Term
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Definition
| Nonliving materials in the environment—such as elements, sunlight, and soil—that influence and are influenced by living (biotic) entities on the planet. |
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Term
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Definition
| A neurotransmitter released by neurons to excite an action potential or trigger a muscle to contract. |
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Term
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Definition
| Hydrogen ion (H+) donors. Acids are very important in the chemical reactions of life because they are highly reactive. Acids have pH values below 7. They are the opposite of bases. |
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Term
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Definition
| Protein filaments that, along with myosin, allow muscles to contract. |
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Definition
| The part of an enzyme that interacts with, or binds to, a substrate. |
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Term
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Definition
| The movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration. Because active transport involves moving the molecule against the natural flow of the concentration gradient, the process requires energy. |
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Term
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Definition
| The evolutionary process by which ancestral forms of an organism are diversified through adaptation to new environments. |
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Term
| adenosine triphosphate (ATP) |
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Definition
| The energy storage molecule for the cell. ATP consists of an adenosine molecule bonded to three phosphate groups. Each phosphate bond contains energy; by breaking these bonds, the cell can get the energy it needs for chemical reactions. Cells build ATP during cell respiration, using the raw material of glucose. |
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Definition
| Two glands, the adrenal cortex and adrenal medulla, located on the kidney. |
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Definition
| A form of cell respiration requiring oxygen (as opposed to anaerobic respiration, which does not need oxygen). Aerobic respiration is much more efficient than anaerobic respiration; it produces 36 ATP for every molecule of glucose. Aerobic respiration proceeds in three stages: glycolysis, the Krebs cycle, and the electron transport chain. |
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Definition
| A specific form or possible version of a gene having multiple versions. Alleles may be dominant or recessive. |
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Term
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Definition
| The frequency with which a particular allele for a certain characteristic appears among all possible alleles for that characteristic in a population. |
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Term
| alternation of generations |
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Definition
| The fluctuation between the diploid (sporophyte) and haploid (gametophyte) life stages that occur in plants. |
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Definition
| The monomer of a protein. A central carbon attached to an amino group (–NH2), a carboxyl group (–COOH), and a hydrogen atom (–H). The fourth group is variable and defines the amino acid’s chemical identity. |
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Definition
| A form of cell respiration that does not use oxygen (as opposed to aerobic cell respiration). Anaerobic respiration is less efficient than the aerobic variety and produces just 2 ATP per molecule of glucose. Anaerobic respiration has two stages: glycolysis and fermentation. |
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Definition
| A trait that is morphologically and functionally similar to that of a different species but that arose from a distinct, ancestral condition. |
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Definition
| The stage of mitosis in which sister chromosomes are separated and pulled to opposite ends of the cell by microtubules; the fourth stage of the first meiotic division (meiosis I), during which maternal and paternal homologous pairs are separated on microtubules; the fourth stage of the second meiotic division (meiosis II), during which either maternal or paternal sister chromatids are separated on microtubules. |
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Definition
| A vascular flowering plant in which seeds are enclosed inside protective ovaries, such as fruit or flowers. Angiosperms can be monocots or dicots. |
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Term
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Definition
| Pollen-producing structure at the top of the stamen, the male reproductive organ of flowers. |
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Term
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Definition
| The sequence of three nucleotides on tRNA that pairs with a codon of mRNA at the A site of a ribosome during translation. |
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Definition
| A protein coat on the surface of red blood cells; a red blood cell may have a protein coat of type A, B, or AB. If the cell has no antigens, it is called type O. The presence of a foreign antigen in a body will cause blood to clot. |
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Term
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Definition
| The largest artery in the body; carries oxygenated blood from the left ventricle of the heart. |
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Term
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Definition
| Literally, zone without light. The aphotic zone is part of the marine pelagic zone and begins 600 feet below the surface of the ocean. Only chemosynthetic organisms, scavengers, and predators are able to survive in this habitat. |
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Term
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Definition
| Vessel that carries blood away from the heart and has thick, elastic, muscular walls that can dilate or contract to control blood pressure within the vessels. Blood in arteries is oxygenated, with the exception of the blood in the pulmonary artery. |
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Term
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Definition
| The involuntary half of the peripheral nervous system. The autonomic nervous system is in two antagonistic parts: the sympathetic and parasympathetic nervous systems. Their interactions control smooth and cardiac muscle, glands, and organs and processes such as heartbeat, the movements of the digestive tract, and the contraction of the bladder. |
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Term
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Definition
| Any chromosome that is not a sex chromosome. Humans have 44 autosomes, in 22 homologous pairs. The two sex chromosomes are the twenty-third pair of chromosomes. |
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Term
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Definition
| An organism that can produce the organic molecules and energy necessary for life through the processes of photosynthesis or chemosynthesis. Autotrophs do not rely on other organisms for food. In a food web, autotrophs are producers. |
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Definition
| One in a class of plant hormones that stimulates (among other things) cell elongation, secondary tissue growth, and fruit development. |
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Term
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Definition
| An ion or compound that removes H+ ions from solution. Often bases are substances that release hydroxide ions (OH–). Bases have pH values above 7. They are the opposite of acids. |
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Term
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Definition
| An emulsifier of fats secreted by the liver and stored in the gallbladder for release in the small intestine. |
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Term
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Definition
| Asexual reproduction found in prokaryotes in which a cell divides into two equal daughter cells by a nonmitotic process. |
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Term
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Definition
| The amount of living matter in a given ecosystem. Because only 10 percent of energy is transferred between trophic levels, the biomass of lower trophic levels is greater than the biomass of subsequent trophic levels: biomass of producers > biomass of primary consumers > biomass of secondary consumers > biomass of tertiary consumers. |
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Term
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Definition
| A particular geographic area with a common climate and characteristic plant and animal life. There are six major terrestrial biomes and two aquatic biomes. The six terrestrial biomes are tropical rain forest, savanna, desert, temperate deciduous forest, taiga, and tundra. The two aquatic biomes are marine and freshwater. Each biome is characterized by specific climax communities. |
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Term
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Definition
| The liquid that carries nutrients and oxygen to the cells and carries carbon dioxide and nitrogenous wastes away. The liquid fluid of blood is called plasma. Red blood cells contain hemoglobin, an iron-containing protein that binds oxygen. White blood cells fight disease. Platelets clot to prevent extreme blood loss resulting from injury. |
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Term
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Definition
| Rigid structures composed of living cells rooted in a matrix of calcium, phosphate salts, and collagen fibers. Bones are the primary component of most vertebrate skeletons. |
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Term
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Definition
| The center of the central nervous system. The brain coordinates the processes of the body. It is composed of various distinct regions, all of which have different functions, including the cerebrum, cerebellum, medulla oblongata, and hypothalamus. |
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Definition
| A lower terrestrial plant (often a moss or liverwort) that lacks a vascular system and is dependent on environmental moisture for reproductive and nutritive functions. |
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Term
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Definition
| Asexual reproductive process in which a small portion of the cell membrane and cytoplasm receive a nucleus and pinch off from the parent cell. |
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Term
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Definition
- Solutions that resist change in pH even when acids and bases are added.
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Term
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Definition
- Roughly spherical underground bud containing additional buds that can develop asexually into new plants.
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Term
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Definition
| Light-independent phase of photosynthesis, where carbon dioxide is fixed to a three-carbon compound used to form glucose. ATP and NADH are consumed in this cycle. Also called the Calvin-Benson cycle or the dark reactions. |
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Term
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Definition
| Tiny blood vessels able to branch through the body and deliver oxygen and nutrients to every cell. |
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Term
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Definition
| The central element of life. Carbon has the ability to form bonds with up to four other elements or molecules at the same time. |
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Term
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Definition
| The maximum number of individuals in a population that can be sustained in a given environment. As populations become increasingly concentrated, competition for food and space, predation, and disease all determine carrying capacity. |
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Term
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Definition
| A firm but flexible substance, found in regions of vertebrate skeletons, such as the ribs, that need to bend. |
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Term
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Definition
| The smallest unit of life, consisting of a solution of organic molecules enclosed by a plasma membrane. |
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Term
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Definition
| A process in which cells reproduce. First the cell replicates its DNA and then divides into two daughter cells. The two main phases of the cell cycle are interphase and mitosis. |
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Term
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Definition
| The phospholipid bilayer that surrounds all cells, regulating the passage of molecules in and out of the cell. |
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Term
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Definition
| The process in which the cell burns glucose to create ATP with the aid of oxygen. Cells have two different methods of turning food into usable fuel: aerobic respiration and anaerobic respiration. |
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Term
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Definition
| The doctrine that every living organism is composed of cells and that all cells come only from other preexisting cells. |
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Term
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Definition
| A rigid structure that surrounds the outer membrane of some cells and helps maintain their shape. In plants the cell wall contains cellulose; in fungi it contains chitin; in prokaryotes it typically contains peptidoglycan. |
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Term
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Definition
| A complex carbohydrate that constitutes the cell walls of plants and protist molds. |
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Term
| central nervous system (CNS) |
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Definition
| The brain and the spinal cord. The CNS acts as the central command center of the body. Mostly made up of interneurons. |
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Term
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Definition
| A structure in the cell that plays an important role in cell replication. During prophase, the centrioles migrate to the poles of the cell and form the mitotic spindle, which allows the chromosomes to be organized and split when the cell divides. |
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Term
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Definition
| Part of the brain. Makes sure that movements are coordinated and balanced. |
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Term
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Definition
| Part of the brain. Controls all voluntary movement, sensory perception, speech, memory, and creative thought. |
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Term
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Definition
| The cycles in which inorganic elements move through the biotic and abiotic aspects of an ecosystem. The two most important chemical cycles are the carbon and nitrogen cycles. |
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Term
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Definition
| Synthesizing organic compounds by energy derived from chemical reactions rather than from the energy of the sun. Chemosynthetic organisms are autotrophs. |
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Term
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Definition
| A rough polysaccharide that constitutes the cell wall of fungi and exoskeleton of arthropods. |
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Term
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Definition
| A pigment located within a chloroplast that absorbs light in plant cells, helping to convert light energy into biological energy through the process of photosynthesis. |
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Term
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Definition
| A double-membrane-bound organelle that contains chlorophyll and is found in plant cells. Chloroplasts are responsible for mediating photosynthesis. |
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Term
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Definition
| The stringy web of genetic material and histone proteins found in the nucleus of eukaryotic cells. During cell division, each strand of DNA coils to form a chromosome. |
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Term
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Definition
| A physical structure composed of a single long strand of DNA (and associated proteins), containing along its length many genes. The human genome consists of 46 chromosomes contained within the nucleus of each cell. |
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Term
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Definition
- Short, hairlike projections found on eukaryotic cells that can help the cell move or can sweep food particles toward the mouth.
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Term
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Definition
| Behavior cycles that depend on time of day. |
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Term
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Definition
| System of organs and blood that brings nutrients and oxygen to cells and carries away wastes. In higher vertebrates, the system has a pulmonary and systemic circuit. The pulmonary circuit carries blood to the lungs to be oxygenated, while the systemic circuit carries oxygenated blood to the body. Vertebrates have a closed circulatory system, while arthropods have an open system. |
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Term
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Definition
| A combination of plant and animal forms that dominate mature ecological communities. Climax communities are unique and shaped by various factors, including temperature, rainfall, and soil acidity. |
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Term
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Definition
| A phenomenon in which two alleles of the same gene are fully expressed in the phenotype when both are present in a heterozygote. Blood type is an example of codominance. |
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Term
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Definition
- A three-nucleotide sequence in a DNA or mRNA molecule. Each codon specifies a single amino acid.
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Term
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Definition
| A compound that regulates activity by binding to an enzyme to tell it when to catalyze a reaction. |
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Term
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Definition
| Animals that are unable to retain heat produced by metabolic activities. Also known as ectothermic. The metabolism of cold-blooded animals is greatly influenced by climate and temperature. |
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Term
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Definition
| The many populations that interact in a given geographical locale constitute ecological communities. Communities exhibit particular interactions such as competition, symbiosis, predation, and food relationships. They also undergo ecological succession. |
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Term
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Definition
| The struggle for survival between organisms or populations that use similar resources and occupy similar niches. Interspecific competition refers to competition between populations that may drive a population out of a community or push it to evolve a different niche to reduce competition. Intraspecific competition refers to competition between individuals of the same species. |
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Term
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Definition
| Consumers are heterotrophic organisms within the food web of a community. In the trophic levels of the food chain, primary consumers consume producers, secondary consumers consume primary consumers, and tertiary consumers consume secondary consumers. |
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Term
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Definition
| An organelle often found in protozoa that pumps excess water out of the cell to keep the cell from bursting in a hypotonic environment (like freshwater). |
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Term
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Definition
| After releasing its ovum (ovulation), the follicle becomes the corpus luteum, which produces progesterone for the continued buildup of the uterine wall. |
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Term
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Definition
| The exchange of genetic information between homologous chromosomes during meiosis I. Crossing-over can disrupt the normal linkage between genes on the same chromosome. |
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Term
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Definition
| The final part of mitosis, in which a cell with duplicated contents splits into two independent cells. |
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Term
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Definition
| The entire content of the cell outside the nucleus, including the membrane-bound organelles and the cytosol. |
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Term
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Definition
| A system of protein filaments found throughout the cytoplasm of eukaryotic cells, which provides structural support for the cell. The cytoskeleton also helps with the movement of organelles within the cell. It is composed of microfilaments and microtubules. |
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Term
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Definition
- The main component of the cytoplasm. It is a grayish, gel-like liquid containing the nucleus, organelles, and cytoskeleton.
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Term
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Definition
| English naturalist (1809–1882) who proposed the modern theory of evolution through natural selection. Darwin traveled aboard the HMS Beagle to the Galápagos Islands, where his revolutionary observations took shape. |
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Term
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Definition
| Organisms that consume waste products and dead organic material and constitute part of the food web, which also includes producers and consumers. Also called saprophytes. Decomposers liberate inorganic elements such as nitrogen and carbon and allow those elements to move back into their respective chemical cycles. Examples of decomposers are bacteria and fungi. |
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Term
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Definition
| A common biochemical reaction in which a new compound is formed by the joining of two compounds to release water. Occurs in the synthesis of polysaccharides and polypeptides. The reverse of hydrolysis. |
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Term
| deoxyribonucleic acid (DNA) |
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Definition
| A type of nucleic acid polymer built from sugar-phosphate backbones and nitrogenous bases. DNA’s sugar, deoxyribose, has one fewer oxygen atom than ribose, found in RNA. The nitrogenous bases adenine, cytosine, guanine, and thymine are used in DNA. |
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Term
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Definition
| A flowering plant (angiosperm) that possesses two cotyledons during embryonic development. Usually has taproots, flower parts in multiples of fours and fives, and branching veins in leaves. |
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Term
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Definition
| The transport or natural drift of molecules traveling from an area of higher concentration to an area of lower concentration. Diffusion does not require outside energy from the cell. |
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Term
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Definition
| The system of organs that converts food to usable nutrients through mechanical and chemical breakdown. Important components of the system are the alimentary canal, glands, esophagus, stomach, small intestine, large intestine, and rectum. |
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Term
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Definition
| The total number of chromosomes present in a somatic cell. The diploid number is twice the haploid number. In humans, the diploid number is 46. |
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Term
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Definition
| A sugar compound consisting of two carbohydrate monomers. |
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Term
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Definition
| Refers to an allele that controls the phenotype even when a different allele is also present, as in a heterozygote. Can also refer to the trait or phenotype produced by a dominant allele. Also known as Mendel’s law of dominance, based on Gregor Mendel’s observations that when two purebred individuals with different forms of the same trait are mated, only one of the two forms appears in the first generation of offspring. Mendel called the apparent form dominant and the suppressed form recessive. |
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Term
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Definition
- Sensory organ capable of detecting sound.
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Term
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Definition
| The progression of plant life and attendant animal life in a given geographic location, from pioneer plant to climax community. |
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Term
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Definition
| The study of the interactions and relationships of populations with each other and their abiotic environments. |
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Term
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Definition
| A community of organisms and its abiotic environment. |
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Term
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Definition
| The female gamete in sexual reproduction; also called an ovum. |
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Term
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Definition
| An instrument that uses an electron beam to form clear and highly magnified images of microscopic structures. Electron microscopes cannot take pictures of living organisms. |
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Term
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Definition
| The final stage of aerobic respiration. The electron transport chain establishes an electrochemical gradient across the inner mitochondrial membrane that powers the synthesis of ATP in oxidative phosphorylation. |
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Term
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Definition
| Before birth, the maturing cells that will grow into a fully formed organism. |
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Term
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Definition
| Control system of the body that functions by releasing hormones into the bloodstream. |
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Term
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Definition
| Process by which liquids or small solid particles are taken into a cell in the form of small vesicles that are produced through the invagination of the cell membrane. |
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Term
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Definition
| A network of membrane-bound tubes and sacs in the cytoplasm. The endoplasmic reticulum is a major site of protein and lipid synthesis. |
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Term
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Definition
| An interior skeleton found in vertebrates made of bone and cartilage. |
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Term
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Definition
| Energy in a community can be depicted as a pyramid of food or biomass. The availability of food, biomass, and energy from the trophic level of producers up through each subsequent level on the food web is approximately 10 percent of that available in the previous trophic level. |
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Term
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Definition
| Biological catalysts made from proteins. Enzymes have attachment locations for substrates called active sites. |
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Term
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Definition
| Hormone that stimulates the growth of the uterine lining during pregnancy and that develops and maintains the female secondary sex characteristics, such as the development of mammary glands, a narrower waist and wider hips, axillary and pubic hair, and a higher-pitched voice. |
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Term
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Definition
- An organism whose cells have membrane-bound intracellular organelles, including a nucleus containing multiple chromosomes. Eukaryotes, unlike prokaryotes, can undergo sexual reproduction via meiosis. Compared to prokaryotes, eukaryotes are more complex and arose later in evolutionary history. Protists, fungi, plants, and animals are all eukaryotic organisms.
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Term
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Definition
| The organ system that filters blood and removes nitrogenous wastes from the body in the form of urea or uric acid. In humans, the two kidneys are the vital organs of blood filtration. In annelids, nephridia fill the filtering role; Malpighian tubules do the same in arthropods. In humans, other important structures of the system are the ureters, the urinary bladder, and the urethra. |
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Term
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Definition
| Process by which molecules are secreted from the cell. Exocytosis occurs when a vesicle fuses with the cell membrane and releases its contents to the outside. |
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Term
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Definition
| A rigid, chitinous protective structure that surrounds the bodies of arthropods and provides support. |
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Term
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Definition
| Sensory organ capable of detecting light. |
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Term
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Definition
| The first generation of offspring from a cross between two varieties or individuals. In Mendel’s experiments, all the F1 offspring were heterozygous hybrids with a dominant phenotype. |
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Term
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Definition
| The second generation of offspring in a breeding experiment; the offspring from a mating between two F1 hybrids. In Mendel’s monohybrid experiments, the ratio of dominant to recessive phenotypes in the F2 generation was 3:1. |
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Term
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Definition
| Diffusion of molecules that cannot pass through the cell membrane independently, but rather through permeable protein channels embedded in the membrane. Facilitated diffusion does not require outside energy. |
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Term
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Definition
| A molecule that stores energy for harvest by the electron transport chain. |
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Term
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Definition
| Duct that connects the ovaries with the uterus; the passage through which the ovulated egg travels from the ovaries to the uterus. |
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Term
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Definition
| The second stage of anaerobic respiration, which produces the NAD+ necessary for glycolysis. There are two types of fermentation: alcoholic fermentation and lactic acid fermentation. Yeast engage in alcoholic fermentation, while muscle cells lacking oxygen produce lactic acid. |
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Term
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Definition
| The name given to an embryo after it has developed organs. |
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Term
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Definition
| A whiplike structure projecting from the surface of some cells and single-celled organisms; coordinated waving of the flagellum allows the organism to swim. Prokaryotic flagella are made of a single helical chain of flagellin proteins; eukaryotic flagella are made of multiple chains of microtubule proteins. |
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Term
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Definition
| Theory describing the cell membrane as a dynamic structure with proteins floating, yet partially embedded, in a sea of phospholipids. |
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Term
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Definition
| A linear relationship of predators and prey. |
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Term
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Definition
| Many connected food chains that exhibit the relationships of all predators to all prey constitute a food web. |
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Term
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Definition
| The grouping of fossilized remains according to relative and absolute age. |
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Term
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Definition
- An organ that stores the bile produced by the liver and releases it to the small intestine during digestion.
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Term
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Definition
| A haploid sex cell (either an egg or sperm cell); male and female gametes join during fertilization to create a diploid zygote. Gametes are created out of germ cells and are passed down to offspring. |
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Term
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Definition
| A haploid plant or plant structure that produces haploid gametes through mitosis. |
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Term
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Definition
| A simple cluster of nerve cells that acts as a coordinating center. In more sophisticated organisms, ganglia evolved into a brain and spinal cord. |
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Term
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Definition
| The fundamental unit of heredity, composed of a stretch of DNA. In general, a single gene encodes the information needed to produce one kind of protein. Each gene resides in a specific spot on a chromosome. |
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Term
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Definition
| The movement of genes, within a population or between populations, through mating. |
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Term
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Definition
| The series of codons that make up an organism’s DNA. |
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Term
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Definition
| The entire set of specific alleles present in an organism or cell: the genetic information that (together with the environment) defines the phenotype. Often refers only to the alleles controlling a particular trait of interest. |
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Term
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Definition
| Cells that lead to the production of gametes. Produced by meiosis. |
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Term
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Definition
| A monosaccharide with the chemical formula C6H12O6. Used as the raw material for cellular respiration. |
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Term
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Definition
| The first step of aerobic and anaerobic respiration. Glycolysis produces ATP while converting glucose to pyruvate, which is the raw material for the rest of aerobic respiration. |
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Term
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Definition
| A series of membrane-bound sacs in the eukaryotic cytoplasm. The Golgi apparatus takes proteins produced by the endoplasmic reticulum and packages and secretes them to various destinations inside and outside of the cell. |
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Term
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Definition
| Sex organs that produce gametes. The gonads also release sex hormones, such as testosterone, estrogen, and progesterone. In humans, the male gonads are the testes; in females, the ovaries. |
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Term
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Definition
| An artificial form of vegetative propagation in which parts of two young plants are joined together, first by artificial means and then by tissue regeneration. |
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Term
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Definition
| A process by which components of bacterial cell walls are bound to Gram’s stain. Depending on the amount of peptidoglycan in their cell walls, bacteria stain differently and are classified as Gram-negative or Gram-positive. |
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Term
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Definition
| Epidermal plant cells found in pairs surrounding the stomata of leaves. By increasing or decreasing their size, guard cells regulate gas exchange by opening and closing individual stoma. |
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Term
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Definition
| A vascular nonflowering plant (commonly known as a conifer) in which seeds are “naked”—collected in a cone and not protected by an ovary. The dispersion of their spermatozoids often relies on wind. |
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Term
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Definition
| The number of homologous pairs in a cell. Equal to half the diploid number. Gametes, cells that are passed on to offspring, contain the haploid number of chromosomes. In humans, the haploid number is 23. |
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Term
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Definition
| The muscular organ that pumps blood through the circulatory system. Mammals and birds have a four-chambered heart, with a left atrium and ventricle and a right atrium and ventricle. The right half of the heart receives deoxygenated blood from the body and pumps it to the lungs, while the left half receives oxygenated blood from the lungs and pumps it to the body. |
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Term
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Definition
| The genetic transmission of traits from parents to offspring, so that offspring resemble their parents. Traits transmitted this way are called hereditary traits. |
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Term
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Definition
| Organisms that can only get the organic molecules and energy necessary for life through the consumption of other organic matter. In the food web, all consumers and decomposers are heterotrophs. Heterotrophs can be herbivores, carnivores, or omnivores. |
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Term
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Definition
| A situation in which an individual (heterozygote) possesses two dissimilar alleles for the same gene. The opposite is homozygous. |
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Term
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Definition
| Chromosomes containing the same series of genes; they may or may not carry the same alleles. Humans receive one set of 23 paternal chromosomes from their male parent and another set of 23 maternal chromosomes from their female parent. Each set matches up to the other for a total of 23 different pairs of homologous chromosomes. During meiosis, homologous pairs line up and are separated. In males, the X and Y chromosomes act as a homologous pair, although they are only partially homologous. |
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Term
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Definition
| A trait found in different species that are morphologically and functionally similar and that comes from the same ancestral condition. A whale’s fin and a human’s arm are homologous structures. |
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Term
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Definition
| A situation in which an individual (homozygote) has the exact same allele on both homologous chromosomes. Mating of two individuals with the same homozygous genotype will produce only offspring with that same identical genotype. The two identical alleles may be dominant or recessive (e.g., RR or rr). The opposite of homozygous is heterozygous. |
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Term
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Definition
| A chemical messenger that can be made of either peptides or lipids. Secreted by glands in one part of the body, hormones affect glands or organs in another part. |
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Term
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Definition
| A genetic mixture; the offspring of two genetically different parents. Hybrids are usually heterozygous for a variety of genes. |
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Term
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Definition
| A weak bond between hydrogen and a set of other elements, including oxygen. Hydrogen bonds are a subset of dipole-dipole interactions. |
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Term
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Definition
| A common biochemical reaction in which the bond between two molecules is split by the addition of a water molecule. Hydrolysis is the process that breaks down polymers and dimers. The reverse is dehydration synthesis. |
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Term
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Definition
| Having an affinity for water; usually polar molecules. For the SAT II Biology, this is principally important in relation to the phospholipid bilayer. |
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Term
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Definition
| Having a reluctance to mix with water; usually nonpolar molecules. The fatty acids that form the interior pocket between the two layers of the cell membrane are hydrophobic. |
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Definition
| A fluid skeleton in many soft-bodied invertebrates, including annelids, that allows an organism to change shape but not volume. |
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Definition
| A situation in which the concentration of solutes in a solution is higher than what it contains. For example, a sodium solution of 10 percent would be hypertonic to an animal cell (with a sodium concentration of about 0.9 percent), causing water to leave the cell by osmosis. |
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Definition
| Part of the brain responsible for temperature regulation, controlling hunger and thirst, and managing water balance. It also helps generate emotion. |
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Term
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Definition
| A situation in which the concentration of solutes in a solution is lower than what an organism contains. An example is a paramecium in pond water: the organism has more solutes than its environment, so water flows into the cell by osmosis. Paramecia have evolved contractile vacuoles to keep from exploding. |
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Definition
- Instinctual behavior in which social bonds are formed during early development. Typically used with the example of a newly hatched bird or other animal identifying and treating the first moving object it sees as its mother.
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Definition
| Occurs when two different alleles of the same gene are both partially expressed in a heterozygote. The resulting phenotype is intermediate between the homozygous phenotypes of the two alleles. Color in a four o’clock flower is an example of incomplete dominance. |
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Term
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Definition
| Mendel’s conclusion that during gamete formation, the segregation of one pair of genes has no influence over the segregation of another pair of hereditary units. Two different traits will thus be inherited independently of each other. This law holds true, except for linked genes. It is often called Mendel’s second law. |
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Term
| inheritance of acquired traits |
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Definition
| A crucial, and incorrect, aspect of Lamarck’s theory of evolution. Lamarck believed that the traits a parent acquired during its lifetime would be passed on to its offspring. |
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Term
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Definition
| Behavior that is hardwired into the brain of an organism; behavior that does not have to be learned. |
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Definition
| Hormone secreted by the pancreas that reduces blood sugar levels. A lack of insulin can result in diabetes. |
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Definition
| The phase of the eukaryotic cell cycle in which the cell prepares for division, primarily by replicating its DNA. After interphase, the cell enters mitosis. |
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Definition
| The most shallow zone in a marine habitat. Periodically dry or wet with the changing tides. Algae, sponges, mollusks, starfish, and crabs inhabit this zone. Also called the littoral zone. |
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Term
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Definition
| An atom or molecule that has lost or gained an electron and consequently has a positive or negative charge. |
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Term
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Definition
| A situation in which the concentration of solutes in a solution is equivalent to what it contains. There is no concentration gradient in isotonic solutions and no net flow of solutes or water. |
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Definition
| A photograph of the chromosomes from an individual cell, usually lined up in homologous pairs, according to size. Missing, extra, or abnormal chromosomes can then be easily identified, aiding in the diagnosis of genetic disorders. |
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Term
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Definition
| The organ of blood filtration in humans. The functional unit of the kidney is the nephron. |
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Definition
| The broadest category of biological taxonomy. |
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Term
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Definition
| A metabolic pathway in aerobic organisms in which acetyl-CoA combines with oxaloacetic acid to form citric acid. For this reason, the Krebs cycle is also known as the citric acid cycle. The cycle produces energy in the forms of ATP, NADH, and FADH2. |
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Term
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Definition
| An evolutionary theory (proved false by Darwin) stating that species change over time by the use and disuse of structures and the inheritance of acquired traits. |
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Term
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Definition
| Behavior that an organism picks up over the course of its life. Three types of learned behavior are habituation, conditioning, and associative learning. |
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Term
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Definition
| Dutch clothing salesman (1632–1723) who made the first observations of bacteria and protozoa using single-lens microscopes of his own design. |
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Definition
| Connective tissue between bones. |
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Term
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Definition
| Genes that are located close together on the same chromosome. Linked genes will not undergo independent assortment during gamete formation, constituting an exception to the law of independent assortment. Crossing-over will disrupt the linkage of two genes on the same chromosome if they are far enough apart. |
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Definition
| A means of returning blood fluid, lymph, that has escaped from capillaries back into the bloodstream. Defended against foreign bodies by lymphocytes. |
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Term
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Definition
| White blood cell that is specialized to kill specific invading bacteria. Three types of lymphocytes work in coordination: B cells, helper T cells, and killer T cells. |
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Term
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Definition
| The organ of blood filtration in arthropods. |
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Term
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Definition
| Part of the brain responsible for the control of involuntary functions such as breathing, cardiovascular regulation, and swallowing. |
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Term
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Definition
| A type of cellular reproduction that results in the formation of four haploid cells from one diploid cell. Contains two cellular divisions, meiosis I and meiosis II, that follow only one round of DNA replication. Meiosis produces germ cells. |
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Term
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Definition
| Gregor Mendel (1822–1884) was an Austrian monk and scientist. Through a series of experiments with pea plants, he discovered the basic laws of heredity, including dominance, segregation, and independent assortment. |
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Term
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Definition
- A 28-day hormone sequence that defines the production, ovulation, and menstruation of eggs in the female reproductive system. If fertilization of the egg occurs, the menstrual cycle stops.
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Term
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Definition
| The internal tissue of a leaf between the epidermal cells; specialized for photosynthesis. Contains the palisade and spongy layer. |
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Term
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Definition
| An RNA molecule that specifies the amino acid sequence of a protein. In transcription, messenger RNA molecules copy the genetic information stored in DNA. The mRNA then bring the recipes for proteins from the nucleus to ribosomes in the cytoplasm. |
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Term
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Definition
| The second stage of mitosis in which microtubules align the chromosomes in the center of the cell along the metaphase plate; the stage of meiosis I and II during which the chromosomes align at the center of the cell. |
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Term
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Definition
| Inorganic molecules required by the body to carry out life processes. Important minerals are iron, a necessary component of hemoglobin; iodine, which is essential for making thyroid hormone; and calcium, which is required by the bones and for many cellular processes. |
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Term
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Definition
| Double membrane-bound organelles that produce most of the energy in eukaryotic cells through the process of aerobic (cellular) respiration, which generates ATP. |
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Term
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Definition
| The phase of the eukaryotic cell cycle in which the cell divides. The four steps of mitosis are prophase, metaphase, anaphase, and telophase. |
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Term
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Definition
| A complex of microtubules that forms between opposite poles of a cell during mitosis. The mitotic spindle is formed by the centrioles and serves to separate and move chromosomes to opposite ends of the cell for division. |
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Term
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Definition
| A molecule or gene sequence that has a constant rate of change through accumulation of neutral substitutions and is therefore a good measuring stick for the relatedness of different species. |
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Term
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Definition
| A flowering plant (angiosperm) that possesses one cotyledon during embryonic development. Usually has fibrous roots, flower parts in threes, and parallel veins in leaves. |
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Term
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Definition
| Each of the repeating units that make up a polymer. |
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Term
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Definition
| A carbohydrate monomer. Glucose and fructose are common examples. |
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Term
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Definition
| Structures that create movement in an organism by contracting under a stimulus from a neuron. There are three types of muscle: skeletal, which is responsible for voluntary movement; smooth, which is responsible for involuntary movement; and cardiac, which makes up the heart. |
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Term
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Definition
| An error in the sequence of nucleotides in DNA or RNA that in turn affects the production of proteins. There are two main types of mutations: substitution mutations and frameshift mutations. A substitution mutation occurs when one nucleotide is replaced by another; these mutations can range from ineffectual to drastic, depending on how the new nucleotide changes the protein coded for. Frameshift mutations occur when a nucleotide is either inserted or deleted into the code; these mutations are always drastic and often fatal, since an insertion or deletion will affect every codon in a particular genetic sequence by throwing the entire three-by-three codon frame out of whack. |
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Term
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Definition
| A structure that speeds the movement of action potentials along the axon of a neuron. The sheath is built of Schwann cells, which wrap themselves around the axon of the neuron, leaving small gaps in between known as the nodes of Ranvier. |
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Term
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Definition
| Protein filaments that, along with actin, allow muscles to contract. |
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Term
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Definition
| An energy-carrying coenzyme produced by glycolysis and the Krebs cycle. NADH carries energy to the electron transport chain, where it is stored in ATP. |
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Term
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Definition
| The theory, first proposed by Darwin, which holds that organisms produce as many offspring as possible, which compete for limited resources. Organisms’ characteristics vary, and certain characteristics will allow organisms to survive and reproduce more effectively. These adaptive characteristics will be more prevalent in subsequent generations. Natural selection is the engine of evolution, choosing the most fit genes to pass from one generation to the next. |
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Term
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Definition
| A blood filtration and excretory organ characteristic of segmented worms. |
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Term
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Definition
| Tiny, tubule structures responsible for the filtering of blood in the kidneys of vertebrates. |
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Term
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Definition
| The medium depth zone of the marine biome. Extends to 600 feet beneath the water’s surface and sits on the continental shelf, hundreds of miles from any shore. Algae, crustaceans, and fish inhabit this region. |
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Term
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Definition
| Control system of the body that functions by sending impulses through neurons to receive information and spur muscles to action. |
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Term
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Definition
| The functional unit of the nervous system. A neuron is a specialized cell able to carry an action potential and made up of dendrites, a cell body, and an axon. There are three types of neurons: sensory, motor, and interneurons. |
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Term
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Definition
| The unique role a population plays in a community. A niche includes all characteristics that define the way a population exists in a community, from where the members live to what they eat, when they sleep, and how they reproduce. |
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Term
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Definition
| One of the nitrogen-containing bases in DNA and RNA nucleotides. There are five nitrogenous bases in living organisms. DNA is composed of adenine, thymine, guanine, and cytosine. RNA is composed of adenine, uracil, guanine, and cytosine. |
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Term
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Definition
| Occurs when a pair of homologous chromosomes fails to separate during gamete formation. The offspring produced from these gametes have either one too many or one too few of a particular chromosome. Nondisjunction is the cause of genetic disorders such as Down syndrome. |
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Term
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Definition
| A longitudinal rod of cells that forms in the least developed chordates and in embryonic stages of more developed chordates. |
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Term
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Definition
| A dense, spherical body inside the nucleus of a cell. The nucleolus makes the RNA that is a structural component of the ribosomes. |
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Term
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Definition
| The monomer of a nucleic acid. Nucleotides consist of (1) a phosphate group, a group of atoms containing phosphorus; (2) a sugar; and (3) a nitrogenous base, a compound containing nitrogen that removes H+ ions from solution. Nucleotides are grouped into two general classes, depending on the sugar group that they carry: deoxyribonucleic acids (DNA) contain the sugar deoxyribose and ribonucleic acids (RNA) contain the sugar ribose. Nucleotides are further divided by the type of nitrogenous base that they carry. DNA is composed of adenine, thymine, guanine, and cytosine. RNA is composed of adenine, uracil, guanine, and cytosine. |
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Term
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Definition
| The large, central organelle of eukaryotes. The nucleus contains the genetic material of the cell and controls cellular activities. |
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Term
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Definition
| Region near the top of the nasal cavity with chemoreceptors and neurons that inform the sense of smell. |
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Term
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Definition
- The process in which haploid egg cells (ova) form through meiotic division.
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Term
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Definition
| A discrete unit of tissues that work together to perform specific functions within the body. |
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Term
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Definition
| Specialized membrane-bound structure in a cell that performs a specific function. Examples of organelles include the endoplasmic reticulum and the mitochondria. |
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Term
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Definition
- Process by which water naturally travels from an area of high water concentration to low water concentration.
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Term
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Definition
| In animals, the female gonad that produces ova and sex hormones. In plants, the ovaries are the structure at the base of the pistil that contains the eggs. |
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Term
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Definition
| Structure that contains the female gametophyte and gametes; after fertilization, develops into a seed. |
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Term
| oxidative phosphorylation |
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Definition
| Part of the electron transport chain. A process occurring in the mitochondria that results in the formation of ATP from the flow of electrons across the inner membrane to bind with oxygen. |
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Term
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Definition
A digestive organ that releases enzymes into the small intestine. Also an endocrine gland that regulates glucose levels in the blood by the release of insulin or glucagon from specialized cells called islets of Langerhans. |
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Term
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Definition
| Four small glands embedded on the posterior surface of the thyroid gland. The parathyroid glands produce a hormone that regulates the level of calcium in the bloodstream. |
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Term
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Definition
| Asexual reproduction in which an unfertilized gamete (usually female) produces female offspring. Parthenogenesis vastly increases the speed at which a population can grow, though it results in a loss of genetic diversity among members of the population. |
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Term
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Definition
| The open-ocean zone at the greatest depth in a marine habitat. This zone is divided into a photic (down to 600 feet below the water’s surface) and aphotic zone. |
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Term
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Definition
| The bond between the amino acids in a protein. Formed by dehydration synthesis. |
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Term
| peripheral nervous system (PNS) |
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Definition
| The pathways by which the central nervous system receives sensory information from the body and sends commands to muscles. The peripheral nervous system is divided into two halves. The sensory system brings information in from the body, while the motor system sends commands out to muscles. |
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Term
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Definition
| The rolling motion of smooth muscle that moves food along the alimentary canal. Includes the passage from the esophagus to the stomach, the churning action of the stomach, and the passage through the small intestine. |
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Term
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Definition
- A scale for measuring the presence or absence of hydrogen ions in solution. Values between 0 and 7 indicate an excess of hydrogen ions. Such solutions are called acids. Values between 7 and 14 indicate the presence of compounds that counteract the effects of hydrogen ions. Such solutions are called bases. At pH 7, solutions are neutral.
- A scale for measuring the presence or absence of hydrogen ions in solution. Values between 0 and 7 indicate an excess of hydrogen ions. Such solutions are called acids. Values between 7 and 14 indicate the presence of compounds that counteract the effects of hydrogen ions. Such solutions are called bases. At pH 7, solutions are neutral.
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Term
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Definition
| A type of white blood cell that kills invading cells by ingesting them. |
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Term
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Definition
| A form of endocytosis in which a cell ingests a solid particle. |
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Term
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Definition
| The entire set of observable characteristics of an organism or cell; the physical traits of an organism. The genotype, together with environmental factors, defines the phenotype. |
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Term
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Definition
- Vascular tissue composed of cells that are living at maturity; transports the products of photosynthesis throughout the plant body.
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Term
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Definition
| Type of lipid found in cell membranes. Phospholipids are made up of a single hydrophilic phosphate head and two nonpolar hydrophobic lipid tails. |
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Term
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Definition
| A double layer of phospholipid molecules that provides the structure of the cell membrane. Formed naturally from the alignment of the two layers of lipids such that their hydrophobic tails point inward toward each other and their hydrophilic phosphate heads point outward into the watery environments inside and outside of the cell. |
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Term
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Definition
| Literally, zone with light. The photic zone is part of the marine pelagic zone and extends to 600 feet below the surface of the ocean. Photosynthetic plankton as well as bony fish, sharks, and whales inhabit this zone. |
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Term
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Definition
| An organism’s response to the length of day and night within a 24-hour period (photoperiod); in many plants, this phenomenon determines when flowering occurs. |
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Term
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Definition
| The process by which plants and other autotrophic organisms convert light energy into organic materials, such as glucose. |
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Term
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Definition
| The evolutionary relationships of a genetically similar group of organisms. |
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Term
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Definition
| Form of endocytosis during which liquids are taken into the cell through the invagination of the cell membrane. |
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Term
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Definition
| The first population to move into a geographic location and begin the process of ecological succession. |
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Term
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Definition
| The female reproductive organ of the flower, composed of a stigma, style, and ovary; sometimes called the carpel. |
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Term
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Definition
| The “master” gland of the endocrine system. The pituitary releases hormones that control the other major glands of the endocrine system. Made up of the anterior and posterior pituitary. Controlled by the hypothalamus. |
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Term
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Definition
| A structure that develops in the uterus during pregnancy; filter through which the embryo gains nutrition from the mother. |
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Term
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Definition
| Circular DNA molecules found in prokaryotes. |
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Term
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Definition
| The male gametophyte of gymnosperms and angiosperms. |
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Term
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Definition
| A large molecule consisting of the same or similar units attached in a series, forming a chain. |
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Term
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Definition
| A group of interbreeding organisms in a particular locale exhibiting a unique set of characteristics such as patterns of growth and reproductive strategies. |
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Term
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Definition
| Term that refers to one organism eating another. Predation covers both carnivorous and herbivorous consumption. |
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Term
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Definition
| Autotrophic organisms such as plants, plankton, and chemosynthetic bacteria that are able to synthesize organic compounds using energy from the sun or chemical reactions. Producers do not have to consume other organisms to attain energy and are the foundation of every food web. |
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Term
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Definition
| Hormone that prepares the uterus for embryo implantation and helps to maintain pregnancy. |
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Term
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Definition
| A single-celled organism that completely lacks membrane-bound intracellular organelles such as a nucleus or mitochondria; prokaryotes possess only a single circular strand of DNA. Prokaryotes are simpler than eukaryotes and arose earlier in evolutionary history. All bacteria are prokaryotes. Taxonomists group all prokaryotes into the kingdom Monera. |
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Term
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Definition
| The first stage of mitosis, meiosis I, and meiosis II, during which the chromosomes become visible and the centrioles move to opposite ends of the cell and begin to form the spindle. |
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Term
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Definition
| Temporary cytoplasmic protrusions of ameboid cells that function in movement and food uptake by phagocytosis. |
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Term
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Definition
| A pictorial method of showing the gene combinations (genotypes) of offspring that might result from an experimental genetic cross of two parents. |
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Term
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Definition
The three-carbon end product of glycolysis. Pyruvate is the raw material of the Krebs cycle. |
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Term
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Definition
| Refers to an allele that cannot control the phenotype unless it is the only kind of allele present, as in a homozygote or hemizygote. Also refers to the trait or phenotype produced when only a recessive allele is present. The opposite of recessive is dominant. |
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Term
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Definition
| The inability of individuals within a species to create offspring with members of any other species. The mark of a species is its reproductive isolation from all other species. |
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Term
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Definition
| The organ system responsible for the intake of oxygen and diffusion of that gas into the blood and the elimination of carbon dioxide from the body. Important structures of the system are the pharynx, larynx, trachea, bronchi, bronchioles, and lungs. Alveoli in the lungs are the location of gas exchange with the blood. The movement of the muscular diaphragm allows the lungs to inhale and exhale. |
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Term
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Definition
| One type of nucleic acid polymer. RNA nucleotides’ sugars contain one more oxygen atom than DNA nucleotides’ sugars. RNA nucleotides can have the nitrogenous bases adenine, cytosine, guanine, and uracil. |
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Term
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Definition
| Organelle responsible for protein synthesis. Ribosomes are located in cytoplasm or endoplasmic reticulum. |
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Term
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Definition
| The part of a plant beneath the soil; responsible for collecting water and minerals from the soil, storing nutrients, and securing the plant to the ground. Can be fibrous or a taproot. |
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Term
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Definition
| An outgrowth of a plant root that provides an increased surface area for the absorption of water and dissolved minerals from the soil. |
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Term
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Definition
| Slender horizontal stem that can form new plants via specialized nodes. |
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Term
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Definition
| Mendel’s conclusion that individuals have two copies of each gene, and that these copies separate randomly during gamete formation, one copy per gamete. This law is true except for genes on sex chromosomes in males, who have only one copy of each such gene. It is often called Mendel’s first law. |
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Term
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Definition
| Fluid-filled structure within the ear that can detect balance. |
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Term
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Definition
| Green, leaflike structure that encloses and protects the unopened flower bud. |
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Term
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Definition
| Refers to a chromosome involved in defining the sex of an individual. Humans have two sex chromosomes and 44 autosomes. In females, both sex chromosomes are X chromosomes. Males have one X chromosome and one Y chromosome. |
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Term
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Definition
| Refers to a gene located on a sex chromosome or to a trait defined by such a gene. Such traits will appear with different frequencies in males and females, and males and females will differ in their ability to transmit the trait to their offspring. In order for a recessive sex-linked trait such as hemophilia or color blindness to manifest in the phenotype of a woman, it must be inherited from both mother and father; such diseases will be present in the phenotype of a man if he inherits it just from his mother. |
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Term
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Definition
| Any plant or animal cell that is not a germ cell, meaning it is not passed down to offspring. The class of cell formed during mitosis. |
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Term
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Definition
| One half of the motor system of the peripheral nervous system. Responsible for voluntary, or conscious, movement. Neurons in this system target skeletal muscles and release the neurotransmitter acetylcholine. |
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Term
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Definition
| The development of a species through evolution. A species forms when its members become reproductively isolated from all other organisms. Speciation can occur through geographic separation that eliminates gene flow or through adaptive radiation. |
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Term
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Definition
| A group of organisms defined by their ability to interbreed with only each other. |
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Term
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Definition
| The male gamete in sexual reproduction. |
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Term
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Definition
| The process in which haploid sperm cells form through meiotic division. |
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Term
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Definition
| A long cylinder of nervous tissue that extends along the vertebral column from the head to the lower back. It controls some autonomic responses and connects the brain to the peripheral nervous system. |
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Term
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Definition
| Usually unicellular and microscopic, spores are produced by protist molds, fungi, and plants and are able to develop into new individuals. Spores are able to survive without food or water for long periods. Most fungi spend part of their life cycle as hyphae and part as spores. |
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Term
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Definition
| A diploid plant or plant structure that produces haploid spores through meiosis. |
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Term
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Definition
| When selection pressures favor the average form of a trait. |
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Term
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Definition
| The male reproductive organ of the flower, consisting of an anther and filament. |
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Term
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Definition
| The top part of the pistil, where pollen grains are received. |
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Term
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Definition
| Small epidermal pores, surrounded by two guard cells, through which gases diffuse and water transpires in and out of a leaf. |
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Term
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Definition
| A codon on mRNA that signals the termination of DNA translation. There are three stop codons: UAA, UAG, or UGA. |
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Term
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Definition
| The shaft of the pistil that leads from the stigma down into the ovary. |
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Term
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Definition
| The starting material that will undergo chemical change in a chemical reaction facilitated by an enzyme. |
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Term
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Definition
| A type of interaction within a community that falls into one of three categories: a parasitic relationship benefits one organism and hurts the other; a commensal relationship benefits one and does not affect the other; a mutualistic relationship benefits both organisms. |
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Term
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Definition
| The gap between two neurons, spanning the space between the axon of one and the dendrites of the other. In order to pass an impulse across a synapse, neurons must release neurotransmitters. |
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Term
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Definition
| Structures on the tongue that contain chemoreceptors, which respond to four main sensations—sour, salty, bitter, and sweet—to create the sense of taste. |
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Term
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Definition
| The study of biological classification. |
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Term
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Definition
| The final stage of mitosis before cytokinesis. In telophase, the nuclear envelope re-forms around separated sister chromatids and kinetochore microtubules disappear. Cell elongation also occurs during this phase. The final stage of the first meiotic division (meiosis I), during which chromosomes arrive at the poles of the cell and begin to recondense; the final stage of the second meiotic division (meiosis II), during which chromosomes arrive at the poles of the cell, the nuclear envelope begins to re-form, and the chromosomes begin to recondense. |
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Term
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Definition
| Connective tissue between bones and muscles. |
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Term
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Definition
| The male gonads; sperm and testosterone are produced here. |
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Term
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Definition
| A hormone necessary for sperm production in men. Also responsible for developing and maintaining the secondary sex characteristics of males, starting at puberty. |
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Term
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Definition
| Gland that produces the hormone thyroxine, which increases the metabolism of most of the cells in the body. Located in the neck. |
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Term
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Definition
| A group of closely connected and similar cells that cooperate to generate a specific structure or specialized function within an organism. |
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Term
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Definition
| A terrestrial plant with a vascular system. |
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Term
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Definition
| Any observable feature or characteristic of an organism. |
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Term
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Definition
| An RNA molecule used in protein synthesis as a link helping to convert messenger RNA into amino acids. |
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Term
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Definition
| The process by which a plant loses water to its environment through evaporation. |
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Term
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Definition
| Steps on a food/biomass pyramid that are defined by organisms within a community that are the same distance from the primary producers in a food web. |
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Term
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Definition
| Long-term growth of a plant toward or away from a stimulus. |
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Term
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Definition
- Fleshy underground storage structure composed of an enlarged portion of the stem that has on its surface buds capable of producing new plants.
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Term
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Definition
| Structure in the female reproductive system in which the embryo develops. |
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Term
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Definition
| Tissue that produces new vascular cells; lies between the xylem and phloem in dicot stems. |
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Term
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Definition
| A conductive component (either xylem or phloem) of the vascular system that transports food and nutrients throughout the plant body. |
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Term
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Definition
| A form of asexual reproduction in which plants produce genetically identical offshoots (clones) of themselves, which then develop into independent plants. |
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| A blood vessel that carries blood back to the heart. The blood in veins is not oxygenated, with the exception of the pulmonary vein. |
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| An animal that has a skeletal rod of bone or cartilage running up its back, surrounding the nerve cord. Segments of this rod are called vertebrae. All vertebrate animals belong to subphylum Vertebrata, part of phylum Chordata. |
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| Bodily structures that developed in the past but no longer serve any function for an organism. |
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| Fingerlike projections in the small intestine that increase surface area and maximize the absorption of nutrients. |
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| Complex molecules that usually serve as coenzymes, assisting in physiological processes. |
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- Animals that have developed fat and fur, hair, or feathers in order to retain heat produced by metabolic activities. Also known as endothermic. Warm-blooded animals are able to thrive in various climates, because they are minimally affected by environmental fluctuations in temperature.
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| Vascular tissue composed of cells that are dead at maturity; transports water and dissolved minerals upward from the roots to the shoot. |
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- In sexual reproduction, the diploid product of the fusion of the father’s haploid sperm cell and the mother’s haploid ovum (egg) cell. The single-celled zygote divides billions of times to form a whole individual.
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