Term
| Distinguish between eukaryotic and prokaryotic cells in terms of their structure and ultrastructure. |
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Definition
Eukaryotic - animal/plant cells - have a nucleus, endoplasmic reticulum, mitochondria, etc...
Prokaryotic - bacteria/single celled organism cells - no nucleus, circular DNA, etc... |
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Term
| Describe the ultrastructure of an animal (eukaryotic) cell and recognise these organelles from EM images. |
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Definition
| nucleus, nucleolus, ribosomes, rough and smooth endoplasmic reticulum, mitochondria, centrioles, lysosomes, and Golgi apparatus - name, label and know their functions. |
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Term
| Explain the role of the rough endoplsmic reticulum (rER) and the Golgi apparatus in protein transport within cells and including its role in formation of extracellular enzymes. |
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Definition
DNA is transcripted in nucleus into mRNA which can leave the nucleus. The mRNA is then made into a primary structure, a chain of amino acids, at the ribosomes lining the edge of the rER and then enters this endoplasmic reticulum. Here it is transformed into its secondary and tertiary structures. Vesicles are pinched of the ends of the rER containing the proteins and join onto the Gogi apparatus where the proteins are further modified. Then the finished product is pinched off the Golgi apparatus in vesicles and leave the cell through exocytosis, thus extracellular enzymes are made.
(Important to know that the membranes are all the same structure so the vesicles can join with the various organelles.) |
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Term
| Explain how mammalian gametes are specialised for their functions. |
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Definition
Egg - Larger than the sperm as it does not need to move around by itself, pushed along the fallopian tube by muscles in the walls. Has a haploid nucleus and lipids as a food source for the embryo's development.
Sperm - acrosome at the head for the acrosome reaction. Haploid nucleus also in head. Mitochondria at the middle to power the tail thus propelling it towards the egg. |
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Term
| Explain the role of meiosis in the production of gametes and genetic variation through recombination of alleles and genes including independent assortment and crossing over (details of the stages of meiosis are not required). |
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Definition
Independent assortment assures variation in that the chromosomes line up during the first stage of meiosis in a completely random order. In animals with many chromosomes, it is very unlikely that the same combination of chromosomes will meet at firtilisation.
Crossing over is when the chromatids come into contact with each other at chiasmata and break and rejoin, exchanging sections of DNA. This can happen at several different points along the chromosomes. |
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Term
| Describe the process of fertilisation in mammals and flowering plants (starting with the acrosome reaction in mammals and pollen tube growth in plants and ending with the fusion of the nuclei). |
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Definition
Mammals - chemicals are released from the cells surrounding the ovum (follicle cells), triggering the acrosome reactiond. The acrosome in the sperm cell bursts releasing digestive enzymes which eat through the cells surrounding the egg and through the ovum's membrane. The nucleus of the sperm cell then enters the egg, lysosomes release enzymes which thicken the zona pellucida, and the two nuclei fuse forming a zygote.
Flowering Plants - Pollen grain lands on the stigma and a pollen tube starts to grow down the style. The two male nuclei in the pollen travel down the tube into the ovule of the plant. The first male nucleus fuses with the egg nucleus of the ovule to form the zygote, whilst the other male nucleus joins with the polar nuclei of the egg, forming the triploid nucleus of the endosperm. |
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Term
| Explain the importance of fertilisation in sexual reproduction. |
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Definition
| Fertilisation is the way in which a new individual of the same species is formed by a haploid nuclei from each parent joining together to create a new individual. |
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Term
| Explain the role of mitosis and the cell cycle for growth and asexual reproduction. |
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Definition
| The cell cycle is the cycle in which a cell is born, replicates its content and the divides to form two new cells. At interphase, a cell goes through three different stages. G1 is the first stage of a new cell. This stage can last from days to years. The second stage is the S phase where DNA is synthesised ready for cell division. The G2 phase sepparates the S phase from cell division. After Interphase, cell division occurs. The production of new cells makes an animal grow, and mitosis is the process used for asexual reproduction. |
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Term
| Describe the stages of mitosis and how to prepare and stain a root tip squash in order to preserve them practivally. |
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Definition
Stages of Mitosis:
After interphase, the cell contains enough genetic material for two cells. The cell progresses to Prophase where the chromosomes condense and form chromatids, centrioles allign themselves around the nuclear envelope and form the poles of the spindle. The nuclear envelope then breaks down. During Metaphase, the chromosomes line up at the centre of the cell attaching themselves to the spindle fibres. During Anaphase the centromeres split, the chromatids are pulled towards opposite sides of the cells and the spindle breaks down. During Telophase, the chromosomes unravel two nuclear envelopes form around the chromatids. Then the cytoplasm divides, forming two new cells.
Preparing and staining a root tip squash: |
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Term
| Explain what is meant by the terms stem cell, pluripotency and totipotency and discuss the way society uses scientific knowlege to make decisions about the use of stem cells in medical therapies. |
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Definition
Stem Cell - A cell from which different kinds of cells can form.
Pluripotency - Cells which can produce most cell types but not all of them.
Totipotency - Cells which can produce each and every cell in the body.
Decisions about the use of stem cells can be made by regulatory authorities relating to human embryo research. Scientific knowledge is used find benefits of using stem cells like them developing into specialised tissues, and how to go about aquiring them, and what risks these processes would pose to humans. |
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Term
| Describe how totipotency can be demonstrated practically using plant tissue culture techniques. |
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Definition
| Most plant cells remain totipotent, so by cutting off small pieces of a plant (explants) you can grow the whole plant. |
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Term
| Explain how cells become specialised through differential gene expression, producing active mRNA leading to synthesis of proteins, which in turn control cell processes or determine cell structure in animals and plants (details of transcription factors are not required at AS) |
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Definition
| Genes can be prevented from being expressed through the attachment of a repressor molecule which will stop the RNA polymerase from transcribing the DNA. |
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Term
| Describe how the cells of multicellular organisms can be organised into tissues, tissues into organs and organs into systems. |
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Definition
| Tissues are a group of specialised cells working together to carry out one function. Organs are a group of tissues working together to carry out a particular function. Organ systems are a group of organs working together to carry out a particular function. |
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Term
| Explain how some phenotypes are affected by alleles at many loci (polygenic inheritance) as well as the environment (e.g. height) and how this can give rise to phenotypes that show continuous variation. |
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Definition
| Phenotypes such as eye colour are determined by many alleles coding, for example, black and blue. So rather than just black and blue eyes, a whole range of colours between black and blue arise which will show continuous variation. |
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Term
| Explain how phenotype is the result of an interaction between genotype and the environment, but the data on the relative contributions of genes and environment is often difficult to interpret. |
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Definition
| The genotype is a result of a combination of particular alleles, but this is not the only factor which determines the phenotype. Height, hair colour, cancers and monoamine oxidase A (MAOA) are all effected by the environment in which an individual is. |
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Term
| [Demonstrate knowledge and understanding of the practical and investigative skills identified in the table of How Science Works in the specification.] |
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Definition
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