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BIOLOGY EDEXCEL A Level (TOPIC 3) Exam Questions with correct Answers latest 2025 100% Verified.
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BIOLOGY EDEXCEL A Level (TOPIC 3) Exam Questions with correct Answers latest 2025 100% Verified.
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Biology Edexcel A Level (TOPIC 3)1.13: Explain why an ovum needs to be large. - ANS- The ovum needs to be large relative to
the sperm so it can be more easily found and act as a bigger target.
2.37: Distinguish between the two types of variation in terms of the number of genes that have
influence and the relative influence of the environment. - ANS- continuous
-many genes
-impacted by the environment
discontinuous
-one/two genes
-not really affected by environment
3.1: Define what prokaryote and eukaryote cells are and give an example of a type of organism
for each group. - ANS- Prokaryote: "before nucleus"- these are bacteria and cyanobacteria
Eukaryotes: "true nucleus"- these are all other cells, including plant and animal cells
3.10: Draw a flowchart that shows how different organelles and nucleus are involved in the
process of protein production and trafficking in a cell. - ANS- 1. transcription of DNA to mRNA
2. mRNA leaves nucleus
3. protein made on ribosomes enter RER
4. protein moves through the ER assuming 3D shape (folding)
5. vesicles pinched off the RER contain the protein
6. vesicles from RER fuse to form the flattened sacs of Golgi Apparatus
7. proteins are modified within the Golgi Apparatus
8. vesicles pinched off the GA contained modified protein
9. vesicles fuse with GA cell surface membrane and releases it by exocytosis
3.11: Describe and explain the role of the RER and golgi apparatus in protein production and
modification. - ANS- RER- produces proteins in ribosomes and folds them assuming 3D shape
Golgi Apparatus- modified within here, e.g.: add glycoprotein
3.12: Draw an ovum (egg cell), label the structures and describe their functions. - ANS- Haploid
Nucleus: contains genetic code
Mitochondria: used for energy
Cortical Granules: involved in cortical reaction to prevent polyspermy
Lipid Droplets: used as an energy store
Cell Surface Membrane: controls what enters and exits the cell
Jelly Coat: prevent polyspermy/protection
, 3.14: Draw a sperm cell, label the structures and describe their function. - ANS- Acrosome:
takes part in acrosome reaction to digest zona pellucida and follicle cells
Haploid Nucleus: contains genetic code
Middle Piece: contains mitochondria
Flagellum: make sperm motile
Mitochondria: energy store
3.15: Draw a flow chart that shows how a sperm reaches an ovum and fertilisation is achieved
(including the stages in the acrosome reaction, the cortical reaction and fertilisation of the
nuclei). - ANS- 1. sperm reaches ovum
2. acrosome reaction is triggered by chemicals from the ovum (follicle cell)
3. acrosome swells and fuses with cell surface membrane of sperm
4. digestive enzymes released
5. enzymes digest follicle cells and jelly coat
6. sperm moves to egg cell surface membrane and fuses
7. sperm nucleus and egg nuclei fuse after sperm nuclei moves through egg cell surface
membrane
8. cortical grannuels release enzymes and thicken jelly coat
3.16: Define the terms chromosome, homologous pair, locus, gamete, haploid, diploid. - ANS-
Chromosome- DNA molecule, histone proteins
Homologous Pair- Pair of chromosomes that have same genes
Locus: Location (of gene on chromosomes)
Gamete: Sex cell, produced in mitosis
Haploid: Half number of chromosomes
Diploid: Regular number of chromosomes
3.17: Explain the terms linkage of genes and sex linkage. - ANS- Genetic Linkage: is the
tendency of alleles that are located close together on a chromosome to be inherited together
during meiosis phase of sexual reproduction
Sex Linkage: colour blindness is an example of sex-linkage; this means that genes involved are
located on the sex chromosomes
3.18: Explain why alleles at adjacent loci on the same chromosomes are more likely to be linked
compared to alleles at distant loci on the same chromosomes. - ANS- See Diagram.
3.19: Explain why it is important for gametes to haploid. - ANS- Gametes have to be haploid
(half the number of chromosomes) because when they join, the original diploid chromosome
number will be restored.
3.2: State the symbols used for millimeters, micrometers and nanometers and be able to convert
measurements - ANS- Millimeters to Micrometers: divide by 1000
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