Voice of the genomeEdexcel A-Level Biology A: Topic test

1. 1
   A student is shown two electron micrographs, one of a bacterium and one of a cell from an animal.

   (a)

   Which structure would be found in the animal cell but not in the bacterium?

   [1 mark]

   • ARibosomes
   • BCircular DNA
   • CPlasmids
   • DA nucleolus

   (b)

   What is the function of the capsule that surrounds many bacteria?

   [1 mark]

   • AIt is the site of protein synthesis
   • BIt protects the bacterium from drying out and from attack by white blood cells
   • CIt propels the bacterium through liquid
   • DIt carries genes for antibiotic resistance

   (c)

   Describe two ways in which the DNA of the bacterium differs from the DNA of the animal cell.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Goblet cells in the lining of the airways make and secrete mucus, which contains a glycoprotein called mucin. The mucin is made inside the cell and released from the cell surface.

   (a)

   Where is the polypeptide of the mucin synthesised?

   [1 mark]

   • AOn ribosomes attached to the rough endoplasmic reticulum
   • BIn the Golgi apparatus
   • CIn lysosomes
   • DOn the smooth endoplasmic reticulum

   (b)

   What is the role of the Golgi apparatus in the production of mucin?

   [1 mark]

   • AIt synthesises amino acids for the polypeptide
   • BIt digests the polypeptide into smaller fragments
   • CIt adds carbohydrate to the protein and packages it into vesicles for secretion
   • DIt translates the mRNA for the polypeptide

   (c)

   Describe how the mucin is moved from the rough endoplasmic reticulum to the outside of the cell.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A kidney contains many different tissues, including epithelial tissue in the tubules, and connective tissue and smooth muscle in the walls of blood vessels. The kidneys of a child grow as the child grows.

   (a)

   Explain what is meant by the terms tissue, organ and system, using the kidney as an example.

   [3 marks]

   (b)

   Explain how mitosis allows the kidney to grow while producing daughter cells that are genetically identical to the parent cells.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Mouse embryos are widely used in research. A mouse has 20 pairs of homologous chromosomes in each body cell, and a male mouse in a breeding colony is heterozygous for two genes, A/a and B/b, that are on different chromosomes.

   (a)

   Explain how meiosis in the male mouse produces gametes that are genetically different from each other, including the number of chromosome combinations that independent assortment alone could produce.

   [6 marks]

   (b)

   Embryonic stem cells from mouse embryos can be grown in culture. Explain how stem cells become specialised and discuss the issues involved in using human embryonic stem cells in medical therapies.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A somatic cell from an animal species has a diploid number of 12 chromosomes. It has just completed interphase and is about to enter mitosis.

   (a)

   How many chromatids are present in the cell at the start of mitosis?

   [1 mark]

   • A6
   • B12
   • C24
   • D48

   (b)

   At which stage of mitosis do the sister chromatids separate?

   [1 mark]

   • AAnaphase
   • BMetaphase
   • CProphase
   • DTelophase

   (c)

   A drug blocks DNA replication during interphase. Explain why a cell treated with this drug cannot complete mitosis normally.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   If two sperm fertilised the same egg, the zygote would have three sets of chromosomes and would not develop normally. Mammalian eggs are surrounded by a layer of glycoprotein called the zona pellucida.

   (a)

   What prevents more than one sperm from fertilising the egg?

   [1 mark]

   • AThe acrosome reaction digests the zona pellucida for all sperm
   • BCortical granules release their contents, making the zona pellucida impenetrable to other sperm
   • CThe sperm tail breaks off as the sperm enters the egg
   • DThe nuclei of the sperm and egg fuse

   (b)

   A human sperm and a human egg each contain 23 chromosomes. How many chromosomes are in the zygote, and in each cell after the first mitotic division of the zygote?

   [1 mark]

   • A23 and 23
   • B46 and 23
   • C23 and 46
   • D46 and 46

   (c)

   Describe the role of the acrosome in fertilisation.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   In Himalayan rabbits the fur on the ears, nose and feet is black but the fur on the rest of the body is white. All the body cells of a rabbit have the same genotype. The allele for black fur codes for a pigment-making enzyme that is inactive above about 34 °C, and the skin of the extremities is cooler than the skin of the rest of the body.

   (a)

   Explain why the fur on the extremities is black although all the cells of the rabbit have the same genotype.

   [3 marks]

   (b)

   Environmental factors can also alter the activity of genes without changing the base sequence of the DNA. Explain how DNA methylation and histone modification can do this, and how the effect may be passed on to daughter cells.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A farmer notices that the milk yield of the cows in a herd varies continuously, from 15 to 40 litres per day. Milk yield depends on many genes and on the cows' diet. The cells of the mammary glands make the milk protein casein, but liver cells do not, although they have the same genes.

   (a)

   Explain why milk yield shows continuous variation, and why the calves of high-yielding cows are not all high-yielding.

   [6 marks]

   (b)

   Explain why mammary gland cells make casein but liver cells do not, and describe how casein is processed and secreted from a mammary gland cell.

   [6 marks]

   Total for question 8: 12 marks

End of questions