1. 1
   A microbiologist inoculates a nutrient agar plate with a single bacterium and incubates it at a suitable warm temperature. Under these conditions the bacteria divide by binary fission once every 20 minutes. The microbiologist later examines a colony from the plate using a light microscope fitted with an eyepiece graticule to measure individual cell dimensions.

   (a)

   Which term describes the type of cell division bacteria use to reproduce, as described above?

   [1 mark]

   • ABinary fission
   • BMitosis
   • CMeiosis
   • DDifferentiation

   (b)

   Which sub-cellular structure found in the bacterial cell would not be present in an animal cell such as a skin cell?

   [1 mark]

   • ACytoplasm
   • BA single circular loop of DNA
   • CCell membrane
   • DRibosomes

   (c)

   The microbiologist starts with a single bacterium on the agar plate. Calculate the number of bacteria present after 2 hours of division at the rate described above. Show your working.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   After a small injury to the liver, surrounding liver cells begin to divide rapidly to replace the damaged tissue. Each new cell produced is genetically identical to the parent cell that divided, and the cell number gradually returns to normal as repair is completed.

   (a)

   What is the name of the type of cell division responsible for producing two genetically identical daughter cells during this repair process?

   [1 mark]

   • AMeiosis
   • BBinary fission
   • CMitosis
   • DFertilisation

   (b)

   During which stage of the cell cycle does the DNA in a liver cell replicate, forming two copies of each chromosome, before division occurs?

   [1 mark]

   • AMitosis
   • BCytokinesis
   • CFertilisation
   • DGrowth

   (c)

   State two ways in which the new liver cells produced by this repair process are similar to the original cell they came from.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A gardener grows tomato plants hydroponically, in a nutrient solution that has a much lower concentration of dissolved mineral ions than the solution inside the plant's root hair cells. The roots absorb both water and mineral ions from this dilute solution.

   (a)

   The roots absorb mineral ions from the dilute nutrient solution into the root hair cells, moving them against their concentration gradient. Name this process and explain why the root hair cells need a good supply of oxygen for it to occur.

   [3 marks]

   (b)

   Explain how water moves from the dilute nutrient solution into the root hair cells, and suggest one feature of a root hair cell that increases the rate at which it can absorb water.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A patient with severe burns to a large area of skin is treated using a sheet of laboratory-grown skin tissue. Scientists produced this tissue by taking a small sample of stem cells from an unaffected area of the patient's own skin and culturing them under controlled conditions in a laboratory, before grafting the resulting tissue onto the wound.

   (a)

   Explain how the stem cells taken from the patient's skin could be used to produce a large sheet of new skin tissue containing different specialised cell types, and give one advantage of using the patient's own stem cells rather than stem cells from a donor embryo.

   [6 marks]

   (b)

   Before implanting the tissue, a scientist examines a sample of the new skin cells using an electron microscope rather than a light microscope. Describe two sub-cellular structures the scientist would expect to see inside a healthy skin cell, and explain why an electron microscope is more suitable than a light microscope for this examination.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A species of earthworm relies entirely on diffusion across its thin, moist skin to obtain the oxygen it needs, with no lungs or gills. A much larger burrowing mammal of similar overall body shape instead obtains oxygen using lungs supplied by a dense network of blood vessels.

   (a)

   Compared with the larger mammal, the earthworm has a much smaller body size. Which statement best explains why diffusion alone can supply the earthworm with enough oxygen?

   [1 mark]

   • AIt has a large surface area to volume ratio, so diffusion distances inside the body are short
   • BIt has a very low metabolic rate, so its cells need almost no oxygen
   • CIts skin is impermeable, which keeps oxygen from escaping once absorbed
   • DIt has fewer mitochondria in its cells than the mammal

   (b)

   Which feature would most effectively increase the rate of diffusion of oxygen across an exchange surface such as the earthworm's skin?

   [1 mark]

   • AIncreasing the distance across the exchange surface
   • BIncreasing the surface area of the exchange surface
   • CDecreasing the blood supply to the exchange surface
   • DDecreasing the concentration gradient across the surface

   (c)

   Explain why the larger mammal needs specialised gas exchange organs (lungs) and a transport system, whereas the earthworm does not.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A palm tree produces both root hair cells at the tips of its roots and phloem cells running through its stem. Both of these specialised cell types develop from unspecialised cells found at the growing tips of the plant.

   (a)

   What name is given to the region of plant tissue where unspecialised cells divide and later differentiate into different cell types?

   [1 mark]

   • AXylem
   • BPhloem
   • CMeristem
   • DCytoplasm

   (b)

   Which statement about plant cell differentiation is correct?

   [1 mark]

   • AOnly cells in a plant embryo are able to differentiate
   • BPlant cells lose the ability to differentiate once the plant is fully grown
   • CDifferentiation only occurs in animal cells, not plant cells
   • DMany plant cells retain the ability to differentiate throughout the life of the plant

   (c)

   Explain how the structure of a root hair cell is related to its function of absorbing water and mineral ions from the soil.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   A research team is trialling a new treatment for a patient with type 1 diabetes, in which stem cells taken from a very early human embryo are used to grow replacement insulin-producing cells in the laboratory, for transplant into the patient's pancreas.

   (a)

   Explain why stem cells taken from a very early embryo are able to develop into insulin-producing pancreas cells in the laboratory.

   [3 marks]

   (b)

   Evaluate the use of embryonic stem cells to treat this patient's diabetes, giving one potential benefit and describing potential risks or concerns with the treatment.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A biotechnology company is developing laboratory-grown cartilage to repair a patient's damaged knee joint. Cartilage-producing cells are grown from a small sample of the patient's own stem cells in a bioreactor, and the resulting tissue is examined under a microscope before being implanted.

   (a)

   Explain how the patient's stem cells can be used to produce a large amount of new cartilage tissue, and give one advantage of using the patient's own stem cells for this treatment rather than stem cells from a donor embryo.

   [6 marks]

   (b)

   Before implanting the tissue, a scientist examines a sample of the new cartilage cells using an electron microscope rather than a light microscope. Describe two sub-cellular structures the scientist would expect to see inside a healthy cartilage cell, and explain why an electron microscope is more suitable than a light microscope for this examination.

   [6 marks]

   Total for question 8: 12 marks

End of questions