1. 1
   A student examines three different specialised cells taken from the human body and from a plant root: a sperm cell, a root hair cell and a nerve cell. Each cell has a distinctive shape that is closely related to the job it performs, even though all three cells originally developed from unspecialised cells.

   (a)

   A student examines a sperm cell, a root hair cell and a nerve cell under a microscope. All three cells are specialised for a particular function, yet each has a very different shape. Which structural feature allows a sperm cell to swim towards an egg cell?

   [1 mark]

   • AA long tail (flagellum) that whips from side to side to propel the cell forward
   • BA large surface area created by finger-like extensions of the membrane
   • CA cell wall made of cellulose that gives the cell extra rigidity
   • DAn extended cytoplasmic branch that carries electrical impulses

   (b)

   Which feature of a root hair cell increases the surface area available for the uptake of water and mineral ions from the soil?

   [1 mark]

   • AA coiled tail that spins to draw water inward
   • BA long hair-like extension that grows out into the soil
   • CMany mitochondria packed into the tip of the cell
   • DA thickened cell wall that resists osmotic pressure

   (c)

   The nerve cell examined by the student has a long, thin extension called an axon and many branched connections at its ends. Explain how these two features relate to the function of a nerve cell.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A patient with type 1 diabetes wants to know whether stem cell treatment could help restore her ability to produce insulin. Doctors explain that stem cells can be obtained from an early embryo, from adult bone marrow, or produced specifically for the patient using therapeutic cloning. The patient and her family have concerns about the risks and ethics of the different approaches.

   (a)

   A patient with type 1 diabetes is being considered for treatment using stem cells taken from her own early embryo produced by therapeutic cloning. Which statement explains the main advantage of using the patient's own cloned embryo as the stem cell source, rather than stem cells from a donor embryo?

   [1 mark]

   • AThe cloned cells cannot carry any viral infection, unlike donor cells
   • BThe cloned cells divide more quickly than donor cells, so treatment takes less time
   • CThe cloned cells contain the patient's own genetic material, so they are less likely to be rejected by her immune system
   • DThe cloned cells are already fully differentiated into pancreas cells

   (b)

   Which of the following is a valid ethical or religious objection that some people raise against the use of embryonic stem cells in medical treatment?

   [1 mark]

   • AAdult stem cells are obtained only from meristem tissue in plants
   • BEmbryonic stem cells cannot differentiate into more than one type of adult cell
   • CBone marrow stem cells are always genetically identical to embryonic stem cells
   • DSome people believe a human embryo has the right to life and should not be destroyed to obtain stem cells

   (c)

   Give one risk, other than an ethical objection, of using embryonic stem cells in medical treatment, and one potential benefit of this treatment for the patient.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A conservation charity is trying to protect a rare orchid species from extinction. Scientists take a small sample of cells from the meristem tissue at the tip of a surviving orchid shoot and use it to grow hundreds of genetically identical plantlets in a laboratory.

   (a)

   Explain why meristem cells, rather than fully differentiated leaf cells, are used to produce the new plantlets.

   [3 marks]

   (b)

   The charity also wants to use the same meristem cloning technique to help a farmer produce large numbers of a crop plant that shows natural resistance to a fungal disease. Explain how cloning this crop plant from meristem cells could benefit the farmer, and suggest one possible disadvantage of growing a large field of genetically identical cloned plants.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A biology textbook explains that stem cells behave differently in animals and plants: 'Most animal cells differentiate at an early stage of development, whereas many plant cells retain the ability to differentiate throughout their life.'

   (a)

   A textbook states that 'most animal cells differentiate at an early stage of development, whereas many plant cells retain the ability to differentiate throughout their life.' Using your knowledge of stem cells and cell differentiation, explain what this statement means and discuss why this difference between animals and plants is biologically important.

   [6 marks]

   (b)

   Bone marrow stem cells can already be used to treat some blood disorders by forming new blood cells, but scientists are also researching the use of embryonic stem cells to treat conditions such as paralysis caused by spinal cord injury. Evaluate the potential benefits and risks of developing embryonic stem cell treatments for conditions like paralysis, compared with continuing to rely on established bone marrow stem cell treatments.

   [6 marks]

   Total for question 4: 12 marks

End of questions