Which statement about chromosomes is correct?
- They are small rings of DNA found in bacteria
- They are found in the nucleus, are made of DNA and carry many genes
- They are the part of the cell where respiration takes place
- They are made of protein and carry one gene each
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Answer: B B (1)
Describe what happens during the cell cycle in a body cell, up to the formation of two daughter cells.
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- the cell grows / increases the number of sub-cellular structures (such as ribosomes and mitochondria) (1)
- DNA replicates to form two copies of each chromosome (1)
- in mitosis, one set of chromosomes is pulled to each end of the cell and the nucleus divides (1)
- the cytoplasm and cell membranes divide to form two identical cells (1)
- Max 3.
A scientist looks at the tip of a growing root. Many of the cells are dividing. Name the type of cell division taking place and explain why it is important in a plant.
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- mitosis (1)
- for growth (of the plant) / development / production of new cells (1)
Describe the function of stem cells in (a) human embryos, (b) adult bone marrow, (c) plant meristems.
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- (a) can differentiate into most types of human cell (1)
- (b) can form many types of cell, including blood cells (1)
- (c) can differentiate into any type of plant cell, throughout the life of the plant (1)
Why are stem cells produced by therapeutic cloning less likely to be rejected by the patient's body?
- The embryo is produced from bone marrow
- The embryo has the same genes as the patient
- The cells have been killed by treatment
- The embryo contains no DNA
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Answer: B B (1)
Give two ways in which stem cells from meristems can be used.
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- to clone rare species to protect them from extinction (1)
- to produce clones of crop plants with special features (such as disease resistance) quickly and economically / in large numbers for farmers (1)
Stem cells from human embryos may one day be used to treat conditions such as diabetes and paralysis. Evaluate the use of stem cells in medical treatments.
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| Level | Marks | What the answer does |
|---|---|---|
| 3 | 5–6 | A balanced evaluation that considers benefits, risks and ethical or religious objections in detail, with a justified conclusion. Scientific terms are used accurately. |
| 2 | 3–4 | Some benefits and some risks or objections are described, but the evaluation is not fully balanced or there is no clear conclusion. |
| 1 | 1–2 | Simple points are made on either benefits or risks only, with little or no development. |
Indicative content
- stem cells can differentiate into many types of cell, so can replace damaged or lost tissue
- may help conditions such as diabetes and paralysis
- in therapeutic cloning, the embryo has the same genes as the patient, so the cells are not rejected
- risk of transfer of viral infection
- some people have ethical or religious objections to using embryos
- conclusion that weighs benefit to patients against risks and objections