Name the three processes involved in the growth of a plant.
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- cell division (1)
- elongation (1)
- differentiation (1)
Explain why cell differentiation is important in the development of an organism.
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- cells become specialised / gain structures for a particular job (1)
- so different cells can carry out different functions / the organism can have different tissues and organs (1)
The table shows the mass of girls aged 12 months on some percentile lines. A girl's mass was on the 50th percentile at 6 months old. At 12 months old her mass is 7.0 kg. Use the table to suggest why a doctor would want to check her growth.
| Percentile | 2nd | 25th | 50th | 75th | 98th |
|---|---|---|---|---|---|
| Mass in kg | 7.0 | 8.2 | 8.9 | 9.7 | 11.3 |
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- she has moved from the 50th percentile to the 2nd percentile (1) allow she has dropped down across the percentile lines
- a large change in percentile may show she is not growing properly / has a health problem (1)
A baby has a mass of 3.5 kg at birth. At 6 weeks old the baby's mass is 4.2 kg. Calculate the percentage gain in mass.
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- change in mass = 4.2 − 3.5 = 0.7 kg and 0.7 ÷ 3.5 × 100 (1)
- 20% (1) correct answer with no working scores 2
Many newborn babies lose some mass in the first few days. A baby had a mass of 3.5 kg at birth and 3.22 kg at 5 days old. Calculate the percentage loss in mass.
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- change in mass = 3.5 − 3.22 = 0.28 kg and 0.28 ÷ 3.5 × 100 (1)
- 8% (1) correct answer with no working scores 2; do not accept 8.7% (divided by final mass)
Describe the function of embryonic stem cells, stem cells in adult animals and meristems in plants.
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- embryonic stem cells can differentiate into any type of cell / produce all the specialised cells of the developing embryo (1)
- stem cells in adult animals can differentiate into a limited range of cell types to replace damaged or worn-out cells, such as blood cells from bone marrow (1)
- meristems produce cells that can differentiate into any type of plant cell, allowing the plant to keep growing (1) allow found at tips of roots and shoots for growth
Discuss the potential benefits and risks associated with the use of stem cells in medicine.
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| Level | Marks | What the answer does |
|---|---|---|
| 3 | 5–6 | Gives a balanced discussion with several benefits and several risks, which are explained, and may include a reasoned conclusion. Scientific terms are used accurately. |
| 2 | 3–4 | Gives at least one benefit and one risk, with some explanation. The discussion may be one-sided or lack detail. |
| 1 | 1–2 | States one or two simple points about benefits or risks, with little or no explanation. |
Indicative content
- benefits: could treat conditions such as diabetes or paralysis
- benefits: could replace damaged or diseased cells with healthy cells
- benefits: new tissues could be grown for transplants
- risks: stem cells may divide out of control and form a tumour
- risks: viruses in donated stem cells could be passed to the patient
- risks: the immune system may reject cells from another person
- ethical or religious objections to using embryos
- a conclusion that weighs the benefits against the risks