The table below shows results from an investigation using red onion cells. Small strips of epidermis were placed in sugar solutions for 20 minutes. A micros...
Question 1 Report
The table below shows results from an investigation using red onion cells. Small strips of epidermis were placed in sugar solutions for 20 minutes. A microscope was then used to find the percentage of cells in which the cell membrane had moved away from the cell wall. Fig. 1 is a drawing of one of these cells. The purple pigment remained inside the large vacuole. The student kept the temperature and the size of each onion strip the same so that concentration was the main variable.
| Sugar concentration / mol dm-3 | Cells with membrane pulled away / % |
|---|---|
| 0.00 | 0 |
| 0.20 | 8 |
| 0.40 | 66 |
| 0.60 | 94 |
(a) What is structure A? [1]
(b) Describe what happened to the percentage of cells as sugar concentration increased. [1]
(c) Explain why the membrane moved away from the cell wall in the 0.60 mol dm-3 solution. [2]
(d) Give one variable that should be controlled in this investigation. [1]
Fig. 1 shows an undrawn scale diagram of cells from the lining of a human small intestine. Each cell has tiny folds called microvilli on its upper surface. Digested food, including glucose, is absorbed from the intestine into blood. Cells in this lining have many mitochondria because some substances are moved by active transport. The doctor uses this diagram to explain why damage to the lining can reduce the amount of food absorbed.
(a) What are the folds labelled A called? [1]
(b) Describe how these folds increase absorption of glucose. [2]
(c) Give one organelle that releases energy for active transport. [1]
(d) When glucose concentration is lower in the intestine than in blood, what process may move glucose into the blood? [1]
Answer Details
Red onion investigation, (a) Structure A is the cell wall. [1]
Red onion investigation, (b) As sugar concentration increased, the percentage of cells with the membrane pulled away from the wall increased. [1]
Red onion investigation, (c) The 0.60 mol dm-3 solution has a lower water potential than the cell sap. Water leaves the cells by osmosis, causing the cytoplasm and vacuole to shrink and the membrane to pull away from the cell wall. [2]
Red onion investigation, (d) One suitable controlled variable is temperature. Time in solution, onion-strip size, and source onion are also valid. [1]
Small-intestine cells, (a) The folds are microvilli. [1]
Small-intestine cells, (b) Microvilli increase surface area, so more glucose can be absorbed per unit time. [2]
Small-intestine cells, (c) The organelle that releases energy for active transport is a mitochondrion. [1]
Small-intestine cells, (d) If glucose concentration is lower in the intestine than in blood, glucose may move into blood by active transport. [1]
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