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Question 1
Plants can respond to their environment during times of stress. |
a) | Suggest two abiotic stresses that might affect plants located next to roads compared to plants located in a woodland.
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b) | Suggest two biotic stresses that might affect plants located next to roads compared to plants located in a woodland.
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c) | Plants that grow nearby roads often need to deal with overcrowding. Describe two ways in which hormones may alter a plant’s growth in response to overcrowding by other plants.
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d) | Both animals and plants use hormones for cell signalling. Describe two similarities between the action of plant and animal hormones.
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Question 2
A scientist investigated how IAA concentration affects the growth of young plants. He removed the tip of the shoot from each plant and removed a 5 mm length of shoot. He placed each shoot into a Petri dish with a glucose solution and a different concentration of IAA solution. He left each dish in the dark for a week and then measured the length of each shoot. His results are shown in the diagram below.
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a) | Suggest why the scientist added glucose solution to each Petri dish.
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b) | Explain why the scientist removed the tip of the shoot from each plant.
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c) | Describe and explain the results shown in the table above.
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d) | Another scientist repeated the investigation using plant roots rather than shoots. Predict the results he would obtain. Explain your answer.
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Question 3
A group of scientists investigated gravitropism in seedlings. They applied different treatments to three seedlings:
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a) | The scientists carried out their experiment in a dark room. Suggest why.
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b) | The scientists placed the seedlings so that their roots were growing horizontally and after a period of time, they recorded the direction of growth of the roots. Their results are shown below.
Explain how IAA may have caused the results for treatments B and C.
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c) | What conclusion can be made from treatment A?
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Question 4
A student investigated phototropism in the shoots of plants. She removed the tip and placed it on one side of the cut shoot as shown in the diagram below.
She allowed the shoot to grow in the presence of a light source for two weeks. The resulting plant shoot is shown in the diagram below.
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a) | Explain the growth curvature of the shoot shown in the diagram above.
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b) | Explain how this behaviour helps to maintain the plant in a favourable environment
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c) | A scientist investigated the effect of temperature on the uptake of IAA by leaves. He sprayed a solution containing IAA onto the lower surface of a leaf at different temperatures. His results are shown in the diagram below.
Describe and explain the results shown in the diagram above.
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d) | Another scientist repeated the same experiment instead spraying the solution onto the upper surface of the leaf. They found that the rate of uptake was lower for all temperatures investigated. Suggest and explain why.
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Question 5
IAA is a specific growth factor found in plants. |
a) | Name the process by which IAA is transported from growing regions to other tissues in the plant.
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b) | The diagram below shows areas of the root in which IAA is distributed during growth.
Describe the relative concentrations of IAA in each of the shaded areas shown above.
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c) | Explain how the distribution of IAA causes the root to bend.
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d) | In the root tips of some plants, IAA is transported out of cells via carrier proteins. The diagram below shows two cells, A and B, in the root tip of a plant.
Explain why this root tip would bend towards the left.
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Question 6
A group of students investigated tropisms in some plant shoots. They placed each shoot in light coming from one direction and used black plastic to cover some parts of the shoots. The treatment for each shoot is described below.
The students left the shoots to grow for three days and then removed the plastic to observe the results. The diagram below shows the shoots after three days. |
a) | The students were investigating phototropism in plant shoots. Name one other tropism. Describe the stimulus the plant responds to in your named tropism.
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b) | Describe two variables the students should control in this investigation.
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c) | What conclusion can be made about the detection of the light stimulus?
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d) | Explain how IAA causes the bending of shoot A.
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Question 7
A group of scientists investigated the role of IAA in how plants respond to light. They cut the tip off the shoot from two seedlings and placed each shoot tip on a block of agar jelly. They then used a piece of glass to separate the sides of the shoot as shown in the diagram below. After 1 day, they measured the amount of IAA in the agar blocks. Their results are shown in the table below.
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a) | The scientists did not use a control experiment in their investigation. Describe how they could set up another shoot to ensure that any response by the shoots was due to the presence of light.
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b) | One of the scientists hypothesised that light causes IAA to move from the illuminated side to the shaded side. Describe the evidence from their results that supports this hypothesis.
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c) | Predict the direction of growth by shoots A and B.
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d) | IAA affects growth in the roots and in the shoots of plants. Describe the difference between how IAA affects the growth of plants in these two places.
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Question 8
A scientist investigated the effect of auxin on some plant stems. He removed the tips of stems and placed them in solutions containing varying concentrations of auxin. He found that higher auxin concentrations resulted in fewer side shoots growing from the stems. |
a) | Explain why higher auxin concentration led to fewer side shoots.
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b) | Auxins are used commercially as weedkillers. Give two other examples of commercial uses of auxin.
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c) | Auxins alter a plant’s growth after the top of shoots are eaten by animals. Suggest how.
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d) | Scientists applied gibberellins and auxins to commercial lemon trees. They observed that these trees grew taller with shorter roots and fewer side branches compared to untreated trees. Suggest explanations for these observations.
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Question 9
Gibberellin is a type of plant hormone that causes an increase in the distance between the leaves on the stem (the internodal length). |
a) | State two other roles of gibberellin in plants.
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b) | Explain why gibberellin is considered a plant hormone.
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c) | An experiment was carried out to investigate the effects of IAA and gibberellin on elongation of seedlings. Internode sections of stems were used and received either IAA, gibberellin, or both hormones. The results of this experiment are shown below.
Describe how a control experiment could have been carried out for this investigation.
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d) | Compare the effects of the three treatments on the elongation of the stems.
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