15.2. Control and coordination in plants
A subsection of Biology, 9700, through 15. Control and coordination
Listing 10 of 32 questions
The passage below summarises the effects of auxin on the growth of a shoot. Complete the passage by using the most appropriate scientific term. Auxin is synthesised in the growing tips of shoots (apical buds). It is transported from here down the shoot by ………………………………… from cell to cell and also to a lesser extent by ………………………………… flow in the ………………………………… . Auxin seems to be involved in determining whether a plant grows upwards or whether it branches sideways. When the apical bud is actively growing, it tends to stop lateral buds from growing. This is called apical ………………………………… . The plant grows upwards rather than branching out sideways. However, if the apical bud is cut off, the lateral buds start to grow. It is thought that removal of the apical bud causes the concentration of auxin in lateral buds to ………………………………… so the buds can now grow by cell ………………………………… and cell ………………………………… .
9700_w13_qp_43
THEORY
2013
Paper 4, Variant 3
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Gibberellin is a plant growth hormone that has a role in germination and in stem elongation. Outline how gibberellin is involved in activating genes for stem elongation. Outline the role played by gibberellin in the germination of wheat seeds. The length of stem in pea plants is controlled by a single gene. Pea plants can be either tall or short. A study was carried out to investigate the effect of applying gibberellin to short pea plants. Two groups of short pea seedlings were used, group P and group Q. • Group P consisted of 20 seedlings to which a paste containing gibberellin had been applied two days after germination. • Group Q consisted of 20 seedlings to which a paste without gibberellin had been applied two days after germination. • The length of stem of the pea plants was recorded at intervals over 20 days. The results are shown in . Explain the role of the gene controlling stem length in pea plants.
9700_w18_qp_42
THEORY
2018
Paper 4, Variant 2
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Gibberellin is a plant hormone that has an important role in seed germination. is a diagram of a section through a barley seed . embryo aleurone layer endosperm On : • Draw one arrow, labelled G, to show the movement of gibberellin during germination. • Draw one arrow, labelled A, to show the movement of amylase during germination. Outline the role of amylase in seed germination. The germination of three groups of seeds of the plant Penstemon digitalis was investigated. The seeds were soaked for 24 hours in distilled water or in a solution of gibberellin. They were then sown on filter paper in dishes and kept moist for 10 days. shows the results for each group. percentage germination group C 1000 mg dm–3 gibberellin solution group B 500 mg dm–3 gibberellin solution group A distilled water time after soaking / days
9700_s22_qp_42
THEORY
2022
Paper 4, Variant 2
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The passage below summarises the effects of gibberellins on seed germination. Complete the passage by using the most appropriate scientific term. When a seed is shed from the parent plant, it is in a state of ………………………………… , which means it is metabolically inactive. When water is absorbed by a seed, it stimulates the production of gibberellin by the ………………………………… within the seed. The gibberellin stimulates the synthesis of amylase by cells in the ………………………………… layer. Amylase hydrolyses starch molecules in the ………………………………… converting them to soluble ………………………………… molecules. These molecules are converted to glucose which is transported to the embryo, providing a source of carbohydrate that can be respired to provide ………………………………… as the embryo begins to grow. Gibberellin causes these effects by regulating genes that are involved in the synthesis of amylase. It has been shown that application of gibberellin to seeds can cause an increase in the ………………………………… of the DNA coding for amylase.
9700_w13_qp_41
THEORY
2013
Paper 4, Variant 1
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The passage below summarises the effects of gibberellins on seed germination. Complete the passage by using the most appropriate scientific term. When a seed is shed from the parent plant, it is in a state of ………………………………… , which means it is metabolically inactive. When water is absorbed by a seed, it stimulates the production of gibberellin by the ………………………………… within the seed. The gibberellin stimulates the synthesis of amylase by cells in the ………………………………… layer. Amylase hydrolyses starch molecules in the ………………………………… converting them to soluble ………………………………… molecules. These molecules are converted to glucose which is transported to the embryo, providing a source of carbohydrate that can be respired to provide ………………………………… as the embryo begins to grow. Gibberellin causes these effects by regulating genes that are involved in the synthesis of amylase. It has been shown that application of gibberellin to seeds can cause an increase in the ………………………………… of the DNA coding for amylase.
9700_w13_qp_42
THEORY
2013
Paper 4, Variant 2
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Bread wheat, Triticum aestivum, is a hexaploid that has developed from diploid wild grasses. Outline the process by which T. aestivum has developed from wild grasses. Wheat seeds begin to germinate when they are in warm conditions and can take up water. shows a germinating wheat seedling. root developing vascular bundles shoot apex coleoptile pericarp and testa aleurone layer endosperm scutellum seed The endosperm contains starch stores. There are also small quantities of sucrose stored in the aleurone layer. Water uptake stimulates the production of a plant growth regulator in the seed, which in turn activates the synthesis of enzymes in the aleurone layer. These enzymes hydrolyse starch to maltose and glucose. Name the plant growth regulator involved in the activation of the synthesis of the enzymes. An investigation was carried out into the role of a gene, TaSUT1, which codes for a sucrose transporter protein, in the germination of wheat seeds. • Wheat seeds were germinated and left to grow for 3, 7 or 10 days. • Samples of tissues from the roots, seeds and shoots of the seedlings were tested for the presence of mRNA transcribed from TaSUT1. • The extracted mRNA was mixed with a probe, and then placed on agarose gel across which a voltage was applied. The results are shown in . root seed days shoot Suggest why the researchers looked for mRNA transcribed from the TaSUT1 gene, rather than for the gene itself. Explain what the results in indicate about the sequence of activity of TaSUT1, from day 3 to day 10, in the root, seed and shoot of a seedling. TaSUT1 codes for the sucrose transporter protein, SUT. This protein transports only sucrose. To investigate where this protein was present in a germinating wheat seedling, a fluorescent antibody for SUT was added to sections of tissues from the seedling. Suggest how this enabled the researchers to determine the areas where SUT was located. Immediately after germination began, SUT was found in the membranes of cells in the aleurone layer. It was also determined that the most common sugar in the endosperm in the first hours after germination was sucrose. Explain how these results support the hypothesis that the first source of sugar for the embryo during germination is sucrose from the aleurone layer and not sugars produced by the hydrolysis of starch. SUT appeared in the developing phloem tissue within three days of the start of germination. Outline how sucrose is transported in phloem.
9700_w15_qp_41
THEORY
2015
Paper 4, Variant 1
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Bread wheat, Triticum aestivum, is a hexaploid that has developed from diploid wild grasses. Outline the process by which T. aestivum has developed from wild grasses. Wheat seeds begin to germinate when they are in warm conditions and can take up water. shows a germinating wheat seedling. root developing vascular bundles shoot apex coleoptile pericarp and testa aleurone layer endosperm scutellum seed The endosperm contains starch stores. There are also small quantities of sucrose stored in the aleurone layer. Water uptake stimulates the production of a plant growth regulator in the seed, which in turn activates the synthesis of enzymes in the aleurone layer. These enzymes hydrolyse starch to maltose and glucose. Name the plant growth regulator involved in the activation of the synthesis of the enzymes. An investigation was carried out into the role of a gene, TaSUT1, which codes for a sucrose transporter protein, in the germination of wheat seeds. • Wheat seeds were germinated and left to grow for 3, 7 or 10 days. • Samples of tissues from the roots, seeds and shoots of the seedlings were tested for the presence of mRNA transcribed from TaSUT1. • The extracted mRNA was mixed with a probe, and then placed on agarose gel across which a voltage was applied. The results are shown in . root seed days shoot Suggest why the researchers looked for mRNA transcribed from the TaSUT1 gene, rather than for the gene itself. Explain what the results in indicate about the sequence of activity of TaSUT1, from day 3 to day 10, in the root, seed and shoot of a seedling. TaSUT1 codes for the sucrose transporter protein, SUT. This protein transports only sucrose. To investigate where this protein was present in a germinating wheat seedling, a fluorescent antibody for SUT was added to sections of tissues from the seedling. Suggest how this enabled the researchers to determine the areas where SUT was located. Immediately after germination began, SUT was found in the membranes of cells in the aleurone layer. It was also determined that the most common sugar in the endosperm in the first hours after germination was sucrose. Explain how these results support the hypothesis that the first source of sugar for the embryo during germination is sucrose from the aleurone layer and not sugars produced by the hydrolysis of starch. SUT appeared in the developing phloem tissue within three days of the start of germination. Outline how sucrose is transported in phloem.
9700_w15_qp_42
THEORY
2015
Paper 4, Variant 2
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Gibberellin is a plant growth regulator involved in barley seed germination. Production of gibberellin is stimulated by the uptake of water. State the location of gibberellin synthesis in a barley seed during germination. Barley seeds germinate when placed on blotting paper soaked in water. The germination of barley seeds placed on blotting paper soaked in solutions of different water potential was investigated. The success of germination was measured as a germination index for: • barley seeds placed on blotting paper soaked in water • barley seeds placed on blotting paper soaked in 5 solutions of different water potential. The results are shown in . The higher the germination index value, the more successful the germination of the barley seeds. 0.0 – 0.5 – 1.0 – 1.5 – 2.0 – 2.5 germination index water potential / MPa With reference to , describe the relationship between the germination index of barley seeds and water potential. Suggest explanations for the relationship shown in . During barley seed germination, gibberellin stimulates the synthesis of enzymes. State the name of one of these enzymes and the precise location of its synthesis. enzyme location Some plants are grown commercially for their flowers. Many of these plants are varieties that have short stems. Two factors that affect the height of stems are: • gibberellin • the Le / le gene. The Le / le gene has two alleles, Le and le. Suggest an advantage of growing a short-stemmed variety of a flowering plant. Explain how the Le / le gene and gibberellin are involved in affecting the height of plant stems.
9700_w21_qp_41
THEORY
2021
Paper 4, Variant 1
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Questions Discovered
32