15.2. Control and coordination in plants
A subsection of Biology, 9700, through 15. Control and coordination
Listing 10 of 32 questions
The leaves of Mimosa pudica plants are made of a number of structures known as pinnae. The pinnae fold when the leaf is touched. This closes the leaf. shows an open leaf of M. pudica before it is touched. shows the same leaf that has closed after being touched. A open (not touched) pinnae B closed A touch stimulus to an M. pudica leaf causes an action potential to be generated. The action potential results in changes in cells, which cause the leaf to close. shows the mechanism in M. pudica cells that causes the leaf to close. action potential after touch stimulus protons pumped into extensor cells Cl − and K+ ions move out of cells water moves out of cells by osmosis cells become flaccid The leaves of M. pudica and the leaves of Venus fly traps move in response to touch stimuli, but the mechanisms that cause the responses are different. Describe the differences between the mechanism shown in and the mechanism that causes the closure of the modified leaves in Venus fly traps. The rate of photosynthesis decreases by 40% when the leaves of M. pudica close. Explain why the rate of photosynthesis decreases when the leaves of M. pudica close. Plants can carry out cyclic photophosphorylation and non‑cyclic photophosphorylation during the light‑dependent stage of photosynthesis. These processes occur at the grana of chloroplasts. Outline the similarities and differences between cyclic photophosphorylation and non‑cyclic photophosphorylation.
9700_w24_qp_41
THEORY
2024
Paper 4, Variant 1
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The leaves of Mimosa pudica plants are made of a number of structures known as pinnae. The pinnae fold when the leaf is touched. This closes the leaf. shows an open leaf of M. pudica before it is touched. shows the same leaf that has closed after being touched. A open (not touched) pinnae B closed A touch stimulus to an M. pudica leaf causes an action potential to be generated. The action potential results in changes in cells, which cause the leaf to close. shows the mechanism in M. pudica cells that causes the leaf to close. action potential after touch stimulus protons pumped into extensor cells Cl − and K+ ions move out of cells water moves out of cells by osmosis cells become flaccid The leaves of M. pudica and the leaves of Venus fly traps move in response to touch stimuli, but the mechanisms that cause the responses are different. Describe the differences between the mechanism shown in and the mechanism that causes the closure of the modified leaves in Venus fly traps. The rate of photosynthesis decreases by 40% when the leaves of M. pudica close. Explain why the rate of photosynthesis decreases when the leaves of M. pudica close. Plants can carry out cyclic photophosphorylation and non‑cyclic photophosphorylation during the light‑dependent stage of photosynthesis. These processes occur at the grana of chloroplasts. Outline the similarities and differences between cyclic photophosphorylation and non‑cyclic photophosphorylation.
9700_w24_qp_43
THEORY
2024
Paper 4, Variant 3
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One example of chemical control and co-ordination in plants is in the breakdown of food reserves during the germination of cereal grains, such as wheat. is a diagram of a grain of wheat. The numbered arrows indicate the sequence of events that occurs after the uptake of water by the grain of wheat. A B C Name structures A, B and C, shown in . A B C With reference to the three numbered arrows in , describe the sequence of events that follows the uptake of water by the grain of wheat. Growth in plants occurs in areas such as shoot and root tips. Growth occurs by cell division and cell elongation. shows the effect of the plant growth regulator auxin on mean cell length in the shoot tips of wheat seedlings. mean cell length / μm time / minutes auxin applied With reference to , calculate the overall rate of increase in mean cell length over the time period shown. overall rate of increase The pH of the cell walls decreased after the application of auxin. Outline the events that occurred to cause this decrease in pH. Explain the increase in the length of the cells following the decrease in pH of the cell walls.
9700_m17_qp_42
THEORY
2017
Paper 4, Variant 2
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An investigation was carried out to study the effect of different intensities of blue light on the percentage germination of barley seeds. Barley seeds were exposed to blue light for a period of seven days. All other variables were kept constant. The results are shown in Table 9.1. Table 9.1 light intensity / arbitrary units percentage germination 0 98.0 76.9 45.0 14.7 The effect of blue light on the concentration of abscisic acid (ABA) was also investigated. ABA concentration was measured at intervals over seven days in barley seeds exposed to blue light at an intensity of 57 arbitrary units. The results are shown in Table 9.2. Table 9.2 day concentration of ABA / arbitrary units 0 For comparison, in the dark the concentration of ABA in barley seeds fell from 100 au at the start (day 0) to 45 au on day 1 and did not increase from day 1 to day 7. ABA is thought to affect gibberellin synthesis or activity. Using the information in Table 9.1 and Table 9.2, describe the effect of blue light on the germination of barley seeds and suggest an explanation for this effect. After germination, auxin is important in the growth of barley plants. Describe and explain the role of auxin in cell elongation.
9700_m24_qp_42
THEORY
2024
Paper 4, Variant 2
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An investigation was carried out into the effects of a plant growth regulator, auxin (IAA), on apical dominance. • The apical buds of 20 pea plants were cut off and discarded. • The cut surfaces of 10 pea plants were coated with an inert paste containing auxin. • The cut surfaces of the other group of 10 pea plants were coated with the inert paste alone. • A further group of 10 pea plants did not have their apical buds removed and were not coated with paste. This was a control group. The lengths of the side shoots of plants in each of the three groups were measured at regular time intervals and mean values calculated. The results are shown in . paste paste alone alone paste paste + auxin auxin control control mean side shoot length / mm days after treatment × × × × × × × × × × × × × control paste + auxin paste alone Explain why the side shoots increase in length when the terminal buds are removed. Calculate the percentage difference, at 13 days, in the mean length of side shoots of plants treated with paste alone compared with the plants treated with paste and auxin. Give your answer to the nearest whole number. Show your working. Answer % Using data from , describe and explain the effect of auxin on the growth of side shoots.
9700_w10_qp_41
THEORY
2010
Paper 4, Variant 1
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An investigation was carried out into the effects of a plant growth regulator, auxin (IAA), on apical dominance. • The apical buds of 20 pea plants were cut off and discarded. • The cut surfaces of 10 pea plants were coated with an inert paste containing auxin. • The cut surfaces of the other group of 10 pea plants were coated with the inert paste alone. • A further group of 10 pea plants did not have their apical buds removed and were not coated with paste. This was a control group. The lengths of the side shoots of plants in each of the three groups were measured at regular time intervals and mean values calculated. The results are shown in . paste paste alone alone paste paste + auxin auxin control control mean side shoot length / mm days after treatment × × × × × × × × × × × × × control paste + auxin paste alone Explain why the side shoots increase in length when the terminal buds are removed. Calculate the percentage difference, at 13 days, in the mean length of side shoots of plants treated with paste alone compared with the plants treated with paste and auxin. Give your answer to the nearest whole number. Show your working. Answer % Using data from , describe and explain the effect of auxin on the growth of side shoots.
9700_w10_qp_42
THEORY
2010
Paper 4, Variant 2
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Questions Discovered
32