14.2. Homeostasis in plants
A subsection of Biology, 9700, through 14. Homeostasis
Listing 10 of 36 questions
Stomata are involved in both transpiration and photosynthesis in plants. is a diagram of an open stoma, its guard cells and surrounding epidermal cells. C D A B Complete Table 9.1 by choosing the correct letter from to match the feature stated in Table 9.1. Each letter may be used once, more than once or not at all. Table 9.1 letter feature location of Calvin cycle made mainly of cellulose The opening and closing of stomata are due to changes in environmental conditions. Hydrogen ions (H+) and potassium ions (K+) are involved in the opening of stomata. Describe how hydrogen ions and potassium ions are involved in the opening of a stoma.
9700_s22_qp_41
THEORY
2022
Paper 4, Variant 1
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Sorghum is a cereal crop that grows well in very dry conditions. Outline two structural features of sorghum that adapt it to survive in arid environments. An investigation was carried out to measure the effect of lack of water on the leaves of sorghum plants. • Several well-watered sorghum plants were kept in conditions of normal light and temperature. • Watering was then stopped for 6 days, and resumed on day 7. • The water potential of the cells in the leaves, the concentrations of abscisic acid in the leaves and stomatal resistance were measured each day. A high stomatal resistance indicates that most stomata are partially or completely closed. The results are shown in . –1600 –1200 –800 –400 time / days watering stopped watering resumed mean concentration of abscisic acid / ngcm–2 mean stomatal resistance / arbitrary units mean leaf water potential / kPa With reference to , describe and explain the changes in abscisic acid concentration over the 10 day period explain the changes in stomatal resistance over this period. Explain how the changes you have described in help sorghum to survive in arid conditions.
9700_w08_qp_4
THEORY
2008
Paper 4, Variant 0
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Most of the water lost from plants passes out through the stomata of leaves. The distance between open guard cells is known as the stomatal aperture, as shown in . stomatal aperture Researchers investigated the effect of stomatal aperture on rates of transpiration in leaves of Tradescantia zebrina under two conditions: • air kept moving by a fan (moving air) • non-moving air. The results are shown in . stomatal aperture / +m rate of transpiration / g m–2 h–1 moving air non-moving air Compare the effect of stomatal aperture on the rate of transpiration in T. zebrina in the two conditions. Explain the effect of stomatal aperture on rates of transpiration in non-moving and moving air. Spruce trees and pine trees are adapted to dry conditions where water can be in limited supply. shows two stomata in a spruce leaf and shows a vertical section through a stoma from a pine leaf. Explain how the stomatal features shown in and give an advantage to plants such as spruce and pine. Some plants that live in very dry conditions close their stomata during the day and open them at night. State one disadvantage of this for these plants. State and explain two adaptations that plant leaves have for survival in dry conditions other than those involving number or structure of stomata. 1. 2.
9700_w15_qp_23
THEORY
2015
Paper 2, Variant 3
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Questions Discovered
36