Module 5-Plant Responses Flashcards
(14 cards)
What do plants regulate growth in response to?
Directional stimuli
Define tropisms
Directional growth responses
Define phototropism and relate it to shoots and roots
-is growth in response to direction of light
-shoots are positively phototropic so will grow towards the light as the shoot tip cells (apiculture bud cells) produce auxin causing cell elongation. If theres unilateral light the auxin will diffuse towards the shaded side of the shoot resulting in a higher concentration of auxin there which causes the shoots to bend towards the light source
-roots are negatively phototropic so grow away from the light as they don’t photosynthesise, therefore don’t require light. A higher concentration of concentration of auxin in roots inhibits cell elongation causing cells to elongate more on the lighter side so the roots bend away from the light. This helps if roots should emerge from the soil to turn rapidly back towards the soil
Define geotropism and link it to roots and shoots
-growth in response to direction of gravity
-shoots are negatively geotropic as they grow upwards (away from the gravity pull). Auxin will diffuse from the upper side to the lower side of the shoot. If a plant is vertical this causes the cells to elongate and grow upwards. If a plant is on its side (horizontal) this will cause the shoot to grow upwards
-roots are positively geotropic as they grow downwards towards the gravitational pull. Auxin moves to the lower side of roots so that the upper side elongates and the roots bend down towards gravity and anchors the plant in
Name and explain chemical defences in plants
Alkaloids e.g caffeine, morphine, cocaine, nicotine are a class of antiherbivory compounds. The presence of alkaloids means plants have a very bitter taste which deters animals from eating them. They inhibit protein synthesis by binding to nucleic acids and inhibit or over activate enzymes to inhibit metabolic systems
Pheromones are secreted by plants as a type of alarm in response to grazing that stimulates the production of tannins. The alarm causes nearby trees to produce Callose to protect them if they are attacked
Name and describe plant responses to abiotic stress
Folding- has evolved to avoid abiotic stress or herbivory by folding leaves. This means a plant exposes its spiny stems and makes itself appear smaller than it actually is. This makes it look less attractive to predators. Folding also reduces exposure to harmful abiotic conditions e.g high temperature or rainfall
Leaf loss (abscission)- is inhibited by auxins. Low auxin levels reduce the levels of cytokinins in the plant.the abscission zone becomes more sensitive to ethylene which promotes cellulose production in cell walls which causes cells to self digest on the leaf side of the abscission zone and causes the leaf to break away from the tree. Leaves of deciduous trees drop in autumn reducing the burden of maintaining in cold temperatures and low light levels
Day length sensitivity- plants are sensitive to a lack of light in their environment known as photoperiodism. This is a result of a light sensitive pigment called phytochrome
Preventing freezing-the cytoplasm of plant cells and sap in vacuoles contain solutes which lower the freezing point. Some plants produce sugars, polysaccharides, amino acids and proteins which act as antifreeze to prevent the stop last from freezing or to protect cells from damage even if they do freeze
Stomata control- leaf cells release ABA when under abiotic stress from temperature or water which causes stomata closure, closing stomata provides a heating effect as theres no evaporation of water which decrease the temperature.
What do auxins do?
-auxins produced in the apicul shoot promote cell elongation and division in the apicul bud but inhibits this in the lateral buds
What does pruning plants do? And where does evidence for this come from?
-pruning plants by removing the apical bud promotes bushier growth of the plant by allowing the lateral buds to develop (inhibiting auxin transport also has the same affect)
-evidence for this is removing the apical bud but then applying the auxin paste has the same affect as if the bud wasn’t removed as lateral buds remain dormant
What is apical dominants?
-auxins maintain apical dominance which is where one main shoot is growing due to the high concentration of auxin in the apical shoot
What do gibberelins do?
-promote seed germination by stimulating amylose synthesis in the aleurone layer of the seed
-synthesising amylose enables the digestion of starch in the endosperm so the developing plant can access energy stored inside
-also a higher concentration of gibberelins the more elongated the stem will become
What does ABA do?
-inhibits seed germination
-causes stomatal closure when the plant is stressed
How can auxins be used commercially?
-auxin sprays cause fruit development in seedless plant varieties
-auxin rooting powers encourage root growth in transplanted cuttings
-auxins are used in selective weed killers, travelling through the phloem of the broad leaved plants and causing them to grow more quickly than they have the reserves to manage, resulting in death. These weed killers don’t affect narrow leaved plants like grasses
How can gibberelins used commercially?
-stimulate seed germination in the crops used in the brewing industry or elsewhere
-they stimulate stem elongation so are used to allow more room for grapes to develop in vineyards
How can ethylene be used commercially?
-gaseous ethylene can be used to ripen fruit more quickly
