OCR A2 Biology: Plant Hormones

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Flashcards by hannawin98, updated more than 1 year ago
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A-Level Biology Flashcards on OCR A2 Biology: Plant Hormones, created by hannawin98 on 05/19/2016.
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Question Answer
What is abiotic stress? Anything that's harmful that's not living e.g a drought or extreme temperatures
What is a tropism? The response of a plant to a directional stimulus (A stimulus coming from a particular direction)
What is a positive tropism? Growth towards the stimuli
Whats is a negative tropism? Growth away from the stimuli
What is phototropism? The growth of a plant in response to light
Are shoots positively or negatively phototrophic? Positively (They grow toward the light)
Are roots positively or negatively phototrophic? Negatively (They grow away from the light)
What are growth hormones? Chemicals that speed up or slow down plant growth
Where are growth hormones produced? In the growing regions of the plant (Shoot tips and leaves)
1. Where are auxins produced? 2. What do they do? 1. They are produced in shoot tips 2. They diffuse backwards to stimulate the the cells just behind the tip to elongate
What is elongation? This is where cell walls become loose and stretchy so the cells get longer.
What happens if the shoot tip is removed? No auxins will be produced, therefore the shoot stops growing.
What happens in high concentration of auxins? Shoots are stimulated to grow, root growth is inhibited
How do auxins move around the plant? 1. Diffusion or active transport in short distances 2. By the phloem in long distances
What is Indoleacetic acid (IAA)? A type of auxin that is involved in phototropism
What is apical dominance? This is where auxins stimulate the growth of the apical bud but inhibit the growth of the side shoots in plants.
Why is apical dominance present in flowering plants? 1. It saves energy and prevents competition from side shoots for light. 2. It enables flowering plants to grow quicker as more energy is used for shoot growth rather than side shoots.
What happens when you remove the apical bud? No auxins are produced so side shoots grow by cell elongation. This is useful to make hedges or other plants more bushy.
What are Gibberellins? Plant hormones involved in the growth of young leaves and seeds.
What do Gibberellins stimulate? 1. Seed germination 2. stem elongation 3. side shoot formation 4. flowering
What is a difference between auxins and gibberellins? Gibberellins don't inhibit plant growth in any way.
Why can auxins and Gibberellins be synergistic? They work together to help the plants grow tall
How can auxins and Gibberellins be antagonistic? Giberellins promote side shoot growth where as auxins inhibit side shoot growth.
What are deciduous plants? Plants that lose their leaves in winter
Why do deciduous plants lose their leaves? Helps plants to conserve water during times when water absorption is difficult (water could be frozen) and when there's less light for photosynthesis.
What triggers leaf loss? The shortening day length, it is controlled by hormones
What hormones effect leaf loss? 1. Auxins (as auxins help promote leaf growth, the plant decreases auxin production) 2. Ethene
How does Ethene promote leaf loss? Ethene stimulates the formation of a layer of cells (The abscission layer) at the bottom of the leaf stalk. This seperates the leaf from the rest of the plant. Ethene then stimulates the expansion of the abscission layer, which breaks the cell walls, causing the leaf to fall off.
How is Ethene used commercially? Ethene stimulates enzymes that break down cell walls, break down chlorophyll and convert starch into sugars. This makes fruit ripe.
How are Auxins and Gibberellins used commercially? They are sprayed onto unpollinated flowers which makes fruit develop without fertilisation e.g seedless grapes.
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