Plant Responses
- Created by: Imogen
- Created on: 28-04-13 10:43
View mindmap
- Plant Responses
- What do plants respond to?
- Water
- Touch
- Chemicals
- Light
- Chemicals
- Types of Plant Response
- Taxis
- Movement of the entire organism, e.g. single celled photosynthesising Protoctista
- Nastism
- Non-growth movement e.g. the closing of a Venus Fly Trap or a Daisy closing its petals at night
- Tropism
- A tropic response is a response in the direction of, and determined by, a directional stimulus
- Taxis
- What controls plant responses?
- Plant Growth Regulators
- Transport
- Diffusion
- Active Transport
- Mass flow in the xylem or phloem
- Features of PGRs
- Effective at very small concentrations
- The same conc. can have different effects on different tissues
- Different conc. can have different effects on the same tissue
- Hormones
- Similarities with PGRs?
- Both have complementary protein receptors on the cell surface membrane of their target tissues
- This ensures specificity in the action of PGRs and Hormones
- Both have complementary protein receptors on the cell surface membrane of their target tissues
- Differences from PGRs
- Hormones are transported in the blood
- PGRs are not excreted from exocrine glands whereas hormones are
- Hormones can target organs, PGRs target tissues and cells
- Similarities with PGRs?
- Transport
- Plant Growth Regulators
- Auxin
- Apical Dominance
- Auxin diffuses down from the apical bud
- It acts as a repressor on the development of the lateral buds
- The further away from the apical bud, the lower the concentration of Auxin and the less repression occurs
- When the source of Auxin is removed cell division begins in the lateral buds
- The further away from the apical bud, the lower the concentration of Auxin and the less repression occurs
- It acts as a repressor on the development of the lateral buds
- Auxin diffuses down from the apical bud
- Phototropism
- Negative
- Positive
- When light shines on a plant a protein called phototropin causes Auxin to collect on the side of the plant furthest from the sun
- When light shines directly above a plant equal amounts of Auxin collect on each side
- Auxin binds to receptors on the plasma cell membrane
- This causes the active transport of H+ ions into the cell wall
- This provides the optimum pH for enzymes called expansins to loosen hydrogen bonds in the cell wall
- Water can diffuse into the cell causing it to expand
- The side furthest from the light source grows at a faster rate causing the plant to bend towards the source
- Water can diffuse into the cell causing it to expand
- This provides the optimum pH for enzymes called expansins to loosen hydrogen bonds in the cell wall
- This causes the active transport of H+ ions into the cell wall
- Light is detected by the tip of the plant
- When light shines on a plant a protein called phototropin causes Auxin to collect on the side of the plant furthest from the sun
- Stimulates cell elongation and cell division
- Apical Dominance
- Gibberellins
- Causes cell elongation and division in the internode region
- Dwarf plants contain two recessive alleles so don't produce the active protein necessary for GA production
- Treating dwarf plants with GA causes them to grow
- Treating normal varieties with GA will have no effect as the plants already produce GA
- Gibberellins are responsible for stem elongation
- Abscission
- The organised shedding of part of a plant
- Cytokinins prevent the leaves of a deciduous tree from senescing
- When cytokinin production drops senescence begins and leaves are shed
- There is an abscission zone at the base of the petriole where cells can easily break away along the middle lamellae
- Below this there is a protective layer. Cells contain waterproof Suberin to prevent water from escaping and pathogens from entering
- Uses of Plant Growth Regulators
- Auxin
- Herbicide
- Promotes flowering in commercial flower production
- Promotes root growth
- Gibberellins
- Delays fruit senescence prolonging their picking season
- Increases sugar cane yield by lengthening the cane
- Ethene
- Causes ripening in e.g. tomatoes, bananas etc.
- Causes fruit to drop
- Auxin
- What do plants respond to?
Comments
Report