Plant Resposnes Flashcards
Define and give examples of tropism
Tropism is growth responses to a directional stimulus
Phototropism - response to light
Geotropism - response to gravity
Chemotropism - chemical gradient
Thigmotropism - growth response to solid structure
What chemicals are released for survival
Survival plants can release
Tannins- toxic to herbivores and microorganisms eating the plant
Alkaloids - give bitter taste,preventing plant being eaten
Pheromones - to elicit behavioural response in other organisms
Auxin is a plant hormone produced in the shoot tip. Auxin causes cell elongation and travels down the stem from the tip. Auxin is destroyed by sunlight. Explain how this leads to positive phototropism in the plant
Auxin is broken down on the sunny side of the plant. Cells on the shaded side will elongate due to auxin, causing curvature of the stem so that the plant grows towards the light
Ivy plants often use walls or other plants as support when growing. State the type of tropism being used
Thigmotropism
Roots grow towards the centre of gravity. State the specific type of tropism being demonstrated
Positive geotropism
Define and explain the role of the hormone auxin
Auxin is thought to inhibit lateral bud growth.
Controls cell elongation , prevent leaf fall
Define and explain the role of of Gibberllins
Causes stem elongation and seed germination. Trigger the mobilisation of food stores in a seed at germination
The La gene,coding for an enzyme that forms gibberliens is expressed in more taller plants
Name a control variable that would be considered in investigating phototropism
Name the independent variable that students change
CO2 concentration
Intensity of light
Students used a control plant placed in the dark. Explain why they did this
Allowed the students to compare how light intensity affected the growth direction of a plant in differing levels of sunlight to a plant not in sunlight
How can you investigate geotropism
By allowing gravity to work on one side of the experiment plant and observing root growth
Control plant is spun on a kilnostat to apply gravity on all sides. Roots normally follow the centre of gravity to support the plant in the ground
Explain why the control plant must be spun
Control plant is spun so that gravity affects the plant root on all sides.,
Means the roots should grow horizontally, compared to the experimental roots, which should grow downwards due to gravity
How can you investigate auxins
Auxin moves shaded side of the shoot causing cells to elongate and bend the shoot towards the light
Serial dilutions of auxin solution can be made to test the effects of different auxin concentration
How can you investigate gibberellins
1) make up serial dilutions of GA concentrations
2) apply each solution to seeds of the same species
3) seeds with higher concentration will have higher mean stem lengths
Explain how gibberellins activate seed germination
When seeds absorb water from environment, embryo of the seed releases gibberellins. This travels to the aleurone layer of the endosperm in the seed. Here gibberellin causes production of enzyme amylase, which breaks starch into glucose. Glucose is used as a substrate for respiration, energy for growth
What is the the commercial use of cytokinins and ethene
Cytokines - delays leaf loss and used in tissue culture to mass produce plants
Ethene- speed up fruit ripening, enhances lateral bud growth. Inhibiting ethene prolongs shelf life
State 2 commercial use of gibberellins with reference to plants
Enhance seed germination in growing malt for beer and delay senescence of citrus fruits, making them available for longer in shop
State 2 commercial use of auxins
Auxins can be used in rotting powder to grow roots in young plant cuttings and can be used as a herbicide to kill weeds
Why are chemicals important in coordinating the growth of plants
Plants are multicellular and often large so need coordination, plants don’t appear to have nervous system so no electrical coordination system, chemicals can carried in plant transport systems and move from cell to cell to coordinate responses
Why is it so important for plants to be able to response to their surroundings
Rooted to the ground so cannot move their bodies therefore very important that they are sensitive so they can grow in the right direction and make the best circumstances where they have germinated
Why do many trees in temperate climates lose all their leaves in winter
Amount of photosynthesis that can take place decreases as day length is reduced and temperature falls- amount of glucose produced by photosynthesis falls.
Amount of glucose needed for respiration to maintain leaves through the winger and produce chemicals to prevent freezing damage increases- more efficient to lose the leaves and became dormant
The explain the process of abscisson
Falling light levels - decreased concentration of auxin - leaves produce hormone ethene - ethene initiates gene switching in abscisson zone at base of leaf stalk - gene switching causes production of new enzymes - new enzymes digest and weaken cell walls in outer layer of abscisson zone (separation zone) - cells separation zone respond to hormonal cues by retaining water and swelling putting more strain on outer layer - further abiotic factors finish process- strain is too much and leaf separates from plant leaving nest waterproof scar max
How do hormones affect stomatal control
Heat and water availability major abiotic stresses for plants
Opening and closing of the stomata in response is under control of hormone ABA
What are tannins
Water soluble carbon compounds in the chemical group known as flavonoids,stored in the vacuoles of plant cells, bitter taste
E.g Gallic acid
What are alkaloids
Nitrogenous compounds derived from AA, bitter tasting and can be toxic,
E.g caffeine
What are pheromones
Chemicals released by one member of a species that affect physiological or behaviour of another member of that species
Trigger other chemical defences in plants
How do abscisic acid trigger stomata closure
ABA binds to receptors on the guard cell membranes - specific ion channels open, allows calcium ions to enter cytosol from vacuole increased concentration of calcium ions in the cytosol causes other ion channels to open. These ion channels allow ions to leave the guard cells, raising the water potential of the cells.
- Water leaves the guard cells via osmosis
- The guard cells become flaccid and the stomata close.
What happens if you remove the apical bud
Plants will not produce auxins, side shoots will therefore start growing
Which hormones inhibit and stimulate leaf loss
Auxins inhibit leaf loss
Ethene stimulate leaf loss
Outline the commercial uses of plant hormones
Selective weed killers - high enough concentrations, rapid growth plant tissues become distorted and damaged, effective against weed in field that occurs in fields of grass lawns
Rooting powders - low doses, stimulate cuttings to grow new roots, lower end of the cutting is dipped into the powder before being planted in compost
Ethene - stimulate fruit to ripen, stimulate enzymes that break down cell walls, break down chlorophyll and convert starch into sugars
