Plant Responses

  • Created by: amyquince
  • Created on: 04-06-19 15:07

PLANT RESPONSES TO STIMULI

CHANGES IN ENVIRONMENT

- grow towards light to maximise absorption for photosynthesis

- roots sense gravity and grow in the right direction

- climbing plants have sense of touch so find things to climb to reach sunlight

RESPONSES TO HERBIVORY - TOXIC CHEMICALS

- Alkaloids - chemicals with bitter taste, bad smells or poisonous

- Tannins - bad taste and in some some herbivores (cattle, sheep) bind to protein in gut making plant hard to digest.

RESPONSES TO HERBIVORY - PHEROMONES

- alarm pheromones - causes nearby plants to detect chemicals and start making their own

- corn plants can produce pheromones to attract parasitic wasps that kill caterpillars eating them. 

LEAF CURLING

- knocks of insects and scares away animals trying to eat

1 of 5

RESPONSES CAUSED BY GROWTH HORMONES

- some plants respond to stimuli using growth hormones - speed up or slow down plant growth

- produced in growing regions (roots and shoots) then move to areas where needed

- GIBBERELIN- seed germination, stem elongation, side shoot formation and flowering

- AUXINS - stimulate growth of shoots by cell elongation (cell walls become loose and stretchy so get longer)

- high concentrations of auxins INHIBITS growth in roots

2 of 5

IAA

- Important auxin

- auxin produced in tis and shoots in flowering plants

- works by stimulating cell elongation

- moved around plant to control tropisms (by diffusion or active transport in short distances, phloem in long)

- different parts of plant have different amounts of IAA so uneven growth in plant

- PHOTOTROPISM - IAA moves to shaded part so uneven growth causes shoot to bend towards light and root to bend away from light (in roots growth is inhibited)

- GEOTROPISM - IAA moves to underside of shoots and roots so uneven growth causes shoot to grow up and causes roots to grow downwards (in roots growth is inhibited)

3 of 5

PRACTICAL INVESTIGATIONS INTO PHOTOTROPISM

1. take 9 wheat shoots and plant in individual pots in same type of soil, each shoot sould be equal in height

2. cover tips of 3 shoots with foil cap, leave 3 without foil, wrap base of 3 shoots with foil leaving only tip exposed

3. set up shoots in front of light source and leave for 2 days. leave same distance from light source, give same intensity of light, temp, exposure to moisture to be controlled also

4. by end of experiments, shoots with exposed tips should have grown towards light source. covering the tip prevents growth towards light (its the most sensitive part to light so will just grow straight up). covering base of shoot will still allow shoots to grow towards light

5. record amount of growth (in mm), as well as direction of growth. 

4 of 5

PRACTICAL INVESTIGATIONS INTO GEOTROPISM

1. Line 3 petri dishes with moist cotton wool (use same vol of water and same amount of cotton)

2. space out 10 cress seeds on surface of cotton wool in each dish

3. tape lid onto each dish and wrap each one in foil (prevents light entering)

4. leave in place where temp is warmish and constant (cupboard)

5. prop one dish upright, one at 90 degree angle and another on slope at 45 degrees. label each dish

6. leave seeds for 4 days then look at shoot and root growth

7. should find that whatever angle the dish was at the shoots should have grown away from gravity and roots towards gravity

8. measure amount of growth of shoots and roots and angle of growth.

5 of 5

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Human, animal and plant behaviour resources »