Summary Life Sciences p1 (CAPS): Responding to the Environment (plants)

RESPONDING TO THE ENVIRONMENT
PLANTS

KEY DEFINITIONS
Tropism
- A plant growth response to an external stimulus
Geotropism
- The growth of a part of a plant in response to gravity
Phototropism
- The growth movement of a part of a plant in response to unilateral light stimulus
Thorns
- Sharp structure found in plants for protection from the herbivores
Abscisic acid
- The plant growth hormone that promotes seed dormancy
Herbicide/weed-killer
- A substance containing plant hormones used to kill unwanted plants

GENERAL FUNCTIONS OF 3 PLANT HORMONES
Auxins
- Stimulates cell elongation
- Cause tropism in stems and roots
- Stimulate the development of fruit
- Stimulate the development of adventitious roots in stem cuttings
- Inhibit the growth of lateral branches
 Apical dominance

Gibberellins
- Stimulate stem elongation
- Stimulate root growth
- Promote flowering
- Stimulate the germination of seeds

Abscisic acid
- Cause dormancy of terminal and lateral buds in winter
- Contributes to the dormancy of seeds by inhibiting germination
- Promotes the abscission of leaves and fruit

THE CONTROL OF WEEDS USING PLANT HORMONES
- Some weed killers contain high concentration of auxins that accelerate the
metabolism of broad-leaved dicotyledonous weeds
- The weeds grow so fast that their water absorption and die

ROLE OF CHEMICALS AND THORNS AS PLANT DEFENSE MECHANISMS
Chemicals
- Many plants produce chemicals that play a role in the defense against herbivores
- Some of these chemicals are toxic or influence the digestibility of plant material
Thorns
- Discourage herbivores from eating plants