Plant Responses 2.0 Flashcards
What is a stimulus?
Anything that causes a reaction in an organism or any of its parts.
What is a response?
Activity of a cell or organism that happens as a result of a stimulus.
What are external factors that cause responses?
Light, day length, gravity, temperature.
What are internal factors that cause responses?
Plants produce chemicals called ‘Growth Regulators’ in the meristematic regions of the plant: Shoot & root tip.
What is tropism?
Change in the growth of a plant due to external stimulus.
What is positive tropism?
Occurs when the growth is towards the stimulus.
What is negative tropism?
Occurs when growth is away from the stimulus.
What is an advantage of tropism?
Plants can achieve more favourable conditions for growth.
What are the types of tropism?
Phototropism, geotropism, thigmotropism, hydrotropism, and chemotropism.
What is phototropism?
Changes in growth of a plant in response to light.
What is positive phototropism?
Stems grow towards light.
What is negative phototropism?
Roots grow away from light.
What is an advantage of phototropism?
Increased photosynthesis.
What is geotropism?
Change in growth of a plant in response to gravity.
What is positive geotropism?
Roots grow with gravity.
What is negative geotropism?
Stem grows away from the direction of gravity.
What is thigmotropism?
Change in growth of a plant in response to touch.
What is positive thigmotropism?
Plants that have tendrils grow around supporting structures.
What is hydrotropism?
Change in growth of a plant in response to water.
What is positive hydrotropism?
Roots grow towards water.
What are growth regulators transported in?
Transported in vascular tissue.
What is chemotropism?
Change in growth of plant in response to chemicals.
What is positive chemotropism?
Roots grow towards minerals in soil. Pollen tube grows towards chemicals in ovule.
What is negative chemotropism?
Most roots will not grow towards acids or heavy metals (Lead & zinc) in soil.
What are growth regulators?
Chemicals that control the growth of a plant.
What are the functions of growth regulators?
Produced in small amounts & transported to another part of the plant to have an effect (Like hormones in us). Can be promoters or inhibitors.
Define auxin.
A plant growth regulator.
What are the uses of growth regulators in agri/horticulture?
Fruit ripening, seedless fruit.
What are growth promoters?
Chemicals that cause increased growth in plants.
What is an example of a growth promoter?
Auxins (IAA - Indole Acetic acid).
Where are auxins made?
Made in meristematic tissue in tips & shoots.
What are the functions of auxins?
Stimulates stem elongation, stimulates root growth, develops fruit, causes phototropism.
What is the inhibitory function of auxins?
Slows mitosis.
What are the types of auxins?
IAA, Ethene & Acetic acid.
What is apical dominance?
If apical bud in stem is present, auxin is produced in tip, preventing lateral buds & side branching.
What happens if the apical bud is removed?
Lateral bud can occur.
How does concentration of IAA affect growth?
Low IAA concentration = Root growth. High IAA concentration = Shoot growth.
What is the mechanism of phototropism?
IAA produced in meristem of stem; when exposed to light, IAA diffuses down the shaded side, causing uneven elongation and bending towards light.
What are growth inhibitors?
Chemical that causes slowed growth in plants.
What is an example of a growth inhibitor?
Ethene Gas.
What are the functions of ethene?
Ripens fruit, causes fruit colour to form, stimulates more ethene production.
What is the commercial use of ethene?
Green bananas picked from trees and transported across the world are exposed to ethene on arrival & allowed to ripen.
What is abscisic acid?
Produced in leaves, stems & root caps.
What are the functions of abscisic acid?
Helps plants withstand harsh conditions, causes stomata to close in dry conditions.
What are commercially prepared growth regulators?
Ethene, root powder - Contains growth regulator NAA.
What are anatomical protective adaptations/features of plants?
Thorns, stinging hairs, bark (prevents pathogen entry + water loss), stomata shrivel to close if there is a shortage of water.
What are chemical protective adaptations/features of plants?
Formation of heat shock proteins to help enzymes maintain their shape in temperatures above 40 degrees, production of phytoalexins: Stress proteins.
What are adverse external environments?
Surroundings that are harmful to an organism.
