Chapter 32 - Plant Responses Flashcards
What is a stimulus?
Anything that causes a reaction in an organism
What is a response?
The activity of a cell in reaction to a stimulus
What four structures are needed for an organism to respond?
Hormonal system
Nervous system
Ability to move and grow
An immune system
What kind of responses are plant responses?
Growth or changes in growth
Why are plant responses different from animal ones?
Plants cannot move
They have no nervous system and instead use chemical coordination
What are growth regulators?
Chemicals that control growth in a plant
What are the internal factors of growth regulators?
Chemicals produced by a plant
What are the external factors of growth regulators?
Light intensity - needed for photosynthesis, produces chlorophyll
Day length - causes plants to flower, seed, ferment
Gravity - roots grow down, shoots grow up
Temperature - affects rate of enzyme reactions
What is a tropism?
A change in the growth of a plant in response to an external stimulus
What is a positive tropism?
Growth towards stimulus
What is a negative stimulus?
Grows away from stimulus
What is the purpose of a tropism?
To help plants obtain the best growing conditions
What are the 5 types of tropisms?
Phototropism Geotropism Thigmotropism Hydrotropism Chemotropism
What is phototropism?
The change in growth of a plant in response to light
Positively phototropic - stems, to carry out more photosynthesis
Negatively phototropic - roots
What is geotropism?
The change in growth of a plant in response to gravity
Positively geotropic - roots, anchor and absorb minerals
Negatively geotropic - stems
What is thigmotropism?
The change in growth of a plant in response to touch
Positively thigmotropic - tendrils
What are tendrils?
They respond to touch by wrapping around supporting structures
Ivy has tendrils
What is hydrotropism?
A change in growth of a plant in response to water
Positively hydrotropic - roots, grow towards damp soil
What is chemotropism?
Change in growth of a plant in response to chemicals
Positively chemotropic - roots, grow towards minerals
Negatively chemotropic - roots, grow away from acids or heavy metals
Where are growth regulators produced?
The meristem
How are growth regulators transported?
Vascular tissue
Why are growth regulators difficult to study?
Active in small amounts
Opposite effects at high and low concentration
Effects depend on location
Interacts in different ways - combine, interfere, or no effect
What are growth promotors?
Increase rate of growth
What are the most known growth promotor?
Auxins
What is the best known auxin?
IAA (indoleacetic acid)
What is the function of IAA?
Made in Shoot Tips, young leaves, seeds
Causes stem and root to grow
Causes fruit formation
What are growth inhibitors?
Decrease rate of growth
What are the two best known growth inhibitors?
Ethene and abscisic acid (ABA)
What is the function of ethene?
Gas made in plant nodes, ripe fruits, decaying leaves
Causes fruit to ripen, leaves to fall
Bananas exposed to ethene before being sent to shops stimulates ripening
What is the function of abscisic acid?
Made in leaves, stems, root caps Causes plants to respond to harmful conditions: Stomata closes at night Bud scales in winter Inhibits seed germination until ready
What are the 7 functions of auxins?
Stimulate stem elongation Stimulate root growth Causes cells to form into different structures Develop fruit Inhibit side branches Causes phototropism Causes geotropism
What are the effects of auxins?
Tropisms Allows cell walls to expand Apical dominance Fruit formation - IAA Root growth - low concentration (used in root powders)
Explain apical dominance?
If apex is present - no side branches
If apex is not present - side branches
Apical dominance - lateral buds do not develop due to inhibition
Lack of apical dominance - side branches form
What 3 ways can growth regulators be used in industry?
Rooting powders
Tissue culturing
fruit ripening
Explain rooting powders
Contains an artificially produced growth regulator (NAA)
Used to stimulate root growth in cuttings
Explain tissue culturing
Piece of plant material growth in high auxin concentration
Explain fruit ripening
Ethene ripens bananas
What are two anatomical plant adaptations?
- Epidermis - physical barrier (bark or cuticle), prevents water loss, entry of pathogens, thorns (cactus), stinging hairs (nettles)
- Stomata - reduces water loss, close by shriveling of guard cells by the release of abscisic acid
What are 2 chemical plant adaptations?
- Heat shock proteins - allow a plant to function properly in high temperatures, normal proteins don’t work above 40°c
- Phytoalexins - stress proteins produced when a plant is infected with micro organisms
Attacks micro organisms, strengthens cell walls to stop infection, alerts outer plant cells
How have plants in deserts adapted?
Spins for leaves Stores water in stem Lighter colour Waxy leaves Long root systems spread out wide and deep Grow slowly
