Plant Responses Flashcards
Stimulus
Anything that causes a reaction in an organism or in any of its parts
Response
The activity of a cell or organism as a result of a stimulus
Sensitivity
The ability to detect change and to respond
External factors affecting growth
~ Light : Provides energy for photosynthesis
~ Day length : Affects fruit and seed formation as well as dormancy
~ Gravity : Causes roots to grow down and shoots to grow up
~ Temperature : Changes the rate of enzyme production
Internal factors
~ Plants produce chemicals called growth regulators
~ Plant growth regulators = Growth promoters and Growth inhibitors
Plant growth inhibitors
Chemicals that cause a reduction in growth in plants e.g. ethene
Ethene
~ Promotes ripening of fruit
~ Promotes the fall of leaves, flowers and fruits
Plant growth promoters
Chemicals that causes growth in plants
Tropisms
~ A growth response to a stimulus
~ Positive tropism = the growth is towards the stimulus
~ Negative tropism = the growth is away from the stimulus
Phototropism
~ Is a change in growth in response to light
~ Positive = stem grows towards the light which increases the amount of photosynthesis
~ Negative = roots grow away from the light
Geotropism
~ Is a change in growth in response to gravity
~ Positive = root grows towards gravity
~ Negative = shoots grow away against gravity
Thigmotropism
~ Is growth in response to touch
~ e.g. ivy climbs up walls which help support the plant
Hydrotropism
~ Is growth in response to water
~ Positive tropism as roots and pollen tubes grow towards water
Chemotropism
~ Is growth in response to chemicals
~ Both positive and negative tropism
~ Roots grow towards favourable minerals but against heavy metal (lead & zinc)
What are plant growth regulators?
~ Is a chemical that controls the growth of a plant
~ Regulators that promote growth e.g. auxins (IAA), gibberellins
~ Regulators that inhibit growth e.g. auxins (IAA) and ethene
Plant growth regulators in detail
~ Active in very small amounts
~ Produced in the meristems; tips of shoots and roots
~ Transported in the xylem and phloem (vascular bundle)
~ Their effects are dependent on concentration i.e. a small amount of growth regulator can have a great effect on growth
How are plant growth regulators similar to animal hormones?
~ Chemical nature
~ Prolonged effects
~ Produced in one place and act in another
Use of plant regulators (in horticulture)
~ Weed killers
~ Seedless fruit
~ Tissue culturing : micropropagation
~ Fruit ripening by spraying it with ethene
Where are auxins (IAA) produced?
Meristematic tissue in the tips of shoots and roots
What are the functions of auxins (IAA)?
~ Stimulating stem elongation and root growth
~ Developing fruit
~ Causes phototropism and geotropism
What are the effects of auxins (IAA)?
~ Tropisms
~ Apical dominance : Prevents the growth of lateral buds and side branching
~ Fruit formation and root growth
Role of auxins (IAA) in phototropism
~ IAA is produced in the meristems
~ If the stem is exposed to light from one side IAA will diffuse down the shaded side
~ The concentration of IAA present in the shaded cells causes them to elongate more than the cells on the bright side of the stem
~ As a result of the uneven elongation, the stem bends towards the light
Adverse external environment
Surroundings that are harmful to organisms
Plant adaptations for protection - structural
~ Cuticle and stomata closing reduces water loss
~ Thorns or stinging hair protects them from being eaten by animals
Plant adaptations for protection - chemical
~ Heat-shock proteins prevent proteins e.g. enzymes from denaturing when the plant is in high temperatures
~ Stress proteins are produced by a plant when it is infected by a micro-organism, they attack the micro-organism and kill them
