Plant growth factors Flashcards
How do organisms increase their chance of survival?
Organisms increase their chance of survival by responding to changes in their environment.
what is tropisms?
Responses to directional stimuli that can maintain the roots and shoots of flowering plants in a favourable environment.
tropisms can be either..?
positive or negative, growing away or from the stimulus.
which three things to plants respond to?
- light
- gravity
- water
why do plants grow/respond towards light?
shoots grow towards light (positively phototropic) because light is needed for photosynthesis (LDR)
why do plants respond to gravity?
plants need to be firmly anchored into the soil. roots are sensitive to gravity and grow in the direction of it’s pull (positively gravitropic)
why do plants respond to water?
almost all plants grow towards water (positively hydrotropic) in order to absorb it for use in photosynthesis and other metabolic processes, as well as for support.
why are plant growth factors used instead of plant hormones?
- they exert their influence by affecting growth, and they may be made by cells located throughout the plant rather than particular organs
- unlike animal hormones, some plant growth factors affect the tissues that release them rather than acting on a distant target organs
what is an example of plant growth factors?
IAA - Indoleacetic acid
What is IAA?
IAA is a type of auxin which controls cell elongation in shoots and inhibits growth of cells in the roots.
where is IAA produced?
it is made in the tip of the shoots or the roots but can diffuse to other cells
what is positive phototropism?
the growth of a plant in response to the direction of light
Describe what causes a plant to bend towards the light?
- Cells in the tip of the shoot produce IAA, which diffuses down the shoot
- The IAA is initially transported evenly throughout all regions as it begins to move down the shoot
- light causes the movement of IAA from the light side to the shaded side of the root
- a greater concentration of IAA builds up on the shaded side of the shoot than the light side.
- as IAA causes cell elongation of the shoot cells and there is a greater concentration of IAA on the shaded side of the shoot, the cells on this side elongate more
- the shaded side of the shoot elongates faster than the light side, causing the shoot tip to bend towards the light.
why does IAA have opposite effects in the roots compared to the shoots?
IAA causes cell elongation in the shoots and a high concentration of IAA inhibits cell elongation in the roots
What is negative phototropism?
growth of a plant away from the light
describe negative phototropism in the roots?
- In the roots, There is a high concentration of IAA on the shaded side
- in roots, high concentration of IAA inhibits cell elongation, causing root cells to elongate more on the lighter side and so root bends away from the light
What is Gravitropism?
a plants growth in response to gravity
what is positive gravitropism?
a plants growth in response to the direction of gravity
describe positive gravitropism in roots?
- cells in the root tip produce IAA, which is then transported along the root
- the IAA is initially transported to all sides of the root
- gravity then influences the movement of IAA from the upper side to the lower side of the root
- a greater concentration of IAA build up on the lower side of the root than the upper side of the root
- A IAA inhibits the elongation of root cells and there is a higher concentration on the lower side, the cells on this side elongate less than those on the upper side
- the relatively greater elongation of cells on the upper side compared to the lower side causes the root to bend downwards towards the force of gravity
what is negative gravitropism?
shoots grow away from gravity
describe negative gravitropism in the shoots?
- IAA will diffuse from the upper side to the lower side of the shoot
- if the plant is vertical, plant cells elongate
- if the plant is on it’s side, it will cause the shoot to bend upwards.
what are the difficulties of studying different growth factors?
The effects of a plant growth factor can depend on:
what other growth factors are present. Another growth factor can increase the effect of the growth factor being studied (synergism) or reduce it (antagonism).
the species of plant
the developmental stage of the plant
the tissue being acted on, e.g. stems or roots
the concentration of the growth factor
TAXES AND KINESES
what is a stimulus?
a stimulus is a detectable change in the internal and external environment of an organism that leads to a response in the organism
what increases a organisms chances of survival?
the ability to respond to stimuli, such as predators or extreme temperatures
What is a taxis?
a simple response whose (motile organisms) direction is determined by the direction of the stimulus
explain how an organism would achieve this?
as a result, a motile organism responds directly to the environmental changes by moving it’s whole body either towards a favourable stimulus or away from an unfavourable one.
how are taxes classified?
they are classed according to whether the movement is towards the stimulus (positive taxis) or away from the stimulus (negative taxis) and also by the nature of the stimulus
give some examples?
- single celled algae - will move towards light (positive phototaxis). this increases their chance of survival, since being photosynthetic, they require light to manufacture their food
- earthworms - will move away from light (negative phototaxis). this increases their chances of survival because it takes them into the soil, where they are better able to conserve water, find food and avoid predators
- some species of bacteria - will move towards a region where glucose is more highly concentrated (positive chemotaxis). this increases their chance of survival because they use glucose as a food source
what is kinesis?
is a form of response in which the organism does not move towards or away from a stimulus. instead it changes the speed at which it moves and the rate at which it changes direction.
what does kinesis mean?
movement in random directions
why do they keep moving?
until they reach desirable conditions
when does kinesis occur?
when an organism crosses a sharp dividing line between a favourable and unfavourable environment , it’s rate of turning increases. this raises it’s chances of a quick return to a favourable environment
- when negative stimulus is coming from all around (less directional) e.g light, temp, humidity
the more unpleasant the stimulus the more..?
the more rapid the animal’s movement and the increase in rate of turns
How does Kinesis help an organisms survival?
In unfavourable conditions animals can increase the probability of randomly finding more favourable conditions by increasing rate of movement and turns
DONE!!
