6A: Responses in plants and animals Flashcards
How do plants increase their chances of survival?
By responding to changes in their environment by;
- Sensing the direction of the light and growing towards it to maximise light absorption for photosynthesis
- Sense gravity so their roots and shoots grow in the right direction
What is a tropism?
The response of a plant to a directional stimulus. Plants respond to stimuli by regulating their growth.
What is phototropism?
The growth of a plant in response to light.
Shoots are positively phototropic and grow towards light.
Roots are negatively phototropic and grow away from light.
What is Gravitropism?
The growth of a plant in response to gravity.
Shoots are negatively gravitropic and grow upwards.
Roots are positively gravitropic and grow downwards.
How do plants respond to directional stimuli?
By using specific growth factors (hormone-like chemicals that speed up or slow down plant growth)
Where are growth factors produced?
In growing regions of the plant, and they move to where they’re needed in other parts of the plant.
How do growth factors like auxin work?
By stimulating the growth of the shoots by cell elongation, which causes the cell walls to become loose and stretchy so the cells get longer
What is the purpose of IAA (Indoleactic acid)?
It is produced in the tips of shoots in flowering plants and is moved around the plant to control tropisms.
How is IAA moved around?
Through diffusion and active tranxport over short distances, and via the phloem over long distances.
What is the effect of high concentrations of auxins?
Inhibit growth in roots
What does IAA result in?
Different parts of plants have different concentrations of IAA - which leads to uneven growth of the plant
How do organisms keep themselves in a favourable environment?
Have simple responses to keep them in a favourable environment. Their response can either be tactic or kinetic.
What are tactic repsonses (taxes)?
The organisms move towards or away from a directional stimulus.
