Responses in Plants and Animals Flashcards
Why do plants need to respond to changes in the environment?
to inc. chances of survival
What is a tropism?
The response of a plant to directional stimulus ( a stimulus from a particular direction).
What are +ve and -ve tropisms?
Plants respond to stimuli by regulating their growth.
A positive tropism is growth towards the stimulus.
A negative tropism is growth away from the stimulus.
Describe phototropism.
Phototropism is 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.
Describe gravitropism.
Gravitropism is the growth of a plant in response to gravity.
Shoots are negatively gravitropic and grow upwards.
Roots are positively gravitropic and grow downwards.
What are growth factors?
these are hormone-like chemicals that speed up or slow down plant growth.
Where are growth factors produced?
Growth factors are produced in the growing regions of the plant (e.g. shoot tips, leaves).
What are auxins?
How do they work?
Growth factors called auxins stimulate the growth of shoots by cell elongation
- this is where cell walls become loose and stretchy, so the cells get longer.
High concentrations of auxins inhibit growth in roots though.
What is indoleacetic acid (IAA)?
Where is it produced?
An important auxin produced in the tips of shoots.
How does indoleacetic acid work?
IAA is moved around the plant to control tropisms
-it moves by diffusion and active transport over short distances, and via the phloem over long distances.
This results in different parts of the plant having different concentrations of IAA.
The uneven distribution of IAA means there’s uneven growth of the plant.
Describe how IAA works in phototropism.
How do simple mobile organisms respond to changes in their environment?
Simple mobile organisms, (e.g. woodlice and earthworms), have simple responses to keep them in a favourable environment.
Their response can either be tactic or kinetic.
What is a tactic response?
Tactic responses (taxes) - the organisms move towards or away from a directional stimulus, e.g. light.
What is a kinetic response?
Kinetic responses (kineses) - the organisms’ movement is affected by a non-directional stimulus, e.g. humidity.
Explain how a tactic response helps a woodlouse to survive.
For example, woodlice show a tactic response to light (phototaxis) -they move away from a light source.
This helps them survive as:
- it keeps them concealed under stones during the day - safe from predators.
- keeps them in damp conditions - reduces water loss.
Describe the difference used to investigate the effect of light intensity and humidity of woodlice responses using a choice chamber.
Place 10 woodlice on the mesh in the centre of the chamber and cover the chamber with the lid. - one half of which is covered with back paper, inc. the sides.
After 10 minutes, take off the lid and record the number of woodlice on each side of the chamber.
To investigate humidity, place some damp filter paper in one side of the base and a desiccating (drying) agent in the other side. Don’t cover the lid with paper. Put the lid on and leave the chamber for 10 minutes to stabilise before adding woodlice.
Q1. The table shows the results some students obtained when they investigated the effect of providing plants with auxins.
a) Describe and explain what the data shows.
b) Suggest why this data might be useful to a commercial tomato producer.
c) Explain the role of auxins in the control of phototropism in the shoots.
1 a) The data shows that the plants provided with auxins grew more
than those not given auxins. This is because auxins stimulate plant growth (by cell elongation).
b) Providing tomato plants with auxins could, potentially, be used to increase the height of tomato plants, which might increase the yield of tomatoes/number of tomatoes grown.
c) Auxin is redistributed to the shaded side of the shoot.
Auxin stimulates cell elongation on the shaded side so the shoot bends to grow towards the light.
