Module 5: Plant responses Flashcards
Give examples on how plants can increase their survival by responding to changes in their environment.
1) They sense the direction of light and grow towards to maximise light absorption for photosynthesis.
2) They sense gravity, so their roots and shoots grow in the right direction.
3) Climbing plants have a sense of touch, so they can find things to climb and reach the sunlight.
What are the two things plants respond to, to increase their chances of survival?
-Abiotic stress
-Herbivory
What is abiotic stress and give an example.
It is anything that is potentially harmful to a plant that is natural, but non-living, like a drought -water stress. (environmental)
An example is that plants respond to extreme cold by producing their own form of anti-freeze.
Carrots produce antifreeze proteins at low temperatures- the proteins bind to ice crystals and lowers the temperature that water freezes at, stopping more ice crystals from growing.
What is Herbivory and give an example.
It is when plants are eaten by animals and insects. However plants protect themselves against herbivory by producing toxic chemicals in response to being eaten. This is known as a chemical defence.
There are 2 examples:
-Alkaloids - These are chemicals with bitter tastes, noxious smells and poisonous characteristics that deter or kill herbivores. For example tobacco plants produce the alkaloid nicotine in response to tissue damage. Nicotine is highly poisonous to many insects.
-Tannins - These taste bitter, and in some herbivores, they can bind to proteins in the gut, making the plant hard to digest. Both of these things deter animals from eating the plant.
What are pheromones and why do plants release this?
Some plants release pheromones in response to herbivory.
They are signalling chemicals that produce a response in other organisms.
Some plants release alarm pheromones into the air in response to herbivore grazing and this can cause nearby plants that detect these chemicals to start making chemical defences such as tannins.
E.g.= when corn plants are being eaten by caterpillars, they can produce pheromones which attract parasitic wasps. These wasps then lay their eggs in the caterpillars, which eventually kills them.
What plant folds up in response to being touched?
If a single leaflet of the plant Mimosa pudica is touched, a signal spread through the entire leaf, causing it to quickly fold up.
It is thought that this could help protect the plant against herbivory in many ways. For example it may help to knock off small insects feeding on the plant. Also it may scare off any animals trying to eat it.
What are tropisms and the different types?
A tropism is the response of a plant to a directional stimulus. Plants respond to stimuli by regulating their growth. A positive tropism is growth towards the stimulus, whereas a negative tropism is growth away from the stimulus.
-Phototropism
-Geotropism
-Hydrotropism
-Thermotropism
- Thigmotropism
What are some tropisms?
Phototropism - is the growth of a plant in response to light. Shoots are positively phototropic and grown towards light whereas roots are negatively phototropic and grow away from light.
Geotropism - is the growth of a plant in response to gravity. Shoots are negatively geotropic and grow upwards whereas roots are positively geotropic and grow downwards.
Hydrotropism - Plant growth in response to water. roots are positively hydrotropic.
Thermotropism - plant growth in response to temperature.
Thigmotropism - plant growth in response to contact with an object.
What are growth hormones and what are the 2 main ones for plants?
Plants respond to some stimuli using growth hormones which are chemicals that speed up or slow down plant growth.
They are produced in the growing regions of the plants such as the shoot tips and the root tips. They move to where they are needed in the other parts of the plant.
- Gibberellin
-Auxins
Describe the function of the growth hormone gibberellin.
-Stimulates seed germination
-Stimulates stem elongation
-Stimulates side shoot formation and flowering.
Describe the function of the growth hormone auxin.
- Stimulates the growth of shoots by cell elongation.
- Auxins are produced in the tips of shoots in flowering plants and diffuse backwards to stimulate the cell just behind the tips to elongate - cell walls become loose and stretchy.
If the tip of a shoot is removed, no auxin will be available and the shoot stops growing.
Auxins stimulate growth in shoots but high concentrations inhibit growth in roots.
What is Indoleacetic acid (IAA)?
It is an important auxin that is produced in the tips of shoots and roots in flowering plants. It is moved around the plant to control tropisms - it moves by diffusion and active transport over short distances and via the phloem for long distances.
This results in different parts of the plant having different amount of IAA. The uneven distribution of IAA means there is an uneven growth of the plant.
Describe the practical investigation into phototropism.
Take 12 small plants of the same age, species and variety.
On four plants, cover the tip of the plant shoot with aluminium foil – this will prove that the phototropic response is dependent on the shoot tip
On a different four plants, cover the stem of the shoot with foil, leaving the tip exposed – this will prove that nothing in the foil is preventing phototropism
Leave the other four plants as they are. Keep control variables (including temperature and humidity) constant.
Place a lamp at specified distance to the plants and leave for 48 hours.
Measure the amount of growth and direction of growth of each plant shoot.
You’re expecting to see growth of the shoot tip for the uncovered plants and the ones where just the stem is wrapped in foil. The four plants with their shoot tip covered will show no directional response (i.e. will grow straight upwards).
Describe the practical investigation into geotropism.
Take three petri dishes and fill with moist cotton wool (adding an equal volume of water to each dish).
Place ten cress seeds in each dish and seal the lid with tape. Label each dish for future reference.
Place one dish horizontally, one vertically (at a 90 degree angle) and the other at 45 degrees in a dark cupboard and leave for 5 days.
Keep all control variables, including temperature and humidity, constant.
Measure the amount of growth and the angle of growth.
You’re expecting that regardless of angle the seeds were placed at, the shoots will have all grown in away from gravity and the roots towards gravity.
What is Apical dominance?
The shoot tip at the top of a flowering plant is called the apical bud.
Auxins stimulate the growth of the apical bud and inhibit the growth of the side shoots from lateral buds.
The apical bud is dominant over the lateral buds.
