Coordination in plants and animals (8) Flashcards
Describe how the hormonal system sends information?
- uses glands and hormones to send chemical messages
- a gland secretes the hormone
- hormones are often proteins but sometimes ar peptides or steriods
How can glands be stimulated (two ways)?
- a change in concentration of a specific substance
- electrical impulses
Compare the hormonal and nervous system (4 differences)
NERVOUS
- uses electrical impulses
- faster response
- localised response
- short-lived response
HORMONAL
- uses chemicals
- slower response
- widespread response
- long-lives response
What type of coordination do plants use?
hormonal
What is IAA?
- Indoleacetic acid (IAA)
- A type of auxin which is a plant growth substance
Describe tropism (include positive and negative phototropism)
When a plant grows according to the light it is exposed to. It occurs due to auxins which are made in the meristem of a shoot.
Positive photropism - growing towards the light
Negative phototropism - growing away from the light
Describe how IAA works.
- made in meristem
- diffuses down to the zone of elongation
- IAA molecules bind to a receptor site on the cell surface membrane
- This activates the pumping of hydrogen ions into the cytoplasm
- The change in hydrogen ion concentration produces the optimum pH for enzymes which break down bonds between adjacent cellulose microfibrils
- Cells absorb water by osmosis and the flexible walls allow the cell to expand
What happens to the IAA once the cell has matured?
IAA is destroyed by enzymes, the pH rises and bonds form between cellulose microfibrils. The cell wall then becomes rigid ans can no longer expand.
How to shoots bend as a result of auxins?
- The side of the shoot exposed to light contains less auxin than the other side.
- light causes auxin to move laterally which means the shoot tip acts as a photoreceptor
- cells elongate on the dark side so the shoot bends towards the light
