Coordination Lesson Objectives: •How do hormonal and nervous coordination differ?•What are the chemical mediators and how do they work? •What changes to plants respond to? •How do plants respond to change? •What are plant growth factors?
No body system can work in isolation• Draw the outline of a body.• Draw one system on the body e.g reproductive.• For that system to work what other systems does it rely on?• Annotate you diagram.
Comparing nerves and hormones. Copy and fill in the table using page 157 Hormonal System Nervous System
Chemical Mediators• Act locally on cells that produce them and other cells in the immediate area.• Released by injured or infected cells.• Cause arteries and small arterioles to dilate.
Prostaglandins• Are mediators of the first three characteristics.• Released from damaged cells at the site of injury.• Have several important effects including: Vasodilatation of arterioles – this allows more blood to flow to the area and more phagocytic white blood cells. Promoting blood clotting – minimises blood loss and entry of microbes.• Pain is a result of pressure on nerve endings and pressure receptors due to an increase of blood.
Histamine• Not produced by damaged cells but by mast cells in the area.• Acts on the capillary walls allowing them to dilate and become more leaky.• This allows some of the plasma, including protein molecules to leave the blood.• Increases the volume of liquid in the tissues causing swelling.• The ‘leakiness’ makes it easier for phagocytes to exit the blood and enter the tissues.
Pus• The liquid in the tissues.• Dead phagocytes continuing bacteria/dead cells they have engulfed.• Escape from the inflamed site as ‘pus’.
Do plants have hormones?• They have chemical messengers, but they aren’t secreted by glands and don’t travel in a transport system.• They are called plant growth factors.• They include: – Auxins – Gibberellins – Abscisic acid – Cytokinins – Ethene
Auxins• Best known growth factor as they were the first to be discovered.• There are several different auxins but they are all similar, chemically, to indole acetic acid (IAA).
Control of phototrophic response by IAA• The way auxins, including IAA act has only recently been discovered.• They act on growth genes turning them on and stimulate cell division and cell elongation.• The growth towards light from one side is a result of the auxin being redistributed to the shaded side of the root.
Gravitrophic Response• Auxins inhibit growth in roots.• It is the absence or low concentrations of auxins that bring about growth.• If a seedling is placed horizontally and left, the roots grow downwards and the shoot upwards.
Gravitrophic Response• In both root and shoot the auxin is redistributed to the lower side.• In the shoot the auxin stimulates growth, so the cells on the lower side grow faster than those on the upper side causing upwards curvature.• In the root auxin inhibits growth, so cells on the lower side grow more slowly than those on the upper causing a downward curvature.
Darwins Experiments 1880Read pages 158-160 and answer the questions.