Responding to Environment = Survival
Plants & Animals - increase chances of survival by responding to external environment changes & internal environment. e.g. temp
Means conditions optimal for metabolism (chem reactions).
Stimulus - any change in internal/external.
- Receptors detect stimuli.
- Specific - detect one particular stimulus. e.g. light, pressure etc.
- Many different types for different stimuli.
- Some are cells e.g photoreceptors connect to nervous system.
- some are proteins on cell surface membranes e.g. glucose receptors on pancreatic cells.
- bring a response to stimulus
- produce an effect
- e.g. muscle cells, cells in glands (pancreas)
Nerve & Hormone Communiction
- Receptors communicate with effectors via nervous / hormonal system or both.
- Both are examples of cell signalling.
Changes in external envir. can affect internal. e.g. blood + tissue fluid
Homeostasis - involves control systems
- keeps internal envir constant which is vital to function normally + to stop damage.
Important - maintaining core body temp as it affects enzyme activity. Enzymes control rate of metabolic reactions.
- Body temp too high (e.g. 40°C) - enzymes denature (molecules vibrate too much, breaks H bonds which holds 3D shape, active site changed + no longer works as catalyst). Metabolic reactions less efficient.
- Body temp too low - enzyme activity reduced. Rate of metabolic reactions slowed down.
- Highest rate of enzyme activity - optimum temp (about 30°C)
Important - maintaining glucose concentration in blood for respiration
- mechanism that restores to around norm.
- e.g. body temp kept within 0.5°C above/below 37°C
- change can't be too big b/c effectors can't counteract
- e.g. big body temp drop from prolonged cold weather - too big a change to counteract
- Amplifies change
- Effectors increase level away from norm
- Rapidly activates something
e.g. blood clot:
- Platelets activiated
- Release chemical
- More platelets activated
- Platelets quickly form blood clot at injury
- Negative feedback - body detects blood clot has formed.
Positive feedback - not involved in homeostasis b/c doesn't keep internal envir. constant.
Homeostatic systems - receptor, communication system, effector.
Receptor - detect too high/low
Communication system - sends stimulus from receptor to effector by hormonal/nervous sys.
Effector - respond to counteract change to norm.
Enzyme conditions - need to be kept constant to be optimum.
Negative feedback - mechanism that restores back to norm.
Positive feedback - amplifies change.