- all living organisms need to detect stimuli and respond to them.
- A stimulus is a change in the environment that causes a response.
- Environment-. external e.g change in air temperature.
internal e.g. change in CO2 concentration in blood.
- response is a change in physiology or behaviour. e.g. stimulus e.g fear Response e.g increase in heartbeat (touch/movement) Venus flytrap stimulus=hair response=eat fly
- plants and animals are multicellular. specialisation means that different parts of the organism have to communicate with each other.
- cells communicate by secreting chemicals in to the surrounding medium(tissue fluid) which will react with receptors and become chemical signals for short distances.
- there are four ways cells can communicate:
1). paracrine system:cells which release chemicals in to tissue fluid (short distances) e.g. histamines in damaged cells + allergen.
2). endocrine system: cells which release chemicals hormones go in to tissue fluid and into blood to target cells. (long)
3). nerve system: specialised cells/neurons info travels as nervous impluses and at end chemicals released e.g. nurotransmitter acet
4). neurosecrition: some nerve cells which secrete chemicals into blood e.g. ADH (made in peturity gland target kidney).
- the maintanence of a constant internal enviroment despite changes
- temeperature has to remain constant (77…