1. Chapter 10 Physiological adaptations for survival V.C.E. Biology Unit 2 – Area of study 1

2. Key knowledge

4. Internal and external environments Internal environment – This refers to the environment inside an organism. For animals in good health, the internal environment remains relatively constant. The internal environment refers to the tissue fluid and plasma form of the body cells.

5. External environments External environment – This refers to the environment outside an organism. Variations to the external environment can vary greatly; temperature (very hot to very cold), humidity (high humidity to very dry). Despite this, the cells of a person (and other animals) exist in a relatively stable and unchanging environment – tolerance range.

6. Homeostasis Homeostasis refers to an animals ability to maintain a stable internal environment, despite fluctuations to their external environment. Homeostasis is an extremely important concept, essential for the survival of an animal.

8. Homeostasis When deviations occur in the internal environment of a healthy organism, mechanisms usually act to restore the changed values to their ‘normal state’. The mechanism that does this is called the ‘Negative feedback mechanism’.

9. Negative feedback If the response by the effector – the gland or organ responding to stimulation – cancels or counteracts the original disturbance or stimulus, the mechanism is referred to as ‘Negative Feedback’.

10. Body systems contribute to homeostasis

11. The nervous system The nervous control system is composed of the brain, the spinal cord and all the nerve cells connecting these to other parts of the body. The brain and the spinal cord make up the central nervous system (CNS). All the other nerve cells, in whole or part that lie outside the CNS form the peripheral nervous system (PNS).

12. CNS or PNS

14. Nerve cells Nerve cells are the basic units of the nervous system. Nerve cells are also known as neurons. This is a neuron

15. Nerve cells A typical neuron has a cell body that contains the nucleus. This is the cell body

16. Nerve cells Extensions arise from the cell body, and carry the information away to another neuron or tissue. These extensions are known as axons. This is the axon

17. Nerve cells Connecting and effector neurons also have extensions known as dendrites. Dendrites are highly branched extensions of the cell body that receive information from other neurons and carry information towards the cell body. These are dendrites

18. Kinds of neurons There are three basic kinds of neurons. There are only a few neurons involved in a reflex arc. A reflex arc comes into play when an immediate response needs to occur, e.g. a hand touching an extremely hot surface will pull away very quickly.