Biology Revision

Keeping Healthy

- Regular exercise and a balanced diet

-Too little food leads to a person being underweight 

this and can lead to... being prone to illnesses 

 - Too much food and not enough exercise leads to a person being overweight

this can lead to...ill health

If someone’s diet consists of food with a lower energy content than the amount of energy their body uses, the person will lose body mass.

Defending against infection

-Pathogens are microorganisms

 such as bacteria and viruses - that cause disease

-Bacteria release toxins

-viruses damage our cells

-White blood cells can ingest and destroy pathogens

- Vaccination involves putting a small amount of an inactive form of a pathogen, or dead pathogen, into the body.

The nervous system

-The nervous system allows the body to respond to changes in the environment in a process usually coordinated by the brain

-Reflex actions are extra-rapid responses to stimuli

this process also involves the nervous system but bypasses the brain.

• sensoryneurones carry signals from receptors to the spinal cord and brain
• relayneurones carry messages from one part of the CNS to another
• motorneurones carry signals from the CNS to effectors.

examples of effectors:

• a muscle contracting
• a gland releasing (secreting) a hormone or other chemical.