Homeostasis - Chp 29

Homeostasis

is the ability of an organism to maintain a constant internal environment

Describe homeostasis in humans

• internal environment of humans is the tissue fluid/intracellular fluid around the cells

• a combination of processes work together to control the internal environment of an organism

• organs and organ system work together and these processes are coordinated by the brain in order to maintain homeostasis - eg skin, kidneys, liver, heart and lungs

Examples of homeostasis in humans

• maintaining a body temperature of 37^oC

• keeping pH of blood at pH7.4

• preventing the build up of toxic chemicals

• maintaining sufficient oxygen levels

• controlling glucose in plasma at 0.01%

What effects an organisms ability to exchange materials with the environment?

• the amount of material to be exchanged

• the surface area available for exchange

• some organisms have special organs for exchange, but single-celled organism do not

What methods are used by organisms to improve diffusion and exchange?

• organ can be flattened to reduce the distance between the two surfaces, and therefore allow materials to be exchanged by diffusion - eg leaves of a plant

• respiratory systems provide increased surface area for the exchange of gas by use of the alveoli

• respiratory and excretory systems take materials to the body surface

  • gases are passed in and out of the lungs while waste products are excreted from the body

Why is homeostasis necessary?

Allows organisms to function efficiently

• homeostasis controls the environment around the cells

• if this environment is constant the cells will be able to operate under optimal conditions, which allows the organism to function properly

  • rate of enzymes will slow down if the body temperature falls below or above 37^oC

Allows organisms to function independently of their external environment

• homeostasis allows organisms to function under adverse conditions

  • if the external temperature drops in winter, humans can continue to function as normal because they can control their internal temperature

  • frogs are ectothermic and cannot control their internal temperature

Allows slight changes in internal environments

• our internal environments have to be allowed to change or fluctuate slightly

  • our body temperature falls by 1^oC at night when we sleep

  • our body temperature rises when we get an infection

  • the internal environment also changes due to hormonal changes during puberty, the menstrual cycle and menopause