Unit B4: Homeostasis

Revision of Unit B4: Homeostasis - Maintenance of a constant internal environment, Control systems, Negative feedback, Function of cells

HideShow resource information

Unit B4: Homeostasis



Maintenance of a constant internal environment; Control systems;

Negative feedback; Function of cells

1 of 6

2 of 6

Maintenance of a constant internal environment

  • Maintains Internal Temperature (37degrees)

< Heat stroke (Too hot)  - Rapid heart rate - Confusion - Dizziness - Increased Temperature - Increase in sweat leads to dehydration - Drink plenty of water

< Hypothermia (Too cold-35degrees) - Confusion - Violent Shivering - Weak pulse - Shallow breathing - Hairs stand up to trap heat - Warm blankets/drinks

  • Maintains Water + Salt Levels - Maintained by Kidneys

< Gain water via food and drink - LOOSE water via sweating, faeces and urine

< Kidneys extract molecules from the blood, then restore the correct levels of salt and water back in to the body. The rest is excreted as urine.

< MORE dilute plasma, LESS ADH released-More dilute urine- Alcohol suppresses ADH - more dilute urine

< LESS dilute plasma (more concentrated), MORE ADH released -More concentrated urine- Ecstasy increases ADH production resulting in too much water in the body creating a more concentrated urine

3 of 6

Control Systems

  • Receptors: Detect stimuli/Change in the environment - Nerve receptors
  • Processing centre: Recieves information + co-ordinates response - Hypothalamus - Brain
  • Effectors: Produce a response to the Stimulus - Muscles or glands


Central Nervous System helps to control homeostasis by detecting a stimulus, co-ordinating and producing a response

Room temperature decreases, Body temperature decreases
RESPONSE: Constriction of Blood vessels, Curling up, Shivering
RESULT: Heat production increases, Heat loss decreases, Body temperature regulates back to its optimum temperature of 37 degrees

4 of 6

Negative Feedback

Negative Feedback is the process in which changes are reversed inside the body. Negative feedback controls:

  • Blood oxygen levels
  • Salt levels
  • Temperature

Examples of Negative Feedback:
Too Hot:
Vasodilation - Blood vessels become larger to lose heat/cool down
Sweating - Releases heat via excess water
Pilorelaxation - Hairs on skin flatten

Too Cold:
Vasoconstriction - Blood vessels become smaller to maintain heat
Shivering - Rapid, Involuntary muscle movement. Heat produced by respiration
Piloerection - Hairs on skin stand up

5 of 6

Function of cells

Cells depend on the movement of chemicals around the body via osmosis and diffusion:
type of diffusion with water
Low concentration to high concentration through a partially permeable membrane

Diffusion: Spreading of particles
- High concentration to low concentration - "Moving down a concentration gradient"

Diffusion in body = Digested food moves from gut to small intestine
- Diffusion in plants = Carbon dioxide moves from air spaces between mesophyll cells to the chloroplast

Work best at optimum temperature, maintained with Homeostasis
- If the temperature increases, so does the reaction rate (more collisions due to greater energy) Denature if too hot
- Active site of an enzyme is where the reaction occurs. Shape of Active site alters by pH and temperature
- Lock and key Model - Only molecules with the correct shape can fit into the enzyme - Only one type of enzyme can speed up a specific reaction

6 of 6


Muskaan Mujahid


Great notes about Homeostasis.

Similar Biology resources:

See all Biology resources »See all Homeostasis resources »