7.10B Explain the importance of homeostasis, including: a thermoregulation…

The idea

Homeostasis keeps internal conditions within narrow limits so cells keep working. For thermoregulation, body temperature affects enzyme activity: enzymes have an optimum temperature, and too high a temperature denatures them so their active site no longer fits the substrate, slowing metabolism; too low a temperature reduces the rate of collisions between enzyme and substrate. For osmoregulation, the water potential of body fluids must be controlled. If surrounding fluid is too dilute, water enters animal cells by osmosis and they may swell and burst; if it is too concentrated, water leaves and cells shrink, so they cannot function. Homeostasis therefore maintains temperature and water balance so enzymes and cells work effectively.

What earns the marks

• States that homeostasis maintains a stable internal environment within narrow limits.
• Explains that enzymes have an optimum temperature at which reaction rate is greatest.
• Explains that temperatures above the optimum denature enzymes, changing the active site so substrate no longer fits.
• Explains that temperatures below the optimum slow reactions because particles collide less often.
• Explains that osmoregulation controls water potential of body fluids.
• Explains that too much water entering animal cells by osmosis causes them to swell and possibly burst.
• Explains that too little water causes animal cells to shrink and stop functioning.

Common mistakes and how to put them right

• Saying high temperature kills or 'breaks down' enzymes.

  Put it right: High temperature denatures enzymes by altering the active site shape.

• Confusing the direction of osmosis.

  Put it right: Water moves from a higher water potential (more dilute) to a lower water potential (more concentrated) solution.

• Treating homeostasis as keeping conditions perfectly constant.

  Put it right: It keeps conditions within narrow limits around a set point.

Exam tips

• Link each condition directly to its effect: temperature to enzyme active sites, water balance to cell volume.
• Use the term 'denature' precisely and explain that the active site shape changes so the substrate no longer fits.
• When describing osmosis, state the direction of water movement and the effect on the cell.