MYP Biology 4.9 Homeostasis Notes

What Is Homeostasis?

1. Homeostasis is the regulation of internal conditions to keep them within a safe, functional range.
2. Cells work efficiently only when conditions such as temperature, water balance, and blood glucose stay stable.
3. Even if the external environment changes, the body keeps these internal factors tightly controlled.

Why Do Living Organisms Need Stable Internal Conditions?

1. Enzymes control nearly all reactions in cells and work only within narrow temperature and pH ranges.
2. If internal conditions drift too far from optimum, enzyme activity slows or stops.
3. Stable conditions ensure cells receive a steady supply of materials and energy.

What Factors Are Controlled by Homeostasis?

1. Homeostasis regulates conditions that directly affect enzyme activity and cell function.
2. Key regulated variables:
   1. Body temperature: ensures enzymes work at optimal rates.
   2. Blood glucose concentration: provides cells with a steady energy supply.
   3. Water content of the blood: maintains osmotic balance and blood pressure.

How Does the Homeostasis Control System Work?

Homeostasis works through a coordinated system of receptors, coordination centres, and effectors:

1. Receptors
   1. Detect changes (stimuli) in the internal or external environment.
2. Coordination centers
   1. Process information from receptors and send instructions.
   2. Includes the brain, spinal cord, and pancreas.
3. Effectors
   1. Carry out responses to restore normal conditions.
   2. Includes muscles and glands.

What Is Negative Feedback and Why Is It Important?

1. Negative feedback reverses a change to bring the body back to its normal range.
2. If a condition becomes too high, effectors bring it down.
3. If a condition becomes too low, effectors bring it up.
4. This constant adjustment keeps internal conditions stable.

How Does the Body Regulate Blood Glucose?

1. Blood glucose levels are controlled by insulin and glucagon, two hormones released by the pancreas.
2. When glucose is too high:
   1. The pancreas releases insulin
   2. Cells absorb more glucose
   3. The liver converts glucose to glycogen for storage.
   4. Blood glucose returns to normal.
3. When glucose is too low:
   1. The pancreas releases glucagon
   2. The liver breaks down glycogen into glucose.
   3. Blood glucose rises back to normal.

What Is Osmoregulation and Why Is Water Balance Important?

1. Osmoregulation is the control of water content in the body.Water levels change constantly through sweating, breathing out, urination, and digestion.
2. Cells need a stable water concentration to avoid shrinking or bursting.

How the body adjusts water balance

1. The kidneys filter the blood
2. Anti diuretic hormones (ADH) controls how much water is reabsorbed
   1. More ADH → more water saved → concentrated urine
   2. Less ADH → more water lost → dilute urine

What Are The Key Homeostatic Processes?