IB MYP Integrated Science- Biology - Enzymes and homeostasis-Study Notes - New Syllabus

Enzymes and Homeostasis

🌟 Introduction

Enzymes and homeostasis are closely linked.
Enzymes speed up chemical reactions, while homeostasis keeps internal conditions stable so enzymes function properly.
Together, they keep metabolism smooth and efficient.

🧪 Enzymes – What They Are

• Enzymes are biological catalysts made of proteins.
• They speed up reactions without being used up.
• Each enzyme works on a specific substrate.

Key properties:

• Highly specific (lock and key).
• Needed in small amounts.
• Affected by temperature, pH, and substrate concentration.
• Lower activation energy of reactions.

How enzymes work:

Lock and Key Model: active site is exactly complementary to substrate.
Induced Fit Model: active site adjusts slightly to fit substrate more precisely.

🌡️ Factors Affecting Enzyme Activity

a) Temperature

• Rate increases until optimum temperature.
• Beyond optimum, enzymes denature.
• Human optimum: around 37°C.

b) pH

• Each enzyme has an optimum pH.
• Example: pepsin works best in acidic pH.
• Extreme pH denatures enzymes.

c) Substrate concentration

• Higher concentration increases rate until saturation point.
• After saturation, all active sites are full.

d) Enzyme concentration

• More enzymes → more active sites available.
• Reaction rate increases as long as enough substrate is present.
• If substrate becomes limited, increasing enzyme amount does not increase the rate.

🏠 Homeostasis – What It Means

Homeostasis is the ability of the body to maintain a stable internal environment despite external changes.

Conditions kept constant:

• Body temperature
• Blood glucose level
• Water balance
• pH of blood and tissues
• Ion balance (Na, K, Ca)

These conditions are vital because enzymes work only within narrow ranges.

🔁 Components of Homeostasis

a) Receptor

• Detects changes like temperature or glucose level.

b) Control center

• Usually brain/hypothalamus.
• Decides the response.

c) Effector

• Muscles or glands that carry out the response.

d) Negative feedback

• The main regulatory mechanism.
• Change occurs.
• Body responds to reverse the change.
• System returns to normal.

Example: body temperature control.

🌡️ Thermoregulation (Temperature Control)

Controlled mainly by the hypothalamus.

If temperature rises:

• Sweating increases.
• Vasodilation.
• More heat lost.

If temperature falls:

• Shivering produces heat.
• Vasoconstriction.
• Hairs stand up to trap air (in some animals).

Stable temperature is essential for enzyme action.

🍬 Blood Glucose Regulation

Maintained by insulin and glucagon from the pancreas.

High blood sugar:

• Insulin released.
• Glucose converted to glycogen and stored in liver.

Low blood sugar:

• Glucagon released.
• Glycogen converted back to glucose.

Stable glucose ensures proper respiration and enzyme function.

💧 Water and Ion Balance (Osmoregulation)

Controlled by: kidneys and ADH hormone.

If body has less water:

• ADH increases.
• Kidneys reabsorb more water.
• Urine becomes concentrated.

If body has excess water:

• ADH decreases.
• Kidneys excrete more water.
• Urine becomes dilute.

🔗 Link Between Enzymes and Homeostasis

• Enzymes need specific internal conditions.
• Homeostasis maintains those conditions.
• If temperature, pH, or water balance shifts, enzymes stop working.
• Without functioning enzymes, metabolism fails.

Homeostasis protects enzyme activity, and enzymes drive homeostasis reactions.

📌 Summary Table

⚡ Quick Recap 
Enzymes speed reactions; homeostasis keeps them in the right environment.
Too high or low temperature or pH leads to denaturation.
Homeostasis uses receptors, control centers, and effectors.
Negative feedback restores balance.
Key areas: thermoregulation, glucose regulation, osmoregulation.
If homeostasis collapses, enzyme activity fails.