MYP Biology 3.4 Cell Respiration Notes

What Is Cellular Respiration?

1. Cellular respiration is the chemical process that releases energy from glucose.
2. Cells break down glucose in a controlled way to release usable energy for life processes.
3. This energy powers everything a cell does, from transport to movement.

Why Do Cells Need Energy?

1. Cells need energy to carry out processes that keep the organism alive.
2. The energy released in respiration is used for:
   1. Muscle contraction for movement.
   2. Active transport, such as moving ions against concentration gradients.
   3. Cell division for growth and repair.
   4. Protein synthesis to build enzymes and structural proteins.

How Is Energy Stored and Released in ATP?

1. Cells cannot use the energy in glucose directly.
2. Respiration transfers this energy to a molecule called ATP.
3. ATP stores energy in its phosphate bonds and releases it when one phosphate is removed.
4. The two key ideas here are:
   1. When ATP → ADP, energy is released
   2. When ADP → ATP, energy is stored (during respiration)

What Are The Types of Respiration?

1. Cells can release energy in two ways:
   1. Aerobic respiration (with oxygen).
   2. Anaerobic respiration (without oxygen).
2. Aerobic respiration releases much more energy because glucose is broken down completely.

How Does Aerobic Respiration Release Energy?

1. Aerobic respiration breaks glucose down completely into carbon dioxide and water.
2. This breakdown releases energy stored in glucose bonds and transfers it to ATP, the molecule that powers cellular work.
3. It's word equation is:

$$Glucose + Oxygen → Carbon dioxide + Water + Energy$$

Why Does Anaerobic Respiration Occur?

1. Anaerobic respiration occurs when oxygen supply can't meet energy demand.
2. During intense exercise or low-oxygen conditions, cells switch to anaerobic pathways to produce some energy quickly, even though it is less efficient.
3. There are two forms of anaerobic respiration:
   1. In animals: Glucose → Lactic acid + Energy
   2. In yeast/plants: Glucose → Ethanol + Carbon dioxide + Energy

Why Does Anaerobic Respiration Release Less Energy?

1. Anaerobic respiration releases less energy because glucose is only partially broken down.
2. Much of the energy remains “locked” in the lactic acid or ethanol molecules.

What Happens to the Body After Anaerobic Respiration?

1. After intense exercise, the body must remove lactic acid and restore normal oxygen levels.
2. The body needs extra oxygen to break it down.
3. This is called oxygen debt.
4. Recovery steps
   1. Lactic acid is transported to the liver.
   2. Oxygen is used to convert lactic acid back into glucose.
   3. Breathing rate and heart rate remain high until this is complete.

How Does Respiration Support Metabolism?

1. Respiration supplies the energy needed for all chemical reactions in cells.
2. These include:
   1. Building molecules (proteins, DNA).
   2. Breaking down molecules for recycling or energy.
3. Without respiration, metabolism would stop and cells would no longer function.

Why Do Plants Also Perform Respiration?

1. Plants make glucose during photosynthesis but still need energy to survive.
2. They use respiration to release the energy stored in glucose.
3. Plants photosynthesize only in light, but respire all the time.