4: Bioenergetics

What is bioenergetics?

The study of how energy flows through living organisms via photosynthesis and respiration.

What is photosynthesis?

An endothermic reaction where plants use light energy to convert carbon dioxide and water into glucose and oxygen.

What is the word equation for photosynthesis?

Carbon dioxide + water → glucose + oxygen

What is the balanced symbol equation for photosynthesis?

6CO2 + 6H2O → C6H12O6 + 6O2

Why is photosynthesis endothermic?

Energy is transferred from light into the chloroplasts.

Where does photosynthesis occur?

In chloroplasts (mainly in leaf cells).

What is chlorophyll?

A green pigment that absorbs light energy for photosynthesis.

What are the limiting factors of photosynthesis?

Light intensity

What is a limiting factor?

The factor in shortest supply that limits the rate of photosynthesis.

How does light intensity affect photosynthesis?

Increasing light increases rate until another factor becomes limiting.

How does carbon dioxide affect photosynthesis?

Higher CO2 increases rate until another factor limits it.

How does temperature affect photosynthesis?

Rate increases with temperature to an optimum

Why does photosynthesis level off on a graph?

Another factor becomes limiting.

What is the inverse square law (HT)?

Light intensity decreases as distance from the light source increases (1/d²).

How do you measure photosynthesis rate in experiments?

By counting oxygen bubbles or measuring volume of oxygen produced.

Why are limiting factors important in greenhouses?

To maximise photosynthesis while keeping costs efficient.

What are the uses of glucose in plants?

Respiration

Why is glucose converted to starch?

Starch is insoluble so it does not affect osmotic balance.

What is cellulose used for?

Strengthening plant cell walls.

How do plants make proteins?

Glucose + nitrate ions → amino acids → proteins.

What is respiration?

An exothermic reaction that releases energy from glucose in cells.

Why is respiration exothermic?

It releases energy for cellular processes.

What is aerobic respiration?

Respiration using oxygen.

What is the word equation for aerobic respiration?

Glucose + oxygen → carbon dioxide + water

What is the symbol equation for aerobic respiration?

C6H12O6 + 6O2 → 6CO2 + 6H2O

What is anaerobic respiration?

Respiration without oxygen.

What is anaerobic respiration in muscles?

Glucose → lactic acid

Why does anaerobic respiration release less energy?

Glucose is only partially broken down.

What is anaerobic respiration in yeast?

Glucose → ethanol + carbon dioxide

What is fermentation?

Anaerobic respiration in yeast used to make bread and alcohol.

What is oxygen debt?

The extra oxygen needed after exercise to oxidise lactic acid.

Why does lactic acid build up?

Insufficient oxygen causes anaerobic respiration.

What causes muscle fatigue?

Build-up of lactic acid.

How does the body respond to exercise?

Increased heart rate

Why do breathing and heart rate increase?

To deliver more oxygen and glucose to muscles.

What happens to lactic acid after exercise (HT)?

Transported to liver and converted back to glucose.

What is metabolism?

The sum of all chemical reactions in a cell or body.

What processes are part of metabolism?

Respiration

How is glucose stored in animals?

As glycogen.

How are lipids formed?

Glycerol + 3 fatty acids.

What happens to excess proteins?

Broken down to form urea for excretion.

Why do organisms need energy?

For movement