Photosynthesis: Key Concepts, Processes, and Gas Exchange in Plants

What is photosynthesis?

The process by which plants convert light energy into chemical energy in glucose.

Why is photosynthesis important?

It produces food and releases oxygen.

What energy change happens in photosynthesis?

Light energy → chemical energy.

Where does photosynthesis take place?

In chloroplasts.

What is the word equation for photosynthesis?

Carbon dioxide + water → glucose + oxygen.

What is the balanced symbol equation for photosynthesis?

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

What conditions are needed for photosynthesis?

Light, carbon dioxide, water, chlorophyll.

How does increasing light intensity affect photosynthesis?

Increases rate until another factor limits.

How does increasing carbon dioxide affect photosynthesis?

Increases rate until another factor limits.

How does temperature affect photosynthesis?

Increases to an optimum then decreases.

Why does photosynthesis decrease at high temperatures?

Enzymes denature.

Why is photosynthesis slow at low temperatures?

Enzymes work slowly.

What is the function of palisade mesophyll cells?

Main site of photosynthesis.

Why are palisade cells near the top of the leaf?

To receive more light.

Why does a leaf have a large surface area?

To absorb more light.

Why is a leaf thin?

Short diffusion distance for gases.

Why do palisade cells contain many chloroplasts?

To absorb more light energy.

Why do plants need mineral ions?

For growth and making substances.

Why are magnesium ions needed?

To make chlorophyll.

Why are nitrate ions needed?

To make amino acids and proteins.

What gas is released during photosynthesis?

Oxygen.

How can oxygen production be investigated using a water plant?

By counting bubbles or collecting gas.

What substance is tested to show photosynthesis has occurred?

Starch.

What test is used for starch in leaves?

Iodine test.

Why must a leaf be destarched before a starch test?

To ensure starch was made during the experiment.

Why is alcohol used in the starch test?

To remove chlorophyll.

Why is chlorophyll needed for photosynthesis?

It absorbs light energy.

What is gas exchange?

The movement of oxygen and carbon dioxide into and out of a leaf.

What process is responsible for gas exchange in leaves?

Diffusion.

What is diffusion?

The movement of particles from high to low concentration.

Which gas enters the leaf for photosynthesis?

Carbon dioxide.

Which gas leaves the leaf during photosynthesis?

Oxygen.

Which gas enters the leaf for respiration?

Oxygen.

Which gas leaves the leaf during respiration?

Carbon dioxide.

How is the leaf adapted for gas exchange?

Large surface area, air spaces, thin structure.

What are air spaces in the spongy mesophyll for?

To allow gases to diffuse easily.

What are stomata?

Pores in the leaf surface.

What is the function of stomata?

Control gas exchange.

Which cells control the opening and closing of stomata?

Guard cells.

When are stomata usually open?

During the day.

Does respiration happen during the day or night?

Both day and night.

Does photosynthesis happen at night?

No.

Why does net gas exchange depend on light intensity?

Because photosynthesis rate changes.

What is meant by net gas exchange?

Overall gas movement after respiration and photosynthesis.

What happens to net gas exchange in bright light?

More oxygen released than carbon dioxide.

What happens to net gas exchange in darkness?

More carbon dioxide released than oxygen.

What is hydrogen-carbonate indicator used for?

To show carbon dioxide concentration.

What colour is hydrogen-carbonate indicator in high carbon dioxide?

Yellow.

What colour is hydrogen-carbonate indicator in low carbon dioxide?

Purple.

What colour is hydrogen-carbonate indicator at normal carbon dioxide?

Red.

What waste gases are produced by plant metabolism?

Carbon dioxide and oxygen.

How do waste gases leave the leaf?

By diffusion through the stomata.