Photosynthesis

What are the raw materials for photosynthesis?

Carbon dioxide and water

Where does photosynthesis take place?

Chloroplasts

What are the products of photosynthesis?

Glucose and oxygen

What does chlorophyll trap?

Light energy

Why is photosynthesis an endothermic reaction?

As sunlight (heat) is being absorbed

State the word equation for photosynthesis

Carbon dioxide + water = glucose + oxygen

State the balanced symbol equation for photosynthesis

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

State how glucose is used in plants

Respiration, storage, used to make other useful substances

How do gases enter/leave the leaf?

Through the stomata

How is light absorption maximized by a leaf?

• Large surface area of the leaf

• Thin so light doesnt have far to travel to cells

• Palisade layer tightly packed with loads of cells rich in chlorophyll, also close to the top of the leaf

• Upper epidermis is transparent to allow light through

By what process does gas exhange take place in the leaf?

Diffusion

How is gas exhange maximised by the leaf?

• Spongy mesophyll layer has intercellular spaces for gas exchange

• Lower epidermis has stomata to allow gases in and out

• There are guard cells to control the opening and closing the stomata

Which cells control the stomata?

Guard cells

What do we use to test for starch?

Iodine

How is a plant destarched?

Placed in the dark for 24-48 hours

Why do we boil the leaf before testing for starch?

To halt the chemical processes

Removes waxy cuticle

What is the purpose of the ethanol in the starch test method?

To remove the chlorophyll to allow iodine colour to be judged more easily

State an important safety precaution in the starch test method

Turn off the bunsen when using ethanol

Why must the bunsen be turned off when using ethanol in the starch test method?

Ethanol is flammable

Why must the leaf be softened with hot water before testing for starch?

Ethanol will make it brittle

What does the rate of photosynthesis depend on?

• Level of carbon dioxide,

• light intensity,

• temperature,

• water availability

Which factor determines the rate of photosynthesis?

The factor that is in shortest supply

What is the compensation point?

The point where the rate of photosynthesis equals the rate of respiration

What colour does hydrogencarbonate indicator become in low carbon dioxide levels?

Purple

What colour does hydrogencarbonate indicator become in high carbon dioxide levels?

Yellow

What colour does hydrogencarbonate indicator become in atmospheric carbon dioxide levels?

red