Chapter 1:Photosynthesis and the carbon cycle, 1.2:More About Photosynthesis

a factor that prevents the rate of photosynthesis from increasing further

Limiting factor

the main factors that affect the rate of photosynthesis

Light intensity

what happens to the rate of photosynthesis when light intensity increases

It usually increases

what happens when another factor becomes limiting

The rate stops increasing

what happens to the rate of photosynthesis when carbon dioxide concentration increases

It usually increases

what happens when carbon dioxide concentration is already high enough

Adding more has little or no effect

what happens to photosynthesis at low temperatures

It happens slowly

what happens to the rate of photosynthesis as temperature increases

It generally increases

what happens when the temperature becomes too high

The rate of photosynthesis decreases

why can very high temperatures reduce photosynthesis

They can damage the enzymes involved in photosynthesis

what is the role of water in photosynthesis

It is a reactant needed for photosynthesis

how does water reach the leaves

Through the xylem

what can happen to photosynthesis when a plant does not have enough water

The rate of photosynthesis decreases

tiny openings on the surface of leaves that allow gases to move in and out

Stomata

what gas enters the leaf through the stomata

Carbon dioxide

what gas leaves the leaf through the stomata

Oxygen

why can closing the stomata reduce photosynthesis

Less carbon dioxide can enter the leaf

why are leaves broad and flat

To provide a large surface area for absorbing light

why are leaves thin

So gases do not have to travel far to reach the photosynthesising cells

which cells contain many chloroplasts and are near the top of the leaf

Palisade cells

what do the veins in a leaf do

Transport water and substances around the plant

what is stored when excess glucose is converted

Starch

what solution is used to test a leaf for starch

Iodine solution

what colour does iodine turn when starch is present

Blue-black

what colour is iodine when starch is absent

Yellow-brown

why is a leaf boiled in water before the starch test

To kill the cells and stop chemical reactions

why is ethanol used during the starch test

To remove chlorophyll

why is a water bath used when heating ethanol

Because ethanol is flammable

why is chlorophyll removed before testing for starch

To make the colour change easier to see

what does a blue-black colour in a leaf show

Starch is present

how can you investigate whether light is needed for photosynthesis

Cover part of a leaf and expose the plant to light

what should happen to the part of the leaf exposed to light

It should turn blue-black

what should happen to the part of the leaf kept in darkness

It should not turn blue-black

what does the light experiment provide evidence for

Light is needed for photosynthesis

how can you investigate whether carbon dioxide is needed for photosynthesis

Remove carbon dioxide from the air around one plant and compare it with a control plant

what does the carbon dioxide experiment provide evidence for

Carbon dioxide is needed for photosynthesis

why is a control plant used in an experiment

To provide a comparison

why should a plant be destarched before investigating photosynthesis

To remove stored starch so the results are more reliable

how can glucose be used by a plant

For respiration

why is photosynthesis important to other organisms

It produces oxygen and provides food and energy stored in plants