The requirements and products of photosynthesis: practical | Combined science

Starter quiz

Cells in the leaves of plants have chloroplasts that contain a green pigment called ______.

'chlorophyll' ✓
The energy required for photosynthesis is transferred to chlorophyll by ...

carbon dioxide.

chloroplasts.

light. ✓

water.
What is the correct word summary for photosynthesis?

carbon dioxide + water --> glucose + oxygen ✓

carbon dioxide + oxygen --> glucose + water

glucose + oxygen --> carbon dioxide + water

glucose + carbon dioxide --> water + oxygen
Some of the glucose made by photosynthesis is stored as starch. Which reagent can be used to test for the presence of starch?

Benedict’s solution

biuret solution

iodine solution ✓

pH indicator
Iodine solution changes colour in the presence of starch. What colour would you expect the iodine solution to be when starch is present?

blue/black ✓

brick red

lilac/purple

yellow/orange
Who correctly predicts what would happen if there was no carbon dioxide available for a plant during the day?

Lucas: This would have no effect on the amount of glucose made.

Izzy: No glucose would be made because photosynthesis needs carbon dioxide. ✓

Laura: Carbon dioxide is just a waste product, so more glucose would be made.

Some of the glucose made by photosynthesis is used to make a larger carbohydrate called ______, which is stored in grains in plant cells.

'starch' ✓
The reagent called ______ solution is used to test for the presence of starch.

'iodine' ✓
True or false? The iodine test result for this leaf shows that it contains starch.

True

False ✓
Foil was attached to this leaf to block out the ...

ethanol.

iodine solution.

light. ✓

water.
Why is a leaf placed in hot ethanol when testing for the presence of starch?

To de-starch the leaf.

To remove green-coloured chlorophyll. ✓

To turn glucose into starch.

To show the presence of starch with a blue/black colour.
The photographs show the same leaf before and after the iodine method was used to test it for starch. Which statement explains why area A turned a darker colour during the test?

Area A had less chlorophyll so less starch was made.

Area A had more chlorophyll so more starch was made. ✓

Area A had less carbon dioxide so less starch was made.

Area A had more carbon dioxide so more starch was made.

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Some of the glucose made by photosynthesis is converted into starch and stored in starch grains in leaf cells.
Iodine solution can be used to test plant leaf tissue for the presence of starch.
A scientific prediction is a testable statement about a possible outcome, which can be tested in an experiment.
Predicting the iodine test result for destarched leaves kept in various conditions, and explaining the predictions.
Observing the iodine test result for destarched leaves kept in various conditions, and explaining the observations.

Mixing up a prediction, an observation and an explanation.

This practical lesson explores predictions, observations and explanations in the context of using iodine solution to test leaves for starch.

Photosynthesis - the process used by producers to make their own food via a series of chemical reactions
Glucose - a type of sugar, which is a simple carbohydrate
Starch - a complex carbohydrate, made of many glucose molecules joined together to form a polymer
Iodine solution - a reagent that can be used to test for the presence of starch
Prediction - a scientific prediction is a testable statement about a possible outcome, which could be tested in an experiment