MakingFood

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2

Slide 10

Plants’ uses of plant glucose

Slide 11

Glucose molecule

Slide 12

Activity – Testing a plant for sugar

Put a piece of raw onion in a pestle and mortar.

Grind it with a little sand and 10cm3 of water.

Filter the liquid into a test tube

Heat the liquid with 10 drops Benedict’s solution in a water bath

What colour change would you expect if sugar was present?

b) Write an explanation of your results.

You need to know the plant experiments in detail, explain the different steps, and results, in each one.

Slide 13

Activity -Testing a leaf for starch

Dip a leaf into boiling water for about a minute (to soften it).

Turn off the Bunsen burner.

Put the leaf into a test-tube of ethanol (to remove chlorophyll).

Stand the test-tube in a beaker of hot water for about 10 minutes.

Wash the leaf in cold water.

Spread the leaf out flat on a petri dish and cover it with iodine solution (tests for starch).

If the leaf goes blue-black,

starch is present.

Slide 14

Activity -Testing a leaf for chlorophyll

Repeat the starch test but this time use a variegated leaf from a geranium plant.

Variegated means that a plant has coloured and white parts on its leaves.

Do the green parts contain chlorophyll? Do the white bits? Which do you think will test positive for starch?

Slide 15

From little acorns do great oaks grow…

Where do the extra 250kg come from?

Explain your answer as fully and scientifically as you can.

A tree is planted in a meadow. After 20 years it has grown into a big tree, weighing 250kg more than when it was planted.

Slide 16

Gas Balance

During the day:

Oxygen released by photosynthesis is greater than the amount of oxygen used up in respiration.

CO2 used in photosynthesis is greater than the amount of CO2 produced by respiration.

glucose + oxygen  carbon dioxide (CO2) + water

Respiration

Photosynthesis

carbon dioxide + water  glucose + oxygen

all the time

daylight only

Slide 17

Fill a jar with water.

Fill a test tube with water too and cover the top as you place it upside down inside the jar.

Take a runner and feed it up inside the test tube.