Chlorophyll Scientific EnquiryChlorophyll Scientific Enquiry

Dave Crowley, 2008

Chlorophyll Scientific EnquiryChlorophyll Scientific Enquiry

To know chlorophyll is needed for photosynthesis

Tuesday, April 18, 2023

Your aimYour aim

The aim of the lesson is for you to be able to come up with a test that can prove that chlorophyll is needed for photosynthesis to take place…

To get us started we need be able to explain what photosynthesis is, as well as what it needs to take place (reactants) and what is produced (products)

PhotosynthesisPhotosynthesis

Photosynthesis is a process which takes place in the leaves of all green plants to produce food for the plant

The food produced is a sugar called glucose

Carbon dioxide + Water Glucose + Oxygen

6CO2 + 6H2O C6H12O6 + 6O2

Light & Chlorophyll

Light & Chlorophyll

ProductsProducts

The products of photosynthesis are glucose and oxygen. The oxygen is a waste product for the plant, it is the glucose that it wants because this is the plants food

What happens to this glucose that has just been made?

• Used for respiration

• Used for making chlorophyll, cell walls, seeds, proteins etc…

• Stored within the plant to be used later

StorageStorage

Why does the plant store some of its food it has produced? How does it store it? Is it stored as glucose?

The glucose the plant produces during photosynthesis is stored as starch (a carbohydrate)

This starch is stored in all areas of the plant, e.g. the leaves, roots and stem

So if a plant is photosynthesising a lot then there will be lots of glucose produced which will be turned into starch

Test for starchTest for starch

A test for starch is to use iodine. If the starch is present then the iodine will change from yellow to a dark blue / black

Starch present - iodine turns from its normal yellow/orange colour to a dark blue / black

Your taskYour task

Your are going to set up an experiment to prove that chlorophyll is needed for photosynthesis to take place

How could you do this?

Your taskYour task

There are special types of leaves called variegated leaves: these have green and white patches on the leaves, e.g. a spider plant

The white patches do not contain any chlorophyll so they do not photosynthesise

Task – Task – What Facts Do I Know NowWhat Facts Do I Know Now

Task 1 - on the what facts do I know now section write down what you know is needed for photosynthesis (including the conditions needed for it to take place) and what the products of photosynthesis are

Key words to help: photosynthesis; sunlight; glucose; chlorophyll

E.g. photosynthesis reactants are… and the products are… and without chlorophyll there would be no…

Task – Task – Can I ExplainCan I Explain

Task 2 - on the can I explain what I know with scientific ideas section explain why plants need to store one of the products of photosynthesis and how you could test for this

Key words to help: roots; photosynthesis; winter; storage; variegated; iodine; colour change; starch

E.g. plants store starch as the roots are unable to… over winter it might not be possible for photosynthesis to… iodine shows the presence of… variegated leaves do not have as much chlorophyll so there will not be as much stored…

Task – Task – What Test To ProveWhat Test To Prove

Task 3 - on the what test could I do to prove my ideas are correct section design a test which could prove that chlorophyll is needed for photosynthesis to take place

Consider the different leaves we have - which contains more chlorophyll?

If there is more chlorophyll what can take place more and what will this mean?

ExperimentExperiment

You now have to set up your experiment to prove that chlorophyll is needed for photosynthesis…

1. Choose 2 leaves; 1 normal and 1 variegated2. Place one leaf into a test tube with ethanol in it; and the other

leaf in a second test tub with ethanol in it3. Label the 2 test tubes: (1) variegated and (2) normal4. Place the 2 test tubes in the water bath and wait for at least 3

minutes5. Remove the leaves and place on a cutting plate. Drop a small

amount of iodine onto both leaves and record your results