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The Role of the Leaf in Photosynthesis

In this worksheet, students will explain how the leaves are used in photosynthesis.

'The Role of the Leaf in Photosynthesis' worksheet

Key stage:  KS 3

Curriculum topic:   Biology: Material Cycles and Energy

Curriculum subtopic:   Photosynthesis

Difficulty level:  

Worksheet Overview

QUESTION 1 of 10

 

The leaves are exceptionally important when it comes to photosynthesis. They are like factories which produce the food that plants need to grow and survive. But how?

Leaves are designed and adapted to allow photosynthesis to take place. They are flat and broad to capture as much of the light energy from the sun as possible.
 

Stomata on leaf


They also contain lots of tiny holes called stomata which allow for the absorption of carbon dioxide and the release of oxygen.    

 

Do all leaves allow photosynthesis?

Surprisingly, no!  The only leaves that can photosynthesise are the ones that contain the chemical chlorophyll.  So how do you know what leaves contain chlorophyll? Easy, chlorophyll is the green pigment in leaves, so if a leaf is green, it will photosynthesise.

 

Leaves



Chlorophyll is the chemical responsible for converting light energy from the sun into chemical energy.  This chemical energy is then used to make glucose (C6H12O6) from carbon dioxide (CO2) and water (H2O).

Light energy   +  CO2  +   H2O   C6H12O6   +   O2

 

What happens to the Glucose?

The glucose produced in photosynthesis has a variety of uses. Some of the glucose is used to create other chemicals needed in the plant such as proteins. Some is converted into starch and stored in the plant for later use and some is used for respiration.

 

Respiration

Respiration is the process that all living organisms use to get the energy they need.  Plants use the glucose produced in photosynthesis and convert it into the energy needed for the living processes in green plants.

C6H12O6    +  O2        CO2 +   H2O   +   Energy

 

 

Leaf processes

 (See if you can spot something wrong in this diagram!!)



Experiment - Testing a leaf for starch

 

A simple experiment can be done to prove that green plants photosynthesise:

 



Step 1:   Boil the leaf in water for around 10 minutes to soften the leaf.  

Step 2:   Place the leaf in a boiling tube containing methylated spirit (or ethanol) and heat for a further 10 minutes to remove the chlorophyll from the leaf (IMPORTANT: Make sure the bunsen burner is switched off before using the methylated spirit as it is highly flammable).

Step 3:   Rinse the leaf with cold water.

Step 4:   Test the leaf with iodine.  If the plant has photosynthesised the iodine should turn from brown to blue/black, indicating the presence of starch.   


The white of a variegated leaf does not contain any chlorophyll. What would you expect to see happen when this type of leaf is tested for starch?

 

Variegated leaf

 

We will now answer some more questions on photosynthesis and the importance of leaves.

 

(Did you spot the mistake in that diagram? All the chemical symbols are written with superscripts rather than subscripts - so like CO2 instead of CO2! You just can't get the scientific graphic designers!!)

What is the name given to the tiny holes on the surface of a leaf that allow the transfer of gases to take place? 

chlorophyll

chloroplast

stomata

photosynthesis

What is the name of the green chemical in plants that converts light energy into chemical energy?

 

Write the word in the answer box.

What is the chemical formula for glucose?

CO2

C2H2O2

C6H12O6

C12H22O11

Some of the glucose produced during photosynthesis is converted into storage for later use.

 

What is the name of the storage chemical that glucose is converted into?  

carbon dioxide

sugar

starch

protein

What are the raw materials needed for respiration?

water

oxygen

starch

glucose

carbon dioxide

chlorophyll

Complete the word equation for respiration.

 

Glucose  +  ____A____  ---------->  Carbon dioxide  +  _____B_____  +  energy

 

Remember to write your answers in lower case.

 Answer
A
B

When using methylated spirit to test a leaf for starch, why is it important to ensure that there are no near by naked flames?

methylated spirit is highly flammable

methylated spirit is a solid and will melt

methylated spirit will burn through the leaf

methylated spirit is non-flammable

In the present of starch, iodine will change from red/brown to what colour?

yellow

orange

blue/black

green/blue

In the answer box below, write the word which completes this sentence:

 

Variegated leaf

yellow

orange

blue/black

green/blue

  • Question 1

What is the name given to the tiny holes on the surface of a leaf that allow the transfer of gases to take place? 

CORRECT ANSWER
stomata
EDDIE SAYS
The tiny holes in the leaf that allow gases in and out are the stomata (singular is a STOMA). They are able to open and close the holes according to what's going on in the plant's environment and also according to the plant's needs.
  • Question 2

What is the name of the green chemical in plants that converts light energy into chemical energy?

 

Write the word in the answer box.

CORRECT ANSWER
chlorophyll
EDDIE SAYS
The green chemical which gives the leaves their green colour and also converts light energy into chemical energy is chlorophyll. Mind you, it's a toughie to spell: pronounced CLAW-ROW-FILL, it's spelt CHLOR - O - PHYLL, so it's just one of those things you have to learn and remember. Sorry!
  • Question 3

What is the chemical formula for glucose?

CORRECT ANSWER
C6H12O6
EDDIE SAYS
The chemical formula for glucose is C6H12O6. That's 6 carbon atoms, twelve hydrogen atoms and 6 carbon atoms. Where do they come from??
  • Question 4

Some of the glucose produced during photosynthesis is converted into storage for later use.

 

What is the name of the storage chemical that glucose is converted into?  

CORRECT ANSWER
starch
EDDIE SAYS
Glucose is converted into starch and stored in the plant. Starch is, basically, a great big long string of glucose molecules all bonded together. As such it's pretty insoluble and so easier to store in a plant that is basically made of water.
  • Question 5

What are the raw materials needed for respiration?

CORRECT ANSWER
oxygen
glucose
EDDIE SAYS
The process of respiration involves glucose and oxygen being converted into carbon dioxide, water and energy. If you think of respiration as the process that releases the energy from food, then food (containing the energy) must be involved; here, it's glucose. Respiration is a form of combustion, or burning, and that needs oxygen. So: food and oxygen.
  • Question 6

Complete the word equation for respiration.

 

Glucose  +  ____A____  ---------->  Carbon dioxide  +  _____B_____  +  energy

 

Remember to write your answers in lower case.

CORRECT ANSWER
 Answer
A
B
EDDIE SAYS
So, reactants: glucose and oxygen. Products: the energy you need plus wastes: CO2 and H20. If you look at it as a chemical symbol equation, you can see where the atoms in the glucose have ended up and the energy stored in the bonds of the sugar has been released to be used for a variety of activities.
  • Question 7

When using methylated spirit to test a leaf for starch, why is it important to ensure that there are no near by naked flames?

CORRECT ANSWER
methylated spirit is highly flammable
EDDIE SAYS
Methylated spirits is based on ethanol (alcohol) and so is very flammable. Indeed, 'meths' was often used as the fuel in old-fashioned camping stoves.
  • Question 8

In the present of starch, iodine will change from red/brown to what colour?

CORRECT ANSWER
blue/black
EDDIE SAYS
Like so many tests, this one is important to learn. It's one of the food tests: any food (bread, pasta, potato, etc.) containing starch will turn a blue/black colour when tested with iodine solution. Leaves containing starch are no different: you just have to remove the green colour and soften it first (the meths dissolves the chlorophyll and breaks down the cell walls). Then the presence of starch can be revealed.
  • Question 9

In the answer box below, write the word which completes this sentence:

 

Variegated leaf

CORRECT ANSWER
EDDIE SAYS
Chlorophyll is the chemical which converts light energy into chemical energy. Without chlorophyll a plant cannot photosynthesise, so that means the white or yellow parts of a variegated leaf do not manufacture starch.
---- OR ----

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