Leaf Structure and Photosynthesis

Leaf structure

Palisade cell

Stoma

Photosynthesis

Flowering Plants

Roots

Leaf

Flower

Stem

The Leaf

Stalk

Vein Lamina

Midrib

The Leaf – Cross-sectionVein Lamina

Midrib

Midrib

Vein

Lamina

Stalk

Extension of the stalk into the leaf

Branch-off from the midrib

The blade of the leaf

Attaches the leaf to the stem

Leaf StructureWaxy cuticle

Epidermis

Palisade mesophyll layer

Spongy mesophyll layer

Epidermis

Stomata

Air space

Waxy Cuticle & EpidermisWaxy cuticle

Epidermis

The waxy cuticle is a thin layer atop the epidermis.

Its function is to reduce the water lost from the leaf.

In arid conditions this cuticle layer ca be quite thick.

Epidermis cells contain no chloroplasts – not true of the stoma cells.

They form layers on the upper and lower surfaces of the leaf.

Their function is to prevent water getting out and stopping unwanted substances/organisms getting in.

Palisade Mesophyll Layer

Palisade mesophyll layer

The palisade mesophyll layer is where most of the photosynthesis occurs in the leaf.

The palisade cells contain a lot of chloroplasts to help them perform this photosynthesis.

The palisade cells are closely packed together to maximize light absorption.

In the leaf cross-section shown the palisade cells are only found in the upper part of the leaf.

Spongy Mesophyll Layer

Spongy mesophyll layer

The cells in the spongy mesophyll layer are not as closely packed as the cells in the palisade mesophyll layer.

This creates air spaces inside the leaf to enable gases to move in and out.

There are not as many chloroplasts in the spongy mesophyll cells as there are in the palisade mesophyll cells – but photosynthesis still occurs in the spongy mesophyll layer.

Stomata

Stomata

There are holes found in leaves called stoma.

These holes allows gases to diffuse in and out of the leaves.

The stoma are formed by two highly specialized epidermis cells.

These cells, called guard cells, are the only epidermis cells that contain chloroplasts.

The stoma open and close depending upon the requirements of the plant.

It is through these stoma that water leaves the leaf, the process that powers transpiration.

Stomata

Stomata open Stomata closed

During photosynthesis carbon dioxide diffuses in and oxygen diffuses out

When the stoma are closed,often at night or in a humid environment, this stops gases diffusing in

and out of the leaf

Key Words

Waxy cuticle

Stoma

Air spaces

Epidermis

Palisade mesophyll cell

Spongy mesophyll cell

Waterproof layer atop the epidermis

Pores that allow gaseous exchange

Found in the spongy mesophyll layer, enable gases to reach the leaf cells

One-cell thick outer layer of cells that prevent water loss from the leaf

Contain numerous chloroplasts and are densely packed

Loosely packed cells that do not contain as many chloroplasts as palisade cells

PhotosynthesisChloroplasts are organelles of plant cells that contain a green substance called chlorophyll.

Scientists believe chlorophyll absorbs light energy and this energy is then used to make food.

The raw materials of photosynthesis are carbon dioxide and water. The waste product of this reaction is oxygen.

The carbon dioxide required is absorbed through the stoma in the leaves – this is how the oxygen is also removed.

The water required is absorbed by the roots.

The word equation for this reaction is...

The chemical equation for this reaction is...

6H2O + 6CO2 C6H12O6 + 6O2

Investigating PhotosynthesisChlorophyll makes leaves green, but is chlorophyll required for photosynthesis?

Your teacher will give you two leaves, one is completely green.

The other leaf is called a variegated leaf. The areas that are not green contain little or no chlorophyll.

Both leaves have previously been destarched. Do you know how to destarch a leaf?

Plan an investigation to discover if chlorophyll is required for photosynthesis.

How will you test to see if photosynthesis has occurred?

What do you predict your results will be?

What apparatus will you require?

What safety precautions will you need to observe?

Investigating PhotosynthesisIs carbon dioxide required for photosynthesis?

Your teacher will give you two plants, one is enclosed in plastic and contains a chemical that absorbs carbon dioxide.

Plan an investigation to discover if carbon dioxide is required for photosynthesis.

What do you predict your results will be?

What apparatus will you require?

Why are two plants used?

How will you evaluate your results?

What chemical will you use to remove carbon dioxide?

Exercise 1: Complete the Table

Broccoli

Potato

CabbageCarrot

Lettuce

Stem Root Leaf Flower

Rhubarb

Turnip

Cauliflower

Celery

BroccoliRhubarb

Celery

Potato

Turnip

Lettuce

Cabbage Cauliflower

Carrot

Exercise 2: The Leaf1. _____ 2. ______

3. _______

Midrib

Vein

Lamina

Stalk

Extension of the stalk into the leaf

The blade of the leaf

Attaches the leaf to the stem

Branch-off from the midrib

Vein Lamina

Midrib

Exercise 3: Label the Parts of a Plant

4. ______

2. _______

1. _______

3. _____

Roots

Leaves

Flower

Stem

Exercise 4: Label the Parts of a Plant

Flower

Roots

Leaf

Stem

Exercise 5: Leaf Structure1. ___________

2. ___________

3. ______________________

5. _____________________

7. __________

6. ________

4. __________

Waxy cuticle

Epidermis

Palisade mesophyll layer

Spongy mesophyll layer

Epidermis

Stomata

Air space

Exercise 6: Link the Boxes

Waxy cuticle

Stoma

Air spaces Waterproof layer atop the epidermis

Pores that allow gaseous exchange

Found in the spongy mesophyll layer, enable gases to reach the leaf

cells

Exercise 7: Link the Boxes

Epidermis

Palisade mesophyll cell

Spongy mesophyll cell

Contain numerous chloroplasts and are densely

packed, where most of the photosynthesis occurs

Loosely packed cells that do not contain as many

chloroplasts as palisade cells

One-cell thick outer layer of cells that prevent

water loss from the leaf

Exercise 8: Short Questions - Leaf

1. What do we call the continuation of the leaf stalk into the leaf-blade?

2. What do we call the specially adapted cells that form holes in the leaves to allow gaseous exchange?

3. What are these holes/pores called?

4. What is the name of the waxy waterproof layer found on top of the epidermis?

5. What is the lamina?

Midrib

Guard cells

Stoma

Cuticle

The leaf-blade

Exercise 9: Short Questions - Leaf

1. What do we call the outer one-cell thick layer of cells that contain no chloroplasts?

2. What is the function of this layer?

3. What are two differences between palisade mesophyll cells (PMC) and spongy mesophyll cells (SMC)?

4. By what process does carbon dioxide enter and leave leaves?

The epidermis

To prevent water loss and to stop substances and

organisms entering the leaf

SMC – more loosely packed, less chloroplasts

Diffusion

PMC – more densely packed, more chloroplasts

Exercise 10: Insert the Missing Words

Chloroplasts __________ of plant cells that contain a green substance called __________.

Scientists believe chlorophyll absorbs _____ energy and this energy is then used to make _____.

The raw materials of photosynthesis are carbon dioxide and _____. This waste product of this reaction is _______.

The carbon dioxide required is absorbed through the ______ in the leaves – this is how the oxygen is also removed.

The water required is absorbed by the _____.

roots organelles light food

water chlorophyll oxygen stoma

organelleschlorophyll

lightfood

water oxygen

stoma

roots

Exercise 11: Short Questions - Photosynthesis

1. Which organelles in plant cells contain a green substance called chlorophyll?

2. Which two raw materials are required by green plants for photosynthesis?

3. What is the waste product of photosynthesis?

4. How does this waste product leave the plant during the day?

5. What process requires this waste product to enable green plants to release energy from their food?

Chloroplasts

Water and carbon dioxide

Oxygen

Through the stoma

Respiration

Exercise 12: Short Questions – Plant Nutrition

1. What do we call the process whereby green plants make glucose using light energy and the raw materials carbon dioxide and water?

2. During the night many green plants perform another process whereby they release the energy from their food they have made. What do we call this process?

3. The sugar glucose, the product of photosynthesis, is changed to starch when it is being stored by the plant. Why?

4. What is the chemical formula of glucose?

Photosynthesis

Respiration

Glucose is soluble in water, starch is insoluble in water. By storing the food starch it means it is easier for the plant to keep the food in the required place

C6H12O6

Exercise 13: Short Questions – Plant Nutrition

1. What is the word equation for photosynthesis?

2. What is the chemical equation for photosynthesis?

3. Name the arrowed organelle.

4. Which substance does this organelle contain that allows green plants to absorb the Sun’s light energy for the process of photosynthesis?

6H2O + 6CO2 C6H12O6 + 6O2

Chloroplast

Chlorophyll

Exercise 14: Variegated LeafA destarched variegated plant was left in a sunny garden during the day for several hours.

At the end of this period a leaf was taken from the plant and tested for starch.

The results are shown below…

Variegated leaf before starch test

Variegated leaf after starch test

Explain the result observed (8 marks)

Exercise 15: Products of PhotosynthesisSome destarched pondweed was set-up as below.

A bright lamp was placed nearby for two hours.

Before lamp turned on

After six hours of lamp shining

Explain the result observed (6 marks)

The following results were observed at the end of this period.

Exercise 16: Short Questions1. What is a variegated leaf?

2. Draw a diagram of a variegated leaf.

3. What is the chemical test for starch?

4. How do you destarch a green plant?

Parts of the leaf do not contain chlorophyll, other parts do

Starch turns orange/brown iodine solution purple/black

You leave it in the dark for several days so that its food stores (starch) are exhausted