Leaf Anatomy

Objectives:1. Identify Internal and External Leaf Anatomy

2. Learn the function of these structures

3. Write the equation for photosynthesis

4. Make quality wet-mount slides to observe these

structures.

The Leaf – External Anatomy

Stalk/petiole

Vein Blade,(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

Internal Leaf AnatomyWaxy 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 can 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 we can see 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 stomata 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

Photosynthesis

Chloroplasts are organelles of plant cells that contain a chlorophyll which 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

Review: Leaf Anatomy1. _____ 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

Review: Internal Leaf Anatomy1. ___________

2. ___________

3. ______________________

5. _____________________

7. __________

6. ________

4. __________

Waxy cuticle

Epidermis

Palisade mesophyll layer

Spongy mesophyll layer

Epidermis

Stomata

Air space

Review: Function

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

Review: Function

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

Review: Insert the Missing WordsChloroplasts are __________ 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 sugar

water chlorophyll oxygen stoma

organelleschlorophyll

lightsugar

water oxygen

stoma

roots

Review: Short Questions - Photosynthesis1. 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. Where does this waste product leave the plant?

5. What process uses this waste product to enable green plants, and us, to release energy from their food?

Chloroplasts

Water and carbon dioxide

Oxygen

Through the stomata (stoma – pl.)

Respiration

Review: Short Questions – Plant Nutrition1. 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 10: 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 2: Label the Parts of a Plant

4. ______

2. _______

1. _______

3. _____

Roots

Leaves

Flower

Stem

Exercise 3: Label the Parts of a Plant

Flower

Roots

Leaf

Stem