Leaf Structure and Photosynthesis Leaf structure Palisade cell

Leaf Structure and Photosynthesis Leaf structure Palisade cell Stoma Photosynthesis

Flowering Plants Flower Leaf Stem Roots

The Leaf Vein Lamina Midrib Stalk

The Leaf – Cross-section Vein Lamina Midrib Extension of the stalk into the leaf Vein Branch-off from the midrib Lamina The blade of the leaf Stalk Attaches the leaf to the stem

Leaf Structure Waxy cuticle Epidermis Palisade mesophyll layer Air space Spongy mesophyll layer Stomata Epidermis

Waxy Cuticle & Epidermis Waxy 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 The palisade mesophyll layer is where most of the photosynthesis occurs in the leaf. Palisade mesophyll layer 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 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. Spongy mesophyll layer 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 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. Stomata It is through these stoma that water leaves the leaf, the process that powers transpiration.

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 Waterproof layer atop the epidermis Stoma Pores that allow gaseous exchange Air spaces Found in the spongy mesophyll layer, enable gases to reach the leaf cells Epidermis One-cell thick outer layer of cells that prevent water loss from the leaf Palisade mesophyll cell Contain numerous chloroplasts and are densely packed Spongy mesophyll cell Loosely packed cells that do not contain as many chloroplasts as palisade cells

Photosynthesis Chloroplasts 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. . . 6 H 2 O + 6 CO 2 C 6 H 12 O 6 + 6 O 2

Investigating Photosynthesis Chlorophyll 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 Photosynthesis Is 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 Stem Root Leaf Flower Rhubarb Potato Lettuce Broccoli Celery Turnip Cabbage Cauliflower Carrot Broccoli Rhubarb Potato Turnip Cabbage Cauliflower Celery Lettuce Carrot

Exercise 2: The Leaf 1. _____ Vein 2. Lamina ______ 3. _______ Midrib Extension of the stalk into the leaf Vein The blade of the leaf Lamina Attaches the leaf to the stem Stalk Branch-off from the midrib

Exercise 3: Label the Parts of a Plant 1. _______ Flower 2. _______ Leaves 3. _____ Stem 4. ______ Roots

Exercise 4: Label the Parts of a Plant Leaf Roots Stem Flower

Exercise 5: Leaf Structure 1. ______ Waxy cuticle 2. ______ Epidermis 3. ___________ Palisade mesophyll layer 4. _____ Air space 5. Spongy ___________ mesophyll layer 6. ____ Stomata 7. _____ Epidermis

Exercise 6: Link the Boxes Waxy cuticle Pores that allow gaseous exchange Stoma Found in the spongy mesophyll layer, enable gases to reach the leaf cells Air spaces Waterproof layer atop the epidermis

Exercise 7: Link the Boxes Epidermis Loosely packed cells that do not contain as many chloroplasts as palisade cells Palisade mesophyll cell One-cell thick outer layer of cells that prevent water loss from the leaf Spongy mesophyll cell Contain numerous chloroplasts and are densely packed, where most of the photosynthesis occurs

Exercise 8: Short Questions - Leaf 1. What do we call the continuation of the leaf stalk into the leafblade? Midrib 2. What do we call the specially adapted cells that form holes in the leaves to allow gaseous exchange? Guard cells 3. What are these holes/pores called? Stoma 4. What is the name of the waxy waterproof layer found on top of the epidermis? Cuticle 5. What is the lamina? 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? The epidermis 2. What is the function of this layer? To prevent water loss and to stop substances and organisms entering the leaf 3. What are two differences between palisade mesophyll cells (PMC) and spongy mesophyll cells (SMC)? SMC – more loosely packed, less chloroplasts PMC – more densely packed, more chloroplasts 4. By what process does carbon dioxide enter and leaves? Diffusion

Exercise 10: Insert the Missing Words organelles of plant cells that contain a green Chloroplasts _____ chlorophyll substance called _____. light energy and this Scientists believe chlorophyll absorbs _____ food energy is then used to make _____. The raw materials of photosynthesis are carbon dioxide and water oxygen _____. This waste product of this reaction is _______. stoma in The carbon dioxide required is absorbed through the ______ the leaves – this is how the oxygen is also removed. The water required is absorbed by the roots _____. roots organelles light food water chlorophyll oxygen stoma

Exercise 11: Short Questions - Photosynthesis 1. Which organelles in plant cells contain a green substance called chlorophyll? Chloroplasts 2. Which two raw materials are required by green plants for photosynthesis? Water and carbon dioxide 3. What is the waste product of photosynthesis? Oxygen 4. How does this waste product leave the plant during the day? Through the stoma 5. What process requires this waste product to enable green plants to release energy from their food? 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? Photosynthesis 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? Respiration 3. The sugar glucose, the product of photosynthesis, is changed to starch when it is being stored by the plant. Why? 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 4. What is the chemical formula of glucose? C 6 H 12 O 6

Exercise 13: Short Questions – Plant Nutrition 1. What is the word equation for photosynthesis? 2. What is the chemical equation for photosynthesis? 6 H 2 O + 6 CO 2 C 6 H 12 O 6 + 6 O 2 3. Name the arrowed organelle. Chloroplast 4. Which substance does this organelle contain that allows green plants to absorb the Sun’s light energy for the process of photosynthesis? Chlorophyll

Exercise 14: Variegated Leaf A 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 Explain the result observed Variegated leaf after starch test (8 marks)

Exercise 15: Products of Photosynthesis Some destarched pondweed was set-up as below. A bright lamp was placed nearby for two hours. The following results were observed at the end of this period. Before lamp turned on Explain the result observed After six hours of lamp shining (6 marks)

Exercise 16: Short Questions 1. What is a variegated leaf? Parts of the leaf do not contain chlorophyll, other parts do 2. Draw a diagram of a variegated leaf. 3. What is the chemical test for starch? Starch turns orange/brown iodine solution purple/black 4. How do you destarch a green plant? You leave it in the dark for several days so that its food stores (starch) are exhausted