4 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 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.
5 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.
6 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.
8 Stoma There are holes found in leaves called stomata. These holes allows gases to diffuse in and out of the leaves. A stoma is formed by two highly specialized epidermis cells. These cells, called guard cells, are the only epidermis cells that contain chloroplasts. The stomata open and close depending upon the requirements of the plant. It is through these stomata that water leaves the leaf, the process that powers transpiration.
9 Stomata Stoma openStoma 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
10 Key Words Waxy cuticle Stomata 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
11 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 stomata 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... 6H 2 O + 6CO 2 C 6 H 12 O 6 + 6O 2
13 Photosynthesis Gaseous Exchange
14 Photosynthesis Gaseous Exchange & Water
15 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?
16 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?
17 Investigating Photosynthesis
18 Using Plants Humans have used plants for thousands of years. There are many different uses of plants by humans. The cotton plant shown is used to produce cotton for clothing etc.
20 Exercise 2: The Leaf 1. _____ 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
21 Exercise 3: Label the Parts of a Plant 4. ______ 2. _______ 1. _______ 3. _____ Roots Leaves Flower Stem
22 Exercise 4: Label the Parts of a Plant Flower Roots Leaf Stem
24 Exercise 6: Link the Boxes Waxy cuticle Stomata 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
25 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
26 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 Stomata Cuticle The leaf-blade
27 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
28 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 _____. rootsorganelles lightfood water chlorophyll oxygenstomata organelles chlorophyll light food wateroxygen stomata roots
29 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 stomata Respiration
30 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 C 6 H 12 O 6
31 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? 6H 2 O + 6CO 2 C 6 H 12 O 6 + 6O 2 Chloroplast Chlorophyll
32 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 Variegated leaf after starch test Explain the result observed (8 marks)
33 Exercise 15: Products of Photosynthesis Some 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.
34 Exercise 16: Short Questions 1.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
35 Exercise 17: Label the Leaf Parts A B C A._______________ B._______________ C._______________ Lamina Vein Midrib