4Waxy 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.
5Palisade Mesophyll Layer The palisade mesophyll layer is where most of the photosynthesis occurs in the leaf.Palisade mesophyll layerThe 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.
6Spongy 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 layerThere 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.
8Stomata 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.Stoma
9Stomata Stoma open Stoma closed During photosynthesis carbon dioxide diffuses in and oxygen diffuses outWhen the stomata are closed,often at night or in a humid environment, this stops gases diffusing in and out of the leaf
10Key Words Waxy cuticle Waterproof layer atop the epidermis Stomata Pores that allow gaseous exchangeFound in the spongy mesophyll layer, enable gases to reach the leaf cellsAir spacesOne-cell thick outer layer of cells that prevent water loss from the leafEpidermisPalisade mesophyll cellContain numerous chloroplasts and are densely packedLoosely packed cells that do not contain as many chloroplasts as palisade cellsSpongy mesophyll cell
11PhotosynthesisChloroplasts 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...6H2O + 6CO2 C6H12O6 + 6O2
15Investigating 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?
16Investigating 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?
24Exercise 6: Link the Boxes Pores that allow gaseous exchangeWaxy cuticleFound in the spongy mesophyll layer, enable gases to reach the leaf cellsStomataWaterproof layer atop the epidermisAir spaces
25Exercise 7: Link the Boxes Loosely packed cells that do not contain as many chloroplasts as palisade cellsEpidermisOne-cell thick outer layer of cells that prevent water loss from the leafPalisade mesophyll cellContain numerous chloroplasts and are densely packed, where most of the photosynthesis occursSpongy mesophyll cell
26Exercise 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?MidribGuard cellsStomataCuticleThe leaf-blade
27Exercise 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 epidermisTo prevent water loss and to stop substances and organisms entering the leafSMC – more loosely packed, less chloroplastsPMC – more densely packed, more chloroplastsDiffusion
28Exercise 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 _____.organelleschlorophylllightfoodwateroxygenstomatarootsroots organelles light foodwater chlorophyll oxygen stomata
29Exercise 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?ChloroplastsWater and carbon dioxideOxygenThrough the stomataRespiration
30Exercise 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?PhotosynthesisRespirationGlucose 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 placeC6H12O6
31Exercise 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 + 6O2ChloroplastChlorophyll
32Exercise 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 testVariegated leaf after starch testExplain the result observed (8 marks)
33Exercise 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 onAfter six hours of lamp shiningExplain the result observed (6 marks)
34Exercise 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 doStarch turns orange/brown iodine solution purple/blackYou leave it in the dark for several days so that its food stores (starch) are exhausted
35Exercise 17: Label the Leaf Parts LaminaVeinMidrib