Leaf structure Photosynthesis

Transcription

1 Leaf Structure and Photosynthesis Leaf structure Photosynthesis Trees ANGIOSPERM GYMNOSPERM 1

2 Gymnosperms or Conifers have needles or scales Deciduous trees like other Angiosperms have leaves 2

3 Angiosperms or Flowering Plants Flower Leaf Stem Roots Vein Lamina The Leaf Midrib Stalk 3

4 The Leaf Cross-section Vein Lamina Midrib 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 Simple and compound leaves 4

5 Simple and Compound leaves Simple leaves 5

6 Palmately compound leaf Pinnately Compound Leaf 6

7 LEAF Structure Wide Helps to catch more light energy Thin Helps get carbon dioxide from bottom to top of leaf for photosynthesis 7

8 Leaf structure Greener on top CO 2 gets in here Leaf Structure Waxy cuticle Epidermis Palisade mesophyll layer Air space Spongy mesophyll layer Stomata Epidermis 8

9 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. 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 we can see the palisade cells are only found in the upper part of the leaf. 9

10 Leaf cell - palisade Position? Upper surface of leaf Features? Box shape Chloroplasts Function? Photosynthesis 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. 10

11 Stoma position 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. 11

12 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 Stoma is a small hole Its size is controlled by 2 guard cells closed open 12

13 Stoma function is for gas exchange in the leaf Guard cell oxygen Provided plant is photosynthesizing Carbon dioxide Gas exchange 13

14 VEIN VASCULAR BUNDLES are continuous with stem & roots Xylem is around the outside, phloem on inside Remember: MONOCOTS veins run parallel along length DICOT DICOTS network of veins Monocot 14

15 Key Words Waxy cuticle Waterproof layer atop the epidermis Stoma Pores that allow gaseous exchange Air spaces Epidermis Palisade mesophyll cell Spongy mesophyll cell 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 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... 6H 2 O + 6CO 2 C 6 H 12 O 6 + 6O 2 15

16 Exercise 1: The Leaf 1. Vein 2. Lamina 3. Midrib 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 2: Label the Parts of a Plant 1. Flower 2. Leaves 3. Stem 4. Roots 16

17 Exercise 3: Label the Parts of a Plant Leaf Roots Stem Flower Exercise 4: Leaf Structure 1. Waxy cuticle 2. Epidermis 3. Palisade mesophyll layer 4. Air space 5. Spongy mesophyll layer 6. Stomata 7. Epidermis 17

18 Exercise 5: 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 6: 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 18

19 Exercise 7: Insert the Missing Words 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 This 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 roots organelles light food water chlorophyll oxygen stoma Exercise 8: 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 19

20 Exercise 9: 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 10: Short Questions Plant Nutrition 1. What is the word equation for photosynthesis? 2. What is the chemical equation for photosynthesis? 6H 2 O + 6CO 2 C 6 H 12 O 6 + 6O 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 20