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 Vein Blade, (Lamina) Midrib Stalk/petiole

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

Palisade mesophyll layer Spongy mesophyll layer Internal Leaf Anatomy Waxy cuticle Epidermis Palisade mesophyll layer Air space Spongy mesophyll layer Stomata 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.

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. It is through these stoma that water leaves the leaf, the process that powers transpiration. Stomata

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

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 Anatomy 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

Review: Internal Leaf Anatomy 1. ___________ Waxy cuticle 2. ___________ Epidermis 3. ______________________ Palisade mesophyll layer 4. __________ Air space 5. _____________________ Spongy mesophyll layer 6. ________ Stomata 7. __________ Epidermis

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

Palisade mesophyll cell Review: Function Loosely packed cells that do not contain as many chloroplasts as palisade 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, where most of the photosynthesis occurs Spongy mesophyll cell

Review: Insert the Missing Words Chloroplasts 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 _____. organelles chlorophyll light sugar water oxygen stoma roots roots organelles light sugar water chlorophyll oxygen stoma

Review: 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. 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 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 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 1. _______ Flower 2. _______ Leaves 3. _____ Stem 4. ______ Roots

Exercise 3: Label the Parts of a Plant Leaf Roots Stem Flower