JWSS Biology Chapter 9 Nutriton Plants

3E Science (Biology) Chapter 8 Notes 1 JURONG WEST SECONDARY SCHOOL SECONDARY THREE – SCIENCE BIOLOGY Chapter 8: NUTRITION IN PLANTS LEARNING OUTCOMES: Candidates should be able to: a) identify the cellular and tissue structure of a dicotyledonous leaf, as seen in cross -section under the microscope and state their functions: (i) distribution of chloroplasts – photosynthesis (ii) stomata and mesophyll cells – gaseous exchange (iii) vascular bundles – transport b) state the equation, in words only, for photosynthesis c) describe the intake of carbon dioxide and water by plants d) state that chlorophyll traps light energy and converts it into chemical energy for the formation of carbohydrates and their subsequent storage e) investigate and state the effect of varying light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis (e.g. in submerged aquatic plants) f) briefly explain why most forms of life are completely dependent on photosynthesis

3E Science (Biology) Chapter 8 Notes 2 VIDEO: Watch the video and fill in the blanks with appropriate terms in the transcript below. Using their leaves, plants combine sunlight, carbon dioxide and water to make glucose and oxygen. The top of a leaf is exposed to the most sunlight, and so the cells specialised for trapping light are on top of the leaf. These specialised cells are called palisade mesophyll cells . They are packed full of chlorophyll - the green chemical that plants used to absorb light. Most leaves have a large surface area so that they can trap as much sunlight as possible. Moving onto carbon dioxide. This is where the bottom of the leaf comes in. There are little pores on the bottom of the leaf called stomata. The stomata open up so that carbon dioxide can diffuse into the leaf. The stomata are controlled by 'sausage shaped' guard cells, which open up to let carbon dioxide in. The guard cells can also close the stomata, to stop other things inside the leaf, like water, from escaping. The carbon dioxide comes in from the stomata, and then makes its way up through the leaf, thr ough the gaps in the spongy mesophyll layer in the bottom part of the leaf and heads up to the palisade cells where photosynthesis occurs. Leaves are thin so that the carbon dioxide doesn't have too far to travel. The final reactant needed for photosynthesis is water. Water comes into the plant through the roots, moves up the stem and enters the leaf through the vascular bundle . The vascular bundle contains a hollow tube specifically for water movement called the xylem. The veins on a leaf are actually the vascular bundle, allowing water to be spread out through the leaf.

3E Science (Biology) Chapter 8 Notes 3 SUMMARY Use the gained knowledge to write the equation for photosynthesis. + + Carbon dioxide diffuses into the plant through the stomata Water enters the plant through the roots and reaches the leaf cells via xylem Light energy enters the leaf cells as the chloroplasts traps light energy. START VIDEO PART 2 How do leaves manage to let in the wanted things (like water and carbon dioxide) but prevent unwanted things like bacteria getting in and also prevent the reactants from escaping before being used? At the top and bottom of the leaf are epidermal cells / epidermis . These produce a protective waxy cuticle layer. The waxy cuticle seals up the leaf so that the only way in and out are through the stomata, which are regulated by the guard cells. CLASS DISCUSSION: What do you think these parts do? (Use the gained knowledge in the video transcript.) Adaptations in the Internal Structure of the leaf. (The first adaptation has been filled in for you.) Structure Function Waxy cuticle Seals up the leaf / waterproof layer to prevent excessive water loss / transparent to allow light energy to pass through Epidermis / Epidermal cells Protect the inner leaf cells Palisade mesophyll cells Has numerous chloroplasts to trap light energy for photosynthesis Spongy mesophyll cells Irregularly shaped to create intercellular air spaces for efficient diffusion of gases Xylem vessels Transport water and dissolved mineral salts from the roots to the rest of the plant Guard cells Regulate the opening of stomata Stomata Opening that allows gases such as carbon dioxide, oxygen and water vapour to enter and exit the leaf Let’s Discuss! Carbon dioxide water glucose oxygen chlorophyll Light energy

3E Science (Biology) Chapter 8 Notes 4 The Internal Structure of Leaf 1. Upper epidermis - Single layer of closely packed cells - Cells do not contain chloroplasts - Function is to protect the internal structure of the leaf - The epidermal cells produce the waxy cuticle to layer to prevent excessive water loss 2. Mesophyll cells: (a) Palisade mesophyll and (b) Spongy mesophyll (a) Palisade mesophyll - One or two layers of closely packed, long and cylindrical cells - Contains numerous chloroplasts to trap light energy for photosynthesis (b) Spongy mesophyll - Irregularly shaped, loosely packed cells - Presence of large intercellular air spaces for rapid diffusion of gases - Presence of vascular bundles (xylem vessels and phloem tubes) 3. Lower epidermis - Single layer of closely packed cells - Protect the inner cells - Presence of guard cells and stomata [Guard cells regulate the size of stomata]

3E Science (Biology) Chapter 8 Notes 5 How does carbon dioxide and water enter the plant? • Carbon dioxide diffuses through the stomata. • Carbon dioxide concentration in intercellular air spaces is lower than in the atmosphere. • CO2 diffuses into the spongy mesophyll layer. • Surfaces of the mesophyll cells are always covered by a thin film of moisture for dissolving gases, such as CO2 • Water enters through the roots. • It enters the root cells via osmosis until it reaches the xylem vessels in the root. • Xylem vessels transport water (osmosis) and dissolved mineral salts (diffusion) from the roots to all parts of the plants. • Since there are xylem vessels in the roots, stem and leaves, water is transported to the leaves eventually. https://www.showme.com/sh/?h=6iXCO5w https://biology-igcse.weebly.com/passage-of-water-through-root-stem-and-leaf.html

3E Science (Biology) Chapter 8 Notes 6 How does guard cell the size of stomata? In sunlight: At night: The guard cell photosynthesizes and converts light energy to chemical energy. This chemical energy is used to pump potassium ions into the guard cells from neighbouring epidermal cells. The water potential in the guard cell is lowered. Water molecules move from a region of higher water potential (epidermal cells) to a region of lower water potential (guard cell) across partially permeable membrane. Now, the guard cell has a thicker cell wall at the stomata pore. The swollen guard cell becomes more curved and the stoma opens. The potassium ions that have accumulated in the guard cell during the day diffuse out of the guard cells. Hence, the water potential of the guard cell increased. Water molecules leave the cells by osmosis down a concentration gradient. The cell becomes flaccid and stoma closes.

3E Science (Biology) Chapter 8 Notes 7 The External Structure of Leaf 1. Network of veins - Veins consist of vascular bundles (xylem vessels and phloem tubes) - Xylem vessels carry water and mineral salts to the cells in the lamina - Phloem tubes carry manufacture food (sucrose and amino acids) from these cells to other parts of the plant 2. Petiole - holds the lamina away from the stem so that the lamina can obt