Nutrition in Plants Notes PDF

Sec 3 Normal Biology Chapter 7: Nutrition in Plants Name: _______________________ ( ) Date: _________________ Class: _______________________ What are you...

Sec 3 Normal Biology Chapter 7: Nutrition in Plants Name: _______________________ ( ) Date: _________________ Class: _______________________ What are you going to learn?  Leaf Structure  Photosynthesis Learning Outcome (a): Identify and label the cellular and tissue structure of a dicotyledonous leaf, as seen in the cross-section under the microscope and describe the significance of these features in terms of their functions such as the  Distribution of chloroplasts in photosynthesis  Stomata and mesophyll cells in gaseous exchange  Vascular bundles in transport Extermal Structure of a leaf External Features of a Leaf Network of veins Lamina Veins carry water and mineral salts to the cells in the lamina The leaf blade or lamina has a large flat surface and carry manufacture food compared to its volume. This enables it to obtain the from these cells to other parts maximum amount of sunlight for photosynthesis. of the plant. A large, thin lamina also means that carbon dioxide In a simple leaf, for example, can rapidly reach the inner cells of the leaf. Hibiscus, there is a main vein (mid-rib) giving off branches repeatedly, forming a network Leaf arrangement of fine veins. Leaves are always organised around the stem in a regular pattern. Petiole In general, leaves grow either in The petiole holds the lamina away pairs (opposite one another on the from the stamen so that the lamina can stem) or singly in an alternate obtain sufficient sunlight and air. arrangement. This ensures that the In some leaves, for example grasses leaves are not blocking one and maize, the petiole is absent. Such stem another from sunlight and that leaves have long laminae. each leaf receives optimum light. Copyright © 2006-2011 Marshall Cavendish International (Singapore) Pte. Ltd. 12 April 2009 7 1  Sec 3 Normal Biology Chapter 7: Nutrition in Plants Internal Structure of the leaf Upper epidermis  Single layer of closely packed cells.  Covered by a waxy cuticle which protects the enclosed leaf tissue and prevents excessive evaporation of water. Being transparent, it allows sunlight to pass through. Palisade mesophyll  Consists of closely packed, long and cylindrical cells.  The cells contain numerous chloroplasts which enables them to absorb maximum sunlight for photosynthesis Spongy mesophyll  Irregularly shaped.  Numerous intercellular airspaces among them to allow for rapid diffusion of gases through the leaf.  Contains chloroplasts but fewer than the palisade mesophyll.  Mesophyll cells are covered with a thin film of moisture so carbon dioxide can dissolve in it.  Vascular bundles containing xylem and phloem are found here.  Xylem transports water and mineral salts from roots to leaf.  Phloem translocates sucrose and amino acids from leaf to all parts of the plant. Lower epidermis  Single layer of closely packed cells covered by outer layer of cuticle. Stoma  Minute openings called stomata (plura) 2  Sec 3 Normal Biology Chapter 7: Nutrition in Plants How do guard cells control the size of the stomata?  In the day, chloroplasts in the guard cells carry out photosynthesis. Light energy converted to chemical energy, causing water from neighboring cells enter the guard cells by osmosis.  The guard cell swells and become turgid and hence the stomata opens  At night, water leaves the guard cell and it becomes flaccid. The stomata closes  Guard cells.ppt  By controlling stomata size: o Regulate rate of diffusion of carbon dioxide and oxygen o Regulate the amount of water vapour escaping from the leaf.  On a very hot and sunny day, the stomata can close to reduce water loss through evaporation to prevent wilting Learning Outcome (c): Outline the intake of carbon dioxide and water by the plants. Carbon dioxide enters the leaf through the stomata  During the day, carbon dioxide in the leaf is rapidly used up due to photosynthesis.  Carbon dioxide concentration in the leaf is lower than that in the air resulting in a diffusion gradient.  Carbon dioxide thus diffuses from the surrounding air through the stomata into the air spaces in the leaf.  A thin film of moisture covers the surfaces of the mesophyll cells so that the carbon dioxide can dissolve in it.  The dissolved carbon dioxide than diffuses into the mesophyll cell as solution  movement.swf 3  Sec 3 Normal Biology Chapter 7: Nutrition in Plants Xylem transports water and mineral salts to the leaf  Veins in the leaf forms fine branches and ends up among the mesophyll cells.  The veins contains xylem and phloem  Xylem transports water and dissolved mineral slats to the leaf from the roots. Once out of the veins, the water and mineral slats move out of the cell to the cell right through the mesophyll of the leaf via osmosis.  movement.swf Learning Outcome (b): State the equation, in words, for photosynthesis Learning Outcome (d): State that chlorophyll traps light energy and converts it into chemical energy for the formation of carbohydrates and their subsequent uses Learning Outcome (f): briefly explain why most forms of life are completely dependent on photosynthesis Photosynthesis Photosynthesis Overall equation: Word equation for photosynthesis light energy Carbon dioxide + water glucose + oxygen + water chlorophyll 4  Photosynthesis Sec 3 Normal Biology Chapter 7: Nutrition in Plants Overall equation: Symbol equation for photosynthesis (not required for N(A) light energy 6CO2 + 6H2O chlorophyll C6H12O6 + 6O2 Definition  Photosynthesis is the process in which light energy absorbed by chlorophyll is transformed into chemical energy. The chemical energy is used to synthesize carbohydrates from water and carbon dioxide. Water and carbon dioxide are raw materials for photosynthesis. Oxygen is released in the process.  In a typical ecosystem, the producer (green plants) are the ones to capture energy from the sun. This captured energy is then converted to glucose (then starch) via photosynthesis. This form of energy is then passed on as plants are consumed by herbivores and subsequently down the food chain Objective 4: State that chlorophyll traps light energy and converts it into chemical energy for the formation of carbohydrates and their subsequent storage. Conditions required for photosynthesis  Sunlight  Carbon dioxide (Substrate in photosynthetic reactions)  Chlorophyll (to capture light energy and convert into chemical energy to power photosynthetic reactions)  Suitable temperature – Photosynthesis depends on enzyme reactions in the chloroplasts  Water N.B.- The absence of any of these conditions will result in no photosynthesis 5  Sec 3 Normal Biology Chapter 7: Nutrition in Plants What happens during photosynthesis?  Photosynthesis occurs in 2 stages, the light stage and the light-independent stage. Light stage  Light energy is absorbed by chlorophyll and then converted into chemical energy.  Light energy is used to split water molecules into oxygen and hydrogen molecules. This reaction is also known as photolysis Light independent stage  Hydrogen produced in photolysis reacts with carbon dioxide to form glucose.  Energy required from this stage comes from the light stage.  Enzymes are required in this stage. 6  Sec 3 Normal Biology Chapter 7: Nutrition in Plants Learning Outcome (e)(i): Investigate and discuss effects of varying light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis (eg. Submerged water plant) Learning Outcome (e)(ii): Discuss light intensity, carbon dioxide concentration and temperature as the limiting factors on the rate of photosynthesis. Limiting factors in photosynthesis  Limiting factor: Any factor that directly affects a process if its quantity is changed is known as a limiting factor.  Photosynthesis is affected by the following factors o Light intensity o Carbon dioxide concentration o Temperature Effect of light intensity on rate of photosynthesis What is the limiting factor in region A? What is represented by the curve at B and C? What does point D represent on the curve? What does point E represent on the curve?  In low light intensity, the rate of photosynthesis increases linearly with increasing light intensity.  Rate falls as the other factors become limiting.  In reality, light is normally not a limiting factor. 7  Sec 3 Normal Biology Chapter 7: Nutrition in Plants Carbon dioxide concentration Compare expt 3 with 1 and expt 4 with 2? What do you  Under normal conditions, CO2 is usually the major limiting factor. observe?  Hence the rate of reaction in Expt 3 increases greatly as the CO2 conc. Increases to 0.4%. Temperature  Photosynthesis is an enzyme-controlled reaction. (Recall: Effect of temperature on enzymes)  Rate of photosynthesis doubles for every 10ºC rise to about 35ºC.  Different type of plants grow best in different optimum temperature (temperate plants thrive at 25ºC) 8