Plant Nutrition and Photosynthesis PDF

# Plant Nutrition ## Photosynthesis - Photosynthesis is the process by which green plants and other organisms containing chlorophyll make glucose and oxygen. - The word derives from the Greek *photo* meaning light and *synthesis* meaning to make - Photosynthesis is a process that combines smal...

# Plant Nutrition ## Photosynthesis - Photosynthesis is the process by which green plants and other organisms containing chlorophyll make glucose and oxygen. - The word derives from the Greek *photo* meaning light and *synthesis* meaning to make - Photosynthesis is a process that combines smaller molecules to form larger ones. - Plants use light energy absorbed by chlorophyll to combine carbon dioxide and water to make glucose and oxygen. - Glucose is an organic molecule that is essential for plant growth and development. - The word equation for photosynthesis is: * carbon dioxide + water → light → glucose + oxygen. - The symbol equation for photosynthesis is: * 6CO₂ + 6H₂O → light → C₆H₁₂O₆ + 6O₂. ## Transfer of light energy into chemical energy - Chlorophyll is the green pigment needed for photosynthesis. - Chlorophyll absorbs light energy which drives the reaction. - The products of photosynthesis contain more chemical energy than the reactants. - This extra energy is supplied by light. - Photosynthesis converts light energy into chemical energy. - The chemical energy is stored in plant material and is then used by other organisms that consume the plant. ## The use and storage of carbohydrates - Glucose is the first product of photosynthesis. - Glucose is used to supply the cell with energy by taking part in cell respiration. - Plants use glucose to produce other organic molecules that they need. - Starch is insoluble in cold water and acts as a store of carbohydrate in plants. - Starch is broken down to release glucose for respiration. ## Conditions Needed for Photosynthesis - Photosynthesis requires five main things: * carbon dioxide * water * light * chlorophyll * a suitable temperature. - Carbon dioxide and water must be available to the plant. - Only parts of the plant containing chlorophyll can absorb light. - Temperature affects enzyme-controlled reactions. - Low temperatures reduce kinetic energy. - High temperatures will cause enzymes to be denatured. ## Testing a Leaf for Starch - The presence of starch in a leaf shows that the plant has carried out photosynthesis. - The test uses iodine solution: - The leaf must be boiled in ethanol to remove the waxy coating and green colour. - The leaf is then placed in a petri dish containing a few drops of iodine solution. - The leaf will turn blue-black if it contains starch. - It is possible to use the starch test to show the conditions needed for photosynthesis. - An experimental plant can be deprived of one condition. - A leaf from the plant is then tested for starch to see whether the plant has been able to photosynthesise. ## Investigating the Need for Chlorophyll, Light and Carbon Dioxide for Photosynthesis - **Light** is needed for photosynthesis. - A plant that has been exposed to light will contain starch. - A plant that has been kept in the dark will not contain starch. - **Carbon Dioxide** is needed for photosynthesis. - A plant in a bell jar containing soda lime (to absorb carbon dioxide) will not contain starch. - A plant in a bell jar containing empty petri dish will contain starch. - **Chlorophyll** is needed for photosynthesis. - A variegated leaf that has been exposed to light will contain starch in the green areas. - A variegated leaf that has been exposed to light will not contain starch in the white areas. ## The Effect of Light, Carbon Dioxide, and Temperature on Rate of Photosynthesis - Rate of photosynthesis can be measured by the rate of production of oxygen. - The rate of oxygen production can be measured by counting the number of bubbles produced by an aquatic plant. - **Light intensity** affects the rate of photosynthesis. - Increasing light intensity increases the rate of photosynthesis until it reaches a plateau. - At high light intensities, another factor becomes a limiting factor. - **Carbon dioxide concentration** affects the rate of photosynthesis. - Increasing carbon dioxide concentration increases the rate of photosynthesis until another factor becomes a limiting factor. - **Temperature** affects the rate of photosynthesis. - The rate of photosynthesis increases with temperature until enzymes become denatured. ## Adaptations of a Leaf - Leaves are specialised for photosynthesis. - Adaptations include: * a large surface area to absorb light * cells containing many chloroplasts * a way to allow carbon dioxide to enter the leaf * a way to allow oxygen and water vapour to exit the leaf * a way to transport the products of photosynthesis away from the leaf. ## Leaf Structure - The leaf blade is thin and has a large surface area. - This allows for maximum light absorption. - The leaf blade has a thin cross-section, so light penetrates to all parts of it. - The leaf is supported by a leaf stalk. - Veins in the leaf contain vessels that carry materials from outside the leaf to the inside. - Tissues in the leaf include: - **Epidermis**: the outer layer of the leaf, which is a transparent layer of cells. - **Mesophyll**: photosynthetic tissue containing chloroplasts. - **Vascular tissue**: the transport tissue that carries water and nutrients to the leaf. ## Importance of Nitrate and Magnesium Ions in Plants - Plants need to obtain 'extra' elements from mineral ions in the soil. - **Nitrate ions (NO3-)**: used to make amino acids and proteins. - Insufficient nitrate leads to slow growth. - **Magnesium ions (Mg2+)**: required for chlorophyll production. - Insufficient magnesium leads to chlorosis, which is the yellowing of leaves.