SASS Bio Nutrition in Plants Notes

6093 Biology Chapter 7 Nutrition in Plants CT_2020 1 ST ANDREW’S SECONDARY SCHOOL Secondary 3 Biology (6093) Chapter 7: Nutrition in Plants Name: ______________________ ( ) Class: _________ Date: _____________ 7.1 Photosynthesis • Plants are able to synthesise their own food by the process of photosynthesis. • Photosynthesis is a process in which light energy is absorbed by chlorophyll and converted to chemical energy. 5. Nutrition in Plants Content • Leaf Structure • Photosynthesis Learning Outcomes Candidates should be able to: a) identify and label the cellular and tissue structure of a dicotyledonous leaf, as seen in transverse section using the light 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 b) state the equation, in words and symbols, 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 uses 
 e) investigate and discuss the effects of varying light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis (e.g. in submerged aquatic plant) f) discuss light intensity, carbon dioxide concentration and temperature as limiting factors on the rate of photosynthesis 
 Use the knowledge gained in this section in new situations or to solve related problems.

6093 Biology Chapter 7 Nutrition in Plants CT_2020 2 • Inorganic molecules of carbon dioxide and water are used for the synthesis of an organic molecule of glucose. • Oxygen is released as a by-product. Where does photosynthesis occur? The light-dependent (light) and light-independent (dark) stages in photosynthesis. 1. Enzymes catalyse a series of reactions involved in the light and dark stages of photosynthesis. Green leaves Leaf’s _________ layer Cytoplasm of the mesophyll cells In an organelle called the chloroplast, which contains the green pigment chlorophyll

6093 Biology Chapter 7 Nutrition in Plants CT_2020 3 2. During the light stage of photosynthesis, the following processes occur: a. Trapping of light energy by chlorophyll b. Conversion of light energy to chemical energy c. Splitting/photolysis of water into hydrogen atoms and oxygen gas. 3. During the dark stage of photosynthesis, the chemical energy and hydrogen atoms produced from the light stage are used to reduce carbon dioxide to form glucose. The overall word equation of photosynthesis: carbon dioxide + water → glucose + oxygen [do not state energy as a product!] The overall chemical equation of photosynthesis: 6 CO2 + 12 H2O → C6H12O6 + 6O2 + 6 H2O The simplified chemical equation for photosynthesis: 6 CO2 + 6 H2O → C6H12O6 + 6O2 Limiting factors • Any factor that directly affects or limits a process if its quantity or concentration is changed is called a limiting factor. • Some factors affecting rate of photosynthesis are: o Light intensity o Carbon dioxide concentration o Temperature A. Light intensity X Beyond point X, the rate of photosynthesis… remains constant, does not increase any further even when the light intensity increases.

6093 Biology Chapter 7 Nutrition in Plants CT_2020 4 Increasing the light intensity will increase the rate of photosynthesis up till a certain point. This is known as the light saturation point. Plants respire (a process that releases carbon dioxide gas) simultaneously when they photosynthesize (a process that takes in carbon dioxide), the light intensity at which net gaseous exchange equals zero is known as the light compensation point. , B. Carbon dioxide concentration When the carbon dioxide concentration is raised from 0.03% to 0.13% while keeping the temperature constant at 20C, the rate of photosynthesis will increase. Considering a different point of view: At which concentration of CO2 is temperature a significant limiting factor? Explain why. 0.13%. At that concentration of carbon dioxide, increasing temperature from 20C to 30C led to a significant increase in rate of photosynthesis. On the other hand, doing the same at 0.03% of CO2 did not lead to a significant increase in rate of photosynthesis. 0.03% of CO2 at 20 °C 0.03% of CO2 at 30 °C 0.13% of CO2 at 20 °C 0.13% of CO2 at 30 °C Light intensity Rate of photosynthesis A B E F

6093 Biology Chapter 7 Nutrition in Plants CT_2020 5 C. Temperature Enzymes catalyse the reactions in photosynthesis. Therefore at temperatures lower or higher than optimum temperatures, enzymes are inactive or denatured respectively, thus affecting the rate of photosynthesis. Practice #1 State and explain the relationship between temperature and photosynthesis. [N11/2/6] (use PEEL strategy. Ensure answers fulfil intellectual standards.) State: Photosynthesis is a chemical reaction that requires the involvement of enzymes. Enzymes are dependent on temperature since they are made of proteins. Therefore, the rate of photosynthesis will be affected on by temperature changes. Explain: At low temperatures such as 0C, enzymes are inactive, due to enzymes having low levels of kinetic energy, hence rate of photosynthesis is slow. As temperature increases, enzymes gain kinetic energy and move faster, thereby increasing the rate of formation of enzyme-substrate complexes and increasing rate of reaction, until the optimum temperature of about 37C. At optimum temperature, rate is the highest. As temperature increases beyond the optimum, enzymes start to lose the nature of their active sites, causing denaturation of the enzyme, and therefore rate of activity drops quickly to zero as temperature continues to increase further.

6093 Biology Chapter 7 Nutrition in Plants CT_2020 6 Fates of glucose in leaves 1. Glucose is used by plant cells for tissue respiration or to form cellulose cell walls. 2. Excess glucose is converted either into sucrose and transported to storage organs or changed into starch for temporary storage in the leaves. 3. Glucose can react with nitrates to form amino acids which are combined to form proteins for the synthesis of new protoplasm in the leaf. 4. Glucose can be used to form fats for storage, cellular respiration or synthesis of new protoplasm. How can we study photosynthesis? To do photosynthetic experiments, the following basic knowledge is required: 1. Glucose is first formed from carbon dioxide during photosynthesis. 2. Presence of starch in the leaves suggests that photosynthesis has taken place. - When glucose is formed more quickly than it is used up, the excess glucose is changed to starch for storage. - Test for starch using the iodine test. 3. Destarching must be carried out on the plants before the experiments. - This ensures that starch is removed in the leaves prior to the experiments. - Put the plants in the dark for two days to stop photosynthesis and change starch to glucose, which is used up by the plant.

6093 Biology Chapter 7 Nutrition in Plants CT_2020 7 Experiments to investigate factors affecting the rate of photosynthesis Factor Experimental set-up Key steps Objective To investigate the effect of light intensity on the rate of photosynthesis Factors kept constant (a) carbon dioxide concentration (b) temperature Manipulation of factor being investigated Vary the distances between the lamp and the plant at intervals of 10cm, 20cm, 30cm, 40cm How to check the effect on the rate of photosynthesis Count the number of bubbles released per unit time Objective To investigate the effect of different carbon d