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ICSE BIOLOGY PHOTOSYNTHESIS NOTES

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~1~ DishaEducentre Exhaustive Notes 5. Photosynthesis PHOTOSYNTHESIS Scope of Syllabus: The internal structure of chloroplast should be explained to give an idea of the site of light and dark reaction. Opening and closing of stomata should be explained. Teachers should stress upon the importance of a correct balanced chemical equation. The terms photochemical for light phase and biosynthetic for dark phase must be introduced. In the light reaction, activation of chlorophyll molecule followed by photolysis, release of O2, formation of ATP and NADPH should be taught. In the dark reaction, (detailed equations are not required) only combination of hydrogen released by NADP with CO2 to form glucose to be discussed. Adaptations in a plant for photosynthesis and experiments with regard to the factors essential for the process should be discussed. I. Definitions and Explanations 1. Photosynthesis 2. Chlorophyll 3. Chloroplasts 4. Photolysis 5. Phosphorylation 6. Photophosphorylation Photosynthesis is an anabolic process by which living plant cells containing chlorophyll produce food substances (glucose and starch) from carbon dioxide and water by using light energy, and releasing oxygen as a waste product. The green colouring pigment found in chloroplasts of the leaves are called as chlorophyll. Chloroplasts are microscopic oval bodies bounded by a double membrane that are present in plant cells. They contain the green pigment chlorophyll. The reaction in which water molecules splits in the influence of light, and forms hydrogen and oxygen is known as photolysis. In any reaction, if the phosphoryl group is added, it is called phosphorylation. The conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP), which occurs in the presence of light and chlorophyll, is known as photophosphorylation. It can be represented as:light , chlorophyll 7. Destarched Plant ADP ATP A plant from whose leaves starch has been removed is known as a destarched plant. This is done by keeping the plant in dark for 5-6 days. 8. 9. II. Questions-Answers 1. What is photosynthesis? Mention its raw materials and its by-products. Write the overall chemical equation involved in photosynthesis. ANSWER Photosynthesis is the process by which living plant cells containing chlorophyll produce food substances (glucose and starch) from carbon dioxide and water by using light energy, and releasing oxygen as a waste product. Raw materials: carbon dioxide, water By-products:glucose, oxygen, water, energy Notes Prepared by Neil Valentine D Silva ~2~ DishaEducentre Exhaustive Notes Photosynthesis Equation: 6CO2 + 12H2 O light energy chlorophyll C6 H12 O6 + 6H2 O + 6O2 2. Give the chemical equations involved in the formation of starch in plants. ANSWER Photosynthesis takes place in green plants to form the carbohydrate glucose. Glucose then undergoes condensation polymerisation to form starch. The equations involved are:- (i) Equation for photosynthesis to produce glucose:6CO2 + 12H2 O (ii) light energy chlorophyll C6 H12 O6 + 6H2 O + 6O2 Equation for condensation of glucose to produce starch:n C6 H12 O6 condensation polymerisation C6 H10 O5 n + nH2 O 3. Describe how photosynthesis is the opposite of respiration. ANSWER The following are the main differences between photosynthesis and respiration (i) In photosynthesis, carbon dioxide and water vapour are absorbed as reactants and oxygen is given out as a by-product. The overall reaction is as follows:light energy chlorophyll 6CO2 + 12H2 O C6 H12 O6 + 6H2 O + 6O2 [ ] However, in respiration, oxygen is utilised and carbon dioxide and water vapour is given out. C6 H12 O6 + 6O2 6CO2 + 6H2 O + 38 ATP [ ] (ii) (iii) 4. Photosynthesis is an anabolic process as it brings about an increase in the dry weight of an organism. Respiration is a catabolic process because it brings about a decrease in the dry weight of the organism. No energy is released in photosynthesis, while 38 ATP of energy is released during aerobic respiration. Describe the structure of the chloroplast with a neat, labelled diagram. chloroplast is an organelle found in plant cells. It contains the green pigment, chlorophyll. ANSWER The The chloroplast is a minute oval body having a double membrane. Its interior contains closely packed flattened sacs known as thylakoids. The thylakoids are arranged in piles known as grana. The entire interior of the chloroplast is filled with a colourless ground substance called stroma. Notes Prepared by Neil Valentine D Silva DishaEducentre Exhaustive Notes ~3~ Photosynthesis The green pigment chlorophyll is contained in the walls of the thylakoids. 5. Give information about the green pigment found in chloroplasts. green pigment found in chloroplasts is known as chlorophyll. It is contained in the walls of the thylakoids present in the chloroplast. Chlorophyll is a highly complex substance, composed of carbon, hydrogen, oxygen, nitrogen and magnesium. There are nine different types of chlorophyll, of which chlorophyll-a and chlorophyll-b are the most abundant. All forms of chlorophyll can absorb light from both ends of the visible spectrum. ANSWER The 6. Where are chloroplasts found in plants? are found in the mesophyll cells located between the upper epidermis and the lower epidermis of leaves. Thus, they are present between the palisade cells and spongy cells of leaves. There may be more than 500,000 chloroplasts in one square millimetre of the leaf surface. They are also found in the guard cells and the outer layers of the young green stems. ANSWER Chloroplasts 7. Describe the Sugar Concentration Theory for the opening and closing of stomata. ANSWER According to the Sugar Concentration Theory, the guard cells of the stomata begin photosynthesis in the daytime. Due to this, starches are produced in them and their osmotic pressure rises. The solution in the guard cells has low water potential now and the adjacent cell solution has higher water pollution. This brings in water from the neighbouring cells by endosmosis and they become turgid. This opens the guard cells. In the night time, photosynthesis stops. The guard cells lose their starches, osmotic pressure decreases, water flows out of them and they become flaccid. This leads them to close. Describe the K+ Ion Concentration Theory for the opening and closing of stomata. + ANSWER According to K Ion Concentration Theory, the guard cells of the stomata begin photosynthesis in the daytime. During photosynthesis, energy molecules ATP are released. Under the influence of ATP, K+ ions are actively pumped into the guard cells from the adjacent cells. Hence, the solution in the guard cells becomes hypertonic. The solution in the guard cells has low water potential now and the adjacent cell solution has higher water pollution. This brings in water from the neighbouring cells by endosmosis and they become turgid. This opens the guard cells. In the night time, photosynthesis stops. The guard cells lose their K+ ion concentration, osmotic pressure decreases, water flows out of them and they become flaccid. This leads them to close. 8. 9. Describe the process of photosynthesis. ANSWER Photosynthesis takes place in the mesophyll of the leaf. The upper layers (palisade) and lower layers (spongy) of the leaf both are involved in photosynthesis. The raw materials required for photosynthesis are light energy (from the sun), carbon dioxide, water and chlorophyll. Light energy of the sun is trapped by the palisade tissue in the daytime. This is the source of energy for the chemical changes occurring in the plant during photosynthesis. Carbon dioxide is taken from the atmosphere by diffusion through the stomata. It travels down the concentration gradient into the leaf. Water is taken from the soil by the roots through osmosis. It moves upward in a cell-to-cell movement and finally reaches the leaves where photosynthesis takes place. Chlorophyll in the leaves is the pigment that absorbs light. The overall equation of photosynthesis is as follows:- Notes Prepared by Neil Valentine D Silva DishaEducentre Exhaustive Notes ~4~ Photosynthesis light energy chlorophyll 6CO2 + 12H2 O C6 H12 O6 + 6H2 O + 6O2 The glucose which is produced is a simple water-soluble molecule. 10. What are the two phases of photosynthesis? ANSWER The two phases of photosynthesis are as follows:Light Dependent Phase Occurs in (a.k.a. Light Phase) thylakoids (a.k.a. Photochemical Phase) Light Independent Phase Occurs in stroma (a.k.a. Dark Phase) of chloroplast (a.k.a. Biosynthetic Phase) Photolysis of water takes place. Oxygen is released into atmosphere. ATP is produced. Glucose is produced. Glucose is later converted into starch. 11. Outline the main steps taking place during the Light Dependent Phase of photosynthesis. ANSWER During the Light Dependent Phase, light energy of the sun is absorbed by the chlorophyll and is used to bring about chemical changes. Hence, this phase is also called as photochemical phase. There are two main steps involved in this phase. (i) Step 1: Activation of Chlorophyll Chlorophyll absorb small individual packets of light energy called photons. This makes them activated. (ii) Step 2: Photolysis of Water Due to the absorbed light energy, water molecules are split into hydrogen and oxygen by releasing electrons. This reaction is known as photolysis. 4 photons of energy 2H2 O 4H + + 4e + O2 Each product of the photolysis reaction is useful in the following ways:a) Hydrogen ions are used to convert nicotinamide adenine dinucleotide phosphate (NADP) into its reduced form NADPH. NADP + H + + e NADPH b) Oxygen is converted into molecular form and released into the environment, from where it is used by all organisms for respiration. 2O O2 c) Electronsactivate inorganic phosphate (P ). This activated inorganic phosphate is taken up by adenosine diphosphate (ADP), which gets converted into adenosine triphosphate (ATP). This reaction is a phosphorylation reaction. ADP + P ATP 12. What is NADP? is nicotinamide adenine dinucleotide phosphate. It is a coenzyme necessary in the photosynthetic process. Its reduced form NADPH is essential for the reduction of carbon dioxide to glucose in the Calvin Cycle (Dark Reaction). ANSWER NADP 13. Explain the photophosphorylation reaction. conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP), which occurs in the presence of light and chlorophyll, is known as photophosphorylation. The electrons released during the photolysis reaction in the Light-Dependent Phase of photosynthesis activate inorganic phosphate. This is represented by P . The activated inorganic phosphate is taken up by adenosine diphosphate (ADP) to form adenine triphosphate (ATP). ADP + P ATP It can be represented as:- ANSWER The ADP light , chlorophyll ATP Notes Prepared by Neil Valentine D Silva DishaEducentre Exhaustive Notes ~5~ Photosynthesis As phosphate is added in this reaction, it is called as phosphorylation. As the addition of phosphate takes place in light energy, it is called as photophosphorylation. 14. Write a note on the Hill Reaction. ANSWER The photolysis reaction taking place during the Light Dependent Phase of photosynthesis is also called as the Hill Reaction because it was discovered by Professor Robert Hill. The activated inorganic phosphate is taken up by adenosine diphosphate (ADP) to form adenine triphosphate (ATP). During this reaction, water molecules are split into hydrogen and oxygen by releasing electrons. 4 photons of energy 2H2 O 4H + + 4e + O2 Each product of the photolysis reaction is useful in the following ways:a) Hydrogen ions are used to convert nicotinamide adenine dinucleotide phosphate (NADP) into its reduced form NADPH. NADP + H + + e NADPH b) Oxygen is converted into molecular form and released into the environment, from where it is used by all organisms for respiration. 2O O2 c) Electrons activate inorganic phosphate (P ). This activated inorganic phosphate is taken up by adenosine diphosphate (ADP), which gets converted into adenosine triphosphate (ATP). This reaction is a phosphorylation reaction. ADP + P ATP 15. What changes take place during the Light Independent Phase of photosynthesis? Light Independent Phase of photosynthesis does not depend on light to carry out the chemical changes. It does not necessarily take place in the dark, and hence it is incorrect to call it as the Dark Reaction, though it was called so formerly. During this reaction, the NADPH formed during photolysis reduces carbon dioxide to glucose. ANSWER The 16. In what form is chemical energy stored in plants at the end of photosynthesis? How does this conversion take place? ANSWER At the end of photosynthesis, glucose is formed. This is eventually converted into starch. Several glucose molecules are combined to form one single large molecule, which is a molecule of starch. This kind of combination reaction is called as polymerisation. In some plants, however, glucose is converted into a disaccharide sugar known as sucrose (cane sugar). This kind of conversion takes place in sugarcane. 17. What are the adaptations seen in leaves to facilitate photosynthesis? show the following adaptations to facilitate photosynthesis:(i) Large surface This causes maximum absorption of light. area (ii) Leaf Leaves arranged perpendicular to the light source can obtain highest amount arrangement of light energy. (iii) Cuticle and Transparent cuticle and upper epidermis allow maximum absorption of light upper epidermis energy. (iv) Large number of This allows more diffusion of carbon dioxide from the atmosphere into the stomata leaves. (v) Thinness of This makes cells of leaf more compact, allowing faster exchange of gases. leaves (vi) Concentration of More chloroplasts in the upper layer of the leaf facilitate faster absorption of chloroplasts light energy. (vii) Extensive vein An intricate vein network helps in rapid transport of gases to and from system mesophyll cells. ANSWER Leaves Notes Prepared by Neil Valentine D Silva ~6~ DishaEducentre Exhaustive Notes 18. Photosynthesis What is translocation? How does it take place? transportation of starch stored in the leaves to the different parts of the plant is known as translocation. The product of photosynthesis is glucose, which is a simple sugar. It is provided to the cells that need energy for metabolism. However, a large part of the glucose is not required immediately. It is polymerised into starch and stored in this form in the leaf. From here, whenever any cell of the plant body requires energy, the starch is reconverted into glucose and transported in solution through the veins of the leaf and the phloem of the stem to that part. The requisite amount of glucose is utilised at that spot, and the remainder is converted back into complex starch. ANSWER The 19. What are the factors affecting photosynthesis? factors affecting photosynthesis are:Light intensity Carbon dioxide concentration Temperature Water content ANSWER The (i) (ii) (iii) (iv) 20. Draw graphs to explain how light intensity and carbon dioxide influence the rate of photosynthesis and explain them. Rate of photosynthesis ANSWER Highest rate of photosynthesis reached with 0.02% CO2 concentration RATE OF PHOTOSYNTHESIS STABILISED 0.02% CO2 concentration 0.02% CO2 concentration S Increasing light intensity GRAPH A: Variation of Rate of Photosynthesis with Light Intensity and CO2 Concentration Rate of photosynthesis Highest rate of photosynthesis reached with 0.05% CO2 concentration RATE OF PHOTOSYNTHESIS STABILISED 0.02% CO2 concentration CO2concentration increased to 0.05% S S Increasing light intensity GRAPH B: Variation of Rate of Photosynthesis with Light Intensity and CO2 Concentration Notes Prepared by Neil Valentine D Silva ~7~ DishaEducentre Exhaustive Notes Photosynthesis The following observations are made in these graphs:Graph A The concentration of CO2 is kept at 0.02%. As the light intensity is increased, the rate of photosynthesis also gradually increases. But, after a point, the rate of photosynthesis remains the same even if the light intensity is increased. This is known as the stabilisation point S . Graph B Now the concentration of CO2 is increased further up to 0.05%. We see that the rate of photosynthesis again begins to increase with increasing light intensity. However, once again, it reaches a stabilisation point after which the rate of photosynthesis becomes constant. This is known as the stabilisation point S . Observations As light intensity increases, rate of photosynthesis also increases. But after a certain point, light intensity does not affect rate of photosynthesis. At this point, photosynthesis gets stabilised. Rate of photosynthesis increases with increasing level of carbon dioxide. 21. Explain how temperature influences the rate of photosynthesis. Draw a suitable graph. rate of photosynthesis rises with increasing temperature. This increase happens up to an optimum temperature of 35 C. After this, the rate falls and stops above 40 C. This is because plant enzymes are destroyed at this temperature. A rise of 10 C below the optimum temperature doubles the rate of photosynthesis. A graph of the variation of rate of photosynthesis with temperature is shown below. ANSWER The Rate of photosynthesis OPTIMUM TEMPERATURE 0 10 20 30 35 40 Increasing temperature in C Graph: Variation of Rate of Photosynthesis with Temperature What happens to the rate of photosynthesis between 30 C and 40 C? ANSWER From 30 C to 35 C, the rate of photosynthesis increases with temperature. At 35 C, the highest rate of photosynthesis is reached. This is known as optimum temperature. From 35 C to 40 C, the rate of photosynthesis begins falling down. After 40 C, the rate of photosynthesis completely stops because enzymes die beyond this point. 22. 23. What is the effect of water content on the rate of photosynthesis? Notes Prepared by Neil Valentine D Silva DishaEducentre Exhaustive Notes ~8~ Photosynthesis ANSWER When water content reduces, the rate of photosynthesis begins dropping as well. Water content may reduce because of scarcity of water in the soil medium or because of an increased rate of transpiration. When this happens, the stomata close and the diffusive intake of CO2 from the atmosphere stops. In fact, only 1% of the total water absorbed by the roots is used in photosynthesis. 24. Describe the internal factors that affect photosynthesis. following are the internal factors that influence photosynthesis:(i) Chlorophyll Chlorophyll may be lost due to reduced nutritional intake. Due to this, enough solar energy is not absorbed and the rate of photosynthesis drops. (ii) Protoplasm Dehydration of protoplasm causes a decrease in the rate of photosynthesis. When protoplasm reduces, potassium levels also reduce. This reduces the ability of plant to convert glucose into starch. The amount of carbohydrate glucose increases in the cells, and further photosynthesis is reduced. (iii) Structure of A thick cuticle and fewer stomata in the leaves reduce the capacity to absorb Leaf CO2 and amount of light. Thus, rate of photosynthesis decreases. ANSWER The 25. What is the role of light energy in photosynthesis? role of light energy in photosynthesis is as a source of energy for the chemical conversions. The term photosynthesis itself means synthesis in the presence of light. Light obtained from the sun provides the energy for the synthesis of organic compounds. Once the light energy is absorbed by chlorophyll, it is converted into chemical energy and utilised for the synthesis of carbohydrates from carbon dioxide and water. ANSWER The 26. What is the role of chloroplasts in photosynthesis? ANSWER The role of chloroplasts in photosynthesis is as an energy converter. The chlorophyll from the chloroplasts absorb the light energy and convert it into chemical energy. This chemical energy is stored in the form of adenosine triphosphate (ATP) and utilised for the synthesis of organic compounds such as glucose, proteins and lipids. 27. Describe the importance of photosynthesis. ANSWER Photosynthesis is significant in the following ways:(i) Production of food for the living kingdom: Green plants, i.e. producers, prepare starches by photosynthesis. This becomes the main source of food for both herbivores and carnivores. (ii) Supply of oxygen: Oxygen is one of the by-products of photosynthesis. Due to photosynthesis, the level of oxygen is maintained in the atmosphere. (iii) Carbon dioxide balance: Green plants absorb carbon dioxide, which is one of the raw materials for photosynthesis. This helps in maintaining the amount of carbon dioxide in the atmosphere, which is 0.03%. 28. Draw an illustration of the carbon cycle and describe the steps involved in it. carbon cycle is a series of chemical reactions in which carbon as a chemical element (in CO2) is removed from the air, used by living organisms in their body processes and is finally returned to the air. ANSWER The Notes Prepared by Neil Valentine D Silva DishaEducentre Exhaustive Notes ~9~ Photosynthesis The following are the essential steps that take place in the carbon cycle:(i) (ii) (iii) (iv) (v) (vi) Photosynthesis: Green plants are the producers who use the carbon dioxide of the air to produce carbohydrates in the form of sugars and starches. Food chains: Through food chains, the food (containing carbon in the carbohydrates and other products) passes on from plants to animals of all body tissues of both plants and animals. Respiration: All plants and animals respire by oxidising carbohydrates in their cells to produce energy and give out carbon dioxide into the atmosphere. Decay: The dead remains of plants and animals are consumed by bacteria and fungi (decomposers), and in the process, they break down the organic matter, releasing carbon in carbon dioxide back into the atmosphere. Combustion (burning): When a fuel such as wood or a fossil fuel like coal, petroleum or natural gas is burnt, the carbon contained in it is oxidised to carbon dioxide, which is given back into the atmosphere. All the fuels named above originally come from living organisms. A certain amount of carbon dioxide is released during heating or burning of limestone in lime kilns. Experiments 1. Outline the steps involved in detecting the starch content in leaves. detect the starch content in leaves, the following steps are carried out:Step Change Purpose Leaf is boiled in water for 10 Destroys cells in the leaf. minutes Leaf is boiled in alcohol for Leaf becomes Destroys chlorophyll in the leaf. 10 minutes colourless. Leaf is washed in water Removes soluble substances from leaf. Leaf is dipped in iodine Regions having starch Detects starch presence. solution turn bluish black ANSWER To The above test is known as the iodine test for detection of starch. Boil in water Boil in alcohol (10 minutes) (10 minutes) Notes Prepared by Neil Valentine D Silva Wash in water Dip in iodine solution Starchy regions turn bluish black DishaEducentre Exhaustive Notes 2. ~ 10 ~ Photosynthesis Demonstrate an experiment to show that chlorophyll is necessary for photosynthesis. ANSWER Aim: To show that chlorophyll is necessary for photosynthesis. Procedure:Take a plant with variegated leaves, having some green and non-green areas, such as that of croton or coleus.Destarch the leaf by keeping it in a dark room for a few days. Then place it in the sun for a few hours. Pluck one leaf. Test the leaf for presence of starch by the iodine test. Observations:Only the green parts of the leaf are stained blue, showing presence of starch in them. The non-green parts do not turn blue. Inference: Chlorophyll was present in the green parts, and hence starch was produced in those regions by photosynthesis. Hence, chlorophyll is necessary for photosynthesis. 3. Demonstrate an experiment to show that sunlight is necessary for photosynthesis. To show that sunlight is necessary for photosynthesis. Procedure: Take a well-watered potted plant. Destarch its leaves by placing it in a dark room for a few days. Cover one of its leaves with a Ganong s light screen (a black paper on which a design is cut out). Place this plant in the sun. After a few hours, pluck the leaf, remove the Ganong s light screen from it, and test it for presence of starch by iodine test. Observation: Only the parts of the leaf that were exposed to light through the cut-out design turn blue black. The covered part does not show this colouration. Inference: The exposed part of the leaf received sunlight and hence produced starch by photosynthesis. The covered part could not produce starch as it received no sunlight. Thus, it is proved that sunlight is necessary for photosynthesis. ANSWER Aim: 4. Demonstrate an experiment to show that carbon dioxide is necessary for photosynthesis. ANSWER Notes Prepared by Neil Valentine D Silva DishaEducentre Exhaustive Notes ~ 11 ~ Photosynthesis Aim: To show that carbon dioxide is necessary for photosynthesis. Procedure:Take a well-watered potted plant. Destarch its leaves by placing it in a dark room for a few days. Take one of its leaves and insert it into a flask containing caustic potash (KOH) through a split cork. Leave the plant in sunlight. After a few hours, test the leaf for starch using iodine test. Observations: The part of the leaf that was outside the flask turns blue black. The part which was inside the flask does not show this colouration. Inference: The part of the leaf which was inside the flask did not get access to carbon dioxide as it was absorbed by KOH. Hence, no photosynthesis took place inside the flask. This shows that carbon dioxide is necessary for photosynthesis. 5. Demonstrate an experiment to show that oxygen is produced during photosynthesis. ANSWER Aim: To show that oxygen is produced during photosynthesis. Procedure: Place some water plants (Elodea or Hydrilla) in a beaker containing pond water. The plant must be completely submerged in the water. Cover them with a short-stemmed funnel. Invert a test tube containing water over the stem of the funnel. Place the apparatus in the sun for a few hours. Observations: Bubbles of gas collect in the test tube. On testing the gas with a glowing splinter, it is proved to be oxygen. Inference: Oxygen gas is released during photosynthesis. Diagram-based Questions 1. a) b) c) d) This experimental setup aims to prove a condition necessary for photosynthesis. Which is the condition? What is the purpose of soda lime? Which plant will show bluish black colour for the iodine test the one on the left or the one on the right? What are the other conditions necessary for photosynthesis? ANSWER a) b) The experimental setup proves that carbon dioxide is necessary for photosynthesis. The function of soda lime is to absorb carbon dioxide present in the air. Notes Prepared by Neil Valentine D Silva DishaEducentre Exhaustive Notes ~ 12 ~ Photosynthesis c) d) The leaves of the plant on the left will show bluish black colouration for the iodine test. The other conditions necessary for photosynthesis are sunlight, chlorophyll and water vapour. 2. The following is an experimental setup to show one of the conditions necessary for photosynthesis. Which condition does it show? What is the role of KOH in the flask? What was done to the plant before commencing the experiment? Will the leaf inside the flask respond to the iodine test at the end of the experiment? Why? Which of the following substances will not be required for this experiment alcohol, acetone, water? a) b) c) d) e) ANSWER a) b) c) d) e) The experimental setup proves that carbon dioxide is necessary for photosynthesis. KOH absorbs the carbon dioxide that is present in the flask. Before commencing the experiment, the plant was destarched by keeping it in a dark room for a few days. The leaf inside the flask will not show a bluish black colouration to the iodine test; i.e. it will not respond to the test. This is because it did not have exposure to carbon dioxide and hence it did not prepare starch by photosynthesis. Acetone is not needed for this experiment. Reasons and Justifications 1. Photosynthesis is an anabolic process. ANSWER Anabolic processes are those in which there is an increase in the protoplasm and dry weight of the organism. In photosynthesis, carbon dioxide and water are taken in by the plant from the atmosphere, and with the help of light energy and chlorophyll are converted into sugars and starches. These are stored within the plant. They increase the protoplasm and dry weight of the organism. Hence, photosynthesis is called as an anabolic process. Distinctions and Comparisons 1. (i) (ii) Photosynthesis and Respiration Photosynthesis It is an anabolic process. It occurs in green plants that have chlorophyll. Notes Prepared by Neil Valentine D Silva Respiration It is a catabolic process. It occurs in all living organisms. DishaEducentre Exhaustive Notes (iii) (iv) (v) 2. OR: (i) (ii) (iii) (iv) (v) 3. ~ 13 ~ Photosynthesis CO2 is taken in and O2 is given out. O2 is taken in and CO2 is given out. There is an increase in the dry weight of the There is a decrease in the dry weight of the organism. organism. It takes place only in the daytime. It takes place throughout the day. Light Dependent Reaction and Light Independent Reaction Light Reaction and Dark Reaction Light Dependent Reaction (Light Reaction) It takes place in the presence of light. It is a photochemical reaction. It takes place in grana of chloroplast. It synthesises ATP and NADPH. It involves photolysis of water and releases O2. Light Independent Reaction (Dark Reaction) It is independent of light. It is a synthetic reaction. It takes place in stroma of chloroplast. It utilises ATP and NADPH. It involves fixation of CO2 to produce carbohydrates. Stroma and Grana (i) (ii) (iii) (iv) Stroma Grana Stroma is the homogeneous matrix of the Grana are the disc-like dark structures in the chloroplast. chloroplast. Stroma is colourless. Grana appears dark green. Stroma contains soluble enzymes. Grana contain chlorophyll. Light Independent Phase takes place in the Light Dependent Phase takes place in the stroma. grana. Diagram-based Questions Flowchart of Sugar Concentration Theory Daytime Photosynthesis begins in guard cells Sugars are produced in guard cells Endosmosis occurs from adjacent cell to guard cells Water fills up in the guard cells making them turgid Turgid guard cells make stomata open The exact opposite of this process takes place in the night time as photosynthesis stops. Flowchart of K+ Ion Concentration Theory Notes Prepared by Neil Valentine D Silva DishaEducentre Exhaustive Notes ~ 14 ~ Photosynthesis Daytime Photosynthesis begins in guard cells ATP is produced in guard cells ATP actively pumps K ion from adjacent cells to guard cells Guard cell solution becomes hypertonic Endosmosis occurs from adjacent cell to guard cells Water fills up in the guard cells making them turgid Turgid guard cells make stomata open The exact opposite of this process takes place in the night time as photosynthesis stops. BOARD EXAMINATION QUESTIONS 2002 1. Choose the correct option for the following:A plant is kept in a dark cupboard for about 48 hours before conducting an experiment on photosynthesis to __________________________. (a) Remove chlorophyll from the leaves. (b) Remove starch from the plant. (c) Ensure that no photosynthesis occurs. (d) Ensure that the leaves are free from starch. ANSWER (d) Ensure that the leaves are free from starch. 2. Define the following term:- Photophosphorylation. conversion of adenosine diphosphate (ADP) to adenosine triphosphate (ATP), which occurs in the presence of light and chlorophyll, is known as photophosphorylation. It can be represented as:- ANSWER The ADP 3. light , chlorophyll ATP Mention the reactants of photosynthesis and respiration. The reactants are carbon dioxide and water (in the presence of chlorophyll and sunlight). Respiration: The reactants are oxygen and glucose. ANSWER Photosynthesis: 2002 4. Name the part of the chloroplast where the dark reaction of photosynthesis takes place. ANSWER Stroma 5. A healthy croton plant bearing variegated leaves was kept in a dark cupboard to destarch it after which it was placed in sunlight for a few hours. One of the leaves was then plucked and an outline of the leaf marking the green and the non-green regions was drawn. The leaf was then tested for starch. Using the above information, answer the following questions:(i) State the aim of the above experiment. (ii) Name the chemical used for testing the presence of starch. (iii) Why is the leaf boiled in water and alcohol before testing it for the presence of starch? (iv) What change is seen in the leaf after the starch test? (v) Give the chemical equation to represent the process of starch formation in plants. Notes Prepared by Neil Valentine D Silva ~ 15 ~ DishaEducentre Exhaustive Notes ANSWER (i) (ii) (iii) (iv) (v) Photosynthesis The aim of the experiment is to prove that chlorophyll is essential for photosynthesis. The chemical used for testing the presence of starch is iodine solution. The leaf is boiled in water to kill all its cells and destroy its active enzymes. It is then boiled in alcohol to remove all its chlorophyll. The green parts of the leaf turn blue-black while the non-green parts turn black. The chemical equations are as follows:a. Equation for photosynthesis to produce glucose:light energy chlorophyll 6CO2 + 12H2 O C6 H12 O6 + 6H2 O + 6O2 b. Equation for condensation of glucose to produce starch:n C6 H12 O6 condensation polymerisation C6 H10 O5 n + nH2 O 2004 6. Name the structure where photophosphorylation takes place. ANSWER Grana 7. Given below are biological statements which are incomplete and hence incorrect. Rewrite the correct form by inserting suitable word/words at the right place. Do not delete any word already given in the statement:(i) The splitting of water molecules into hydrogen ions and hydroxyl ions is termed as photolysis. (ii) Destarching a plant means removing the starch from the plant. ANSWER (i) The splitting of water molecules into hydrogen ions and hydroxyl ions in the presence of light is known as photolysis. (ii) Destarching a plant means removing the starch from the leaves of the plant. 8. A tiger owes its existence to chlorophyll. Give reasons. ANSWER Green plants produce starch through the process of photosynthesis. For this, carbon dioxide and water vapour from the atmosphere are taken into the plant and converted into starches with the help of chlorophyll pigment. As green plants prepare their own food, they are called as producers. Tiger is a consumer. It is a carnivore who feeds on herbivorous animals. Herbivores get their nutrition from the green plants that they eat. The entire food chain can be represented as:Tiger Green plants Herbivores (second level consumer) (first level consumer) (producer) Thus, indirectly, the tiger gets its nutrition from green plants. Hence, it owes its existence to green plants. 2005 9. Give the exact location and one function of the following structure:- Thylakoid They are disc-like structures present in each granum of the chloroplast in plant cells. Function: Thylakoid contain photosynthetic pigments in their inner walls (chlorophyll), which convert light energy to chemical energy in photosynthesis. ANSWER Location: 10. Enumerate the steps involved in testing a green leaf for the presence of starch. detect the starch content in leaves, the following steps are carried out:Step 1: Leaf is boiled in water for 10 minutes. This destroys the cells and active enzymes in the leaf. Step 2: Leaf is boiled in alcohol for 10 minutes. This destroys the chlorophyll in the leaf. ANSWER To (i) (ii) Notes Prepared by Neil Valentine D Silva DishaEducentre Exhaustive Notes (iii) (iv) ~ 16 ~ Photosynthesis Step 3: Leaf is washed in water. This removes soluble substances from the leaf. Step 4: Leaf is dipped in iodine solution. If starch is present, that region of the leaf turns bluish black. 2006 11. State whether the following statement is true or false. Correct if false by changing the first word only. Respiration is the only biological process in which oxygen is produced. ANSWER The statement is false. The correct statement is:Photosynthesis is the only biological process in which oxygen is produced. 12. Explain the term photolysis. photolysis reaction taking place during the Light Dependent Phase of photosynthesis. During this reaction, activated inorganic phosphate is taken up by adenosine diphosphate (ADP) to form adenine triphosphate (ATP). During this reaction, water molecules are split into hydrogen and oxygen by releasing electrons. ANSWER The 2H2 O 4 photons of energy 4H + + 4e + O2 2007 13. State whether the following statement is true or false:The dark reaction of photosynthesis is light independent. ANSWER The statement is true. Oxygen stoma respiratory cavity mesophyll cells oxidation of glucose 2 ATP Of these, only one term is incorrect. Identify the incorrect term and replace it with the correct one. ANSWER Carbon dioxide stoma respiratory cavity mesophyll cells oxidation of glucose 2 ATP 14. 15. (i) (ii) (iii) ANSWER (i) (ii) Draw a neat well-labelled diagram of the chloroplast. List the events taking place in the photochemical phase of photosynthesis. If you are planning an experiment to show the effect of light on photosynthesis:a) Will you select white light or green light? Justify your answer. b) Why would you select a destarched plant? The diagram of chloroplast is as follows:- The events taking place during the photochemical phase of photosynthesis are:a) Activation of chlorophyll b) Splitting of water (photolysis) according to the following reaction:2H2 O 4 photons of energy Notes Prepared by Neil Valentine D Silva 4H + + 4e + O2 DishaEducentre Exhaustive Notes (iii) ~ 17 ~ Photosynthesis a) I will select white light for photosynthesis. Maximum photosynthesis occurs in white light and minimum in green light. Chlorophyll pigment is most sensitive to white light. b) A destarched plant is selected because we have to only determine if photosynthesis occurs to produce starch. Hence, all previous starch must be removed. By using a destarched plant, we can show that light is essential for photosynthesis. 16. Give reasons: Green leaves are thin and broad. ANSWER The following reasons justify the thin and broad shape of green leaves: Broad leaves means more surface area. This improves the absorption of light by chlorophyll. Thin leaves reduces the distance between cells. This facilitates rapid transport of substances within the leaves. Hence, by being thin and broad, photosynthesis is increased in leaves. 2008 17. Name the ground substance present in a chloroplast. ANSWER Stroma 18. Rearrange the following terms so as to be in a logical sequence:Destarched plant, iodine added, washed in water, a leaf boiled in alcohol, placed in sunlight (testing for presence of starch) ANSWER Destarched plant placed in sunlight a leaf boiled in alcohol washed in water iodine added 19. State whether the following statement is true or false. If false, correct it by changing the last word only:Plants that manufacture their own food are termed heterotrophs. ANSWER The given statement is false. The correct statement is:Plants that manufacture their own food are termed autotrophs. 20. Given below is an incomplete explanation of a biological process/term where a key word has been left out. Rewrite the completed explanation by inserting the key word in the space indicated by ^ . Photolysis is the splitting of water molecules into hydrogen ions and hydroxyl ions in the presence of ^ and light. ANSWER Photolysis is the splitting of water molecules into hydrogen ions and hydroxyl ions in the presence of chlorophyll and light. 21. Briefly explain the term: Destarched plant plant from whose leaves starch has been removed is known as a destarched plant. This is done by placing the plant in the dark for 5-6 days, during which the starch present in its leaves is all used up. During photosynthesis experiments, plants are destarched before starting. ANSWER A 22. Given below is a diagrammatic representation of the internal structure of an organelle found in a plant cell. Study the same and then answer the questions that follow:(i) Identify the organelle. (ii) Name the physiological process occurring in this organelle. (iii) Mention one way in which this process is beneficial to man. Notes Prepared by Neil Valentine D Silva ~ 18 ~ DishaEducentre Exhaustive Notes (iv) (v) (vi) ANSWER (i) (ii) (iii) (iv) (v) Photosynthesis Name the phases of the process occurring in the parts labelled 1 and 2. A chemical substance NADP plays an active part in one of the phases. Give the expanded form of NADP and state its role in the above process. Represent the physiological process mentioned in (ii) above in the form of a chemical equation. The organelle is a chloroplast. The physiological process occurring in it is photosynthesis. Photosynthesis is important to man because this is the primary way in which food is produced for all living organisms. Thus, is acts as a source of energy for all physiological processes in all living organisms. The processes that occur in 1 and 2 are:1 (stroma): Reaction occurring is dark reaction, i.e. light independent phase. 2 (grana): Reaction occurring is light reaction, i.e. light dependent phase. The chemical equation for photosynthesis is:6CO2 + 12H2 O light energy chlorophyll C6 H12 O6 + 6H2 O + 6O2 23. Give the biological term for the following:The process of conversion of ADP to ATP during the first phase of photosynthesis. ANSWER Photophosphorylation 24. Account for the following:- Animals owe their existence to chlorophyll. plants produce starch through the process of photosynthesis. For this, carbon dioxide and water vapour from the atmosphere are taken into the plant and converted into starches with the help of chlorophyll pigment. As they prepare their own food, they are called as producers. Animals are consumers. Herbivorous animals eat green plants directly and carnivorous animals consume them indirectly. Thus, directly or indirectly, all animals owe their existence to chlorophyll. ANSWER Green 2009 25. Name the following:- The cell organelle responsible for photosynthesis. ANSWER Chlorophyll 26. State whether the following statement is true or false. If false, then correct it by changing only the first or last word. Photosynthesis occurs in all the cells of the plant. ANSWER The given statement is false. The correct statement is:Respiration occurs in all the cells of the plant. 27. Explain the term: Photolysis in photosynthesis. photolysis reaction taking place during the Light Dependent Phase of photosynthesis. During this reaction, activated inorganic phosphate is taken up by adenosine diphosphate (ADP) to form adenine triphosphate (ATP). During this reaction, water molecules are split into hydrogen and oxygen by releasing electrons. ANSWER The 2H2 O 28. 4 photons of energy 4H + + 4e + O2 Given below is a statement followed by four choices. Select and rewrite the correct answer of the given statement:A destarched plant is one whose: a) Leaves are free from chlorophyll. Notes Prepared by Neil Valentine D Silva ~ 19 ~ DishaEducentre Exhaustive Notes Photosynthesis b) Aerial parts are free from chlorophyll. c) Leaves are free from starch. d) Plant is free from starch. ANSWER A destarched plant is one whose: c) leaves are free from starch. 29. Mention any three adaptations found in plants to favour the process of photosynthesis. following are some adaptations found in plants to favour photosynthesis:Large surface area (broad lamina) for maximum absorption of light. Leaves arranged perpendicular to light source so as to obtain highest amount of light. Large number of stomata to provide for more diffusion of carbon dioxide from atmosphere into the leaves. ANSWER The (i) (ii) (iii) 30. The diagram below represents an experiment conducted to prove the importance of a factor in photosynthesis. Study the same and then answer the questions that follow:(i) Name the factor being studied in the experiment. (ii) Why was the plant kept in a dark room before conducting the experiment? (iii) Why was the experimental leaf then kept in:- 1. Boiling water 2. Methylated spirit? (iv) Name the solution used to test for presence of starch in the leaf. (v) What will we observe in the experimental leaf at the end of the starch test? (vi) Give a balanced chemical equation to represent the process of photosynthesis. ANSWER (i) The factor being studied is light. The experiment proves that light is necessary for photosynthesis. (ii) The plant was kept in a dark room before the experiment to destarch its leaves. (iii) 1. The experimental leaf was boiled in water to kill its cells and active enzymes. 2. The experimental leaf was kept in methylated spirit (alcohol) to destroy the chlorophyll in it. (iv) The solution used to test presence of starch in the leaf is iodine solution. (v) At the end, the parts of the leaf exposed to sunlight will turn bluish black, while the parts that were covered will turn brown. (vi) The chemical equation of photosynthesis is:6CO2 + 12H2 O light energy chlorophyll C6 H12 O6 + 6H2 O + 6O2 31. Complete the following by filling in the blanks numbered 1 to 10 with the appropriate word/term:Photosynthesis involves light reaction and dark reaction. During light reaction, the chlorophyll present in the ____(1)____ gets activated by absorbing light energy. This energy splits ____(2)____ molecules to ____(3)____ and oxygen and releases two electrons. This process is called ____(4)____. The ____(5)____ ions are picked up by NADP to form ____(6)____. The ADP is converted to ____(7)____. This process is called ____(8)____. During the dark phase, the compound produced at the end of light reaction reacts with carbon dioxide to form ____(9)____. This product is converted to starch. The process is called ____(10)____. ANSWER (1) chloroplasts (2) water (3) hydrogen (4) photolysis (5) hydrogen (6) NADPH (7) ATP (8) photophosphorylation (9) glucose (C6H12O6) (10) polymerisation 2010 Notes Prepared by Neil Valentine D Silva ~ 20 ~ DishaEducentre Exhaustive Notes Photosynthesis 32. State whether the following statements are true or false. If false, rewrite the correct form by changing the first or last word only:Photolysis is the process of splitting of water molecules in the presence of grana and temperature. ANSWER The given statement is false. The correct statement is:Photolysis is the process of splitting of water molecules in the presence of grana and light. 33. The figure below represents an experimental setup to study a physiological process in plants. (i) Name the physiological process being studied. (ii) Explain the process. (iii) What is the aim of the experiment? (iv) Give a well-balanced equation to represent the process. ANSWER (i) The physiological process being studied is photosynthesis. (ii) Photosynthesis is an anabolic process by which living plant cells containing chlorophyll produce food substances (glucose and starch) from carbon dioxide and water by using light energy, and releasing oxygen as a waste product. (iii) The aim of the experiment is to demonstrate that oxygen is released during photosynthesis. (iv) The chemical equation of photosynthesis is:6CO2 + 12H2 O light energy chlorophyll C6 H12 O6 + 6H2 O + 6O2 34. Explain the following term:- Destarched plant ANSWER A plant from whose leaves starch has been removed is known as a destarched plant. This is done by placing the plant in the dark for 5-6 days, during which the starch present in its leaves is all used up. During photosynthesis experiments, plants are destarched before starting. 35. Give one point of difference between the following terms on the basis of what is given in brackets:Light Reaction and Dark Reaction (site of occurrence) ANSWER The difference is as follows:Light Reaction Dark Reaction It occurs in the grana of the chloroplast. It occurs in the stroma of the chloroplast. 36. Give the biological/technical term for the following:Process of conversion of several molecules of glucose to one molecule of starch. ANSWER Polymerisation 2011 37. Name the following:That part of the chloroplast where the light reaction of photosynthesis takes place. ANSWER Thylakoids 38. Copy and complete the following by filling in the blanks 1 to 5 with appropriate words/terms/phrases:To test the leaf for starch, the leaf is boiled in water to ____(1)____. It is next boiled in methylated spirit to ____(2)____. The leaf is placed in warm water to soften it. It is then placed in a dish and ____(3)____ solution is added. The region which contains starch turns ____(4)____ and the region which does not contain starch turns ____(5)____. Notes Prepared by Neil Valentine D Silva DishaEducentre Exhaustive Notes ~ 21 ~ Photosynthesis ANSWER To test the leaf for starch, the leaf is boiled in water to (1) kill the cells and active enzymes. It is next boiled in methylated spirit to (2) destroy the chlorophyll. The leaf is placed in warm water to soften it. It is then placed in a dish and (3) iodine solution is added. The region which contains starch turns (4) bluish black and the region which does not contain starch turns (5) brown. 39. Give reasons:- Photosynthesis is considered as a process supporting all life on earth. plants produce starches by utilising carbon dioxide and water vapour taken from the environment in the presence of light and chlorophyll. This process is called green plants. Thus, green plants are producers who can prepare their own food. This food is consumed by herbivorous animals, who are in turn consumed by carnivorous animals.In this manner, all animals depend either directly or indirectly on the food they consume from the green plants. Also, photosynthesis releases oxygen into the environment, which is used by all living organisms for respiration. ANSWER Green 40. Write down the answer as indicated within brackets:NADP (expand the abbreviation) ANSWER NADP = Nicotinamide Adenine Dinucleotide Phosphate 41. Match the item in Column I with that which is most appropriate in Column II:Column I Column II Stroma a) Site of light reaction b) Site of dark reaction ANSWER Stroma site of dark reaction Notes Prepared by Neil Valentine D Silva

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Additional Info : ICSE Biology Notes by Bhomik Acharya (bhomik1018)
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