Photosynthesis
Overview
Weigh a young oak sapling, plant it, come back thirty years later and weigh the tree. It has gained tonnes. Dig up the soil around it and weigh that too: almost nothing has gone. So where did the tree come from? Overwhelmingly, from thin air and rainwater, assembled by a reaction that runs on sunlight inside the green cells of its leaves.
This lesson takes you through that reaction. You will write both equations for photosynthesis, find out exactly what chlorophyll does with the light it catches, and learn why the rate of the reaction so often stalls even in bright sun. You will then use that idea where it actually earns money: inside a commercial greenhouse, where a grower has to decide whether paying for extra heat, extra light or extra carbon dioxide will return more in crop than it costs in fuel.
Objectives
- Photosynthesis is represented by the equations: light carbon dioxide + water → glucose + oxygen light 6CO2 + 6H2O → C6H12O6 + 6O2
- During photosynthesis: light is absorbed by a green substance called chlorophyll, which is found in chloroplasts in some plant cells and in algae; light is used to convert carbon dioxide (from the air) and water (from the soil) into sugar (glucose); oxygen is released as a by-product.
- The rate of photosynthesis may be limited by: low temperature; shortage of carbon dioxide; shortage of light. These factors interact and any one of them may be the factor that limits photosynthesis. Students should be able to relate the principle of limiting factors to the economics of enhancing the following conditions in greenhouses: temperature; carbon dioxide concentration; light intensity. Required practical: Investigate how variables affect the rate of photosynthesis.
- The glucose produced in photosynthesis may be used as a source of chemical energy or converted to larger molecules for storage and use later. The glucose can be: used for respiration; converted into insoluble starch for storage; used to produce fat or oil for storage; used to produce cellulose, which strengthens the cell wall; used to produce proteins.
- To produce proteins, plants also use nitrate ions that are absorbed from the soil.
Mind map
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Photosynthesis. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- Which substance absorbs the light used in photosynthesis? A. Cellulose B. Chlorophyll C. Starch D. Nitrate Answer: B
- Which is the correct balanced symbol equation for photosynthesis? A. C6H12O6 + 6O2 -> 6CO2 + 6H2O B. 6CO2 + 6H2O -> C6H12O6 + 6O2 C. CO2 + H2O -> C6H12O6 + O2 D. 6CO2 + 6O2 -> C6H12O6 + 6H2O Answer: B
- Which of these is NOT something a plant makes from the glucose produced in photosynthesis? A. Insoluble starch for storage B. Cellulose for the cell wall C. Nitrate ions absorbed by the roots D. Fats and oils for storage Answer: C
- A graph of rate of photosynthesis against light intensity becomes horizontal at high light intensities. What does the horizontal section show? A. The plant has stopped photosynthesising B. Light intensity is the limiting factor C. A factor other than light intensity is limiting the rate D. The enzymes have been denatured Answer: C
- In July a greenhouse is brightly lit and warm. Which change is most likely to increase the rate of photosynthesis of the crop inside it? A. Switching on extra lamps B. Raising the temperature to 30 degrees Celsius C. Increasing the carbon dioxide concentration D. Watering the plants more often Answer: C
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