Sila Science 7.3 PDF - Photosynthesis

- Photosynthesis is the process by which green plants and some other organisms use sunlight, carbon dioxide and water to produce glucose (sugar) and oxygen. The word equation and chemical equation for photosynthesis are provided. - We can test if a plant has carried out photosynthesis by testing for...

- Photosynthesis is the process by which green plants and some other organisms use sunlight, carbon dioxide and water to produce glucose (sugar) and oxygen. The word equation and chemical equation for photosynthesis are provided. - We can test if a plant has carried out photosynthesis by testing for starch, which is produced during photosynthesis and stored in leaves. Iodine turns dark blue/black in the presence of starch. - Oxygen is one of the by-products of photosynthesis. An experiment is described to collect and test the oxygen produced by a water plant. Gas is collected in a test tube containing sodium hydrogencarbonate solution and tested with a glowing splint. - Plants gain mass and weight from absorbing water and minerals from the soil through their roots, and energy from sunlight through their leaves during photosynthesis. - An experiment using a Coleus plant with variegated leaves showed that only the green parts of leaves containing chlorophyll contained starch after an iodine test. This indicates chlorophyll is necessary for photosynthesis. - An experiment wrapping some leaves of a plant in aluminum foil and leaving others uncovered showed only uncovered leaves contained starch after 2 days. This shows light is necessary for photosynthesis. - Photosynthesis is important for both plants and animals. Animals cannot produce their own food and rely on plants or other animals for food either directly or indirectly through food chains. - Food chains show the transfer of energy from producers to consumers. Producers like plants are the first link, with grass, trees and algae as common examples. Consumers can be primary, secondary or tertiary depending on what they feed on. - Decomposers like fungi and bacteria break down dead or waste organic materials and return nutrients to the soil/environment for reuse by plants. - Respiration and photosynthesis have opposite but combined effects on atmospheric oxygen and carbon dioxide levels. Respiration releases CO 2 while photosynthesis absorbs it, maintaining balance. - A food web shows the interconnected food chains in an ecosystem and energy transfer between organisms. Disruptions can impact the whole ecosystem. The steps to test for starch using iodine solution included the following: 1. Prepare the materials needed which include iodine solution, a white tile, Petri dishes, and a leaf sample from the plant being tested. 2. Add a drop of iodine solution to a Petri dish on the white tile as a control. Observe and record the color. 3. Add a drop of starch solution and a drop of water to two separate parts of another Petri dish on the white tile. 4. Add a drop of iodine solution to the starch solution and to the water separately. 5. Observe and record any changes in color. The starch solution should turn dark blue/black while the water should remain unchanged. 6. Take a leaf sample from the plant being tested. It should first be destarched by keeping it in darkness for 1-2 days. 7. Carry out the heating and bleaching process on the leaf sample as described. 8. Carefully spread the processed leaf on a Petri dish on a white tile. 9. Add a few drops of iodine solution to cover the whole leaf. 10. Observe if any parts of the leaf turn dark blue/black, indicating the presence of starch and confirming photosynthesis has occurred.