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Photosynthesis - revision notes

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Introduction

Biology revision notes. Photosynthesis = The process that makes food (glucose) in plants. * It takes place in the green leaves of plants. * Sun light is very essential and is taken in by the green pigment in plants: Chlorophyll. * Chlorophyll is in the chloroplasts. Chlorophyll changes the light energy from the sun to chemical energy. * The raw materials = carbon dioxide and water. * The products = glucose (which is later turned into other substances like starch) and oxygen. * The word equation = carbon dioxide + water sun light energy absorbed by chlorophyll glucose + oxygen or the chemical equation: 6CO2 + 6H2O sun light energy absorbed by chlorophyll C6H12O6 + 6O2 Experiments for photosythesis: * Iodine shows if starch is present. * The factor/thing we want to investigate is taken away from the plant. * We use a control as a comparison. This is a plant that is given normal conditions INCLUDING the factor we are investigating. Detailed notes: Plants make their own organic food such as starch, but how do they do it????? What does a plant need for photosynthesis?? Experiments to show factors needed for photosynthesis: (1) Remove all starch from leaves of plant (de-starch). (Put it in the dark for a few days) ...read more.

Middle

bubbles / time The internal structure of the leaf. * Waxy cuticle on top of leaf so it's water-proof (prevent water loss). * Lined above and below by the epidermis. (Upper and lower) * In between = lots of cells which make up the mesophyll. * Mesophyll is divided into the palisade mesophyll (above) and the spongy mesophyll (below). * The palisade mesophyll is tightly packed together whereas the spongy mesophyll contains large air spaces. * In middle of leaf = vascular bundle-contains two main types of vessel: xylem vessels (top) and phloem vessels (below) ==> The xylem vessels transport water The phloem vessels transport glucose. * There are stomata under the surface of the leaf. They open during the day to let in carbon dioxide and let out oxygen and close during the night to stop water loss. SEE A DIAGRAM! Questions about the structure of the leaf. Why do the mesophyll cells contain chloroplasts?? Photosynthesis takes place in the mesophyll cells. Both the spongy mesophyll and the palisade cells contain chloroplasts for photosynthesis. But there are more chloroplasts in the palisade cell so photosynthesis mainly takes place here. Why do leaves have a large surface area? ==> Large area to absorb max amount of carbon dioxide from air. ...read more.

Conclusion

and the spongy mesophyll cell (at the bottom). There is a small vein in the middle of the leaf which is made up of two cells the xylem (top) and the phloem (bottom). Why are leaves so thin? Leaves are so thin to provide the smallest distance for the CO2 to diffuse through after entering the stomata. Leaves have veins as a sort of skeleton. The veins hold the leaf out flat. Experiments. What is needed for photosynthesis???? Always take these steps for these experiments: (1) De-starch plant (leave it in darkness for a few days) (2) An experiment to find out if light is needed for photosynthesis. A plant is put in darkness for a few days. Then the leaf is tested for starch using the starch test. If starch is not present it means that light is needed for photosynthesis to take place. An experiment to find out if chlorophyll is needed for photosynthesis. Impossible to get rid of chlorophyll without killing plant. Luckily there are plants with variegated leaves. (leaves partly green, partly not) For example: Certain types of ivy. Leaf is tested for starch. An experiment to show if CO2 is needed for photosynthesis. One plant is put in a sealed place with sodium hydroxide solution (to absorb all of CO2) Everything I know. Photosynthesis: The process in which plants make their own food using carbon dioxide and water. Respiration: The process in which living things produce energy from glucose and oxygen. ...read more.

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