CORE Biology (Short Course) - 9221 OxfordAQA

Photosynthesis

Akopọ

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 the equation 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 take that idea into the laboratory, where a single stem of pondweed in a tube of water lets you measure the rate for yourself and prove which of three conditions is the one holding everything back.

Awọn Afojusun

  1. Photosynthesis is represented by the equation: light carbon dioxide + water → glucose + oxygen
  2. 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.
  3. 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. Required practical: Investigate how variables affect the rate of photosynthesis.

Àwòrán ọpọlọ

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Akọ̀wé Ẹ̀kọ́

Trace any meal backwards far enough and it ends at a leaf. The wheat in the bread, the grass the cow ate, the plankton the fish ate: at some point a green cell caught light and used it to build a sugar molecule out of a gas and some water. Nothing else on the planet does this at any scale. Every heterotroph, including you, is living off energy that a plant or an alga captured first. That is why photosynthesis sits at the front of the Bioenergetics section, and why questions on it turn up in contexts as different as a crop yield, a sealed jar of pondweed and a rainforest canopy.

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Ìdánwò Ẹ̀kọ́

Oriire fun ipari ẹkọ lori Photosynthesis. Ni bayi ti o ti ṣawari naa awọn imọran bọtini ati awọn imọran, o to akoko lati fi imọ rẹ si idanwo. Ẹka yii nfunni ni ọpọlọpọ awọn adaṣe awọn ibeere ti a ṣe lati fun oye rẹ lokun ati ṣe iranlọwọ fun ọ lati ṣe iwọn oye ohun elo naa.

Iwọ yoo pade adalu awọn iru ibeere, pẹlu awọn ibeere olumulo pupọ, awọn ibeere idahun kukuru, ati awọn ibeere iwe kikọ. Gbogbo ibeere kọọkan ni a ṣe pẹlu iṣaro lati ṣe ayẹwo awọn ẹya oriṣiriṣi ti imọ rẹ ati awọn ogbon ironu pataki.

Lo ise abala yii gege bi anfaani lati mu oye re lori koko-ọrọ naa lagbara ati lati ṣe idanimọ eyikeyi agbegbe ti o le nilo afikun ikẹkọ. Maṣe jẹ ki awọn italaya eyikeyi ti o ba pade da ọ lójú; dipo, wo wọn gẹgẹ bi awọn anfaani fun idagbasoke ati ilọsiwaju.

  1. Which substance absorbs the light used in photosynthesis? A. Cellulose B. Chlorophyll C. Starch D. Glucose Answer: B
  2. Which is the correct word equation for photosynthesis? A. glucose + oxygen -> carbon dioxide + water B. carbon dioxide + water -> glucose + oxygen C. carbon dioxide + oxygen -> glucose + water D. glucose + water -> carbon dioxide + oxygen Answer: B
  3. In which organelle does photosynthesis take place? A. Mitochondrion B. Nucleus C. Chloroplast D. Ribosome Answer: C
  4. 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
  5. Water plants growing 4 m below the surface of a warm lake photosynthesise more slowly than plants of the same species just below the surface, although the temperature and the dissolved carbon dioxide concentration are the same at both depths. What is the most likely limiting factor at 4 m? A. Water B. Carbon dioxide concentration C. Light intensity D. Temperature Answer: C

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