IGCSE Biology Paper-1: Specimen Questions with Answers 177 - 177 of 208

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Question 177



In which natural cycles do respiration and photosynthesis both play a part?


Choice (4)


carbon cycle-Yes, water cycle-No


carbon cycle- Yes, water cycle- Yes


carbon cycle- No, water cycle-Yes


carbon cycle- No, water cycle- No




The Carbon Cycle
The Water Cycle
  • Green plants remove carbon dioxide from the atmosphere because of their photosynthesis. The carbon from the carbon dioxide is built first into a carbohydrate such as sugar. Some of this is changed into starch or the cellulose of cell walls, and the proteins, pigments, and other compounds of a plant. When the plants are eaten by animals, the organic plant material is digested, absorbed, and built into the compounds making up the animals tissues. Thus, the carbon atoms from the plant become part of the animal.
  • Plants and animals obtain energy by oxidizing carbohydrates in their cells to carbon dioxide and water. The carbon dioxide and water are excreted so the carbon dioxide returns once again to the atmosphere. The water cycle is different from other cycles because only a tiny proportion of the water that is recycled passes through living organisms. Animals lose water by evaporation, defecation, urination, and exhalation. They gain water from their food and drink. Plants take up water from the soil and lose it by transpiration. Millions of tons of water are transpired, but only a tiny fraction of this has taken part in the reactions of respiration or photosynthesis.

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