Unit 2 - Photosynthesis
Plants can convert the sugars made during photosynthesis into starch.

Unit 2 - Photosynthesis

Photosynthesis is the process in which plants, using sunlight, create sugars by combining carbon dioxide with water. It is important that students of GCSE Biology understand photosynthesis and this quiz will help them to revise.

Simply put, photosynthesis is the process by which plants feed. Since they are at the start of all food chains and food webs, you could say that they make all of the food for the planet! Photosynthesis is the making of sugars from carbon dioxide and water. It requires energy in the form of light, hence the name of the process (photo means relating to light and in terms of chemicals, synthesis means building a more complex compound from simpler substances). The waste product is oxygen which is needed for aerobic respiration in living organisms. Until green plants had built up sufficient oxygen in the Earth's atmosphere to create an ozone layer, animal life was restricted to living under water, where it was protected from the UV radiation from the Sun.

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Light energy is absorbed by the chlorophyll in green plants and algae. This energy is used to convert carbon dioxide from the air and water from the soil into glucose. This glucose can be stored as starch, converted into cellulose for making cell walls, converted into proteins or used in respiration. Plant cells respire at the same time as photosynthesis takes place but during the day, photosynthesis produces more oxygen than is used up in respiration.

Most plants have evolved leaves to make the process of photosynthesis more effective. Leaves have a large surface area and are very thin. This means that gases can get in and out more easily and it also maximises the amount of light energy reaching the chlorophyll. Chlorophyll is found in most plant cells and is contained within structures named chloroplasts. Chlorophyll absorbs the red and blue wavelengths of light from the sun but reflects the green, which is why plants appear green. There are types of chlorophyll that absorb other wavelengths, making certain plants and algae appear more red. It is possible to grow plants under artificial lighting but sunlight is the best source of light for photosynthesis.

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  1. Photosynthesis is a process in...
    Animals cannot photosynthesise and rely on plants to provide their food either directly (herbivores) or indirectly by eating other animals
  2. Various factors can limit the rate of photosynthesis. Which of these variables can limit photosynthesis?
    In practice, there is normally sufficient carbon dioxide in the atmosphere to keep plants fully supplied
  3. If the rate of photosynthesis is reduced, which of the following important processes is also reduced?
    Photosynthesis makes sugars which are then used to make the biomass of the plant itself. More photosynthesis means more sugars which can be used to grow a bigger plant
  4. Where does the water needed for photosynthesis usually come from in plants?
    Root hairs absorb the water needed by the plant for photosynthesis from the soil
  5. Plants can convert the sugars made during photosynthesis into which insoluble stored form of energy?
    Starch is made from long chains of glucose molecules that have been chemically joined together
  6. Which very important gas is given off as a by-product of photosynthesis?
    Oxygen makes up about 20% of the air we breathe. Plants and algae are responsible for producing the oxygen we need!
  7. Farmers will use heated greenhouses for faster growth of crops. This increases photosynthesis by increasing the...
    Photosynthesis is a series of chemical reactions. Chemical reactions usually increase in speed as temperature is increased
  8. Plants can convert sugars into protein using which mineral ion obtained from the soil?
    Proteins and amino acids contain nitrogen which enters the plant from the soil in the form of nitrate ions
  9. Photosynthesis takes place in which part of a plant cell?
    This is where the chlorophyll is located
  10. Photosynthesis requires which type of energy?
    The light energy is trapped by chlorophyll molecules which are packed into the chloroplasts

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