Photosynthetic Organisms as Producers (OCR Gateway GCSE Biology: Combined Science)

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Photosynthesis is Food Making

  • Plants and algae are autotrophs – this means that they can make their own food
    • Autotrophic organisms make complex molecules (that can be used as an energy store) from simple molecules (carbon dioxide and water) 
  • Plants and algae make glucose using light energy, water and carbon dioxide in the process of photosynthesis
    • The glucose can be used as a source of energy in cellular respiration or used to make more complex molecules that are used to help the plant or algae grow
    • This makes-up the organism's biomass (mass of living material)
  • This is why autotrophs such as plants are called producers in food chains
    • The energy stored in the biomass makes its way through the food chain
    • Photosynthetic organisms help support nearly all life on earth

The Process of Photosynthesis

  • Photosynthesis can be defined as the process by which plants manufacture carbohydrates from raw materials using energy from light
  • The reactants of photosynthesis are carbon dioxide and water
  • The products of photosynthesis are glucose and oxygen
  • These reactions can be summarised into a simple equation

Photosynthesis word equation, IGCSE & GCSE Biology revision notes

Word equation for photosynthesis

How plants get the materials they need, IGCSE & GCSE Biology revision notes

Where do the reactants come from and where do the products go?

  • This equation can also be shown as a balanced chemical equation
    • Six carbon dioxide molecules combine with six water molecules to make one glucose molecule and six oxygen molecules

Balanced chemical equation for photosynthesis, IGCSE & GCSE Biology revision notes

The balanced chemical equation for photosynthesis

  • Photosynthesis takes place in specialised sub-cellular structures called chloroplasts
    • The chloroplasts contain chlorophyll to help absorb as much light energy as possible
  • The leaves of most plants contain specialised mesophyll cells which are packed with chloroplasts
    • This helps maximise the amount of photosynthesis
  • Photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplasts by light

Photosynthesis is a two-stage process

  • Photosynthesis occurs in two main stages
    • Energy transferred from light is used to split water into oxygen gas and hydrogen ions
    • Carbon dioxide gas taken from the atmosphere then combines with the hydrogen ions to make glucose

Exam Tip

Photosynthesis is essential for the majority of all food chains on Earth, so learning the equation above is essential. Be careful not to confuse the photosynthesis equation with respiration and remember, plants respire as well as photosynthesise!

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Author: Phil

Phil has a BSc in Biochemistry from the University of Birmingham, followed by an MBA from Manchester Business School. He has 15 years of teaching and tutoring experience, teaching Biology in schools before becoming director of a growing tuition agency. He has also examined Biology for one of the leading UK exam boards. Phil has a particular passion for empowering students to overcome their fear of numbers in a scientific context.