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HSC Biology

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Lesson 2, Topic 3
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Photosynthesis, Respiration and Waste

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All living things fall under one of two categories:

  • Autotrophs: Create their own food; plants, for example.
  • Heterotrophs: Consume other organisms for food; humans, for example.


Photosynthesis is used by plants to create glucose.

Chlorophyll (in the chloroplast) traps sunlight and uses the energy to react water and carbon dioxide to form glucose.

\text{carbon dioxide} + \text{water} \xrightarrow{sunlight} \text{glucose} + \text{oxygen}

Two Stages of Photosynthesis

Light-Dependant Stage

Chlorophyll captures solar energy and uses it to produce ATP. Photolysis occurs, which is the splitting of water into hydrogen and oxygen.

\text{water} \xrightarrow{sunlight} \text{hydrogen} + \text{oxygen} + \text{ATP}

Light-Independent Stage

Glucose, water and ATP are produced. This stage does not require sunlight to function.

Cellular Respiration

Cellular respiration converts glucose to energy which organisms can use to function.

Glucose is broken down in two ways during cellular respiration:

  • Aerobic respiration (in the presence of oxygen)
  • Anaerobic respiration (without oxygen)