AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Life on Earth is dependent on photosynthesis in which green plants and…
Full specification wording
Key ideas: life on Earth is dependent on photosynthesis in which green plants and algae trap light from the Sun to fix carbon dioxide and combine it with hydrogen from water to make organic compounds and oxygen
Photosynthesis is the process that transfers light energy into chemical energy stored in organic compounds.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 5 of 26
Study notes
From the checked teaching notes for this specification point.
The idea
Photosynthesis is the process that transfers light energy into chemical energy stored in organic compounds. Green plants and algae trap sunlight using chlorophyll in chloroplasts. Plants take in carbon dioxide through stomata and water through roots, whereas algae absorb these directly over their surface from the surrounding water. Light energy splits water into hydrogen and oxygen. The hydrogen combines with carbon dioxide to make glucose, an organic compound, and oxygen is released as a by-product. The balanced symbol equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Life on Earth depends on this process because it produces the organic compounds that form food chains and releases the oxygen used in aerobic respiration.
What earns the marks
- State that green plants and algae trap light from the Sun using chlorophyll in chloroplasts.
- Identify carbon dioxide and water as the raw materials, and glucose and oxygen as the products.
- Describe how plants use stomata and roots for raw materials, while algae absorb them over their surface.
- Describe how light energy splits water into hydrogen and oxygen, and how hydrogen combines with carbon dioxide to form glucose.
- Write the balanced symbol equation 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.
- Explain that life on Earth depends on photosynthesis because it produces food and releases oxygen for aerobic respiration.
Common mistakes and how to put them right
Assuming algae have roots and stomata like plants.
Put it right: Algae are aquatic and absorb water and dissolved carbon dioxide directly across their surface.
Writing the equation with the wrong products or unbalanced formulae.
Put it right: Learn the balanced equation 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ and check that each element is balanced.
Confusing the role of water with that of carbon dioxide.
Put it right: Water is split by light energy to provide hydrogen and release oxygen; carbon dioxide is fixed by combining with hydrogen to make glucose.
Exam tips
- When describing photosynthesis, name the energy transfer from light to chemical and refer to chlorophyll as the pigment that traps light.
- Remember to distinguish between plants and algae if asked about how they obtain their reactants.
Try the lesson
The start of the Key ideas: life on Earth is dependent on photosynthesis in which green plants and algae trap light from the Sun to fix carbon dioxide and combine it with hydrogen from water to make organic compounds and oxygen lesson, made from checked teaching notes for this specification point.
Have a go first
Which gas from the air is fixed by green plants and algae during photosynthesis?
Listen
Photosynthesis is the process that transfers light energy into chemical energy stored in organic compounds. Green plants and algae trap sunlight using chlorophyll in chloroplasts. Plants take in carbon dioxide through stomata and water through roots, whereas algae absorb these directly over their surface from the surrounding water. Light energy splits water into hydrogen and oxygen. The hydrogen combines with carbon dioxide to make glucose, an organic compound, and oxygen is released as a by-product. The balanced symbol equation is 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. Life on Earth depends on this process because it produces the organic compounds that form food chains and releases the oxygen used in aerobic respiration. A strong answer earns marks for these points. State that green plants and algae trap light from the Sun using chlorophyll in chloroplasts. Identify carbon dioxide and water as the raw materials, and glucose and oxygen as the products. Describe how plants use stomata and roots for raw materials, while algae absorb them over their surface. Describe how light energy splits water into hydrogen and oxygen, and how hydrogen combines with carbon dioxide to form glucose. A common slip: Assuming algae have roots and stomata like plants. Instead, algae are aquatic and absorb water and dissolved carbon dioxide directly across their surface. Exam tip: When describing photosynthesis, name the energy transfer from light to chemical and refer to chlorophyll as the pigment that traps light.
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