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B3 Life on Earth

B3 Life on Earth. Lesson 4: Recycling Nutrients. Objectives. MUST describe the carbon cycle SHOULD describe the nitrogen cycle. Key Words. You need to be able to define the following: Carbon Carbon cycle Carbon dioxide Combustion Respiration Decomposition Nitrogen cycle Nitrates

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B3 Life on Earth

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  1. B3 Life on Earth Lesson 4: Recycling Nutrients

  2. Objectives • MUSTdescribe the carbon cycle • SHOULD describe the nitrogen cycle

  3. Key Words • You need to be able to define the following: • Carbon • Carbon cycle • Carbon dioxide • Combustion • Respiration • Decomposition • Nitrogen cycle • Nitrates • Proteins • Nitrogen-fixing bacteria (Higher tier only) • Denitrifying bacteria (Higher tier only)

  4. Textbook Answers 1) a) Through combustion (burning); decomposition and respiration. b) By photosynthesis. 2) Increased combustion of fossil fuels; the reduction of forest cover on Earth. 3) In the form of proteins that plants have made; in food as proteins from other animals (or animal products). 4) By decomposition.

  5. Textbook Answers 5) Some bacteria and fungi decompose dead matter, releasing nitrates into the soil; denitrifying bacteria turn these nitrates back into nitrogen; nitrogen-fixing bacteria in the roots of beans and peas turn nitrogen gas from the air into nitrates that plants can use to make proteins. 6) Peas and beans contain nitrogen-fixing bacteria in their roots that can ‘fix’ atmospheric nitrogen into nitrates; this means these plants are able to access more nitrates than most other plants; these nitrates are used to make proteins.

  6. Worksheet Answers • Activity 1 (Low demand) a) Photosynthesis; b) combustion; c) respiration; d) decomposition

  7. Worksheet Answers Activity 2 (Standard demand) • Plants absorb nutrients from the soil for growth • nitrates  proteins in plants • Plants and animals die and decay • proteins in plants and animals  nitrates in the soil • Animals excrete waste • products from breakdown of proteins  nitrates in soil • Animals eat plants • protein in plants  proteins in animals

  8. Worksheet Answers Activity 3 (High demand) 1) Lightning; nitrogen-fixing bacteria in the roots of beans and peas; nitrogen-fixing bacteria in the soil; decomposition by bacteria and fungi. 2) By the decay of nitrogen-containing plants and animals and their urine and faeces; and by denitrifying bacteria. 3) Fertilisers contain nitrates; plants need nitrates to create proteins, which help them grow; fertilisers are added to help plants grow.

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