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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

B3 Life on Earth

Lesson 4: Recycling Nutrients


Objectives
Objectives

  • MUSTdescribe the carbon cycle

  • SHOULD describe the nitrogen cycle


Key words
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)


Textbook answers
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.


Textbook answers1
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.


Worksheet answers
Worksheet Answers

  • Activity 1 (Low demand)

    a) Photosynthesis;

    b) combustion;

    c) respiration;

    d) decomposition


Worksheet answers1
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


Worksheet answers2
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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