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Photosynthesis, Food Production and Management of the Environment

Microorganisms, the nitrogen cycle and biosensors

  • 3 things to know
  • Components 01, 02 and 03

Overview

Recall questions on nitrogen fixation by Azotobacter and Rhizobium, nitrogenase and leghaemoglobin, nitrification by Nitrosomonas and Nitrobacter, ammonification, legumes in crop rotation, culturing Rhizobium aseptically from root nodules, and luminescent bacteria as biosensors of water toxicity.

What you need to know

Answer each one before you reveal it.

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Process

What is nitrogen fixation, which enzyme carries it out, and how is that enzyme protected in a root nodule?

Key term

What is nitrogen fixation?

Key term

Which enzyme carries out nitrogen fixation, and what conditions does it need?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is nitrogen fixation?

    Model answer

    Nitrogen fixation is the conversion of atmospheric nitrogen gas into ammonia or ammonium ions that plants are able to use.

  2. 2

    Name the free-living soil bacterium that fixes atmospheric nitrogen.

    Model answer

    Azotobacter.

  3. 3

    Which genus of bacteria fixes nitrogen inside the root nodules of legumes?

    Model answer

    Rhizobium.

  4. 4

    Which enzyme carries out nitrogen fixation, and what conditions does it need?

    Model answer

    Nitrogenase, which requires a large supply of ATP and must be kept in near-anaerobic conditions.

  5. 5

    Describe the mutualistic relationship between Rhizobium and a legume.

    Model answer

    The bacteria supply the plant with fixed nitrogen as ammonium, and the plant supplies the bacteria with carbohydrate and a protected low-oxygen environment inside the nodule.

  6. 6

    What is the role of leghaemoglobin in a root nodule?

    Model answer

    Leghaemoglobin binds oxygen and keeps its free concentration very low, protecting nitrogenase from being inactivated.

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