Level: JHS, Basic 9 | Subject: Integrated Science | Strand: Cycles | Topic: The Nitrogen Cycle (Earth Science)
Read the summary notes first: Basic 9 Integrated Science Summary Notes: The Nitrogen Cycle
Test Yourself: 20 Objective Questions
Tick one answer for each question, then press Review answer. If your answer is wrong, it will be marked first, then the correct answer will show in green.
Essay Questions
- Explain two natural ways by which nitrogen gas in the air is changed into forms that plants can use. (6 marks)
- Name, in the correct order, the five main processes of the nitrogen cycle and say in one line what happens in each. (5 marks)
- Explain why growing beans or groundnut improves the fertility of the soil. (4 marks)
- State two ways human activities upset the nitrogen cycle and three ways a farmer can keep the soil rich in nitrogen. (5 marks)
- Air is about 78% nitrogen, yet plants cannot use it directly. Explain why, and say what form of nitrogen plants take in. (4 marks)
Essay Questions: Marking Guide for Teachers and Parents
- (6 marks) Lightning (3): the heat and energy make nitrogen and oxygen in the air combine to form nitrogen oxides (1), rain washes them into the soil (1), where they become nitrates that plants can absorb (1). Nitrogen-fixing bacteria (3): Rhizobium lives in root nodules of legumes (1), it changes nitrogen gas to ammonia (1), and the plant uses it while the bacteria get food and shelter (1). Free living bacteria such as Azotobacter may also be accepted.
- (5 marks, 1 each) Nitrogen fixation: nitrogen gas changed into ammonia or nitrates. Nitrification: bacteria change ammonia to nitrites and then nitrates. Assimilation: plants absorb nitrates and make proteins, and animals eat plants. Ammonification (decay): decomposers break down dead matter and release ammonia. Denitrification: bacteria change nitrates back to nitrogen gas.
- (4 marks) Legumes have root nodules containing Rhizobium bacteria (1). The bacteria change nitrogen gas into ammonia and nitrates (1). Some of it stays in the soil when the roots and leaves decay (1). The next crop such as maize can then use it, so farmers use rotation or intercropping (1).
- (5 marks) Any two disturbances (1 mark each): too much fertiliser washing into rivers, bush burning, cutting down trees, waterlogging. Any three good practices (1 mark each): crop rotation, planting legumes, using compost or manure, applying fertiliser in the right amount, keeping soil well drained.
- (4 marks) Nitrogen gas is very stable and unreactive (1). Plant roots cannot take it in as a gas (1). It must first be fixed by bacteria or lightning (1). Plants take in nitrates through their roots (1).
Education Always (education.inspiringalways.com). Original practice questions, not official WAEC or BECE questions.