Lesson Notes By Weeks and Term v4 - JHS 3
EARTH SCIENCES
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EARTH SCIENCES
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Subject: Science
Class: JHS 3
Term: 1st Term
Week: 7
Grade code: B9.2.1.1.2
Strand code: 2
Sub-strand code: 1
Content standard code: B9.2.1.1
Indicator code: B9.2.1.1.2
Theme: CYCLES
Subtheme: EARTH SCIENCES
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Nitrogen is one of the most important nutrients for living things, yet most organisms cannot use nitrogen gas (N₂) directly from the air. The nitrogen cycle is the natural process that changes nitrogen into forms plants and animals can use, and then returns it to the atmosphere. In Ghana, this matters in everyday life because it affects: Soil fertility and crop yield (maize, rice, cassava, vegetables) Cost of farming (need for fertiliser) Water quality (pollution of rivers/streams from fertiliser run-off) Bush burning and land degradation (loss of soil nutrients)
A. What is Nitrogen and why is it important? Nitrogen (N) is a chemical element found in the air, soil, and living things. About 78% of the air is nitrogen gas (N₂), but plants cannot use N₂ directly. Importance of nitrogen to living things Nitrogen is needed to make: Proteins (for growth and repair of body tissues in humans/animals; for plant growth) DNA and RNA (genetic material in all living things) Chlorophyll (green pigment in plants used for photosynthesis)
If soil lacks nitrogen, plants show: Yellowing of leaves (especially older leaves) called chlorosis Stunted growth Low yield (small cobs, fewer grains, poor leaf development)
B. The Nitrogen Cycle (meaning and stages) Nitrogen cycle: the continuous movement of nitrogen through the atmosphere, soil, plants, animals, and microorganisms. Nitrogen Fixation (N₂ → ammonia/ammonium) This is the process of converting nitrogen gas (N₂) into forms plants can use.
Ways nitrogen is fixed: Biological fixation (most important): Certain bacteria convert N₂ into ammonia (NH₃) or ammonium (NH₄⁺). Example: *Rhizobium* bacteria in the root nodules of leguminous plants (cowpea, groundnut, soyabean, pigeon pea). Lightning: Lightning energy helps form nitrates that enter soil with rain. Industrial fixation: Factories produce nitrogen fertilisers (e.g., urea, ammonium sulphate).