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: 6
Grade code: B9.2.1.1.1
Strand code: 2
Sub-strand code: 1
Content standard code: B9.2.1.1
Indicator code: B9.2.1.1.1
Theme: CYCLES
Subtheme: EARTH SCIENCES
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Nitrogen is one of the most important elements for life because it is needed to make proteins (for growth and repair) and DNA (genetic material). Although about 78% of air is nitrogen gas (N₂), most plants and animals cannot use nitrogen directly from the air. Nature therefore “recycles” nitrogen through a repeated pattern called the nitrogen cycle. In Ghana, understanding the nitrogen cycle helps learners to: explain why farmers apply fertilisers (e.g., NPK, urea), understand why legumes (beans, cowpea, groundnut) improve soil fertility, connect pollution (eutrophication of water bodies) to excess nitrates, appreciate how microbes in soil keep ecosystems functioning.
A. Key Terms (Definitions) Nitrogen (N): An element needed by living things to make proteins and nucleic acids. Nitrogen gas (N₂): The form of nitrogen in the atmosphere; very stable and not easily used by most organisms. Nitrogen cycle: The continuous movement of nitrogen through the atmosphere, soil, water, plants, animals, and microorganisms. Microorganisms (microbes): Tiny living things (especially bacteria) that drive many steps of the nitrogen cycle.
B. Why organisms need nitrogen Living things need nitrogen to make: Amino acids → proteins (muscles, enzymes, hormones) Nucleic acids → DNA and RNA (growth, reproduction)
Plants need nitrogen mainly to make chlorophyll and proteins for growth. When nitrogen is lacking, plants show: yellowing leaves (chlorosis), stunted growth, poor yield (important in maize, rice, vegetables).
C. The Nitrogen Cycle: Step-by-step Processes (Core of Indicator B9.2.1.1.1) 1) Nitrogen Fixation (Making nitrogen usable) Meaning: Conversion of atmospheric nitrogen gas (N₂) into ammonia (NH₃) or ammonium (NH₄⁺) which plants can eventually use.