Lesson Notes By Weeks and Term v4 - JHS 2
LIFE CYCLE OF ORGANISMS
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LIFE CYCLE OF ORGANISMS
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Subject: Science
Class: JHS 2
Term: 1st Term
Week: 8
Grade code: B8.2.2.1.1
Strand code: 2
Sub-strand code: 2
Content standard code: B8.2.2.1
Indicator code: B8.2.2.1.1
Theme: CYCLES
Subtheme: LIFE CYCLE OF ORGANISMS
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All living things grow, reproduce and die. The life cycle is the series of stages an organism passes through from birth/egg to adult and back to producing young ones again. In Ghana, understanding the life cycle of the Anopheles mosquito is very important because it helps us prevent malaria, which affects families, school attendance and the national economy. When learners know where and how mosquitoes breed, they can help their homes and communities reduce mosquito numbers.
A. Key Terms Life cycle: The sequence of developmental stages an organism goes through from the beginning of life to reproduction and death, repeating in the next generation. Metamorphosis: A major change in body form during development. Mosquitoes undergo complete metamorphosis (egg → larva → pupa → adult). Breeding site: A place where an organism lays eggs and young ones develop (for mosquitoes, usually standing water). Vector: An organism that carries and transmits disease-causing organisms from one host to another. The female Anopheles mosquito is a vector for malaria parasites. B. Life Cycle of the Anopheles Mosquito (Complete Metamorphosis) The Anopheles mosquito has four stages. The first three stages occur in water, and the adult stage is air/land. 1) Egg stage Where laid: On the surface of clean, still or slow-moving water (e.g., puddles, uncovered water containers, gutters with stagnant water, tyre tracks, rice fields). Features: Eggs are small and may be laid singly; they float. Time: Often hatch within 1–3 days depending on temperature and conditions.
Key idea: If there is no standing water, eggs cannot survive. 2) Larva stage (“wriggler”) Where found: In water. What it does: Feeds on microorganisms and organic matter in the water; grows and moults several times. Movement: Larvae wriggle actively. Breathing: Larvae come to the surface to breathe air (Anopheles larvae often lie parallel to the water surface).
Key idea: Larvae are easier to target with control methods (e.g., draining water, larvicides). 3) Pupa stage (“tumbler”) Where found: In water. What it does: Does not feed much; it is a resting and transformation stage where the body changes into an adult. Movement: Pupae tumble when disturbed.
Key idea: Pupae still need water; removing water stops them from becoming adults. 4) Adult mosquito stage Where found: Flies in air; rests on walls, dark corners, bushes. Feeding: Male mosquitoes feed on plant juices/nectar. Female mosquitoes need a blood meal to develop eggs. Disease transmission: When a female Anopheles bites an infected person, it can pick up malaria parasites and later transmit them to another person.