Lesson Notes By Weeks and Term v4 - JHS 3
LIVING CELLS
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LIVING CELLS
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Subject: Science
Class: JHS 3
Term: 1st Term
Week: 4
Grade code: B9.1.2.1.1
Strand code: 1
Sub-strand code: 2
Content standard code: B9.1.2.1
Indicator code: B9.1.2.1.1
Theme: DIVERSITY OF MATTER
Subtheme: LIVING CELLS
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All living things in Ghana—humans, goats, maize, cassava, mango trees—are made of cells. Although cells share basic parts, many cells become specialised (modified) to do particular jobs very well. Understanding specialised cells helps learners explain everyday life processes such as breathing, movement, digestion, wound healing, growth in plants, and transport of water and food in crops. It also supports health and agriculture decisions (e.g., why anaemia affects energy, why plants wilt, why roots absorb water).
A. Meaning of Specialised Cells Specialised cells are cells that have developed special structures to perform specific functions efficiently. All cells start from a single cell (zygote in humans; fertilised egg in plants). As the organism grows, cells divide and then some cells change in structure and function. This process is called cell differentiation.
Why specialisation is important It creates division of labour: different cells do different jobs. It makes the organism more efficient and able to survive.
B. How Specialised Cells Are Formed in Humans (Differentiation) Humans begin as a single fertilised egg (zygote). Through mitosis, the zygote forms many cells. Early in development, many cells are stem cells. Key idea: Stem cells Stem cells are unspecialised cells that can: Divide to make more stem cells, and Differentiate into specialised cells (e.g., nerve cells, muscle cells, red blood cells). How differentiation happens (step-by-step) Cell division (mitosis) increases the number of cells. Cells receive signals (chemical messages) from nearby cells and the body. These signals cause certain genes to be switched on or off. The cell begins to make specific proteins, changing its structure and function. The cell becomes specialised (e.g., a muscle cell produces many contractile fibres). Important note for JHS level In humans, many specialised cells cannot divide anymore (e.g., nerve cells). Some tissues still have stem cells for repair (e.g., bone marrow makes blood cells; skin cells replace dead skin).
C. How Specialised Cells Are Formed in Dicotyledonous Plants Dicot plants include beans, groundnut, mango, hibiscus, cassava, cocoa seedlings (many common Ghanaian examples).