Primary 5 Science · Cells - study notes & mind map

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Cells are the Building Blocks of Life

Every living thing is made of tiny units called cells. Cells divide to produce new cells for growth and to repair damaged parts of an organism.

Parts Found in Both Plant and Animal Cells

Both plant and animal cells contain a nucleus, cytoplasm, and a cell membrane. These three essential parts work together to keep the cell alive and functioning.

Cell Part	Location	Main Function
Nucleus	Inside the cell	Controls all cell activities and holds genetic material
Cytoplasm	Jelly-like substance filling the cell	Allows chemical reactions and cell activities to take place
Cell Membrane	Outer layer of animal cell, beneath cell wall in plant cell	Controls the movement of substances in and out of the cell

Functions of common cell parts

Special Parts in Plant Cells

Plant cells have a stiff cell wall outside the membrane that gives the cell a regular shape and support. Green plant cells also have chloroplasts containing chlorophyll to trap sunlight for photosynthesis.

Not All Plant Cells Have Chloroplasts

Chloroplasts are only found in plant parts that are exposed to light, such as green leaves. Underground parts like roots and onion bulbs do not make food, so their cells do not have chloroplasts.

Single-Celled and Multi-Celled Organisms

Some organisms like amoeba and bacteria consist of only a single cell that carries out all life functions. Complex organisms like humans and trees are multicellular and have specialised cells with specific jobs.

Worked examples

Sarah looked at an onion skin cell under a microscope. She saw a cell wall, a nucleus, cytoplasm, and a cell membrane, but no chloroplasts. Explain why the onion skin cell is still a plant cell even without chloroplasts.

Identify the feature unique to plant cells present in the sample: The onion cell has a cell wall, which is found in plant cells but absent in animal cells.
Explain the absence of chloroplasts based on location: Onions grow underground in the dark where there is no sunlight, so they do not need chloroplasts to make food.
Conclude clearly: The presence of a cell wall confirms it is a plant cell, even though it lacks chloroplasts.

What would happen to an animal cell if its nucleus is removed? Explain your answer.

Recall the function of the nucleus: The nucleus controls all cell activities, including growth, repair, and reproduction.
State the direct consequence: Without a nucleus, the cell cannot carry out its life processes or divide.
Conclude the final outcome: The animal cell will eventually die.

State one difference between the function of the cell membrane and the function of the cell wall.

Identify the function of the cell membrane: It is partially permeable and controls what substances enter or leave the cell.
Identify the function of the cell wall: It is a stiff, fully permeable layer that provides support and gives the plant cell a regular shape.
State the comparison: The cell membrane regulates the entry and exit of substances, whereas the cell wall provides mechanical support and shape.

Cells