ACARA v9 CONTENT DESCRIPTION “recognise cells as the basic units of living things, compare plant and animal cells, and describe the functions of specialised cell structures and organelles”
Builds on grouping and classifying living things. Here we look inside them: every living thing, whatever its size, is built from cells, and the same set of working parts appears again and again across the living world.
Cells are the basic units of living things
Every living thing is made of cells. Some, like bacteria, are a single cell; others, like a tree or a person, are built from many millions. A cell is the smallest part of a living thing that is still alive, which is why we call it the basic unit of life. Zoom into any organism far enough and you arrive at cells.
Zoom in to a single cell
Step inward from a whole plant down to one cell. Every living thing is built from cells, and a cell is the smallest piece that is still alive.
Whole plant (organism). A whole living thing. You can see it without any help. Keep zooming in to reach a single cell.
Plant and animal cells share a core plan
Plant cells and animal cells are built to the same basic plan. Both have a cell membrane holding them together, a nucleus in charge, cytoplasm filling the space, and mitochondria releasing energy. Plant cells then add three parts of their own: a stiff cell wall around the outside, chloroplasts that capture light, and a large vacuole that stores sap and keeps the cell firm.
Plant cell and animal cell
Plant and animal cells share the same core parts. Toggle between them to see what they have in common and the three extra parts found only in plant cells.
A plant cell has every shared part plus three of its own: cell wall, chloroplast, large vacuole. The cell wall holds the cell stiff, chloroplasts capture light, and the large vacuole stores sap.
Inside the cell: organelles and their jobs
A cell is not an empty bag. It is packed with tiny working parts called organelles, each built for a particular job. The nucleus stores the instructions and runs the cell; the mitochondria release energy; the cell membrane controls what crosses the border; and the cytoplasm is the jelly where many reactions take place. Naming the parts is really about knowing what each one does.
Organelles and their jobs
A cell is not empty. It is packed with tiny working parts called organelles. Pick one to highlight it and read what it does.
Nucleus: Holds the cell instructions and controls what the cell does.
A specialised structure doing its job
The shape and contents of an organelle suit the job it performs. A chloroplast is full of green pigment so it can capture light; following it step by step shows that structure at work, turning light, water and carbon dioxide into stored sugar. Each stage depends on the one before, and the result is energy the cell can keep for later.
A specialised structure in action
A chloroplast is built for one job: turning light into stored energy. Step through the process to watch that structure work.
Step 1. Sunlight falls on a leaf and reaches the chloroplasts inside its cells.
Why specialised structures matter
Cells take on different jobs in a living thing, and each one builds up whichever organelle its work depends on. A leaf cell, which makes food from light, is full of chloroplasts. A muscle cell, which needs energy to move, is packed with mitochondria. Matching a structure to a job shows why cells are specialised rather than all the same.
Match the structure to the job
A cell builds extra copies of whatever organelle does its main job. Read what each cell must do, then pick the structure built for it.
Pick the organelle built for this cell job. Only one structure does it well.
Why this matters
Understanding cells is the foundation of all biology. Knowing that living things are built from cells, that plant and animal cells share a plan, and that each organelle has a job lets us explain how a whole organism works from the inside out. Every later idea in the life sciences rests on this basic unit.
Quick self-check
1. What is the smallest unit that is still alive?
2. Which part is found in a plant cell but not in an animal cell?
3. What does the nucleus do?
4. A chloroplast is built mainly to...
5. Why does a busy muscle cell hold many mitochondria?