Cell Organelles and Their Functions
Why can a plant cell sit in pure water and keep its shape, while an animal cell might burst? And why does a leg muscle cell need so many tiny "power plants"? The answer is in the structures inside the cell. Think of a cell as a tiny factory: each part has a job, and the cell stays alive only when they all work together.
Organelles: the parts of a cell
An organelle is a structure inside a cell that carries out a specific job. Just as your body has organs (heart, lungs, stomach), a cell has organelles. You need a microscope to see them.
Every cell has a few basic parts:
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Cell membrane: a thin, flexible boundary that controls what enters and leaves the cell.
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Cytoplasm: the jelly-like fluid inside the cell. The organelles float in it, and many chemical reactions happen there.
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Nucleus: holds the cell's DNA (its genetic instructions) and controls the cell's activities.
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Ribosomes: tiny structures that build proteins by following instructions from the nucleus.
Name the organelle that contains a cell's DNA and controls the cell's activities. Then state whether this organelle is found in plant cells, animal cells, or both.
Name the organelle that contains a cell's DNA and controls the cell's activities. Then state whether this organelle is found in plant cells, animal cells, or both.
Energy and storage organelles
Cells need energy and need places to keep materials.
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Mitochondria (one is a mitochondrion): break down food molecules, such as sugar, using oxygen to release usable energy for the cell. This process is called cellular respiration. Both plant and animal cells have mitochondria.
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Chloroplasts: contain a green pigment called chlorophyll. They capture light energy and use it to make sugar from carbon dioxide and water (photosynthesis). Only plant cells (and some other organisms such as algae) have chloroplasts.
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Vacuoles: sacs that store water, nutrients, or wastes. Plant cells usually have one large central vacuole. Animal cells have only small ones, if any.
Notice the difference: chloroplasts make food; mitochondria use food to release energy. Plants need both.
Chloroplasts and mitochondria both help a cell get usable energy. State the function of each organelle in one sentence, and say which one is found only in plant cells.
Chloroplasts and mitochondria both help a cell get usable energy. State the function of each organelle in one sentence, and say which one is found only in plant cells.
A muscle cell in an athlete's leg needs far more energy than a skin cell does. Predict which of the two cells has more mitochondria and explain why. In your answer,…
A muscle cell in an athlete's leg needs far more energy than a skin cell does. Predict which of the two cells has more mitochondria and explain why. In your answer, describe what mitochondria do with the food molecules that enter the cell.
Support and protection: cell wall and membrane
All cells have a cell membrane. It is selective: it lets water and some materials pass but keeps others out or in. It works like a security gate.
Plant cells also have a cell wall, a rigid layer outside the membrane. It gives the cell a fixed shape, supports the plant, and protects the cell. Animal cells have no cell wall, which is why they are usually rounder and more irregular.
| Structure | Function | Plant cell | Animal cell |
|---|---|---|---|
| Cell membrane | Controls what enters and leaves | Yes | Yes |
| Cell wall | Rigid support and protection | Yes | No |
| Nucleus | Holds DNA, controls the cell | Yes | Yes |
| Ribosomes | Build proteins | Yes | Yes |
| Cytoplasm | Holds organelles; reactions happen here | Yes | Yes |
| Mitochondria | Release energy from food | Yes | Yes |
| Chloroplasts | Make sugar by photosynthesis | Yes | No |
| Vacuole | Stores water, nutrients, wastes | Large | Small or none |
Water moves across the cell membrane into a cell placed in pure water. An animal cell has nothing to hold it back, so it can swell and burst. In a plant cell, the cell wall pushes back and keeps the shape, so the cell just becomes firm.
Match each structure to its function: (a) cell wall, (b) cell membrane, (c) ribosomes, (d) vacuole. The functions, in scrambled order, are: (1) stores water, nutrients,…
Match each structure to its function: (a) cell wall, (b) cell membrane, (c) ribosomes, (d) vacuole. The functions, in scrambled order, are: (1) stores water, nutrients, or wastes; (2) controls what enters and leaves the cell; (3) builds proteins; (4) gives a plant cell rigid support and protection.
Emma looks at two cells under a microscope. Cell A has a rectangular shape, a large central vacuole, and green organelles. Cell B is round and irregular, with no green…
Emma looks at two cells under a microscope. Cell A has a rectangular shape, a large central vacuole, and green organelles. Cell B is round and irregular, with no green organelles and no rigid outer layer. Identify which cell is a plant cell and which is an animal cell. Name two structures from the description that support your answer and explain what each does.
Jayden places a plant cell and an animal cell in pure water. The animal cell may burst, but the plant cell keeps its shape. Explain this difference using the cell…
Jayden places a plant cell and an animal cell in pure water. The animal cell may burst, but the plant cell keeps its shape. Explain this difference using the cell membrane and the cell wall. Say what job each structure does in this situation.
Organelles working together
Organelles do not work alone. Follow how a cell makes a protein and sends it out:
Answer to "Your turn": hormone production stops, because ribosomes are the only organelles that build proteins, and the nucleus's instructions cannot be carried out.
Structure matches function, so cells in different parts of an organism have different organelles. Use claim, evidence, reasoning (CER) to explain this:
A pancreas cell makes large amounts of a protein hormone and sends it out of the cell. Trace the path of the instructions and materials by naming and describing the…
A pancreas cell makes large amounts of a protein hormone and sends it out of the cell. Trace the path of the instructions and materials by naming and describing the roles of the nucleus, the ribosomes, the cytoplasm, and the cell membrane. Then predict what would happen to hormone production if the ribosomes stopped working, and justify your prediction.
A scientist studies a leaf cell and a root cell from the same plant. The leaf cell has many chloroplasts. The root cell has none but has many mitochondria and a large…
A scientist studies a leaf cell and a root cell from the same plant. The leaf cell has many chloroplasts. The root cell has none but has many mitochondria and a large vacuole. Compare the two cells and explain why each has the organelles it does. Then explain why the root cell can survive without chloroplasts, and describe what the plant must supply to it. Use a claim, evidence, and reasoning format.
Back to the start: the animal cell can burst in pure water because it has only a flexible membrane, while the plant cell's rigid wall holds its shape. A muscle cell has many mitochondria because it needs a lot of energy.