The Structures Inside an Animal Cell
Definition
Organelle
A structure inside a cell that carries out a particular function, such as the nucleus, mitochondria or ribosomes.
- An animal cell is a eukaryotic cell built from several sub-cellular structures, also called organelles.
- The nucleus is a large, membrane-bound structure that holds the cell's DNA.
- The cytoplasm is the jelly-like liquid that fills the cell and holds the other structures.
- The cell membrane is a thin layer around the cell.
- Mitochondria are small, rod-shaped organelles in the cytoplasm.
- Ribosomes are tiny structures in the cytoplasm, too small to see with a light microscope.
- An animal cell does not have a cell wall, a permanent vacuole or chloroplasts.
Common Mistake
- An animal cell is surrounded by a cell membrane, not a cell wall.
What Each Structure Does in the Cell
Definition
Nucleus
The organelle that contains the cell's DNA and controls the cell's activities.
- The nucleus controls the cell's activities and holds the DNA that codes for proteins.
- The cytoplasm is where most of the cell's chemical reactions take place.
- The cell membrane is partially permeable and controls which substances move into and out of the cell.
- Mitochondria are the site of aerobic respiration, which transfers the energy the cell needs.
- Cells that use a lot of energy, such as muscle cells, contain many mitochondria.
- Ribosomes are the site of protein synthesis, where proteins are made.
Analogy
- The nucleus is like the control centre of the cell, giving the instructions that run everything else.
The Extra Structures Found in Plant Cells
Definition
Cell wall
A rigid outer layer around the cell membrane that supports and strengthens the cell; in plant and algal cells it is made of cellulose.
- A plant cell has everything an animal cell has, plus three extra structures, and algal cells have them too.
- A cell wall made of cellulose surrounds the cell membrane.
- A large permanent vacuole filled with cell sap sits in the middle of the cell.
- Chloroplasts are found in cells that receive light, such as leaf and stem cells.
- Cells that are not in the light, such as root cells, have no chloroplasts.
Hint
- In a diagram, a thin outer line is the cell membrane, while a thick outer layer around it is a cell wall.
- A cell with a wall, a permanent vacuole and chloroplasts is a plant cell.
What the Plant-Only Structures Do
Definition
Chloroplast
The organelle in plant and algal cells where photosynthesis takes place; it contains the green pigment chlorophyll, which absorbs light.
- The cell wall is made of cellulose and strengthens and supports the cell, helping it keep its shape.
- The permanent vacuole is filled with cell sap and helps keep the cell firm, which supports the plant.
- Chloroplasts are the site of photosynthesis and contain the green pigment chlorophyll, which absorbs light.
- These structures let a plant cell make its own food and stay rigid, which an animal cell cannot do.
Self review
- Name the five sub-cellular structures found in a typical animal cell.
- What is the function of the nucleus?
- Why do muscle cells contain many mitochondria?
- Name the three structures found in plant cells but not animal cells.
- What happens in the chloroplasts, and which pigment do they contain?