Plant and animal cell comparison

Plant and animal cells share several structures that carry out the same basic activities. A typical plant cell also has structures that support it and enable photosynthesis.

Structures shared by plant and animal cells

The cell membrane controls the movement of substances into and out of the cell.
The cytoplasm is where many chemical reactions occur.
The nucleus contains genetic material and controls the activities of the cell.
Ribosomes make proteins.
Mitochondria are the sites of aerobic respiration, which releases energy for the cell.

Structures of a typical plant cell

A typical plant cell has three additional structures:

The cell wall lies outside the cell membrane. It supports the cell and helps maintain its shape.
Chloroplasts absorb light for photosynthesis.
A large vacuole contains cell sap and helps keep the cell firm.

Animal cells do not have a cell wall or chloroplasts. Not every plant cell contains chloroplasts, but in diagrams and images, the combination of a cell wall, chloroplasts and a large vacuole identifies a typical plant cell. The shared structures can be identified in both plant and animal cells.

Bacterial cell structure

A bacterial cell has an outer cell wall surrounding a cell membrane. Inside the membrane are the cytoplasm, ribosomes and genetic material. Unlike a cell with a nucleus, a bacterial cell has its main DNA in the cytoplasm, not enclosed inside a nucleus.

Bacterial cell structures and their functions

Cell wall: supports and protects the cell. In a diagram, it forms the outer layer around the cell membrane.
Cell membrane: controls the movement of substances into and out of the cell. It lies just inside the cell wall.
Cytoplasm: the material filling the inside of the cell, where many chemical reactions occur.
Ribosomes: small structures in the cytoplasm that make proteins. They are often shown as dots in diagrams.

Bacterial DNA and plasmids

The bacterium’s main genetic material is circular DNA in the cytoplasm. In a diagram, it is often drawn as a large loop, which may appear tangled or folded.

Some bacterial cells also contain plasmids: smaller circles of DNA separate from the main circular DNA. In a diagram, these can be recognised as small loops in the cytoplasm. Plasmids are not present in every bacterial cell.

Cell specialisation

Cells can be suited to different jobs. A specialised cell carries out a particular function, and its features help it perform that function. Cells within an organism do not all have the same role, and different organisms have cells specialised for different functions.

Ciliated cells line the trachea and bronchi. Tiny hair-like structures called cilia beat to move mucus along the airways.
Root hair cells absorb water and mineral ions from the soil. Their long projections provide a large surface area for absorption.
Palisade mesophyll cells carry out photosynthesis in leaves. They contain many chloroplasts, which absorb light for photosynthesis.
Neurones conduct electrical impulses, carrying information from one part of the body to another.
Red blood cells transport oxygen from the lungs to body tissues. They contain haemoglobin, which binds oxygen.

Sperm cells and egg cells are specialised reproductive cells called gametes. A sperm cell and an egg cell join during fertilisation, bringing together genetic material from each parent.

Levels of biological organisation

A cell is a basic living unit. New cells are produced when existing cells divide. In a multicellular organism, many cells work together and are organised into increasingly larger structures.

A tissue is a group of cells working together. Different tissues work together to form an organ, and organs work together to form an organ system. An organism is an individual living thing made up of these coordinated parts.

The levels can be followed from the smallest to the largest:

Cell → tissue → organ → organ system → organism

Organisation in the human respiratory system

Ciliated cells form part of the tissue lining the trachea, or windpipe. The trachea is an organ made of different tissues working together. It is part of the respiratory system, an organ system within a human organism.