Specialisation of eukaryotic cells

In a complex multicellular organism, different cells perform different functions. A specialised cell has features that help it carry out a particular role. These features may include its shape, the abundance of a cell structure, or the way structures are arranged.

For example, a root hair cell absorbs water from the soil. Its long, thin extension gives it a large surface area in contact with the soil, allowing more water to enter the cell.

A sperm cell has a tail that propels it towards an egg. It also has many mitochondria, which release energy needed for the tail to move. Both features are suited to the sperm cell’s role in reaching the egg.

To explain a cell’s adaptation, name a specific feature and link it to the function it helps the cell perform. For a root hair cell, stating that it has a long extension identifies the feature; explaining that the extension increases the surface area for water absorption shows how the feature helps.

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.

Sperm cell adaptations

A sperm cell is specialised to reach and fertilise an egg cell. Its structures help it swim to the egg, penetrate its outer layers and deliver genetic information.

Swimming towards the egg

The sperm’s tail beats to propel it through fluid towards the egg. The sperm contains many mitochondria, which carry out respiration and release energy to power the tail’s movement.

Entering the egg

At the head of the sperm is a cap called the acrosome. It contains enzymes that help digest through the outer layers of the egg, allowing the sperm nucleus to enter.

Delivering genetic information

The sperm’s nucleus is haploid: it contains one set of chromosomes, rather than the two sets usually found in body cells. The egg nucleus is also haploid. When the sperm and egg nuclei fuse, their chromosome sets combine, restoring the normal diploid number in the fertilised egg.