1.1.2 Cell Specialisation

In this lesson, we will investigate cell specialisationThe development of specific structures in a cell to enable it to perform a particular function. and how different cells are adapted for specific functions. We will examine specialised animal cells such as sperm, nerve and muscle cells, and specialised plant cells including root hair, xylemPlant tissue that transports water and mineral ions from roots to the rest of the plant. and phloemPlant tissue that transports dissolved sugars around the plant. cells. We will link the structural features of these cells directly to their functions within tissues, organs and organA structure made of different tissues working together to perform a specific function. systems in multicellular organisms.

What is Cell Specialisation?

Cell specialisation is the process by which a cell develops particular structures that allow it to carry out a specific function. In multicellular organisms, cells become specialised so that the whole organism can function efficiently. Groups of specialised cells form tissues, tissues form organs, and organs work together in organ systems.

Specialised Cells in Animals

In animals, specialised cells are adapted to carry out important functions necessary for survival, including reproduction, movement and communication. Specialised cells in animals include sperm cells, nerve cells, and muscle cells.

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Sperm Cells

Sperm cells are specialised male reproductive cells designed to reach and fertilise an egg cell. A sperm cellA specialised male reproductive cell adapted to fertilise an egg. has several adaptations that increase the chance of fertilisation. It has a long tail called a flagellum, which allows it to swim towards the egg. The mid-piece contains many mitochondriaAn organelle where aerobic respiration occurs and energy is released. to release energy for movement. The head contains a nucleusA membrane-bound organelle in eukaryotic cells that contains DNA. with half of the genetic materialDNA that carries the instructions for cell structure and function. needed to form a new organism. At the tip of the head is the acrosome, which contains enzymes that help the sperm penetrate the outer layers of the egg.

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Nerve Cells

Nerve cells, also called neurons, are specialised cells that carry electrical impulses around the body. A nerve cellA specialised cell that transmits electrical impulses around the body. has a long extension called an axonA long extension of a neuron that carries electrical impulses away from the cell body., which allows electrical impulses to travel long distances. It also has branched endings called dendrites that allow it to connect to other nerve cells. The long structure of the neuronA specialised cell that transmits electrical impulses around the body. makes rapid communication possible between different parts of the body, enabling coordination and response to stimuli. Neurons are essential for sensory perception, movement, and overall coordination in the body.

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Muscle Cells

Muscle cells are specialised to contract and produce movement. Muscle cells are long and contain special protein filaments that can slide past each other, causing the cell to shorten. This shortening is called contraction and produces movement. Muscle cells contain many mitochondria to provide the energy needed for contraction. Many muscle fibres also contain multiple nuclei, which support the production of proteins required for repeated contraction.

Specialised Cells in Plants

Plants also contain specialised cells that allow them to absorb water and minerals and transport substances around the plant. This ensures the plant can grow, reproduce, and thrive in different environments. Specialised cells in plants include root hair cells, xylem cells, and phloem cells.

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Root Hair Cells

Root hair cells are specialised for absorbing water and mineral ions from the soil. A root hair cellA specialised plant cell adapted to absorb water and mineral ions from the soil. has a long projection (the root hair) that greatly increases its surface area, allowing more water and mineral ions to be absorbed. It has a thin cell wallA rigid outer layer that strengthens and supports the cell; made of cellulose in plants and peptidoglycan in bacteria. to reduce the distance substances must travel into the cell. A large vacuoleA fluid-filled space in plant cells that maintains internal pressure. helps maintain a concentration gradientA difference in concentration between two areas. for water movement by osmosisThe movement of water across a partially permeable membrane from a dilute solution to a more concentrated solution.. Root hair cells also contain many mitochondria to provide energy for the active transportThe movement of substances against a concentration gradient using energy from respiration. of mineral ions. They do not contain chloroplasts because they are found underground where there is no light.

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Xylem Cells

Xylem tissueA group of similar specialised cells working together to perform a function. is specialised for transporting water and mineral ions from the roots to the rest of the plant. Xylem vessels are made from cells that have lost their contents and become hollow tubes. The end walls break down so the cells form a continuous column. Their walls are thickened with lignin, which strengthens the vessel and prevents it from collapsing. This structure allows water to move upwards through the plant efficiently and also provides support.

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Phloem Cells

Phloem tissue is specialised for transporting dissolved sugars produced during photosynthesisThe process by which plants use light energy to produce glucose.. Phloem is made of living cells called sieve tube elements. These cells are arranged end to end, and their end walls form sieve plates that allow sap to flow between cells. Phloem transport sugars such as sucrose from the leaves to other parts of the plant where they are needed for growth or storage. Transport in the phloem can occur in both directions, depending on the plant’s needs.