Cell Specialisation (1.1.3)

Cell Specialisation (1.1.3)

• Cells specialise through a process called differentiation. Differentiation involves cells acquiring new sub-cellular structures to fulfil specific roles.
• Cells can differentiate either once early in their development or throughout their entire lifespan. Stem cells are an example of the latter.
• In animals, most cells differentiate only once, but in plants many cells retain the ability to differentiate throughout their lives.

Examples of Specialised Animal Cells

• Sperm cells: Designed for reproduction. Features include a streamlined head and long tail for motility, many mitochondria for energy, and acrosome enzymes to penetrate the egg's outer layer.
• Nerve cells: Transmit electrical signals rapidly throughout the body. Key features are a long axon for signal transmission, branched dendrites for connections with other cells, and numerous mitochondria for energy. Neurotransmitters allow signals to pass between cells.
• Muscle cells (striated): Responsible for rapid contractions to move bones. Contain special proteins which slide over each other, causing the muscle to contract, and many mitochondria to provide energy. These cells can also store glycogen for respiration. Smooth muscle allows variations in blood pressure, for example.

Examples of Specialised Plant Cells

• Root hair cells: Absorb water and mineral ions from the soil. Root hairs increase surface area for absorption. A large permanent vacuole affects water movement, and mitochondria facilitate active transport of mineral ions.
• Xylem cells: Transport water and mineral ions throughout the plant. Lignin deposition in these cells enables them to withstand pressure from water movement through the plant. To conduct water, these cells form tubes by joining together.
• Phloem cells: Transport food produced in photosynthesis to other parts of the plant. Phloem cells lose most of their subcellular structures but still need energy from companion cells' mitochondria to survive. Sieve plates aid transport within the phloem.