Specialist cells: structure and function across systems
Cell biology • Cell structure
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General principle: structure determines function
Cells develop specialised features that increase efficiency for a single task. A larger surface area increases exchange rates so that absorption or secretion happens faster; internal organelle abundance, such as many mitochondria, increases ATP supply so that energy-demanding processes proceed at required rates. Structural loss of some components, such as removal of a nucleus, creates space for increased transport or storage, improving a cell’s primary role.
Animal specialised cells and their adaptations
Sperm cells have a long tail (flagellum) to move through fluid and many mitochondria near the midpiece to supply ATP for flagellar beating; the nucleus contains condensed genetic material for fertilisation so a haploid genome delivers half the DNA to the zygote. These structures allow a sperm cell to travel and fuse with an ovum. Nerve cells have long extensions (axons) to transmit electrical impulses over distance and many branched endings (synaptic terminals) to form junctions with many other cells; insulating myelin speeds conduction, allowing rapid communication across tissues. Muscle cells contain contractile proteins and many mitochondria so contraction occurs repeatedly and with high energy supply; tissue-level force arises from many muscle cells acting together.
Plant specialised cells and their adaptations
Root hair cells form long thin projections that increase surface area in contact with soil; increased surface area causes higher rates of water and mineral uptake by diffusion and active transport. Xylem consists of elongated dead cells joined into continuous tubes with lignified walls; absence of end walls and cell contents removes resistance to bulk water flow and lignin reinforces the tubes to resist collapse while supporting the plant. Phloem consists of living sieve tube elements with reduced organelles and sieve plates between cells; reduced contents lower resistance to flow of sap while companion cells supply ATP and proteins to maintain transport of sucrose. Together xylem and phloem form transport tissues that meet whole-plant water and nutrient demands.
Cell differentiation and limits
Cell differentiation is the process by which generalised cells develop specialised structures and functions through changes in gene expression and organelle composition. Differentiation allows multicellular organisms to form tissues and organs with division of labour, increasing overall efficiency. Animal cells often differentiate during development and many lose the ability to divide; plant cells retain the ability to differentiate for longer, enabling growth from meristems and regeneration from cuttings. Limiting factors include availability of nutrients, oxygen, and signals that regulate differentiation, and loss of stem-cell potential in many adult animal tissues restricts regeneration.
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