All cells are designed to perform a particular job within an organism, that is, to sustain life. Cells can become specialized to perform a particular function within an organism, usually as part of a larger tissue consisting of many of the same cells working together for example muscle cells. The cells combine together for a common purpose. All organisms will contain specialised cells. There are hundreds of types of specialised cells. Below is listed some of the major ones found in plants and animals.
Plant Cell Specialisation. Guard cells (a pair form a stoma hole) – kidney shapes cells that change shape depending on water content. Regulate the exchange of gases in and out of the plant, and the amount of water lost through the leaves of the plant. Pollen grains – circular cells with an extremely hard protective cell wall containing sperm cells, pollen grains germinate when they come in contact with female stamens, producing a pollen tube through which the sperm travel to reach the ova (ovary). These pollen tubes can easily be seen in a corn cob.
Root hair cell – designed to increase the surface area of the root for absorption of water and mineral nutrients into the plant. These cells have a very thin cell wall that is fully permeable that allows the absorption of mineral nutrients as ions by cation and anion exchange. Contain large vacuoles for the short term storage of these nutrients. Epidermal cells – feature a waxy cuticle (covering) to help prevent water loss from the plant, the cells on the top side of the leaf tend to be more waxy due to higher exposure to the elements.
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Palisade cell (mesophyll) – designed for photosynthesis, it is a tall cell with a large surface area contained many chloroplasts. Located on top side of the leaf in plants to allow optimum absorption of light and carbon dioxide (inputs for photosynthesis). Xylem and Phloem cells (combined referred to as vascular bundles) – cells responsible for the transport of water and nutrients around the plant. Vascular bundles are located in a ring around the outside of the stem in higher order plants. This provides structural support for the plant (plant can die if ‘ring barked’as equivalent to strangulation ).
Xylem carries water and mineral ions up through the plant to the leaves. The phloem transport products of photosynthesis to other areas within the plant for storage (growth). Stone cells (sclereids) – extremely hard to provide protective covering to the seed in stone fruit. Animal Cell Specialisation White blood cells (phagocytes) – part of the body’s immune system, it is responsible for engulfing, breaking down foreign material (bacteria)and cellular debis in the blood in a process called phagocytosis. They are highly mobile, able to move between body cells.
Red blood cells – have no nucleus and contain haemoglobin, the molecule that carries the oxygen around the body to the cells undergoing respiration. Red blood cells with a high oxygen content appear bright red, with low oxygen concentration dark blue/red. Retina cells – the cone and rod shaped cells of the retina are sensitive to light. These cells send electrical messages via the optic nerve to the brain. Muscle cells (fibres)– these cells are long and smooth in structure. The flexible nature of the cell allows them to move by contracting and expanding.
This contractile ability allows to cell o quickly change length. Microvilli (cells lining the small intestine) – these cells have finger like extensions to the surface of the cell to allow greater absorption into the cell by increased surface area. Nerve cells – these cells are elongated with trendril like extensions at each end, and capable of transmitting electrical impulses along the cell body. These electrical impulses are able to contract muscle fibres and stimulate brain cells. Cilia – tiny hair like cells designed to prevent damage to the lungs by airborne particles.
Cilia cells line the surface of the nasal passages and secrete a mucas (snot), a sticky substance that collects the dust particles captured by the hairs , where it is swept towards the back of the throat and then swallowed. Sperm cells – designed to fertilise egg cells, they are very small with a tail to allow movement by swimming. The head of the cell contains enzymes that can digest the outer surface of the egg so that the two nuclei can fuse. A sperm cell contains half the number of chromosomes of the parent organism (genetic material from the father), which will be passed onto the offspring.
Ovum (egg cell) - designed to be fertilized, the cell is large, bulky and not designed to move easily. Like the sperm the ova contains half the number of chromosomes of the adult organism (mother’s genetic material). The ova contains a large food store in the cytoplasm, needed for the developing offspring once the ova has been fertilized. Osteocyte (bone cell) – calcium carbonate and calcium phosphate are deposited around the outside of the cell to form a hard outer covering (bone).
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