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understanding cell structure / tissue types and functions

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Understanding the basic structure of a cell Cells Structure All cells have organelles; these are the specialised structures within a cell that help it to perform the specific functions. Organelle Structure / Function Cell Membrane The cell membrane keeps the cell together by containing the organelles within it. Cell membranes are selectively-permeable, allowing materials to move both into and outside of the cell. Centrosomes also known as the MTOC is where the microtubules are produced During cell division the centrioles replicate and the centrosome divides. The result is two centrosomes, each with its own pair of centrioles. The two centrosomes move to opposite ends of the nucleus, and from each centrosome, microtubules grow into a "spindle" which is responsible for separating replicated chromosomes into the two daughter cells. Centriole A ring of nine groups of microtubules, each group has three microtubules (centriole), and is part of the cytoskeleton Cytoplasm Cytoplasm is a jelly-like substance that is sometimes described as "the cell-matrix". It holds the organelles in place within the cell. It is where the entire cell metabolism occurs. The cytosol is made up of mostly water it is full of proteins that control the cell metabolism including signal transduction pathways, glycolysis, intercellular receptors Golgi apparatus Normally connected to the ER, it stores and transports the proteins made within the ER Lysosomes Lysosomes are tiny sacs filled with enzymes essential for intracellular digestion. They also destroy the cell after it has died. Microvilli Microvilli are finger-like projections on the outer-surface of the cell. Not all cells have microvilli. Their function is to increase the surface area of the cell, which is the area through which diffusion of materials both into, and out of, the cell is possible. Nuclear membrane Nuclear membrane separates the nucleus and the nucleolus from the contents in the rest of the cell Nuclear pores These allow substances such as nutrients, waste and cellular information to pass into and out of the nucleus Nucleolus This is responsible for the cell organelles


At this point maternal and paternal chromatids can exchange bits of DNA to recombine their genetic material and increase the potential for variation. The homologous pairs of chromosomes then separate and move to the poles of the parent nucleus. For each of the 23 pairs there is a 50-50 chance as to which pole the paternal or maternal pair of chromatids goes. With over 8 million possibilities there are many opportunities for variation. The nucleus now divides to form two daughter nuclei, each with a mixture of paternal and maternal chromosomes but with half the full complement of genetic material (and no pairs at all). This division is called Meiosis 1. Finally the two daughter nuclei themselves divide to form gametes. This second division - Meiosis 2 - works just like mitosis. The chromosomes (really pairs of chromatids) split apart to form the genetic material of the four new cells. The end result is four sex cells each with a complete but single set of 23 chromosomes. On fertilisation the nuclei of the sperm and the egg join to form a new nucleus, called the zygote. The zygote contains 23 pairs of chromosomes - 23 single chromosomes from the sperm, and 23 single chromosomes from the egg. Understand the nature of multi - cellular organisms Multi-cellular Organisms Humans are multicellular; the largest cell in the human body is the egg cell, ovum. It needs to be larger than the other cells as it needs to store food reserves. The body systems consist of complex organs and tissues which interact and co-operate to keep the cells in the best possible environment. Different groups of cells carry out different functions and tasks, they are differentiated and become specialised. The different types of cell develop to perform their specific functions, which contributes to the success of the organism. This is also known as the division of labour.


flexibility), the muscular system (muscles receive additional blood flow in response to the secretion of the hormone adrenaline at times of stress), the circulatory system (hormones are secreted and carried to their target organs). The reproductive system is linked to the skeletal system (the pelvis protects the uterus), the muscular system (smooth muscle is responsible for the passage of ova from the ovaries to the vagina and sperm from the testes to the urethra), the circulatory system (during erection of the penis the vascular spaces become engorged with blood), the nervous system (semen moves as a result of sympathetic reflexes) and the endocrine system (ovaries and testes responsible for development of secondary sexual characteristics). The digestive system is linked to the skeletal system (the larger bines in the mouth support the jaw and teeth when food is ingested), the muscular system (helps to propel the food through digestive tract, and assist in chewing), the circulatory system (nutrients are carried to nourish the cells and tissues, waste products are carried away through blood)m the lymphatic system (absorb products of fat digestion), the respiratory system (oxygen activates glycogen from the digestive system which produces energy for cell metabolism), the nervous system (nerve impulses stimulate the digestive system) and the endocrine system (pancreas secretes insulin which helps to control blood sugar levels). The urinary system is linked to the skeletal system (the kidneys and the bones of the skeleton helps control the amount of calcium in blood by storing some in bones and excreting some in urine), the muscular system (smooth muscle responsible for passage of urine through urinary tract), the circulatory system (kidneys filter blood to avoid poisons accumulating in the body), the nervous system (relaxation and contraction of the bladder, closing and opening the sphincter muscles is controlled by autonomic nervous system) and digestive system (water is an essential nutrient needed by all body parts, it is taken in through digestion to aid metabolic process, colon absorbs most of water to conserve moisture in body).

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