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How and Why do Organisms maintain, a Constant Internal Environment?

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Photosynthesis xerophytes Plan Thermoregulation Blood glucose Blood water potential O2 and CO2 Levels Blood urea The maintenance of a constant internal environment requires control systems that detect stimuli and make the necessary adjustments to return the environment to normal. They do this is by homeostasis. One example of homeostasis is thermoregulation. Heat can be lost and gained by radiation, conduction and convection. Evaporation also plays an important part in heat loss by using heat from the body to evaporate water, and therefore cooling the body down. Heat is also lost in substances leaving the body, such as exhaled air, urine and faeces. Heat can also gained through metabolic activities inside the body cells, such as respiration. In mammals, body temperature is controlled by the hypothalamus, which acts like a thermostat. Sensory cells called thermoreceptors detect changes in body temperature. The central thermoreceptors in the hypothalamus measure the temperature of the blood passing through the hypothalamus. This is known as the core body temperature. There are also peripheral thermoreceptors in the skin, which measure the skin temperature. Both receptors send nerve impulses to the hypothalamus. If the central thermoreceptors detect a decrease in core body temperature then the hypothalamus send impulses to the sweat glands, which reduce sweating, to the erector pilli muscles, which cause hairs to stand on end and to muscles in arterioles, which cause vasoconstriction to take place. ...read more.


A level of amino acids is also maintained within the body. Amino Acids from the gut enter the bloodstream, and are used in protein synthesis. Excess amino acids that are not needed for use in protein synthesis are modified fro use in respiration. This is known as deamination and takes place in the liver. During this deamination process, the amino group, and a hydrogen atom are removed from the amino acid, forming ammonia. This leaves an organic acid, called carboxylic acid that can be used in respiration. Ammonia is then converted into urea in the liver. The kidneys regulate Blood urea content, blood water content and ion content. This is carried out in stages. The first of which is ultra filtration. When blood enters the glomerulus from the afferent arteriole, it is under pressure. The efferent arteriole, which is much narrower causes there to be high pressure in the capillaries of the glomerulus, which means that the blood passes through the glomerulus and, due to the pressure, some water, ions and small molecules pass across the filtering system to the renal space. Many of the substances in the glomerular filtrate, such as glucose, amino acids and mineral ions, are then reabsorbed by active transport by epithelial cells lining the proximal convoluted tubule. ...read more.


They could also have a long, shallow root system, allowing them easier access to rain water as it moves through the soil profile. All these factors allow these plants to live in dry areas and conserve as much water as possible. Plants also regulate their internal environment by photosynthesis. This process involves a series of reactions during which light energy is converted into chemical energy, which other living organisms can use. The process involves using light energy to obtain hydrogen ions and electrons from water. These are then used in the synthesis of ATP and reduced NADP. Carbon dioxide is used to synthesise sugars using reduced NADP and ATP. The whole process occurs by two interconnected, enzyme catalysed metabolic pathways: light-independent reactions and light-dependent reactions. These are just a few ways in which organisms maintain a constant internal environment. They must do this in order to make sure physiological processes, which depend on enzymes and other globular proteins, work properly. Enzymes and other globular proteins need optimum conditions, such as the right temperature etc, to maintain full activity. Living organisms must constantly take substances from their environment, such as nutrients and gasses, and waste materials need to be removed. This means that living organisms must have the systems mentioned above in order to regulate their internal environment, while constantly exchanging substances with their external environment, otherwise they simple could not survive. ...read more.

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