Homeostasis Why is homeostasis important for cells Living

Homeostasis Why is homeostasis important for cells? Living cells depend on the movement of chemicals around the body. Chemicals such as oxygen, carbon dioxide and dissolved food need to be transported into and out of cells. This is done by the processes of diffusion and osmosis and active transport. These processes depend on the body's water and salt balance, which are maintained by homeostasis. DIFFUSION VS. OSMOSIS 2 of 18 © Boardworks Ltd 2007

Diffusion The process by which molecules spread from areas of high concentration, to areas of low concentration. When the molecules are even throughout a space - it is called EQUILIBRIUM 3 of 18 © Boardworks Ltd 2007

What is diffusion? 4 of 18 © Boardworks Ltd 2007

Diffusion in action: one gas 5 of 18 © Boardworks Ltd 2007

Diffusion and digestion Carbohydrates, proteins and fats are made up of large molecules that cannot be absorbed by the body. Digestion breaks down large nutrient molecules into simpler forms such as glucose, amino acids and fatty acids that can be easily absorbed. In which part of the digestive system is most food absorbed? Small food molecules are usually absorbed in the small intestine, diffusing across the intestine wall and into the bloodstream. 6 of 18 © Boardworks Ltd 2007

Diffusion and the small intestine Only some food molecules are small enough to diffuse through the villi and into the bloodstream. Fats, fat-soluble vitamins and glucose can move into the bloodstream by diffusion. These small molecules diffuse from the small intestine into the blood, moving from higher to lower concentration. 7 of 18 glucose © Boardworks Ltd 2007

Osmosis - the diffusion of water (across a membrane) Water will move in the direction where there is a high concentration of solute (and hence a lower concentration of water. A simple way to remember is: Salt is a solute, when it is concentrated inside or outside the cell, it will draw the water in its direction. This is also why you get thirsty after eating something salty. 8 of 18 © Boardworks Ltd 2007

Osmosis and animal cells 9 of 18 © Boardworks Ltd 2007

Osmosis in action 10 of 18 © Boardworks Ltd 2007

Osmosis and digestion In order to remain healthy, animal cells need to maintain homeostasis in water balance. This means that the water concentration both inside and outside the cell are equal. In the large intestine water is absorbed back in the body cells by osmosis. This also makes the feces solid. Good bacteria in the large intestine produce vitamins like Vitamin K which is also reabsorbed by osmosis. These bacteria also produce flatus, a mixture of nitrogen and carbon dioxide, with small amounts of the hydrogen, methane, and hydrogen sulphide. 11 of 18 © Boardworks Ltd 2007

Passive Transport Diffusion and osmosis do not require energy so they are called passive transport. Y G R E N E O N D E D NEE high concentration 12 of 18 low concentration © Boardworks Ltd 2007

Active Transport Sometimes dissolved molecules are larger or at a higher concentration inside the cell than outside, but, because the organism needs these molecules, they still have to be absorbed. Active transport is the process by which dissolved molecules move across a cell membrane from a lower to a higher concentration. In active transport, particles move against the concentration gradient and therefore require an input of energy from the cell. 13 of 18 © Boardworks Ltd 2007

Active transport and digestion During digestion, the villi in the small intestine absorb the soluble nutrients. Over time, the concentration of nutrients in the villi reach an equilibrium with the concentration in the gut. glucose Active transport is used to continue the transport of the small amounts of remaining nutrients against the concentration gradient. 14 of 18 © Boardworks Ltd 2007

Active transport and digestion Amino acids are also absorbed by active transport. Active Transport 15 of 18 © Boardworks Ltd 2007

What is active transport? 16 of 18 © Boardworks Ltd 2007

Glossary l active transport – The movement of molecules against a concentration gradient, and which requires energy. l concentration gradient – The difference in concentration across a given area. l diffusion – The movement of molecules from an area of high concentration to low concentration. l osmosis – The diffusion of water molecules from a dilute solution to a more concentrated solution. l partially-permeable membrane – A membrane that allows only certain sized molecules to pass through it. l villi – Tiny finger-like projections on the inner surface of the small intestine, across which nutrients diffuse. 17 of 18 © Boardworks Ltd 2007

Multiple-choice quiz 18 of 18 © Boardworks Ltd 2007