Homeostasis+Exploration

- despite changing environment - understand cell membrane - osmosis: the movement of water from a region of higher water potential through a partially permeable membrane to a region of lower water potential - definition, explain, example
 * Homeostasis:** The maintaining of equilibrium between the the external and internal environment of an organism/living thing/living system through active or passive transport.



In this experimental setup, the control was tube A. To ensure that a fair test is conducted, all the beetroot slices had to be cut into as equal pieces as possible and washed thoroughly. The tube which colour of the solution was the most intense after 15 minutes is tube C (50% alcohol), followed by tube B (25% alcohol). This is because alcohol enhances the fluidity of the cell membrane, breaks down the phospholipid bilayer and denatures the proteins by breaking the hydrogen bonds. The colour of the solution in tube D (hot water) after 15 minutes was pinkish as high temperatures denature the carrier proteins in the cell membrane, hence more betacyanin leaks out of the cell membrane than in the beetroot cells in tube A. In tube E, the colour of the solution was the same shade of pink as that in tube D due to the increased surface area to volume ratio of the beetroot discs resulting in a higher rate of diffusion. Other factors that would affect the leaking of betacyanin out of the beetroot cells are pH level and the presence of oxidants. The properties of proteins in the cell membrane change with pH level as this affects the charge (positive or negative) of amino acids due to hydrogen bonds. In acid pH, the amino acids become positively charged (H+ ions are added) and in alkaline pH, they become negatively charged (H+ ions are lost). Thus, high and low pH cause the proteins in the cell membrane to change shape and become unable to function properly. However, a neutral pH should have no or little effect on cell membranes.
 * __4A) Beetroot Experiment Discussion__**

__**4B) Agar Experiment Discussion**__ When agar cubes are placed in water, the bonds between the ions in the agar break and diffuse into the water. Thus, the conductivity probe is used to test the amount of ions in the solution. The surface area to volume ratio increases with increased surface area. Diffusion is more efficient for the 64 agar cubes as compared to the 8 cubes and 1 cube as it has the highest rate of conductivity change of 9.88. Thus, when the surface area to volume ratio increases, the rate of conductivity change increases as seen from the results, meaning that the greater the surface area of the agar, the faster the rate of diffusion. This experiment allows us to relate this property to the shape of simple to complex organisms. As a cell grows, the surface area of its cell membrane gets less and less efficient relative to its volume as the ratio decreases. Likewise, as organisms get bigger, their surface area to volume ratios decrease. Single-celled organisms can efficiently transport all substances through diffusion as it has a large surface area to volume ration. However, multi-cellular complex organisms are unable to depend on diffusion alone as the transport of substances would be too slow and would probably not reach all cells. Thus, as it is more difficult for them to exchange materials with the surroundings, they have adaptations which cleverly maximise surface area to maximise diffusion and absorption such as villi in the small intestine.