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How Temperature Affects the Movement of Pigment Through Cell Membranes

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How Temperature Affects the Movement of Pigment Through Cell Membranes Aim: To use beetroot to examine the effect of temperature on cell membranes and relate the effects observed to membrane structure. Hypothesis: An increase in temperature will damage and denature the membrane and cause the substances contained within it to leak out. Overview: The experiment below displays the effects of temperature on the pigment in uncooked beetroot cells. The pigment in beetroot cells lies within the cell vacuole and is called betalain, each vacuole is surrounded by a tonoplast membrane and outside it, the cytoplasm is surrounded by the plasma membrane, therefore the foundation of this experiment lies with the temperature at which the membranes will rupture and therefore leak the pigment. To do this a series of uncooked beetroot cylinders will be exposed to different temperatures and then to distilled water at room temperature (20�C). The colour of the distilled water is the variable here. Theory - To understand how the red pigment leaks out of the beetroot it is essential that we understand the molecular Structure of a plasma membrane. If you read a recipe for cooked beetroot it will usually recommend that you don't remove the outer skin of the beetroot and don't cut off al the stalk and root if you want to avoid getting lots of red dye in the cooking water. Background; Beetroot contains red pigments called betalains, located within the cell vacuole. Normally the pigments can't pass through membranes but they leak out when the beetroot is cooked. A membrane is a phospholipids bilayer. This means that it has two layers of molecules called phospholipids. ...read more.


Half-life: The half-life of beetroot pigment is 413 mins at 250C but only 83.5 mins at 600C. These values are doubled in 0.1% ascorbic acid. Metal ions speed up the breakdown - iron is particularly effective. They are stable between pH 4.0 and 7.0 - indeed, at high temperatures they are most stable in a pH between 4.0 and 5.0 - and most fruits and vegetables are acidic! * When the beetroot has been cut some of the cell membranes are broken, which means some betalain will leak out. This must be completely washed off in order to maintain the reliability of the results. * I will use distilled water to so that I have a reliable substance to test with a colorimeter. Each piece of beetroot will be the same size (3 cm), by using a segregated knife to maintain the thickness of the surface. The reason why the amount of betalain pigment released (colorimeter reading) from the vacuole increased directly proportionally to the temperature of the water bath (from 20oC to 40oC) is because the amount of random movement of betalain molecules out through the cell membrane depends on the amount of heat energy the betalain molecules are given to convert into kinetic energy- hence the higher the temperature the more betalain lost from the vacuole. This is because the betacyanin pigment of beet root cells is normally sequestered in the vacuole and by means of the cell membrane which maintains the integrity of the cell and the tonoplasts, it does not leak into the cytosol or the extra-cellular sap of the beet root. ...read more.


The plasma membrane also provides a boundary to cell cytoplasm separating it from other cells. Phospholipids have a polar head, which is hydrophilic and a non polar tail which is hydrophobic. Proteins have a hydrophobic part which is buried in the lipid bilayer and a hydrophilic part which can be involved in a variety of activities. Some proteins move freely some are fixed in one place. Some proteins only span the top bilayer which is the extrinsic or the bottom which is the intrinsic or they may span the entire membrane. Some proteins on the outer edge of the membrane have carbohydrates molecules attached, usually short sugar chains called glycoprotein or lipids with carbohydrates attached to them called glycolipids. These are important in cell recognition and the immune system. Membranes are therefore vital to cellular function. As long as the temperature does not go beyond what the membrane is supposed to withstand, the permeability of the plasma membrane (PM) should not be affected. There might be a higher controlled permeability for such compounds that are supposed to transit the PM, but it will not break down, spewing out red beet colour. So what happens when the temperature goes beyond these limits? Water expands, putting pressure on the membranes from within. The lipid part of the membrane liquefies, making it more prone to leakage. The proteins that span the membrane fall apart, creating holes in the fabric. All this combined will allow compounds to exit the cell. Why does this happen? That is physics. Higher temperature makes all molecules shake and vibrate more. The faster movement disrupts any ordered structure there might have been, eventually destroying the structure altogether. ...read more.

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