Cell Size Surface Area- Volume

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Cell Biology- Osmosis, Cell Size and Diffusion and Enzymes
Cells are the basic building blocks of all living things. They provide structure for the body, take in nutrients from the food, convert those nutrients into energy, and carry out specialized functions. Cells also contain the body’s genetic material and can make copies of themselves. A cell is also a metabolic compartment where many different chemical reaction occur. There are two types of cells, eukaryotic and prokaryotic. Prokaryotic cells are usually unicellular, while eukaryotic cells can either exist as a single celled organism or be found in multicellular organisms. The unicellular and multicellular organisms are linked to cell size and surface area to volume ratio. The experiment for cell size and diffusion was set to see how and how much water can go to the cells. This movement of water is called Osmosis. Osmosis is the movement of water molecules from an area of low concentration (lots of water) to an area of high concentration (little water) through a semi permeable membrane, demonstrated in ‘figure 1’. A semi permeable membrane is a membrane that only lets selected molecules to pass through it. In a plant water is taken into the roots by the process of Osmosis. This is because the cells inside the roots have a higher concentration of solutes than the soil outside the roots, water diffuses from an area on high concentration to an area of low concentration. When a large volume of water enters the cell, it swells causing the membrane to push against the cell wall which is called turgor pressure. When the water moves out of the cell, the membrane shrinks away from the cell wall and becomes a loose cell, plasmolysis. This causes the plant to wilt, as the cells can no longer provide support for the leaves.  Figure1. How Osmosis works

As already known, proteins in our cells do many things. One of the most important things they do is act as an enzyme. An enzyme is a biological catalyst, and a biological catalyst is something that changes chemical reactions without being changed itself. Enzymes are the catalysts for chemical reactions. They work by lowering the activation energy of a reaction therefore making the reaction easier to proceed to the products...this increases the reaction rate. Chemical reactions keep our bodies going, without them, we’d die. So enzymes are very, very important. Enzymes are not changed when they perform their function as seen in ‘figure 2’. This means that the same enzyme can be used over and over again. Some enzymes may even be used repeatedly on the same set of small molecules to build a long chain of repeating subunits. As with all proteins, the shape of an enzyme is what determines its function. An organism has the ability to make many different enzymes, and each enzyme has one particular function. There are enzymes in all the tissues and fluids of our bodies and these enzymes are very specific. The substances they work on are called substrates. The factors effecting enzymes shape of a molecule are substrate concentration (salinity), pH, temperature, activators and inhibitors. This process is called denaturing and will also make the enzyme less effective, possibly even useless. Figure 2. An Animated Demonstration of How Enzymes Work

2.0 Cell Size and diffusion
2.1 AIM
To determine the influence of the surface area : volume ratio on the effectiveness of the rate and percentage of diffusion in various cell sizes. 2.2 HYPOTHESIS
If the agar cubes are reactant to the Hydrochloric Acid, then the cube will become clear because the acid is defusing the cubes and the clear parts are the indicator of the cell size and surface area to volume ratio. As the size of the cell increases, so does the surface area and volume.

* 3 cubes of Agar with NaOH & phenolphthalein indicator (1cm3, 2cm3, 3cm3) * 200-250mL 2M HCl solution
* 250mL beaker
* forceps
* glass petri...
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