Osmosis

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DESIGN ASPECT 1: Defining the Problem and Selecting Variables

CELLS are the basic unit of structure in all organisms and the smallest unit of life. All living things are made of cells. Multicellular organisms (humans) are composed of many cells. Unicellular organisms (bacteria) are composed of only one cell. Existing cells come from other pre-existing cells and cannot be created from non-living materials. All cells are surrounded with membrane called CELL MEMBRANE (PLASMA MEMBRANE). Plasma membrane is semipermeable (selectively permeable) membrane, which means that it only allows certain molecules or ions to get in or to get out of the cell. There are three types of movement of particals across the cell: diffusion(and also facilitated diffusion), osmosis and active transport. Diffusion and osmosis are passive movements and they don't require any energy. Active transport requires ATP energy.

OSMOSIS is the passive movement of water molecules across a partially permeable (semipermeable) membrane, from a region of lower solute concentration to a region of higher solute concentration in order to equalize the solute concentrations on the two sides.

Tonicity is a measure of the osmotic pressure of two solutions separated by a semipermeable membrane. There are three types of tonicity that one solution can have relative to another. Those are hypertonic, hypotonic, and isotonic.

Hypertonic solutions(more dissolved solute)-the solution with a higher concentration of a solute. Water leaves the cell and the cell shrinks.

Hypotonoic solution(less dissolved solute)-the solution with the lower solute concentration. Water molecules enter the cell and the cell becomes larger.

Isotonic solution(same amount of dissolved solute)-the solution of equal solute concentration.

PROBLEM QUESTION: What is the effect of different concentration of sugar in water on raisins's mass and change of shape in that water?

HYPOTHESIS: Raisins that have been put in the water with a lower sugar concentration will increase in volume and mass, and raisins that have been put in water with a higher sugar concentration will shrink and lose some mass.

This hypothesis is based on the usual effect of hypertonic and hypotonic solutions. SOLUTE+SOLVENT=SOLUTION. Solute is sugar, solvent is water. In the first glass we had higher concentration of sugar(solute) which means that water with more dissolved sugar(saturated water) is HYPERTONIC SOLUTION. In hypertonic solution cells shrink because water leaves the cell. As raisins's cells shrink, raisins will shrink themselves and lose certain mass. In the second glass we had lower concentration of solute-sugar, water with less dissolved sugar and that water was HYPOTONIC SOLUTION. In hypotonic solution water enters the cells and the cell becomes larger. As raisins's cells become larger, raisins will become larger and their mass will increase.

VARIABLES

MANIPULATED VARIABLE: concentration of sugar

Sugar-SUCROSE (molecular formula C12H22O11 ) also known as table sugar, sugar we use everyday. We had two levels of MV:

1. Small amount of sugar

2. Large amount of sugar

RESPONDING VARIABLE: mass and shape of raisins

Quantitative data-mass of raisins, qualitative data-shape of raisins.

DESIGN ASPECT 2: Controlling Variables

|Controlled variables |Why it must be controlled? |How it was controlled? | |Mass of raisins |Mass of raisins have to be controlled so we |By measuring and using the same amount | | |could see clearly later the actual increase or| | | |decrease of mass. | | |Water |Water have...
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