Osmosis and Active Transport

define osmosis

the net movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane

define water concentration

the amount of water as compared to other molecules like suagrs or salts that are dissolved in the water

define hypotonic

when the concentration of solutes in the solution outside the cell is lower than the internal concentration

define isotonic

when the concentration of solutes in the solution outside the cell is the same as the internal concentration

define hypertonic

when the concentration of solutes in the solution outside the cell is higher than the internal concentration

what molecules can diffuse via osmosis through a cell membrane?

smaller molecules like oxygen and carbon dioxide

what happens if there's not enough water taken into an animal cell?

the cell will shrivel/shrink(crenation) this occurs when the solution outside the cell is severely hypertonic(more concentrated) so water will move out of the cell

what happens if there's too much water inside an animal cell?

the cell will burst(lysis) and the contents of the cell will spill out this occurs when the solution outside the cell becomes much more hypotonic(dilute) so water will move into the cell

what happens if there's too much water in a plant cell?

it just becomes turgid as the cell membrane swells up which keeps the leaves and stem rigid ad firm

what happens if there's not enough water in a plant cell?

the plant cell wilts and the cell membrane moves away from the cell wall(plasmolysis)

what concentration do plant cells need the fluid surrounding them to be?

hypotonic to the cytoplasm with a lower concentration if solutes and higher concentration of water than the plant cells so that water is constantly moving into the cell

method of potato osmosis practical

1. use a Cork borer to cut potato cylinders of the same diameter

2. trim the cylinders to the same approximate length usung a knife

3. measure out 10cm³ of the first sugar solution and place this in a labelled boiling tube

4. weigh one of your potato cylinders and add this to the tube. repeat the steps above for each sugar concentration.

5. leave the potato in the tube for 15 mins.

6. plan and draw ur results table.

7. After 15 mins remove the cylinders from the tubes and blot them dry

8. using ur results table calculate change in mass for each concentration and plot ur results on graph paper

independent variable for the osmosis experiment

change in mass of potato

dependent variable for the osmosis experiment

the molarity/concentration of the sucrose

controlled variable in osmosis experiment

size of the potato/volume of the solution

what is active transport

the movement of molecules into or out of a cell against a concentration gradient, therefore it requires energy from the cell from respiration(active process)