Download Diffusion, Osmosis and Active Transport

Diffusion, Osmosis and
Active Transport
I. Diffusion
Diffusion is the movement of particles from a high concentration to a low concentration, until they are evenly distributed. For example, when food is cooking in the kitchen, you can smell it at the other end of the house. This is because molecules are leaving the food (where there is high concentration of them) as a gas and moving around rapidly in the air to spread themselves throughout the house (where there is a low concentration of them). Diagram cited from: http://www.biologycorner.com/ 1. Diffusion in the body
Our cell membranes are in charge of what enters and exits the cell. Dissolved substances and very small molecules (i.e. oxygen, glucose, amino acids and water) can move in and out of cells by diffusion. These molecules are carried around the body in our blood stream. When the blood reaches the cell, the food and oxygen molecules diffuse out of our blood and into our cells. As the cells use up the food and oxygen, waste products are produced (i.e. carbon 1 dioxide). These diffuse out of the cells and into the blood, as they become toxic if they build up in our cells. Diagram cited from: https://anatomygroup.wordpress.com/cardiovascular-­‐system 2. Rates of Diffusion
Diffusion will take place quickly if there is a large difference in the concentration of two areas. This will cause many particles to move randomly towards the area of low concentration. If there is only a small difference in concentration between two areas then the net movement by diffusion will be quite slow. In general, the greater the difference in concentration is, the faster the rate of diffusion will be. This difference in concentration in two areas is called the concentration gradient. II. Osmosis
Osmosis is a specific type of diffusion involving water molecules and occurs when a partially permeable membrane separates two solutions. It is the movement of water molecules from an area of high water concentration to an area of low water concentration across a partially permeable membrane. Tiny holes in the cell membrane allow small water molecules to pass through but large solute molecules are unable to. 2 Diagram cited from: http://bankofbiology.blogspot.fr/ 1. Osmosis in plant cells
Osmosis is the way in which plants take up water. -­‐
The cell membrane of the plant acts as a partially permeable membrane -­‐
The cell sap inside the vacuole is a strong solution -­‐
Water therefore, passes into the plant cell by osmosis -­‐
The concentration of sap inside the vacuole is now weaker -­‐
Water passes from the weak solution into the strong solution in the next cell by osmosis When a plant cell has equal concentrations both outside and inside the cell (isotonic), or higher concentrations of solution inside the cell (hypotonic), then it will become turgid. When a plant cell has a higher concentration of solution outside the cell (hypertonic), then water will leave the cell by osmosis and the cell will become flaccid. If too much water is lost, the cell membrane will come away from the cell wall and they will become plasmolysed. 3 Diagram cited from: http://visualvocabulary.blogspot.fr/ 2. Osmosis in animal cells
In animal cells, the cell membrane is the partially permeable membrane that allows osmosis to occur. If red blood cells are placed into a hypotonic solution (i.e. distilled water), the water will cross the membrane into the cell, as the cell contains a strong solution in the cytoplasm. Animal cells do not have a strong cell wall to stop them swelling too much so if too much water passes into the cell by osmosis, they will burst. This is called haemolysis. If red blood cells are placed into a hypertonic solution (i.e. one with a higher concentration solution than that in the cytoplasm), the water cross the membrane out of the cell and the cells will shrivel. An isotonic solution is one that has the same concentration both inside and outside of the cell. Diagram cited from: http://bio1100.nicerweb.com/ 4 III. Active transport
Active transport is the uptake of particles by cells against a concentration gradient. It requires energy, in order to be carried out. A carrier protein embedded in the cell membrane can use energy from respiration to transport molecules across the membrane, into or out of the cell. Active transport is generally associated with the accumulation of a high concentration of molecules that the cell needs (i.e. glucose, amino acids etc). Diagram cited from: http://www.daviddarling.info/encyclopedia 5 MCQ
1. Cell membranes are: a) Permeable b) Partially permeable c) Impermeable d) Water resistant 2. The movement of molecules from an area of high concentration to an area of low concentration is called: a) Diffusion b) Osmosis c) Isotonic d) Active transport 3. When the concentration of solute molecules is higher outside the cell, water will move out of the cell. This solution is called …………………….. a) Hypotonic b) Isotonic c) Hypertonic d) Homostasis 4. When the concentration of solute molecules is higher inside the cell, water will move into of the cell. This solution is called …………………….. a) Hypotonic b) Isotonic c) Hypertonic d) Homostasis 6 5. When the concentration of solute molecules is the same both inside and outside the cell. This is called …………………….. a) Hypotonic b) Equilibrium c) Hypertonic d) Isotonic 6. The movement of water from an area of high water concentration to an area of low water concentration is called: a) Diffusion b) Osmosis c) Isotonic d) Active transport 7. As molecules diffuse, they create a difference in concentrations across space, this is called a: a) Partially permeable membrane b) Osmosis c) Diffusion d) Concentration gradient 8. A substance can only be accumulated against its concentration gradient by: a) Active transport b) Osmosis c) Diffusion d) Facilitated diffusion 7 9. If a cell's contents are higher in concentration than outside of the cell, it is likely that the cell will become: a) Turgid b) Flaccid c) Isotonic d) Burst 10. If a cell's contents are lower in concentration than outside of the cell, it is likely that the cell will become: a) Turgid b) Flaccid c) Isotonic d) Burst 8