FINAL NOTES Chp 3 PDF

 Diffusion − The net movement of molecules and ions from a region of their higher concentration to the lower concentration down concentration gradient as a result of their random movement − Energy of diffusion comes from...

 Diffusion − The net movement of molecules and ions from a region of their higher concentration to the lower concentration down concentration gradient as a result of their random movement − Energy of diffusion comes from kinetic energy of random movement of molecules and ions making them moving. − Diffusion can occur in liquids, gases even solid molecules vibrate in place. − Each molecule just moves by chance, changing direction when it bumps into another molecule Importance of diffusion of gases and solutes in living organisms: In plants: − CO2 needed for photosynthesis enter the leaves through stomata from atmosphere during the day because CO2 concentration is lower inside the leaf than outside as it is used up. − O2 diffuses out of the plant leaves through stomata during the day because its concentration in the leaf is higher than outside as it is made during photosynthesis. − CO2 diffuses out of the leaf during night because its concentration is higher as it is a waste product of respiration. − O2 diffuses into leaf at night to be used in respiration. O2 & CO2 diffuse freely through cell membrane into& out of the cell down concentration gradient. In animals: − Some digested food is absorbed by diffusion in ileum down diffusion gradient. − CO2 and O2 molecules exchange in lungs occurs by diffusion. Dr.Gehan Fares Bio O.L CIE 27 | P a g e  Factors affecting rate of diffusion: 1. Temperature: increases in the kinetic energy of the molecules increasing the rate of diffusion. 2. Concentration gradient: the rate of diffusion increases as the difference between the number of molecules between the two areas increases. 3. Surface area of membranes through which the molecule pass: the rate of diffusion increases as the surface area of membrane increases. 4. The distance travelled by molecules: rate of diffusion increase as the distance travelled DECREASES. Investigate the effect of one of the following factors on the rate of diffusion: 1. The surface area to volume ratio 2. Temperature. 3. Distance. 4. Concentration gradient. 1. The surface area to volume ratio − A larger surface area in proportion to the volume will increase the rate of diffusion − Agar blocks made with indicator and alkali will turn colorless when acid diffuse into block. − We determine the rate of diffusion by timing how long it takes for acid to diffuse into blocks of different sizes. 2. The temperature − The rate of diffusion is greater at higher temperatures. − This is because a high temperature provides the particles with more kinetic energy. 3. The distance: The greater the distance over which diffusion has to take place, the slower the rate of diffusion. Measure time taken for each litmus paper to change colour. Dr.Gehan Fares Bio O.L CIE 28 | P a g e  Osmosis The net movement of water molecule from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane Water molecules are also very small. Each one is made of two hydrogen atoms and one oxygen atom. Sugar molecules are many times larger than this. In dialysis tubing, the holes are big enough to let the water molecules through, but not the sugar molecules. Dialysis tubing is called a partially permeable membrane We say that a dilute solution (where there is a lot of water) has a high water potential. A concentrated solution (where there is less water) has a low water potential. Dr.Gehan Fares Bio O.L CIE 29 | P a g e  Osmosis and animal cells Animal cell in pure water or dilute solution (higher water potential): − The pure water or dilute solution has a higher water potential than the cytoplasm. − Water molecules pass from pure water into the cell by (endosmosis) down water potential gradient through partially permeable cell membrane. − The cell swells and the cell membrane stretches and eventually the cell bursts. Animal cells in a concentrated solution (lower water potential): − Water moves out of the cell by (osmosis) down water potential gradient through the partially permeable cell membrane. − The cytoplasm shrinks and the cell shrivels up. Animal cell in a solution with same concentration as the cytoplasm (same water potential): − Net movement of water is zero, cells remain as they are. − Suggest a name of solution with the same water potential as the cytoplasm of blood cells. Osmosis and plant cells Plant cell in pure water or diluted solution: − Water enters by endosmosis through the partially permeable cell membrane into the cytoplasm, then the vacuole which swells pressing the cytoplasm and cell membrane against cell wall. − The cell wall is strong and inelastic will press back on the contents causing turgor pressure to build up in the cytoplasm preventing entry of any more water and stopping the plant cell from bursting. − Now the cell is turgid. − Importance: 1. Plants with non woody stem stay upright. 2. Keeps leaves firm and flat to be exposed to more light for more photosynthesis Dr.Gehan Fares Bio O.L CIE 30 | P a g e  Plant cell in concentrated solution: − Water moves by exosmosis out of the cell down water potential gradient through partially permeable membrane. − The cytoplasm shrinks and stops pushing outwards on the cell wall. − Now the cell is flaccid. − The whole plant is wilting. Plant cell in very concentrated solution: − More loss of water by osmosis, causing cytoplasm and vacuole to shrink more, cell membrane surrounding the cytoplasm is pulled away from the cell wall, the cell is said to be plasmolysed, and cells may die due to damage of cell membrane. Importance of osmosis for absorption of water by root hair cells: − Without osmosis water could not be absorbed by root hair cells. − Inside the root hair cell cytoplasm and cell sap are more concentrated than the solution in soil. − Therefor water moves into the root hair cells down water potential gradient through partially permeable membrane. Describe and explain what happens to a plant grown in a soil flooded with concentrated salt?? Importance of water potential and osmosis on animal cells and tissues: − Every cell in organism's body has water inside and outside with different solutes dissolved in it. − The concentration of these solutes determines the water potential inside and outside the cells. − Movement of water into and out of the cells is determined by water potential gradient. − Plasma surrounding blood cell must have water potential equal to that of cytoplasm of the cell. Dr.Gehan Fares Bio O.L CIE 31 | P a g e  Active transport − Active transport is the movement of molecules and ions in and out of the cell through the cell membrane, against concentration gradient, using energy from respiration. − This happens in occasions when cells need to take in substances that are found in small quantities around. In this case cells move these substances by active transport process How do cells do active transport? − The cell membranes carry special transporter proteins that pick up the ions from outside, then change shape to push the ions into the cell against concentration gradient. − Energy from respiration is required to change the shape of the transporter protein. − In active transport the chemical energy released from glucose is changed to kinetic energy Importance of active transport in plants: − Absorption of minerals such as nitrate from soil by root hair cells is by active uptake. Importance of active transport in humans: − Glucose absorption from the lumen of the small intestine into the cells of villi is by active transport. − Glucose reabsorption out of renal tubule is by active transport. Dr.Gehan Fares Bio O.L CIE 32 | P a g e Dr.Gehan Fares Bio O.L CIE 33 | P a g e