[BIO] Chapter 2 - Movement of Substances

© Hee Xin Wei (Copyrighted) Topic 2: Movement of substances

Chapter Analysis FOCUS EXAM WEIGHTAGE © Hee Xin Wei (Copyrighted) •diffusion, osmosis and active transport •straightforward chapter •heavily tested •foundation of many future chapters •heavy weightage especially as a concept incorporated with other chapters

diffusion osmosis & effect of osmosis active transport Key Concept © Hee Xin Wei (Copyrighted)

Diffusion •Diffusion is the net movement of molecules from a region of higher concentration to a region of lower concentration, down a concentration gradient. •it is a passive process as energy is not required •When the molecules have reached equilibrium between the two regions, the concentrations are the same and there will be no net movement of molecules. ROLE OF DIFFUSION IN LIVING ORGANISMS •Its role in nutrient uptake and gaseous exchange in plants and humans •Diffusion enables living organisms, unicellular or multicellular, to survive by allowing the exchange of nutrients such as glucose, amino acid and fats, gases such as oxygen and waste substances such as carbon dioxide and urea * diffusion is a extremely relevant concept in future chapters © Hee Xin Wei (Copyrighted)

Diffusion FACTORS THAT AFFECT RATE OF DIFFUSION FACTORS THAT AFFECT RATE OF DIFFUSION 1.Temperature •↑ in temperature, ↑ in kinetic energy of molecules 2.Concentration gradient •Concentration gradient is the difference in concentration between two regions •The steeper the concentration, the higher rate of diffusion 3.Size of molecules •Heavier molecules move more slowly than light molecules 4.Diffusion distance •Molecules do not have to travel far thus rate of diffusion is faster Slide A represents a steeper concentration gradient and will allow you (the molecules) to move down faster © Hee Xin Wei (Copyrighted)

Osmosis •Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane •Water potential refers to the tendency of water to move from one area to another •Plasma membrane or visking tubing are examples of partially permeable membranes that only allow allow some substances such as water, gases like oxygen and carbon dioxide to pass through freely but not some other substances 10% conc 20% conc Examples: •The 20% solution is more concentrated than the 10% solution. Hence, 10% solution has a higher water potential than 20% solution. The partially permeable membrane does not allow solute molecules to pass through as it is too big. •As a result, water molecules will move from the arm with the 10% solution which has a higher water potential to the arm with the 20% solution which has a lower water potential, passing through semi permeable membrane via osmosis. © Hee Xin Wei (Copyrighted)

Effect of osmosis on animal cells When an animal cells is immersed in a solution with a higher water potential relative to its cytoplasm, •Water moves into the cell by osmosis. •Animal cells do not have cell walls to protect the cells from overexpansion. As more water enters the cell, it swells to such an extent that it bursts. •CYTOLYSIS / the cell is lysed When an animal cell is immersed in a solution with a lower water potential, relative to its cytoplasm, •Water moves out of the cell by osmosis. •The cell shrinks and become dehydrated. In red blood cells, little spikes appear on the cell surface membrane. •CRENATION / the cell is crenated © Hee Xin Wei (Copyrighted)

Effect of osmosis on plant cells When a plant cell is immersed in a solution of higher water potential relative to its cell sap, •Water molecules enter the cell by osmosis. •The vacuole increases in size •The cellulose cell wall of a plant cell is rigid and exerts an opposing pressure on the cell contents, preventing the entry of more water. This prevents the cell from overexpanding and bursting. •At this point, the plant cell is very turgid. TURGOR PRESSURE provides mechanical support for many non-woody plants When a plant cell is immersed in a solution with a lower water potential relative to its cell sap, •Water moves out of the cell into the solution by osmosis. •The vacuole decreases in size and the cell is flaccid •If more water leaves the cell, the vacuole and cytoplasm shrink to such an extent that the cell surface membrane pulls away from the cell wall •PLASMOLYSIS / the cell is plasmolyse © Hee Xin Wei (Copyrighted)

Effect of osmosis summary Hypotonic solution (water potential is higher than cell content) Isotonic solution (water potential is same as cell content) Hypertonic solution (water potential is lower than cell content) Animal Cells Lysed Normal Crenated Plant Cells Turgid Normal Plasmolysed © Hee Xin Wei (Copyrighted)

Active Transport •Both diffusion and osmosis is passive transport where energy is not required •Active transport is the process where energy is used to move substances, across a cell membrane, from a region of lower concentration to a region of higher concentration, against concentration gradient. •Since energy is required, amount of mitochondria to carry out aerobic respiration and availability of oxygen is important •Example: Uptake of dissolved mineral salts by root hair cells and glucose uptake by cells in the villi of the small intestine © Hee Xin Wei (Copyrighted)