JWSS Biology Chapter 2 Movemenst of Substances

Sec3 G3 Science (Biology) Chapter 2 Notes 1 Prepared by Ms Pui LX JURONG WEST SECONDARY SCHOOL SECONDARY THREE – SCIENCE BIOLOGY Chapter 2: MOVEMENT OF SUBSTANCES Learning Outcomes: Candidates should be able to: a) define diffusion and describe its role in nutrient uptake and gaseous exchange in plants and humans b) define osmosis, investi gate and describe the effects of osmosis on plant and animal tissues Use the knowledge gained in this section in new situations or to solve related problems. Lesson Trigger After a game of floorball, some students apply perfume to smell pleasant. How has the smell travelled to your nose? Think of the last time you detected the smell of perfume in a room after PE lesson. DIFFUSION Definition: Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient till equilibrium is reached.

Sec3 G3 Science (Biology) Chapter 2 Notes 2 Prepared by Ms Pui LX What is a concentration gradient and how is it related to diffusion? Concentration gradient is the difference in concentration between two regions. • The particles in fluids possess kinetic energy. • Particles will diffuse down their concentration gradient. • The steeper the concentration gradient, the faster the rate of diffusion. How diffusion occurs Example 1 • Membrane is partially permeable. • Particles like potassium iodide and copper sulfate is able to pass through. • Explanation: there is a net movement of particles from region of higher concentration to a region of lower concentration via diffusion till equilibrium is reached.

Sec3 G3 Science (Biology) Chapter 2 Notes 3 Prepared by Ms Pui LX Example 2 • Visking tubing is partially permeable. 1. Which side has a higher concentration of glucose? ✓ Inside Visking tubing 2. Which direction will there be a net movement of glucose molecules? ✓ Ans: There is a net movement of Glucose molecules move out of the visking tubing, as the 10ml glucose solution has higher concentration of glucose, down a concentration gradient 3. Will equilibrium be achieved? (end: 6ml glucose inside and outside visking tubing) ✓ Yes Explanation (similar to definition. Need to write the location) ✓ there is a net movement of glucose molecules ✓ from a region of higher concentration inside the visking tubing ✓ to a region of lower concentration outside the visking tubing, ✓ via diffusion, ✓ down a concentration gradient, till equilibrium is reached. visking tubing 2ml glucose

Sec3 G3 Science (Biology) Chapter 2 Notes 4 Prepared by Ms Pui LX Example 3 Explanation: ✓ there is a net movement of glucose molecules (which are small enough) ✓ from the region of higher concentration outside the Visking tubing ✓ to the region of lower concentration inside the Visking tubing, ✓ via diffusion, ✓ down the concentration gradient until equilibrium is reached. Example 4 visking tubing (partially permeable) 2ml glucose diffusion of sucrose molecules from within the Visking tubing to the outside will not occur as the sucrose molecules are too large to pass through the partially permeable membrane. With membrane • Iodine solution contain iodine molecules and water molecules that are small enough to pass through the partially permeable membrane. • Starch is a large molecule and cannot pass through the partially permeable membrane. • Description: o Iodine solution inside the visking tubing turns from yellowish brown (initial colour) to blue black (final colour). o Iodine solution outside of the visking tubing remains yellowish brown. CANNOT WRITE NO CHANGE • Explanation: There is a net movement of Iodine molecules from a region of higher concentration outside the dialysis tubing to a region of lower concentration inside the tubing via diffusion, down a concentration gradient. Visking tubing containing starch solution

Sec3 G3 Science (Biology) Chapter 2 Notes 5 Prepared by Ms Pui LX Example 5 Factors affecting the speed of diffusion 1. State of particles Speed of diffusion slow medium fast • Having more energy allows the particles to spread diffuse out randomly at a higher speed. Without membrane • There is a net movement of red dye molecules from a region of higher concentration to a region of lower concentration via diffusion, down a concentration gradient until equilibrium is reached. Zxn n xn jkn jk

Sec3 G3 Science (Biology) Chapter 2 Notes 6 Prepared by Ms Pui LX 2. Difference in concentration Corner of the room [High concentration] [Low concentration] • The higher the difference in concentration, the faster the speed of diffusion. 3. Temperature of the particles • The higher the temperature, the more kinetic energy the particles have, hence they spread diffuse out randomly at higher speed.

Sec3 G3 Science (Biology) Chapter 2 Notes 7 Prepared by Ms Pui LX What is the importance of diffusion in animals and plants? 1. Gaseous exchange via diffusion in the lungs Movement of oxygen • When we breathe in, air enters the air sacs (alveoli) in our lungs. • Oxygen concentration thus becomes higher in the alveolus than in the blood within the blood vessel (capillary). • Oxygen thus enters the blood through diffusion, from the region of higher concentration within the alveolus to the region of lower concentration (blood capillary), down a concentration gradient. Movement of carbon dioxide • During respiration in the body cells, carbon dioxide is produced and released as waste. • Carbon dioxide is carried by the blood to the alveoli. • The carbon dioxide concentration is higher in the blood capillary than the alveoli. • Carbon dioxide molecules thus diffuse from the region of higher concentration in the blood capillary to the region of lower concentration in the alveoli, down the concentration gradient. • Carbon dioxide is then exhaled out from the lungs when we breathe out.

Sec3 G3 Science (Biology) Chapter 2 Notes 8 Prepared by Ms Pui LX 2. Gaseous exchange via diffusion in the plants during photosynthesis Movement of oxygen • During day time, plant s photosynthesize and release oxygen into the air spaces found in the leaves. • As a result, these air spaces have a higher concentration of oxygen than the outside atmosphere. • Oxygen molecules thus move from the region of higher concentration within the air space to the region of lower concentration in the atmosphere through the stomata, down a concentration gradient. Movement of carbon dioxide • During day time, plant photosynthesizes and uses carbon dioxide. • The air spaces within the leaves have a lower concentration of carbon dioxide than the outside atmosphere. • Carbon dioxide molecules thus move from the region of higher concentration in the atmosphere to the region of lower concentration in the air spaces through the stomata, down a concentration gradient.

Sec3 G3 Science (Biology) Chapter 2 Notes 9 Prepared by Ms Pui LX OSMOSIS Definition: Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential, down a water potential gradient, through a partially permeable membrane. Water potential High concentration of glucose Low concentration Low water potential 50% glucose (50% water) How osmosis occurs • Sucrose molecules are too large to pass through the partially permeable membrane • Water potential in B is higher than in A • Explanation: There is a net movement of water molecules from a region of higher water potential (B) to a region of lower water potential (A) via osmosis across the partially permeable membrane till equilibrium is reached. • There is a rise in level as solution in A as a result. Lower concentration of glucose