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Transcript
ACTIVE AND PASSIVE TRANSPORT Dear Reader An organism or cell is said to be living as it shows different kinds of movements. Movement can be at the molecular level too. Movement of molecules, circulation of materials and translocation of water and nutrients is governed by different means of transport, namely, active and passive. Passive Transport Movement of molecules along the concentration gradient, without expenditure of energy. The process may or may not require membrane proteins. Passive Transport includes: Diffusion Facilitated Diffusion Osmosis Ion Channels Active Transport Movement of molecules against the concentration gradient, with expenditure of energy. The process involves membrane proteins. Active Transport includes: Sodium Potassium Pump Proton Pump Passive Transport Diffusion- the movement of molecules, from a region of high concentration to a region of low concentration e.g. diffusion of gases across the membrane in Amoeba, diffusion of gases in plants. 232 Figure 1: Diffusion Osmosis- movement of water from a region of its high concentration to a region of its low concentration, across a semi-permeable membrane, e.g. movement of water into the cell, upon placing it in a hypotonic solution (endosmosis). Semi-permeable Membrane Figure 2: Osmosis 233 Facilitated Diffusion- the movement of molecules, from a region of its high concentration to a region of its low concentration, through membrane proteins, e,g. movement of fructose across the membrane, via the membrane protein. Ion Channels- Specific membrane proteins (ion channels) allow movement of particular ions e.g. Na+ channels in nerve fibre, water channels. IONS Figure 3: Ion Channel Active Transport Sodium-Potassium Pump- a membrane protein that plays a role in transporting 3 Na+ outside and 2 K+ inside as in axon, while utilizing ATP. https://sp.yimg.com/xj/th?id=OIP.Mf69dc0c6bdeb6cbb5fb11e057650443co0&pid=15.1 &P=0&w=288&h=163 Proton Pump- during photosynthesis, a proton gradient is established due to the passage of protons into the thylakoid (of chloroplast) using proton pump Absorption of digested products is carried out by both passive and active mechanisms e.g. amino acids are initially absorbed by facilitated diffusion and then, also by active transport when their concentration is low in the small intestine. 234 Reabsorption by renal tubules of the kidney is either by active or passive mechanisms e.g. glucose and Na+ are reabsorbed actively, whereas Urea is absorbed passively. Passive Transport Active Transport Figure 4: Absorption and Reabsorption through Active and Passive Transport DO IT YOURSELF 1. Make a table to compare active and passive transport. 2. (i) What are K+ channels ? (ii) Aquaporins is the term used for denoting ---------------------- . (ion channels/ proton channels/ water channels) 3. You are familiar with the term osmosis. What is reverse osmosis ? Do you have any equipment at home that works on the principle of reverse osmosis ? Name it. 4. Suggest an experiment that would demonstrate exosmosis. 5. In the given diagram, several trans-membrane proteins are shown. Which kinds of transport are possible across these proteins ? 235 236