Download Active and Passive Transport

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.
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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
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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.
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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.
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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 ?
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