2. Passive transport differs from active transport in that it always operates from regions of greater concentration to regions of lesser concentration. It also does not require external source of energy.
3. Examples include the simple diffusion of oxygen and carbon dioxide; osmosis of water, and the exchange of oxygen and carbon dioxide in the alveoli of the lungs is an example of facilitated diffusion.
4. Passive transport involves carriers, channels, or direct diffusion through a membrane.
Simple diffusion
1. Diffusion is the net movement of a substance (liquid or gas) from an area of higher concentration to one of lower concentration along the concentration gradient.
2. Diffusion is one principle method of movement of substances within cells, as well as the method for essential small molecules to cross the cell membrane
3. Gas exchange in gills and lungs operates by this process.
4. In the human body, waste products are removed from the bloodstream in the kidneys via dialysis, is an example of diffusion.
Osmosis: the diffusion of water
1. Osmosis is the diffusion of water across a semi-permeable membrane from a solution with a low solute concentration (high water concentration) to a solution with a higher solute concentration (low water concentration) until there is an equal concentration of fluid on both sides of the membrane.
2. The semi permeable membrane allows water molecules to pass through, but not the solutes molecules.
3. Examples of osmosis include the movement of water from one cell to another, absorption of water by root hairs and absorption of water in the alimentary canal- stomach, small intestine and colon.
Facilitated diffusion
1. Facilitated diffusion is the carrier-mediated transport of large molecules through the cell membrane using transport proteins embedded within the cell membrane.
2. These molecules would otherwise not be able to breach the cell membrane, but the transport proteins effectively "transport" them through.
3. Facilitated diffusion is assisted either by pore proteins or by carrier proteins, and direction of movement of the molecules involved is down the concentration gradient .
4. This process is still diffusion, so the concept of the molecules moving from a higher concentration (outside the cell) to a lower concentration (inside the cell) without utilizing any chemical energy still applies
5. Pore proteins open up pores or channels across the membrane to allow entry or exit. Each pore or channel is specific and will allow only particular type of ion to pass through.
6. Pores also can open or close, acting as gates, to cater to the needs of the cells..
7. Substances which pass through pores include charged ions such as Na+, Ca+, K+ and Cl-.
8. Carrier proteins allow larger polar molecules such as sugars and amino acid to pass through.
9. A specific protein attaches itself to the binding site of a carrier protein,t then the carrier protein changes shape and delivers the molecules across the plasma membrane.
10. Examples of facilitated diffusion include the absorption of amino acids, the absorption of glucose from blood into the cell.
Active transport
1. Active transport is the pumping of molecules or ions across a cell membrane against their concentration gradient.
2. The cell uses active transport in three situations: when a particle is going from low to high concentration (against concentration gradient), when particles need help to enter the membrane because they are selectively impermeable , and when very large particles enter and exit the cell.
3. Active transport requires the cell to spend energy, usually in the form of ATP. It can only take place in living organisms.
4. Sodium-potassium pump is a example of primary active transport. The concentration of sodium ions outside the cell is higher than the concentration of sodium ions inside the cell.The sodium-potassium pump transport sodium ions out of the cells and potassium ions into the cell.
5. Other examples of active transport include the absorption of dissolved mineral salts by root hairs, absorption of glucose and amino acids by cells in the small intestine and a single-cell alga Nitella, sp. collect and concentrate ions, minerals and nutrients in the cells (where those substances are low concentrations outside of the cells)
The Process of Passive Transport and Active Transport in Living Organisms.
***FAQ in SPM for Structure and Essays....
Gaseous Exchange in the Alveoli and Blood Capillaries by Simple Diffusion
All gases move across the alveolar wall according to the principle of simple diffusion: gas moves from areas of higher concentration to lower concentration.
In the alveoli, oxygen diffuse from the air where its partial pressure is high, into the blood capillary, where the partial pressure of oxygen is low.
The blood circulatory system takes the oxygen-rich blood away and replaces it with blood low in oxygen, but high in carbon dioxide.
Carbon dioxide diffuses out of the blood capillary, where its partial pressure is higher, into the air in the alveoli with the low partial pressure of carbon dioxide.
Absorption of Digested Food in the Villi
-The villus has the epithelial layer which allows the passage of digested food stuffs to the blood vessels & lacteal vessel in each villus.
-This layer has micro villi to help increase surface area of absorption.
-Sucrose, lactose, maltose and the glucose chains are broken down into monosaccharides: glucose, fructose and galactose, by enzymes on the microvilli of the small intestine.
-The sugars then cross the epithelium into the blood.
This is by active transport or facilitated diffusion. The sugars are too big for simple diffusion across the membrane.
-Fatty acids enter by diffusion. Amino acids are transferred into the epithelium by active transport coupled to sodium transport.
-Water soluble vitamins are absorbed by diffusion or facilitated diffusion.
-Water is the most abundant substance in chyme. Most water is reabsorbed in the wall of the small intestine, which is very permeable to water. Water follows solutes via osmosis.
-Sodium is the most abundant solute in chyme. It is absorbed using Na,K-ATPase pumps similarly to the renal tubules.
Absorption of Water in Root hairs of Plants by osmosis.
1. Osmosis is very important in root hair cells. Provided that the soil is moist, it is possible for water to enter the root hair by osmosis.
2. Water passes from a region of high water concentration (wet soil) through a semi-permeable membrane (the cell membrane) to a region of lower water concentration (the cytoplasm). This makes the cell turgid.
3. As these cells develop they absorb water by osmosis and the hair can be pushed between soil particles.
4. The root hairs increase the surface area between the root and the soil: this is necessary for the absorption of water and mineral salts-
Ion uptake by root hairs of a Plant through Active Transport
-Absorption of water and mineral salt take place mainly in the area of the root hair.
-Dissolved mineral salts are present in the soil water. Therefore the water surrounding each root hair is a dilute solution of mineral salts.
-The concentration of ions inside the root hair cell is normally greater than that in the soil solution.
-The uptake of mineral ions is therefore against the concentration gradient, as a result, require active transport.
-This is achieved by using special carrier protein which use ATP to provide energy to transport particular ions from the soil solution where they are in low concentration to the root hair cytoplasm and vacuole, where they are in higher concentration.
-There is occasion where a particular ion is in a greater concentration in the soil than in the root hair cell, the ion then simply moves into the cell by the passive process of diffusion.
SUMMARY:
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