Diffusion, Osmosis, and Active Transport PDF

Diffusion, Osmosis, and Active Transport This document covers key concepts in cellular transport mechanisms, including diffusion, osmosis, and active transport. It explores how molecules move within and between cells, the factors that influence these processes, and their importance in biological sys...

Diffusion, Osmosis, and Active Transport This document covers key concepts in cellular transport mechanisms, including diffusion, osmosis, and active transport. It explores how molecules move within and between cells, the factors that influence these processes, and their importance in biological systems. Diffusion: Definition and Examples Diffusion is the net movement of molecules from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as result of their random motion. Ink in Water The molecules of dye in a drop of ink (solute) placed in a jar of water (solvent) will also move randomly through the water until the colour is evenly spread. Perfume in Air When the lid of a perfume bottle is taken off, perfume molecules (solute) move out and spread all over in the air (solvent). In above examples, solute molecules move from an area of high concentration to an area of low solute concentration. This process is called diffusion. A difference between solute concentrations is called a concentration gradient. Therefore, each substance moves down its concentration gradient. The energy for diffusion of these molecules come from the kinetic energy due to random movement of the molecules. Diffusion occurs until equilibrium is reached, that is when all the molecules have spread evenly. Diffusion Through Membranes (a) Diffusion results in the random dispersal of solute molecules throughout a solvent. If a membrane is present, that is permeable to both the solute and the solvent, it does not affect the pattern of diffusion. A partially permeable membrane such as a cell membrane (which allows the solvent molecules to pass through, but not the solute molecules) stops the solute from diffusing past the membrane. Diffusion also occurs in and out of a living cell. Diffusion is very important for obtaining nutrient molecules and removing wastes out from a cell and exhange of gases for respiration However molecules move through the partially permeable cell membrane of the cell either passively by diffusion and osmosis or actively by active transport. Examples of Diffusion in Biological Systems Gas Exchange in Human Lungs Absorption of Products of Digestion 1 2 There is higher concentration of oxygen in the air Carbohydrates, proteins and fats are digested using inside the alveolus but lower concentration in the enzymes and then small, soluble food molecules are blood capillary. So, oxygen moves down a absorbed into the bloodstream from the small concentration gradient, by diffusion from the alveolus intestine. Absorption of some of the digested food into the capillary and combines with haemoglobin molecules takes place by diffusion through epithelial then it is carried away inside the red blood cells all cells in villi into the blood capillaries. around the body. In the same manner carbon dioxide gas diffuses out of the blood where it is in higher concentration into alveolus where it is in lower concentration. Exchange of Food and Wastes Diffusion in Plants 3 Through Placenta 4 As CO₂ molecules get used up in photosynthesis, therewill a low concentration of CO in mesophyll cells than The surface of the placenta is highly folded to increase in airspaces. This creates a concentration gradient and the surface area. The food molecules move by so CO2 moves into the air spaces of leaf from air diffusion from the mother's blood to the developing outside through stomata by diffusion. The path taken fetus and the waste produced by fetus diffuse into by Carbon dioxide molecules is: Air--stomata--air pace mother's blood. in spongy mesophyll--mesophyll cell Factors Influencing Rate of Diffusion There are several factors that affect the rate of diffusion, Le, how fast or slow diffusion happen, such as temperature, distance, concentration gradient/concentration difference , surface area to volume ratio. Temperature Distance of Diffusion Concentration Gradient At lower temperature, the rate of As the distance/thickness of the Higher the concentration gradient diffusion is slower. and at higher barrier increases, diffusion rate higher the rate of diffusion and vice temperatures the rate of diffusion is becomes lower. This is why, the versa. This is because of more number faster, this occurs because the kinetic surfaces such as alveoli in the lungs, of molecules present in a energy of the molecules increases due epithelial cells in the villi, the wall concentrated environment, so a to heat energy. blood capillaries are all one cell think steeper gradient is present. and the cell wall of the root hair cell is also thin to increase the rate of diffusion. Surface Area: The larger the surface area, the higher the rate of diffusion. The extension of root hair cells, alveoli in lungs, villiand microvilli in intestines, and villi in placenta, all increase the surface area to volume ration, which increases the rate ofdiffusion. Osmosis: Definition and Types of Solutions Osmosis is the diffusion of water molecules from a region of high water potential (dilute solution) to a region of low water potential (concentrated solution), through a partially permeable membrane. Osmosis in a special kind of diffusion, involving water molecules. TYPES OF SOLUTIONS: A solution consists of solvent (liquid part) and solute (dissolved part). 1. Solutions with equal solute concentration are known as Isotonic solution. 2. A solution with greater solute concentration is known as Hypertonic solution. 3. A solution with lower solute concentration is known as Hypotonic solution. Effects of Osmosis in Animal and Plant Tissues EFFECTS OF OSMOSIS IN ANIMAL TISSUES If the animal cell such as an RBC is surrounded by a concentrated solution(hypertonic solution)water leaves the cell by osmosis, through partially permeable membrane, and the cell shrinks, shrivel and become crenated. If the animal cell such as an RBC is surrounded by a dilute solution or pure water(hypotonic solution) more and more water enter the cell by osmosis through partially permeable membrane and the cell swells up.After a while , it may get so big that it bursts. The content will escape and the cell dies. When the concentration of solutes in the cytoplasm of an animal cell is equal to the solution (isotonic solution) surrounding it, net osmosis will be zero. The importance of water potential and osmosis in animal tissues The fluid which bathes the cells in animals, such as tissue fluid or blood plasma always has the same water potential as the cell contents. This prevents any net flow of water into or out of the cells. If the bathing fluid has a higher water potential than the cells, water will move into the cells by osmosis causing them to swell up. As animal cells have no cell wall and the membrane has little strength, water would continue to enter and the cells will swell up, eventually burst, and die. EFFECTS OF OSMOSIS IN PLANT TISSUE 1. PLANT CELLS IN HYPOTONIC SOLUTION (FRESH WATER/DILUTE SOLUTION) In a hypotonic solution, water diffuses into the plant cell (endosmosis), the vacuole is filled to capacity, and the cell becomes turgid. The water entering the cell creates Turgor pressure, which pushes the plasma membrane against the inelastic cell wall. The cells of a well-watered plant are all turgid. This helps to keep the soft parts of a plant, such as its leaves and flower petals, firm and in shape. Turgidity helps to support the plant. 2. PLANT CELLS IN HYPERTONIC SOLUTION (MORE CONCENTRATED SOLUTION) In hypertonic solution, water diffuses out of the plant cell (exosmosis), the cell surface membrane pulls away from the cell wall, and the cytoplasm and vacuole get smaller. They stop exerting pressure on the cell wall. Instead of being firm and turgid, the cell becomes soft. It is said to be flaccid If water keeps on going out of the cell, and the cytoplasm keeps on shrinking, the cell surface membrane will eventually be pulled away from the cell wall. The cell is said to be plasmolysed and internal pressure is lost in plant cells, and the plant wilts. PLANT CELLS IN ISOTONIC SOLUTION: Plant cells behave in the same way as animal cells in an isotonic solution: they neither gain nor lose water. Water potential in and out is equal. So, no net movement of water molecules and no change in mass. Active Transport and Its Importance Active transport is defined as the movement of jons through the cell membrane, from region of lower concentration to a region of higher concentration against the concentration gradient, using energy released by respiration. Mechanism of active transport: There are special protein molecules, called carrier proteins/transport proteins, embedded in the cell membranes of the root hair cells.. Carrier proteins pick up nitrate ions from outside the cell, and then change shape in such a way that they push the nitrate ions through the cell membrane into the cytoplasm of the cell. Energy is needed to produce the shape change in the carrier protein.. This energy is provided by respiration inside the root hair cells and produces the energy-rich substance called ATP. Active transport allows a plant to take in mineral ions from the soil which explains why many mitochondria are found in the root hair cells. The membrane proteins are very specific. One protein that moves glucose will not move calcium ions. There are hundreds of types of membrane proteins in our cells. Presence of a respiratory poison will stop active transport so carrier proteins which need energy to move ions will stop functioning in the absence of energy from respiration. Importance of active transport in living things: 1. Absorption of mineral lons by root hairs. 2. in human small intestine, glucose and amino acids can be actively transported from the lumen of the intestine into the epithelial cells of the villi, if their concentration outside is low. 3. In kidneys dissolved glucose, amino acids and lons are actively reabsorbed back into the blood stream from the kidney tubules by active transport. 4. Movement of sucrose into companion cells in translocation occurs by active