When crystals of dye are placed in water, they are concentrated in one area.
Define diffusion and describe the role of diffusion in nutrients uptake and gaseous exchange in plants and humans. Define osmosis and describe the effects of osmosis on plant and animal tissues. Define active transport and discuss its importance as an energy-consuming process (Pure)
•Diffusion is the net movement of moleculesfrom a region of higher concentration to aregion of lower concentration, down aconcentration gradient.•The difference in concentrations of thesubstance between the two regions isknown as concentration gradient ordiffusion gradient.
Examples of diffusion: Carbon dioxide diffuses from blood capillary into alveoli and oxygen diffuses from alveoli into surrounding blood capillaries. The diffusion of carbon dioxide through the stomata into the mesophyll cells. The diffusion of water vapour from the leaves during transpiration.
Osmosis is …• the net movement of water molecules• from a region of higher water potential to a region of a lower water potential• through a partially permeable membrane• Involves only water molecules
Concentrations of Solutions Dilute solutions: - larger number of water molecules (solvent) compared to another similar solution. - dilute solutions have a higher water potential, compared to another similar solution. - Eg) 5% sugar solution means: 5% sugar molecules; 95% water molecules
Concentrated solutions: - smaller number of water molecules (solvent) compared to another similar solution. - concentrated solutions have a lower water potential, compared to another similar solution. - Eg) 10% sugar solution means: 10% sugar molecules; 90% water moleculesQUESTION:Compare between a 5% and 10% sugar solution.Which one has a higher water potential?
Osmosis Sugars such as starch molecules CANNOT pass through the partially permeable membrane (Too big) However, sugar such as glucose CAN pass through the partially permeable membrane (Small enough)
Partially permeable membraneHigher water Lower waterpotential potential
Another example of osmosis5% sucrose solution 10% sucrose solution Point A Point B Partially permeable membrane
Demonstrations of OsmosisQuestion:What will happen to the water level in glasstube?
The surroundingsolution has ahigher waterpotential than thesolution in thevisking tubing. Increase. Water enters the visking tubing by osmosis. The Visking tubing swells and becomes firm and turgid.
Surroundingsolution has alower waterpotential than thesolution in thevisking tubing. Decrease. Water leaves the visking tubing by osmosis. The Visking tubing shrinks and becomes soft and flaccid.
The surroundingsolution has thesame waterpotential as thesolution in thevisking tubing. Water level and Visking tubing remain unchanged. No net movement of water molecules into and out of the visking tubing.
MicroQues 1Describe the changes that took place in thewater levels of the solution in the glass tube andbeaker.
MicroQues 1Dilute solution= high ____water potentialConcentrated solution low= ____ water potential Decrease. Water leaves the Visking tubing by osmosis. The Visking tubing shrinks and becomes soft.
MicroQues 2(a)State the similarities between osmosis and diffusion.Both involves movement of substances.Both involves movement of substances from aregion of its higher concentration to a region oflower concentration.Bothinvolves movement of substances down aconcentration gradient.
MicroQues 2(B)State two differences between osmosis and diffusion.
Diffusion Osmosis How are they alike? Both involve the movement of molecules from a region of their higher concentration to a region of their lower concentration How are they different?1. Involves movement 1. Involves movement of of all types of only water molecules molecules. 2. Involve the movement2. Do not involve a of water molecules partially permeable passing through a membrane partially permeable membrane
Quiz Time1. Which of the following processes causes juice the chilli to curl outwards?a. Diffusionb. Transpirationc. Osmosisd. PlasmolysisWatch video: Chilli bloom practical
Quiz Time2. How could a lettuce, which has just wilted, be made firm and crispy again?a. Submerge in waterb. Submerge in a 20% sugar solutionc. Submerge in a 30% sugar solutiond. Submerge in a 50% salt solution
The cell membrane of living cells are partially permeable. The cell wall, however, is non-living, tough and fully permeable. In a plant cell, the vacuole membrane (tonoplast) is also partially permeable. The cell sap in the large central vacuole of a plant cell is highly concentrated (low water potential) as it contains a complex mixture of substances.
Cells in a Solution with High Water Potential Water enters the cell by osmosis. Plant cell Vacuole increases in size. Plant cell becomes firm and turgid. Animal cell Animal cell swells and may burst. Why?
Why animal cell will burst? Due to the absence of a cell wall. Cell wall is strong and relatively inelastic.
Cells in a Solution with Low Water PotentialWater leaves the cell by osmosis. Plant cell Vacuole decreases in size and cell becomes soft and flaccid. Cytoplasm shrinks away from cellulose cell wall, through a process known as plasmolysis. Watch animation: Plant cell when placed in low/high water potential
Cells in a Solution with Low Water Potential Animal cell The animal cell shrinks. Little spikes appear on the plasma membrane. This process is called crenation.Watch animation: Animal cell when placed in low/high water potential
Importance of turgor pressurein plants• Help maintain shape of soft tissues in plants, especially young stems and leaves• Changes in movement of plants due to turgor• Plasmolysed leaves are flaccid and the cells can die
MicroQues 3Four plant cells were placed in 20% sucrosesolution, 50% sucrose solution, 80% sucrosesolution and pure water separately.In the table below,(a) describe the appearance of the plant cells.(b) identify the solution that the cells have beenplaced in.
MicroQues 3Cell become No change. Cell become Cell becometurgid. flaccid. plasmolysed.Pure water 20% sucrose 50% sucrose 80% sucrose
Question What happens to animal and plant cells when placed in solutions with differing water potentials?
Active Transport (PURE) Requires energy When substances move from a region of lower concentration to a region of higher concentration against a concentration gradient Occurs only in living cells as only living cells respire Respiration will release energy where part of it will be used in active transport
Active transport is the process in which particles move from a region of low concentration to a region of highconcentration, against the concentration gradient, with the use of energy.
Examples of active transport: The absorption of mineral salts from the surrounding soil solution by root hair cells. The absorption of glucose and amino acids by the epithelium cells in the small intestines of man, when they are low in concentration.
Micro Ques 4Which of the following diagram illustrates the most likelyappearance of a red blood cell that has been placed indistilled water? ( D )
Micro Ques 5A strip of potato, originally 50 mm in length, was measuredafter it was soaked in distilled water. Which of the followinggraphs A, B, C or D best represents the results? length of potato strips/mm ( A )
Micro Ques 6 The apparatus shown in the diagram was set up. After one hour, the water in the beaker turned red. What is the most likely reason for this colour change?A Molecules of red ink move through the membrane by diffusion.B Molecules of red ink move through the membrane by osmosis.C Molecules of water move through the membrane by diffusion.D Molecules of water move through the membrane by osmosis. ( A )