School Science Lessons
2024-01-03
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(UNBiol7.html)
Plant Physiology
Table of contents
9.1.0 Colloids, diffusion
9.2.0 Osmosis
9.3.0 Plasmolysis
9.4.0 Tests for reducing sugars, Benedict's test
9.5.0 Tests for reducing sugars, Fehling's test
9.6.0 Vitamins
9.1.0 Colloids, diffusion
See: Diffusion (Commercial).
7.8.0 Colloids and crystalloids
Experiments
9.1.1 Cellophane as a semipermeable membrane
9.1.2 Copper ferrocyanide as a semipermeable membrane
9.1.3 Colloidal nature of egg white
9.1.4 Colloidal solution of starch
9.1.5 Diffusion through a colloidal gel
9.1.6 Diffusion with copper (II) sulfate solution
9.1.7 Measure osmosis
9.1.8 Prussian blue as a semipermeable membrane
9.1.9 Sausage skin as a semipermeable membrane
9.1.10 Separate a colloid from a crystalloid by dialysis
9.2.0 Osmosis, osmotic pressure, reverse osmosis
See: Osmosis (Commercial).
9.2.1 Osmosis and osmotic pressure, reverse osmosis
Experiments
24.1.06 Morse equation, osmotic pressure equation
9.2.2 Imbibition in seeds and dried fruit, broad bean, pea, bean
9.2.3 Osmometer, carrot or potato osmometer
9.2.4 Osmosis with a carrot
9.2.5 Osmosis with a chicken egg
9.2.6 Osmosis with dialysis tubing
9.2.7 Osmosis with honey on bread
9.216 Osmotic behaviour of red blood cells
9.2.8 Osmotic pressure and suction potential in dandelion
9.2.10 Turgor pressure in a potato
9.3.0 Plasmolysis
Experiments
9.3.1 Effect of different temperatures on the cell membranes of beetroot
9.3.2 Effects of factors of environmental stress on the cell membranes of beetroot
9.3.3 Plasmolysis in beetroot
9.3.4 Plasmolysis in Elodea
9.3.5 Plasmolysis in hairs on the stamens of spiderwort, Tradescantia
9.3.6 Plasmolysis in onion epidermis
9.3.7 Plasmolysis in Spirogyra
9.3.8 Suction potential and tissue tension in celery
9.4.0 Tests for reducing sugars, Benedict's test
Benedict's solution (test: diabetes, reducing sugars), Local Purchase
Reducing sugars: glucose, fructose, glyceraldehyde, lactose, arabinose, (C5H10O5), turanose (C12H22O11), maltose
Non-reducing sugars: Sucrose, trehalose (diglucose)
A reducing sugar acts as a reducing agent by giving electrons to other molecules.
Reducing sugars are monosaccharides or disaccharides with a free ketone group, -CO-, e.g. fructose, or, a free aldehyde group, -CHO, e.g. glucose.
So fructose is a ketose or ketohexose and glucose is an aldose or aldohexose.
Reducing sugars use a citrate ion-Cu2+ complex.
Nowadays, Benedict's test is used instead of Fehling's tests for detecting reducing sugars.
Oxidation of aldose sugars: RCH=O + 2Cu2+ (blue solution) + 5OH- --> R(C=O)O- + Cu2O (red precipitate) + 3H2O.
9.4.1 Benedict's test for reducing sugars
9.4.2 Prepare Benedict's solution
3.10.0 Poisons and First Aid (Table), (See: Benedict's solution)
9.4.3 Tests for reducing sugars in urine, Benedict's solution
9.6.0 Vitamins
Originally "vitamine", (Latin vita life), but no vitamin contains an amine, e.g. methylamine, CH3.NH2.
9.6.1 Vitamin A
9.6.2 Vitamin B
9.6.2a Thiazole
9.6.3 Vitamin C
9.6.4 Vitamin D
9.6.5 Vitamin E
9.6.6 Antioxidants, vitamin E
9.6.7 Free radicals and antioxidants
9.1.1 Cellophane as a semipermeable membrane
See: Cellophane.
1. Mix cornstarch with water then test a sample of it with drops of iodine solution.
The cornstarch turns dark blue.
Put the sample aside and put the rest of the cornstarch in a cellophane bag.
Wash outside the bag under the tap.
Half fill a beaker with water and add drops of iodine solution or tincture of iodine.
Suspend the cellophane bag containing cornstarch solution in the iodine solution.
The cornstarch in the cellophane bag starts to turn blue showing that iodine solution is moving through the wall of the cellophane bag.
However, the iodine solution in the beaker does not change colour, because the cornstarch cannot pass through the walls of the cellophane bag.
The cellophane is semipermeable.
It is permeable to the iodine solution. but not permeable to the cornstarch solution.
2. Tie a piece of cellophane over the mouth of a funnel.
Invert the funnel and partly fill it with a concentrated sugar solution coloured with red ink.
Tie tightly the string around the funnel and cellophane so that no leaks occur.
Place the funnel with its mouth in a beaker of water and clamp it to a stand.
Set the apparatus aside and note the rising level of the sugar solution in the stem of a funnel.
Note the decrease in the red colour as the level of sugar solution in the stem of the funnel rises.
Note the height when the level of the sugar solution stops rising.
This height gives a measure of the difference in concentration of the two solutions.
Repeat the experiment with sugar solution in the beaker and water in the funnel.
The water level now falls in the funnel.
In osmosis, the net movement of water is from the weaker solution to the stronger solution until both solutions are isotonic.
The result is to dilute the more concentrated solution.
3. Pour molasses or "golden syrup" on the centre of a square piece of cellophane.
Lift the corners of the cellophane then tie a string around the cellophane above the molasses to make a "pudding".
Hang the pudding in water, keeping where it is tied above the surface of the water.
The "pudding" swells as water enters by osmosis.
9.1.2 Copper ferrocyanide as a semipermeable membrane
Drop a concentrated solution of potassium ferrocyanide into dilute copper (II) sulfate solution.
A layer of copper ferrocyanide will surround the drop formed.
The drop sinks. but later rises, because of osmosis causing alteration in density.
2CuSO4 + K4Fe(CN)6 --> 2K2SO4 + CU2Fe(CN)6
2Cu2+ + Fe(CN)64- --> Cu2Fe(CN)6 (s)
9.1.3 Colloidal nature of egg white
Note the irreversible coagulation of egg white by warming some egg white in a test-tube placed in boiling water.
Examine the reversible precipitation of a colloid, with egg white.
The colloidal nature of egg white is due chiefly to the presence of the protein albumen.
Mix the white of an egg with 100 mL of water.
Filter with a filter pump.
To about half the clear solution add powdered ammonium sulfate while continuously shaking.
As the sulfate approaches saturation, the albumen will precipitate as a white curd.
Then shake this liquid with about the same volume of water and note that the precipitated albumen re-enters the colloidal solution.
9.1.4 Colloidal solution of starch
Shake 2 g of starch with a little cold water in a test-tube until it forms a paste.
Boil 100 mL of water in a beaker, and while the water is boiling, slowly pour the paste from the test-tube, drop by drop, into it.
After cooling, note that this colloidal solution is opaque.
Test the solution for starch by adding a few drops of iodine solution.
9.1.5 Diffusion through a colloidal gel
See: Diffusion (Commercial).
1. Make a 10% solution of gelatine by warming in water and add a few drops of phenolphthalein solution.
Be careful! Phenolphthalein may cause eye, skin and respiratory irritation.
Use safety glasses and insulated heat-proof gloves and work in a fume cupboard, fume hood.
Fill a wide test-tube, with a stopper at one end, with the warm solution and leave to cool.
When it has set, invert the test-tube over a 10% solution of caustic soda.
A reddening of the gelatine will show the upward diffusion of the alkali through the colloidal gel.
2. Note how gelatine absorbs dye.
Cut three rectangles of exactly equal dimensions from sheet gelatine.
Let one rectangle remain dry as a control.
Place a second rectangle in water.
Note that its dimensions increase, because of the imbibition of water.
Measure its final area and compare it with the control.
Place the third rectangle in a very dilute aqueous solution of methylene blue.
A progressive staining of the gelatine accompanies the swelling.
Eventually the gelatine adsorbs practically all the dye from the solution.
Imbibition is the absorption of fluid by a solid.
9.1.6 Diffusion with copper (II) sulfate solution
See: Diffusion (Commercial).
Put 75 mL of water in a 100 mL beaker.
Using a graduated pipette, put 10 mL of copper (II) sulfate solution under the water layer.
Mark the boundary between the two liquids with a grease pencil.
Leave the beaker to stand in a place free from vibrations.
During the following days, the boundary between the demineralized water and the saturated copper (II) sulfate solution becomes more indistinct and moves upwards.
After three weeks, the liquid in the beaker appears uniformly coloured.
Compared with the original saturated solution the colour is less intense.
At first, the lower layer of saturated copper (II) sulfate solution is sharply separated from the demineralized water above it, because of its greater density.
However, because of the individual movement of the molecules of both layers, the initial marked difference in concentration at the boundary becomes diffuse, because of mixing of a sequence of layers of lower concentration.
The result is equalization of concentration.
9.1.7 Measure osmosis
See: Osmosis (Commercial).
See diagram 9.171: Measure osmosis.
Diffusion occurs when two substances flow into each other until both substances are completely mixed.
Osmosis occurs when a semipermeable membrane separating a water and sugar solution allows only water molecules to diffuse through it and so decrease the concentration of the sugar solution.
One mole of a non-electrolyte dissolved in water and made up to 22.4L of solution causes an osmotic pressure, at 0oC of 760 mm of mercury (1 atmosphere).
The cell membrane inside the cell wall of plant cells allows water to diffuse in when the cell is surrounded by a lower concentration solution.
The cell swells with the absorbed water and develops an extra pressure, called turgor pressure.
However, if the cell is surrounded by a higher concentration solution, water diffuses out of the cell, and the protoplasm shrinks away from the cell wall.
This process is called plasmolysis.
9.1.8 Prussian blue as a semipermeable membrane
Put a solution of 0.5 g in 1 litre of potassium ferrocyanide in an evaporating basin and add a lump of solid iron (III) chloride.
A semipermeable membrane layer of Prussian blue forms at the surface of the concentrated solution of iron (III) chloride.
Then water passes from the dilute potassium ferrocyanide solution through the semipermeable membrane and the layer of Prussian blue swells.
9.1.9 Sausage skin as a semipermeable membrane
Immerse a specimen tube in a concentrated solution of cane sugar or common salt.
Work under the solution to avoid air bubbles.
Fix sausage skin across the mouth of the specimen tube and secure with wire.
Wash outside the specimen tube and sausage skin membrane under the tap to remove any concentrated solution.
Immerse the filled specimen tube in tap water.
The sausage skin membrane stretches outwards as water moves through it into the concentrated solution.
9.1.10 Separate a colloid from a crystalloid by dialysis
See: Dialysis tubing, (Commercial).
Dialysis is the use of a semipermeable membrane to separate a colloidal solution from a true solution, i.e. separating small molecules from large molecules.
A Soxhlet thimble is a filter made usually of cellulose or thick paper.
It looks like a white test-tube.
Collodion, cellulose tetranitrate, is made by dissolving nitrocellulose (gun cotton, nitrate movie film) in acetone.
It was used in medicine to cover wounds and with salicylic acid as a wart remover.
Also, it was used in wet plate photography.
1. Dip a finger in collodion, wave it in the air until the collodion dries, then pull off your dialyser thimble.
Wash the dialyser with tap water.
Add sodium chloride solution to a 2% colloidal solution of gelatine to produce a mixture of a colloidal solution and true solution.
Put the mixture in the dialyser.
Put the dialyser in a beaker of water so that the level of water in the beaker and in the dialyser are the same.
After one day, test the liquid in the dialyser with tannic acid that precipitates gelatine out of solution.
2. Test the liquid in the beaker with silver nitrate solution that reacts with sodium chloride to produce a white precipitate of silver chloride.
The crystalloid sodium chloride passes through the membrane. but the colloid collodion does not.
An artificial kidney works in the same way.
Be careful!
Silver nitrate is poisonous if swallowed or inhaled and leaves silver to black stains on the skin that cannot be removed with soap and water.
Students should not do the silver nitrate test.
Repeat the experiment with a colloidal solution of starch.
Test the liquid in the dialyser with the iodine tests for starch.
3. Make a dialyser by soaking a Soxhlet thimble in a 5% solution of collodion in glacial acetic acid.
Alternatively, you can try making a dialyser by dipping your finger in collodion then waving you finger in the air.
Wash the dialyser with tap water.
Add sodium chloride solution to a 2% colloidal solution of gelatine to produce a mixture of a colloidal solution and true solution.
Put the mixture in the dialyser.
Put the dialyser in a beaker of water with the water level with the mixture in the dialyser.
After one day test the liquids.
Test the liquid in the dialyser with tannic acid that precipitates gelatine out of solution.
Test the liquid in the beaker with silver nitrate solution that reacts with sodium chloride to produce a white precipitate of silver chloride.
The crystalloid sodium chloride passes through the membrane. but the colloid collodion does not.
An artificial kidney works in the same way.
Repeat the experiment with a colloidal solution of starch.
Test the liquid in the dialyser with the iodine tests for starch.
9.2.1 Osmosis and osmotic pressure, reverse osmosis
See: Reverse Osmosis (Commercial).
See 24.1.06 Morse equation, osmotic pressure equation.
See diagram 9.164: Osmosis.
Osmosis is a modification of diffusion, namely the penetration of liquids and solutions through a porous membrane.
Some membranes that are permeable to one type of liquid or solution, are partially or completely impermeable to other liquids or solutions.
Such membranes are called semipermeable membranes.
Reverse osmosis membrane elements are used in a variety of applications, desalination of seawater and brackish water to produce pure water, treatment and recycling of effluent for the recovery of valuable process materials and the concentration of foodstuffs, e.g. milk.
Osmosis is the process by which a solvent passes through a semipermeable membrane from a region of lesser solute concentration into a region of greater solute concentration until the concentrations are equal.
Osmotic pressure is the pressure that must be applied to a solution to keep it in equilibrium with the pure solvent separated only by a semipermeable membrane.
If a container is separated by two parts A and B by a semipermeable membrane, e.g. a bladder or film of copper ferrocyanide.
A containing water and B containing a substance dissolved in water.
Water molecules pass through the semipermeable membrane from A into B to dilute the solution in it.
The osmotic pressure of the solution is the pressure that must be applied to it to prevent water entering it by osmosis.
If the solutions A and B originally had the same level in the container and osmosis ceased when the level of the solution in B had risen to h cm the original osmotic pressure of B was:
[h X density of solution X g (gravity acceleration)].
The osmotic pressure obeys the gas laws so osmotic pressure increases proportionally to the absolute temperature.
Osmotic pressure depends on the number of particles so when a solute dissociates in solution the osmotic pressure increases.
The approximate value of the osmotic pressure, Π (capital pi) of a dilute solution (atmosphere or bar) can calculated from the Morse equation (osmotic pressure equation).
Isotonic solutions have the same osmotic pressure, at the same temperature they contain the same number of particles of the solute per litre if they are neither dissociated or nor coagulated.
If a solution is more concentrated than another solution, it is the hypertonic solution and if less concentrated than another solution, it is the hypotonic solution.
Reverse osmosis uses pressure to drive solutes out of a solution through a semipermeable membrane by applying pressure to the solution, e.g. desalination of seawater, concentration of milk.
9.2.2 Imbibition in seeds and dried fruit, broad bean, pea, bean
1. Measure the displacement of dry broad bean or pea seeds with a measuring cylinder partly filled with water.
Put the seeds in moist sawdust for two days and then again measure their displacement.
Estimate the percentage increase in volume, because of the imbibition of water.
2. Put sultanas, grains, dried apricots in pure water and leave them for some time.
Then place them into a concentrated solution of sugar or salt.
Each gains water and swells when placed in pure water, then shrinks in the concentrated solution.
9.2.3 Osmometer, carrot or potato osmometer
See: Osmosis (Commercial).
See diagram 9.3.47: Osmosis with a carrot.
Prepare a one-hole stopper with a long glass tube inserted through the hole, 2 cm below the stopper and 20 cm or more above the stopper.
Be careful when inserting the stopper!
Cut a hole in the side of a large carrot, or potato, the same diameter as the middle of the one-hole stopper.
Insert a spoon or knife into the hole to make the carrot hollow.
Fill the carrot with concentrated sucrose solution, containing drops of ink, by pouring through the hole.
Put some petroleum jelly on the rim of the hole.
Insert the stopper with the glass tube into the hole of the carrot.
It must fit tightly.
By moving the glass tube through the stopper you can adjust the height of the coloured sugar solution in the tube.
Fill any gap between the carrot and the stopper with hot candle wax.
Hold the carrot in a tall beaker.
Pour water into the beaker to submerge the carrot and a short length of the glass tube.
Clamp the carrot upright without squeezing it.
Record the height of the coloured sugar solution in the glass tube and note the depth of the ink colour.
Also, record the height of the water in the beaker.
Later, record the heights again and note depth of colour in the glass tube.
Water penetrates the wall of the carrot to dilute the colour of the sugar solution that rises in the tube.
The level of water in the beaker falls.
9.2.4 Osmosis with a carrot
See: Osmosis (Commercial).
See diagram 9.3.47: Osmosis with a carrot.
1. Select a carrot that has a large top and is free of breaks in its surface.
In the centre of the carrot, cut a 5 cm deep round hole with a cork borer so that the diameter is the same as a one-hole stopper fitted with a length of glass tubing.
Add ink to a concentrated sugar solution in a beaker and note the resulting colour of the solution.
Fill the hole with the concentrated sugar solution coloured with red ink.
Fit the one-hole stopper into the entrance of the hole.
Put the carrot in a tall beaker of water.
Seal around the stopper with wax from a burning candle.
Be careful! Melted wax can cause skin burns so wear safety glasses and insulated heat-proof gloves.
Move the glass tube through the stopper to adjust the height of the coloured sugar solution in the tube.
Observe the coloured sugar solution rising inside the glass tubing.
Record the height and note any change in the colour of the coloured sugar solution.
2. Repeat the experiment using a potato.
3. Use a carrot or potato that has been stored for a long time.
Squeeze the carrot and notice the limp feel.
Put the carrot in water and squeeze again later.
The carrot now feels firm, because water has entered its cells, because of osmosis.
9.2.5 Osmosis with a chicken egg
See: Osmosis (Commercial).
See diagram 50.6.10: Parts of a chicken egg.
1. Cover a fresh egg, or hard-boiled egg, in dilute (10%) hydrochloric acid or white vinegar (about 10% acetic acid in water).
The egg shell is mainly calcium carbonate, with some magnesium carbonate, calcium phosphate and organic matter.
Note any bubbles from the eggshell.
A film may develop on the surface of the vinegar.
Place the beaker containing the egg and vinegar overnight in a refrigerator.
The next day, replace the vinegar and leave the egg and vinegar in the refrigerator for up to seven days.
Use a tablespoon to remove the egg carefully that has now lost the eggshell.
Feel the rubber-like surface of the egg, now covered with the double shell membranes, by plucking it with the fingers.
The size of the egg has increased, because of the movement of water in the vinegar through the double shell membranes.
2. Weigh the egg with no shell membranes, measure the diameter and then observe the osmotic properties of the double shell membranes by putting it in the following solutions:
2.1 Water, dilute fountain pen blue ink
The egg swells, because by endosmosis.
Water passes in through the double shell membranes.
Some dye from the ink may pass through the double shell membranes.
2.2 Concentrated salt solution, molasses, honey, corn syrup
The egg shrinks, because of exosmosis.
Water passes out through the double shell membranes.
A thin layer of water may be seen on the molasses.
After one day in the hypertonic or hypotonic solutions the change in volume is not easy to observe.
However, the change is more obvious with a very small egg, e.g. a quail's egg.
After a few days the egg will harden again as a new eggshell is formed using the carbon dioxide in the air.
2.3 Equation
2CH3COOH + CaCO3 --> Ca(CH3COO)2 + H2O + CO2
acetic acid + calcium carbonate --> calcium acetate + water + carbon dioxide (the bubbles seen on the eggshell).
3. Recipe for pickled eggs
Place eggs in a saucepan and cover with cold water.
Bring water to the boil and immediately remove from heat.
Cover and let eggs stand in hot water for 10 to 12 minutes.
Remove from hot water, cool and peel.
In a medium saucepan over medium heat, mix together the vinegar, water and pickling spice.
Bring to the boil and mix in the garlic and bay leaf.
Remove from heat.
Transfer the eggs to sterilized containers.
Fill the containers with the hot vinegar mixture, seal and refrigerate 8 to 10 days before serving.
9.2.6 Osmosis with dialysis tubing
See: Dialysis tubing (Modern Teaching Aids).
See diagram 9.36.12: Osmosis with dialysis tubing.
1. An osmometer measures osmotic pressure.
Tie a length of dialysis tubing filled with a sugar solution to a capillary tube and note the rise in the level of the sugar solution.
However, in this osmometer, achieving a watertight junction between the dialysis tubing and the capillary tube is difficult, because the thread is not elastic and the wall of the glass capillary tube is slippery.
Note any small initial rise in the level of sugar solution in the capillary tube followed by a steady drop.
Leakage at the junction usually causes this drop when enough hydrostatic pressure has built up in the liquid column.
2. Make a watertight junction between the dialysis tubing and the glass tubing using a polypropylene connector with a wide end of bore diameter 10 mm and a narrow tapered end of bore diameter 5 mm
(or fix the dialysis tubing to the T-shape connector with a rubber band, taking care not to trap air bubbles in the dialysis tubing when filling with the sugar solution).
Tie a knot tightly at one end of a length of soaked dialysis tubing about 16 cm long.
Fix the other end of the dialysis tubing to the wide end of a polypropylene connector by winding a rubber band tightly around it to form a watertight junction.
Fill the dialysis tubing with a sugar solution.
Join the tapered end of the polypropylene connector to a T-shape connector with rubber tubing.
Join the other two ends of the T-shape connector to a 10 mL syringe filled with the sugar solution and to a calibrated 1 cm3 pipette.
Rinse the outer wall of the dialysis tubing with water to remove any trace of sugar solution.
Immerse the dialysis tubing into a beaker of water.
Move the plunger of the syringe to adjust the position of the meniscus of the sugar solution in the pipette to a suitable position.
Start taking measurements.
When the meniscus reaches the top of the pipette, move it to the starting position by adjusting the plunger to make more measurements.
Add a few drops of Congo red (blue in acid and red in alkali) to the sugar solution to see the liquid column in the pipette.
Congo red may be harmful if swallowed or inhaled so use amyloid red dye as a safer substitute.
3. Investigate the following:
3.1 The effect of temperature or solute concentration on the initial rate of osmosis of a sugar solution.
3.2 Compare the initial rates of osmosis of different solutions, starch, sucrose and glucose solutions.
9.2.7 Osmosis with honey on bread
Spread honey on a flat slice of bread. but do not use any butter.
Pick up the slice of bread by holding the opposite crusts and hold the slice horizontally.
The middle of the slice dips down.
The concentrated sugar solutions in honey have attracted moisture out of the side of the bread next to the honey bread by osmosis that shrinks causing the concave bowing of the slice of bread.
9.2.8 Osmotic pressure and suction potential in dandelion
See diagram 9.36.11: Circular strips of dandelion in sucrose solutions.
Cut the stalk into circular segments.
Then make a vertical cut through one side of each segment to form circular strips.
After you make the vertical cut, each strip curves outwards, because of the expansion of the stalk cells.
Put the strips in demineralized water.
The stalk cells can still absorb water so the strip curves more outwards.
If the stalk cells had no suction potential they could not absorb water and no change in curvature would occur.
If the cells lost water the curvature of the strip would be reduced and eventually the strip would become straight.
Put a circular strip in each of the following concentrations of sucrose: 0.3M, 0.4 M, 0.5 M, 0.6 M, 0.7 M.
The concentration that causes no change in the curvature of the strip is equal to the suction potential of the cells of the strip.
A lower concentration causes more curvature and the circle becomes a spiral, at 0.3M and 0.4 M.
A higher concentration causes an opening out of the circle, at 0.6 M, 0.7 M.
So the suction potential is equivalent to a 0.5 M solution of sucrose where no change of curvature occurs.
9.2.10 Turgor pressure in a potato
1. Make a potato thimble by peeling the potato then scooping out the inside.
Half fill the potato thimble with 10% sugar solution.
Suspend the filled potato thimble in a beaker of pure water.
Note the rise in level of the sugar solution in the potato thimble.
>2. Cut 3 mm thick slices from a potato tuber.
Bend the slices between the fingers to test their comparative firmness.
The cells are full of water and thus turgid.
Put the slices in a 3% solution of common salt and leave for about half an hour.
Again bend the slices between the fingers to test their comparative firmness.
The slices become flabby.
Put the slices in demineralized water and leave for half an hour.
Again bend the slices between the fingers to test their comparative firmness.
The cells regain their firm texture.
If a slice of potato is put in a solution that is hypertonic to the cytoplasm, the size of the cells will decrease slightly and the slice of potato will feel soft.
3. Prepare 30 identical thickness and area slices of potato or cut discs from a 3 cm thick slice with a large cork borer.
Dry the slices or discs with absorbent paper and weigh them.
Half fill test-tubes with 20%, 15%, 10%, 7.5%, 5%, and 0% sucrose solutions.
Put a potato slice or disc into each test-tube with just enough sucrose solution to cover the strip and take them out after 40 minutes.
Dry the slices or discs with absorbent paper and weigh them.
Plot a graph of final weight divided by initial weight against percentage of sucrose solution.
From the graph, note which sucrose concentration is isotonic with the potato cell contents.
If sucrose is the only osmotically active material in the cell, determine the sucrose concentration of the cytoplasm.
A 1 molar sucrose solution contains 342 g of sucrose in 1000 mL of solution, equivalent to 25.69 atmospheres.
A 0.1 molar solution is 34.2%, so if the isotonic solution is 5%, then the turgor pressure will be 5 divided by 34.2 of the osmotic pressure of the 1 molar solution.
9.3.1 Effect of different temperatures on the cell membranes of beetroot
Each beetroot cell has a large central vacuole bounded by a membrane.
The vacuole contains the red pigment anthocyanin, which gives the beetroot its typical colour.
The whole beetroot cell is also surrounded by the cell membrane.
If the two membranes remain intact, the anthocyanin cannot escape into the surrounding environment.
If the membranes are stressed or damaged, the red colour can leak out.
The cell wall surrounding plant cells provides a plant structure, but it does not control movement of substances into and out of cells.
1. Put slices of 40 beetroot in a 100 mL beaker of water.
2. Label eight test-tubes -5, 5, 30, 40, 50, 60, 70, 80, for oC.
3. Check the temperatures in a refrigerator and its freezer, probably 5oC and -5oC.
Put five beetroot slices in the -5oC test-tube, place it in a freezer for 30 minutes, then 10 mL of tap water and leave to stand.
Put five beetroot slices in the 5oC test-tube, place it in a refrigerator for 30 minutes, then add 10 mL of tap water and leave to stand.
Put five beetroot slices in the other test-tubes and just cover the slices with water at 30, 40, 50, 60, 70, 80oC.
4. After 30 minutes, shake each test-tube, hold it against a white background and record the colour of each of the solutions.
5. Note which temperatures caused damage to the cell membranes that allowed red anthocyanin pigment to leak out.
9.3.2 Effects of factors of environmental stress on the cell membranes of beetroot
1. The factors of environmental stress are as follows
* Solutions of pH 2, 4, 6, 8, 10
* Ethanol solutions: 1%, 25%, 50%
* Detergent solution: 1%, 5%
The controls are as follows
* Boiled distilled water
* Aerated distilled water.
2. Prepare 60 washed beetroot slices and store them in aerated water.
3. Put 10 mL of each of the ten environmental stress solutions in Petri dishes and add five beetroot slices to each solution.
4. Add five beetroot slices to beakers of each control solution.
5. Note which factors of environmental stress caused damage to the cell membranes that allowed red anthocyanin pigment to leak out.
9.3.3 Plasmolysis in beetroot
Cut thin sections of beetroot and mount them in water on a microscope slide.
Cut the section as a very fine wedge then find an area of the section where you can see cells clearly.
Place drops of 30% sugar solution next to the coverslip.
Use absorbent paper to draw the sugar solution across the section of beetroot tissue.
Note the cells that plasmolyse.
Place drops of tap water next to the coverslip.
Use absorbent paper to draw the water across the section of beetroot tissue.
Note the cells that deplasmolyse.
9.3.4 Plasmolysis in Elodea
See diagram 9.3.68: Plasmolysis in Elodea.
1. Mount a complete leaf in water on a slide and examine cells under the high power.
Note the small green granules, chloroplasts, which contain the chlorophyll.
Then irrigate the leaf with a strong solution of sugar or salt.
The green chloroplasts help one to see plasmolysis taking place more easily.
Place a small sprig of Elodea in boiling water for a few minutes.
This kills the cells.
Then mount one leaf and treat it as before.
Note that plasmolysis does not occur now.
This shows that only living cells possess semipermeable membranes and are therefore able to absorb water by osmosis.
2. Note absorption of methylene blue by Elodea.
Place a shoot of Elodea in a very dilute solution of methylene blue.
Leave for a few hours and note that the Elodea plant becomes deeply coloured by adsorption of the dye.
9.3.5 Plasmolysis in hairs on the stamens of spiderwort, Tradescantia
See diagram 9.36.16: Plasmolysis in Tradescantia.
1. Mount a complete leaf in water on a slide and examine cells under the high power.
Note the green chloroplasts that help to define the extent of the cytoplasm.
Use absorbent paper to draw concentrated sugar or salt solution across the cell while still looking down the microscope.
The cytoplasm shrinks into the centre of the cell away from the cell wall, taking the chloroplasts with it.
Plasmolysis has occurred.
2. Repeat the experiment by drawing pure water across the same waterweed cells.
The cytoplasm and chloroplasts spread out through the cell.
Plasmolysis has been reversed.
3. Repeat the experiment with waterweed, Elodea, dipped in boiling water for two minutes.
Use absorbent paper to draw concentrated sugar or salt solution across the cell while still looking down the microscope.
Plasmolysis does not occur, because only living cells possess semipermeable membranes that control plasmolysis.
9.3.6 Plasmolysis in onion epidermis
See diagram 9.36.15: Drawing stain across specimen under coverslip.
Remove the outer layer of skin from an onion with a razor blade to expose the leaf scales.
Use forceps to detach a small piece of the epidermis from the external convex side of a leaf scale.
Put this piece immediately in a drop of demineralized water on a microscope slide.
Cover the drop with a coverslip and examine the epidermis under low power.
Place drops of 6% sodium chloride solution to one side of the cover slip and draw it across under the coverslip with absorbent paper at the other side.
Note any change in the cells.
Place drops of demineralized water to one side of the coverslip and draw them across under the coverslip with absorbent paper at the other side.
Note any change in the cells.
Repeat the experiment with red rhubarb stalks.
9.3.7 Plasmolysis in Spirogyra
Put the algae, Spirogyra, in water on a microscope slide.
While looking at the cells under the microscope add drops of sodium chloride solution near the algae.
The cytoplasm shrinks away from the cell walls and forms a clump.
Absorb the salt water with absorbent paper.
While looking at the algae cells under the microscope, add drops of water near the algae and absorb excess water with absorbent paper.
The cytoplasm swells to occupy most of the space in the cell.
When you put salt water near the algae, water diffused out of the cytoplasm causing it to shrink.
When you mop up the salt water and put pure water near the algae, water diffused back into the cytoplasm in the cells making it swell.
9.3.8 Suction potential and tissue tension in celery
1. Use a segment of celery "stalk" stored in a dry place for a few days, i.e. you can bend it and it is not crisp.
Celery "stalks" are enlarged petioles or leaf stalks.
Cut a thin transverse section, put it in water, and examine it with a magnifying glass.
On the outer convex side is a dark green epidermis in folds.
It is a single layer of cells with a thick cuticle on the outer surface.
Associated with each of the outer folds is a vascular bundle that appears as a white circle.
If you rub your finger across a dry transversely cut surface, you can feel them.
Each vascular bundle has phloem on the outside, then cambium then xylem.
Phloem cells have cytoplasm and carry organic food materials.
Cambium cells are closely packed and produce new cells by repeated cell division.
Xylem cells have no cytoplasm and conduct water.
A cap of woody sclerenchyma cells strengthens the vascular bundles.
Inside the epidermis and around the vascular bundles are collenchyma cells with cellulose thickening in the corners.
Most of the cross-section consists of the light green parenchyma cells, a packing tissue with thin cellulose cell walls.
On the inside concave surface is a second layer of epidermis.
In contrast to the outer convex layer, this epidermis consists of thin cells with no cuticle.
2. Cut across the celery stalk to make a segment 8 cm long.
Measure the length of the segment.
Then put it in water to allow the cells to become turgid and measure the length again.
Cut longitudinally between the folds to produce strips.
Put the strips in water and note how the strips curl with the whiter parenchyma tissue on the outside of the curl and the greener epidermis on the inside of the curl.
The parenchyma cells take up water and expand, because the longitudinal cuts reduce tissue tension.
Wall pressure in this tissue is low, because the cells have thin extensible walls.
Suction potential increases in the parenchyma cells, water moves in and they increase in size.
Curling occurs, because the inner cut surface increases in length, while the outer cut surface remains the same, because of the epidermis with its thick cuticle on the outside and the collenchyma confined by its own cell walls.
Wall pressure remains high, so no change in suction potential, no water uptake and no increase in length of this surface.
Salad cooks know how to cut celery, radishes and other uncooked vegetable to make them curl attractively.
9.4.1 Benedict's test for reducing sugars
See 16.3.7.1: Reducing sugars and non-reducing sugars.
See: Urine test, (Commercial).
Benedict's solution is a blue solution of sodium or potassium citrate, sodium carbonate and copper sulfate, which forms a red, orange or yellow precipitate with reducing sugars, e.g. glucose, and is used to test urine for diabetes.
Benedict's tests for reducing sugars uses a citrate ion-Cu2+ complex.
Benedict's solution is a mixture of copper (II) sulfate, hydrated sodium citrate and hydrated sodium carbonate.
Add Benedict's solution to a test solution and heat to boiling.
A high concentration of reducing sugars gives a red precipitate and a lowconcentration gives a yellow precipitate.
Benedict's test is more sensitive than Fehling's test and is easier to do, because only one solution is needed.
However, it may be more expensive.
Nowadays, Benedict's test is used instead of Fehling's tests for detecting reducing sugars.
This test was discovered by S. R. Benedict, 1884-1936, USA.
The oxidation methods for blood glucose are based on the reducing properties of glucose.
Copper reduction tests are among the oldest methods for glucose determination.
In a hot alkaline solution, glucose will reduce cupric salts to cuprous salts.
The quantity of cuprous salts produced is directly proportional to the glucose concentration.
Other procedures make use of the reduction of yellow alkaline ferricyanide to a colourless ferrocyanide.
The decrease of yellow colour depends the concentration of glucose.
9.4.2 Prepare Benedict's solution
Purchase: Benedict's solution for the quantitative determination of sugars
Prepare Benedict's solution:
1. Dissolve 173 g of sodium citrate and 100 g of anhydrous sodium carbonate in 800 mL of water then filter the solution.
2. Dissolve 17.3 g of copper sulfate in 100 mL of water and add this to the filtered solution.
Make up to 1 L with water.
3. Solution A: Dissolve with heat 173 g sodium citrate, 100 g anhydrous sodium carbonate, Na2CO3, in 800 mL water.
Filter and dilute to 850 mL.
Solution B: Dissolve 17.3 g copper sulfate crystals, CuSO4.5H2O in 100 mL water.
Pour Solution B with stirring, into Solution A, and make up to 1 litre.
4. Solution A: Dissolve 17.3 g of sodium citrate and 10 g of anhydrous sodium carbonate in 60 mL of water.
Solution B: Dissolve 1.73 g of copper sulfate crystals in 20 mL of water.
Pour solution B into solution A while stirring, and make up to 1 litre.
9.4.3 Tests for reducing sugars in urine, Benedict's solution
See: Urine test, (Commercial).
Add 8 drops of urine to 5 mL of Benedict's solution, heat to boiling for 2 minutes and leave to cool.
Reducing sugars produce precipitates: light green turbidity 0.1-0.5% sugar, green precipitate 0.5-1.0% sugar, yellow precipitate 1.0 to 2.0% sugar, red precipitate > 2.9% sugar.
9.5.0 Tests for reducing sugars, Fehling's test
Rochelle salt, potassium sodium tartrate-4-water
Fehling's solution (Herman von Fehling, 1812-1885, Germany), is an alkaline solution of copper (II) sulfate and which reacts with aldehydes as a test for aldose sugars.
Benedict's test is more sensitive than Fehling's test, and is easier to do, because only one solution is needed, but it may be more expensive.
Fehling's test is the reaction of Fehling's solution with aldehydes.
It is used as an analytical test, especially for aldose sugars, i.e. any sugar which is also an aldehyde.
Fehling's solution is an alkaline solution of copper (II) sulfate and a tartrate.
Fehling's test is used to test for water-soluble carbohydrates, ketone functional groups, and monosaccharides.
Fehling's Test is also used as a test for reducing sugars, but fructose gives a positive test.
Fehling's solution No. 2, COR, 1 litre
Fehling's solution No. 1, 1 litre
9.5.1 Prepare Fehling's solution
9.5.2 Tests for aldehydes with Fehling's solution
9.5.3 Tests for starch with Fehling's solution
9.10.1 Tests for hydrolysis of starch, iodine test, Fehling's solution
9.5.4 Tests for glucose and fructose with Fehling's solution
9.5.5 Tests for sucrose with Fehling's solution
9.5.6 Tests for cellulose, Fehling's solution
9.5.7 Tests for sugars in plant parts, Fehling's solution
9.5.1 Prepare Fehling's solution
To prepare Fehling's solution, the following solutions must be prepared by school staff before the experiment.
Do not ask students to prepare these solutions or weigh out sodium hydroxide.
Use safety glasses and nitrile chemical-resistant gloves.
1. The two solutions used are as follows:
Fehling's A solution (Fehling's copper sulfate solution), 7 g CuSO4.5H2O in distilled water with 2 drops dilute sulfuric acid.
Fehling's B solution (Fehling's alkaline tartrate solution), 35g potassium tartrate + 12g NaOH in 100 mL distilled water.
Fehling's test: 1.15 mL Fehling's A solution + 15 mL Fehling's B solution.
2. Put 2 mL of this mixture in a test-tube.
3. Add 3 drops of compound to be tested.
4. Put test-tube in 60oC water bath.
5. Positive test is a red precipitate in green suspension.
6. Simple sugars, e.g. glucose and fructose, reduce blue copper (II) oxide in Fehling's solution to brick-red copper (I) oxide.
To make Fehling's A solution, dissolve 17 g of copper (II) sulfate crystals in water and make up to 250 mL.
To make Fehling's B solution, dissolve 87 g of sodium potassium tartrate-4-water (Rochelle salt) and 35 g of sodium hydroxide in water and make up to 250 mL.
Just before doing the test, prepare Fehling's solution by mixing equal volumes of Fehling's A solution and Fehling's B solutions to form a clear deep blue solution.
3. Prepare the solution in separate parts, Fehling's solution A and Fehling's solution B.
Prepare Fehling's A solution by dissolving 34.6 g of copper sulfate in 500 mL deionized water.
Prepare Fehling's B solution by dissolving 175 g of Rochelle salt and 50 g of sodium hydroxide in 500 mL distilled water.
The complete solution is prepared when required for use by mixing equal quantities of the A and B solutions.
7. Prepare Fehling's solution just before the estimation of sugar test as follows:
Fehling's A solution: 69.28 grams copper (II) sulfate pentahydrate dissolved in 1 litre of distilled water
Fehling's B solution: 346 grams Rochelle salt (potassium sodium tartrate tetrahydrate), and 120 grams sodium hydroxide in 1 litre of distilled water
Add Fehling's B solution to 1 mL of Fehling's A solution until the blue precipitate just dissolves to give a deep blue solution.
Fehling's solution is used as an oxidizing agent to detect reducing sugars, e.g. (+) glucose, fructose, and aldehydes, e.g. methanal (formaldehyde).
After boiling, the deep blue Fehling's solution is reduced to a red-yellow (brick-red) precipitate of copper (I) oxide, Cu2O.
Ketones (except α-hydroxy ketones) do not react with Fehling's solution.
Rochelle salt (potassium sodium tartrate tetrahydrate, Seignette's salt), is a double salt, [KNa(C4H4O6).4H2O], that has a cooling saline taste and is piezoelectric.
9.5.2 Tests for aldehydes with Fehling's solution
1. Add 3 drops acetaldehyde solution to Fehling's solution and boil the solution until the red copper (I) oxide precipitate indicates the presence of a reducing agent.
CH3CHO (aq) + 2CuO --> CH3COOH + Cu2O(s)
2. Add drops of methanal (formaldehyde) solution (formalin), HCHO, to a test-tube one quarter filled with Fehling's solution and heat to boiling.
Note the yellow then orange then red precipitate of copper (I) oxide.
The copper from the copper (II) sulfate solution has been reduced from copper (II) to copper (I).
Methanal is a strong reducing agent.
The ketones do not react with Fehling's solution.
Be careful! Formaldehyde as at concentrations above 0.1 ppm in air it can irritate the eyes and mucous membranes, cause headaches, difficulty breathing or aggravate asthma symptoms.
Students should not do this test.
3. Add drops of formalin (formaldehyde) to a test-tube one quarter filled with Fehling's A and B solutions and heat to boiling.
Note the yellow then orange then red precipitate of copper (I) oxide.
The copper from the copper (II) sulfate solution has been reduced from copper (II) to copper (I).
4. Repeat the experiment using acetaldehyde instead of formalin, Fehling's solution
Note the similar reaction.
In this reactions, the aldehyde is oxidized to carboxylic acids and the Cu2+ ion (cupric ion), complexioned with tartrate ion is reduced to Cu+ ion (cuprous ion).
RCHO + 2Cu2+ + 4OH- --> RCOOH + Cu2O + 2H2O
9.5.3 Tests for starch with Fehling's solution
1. Test a dilute starch solution.
Starch does not react with Fehling's solution.
2. Hydrolyse starch solution by boiling it with equal volume of dilute sulfuric acid for about 10 minutes, with constant stirring.
Neutralize and apply the Fehling's solution.
1. No reaction occurs with starch solution if it is pure.
Test 1% pure starch solution with Fehling's test.
The test is negative.
Add 10 drops of concentrated hydrochloric acid to 10 mL of 1% starch solution.
Stand the test-tube in boiling water for 10 minutes then leave to cool.
2. Use 5 mL of this solution and neutralize by adding 1 mL of sodium hydroxide solution.
Tests for Fehling's solution.
If the test is positive, the starch is converted to reducing sugars by acid hydrolysis.
If the tests for glucose is not positive, heat for a longer period and test again.
3. Fehling's test on a colloidal solution of starch.
Note the reaction is negative.
Then hydrolyse a portion of the starch solution by boiling with equal volume of dilute sulfuric acid for 10 minutes, stirring all the time.
Test the solution periodically by applying the iodine test on a drop on a tile.
Note the stages of colour changes.
Finally neutralize, apply the Fehling's test.
4. Prepare a 1% suspension of starch in a little water, notice how the starch breaks up, but does not dissolve.
Boil the suspension and again examine.
Add one drop of iodine solution to 5 mL of water and then add several drops of starch paste.
The blue colour produced is the best tests for starch.
Apply the Fehling's test and note the result.
5. Tie a teaspoonful of plain wheat flour in a fine cloth, like a handkerchief, and pummel it up and down in a saucer of water.
Allow the white suspension in the dish to settle and decant the water.
To test the solid for starch, apply the Fehling's test and note the result.
Examine the sticky mass left in the cloth.
It is mainly gluten and cellulose.
9.5.4 Tests for glucose and fructose with Fehling's solution
1. Mix equal parts of Fehling's A solution and Fehling's B solution.
Use 3 mL of this deep blue solution and add 3 mL of 1% glucose solution.
Stand the test-tube in boiling water for some minutes or warm the solution gently over a Bunsen burner, with constant shaking.
The blue colour gradually disappears and a bright red precipitate of copper oxide forms to indicate the presence of glucose.
A red precipitate shows that glucose is a reducing agent.
Fructose gives the same reaction.
2. Add glucose crystals to a test-tube a quarter filled with water.
Close the test-tube with your thumb and shake until the glucose dissolves.
Pour into a second test-tube the same quantity of Fehling's A solution and Fehling's B solution.
Heat the contents of the test-tube not at the bottom, but at just below the surface of the liquid.
Hold the test-tube so the mouth points away from people.
As soon as the solution boils, add the contents to the glucose solution.
Heat the contents of the test-tube.
A green then a brick-red (orange red) precipitate forms of copper (I) oxide forms that shows the presence of glucose sugar.
Fructose and methanal give the same reaction.
Repeat the experiment by testing cane sugar or beet sugar (sucrose) starch and cellulose.
They do not change the colour of Fehling's solution.
3. Test juice squeezed from crushed leaves, stems, and fruit.
The test is positive, showing the presence of simple sweet tasting sugars.
However, roots and seeds test negative, because they contain mainly starch.
Repeat the experiment with crumbled cake, biscuit, rice, starch and other common foods.
9.5.5 Tests for sucrose with Fehling's solution
1. Do Fehling's test on a 1% cent solution of sucrose, cane sugar or beet sugar.
No reaction occurs with sucrose solution if it is pure.
Hydrolyse the solution of sucrose in a test-tube by adding 10 drops of dilute hydrochloric acid to the 1% cent sucrose solution.
Boil for a few minutes, cool and add 10 drops of sodium hydroxide solution to neutralize the acid.
Add freshly made Fehling's A and B solutions.
Stand the test-tube in boiling water.
The reaction produces red precipitate in the sucrose solution.
The intensity of the colour depends on the extent of the hydrolysis.
If no red colour appears, again add acid and boil the solution until a red colour appears.
2. To a 3 mL sample of 1% sucrose solution, add 10 drops of dilute hydrochloric acid.
Boil for a few minutes, cool and add 10 drops of sodium hydroxide solution to neutralize the acid and then 3 mL of deep blue Fehling's solution.
Stand the test-tube in boiling water.
If no red colour appears, again add acid and boil the solution until a red colour appears.
9.5.6 Tests for cellulose, Fehling's solution
Cellulose does not change the colour of Fehling's solution.
9.5.7 Tests for sugars in plant parts, Fehling's solution
1. Test juice squeezed from crushed leaves, stems, and fruit.
The test is positive indicating the presence of simple sweet tasting sugars.
However, roots and seeds test negative, because they contain mainly starch.
Repeat the experiment with crumbled cake, biscuit, rice, starch and other common foods.
2. Test plant organs for glucose and fructose, e.g. seeds, leaves, roots, stems, tubers.
Extract some of the juice from the plant organ to be tested.
Cut the tissues into fine pieces, and then crush the material with a pestle and mortar.
If little juice is expressed, add a few mL water and continue to crush.
Then apply the Fehling's solution on the plant extracts obtained.
3. Test juice squeezed from crushed leaves, stems, and fruit.
The test is positive, showing the presence of simple sweet tasting sugars.
However, roots and seeds test negative, because they contain mainly starch.
Repeat the experiment with crumbled cake, biscuit, rice, starch and other common foods.
9.6.1 Vitamin A
Vitamin A is a group of fat-soluble, unsaturated organic compounds which cannot be synthesized by mammals, so must be in diet for good vision, healthy skin and the immune system.
It is in dairy products and is supplied by adequate breast feeding
1. Retinol, vitamin A1, (C20H30O), diterpenoid alcohol, fat soluble retinoid, from liver, eggs, carrot, spinach, converted into vitamin A pigments, essential functioning of the retina, immune function, growth and differentiation, reproductive organs.
2. Retinal (retinaldehyde), (C20H28O), essential for vision, because converts energy in light photons to electrical impulses in retina
3. Retinoic acid, (C20H28O2), skin health, treatment for acne, in fruits and vegetables
4. β-carotene, (C40H56), provitamin A carotenoid, major vitamin A precursor, antioxidant, most important provitamin A.
Orange colour of carrots and other fruits and vegetables, the most common form of carotene in plants, in almost all green leaves, and many roots and seeds, the most important vitamin A precursors, used as yellow food colouring in margarine, used as sunscreen agent.
Highest concentration is in sweet potato, pumpkin, carrot juice, spinach, yellow fruit and vegetables, green leaves.
Dietary supplement not recommended, may reduce incidence of cancers, but not lung cancers, may decrease sensitivity to the sun.
β-carotene (C40H56), is a precursor to be digested to form the antioxidant vitamin A (C20H28O), retinol.
Sold as: β-Carotene, Type I, synthetic, 93% (UV), powder, β, β-Carotene, Provitamin A, (C40H56 )
Sold as: β-Carotene, Type II, synthetic, 95% (HPLC), crystalline, β, β-Carotene, Provitamin A, (C40H56)
Sold as: β-Carotene, 95%, trans-β-Carotene, Provitamin A, (C40H56)
Sold as: β-Carotene, 97.0% (UV), β, β-Carotene, Provitamin A, (C40H56)
5. α-Carotene, (C40H56), less than half the vitamin A activity of beta-carotene, in carrots, pumpkin, maize seeds, orange, tangerine, tomato.
Vitamin A precursor is used as yellow food colouring.
6. γ-Carotene, (C40H56), small amounts in roots, stems, leaves, half as active as beta-carotene vitamin A precursor, derived from lycopene.
Xanthophylls
7. β-Cryptoxanthin, cryptoxanthin, (C40H56O), (converts to retinol, so is a provitamin A), antioxidant, inhibits urinary bladder cancer.
Cryptoxanthin, (C40H56O), orange rind, papaya, egg yolk, butter, apples, food additive E161c.
International programmes to address vitamin A deficiency by oral high-dose supplements by GAVA (Global Alliance for Vitamin A).
8. δ-Carotene C40H56, zeta-Carotene, no provitamin A activity.
9. β-Carotene 5,6-epoxide, C40H56O, vitamin A precursor, epoxycarotenoid of beta-carotene, plant metabolite derived from a beta-carotene.
Vitamin A is used to maintain epithelial tissue.
Normal blood contains 15 to 60 mg retinol per 100 mL of serum.
Deficiency of vitamin A leads to anaemia and night blindness, because rhodopsin in the retinal rods not reformed.
Excessive intake of vitamin A may cause orange-yellow skin, headaches, blurred vision and bone fractures.
When light strikes the retinal / opsin complex in the retina, a double bond in retinal is converted from (cis-) to (trans-) to send a signal to the optic nerve.
Retinoids are oxygenated derivatives of 3,7-dimethyl-1-(2,6,6-trimethylcyclohex-1-enyl)nona-1,3,5,7-tetraene.
Retinoids are not carotenoids, but are related to vitamin A, e.g. Retinol.
9.6.2 Vitamin B
Vitamin B, water soluble vitamins, necessary for growth and metabolism, not synthesized in adequate amounts by humans.
Vitamin B includes:
Vitamin B1 (thymine): Thymine
Vitamin B2 (riboflavin): Riboflavin
Vitamin B3 (niacin): Niacin
Vitamin B6 (pyridoxine): Pyridoxine
Vitamin B12 (cyanocobalamin), (C63H88CON14O14P)
Pantothenic acid, (C9H17NO5), vitamin B5
9.6.2a Thiazole
"Thiazole" may refer to many derivatives.
Thiazole, 1,3-Thiazole, (C3H3NS), flavouring ingredient, part of vitamin B1 (thiamine), firefly chemical luciferin, colourless to pale yellow, flammable liquid, aromatic bad smell like pyridine, 5-membered ring, thiazole functional group, flavouring ingredient, part of vitamin B1 (thiamine) and epothilone.
Benzothiazoles, the firefly chemical luciferin.
See diagram: Thiazole molecule, Thiazole group.
9.6.3 Vitamin C (ascorbic acid)
Vitamin C, ascorbic acid, C6H8O6 or HC6H7O6, is a water soluble antioxidant and reducing agent.
It is used to treat bacterial infections, for detoxifying.
It takes part in the formation of collagen in fibrous tissue, bone, teeth, and tendons.
It has a role in amino acid metabolism.
It is used to treat bacterial infections and for detoxifying.
Lack of ascorbic acid results in scurvy that can be prevented by a Recommended Daily Allowance, RDA of 60 m for young adult males.
It occurs in citrus fruits and green vegetables, in chilli, and chocolate.
For a vitamin C Redox titration with KI/I2 and starch as indicator.
If temperature is the independent variable, there will be no loss of vitamin C below 70 degrees C, but at a range of temperatures from being held at 70 degrees C to 90 degrees C for 30 minutes, for every 10 degrees C above 70 degrees C, about twice as much vitamin C decomposes.
See: 9.143 Tests for vitamin C (L-ascorbic acid), (Commercial).
See diagram 9.4.1.3: L-Ascorbic acid (vitamin C)
See: Vitamin C ascorbic acid, (Commercial).
See: Vitamin C ascorbic acid, (Commercial).
9.6.4 Vitamin D
Vitamin D is a group of compounds including pyridoxine, pyridoxal and pyridoxamine.
The latter two are cofactors for some metabolic enzymes for catalysis, biosynthesis and degradation of amino acids.
Sunscreen inhibits the production of vitamin D.
People need 15 minutes per day of direct exposure to the sun outside peak UV times, i.e. 10 am to 2 pm.
Office workers who always wear long-sleeved clothing and women from Middle East countries living in the Northern hemisphere may have insufficient levels of vitamin D.
However, people who eat oily fish may have sufficient levels of vitamin D at the end of winter.
9.6.5 Vitamin E
Vitamin E is the name collectively for a group of fat-soluble compounds that contain antioxidant distinctive activities.
It can be found in vegetable oils, nuts, seeds, green vegetables like broccoli, or taken as a dietary supplement.
Vitamin E exists in 8 chemical forms; alpha, beta, and delta-tocopherol and alpha-, beta-, gamma-, and delta-tocotrienol, with most common forms in a natural diet being gamma-tocopherol, followed by alpha-tocopherol.
Vitamin E is a fat-soluble antioxidant that prevents the production of reactive oxygen species formed during the process of the oxidation of fat, and may help prevent or slow the chronic diseases associated with free radicals.
Alpha tocopherol, an antioxidant in humans, is a fat soluble molecule, prevents free radicals from destroying through oxidation of fats in the body essential for cell membranes.
Alpha-tocopherol inhibits activity of protein kinase C, an important molecule for cell-signalling.
Alpha-tocopherol affects the activity of enzymes in immune and inflammatory cells.
Vitamin E, α-tocopherol, an oil soluble antioxidant found in polyunsaturated oils in amounts necessary to protect the them against oxidation (vegetables, soy, wheat germ, maize) (antioxidant prevents oxidation of vitamin A) (in margarine, salad dressing) (Antioxidants, food additives, E309).
Antioxidants are related to the "natural" antioxidant, vitamin E, α-tocopherol and have similar properties.
Vitamin E occurs in vegetable oils, e.g. in wheat germ oil and prevents olive oil from turning rancid.
Used in processed meat, cheese, vitamin enriched food.
It prevents the oxidation of unsaturated fatty acids in cell membranes and removes toxins.
Deficiency in vitamin E can cause liver damage and infertility, nerve and muscle damage to the point of loss of feeling in arms and legs, muscle weakness, vision disorders and weakened immune system.
Vitamin E deficiency is linked Crohn's disease and cystic fibrosis - diseases where fat is not properly absorbed/digested.
The amount of vitamin E needed in the human diet depends on the amount of polyunsaturated fat consumed, but excess may be harmful.
19.2.1.6 Vitamin E, Antioxidants
19.3.05 Vitamins in canned food
9.6.6 Antioxidants, vitamin E
Antioxidants reduce damage by reactive oxygen.
Antioxidants inhibits oxidation or reaction with oxygen, are soluble in oil and cheap to produce.
Antioxidants are preservatives for fatty products and oils that are themselves oxidized instead of the added substance to prevent the occurrence of oxidation, i.e. rancidity.
E319, tertiary butylhydroquinone (TBHQ), a phenol, C10H14O2
E310-E312 are antioxidant esters allowed in edible oils, margarine, table spreads, and salad oils.
Antioxidants are related to the "natural" antioxidant, vitamin E, α-tocopherol and have similar properties.
Antioxidants in green tea may be at a concentration of 21 mg of total polyphenols per 100 mL.
9.6.7 Free radicals and antioxidants
A free radical is a molecule carrying an impaired electron and free radicals are extremely reactive.
As free radicals take an electron from the other molecules, they convert these molecules into free radicals or breakdown or alter their chemical structure.
Free radicals can damage proteins, sugars, fatty acids and nucleic acids that combine and accumulate as "age pigment".
The main free radicals are superoxide radical (SOR), hydroxyl radical (OHR), hydroperoxyl radical (HPR), alkoxyl radical (AR), peroxyl radical (PR), and nitric oxide radical (NOR).
Other molecules that are not free radicals, but act much like them, are singlet oxygen, hydrogen peroxide (H2O2) and hypochlorous acid (HOCl).
For example, the hydroxyl radical, -OH, is the most destructive free radical.
It can seize a hydrogen atom, H, from a protein to form water and a damaged protein which is now a free radical.
Free radical damage to LDL cholesterol causes atherosclerosis.
Oxidants
The free radicals and non-free radical mimics are called "oxidants" or "reactive oxygen species" (ROS).
Free radicals live for only a few seconds, because of their extreme reactivity.
Free radical damage includes ageing, cancer, heart / artery disease, hypertension disease, ageing immune deficiency, cataracts, diabetes, inflammatory disease, and just "ageing".
Free radicals and oxidants are produced by normal physiological processes and by enzymes that detoxify pollutants.
Monosaturated fats, cholesterol, and saturated fats are subject to free radicals, but polyunsaturated fatty acids are the most susceptible.
Antioxidants
Antioxidants are molecules that can react with free radicals to accept or donate an electron to eliminate unpaired electrons and so neutralize the action of the free radicals.
In humans, the first line of antioxidant defence are the antioxidant enzymes, e.g. glutathione peroxidase (GPX), and tripeptide glutathione (GSH) that help destroy SOR, H2O2 and lipid peroxides.
Also, vitamins C and E, and the mineral selenium have a major antioxidant role, besides various drugs.
Vitamin C may be the most important nutrient antioxidant.
Vitamin E is the chief fat-soluble antioxidant, and occurs in all membranes.
The α-lipoic acid (ALA) is a quasi-vitamin anti-oxidant that can be made by the body, but also absorbed from diet or supplements