School Science Lessons
2024-03-12 Plant physiology, Respiration, Transpiration
(UNBiology7)
Contents 9.1.0 Respiration in plants, plant respiration 9.2.0 Transpiration in plants 9.1.0 Respiration in plants, plant respiration 9.1.1 Alcoholic fermentation, Yeast, Saccharomyces cerevisiae 9.1.2 Butyric acid fermentation 9.1.3 Carbon dioxide gas is produced during respiration 9.1.4 Glucose fermentation 9.1.5 Energy from breakfast cereal 9.1.6 Energy from peanuts 9.1.7 Food used in plant respiration 9.1.8 Heat energy from respiration of peas 9.1.9 Heat of respiration, bakers' yeast 9.1.10 Production of carbon dioxide during plant respiration 9.1.11 Respiration of flower heads over mercury 9.1.12 Respiration of small animals and temperature 9.1.13 Respiration of soaked peas over mercury 9.1.14 Respiratory quotient, Compositae flowers, mung bean seedlings 9.1.15 Respiratory quotient using an alternative design respirometer 9.1.16 Rotting banana and rotting grass 9.1.17 Study respiration with a respiration apparatus 9.1.18 Tests for carbon dioxide in the breath with limewater 9.1.19 Tests for gases collected in a respirometer 9.1.20 Tests for oxygen absorption during plant respiration 9.1.21 Tests for respiration of soaked peas with limewater, respiration apparatus 9.2.0 Transpiration in plants 9.2.1 Conduction of water and salts through the stems 9.2.2 Conduction of water in plants, cut flowers in coloured water 9.2.3 Control of evaporation by potato skin, apple peel 9.2.4 Guttation 9.2.5 Path of the transpiration stream, cut flower stems in ink 9.2.6 Plastic bag over leaves 9.2.7 Root pressure, water transport in plants 9.2.8 The "heartbeats" of trees 9.2.9 Transpiration and water transport in plants 9.2.10 Transpiration and weight of plants 9.2.11 Transpiration and temperature 9.2.12 Transpiration by leaves exerts suction 9.2.13 Transpiration causes a drop in water level 9.2.14 Transpiration rates using a potometer 9.2.15 Transpiration sites 9.2.16 Transpiration through stomates 9.1.3 Carbon dioxide gas is produced during respiration See diagram 9.154: Limewater test for carbon dioxide in the breath.
Plants (and animals) breathe in oxygen gas from the air to breakdown food into carbon dioxide gas and water.
The energy stored in the food is then let out and can be used for growth, movement and to keep the plant (or animals) alive.
This process is called respiration.
Respiration equation: oxygen gas + simple sugar (food) --> carbon dioxide gas + water + energy.
The carbon dioxide gas produced by respiration goes out into the air.
Experiment
Prepare limewater to test for carbon dioxide.
Heat calcium carbonate (coral, shells), strongly to change it into quicklime, (calcium oxide).
Add this to water, shake and stand for a few days until the top of the liquid is clear.
To show the presence of carbon dioxide gas, breathe down a tube or a drinking straw to make bubbles in the clear liquid.
The carbon dioxide gas will turn the clear liquid a white milky colour. 9.5.1 Carbon dioxide in the air is necessary for photosynthesis See diagram 9.151: Split rubber stopper.
1. Insert a split rubber stopper firmly.
Smear petroleum jelly over the surface of the stopper to prevent any air entering the vessel either between the stopper and the neck or between the stopper and the plant stem.
Place the apparatus in sunlight.
Leave for two days, then do the iodine tests for starch on a leaf from that part of the twig inside the vessel and also a leaf outside the vessel.
The potassium hydroxide has absorbed the carbon dioxide in the enclosed air.
2. Put a mature nasturtium plant in a plant pot in a dark place in the evening. See diagram 9.146: Nasturtium.
On the following morning, fill a glass container one third full with 20% potassium hydroxide solution.
Place the nasturtium plant beside the glass container.
Bend a leaf stem without breaking it and insert one leaf into the upper air filled section of the glass container.
Cover the jar with a slotted cover to let the leaf stem to pass through the slot.
Seal the slot around the stem with adhesive tape.
Completely seal the glass container with adhesive tape.
Potassium hydroxide absorbs carbon dioxide, so the leaf sealed inside the glass container is in air without carbon dioxide.
Put the plant and culture jar in direct sunlight so that the leaf inside the glass container is exposed to the light source.
After three hours, detach the leaf inside the glass container from the plant.
Detach some other leaves, which have had equal exposure to light.
Kill the cells in the leaves by dropping them into boiling water.
After one minute, remove them with tweezers and place them in 96% ethanol.
After 2 hours the leaves become almost colourless.
Rinse the leaves in water and pour potassium iodide solution over them.
Note which leaf is coloured blue violet by the iodine potassium iodide solution. 9.1.11 Respiration of flower heads over mercury See diagram 9.156.2: Flowers in a flask. Do NOT use elemental mercury for school experiments!
Collect living flowers and push them down into a flask.
Invert the flask over mercury, so that the mouth of the flask is below the surface.
Use a bent tube to introduce strong caustic potash solution to the surface of the mercury inside the neck of the flask.
After a few hours, the mercury will rise inside the flask, because of the respiratory activity of the flowers.
During the process, oxygen is absorbed from the enclosed atmosphere of the flask, and an almost equal volume of carbon dioxide is given off.
The reduced volume of gases in the flask is owing to the absorption of carbon dioxide by the caustic potash. 9.1.13 Respiration of soaked peas over mercury See diagram 9.156.4: Soaked peas over mercury. Do NOT use elemental mercury for school experiments!
1. Fill a test-tube with mercury and, sealing the end with the finger, invert it over a dish of mercury, with the mouth of the tube below the surface.
Insert soaked peas, one at a time, into the mouth of the tube.
These peas will rise to the top of the tube.
Support the tube in this position with a clamp.
After 24 hours, the peas will have given off a gas that has forced the mercury some distance down the tube.
Show this gas to be carbon dioxide by allowing a strong caustic potash solution to rise into the test-tube from a bent tube inserted at the mouth.
The potash, now in contact with the carbon dioxide, absorbs it, and the mercury rises again in the tube.
2. To measure the respiration rate of soaked peas over mercury, insert the short end of an L-shaped tube into a flask containing soaked peas.
Insert the long end of the tube into a reservoir of mercury and note the level of mercury in the tube.
In time, the soaked peas will use all the oxygen in the flask and tube and change to anaerobic respiration with breakdown of starch reserves.
Note the level of mercury in the tube at equal time intervals, e.g. every hour. 9.1.20 Tests for oxygen absorption during plant respiration See diagram 9.157 Burning time of candle flame.
Plants take oxygen in and give carbon dioxide out during respiration.
Green plants also take in carbon dioxide and give out oxygen during photosynthesis.
Plant respiration can only be noted when there is no photosynthetic activity.
So this experiment uses plants or parts of plants that have no chlorophyll necessary for photosynthesis, e.g. mushrooms or flowers of Compositae.
Use the burning time of a candle in an enclosed known volume of air to prove the presence of oxygen.
Smear the bottom edge of a 5 litre polystyrene bell jar with glycerine to provide a good seal, and is then put on a glass plate.
Put a lighted candle in the bell jar using the candle holder.
Close the neck of the bell jar immediately with the rubber stopper of the candle holder.
Record the burning time of the candle.
The candle burns for 90 to 120 seconds enclosed in the bell jar. 9.1.14 Respiratory quotient, Compositae flowers, mung bean seedlings See diagram 9.156.2: Flower heads.
The ratio of the quantity of carbon dioxide given out during respiration to the quantity of oxygen taken in CO2:O2, is called the respiratory quotient, RQ.
If sugars are consumed in respiration, 6 moles of carbon dioxide and 6 moles of water are produced by the complete combustion of one mole of glucose by 6 moles of oxygen.
C6H12O6 + 6O2 --> 6CO2 + 6H2O
The carbon dioxide given out and the oxygen taken in are in the ratio 1.1, the respiratory quotient = 1.
If during respiration substances low in oxygen are consumed, oil, more oxygen must be used for the complete combustion to carbon dioxide and water.
So the respiratory quotient is less than 1. If substances rich in oxygen are consumed, organic acids, the respiratory ratio rises above 1. Experiments:
1. Respiratory quotient of Compositae flowers
Attach a double burette clamp to a Bunsen burner stand and clamp a respiration vessel to each side.
Fill both two thirds filled with small flowers of Compositae with the green leaflets of the calyx removed to prevent photosynthesis.
In one respiration vessel is placed a specimen tube containing 6 pellets of potassium hydroxide.
Smear the ground glass stoppers with glycerine to provide a good seal and insert in the respiration vessels.
Half fill two 100 mL beakers with deionized water and place them under the two respiration vessels.
Adjust the latter such that their capillary ends are immersed to a depth of 2 cm in the water.
Attach a scale to each capillary.
Warm both respiration vessels by placing a hand around them so that a few air bubbles escape from the capillaries.
On cooling, the deionized water rises into the region of the scale.
After 15 minutes record the level of the water in the two capillaries.
Repeat this every quarter of an hour.
The meniscus in the capillary of the respiration vessel containing potassium hydroxide rises uniformly.
The reduction in volume indicates the uptake of oxygen owing to the respiration of the flowers.
Only a small rise in the water level is noted in the other respiration vessel so the amount of carbon dioxide given out must be almost as much as the oxygen taken in.
The respiratory ratio of the flowers is thus 1. In general this applies for all higher plants.
It clearly indicates that sugar is the predominant substance consumed in the respiration process.
2. Respiratory quotient calculation for mung bean seedlings: See diagram 9.72.1: Mung bean.
Table 9.6.9
Mung bean seedlings
1. with foliage leaves developed
2. with radicle just emerged
A
0.72 cm3 per hour
3.24 cm3 per hour
B
0. 06 cm3 per hour
1.20 cm3 per hour
(A - B)
0.66 cm3 per hour
2. 04 cm3 per hour
RQ = (A - B) / A
0.92
0.63
9.1.18 Tests for carbon dioxide in the breath with limewater See diagram 9.154: Limewater test for carbon dioxide in the breath, (GIF)
1. Prepare limewater.
Calcium hydroxide is only slightly soluble in water.
Prepare the weak alkali calcium hydroxide solution, limewater, by adding
solid calcium hydroxide, slaked lime, to demineralized water.
Shake vigorously and leave to stand.
Calcium hydroxide solid is only slightly soluble in water.
When the white solid has settled as a fine white sediment, decant the
clear limewater above the sediment.
To replenish the limewater, add more demineralized to the sediment in
the stock bottle, shake and leave to settle.
The settling process may take several days.
2. Pass carbon dioxide from a gas cylinder or experiment
through the clear limewater.
The solution becomes milky, because of a fine precipitate of calcium carbonate.
Ca(OH)2 (aq) + CO2 (g) --> Ca(CO3)2 (s) + 2HCl (l)
Pass more carbon dioxide through the limewater.
The solution becomes clear again, because of the formation of soluble
calcium hydrogen carbonate.
CaCO3 (s) + CO2 (g) + H2O (l) --> Ca(HCO3)2 (aq)
3. Pass air through freshly made limewater.
After a long time you may see a faint cloudy precipitate.
The air contains about 0.4% carbon dioxide.
4. Pass the breath through freshly made limewater. See diagram 9.154: Limewater test for carbon dioxide in the breath.
Use a drinking straw to exhale into the limewater.
A cloudy precipitate soon forms, because your exhaled breath contains
about 4% carbon dioxide. 9.1.12 Respiration of small animals and temperature See diagram 4.9.12.2d: Effect of temperature.
Use a U-tube to connect the syringe to the pipette and put the apparatus in a water bath.
At each new temperature wait 10 minutes before taking readings.
Do not use temperatures that cause discomfort to small animals.
See graph 4.9.12.2.1 of respiration rates of ten worms measured at 20oC, 30oC and 40oC. 9.1.19 Tests for gases collected in a respirometer See diagram 4.9.12.0: Effect of temperature.
1. Invert the apparatus so that the collected gas is near the open end of the syringe.
Push the plunger to introduce a column of gas into the pipette.
2. Seal the end of the gas column with the solution in the syringe to trap a column of 0.8 cm3 gas inside the pipette.
Fix the apparatus in a vertical position.
3. Record the volume of gas in the pipette, V1.
4. Expel most of the solution at the lower end of the gas column.
Draw in some 2 M sodium hydroxide solution.
Keep the tip of the pipette in the sodium hydroxide solution and move
the gas column up and down to assist the absorption of carbon
dioxide.
5. Record the volume of the gas column every five minutes until the reading,
V2, becomes steady.
V2 measures the volume of the gas column without carbon dioxide.
% carbon dioxide =, V 1 - V2, / V1 × 100
Example result for pond Selaginella:
Initial volume of gas column, v = 0.75 cm3
Volume of gas column after absorbing carbon dioxide, v2, =
0.74 cm2
Percentage of carbon dioxide = V1 - V2 × 100 = 1.33%
6. The percentage of oxygen in the gas collected in the syringe can
be estimated using alkaline pyrogallol solution.
However, this chemical is too dangerous for use in school science experiments. 9.1.15 Respiratory quotient using an alternative design respirometer See diagram 4.9.12.1: Alternative respirometer, grasshopper. See diagram 4.9.12.3: Alternative respirometer, pond weed.
Make sure that the joints are airtight, e.g. between the rubber stopper and the boiling tube.
If the rubber stopper loses its elasticity after a long period of storage, +ve an airtight condition is difficult.
The respirometer is sensitive to volume changes owing to slight fluctuations in air temperature so errors in measurement may arise if you do not set up a control for comparison.
When measuring the rate of photosynthesis by collecting the oxygen evolved from a pond weed, Figure I c, errors may occur if the gas bubbles generated from the cut ends of the aquatic stem are released at an erratic rate or in variable size, or when the gas bubbles are trapped on the leaf surface or wall of the apparatus.
These errors make counting the number of gas bubbles evolved or measuring the volume of gas collected a less than reliable method for assessing the rate of photosynthesis. 9.1.6 Energy from peanuts
Put 20 mL of water in a test-tube.
Weigh a peanut (about 1 gram).
Push the blunt end of a needle into a cork then stick the sharp end into
the peanut.
Record the temperature of the water in the test-tube.
Set alight the peanut with a Bunsen burner then immediately hold it under
the test-tube.
Record the temperature of the water in the test-tube.
Weigh the burnt remains of the peanut.
Heat in calories = weight of water multiplied by the specific heat of
water multiplied by the rise in temperature of the water.
One calorie = 4.186 joules, J.
Nutrition information often uses the kilocalorie, food Calorie = 1000
calories.
Most school experimenters get values of about 12 kJ per gram, but nutrition
information on food labels usually quote peanuts at 25 kJ
per gram and peanut butter at 27 kJ per gram.
Repeat the experiment with cashew, marshmallow and popcorn. 9.1.5 Energy from breakfast cereal
Repeat the previous experiment with breakfast cereal.
Compare the result of the experiment with the information on the packet.
The packet information is more accurate than this experiment, because
in a science laboratory, a "bomb calorimeter" is used to burn
food samples and calculate the energy stored from the increase in temperature
of water around the bomb calorimeter.
No heat is lost or unaccounted for during this procedure so may find
that the calorific value on the packet may be three times the result
of this experiment. 9.1.1 Alcoholic fermentation, Yeast, Saccharomyces cerevisiae See diagram 9.156.1: Yeast with sucrose solution. See diagram 9.204: Yeast cell forming bud. See diagram 11.209.3: Wine and spirits hydrometer.
Many organisms can breakdown organic substances without atmospheric oxygen, anaerobic degradation.
The process is called fermentation.
The amount of energy produced is less than in an aerobic reaction since further substances of varying energy content are formed.
Instead of atmospheric oxygen the intermediate products of the decomposition are used here as hydrogen acceptors.
Because the decomposition results from the splitting of molecules, the fermentation can also be defined as a dissimulation.
Fission respiration, the most familiar example, is alcoholic fermentation.
In the Bible is caution against putting new wine into old wine-skin containers.
This action would burst the containers by the gases released by further fermentation: "Neither do men put new wine into old bottles [wine-skins]; else the bottles break, and the wine runneth out, and the bottles perish [are spoilt]" Matthew, ix, 17. 9.6.18.1 Alcoholic fermentation, yeast
1. Half fill a test-tube with water, add a piece of yeast the size of
a pea, and stir the mixture to produce a uniform suspension of the
yeast cells.
Three quarters fill two test-tubes with 10%t sucrose solution, and fill
a third test-tube with the same amount of water.
Add 10 drops of water to one of the test-tubes containing sucrose solution,
and add 10 drops of the yeast suspension to the other two
test-tubes.
The contents of each of the test-tubes are poured into fermentation
tubes, taking care that the upright limbs of the tubes are completely
filled with liquid and contain no air bubbles.
During the next few days a gas collects in the upright limb of the fermentation
tube containing sugar and yeast suspension.
No gas collects in the two control tubes, containing sucrose and water,
or water and yeast suspension.
2. Insert two pellets of potassium hydroxide in
the fermentation tube in which gas was produced.
The gas soon disappears, indicating the presence of carbon dioxide.
Pour the contents of this fermentation tube into a flat glass dish and
note the distinct smell of alcohol.
Yeasts ferment sugar to produce alcohol and carbon dioxide.
3. Half fill a test-tube with water, add a piece
of yeast the size of a pea, and stir the mixture to produce a uniform
suspension of the
east cells.
Three quarters fill two test-tubes with 10% sucrose solution, and fill
a third test-tube with the same amount of water.
Add 10 drops of water to one of the test-tubes containing sucrose solution,
and add 10 drops of the yeast suspension to the other
two test-tubes.
The contents of each of the test-tubes are poured into fermentation tubes, taking care that the upright limbs of the tubes are completely filled with liquid and contain no air bubbles.
In the course of the next few days a gas collects in the upright limb of the fermentation tube containing sugar and yeast suspension.
This does not happen in the control tubes, containing sucrose and water, or water and yeast suspension.
If 1-2 pellets of potassium hydroxide are inserted in the fermentation
tube in which gas was produced, the gas disappears within a few
minutes, indicating the presence of carbon dioxide.
On pouring out the contents of this fermentation tube into a flat glass
dish, the smell of alcohol is very distinct.
Yeasts ferment sugar to give alcohol and carbon dioxide.
4. Experiments, which students can do at home, e.g. bread yeast, Kombucha, junket, rennin
Students must set up a consistent way of measuring if a reaction has happened or not, using observations.
Instead of waiting for proof of 'setting', it is easier for students to observe precipitation by mixing and allowing time to settle.
This also means that with temperature reactions where you need to cool down quickly, the mixing helps this process.
Experiment:
Measure reaction time at different temperatures by mixing up yeast solutions at different temperatures and collecting multiple samples of the solution in pipettes.
Placed these samples into test tubes filled with water and counted the bubbles produced per minute. 9.1.2 Butyric acid fermentation
See diagram 9.161: Cut potato.
The soil contains micro-organisms, among which are spores and vegetative
rods of Bacillus amylobacter.
This bacillus is able to breakdown the middle lamella of plant cells forming,
among other things, butyric acid CH3-CH2-CH2-COOH.
From this breakdown it obtains the energy necessary for the maintaining
of its metabolic processes.
Butyric acid fermentation is of practical importance in flax and hemp
production since it loosens the bundles of fibres from the
structural matter of the stalks. Bacillus amylobacter is the most important butyric acid producer
in the soil.
The following experiment shows its activity:
Make a cut in a medium size potato, infected by rubbing soil into it.
It is well covered with water, contained in a 600 mL beaker, and left
to stand at room temperature.
After 5 days a vigorous fermentation process can be seen to be taking
place.
Bubbles of gas rise from the cut made in the potato.
It smells of butyric acid.
The spores and vegetative rods of Bacillus amylobacter present
in the garden or arable soil can develop and propagate under the
above experimental conditions.
The bacillus breaks down the middle lamella of the potato cells, wet
rot, thus forming butyric acid. Bacillus amylobacter is anaerobic, dislikes oxygen, so potatoes
must be covered with water to keep them away from atmospheric
oxygen. 9.1.4 Glucose fermentation See diagram 6.6.20: Gas produced from fermentation.
Wear safety glasses and rubber gloves to complete all tasks.
1. Prepare 180 mL of glucose solution at 10% (w/v).
Dissolve 18 g of glucose powder in distilled water and make up to 180
mL.
Add the glucose solution to a 250 mL conical flask and warm to the ideal
temperature for yeast activity using the thermometer, a hot
plate, incubator, water bath or Bunsen burner.
Weigh 1.5 g of dried brewer's yeast onto filter paper and add the yeast
to the glucose solution in the conical flask.
Gently stir the yeast and glucose solution.
To allow gases to escape, reduce loss of alcohol by evaporation, and
avoid bacteria or fungi contamination, fix cotton balls firmly into
the neck of the flask and put 5 cm square of aluminium foil to sit on
top of the flask.
2. Weigh the flask, solution, cotton wool balls
and aluminium foil square and record the initial mass, M1.
Maintain the solution at 20-25oC, if not specified differently
on the yeast packet.
The time required for fermentation may be 24 hours at ideal temperature
and gently stirred, or aerated, or up to 5-6 days, if just left on
a window sill.
Fermentation is completed when no more bubbles are released.
Reweigh the flask, fermented solution, cotton wool balls and aluminium
foil square, M2.
Calculate any changes in mass, M1- M2.
3. Secure the rubber stopper into the top of
the flask with the tubing fitted snugly through the stopper.
Maintain the solution at the ideal temperature for fermentation.
When bubbles form to show that fermentation is taking place, measure
25 mL limewater into a test-tube and immerse the end of the
tubing into the limewater.
Observe and record any changes in the appearance of the limewater.
4.See diagram 6.6.20 Gas produced from fermentation.
Insert the stopper in the top of the flask with the tubing passing through
the stopper.
Fill the beaker and the measuring cylinder with water and arrange the
equipment to allow measurement of the volume of gas produced
from the fermentation.
Maintain the solution at the ideal temperature for fermentation.
When fermentation is completed, observe and record the amount of gas
produced in the upturned measuring cylinder.
5. Teacher demonstration, wear safety glasses,
rubber gloves and a lab coat.
Concentrated sulfuric acid is dangerous!
Use a pipette to collect 5 mL of the fermented solution in a test-tube,
secured safely in a test tube rack.
Use a control using 5mL of distilled water to allow comparison of the
results.
Use a clean pipette to add 2 drops of concentrated sulfuric acid to the
fermented solution in the test-tube.
Put a small amount of potassium dichromate on the wooden end of a matchstick
and put it in the solution in the test-tube.
If the colour change is not immediately obvious, gently heat the solution
by sitting it in a beaker of hot water for a few minutes.
Observe and note any colour changes. 9.1.17 Study respiration with
a respiration apparatus See diagram 9.3.42: Respiration of a mouse.
The respiratory activity of organisms can be shown with an apparatus
that moves air over leaves, insects or a small animal and bubbles
it through a weak solution of limewater, Ca(OH)2.
The system must be isolated from atmospheric carbon dioxide.
Set up the apparatus as shown in the diagram, but leave the third bottle
empty.
Run the apparatus by siphoning the large container, a carboy, until it
is empty.
Note the results.
Replace the solutions in all bottles, and this time put loosely packed
leaves or an animal into the third bottle.
Compare the results of the first run, the control, with the second run.
Limewater turns from clear to cloudy in the presence of carbon dioxide.
This can be shown by blowing through a drinking straw into a container
of clear limewater.
Plant leaves produce oxygen and carbon dioxide in the light and produce
carbon dioxide in the dark. 9.1.21 Tests for respiration
of soaked peas with limewater, respiration apparatus See diagram 9.155: Respiration of soaked peas.
1. The respiratory activity of organisms can be shown with an apparatus
that moves air over leaves, insects or a small animal and
bubbles it through a weak solution of limewater, Ca(OH)2.
The system must be isolated from atmospheric carbon dioxide.
Set up the apparatus as shown in the diagram, but leave the fourth container
empty.
Note the results.
Replace the solutions in all bottles.
Put peas in the fourth container.
Draw air slowly through the apparatus with a filter pump.
When the air current bubbles through limewater before passing the soaked
peas the limewater remains clear.
When the air current bubbles through limewater after passing the soaked
peas the limewater becomes milky.
As limewater turns from clear to cloudy in the presence of carbon dioxide,
the peas must have been respiring.
2. Draw air slowly through the apparatus with a
filter pump.
The air current bubbles through limewater before passing the soaked
peas.
That limewater remains clear.
The air current bubbles through limewater after passing the soaked peas.
That limewater becomes milky. 9.1.8 Heat energy from respiration
of peas See diagram 9.156.3: Heat of respiration.
Prepare two thermos flasks fitted with one-hole stoppers for the insertion
of thermometers.
Put dry pea seeds and water to the first thermos flask.
Boil the same number of seeds and put them and water in the second thermos
flask.
Adjust the thermometers in both thermos flasks so that the bulb of each
thermometer touches the peas.
Note the rising temperature in the first thermos flask.
Actively respiring plants generate heat.
Note the steady temperature in the second thermos flask until the activity
of micro-organisms causes a sharp rise in temperature.
Examine the contents of the two thermos flasks. 9.1.10 Production of carbon dioxide
during plant respiration See diagram 9.157: Production of carbon dioxide during plant respiration.
1. Plant respiration can only be observed where no photosynthetic activity
occurs.
So use fungi or parts of plants that have no chlorophyll necessary for
photosynthesis, e.g. mushrooms or the white flowers of the
Compositae family, e.g. daisy.
Remove the green leaflets of the calyx to prevent photosynthesis.
Use the burning time of a candle in an enclosed known volume of air to
prove the presence of oxygen.
Smear the bottom edge of a big jar with petroleum jelly then put it on
a glass plate.
Open the neck of the jar then put a lighted candle down the neck on to
the glass plate.
Be careful! Melting wax from a burning candle can cause severe skin burns
so use safety glasses and insulated heat-proof gloves.
Close the neck of the jar immediately.
Record the burning time of the candle.
Put mushrooms or white flowers in the jar.
Close the neck of the jar.
Two hours later, put the lighted candle into the jar.
Record the burning time of the candle.
The candle burns a shorter time, because plants extract oxygen from the
air during respiration.
2. Repeat the experiment by pumping air from the
jar through limewater.
Continue pumping until the limewater becomes milky to show the presence
of carbon dioxide. 9.1.9 Heat of respiration, bakers' yeast
Yeast, Saccharomyces cerevisiae See diagram 9.156.1: Heat of respiration of yeast.
Heat 450 mL 10% sucrose solution to 35oC then add 25 g of
baker's yeast, Saccharomyces cerevisiae.
Stir the suspension then pour it into a thermos flask.
Fit a two-holes stopper with a thermometer inserted through one hole.
As a control, heat 450 mL 10% sucrose solution to 35oC then
pour the solution into an identical thermos flask, with a two-holes
stopper with a thermometer inserted through one hole.
Record the temperatures every 15 minutes.
The temperature in the thermos flask containing the sugar solution and
yeast rises, but the temperature in the control decreases.
Energy is liberated during respiration.
Part of it is given off to the outside as heat. 9.1.16 Rotting banana and rotting grass
1. Squeeze very ripe fruit into a watery mash, banana.
Put the mash in a small bottle then fill the bottle with water.
Attach a balloon to the mouth of the bottle.
Put the bottle and balloon in a warm place.
Measure the size of the balloon at the same time each day.
The balloon inflates, because of the carbon dioxide gas produced by the
action of bacteria on the sugars in the rotting fruit.
Bananas contain polyphenol oxidase and other iron-containing chemicals which react with the oxygen in the air when the cells are cut open.
When exposed to the air, these chemicals react in a process known as oxidation, turning the fruit brown.
2. Sterilize rotting grass by boiling in water.
Prepare sterile agar containing beef broth in test-tubes sealed with cotton
wool.
Remove the cotton wool and pour into 2 sterilized dishes, Dish 1 and
Dish 2.
After pouring the agar immediately replace the dish lids.
When the agar is set, use sterilized forceps to rub the sterilized rotten
grass over the agar in Dish 1, the control.
Replace the lid, and seal with adhesive tape.
Rub rotting grass over the agar in Dish 2 and seal with adhesive tape.
Leave the dishes upside down and undisturbed in a warm dark place for
4 days.
Examine the dishes each day for bacteria and fungi growing in small
colonies like dots.
The bacterial colonies are usually shiny and smooth.
The fungal colonies are usually fuzzy or furry.
Note whether bacterial or fungal colonies appeared first and whether
they appeared in Dish 1 or Dish 2. 9.1.7 Food used in plant respiration See diagram 9.113.2d: Bean seed germination.
Put absorbent paper in two aluminium foil trays and add 50 g of wheat
grains to each tray.
To one tray add water shaken with thymol or chloroform prevent mould
growth.
Put the trays under jars raised to admit air.
Put both trays in the dark.
When the yellow seedlings are more than 5 cm long, dry both dishes in
an oven until the weight is constant.
Record the results as the weight of 1. dry seeds 2. dry seeds after
heating 3. germinated seeds after heating. 9.2.6 Plastic bag over leaves See diagram 9.194.1: Plastic bag over leaves.
Two hours before the lesson, place a dry clear plastic bag over a small
branch of a plant growing in the sun.
Tie the mouth of the bag tightly around the stem with string.
Also find a similar branch, pull all the leaves off and tie another dry
clear plastic bag over the bare branch.
Be prepared to show what happens when a newly picked leaf is placed in
water that is nearly boiling.
Bubbles come out from the leaf.
Show the students the leafy branch and the bare branch, each covered
with a plastic bag.
Look carefully inside the bags.
What do you see? [Water]
What is the difference between the two branches? [One has leaves and
the other has no leaves.]
What is the difference between the two plastic bags? [The bag over the leafy branch has water on the inside.
The bag over the bare branch has no water in it.
Both bags were dry when put on the branches.].
Where did the water come from? [The leaves.].
The loss of water by leaves is called transpiration.
Leaves give out water when they are growing in the sunlight.
The sunlight heats the water and turns it into water vapour.
This is called evaporation.
When a liquid is heated, it forms a gas.
This gas is called a vapour.
The water vapour comes out through holes in the lower side of the leaf.
The loss of water by evaporation cools the leaf.
(Special note: This is a difficult idea.
The sun heats the water in the leaf, but the water evaporating cools the leaf.).
Plastic bag over leaves See diagram 9.194.1: Transpiration in plastic bag.
1. Tie a dry plastic bag over the leaves of a small tree.
Wind wire or string around the mouth of the bag to make it air tight.
Examine the bag after a few hours.
Note the drops of water inside the plastic bag.
Tie the plastic bag around the stem with the leaves pulled off.
No water forms in the bag.
The water comes from the leaves.
2. Tie a piece of polythene around a pot containing
a young growing plant.
Put the pot under a large jar or plastic container on a sheet of glass.
Set up a similar large empty large jar as a control.
Apply petroleum jelly to where the large jar touches the glass to ensure
that the apparatus is airtight.
Droplets of liquid appear on the walls of the large jar after two hours. 9.2.5 Path of the transpiration
stream, cut flower stems in ink
Herbaceous plants lose several hundred times their own weight of water
in a day, mostly through stomata on the leaves.
Within the mesophyll of the leaf a large wet surface is exposed to enable
the adsorption of carbon dioxide for photosynthesis.
When the air outside the leaf is drier than the air within, water vapour
can diffuse out through the stomates causing more water to
evaporate from the leaf cells.
Then the suction pressure of the leaf cells rises, draws water from the
veins and creating negative hydrostatic pressure in them to draw
water up the xylem vessels.
The xylem vessels are merely pipes and the water flows passively so water
can be made to flow in the reverse direction by sealing the
normal base end, cutting off the apex of the shoot and dipping the cut
stem into water.
Experiments
1. To show that the leaves are mainly responsible for causing the flow
of water, you can remove leaves and compare the rates of water
movement.
Use two leafy shoots of balsam to study of water conduction in stems.
Cut a fresh surface on the lower end of each shoot with a sharp razor
blade, keeping the end wet under water as you cut.
Leave in water for at least two minutes.
Place one shoots in a tube of dye provided and watch continuously until
you see colour rise in the vascular bundles in the stem and has
reached the leaves.
Remove the other shoot from the water, dry the cut end and seal with
petroleum jelly.
Cut the stem under water near the terminal rosette and leave inverted
in water for two minutes.
Transfer the shoot to the dye provided and watch continuously until you
see colour flow.
Note that the direction of flow is the reverse of that previously noted.
2. Stand the cut stems of white flowers and some
cut shoots in dilute red ink or eosin dye.
Note the stain reaching the petals and leaves.
Cut across the stems to see the dye in the xylem of the vascular bundles in the veins. 9.2.12 Transpiration by leaves exerts suction Do NOT use elemental mercury for school experiments!. See diagram 9.192.1: Suction pressure.
Make all joints air tight and do not include any air bubbles.
The mercury will rise in the narrow glass tube. 9.2.2 Conduction of water in
plants, cut flowers in coloured water
Water is distributed in a plant through the xylem vessels in the vascular
bundles.
The water absorbed by the roots of plants goes to all cells and to replace
water lost through transpiration.
Water travels up cut stems by capillary action.
1. Cut the stem of a white flower, e.g. carnation
or lily, under water with a one-sided razor blade or exacto knife.
Keep the cut end wet then put it into a red dye, e.g. red ink diluted
with water.
After some hours the petal will change colour.
1a. Repeat the experiment by carefully cutting the flower stem lengthways.
Put one cut end in red ink solution and the other cut end in blue ink solution.
After some hours the white flower will have two colours.
2. Examine the arrangement of vascular bundles
in the stalk.
Use a one-sided razor blade to cut thin wedge-shaped slices, e.g. maize,
buttercup, tulip, iris.
Cut off a small piece at the end of the stalk with a cut perpendicular
to the axis and cut away from you or cut plant material down on a
bench top and wear protective gloves.
Drop the sections into a beaker of water.
Examine the sections under low power.
Identify the vascular bundles and note how their distribution is different
in monocotyledons and dicotyledons.
3. Put ink or food colouring or 0.5% of the magenta
dye acid fuchsine in test-tubes.
Put a small flowering sprig in the test-tubes, e.g. camomile.
The white florets of camomile become pale red within 10 minutes.
The solution of dye rises with the transpiration stream into the flowers.
4. Use a white carnation flower with a long stem.
Cut the stem in half along its length and put the half stems in test-tubes
containing different water colours to create a flower with two
colours.
5. Repeat the above experiments with a celery
stem.
Cut a length of a stem under water and add red ink to the water.
Watch the red ink moving up the celery stem.
Calculate the speed of movement of the ink up the stem. 9.2.7 Root pressure, water transport in plants
1. Use two white flowers with stalks cut with a slanting cut.
Fill a test-tube two-thirds full with 1% of the magenta dye fuchsine
acid solution and put in the two white flowers.
Note any changes in the colour of the petals.
2. Fill a test-tube two-thirds full with 1% fuchsine
acid solution.
Cut off a side shoot from a pot plant and put it in the coloured solution.
After 15 minutes cut through the side shoot and note any change in colour.
Make a horizontal cut 5 cm above the soil level of a pot plant.
Fix a glass tube to the cut end.
Note any water moving up the glass tube.
The process of osmosis takes up water from the soil through the roots,
even if the foliage of a plant has been removed.
Root pressure raises the water level in the glass tube. 9.2.1 Conduction of water and
salts through the stems
Water is speedily distributed over a plant along special pathways, vascular
bundles.
1. To examine the arrangement of vascular bundles in the stalk, use a
razor blade to cut thin wedge-shaped slices, e.g. maize, buttercup,
tulip, iris.
Cut off a small piece at the end of the stalk with a cut perpendicular
to the axis.
If right-handed, take the stalk in the left hand and hold it with the
thumb and first two fingers.
Hold a razor blade between the thumb and index finger of the right hand.
Pull the blade along its whole length from left to right and towards
the body.
Drop the sections into a beaker of water.
Examine the sections under low power.
Identify the vascular bundles and note how their distribution is different
in monocotyledons and dicotyledons.
2. Put a young plant, e.g. balsam, in a beaker
with its roots in water containing red ink or eosin or 5% of the magenta
dye acid fuchsine.
After two hours, cut thin sections of the stem above the level of the
solution and examine them under low power.
Note the xylem vessels are coloured, but the phloem is not coloured.
The xylem vessels, not the phloem, conduct water and other dissolved
salts up the stem. 9.2.15 Transpiration sites See diagram 9.186: Sites of transpiration.
1. Smear the rim of a large jar with petroleum jelly.
Put a potted plant and a dish containing a known weight of calcium chloride
on a piece of glass.
Invert the large jar and place it over the potted plant and dish of calcium
chloride.
Leave to stand for six hours then again weigh the calcium chloride.
2. Cover the leaves of a potted plant with a thin
layer of petroleum jelly then put the plant under a large jar.
Also, put a dish containing a known weight of calcium chloride in a large
jar.
Leave to stand for 6 hours then again weigh the calcium chloride.
Note an increase in the weight of calcium chloride in 1.1 whereas in
1.2 there is no change in weight of calcium chloride.
The calcium chloride becomes heavier, because it absorbed water from transpiration.
The calcium chloride in 1.2 did not absorb any water and remained the
same weight, because the leaves were covered by the petroleum
jelly that prevented the loss of any water vapour by transpiration.
3. Find the surface of the leaf through which
transpiration takes place more rapidly.
Fix one piece of dry cobalt (II) chloride paper on the upper surface
of one leaf of the potted plant with adhesive tape.
Fix another piece of dry cobalt (II) chloride paper on the lower side
of another leaf of the same potted plant.
Put the pot plant on a piece of glass and cover it with a glass jar.
Apply petroleum jelly to where the jar touches the glass to ensure that
the apparatus is airtight.
Leave the experiment for two hours then note how fast any change in
colour takes place in the cobalt (II) chloride papers.
The piece of dry cobalt (II) chloride paper attached to the lower surface
of the leaf changed from blue to pink much more rapidly than
that fixed to the upper surface of a leaf of the same potted plant.
So the lower surface of leaves gives off more water than the upper surface. 9.2.3 Control of evaporation by potato skin, apple peel
1. Plants continually lose water from their surfaces through evaporation,
transpiration.
The water lost by transpiration must be replaced.
Many plants have protective devices to control transpiration.
Compare the water lost by an unpeeled and a peeled potato.
Use two potatoes of different size.
Peel the larger potato and weigh it.
After peeling it should still be heavier than the unpeeled potato.
Cutting small slices from the peeled potato until the peeled and unpeeled
potato have the same weight.
Put each potato in an open flat glass dish and leave them at room temperature.
Weigh both potatoes at the same time each day and record the results.
2. Apple peel provides protection against loss
of water by evaporation.
Select two apples of equal size.
Peel one apple as thinly as possible and leave the other apple as a control.
Put each apple in a beaker and weigh the apple + beaker.
Leave the apples to stand for some days.
During the next few days, the peeled apple shrinks and becomes increasingly
wrinkled.
However, the unpeeled apple shows no noticeable changes.
Weigh each apple + beaker again.
Calculate the percentage loss in weight of the two apples.
The peel of an apple is only very slightly permeable to water so water
can only evaporate only slowly from the fruit pulp inside it.
If the skin is not removed or damaged, fruit can be stored for a long
time. 9.2.11 Transpiration and temperature See diagram 9.189: Effect of temperature on transpiration.
1. Set up a vertical metal heating sheet with its lower edge 20 cm above
the surface of the bench.
Place a Bunsen burner below the heating sheet.
Be careful! Use safety glasses and insulated heat-proof gloves.
Do not get too close to the flame.
Prepare 4 fresh cuttings, e.g. poplar, with about the same leaf area
and the bottom 5 cm of stem cut off diagonally to promote good
suction.
Do the cutting by cutting down on the stem under water.
Put each cutting in a graduated cylinder containing water.
Fill the graduated cylinders to the 100 mL mark with water and cover
the surface of the water with paraffin oil or hot wax to prevent
evaporation.
Place one cutting near the heating sheet and the rest farther distances
away from the heating sheet.
Compare the levels of water in the measuring cylinders after two hours.
The losses of water are caused only by the transpiration of the cuttings.
The cuttings placed at a higher temperature transpire more. 9.2.9 Transpiration and water transport in plants
1. To show transpiration under a variety of conditions use a plaster
of Paris pot, with a rubber stopper and glass tube, held upside
down.
The glass tube sits in coloured water.
A fan heater is blown over the pot, water evaporates, drawing up water
from the beaker, as shown by a bubble moving up.
2. Make dry cobalt (II) chloride paper by putting
1 cm squares of absorbent paper or white newspaper into a 5% solution
of
cobalt (II) chloride then dry in an oven.
The dry cobalt (II) chloride paper is blue when dry, but turns pink when
exposed to a humid atmosphere or dipped in water.
Store the dry cobalt (II) chloride paper in a sealed test-tube or in
a desiccator or over anhydrous calcium chloride.
Put a piece of dry cobalt (II) chloride paper in contact with the upper
and lower surface of a leaf and quickly apply a coverslip.
Note the time required for the blue colour to fade for each piece of
dry cobalt (II) chloride paper.
3. Do a similar experiment with dried copper (II)
sulfate paper.
This liquid turns white anhydrous copper (II) sulfate to blue.
This liquid turns blue paper soaked in cobalt (II) chloride solution
pink.
So the liquid is water.
This water could not have come from any other source except the plant.
4. Plants continuously evaporate water and absorb
water.
Fill a 100 mL measuring cylinder with tap water to 2 cm below the 100 mL mark.
Insert rooted shoots of Tradescantia with well-developed leaves.
Pour paraffin oil on the water so that no water can evaporate from the surface.
The leaves of the Tradescantia shoots, inside the measuring cylinder
above the layer of paraffin, and outside the measuring cylinder must
all be completely dry.
Wipe any drops of water off them with absorbent paper.
Record the level of the water surface in the measuring cylinder, e.g.
98.5 mL.
Put the measuring cylinder on a sheet of glass and place a large jar
over the measuring cylinder.
Where the rim of the large jar touches the glass make a seal with petroleum
jelly so no air or water can enter or leave the large jar.
By the following day, drops of water have appeared on the inside surface
of the large jar and the level of the water in the measuring
cylinder has fallen.
The Tradescantia shoots have absorbed water then lost water through
their leaves as water vapour that has condensed on the inside
surface of the large jar.
Absorbing water through the roots must compensate for loss of transpired
water from the leaves.
5. Pick a green leaf then immediately put it in
cold water.
Nothing happens.
Put a green leaf in hot water.
Bubbles of air come from holes in the lower side of the leaf where the
stomates are situated. 9.2.10 Transpiration and weight
of plants
Use a well-watered plant in a flowerpot, e.g. Pelargonium (geranium)
or Fuchsia.
Cover the surface of the soil and the sides and base of the flowerpot
with plastic sheet.
Cover the soil surface in the flowerpot with a plastic sheet with a
slit for the stem.
Seal around the stem with rubber solution.
Fix the ends of the plastic sheet to the flowerpot so no moisture can
be lost to the air.
Weight the whole apparatus then stand in sunlight for several hours.
Weigh the whole apparatus again and note any loss in weight, because of
transpiration. 9.2.14 Transpiration rates using a potometer See diagram 9.3.43: Potometer to measure transpiration. (It may be called "Ganong's potometer".)
1. A potometer measures the rate of water intake rather than transpiration.
However, assume that water intake equals water loss by evaporation in the transpiration stream.
Select a leafy shoot from a plant that has leaves with thin waxy cuticles, e.g. Hibiscus, Bauhinia, Ligustrum, Pelargonium, (geranium).
Bend the stem of the shot under water and cut the stem so that no bubbles attach to the cut end.
Trim the cut with a razor blade.
Select a cork borer of slightly bigger diameter than the stem of the shoot and apply petroleum jelly to the outside of the cylinder.
Pass the cork borer through a hole in a 3-hole cork stopper, working from below then place the stopper and attached cork borer under water.
Flood the apparatus to eliminate any air bubbles.
Air bubbles in the xylem may prevent potometer working properly.
Still working under water, slide the end of the shoot into the end of the cork borer working from above.
Remove the cork borer by pulling downward.
The end of the capillary tube must not stick out below the cork stopper because air may become trapped there.
When all the air is eliminated from the apparatus, close the reservoir tap, remove the apparatus from the water.
Leave the apparatus for four hours.
2. Lift the end of the bent capillary glass tube to introduce a small bubble into it.
After the bubble moves around the bend in the capillary tube and parallel to the scale, note the time taken by the bubble to move towards the cut shoot.
This movement is a measure of the rate of transpiration.
Measure the rate of transpiration under different conditions, e.g. wind velocity with fast and slow fan, and temperature.
3. Put a leaf on graph paper and draw a line around the leaf margin to measure the leaf area then calculate the rate of transpiration per cm2 of leaf. 9.2.16 Transpiration through stomates See diagram 9.193: Transpiration through stomates.
1. Half fill with water four identical containers, A, B, C, D.
Prepare two similar leafy shoots A1 and B1, each with two similar leaves.
Smear petroleum jelly over both sides of the leaves of B1.
A1 is the control.
Cut the ends of both stems under water.
Pick up each stem carefully so that a drop of water sticks to the cut end.
Put each stem in its container.
Adjust the level of water in the four containers to the same height.
Add 0.5 cm of cooking oil to containers A, B and C.
Use a grease pencil to mark the original water level on each container.
Leave the stems in the sunlight for hours then the next day record the water levels in each container.
Repeat the experiment using an electric fan.
Container, B is the experiment and containers A, C and, D are controls.
2. Choose four similar leaves of a plant with thin
leaves and stomates only on the lower sides of the leaves.
2.1 Smear both surfaces of leaf 1 with petroleum jelly.
2.2 Smear only the upper surface of leaf 2 with petroleum jelly.
2.3 Smear only the lower surface of leaf 3 with petroleum jelly.
2.4 Let leaf 4 hang freely in the air as a control without smearing it with petroleum jelly.
The next day, examine the leaves.
Leaf 1 and leaf 3 show signs of wilting.
Leaf 2 and leaf 4 show no signs of wilting. 9.2.13 Transpiration causes a drop in water level See diagram 9.195: Water level drops.
1. Remove a nasturtium plant from a pot or the soil.
Wash the plant and put it into a jar of water.
Pour oil on the surface of the water.
Note the level of the oil in the jar.
Hours later, note the level of the oil again.
Water has been lost from the jar by transpiration through the plant.
2. Put water in a jar.
Mark the water level.
Fix plastic cling film over the top of the jar.
Cut a slit in the cling film just long enough to insert through it the stem of a plant.
Use some glue to seal the slit.
The water level will drop as the plant stem absorbs water.
3. Use measuring cylinders of water with stem
sample inserted then a thin layer of vegetable oil to stop evaporation.
This experiment can be left set up in sunny, shaded, warm, hot, cold areas for weeks if the students maintain the water level.
Use larger test-tubes in racks if not enough measuring cylinders and let students devise their own scales. 9.2.4 Guttation
If you observe a heavy dew on grass early in the morning, some of the moisture may not have come from the air, but from guttation by the grass.
Guttation occurs on cool clear nights when stomates are closed to reduce water lost by transpiration.
However, water lost occurs by xylem through modified stomates called hydathodes along the edges of leaves or at leaf blade tips.
Although observed usually in grasses, guttation occurs in hundreds of genera.
It may occur during the day in very humid tropical regions with high soil temperature to assist in loss of water by transpiration.
Also, it may cause negative osmotic pressure in the xylem compared to the osmotic pressure of the soil water. 9.2.8 The "heartbeats" of trees
Until now, scientists thought water moved through trees by osmosis, in a somewhat continuous manner.
The trunks and branches of trees are actually contracting and expanding to "pump" water up from the roots to the leaves, similar to how our heart pumps blood.
However, a tree's pulse is much slower, "beating" once every two hours or so.
Instead of regulating blood pressure, the heartbeat of a tree, regulates water pressure.
Most trees have regular periodic changes in shape, synchronized across the whole plant, which imply periodic changes in water pressure.
Andras Zlinszky of Aarhus University in the Netherlands used terrestrial laser scanning to monitor 22 tree species to see how the shape of their canopies changed.
The measurements were taken in greenhouses at night to rule out sun and wind as factors in the trees' movements.
In several of the trees, branches moved up and down by about a centimetre or so every couple of hours.
They have charted the changing of movement in a magnolia tree.
After studying the nocturnal tree activity, the researchers came up with a theory about what the movement means.
They believe the motion is an indication that trees are pumping water up from their roots, so it is a type of "heartbeat.".
"In classical plant physiology, most transport processes are explained as constant flows with negligible fluctuation in time".
"No fluctuations with periods shorter than 24 hours are assumed or explained by current models".
He said: "The trunk gently squeezes the water, pushing it upwards through the xylem, whose main job is to transport water and nutrients from roots to shoots and leaves.
Their new discovery is something entirely different, they say, because the these movements happen at much shorter intervals.