Biology Experiments for Teachers. Measuring The Transpiration Rate of an Uprooted Plant

Outline. The mass lost by an uprooted plant in a flask of water is compared with the mass lost from an identical flask with no plant.

Prior knowledge. Evaporation takes place from an exposed water surface

Advance preparation and materials

Biology Experiments for Teachers. Measuring The Transpiration Rate of an Uprooted Plant

Flask or bottle. Any pair of small, narrow-necked vessels will do, e.g. 100 cm3 conical flasks,
small fruit-juice bottle, small 'medicine' bottles. Allow one matched pair per group.

Plants. Any small plants which can easily be dug up. Wash the soil off the roots and store the plants in a container of water from which the student can collect them. One plant per group.

Balance. One or two per class.

Experiment

(a) Label each bottle or flask with your initials.

(b) Fill each vessel with water to within 1 cm of the rim.

(c) Place the uprooted plant in one of the vessels.

(d) Weigh the vessel with the plant and record its mass. Weigh the other vessel
(with no plant) and record its mass.

(e) Leave both vessels in a (potentially) sunny position in the laboratory.

(f) After one day, weigh both vessels again and record their masses.

(g) If there has been little change of mass in the vessel with the plant, the experiment can be
continued for several more days.

(h) At the end of the experiment, work out the mass lost by each vessel. Subtract the mass lost by the vessel with water only, from the mass lost by the vessel with the plant. This will give the loss in mass resulting from the plant's transpiration.

(i) Calculate the rate of transpiration in grams per day.

Discussion

1 The vessel with the plant will be losing water (a) from the shoot and (b) directly from the exposed water surface. The vessel lacking a plant enables us to calculate the amount of mass loss resulting from (b).

2 The mass loss in the vessel with the plant is made up of these two components. By deducting the mass loss resulting from direct evaporation, we are left with the mass loss caused by transpiration from the plant.

3 (a) The plant will interfere with the direct evaporation from the vessel, depending on the shape and size of the stem and the position of the lower leaves.

(b) In the vessel with the plant, the water level may drop below the neck, exposing a greater surface area of water for evaporation.

Biology Experiments for Teachers. Measuring The Transpiration Rate of an Uprooted Plant
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D G Mackean is the author of GCSE Biology, IGCSE Biology, and many other Biology text books. He has a site of Biology Teaching Resources at http://www.biology-resources.com which includes a bank of experiments for teachers, sample PowerPoint presentations, and many biological drawings

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Biology Experiments for Teachers. Human Senses: Sensitivity to Temperature

Outline. One finger of each hand is acclimatized to hot or cold water and then dipped into lukewarm water.

Prior knowledge. The general idea of receptors sending impulses to the brain

Advance preparation and materials
A supply of hot and cold water

Biology Experiments for Teachers. Human Senses: Sensitivity to Temperature

Apparatus - per group
3 jars or beakers large enough to accommodate a finger
Thermometer

Experiment

(a) Collect three jars or beakers of about the same size. Fill one with cold water (10-15 °C), one with hot water (40-50 °C) and the third with warm water (about 25 °C).

(b) Place the first finger of the left hand in the cold water and the first finger of the right hand in the hot water. Leave both fingers immersed for at least one minute.

(c) After one minute, remove both fingers from the jars and dip them repeatedly but alternately in the warm water for about a second at a time Notice the temperature sensation in each finger.

Discussion

1 What impression did (i) the left finger, (ii) the right finger give about the temperature of the
warm water?

2 Why should there be any difference in the sensory information from the two fingers? How could you modify the experiment to test your suggestion?

3 Does the result mean that the skin of your fingers is incapable of judging whether an object is hot or cold?

4 What does the result suggest about the way in which the skin responds to temperature

Discussion - answers

1 The finger which has been immersed in cold water will register warmth. The finger previously held in hot water will register coldness.

2 The difference in sensations can be attributed to the difference in the temperature of the fingers after one minute's immersion. This can be tested by repeating the experiment with the left-hand finger in the hot water and the right-hand finger in the cold water. The sensation on dipping them both into warm water should be the reverse of the first experiment.

An alternative explanation is that the warmth receptors in the hot water become adapted, i.e. after prolonged immersion they no longer send impulses to the brain. Consequently, on transfer to lukewarm water, there are few impulses sent to the brain from the warmth receptors of this finger, whereas the warmth receptors in the cold finger fire normally.

3 The results suggest that the fingers detect whether they are gaining or losing heat rather than the actual temperature of an object. Metal objects at room temperature will feel cold to the touch because heat is conducted away from the fingers, while wooden objects at the same temperature feel less cold.

4 The results seem to imply that the thermoreceptors respond to change in temperature rather than to any particular temperature. In fact, there is a steady discharge of nerve impulses from cold and warmth receptors at all temperatures within certain limits but increased bursts of impulses occur during sudden changes of temperature.

Biology Experiments for Teachers. Human Senses: Sensitivity to Temperature
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D G Mackean is the author of GCSE Biology, IGCSE Biology, and many other Biology text books. He has a site of Biology Teaching Resources at http://www.biology-resources.com which includes a bank of experiments for teachers, sample PowerPoint presentations, and many biological drawings

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Biology Experiments for Teachers. Binocular Vision, Eye Dominance and Location of Stimuli

Binocular Vision: Experiment

(a) Keep both eyes open and hold a pen or pencil upright at arm's length.

(b) Quickly move the pencil to come exactly in line with a more distant vertical object, such as a window frame or lamp-post.

Biology Experiments for Teachers. Binocular Vision, Eye Dominance and Location of Stimuli

(c) Close and open the left eye.

(d) Close and open the right eye.

(e) Note any change in the apparent position of the pencil and whether it was the closure of the left or right eye which produced it.

(f) Which eye did you use in lining up the two objects?

Discussion

Although both eyes are kept open to line up the pencil and the distant object, only one eye, the dominant eye, is used to determine the alignment. When this eye is closed, the pencil will appear to 'jump' sideways. It is closure of the dominant eye which produces the jump because, according to the eye now remaining open, the pencil and distant object are not in line. If the student is slow to line up the two objects he or she may be aware of a double image of the near object. Nevertheless, the student is still likely to select the image from the dominant eye.

Awarness of Location of Stimuli. Experiment

(a) Place a glass marble on a non-slippery surface, e.g. on the page of an open notebook.

(b) Cross the first and second fingers of one hand and press on the marble with the tips of these fingers.

(c) Close your eyes and roll the marble firmly, forwards and backwards, side to side and then with a circular motion for about 30 seconds.

(d) Notice any unusual impressions you receive from the fingers.

Discussion

1 The subjective impression should be as if there were two marbles with the fingers pressing
between the two.

2 The areas of the finger-tips employed, with the fingers not crossed, would normally be stimulated only by two surfaces separated in space.. The connections that exist between the receptors and the brain are, presumably, the foundation for this interpretation. When the two areas are stimulated simultaneously by the same object in the absence of visual evidence, the brain makes its usual interpretation, giving the sensation of two objects.

The results also show that we normally rely on information from several sources for our
interpretations. If the subject watches the fingers and marble, it is far more difficult to elicit the impression of two objects.

Biology Experiments for Teachers. Binocular Vision, Eye Dominance and Location of Stimuli
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D G Mackean is the author of GCSE Biology, IGCSE Biology, and many other Biology text books. He has a site of Biology Teaching Resources at http://www.biology-resources.com which includes a bank of experiments for teachers, sample PowerPoint presentations, and many biological drawings

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How Teachers Influence The Performance Of Biology In High Schools

Biology plays a key role in industrialization and other sectors of the economy. Biology is a practical subject, which equips students with concepts and skills that are useful in solving the day-today problems of life. The study of biology aims at providing the learner with the necessary knowledge with which to control or change the environment for the benefit of an individual, family or community.

In general, the importance of biology to humanity can be outlined as follows:

Biology

(i) The learning of biology helps us to know how to use natural resources more efficiently in industry e.g. in bio-technology, food production, building and textile and paper industries.

How Teachers Influence The Performance Of Biology In High Schools

(ii) The learning of biology helps us to understand changes in the environment and the factors affecting these changes, in order to know how human needs are influenced.

(iii) The learning of biology is important in helping mankind to find effective ways of preventing, treating and curing diseases and home management techniques e.g. better methods of food preservation, efficient food preparation and care of the family

(iv) The learning of biology is important in helping the improvement of agricultural yields through scientific research.

There has been public outcry and concern by parents, teachers, educationists in Kenya about poor performance in science subjects and mathematics in national examinations.

But do you know the biology teacher has a role to play in this poor performance?

Biology as a science subject requires an integration of both theoretical and practical work to make it easily understood by the students. The largest proportion of teachers still use the conventional lecture method while teaching biology.

Teacher expectations have a bearing on the attitude and science anxiety levels of the learners particularly when the learners are aware of the level of expectation the teacher has of them.

In relation to the teaching and learning of biology, attitudes begin to develop on the first encounter between the teacher and the learner, once formed they play a key role in determining students' learning and performance in biology.

Authoritarian and impersonal teacher- student interaction in class could be the major factor that contributes to negative attitude of the students towards learning biology. On the other hand, democratic and personal teacher-student interaction in class elicits positive attitude towards learning biology

The teaching approach, methodology and how the professional skills and practices of the teacher are displayed may be dependent on the level of science anxiety the biology teacher has.

A teacher who suffers from career dissatisfaction is likely to contribute negatively in terms of performance of the learners in biology; this is because the teacher will have lower self-efficacy and high levels of anxiety. This kind of teacher is likely to develop negative attitude towards the students and his/her interaction with the students will be negative and this may contribute to a negative attitude of the students towards biology with the likelihood of the students developing high levels of anxiety towards the subject.

Therefore, teacher perceptions, teaching methods applied, the type of teacher -pupil classroom interactions, teacher expectations of students in terms of performance and science anxiety levels of the teachers- partly contributed by lack of job dissatisfaction or satisfaction are the key factors that influence performance in biology in Kenyan secondary schools.

How Teachers Influence The Performance Of Biology In High Schools

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Biology Experiments for Teachers - Enzymes: Catalase

Safety. Although the hazards in the following experiments are negligible, you are advised to consult the latest edition of 'Safeguards in the School Laboratory' published by The Association for Science Education (ase.org.uk) before embarking on any experiment.

Outline. Catalase is an enzyme which occurs in the cells of many living organisms. Certain of the energy-releasing reactions in the cell produce hydrogen peroxide as an end-product. This compound, which is toxic to the cell, is split to water and oxygen by the action of catalase. 2H2O2 = 2H2O + O2

Biology

Samples of liver and yeast are dropped into hydrogen peroxide. Oxygen is evolved and the student is asked to extend the experiment to try and decide if an enzyme in the tissues is responsible. The experiments and the questions take about one hour.

Biology Experiments for Teachers - Enzymes: Catalase

Prior knowledge. The existence of inorganic catalysts; enzymes denatured on boiling; oxygen relights a glowing splint.

Advance preparation and materials - per group

20 volume hydrogen peroxide 50 cm3

splint

liver, about 1 cm cube

distilled water 20 cm3

dried yeast about 1 g

clean sand about 1 g

activated charcoal granules, about 1 g

Apparatus - per group

test-tube rack and 4 test-tubes

forceps or seeker for pushing liver into test-tube

4 labels or spirit marker

filter funnel

Bunsen burner

filter paper

test-tube holder

mortar and pestle

Experiment

The investigation below is a fairly critical examination of plant and animal tissues to see if
they contain catalase.

(a) Label three test-tubes 1-3.

(b) Pour about 20 mm (depth) hydrogen peroxide into each tube.

(c) Cut the liver into 3 pieces.

(d) To tube 1 add a small piece of liver, and to tube 2 add a pinch of dried yeast.

(e) Insert a glowing splint into tubes 1 and 2, bringing it close to the liquid surface or into the upper part of the froth.

1 Describe what you saw happening and the effect on the glowing splint.

2 How do you interpret these observations?

3 Is there any evidence from this experiment so far, to indicate whether the gas is coming from the hydrogen peroxide or from the solid?

4 Is there any evidence at this stage that an enzyme is involved in the production of gas in this reaction?

(f) In tube 3 place a few granules of charcoal and observe the reaction.

5 Could charcoal be an enzyme? Explain your answer.

6 Assuming (i) that the gas in (f) is the same as before and (ii) that the charcoal is almost pure carbon, does the result with charcoal help you to decide on the source of the gas in this and the previous experiments?

(g) Suppose the hypothesis is advanced that there is an enzyme in the liver and yeast, which decomposes hydrogen peroxide to oxygen and water; design and carry out a control experiment to test this hypothesis.

7 Record (i) the experiment, (ii) the reasons which led you to conduct it, (iii) the observed
results and (iv) your conclusions.

(h) Wash out the test-tubes. Design and carry out an experiment to see if the supposed enzyme in the plant and animal material can be extracted and still retain its properties. The experiment should include a control.

8 Describe briefly your procedure, your results and your conclusions.

9 Assuming that liver and yeast each contain an enzyme which splits hydrogen peroxide, is there any evidence to show that it is the same enzyme? What would have to be done to find this out for certain?

Discussion - answers

1 Effervescence should be observed in each case but it is more vigorous with yeast than with liver. The glowing splint should relight.

2 Oxygen is being produced.

3 There is no evidence to indicate whether the liquid or solid is giving the gas. If the students think that a solid is unlikely to give off a gas they could be reminded of marble and hydrochloric acid in which it is the solid producing the carbon dioxide. It seems less likely, however, that yeast and liver would both give off oxygen when treated with hydrogen peroxide, than that hydrogen peroxide should give oxygen when treated with diverse substances.

4 So far, there is no evidence of an enzyme being involved.

5 A gas will come off but not sufficiently rapidly to relight a glowing splint. Charcoal could not
be an enzyme because (a) it is an element and (b) it has been produced by very high temperatures that would destroy enzymes.

6 Charcoal, as an element, could not be giving off oxygen. The gas must be coming from the
hydrogen peroxide.

7 (i) The experiment should involve boiling the tissues and then putting them into hydrogen peroxide.
(ii) If an enzyme is involved,
(iii) no gas will be produced.

8 The student should grind the samples with a little sand and distilled water, filter and test the filtrate with hydrogen peroxide. Oxygen will be evolved with a vigour proportional to that witnessed when the original substances were tested.

The student should boil half of each extract and show that it loses its activity.

9 There seems no fundamental reason why yeast and liver should not have different enzymes which catalyse the decomposition of hydrogen peroxide. To be certain on this point, the enzymes would have to be extracted and their chemical composition determined.

Biology Experiments for Teachers - Enzymes: Catalase

D G Mackean is the author of GCSE Biology, IGCSE Biology, and many other Biology text books. He has a site of Biology Teaching Resources at http://www.biology-resources.com which includes a bank of experiments for teachers, sample PowerPoint presentations, and many biological drawings

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