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Sunday, January 20, 2013

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.

(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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Monday, January 14, 2013

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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Wednesday, January 2, 2013

High School Science Fair Projects - Topic Ideas For Winning Experiments

High school science fair projects can be on any number of topics, depending upon the science course being taken. In the high school years students are allowed to take more advanced biology, chemistry, Earth Science and in some cases, rudimentary physics and astronomy courses. With this diversity, projects can be designed that even are cross disciplinary, like combining physics and astronomy to design a project that could answer problems faced by space travelers, for example. A few ideas for high school level science projects follow:

o Experts are saying that global warming could be the cause of the disappearance of many of the world's fields of glaciers in the next 50 years. What evidence is there that these changes are already occurring? Why is there a debate among scientists that global warming may or not be occurring? Do you think this debate may be financially or politically motivated? What effects will global warming have on the planet if it is happening? How do scientists that do not believe in global warming explain the discrepancies? Show both sides of the argument so that the average American can be better educated on how it affects everyone's daily life, especially if something isn't done soon.

o High school science fair projects involving "going green" are highly popular. Biodiesal fuels seem to be the next answer when it comes to finding a solution to the current oil crisis. What constitutes a "biofuel"? How is it manufactured and from what? Are these sources considered renewable? If so, why? How does the use of a biofuel affect CO2 emissions? Are biofuels as efficient as the fossil-fuels now being used? What adaptations are needed for a vehicle to utilize a biofuel?

High School Science Fair Projects - Topic Ideas For Winning Experiments

o President Obama signed legislation in June of 2009 that will be providing incentives through the Department of Energy to businesses and individual homeowners that install small solar or wind-powered generators. He is hoping that these smaller generators will hook into the local utility grids to provide more wattage that can be purchased by other users. What exactly constitutes a solar generator? What constitutes a wind generator? How will these benefit the local power utility? Are there regions of the country that would be better suited to one type of generation system over the other? How would the individual installing the small system determine this? Is the savings to energy consumers projected between the years 2012 and 2042 realistic? Why or why not?

o There is a huge debate raging over the use of genetically modified foods. What constitutes an engineered food? What are some of the dangers that some scientists believe that genetically altered foods could pose? Why do some farmers fear the planting of genetically altered crops near those that are not? Do you feel this concern is justified or not? If so, what can be done about it? Provide a sheet that can be presented to the average citizen to educate them on the subject, and who to contact to voice objections to.

High School Science Fair Projects - Topic Ideas For Winning Experiments
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For more high school science fair projects and step-by-step instructions, visit http://www.easy-kids-science-experiments.com. Be sure to check out the site for tons of simple science projects elementary science experiments, middle school, and high school science.

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Friday, November 30, 2012

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

(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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Wednesday, August 22, 2012

Biology Science Fair Projects For Winning Science Experiments

Biology science fair projects are focused on the study of all living things and the relationships between them. Biology refers to any living thing; plants or animals and how they live, how they grow, how they interact with one another and their environment and so on.

Biology can be broken down into three separate categories; botany, which is the study of plants, zoology, the study of animals, and microbiology, which is the study of microorganisms. To do a successful biology science project, you should choose the category that interests you the most. If you like animals, you might choose a project on finding out how fire flies glow and what they can teach us about life. If you enjoy plants you might choose a project that focuses on plants, such as finding out if seeds can germinate without soil. If microorganisms interest you, you might choose a project like researching to find out if yeast is a living organism.

Whichever biology science projects you choose to do your science fair project on, you should make sure you are capable of explaining your entire project. The judges want to know that you are knowledgeable about the subject you have chosen. You will also want to make your presentation pleasing to the eye, so be sure it's very organized and tidy. There are many different topics to choose from when it comes to biology, so you should have no problem finding one that interests you and will capture the attention of you audience and the judges. Good luck!

Biology Science Fair Projects For Winning Science Experiments

For more biology science fair projects and step-by-step instructions, visit www.easy-kids-science-experiments.com. Be sure to check out the site for tons of simple science projects elementary science experiments, middle school, and high school science.

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Wednesday, June 13, 2012

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.

(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

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