BIOLOGY INVESTIGATIONS

NOTE: This page does not provide full lab reports for different experiments, rather aims and procedures of many different investigations as a means to further understand how theoretical understanding can be applied practically. This information can be very helpful when trying to attempt lab report questions in the MYP e-Assesments.

Animal & Plant cells under a microscope

Aim

To view animal and plant cells under a compound microscope and record the visible differences between the two.

Method

Human Cheek Cells – Wear glasses and lab coat.
Add a drop of 0.9% Sodium Chloride onto glass slide.
Take a toothpick and roll it on the inside of your mouth, so that cheek cells are covered on it.
Take the toothpick and rub it on the prepared glass slide.
Add a drop of Methylene Blue Solution on the glass slide.
Using a needle and forceps very carefully put the cover on top of the solution, making sure that no air pockets are formed in the process.
Using a tissue dab excess liquid of off of the glass slide.
View the cells under a microscope under the magnifications of 4x, 10x, 50x, and 100x.
Draw observations on a paper, making sure to write down the magnification. Note the change when viewing the cell.
Onion Cells – Cut up 1 onion into 4 pieces.
Take the inner most part of the onion and put it aside. Using forceps pull a thread like piece of the onion and put it on the watching slide.
Add a few drops of water and safranin dye onto the watching glass.
After 30-40 seconds using a brush, take the onion and move it on to the glass slide.
Put the cover on top of the onion using a needle and forceps. Be careful of air pockets.
Dab of any excess liquid with a tissue.
View under a microscope with the magnifications of 4x, 10x, 50x and 100x.
Draw observations on paper, making sure to write down the magnification. Note the change when viewing the cell.

Enzyme Activity

Aim

To find out which temperature enzymes function best in. This will be found by using a potato and hydrogen peroxide. Potatoes contain an enzyme called catalase which will help in the experiment.

Method

Wash and peel a potato.
Cut the potato in half and place it on a petri dish with some water present.
Cut 3 pieces from the potato with masses between 1.80g-2.20g. Use the weighing machine for accurate masses.
In a large beaker add 500 ml of water and place over a Bunsen burner.
Measure 25 ml of hydrogen peroxide in a granulated cylinder and pour into a test tube.
When water starts to boil in the large beaker take off the heat and measure the temperature of the water. Record the temperature.
Take a piece of the potato and record its weight and length. Put the potato piece in the test tube containing hydrogen peroxide and place in the large beaker (containing warm water).
Measures 5 minutes on the stopwatch and after exactly 5 minutes use the forceps to extract the potato piece.
Measure the temperature of the warm water present in the large beaker and record it.
Measure the mass and length of the potato piece, extracted from the test tube.
Again, using the granulated cylinder measure 25 ml of hydrogen peroxide and place in a test tube.
Measure the temperature of the hydrogen peroxide at room temperature and record it.
Take the second potato piece and measure its mass and length.
Place the potato piece in the test tube and wait for 5 minutes.
After 5 minutes, take out the potato piece and record its new mass and length.
Measure the temperature of the hydrogen peroxide in the test tube after the experiment and record it.
Take 25 ml of hydrogen peroxide in a test tube and place it in the fridge for 3 minutes.
Measure the temperature of the hydrogen peroxide in the fridge after 3 minutes and record it.
Take the third potato piece, measure its mass and length and record it.
Place the potato piece inside the hydrogen peroxide, and place it in the fridge for 5 minutes.
After 5 minutes take out the potato piece and record its new mass and length.
Record the temperature of the hydrogen peroxide after the reaction has taken place.

Extracting DNA from Kiwi fruit

Aim

To understand and visually see the amount of DNA (deoxyribonucleic acid), present in Kiwi. Through this experiment, it can be shown that DNA is present in all living organisms.

Method

Peel and chop up into small pieces, half a kiwi fruit. Grind the pieces of Kiwi to a paste in the mortar using the pestle.
Fill up half a beaker with hot tap water (60 degrees Celsius). Add 10 g of salt and stir until the salt has dissolved. Mix in about 6 ml of washing-up liquid.
Add the mashed Kiwi fruit to this mixture. Stand the beaker in the water bath (60 C) for 10 minutes, continuing with stirring the kiwi fruit.
Transfer this mixture in the beaker to the ice bath, leave for 5 minutes. Continue stirring.
Filter the mixture into a cold boiling tube.
Use about 10 ml of the filtrate (remove any bubbles there are on the surface of the liquid). Add about 15 ml of absolute alcohol. Add all the alcohol very gently down the side of the tube so that it sits on top of the salt solution and kiwi mixture. Do not shake the tube – keep it still to get a good yield of DNA. The DNA appears as white strands entangled at the interface of the two liquids.

Testing for the presence of reducing sugars

The Benedict’s test

Place 2 cubic centimeters of food sample into a test tube.
Add 2 cubic centimeters of Benedict’s solution to the food sample.
Shake the mixture and place the tube in a boiling water bath for 2-3 minutes.
The presence of reducing sugars is indicated by color changes in the solution as listed below:

a. Solution remains blue – No reducing sugar

b. Blue to green precipitate – Traces of reducing sugar

c. Blue to yellow or orange precipitate – Moderate amount of reducing sugar

d. Blue to brick-red precipitate – Large amount of reducing sugar

Testing for the presence of starch

Starch can be detected by the iodine test. A few drops of iodine solution added to any substance containing starch will produce a blue-black color.

Add few drops of iodine solution to a piece of potato.
What do you observe?

Testing for the presence of fat

A cloudy white emulsion is formed when ethanol and water are added to fats. An emulsion is a suspension of small drops of a liquid in another liquid.

Ethanol (alcohol) emulsion test

On liquid food:

Add 2 cubic centimeters of ethanol to a drop of coconut oil in a test tube and shake the mixture thoroughly. What do you observe?
Add 2 cubic centimeters of water to the mixture and shake the mixture. What do you observe?

On solid food:

Cut a peanut into small pieces and place the pieces in a test tube. Add 2 cubic centimeters of ethanol and shake thoroughly.
Allow the solid particles to settle. Carefully decant the ethanol (pour off the top layer of ethanol) into another test tube containing 2 cubic centimeters of water. What do you observe? How can you explain your observation?

Testing for the presence of protein

The biuret solution is a blue solution made up of sodium hydroxide and copper (II) sulfate. It turns violet (deep purple) when proteins are present.

Biuret test

Add 2 cubic centimeters of sodium hydroxide solution (40% or bench solution) to 2 cubic centimeters of egg white solution in a test tube and shake it thoroughly.
Add 1% copper (II) sulphate solution, drop by drop, shaking after every drop. What color changes do you observe?

Effect of pH on enzyme action

This experiment is based on the fact that egg white contains protein. Pepsin is a protein-digesting enzyme produced by the stomach. This experiment is designed to test how pH affects the activity of pepsin.

The contents of four test tubes used in the experiment are as follows:

A – 3 cubic centimeters of egg white + 10 drops dilute HCL + 3 cubic centimeters pepsin

B – 3 cubic centimeters of egg white + 10 drops dilute HCL + 3 cubic centimeters distilled water

C – 3 cubic centimeters of egg white + 10 drops dilute NA2CO3 + 3 cubic centimeters pepsin

D – 3 cubic centimeters of egg white + 10 drops distilled water + 3 cubic centimeters pepsin

What would you observe in a test tube where pepsin is active?
What are the purposes of test tube B and test tube D?
Which of the above test tubes can be replaced by one containing 3 cubic centimeters egg white and heat-treated pepsin?

How can we test for starch in a leaf?

Remove a green leaf from a plant that has been exposed to sunlight for a few hours.
Immediately put the leaf in a boiling tube for two minutes.
Put the boiled leaf in a boiling tube containing some alcohol or ethanol. Place the boiling tube in a beaker of hot water.
What is the colour of the alcohol

a. Before the leaf is put in; and

b. 10 minutes after the leaf is put in?

What is the colour of the leaf after 10 minutes?
What has the alcohol done to the leaf?
The leaf is now brittle. Gently remove the leaf and put it back into the hot water. This softens the leaf and makes it more permeable to iodine solution.
Remove the lead and spread it evenly on a white tile. Add a few drops of iodine solution to the leaf. Explain your observation.
What is the purpose of putting the leaf in boiling water in step 2?

Is sunlight necessary in photosynthesis?

Destarch a potted plant by placing it in the dark for two days.
Remove one leaf. Test it for starch as described in the previous investigation.
Sandwich a leaf, which is still attached to the plant, between two pieces of black paper. Each paper has a certain pattern cut out from it. Fasten the papers with paper clips. Place the plant in strong sunlight.
After a few hours, remove the leaf and test it for starch.
Make a drawing of the leaf to show the regions that are stained blue-black. What conclusion can you draw from this investigation?
Why must you test a leaf for starch before carrying out this investigation?

Is chlorophyll necessary in photosynthesis?

Destarch a plant with variegated leaves, e.g. Duranta, by placing it in the dark for two days.
Expose the plant to strong sunlight for a few hours.
Remove one leaf. Make a drawing to show the distribution of the green parts, i.e. the parts that contain chlorophyll
Decolourise the leaf and test it for starch.
Make a drawing of the leaf to show the distribution of the blue-black colour. Compare this with your drawing in step 3.
Suggest an explanation for your observation.

Is carbon dioxide necessary in photosynthesis?

Destarch two planted plants by placing them in the dark for two days.
Enclose the pots in polythene bags. Secure the bags to the plant stems.
Place one pot in a bell jar which does not have a supply of CO2 (Hint: Use soda lime) and one pot in a bell jar with a supply of CO2. Leave both bell jars in strong sunlight for a few hours.
Remove a leaf from each plant and test them for starch.
What do you observe? Draw a conclusion from this investigation.

Figure 1. CO2 in photosynthesis experiment set up

What gas is given off during photosynthesis?

Set up some fresh water plants, e.g. Hydrilla or Elodea as shown.
Dissolve 2-10 g of sodium hydrogencarbonate in the water in the beaker. This provides CO2 to the plant.
Place the apparatus in strong sunlight for a few hours.
You will notice that gas bubbles form on the leaves in the beaker placed in sunlight. These bubbles will rise up the test tube and displace the water downwards. When the tube is about half-filled with the gas, remove the tube by placing a thumb over its mouth.
Test the gas with a glowing splinter. Record your observation.
What gas is given off by the water plants exposed to sunlight? What happens in the controlled experiment?
Why is it important that no air is trapped in the test tube at the beginning of the experiment?
What does the rate of gas production indicate?

Effect of light intensity on the rate of photosynthesis

Figure 2. Gas given out during photosynthesis set up

(This experiment assumes that the rate of oxygen produced is directly proportional to the rate of photosynthesis.)

Set up the apparatus as shown in the diagram, with the cut end of the water plant positioned upwards.
Air bubbles are given off from the cut end of the plant. Allow some time for the plant to adapt to the conditions provided before taking readings.
When the bubbles are produced at a regular rate, count the number of bubbles over a period of 5 minutes. Repeat this a few times to obtain the average rate.
Repeat step 3 with the light source closer to the plant, e.g. 80 cm, 40 cm, 30 cm, 20 cm, 15 cm, and 10 cm. Note that the nearer the light source is to the beaker, the higher is the light intensity that the plant is exposes to.
Record your results in a table. Plot a graph to show the rate of bubbling per minute against the distance between the lamp and the plant.
From your investigation, what is the effect of light intensity on photosynthesis? (Assume that the higher the rate of air bubbles given off [oxygen], the higher the rate of photosynthesis).
What is sodium hydrogencarbonate solution used instead of water?
What conditions are you allowing for in step 2? Why do you wait for some time before taking the readings?

Figure 3. Light intensity experiment set up

Effect of temperature on the rate of photosynthesis

Repeat step 1 as in previous investigation.
Place a lamp 10 cm away from the plant. Keep this distant constant throughout the investigation.
Add ice-cold water to the water bath to keep the temperature at 5 C. Allow some time for the plant to adapt to the conditions provided before taking the readings.
Count the number of bubbles over a period of 5 minutes. Repeat this a few times to obtain an average rate.
Repeat step 4 at different temperatures, e.g. 15 C, 25 C, 35 C, 45 C, 55 C, 65 C, and 75 C.
Record your results in a table. Plot a graph to show the rate of bubbling per minute against the temperature.
From your investigation, what is the effect of increasing the temperature from 5 C to 35 C?
At what temperature is the rate of bubbling the fastest? This is the optimum temperature.
What happens when the temperature is increased beyond the optimum temperature? Explain your observation.

Effect of CO2 concentrations on the rate of photosynthesis

Repeat step one as mentioned in the previous investigation
Repeat step two as mentioned in the previous investigation
Conduct the investigation at room temperature
Use different concentrations of sodium hydrogencarbonate solutions, e.g. 0.01 mol dm^3, 0.02 mol dm^3, 0.04 mol dm^3, 0.05 mol dm^3, 0.06 mol dm^3, up to 0.1 mol dm^3 (These are proportional to the carbon dioxide concentrations in the solution).
When the bubbles are coming out at a regular rate, measure the rate of bubbling for each concentration of the sodium hydrogencarbonate solution.
Plot a graph to show the rate of bubbling against the concentration of sodium hydrogencarbonate of the solution.
How do the concentrations of sodium hydrogencarbonate solutions affect the rate of photosynthesis?

How can we demonstrate the presence of stomata in a leaf?

Pick up a fresh leaf with a pair of forceps and hold the leaf below the surface of the water. The water should be approximately 75 C. Observe carefully what happens on the surface of the leaf.

Record your observations
Explain what had taken place in the lead as fully as you can (Hint: Air expands when heated)
Why must the water temperatures be approximately 75 C before taking the readings?

How can we show the path of water through a plant?

Take a celery plant and wash it with water to remove the soil
Allow the plant the stand with its stem immersed in dilute red ink (or methylene blue) solution
After a few hours, you can see that red ink has risen up the plant. Cut thin transverse sections of the stem.
Place the sections on a glass slide. Examine the sections under a microscope.
Which tissue has been stained red?
What conclusion can you draw from the investigation?

The 'Ringing' Experiment

This experiment shows how the phloem carries material from the leaves to other parts of the plant.

Cut off a complete ring of bark including the phloem and cambium from the main stems of a woody twig (e.g. Hibiscus) this will leave the xylem exposed. Place the twig in water with the cut ring above the water level (twig A)
Set up a control using an unringed twig (twig B)
Observe the twigs daily. Note where roots or swellings appear. Make drawings of your observations.
What does this experiment tell you about the phloem?
Suggest an explanation for your observations.

Figure 4. The Ringing Experiment

Transpiration in a plant

Take a potted plant and wrap a polythene bag around the pot and the stem of the plant. Water may evaporate from the soil surface. The bag prevents such water vapour from entering the bell jar.
Place the pot on a glass plate and cover it with a dry bell jar.
Set up a control using similar apparatus but without a plant. Place the two bell jars side by side near an open window for two hours. What do you observe after two hours?
Test any liquid on the onside of the bell jar with anhydrous copper (II) sulfate. What do you observe? Given an explanation for your observations.

Transpiration occurring through leaves in a plant

Take two leafy twigs of about the same size from the same plant. Cut the end of each twig under water to prevent air from entering the xylem vessels. Any air trapped in the xylem vessels would interfere with the absorption of water by the twig.
Place each twig in a beaker of water and add a little oil into the water to prevent evaporation.
Strip off all the leaves of one twig and put petroleum jelly on the ends of the petioles. Also put petroleum jelly on the stem of the leafy twig. Place each beaker under a large bell jar and allow them to stand so that they receive sunlight.
What do you observe after a few hours? Explain your observations.

Figure 5. Set up of transpiration experiment

chapter-10-respiration-lesson-1-aerobic-

Is carbon dioxide given off during alcoholic fermentation (anaerobic respiration)?

Add a few grains of dry yeast to some distilled water in a boiling tube. Stir well.
After 20 minutes, add an equal volume of boiled and cooled dilute glucose solution to the yeast suspension and mix well. Why do you need to boil the glucose solution before carrying out the experiment?
Add a little oil. What does the layer of oil serve as?
What would you add to the boiling tube in a control experiment?

Figure 6. Set up of fermentation experiment