Various Experiments To Learn

Question 0

Describe an experiment to demonstrate the production of carbon dioxide by small living organisms…

Answer 0

Hydrogencarbonate solution is orange, but turns yellow if carbon dioxide is added.

1) place organisms on a gauze platform in a stoppered boiling tube, with hydrogencarbonate indicator solution in the bottom of the tube
2) measure the rate at which the indicator changes colour

Question 1

Describe an experiment to demonstrate that heat is produced by respiration..

Answer 1

1) soak one set of peas in water for 24 hours so they begin to germinate
2) boil another batch of peas to kill them
3) wash both sets of peas in a 1% bleach solution, surface sterilising and killing any bacteria
4) rinse twice in distiller water to remove all bleach
5) put each batch of peas in inverted vacuum flasks, leaving some air in each flask
6) each flask is plugged with a thermometer and cotton wool - this allows the carbon dioxide gas that the seeds produce to escape
7) measure the temperature of the flasks
8) leave the flasks for a couple of days
9) measure the temperature again

Question 2

Describe an experiment to demonstrate the effect of temperature on an enzyme, using the enzyme amylase as an example..

Answer 2

Amylase breaks down starch into the sugar maltose.

By recording the speed at which the starch disappears we can measure the activity of the amylase.

1) spots of iodine are put into the depressions on a spotting tile
2) 5cm 3 of starch suspension is placed in one boiling tube and 5cm 3 of amylase solution is placed in another (separate syringes must be used to transport each solution)
3) a beaker is filled with water at room temperature and both boiling tubes are placed in the water for 5 minutes, recording the temperature
4) the amylase solution is poured into the starch suspension, leaving the tube with the mixture in the water bath
5) immediately, a small sample of the mixture is removed from the tube using a pipette and added to the first drop of iodine
6) the colour of the iodine is recorded
7) a sample of the mixture is then taken every 30 seconds for 10 minutes and tested for starch as above, until the iodine remains yellow, showing that all the starch is used up
8) the experiment is repeated, maintaining the water bath at different temperatures between 20 deg C and 60 deg C

• the results can be plotted on a table with temperature along the top, time down the side, and the relative colours written within the table itself
• the rate of the reaction can be calculated by dividing the volume of the starch (in this case, 5cm 3) by the time

Eg: rate = 5 cm 3 / 3.5 minutes = 1.4 cm 3 / minute

Question 3

Describe an experiment to show the effect exersise can have on breathing rate..

Answer 3

• subject sits for 5 minutes, getting completely relaxed
• next, count the number of breaths taken in one minute, recording the results
• wait for one minute then repeat
• repeat this until there is a steady value recorded for breathing rate
• carry out a vigorous exercise for 5 minutes
• once finished, record breathing rate as above, until it returns to normal
• results can then be recorded in a results table and a line graph can be constructed

Question 4

Describe how you can test for starch..

Answer 4

• glucose is sweet and dissolves in water while starch is not sweet and does not dissolve
• a further test is to shine a beam of light through solutions of each
• this is the “Tyndall beam effect” and dispersal only happens in starch as the large starch molecules are big enough to affect the light
• you can also add iodine solution (red) and see if it turns black, eg: if you add iodine to a peeled potato it will turn black

Question 5

What experiments can be carried out to investigate osmosis outside the body of an organism?

Answer 5

• construct an artificially permeable membrane using visking tubing
• fill the visking tube with concentrated sucrose solution, attaching it to a capillary tube and placing the visking tube in a beaker of water
• the level of water in the capillary tube rises as water moves from the beaker to the inside of the visking tube

OR..

• place a drop of sucrose solution on one microscope slide and a drop of tap water on another
• transfer two small squares of inner epidermis from the outer layer of an onion onto each one
• out a drop of the correct solution on top of each an then cover slips
• any excess liquid is blotted up with filter paper
• observe through a microscope for several minutes
• the specimen in water will show turgid cells
• the other will gradually plasmolyse (shrink away from the cell wall due to water loss)
• if the cell is placed in a solution with the same concentration as inside the cell, it will become flaccid

Question 6

Describe testing for glucose..

Answer 6

• Benedict’s or Fehling’s reagent is used to test for glucose but not sucrose
• you heat sugar with either of these chemicals and observe the colour change from blue to orange
• this reaction occurs because glucose is a reducing sugar, ie: it can help another chemical to be reduced

Question 8

Describe how photosynthesis can be investigated to show the production of starch and the importance of chlorophyll.

Answer 8

Iodine solution is used to test leaves for the presence of starch.

You need to:

• heat a plant leaf in boiling water for 30 seconds (this stops its chemical reactions)
• heat it in boiling ethanol for a few minutes (this removes most of its colour)
• wash with water and spread onto a white tile
  add iodine solution from a dropping pipette
• After a few minutes, the parts of the leaf that contain starch turn blue-black.

Note that ethanol is heated using a hot water bath. Ethanol boils at 78°C, so a tube of it boils when placed in a beaker of hot water. This is safer than using a Bunsen burner because ethanol is flammable.

Variegated leaves have green parts (where the cells contain chlorophyll) and white parts (where there is no chlorophyll). Only the parts that were green become blue-black with iodine solution, showing the importance of chlorophyll in photosynthesis.

A plant can be ‘de-starched’ by leaving it in the dark for a few hours. Parts of its leaves are covered with dark paper, and the plant is left in the light for a few hours. Only the uncovered parts become blue-black with iodine solution, showing the importance of light in photosynthesis.