Practicals Flashcards
What is submerging vegetables an experiment for?
Submerging vegetables shows osmosis.
What is the experiment of submerging vegetables to show osmosis? How does it work?
1) Use a cork borer to cut 5 potato cylinders of the same diameter.
2) Use a scalpel and ruler to trim each potato cylinder so they are all the same length.
3) Measure the mass of each potato cylinder and record in a table of results.
4) Measure 10cm3 of each sugar or salt solution and pour into each boiling tube. Label each boiling tub clearly. - different concentration os sugar solutions, and one should be distilled water.
5) Add one potato cylinder to each boiling tube and leave for a specific amount of time.
6) After a while, trove the potatoes and blot hem dry and record the final mass.
What are the variables in the experiment of submerging vegetables to show osmosis?
Independent variable (one we change to see the effect): Solute concentration.
Dependent variable (one we measure): change in mass of potato cylinders.
Control variables (must stay constant):
-Temperate surrounding potato.
-Surface area of potato.
-Volume of solute solution.
What are the possible results of the osmosis experiment?
If the potato cylinder is immersed in a solution of a higher solute concentration compared to the cytoplasm of its cells will lose water. Water moves out of the cells due to osmosis.
- Decreased mass indicates net movement out of the cell.
This is because water moves from a region of high concentration (high water potential) to a region of lower concentration (low water potential), down a concentration gradient.
If the potato cylinder is immersed in a solution of a lower solute concentration compared to the cytoplasm leads to the potato gaining mass because there is net movement into the cell. This means mass increases.
What if there is no change in mass of the cell? -osmosis
If there is no change in the mass of the cell, the potato is immersed in a solution of the same solute concentration as the cytoplasm of the cell. Water moves into and out of the cell at the same rate.
What is dialysis tubing?
Dialysis or visking tubing is used as a model to show osmosis. It is a partially permeable material that acts as the membrane.
How does dialysis tubing work as an experiment to show osmosis?
1) Fill a section of dialysis tubing with concentrated sucrose solution. - cannot pass through the pores.
2) Suspend the tubing in a boiling tube (beaker) of water for a set period of time.
3) Note whether the water level outside of the tubing decreases as water moves into the tubing via osmosis.
-The distilled water moves into the dialysis tube through the membrane and via osmosis. This is because water moves from a region of higher water potential (dilute) to a region of lower water potential (conc solution), through a partially permeable membrane.
What is amylase?
Amylase is an enzyme that breaks down starch to maltose.
We can use iodine solution to test for the presence of starch. Changes from orange to blue-black if present.
How can amylase be used to investigate the effect of temperature and pH?
We can use the effect that the iodine solution will turn blue-black is starch is present. But if maltose and iodine react, it doesn’t change colour meaning it has already been broken down. This can be sued to investigate how the rate of reaction of amylase changes at different temperatures and pH levels.
What is the experiment for the effect of temperature on an enzyme?
-Amylase.
1) Heat a starch solution to a set temperature.
2) Add iodine to each well on the spotting tube.
3) Add the enzyme amylase and start timer immediately.
4) Once a minute has passed, a sample is transferred to the spotting tile - one of the wells.
5) At this temperature, the starch should not be digested yet so turns blue-black.
6) Repeat this for every minute that passes.
7) When all of the starch has been broken down, the iodine remains orange.
8) Repeat this at different temperatures.
9) At a higher temperature, it takes less time to break down all of the starch because they have more kinetic energy leading to more collisions between substrate and active site.
10) However, if the temperature gets too high, there will be no digestion because the amylase has denatured.
What is the experiment for the effect of pH on an enzyme?
-Amylase.
1) Prepare a spotting tile with drops of iodine in each well.
2) Measure out all of solutions.
e.g. 1cm3 pH7 buffer solution, 2cm3 amylase solution, starch solution.
3) Add the amylase and buffer to a test tube, mix then add starch solution. Start the stopwatch.
4) The amylase will start breaking the starch down into maltose.
5) Use a pipette to transfer a couple of drops of solution to iodine in spotting tile. This should turn blue-black because the starch has not yet fully been broken down.
6) Transfer more drops.
7) When the solution remains orange, it means that all of the starch has been broken down.
8) Repeat using buffer solutions of different pH.
9) At a too high pH (pH14), there is no reaction because the enzyme has denatured.
What is the experiment for investigating the need for carbon dioxide?
-Destarch 2 plants by placing in the dark for prolonged period of time.
-Place one plant in a bell jar which contains a beaker of sodium hydroxide (which will absorb carbon dioxide from the surrounding air).
-Place both plants in bright light for several hours.
-Test plants of starch using iodine.
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What are the results of investigating the need for carbon dioxide in plants experiment?
-The leaf from plant placed near the sodium hydroxide will remain orange/brown as it could not photosynthesise due to a lack of carbon dioxide.
-The leaf from plant placed near water should turn blue.black as it had all of the necessary requirements for photosynthesis.
What is the experiment for investigating the need for light?
-Plant needs to be destarched by placing in a dark cupboard for 24 hours.
-Following destarching, a leaf of the plant needs to be partially covered with aluminium foil and plant placed in sunlight for a day.
-The leaf can then be removed and tested for starch using iodine.
What are the results of investigating the need for light experiment?
-The area of the leaf that was covered with aluminium foil will remain orange/brown as it did not receive any sunlight and could therefore not photosynthesise.
-The area exposed to the sun will turn blue-black.
This proves that light is necessary for photosynthesis and production of starch (glucose/carbohydrates).
