Biological Molecules - GSCE

Question 1

Identify the chemical elements present in carbohydrates

Answer 1

Carbon, Hydrogen, Oxygen

Question 2

Identify the chemical elements present in proteins

Answer 2

Carbon, Hydrogen, Oxygen, Nitrogen (Sulfur)

Question 3

Identify the chemical elements present in lipids (fats and oils)

Answer 3

Carbon, Hydrogen, Oxygen

Question 4

Describe the structure of carbohydrates as large molecules made up from smaller basic units

Answer 4

Carbohydrates from Saccharide Unit (sugar)

Starch and Glycogen from simple sugars

Question 5

Describe the structure of proteins as large molecules made up from smaller basic units

Answer 5

Proteins from Amino Acids

Question 6

Describe the structure of lipids as large molecules made up from smaller basic units

Answer 6

Lipids from Fatty Acids and Glycerol

Question 7

Practical: investigate food samples for the presence of glucose

Answer 7

METHOD:
Add a few drops of Benedict’s solution into a test tube of the test solution
Heat test tube placed in a water bath set at 60 - 70 °C for 5 minutes
Remove the test tube from the water bath and observe the color change
RESULT:
If Glucose is present, the solution will turn brick red
If Glucose is not present, the solution will stay blue

Question 8

Practical: investigate food samples for the presence of starch

Answer 8

METHOD:
Use a pipette to transfer sample solution into wells on tile
Add a few drops of Iodine solution and observe the color change
RESULT:
If Starch is present, the solution will turn blue-black
If Starch is not present, the solution will stay brown

Question 9

Practical: investigate food samples for the presence of protein

Answer 9

METHOD:
Add a few drops of Biuret solution into a test tube of sample solution
Observe color change
RESULT:
If Protein is present, the solution will turn violet
If Protein is not present, the solution will stay blue

Question 10

Practical: Investigate food samples for the presence of fat

Answer 10

METHOD:
Test tube of the sample solution is mixed with 2cm³ of Ethanol and 2cm³ of distilled water
Observe color change
RESULT:
If Fat is present, a milky - white emulsion will form
If Fat is not present, the solution will remain colorless

Question 11

The role of enzymes as biological catalysts in metabolic reactions

Answer 11

The most important thing to know about enzymes is that they are chemically unchanged throughout the reaction. Enzymes speed up a reaction by lowering the activation energy of a reaction. Making a reaction faster and being unchanged are the basic characteristics of a catalyst, therefore, as enzymes speed up reactions and are chemically unchanged throughout the reaction, they are known as biological catalysts.

Question 12

How does temperature change affect enzyme function, including changes to the shape of the active site

Answer 12

As with many chemical reactions, the rate of an enzyme-catalyzed reaction increases as the temperature increases. However, at high temperatures, the rate decreases again because the enzyme becomes denatured and can no longer function. As the temperature increases so do the rate of enzyme activity. Optimum activity is reached at the enzyme’s optimum temperature. A continued increase in temperature results in a sharp decrease in activity as the enzyme’s active site changes shape. It is now denatured.

Question 13

Practical: Investigate how enzyme activity can be affected by changes in temperature

Answer 13

Put starch into a test tube; either heat or cool it.
Add amylase
With this mixture on white tiles, add iodine
Time how long it takes for the iodine to stop being blue-black
Repeat at different temperatures and compare
When the iodine stops being blue/black there is no starch present, so it must have been digested by the enzymes.

Question 14

Understand how enzyme function can be affected by changes in pH altering the active site

Answer 14

Change in PH can denature enzymes by breaking the bonds that hold the structure in place. So the active site no longer fits with the substrate it is meant to be breaking down. The PH at which this happens is different for different enzymes, but generally, an extreme PH will denature any enzyme.

Question 15

Practical: investigate how enzyme activity can be affected by changes in pH

Answer 15

Set up a Bunsen burner, heatproof mat, tripod, and gauze.
Now put two drops of iodine solution into each spot of a spotting tile.
Add 2 cm³ of amylase enzyme solution to a test tube.
Place 2 cm³ of starch solution into the same tube.
Finally, add 1 cm3 of pH solution to the tube. This will keep the pH constant.
Mix the solution in the test tube and place it into the beaker of water on the Bunsen burner.
Use a pipette to remove a few drops of solution every 20 seconds from the test tube and put them into a different well of the spotting tile.
Repeat until the iodine solution stops turning black.
Record the time this takes.
Repeat with different pH solutions.

Question 16

Understand the processes of diffusion, osmosis and active transport by which substances move into and out of cells

Answer 16

Active transport is the movement of dissolved molecules into or out of a cell through the cell membrane, from a region of lower concentration to a region of higher concentration. The particles move against the concentration gradient, using the energy released during respiration.

Question 17

Understand how factors affect the rate of movement of substances into and out of cells, including the effects of surface area to volume ratio, distance, temperature, and concentration gradient

Answer 17

Changed in kinetic energy (a decrease in temperature will decrease the rate of diffusion/osmosis as it will decrease the amount of kinetic energy in the molecules)
Surface area for diffusion and the surface area to volume ratio
The size of the concentration gradient
The thickness/distance molecules have to diffuse

Question 18

Practical: investigate diffusion using living and non-living systems

Answer 18

Diffusion
Put a colored substance (like food coloring) into a clear one (like water)
Time how long it takes for all the liquid to be the same color.
Change the temperature of the liquid and make observations.
The higher the heat, the more kinetic energy meaning the color moves through the liquid faster.

Question 19

Practical: investigate osmosis using living and non-living systems

Answer 19

Osmosis
Cut two roughly equal pieces of potato and weigh them.
Put one in distilled water and one in saltwater.
After a given amount of time weigh them.
The one in saltwater will have lost mass as the water in the potato moves to the more highly concentrated saltwater. Whereas in the pure water the potato will have gained mass as it was less