Biological Molecules Prepared Questions With Answers

Welcome to Biologised prepared questions and Answers. You may screenshot and print out for practice if necessary.

Questions

1. A) Which three elements are contained in all carbohydrates?
B) The molecular formula for glucose is C₆H₁₂O₆. What does this tell you about a glucose molecule?
C) Why is glucose described as a simple sugar, whereas starch and glycogen are described as more complex carbohydrates?
D) Why do animals need carbohydrates?

2. A) Name two elements found in proteins that are not found in carbohydrates.
B)  In what way are protein molecules similar to starch molecules?
C) State two uses of proteins in the human body.

3. Briefly explain the role of water in your body.

4.This is a practical activity to investigate the distribution of carbohydrates, fats and proteins in different parts of a seed or fruit.
You will need:
- porcelain tile
- cooked maize
- boiling tube
- iodine solution
- Bunsen burner
- Benedict's solution
- dropper
- raisins.
Method:
A) Take the cooked maize, and mix it with some water. Put a drop of iodine solution on a tile, and add some of the maize water. What happens to  the iodine solution? What does this colour change tell you about what is present in the maize?
B) Pour some cooked maize into a boiling tube, and add some Benedict's solution. Boil the mixture. What happens to the mixture? What does this result tell you about the maize?
C) Take a few raisins. Chop them up into small pleces, and carry out the same two tests as with the maize. want happens to the iodine solution? What happens to the Benedict's solution? What does tnis resuit tell you about the raisins?

5. A) Name the three elements found in fats.
B) Name the two smaller molecules from which a fat molecule is made.
C) List three reasons why humans need fat in their diet.
D) Complete this paragraph by filling in the missing words:
- To test food for fat, put a little food into a dry test-tube, and then add some a)______. Shake the food up, and then leave the food to settle. Take another test-tube, and put water in it. Then pour the b)_____ from the first tube into the second tube. If there is fat in the food, the liquid will turn c)_______.

6. In Experiment 6 you did a simple chemical test that shows the presence of Vitamin C in foods. The chemical used is the test reagent DCPIP, a dark blue Solution. A few drops of fruit juice added to DCPIP causes the blue colour to disappear. The vitamin C in the juice removes the blue colour from DCPIP.
Answer these questions
a) If you need more fruit juice than ascorbic acid solution to take the colour out of DCPIP, does it mean that the juice contains more vitaminC than the ascorbic acid test solution?
b) According to your results, which of your fruit juices contained the most vitamin C?
c) In what ways did the canned fruit juices differ from the fresh fruit juices in their Vitamin content?
d) The vitamin C content of food is reduced by cooking it. In fresh fruit and vegetables, there is a great deal of vitamin C. Use this information to  plan a diet to increase the vitamin C intake of an individual.

7. The table below shows the composition of four foods.

A) Which one would provide the most energy, if the foods were eaten in equal quantities?

8. Which substances join to form protein molecules?
A) amino acid molecules
B) fatty acid molecules
C) glycerol molecules
D) glucose molecules

9. Why is yeast used in making bread?
A)  it produces alcohol
B) it preserves the bread
C) it produces carbon dioxide
D) it provides carbohydrates

10. A) Describe a test that would allow you to find out if a food sample contains:
- protein   - reducing sugar
For each test, describe the observations that would indicate a positive result.
i) Protein test:
   Method:
   Observation:
ii) Reducing sugar test:
    Method:
    Observation:
B) Four different mixtures of starch, sugar, fat and protein were made up as follows and placed in separate containers:

Unfortunately, all the labels on the containers fell off. A learner was given the job of correctly re-labelling the containers. She carried out food tests on the contents of each container and obtained the following results.

From these results, work out which mixture, A, B, C or D, is in each container and complete the table below.

11. What is DNA?

12. What are the four pairs of DNA bases that form in the double helix?

13. How many strands make up a DNA double helix?

14. What is the primary structure ot a protein?

Answers

1. A) Carbon, hydrogen and oxygen
B) It contains six carbon atoms, twelve hydrogen atoms and six oxygen atoms.
C) Glucose contains only one molecule, whereas starch is made of many molecules linked together.
D) Carbohydrates are needed for energy.

2. A) Nitrogen and sulphur
B) Protein and starch molecules are both long molecules made up of smaller units.
C) Any two: growth; to make new cells; to make enzymes; to make haemoglobin (the red pigment in blood that carries oxygen); to make antibodies (chemicals that fight disease); to make new cell membranes; to make hair and skin (which contain the proteins keratin and collagen); and sometimes for energy.

3. Water is a solvent and all metabolic reactions take place in solutions. Blood plasma, tissue fluid and lymph and tissues to help regulate its temperature and maintain other bodily functions. Because your body lose water through breathing, sweating, and digestion, it's important to rehydrate by drinking fluids and are all mostly water. It is a means of transport in the body. Your body uses water in all its cells, organs, eating foods that contain water.

4. Practical investigation: Investigate the distribution of Carbonydrates, tats and proteins in different parts of a seed or fruit
A) The maize must contain starch.
B) The maize contains a little bit of reducing sugar.
C) The raisins do not contain starch, but they contain a lot of reducing sugar.

5. A) Carbon, hydrogen and oxygen
B) Fatty acids and glycerol
C) For energy. Humans need fat in their diet to make cell membranes and for insulation.
D) a) ethanol
     b) water
     c)cloudy or milky

6. a) Yes, it you need more fruit juice than ascorbic acid solution to take the colour out of DCPIP, it means that the juice contains more vitamin C than the ascorbic acid test solution.
b) The one that removes the blue colour trom DCPIP. Divide the orange juice into two samples of equal volume. You could freeze one of the samples and then defrost it. You could then see how many drops ot each juice was needed to remove the blue colour from DCPIP. If more of the frozen juice was needed to decolourise DCPIP, then you could conclude that freezing destroys the vitamin C content.
c) Vitamin C is sensitive to heat, light, and oxygen. If fresh produce is stored at the appropriate temperature and consumed in a relatively short period of time, then it is the best source of vitamin C. However, during prolonged storage, vitamin C degrades rapidly. It is also lost with blanching (thougn some fruits with ascorbic acid that undergo freezing may retain more vitamin C than even the fresh produce). A large percentage of vitamin C is lost with the initial canning process.
d) he diet should contain papaya, broccoli, strawberries, pineapple, oranges, kiwifruit, and caulitlower.

7. B, It has a lot of fat, which contains twice as much energy per gram as either carbohydrate or protein
8. A

9. C

10. A) i) Add Biuret reagent. Do not heat. A purple colour indicates protein.
ii)Add Benedict's solution. Boil. A red-brown colour indicates reducing sugar. If there were more marks allocated for these answers, you should describe how the food would first be chopped or crushed, and then mixed into some water before doing the test.
B) 1 Mixture C
    2 Mixture D
    3 Mixture A
    4 Mixture B

11. DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organsms

12. Guanine, thymine, adenine and cytosine

13. Two

14. The primary structure of a protein is the linear sequence of amino acids that form the molecule.

Food Tests Experiments Answers

EXPERIMENT 1
Practical investigation: Using iodine to test food for starch (iodine test)
- lodine solution should change to black when dropped onto the potato and bread. These two foods contain starch. lodine solution will stay brown when dropped onto the sugar, showing that sugar does not contain starch.

EXPERIMENT 2
Practical investigation: Using Benedict's solution to test food for a reducing sugar (Benedict's test)
- If there is a lot of sugar present, the solution will turn orange-red. If there is a small amount of sugar present, the solution will turn greenish-yellow.

EXPERIMENT 3
Practical investigation: Using Biuret solution to test food for proteins (Biuret test)
- A purple colour appears if protein is present. If the colour remains blue, there is no protein present.

EXPERIMENT 4
Practical investigation: Using ethanol solution to test food for fats (emulsion test)
- if there is fat present, the water turns milky.

EXPERIMENT 5
Practical investigation: Using DCPIP solution to test for ascorbic acid (vitamin C)
- The fewer the drops needed to remove the blue colour from the solution, the more concentrated the vitamin C in the food sample.

The end, Posted by Miss Fang Xiu.