Biological molecules

Question 1

What is the formula for each of these cations?
- Calcium ions (1)
- Sodium ions (1)
- Potassium ions (1)
- Hydrogen ions (1)
- Ammonium ions (1)

Answer 1

• Calcium ions; Ca^2+ (1)
• Sodium ions: Na^+ (1)
• Potassium ions; K^+ (1)
• Hydrogen ions; H^+ (1)
• Ammonium ions; NH4^+ (1)

Question 2

What is the formula for each of these anions?
- Nitrate ions (1)
- Hydrogen carbonate ions (1)
- Chloride ions (1), how does it play a role in the breakdown of starch? (1)
- Phosphate ions (1)
- Hydroxide ions (1)

Answer 2

• Nitrate ions; NO3^- (1)
• Hydrogen carbonate ions; HCO3^- (1)
• Chloride ions; Cl^- (1), coenzyme for amylase. (1)
• Phosphate ions; PO4^3- (1)
• Hydroxide ions; OH^- (1)

Question 3

What makes water molecules polar and interact with one another? (2)

Answer 3

• Electrons shared unequally (oxygen has a greater share than hydrogen). (1)
• The slightly positive region of the water molecule (H2) is attracted to the slightly negative region of another water molecule (O). (1)

Question 4

Water has a very high boiling point; why? (1)

Answer 4

Abundant hydrogen bonds between water molecules means more energy is required to increase the temperature of water (high specific heat capacity). (1)

Question 5

Describe three properties of water that contribute to the increased likelihood of the survival of organisms. (6)

Answer 5

• Ice is less dense than water (floats). (1)
• Provides habitat for some species/ice insulates water below/organisms can move/organisms (like amphibians) can float/be buoyant. (1)
• Water is a good coolant. (1)
• Sweating/transpiration cools organisms (1)
• Water has a high specific heat capacity/boiling point. (1)
• Stable habitat (for aquatic organisms)/internal temperature of organisms changes slowly. (1)
• Water is a good solvent. (1)
• Oxygen is abundant in water/the cytosol is mostly water/medium for chemical reactions/transports soluble materials in and out of cells (e.g glucose in blood)/plasma is primarily water. (1)
• Water is cohesive and adhesive. (1)
• Exhibits capillary action useful in transport. (1)

Question 6

What elements do the following biological molecules contain:
- Carbohydrates (1)
- Proteins (1)
- Lipids (1)
- Nucleic acids (1)

Answer 6

• Carbohydrates; Carbon, hydrogen, oxygen (1)
• Proteins; Carbon, hydrogen, oxygen, nitrogen, sulphur (1)
• Lipids; Carbon, hydrogen, oxyen (1)
• Nucleic acids; Carbon, hydrogen, oxygen, nitrogen, phosphorus (1)

Question 7

Fill in the blanks (3):
The monomers (single units) of saccharides are called ___.
Two of these monomers bonded together forms a ___.
Many of these monomers bonded together forms a ___.

Answer 7

• Monosaccharide (1)
• Disaccharide (1)
• Polysaccharide (1)

Question 8

What is the bond formed between glucose and fructose to produce sucrose? (1)

Answer 8

• (Alpha) glycosidic (1)

Question 9

What type of reaction is required to break down lactose into galactose and glucose? (1)

Answer 9

• Hydrolysis (1)

Question 10

What type of reaction forms cellulose and what is the molecule that is polymerised? (2)

Answer 10

Condensation (1) reaction polymerises beta glucose (1)

Question 11

Which of the following statements about amylopectin are true? (2)

1. Contains only 1,6 glycosidic bonds.
2. Contains both 1,4 and 1,6 glycosidic bonds.
3. It is a soluble molecule.
4. It is a chain of beta glucose.
5. It is uncoiled.

Answer 11

• Statement 2 (1)
• Statement 5 (1)

Question 12

What inorganic ion is required as a cofactor for the activation of the enzyme that breaks down starch? (1)

Which enzyme catalyses the hydrolysis of starch? (1)

Answer 12

• Cl^- (1)
• Amylase (1)

Question 13

Describe the structure of amylose. (3)

Answer 13

• 1,4 glycosidic bonds (1)
• Alpha glucose (1)
• Coils (1)

Question 14

Reducing sugars are capable of donating electrons and therefore reduce the Cu^2+ ions in Benedict’s reagent into Cu+ ions.

Provide three examples of reducing sugars. (3)

Answer 14

• Glucose (1)
• Galactose (1)
• Fructose (1)

Question 15

Non-reducing sugars are dissacharides such as sucrose. Describe a method that can be used to test for carbohydrates in non-reducing sugars. (4)

Describe a positive result.

Answer 15

• Place the sample in a boiling tube (1)
• Boil sample in water bath with dilute hydrochloric acid (to hydrolyse it into its monosaccharides). (1)
• Add (equal volume of) Benedict’s reagent. (1)
• Heat the sample for (given time around 5 minutes). (1)
• Blue to green/yellow/orange/red. (1)

Question 16

Describe the colour change that will occur if iodine (dissolved in potassium iodide) is added to a sample of starch. (2)

Answer 16

Yellow/orange (1) to blue/black (1)

Question 17

Name the carbohydrates used for energy storage in :
- Plants (1)
- Animals (1)

Answer 17

• Starch (amylose and amylopectin) (1)
• Glycogen (1)

Question 18

• What type of reactions form a triglyceride? (1)
• What molecules make up triglycerides? (1)
• What bonds iare formed between the molecules? (1)

Answer 18

• Condensation (1)
• 3 fatty acids, 1 glycerol (1)
• Ester bonds (1)