Biology Topic 1B Exam Questions

Explain how the structure of glycogen allows it to be an energy store? (3)

• M1: Polymer of glucose

• M2: To provide glucose for respiration

• M3: {branched/contains 1-6 glycosidic bonds/ has many terminal ends} for rapid hydrolysis

• M4: Compact to allow large amount of glucose/ energy to be stored in a small space/ insoluble hence no osmotic effect on cells

Explain how the structures of amylopectin and glycogen make them suitable for storing energy. (3)

• M1: Branched so can hence be rapidly hydrolysed to release glucose

• M2: Compact so more energy can be stored

• M3: Insoluble so therefore does not affect osmosis

• M4: Moleclues too large too diffuse across cell surface membrane

Compare and contrast the structure of a disaccharide with glycogen. (4)

• M1: Both contain C, H, O

• M2: Both contain glycosidic bonds

• M3: Both contain glucose

• M4: Glycogen contains 1,4 and 1,6 glycosidic bonds but disaccharide only contains one type

• M5: Glycogen can contain one glucose whereas disaccharides can contain glucose and other monosaccharides.

Explain why high levels of sugars in a persons diet could lead to obesity? (3)

• M1: Energy intake is greater than energy output

• M2: Excess {energy/sugars} can be {stored as/ converted to} fat

• M3: Leading to weight gain (greater than overweight)

• M4: Obesity as indicated by a {BMI above 30/ waist to hip ratio greater than 0.85 in women or 1.0 in men}

Assess the relative importance of carbohydrates to plants and animals. (6)

Basic Knowledge:

• Glucose for respiration in both

• starch for energy store in plants/ glycogen for energy store in animals

• cellulose for cell wall in plants

Linkage:

• starch composed of amylose and amylopectin in plants

• sucrose as transport sugar in phloem in plants, glucose in animals

• lactose in milk for energy

• a judgement of importance: cellulose as structural carbohydrate in plants hence a greater proportion carbohydrate in plants than animals or animals require more energy, hence need more carbohydrate.

Comprehensive biological knowledge with sustained linkages:

• pentose sugars, ribose and deoxyribose {in nucleic acids/ DNA/ RNA/ ATP/} in both

• Ribulose as part of the calvin cycle in plants

• glycoprotein in {mucus/ receptors on cell surface membrane/ antibodies}

• glycolipids in cell membranes

• Sustained judgement: animals store more energy in lipids than carbohydrates, hence carbohydrate more important as a storage molecule in plants/ or the idea of carbohydrates as part of complex molecules/ or the proportion of carbohydrates present is not as same as importance

Explain how the properties of water make it an ideal transport medium? (3)

• M1: water is a solvent

• M2: because water molecules surround {polar molecules/ ions}/ hydrogen bonds form between water molecules and polar molecules

• M3: water is liquid so has the ability to flow (cohesion between water molecules)

Describe how lactose is formed from two monosaccharides. (3)

• M1:Glucose and galactose

• M2: Joined by glycosidic bond

• M3: By condensation reaction