02.07 Lipids & Triglycerides

Question 1

Describe the structure of a triglyceride. (6 marks)

Mark Scheme:

1. Triglycerides consist of one glycerol molecule and three fatty acid molecules. (1 mark)
2. Glycerol is an alcohol with three hydroxyl (–OH) groups. (1 mark)
3. Each fatty acid contains a carboxyl group (–COOH) and a hydrocarbon tail. (1 mark)
4. The fatty acids bind to the hydroxyl groups of glycerol through ester bonds. (1 mark)
5. The formation of each ester bond occurs via a condensation reaction, releasing three water molecules. (1 mark)
6. Triglycerides have non-polar, hydrophobic hydrocarbon tails, making them insoluble in water but soluble in organic solvents. (1 mark)

Question 2

Explain how triglycerides are adapted for energy storage. (6 marks)

Mark Scheme:

1. Triglycerides have a high density of carbon-hydrogen bonds, which release large amounts of energy upon oxidation. (1 mark)
2. They provide a higher energy yield per gram than carbohydrates or proteins. (1 mark)
3. Being hydrophobic, triglycerides are stored without attracting water, reducing storage weight. (1 mark)
4. This makes them efficient for long-term energy storage, especially in animals. (1 mark)
5. Triglycerides are stored in adipose tissue, where they act as energy reserves during fasting or energy-demanding activities. (1 mark)
6. The compact and dense nature of triglycerides ensures maximum energy storage in minimal space. (1 mark)

Question 3

What is the role of triglycerides in thermal insulation and organ protection? (5 marks)

Mark Scheme:

1. Triglycerides stored under the skin act as a thermal insulator, reducing heat loss in cold environments. (1 mark)
2. This insulation is particularly important for endothermic animals, maintaining a stable body temperature. (1 mark)
3. Deposits of triglycerides around vital organs (e.g., kidneys) provide cushioning and protection from mechanical shocks. (1 mark)
4. In marine animals, large fat deposits (e.g., blubber) also aid in buoyancy and thermal insulation in cold water. (1 mark)
5. These adaptations enhance survival in diverse environmental conditions, from terrestrial cold climates to aquatic habitats. (1 mark)

Question 4

How do triglycerides provide a source of metabolic water? (5 marks)

Mark Scheme:

1. When triglycerides are oxidized during respiration, they produce carbon dioxide, energy, and water. (1 mark)
2. This water, known as metabolic water, is crucial for hydration in animals living in arid environments. (1 mark)
3. Example: Desert animals like the kangaroo rat rely on metabolic water to survive in environments with limited water availability. (1 mark)
4. Triglycerides are particularly efficient as they produce more water per gram than carbohydrates or proteins during oxidation. (1 mark)
5. This function illustrates the versatility of triglycerides in meeting both energy and water needs. (1 mark)

Question 5

Compare the energy yield of triglycerides and carbohydrates. (5 marks)

Mark Scheme:

1. Triglycerides provide approximately twice the energy per gram compared to carbohydrates. (1 mark)
2. The higher energy density is due to the greater number of carbon-hydrogen bonds in triglycerides. (1 mark)
3. Carbohydrates are more suitable for short-term energy storage, as they are rapidly mobilized and metabolized. (1 mark)
4. Triglycerides are ideal for long-term energy storage, providing sustained energy over extended periods. (1 mark)
5. The hydrophobic nature of triglycerides allows compact storage without water, unlike carbohydrates, which attract water and are bulkier. (1 mark)

Question 6

Explain the role of triglycerides in buoyancy and survival in marine animals. (5 marks)

Mark Scheme:

1. Triglycerides are stored as blubber in marine animals like whales and seals. (1 mark)
2. Blubber provides buoyancy by reducing the overall density of the animal. (1 mark)
3. It also acts as a thermal insulator, protecting the animal from cold water temperatures. (1 mark)
4. Triglycerides serve as an energy reserve, which is crucial for long migrations or periods of fasting. (1 mark)
5. These combined roles enhance the survival and functionality of marine animals in challenging aquatic environments. (1 mark)

Question 7

What are the differences between triglycerides and phospholipids? (6 marks)

Mark Scheme:

Question 8

Why are triglycerides considered an efficient energy storage molecule? (6 marks)

Mark Scheme:

1. Triglycerides are energy-dense, with many C–H bonds that release significant energy upon oxidation. (1 mark)
2. They provide approximately 37 kJ/g, making them more efficient than carbohydrates (16 kJ/g). (1 mark)
3. Being hydrophobic, triglycerides are stored without water, minimizing storage weight. (1 mark)
4. Their compact structure allows storage of large energy reserves in small spaces, such as in adipose tissue. (1 mark)
5. Triglycerides are metabolized into fatty acids and glycerol, which enter pathways like beta-oxidation and glycolysis for ATP production. (1 mark)
6. Their long-term energy storage capability supports survival during prolonged fasting or migration. (1 mark)

Question 9

Explain how triglycerides are formed and broken down in living organisms. (6 marks)

Mark Scheme:

1. Formation: Triglycerides are formed when glycerol reacts with three fatty acids through condensation reactions. (1 mark)
2. Each hydroxyl group (–OH) of glycerol reacts with the carboxyl group (–COOH) of a fatty acid, forming ester bonds. (1 mark)
3. Three water molecules are released as by-products of the condensation reaction. (1 mark)
4. Breakdown: Triglycerides are hydrolyzed into glycerol and fatty acids by adding water, catalyzed by enzymes like lipase. (1 mark)
5. Fatty acids are metabolized via beta-oxidation to produce ATP, while glycerol enters glycolysis or gluconeogenesis. (1 mark)
6. This reversible process allows triglycerides to function in both energy storage and release. (1 mark)

Question 10

How does the hydrophobic nature of triglycerides influence their biological roles? (5 marks)

Mark Scheme:

• Triglycerides are hydrophobic, meaning they do not mix with water. (1 mark)
• This property allows them to be stored in a compact, anhydrous form, minimizing storage weight. (1 mark)
• In adipose tissue, triglycerides provide an efficient long-term energy reserve. (1 mark)
• Their hydrophobic nature also ensures they do not dissolve in cytoplasm, preventing interference with cellular processes. (1 mark)
• This makes triglycerides ideal for functions such as energy storage, insulation, and organ protection. (1 mark)

Question 1

Describe the structure of a fatty acid and differentiate between saturated and unsaturated fatty acids. (6 marks)

Mark Scheme:

1. A fatty acid consists of a carboxyl group (–COOH) as the head and a long hydrocarbon tail. (1 mark)
2. The hydrocarbon tail is a chain of carbon atoms bonded to hydrogen atoms, typically 15–17 carbons long. (1 mark)
3. Saturated fatty acids have no double bonds between carbon atoms in their tails. (1 mark)
4. Saturated fatty acids are straight, allowing them to pack closely together, and are solid at room temperature (e.g., animal fats). (1 mark)
5. Unsaturated fatty acids have one or more double bonds (–C=C–), creating kinks in the tail. (1 mark)
6. These kinks prevent close packing, making unsaturated lipids liquid at room temperature (e.g., plant oils). (1 mark)

Question 2

Explain the difference between fats and oils in terms of structure and properties. (5 marks)

Mark Scheme:

1. Fats are lipids that are solid at room temperature, while oils are liquid. (1 mark)
2. Fats are typically composed of saturated fatty acids with straight hydrocarbon tails. (1 mark)
3. Oils are mostly made of unsaturated fatty acids, containing one or more double bonds. (1 mark)
4. The kinks in unsaturated fatty acid tails prevent tight packing, increasing fluidity in oils. (1 mark)
5. Fats are common in animal sources, whereas oils are typically derived from plants (e.g., sunflower oil, olive oil). (1 mark)

Question 3

What are the structural and functional differences between monounsaturated and polyunsaturated fatty acids? (6 marks)

Mark Scheme:

1. Monounsaturated fatty acids have one double bond in their hydrocarbon tails. (1 mark)
2. Polyunsaturated fatty acids have multiple double bonds. (1 mark)
3. Double bonds in both types cause kinks in the tail, reducing packing ability and increasing fluidity. (1 mark)
4. Monounsaturated fatty acids are typically found in olive oil and avocado, providing moderate fluidity. (1 mark)
5. Polyunsaturated fatty acids (e.g., in fish oil, sunflower oil) provide greater fluidity due to more kinks. (1 mark)
6. Both are considered healthier than saturated fatty acids, contributing to heart health by reducing bad cholesterol levels. (1 mark)

Question 4

Why are unsaturated fatty acids liquid at room temperature while saturated fatty acids are solid? (6 marks)

Mark Scheme:

1. Unsaturated fatty acids have one or more double bonds (–C=C–), creating kinks in their hydrocarbon tails. (1 mark)
2. These kinks prevent the fatty acid molecules from packing closely together. (1 mark)
3. The reduced packing results in weaker intermolecular forces, making the lipid liquid at room temperature. (1 mark)
4. Saturated fatty acids lack double bonds, so their tails are straight. (1 mark)
5. This allows tight packing of molecules, leading to stronger intermolecular forces. (1 mark)
6. Consequently, saturated fatty acids are solid at room temperature, as seen in animal fats. (1 mark)

Question 5

Explain the structural features of saturated and unsaturated fatty acids that influence their physical state. (5 marks)

Mark Scheme:

1. Saturated fatty acids have straight hydrocarbon tails due to the absence of double bonds. (1 mark)
2. This structure allows molecules to pack closely, forming strong intermolecular forces. (1 mark)
3. As a result, saturated fatty acids are solid at room temperature (e.g., butter, lard). (1 mark)
4. Unsaturated fatty acids contain double bonds, creating kinks in their hydrocarbon tails. (1 mark)
5. The kinks reduce close packing, weakening intermolecular forces and making them liquid at room temperature (e.g., sunflower oil, olive oil). (1 mark)

Question 6

What is the relationship between fatty acid structure and lipid function in biological membranes? (6 marks)

Mark Scheme:

1. Biological membranes are composed of phospholipids, which include two fatty acid tails. (1 mark)
2. Saturated fatty acid tails are straight, leading to less fluid and more rigid membranes. (1 mark)
3. Unsaturated fatty acid tails, with kinks from double bonds, increase membrane fluidity by reducing tight packing. (1 mark)
4. Membrane fluidity is critical for processes such as diffusion, endocytosis, and exocytosis. (1 mark)
5. A balance of saturated and unsaturated fatty acids ensures the membrane is flexible yet stable. (1 mark)
6. Cholesterol also plays a role in regulating membrane fluidity by interacting with fatty acid tails. (1 mark)

Question 7

Why are unsaturated fats considered healthier than saturated fats? (5 marks)

Mark Scheme:

1. Unsaturated fats contain double bonds, which create kinks in their structure, preventing tight packing. (1 mark)
2. They tend to be liquid at room temperature and are less likely to accumulate as plaque in arteries. (1 mark)
3. Unsaturated fats help reduce LDL cholesterol (bad cholesterol) levels. (1 mark)
4. They increase HDL cholesterol (good cholesterol), improving heart health. (1 mark)
5. Saturated fats, with straight chains, are solid at room temperature and contribute to cardiovascular diseases by raising LDL cholesterol levels. (1 mark)

Question 8

Discuss the role of double bonds in determining the properties of fatty acids. (6 marks)

Mark Scheme:

1. Double bonds in fatty acids create kinks in the hydrocarbon tail, altering their structure. (1 mark)
2. These kinks reduce the ability of fatty acids to pack tightly together. (1 mark)
3. Fewer intermolecular forces result in lower melting points, making unsaturated fats liquid at room temperature. (1 mark)
4. Double bonds can be cis (same side) or trans (opposite side), affecting the shape and health impact of fatty acids. (1 mark)
5. Cis double bonds promote fluidity, while trans double bonds behave more like saturated fats, increasing health risks. (1 mark)
6. The number of double bonds determines if the fatty acid is monounsaturated or polyunsaturated, affecting its properties and biological function. (1 mark)

Question 9

How do the structural differences between saturated and unsaturated fatty acids affect their storage and biological roles? (6 marks)

Mark Scheme:

1. Saturated fatty acids, with straight chains, pack tightly, forming dense, solid fats that are efficient for energy storage. (1 mark)
2. These fats are found in animal tissues and are stored as long-term energy reserves. (1 mark)
3. Unsaturated fatty acids, with kinks from double bonds, pack less tightly and form oils. (1 mark)
4. Oils, being liquid, are more dynamic and often used in metabolic processes rather than long-term storage. (1 mark)
5. Unsaturated fats are common in plant seeds, where fluidity aids in nutrient transport. (1 mark)
6. Saturated fats play structural roles, such as insulation and protection, while unsaturated fats are precursors for hormones and signaling molecules. (1 mark)

Question 10

Explain the significance of the hydrocarbon tail length in determining the properties of fatty acids. (6 marks)

Mark Scheme:

• Longer hydrocarbon tails increase intermolecular forces, raising the melting point of fatty acids. (1 mark)
• Shorter tails have weaker forces, making the fatty acid more fluid and reducing the melting point. (1 mark)
• In biological membranes, shorter or unsaturated tails increase fluidity, enhancing membrane flexibility. (1 mark)
• Longer, saturated tails create more rigid membranes, which can reduce permeability. (1 mark)
• Organisms in colder environments often have shorter or unsaturated fatty acids to maintain membrane fluidity. (1 mark)
• Hydrocarbon tail length also affects lipid solubility in water, with longer tails being more hydrophobic. (1 mark)