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To study lipid digestion, a scientist placed a tube into the gut of a healthy 20-year-old man - AQA - A-Level Biology - Question 2 - 2020 - Paper 1
Question 2
To study lipid digestion, a scientist placed a tube into the gut of a healthy 20-year-old man. The end of the tube passed through the stomach but did not reach as fa... show full transcript
Worked Solution & Example Answer:To study lipid digestion, a scientist placed a tube into the gut of a healthy 20-year-old man - AQA - A-Level Biology - Question 2 - 2020 - Paper 1
Step 1
Use your knowledge of lipid digestion to explain the differences in the results for samples A and B shown in Table 1.
Answer
In sample A taken at 45 minutes after the meal, the concentration of triglycerides is 0.6 mg cm⁻³ while the concentration of fatty acids is 2.7 mg cm⁻³. This suggests that triglycerides are being hydrolyzed into fatty acids, which is a result of lipase activity that breaks down triglycerides.
In sample B taken at a later time of 75 minutes, the concentration of triglycerides has increased to 0.9 mg cm⁻³ and the concentration of fatty acids has increased to 3.3 mg cm⁻³, indicating continued hydrolysis. The increase in fatty acids suggests that lipase continues to act on triglycerides, leading to an increase in their concentration as their breakdown continues. This result confirms that digestion is an ongoing process, and these variances can be attributed to the rates of enzymatic activity over time.
Step 2
Explain why.
Answer
The samples were heated to 70 °C to denature the enzymes present, particularly lipases. Denaturation means the enzymes are rendered inactive, thereby stopping further digestion and hydrolysis of the lipids. This is critical in ensuring that the results accurately reflect the state of lipid digestion at the time of sampling, without interference from ongoing enzymatic activity.
Step 3
Describe the role of micelles in the absorption of fats into the cells lining the ileum.
Answer
Micelles play a crucial role in the absorption of fats due to several functions:
- They are formed from bile salts and fatty acids, which increase the solubility of lipids in the aqueous environment of the intestine, enabling their transport.
- Micelles facilitate the release of fatty acids into the cells lining the ileum by creating a high concentration gradient that drives diffusion.
- They bring fatty acids close to the intestinal epithelial cells, allowing for efficient uptake.
- Once inside the cells, fatty acids can be re-esterified into triglycerides, which are then packaged into chylomicrons for transport in the lymphatic system. The process of absorption is greatly enhanced by micelles acting as carriers of these hydrophobic substances.