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Figure 1 shows a cell from the lining of the ileum specialised for absorption of products of digestion - AQA - A-Level Biology - Question 1 - 2020 - Paper 1
Question 1
Figure 1 shows a cell from the lining of the ileum specialised for absorption of products of digestion. SGLT1 is a carrier protein found in the cell-surface membran... show full transcript
Worked Solution & Example Answer:Figure 1 shows a cell from the lining of the ileum specialised for absorption of products of digestion - AQA - A-Level Biology - Question 1 - 2020 - Paper 1
Step 1
The action of the carrier protein X in Figure 1 is linked to a membrane-bound ATP hydrolase enzyme. Explain the function of this ATP hydrolase.
Answer
The ATP hydrolase enzyme catalyzes the conversion of ATP to ADP and inorganic phosphate (Pi). This process releases energy, which is critical for active transport, enabling Na+ ions to be moved against their concentration gradient into the cell.
Step 2
The movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum. Explain how.
Answer
The movement of Na+ out of the cell creates a concentration gradient, allowing Na+ to move back into the cell via co-transport with glucose. This process is facilitated by SGLT1, which transports glucose into the cell along with Na+.
Step 3
Describe and explain two features you would expect to find in a cell specialised for absorption.
Answer
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Microvilli: These are tiny projections that increase the surface area of the cell, facilitating greater absorption of nutrients.
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Numerous Mitochondria: These organelles provide ATP, the energy currency of the cell, which is essential for active transport mechanisms involved in nutrient absorption.
Step 4
Draw phospholipids on Figure 2 to show how the carrier protein, SGLT1, would fit into the cell-surface membrane.
Answer
Phospholipids should be drawn with hydrophilic heads pointing outward and hydrophobic tails oriented inward, forming a bilayer around the SGLT1 protein, which resides within the membrane.
Step 5
Describe how amino acids join to form a polypeptide so there is always NH2 at one end and COOH at the other end.
Answer
Amino acids join together through peptide bonds formed between the carboxyl group (COOH) of one amino acid and the amino group (NH2) of another, creating a chain. The sequence starts with an NH2 terminal at one end and ends with a COOH terminal at the other, maintaining the polarization.