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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 membrane... 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
Explain the function of this ATP hydrolase.
Answer
The ATP hydrolase enzyme catalyzes the breakdown of ATP (adenosine triphosphate) into ADP (adenosine diphosphate) and inorganic phosphate (Pi).
This reaction releases energy, which is then used to transport ions against their concentration gradient. In this context, it allows the movement of Na+ ions out of the cell, maintaining a concentration gradient that is essential for the co-transport of glucose.
Step 2
Explain how the movement of Na+ out of the cell allows the absorption of glucose into the cell lining the ileum.
Answer
The movement of Na+ out of the cell creates a concentration gradient that facilitates its re-entry into the cell via the SGLT1 transporter, where it co-transports glucose along with it. As Na+ moves back into the cell by facilitated diffusion, glucose is then carried along, resulting in effective absorption of glucose into the ileal cells.
Step 3
Describe and explain two features you would expect to find in a cell specialised for absorption.
Answer
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The cell would have a highly folded membrane or microvilli to increase the surface area available for absorption, thereby enhancing the rate of nutrient uptake.
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A large number of co-transport proteins would be present, such as SGLT1, to facilitate the rapid transport of glucose and ions, ensuring efficient nutrient absorption.
Step 4
Draw phospholipids on Figure 2 to show how the carrier protein, SGLT1, would fit into the cell-surface membrane.
Answer
The phospholipids should be represented with hydrophilic 'heads' facing outward and hydrophobic 'tails' oriented inward, creating a bilayer. The SGLT1 protein will be embedded within this bilayer, allowing its hydrophobic regions to interact with the fatty acid tails while positioning its hydrophilic regions towards the extracellular and intracellular environments.
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 are joined together by peptide bonds during a condensation reaction where the amino group (NH2) of one amino acid reacts with the carboxyl group (COOH) of another, releasing a molecule of water. This results in a chain of amino acids, maintaining a free amino group at one end (the N-terminus) and a free carboxyl group at the other end (the C-terminus), which is a characteristic of polypeptide formation.