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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
1. Explain the function of this ATP hydrolase.
Answer
The ATP hydrolase enzyme breaks down ATP into ADP and inorganic phosphate (Pi), releasing energy. This energy is utilized to transport sodium ions (Na+) against their concentration gradient into the cell, which is essential for establishing a sodium concentration gradient that is crucial for the subsequent uptake of glucose via the SGLT1 protein.
Step 2
2. Explain how Na+ movement out of the cell allows the absorption of glucose into the cell lining the ileum.
Answer
The active transport of Na+ out of the cell creates a low concentration of Na+ inside the cell. This concentration gradient enables Na+ to move back into the cell through co-transport with glucose via the SGLT1 protein. As Na+ enters, it brings glucose along with it, facilitating the absorption of glucose into the cell lining the ileum.
Step 3
3. Describe and explain two features you would expect to find in a cell specialised for absorption.
Answer
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Folded membrane (microvilli) to increase surface area, enhancing the capacity for absorption.
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A large number of co-transport proteins to facilitate the rapid absorption of nutrients, ensuring efficient transport mechanisms are in place to maximize nutrient uptake.
Step 4
4. Draw phospholipids on Figure 2 to show how the carrier protein, SGLT1, would fit into the cell-surface membrane.
Answer
In your drawing, ensure to represent phospholipids as a bilayer with hydrophilic heads oriented toward the outside and inside of the cell, while the hydrophobic tails face inward. Position the SGLT1 protein within this membrane bilayer, ensuring it spans the membrane at least partially.
Step 5
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 to form a polypeptide through peptide bonds. The amino group (NH2) of one amino acid reacts with the carboxyl group (COOH) of another, releasing water (condensation reaction). This process continues, resulting in a chain of amino acids with an NH2 group at one end (the N-terminus) and a COOH group at the other end (the C-terminus), ensuring the proper orientation of functional groups.