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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
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
ATP hydrolase plays a crucial role in energy metabolism within the cell by catalyzing the hydrolysis of ATP into ADP and inorganic phosphate (Pi). This reaction releases energy, which is then used to move ions against their concentration gradient, thereby aiding in the active transport of sodium ions (Na+) out of 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 sodium ions (Na+) out of the cell creates a lower concentration of Na+ inside the cell compared to the outside. This concentration gradient allows Na+ to re-enter the cell through the co-transport mechanism alongside glucose. As sodium ions move back into the cell, driven by the concentration gradient, they facilitate the concurrent transport of glucose molecules into the cell, hence aiding in glucose absorption.
Step 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: Cells specialized for absorption, such as those lining the ileum, often have a folded membrane or microvilli, which increase the surface area available for absorption. A larger surface area allows for more transport proteins and channels, enhancing the absorption rate of nutrients.
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Numerous Mitochondria: These cells typically contain a large number of mitochondria, which provide the necessary ATP for active transport processes. The increased energy from ATP is crucial for maintaining concentration gradients for sodium and glucose transport.
Step 4
Draw phospholipids on Figure 2 to show how the carrier protein, SGLT1, would fit into the cell-surface membrane. Do not draw more than eight phospholipids.
Answer
Phospholipids should be illustrated as a bilayer with hydrophilic heads facing outwards and hydrophobic tails inward, encapsulating the SGLT1 protein, which spans the membrane. Ensure that the heads extend into the aqueous environment both inside and outside the cell, while placing at least six to eight phospholipids appropriately without overlapping with the protein illustration.
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, which are formed by a condensation reaction between the amino group (NH2) of one amino acid and the carboxyl group (COOH) of another. In this reaction, a molecule of water is released. This process results in a polypeptide chain where the NH2 group remains at one end (the N-terminus) and the COOH group is located at the opposite end (the C-terminus), thus maintaining the distinct ends of the polypeptide.