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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
The ATP hydrolase enzyme facilitates the breakdown of ATP to ADP and inorganic phosphate (Pi). This reaction releases energy, which is crucial for the active transport of sodium ions (Na+) against their concentration gradient. Consequently, this enzyme helps to maintain the concentration gradient necessary for the co-transport of glucose and Na+ 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 is essential for the establishment of a sodium gradient. Sodium ions move into the cell through the SGLT1 co-transporter, which also brings glucose along with them into the cell by facilitated diffusion. This co-transport mechanism enhances the absorption of glucose as it relies on the favorable concentration gradient created by the ATP hydrolase enzyme.
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: The presence of microvilli increases the surface area available for absorption, allowing for a greater number of nutrient molecules to be absorbed.
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Large number of mitochondria: These organelles provide the ATP needed for active transport processes, such as the uptake of glucose and Na+ ions, thus enhancing the overall efficiency of absorption.
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
To represent how SGLT1 fits into the phospholipid bilayer, draw phospholipids in a bilayer with their hydrophilic (polar) heads facing outward and their hydrophobic (non-polar) tails facing inward. Ensure to show that part of SGLT1 extends through the membrane, illustrating its position as an integral membrane protein.
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 linked together by peptide bonds, which form through a condensation reaction between the amino group (NH2) of one amino acid and the carboxyl group (COOH) of another. This process results in the release of a water molecule. The polypeptide chain continues to grow in this manner, always maintaining an NH2 at one end (N-terminus) and a COOH at the other end (C-terminus), ensuring the directionality of the polypeptide.