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The diagram below shows a cross section of part of the plasma membrane of a typical mammalian cell - VCE - SSCE Biology - Question 1 - 2008 - Paper 1
Question 1
The diagram below shows a cross section of part of the plasma membrane of a typical mammalian cell. The substances labelled X and Y are about to be transported acros... show full transcript
Worked Solution & Example Answer:The diagram below shows a cross section of part of the plasma membrane of a typical mammalian cell - VCE - SSCE Biology - Question 1 - 2008 - Paper 1
Step 1
Structure A Chemical composition
Answer
Structure A is primarily composed of phospholipids, which have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails. This unique arrangement leads to the formation of a bilayer that is fundamental to cell membrane structure, allowing selective permeability.
The hydrophobic interior serves as a barrier to most water-soluble substances while enabling lipid-soluble molecules to pass freely through the membrane. This property is crucial for maintaining cellular homeostasis and regulating the internal environment of the cell.
Step 2
Structure B Chemical composition
Answer
Structure B is likely a protein structure embedded in the plasma membrane, which can be either integral or peripheral. Integral proteins typically span the membrane and are characterized by hydrophobic regions that interact with the lipid bilayer.
These proteins serve various functions, such as acting as channels or transporters for substances like substance Y, which may require energy to move across the membrane. The specific amino acid composition of these proteins allows for specific interactions with the substrate, thereby facilitating the transport process effectively.