Question 1
What are the most abundant molecules in the cell surface membranes of plant cells?
Options:
A) Cholesterol
B) Glycolipids
C) Phospholipids
D) Proteins
Answer:
Correct Answer: C) Phospholipids
Explanation:
They are essential for various functions (transport, signaling), but they are not as abundant as phospholipids in forming the bilayer structure.
Cell Membrane Structure
The cell membrane primarily consists of a phospholipid bilayer, which forms the basic structure.
Phospholipids are arranged in a double layer, providing both flexibility and a barrier to many molecules.
They play a critical role in maintaining the membrane’s semi-permeable nature.
Role of Phospholipids
Phospholipids have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.
This arrangement allows the cell membrane to control the passage of substances in and out of the cell, essential for cell function.
Why Other Options Are Incorrect
A) Cholesterol
Present in animal cell membranes to provide fluidity and stability.
In plant cells, cholesterol is much less abundant, as plant membranes rely more on sterols like sitosterol.
B) Glycolipids
These are present in the membrane, especially in animal cells, where they play roles in cell recognition.
However, they are much less abundant than phospholipids.
D) Proteins
Integral and peripheral proteins are embedded within or attached to the membrane.