A beetroot slice is first washed and then placed in cold water and it does not lose its anthocyanin. This shows that the plasma membrane is
A)Impermeable to anthocyanins
B)Permeable to anthocyanins
C)Differentially permeable to anthocyanins
D)Dead

Hint: The plasma membrane consists predominantly of phospholipids, which are composed of alcohol and fatty acids. Phospholipids are found in the plasma membrane, called a phospholipid bilayer, and are arranged into two layers. A phospholipid molecule has two tails and a head. Water (hydrophilic) and the tails "fear" water "loves" the head (hydrophobic). On the inside of the membrane, the water-fearing tails are, while the water-loving heads point forward, either into the cytoplasm or the cell-surrounding fluid.

Complete answer:
The red colored pigment found in the beetroot is anthocyanin. The interior of the cell contains the pigment. The membrane of the plasma is impermeable and does not allow leakage of the pigment. The slices were washed and put in cold water that did not kill the plasma membrane and did not release the pigment. The fatty acid tails of the phospholipids shift less and become more stable at a low temperature. This lowers the membrane's total fluidity, also reducing its permeability and theoretically preventing the entry into the cell of essential molecules such as oxygen and glucose.

Factors that affect fluidity in bilayers –
1)Length of tail of fatty acids. The length of the tail of the fatty acid impacts the membrane's fluidity.
2)Temperature. If the temperature increases, so does the fluidity of phospholipid bilayers.
3)Bi-layer cholesterol content.
4)The saturation level of the tails of fatty acids.

Hence, the correct answer is option (A)

Note: A phospholipid bilayer, consisting of two layers of phospholipid molecules, forms part of the cell membrane. However, other macromolecules, such as membrane proteins and carbohydrates, are also found in the cell membrane. Therefore, we can assume that a phospholipid bilayer is made of the cell membrane, but not only is it made of it.