Chapter 5, Problem 1MC

Animal cells are surrounded by ______ fluid. This fluid is_____ to thecytosol.

a. phospholipid; isotonic

b. plasma; hypertonic

c. interstitial; isotonic

d. interstitial; hypotonic

Summary Introduction

Introduction:

Animals are eukaryotes and therefore their cells are highly organized. They have a phospholipid membrane, which is bilayered and encloses the cell’s contents like organelles, proteins, and ribosomes in the cytosol.

Answer to Problem 1MC

Correct answer:

Interstitial fluid surrounds animal cells and is isotonic with respect to the cytosol.

Explanation of Solution

Justification for the correct answer:

Option (c) is given that isotonic, interstitial fluid surrounds the animal cells. This is a true statement as interstitial fluid is a part of the extracellular matrix (ECM). The water cannot enter or exit the cell because of equal concentration of solute and water in the cytosol and the interstitial fluid. Hence, option (c) is correct.

Justification for incorrect answers:

Option (a) is given that a phospholipid fluid encloses the animal cell and this fluid is isotonic. This is false as phospholipid is a component of the cell membrane and not the area surrounding it. Also, the lipid component of the membrane makes it permeable and therefore it cannot be isotonic. So, it is an incorrect option.

Option (b) is given that the hypertonic blood plasma encloses the animal cells. This is only partially true as the interstitial fluid that is a major component of the ECM actually forms the blood plasma in case of animals, but this plasma is not hypertonic. If it was true, the cells will always be in a shrunken state. So, it is an incorrect option.

Option (d) is given that an interstitial fluid surrounds the cells in animals, which is hypotonic in nature. This is a wrong statement because if the fluid surrounding the cells were to be hypotonic, the cells would always be swollen and will burst to result in cell death. So, it is an incorrect option.

Hence, options, (a), (b), and (d) are incorrect.

Conclusion

Thus, it can be concluded that it is the interstitial fluid, which is a part of the ECM surrounds the cells of animals. This provides an isotonic solution and hence maintains the osmotic pressure in and out of the cell.