Question

The bulk movement of liquid into a cell through vesicular infoldings is known as: (A) \(\quad\) phagocytosis. (B) \(\quad\) pinocytosis. (C) \(\quad\) exocytosis. (D) \(\quad\) drinking.

Short answer

Option B: pinocytosis.

Step-by-step solution

- Understand the Terminology

First, understand the key terms presented in the options. Phagocytosis involves the engulfing of large particles; pinocytosis is the process of taking in liquid into the cell; exocytosis is the process of vesicles merging with the plasma membrane to release contents out of the cell; and 'drinking' is not a biological term used in this context.

- Identify the Correct Term

Since the question refers to the bulk movement of liquid into a cell, the correct term is the one associated with the uptake of extracellular fluid. This process is known as pinocytosis.

- Confirm Your Answer

Review the definitions once more to ensure accuracy. Phagocytosis (option A) involves solid particles, exocytosis (option C) is about exporting material out of the cell, and 'drinking' (option D) is not a proper term in this context. Therefore, pinocytosis is the correct answer.

Key concepts

Pinocytosis

Pinocytosis, often referred to as 'cell drinking', is a cellular process where cells ingest extracellular fluid and its dissolved solutes. This process involves the invagination of the cell membrane, creating small vesicles that encapsulate the liquid. These vesicles then move into the cell, releasing their contents into the cytoplasm.

Key characteristics of pinocytosis include:

• Ingestion of liquid: Unlike phagocytosis, which deals with solid particles, pinocytosis is specific to fluids.
• Vesicle formation: The cell membrane wraps around the fluid to form vesicles.
• Non-selective process: Pinocytosis is less specific than other transport mechanisms, meaning it doesn't select which fluids to ingest.

Pinocytosis plays a crucial role in nutrient absorption, especially in cells lining the gut, that partake in absorbing nutrients from the digestive tract into the bloodstream.

Phagocytosis

Phagocytosis is a type of endocytosis where the cell ingests large particles, such as bacteria, dead cells, or other sizable objects. This mechanism is critical for the immune system, as it helps in removing pathogens and cellular debris. During phagocytosis, the cell's membrane engulfs the target particle, forming a phagosome which is then internalized.

Important aspects of phagocytosis include:

• Ingestion of solids: Unlike pinocytosis, phagocytosis targets large particles.
• Selective process: Cells often recognize specific particles to ingest, usually tagged by molecules such as antibodies.
• Phagosome formation: The engulfed particle is enclosed in a membrane-bound vesicle known as a phagosome.

Phagosomes usually fuse with lysosomes, resulting in the digestion of the engulfed material. Phagocytes, for instance, are specialized cells that perform phagocytosis, playing a pivotal role in the immune response by defending the body against infections.

Exocytosis

Exocytosis is the process by which cells expel materials. This involves vesicles within the cell moving toward the plasma membrane, fusing with it, and releasing their contents outside the cell. Exocytosis is essential for functions such as neurotransmitter release, hormone secretion, and waste removal.

Key elements of exocytosis are:

• Export of substances: Materials are moved out of the cell, contrasting with endocytosis processes like pinocytosis and phagocytosis.
• Vesicle fusion: Vesicles containing the substances to be expelled merge with the cell membrane.
• Release to exterior: Contents of the vesicles are discharged into the extracellular environment.

Exocytosis is vital for maintaining cellular homeostasis and communication between cells. For example, neurons use exocytosis to release neurotransmitters into synapses, thereby facilitating neuronal signaling.