A cell may allow a large or charged chemical to move across the cytoplasmic membrane, down the chemical’s electrical and chemical gradients, in a process called _________ .                   .


a. active transport
b. facilitated diffusion
c. endocytosis
d. pinocytosis

Verified step by step guidance

1. Step 1: Understand the key terms in the question. The question describes a process where a large or charged chemical moves across the cytoplasmic membrane down its electrical and chemical gradients. This means the movement is passive, not requiring energy input from the cell.
2. Step 2: Recall that active transport requires energy (usually ATP) to move substances against their gradients, so option (a) active transport is unlikely here because the movement is down the gradients.
3. Step 3: Consider endocytosis and pinocytosis (options c and d), which involve the cell engulfing substances by forming vesicles. These processes are not typically described as movement down gradients across the membrane but rather internalization of substances.
4. Step 4: Facilitated diffusion (option b) is a passive transport mechanism where proteins help large or charged molecules cross the membrane down their concentration or electrical gradients without energy expenditure.
5. Step 5: Based on the definitions and the description, the correct term to fill in the blank is the process that allows passive movement of large or charged molecules with the help of membrane proteins, which is facilitated diffusion.

Key Concepts

Facilitated Diffusion

Facilitated diffusion is a passive transport process where specific carrier proteins or channels help large or charged molecules cross the cell membrane down their concentration gradient, without using cellular energy. It allows substances that cannot diffuse freely through the lipid bilayer to enter or exit the cell efficiently.

Active Transport

Active transport involves moving molecules against their concentration or electrical gradients using energy, usually from ATP. This process requires specific transport proteins and is essential for accumulating substances inside the cell or expelling waste, unlike passive processes that rely on gradients.

Endocytosis and Pinocytosis

Endocytosis is a cellular process where the membrane engulfs extracellular material to bring it into the cell, often forming vesicles. Pinocytosis is a type of endocytosis specifically for the uptake of fluids and dissolved substances. Both require energy and are distinct from passive transport mechanisms.