Cells must sometimes move ions and other small substances across the plasma membrane in a direction that passive processes would not favor. This lesson explains why that movement requires energy and how cells use primary and secondary active transport to maintain essential conditions.
A concentration gradient is a difference in the concentration of a substance across a space or membrane. Particles tend to diffuse from regions of higher concentration toward regions of lower concentration.
All flashcards
What is an electrochemical gradient?
The combined influence of concentration and electrical differences across a membrane on an ion’s movement.
Why do sodium ions tend to move into a typical cell?
Sodium is usually more concentrated outside, and the negatively charged cell interior attracts positive sodium ions.
How does primary active transport move substances?
It uses ATP directly to move substances across a membrane, often against their gradients.
How does receptor-mediated endocytosis select materials for uptake?
Specific membrane receptors bind particular substances, which are then brought into the cell in vesicles.
How does exocytosis release material from a cell?
An internal vesicle fuses with the plasma membrane and releases its contents outside the cell.
Quiz questions
In the sodium-potassium pump’s typical exchange, how many ions move in each direction per cycle?Answer: Three sodium ions move out and two potassium ions move in.
How does secondary active transport obtain energy to move a substance?Answer: It uses energy stored in an electrochemical gradient established by another transport process.
Which material is characteristically taken up by phagocytosis?Answer: Large particles, including microorganisms or whole cells.
What makes receptor-mediated endocytosis selective?Answer: Membrane receptors bind particular substances before the membrane encloses them.
What directly enables a cell to release vesicle contents by exocytosis?Answer: Fusion of the vesicle membrane with the plasma membrane.
Based on Concepts of Biology by Samantha Fowler, Rebecca Roush, James Wise (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.