Question

Suppose you discover a new bacterium that has a concentration of 15 nM Cu²⁺ inside the cell, and 1 mM Cu²⁺ outside the cell. When a facilitated diffusion Cu²⁺ transporter opens, you expect the Cu²⁺ ions to flow.... (

Remember, to move with/down a concentration gradient is to move from high to low concentration; against/up a concentration gradient is low to high.)
a. inside the cell, with its concentration gradient
b. inside the cell, against its concentration gradient
c. outside the cell, with its concentration gradient
d. outside the cell, against its concentration gradient

Answer 1

Copper ions (Cu²⁺) will move inside the cell, with its concentration gradient, during facilitated diffusion since they flow from high to low concentration without requiring cellular energy.

Step-by-step explanation:

When considering the movement of ions across a cell membrane, facilitated diffusion is a process that enables ions like copper ions (Cu²⁺) to move across the membrane without the input of cellular energy. This process relies on the existence of a concentration gradient. The concentration gradient is simply the difference in the concentration of a substance (in this case, copper ions) between two areas. For facilitated diffusion to occur, ions will move down their concentration gradient, meaning they will flow from an area of higher concentration to an area of lower concentration - this is a form of passive transport.

Given the concentrations mentioned in the question, with a high concentration of Cu²⁺ ions outside the cell (1 mM) and a lower concentration inside the cell (15 nM), when a facilitated diffusion Cu²⁺ transporter is opened, the copper ions would naturally flow inside the cell because they are moving from an area of higher concentration outside the cell to an area of lower concentration inside the cell. This is known as moving with or down the concentration gradient. This principle is illustrated in Figure 8.9 which shows facilitated transport of substances down their concentration gradients with the aid of channel proteins. Additionally, as opposed to active transport which requires energy, facilitated diffusion does not require an input of energy because it's utilizing the natural kinetic energy of the ions to move down the gradient.