Question

Following figure shows different transport mechanisms used by a cell. If the circles represents transport proteins then choose the correct option showing type of transport.

• A. $$\begin{array}{cccc}\text{Simple diffusion}& \text{Facilitated diffusion}& \text{Primary active transport}& \text{Secondary active transport}\\ 3& 1& 4& 2\end{array}$$
• B. $$\begin{array}{cccc}\text{Simple diffusion}& \text{Facilitated diffusion}& \text{Primary active transport}& \text{Secondary active transport}\\ 3& 2& 1& 4\end{array}$$
• C. $$\begin{array}{cccc}\text{Simple diffusion}& \text{Facilitated diffusion}& \text{Primary active transport}& \text{Secondary active transport}\\ 4& 0& 4& 1\end{array}$$
• D. $$\begin{array}{cccc}\text{Simple diffusion}& \text{Facilitated diffusion}& \text{Primary active transport}& \text{Secondary active transport}\\ 3& 4& 2& 1\end{array}$$

Answer 1

The correct option is A $$\begin{array}{cccc}\text{Simple diffusion}& \text{Facilitated diffusion}& \text{Primary active transport}& \text{Secondary active transport}\\ 3& 1& 4& 2\end{array}$$

Simple diffusion does not involve transport protein so 3 is Simple diffusion.

Facilitated diffusion and both types of active transport involves transport protein.

Active transport may involve transport of 1 or 2 substances simultaneously but it is not possible in facilitated diffusion so 2 and 4 are types of active transport and 1 is facilitated diffusion.

4 is counter transport of $N{a}^{+}$ and $K^{+}$ and it directly uses ATP so it is primary active transport while 2 is Secondary active transport which doesn’t require ATP directly.

Secondary active transport is a form of active transport across a biological membrane in which a transporter protein couples the movement of an ion (typically $N{a}^{+}or{H}^{+})$ down its electrochemical gradient to the uphill movement of another molecule or ion against a concentration/electrochemical gradient. Thus, energy stored in the electrochemical gradient of an ion is used to drive the transport of another solute against a concentration or electrochemical gradient.