Question

Identify A, B and C shown in this table: \(\begin{array}{lccc}\text { Property } & \begin{array}{c}\text { Simple } \\\ \text { Diffusion }\end{array} & \begin{array}{c}\text { Facilitated } \\\ \text { Transport }\end{array} & \begin{array}{c}\text { Active } \\ \text { Transport }\end{array} \\ \text { Requires special membrane proteins } & \text { A } & \text { Yes } & \text { Yes } \\ \text { Highly selective } & \text { No } & \text { Yes } & \text { Yes } \\ \text { Transport Saturates } & \text { No } & \text { B } & \text { Yes } \\ \text { Uphill transport } & \text { No } & \text { No } & \text { C } \\ \text { Requires ATP energy } & \text { No } & \text { No } & \text { Yes } \\ \begin{array}{lc}\text { (a) A-Yes, B-Yes, C-Yes } & \text { (b) A-Yes, B-No, C-Yes }\end{array}\end{array}\) a) (a) A-Yes, B-Yes, C-Yes A-Yes, B-No, C-Yes (c) \(\mathrm{A}-\mathrm{No}, \mathrm{B}-\mathrm{Yes}, \mathrm{C}-\mathrm{Yes}\) (d) A-No, B-No, C-Yes

Short answer

(c) A-No, B-Yes, C-Yes

Step-by-step solution

Identification of A

A refers to whether Simple Diffusion requires special membrane proteins or not. As per the table, under Simple Diffusion, for the property 'Requires special membrane proteins', A is marked. But since 'Simple Diffusion' does not require special membrane proteins, so, A is 'No'.

Identification of B

B denotes whether Facilitated Transport can saturate or not. As per the table, under Facilitated Transport, for the property 'Transport Saturates', B is marked. But 'Facilitated Transport' can saturate because of the limited number of transport proteins available. Hence, B is 'Yes'.

Identification of C

C refers to whether Active Transport can move particles uphill or against the concentration gradient or not. As per the table, under Active Transport, for the property 'Uphill Transport', C is marked. In fact, 'Active Transport' can move molecules against a concentration gradient, so C is 'Yes'.

Key concepts

Simple Diffusion

Simple diffusion is a fundamental process in cellular transport, allowing molecules to move across the cell membrane without the need for energy or special proteins. In simple terms, it's like letting molecules go with the flow.
This process occurs when molecules move from an area of higher concentration to an area of lower concentration.
This natural movement continues until there's an equal concentration of molecules on both sides of the membrane, achieving equilibrium. Here are some key points to remember:

• Molecules move down their concentration gradient.
• No energy (ATP) is required from the cell.
• No special membrane proteins are needed.

Simple diffusion is crucial for the transport of small, nonpolar molecules such as oxygen, carbon dioxide, and small lipids. It's important for students to understand that this process directly ties into how cells maintain homeostasis by regulating the movement of substances without expending energy.

Facilitated Transport

Facilitated transport is a step up from simple diffusion, mainly because it involves the help of membrane proteins to move molecules across the cell membrane. While it does not require energy, it does rely heavily on these proteins to operate.
In facilitated transport, molecules move from areas of high concentration to areas of low concentration, but they need a bit of assistance:

• Special proteins, such as carrier and channel proteins, provide this assistance.
• The process is selective, meaning only certain molecules can pass through.
• Transport can saturate, meaning if all proteins are busy, no additional molecules can pass through simultaneously.

Facilitated transport is specifically important for larger or polar molecules that cannot easily diffuse through the lipid bilayer on their own. This includes ions, glucose, and amino acids. Understanding this concept helps students grasp how cells control the intake and output of these essential substances without using energy, focusing instead on the availability and function of specific proteins.

Active Transport

Active transport takes things to a whole new level by moving molecules against their concentration gradient, which means going from an area of low concentration to an area of high concentration.
This process requires energy and is crucial for maintaining cellular functions and homeostasis. Let's explore the important features of active transport:

• Energy is needed in the form of ATP since molecules move against the gradient.
• Specialized membrane proteins act as "pumps" to facilitate this movement.
• It allows cells to maintain concentration differences that are essential for vital processes like nerve impulse transmission and nutrient absorption.

Active transport is necessary for transporting ions like sodium and potassium across cell membranes, keeping an electrical balance, and ensuring cells have the right conditions to function properly. Students need to grasp the idea that this process is crucial for life, as it allows for an unequal distribution of ions, which is necessary for many cellular processes.