Problem 166 - Objective Biology for NEET

Question

Assertion: Movement by diffusion is passive process. Reason: No energy expenditure takes place during diffusion.

Step-by-Step Solution

Answer

The Assertion and Reason are correct, and the Reason validates the Assertion.

Step 1: Understand the Assertion

The Assertion states that 'Movement by diffusion is a passive process'. In terms of cellular biology, passive processes refer to the movement of biochemicals and other atomic or molecular substances across cell membranes without the need for energy input. Let's confirm this statement by comparing it with the principle of diffusion.

Step 2: Analyze the Reason

The stated Reason is 'No energy expenditure takes place during diffusion'. By definition, diffusion is a process resulting from the random motion of particles where substances move from an area of higher concentration to an area of lower concentration until equilibrium is reached. It does not require energy, and thus, is considered as passive transport.

Step 3: Confirm the interconnection

Considering our understanding from Step 1 and Step 2, the Reason supports the Assertion. Movement by diffusion is indeed a passive process because it does not involve the expenditure of energy.

Key Concepts

Passive Transport

Passive transport is a fundamental concept in cellular biology, describing the movement of molecules across cell membranes without any need for external energy. This kind of transport relies on the natural motion of particles, often driven by concentration gradients. In simpler terms, molecules move from areas of high concentration to low concentration naturally.

This movement does not rely on energy, which means the cells do not use any of their energy stores to make it happen. The process is instead powered by the natural kinetic energy of molecules, which constantly move and collide randomly. Common examples of passive transport include osmosis and diffusion. By understanding passive transport, we can appreciate how cells efficiently manage intake and release of substances.

• Occurs without energy
• Driven by concentration gradients
• Key examples: diffusion and osmosis

Cell Membranes

Cell membranes are critical structures that protect and organize cells. They are primarily composed of a double layer of phospholipids, which allows them to be both flexible and selectively permeable. This feature is essential because it lets certain molecules pass through while keeping others out, maintaining the internal balance of the cell.

Cell membranes facilitate passive transport such as diffusion, allowing molecules like oxygen and carbon dioxide to pass freely in and out of the cell. Proteins embedded in the cell membrane can help with the transport of larger or charged molecules which can't diffuse freely. The structure and composition of cell membranes are crucial for effective cellular function, acting as both a barrier and gateway for different substances.

• Double layer of phospholipids
• Selectively permeable
• Facilitates diffusion and osmosis

Energy Expenditure

Energy expenditure refers to how organisms, including cells, use energy to perform tasks. In biology, not all processes require an energy expenditure. Passive transport, including diffusion, does not require external energy, which distinguishes it from active transport that needs energy from ATP.

During passive transport, substances move down their concentration gradient without energy input, showcasing how cells can efficiently support certain processes. This lack of energy requirement is a significant advantage for cells because it allows them to conserve energy, ensuring it's available for other cellular activities that do require energy, like cell division or active transport.

• Passive transport requires no energy
• Active transport requires ATP
• Conserves energy for vital cell functions