Problem 94 - Objective Biology for NEET

Question

In which kind of transport, the molecules move across without the utilization of energy? (a) Passive transport (b) Osmosis (c) Both (a) and (b) (d) Active transport

Step-by-Step Solution

Answer

The answer is (c) Both (a) and (b).

Step 1: Understanding the Transport Types

Passive transport is a method that allows molecules to move across the membrane without energy input like diffusion, facilitated diffusion. Osmosis is a specific type of passive transport involving the movement of water molecules without the use of energy. Active transport uses energy to transport molecules against their concentration gradient.

Step 2: Matching the Question Criteria

We are asked to identify the transport where molecules move without using energy. So, we can eliminate the option of active transport as it requires energy.

Step 3: Selecting the Correct Options

From the definition outlined in Step 1, both passive transport and osmosis fulfill the criteria. Therefore, both (a) Passive transport and (b) Osmosis are correct and the answer is (c) Both (a) and (b).

Key Concepts

Passive Transport

Imagine a river flowing naturally from a high mountain towards the sea - this is how passive transport works in the cellular world. It is a spontaneous movement of molecules across the cell membrane from an area of higher concentration to an area of lower concentration, and it does not require the cell to expend energy. Think of it as letting a ball roll downhill; the ball moves effortlessly due to gravity, just like molecules drift across the membrane because of a process called diffusion.

In living organisms, passive transport is essential for the regulation of substances entering or exiting the cell. For example, oxygen and carbon dioxide diffuse passively across the membrane, vital for cellular respiration and energy production. There is also a special type of diffusion known as facilitated diffusion, where molecules move through protein channels or carriers within the cell membrane, but still without using cellular energy.

Osmosis

Now, let's focus on a specific category of passive transport called osmosis. If diffusion is the general movement of substances, osmosis is the VIP, solely responsible for the movement of water. Osmosis occurs when water molecules pass through a selectively permeable membrane from a region with a lower solute concentration (more water) to a region with a higher solute concentration (less water).

This movement helps maintain the cell's internal balance, known as homeostasis. For example, plant cells use osmosis to absorb water from the soil, which gives them the turgor pressure necessary to maintain structure and growth. In the human body, osmosis regulates fluid balance across various compartments like blood vessels and tissues. This mechanism is so fundamental that if cells couldn’t perform osmosis, they would either swell up and burst or shrivel and die, depending on the surrounding water concentration.

Active Transport

In contrast to the effortless journey molecules take during passive transport, active transport is like swimming upstream – it requires energy! Cells perform active transport to move molecules from areas of lower concentration to areas of higher concentration, known as 'against the concentration gradient.' This is the cellular equivalent of pushing a boulder uphill.

Active transport often involves carrier proteins called pumps which need energy in the form of ATP (adenosine triphosphate). The sodium-potassium pump is a classic example, where the cell expends energy to maintain a high concentration of sodium ions outside and potassium ions inside. This process is crucial for many physiological functions, including nerve impulse conduction and muscle contraction. Without active transport, cells would not be able to maintain their necessary concentrations of various substances, which is vital for proper cellular function.