Problem 11 - Objective Biology for NEET

Question

Find out the total number of false statements from the following. (1) The diffusion rate depends on the size of substrate. (2) Diffusion across membrane depends upon the solubility of lipids. (3) Membrane protein provide sites for hydrophilic substance to cross membrane. (4) Facilitated diffusion do not require concentration gradient. (a) 1 (b) 2 (c) 3 (d) 4

Step-by-Step Solution

Answer

The total number of false statements is 1 (d).

Step 1: Evaluate Statement 1

The first statement is: 'The diffusion rate depends on the size of substrate.' This statement is true. Diffusion rate is indeed influenced by the size of the particles or molecules. Smaller particles diffuse faster than larger particles because they can move more easily.

Step 2: Evaluate Statement 2

The second statement is: 'Diffusion across membrane depends upon the solubility of lipids.' This statement is true as well. The lipid solubility of a substance directly affects its ability to pass through the cell membrane by simple diffusion.

Step 3: Evaluate Statement 3

The third statement is: 'Membrane protein provide sites for hydrophilic substance to cross membrane.' This is also true. Membrane proteins can act as channels or transporters to help substances, especially polar or charged substances, to cross the cell membrane.

Step 4: Evaluate Statement 4

The fourth statement is: 'Facilitated diffusion do not require concentration gradient.' This is a false statement. Facilitated diffusion relies on the concentration gradient because substances move from an area of higher concentration to an area of lower concentration through specific transport proteins.

Key Concepts

Diffusion in Biological Systems

Diffusion is a key process in biological systems, ensuring substances such as gases, ions, and molecules can move from areas of high concentration to areas with lower concentration. This movement relies solely on kinetic energy and proceeds until equilibrium is reached.

Factors affecting the diffusion rate includes the size of diffusing substances, the concentration gradient, and the temperature. Smaller molecules can move between phospholipids in the cell membrane more easily than larger ones, explaining why size influences diffusion rate. Additionally, an increase in temperature typically speeds up diffusion because molecules have more kinetic energy.

In living organisms, this natural phenomenon is critical for various functions, such as cellular respiration where oxygen diffuses into cells and carbon dioxide diffuses out. Maintaining proper diffusion rates is essential for homeostasis, highlighting the importance of this spontaneous process in biology.

Membrane Transport Mechanisms

Cell membranes are selectively permeable barriers that regulate the entry and exit of substances. The transport across cell membranes occurs via several mechanisms, with diffusion being just one.

• Simple Diffusion: Nonpolar and small polar molecules pass directly through the lipid bilayer without assistance.
• Osmosis: The diffusion of water across a semipermeable membrane, guided by the water potential gradient.
• Active Transport: Movement of molecules against the concentration gradient using energy, typically ATP, and often involves carrier proteins.
• Endocytosis and Exocytosis: Processes for large molecules or particles to enter (endocytosis) or exit (exocytosis) the cell via vesicles.

Note that lipid solubility greatly influences the ability of molecules to diffuse directly through the cell membrane; more soluble substances diffuse more readily.

Facilitated Diffusion Process

Facilitated diffusion is a specific transport mechanism where molecules that cannot cross the lipid bilayer freely, such as ions and large polar molecules, diffuse through the membrane with the help of transport proteins.

There are two main types of proteins involved:

• Channel Proteins: Provide a water-filled passage for ions and other small, hydrophilic substances to pass through.
• Carrier Proteins: Bind to specific molecules and change shape to shuttle them across the membrane.

Despite aiding diffusion, these proteins do not provide energy to the molecules. Instead, facilitated diffusion is a passive process and absolutely relies on a concentration gradient, where molecules move from an area of higher to an area of lower concentration until equilibrium is achieved. This crucial process allows for selective permeability and contributes to the regulation of substance concentration within cells.