Question

Simple long distance transport cannot be achieved by (a) Diffusion (b) Facilitated diffusion (c) Active transport (d) All of these

Short answer

None of the listed methods - Diffusion, Facilitated diffusion, or Active transport - can effectively be used for long-distance transport in an organism, so the answer is (d) All of these.

Step-by-step solution

Understanding Diffusion

Diffusion is a process that allows particles to spread out from a region of high concentration to a region of low concentration until equilibrium is reached. This process is slow and entirely dependent on the activity of the particles themselves. Given the inherent energy and time constraints, it's not sufficient for long-distance transport in cells.

Understanding Facilitated Diffusion

Facilitated diffusion, unlike simple diffusion, uses carrier proteins to transport substances across cell membranes. However, it still depends on concentration gradients and can't be relied on for the long-distance transport of particles.

Understanding Active Transport

Active transport is the only mode that effectively moves particles against a concentration gradient using energy in the form of ATP. However, due to energy constraints and the transport specifically occurring at the cellular level, it's not ideal for long-distance transport in the organism.

Key concepts

Diffusion

Diffusion is a natural process where particles move from an area of higher concentration to an area of lower concentration. This movement occurs due to the random motion of particles, which drives them to spread out evenly in the available space. A classic example of diffusion is the way a drop of ink spreads in a glass of water until the color is uniform. Diffusion is a passive process, meaning it does not require energy from the cell. However, due to its reliance on concentration gradients and the slow nature of particle movement, diffusion alone is not effective for transporting substances over long distances within an organism. Instead, diffusion is useful for short-distance transport, such as the exchange of gases like oxygen and carbon dioxide in small areas around cells.

Key characteristics of diffusion include:

• Passive transport mechanism
• Driven by concentration gradients
• Effective for short distances only
• No cellular energy requirement

Facilitated Diffusion

Facilitated diffusion expands on the concept of diffusion by involving specific proteins to expedite the transport of substances across cell membranes. These proteins, known as carrier proteins or channels, help move molecules that might not easily pass through the lipid bilayer of the cell membrane on their own, such as glucose and certain ions. Although facilitated diffusion enables these substances to cross cell membranes more efficiently, it still relies on existing concentration gradients, meaning substances move from areas of higher concentration to lower concentration without the input of cellular energy.

While more efficient than simple diffusion, facilitated diffusion is still limited by its reliance on concentration gradients. It is not suitable for transporting molecules over long distances within the organism. This type of transport mainly supports processes like nutrient uptake at the cellular level.

Main features of facilitated diffusion:

• Utilizes carrier proteins or channels
• Does not require energy (passive)
• Higher efficiency than simple diffusion
• Ineffective for long-distance transport

Active Transport

Active transport is a crucial process for moving substances against their concentration gradients, meaning from an area of lower concentration to an area of higher concentration. To accomplish this, cells expend energy in the form of ATP. This energy requirement distinguishes active transport from diffusion and facilitated diffusion.

Active transport involves specific transport proteins, often referred to as pumps. These proteins bind to the substance to be transported and change shape, effectively shuttling the substance from one side of the membrane to the other. An example of active transport is the sodium-potassium pump, which maintains essential concentration gradients of sodium and potassium ions in our cells.

Although active transport is highly effective for concentrating essential molecules within cells and removing waste products, it is not suitable for long-distance transport of substances across the whole organism. The vast energy expenditure and cellular specificity make it impractical for transport across larger regions.

• Requires cellular energy (ATP)
• Transport against concentration gradients
• Involves specific transport proteins or pumps
• Ideal for maintaining concentrations and gradients at the cellular level