Diffusion

The scent particles start concentrated in one corner and spread throughout the room. This matches the definition of diffusion: net movement of particles from high to low concentration.

Diffusion is a passive process — it requires no energy (ATP). Particles move randomly due to their kinetic energy, and the net result is spreading from high to low concentration.

The correct answer states that particles spread from high to low concentration and without using energy, which precisely matches the definition of diffusion.

The question asks which statement best describes the spreading of scent particles — we need to find the option that matches diffusion correctly.

'Particles moved from low to high concentration using energy' is wrong on two counts — diffusion moves from high to low, and it requires no energy. This describes active transport instead.

'Actively pumped by the ventilation system' implies an external energy source driving the movement. Diffusion is passive and does not require any pumping mechanism.

'Particles remained near the spray source' contradicts what we observe — the scent clearly spreads throughout the room, so this option is factually incorrect.

The remaining option — particles spread from high to low concentration without using energy — correctly describes diffusion as a passive process down the concentration gradient.

Respiration produces CO₂ inside the cell, so CO₂ concentration inside the cell is higher than outside. The concentration gradient runs from inside → outside.

Diffusion always moves particles down the concentration gradient — from high to low concentration. Since CO₂ is higher inside, it diffuses out of the cell.

CO₂ is a small, non-polar molecule that can cross the cell membrane freely. No energy is needed — this is simple diffusion.

The correct answer is: CO₂ diffuses out of the cell because its concentration inside is higher than outside.

The question asks what happens to CO₂ produced inside a cell — specifically, in which direction it moves and why.

'Diffuses into the cell' is incorrect. Since CO₂ is being produced inside, its concentration is already higher inside. Diffusion would move it out, not in.

'Actively transported using ATP' describes active transport, not diffusion. CO₂ is a small non-polar molecule that crosses membranes freely by simple diffusion — no energy is needed.

'Remains inside until gates open' is incorrect. CO₂ does not need special gated channels — it passes directly through the phospholipid bilayer by diffusion.

The correct answer is that CO₂ diffuses out because its concentration inside is higher than outside — this correctly applies the principle of diffusion down the concentration gradient.