Diffusion
Define diffusion.
Net movement of particles from high to low concentration
What did Robert Brown observe under his microscope?
Pollen grains moving in a random, jittery zigzag pattern in water
Name the three states of matter.
Solid, liquid, gas
What is the name of the change from liquid to gas?
Evaporation / vaporisation
What do we call an organism that makes its own food using sunlight?
Producer
In which direction do particles move during diffusion?
Down the concentration gradient (high to low)
What causes the random movement of particles in Brownian motion?
Uneven collisions from surrounding fluid molecules hitting the particle from all sides
In which state do particles have the most kinetic energy?
Gas
What happens to particles when water freezes?
They slow down, lose kinetic energy, and form a fixed regular arrangement
In the chain: grass → rabbit → fox, what is the rabbit?
Primary consumer / herbivore
How does temperature affect the rate of diffusion?
Higher temperature = faster diffusion, as particles have more kinetic energy
How does increasing temperature affect Brownian motion?
Motion becomes more vigorous — particles have more kinetic energy so collisions are stronger
Why can liquids flow but solids cannot?
Liquid particles can slide past each other; solid particles are fixed in position and can only vibrate
What is sublimation? Give an example.
Direct change from solid to gas; e.g. dry ice (solid CO₂) or iodine crystals
What percentage of energy is typically passed on from one trophic level to the next?
10%
Why does diffusion happen faster in gases than in liquids?
Gas particles are further apart and move faster, so they spread with less resistance
How does Brownian motion support the particle model of matter?
It shows matter consists of tiny, invisible, constantly-moving particles that exert forces through collisions
Why can gases be compressed but liquids cannot?
Gas particles have large spaces between them; liquid particles are already tightly packed
Why does sweating cool you down? Link your answer to a phase change.
Sweat evaporates from the skin; the particles that escape carry kinetic energy away, removing heat from the body
Why do food chains rarely have more than 4–5 links?
Too much energy is lost as heat at each level, leaving too little to support another consumer
A cell produces CO₂ continuously. Explain why diffusion alone is enough to remove it.
CO₂ concentration inside is always higher than outside, maintaining a concentration gradient so it continuously diffuses out
Why does a larger particle show less Brownian motion than a smaller one?
It is struck by more molecules simultaneously from all directions, so forces cancel out and net movement is smaller
Explain why a gas fills its entire container but a liquid does not.
Gas particles move rapidly in all directions with enough energy to spread throughout; liquid particles are held together by intermolecular forces and settle under gravity
Why does temperature stay constant during melting, even when heat is being added?
Energy is used to break intermolecular bonds rather than increase kinetic energy, so temperature does not rise until the change of state is complete
A pesticide accumulates in organisms along a food chain. Why does the top predator suffer most?
Bioaccumulation — the toxin builds up at each level, so the top predator ingests the highest concentration