Understanding Key Concepts in Biology and Physics: Diffusion, Energy, and Heat Transfer

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Cellular Transport and Water Potential


The movement of molecules from an area of high concentration to an area of low concentration through a partially permeable membrane. (Osmosis is the same but with water molecules)

Concentration Gradient

The difference in concentration of a substance between two different areas.

Active Transport

The uptake of particles by cells against a concentration gradient. It requires energy and a carrier protein.

Partially Permeable Membrane

A membrane that allows small molecules of water and certain solutes but does not allow the passage of large solute molecules.

Kinetic Energy

The energy of movement

Brownian Motion

The random movement of particles

Water Potential

The ability for a substance or cell to accept more water. Pure water has a water potential of zero.

Calculating Percent Change in Mass

% change in mass = (change in mass / initial mass) x 100

Plant Biology: Photosynthesis and Transpiration


The process where plants produce carbohydrates from carbon dioxide and water using energy from light.

Photosynthesis Equation

6CO2 + 6H2O —> C6H12O6 + 6O2

Carbon dioxide + water —> glucose + oxygen


The evaporation of water from the leaves through the stomata.


Can open and close, allows carbon dioxide to diffuse into the plant, allows water and oxygen to diffuse out of the plant.

Temperature and Heat Transfer


A measurement of the average kinetic energy of the particles that make up a system.

Thermal Equilibrium

When two objects are in thermal equilibrium, the particles of both objects will have the same average kinetic energy.

When hot particles (high energy) collide with cold particles (low energy), energy is exchanged over time. This phenomenon causes systems to reach thermal equilibrium.


The energy exchanged between systems that have different temperatures (when they are interacting).

Evaporation vs. Boiling

Evaporation is a change of state from liquid to gas, but it is different from boiling.

Methods of Heat Transfer


The particles that are directly heated gain energy and move more. Then they collide with nearby particles, transferring energy. Eventually, all of the system will gain energy, but not necessarily the same amount.


The heated particles tend to rise, while the colder particles sink and get heated. A convection current is created, and the energy is distributed rapidly throughout the system.

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