Energy and transport

This course is a part of High school biology, a 9-course Topic series from Khan Academy.

Learn more about types of transfer and how organisms use photosynthesis and cellular respiration to convert and transfer energy.

This course contains 6 segments:

Introduction to metabolism

Can you feel the energy flowing through your body? The answer may be no (unless you’ve had something caffeinated recently), but it’s true: energy is constantly being transformed in your body.

Enzymes

Every second of the day, tiny molecular machines called enzymes are working away busily inside your cells, catalyzing and directing the chemical reactions that keep you alive. Learn more about how enzymes speed up reactions in cells.

Passive and active transport

Sometimes it pays to go with the flow! Learn about passive transport, in which molecules travel across the plasma membrane by moving down their concentration gradients (no energy expenditure required), and active transport.

Osmosis and tonicity

Ever wonder why plants wilt if you don't water them? Find out here, and learn more about the basic principles of probability that underlie movement of water and other molecules in biological systems.

Photosynthesis

There's a lot of carbon in your body - in DNA, proteins, carbohydrates, fats, and other key biological molecules. How did that carbon get there? Drumroll... photosynthesis! Learn how plants and other photosynthetic organisms use light energy to make sugars from carbon dioxide and water, bringing both chemical energy and readily usable carbon into Earth’s global ecosystem.

Cellular respiration

How do your cells extract energy from the food that you eat? As it turns out, cells have a network of elegant metabolic pathways dedicated to just this task. Learn more about cellular respiration, fermentation, and other processes that extract energy from fuel molecules like glucose.