Chemistry Basics
Human Body Systems
Earth & Space
Physics Fundamentals
Ecology & Plants
100
This element, with atomic number 8, is the gas most people need to breathe.
What is oxygen?
100

This muscular organ pumps blood through the body and is roughly the size of a fist.

What is the heart?

100

This star at the center of our solar system provides nearly all of Earth's energy.

What is the sun?

100

This unit of force accelerates one kilogram at one meter per second squared.

What is the newton?

100

This green pigment captures light energy for photosynthesis.

What is chlorophyll?

200

The number of protons in an atom's nucleus, which defines the element, is called this.

What is atomic number?

200

This organ filters blood to produce urine and helps regulate water and electrolyte balance.

What is the kidney?

200

This planet is the largest in our solar system and has a giant storm called the Great Red Spot.

What is Jupiter?

200

This quantity, equal to mass times velocity, is conserved in an isolated system.

What is momentum?

200

This organelle is the site of photosynthesis in plant cells.

What is the chloroplast?

300

Balancing 2H₂ + O₂ → 2H₂O shows this law, which states that matter is neither created nor destroyed in a reaction.

What is the law of conservation of mass?

300

This is the largest and strongest bone in the human body, located in the thigh.

What is the femur?

300

This type of rock forms from cooled magma or lava, such as basalt and granite.

What is igneous rock?

300

Ohm's law states that voltage equals current multiplied by this quantity.

What is resistance?

300

Organisms that eat only plants are called this.

What are herbivores?

400

At standard temperature and pressure, one mole of any ideal gas occupies about this many liters.

What is 22.4 liters?

400

This hormone, made by the pancreas, lowers blood glucose by helping cells take up sugar.

What is insulin?

400

This layer of Earth, between the crust and the core, is the thickest layer.

What is the mantle?

400

This law states that a gas's pressure is inversely proportional to its volume at constant temperature.

What is Boyle's law?

400

This term describes the variety of life in an ecosystem, measured at the genetic, species, and ecosystem levels.

What is biodiversity?

500

This type of bond forms when atoms share electrons, as in the H–H bond of H₂.

What is a covalent bond?

500

This iron-containing protein in red blood cells carries oxygen from the lungs to the tissues.

What is hemoglobin?

500

This layer of the atmosphere contains most of the ozone that absorbs ultraviolet radiation.

What is the stratosphere?

500

This constant, about 6.674 × 10⁻¹¹ N·m²/kg², appears in Newton's law of universal gravitation.

What is the gravitational constant (G)?

500

This gradual change in a community's species over time, after a disturbance, is called this.

What is ecological succession?