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Red blood cells contain hemoglobin, a protein that binds to oxygen in the lungs and releases it to tissues throughout the body.

A renewable resource is one that can be used repeatedly and is naturally replenished on a human timescale, like energy from the sun.

Coca alkaloids, such as cocaine, are central nervous system stimulants. They work by increasing the levels of neurotransmitters like dopamine in the brain, leading to heightened alertness and euphoria.

Mars appears red because its surface is covered in iron oxide, or rust, which gives the landscape a reddish hue.

The chemical formula H2O represents one oxygen atom covalently bonded to two hydrogen atoms.

In a series circuit, the current flows through a single path. If that path is broken by a burnt-out bulb, the current cannot flow to the other bulbs.

Gravity is the attractive force between all objects with mass. The Sun’s immense gravitational pull keeps the planets in their elliptical orbits.

During photosynthesis, plants use sunlight, water, and carbon dioxide to create glucose (their food) and release oxygen as a byproduct.

The three most common states of matter on Earth are solid, liquid, and gas. Heat is a form of energy, not a state of matter.

The skin is the body’s largest organ, making up about 15% of your total body weight. It serves as a protective barrier against the environment.