General Science: Biology, Chemistry, Physics, and Earth Science

General Information hands you free points in science if you know the everyday facts. You will not be asked to derive equations. You will be asked to name a process, match a unit, or read a simple situation and say what is happening. This lesson gathers the settled science that repeats, grouped so you can recall it fast.

Life science: the cell, the body, and living things

The cell is the basic unit of life: every plant and animal is built from cells. Groups of similar cells form tissues, tissues form organs, and organs working together form a system.

Learn the main body systems by their one-line job:

• Circulatory: the heart and blood vessels move blood.
• Respiratory: the lungs take in oxygen and release carbon dioxide.
• Digestive: breaks food into nutrients the body can absorb.
• Nervous: the brain, spinal cord, and nerves carry signals and control the body.

In an ecosystem, green plants are producers: they make their own food. Animals that eat other organisms are consumers, and organisms that break down dead matter are decomposers. A plant's roots anchor it and absorb water and minerals from the soil, while its leaves make the food.

Matter and its changes

Matter exists in three common states: solid, liquid, and gas (plasma is a fourth). Adding or removing heat changes the state.

Change	From ... to	Everyday example
Melting	solid to liquid	ice turning to water
Freezing	liquid to solid	water turning to ice
Evaporation	liquid to gas	a puddle drying up
Condensation	gas to liquid	dew forming on grass
Sublimation	solid straight to gas	a mothball shrinking away

Watch the traps: condensation is gas turning to liquid, the reverse of evaporation, and sublimation skips the liquid stage entirely.

Elements, compounds, and mixtures

An atom is the smallest particle of an element that still has that element's properties. When atoms of different elements bond in a fixed ratio, they form a compound: water and ordinary table salt (sodium chloride, made of sodium and chlorine) are compounds.

A mixture is two or more materials combined without a fixed ratio, and each part keeps its own properties. When one material dissolves evenly in another, like salt in water, the result is a solution, a uniform mixture you cannot separate by filtering. Because the parts of a mixture keep their properties, you can separate them physically: a magnet pulls iron filings out of a pile of sand, and a filter traps sand out of water. Keep the ladder straight: an atom is a piece of an element, a compound is elements chemically bonded, and a mixture is materials only physically combined.

Force, motion, and energy

A force is a push or a pull that can start, stop, or change the motion of an object. An object at rest stays at rest, and a moving object keeps moving, until a force acts on it. This resistance to a change in motion is inertia, stated in Isaac Newton's first law.

Energy is the ability to do work. Two forms to know:

• Kinetic energy is the energy of motion. A moving patrol car has kinetic energy.
• Potential energy is stored energy that depends on position, like a rock resting at the edge of a cliff.

The SI (metric) units let you match a quantity to its unit: length in meters, mass in kilograms, time in seconds, and force in newtons.

Electricity and magnetism

A conductor lets electricity pass through easily. Metals such as copper are good conductors, which is why wires have a copper core. An insulator resists the flow: rubber and plastic are insulators, which is why wire coatings are plastic.

A magnet has two poles, north and south. Like poles repel; unlike poles attract. Only a few metals, mainly iron, nickel, and cobalt, are attracted to a magnet. Gold, aluminum, and copper are not.

Earth and space

Our solar system has eight planets orbiting the Sun, which is a star. Two quick anchors:

• Mars is the "Red Planet," colored by its iron-rich, reddish dust.
• The Moon is Earth's only natural satellite. It makes no light of its own and shines only by reflecting sunlight.

The atmosphere is layered. Clouds, rain, and most weather sit in the lowest layer, the troposphere, which is the air closest to the ground. Higher up, an ozone layer screens harmful rays.

The Earth itself has layers. From the outside in they are the thin, solid crust we live on, the thick mantle beneath it, and the metal core at the very center.

Rocks come in three families: igneous rock forms when melted magma or lava cools and hardens, sedimentary rock forms from pressed layers of sediment, and metamorphic rock forms when heat and pressure change an existing rock.

The water cycle keeps water moving. The Sun's heat drives evaporation (liquid to vapor), the vapor cools and condenses into clouds, water falls as precipitation, and it collects in rivers and seas to begin again.

Exam-day strategy

Most science items test one plain fact wrapped in a longer sentence. Read to the end, then answer:

• If the item names a process (condensation, inertia, sublimation), match it to its one-line definition.
• If it gives a scenario (a shrinking mothball, dew on the grass, a car speeding up), name the process or force behind it.
• If it asks for a unit, match the quantity: force to newtons, mass to kilograms.
• When unsure, trust the everyday science around you. The obvious, ordinary answer is usually right, and the exotic-sounding choice is usually the trap.