Body Systems, Atoms and Matter, Forces

Tissue

A group of similar specialized cells that work together to perform a specific function in the body.

Organ

A distinct body structure composed of different types of tissues working together to carry out a specific job.

Organ system

A group of organs that cooperate to perform major life functions, such as the digestive or circulatory system.

ATP (Adenosine triphosphate)

The main energy-carrying molecule in cells that stores and releases usable energy for cellular processes.

Cellular respiration chemical word equation

$$\text{Glucose} + \text{Oxygen} \rightarrow \text{Carbon Dioxide} + \text{Water} + \text{Energy (ATP)}$$

Epithelial tissue

A protective layer of tightly packed cells that covers body surfaces and lines internal cavities and organs.

Connective tissue

A supportive tissue type that connects, binds, cushions, and protects organs and other structures in the body.

Nervous tissue

Specialized body tissue made of nerve cells that sends and receives electrical messages throughout the body.

Mechanical digestion

The physical breakdown of food into smaller pieces by chewing, grinding, and churning without altering chemical structures.

Chemical digestion

The process of using digestive enzymes and acids to break complex food molecules into simple nutrients the body can absorb.

Peristalsis

Wave-like muscle contractions that push food and liquids through the digestive tract.

Bile (Production and storage)

A digestive fluid made by the liver to break down fats into small droplets, stored in the gallbladder until released.

Small intestine

The long, narrow section of the digestive tract where chemical digestion finishes and nutrients are absorbed into the blood.

Large intestine

The digestive organ that reabsorbs water and minerals from indigestible food waste and compacts the remainder into solid stool.

Red blood cells (Erythrocytes)

Disc-shaped cells containing haemoglobin that pick up oxygen in the lungs and deliver it to cells throughout the body.

Platelets

Small cell fragments in the blood that stick together to form clots and stop bleeding at wound sites.

Blood plasma

The liquid portion of blood that transports blood cells, nutrients, hormones, and dissolved waste substances.

Arteries

Thick, elastic blood vessels that transport high-pressure blood away from the heart to body tissues.

Capillaries

Extremely thin, microscopic blood vessels where oxygen, nutrients, and waste materials pass between blood and tissues.

Right ventricle

The lower right heart chamber that pumps oxygen-poor blood to the lungs through the pulmonary artery.

Left ventricle

The thick, muscular lower heart chamber that pumps oxygen-rich blood out to the rest of the body through the aorta.

Tricuspid valve

The one-way heart valve between the right atrium and right ventricle that prevents blood from flowing backward.

Alveoli

Microscopic air sacs inside the lungs surrounded by capillaries, where gas exchange between air and blood takes place.

Inhalation mechanism

Breathing in: the diaphragm contracts downward and rib muscles expand the chest, lowering lung pressure so air rushes inward.

Homeostasis

The process by which the body maintains a stable, balanced internal environment despite external changes.

Proton

A subatomic particle in the atomic nucleus that has a positive charge of $+1$ and a relative mass of $1$.

Neutron

A neutral subatomic particle located in the atomic nucleus that carries no electrical charge and has a relative mass of $1$.

Electron

A very light subatomic particle with a negative charge of $-1$ that orbits the nucleus in electron shells.

Valence shell

The outermost electron shell of an atom, which determines how that atom chemically reacts and bonds with others.

Atomic number

The total number of protons in the nucleus of an atom, identifying which chemical element it is.

Mass number (Atomic mass number)

The combined total count of protons and neutrons located inside an atom's nucleus.

Maximum electron shell capacity formula

The formula $2n^2$, where $n$ is the shell number, used to find the maximum number of electrons an electron shell can hold.

Dalton's Solid Sphere Model

An early atomic model that envisioned atoms as solid, indivisible balls that cannot be created, split, or destroyed.

Thomson's Plum Pudding Model

An atomic model that pictured negatively charged electrons scattered inside a sphere of positive electrical charge.

Rutherford's Nuclear Model

An atomic model established through the gold foil experiment, showing that an atom has a tiny, dense, positively charged nucleus surrounded by empty space.

Bohr's Electron Shell Model

An atomic model proposing that electrons travel in fixed circular orbits around the nucleus at specific energy levels.

Schrödinger's Quantum Model

The modern atomic model that represents electrons as matter waves situated within 3D probability clouds called orbitals.

Lustre

A physical appearance property describing how well the surface of a metal or mineral reflects light and shines.

Malleability

The physical ability of a metal to be hammered, flattened, or rolled into thin sheets without cracking or breaking.

Ductility

The physical ability of a solid material to be pulled and stretched into long, thin wires without snapping.

Metalloids

Elements that share both metallic and non-metallic physical and chemical characteristics, such as silicon.

Ionic compound

A chemical substance made when metal atoms transfer electrons to non-metal atoms, forming oppositely charged ions held by electrostatic attraction.

Covalent compound

A chemical substance formed when non-metal atoms share pairs of valence electrons to achieve full electron shells.

Cation

A positively charged ion formed when a neutral atom loses one or more valence electrons.

Anion

A negatively charged ion formed when a neutral atom gains one or more additional electrons.

Isotopes

Atoms of the same element that share the same number of protons but have different numbers of neutrons.

Mixture

A physical combination of two or more substances that keep their original properties and can be separated by physical means.

Octet rule

The chemical guideline stating that atoms tend to gain, lose, or share electrons until their outer shell contains eight valence electrons.

Law of Conservation of Mass

The scientific principle stating that matter cannot be created or destroyed in a chemical reaction; the total mass of the reactants equals the mass of the products.

Catalyst

A substance that speeds up a chemical reaction by lowering its activation energy, without being consumed or permanently changed.

Force

A push or pull acting on an object that can change its speed, direction, or shape, measured in newtons ($\text{N}$).

Vector quantity

A physical quantity that has both a numerical size (magnitude) and a specific direction, such as velocity or weight.

Friction

A contact force that resists sliding motion between two surfaces in contact and converts mechanical energy into heat.

Air resistance (Drag force)

A frictional force exerted by air that pushes against and slows down an object moving through the atmosphere.

Terminal velocity

The constant maximum speed a falling object maintains when the upward drag force balances the downward force of gravity.

Tension force

A pulling force transmitted through an object, like a rope, string, or cable, when it is pulled tight from opposite sides.

Normal force

The perpendicular upward support force exerted by a solid surface against any object pressing down on it.

Buoyant force

The upward force that a fluid exerts on a floating or submerged object, supporting some or all of its weight.

Factors affecting gravitational force

The attractive non-contact force between two masses increases as their masses grow, and decreases as the distance between them increases.

Ferromagnetic materials

Metals such as iron, nickel, and cobalt that are strongly attracted by magnets and can be turned into permanent magnets.

Electrostatic force

The attractive or repulsive non-contact force that occurs between stationary electric charges.

Balanced forces

Forces that are equal in size and opposite in direction, canceling each other out so an object remains at rest or at a steady speed.

Unbalanced forces

Forces that do not cancel out, producing a net force that causes an object to accelerate, decelerate, or change direction.

Mass vs. weight

Mass is the amount of matter in an object, while weight is the downward force exerted on that mass by gravity.

Mechanical advantage

The number of times a simple machine multiplies the user's input effort force, calculated as output load divided by input effort.

First-class lever

A lever where the fulcrum (pivot point) sits between the applied effort force and the load, like a seesaw or crowbar.

Second-class lever

A lever where the load is positioned in the middle, between the fulcrum and the applied effort force, like a wheelbarrow.

Third-class lever

A lever where the effort force is applied in the middle, between the fulcrum and the load, like tweezers or a broom.

Wedge

A simple machine made of two inclined planes placed back-to-back, used to split, lift, or hold materials in place.

Inclined plane

A flat, sloping ramp that reduces the force needed to raise an object by extending the distance over which it is moved.

Screw

A simple machine made by wrapping an inclined plane spirally around a central cylinder, converting rotational motion into linear force.

Wheel and axle

A simple machine made of a large wheel locked to a smaller central rod or axle, turning together to multiply force or distance.

Gears

Wheels with interlocking teeth that rotate together to transfer power and change speed, force, or direction of motion.

Fixed pulley

A grooved wheel anchored in place with a rope running over it, changing the direction of a pulling force without altering the required effort.

Charging by friction

A method of creating static electricity where rubbing two different insulators together transfers electrons from one to the other.