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Connective tissue

Binds organs, provides support, and stores fat.

11 organ systems

There are 11 organ systems in the human body.

Skeletal system

Produces blood cells (bone marrow hematopoiesis).

Compound

A substance made of two or more different elements bonded together.

Molecule

Two or more atoms bonded together; molecules interact to form cells.

Atomic number

The number of protons in an atom's nucleus; in a neutral atom, it also equals the number of electrons.

Proton

A positively charged subatomic particle located in the nucleus.

Neutron

An electrically neutral subatomic particle located in the nucleus; contributes to atomic mass.

Electron

A negatively charged subatomic particle that orbits the nucleus in electron shells or orbitals.

Nucleus

The center of an atom that contains protons and neutrons and is the atom's dense, positive core.

Orbital (shell)

A region around the nucleus where electrons are likely to be found; electrons occupy electron shells.

Electron cloud

The region around the nucleus where electrons are likely to be found, reflecting probabilistic locations.

CHONPS

The six elements—Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, and Sulfur—that make up about 95% of living organisms by weight.

Molecule

Two or more atoms bonded together.

Compound

A substance formed when two or more elements are chemically bonded; example: H2O.

Isotope

Atoms of the same element that have different numbers of neutrons, resulting in different mass numbers.

Carbon-14 (14C)

An isotope of carbon with 6 protons and 8 neutrons; mass number 14.

Valence electrons

Electrons in the outermost shell of an atom; determine chemical bonding. For atomic number 12, there are 2 valence electrons.

Cell

The smallest unit of life; the basic unit that carries out life processes in organisms.

Tissue

A group of similar cells that perform a specific function.

Biological organization (levels of organization)

A hierarchical sequence from smallest to largest: atom → molecule → organelle → cell → tissue → organ → organ system → organism.

Matter

Anything that takes up space and has mass.

Nucleus

The central part of an atom that contains protons and neutrons.

Electron

A subatomic particle that orbits the nucleus and carries a negative charge.

Balanced equation coefficients

Numbers placed before reactants and products to balance atoms on both sides of a chemical equation; e.g., 2Na + Cl2 → 2NaCl has coefficients 2, 1, and 2.

Synthesis reaction

A reaction in which two or more reactants combine to form a single product; often involves dehydration synthesis (e.g., glucose + glucose → maltose + H2O).

Polar covalent bond

A covalent bond where electrons are shared unequally, creating partial charges; water (H2O) has polar covalent bonds.

Lactose hydrolysis products

Hydrolysis of lactose yields glucose and galactose.

Electronegativity in water

Oxygen is more electronegative than hydrogen, giving water its polar nature.

Ionic bond formation

A bond formed by transfer of electrons from one atom to another, producing oppositely charged ions that attract.

Electron transfer in NaCl

Sodium donates one electron to chlorine; Na becomes Na⁺ and Cl becomes Cl⁻, forming an ionic bond.

Polar covalent bond

A covalent bond in which electrons are shared unequally between atoms, resulting in partial charges.

Ionic bond

A bond formed by transfer of electrons from one atom to another, creating oppositely charged ions; NaCl is a classic example.

Hydrogen bond

A weak attraction between a hydrogen atom bonded to a highly electronegative atom (like O or N) and another electronegative atom; important for DNA base-pairing.

Ionic bond electron sharing

Not shared; electrons are transferred, leading to charged ions held together by electrostatic attraction.

Valence electrons

Electrons in the outermost shell that participate in bonding; inner-shell electrons generally do not participate in bonding.

O–H polar covalent bond in water

A polar covalent bond between oxygen and hydrogen where electrons are shared unequally, giving water its polarity.

Hydrolysis

A chemical reaction in which water is added to break bonds in polymers, producing smaller units (monomers).

Dehydration synthesis

A condensation reaction in which water is removed to form a bond, building polymers from monomers.

Balanced chemical equation for H2SO4 + NaOH → Na2SO4 + H2O

Coefficients: 1 H2SO4, 2 NaOH, 1 Na2SO4, 2 H2O (i.e., H2SO4 + 2 NaOH → Na2SO4 + 2 H2O).

Dehydration synthesis (condensation reaction)

A chemical reaction in which two monomers are joined by removing a water molecule, forming a polymer.

Hydrolysis

A chemical reaction in which water is added to break polymers into monomers.

Monomer

A small molecule that can join with other monomers to form a polymer.

Polymer

A large molecule made of repeating monomer units.

Synthesis (condensation) reaction

A reaction that combines subunits to form a larger molecule or polymer.

Balanced chemical equation

An equation where the number of atoms of each element is the same on both sides; achieved by using coefficients; subscripts must not be changed.

Coefficient

A number placed in front of a chemical formula that multiplies all atoms in that formula in the equation.

Subscript

A small number written after an element in a chemical formula indicating how many atoms of that element are present in the molecule; it cannot be changed when balancing.

Balancing chemical equations

The process of adjusting coefficients to equalize the number of atoms of each element on both sides of the equation; only coefficients are changed.

Balanced example: Al + O2 → Al2O3

The balanced form is 4 Al + 3 O2 → 2 Al2O3.

Isotopes

Atoms of the same element with different numbers of neutrons.

Ionic bond

Chemical bond formed when one atom transfers electrons to another, producing ions.

Polar covalent bond

A covalent bond with unequal sharing of electrons; example: water (H2O).

Hydrogen bond

Weak attraction between a hydrogen atom and an electronegative atom (O, N, or F).

Water polarity

Water is a polar molecule because oxygen is more electronegative than hydrogen, pulling electrons toward itself.

Valence electrons

Electrons available for bonding in the outer electron shell.

Radioactive isotopes in medicine

Isotopes used in medicine to treat cancer cells.

Sodium chloride ionic bond

Sodium donates an electron to chlorine, forming Na+ and Cl− and an ionic bond.

Chemical reaction

A process in which chemical bonds are broken and/or new bonds are formed.

Monomer

The small repeating unit that makes up polymers.

Lactose monomers

Glucose and galactose.

Biological organization (smallest to largest)

Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ System.

Mass number (A)

Total number of protons and neutrons in the nucleus; A = Z + N.

Atomic number (Z)

Number of protons in the nucleus; equals the number of electrons in a neutral atom.

Proton

Positively charged subatomic particle located in the nucleus.

Neutron

Electrically neutral subatomic particle located in the nucleus.

Electron

Negatively charged subatomic particle orbiting the nucleus in electron shells.

Neutral atom

An atom with equal numbers of protons and electrons; overall charge is zero.

Oxygen-16 (isotope of oxygen)

Isotope with 8 protons and 8 neutrons (A = 16); in neutral form, 8 electrons.

Magnesium electron configuration (Z = 12)

1s2 2s2 2p6 3s2; electron distribution across shells: 2, 8, 2.

Neutron number (N)

Number of neutrons in the nucleus; N = A − Z.

Isotope

Atoms of the same element with different neutron numbers and mass numbers.

Charge balance in a neutral atom

In a neutral atom, the number of protons equals the number of electrons; net charge = 0.

Chemical reaction

A process in which reactants are transformed into products by breaking and forming chemical bonds.

Monomer

A small repeating unit that builds up polymers.

Polymer

A large molecule composed of many repeated subunits (monomers) joined together.

Dehydration synthesis (condensation reaction)

A synthesis reaction where a water molecule is removed to join two monomers into a polymer.

Hydrolysis

A reaction in which water is added to break bonds, producing smaller molecules.

Coefficient

The number in front of a chemical formula in an equation that multiplies the entire molecule or formula.

Subscript

The small number written after an atom within a chemical formula indicating how many atoms of that element are present in the molecule.

Synthesis reaction

A reaction that combines two or more subunits to form a larger molecule or polymer.

Balanced chemical equation

An equation in which the number of atoms of each element is the same on both sides, achieved by adjusting coefficients (without changing subscripts).

Reactant

Substances that participate in a chemical reaction and are transformed into products.

Product

Substances formed as a result of a chemical reaction.