Grade 12 Biology Unit 1

Elements

Pure substances made of only one type of atom

Atoms

Smallest particles of an element that can exist by themselves

Relationship between elements and atoms

Elements are made of only one type of atom; atoms are the smallest particles of an element

Six building blocks of life

Carbon C, hydrogen H, oxygen O, nitrogen N, phosphorus P, and sulfur S

Four most common elements in living systems

Carbon C, hydrogen H, oxygen O, and nitrogen N

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons, giving them different masses

Carbon-12 vs carbon-14

Both have 6 protons and 6 electrons; carbon-12 has 6 neutrons and is stable, while carbon-14 has 8 neutrons and is radioactive

Radioisotopes

Unstable isotopes that emit radiation as their nuclei decay

Uses of radioisotopes

Can be attached to substances that target cancer cells to locate cancerous tissue; can also be added to food to trace where nutrients are broken down, absorbed, and transported during digestion

Biochemistry

Study of the properties and interactions of biologically important molecules

Organic molecules

Carbon-based molecules, usually bonded to carbon and hydrogen

Atom to molecule connections

Atoms bond together to form molecules; organic molecules are carbon-based molecules; molecules can contain functional groups

Ion

An atom that has gained or lost electrons to obtain a full valence shell and therefore has a charge

Cation

A positively charged ion formed when an atom loses electrons

Anion

A negatively charged ion formed when an atom gains electrons

Biologically important cations

K+ is important for nerve impulses and Na+ is also important in biological systems

Biologically important polyatomic ion

HCO3− is the main form by which CO2 is transported in blood

Intramolecular forces

Chemical bonds between atoms within a molecule

Intermolecular forces

Attractions between different molecules or different parts of the same molecule; weaker than intramolecular forces

Covalent bond

A bond where non-metal atoms share valence electrons

Polar covalent bond

A covalent bond where electrons are shared unequally because one atom attracts the electrons more strongly (results in partial positive charge and partial negative charge)

Ionic bond

A bond formed when electrons are transferred from one atom to another, creating oppositely charged ions

Electronegativity

The ability of an atom to attract electrons in a chemical bond

Electronegativity trend for common elements

O, N, and Cl have relatively high electronegativity; H, C, and P have relatively low electronegativity

Polar molecule

A molecule with unequal electron sharing that creates partial positive and negative regions

Non-polar molecule

A molecule with equal or nearly equal electron sharing because the atoms have similar electronegativities

Water polarity

H2O is polar because oxygen attracts the shared electrons more strongly than hydrogen; O is partially negative and H is partially positive

Water molecule bonds

The O-H bonds in water are polar covalent bonds

Hydrogen bond

An intermolecular attraction between a slightly positive H and a slightly negative electronegative atom such as O

Hydrogen bonds in life

Weaker than covalent bonds individually but collectively important; help stabilize DNA and are important for the 3D shape and function of biological molecules

Intramolecular vs intermolecular strength

Intramolecular forces such as covalent bonds are stronger than intermolecular forces such as hydrogen bonds because they must hold molecules together

O-O bond

Non-polar because the atoms have equal electronegativity

H-N bond

Polar because nitrogen attracts electrons more strongly than hydrogen

C-Cl bond

Polar because chlorine attracts electrons more strongly than carbon

P-O bond

Polar because oxygen attracts electrons more strongly than phosphorus

Carbon-fluorine bond

Likely polar covalent because fluorine has much higher electronegativity than carbon

Hydrocarbons and hydrogen bonding

Hydrocarbons do not form hydrogen bonds because their H atoms are bonded to carbon and C-H bonds are not polar enough

Hydrophilic

Attracted to water; usually polar or ionic substances that can form intermolecular attractions with water and often dissolve in it

Hydrophobic

Not attracted to water; usually non-polar substances that do not dissolve well in water

Hydrophobic effect

Non-polar molecules group together because water molecules are more strongly attracted to each other than to the non-polar molecules

Oil and water

Oil is non-polar and hydrophobic, so water molecules attract each other more strongly and oil separates from the water-based mixture

Molecular formula

Shows the types and numbers of atoms in a molecule or compound, such as CH4 or H2O

Structural formula

Shows how atoms in a molecule are connected and bonded

Advantage of a molecular formula

Quickly shows which atoms and how many of each are present

Advantage of a structural formula

Shows how atoms are arranged and bonded, which helps reveal the molecule's structure

Space-filling model

A 3D model that represents the approximate size and arrangement of atoms

Ball-and-stick model

A 3D model that shows atoms as balls and bonds as sticks

Functional group

A specific group of atoms attached to a molecule that gives it particular physical and chemical properties and is often reactive

Hydroxyl group

-OH; one oxygen covalently bonded to one hydrogen; found in alcohols and carboxylic acids

Carbonyl group

C=O; a carbon atom double-bonded to an oxygen atom

Aldehyde

A carbonyl group located at the end of a carbon chain

Ketone

A carbonyl group located within a carbon chain

Carboxyl group

-COOH or COO−; made of a carbonyl group and a hydroxyl group attached to the same carbon; found in fatty acids

Carboxyl group components

Carbonyl C=O plus hydroxyl -OH

Amino group

-NH2; a nitrogen atom bonded to two hydrogen atoms

Amine

A molecule containing an amino functional group

Sulfhydryl group

-SH; also called a thiol group; involved in protein folding

Phosphate group

A phosphorus atom bonded to four oxygen atoms; commonly represented as -PO4³− and is important in biological molecules

Functional group quick review

Hydroxyl -OH; carbonyl C=O; carboxyl -COOH or COO−; amino -NH2; sulfhydryl -SH; phosphate -PO4³−

Water and intermolecular forces

Water molecules are polar, so the partially positive H of one water molecule can attract the partially negative O of another through hydrogen bonding

Water and hydrophilic interactions

Polar molecules and ions interact with water because they can form intermolecular attractions with water

Water and hydrophobic interactions

Non-polar molecules do not interact strongly with water, so water molecules tend to group around themselves instead

Magnet analogy for water

Water molecules can be compared to tiny magnets because partially positive H attracts partially negative O; the limitation is that water is not actually magnetic and the attraction comes from partial electrical charges

Bridging scientific disciplines

Biophysics combines biology and physics to study physical forces in living systems; geochemistry combines geology and chemistry to study the chemical composition and processes of Earth ```