❌ are the basic building blocks of matter. They are composed of ❌ and ❌ that form the ❌ at the center of the atom as well as ❌ that orbit the nucleus. Atoms have an ❌ of protons and electrons, and the majority of an atom’s properties are determined by the ❌ it has.

The more important biological elements and their abbreviations (in parentheses) are: ❌ (C), ❌ (H), ❌ (O), ❌ (N), ❌ (P), and ❌ (S)

“Sulfur-32” is the name of a specific ❌, while “sulfur” is the name of an ❌.

When atoms link together, they form ❌. A molecule of ethyl alcohol, C2H6O, has ❌ carbon atoms, ❌ hydrogen atoms, and ❌ oxygen atom.

Even though they both contain ❌ and ❌ atoms, CO and CO2 are ❌ molecules.

When sucrose is dissolved in water, a ❌ change has taken place. On the other hand, when sucrose reacts with water with the help of an enzyme to make glucose and fructose, a ❌ change has occurred. In general, ❌ are reversible, while ❌ are not.

All matter can exist in one of three phases: ❌, ❌, and ❌. Adding energy turns ❌ into ❌ and liquids into ❌, while taking away energy tends to reverse the process.

When ❌ is dissolved in ❌, salt is the solute, water is the solvent, and the solution is ❌.

When a solute travels across a membrane in order to even out concentration, ❌ has occurred. When the solvent travels across a membrane in order to even out concentration, ❌ has occurred. Osmosis happens when a semipermeable membrane separates ❌.

A cell sits in a solution that has a higher concentration of solutes than that found in the cell. Water will tend to travel ❌ and ❌.

In the balanced chemical equation:
C18 H32 O16 + 2H2O → 3C6H12O6

❌ molecule of C18H32O16 reacts with ❌ molecules of H2O to make ❌ molecules of C6H12O6.

Photosynthesis requires ❌, ❌, ❌, and ❌ (which acts as a catalyst). It produces ❌ and ❌ via the chemical equation:

❌ + ❌ → ❌ + ❌

Glucose and fructose both have the same chemical formula, ❌, which means they are ❌. They have different ❌ formulas. A molecule can have more than one ❌. Glucose and fructose, for example, have both a ❌ structure and a ❌ structure.

A simple sugar is called a ❌. Two such simple sugars can join to make a
❌. If three or more join, they form a ❌. Simple sugars join together through
❌ reactions.

People and animals store excess sugars as a ❌ known as ❌. When they need the simple sugars again, they break down this molecule into ❌ via ❌ reactions.

The pH scale runs from ❌ to ❌. A pH of ❌ is neutral. A pH ❌ indicates an ❌ solution, while a pH ❌ indicates an ❌ solution.

Lipids are formed in ❌ reactions where three ❌ are joined to one ❌ molecule. Lipids are ❌, meaning they are not attracted to water. If the ❌ molecules that make up the lipid have no double bonds between the carbon atoms, it is a ❌ and is generally ❌ at room temperature. If there are double bonds between the carbon atoms, it is an ❌ and is generally ❌ at room temperature.

Proteins are formed in ❌ reactions where ❌ are joined together. The bond that forms between them is called a ❌. ❌ make up a special class of proteins that serve as ❌ for many biologically-important chemical reactions, and they typically work according to the ❌, in which an active site complements the shape of a reactant. Many of these molecules are quite ❌, breaking down soon after they are formed.

❌ is a double chain of chemical units known as ❌ that twist around one another in a double helix. The units that make up these chains are composed of three basic constituents: ❌, a ❌, and a ❌. The double helix is held together by ❌ that link certain ❌ together. In DNA, ❌ can link only to ❌ (and vice-versa), while the nucleotide base ❌ can link only to ❌ (and vice-versa).