The structure of a given amino acid consists of an alpha carbon, amino group, carboxyl group, hydrogen, and a R-side group. R-side groups can have a variety of characteristics. They can be non-polar, polar, acidic, or basic. Amino acids can bond together through a peptide bond via dehydration synthesis—the loss of a single oxygen from one amino acid’s carboxyl group and two hydrogens from the other amino acid’s amine group.

Polypeptides are polymers of amino acids formed by this process. Glycerol is a component of a phospholipid.

The cysteine-cysteine disulfide bond is an example of a tertiary bond. Tertiary bonds are bonds between R-side groups. Other examples include non-polar associated bonds, polar associations with a polar aqueous environment, and ionic bonds. Primary level bonds are described as the sequence of amino acids. Secondary bonds consist of local folding due to bonds between an oxygen on a carboxyl group with a hydrogen from an amino group. This bonding includes alpha helixes and beta sheets. Quaternary bonds are defined as the association between polypeptides. 

All proteins have at least a primary, secondary, and tertiary structure, but only some, such as hemoglobin, have a quaternary structure. Secondary structures are determined by hydrogen bonding between different amino acids in the polypeptide chain that form the primary structure. There may be multiple and different secondary structures in a single protein.

Amino acids link together by peptide bonds to form proteins. Nucleotides link together to form nucleic acids like DNA and RNA. Monosaccharides are sugars that form links to form carbohydrates. Fatty acids attach to a glycerol backbone to form lipids, except those that are derived from cholesterol. 

Phosphorous is found in nucleotides, but not amino acids. In certain reactions, proteins can be modified by kinases to contain phosphate groups. Kinases are enzymes that catalyze the transfer of phosphate groups onto substrates. They function in signal transduction pathways. 

There are only a few residues (amino acids in proteins) which can be phosphorylated: Serine, threonine, tyrosine, histidine, arginine, and lysine. 

Ribosomes may be attached to the endoplasmic reticulum or may float around in the cytoplasm freely. Ribosomes synthesize proteins using mRNA during transcription.

Vacuoles store waste to be excreted by the cell, as well as water to maintain cell volume and shape.

Golgi apparatus packages proteins, lipids, and other materials for transport and secretion outside of the cell.  

Lysosomes are structures in the cell that digest waste products.

Chloroplasts are found in plant cells and are the location of photosynthesis.

The basic structure of a carbohydrate contains carbon, hydrogen, and oxygen.

Lipids are made of carbon, hydrogen, oxygen, and occasionally phosphorous.

Proteins are made of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.

The only elements that will always be found in all three (lipids, proteins, and carbohydrates) are carbon, hydrogen, and oxygen.  

Cell are the basic functional unit of biology, representing the smallest form of biological organization. Tissues are made of groups of specialized cells that operate together. Organs are made of multiple tissue types and perform biological functions. Organ systems are comprised of multiple organs that work together to accomplish a biological process. Together, several organ systems form a full living organism, making organisms the highest level of biological organization.

For example, a goblet cell secretes mucus. Goblet cells are part of epithelial tissue, found in the stomach. The stomach is an organ made of smooth muscle, epithelium, and connective tissue. Together, the stomach, intestines, esophagus, and other organs form the digestive system. The full organism is composed of the digestive system, respiratory system, circulatory system, etc.

An ecosystem will have abiotic and biotic factors that interact with each other for survival and reproduction. An abiotic factor is non-living and is generally a part of the surroundings where an organism is found. Examples include soil, water, and oxygen. Biotic factors are referred to as living or were alive at one point, but are now dead. Examples of these are bacteria, mammals, and plants.

Transpiration is the process by which plants return water back into the atmosphere as vapor. This pathway is an important step in the water cycle. The stomata are pores found in the leaves, and participate in gas exchange with the air via transpiration. The opening of the pore is enveloped by a pair of cells called the guard cells, which control access to the pore. Roots are a part of the plant that are generally found underground and anchor the plant to the soil. They also absorb water and nutrients for the plant. The stem provides structural support for the plant, and the seeds are a means by which a plant can reproduce.