AP Biology - Core Concepts

Front

Why is water an effective solvent for polar and ionic substances?

Back

Water's polarity creates a partial negative charge on oxygen and partial positive charge on hydrogen atoms. These partial charges allow water to form hydrogen bonds with polar molecules and surround ions (hydration shells), effectively dissolving them. This property is essential for cellular reactions and transport.

Front

What are the four categories of biological macromolecules and their monomers?

Back

1. Carbohydrates (monosaccharides like glucose); 2. Lipids (not true polymers, but built from fatty acids and glycerol); 3. Proteins (amino acids); 4. Nucleic acids (nucleotides). Each monomer type connects via dehydration synthesis and breaks apart via hydrolysis reactions.

Front

How does the structure of a phospholipid contribute to membrane formation?

Back

Phospholipids have a hydrophilic phosphate head and two hydrophobic fatty acid tails. This amphipathic nature causes them to spontaneously form bilayers in aqueous environments, with heads facing water and tails facing inward, creating the selective barrier of the plasma membrane.

Front

What is the role of the R-group in determining protein structure?

Back

The R-group (side chain) of each amino acid determines its chemical properties (hydrophobic, hydrophilic, acidic, basic). These properties drive protein folding: hydrophobic R-groups cluster in the interior while hydrophilic ones face the surface, determining the protein's 3D conformation and function.

Front

Explain the relationship between surface area-to-volume ratio and cell size.

Back

As cells grow, volume increases faster than surface area (volume grows cubically, surface area grows squarely). A lower SA:V ratio limits material exchange across the membrane relative to metabolic needs. Cells remain small or develop adaptations (folds, microvilli) to maintain efficient exchange.