Quick Reference
Structure → function
When a question gives you a structure, ask what property of that structure explains its function.
Process → purpose
For pathways, remember what enters, what leaves and why the pathway exists.
Comparison tables
Closely related terms are ideal distractors; compare them side-by-side.
Exact wording
Biology options often differ by one word. Read qualifiers such as mainly, directly, first, only and most carefully.
1. Biological Molecules
Carbohydrates, lipids, proteins and nucleic acids are easier to retrieve when organized by building blocks, linkage, major function and representative examples. Proteins are polymers of amino acids connected by peptide bonds; nucleic acids are built from nucleotides; polysaccharides are carbohydrate polymers with linkage patterns that affect structure and function.
| Class | Building block | High-yield structural idea | Typical role |
|---|---|---|---|
| Carbohydrates | Monosaccharides | Glycosidic linkages; branching matters. | Energy and structure. |
| Lipids | Not one single repeating monomer class | Hydrophobic character; fatty acids in many lipid types. | Energy storage, membranes, signaling. |
| Proteins | Amino acids | Peptide backbone; 3-D folding determines function. | Enzymes, transport, structure, signaling. |
| Nucleic acids | Nucleotides | Sugar-phosphate backbone + nitrogenous bases. | Information storage and expression. |
2. Enzymes & Metabolic Control
Enzymes are biological catalysts. Their central role is to lower the activation-energy barrier for reactions; they do not change the reaction’s overall Gibbs free-energy difference between reactants and products. Enzyme activity is influenced by factors such as temperature, pH, substrate concentration and inhibitors.
3. Cell Biology
Selective transport
Different substances move through membranes by different mechanisms depending on gradients, proteins and energy requirements.
Genetic information
In eukaryotic cells, most genomic DNA is housed in the nucleus.
ATP production
A major site of aerobic cellular respiration in eukaryotes; not the site of glycolysis.
Protein synthesis
Translates messenger RNA information into a polypeptide sequence.
4. Bioenergetics & Respiration
Glycolysis takes place in the cytoplasm and converts one glucose into two pyruvate molecules while producing a net gain of 2 ATP and 2 NADH. In aerobic respiration, pyruvate is further processed and reducing equivalents drive oxidative phosphorylation. Keep the location and net outputs straight; these are frequent high-value distinctions.
5. Human Physiology: Think in Control Systems
Homeostasis is dynamic stability, not a frozen state. A stimulus is detected, a control center processes information, and an effector produces a response. Negative feedback tends to oppose a deviation from a set point; positive feedback reinforces the direction of a change and is used in specific physiological processes such as childbirth and clot formation.
| System | Core idea | Common confusion |
|---|---|---|
| Respiratory | Gas exchange + ventilation + transport | Ventilation is not the same as cellular respiration. |
| Circulatory | Transport by blood through vessels and heart | Arteries/veins describe direction relative to the heart, not oxygen content alone. |
| Renal | Filtration, reabsorption, secretion, excretion | These are distinct processes. |
| Nervous/endocrine | Coordination via electrical and chemical signals | Speed and duration of signaling differ. |
6. Genetics & Evolution
Genotype describes the genetic constitution; phenotype is the observable outcome produced through genotype–environment interaction. In a simple Mendelian framework, alleles separate during gamete formation and recombine at fertilization. Punnett squares are probability models for expected genotype and phenotype distributions under specified assumptions.
Do not confuse “dominant” with “more common,” “stronger,” or “more adaptive.” Dominance describes the relationship between alleles in the phenotype of a heterozygote.
7. Acellular Life, Prokaryotes & Diversity
Keep taxonomic terms and cellular architecture separate. Viruses are acellular infectious entities rather than cells; prokaryotic organisms lack a membrane-bound nucleus; eukaryotic cells possess membrane-bound organelles. Comparative questions often test one structural distinction rather than a large amount of narrative biology.
8. Rapid-Fire Distinctions
| Do not mix up | Keep the distinction |
|---|---|
| Diffusion vs osmosis | Osmosis is water movement across a selectively permeable membrane; diffusion is broader net movement down a gradient. |
| Active vs facilitated diffusion | Active transport requires an energy source; facilitated diffusion is passive. |
| Genotype vs phenotype | Genotype = genetic makeup; phenotype = observable characteristics. |
| Antigen vs antibody | Antigen is a molecule recognized by the immune system; antibody is an immune protein that binds specific targets. |
| Hormone vs neurotransmitter | Both signal, but their transport route, timing and range differ. |
Frequently Asked Questions
PM&DC — Uniform Curriculum MDCAT-2025 (official PDF) · PM&DC — Public Notice regarding MDCAT-2026 · OpenStax — Biology 2e: Enzymes · OpenStax — Biology 2e: Glycolysis · OpenStax — Biology 2e: Homeostasis · OpenStax — Biology 2e: Characteristics and Traits
Scope: scientific explanations are written for student use and simplified where appropriate. Exact exam wording, syllabus scope and current administrative rules should be checked against PM&DC documents.