TEAS Chemistry and Biology Review: Key Concepts You Must Know for the Science Section

The TEAS Science section is 50 questions in 60 minutes and consistently ranks as the hardest section of the exam. While anatomy and physiology get most of the attention, biology and chemistry questions make up a significant portion of the test — and they're where many students lose easy points because they skipped the review.

This guide covers every biology and chemistry concept tested on the ATI TEAS, organized by topic, with clear explanations and practical memory aids. Whether you're starting from scratch or brushing up, this is your one-stop review.

Biology: Cell Structure and Function

Understanding cell biology is foundational to the TEAS Science section. You need to know the key organelles, their functions, and the differences between cell types.

Prokaryotic vs. Eukaryotic Cells: Prokaryotes (bacteria) lack a nucleus and membrane-bound organelles. Eukaryotes (plants, animals, fungi) have a nucleus, mitochondria, endoplasmic reticulum, and other organelles enclosed by membranes. The TEAS frequently tests this distinction.

• Nucleus: Contains DNA; controls cell activities and gene expression. Think of it as the cell's "control center."
• Mitochondria: Produce ATP through cellular respiration. Known as the "powerhouse of the cell." Remember: more active cells (like muscle cells) have more mitochondria.
• Ribosomes: Synthesize proteins. Found free in the cytoplasm or attached to the rough endoplasmic reticulum.
• Endoplasmic Reticulum (ER): Rough ER (has ribosomes) processes proteins; Smooth ER synthesizes lipids and detoxifies chemicals.
• Golgi Apparatus: Packages and ships proteins to their destinations. Think of it as the cell's "post office."
• Cell Membrane: Phospholipid bilayer that controls what enters and exits the cell. Selectively permeable.
• Lysosomes: Contain digestive enzymes that break down waste. The cell's "recycling center."
• Chloroplasts: Found only in plant cells. Convert sunlight to glucose via photosynthesis.

Biology: Cell Transport Mechanisms

The TEAS tests your understanding of how substances move across cell membranes. There are two main categories: passive transport (no energy required) and active transport (requires ATP).

• Diffusion: Movement of molecules from high to low concentration. Example: oxygen moving from alveoli into blood capillaries.
• Osmosis: Diffusion of water across a selectively permeable membrane. Water moves toward higher solute concentration.
• Facilitated Diffusion: Uses transport proteins to move molecules across the membrane. Still passive — no ATP needed. Example: glucose entering cells via GLUT transporters.
• Active Transport: Uses ATP to move molecules against the concentration gradient (low to high). Example: sodium-potassium pump (Na⁺/K⁺ ATPase).
• Endocytosis: Cell engulfs large particles by wrapping the membrane around them. Phagocytosis = "cell eating"; Pinocytosis = "cell drinking."
• Exocytosis: Cell expels materials by fusing vesicles with the cell membrane. Example: neurotransmitter release at synapses.

Tonicity is a related concept the TEAS loves to test. In a hypertonic solution (more solute outside), water leaves the cell and it shrivels (crenation in animal cells, plasmolysis in plant cells). In a hypotonic solution (less solute outside), water enters the cell and it swells (and may lyse). In an isotonic solution, there is no net water movement.

Biology: DNA, RNA, and Protein Synthesis

Genetics questions on the TEAS focus on DNA structure, replication, and the process of turning genetic information into proteins.

• DNA Structure: Double helix made of nucleotides. Each nucleotide has a phosphate group, deoxyribose sugar, and a nitrogenous base (A, T, G, C). Base pairing: A–T, G–C.
• RNA Structure: Single-stranded. Uses ribose sugar and uracil (U) instead of thymine (T). Base pairing with DNA: A–U, G–C.
• Transcription: DNA → mRNA. Occurs in the nucleus. RNA polymerase reads the template strand and builds a complementary mRNA strand.
• Translation: mRNA → Protein. Occurs at ribosomes. Transfer RNA (tRNA) brings amino acids that match mRNA codons (three-base sequences).
• Codons: Each three-nucleotide sequence on mRNA codes for one amino acid. AUG is the start codon (codes for methionine). UAA, UAG, UGA are stop codons.
• Mutations: Changes in DNA sequence. Point mutations affect one base; frameshift mutations (insertions/deletions) shift the entire reading frame and usually cause nonfunctional proteins.

Biology: Genetics and Heredity

The TEAS tests basic Mendelian genetics, including dominant and recessive traits, Punnett squares, and inheritance patterns.

• Genotype vs. Phenotype: Genotype is the genetic makeup (e.g., Bb); phenotype is the observable trait (e.g., brown eyes).
• Homozygous vs. Heterozygous: Homozygous = two identical alleles (BB or bb). Heterozygous = two different alleles (Bb).
• Dominant and Recessive: A dominant allele (B) masks a recessive allele (b). The recessive trait only shows when homozygous recessive (bb).
• Punnett Squares: Cross Bb × Bb → 25% BB, 50% Bb, 25% bb. Phenotype ratio: 3 dominant : 1 recessive.
• Incomplete Dominance: Neither allele is fully dominant. Heterozygotes show a blended phenotype (e.g., red × white = pink flowers).
• Codominance: Both alleles are fully expressed. Example: AB blood type — both A and B antigens are present.
• Sex-Linked Traits: Genes on the X chromosome. Males (XY) are more likely to express X-linked recessive traits because they have only one X.

Chemistry: Atoms and the Periodic Table

Chemistry on the TEAS starts with atomic structure. You need to know the parts of an atom, how to read the periodic table, and how elements are organized.

• Subatomic Particles: Protons (positive charge, in nucleus), Neutrons (no charge, in nucleus), Electrons (negative charge, orbit the nucleus). Atomic number = number of protons.
• Mass Number: Protons + Neutrons. Isotopes are atoms of the same element with different numbers of neutrons.
• Electron Configuration: Electrons fill energy levels (shells) from lowest to highest. First shell holds 2 electrons, second holds 8, third holds 8 (simplified for TEAS).
• Periodic Table Organization: Rows = Periods (energy levels). Columns = Groups (similar properties). Group 1 = Alkali metals, Group 17 = Halogens, Group 18 = Noble gases.
• Trends: Atomic radius increases going down a group and left across a period. Electronegativity increases going up a group and right across a period. Ionization energy follows the same trend as electronegativity.
• Valence Electrons: Electrons in the outermost shell. They determine an element's reactivity and bonding behavior. Group number = number of valence electrons (for main group elements).

Chemistry: Chemical Bonds

Understanding how atoms bond is essential for TEAS chemistry questions. There are three main types of chemical bonds:

• Ionic Bonds: Formed when one atom transfers electrons to another. Usually between metals and nonmetals. Example: NaCl (sodium chloride). Na loses an electron → Na⁺; Cl gains an electron → Cl⁻. Ionic compounds form crystal lattices and have high melting points.
• Covalent Bonds: Formed when atoms share electrons. Usually between two nonmetals. Example: H₂O (water). Can be single (1 pair shared), double (2 pairs), or triple (3 pairs). Polar covalent bonds occur when sharing is unequal (e.g., O–H bond in water).
• Hydrogen Bonds: Weak attractions between a hydrogen atom bonded to an electronegative atom (N, O, F) and another electronegative atom nearby. Important in water properties and DNA base pairing. Not true chemical bonds — they're intermolecular forces.

Chemistry: Chemical Reactions and Equations

The TEAS expects you to understand basic reaction types, how to balance equations, and the law of conservation of mass.

• Law of Conservation of Mass: Matter is neither created nor destroyed in a chemical reaction. The number of each type of atom must be equal on both sides of the equation.
• Balancing Equations: Adjust coefficients (not subscripts) so that atoms are equal on both sides. Start with the most complex molecule first.
• Synthesis (Combination): A + B → AB. Two or more reactants combine to form one product.
• Decomposition: AB → A + B. One compound breaks down into two or more simpler substances.
• Single Replacement: A + BC → AC + B. One element replaces another in a compound.
• Double Replacement: AB + CD → AD + CB. Two compounds exchange partners.
• Combustion: Hydrocarbon + O₂ → CO₂ + H₂O. Always produces carbon dioxide and water.
• Catalysts: Speed up reactions without being consumed. Enzymes are biological catalysts.

Chemistry: Acids, Bases, and the pH Scale

Acid-base chemistry is a high-yield topic on the TEAS. You need to understand the pH scale, properties of acids and bases, and buffer systems.

• pH Scale: Ranges from 0 to 14. pH < 7 = acidic, pH = 7 = neutral, pH > 7 = basic (alkaline). Each whole number change represents a 10-fold change in hydrogen ion concentration.
• Acids: Donate H⁺ ions in solution. Taste sour, turn blue litmus red. Examples: HCl (stomach acid), H₂SO₄ (sulfuric acid), citric acid.
• Bases: Accept H⁺ ions (or donate OH⁻). Taste bitter, feel slippery, turn red litmus blue. Examples: NaOH (sodium hydroxide), baking soda, ammonia.
• Neutralization: Acid + Base → Salt + Water. Example: HCl + NaOH → NaCl + H₂O.
• Buffers: Solutions that resist changes in pH. Critical in the human body — blood is buffered at pH 7.35–7.45. The bicarbonate buffer system (H₂CO₃/HCO₃⁻) is the most important for TEAS.
• Clinical Relevance: Acidosis (blood pH < 7.35) and alkalosis (blood pH > 7.45) are life-threatening conditions. Respiratory acidosis is caused by CO₂ retention; metabolic acidosis by excess acid or loss of bicarbonate.

Chemistry: States of Matter and Solutions

The TEAS may ask about the three states of matter, phase changes, and solution properties.

• Solids: Fixed shape and volume. Particles are tightly packed in a fixed arrangement. Low kinetic energy.
• Liquids: Fixed volume but take the shape of their container. Particles are close but can slide past each other.
• Gases: No fixed shape or volume. Particles move freely with high kinetic energy. Compressible.
• Phase Changes: Solid → Liquid (melting), Liquid → Gas (evaporation/boiling), Gas → Liquid (condensation), Liquid → Solid (freezing), Solid → Gas (sublimation).
• Solutions: A homogeneous mixture of a solute (dissolved substance) and a solvent (the dissolver, usually water). Concentration = amount of solute per amount of solution.
• Solubility Factors: Temperature (most solids dissolve faster in hot water), pressure (affects gas solubility — think carbonated beverages), and molecular polarity ("like dissolves like").

Biology: Cellular Respiration and Photosynthesis

These two metabolic processes are mirror images of each other and are commonly tested on the TEAS.

• Cellular Respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP. Occurs in the mitochondria. Breaks down glucose to produce energy (ATP). Three stages: Glycolysis (cytoplasm), Krebs Cycle (mitochondrial matrix), Electron Transport Chain (inner mitochondrial membrane).
• Photosynthesis: 6CO₂ + 6H₂O + Light Energy → C₆H₁₂O₆ + 6O₂. Occurs in chloroplasts. Converts light energy into chemical energy (glucose). Two stages: Light-dependent reactions (thylakoid membranes) and the Calvin Cycle (stroma).
• Key Relationship: The products of one process are the reactants of the other. Animals depend on cellular respiration; plants perform both photosynthesis and cellular respiration.
• ATP: Adenosine triphosphate. The cell's "energy currency." When a phosphate bond is broken (ATP → ADP + P), energy is released for cellular work.
• Anaerobic Respiration: Occurs without oxygen. Produces much less ATP. Lactic acid fermentation occurs in human muscles during intense exercise; alcoholic fermentation occurs in yeast.

Quick-Reference Review Table

Use this summary to do a final review before test day. If any concept feels unfamiliar, go back to the relevant section above and study the details.

• Cell organelles → Know the function of each (nucleus, mitochondria, ribosomes, ER, Golgi, lysosomes)
• Cell transport → Passive (diffusion, osmosis, facilitated) vs. Active (pump, endocytosis, exocytosis)
• DNA/RNA → Structure differences, transcription, translation, codons
• Genetics → Punnett squares, dominant/recessive, incomplete dominance, codominance, sex-linked
• Atomic structure → Protons, neutrons, electrons, atomic number, mass number
• Chemical bonds → Ionic (metal + nonmetal), Covalent (nonmetal + nonmetal), Hydrogen bonds
• Reactions → Synthesis, decomposition, single/double replacement, combustion, balancing
• Acids & Bases → pH scale, properties, neutralization, buffers, clinical relevance
• States of matter → Solid, liquid, gas, phase changes, solutions, solubility factors
• Energy metabolism → Cellular respiration equation, photosynthesis equation, ATP

Chemistry and biology together make up a large portion of the TEAS Science section. Mastering these fundamentals will not only boost your Science score but also help you understand the anatomy and physiology concepts that build on this foundation. Study smart, review often, and use practice questions to test your retention.