High School Biology practice questions and exam guide

What are the building blocks of proteins?

1. Nucleotides
2. Fatty acids
3. Glucose
4. Amino acids (20 standard ones, linked by peptide bonds)
5. DNA bases

Answer: D — Amino acids (20 standard ones, linked by peptide bonds)

Proteins composed of amino acids. 20 standard amino acids in humans. Linked by peptide bonds. Sequence determines structure → function. Nucleotides → nucleic acids. Glucose/sugars → carbohydrates. Fatty acids → lipids. Foundation of biochemistry.

Controlled experiment:

1. Only one variable
2. Has no controls
3. Random observations
4. Has independent variable (manipulated), dependent variable (measured), control group (no treatment or baseline), constants/controlled variables; random assignment, replication, blinding (where possible) reduce bias; allows causal inference

Answer: D — Has independent variable (manipulated), dependent variable (measured), control group (no treatment or baseline), constants/controlled variables; random assignment, replication, blinding (where possible) reduce bias; allows causal inference

D) Standard. A/B/C) Each is incomplete.

Mitosis phases in order:

1. Random
2. Telophase first
3. Prophase (chromatin condenses, nuclear envelope breaks down, spindle forms), Metaphase (chromosomes align at the equator), Anaphase (sister chromatids separate to opposite poles), Telophase (nuclear envelopes reform, chromosomes decondense), cytokinesis splits the cell
4. Mitosis has no phases

Answer: C — Prophase (chromatin condenses, nuclear envelope breaks down, spindle forms), Metaphase (chromosomes align at the equator), Anaphase (sister chromatids separate to opposite poles), Telophase (nuclear envelopes reform, chromosomes decondense), cytokinesis splits the cell

C) Standard PMAT. A/B/D) Each is incorrect.

Which is the BEST description of the cell membrane?

1. Solid wall
2. Single layer of protein
3. Rigid structure
4. Made of cellulose only
5. Phospholipid bilayer with embedded proteins; selectively permeable (fluid mosaic model)

Answer: E — Phospholipid bilayer with embedded proteins; selectively permeable (fluid mosaic model)

Cell membrane: phospholipid bilayer (hydrophilic heads outside, hydrophobic tails inside). Embedded proteins (channels, receptors, enzymes). Cholesterol regulates fluidity. Selectively permeable. Fluid mosaic model (Singer-Nicolson, 1972).

Which best describes 'CONVERGENT EVOLUTION'?

1. Same species evolving twice
2. Reverse evolution
3. Single lineage
4. Unrelated species independently evolving similar traits in response to similar environments (e.g., wings in birds, bats, insects; streamlined body of dolphins, sharks, ichthyosaurs)
5. No evolution

Answer: D — Unrelated species independently evolving similar traits in response to similar environments (e.g., wings in birds, bats, insects; streamlined body of dolphins, sharks, ichthyosaurs)

Convergent evolution: similar selective pressures yield similar adaptations in unrelated lineages. Analogous structures (similar function, different ancestry). Compare homologous (shared ancestry, similar structure). Examples: streamlined body in aquatic vertebrates. NGSS HS-LS4-1.

The structure of an enzyme is critical because:

1. Only color matters
2. Has no effect
3. Only mass matters
4. Its three-dimensional shape (especially the active site) determines substrate specificity — enzymes catalyze reactions by lowering activation energy without being consumed; affected by temperature, pH, inhibitors

Answer: D — Its three-dimensional shape (especially the active site) determines substrate specificity — enzymes catalyze reactions by lowering activation energy without being consumed; affected by temperature, pH, inhibitors

D) Standard. A/B/C) Each is incorrect.

Sex chromosomes and sex determination in humans:

1. XX = typical female, XY = typical male; Y chromosome carries SRY gene initiating male development; X-linked traits (hemophilia, red-green color blindness) more common in males due to single X copy; variations exist
2. ZW system
3. Random
4. Determined by mother only

Answer: A — XX = typical female, XY = typical male; Y chromosome carries SRY gene initiating male development; X-linked traits (hemophilia, red-green color blindness) more common in males due to single X copy; variations exist

A) Standard. B/C/D) Each is incorrect.

What is the function of DNA?

1. Protein production
2. Stores genetic information used to make proteins via transcription and translation
3. Cell movement
4. Energy storage
5. Cell wall structure

Answer: B — Stores genetic information used to make proteins via transcription and translation

DNA: deoxyribonucleic acid. Stores genetic info. Double helix. Bases: A-T, G-C. Genes (regions) coded by base sequence. Transcribed to mRNA, translated to proteins. Foundation of molecular biology.

Which membrane transport process moves glucose into a red blood cell down its concentration gradient using a specific carrier protein, WITHOUT ATP?

1. Simple diffusion
2. Facilitated diffusion
3. Primary active transport
4. Endocytosis

Answer: B — Facilitated diffusion

B) Facilitated diffusion uses transport proteins to move polar/charged molecules down a gradient without energy. A) Simple diffusion doesn't use carriers. C) Requires ATP. D) Bulk transport via vesicles.

What is the function of the IMMUNE SYSTEM?

1. Digestion
2. Energy production
3. Movement
4. Reproduction
5. Defend against pathogens and abnormal cells; innate (nonspecific) + adaptive (specific, memory) responses

Answer: E — Defend against pathogens and abnormal cells; innate (nonspecific) + adaptive (specific, memory) responses

Immune system: 2 branches. Innate (skin, phagocytes, inflammation — fast, broad). Adaptive (B cells make antibodies, T cells kill infected — slower, specific, memory). Vaccines induce memory without disease.

An enzyme is a biological catalyst that:

1. Increases activation energy
2. Replaces substrate
3. Becomes part of product
4. Generates energy
5. Lowers activation energy of a reaction, unchanged by reaction itself, specific to substrate (induced-fit / lock-and-key), can be denatured by heat/pH

Answer: E — Lowers activation energy of a reaction, unchanged by reaction itself, specific to substrate (induced-fit / lock-and-key), can be denatured by heat/pH

Enzymes: typically proteins. Specific to substrate (active site). Lower activation energy → speed up reactions. Affected by temperature, pH, substrate concentration. Denaturation = loss of 3D structure → loss of function. Foundation of biochemistry.

The human respiratory system's primary function is to:

1. Digest food
2. Filter blood
3. Exchange gases — O₂ in, CO₂ out — at the alveoli; supports cellular respiration throughout the body
4. Produce hormones

Answer: C — Exchange gases — O₂ in, CO₂ out — at the alveoli; supports cellular respiration throughout the body

C) Defining role. A/B/D) Each is a different system.

What is sex-linked inheritance?

Genes located on sex chromosomes (most often X). X-linked recessive traits affect males more often (e.g., colorblindness, hemophilia).

What is homozygous vs. heterozygous?

Homozygous: two identical alleles (TT or tt). Heterozygous: two different alleles (Tt).

WORKED EXAMPLE — Chromosome counting through mitosis: A human somatic cell (2n = 46). Count chromosomes and chromatids at each stage.

STEP 1 — G1 (before S phase): 46 chromosomes, each unreplicated → 46 chromatids. STEP 2 — After S phase / G2: DNA replicated. Still 46 chromosomes, but each is now 2 sister chromatids → 92 chromatids. STEP 3 — Prophase/Metaphase: 46 chromosomes (each with 2 chromatids), 92 chromatids total. STEP 4 — Anaphase: Sister chromatids separate; each pole now has 46 chromatids = 46 chromosomes. STEP 5 — Telophase/cytokinesis: Each daughter cell has 46 chromosomes, 46 chromatids (unreplicated). ANSWER: Chromosome NUMBER stays 46 throughout; chromatid count goes 46 → 92 → 46 per daughter.

What is the monomer of nucleic acids?

Nucleotides (nitrogenous base + sugar + phosphate).

Why is water essential to life?

Polar molecule, universal solvent, high specific heat, cohesion/adhesion, density (ice floats), participates in many biochemical reactions.

What is the function of the Golgi apparatus?

Modifies, sorts, packages, and ships proteins/lipids.