TEAS Science: Biology and Life Science 1 — Questions and Answers

Question 1: The Hardy-Weinberg principle states that allele frequencies in a population will remain constant if:

Natural selection is strong
The population is small
There is no mutation, migration, selection, genetic drift, or non-random mating (Correct answer)
Gene flow between populations is high

Correct answer: There is no mutation, migration, selection, genetic drift, or non-random mating

Hardy-Weinberg equilibrium requires five conditions: no mutation, no gene flow (migration), random mating, large population, and no natural selection.

The Hardy-Weinberg principle is a null model for population genetics stating that allele and genotype frequencies remain stable generation after generation IF: (1) no mutations occur, (2) no migration (gene flow) in or out, (3) random mating, (4) very large population (no genetic drift), and (5) no natural selection. Real populations violate these conditions, causing allele frequency changes (evolution). The principle provides a baseline — deviations from Hardy-Weinberg equilibrium indicate that one or more evolutionary forces are acting on the population.

Question 2: Which molecule carries amino acids to the ribosome during translation?

mRNA
rRNA
tRNA (Correct answer)
snRNA

Correct answer: tRNA

Transfer RNA (tRNA) has an anticodon that matches mRNA codons and carries the corresponding amino acid to the ribosome for incorporation into the growing protein.

tRNA (transfer RNA) is the adapter molecule of translation. It has a distinctive cloverleaf/L-shaped structure with two key regions: the anticodon loop (a triplet of nucleotides complementary to the mRNA codon) and the 3' acceptor stem (where the specific amino acid is attached by aminoacyl-tRNA synthetase enzymes). At the ribosome, tRNA anticodons base-pair with mRNA codons in the A site, the amino acid is added to the growing polypeptide, and the 'empty' tRNA exits through the E site. Each of the 20 amino acids has at least one tRNA.

Question 3: Which term describes the movement of water across a semipermeable membrane from high to low water concentration?

Active transport
Diffusion
Osmosis (Correct answer)
Endocytosis

Correct answer: Osmosis

Osmosis is the passive movement of water across a semipermeable membrane from a region of high water concentration (low solute) to low water concentration (high solute).

Osmosis is a special case of diffusion specifically involving water molecules moving through a selectively permeable membrane. Water moves from hypotonic (low solute, high water) to hypertonic (high solute, low water) solutions. Osmotic pressure is the pressure needed to prevent net water movement. In biology: red blood cells in a hypertonic solution shrink (crenation) as water leaves; in a hypotonic solution, they swell and may lyse (hemolysis). Plant cells placed in hypotonic solutions become turgid (rigid); in hypertonic solutions, they undergo plasmolysis. Osmosis drives many physiological processes including kidney filtration.

Question 4: What is the product of glycolysis?

Acetyl-CoA and CO2
ATP only
Two pyruvate molecules (plus net 2 ATP and 2 NADH) (Correct answer)
Glucose-6-phosphate only

Correct answer: Two pyruvate molecules (plus net 2 ATP and 2 NADH)

Glycolysis converts one glucose (6-carbon) into two pyruvate (3-carbon) molecules, with a net yield of 2 ATP and 2 NADH.

Glycolysis occurs in the cytoplasm and consists of 10 enzymatic reactions. One glucose (C6) is: phosphorylated twice (using 2 ATP), split into two 3-carbon molecules (glyceraldehyde-3-phosphate), and oxidized to produce 2 pyruvate, generating 4 ATP (net 2 ATP after investment) and 2 NADH. Under aerobic conditions, pyruvate enters mitochondria for the Krebs cycle. Under anaerobic conditions, pyruvate is reduced to lactate (animal cells) or ethanol+CO2 (yeast) to regenerate NAD+ and keep glycolysis running. Glycolysis doesn't require oxygen and is the first step in both aerobic and anaerobic respiration.

Question 5: Which level of protein structure describes the coiling or folding of a polypeptide chain into alpha helices and beta pleated sheets?

Primary structure
Secondary structure (Correct answer)
Tertiary structure
Quaternary structure

Correct answer: Secondary structure

Secondary structure refers to local folding of the polypeptide backbone into alpha helices and beta-pleated sheets, stabilized by hydrogen bonds between backbone atoms.

Protein structure has four levels: (1) Primary — the linear sequence of amino acids (determined by DNA); (2) Secondary — local regular folding patterns (alpha helices and beta-pleated sheets) stabilized by hydrogen bonds between the carbonyl O and amide NH groups of the peptide backbone; (3) Tertiary — the overall 3D shape of a single polypeptide, stabilized by R-group interactions (hydrophobic, disulfide bonds, ionic bonds, H-bonds); (4) Quaternary — the arrangement of multiple polypeptide subunits (e.g., hemoglobin has 4 subunits). Denaturation disrupts secondary, tertiary, and quaternary structures.

Question 6: Which of the following correctly describes the central dogma of molecular biology?

RNA → DNA → Protein
DNA → RNA → Protein (Correct answer)
Protein → RNA → DNA
DNA → Protein → RNA

Correct answer: DNA → RNA → Protein

The central dogma describes the flow of genetic information: DNA is transcribed to RNA, which is translated to protein.

Crick's central dogma (1958) describes the general flow of genetic information: DNA → RNA → Protein. Specifically: (1) Replication: DNA → DNA (copying the genome before cell division); (2) Transcription: DNA → RNA (making mRNA copies of genes); (3) Translation: RNA → Protein (ribosomes decode mRNA to make proteins). Notable exceptions exist: retroviruses (like HIV) use reverse transcriptase to copy RNA back into DNA. Prions are misfolded proteins that can template other proteins to misfold — sometimes considered a fourth transfer not in the central dogma (protein → protein conformational change).

Question 7: What is the role of decomposers in an ecosystem?

Producing energy from sunlight
Converting atmospheric nitrogen to usable forms
Breaking down dead organic matter and recycling nutrients (Correct answer)
Transferring energy from plants to herbivores

Correct answer: Breaking down dead organic matter and recycling nutrients

Decomposers (fungi and bacteria) break down dead organisms and waste, releasing nutrients back into the environment for uptake by producers.

Decomposers (primarily bacteria and fungi) are saprotrophic organisms that break down complex organic compounds in dead organisms and waste into simpler inorganic substances (CO2, water, mineral salts) through chemical decomposition. This releases nutrients like nitrogen, phosphorus, and carbon back into the soil and atmosphere, making them available for uptake by producers (plants). Without decomposers, nutrients would remain locked in dead organic matter, ecosystems would accumulate waste, and producer growth would be severely limited. They occupy the final trophic level and are essential for nutrient cycling.

Question 8: A mutation that changes a single nucleotide base and results in a different amino acid being inserted is called a:

Silent mutation
Frameshift mutation
Missense mutation (Correct answer)
Nonsense mutation

Correct answer: Missense mutation

A missense mutation is a single nucleotide substitution that changes one amino acid in the resulting protein to a different amino acid.

Point mutations (single nucleotide changes) include three types: (1) Silent/synonymous — codon changes but same amino acid is incorporated (due to genetic code degeneracy), no effect on protein; (2) Missense — codon changes to code for a different amino acid (may alter protein function — e.g., sickle cell anemia involves a single missense mutation in beta-globin); (3) Nonsense — codon changes to a stop codon, prematurely terminating the protein. Frameshift mutations (insertions/deletions of non-multiple-of-3 nucleotides) shift the entire reading frame and are typically more severe.

Question 9: Which type of organism can perform photosynthesis?

Heterotrophs
Autotrophs (Correct answer)
Decomposers only
Carnivores

Correct answer: Autotrophs

Autotrophs (producers) can perform photosynthesis, using light energy to synthesize organic compounds from CO2 and water.

Autotrophs are organisms that synthesize their own organic nutrients from inorganic sources. Photoautotrophs (plants, algae, cyanobacteria) use light energy for photosynthesis. Chemoautotrophs (certain bacteria) use energy from inorganic chemical reactions. In contrast, heterotrophs (animals, fungi, most bacteria) must consume organic molecules made by other organisms. This distinction defines trophic levels: autotrophs are producers (first trophic level); herbivores (primary consumers), carnivores, and omnivores are heterotrophs occupying higher trophic levels. Only ~10% of energy is transferred between trophic levels (ten percent rule).

Question 10: Which of the following best defines 'homeostasis'?

The process of cell division
The maintenance of a stable internal environment despite external changes (Correct answer)
The genetic variation within a population
The storage of energy in chemical bonds

Correct answer: The maintenance of a stable internal environment despite external changes

Homeostasis is the ability of an organism to maintain a stable internal environment (body temperature, pH, blood glucose, etc.) through negative feedback mechanisms.

Homeostasis is fundamental to life. The body uses negative feedback loops to maintain physiological variables within narrow ranges: a stimulus causes a change → receptors detect the change → control center (often the brain or endocrine gland) processes information → effectors produce a response that counteracts the change, restoring balance. Examples: thermoregulation (sweating/shivering maintain 37°C), blood glucose regulation (insulin/glucagon maintain 70–100 mg/dL), and blood pressure regulation. Positive feedback (rare) amplifies changes (e.g., childbirth contractions, blood clotting) — it moves away from setpoint until a specific endpoint is reached.

Question 11: Which kingdom includes organisms that are multicellular, obtain nutrients through absorption, and have cell walls made of chitin?

Animalia
Plantae
Fungi (Correct answer)
Protista

Correct answer: Fungi

The kingdom Fungi includes multicellular organisms (most) with chitin cell walls that absorb nutrients from their environment through decomposition or symbiosis.

Kingdom Fungi characteristics: (1) Eukaryotic; (2) Cell walls containing chitin (unlike plant cell walls which contain cellulose); (3) Absorptive heterotrophs — secrete digestive enzymes externally and absorb the resulting nutrients; (4) Most are multicellular (except yeasts); (5) Reproduce via spores. Examples: mushrooms, molds (Aspergillus, Penicillium), yeasts (Candida, Saccharomyces). Medical significance: fungi cause diseases like athlete's foot (tinea pedis), ringworm, thrush (Candida albicans), and opportunistic infections in immunocompromised patients. Antibiotics are derived from fungi (penicillin from Penicillium).

Question 12: What is the primary role of the spleen in the body?

Producing digestive enzymes
Filtering blood and recycling old red blood cells (Correct answer)
Producing insulin
Synthesizing vitamin D

Correct answer: Filtering blood and recycling old red blood cells

The spleen filters blood, removes old and damaged red blood cells, recycles hemoglobin, and houses immune cells that fight bloodborne pathogens.

The spleen has two main functions: (1) Red pulp — filters blood, removes old/damaged RBCs (lifespan ~120 days), platelets, and pathogens; macrophages break down hemoglobin, recycling iron back to bone marrow. (2) White pulp — contains lymphocytes and macrophages that mount immune responses against bloodborne antigens. The spleen also serves as a blood reservoir. Asplenic patients (after splenectomy) are at increased risk of infection by encapsulated bacteria (Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis) and require vaccinations.

Question 13: Which of the following correctly describes the process of transpiration in plants?

Absorption of water through leaves
Loss of water vapor through stomata in leaves (Correct answer)
Transport of sugars from leaves to roots
Conversion of light energy to chemical energy

Correct answer: Loss of water vapor through stomata in leaves

Transpiration is the evaporation of water vapor through stomata (pores) in leaves, creating a water potential gradient that drives water uptake from roots.

Transpiration occurs when stomata (tiny pores in leaves, surrounded by guard cells) open to allow CO₂ uptake for photosynthesis — water vapor simultaneously escapes. This creates negative water potential in leaves, pulling water up through the xylem from roots via a transpiration-cohesion-tension mechanism. Water molecules cohere (stick together due to hydrogen bonds) as a continuous column from roots to leaves. Transpiration is affected by temperature, humidity, wind, and light. Guard cells control stomatal aperture in response to water availability (stomata close during drought to prevent wilting).

Question 14: The process by which a cell engulfs and destroys large particles such as bacteria is called:

Exocytosis
Pinocytosis
Phagocytosis (Correct answer)
Facilitated diffusion

Correct answer: Phagocytosis

Phagocytosis ('cell eating') is the endocytosis of large solid particles — used by white blood cells (neutrophils, macrophages) to engulf and destroy pathogens.

Types of endocytosis (cell bringing material IN): (1) Phagocytosis ('cell eating') — engulfment of large solid particles (bacteria, dead cells) by pseudopods; forms a phagosome that fuses with lysosomes for digestion. (2) Pinocytosis ('cell drinking') — engulfment of small droplets of extracellular fluid. (3) Receptor-mediated endocytosis — specific molecules bind receptors, triggering targeted uptake. Neutrophils and macrophages are professional phagocytes in the immune system. Macrophages also present antigens after phagocytosis, linking innate and adaptive immunity. Exocytosis is the reverse process — moving material OUT.

TEAS Science: Biology and Life Science 1

The Hardy-Weinberg principle states that allele frequencies in a population will remain constant if:

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