HESI A2 Biology Practice Questions: 25 Questions With Explanations
Biology preparation can involve many topics, so students benefit from reviewing foundational concepts before attempting more advanced questions. Understanding cell structures, genetics, energy production, and the relationship between organisms and their environments provides a useful base for further study. These original Naxles questions are intended for revision. They are not official HESI questions, and the subjects covered by your particular exam may vary.
Practice questions
1. Which structure controls many of the activities of a eukaryotic cell and contains most of its DNA?
- A. Ribosome
- B. Nucleus
- C. Cell membrane
- D. Golgi apparatus
Answer: B. Nucleus. The nucleus houses most of the cell's genetic material and helps regulate gene expression.
2. What is the primary function of mitochondria?
- A. Produce most cellular ATP through aerobic respiration
- B. Store genetic information outside the cell
- C. Make every protein directly
- D. Digest food in the stomach
Answer: A. Mitochondria are major sites of ATP production during aerobic cellular respiration.
3. Which molecule carries genetic information in most living organisms?
- A. DNA
- B. Glucose
- C. Water
- D. Hemoglobin
Answer: A. DNA. DNA stores hereditary information used in development and cellular function.
4. What is the basic function of ribosomes?
- A. Protein synthesis
- B. Lipid storage only
- C. Oxygen transport
- D. Waste removal from the body
Answer: A. Ribosomes assemble amino acids into proteins according to genetic instructions.
5. Which process produces two genetically similar daughter cells for growth and repair?
- A. Mitosis
- B. Meiosis
- C. Fertilization
- D. Pollination
Answer: A. Mitosis. Mitosis produces daughter nuclei with the same chromosome number as the parent cell, barring errors.
6. Which process normally produces gametes with half the usual chromosome number?
- A. Mitosis
- B. Meiosis
- C. Diffusion
- D. Osmosis
Answer: B. Meiosis. Meiosis reduces the chromosome number and contributes to genetic variation.
7. What is the main function of the cell membrane?
- A. Regulate what enters and leaves the cell
- B. Produce sunlight
- C. Store all body minerals
- D. Form bones
Answer: A. The cell membrane acts as a selectively permeable barrier.
8. Which process allows water to move across a selectively permeable membrane?
- A. Osmosis
- B. Transcription
- C. Translation
- D. Mitosis
Answer: A. Osmosis. Osmosis is the movement of water across a selectively permeable membrane in response to differences in water potential.
9. Which organelle modifies, sorts, and packages many proteins for transport?
- A. Golgi apparatus
- B. Nucleus
- C. Centriole
- D. Nucleolus alone
Answer: A. The Golgi apparatus processes and packages proteins and lipids for delivery.
10. What is photosynthesis?
- A. The conversion of light energy into chemical energy by organisms such as plants
- B. The breakdown of bones
- C. The movement of blood through arteries
- D. The production of urine
Answer: A. Photosynthesis uses light energy to produce energy-rich compounds, typically using carbon dioxide and water.
11. Which gas is released as a by-product of oxygenic photosynthesis?
- A. Oxygen
- B. Nitrogen
- C. Helium
- D. Methane in every case
Answer: A. Oxygen. Oxygen is released when water is split during oxygenic photosynthesis.
12. Which type of biomolecule is made from amino acids?
- A. Protein
- B. Carbohydrate
- C. Nucleic acid
- D. Mineral
Answer: A. Protein. Amino acids are joined by peptide bonds to form proteins.
13. What is a gene?
- A. A segment of DNA associated with a functional product or trait
- B. A type of blood vessel
- C. A complete organ system
- D. A digestive enzyme in every case
Answer: A. Genes contain instructions for functional RNA or proteins and contribute to inherited characteristics.
14. What does a dominant allele generally mean in introductory genetics?
- A. Its effect can appear in a heterozygote
- B. It is always more common in a population
- C. It is always beneficial
- D. It cannot be inherited
Answer: A. In a simple dominant-recessive model, one copy of a dominant allele can produce the associated phenotype. Dominance does not necessarily mean commonness or advantage.
15. If a parent cell has 46 chromosomes and undergoes normal mitosis, how many chromosomes will each daughter cell generally have?
- A. 23
- B. 46
- C. 92
- D. 12
Answer: B. Mitosis normally preserves the chromosome number.
16. Which process describes the production of RNA from a DNA template?
- A. Transcription
- B. Translation
- C. Replication only
- D. Digestion
Answer: A. Transcription uses DNA as a template to produce RNA.
17. What happens during translation?
- A. Ribosomes use information in messenger RNA to build a polypeptide
- B. DNA is always destroyed
- C. Water becomes glucose directly
- D. Chromosomes leave the organism permanently
Answer: A. Translation converts the coded message in messenger RNA into an amino-acid sequence.
18. What is an ecosystem?
- A. Living organisms interacting with one another and their physical environment
- B. A single cell only
- C. A type of chromosome
- D. One isolated protein
Answer: A. An ecosystem includes organisms and the nonliving environment with which they interact.
19. Which organisms are commonly described as producers in a food chain?
- A. Organisms that make organic material from inorganic sources, such as plants
- B. Animals that eat only meat
- C. Decomposers only
- D. All consumers
Answer: A. Producers capture energy, often through photosynthesis, and form the base of many food webs.
20. What is natural selection?
- A. A process in which heritable traits affecting survival or reproduction influence how common they become
- B. A process in which every organism changes intentionally
- C. A guarantee that all species survive
- D. A type of cell division
Answer: A. Natural selection changes trait frequencies over generations when heritable variation affects reproductive success.
22. Which type of molecule forms much of the structure of cell membranes?
- A. Phospholipids
- B. Starch alone
- C. DNA alone
- D. Hemoglobin
Answer: A. Phospholipids form a bilayer that provides the basic structure of many cell membranes.
23. What is homeostasis?
- A. Maintaining relatively stable internal conditions
- B. The permanent elimination of all change
- C. The production of offspring only
- D. The breakdown of every protein
Answer: A. Homeostasis involves regulating internal conditions within suitable ranges despite external changes.
24. What is the main role of decomposers in an ecosystem?
- A. Break down dead organic matter and recycle nutrients
- B. Produce sunlight
- C. Stop every organism from reproducing
- D. Remove all oxygen from the atmosphere
Answer: A. Decomposers help return nutrients to the environment.
25. Which statement about enzymes is generally correct?
- A. They speed up chemical reactions by lowering activation energy.
- B. They are consumed permanently in every reaction.
- C. They work only at boiling temperatures.
- D. They always change the final equilibrium of a reaction.
Answer: A. Enzymes are biological catalysts. Their activity can be affected by temperature, pH, and other conditions.
How to study biology effectively
Group your revision into themes: cell structure, genetics, energy processes, and ecology. After reviewing each theme, answer practice questions without looking at your notes. Explain why each incorrect option is wrong, not just why the correct answer is right.
