RIO BIO 156 – Introductory Human Biology Exam 1 (2025/2026)
Verified Questions, Correct Answers & Rationales
Mixed Exam Style | Set 1: Questions
1. Which level of biological organization includes all the other levels below it?
A. Organ system
✅
B. Cell
C. Organism
D. Tissue
Rationale: The organism is the total living being composed of all systems, organs, tissues, and
cells.
2. Which of the following best describes homeostasis?
✅
A. Maintaining a constant external environment
B. Maintaining internal stability despite external changes
C. Breaking down nutrients for energy
D. The process of reproduction
Rationale: Homeostasis keeps body conditions stable (e.g., temperature, pH) despite external
changes.
3. The smallest living unit in the human body is the:
A. Atom
✅
B. Molecule
C. Cell
D. Tissue
Rationale: The cell is the fundamental unit of life capable of all vital functions.
4. Which organ system is primarily responsible for transporting nutrients and oxygen throughout
the body?
A. Nervous system
✅
B. Digestive system
C. Circulatory system
D. Respiratory system
Rationale: The circulatory system delivers oxygen and nutrients to tissues and removes waste.
,5. Which macromolecule serves as the body’s main source of energy?
A. Proteins
✅
B. Lipids
C. Carbohydrates
D. Nucleic acids
Rationale: Carbohydrates are broken down into glucose, the body’s primary fuel.
6. Which of the following statements about enzymes is TRUE?
A. They slow down chemical reactions
✅
B. They are used up during reactions
C. They lower activation energy
D. They are carbohydrates
Rationale: Enzymes act as catalysts, lowering the activation energy to speed up reactions.
7. DNA is found mainly in which part of the cell?
A. Ribosome
✅
B. Cytoplasm
C. Nucleus
D. Mitochondria
Rationale: The nucleus stores DNA in the form of chromatin or chromosomes.
8. The plasma membrane is described as “selectively permeable” because it:
A. Allows all molecules to pass
✅
B. Blocks all materials
C. Controls what enters and leaves the cell
D. Is solid and rigid
Rationale: The plasma membrane regulates passage of substances in and out of the cell.
9. Which of the following organelles is the “powerhouse” of the cell?
✅
A. Ribosome
B. Mitochondrion
C. Lysosome
D. Endoplasmic reticulum
Rationale: Mitochondria produce ATP, the main energy molecule for cellular activities.
,10. Which process moves molecules from high concentration to low concentration without
energy use?
A. Active transport
✅
B. Osmosis
C. Diffusion
D. Endocytosis
Rationale: Diffusion is passive movement along a concentration gradient.
11. Which organ system includes the skin, hair, and nails?
✅
A. Muscular system
B. Integumentary system
C. Skeletal system
D. Endocrine system
Rationale: The integumentary system protects and regulates body temperature.
12. The atomic number of an element is determined by its:
A. Neutrons
✅
B. Electrons
C. Protons
D. Isotopes
Rationale: The number of protons defines the atomic number and identity of the element.
13. Which of the following describes a neutral solution?
✅
A. pH 2
B. pH 7
C. pH 10
D. pH 12
Rationale: A pH of 7 indicates a neutral balance between hydrogen and hydroxide ions.
14. What type of feedback mechanism enhances or increases the original stimulus?
✅
A. Negative feedback
B. Positive feedback
C. Homeostatic balance
D. Reverse regulation
Rationale: Positive feedback amplifies a process (e.g., childbirth contractions).
, ✅
15. The human body is primarily composed of which elements?
A. Carbon, hydrogen, oxygen, nitrogen
B. Sodium, chlorine, potassium, calcium
C. Iron, zinc, magnesium, phosphorus
D. Helium, neon, argon, krypton
Rationale: CHON are the four most abundant elements in the human body.
✅
16. Which structure controls entry and exit of substances in the nucleus?
A. Nuclear membrane
B. Nucleolus
C. Chromatin
D. Ribosome
Rationale: The nuclear membrane contains pores that regulate nuclear transport.
17. The process of converting glucose into ATP occurs mainly in the:
✅
A. Cytoplasm
B. Mitochondria
C. Ribosomes
D. Nucleus
Rationale: Cellular respiration in mitochondria produces ATP from glucose.
18. Which of the following best describes mitosis?
✅
A. Reduction division producing gametes
B. Cell division for growth and repair
C. Production of genetic variation
D. DNA replication only
Rationale: Mitosis produces identical daughter cells for tissue growth and repair.
19. Which tissue type conducts electrical impulses?
✅
A. Muscle
B. Nervous
C. Epithelial
D. Connective
Rationale: Nervous tissue carries signals via neurons and neuroglia.
Verified Questions, Correct Answers & Rationales
Mixed Exam Style | Set 1: Questions
1. Which level of biological organization includes all the other levels below it?
A. Organ system
✅
B. Cell
C. Organism
D. Tissue
Rationale: The organism is the total living being composed of all systems, organs, tissues, and
cells.
2. Which of the following best describes homeostasis?
✅
A. Maintaining a constant external environment
B. Maintaining internal stability despite external changes
C. Breaking down nutrients for energy
D. The process of reproduction
Rationale: Homeostasis keeps body conditions stable (e.g., temperature, pH) despite external
changes.
3. The smallest living unit in the human body is the:
A. Atom
✅
B. Molecule
C. Cell
D. Tissue
Rationale: The cell is the fundamental unit of life capable of all vital functions.
4. Which organ system is primarily responsible for transporting nutrients and oxygen throughout
the body?
A. Nervous system
✅
B. Digestive system
C. Circulatory system
D. Respiratory system
Rationale: The circulatory system delivers oxygen and nutrients to tissues and removes waste.
,5. Which macromolecule serves as the body’s main source of energy?
A. Proteins
✅
B. Lipids
C. Carbohydrates
D. Nucleic acids
Rationale: Carbohydrates are broken down into glucose, the body’s primary fuel.
6. Which of the following statements about enzymes is TRUE?
A. They slow down chemical reactions
✅
B. They are used up during reactions
C. They lower activation energy
D. They are carbohydrates
Rationale: Enzymes act as catalysts, lowering the activation energy to speed up reactions.
7. DNA is found mainly in which part of the cell?
A. Ribosome
✅
B. Cytoplasm
C. Nucleus
D. Mitochondria
Rationale: The nucleus stores DNA in the form of chromatin or chromosomes.
8. The plasma membrane is described as “selectively permeable” because it:
A. Allows all molecules to pass
✅
B. Blocks all materials
C. Controls what enters and leaves the cell
D. Is solid and rigid
Rationale: The plasma membrane regulates passage of substances in and out of the cell.
9. Which of the following organelles is the “powerhouse” of the cell?
✅
A. Ribosome
B. Mitochondrion
C. Lysosome
D. Endoplasmic reticulum
Rationale: Mitochondria produce ATP, the main energy molecule for cellular activities.
,10. Which process moves molecules from high concentration to low concentration without
energy use?
A. Active transport
✅
B. Osmosis
C. Diffusion
D. Endocytosis
Rationale: Diffusion is passive movement along a concentration gradient.
11. Which organ system includes the skin, hair, and nails?
✅
A. Muscular system
B. Integumentary system
C. Skeletal system
D. Endocrine system
Rationale: The integumentary system protects and regulates body temperature.
12. The atomic number of an element is determined by its:
A. Neutrons
✅
B. Electrons
C. Protons
D. Isotopes
Rationale: The number of protons defines the atomic number and identity of the element.
13. Which of the following describes a neutral solution?
✅
A. pH 2
B. pH 7
C. pH 10
D. pH 12
Rationale: A pH of 7 indicates a neutral balance between hydrogen and hydroxide ions.
14. What type of feedback mechanism enhances or increases the original stimulus?
✅
A. Negative feedback
B. Positive feedback
C. Homeostatic balance
D. Reverse regulation
Rationale: Positive feedback amplifies a process (e.g., childbirth contractions).
, ✅
15. The human body is primarily composed of which elements?
A. Carbon, hydrogen, oxygen, nitrogen
B. Sodium, chlorine, potassium, calcium
C. Iron, zinc, magnesium, phosphorus
D. Helium, neon, argon, krypton
Rationale: CHON are the four most abundant elements in the human body.
✅
16. Which structure controls entry and exit of substances in the nucleus?
A. Nuclear membrane
B. Nucleolus
C. Chromatin
D. Ribosome
Rationale: The nuclear membrane contains pores that regulate nuclear transport.
17. The process of converting glucose into ATP occurs mainly in the:
✅
A. Cytoplasm
B. Mitochondria
C. Ribosomes
D. Nucleus
Rationale: Cellular respiration in mitochondria produces ATP from glucose.
18. Which of the following best describes mitosis?
✅
A. Reduction division producing gametes
B. Cell division for growth and repair
C. Production of genetic variation
D. DNA replication only
Rationale: Mitosis produces identical daughter cells for tissue growth and repair.
19. Which tissue type conducts electrical impulses?
✅
A. Muscle
B. Nervous
C. Epithelial
D. Connective
Rationale: Nervous tissue carries signals via neurons and neuroglia.
