IB Biology (International Baccalaureate) SL & HL Exam Questions &
Answers
IB Biology SL & HL 300 Exam Practice Questions & Answers
Topics Covered:
300 questions as follows:
🧬 Core Topics (SL & HL) – 150 Questions
1. Cell Biology – 25 Qs
2. Molecular Biology – 25 Qs
3. Genetics – 25 Qs
4. Ecology – 20 Qs
5. Evolution & Biodiversity – 20 Qs
6. Human Physiology – 35 Qs
🔬AHL Topics (HL only) – 90 Questions
1. Nucleic Acids – 15 Qs
2. Metabolism, Cell Respiration, Photosynthesis – 20 Qs
3. Plant Biology – 15 Qs
4. Genetics & Evolution – 15 Qs
5. Animal Physiology – 25 Qs
🌍 Options (SL & HL) – 60 Questions
Option C: Ecology & Conservation – 30 Qs
Option D: Human Physiology – 30 Qs
IB Biology SL & HL – Exam Questions & Answers
📦 Part 1: Questions 1–50
Topics Covered:
Cell Biology (Qs 1–20)
, Molecular Biology (Qs 21–35)
Genetics (Qs 36–50)
🔬 Topic 1: Cell Biology
1. Describe the principles of cell theory.
Answer:
Cell theory states that:
1. All living organisms are composed of cells.
2. Cells are the smallest units of life.
3. All cells come from pre-existing cells.
This theory is supported by extensive microscopic observations and
experiments, including Pasteur’s swan-neck flask experiment, which
disproved spontaneous generation.
2. Explain how the surface area to volume ratio limits cell size.
Answer:
As a cell grows, its volume increases faster than its surface area, reducing the
surface area:volume ratio. This limits the rate of material exchange (e.g., oxygen,
nutrients) relative to the cell’s needs, making large cells inefficient. Cells divide to
maintain an optimal ratio for efficient diffusion and metabolic processes.
3. List three atypical examples that challenge the cell theory.
Answer:
1. Striated muscle fibers – large and multinucleated.
2. Giant algae (e.g., Acetabularia) – single cells that are very large.
3. Aseptate fungal hyphae – not divided into individual cells.
These examples show that not all living cells fit the classical definitions of
cell theory.
,4. Distinguish between prokaryotic and eukaryotic cells.
Answer:
Prokaryotes: No nucleus, DNA in nucleoid region, 70S ribosomes, no
membrane-bound organelles.
Eukaryotes: DNA in nucleus, 80S ribosomes, many membrane-bound
organelles (e.g., mitochondria, ER, Golgi).
Eukaryotes are generally larger and more complex.
5. Outline the function of the following organelles: nucleus, mitochondrion,
Golgi apparatus, rough ER.
Answer:
Nucleus: Stores genetic information, controls cell activities.
Mitochondrion: Site of aerobic respiration (ATP production).
Golgi apparatus: Processes and packages proteins.
Rough ER: Synthesizes proteins (with attached ribosomes).
6. Compare the structures of plant and animal cells.
Answer:
Both have a nucleus, cytoplasm, plasma membrane, mitochondria, and ribosomes.
Plant cells additionally have:
Cell wall (cellulose)
Chloroplasts (photosynthesis)
Large central vacuole
Animal cells have:
Centrioles
Smaller vacuoles
Only plant cells perform photosynthesis.
7. State the role of cholesterol in the plasma membrane.
Answer:
Cholesterol maintains membrane fluidity by:
, Reducing membrane permeability to small water-soluble molecules.
Preventing phospholipids from packing too closely in cold temperatures.
Stabilizing membrane in higher temperatures.
8. Draw and label a diagram of the fluid mosaic model of the plasma
membrane.
Answer:
(Diagram should include: phospholipid bilayer, integral proteins, peripheral
proteins, glycoproteins, glycolipids, cholesterol.)
9. Explain the process of osmosis.
Answer:
Osmosis is the passive movement of water molecules across a semi-permeable
membrane from a region of low solute concentration to high solute concentration,
until equilibrium is reached. No energy input is required.
10. Describe how vesicles are used to transport proteins within a cell.
Answer:
Proteins synthesized by ribosomes on the rough ER are packaged into vesicles,
which bud off and move to the Golgi apparatus. After modification, proteins are
packaged into secretory vesicles that fuse with the plasma membrane to release
contents (exocytosis).
11. Explain the significance of Pasteur’s experiment in supporting cell theory.
Answer:
Pasteur’s swan-neck flask experiment showed that no microorganisms grew in
sterilized broth unless exposed to air with microbes. This disproved spontaneous
generation and supported that cells arise from pre-existing cells.
12. Outline the events of the cell cycle.
Answer:
Answers
IB Biology SL & HL 300 Exam Practice Questions & Answers
Topics Covered:
300 questions as follows:
🧬 Core Topics (SL & HL) – 150 Questions
1. Cell Biology – 25 Qs
2. Molecular Biology – 25 Qs
3. Genetics – 25 Qs
4. Ecology – 20 Qs
5. Evolution & Biodiversity – 20 Qs
6. Human Physiology – 35 Qs
🔬AHL Topics (HL only) – 90 Questions
1. Nucleic Acids – 15 Qs
2. Metabolism, Cell Respiration, Photosynthesis – 20 Qs
3. Plant Biology – 15 Qs
4. Genetics & Evolution – 15 Qs
5. Animal Physiology – 25 Qs
🌍 Options (SL & HL) – 60 Questions
Option C: Ecology & Conservation – 30 Qs
Option D: Human Physiology – 30 Qs
IB Biology SL & HL – Exam Questions & Answers
📦 Part 1: Questions 1–50
Topics Covered:
Cell Biology (Qs 1–20)
, Molecular Biology (Qs 21–35)
Genetics (Qs 36–50)
🔬 Topic 1: Cell Biology
1. Describe the principles of cell theory.
Answer:
Cell theory states that:
1. All living organisms are composed of cells.
2. Cells are the smallest units of life.
3. All cells come from pre-existing cells.
This theory is supported by extensive microscopic observations and
experiments, including Pasteur’s swan-neck flask experiment, which
disproved spontaneous generation.
2. Explain how the surface area to volume ratio limits cell size.
Answer:
As a cell grows, its volume increases faster than its surface area, reducing the
surface area:volume ratio. This limits the rate of material exchange (e.g., oxygen,
nutrients) relative to the cell’s needs, making large cells inefficient. Cells divide to
maintain an optimal ratio for efficient diffusion and metabolic processes.
3. List three atypical examples that challenge the cell theory.
Answer:
1. Striated muscle fibers – large and multinucleated.
2. Giant algae (e.g., Acetabularia) – single cells that are very large.
3. Aseptate fungal hyphae – not divided into individual cells.
These examples show that not all living cells fit the classical definitions of
cell theory.
,4. Distinguish between prokaryotic and eukaryotic cells.
Answer:
Prokaryotes: No nucleus, DNA in nucleoid region, 70S ribosomes, no
membrane-bound organelles.
Eukaryotes: DNA in nucleus, 80S ribosomes, many membrane-bound
organelles (e.g., mitochondria, ER, Golgi).
Eukaryotes are generally larger and more complex.
5. Outline the function of the following organelles: nucleus, mitochondrion,
Golgi apparatus, rough ER.
Answer:
Nucleus: Stores genetic information, controls cell activities.
Mitochondrion: Site of aerobic respiration (ATP production).
Golgi apparatus: Processes and packages proteins.
Rough ER: Synthesizes proteins (with attached ribosomes).
6. Compare the structures of plant and animal cells.
Answer:
Both have a nucleus, cytoplasm, plasma membrane, mitochondria, and ribosomes.
Plant cells additionally have:
Cell wall (cellulose)
Chloroplasts (photosynthesis)
Large central vacuole
Animal cells have:
Centrioles
Smaller vacuoles
Only plant cells perform photosynthesis.
7. State the role of cholesterol in the plasma membrane.
Answer:
Cholesterol maintains membrane fluidity by:
, Reducing membrane permeability to small water-soluble molecules.
Preventing phospholipids from packing too closely in cold temperatures.
Stabilizing membrane in higher temperatures.
8. Draw and label a diagram of the fluid mosaic model of the plasma
membrane.
Answer:
(Diagram should include: phospholipid bilayer, integral proteins, peripheral
proteins, glycoproteins, glycolipids, cholesterol.)
9. Explain the process of osmosis.
Answer:
Osmosis is the passive movement of water molecules across a semi-permeable
membrane from a region of low solute concentration to high solute concentration,
until equilibrium is reached. No energy input is required.
10. Describe how vesicles are used to transport proteins within a cell.
Answer:
Proteins synthesized by ribosomes on the rough ER are packaged into vesicles,
which bud off and move to the Golgi apparatus. After modification, proteins are
packaged into secretory vesicles that fuse with the plasma membrane to release
contents (exocytosis).
11. Explain the significance of Pasteur’s experiment in supporting cell theory.
Answer:
Pasteur’s swan-neck flask experiment showed that no microorganisms grew in
sterilized broth unless exposed to air with microbes. This disproved spontaneous
generation and supported that cells arise from pre-existing cells.
12. Outline the events of the cell cycle.
Answer:
