IB BIOLOGY SL STUDY GUIDE
Practice Questions
Here are 15 practice questions for your IB Biology SL exam, covering key topics such as cells, molecular biology, genetics, ecology, evolution, and human physiology. I've included a mix of multiple choice, short answer, and data-based questions similar to those you might see on Papers 1, 2, and 3.
🔬 Topic 1: Cell Biology
1. Multiple Choice:
Which of the following statements best describes the function of the rough endoplasmic reticulum?
A. Synthesizes lipids
B. Modifies and packages proteins for secretion
C. Produces ATP through aerobic respiration
D. Digests old or damaged cell parts
2. Short Answer:
Explain how the structure of phospholipids allows them to form membranes.
3. Short Answer:
Outline the evidence for the endosymbiotic theory.
🧬 Topic 2: Molecular Biology
4. Data-Based Question:
Given a graph showing the activity of amylase at different pH levels,
a) Identify the optimum pH.
b) Explain why enzyme activity decreases outside this range.
5. Short Answer:
Describe the structure of DNA and how it allows replication to occur.
6. Multiple Choice:
Which enzyme is responsible for forming the complementary RNA strand during transcription?
A. DNA polymerase
B. RNA polymerase
C. Ligase
D. Helicase
🌱 Topic 3: Genetics
7. Short Answer:
Define the terms dominant allele, recessive allele, and codominant alleles.
8. Genetics Problem:
In peas, green pods (G) are dominant over yellow pods (g). Two heterozygous plants are crossed.
a) Draw a Punnett square.
b) State the genotypic and phenotypic ratios of the offspring.
🌎 Topic 4: Ecology
9. Short Answer:
Distinguish between autotrophs and heterotrophs, giving one example of each.
10. Data-Based Question:
You are given a table showing carbon dioxide concentrations in different parts of an ecosystem.
a) Identify the carbon sinks.
b) Explain how human activities impact the carbon cycle.
🧪 Topic 5: Evolution and Biodiversity
11. Short Answer:
Outline the process of natural selection using an example.
12. Multiple Choice:
Which statement is evidence for evolution?
A. Fossils show changes in organisms over time
B. Organisms adapt to their environments through use and disuse
C. Individuals evolve during their lifetime
D. All mutations are beneficial
🫀 Topic 6: Human Physiology
13. Short Answer:
Explain the role of the pancreas in maintaining blood glucose levels.
14. Multiple Choice:
Which of the following is NOT part of the defense against pathogens?
A. Phagocytes
B. Antibodies
C. Memory cells
D. Ribosomes
15. Data-Based Question:
Given a graph of heart rate before, during, and after exercise:
a) Describe the trend.
b) Explain how the body returns to resting heart rate after exercise.
Answers
Here are the markschemes and model answers for the 15 IB Biology SL practice questions I gave you earlier:
🔬 Topic 1: Cell Biology
1. MC Answer:
B. Modifies and packages proteins for secretion
Explanation: Rough ER has ribosomes on its surface that synthesize proteins, which are then processed and transported.
2. Markscheme / Model Answer:
Phospholipid Membranes (2–3 marks):
Phospholipids have hydrophilic heads and hydrophobic tails.
In aqueous environments, they form a bilayer with heads facing outwards and tails inwards.
This structure forms a selectively permeable membrane.
3. Markscheme / Model Answer:
Endosymbiotic Theory (3–4 marks):
Mitochondria and chloroplasts have their own DNA, similar to prokaryotes.
They reproduce by binary fission.
They have double membranes and 70S ribosomes.
Suggests they originated from free-living prokaryotes engulfed by a larger cell.
🧬 Topic 2: Molecular Biology
4. Markscheme / Model Answer (Data):
a) The optimum pH is the peak of the graph (e.g., pH 7).
b) Enzyme structure is altered (denatured) at extreme pH values, reducing activity.
5. Markscheme / Model Answer:
Structure and Replication of DNA (3–4 marks):
DNA is a double helix with complementary base pairing (A-T, C-G).
Strands are antiparallel.
During replication, helicase unwinds DNA and DNA polymerase adds new nucleotides.
6. MC Answer:
B. RNA polymerase
Explanation: It synthesizes RNA using the DNA template during transcription.
🌱 Topic 3: Genetics
7. Markscheme / Model Answer:
Dominant allele: Expressed even if only one copy is present (e.g., G).
Recessive allele: Only expressed when two copies are present (e.g., g).
Codominant alleles: Both alleles are expressed equally in the phenotype (e.g., AB blood group).
8. Markscheme / Model Answer (Punnett Square):
G | g | |
|---|---|---|
G | GG | Gg |
g | Gg | gg |
a)
Genotypes: GG, Gg, Gg, gg
b)Genotypic ratio: 1 GG : 2 Gg : 1 gg
Phenotypic ratio: 3 green : 1 yellow
🌎 Topic 4: Ecology
9. Markscheme / Model Answer:
Autotrophs: Produce their own food via photosynthesis or chemosynthesis (e.g., plants).
Heterotrophs: Consume organic matter from other organisms (e.g., animals).
10. Markscheme / Model Answer (Data):
a) Carbon sinks include forests, oceans, and soil.
b) Human activities like burning fossil fuels and deforestation increase atmospheric CO₂, disturbing the carbon cycle.
🧪 Topic 5: Evolution and Biodiversity
11. Markscheme / Model Answer (Natural Selection):
Variation exists in populations.
Some individuals have advantageous traits.
These survive and reproduce more.
Their traits are passed on, leading to gradual evolution (e.g., peppered moths).
12. MC Answer:
A. Fossils show changes in organisms over time
Explanation: Fossils provide historical evidence of gradual change and extinction, supporting evolution.
🫀 Topic 6: Human Physiology
13. Markscheme / Model Answer:
When blood glucose is high: The pancreas secretes insulin → cells take up glucose → stored as glycogen in liver.
When blood glucose is low: The pancreas secretes glucagon → glycogen broken down to glucose.
14. MC Answer:
D. Ribosomes
Explanation: Ribosomes synthesize proteins; they are not part of the immune system.
15. Markscheme / Model Answer (Graph):
a) Heart rate increases during exercise and decreases after.
b) Increased demand for oxygen/energy during exercise → heart rate rises. Afterward, less demand → parasympathetic nervous system lowers heart rate.