Below is a **faithful ZIMSEC O-Level Biology Paper 2 (4025/2)-style exam** complete with **full marks
allocations** and a **comprehensive answer scheme**. Treat it as a self-testing booklet: first try the
questions under exam conditions, then check your answers against the model scheme.
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## ZIMSEC O-LEVEL BIOLOGY 4025/2
**Paper 2 – Theory**
**Time allowed: 1 hour 30 minutes**
**Total marks: 80**
**Instructions to candidates**
- Answer **ALL** questions in **Section A**.
- Answer **ONLY ONE** question from **Section B**.
- Write your answers in the spaces provided.
- Where diagrams are required, you must label the parts indicated.
---
### Section A (60 marks)
#### Question 1 – Classification (6 marks)
(a) Define “kingdom” in biological classification. [2]
(b) List **three** features that distinguish Kingdom Fungi from Kingdom Plantae. [3]
(c) Give **one** example of a unicellular organism from Kingdom Protista. [1]
#### Question 2 – Cell Structure & Transport (6 marks)
(a) State **two** differences between prokaryotic and eukaryotic cells. [4]
(b) Briefly explain:
(i) **Diffusion** across a cell membrane. [1]
(ii) **Osmosis** across a cell membrane. [1]
#### Question 3 – Nutrition & Digestion (8 marks)
(a) List **three** roles of the liver in human digestion. [3]
(b) State the function of each enzyme:
(i) **Amylase**. [1]
(ii) **Lipase**. [1]
(c) Draw and label a transverse section of a **villus**. [3]
#### Question 4 – Transport in Plants (8 marks)
(a) Explain the **cohesion–tension theory** of water transport in xylem. [4]
(b) Describe **two** structural adaptations of root hair cells. [4]
#### Question 5 – Photosynthesis & Respiration (8 marks)
(a) Give the balanced equation for **photosynthesis**. [2]
(b) State **two** factors affecting the rate of photosynthesis. [2]
(c) Contrast **aerobic** vs **anaerobic** respiration in terms of energy yield and end-products. [4]
#### Question 6 – Growth & Reproduction (8 marks)
(a) Differentiate **self-pollination** from **cross-pollination**. [2]
(b) Outline the role of **gibberellin** in seed germination. [2]
(c) Describe **metamorphosis** in the frog life cycle. [4]
#### Question 7 – Ecology (8 marks)
(a) Define “ecological niche.” [2]
(b) Using a simple food chain (e.g. grass → rabbit → fox), explain how energy flows through trophic
levels. [3]
(c) Describe **two** human activities that reduce biodiversity. [3]
#### Question 8 – Health & Disease (8 marks)
(a) Describe the role of:
(i) **Antibodies** in immunity. [3]
(ii) **Vaccination** in disease prevention. [3]
(b) For malaria, give **one** mode of transmission and **one** control measure. [2]
---
### Section B (20 marks)
**Answer only one** of the following.
#### Question 9(a) – Homeostasis (20 marks)
Discuss how blood glucose concentration is maintained within narrow limits. In your answer include:
- The roles of the **pancreas**, **insulin** and **glucagon** [8]
- **Negative feedback** mechanisms [6]
- Consequences of **failure** in regulation (e.g. diabetes) [6]
**OR**
#### Question 9(b) – Exercise Physiology (20 marks)
(a) Describe the physiological changes that occur in the **muscular** and **respiratory** systems
during strenuous exercise. [10]
(b) Explain how these changes help the body meet increased **energy** demands. [10]
---
## Marking Scheme & Model Answers
### Section A
**1. Classification**
(a) Kingdom = highest taxonomic rank grouping organisms sharing fundamental features (e.g. cell type,
nutrition) [2]
(b) Fungi vs Plantae:
- Fungi have cell walls of chitin (not cellulose)
- Fungi are heterotrophic saprophytes (not autotrophic)
- Body composed of hyphae/mycelium (not roots/stems/leaves) [3]
(c) Example Protista: **Amoeba**, **Paramecium**, **Euglena** [1]
---
**2. Cell Structure & Transport**
(a) Prokaryote vs Eukaryote (any two):
- No nucleus vs true nucleus
- 70S ribosomes vs 80S ribosomes
- No membrane-bound organelles vs organelles present
- Circular DNA vs linear chromosomes [4]
(b)(i) Diffusion = net movement of molecules from high → low concentration down a concentration
gradient [1]
(b)(ii) Osmosis = diffusion of water across a partially permeable membrane from low solute → high
solute concentration [1]
---
**3. Nutrition & Digestion**
(a) Liver roles (any three):
- Produces bile (emulsifies fats)
- Glycogen synthesis & storage
- Detoxification of poisons
- Deamination of excess amino acids [3]
(b)(i) Amylase hydrolyses starch → maltose/glucose [1]
(b)(ii) Lipase hydrolyses lipids → glycerol + fatty acids [1]
(c) Villus diagram must show:
- Single-layer epithelial cells (enterocytes)
- Lacteal (central lymph vessel)
- Blood capillary
- Microvilli labeled on epithelium [3]
---
**4. Transport in Plants**
(a) Cohesion–tension theory: water evaporates from mesophyll (transpiration pull), creating tension;
cohesion between water molecules transmits pull down xylem; adhesion to xylem walls helps capillary
rise [4]
(b) Root hair cell adaptations:
- Long hair increases surface area
- Thin cell wall (short diffusion path)
- Many mitochondria (energy for active uptake)
- Carrier proteins in membrane for mineral ions [4]
---
**5. Photosynthesis & Respiration**
(a) 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ [2]
(b) Factors: light intensity, CO₂ concentration, temperature, chlorophyll concentration [2]
(c) Aerobic vs Anaerobic:
- Energy yield: ~38 ATP vs 2 ATP per glucose [2]
- End products: CO₂ + H₂O vs lactic acid (animals) or ethanol + CO₂ (plants/yeast) [2]
---
**6. Growth & Reproduction**
(a) Self-pollination = pollen to stigma of same flower/plant vs cross-pollination = pollen to stigma of
different plant of same species [2]
(b) Gibberellin breaks seed dormancy, stimulates synthesis of amylase, mobilizes food reserves for
embryo growth [2]
(c) Frog metamorphosis: egg → tadpole (gills, tail, herbivore) → developing legs, lungs → adult frog
(lungs, no tail, carnivore) [4]
---
**7. Ecology**
(a) Ecological niche = the role and position of an organism in its ecosystem, including habitat, resources,
and interactions [2]
(b) Energy flow: producers convert light → chemical energy; primary consumers eat producers, tertiary
consumers eat others; ~10% energy transfer per trophic level, rest lost as heat [3]
(c) Human impacts (any two):
- Deforestation → habitat loss
- Pollution (eutrophication, oil spills)
- Overfishing/hunting → population decline
- Introduction of invasive species [3]
---
**8. Health & Disease**
(a)(i) Antibodies bind specific antigens on pathogens, neutralizing or marking for destruction by
phagocytes [3]
(a)(ii) Vaccination introduces antigenic material to stimulate memory lymphocytes without causing
disease [3]
(b) Malaria:
- Transmission = bite of infected female Anopheles mosquito [1]
- Control = insecticide-treated bed nets or antimalarial drugs [1]
---
### Section B
#### 9(a) Homeostasis [20]
- **Pancreas**: islets of Langerhans; β-cells secrete insulin when blood glucose high; α-cells secrete
glucagon when low [8]
- **Negative feedback**: rising glucose → insulin release → glucose uptake & glycogenesis → blood
glucose falls → insulin secretion decreases; conversely for glucagon [6]
- **Failure**: Type I diabetes (no insulin), Type II (insulin resistance); hyperglycaemia, ketoacidosis,
neuropathy, coma [6]
#### 9(b) Exercise Physiology [20]
(a) Changes during exercise:
- Muscular: increased muscle temperature, lactic acid production, vasodilation, increased blood flow
- Respiratory: increased breathing rate & tidal volume, increased lung ventilation, deeper breaths,
widened alveoli capillary gap [10]
(b) How changes meet demand:
- Faster O₂ uptake & CO₂ removal
- Increased cardiac output & muscle perfusion
- Enhanced glycolysis & aerobic respiration in muscles
- Buffering of lactic acid via increased blood flow [10]
---
**End of Paper**
