Biology Examination — Questions and Complete Solutions
Questions
Question 1
(a) Citing relevant examples, write explanatory notes on the following terms:
i. Continuous variables
ii. Histogram
iii. Variance
iv. Data
(b) The following data represents the number of Covid-19 positive cases from ten (10) towns in Nigeria.
| Location | January | February | March | April | May |
|---|---|---|---|---|---|
| Abuja | 7 | 8 | 10 | 7 | 4 |
| Sokoto | 8 | 8 | 8 | 6 | 3 |
| Nnewi | 6 | 9 | 11 | 5 | 5 |
| Mubi | 7 | 7 | 7 | 6 | 3 |
| Ekpoma | 6 | 7 | 9 | 5 | 5 |
| Babura | 8 | 9 | 9 | 6 | 2 |
| Jibia | 7 | 7 | 10 | 7 | 3 |
| Ilela | 6 | 8 | 8 | 6 | 4 |
| Otuoke | 7 | 9 | 7 | 5 | 3 |
| Zuba | 8 | 8 | 11 | 5 | 4 |
Use the information in the table to answer the questions that follow:
i. Calculate the percentage change in the number of positive cases recorded in each town between January and May.
ii. State the method of sampling used if samples were collected only from persons showing symptoms of Covid-19.
iii. Which town(s) had the highest percentage change in the two months considered in b(i)?
iv. Which town(s) had the lowest rate of change in the two months considered in b(i)?
© Fill in the blank spaces:
i. Plants with seeds borne on exposed surfaces are called __________
ii. The male gametophyte in seed plants is called __________
iii. The pattern of arrangement of ovules in a flower is called __________
iv. __________ refers to the type of reproduction in algae in which the male and female gametes are morphologically identical.
v. The spores produced after sexual reproduction in fungi are called __________
vi. Spherical bacterial cells are called __________
vii. The structure responsible for the absorption of water and nutrients in vascular plants is called __________
viii. Leaves in the pteridophyta are called __________
ix. Organisms with membrane-bound organelles in their cells are referred to as __________
x. The mode of nutrition in fungi is generally termed __________
Question 2
Write concise notes on the economic importance of fungi.
Question 3
Give a brief explanation of the following terms:
i. Chemosynthesis
ii. Respiration
iii. Plasmolysis
iv. Fermentation
Question 4
a) Discuss the different methods of control of bacterial activity in food.
b) Write explanatory notes on integrated pest management.
Question 5
Write an essay on environmental pollution.
Question 6
a) Outline the general characteristics of the bryophytes.
b) What are the differences between the gymnosperms and angiosperms?
Solutions
Question 1(a) — Explanatory notes
i. Continuous variables
Quantitative variables that can take any value within a given range, including fractions and decimals. They are measured rather than counted and have an infinite number of possible values between any two points. Examples include height, body temperature, blood pressure, and plant growth rate. Continuous data is typically displayed using a histogram or a line graph.
ii. Histogram
A graphical representation of the frequency distribution of continuous data. It consists of adjacent (touching) bars, where the x-axis represents class intervals and the y-axis represents frequency or frequency density; the area of each bar is proportional to the frequency of that class. Unlike bar charts, histogram bars have no gaps, reflecting the continuous nature of the data.
iii. Variance
A statistical measure of the spread or dispersion of data values around the mean, calculated as the average of the squared deviations from the mean:
Formula: s² = Σ(x − x̄)² / (n − 1)
A high variance indicates data points are widely spread from the mean; a low variance means they are closely clustered. Variance is always expressed in squared units.
iv. Data
Raw facts, figures, measurements, or observations collected from an experiment, survey, or study for analysis and interpretation. Data can be qualitative (categorical, descriptive, e.g. flower colour) or quantitative (numerical, either discrete, e.g. number of seeds, or continuous, e.g. height). Data must be organized, analyzed, and interpreted to become meaningful information.
Question 1(b) — Covid-19 data analysis
i. Percentage change (January to May)
Formula: % change = [(May − January) / January] × 100
| Town | January | May | Change | % Change |
|---|---|---|---|---|
| Abuja | 7 | 4 | −3 | −42.86% |
| Sokoto | 8 | 3 | −5 | −62.50% |
| Nnewi | 6 | 5 | −1 | −16.67% |
| Mubi | 7 | 3 | −4 | −57.14% |
| Ekpoma | 6 | 5 | −1 | −16.67% |
| Babura | 8 | 2 | −6 | −75.00% |
| Jibia | 7 | 3 | −4 | −57.14% |
| Ilela | 6 | 4 | −2 | −33.33% |
| Otuoke | 7 | 3 | −4 | −57.14% |
| Zuba | 8 | 4 | −4 | −50.00% |
All towns showed a decrease in cases from January to May.
ii. Method of sampling
If samples were collected only from persons showing symptoms of Covid-19, this is purposive (judgmental) sampling, also called selective or symptom-based sampling — a non-random method where individuals are chosen based on a specific criterion rather than randomly from the general population.
iii. Town with the highest percentage change
Babura, with the greatest reduction at −75.00%.
iv. Town(s) with the lowest rate of change
Nnewi and Ekpoma, both at −16.67%.
Question 1© — Fill in the blanks
i. Gymnosperms
ii. Pollen grain
iii. Placentation
iv. Isogamy
v. Ascospores (in Ascomycota) / zygospores
vi. Cocci (coccus)
vii. Root hair (root hair cells)
viii. Fronds
ix. Eukaryotes
x. Saprotrophic (saprophytic)
Question 2 — Economic importance of fungi
Fungi have both beneficial and harmful economic significance.
Beneficial roles:
- Food production: mushrooms (Agaricus, Pleurotus) are eaten directly; yeast (Saccharomyces cerevisiae) is used in baking and brewing.
- Antibiotic production: Penicillium notatum produces penicillin; other antifungal and antibacterial drugs are also derived from fungi.
- Fermentation industry: fungi are used in producing cheese (Penicillium camemberti, P. roqueforti), soy sauce, yogurt, and alcoholic beverages.
- Decomposition and nutrient cycling: fungi break down dead organic matter, recycling carbon and nitrogen back into the soil.
- Mycorrhizal associations: symbiotic relationships with plant roots enhance water and mineral absorption, improving agricultural productivity.
- Research and biotechnology: yeast is used as a model organism in genetics research, and in producing enzymes, citric acid (Aspergillus niger), and hormones such as insulin via recombinant DNA.
Harmful roles:
- Plant diseases: maize smut (Ustilago), wheat rust (Puccinia), and potato blight (Phytophthora) reduce agricultural yield.
- Food spoilage: molds such as Rhizopus, Aspergillus, and Mucor spoil stored food, causing significant post-harvest losses.
- Mycotoxin production: Aspergillus flavus produces aflatoxins, which are toxic and carcinogenic contaminants of groundnuts and maize.
- Human and animal diseases: fungi cause ringworm, athlete’s foot (Tinea), candidiasis (Candida albicans), and cryptococcal meningitis in immunocompromised individuals.
- Damage to materials: fungi cause rotting of timber and deterioration of leather, textiles, and paper.
Question 3 — Brief explanations
i. Chemosynthesis
The process by which certain chemoautotrophic microorganisms, such as nitrifying bacteria (Nitrosomonas, Nitrobacter) and sulfur bacteria, synthesize organic compounds using energy from the oxidation of inorganic substances such as ammonia, hydrogen sulfide, or iron, rather than from sunlight. Chemosynthesis is important in the nitrogen cycle and sustains life in deep-sea hydrothermal vent ecosystems.
ii. Respiration
The biochemical process by which organisms break down organic molecules (glucose) to release energy as ATP. Aerobic respiration uses oxygen and yields about 38 ATP per glucose molecule, occurring in the cytoplasm (glycolysis) and mitochondria (Krebs cycle and oxidative phosphorylation). Anaerobic respiration occurs without oxygen, yielding lactic acid or ethanol and carbon dioxide, and only about 2 ATP.
iii. Plasmolysis
The process by which the cytoplasm and cell membrane of a plant cell shrink away from the cell wall due to water loss by osmosis, when the cell is placed in a hypertonic solution. The protoplast contracts and the cell becomes flaccid and wilts. Plasmolysis is reversible: placing the cell in a hypotonic solution causes deplasmolysis, restoring turgidity.
iv. Fermentation
An anaerobic metabolic process in which microorganisms partially break down sugars to release energy without oxygen, producing simpler compounds as by-products. Alcoholic fermentation (by yeast) produces ethanol and carbon dioxide and is used in brewing and bread-making; lactic acid fermentation (by bacteria or muscle cells) produces lactic acid and is used in yogurt and cheese production. Fermentation yields only 2 ATP per glucose molecule.
Question 4
a) Methods of control of bacterial activity in food
- Heat treatment: pasteurization (heating milk to 72°C for 15 seconds), sterilization/UHT (135°C+ for 2 seconds), and boiling/cooking kill most pathogenic bacteria.
- Refrigeration and freezing: low temperatures slow or halt bacterial metabolism and reproduction.
- Drying/dehydration: removing moisture inhibits bacterial growth, as in dried fish or powdered milk.
- Salting (curing): high salt concentration draws water out of bacterial cells by osmosis, inhibiting or killing them.
- Sugaring: high sugar concentration similarly creates osmotic stress on bacteria, as in jams and condensed milk.
- Pickling: vinegar or lactic acid fermentation lowers pH, creating conditions hostile to most bacteria.
- Smoking: chemicals in smoke have bactericidal properties and, combined with dehydration, preserve meat and fish.
- Chemical preservatives: substances such as sodium benzoate, sodium nitrite, potassium sorbate, and sulfur dioxide inhibit bacterial growth.
- Irradiation: exposure to ionizing radiation destroys bacterial DNA without making food radioactive.
- Canning: sealing food in airtight containers with prior heat sterilization prevents bacterial growth.
b) Integrated pest management (IPM)
IPM is a sustainable, ecosystem-based strategy for managing pests by combining multiple control methods to minimize economic damage, environmental impact, and health risks while reducing reliance on chemical pesticides.
Key components:
- Biological control: using natural enemies such as predators, parasites, and pathogens, e.g. ladybirds against aphids, or Bacillus thuringiensis against caterpillars.
- Cultural/agronomic control: farming practices such as crop rotation, intercropping, timely planting, and removal of crop residues that make conditions less favorable to pests.
- Mechanical/physical control: traps, nets, hand-picking, and mulch used to exclude or remove pests.
- Chemical control (last resort): targeted, low-toxicity pesticides applied only when pest populations exceed economic injury levels.
- Monitoring and economic thresholds: regular field scouting to assess pest levels, with control action taken only once numbers exceed the economic threshold.
- Genetic/host resistance: use of crop varieties bred for resistance to specific pests or diseases.
IPM reduces pesticide use and associated health and environmental risks, is cost-effective over time, preserves beneficial organisms and biodiversity, and lowers the risk of pesticide resistance.
Question 5 — Essay on environmental pollution
Environmental pollution is the introduction of harmful substances or contaminants into the natural environment — air, water, or soil — at levels that cause adverse effects on living organisms and ecosystems. It is largely a consequence of industrial, agricultural, and domestic human activities.
Types of environmental pollution:
Air pollution results from the release of harmful gases and particles into the atmosphere, from sources such as fossil fuel combustion, industrial emissions, and bush burning. Pollutants include carbon monoxide, sulfur dioxide, nitrogen oxides, particulate matter, and chlorofluorocarbons, contributing to respiratory disease, acid rain, global warming, and ozone layer depletion.
Water pollution arises from industrial effluents, oil spills, agricultural runoff, and sewage discharged into rivers, lakes, and groundwater. Effects include death of aquatic organisms, eutrophication, waterborne diseases, and bioaccumulation of toxins in food chains.
Soil pollution results from excessive fertilizer and pesticide use, industrial waste, mining, and improper waste disposal, leading to reduced soil fertility, destruction of soil microorganisms, and groundwater contamination.
Noise pollution, from traffic, construction, and industry, causes hearing loss, stress, and cardiovascular problems. Thermal pollution, from heated industrial discharge into water bodies, reduces dissolved oxygen and harms aquatic life. Radioactive pollution, from nuclear plants, weapons testing, or accidents, can cause cancer, genetic mutations, and death of organisms.
Effects of environmental pollution include loss of biodiversity, human health problems, climate change, destruction of ecosystems, and economic losses across agriculture, tourism, and healthcare.
Control measures include enforcement of environmental regulations, treatment of waste before discharge, promotion of renewable energy, reforestation, recycling and waste reduction, use of catalytic converters, public environmental education, and international agreements such as the Paris Agreement.
Question 6
a) General characteristics of bryophytes
- Non-vascular — lack true xylem and phloem; water and nutrients move by diffusion and osmosis.
- Terrestrial but water-dependent — found in moist, shaded habitats and require water for fertilization.
- No true roots, stems, or leaves — possess rhizoids, cauloids (stem-like), and phylloids (leaf-like structures).
- Dominant generation is the gametophyte (haploid); the sporophyte is dependent on it.
- Show alternation of generations between gametophyte and sporophyte phases.
- Reproductive organs: antheridia (male, produce antherozoids) and archegonia (female, contain egg cells).
- Spores are produced in a sporangium/capsule and dispersed by wind.
- Generally small in size.
- Reproduce by spores; no seeds or flowers.
- Three classes: Hepaticopsida (liverworts), Anthocerotopsida (hornworts), and Bryopsida (mosses).
- Play an ecological role as pioneer species in succession, reducing soil erosion and retaining moisture.
b) Differences between gymnosperms and angiosperms
| Feature | Gymnosperms | Angiosperms |
|---|---|---|
| Seed enclosure | Naked (borne on open scales/cones) | Enclosed in a fruit (ovary wall) |
| Flowers | Absent — reproduce via cones (strobili) | Present — true flowers with petals and sepals |
| Ovary/Fruit | No true ovary; no fruit formed | True ovary present; develops into fruit |
| Ovules | Exposed on cone scales | Enclosed within the ovary |
| Pollination | Mostly by wind | By wind, insects, animals, or water |
| Fertilization | Simple fertilization | Double fertilization (unique to angiosperms) |
| Endosperm | Haploid, formed before fertilization | Triploid, formed after fertilization |
| Leaves | Mostly needle-like or scale-like, often evergreen | Broad, flat leaves, deciduous or evergreen |
| Vascular tissue | Xylem lacks vessels, has tracheids only | Xylem has both vessels and tracheids |
| Examples | Pine, cedar, cycad, Gnetum | Mango, maize, beans, roses, grasses |
| Economic use | Timber, resin, ornamentals | Food, medicine, timber, fiber, ornamentals |
| Diversity | Less diverse (about 1,000 species) | Most diverse plant group (over 300,000 species) |