Questions
1. a) The following table presents a sampled data set obtained from a plant growth experiment conducted on 88 seedlings in a school nursery garden. Use the data to answer the questions that follow.
| S/No | Species | Height (cm) | Leaf Count | Light Condition | Growth Rate |
|---|---|---|---|---|---|
| 1 | Bean | 18.5 | 6 | Full sun | Fast |
| 2 | Maize | 25.0 | 4 | Full sun | Fast |
| 3 | Bean | 12.0 | 4 | Shade | Slow |
| 4 | Okra | 15.5 | 5 | Partial shade | Medium |
| 5 | Maize | 22.0 | 5 | Partial shade | Medium |
| 6 | Bean | 19.0 | 6 | Full sun | Fast |
| 7 | Okra | 10.5 | 3 | Shade | Slow |
| 8 | Maize | 14.0 | 3 | Shade | Slow |
| 9 | Bean | 16.5 | 5 | Partial shade | Medium |
| 10 | Okra | 17.0 | 5 | Full sun | Fast |
i. What is the proportion of the sample to the total number of seedlings in the nursery?
ii. If the seedlings were selected by assigning each a number and using a table of random numbers to pick them, give the appropriate name for the sampling technique used.
iii. Represent the whole data of Growth Rate on a pie chart.
iv. If the sample collected is a representative sample of the nursery seedlings, what is the median height of the seedlings?
v. On the basis of Light Condition, represent the data of Species on a bar chart.
vi. Write short notes on observation as a method of data collection.
b) Give the most appropriate word(s) or phrases which fill in the blank spaces in the questions below. Spellings of one-word answers must be correct to score.
i. A supportive, dead cell with thick lignified walls and no living contents at maturity is a ______ cell.
ii. Growth movement of a plant part in response to light is called ______.
iii. Fibrous roots that arise in a cluster from the base of the stem, replacing the primary root, are called ______.
iv. An inflorescence in which the main axis branches repeatedly, each branch bearing flowers, is called a ______.
v. A blue-green pigment found alongside chlorophyll in cyanobacteria is called ______.
vi. A dry, indehiscent, one-seeded fruit with the pericarp fused to the seed coat, typical of grasses, is called a ______.
vii. A colourless plastid involved in the storage of oils, proteins, or starch is called a ______.
viii. Spores produced asexually at the tip of a sporangiophore in Rhizopus are called ______.
ix. Underground stems that grow horizontally and produce roots and shoots at nodes are called ______.
x. The general name for non-flowering seed plants bearing naked seeds is ______.
2. Write short notes on ALL of the following:
a) Nitrogen fixation
b) Deforestation
c) Vernalization
d) Regeneration
3. Discuss the economic importance of Protozoa.
4. a) Citing relevant examples, describe three adaptations of xerophytes to water scarcity.
b) What is soil texture?
5. Write explanatory notes on the following:
a) Citrus canker
b) Ozone layer depletion
6. a) Describe the morphological range of forms of Protozoa, giving NAMED examples.
b) Write short notes on the nucleus.
Answers
Question 1
a) i) Proportion of the sample to the total number of seedlings
Sample size = 88; total number of seedlings in the nursery = 88.
Proportion = 88/88 = 1 (i.e., the sample represents 100% of the seedlings).
ii) Sampling technique
Systematic Random Sampling (using random number tables).
iii) Pie chart of Growth Rate
Steps: Determine the frequency of each growth rate category (Fast, Medium, Slow) in the full data set of 88 seedlings. For each category, calculate:
Angle = (Frequency of category ÷ 88) × 360°
Draw a circle and use a protractor to mark out each sector according to its calculated angle, labeling each sector with its category and percentage.
iv) Median height
Steps: Arrange all 88 height values in ascending order. Since n = 88 (even), the median is the average of the values at positions:
n/2 and (n/2 + 1) = 44th and 45th values
Median = (44th value + 45th value) / 2
v) Bar chart of Species by Light Condition
Steps: Separate the data into Full sun, Partial shade, and Shade groups. Within each group, count the frequency of each species (Bean, Maize, Okra). Plot a grouped (clustered) bar chart with Species on the x-axis, Frequency on the y-axis, and paired/grouped bars for each light condition category, using a key/legend to distinguish light condition.
vi) Observation as a method of data collection
Observation is a method of data collection in which the researcher watches and records phenomena, behaviours, or characteristics as they naturally occur, without manipulating any variables. It may be direct (the observer is physically present) or indirect (using recording instruments), and participant (observer is involved in the setting) or non-participant (observer remains detached). This method is useful for studying behaviour or conditions in their natural setting and provides first-hand, often qualitative, data, but it can be time-consuming, and the presence of an observer may sometimes influence the behaviour being observed. Unlike experimentation, observation does not involve deliberate control or manipulation of variables.
b) Fill in the blanks
i. Sclerenchyma
ii. Phototropism
iii. Adventitious (fibrous) roots
iv. Panicle
v. Phycocyanin
vi. Caryopsis
vii. Leucoplast
viii. Sporangiospores
ix. Rhizomes
x. Gymnosperms
Question 2
a) Nitrogen fixation
Nitrogen fixation is the biological process by which atmospheric nitrogen gas (N₂), which is inert and unusable by most organisms, is converted into ammonia or related nitrogenous compounds that plants can absorb and utilize. It is carried out mainly by nitrogen-fixing bacteria, such as Rhizobium species living symbiotically in root nodules of leguminous plants, and free-living forms such as Azotobacter and Cyanobacteria (e.g., Anabaena). The enzyme nitrogenase catalyzes the conversion of N₂ to ammonia, which is then assimilated into amino acids and other organic nitrogen compounds. This process is essential for soil fertility and forms a key step in the nitrogen cycle, replenishing nitrogen removed from the soil by plant uptake and leaching.
b) Deforestation
Deforestation is the large-scale clearing or removal of forest cover, primarily due to logging, agricultural expansion, urbanization, and infrastructure development. Its consequences include loss of biodiversity and habitat destruction, soil erosion due to loss of protective root systems, disruption of the water cycle and reduced rainfall, increased atmospheric carbon dioxide levels (contributing to climate change, since trees act as carbon sinks), and desertification in vulnerable regions. Mitigation strategies include afforestation and reforestation programs, sustainable logging practices, establishment of forest reserves and protected areas, and promotion of agroforestry.
c) Vernalization
Vernalization is the process by which certain plants require a prolonged period of exposure to low temperature (cold treatment) during a specific developmental stage in order to subsequently flower. This ensures that flowering occurs at an appropriate time, typically in spring following winter cold, preventing premature flowering before conditions are favourable for seed development. Vernalization is of particular importance in temperate cereal crops such as wheat and rye, where farmers may artificially chill seeds before planting to induce or accelerate flowering, ensuring a synchronized and timely harvest.
d) Regeneration
Regeneration is the biological process by which an organism regrows or replaces lost, damaged, or amputated body parts, restoring the original structure and function. It ranges from the replacement of individual cells and tissues to the regrowth of complex organs or entire body parts, and its extent varies widely among organisms; for example, planarians can regenerate an entire body from a small fragment, starfish can regrow lost arms, and lizards can regrow a severed tail. Regeneration relies on the activity of specialized, undifferentiated cells capable of proliferating and differentiating into the various cell types needed to reconstruct the missing part, and is of interest in medical research for its potential applications in tissue repair and regenerative medicine.
Question 3
Economic Importance of Protozoa
Beneficial roles:
- Ecological role: Protozoa, such as amoebae and ciliates, feed on bacteria and organic debris in soil and water, helping to regulate microbial populations and contributing to nutrient cycling and decomposition.
- Food chain/aquatic ecosystems: Protozoa such as Foraminifera and other planktonic forms serve as an important food source for small aquatic animals, forming a key link in aquatic food chains.
- Sewage/wastewater treatment: Certain protozoa consume bacteria in sewage treatment plants, helping to purify wastewater and reduce microbial load before discharge.
- Geological/scientific use: Fossilized shells of Foraminifera and Radiolaria are used by geologists to date rock strata and locate oil deposits, since different species are characteristic of particular geological periods.
- Research/biotechnology: Protozoa such as Paramecium and Tetrahymena are used as model organisms in genetic and cell biology research.
Harmful effects:
- Protozoa are responsible for serious human diseases, including malaria (Plasmodium), sleeping sickness (Trypanosoma), amoebic dysentery (Entamoeba histolytica), and toxoplasmosis (Toxoplasma).
- Certain protozoa cause diseases in livestock, such as East Coast fever (Theileria) and trypanosomiasis (nagana) in cattle, resulting in significant economic losses to farmers.
- Some parasitic protozoa reduce the productivity and health of infected animals and humans, increasing healthcare and veterinary costs.
Question 4
a) Adaptations of xerophytes to water scarcity
Reduction of leaf surface area: Many xerophytes have small, needle-like, or reduced leaves (or leaves modified into spines) to minimize the surface area available for water loss through transpiration. Example: Cactus (leaves reduced to spines, with the stem taking over photosynthesis).
Water storage tissue (succulence): Some xerophytes possess thick, fleshy stems or leaves with specialized parenchyma tissue for storing water, enabling survival during prolonged dry periods. Example: Cactus stems, Aloe vera leaves.
Deep or extensive root systems: Xerophytes often develop very long taproots that penetrate deep into the soil to access groundwater, or extensive shallow root systems that quickly absorb any available surface moisture after rainfall. Example: Acacia (deep taproot), desert grasses (shallow, widespread roots).
Other adaptations include thick, waxy cuticles to reduce water loss, sunken stomata (often in pits) to reduce transpiration, and a reduced number of stomata overall.
b) Soil texture
Soil texture refers to the relative proportions of different-sized mineral particles—sand, silt, and clay—that make up a soil. Sand particles are the largest and give soil good drainage and aeration but poor water and nutrient retention; clay particles are the smallest and give soil high water and nutrient retention but poor drainage and aeration; silt particles are intermediate in size and properties. The proportion of these particles determines a soil's classification (e.g., sandy soil, clay soil, loamy soil) and influences its water-holding capacity, drainage, aeration, and suitability for particular crops, with loamy soil (a balanced mixture of sand, silt, and clay) generally considered most favourable for plant growth.
Question 5
a) Citrus canker
Citrus canker is a bacterial disease of citrus plants (oranges, lemons, limes) caused by the bacterium Xanthomonas citri. It affects leaves, stems, and fruits, producing raised, corky, brown lesions surrounded by a yellow halo (water-soaked margin). Severely infected leaves may fall prematurely, fruits become blemished and unmarketable, and heavily infected trees show reduced vigour and yield. The disease spreads through wind-driven rain, contaminated tools and equipment, and infected plant material, and is especially severe in warm, humid climates. Control measures include planting disease-free certified stock, removing and destroying infected plant material, applying copper-based bactericides, and establishing windbreaks to reduce the spread of wind-driven rain carrying bacteria.
b) Ozone layer depletion
Ozone layer depletion refers to the thinning of the ozone (O₃) layer in the stratosphere, which normally absorbs and filters out most of the sun's harmful ultraviolet (UV) radiation before it reaches the Earth's surface. It is caused primarily by the release of ozone-depleting substances, particularly chlorofluorocarbons (CFCs), which were widely used in refrigerants, aerosol propellants, and industrial solvents; these compounds break down ozone molecules in the stratosphere through catalytic reactions. Consequences of ozone depletion include increased UV radiation reaching the Earth's surface, leading to higher rates of skin cancer and cataracts in humans, damage to phytoplankton and disruption of marine food chains, and reduced crop yields. International measures to address this issue include the Montreal Protocol, an agreement that phased out the production and use of CFCs and other ozone-depleting substances worldwide.
Question 6
a) Morphological range of forms of Protozoa, with named examples
- Amoeboid (rhizopod) forms: Lack a fixed shape and move using temporary cytoplasmic extensions called pseudopodia. Example: Amoeba, Entamoeba.
- Flagellate forms: Possess one or more whip-like flagella used for locomotion. Example: Euglena, Trypanosoma.
- Ciliate forms: Covered with numerous short, hair-like cilia used for locomotion and feeding, and possess a fixed body shape. Example: Paramecium, Vorticella.
- Sporozoan (non-motile/spore-forming) forms: Lack locomotory organelles in their mature stage and reproduce by forming spores, typically as obligate parasites with complex life cycles. Example: Plasmodium (malaria parasite).
- Shelled (testate) forms: Possess a hard external shell or test, often composed of calcium carbonate or silica. Example: Foraminifera, Radiolaria.
b) The nucleus
The nucleus is a large, membrane-bound organelle found in eukaryotic cells, often referred to as the "control centre" of the cell because it houses the cell's genetic material (DNA) organized into chromosomes. It is enclosed by a double membrane called the nuclear envelope, perforated by nuclear pores that regulate the movement of substances such as RNA and proteins between the nucleus and the cytoplasm. Within the nucleus, a dense region called the nucleolus is responsible for the synthesis of ribosomal RNA and assembly of ribosomal subunits. The nucleus controls cell activities by regulating gene expression (determining which proteins are synthesized) and is essential for cell division, since it contains the DNA that must be accurately replicated and distributed to daughter cells during mitosis and meiosis.