## SECTION A: MULTIPLE CHOICE QUESTIONS
1\. Which of the following diseases could be exclusively associated with a river basin?
A. Malaria B. Syphilis C. Onchocerciasis D. Cholera
2\. In mammals, the function of the sebaceous gland is to ______
A. produce sweat B. secrete sodium C. secrete water D. produce sebum
3\. Osteoporosis is a disease of the ______
A. lungs B. skin C. bones D. eyes
4\. The type of reproduction that is common to both Hydra and yeast is ______
A. grafting B. budding C. conjugation D. binary fission
5\. The difference between the largest and the smallest data values is the ______
A. variance B. interquartile range C. range D. coefficient of variation
6\. The function of ribosomes in cells is ______
A. protein synthesis B. starch synthesis C. transport of materials D. lipid storage
7\. Which statement correctly describes homologous chromosomes?
A. They are formed during meiosis B. They are held together by centromeres C. They are identical D. They carry the same gene loci
8\. Which one of the following is a correct outline of the main events in photosynthesis?
A. Oxygen reacts with a carbohydrate to produce water and carbon dioxide in the presence of light.
B. Light joins carbon dioxide to an acceptor compound which is then reduced by hydrogen obtained from water.
C. Light splits water and the resulting hydroxyl group combines with a compound which has incorporated carbon dioxide.
D. Carbon dioxide combines with an acceptor compound and this is reduced by hydrogen split from water by light.
9\. Breathing movement in mammals is accompanied by regular movement of the diaphragm and the ______
A. intercostal muscles B. vertebral column C. clavicle D. pleural cavity
10\. Organisms that require oxygen to grow are called ______
A. psychrophilic organisms B. thermophilic organisms C. aerobes D. hyperthermophiles
11\. Organisms that retain the blue/purple colour in their cell wall in the Gram staining technique are ______
A. microaerophiles B. viable cells C. Gram-positive organisms D. Gram-negative organisms
12\. Which of the following nitrogenous bases is found in RNA but not in DNA?
A. Adenine B. Thymine C. Uracil D. Guanine
13\. The study of groups of organisms is called ______
A. Ecology B. Autecology C. Gynaecology D. Synecology
14\. Genetic rearrangement between non-sister chromatids is known as ______
A. crossing over B. synapsis C. random fertilisation D. character
15\. One of the following is not a type of dormancy.
A. Induced B. Innate C. Enforced D. Applied
16\. The terrestrial species of class Gastropoda prevent water loss by means of ______
A. Apiphragm B. Nephridia C. Radula D. Epiphragm
17\. The first forms of life on Earth were thought to be ______
A. single-celled plants B. prokaryotes C. insects D. large animals such as dinosaurs
18\. Which polysaccharide is usually found in the cell walls of fungi?
A. Starch B. Glycogen C. Chitin D. Cellulose
19\. What adaptation do seed plants have in addition to the seed that is not found in seedless plants?
A. Gametophytes B. Vascular tissue C. Pollen D. Chlorophyll
20\. Prokaryotes stain as Gram-positive or Gram-negative because of differences in the ______
A. Cell wall B. Cytoplasm C. Nucleus D. Chromosome
21\. External fertilisation occurs in ______ type of environment?
A. Aquatic B. Forested C. Savanna D. Steppe
22\. What kind of ecosystem are exotic species especially threatening to?
A. Deserts B. Marine ecosystems C. Islands D. Tropical forests
23\. Each neurone contains ______
A. soma, dendrites and axon B. sensory, association and motor C. cerebrum, cerebellum and hypothalamus D. afferent, efferent and mixed
24\. One of these statements is not true about Berry and Drupe.
A. They both have thin epicarp B. They both have fleshy succulent mesocarp C. Their endocarp is edible D. They both have seeds
25\. Antibiotic discovery was done by the Scottish bacteriologist ______
A. Alexander Penicillius B. Alexander Fleming C. Alexandes Fleming D. AlexandesPenicillius
26\. The type of cell division which forms the basis of Mendel's law of segregation is ______
A. Mitosis B. Meiosis C. Somatic D. Synoptic
27\. Archaebacteria is simply ______
A. A prokaryote without a cell wall B. A eukaryote without a cell wall C. A prokaryote without a peptidoglycan cell wall D. A eukaryote without a peptidoglycan cell wall
28\. *Leucosolenia* belongs to class ______
A. Calcispongiae B. Hexactinellida C. Demospongiae D. Porifera
29\. A pseudopodium that is threadlike, branched, and interconnected is known as ______
A. Lobopodia B. Actinopodia C. Filopodia D. Reticulopodia
30\. Photosynthetic microphylls are found in ______
A. Division Psilophyta B. Division Lycophyta C. Division Sphenophyta D. Division Pterophyta
31\. Poliomyelitis is an infectious disease caused by ______
A. virus B. protozoan C. bacterium D. fungus
32\. Which of these is a trace element?
A. Iron B. Copper C. Calcium D. Sulphur
33\. Which of these diseases cannot be prevented by immunisation?
A. Poliomyelitis B. Tuberculosis C. Cholera D. Onchocerciasis
34\. Hydra removes undigested food by ______
A. passing it through the anus B. passing it through the mouth C. means of contractile vacuole D. digesting it through the body surface
35\. Which of the following is INCORRECT? The prothallus of a fern ______
A. is a flattened heart-shaped structure B. is green because its cells contain chloroplasts C. is the dominant plant D. bears the sexual organs
36\. The science of taxonomy has two branches, namely ______ and ______
A. Biology naming and biochemistry B. Nomenclature and Classification C. Botany and Systematics D. Microbiology and Systematics
37\. To complement biotic analysis in measuring environmental factors, the following are studied EXCEPT ______
A. Soil B. Water C. Topography D. Geography
38\. The period between inoculation of bacteria in culture medium and the beginning of multiplication is known as ______
A. log phase B. lag phase C. stationary phase D. decline phase
39\. Small proteinaceous infectious particles that do not contain a nucleic acid genome that codes for their progeny are ______
A. bacteria B. viruses C. HIV D. prions
40\. An example of all-purpose media used in cultivation of bacteria by a bacteriologist is ______
A. Selenite A agar B. blood agar C. nutrient agar D. tryptone soy agar
41\. Which of the following is not a characteristic feature of the phylum Cnidaria?
A. Polymorphism B. Cephalisation C. Body of two germ layers D. Nematocysts
42\. Which of the following groups of plants are not considered lower plants?
A. Pteridophytes B. Bryophytes C. Cryptogams D. Spermatophytes
43\. Non-living bodies in the cell include one of these ______
A. Starch grains B. Chloroplast C. Ribosomes D. Cell wall
44\. Alternation of generation in plants involves which of the following?
A. Processes in two sexual pathways B. Processes in one single sexual pathway C. Spore dispersal alone D. Processes in homogamy alone
45\. Which of these is not a form of respiration in Amphibians?
A. Cutaneous B. Tubular C. Pulmonary D. Buccal-pharyngeal
46\. The factor that least affects food shortage in sub-Saharan Africa is ______
A. flooding B. pests C. mixed cropping D. drought
47\. Which one of the following factors may not directly affect population density of organisms?
A. Edaphic B. Nutritional C. Mortality D. Emigration
48\. One of the major causes of laboratory-acquired infection is inhalation of ______
A. air B. water C. particles D. infectious aerosol
49\. The major cell of the specific immune system is ______
A. bone marrow cells B. erythrocytes C. lymphocytes D. monocytes
50\. The normal microbiota of the stomach include all of the following EXCEPT:
A. *Streptococcus* B. *Staphylococcus* C. *Lactobacillus* D. Diphtheroids
---
## SECTION B: ESSAY QUESTIONS
*Answer FOUR questions in all; ONE from each Course. Time: 2 Hours*
---
**Question 1** *(BIO 001: General Biology)*
(a) State six (6) differences between sexual and asexual reproduction. *[6 marks]*
(b) Write short notes on any TWO of the following:
i. Haplontic life cycle
ii. Diplontic life cycle
iii. Haplodiplontic life cycle *[4 marks]*
---
**Question 2** *(BIO 001: General Biology)*
(a) Define the following terms:
i. Genotype ii. Phenotype iii. Hybrid iv. Dominant character *[4 marks]*
(b) State clearly Mendel's first and second laws of inheritance. *[2 marks]*
(c) If a pure-breeding brown-coloured rat (BB) is crossed with a pure-breeding white rat (bb), using diagrams only, show the genotype of the offspring up to the second filial generation. *[4 marks]*
---
**Question 3** *(BIO 003: Microbiology)*
Describe the formation of two molecules of pyruvate during respiration. *[10 marks]*
---
**Question 4** *(BIO 003: Microbiology)*
(a) Define the following terms:
i. Aseptic technique ii. Antigens iii. Antibodies iv. Immunity *[4 marks]*
(b) List six (6) rules that must be observed in any aseptic technique. *[6 marks]*
---
**Question 5** *(BIO 002: Basic Botany)*
(a) How does water in the soil enter the root hair of a plant? *[6 marks]*
(b) Name the tissue that conducts water from the root to the stem and leaves in a flowering plant. *[4 marks]*
---
**Question 6** *(BIO 004: Fundamentals of Zoology)*
(a) State five (5) functions of testosterone. *[5 marks]*
(b) With the aid of a diagram only, describe the structure of a mature spermatozoon. *[5 marks]*
---
**Question 7** *(BIO 002: Basic Botany)*
(a) What is a tissue? *[1 mark]*
(b) How are plant tissues formed? *[3 marks]*
(c) Describe the structure and function of two vascular tissues. *[6 marks]*
---
**Question 8** *(BIO 004: Fundamentals of Zoology)*
(a) List any six (6) characteristics of the phylum Mollusca. *[6 marks]*
(b) Give four (4) economic importances of the subclass Pulmonata. *[4 marks]*
---
---
# ANSWERS
## SECTION A: MCQ ANSWERS
| Q | Ans | Q | Ans | Q | Ans | Q | Ans | Q | Ans |
|---|---|---|---|---|---|---|---|---|---|
| 1 | C | 11 | C | 21 | A | 31 | A | 41 | B |
| 2 | D | 12 | C | 22 | C | 32 | B | 42 | D |
| 3 | C | 13 | D | 23 | A | 33 | D | 43 | A |
| 4 | B | 14 | A | 24 | C | 34 | B | 44 | A |
| 5 | C | 15 | D | 25 | B | 35 | C | 45 | B |
| 6 | A | 16 | D | 26 | B | 36 | B | 46 | C |
| 7 | D | 17 | B | 27 | C | 37 | D | 47 | A |
| 8 | D | 18 | C | 28 | A | 38 | B | 48 | D |
| 9 | A | 19 | C | 29 | D | 39 | D | 49 | C |
| 10 | C | 20 | A | 30 | B | 40 | C | 50 | A |
**Selected explanations:**
**Q1 — C (Onchocerciasis):** River blindness (*Onchocerca volvulus*) is transmitted by blackflies (*Simulium* spp.) that breed exclusively in fast-flowing, well-oxygenated rivers — making it uniquely river-basin-associated. Malaria and cholera occur in diverse water environments; syphilis is sexually transmitted.
**Q24 — C (Their endocarp is edible):** In a Drupe (e.g., mango, coconut), the endocarp is hard, woody, and inedible (it forms the stone/shell). In a Berry (e.g., tomato, grape), the endocarp is thin and fleshy/edible. The statement that both have an edible endocarp is therefore false.
**Q35 — C (Is the dominant plant):** The prothallus is the gametophyte generation — it is the small, inconspicuous, heart-shaped, photosynthetic, haploid plant. It is NOT the dominant generation; the dominant plant in ferns is the diploid sporophyte (the familiar leafy fern). Options A, B, and D are all correct statements about the prothallus.
**Q50 — A (*Streptococcus*):** The stomach has an extremely acidic environment (pH 1–3) that limits microbial colonisation. *Lactobacillus*, *Staphylococcus*, and diphtheroids can survive in small numbers, but *Streptococcus* is not a typical constituent of the normal gastric microbiota. *(Note: Some sources vary; the most defensible answer based on standard microbiology texts is A.)*
---
## SECTION B: ESSAY ANSWERS
### Question 1(a) — Six Differences Between Sexual and Asexual Reproduction
| Feature | Sexual Reproduction | Asexual Reproduction |
|---|---|---|
| Number of parents | Requires two parents (male and female) | Requires only one parent |
| Gametes | Involves the formation and fusion of specialised sex cells (gametes) | No gametes are formed or fused |
| Genetic variation | Offspring are genetically diverse due to meiosis and fertilisation | Offspring are genetically identical to the parent (clones) |
| Type of cell division | Meiosis is involved in gamete production | Only mitosis is involved |
| Time and energy | Generally slower and more energy-expensive | Rapid and energetically economical |
| Occurrence | Common in higher animals and plants under favourable and normal conditions | Common in lower organisms and plants under favourable conditions or in stable environments |
---
### Question 1(b) — Short Notes on Life Cycles
**i. Haplontic Life Cycle**
In a haplontic life cycle, the dominant, free-living, photosynthetic phase is the **haploid (n) gametophyte**. The only diploid structure present is the zygote, which immediately undergoes meiosis to restore the haploid state. No multicellular diploid sporophyte exists. This cycle is characteristic of many green algae (e.g., *Chlamydomonas*, *Spirogyra*) and some fungi. The sequence is: haploid organism → gametes (by mitosis) → zygote (2n) → meiosis → haploid organism.
**ii. Diplontic Life Cycle**
In a diplontic life cycle, the dominant, free-living phase is the **diploid (2n) sporophyte**. The haploid phase is extremely reduced and transient, represented only by the gametes themselves, which are produced by meiosis and exist only briefly before fertilisation restores the diploid condition. This is the life cycle characteristic of most animals and some algae (e.g., *Fucus*). The sequence is: diploid organism → gametes (n, by meiosis) → fertilisation → diploid organism.
**iii. Haplodiplontic Life Cycle**
In a haplodiplontic (or diplohaplontic) life cycle, both a multicellular haploid **gametophyte** generation and a multicellular diploid **sporophyte** generation exist and are free-living — a phenomenon called **alternation of generations**. The relative dominance of each phase varies by group: in bryophytes the gametophyte dominates; in ferns the sporophyte dominates; in flowering plants the sporophyte dominates while the gametophyte is microscopic and dependent. This cycle is characteristic of all land plants and some algae (e.g., *Ulva*).
---
### Question 2(a) — Definitions
**i. Genotype:** The complete genetic constitution of an organism — the full set of alleles it carries at all loci — whether or not those alleles are expressed in the observable phenotype. The genotype is inherited from the parents and remains constant throughout the organism's life (barring mutation).
**ii. Phenotype:** The observable or measurable physical, physiological, and behavioural characteristics of an organism, resulting from the interaction between its genotype and the environment. Examples include height, blood group, eye colour, and coat colour.
**iii. Hybrid:** The offspring produced by a cross between two parents that differ in one or more heritable characteristics — either between different alleles at a single locus (monohybrid), between alleles at two loci (dihybrid), or between different species or varieties. A hybrid at a single gene locus is heterozygous (e.g., Bb).
**iv. Dominant character:** A character (trait) controlled by a dominant allele that is fully expressed in the phenotype whenever that allele is present — whether in the homozygous (BB) or heterozygous (Bb) condition. The dominant allele masks or suppresses the expression of the recessive allele in heterozygotes.
---
### Question 2(b) — Mendel's Laws
**First Law — Law of Segregation:**
The two alleles of a gene (one inherited from each parent) separate (segregate) from each other during the formation of gametes (meiosis), so that each gamete carries only one allele of each gene. Fertilisation randomly reunites alleles from two parents. Therefore, each offspring has an equal probability of receiving either allele from a heterozygous parent.
**Second Law — Law of Independent Assortment:**
The alleles of different genes (located on different, non-homologous chromosomes) segregate independently of one another during gamete formation. That is, the allele of one gene that passes into a gamete does not influence which allele of a different gene is included in the same gamete. This law applies specifically to genes on non-homologous chromosomes (or genes sufficiently far apart on the same chromosome).
---
### Question 2(c) — Genetic Cross: BB × bb (F1 and F2)
**Parental Cross:**
```
Parents: BB × bb
(Brown) (White)
Gametes: B b
B b
F1 Offspring:
| b | b |
| B | Bb | Bb |
| B | Bb | Bb |
F1 Genotype: All Bb (heterozygous brown)
F1 Phenotype: All brown (B is dominant)
```
**F1 × F1 Cross (to produce F2):**
```
F1 Parents: Bb × Bb
Gametes: B, b B, b
F2 Punnett Square:
| B | b |
| B | BB | Bb |
| b | Bb | bb |
F2 Genotypes: 1 BB : 2 Bb : 1 bb
F2 Phenotypes: 3 Brown (BB + Bb) : 1 White (bb)
Phenotypic ratio = 3 : 1
```
---
### Question 3 — Formation of Two Molecules of Pyruvate During Respiration (Glycolysis)
The formation of pyruvate from glucose occurs via the metabolic pathway known as **glycolysis** (also called the Embden–Meyerhof–Parnas pathway), which takes place entirely in the **cytoplasm** and does not require oxygen. The ten sequential enzymatic steps can be summarised in two phases:
**Phase 1 — Energy Investment Phase (Preparatory Phase):**
**Step 1 — Phosphorylation of glucose:** One molecule of glucose (6-carbon) receives a phosphate group from ATP, forming **glucose-6-phosphate**. This consumes 1 ATP and is catalysed by the enzyme hexokinase. The phosphorylation traps glucose inside the cell.
**Step 2 — Isomerisation:** Glucose-6-phosphate is converted to **fructose-6-phosphate** by the enzyme phosphoglucose isomerase.
**Step 3 — Second phosphorylation:** A second ATP is consumed to phosphorylate fructose-6-phosphate, producing **fructose-1,6-bisphosphate**, catalysed by phosphofructokinase. Net cost so far: **2 ATP invested**.
**Step 4 — Cleavage:** Fructose-1,6-bisphosphate is split by aldolase into two interconvertible 3-carbon compounds: **dihydroxyacetone phosphate (DHAP)** and **glyceraldehyde-3-phosphate (G3P)**. DHAP is rapidly converted to G3P by triose phosphate isomerase, so effectively **two molecules of G3P** proceed through the rest of glycolysis.
**Phase 2 — Energy Recovery Phase (Pay-off Phase):**
*(Each step below occurs twice — once for each G3P molecule)*
**Step 5 — Oxidation and phosphorylation:** Each G3P is oxidised by NAD⁺ (which is reduced to **NADH**) and simultaneously phosphorylated (using inorganic phosphate, not ATP), producing **1,3-bisphosphoglycerate**. This is catalysed by glyceraldehyde-3-phosphate dehydrogenase.
**Step 6 — ATP generation (Substrate-level phosphorylation):** The high-energy phosphate group is transferred from 1,3-bisphosphoglycerate to ADP, producing **3-phosphoglycerate** and **1 ATP** per molecule (2 ATP total). Catalysed by phosphoglycerate kinase.
**Step 7 — Isomerisation:** 3-Phosphoglycerate is converted to **2-phosphoglycerate** by phosphoglycerate mutase.
**Step 8 — Dehydration:** Enolase removes a water molecule from 2-phosphoglycerate, forming the high-energy compound **phosphoenolpyruvate (PEP)**.
**Step 9 — Second ATP generation:** The phosphate group of PEP is transferred to ADP, producing **pyruvate** and **1 ATP** per molecule (2 ATP total). Catalysed by pyruvate kinase.
**Net balance of glycolysis:**
| | |
|---|---|
| Glucose consumed | 1 molecule (6C) |
| Pyruvate produced | **2 molecules** (3C each) |
| ATP consumed | 2 |
| ATP produced | 4 |
| **Net ATP gain** | **2 ATP** |
| NADH produced | **2 NADH** |
The two pyruvate molecules then proceed to the mitochondrial matrix (under aerobic conditions) to enter the **pyruvate oxidation** step (conversion to acetyl-CoA) and subsequently the Krebs cycle.
---
### Question 4(a) — Definitions
**i. Aseptic technique:** A set of practices and procedures carried out under carefully controlled conditions to prevent contamination of cultures, specimens, surgical wounds, or sterile materials by unwanted microorganisms from the environment, the operator, or other sources. It involves the use of sterilised equipment, working near a flame or within a biosafety cabinet, and minimising exposure of sterile materials to the open environment.
**ii. Antigens:** Substances — typically proteins, polysaccharides, or glycoproteins found on the surface of pathogens, foreign cells, or other particles — that are recognised as non-self by the immune system and are capable of stimulating a specific immune response, including the production of antibodies. An antigen has one or more specific regions called **epitopes** (antigenic determinants) to which antibodies or T-cell receptors bind.
**iii. Antibodies:** Glycoprotein molecules (immunoglobulins) produced and secreted by B lymphocytes (plasma cells) in response to a specific antigen. They have a characteristic Y-shaped structure with two identical antigen-binding sites (Fab regions) that bind specifically to the complementary epitope of the stimulating antigen. Antibodies neutralise pathogens, opsonise targets for phagocytosis, activate complement, and participate in agglutination.
**iv. Immunity:** The ability of an organism to resist infection, disease, or the harmful effects of foreign substances by means of physiological mechanisms that recognise and eliminate pathogens and foreign molecules. Immunity may be innate (non-specific, present from birth) or adaptive/acquired (specific, developed through exposure to antigens); it may also be active (generated by the individual's own immune response) or passive (transferred from another individual, e.g., maternal antibodies or antiserum).
---
### Question 4(b) — Six Rules of Aseptic Technique
1. **Work in a clean, designated area:** Always conduct microbiological work in a biosafety cabinet (laminar flow hood) or near a lit Bunsen burner, which creates an updraft of hot air that prevents microbial particles from settling into cultures.
2. **Sterilise all equipment before and after use:** All glassware, media, instruments (loops, spreaders, forceps), and surfaces must be sterilised by autoclaving, dry heat, flaming, or appropriate chemical disinfection before contact with cultures or specimens.
3. **Minimise exposure of sterile materials:** Open containers (flasks, tubes, Petri dishes) only when necessary and for the shortest possible time; tilt containers at an angle when opened and keep them near the flame to prevent aerial contamination.
4. **Flame inoculating loops and needles before and after use:** Heat the metal loop or needle to red heat in the Bunsen flame before use (to sterilise) and after use (to incinerate any remaining culture), then allow it to cool briefly before contacting a culture to avoid heat-killing organisms.
5. **Never allow sterile surfaces to contact non-sterile surfaces:** Sterile pipettes, loops, and the inside of container caps must never touch the bench, skin, or clothing; lids and caps must not be placed down on the bench surface but held in the hand or placed inverted.
6. **Label all cultures clearly and work with only one organism at a time where possible:** This prevents mix-ups and reduces the risk of cross-contamination; all inoculated plates and tubes must be labelled with the organism, date, and operator's name before incubation.
---
### Question 5(a) — How Water Enters the Root Hair of a Plant
Water enters root hair cells from the soil by the process of **osmosis** — the passive movement of water molecules across a selectively permeable membrane from a region of higher water potential (lower solute concentration) to a region of lower water potential (higher solute concentration).
The detailed mechanism proceeds as follows:
**1. Soil water potential:** The soil solution surrounding root hairs is a dilute solution of mineral salts; its water potential is relatively high (less negative).
**2. Root hair cell water potential:** The cell sap within the root hair vacuole contains a higher concentration of dissolved solutes (sugars, amino acids, mineral ions) than the soil solution; its water potential is therefore lower (more negative).
**3. Osmotic gradient:** Because the water potential of the soil solution is higher than that of the root hair cell sap, water moves down this water potential gradient — from the soil, across the thin, permeable cell wall, and then across the selectively permeable plasma membrane — into the vacuole of the root hair cell by osmosis.
**4. Pathways of water movement across the root:** Once inside the root hair, water continues to move across the root cortex toward the xylem by three pathways:
- **Apoplast pathway:** Water moves through the porous cell walls and intercellular spaces without crossing membranes, until it is blocked by the **Casparian strip** (a band of suberin in the cell walls of the endodermis).
- **Symplast pathway:** Water moves through the cytoplasm and plasmodesmata (cytoplasmic connections between cells) from cell to cell.
- **Vacuolar pathway:** Water passes from vacuole to vacuole through intervening cytoplasm and tonoplast membranes.
At the endodermis, the Casparian strip forces all apoplastic water into the symplast, giving the plant control over what enters the xylem. Water then passes into the xylem vessels of the stele for upward transport.
---
### Question 5(b) — Tissue that Conducts Water from Root to Stem and Leaves
The tissue responsible for conducting water and dissolved mineral salts upward from the root through the stem to the leaves is **xylem**.
Within the xylem, the conducting elements are primarily the **vessel elements** (wide, long, dead cells joined end-to-end to form continuous hollow tubes called **vessels**) and **tracheids** (elongated, tapering dead cells with pitted walls). Both cell types are dead at functional maturity, have thick, lignified secondary cell walls (which provide structural support), and have no cross-walls obstructing water flow (or have perforated end walls in tracheids).
Water is drawn upward through the xylem primarily by **transpiration pull** (the cohesion-tension mechanism): water evaporating from leaf mesophyll cells through stomata (transpiration) creates a tension that pulls water columns upward through the xylem, supported by the cohesion of water molecules to each other and their adhesion to xylem walls.
---
### Question 6(a) — Five Functions of Testosterone
1. **Development of primary sex characteristics:** Testosterone drives the differentiation and growth of the male reproductive organs — testes, epididymis, vas deferens, seminal vesicles, and prostate gland — during embryonic development (under the influence of the SRY gene) and at puberty.
2. **Development of secondary sexual characteristics:** At puberty, testosterone is responsible for the development of male secondary sex characteristics including deepening of the voice (laryngeal growth), growth of facial, axillary, and pubic hair, broadening of the shoulders, and development of the characteristic male body shape.
3. **Spermatogenesis:** Testosterone is essential for the initiation and maintenance of sperm production (spermatogenesis) within the seminiferous tubules of the testes, acting in concert with FSH on Sertoli cells.
4. **Anabolic effects on muscle and bone:** Testosterone stimulates protein synthesis in skeletal muscle (promoting muscle mass and strength) and stimulates bone growth and increased bone density at puberty; it eventually causes closure of the epiphyseal plates, ending longitudinal growth.
5. **Influence on behaviour and libido:** Testosterone influences the central nervous system, contributing to the male sex drive (libido), assertive or competitive behaviour, and is involved in the maintenance of mood and cognitive function in adult males.
---
### Question 6(b) — Structure of a Mature Spermatozoon (Labelled Diagram)
*(A fully labelled diagram is required in the examination. Key structures to illustrate and label are listed below.)*
```
┌─────────────────────┐
│ ACROSOME │ ← Contains hydrolytic enzymes
│ (acrosomal cap) │ (acrosin, hyaluronidase)
├─────────────────────┤
│ NUCLEUS │ ← Condensed, haploid (n) DNA
│ (haploid, dense) │
HEAD ───────────────┤─────────────────────│
│ NUCLEAR ENVELOPE │
└──────────┬──────────┘
│
NECK ──────────────────────────┤ ← Centriole (basal body of flagellum)
│
┌──────────┴──────────┐
│ MIDDLE PIECE │ ← Mitochondrial helix wrapped
MIDDLE PIECE ───────│ (mitochondrial │ around axoneme; generates ATP
│ sheath) │ for flagellar movement
└──────────┬──────────┘
│ Axoneme (9+2 arrangement of
PRINCIPAL ─────────────────────┤ microtubule doublets + central pair)
PIECE (TAIL) │
│ ← Fibrous sheath
│
END PIECE ─────────────────────┴──→ (axoneme only; fibrous sheath ends)
```
**Summary of regions and functions:**
| Region | Key Components | Function |
|---|---|---|
| Head | Nucleus (haploid DNA), acrosome | Carries genetic material; acrosome releases enzymes to penetrate egg |
| Neck | Centriole, connecting piece | Anchors tail to head; organises axoneme |
| Middle piece | Mitochondrial helix around axoneme | ATP production for flagellar motility |
| Principal piece | Axoneme + fibrous sheath | Main propulsive segment of flagellum |
| End piece | Axoneme only | Terminal portion of flagellum |
---
### Question 7(a) — Definition of Tissue
A tissue is a group of cells that are similar in origin, structure, and function, organised together to perform a specific physiological role within an organism.
---
### Question 7(b) — How Plant Tissues Are Formed
Plant tissues are formed through the activity of **meristems** — regions of actively dividing, undifferentiated (totipotent) cells found at specific locations in the plant body. The process involves three stages:
1. **Cell division (proliferation):** Meristematic cells divide repeatedly by mitosis, producing new cells. Apical meristems (at shoot and root tips) bring about primary growth in length, while lateral meristems (vascular cambium and cork cambium) bring about secondary growth in girth.
2. **Cell enlargement:** Newly produced meristematic cells absorb water and expand, often increasing many times in volume, driven by turgor pressure acting against the elastic primary cell wall.
3. **Cell differentiation:** Enlarged cells undergo structural and biochemical specialisation — developing characteristic shapes, wall thickening, and organelle complements — to become the various permanent tissue types (parenchyma, collenchyma, sclerenchyma, xylem, phloem, epidermis). Once differentiated, most plant cells lose the ability to divide (except parenchyma cells which retain some meristematic potential).
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### Question 7(c) — Structure and Function of Two Vascular Tissues
**1. Xylem**
*Structure:* Xylem is a complex tissue composed of several cell types. The principal conducting elements are **vessel elements** — wide, cylindrical cells arranged end-to-end; at maturity they are dead, with their cross-walls perforated or completely dissolved (forming **perforation plates**) to produce long, unobstructed tubes called vessels. **Tracheids** are narrower, elongated, dead cells with tapered ends and numerous pits in their lateral walls through which water passes between cells. Both vessel elements and tracheids have thick, **lignified** secondary cell walls that resist collapse under the tension of water transport and provide considerable mechanical support. Xylem also contains living **xylem parenchyma** (for storage and lateral transport of water and minerals) and **xylem fibres** (for additional mechanical support).
*Function:* The primary function of xylem is the **unidirectional conduction of water and dissolved mineral ions** (the xylem sap) from the roots upward through the stem to the leaves, driven mainly by the cohesion-tension mechanism (transpiration pull). Lignified xylem also provides **mechanical support** (wood in trees is largely secondary xylem) to keep the plant upright.
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**2. Phloem**
*Structure:* Phloem is also a complex tissue. The main conducting elements are **sieve tube elements** — living cells (lacking a nucleus and most organelles at maturity) with perforated end walls called **sieve plates** through which cytoplasmic strands connect adjacent sieve tube elements. Each sieve tube element is closely associated with one or more **companion cells** — nucleated, metabolically active cells connected to the sieve tube element by numerous plasmodesmata; companion cells regulate the loading and unloading of solutes into and out of the sieve tube. Phloem also contains **phloem parenchyma** (storage) and **phloem fibres** (support).
*Function:* The primary function of phloem is the **translocation of organic solutes** — principally sucrose (the main transport sugar in most plants), amino acids, plant hormones, and other metabolites — from sources (e.g., photosynthetically active mature leaves, or storage organs during mobilisation) to sinks (e.g., growing meristems, developing fruits and seeds, roots). Unlike xylem flow, phloem translocation is **bidirectional** (moving up or down the plant depending on source and sink locations) and is an active, energy-requiring process explained by the **pressure-flow hypothesis** (Münch model).
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### Question 8(a) — Six Characteristics of Phylum Mollusca
1. Molluscs are **soft-bodied**, bilaterally symmetrical (though some, like gastropods, undergo torsion), unsegmented (or show only vestigial segmentation in Polyplacophora) animals.
2. The body is typically divided into three regions: a **head** (bearing sense organs and mouth), a **muscular foot** (used for locomotion), and a **visceral mass** (containing internal organs).
3. Most molluscs possess a dorsal fold of tissue called the **mantle**, which secretes the **calcareous shell** (one, two, or eight valves depending on the class) and encloses a **mantle cavity** containing the gills (ctenidia) and/or lungs.
4. They possess a unique feeding structure called the **radula** — a flexible, ribbon-like rasping organ bearing rows of chitinous teeth, used to scrape, cut, or drill food — absent only in bivalves.
5. They have a **true coelom** (haemocoel serving as the main body cavity in most groups) and an open circulatory system (except in cephalopods, which have a closed system) with a dorsal heart consisting of one or two atria and a ventricle.
6. Excretion is carried out by paired **nephridia** (kidneys), and the nervous system consists of paired cerebral, pleural, pedal, and visceral ganglia connected by nerve cords; sensory organs include eyes (ranging from simple ocelli to the highly sophisticated camera eyes of cephalopods), statocysts, and osphradia (chemosensory organs).
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### Question 8(b) — Four Economic Importances of Subclass Pulmonata
The Pulmonata (pulmonate gastropods) are air-breathing snails and slugs that have a lung (modified mantle cavity) instead of gills. They include garden snails (*Helix* spp.), land slugs, and many freshwater snails.
1. **Food source:** Many pulmonate snails (e.g., *Helix pomatia* — the Roman or edible snail, and *Achatina fulica* — the giant African land snail) are consumed as protein-rich food by human populations in Africa, Europe, and Asia. Snail farming (heliciculture/snail rearing) is an economically significant industry in several countries.
2. **Agricultural and horticultural pests:** Land slugs and snails cause significant economic damage to crops (vegetables, cereals, fruits) and ornamental plants by feeding on leaves, stems, and roots; the cost of control measures (molluscicides, barriers, biological controls) and crop losses runs into millions annually.
3. **Intermediate hosts of parasites:** Certain freshwater pulmonate snails (e.g., *Biomphalaria* spp. and *Bulinus* spp.) serve as obligate intermediate hosts for **Schistosoma** parasites (blood flukes), which cause **schistosomiasis (bilharzia)** — a major debilitating parasitic disease affecting hundreds of millions of people in tropical regions. Control of these snail hosts is therefore central to schistosomiasis control programmes.
4. **Biomedical and research use:** Pulmonate snails, particularly *Aplysia californica* (a sea hare, which some classifications include in the group) and *Helix* species, have been extensively used in neurobiological research due to their large, identifiable neurons; this research has contributed significantly to the understanding of neural circuits, learning, and memory. Additionally, compounds derived from molluscs are being investigated for pharmaceutical applications.