## QUESTION 1
**(a)** Explain the following terms:
- (i) Recessive gene (2½ marks)
- (ii) Homeostatic imbalance (2½ marks)
- (iii) Nitrogenous waste products (2½ marks)
- (iv) Inbreeding (2½ marks)
**(b)** Assuming a hairless cat has a genotype of (Hh) and inheriting a dominant allele (H) makes the cat hairless. Inheriting two of the dominant allele is lethal.
- (i). Use the Punnet Square to show the offspring's of a cross between a male and a female hairless cat.
- (ii). Show the genotypes and phenotypes from the cross.
- (iii). What is the genotypic ratio of the cross?
- (iv). Show the phenotypic ratio of the cross
- (v). Calculate the percentages for mortality, hairless and hairy offspring from the cross.
(20 marks)
**(c)** Fill in the blank spaces. Spellings of one word answer and scientific names must be correct to score. (10 marks)
- (i) Sebaceous and sweat glands secrete \_\_\_\_a\_\_\_\_ and \_\_\_\_b\_\_\_\_ respectively.
- (ii) Urea is formed in the \_\_\_\_c\_\_\_\_ of vertebrates and excreted by \_\_\_\_d\_\_\_\_
- (iii) The function of the valve-like structures in the spiracles of insects is to \_\_\_\_e\_\_\_\_
- (iv) \_\_\_\_f\_\_\_\_ and \_\_\_\_g\_\_\_\_ are the major minerals in the synthesis of bones and ATP respectively.
- (v) \_\_\_\_h\_\_\_\_ are the building blocks of proteins.
- (vi) The elephant uses \_\_\_\_i\_\_\_\_ for digging, feeding, offence and defence.
- (vii) The action in reaction to stimuli without prior thought or planning is called \_\_\_\_j\_\_\_\_
---
## PAGE 2 — 2025 IJMBE BIOLOGY II contd.
## QUESTION 2
**(a).** Draw and label the diagram of a mammalian brain, giving one function of any five (5) labeled parts. (15 marks)
**(b).** Outline ten (10) functions of the mammalian liver. (5 marks)
---
## QUESTION 3
Explain the following:
- (a) Cytokinesis in cell division (10 marks)
- (b) Diploblastic organization in Hydra (5 marks)
- (c) Reproduction in reptiles (5 marks)
---
## QUESTION 4
Briefly explain the four (4) main types of organic molecules in a cell (20 marks)
---
## QUESTION 5
With the aid of well labeled diagram, explain the mechanism of perception of taste in man. (20 marks)
---
## QUESTION 6
**(a).** Copy and complete (*) the table below: (5 marks)
| S/No. | Vector | Disease | Pathogen |
|---|---|---|---|
| 1 | * | Lymphatic filariasis, Malaria | Parasite |
| 2 | Lice | Typhus, Louse-borne relapsing fever | Parasite |
| 3 | * | Leishmaniasis | Bacteria |
| 4 | Ticks | * | * |
| 5 | Tsetse flies | Sleeping sickness (African trypanosomiasis) | * |
**(b).** Explain the process of excretion in protozoa (5 marks)
**(c).** Outline five (5) disadvantages of asexual reproduction. (5 marks)
**(d).** Briefly explain divergent evolution. (5 marks)
---
COMPLETE SOLUTIONS
# QUESTION 1
## (a) Explanation of Terms
### (i) Recessive Gene
A recessive gene is an allele that only expresses its trait/phenotype when present in homozygous form (two copies). It is masked or suppressed by a dominant allele when both are present together in a heterozygous organism. It is usually represented by a lowercase letter (e.g., h). Example: the allele for smooth seeds in pea plants.
### (ii) Homeostatic Imbalance
Homeostatic imbalance is a disruption or failure of the body's ability to maintain a stable internal environment (homeostasis). It occurs when the body's regulatory mechanisms cannot adequately respond to internal or external changes, leading to disease or dysfunction. Examples include diabetes mellitus (failure to regulate blood glucose) and hypertension (failure to regulate blood pressure).
### (iii) Nitrogenous Waste Products
These are metabolic waste products containing nitrogen, produced from the breakdown of proteins and nucleic acids in living organisms. They include:
- **Ammonia** — produced by aquatic animals (ammonotelic)
- **Urea** — produced by mammals (ureotelic)
- **Uric acid** — produced by birds, reptiles, insects (uricotelic)
### (iv) Inbreeding
Inbreeding is the mating or crossing of closely related individuals within the same family, population, or breed over successive generations. It increases homozygosity in the offspring and can lead to expression of harmful recessive traits (inbreeding depression). It is used in selective breeding to fix desirable traits but can reduce genetic diversity and overall fitness.
---
## (b) Genetics of Hairless Cat Cross
**Given information:**
- Hh = hairless cat
- HH = lethal (dies)
- hh = hairy cat
- H is dominant; inheriting two H alleles is lethal
**Parents:** Hairless male (Hh) × Hairless female (Hh)
### (i) Punnet Square
| | **H** | **h** |
|---|---|---|
| **H** | HH | Hh |
| **h** | Hh | hh |
---
### (ii) Genotypes and Phenotypes
| Genotype | Phenotype |
|---|---|
| HH | Lethal (dies) |
| Hh | Hairless cat |
| Hh | Hairless cat |
| hh | Hairy cat |
---
### (iii) Genotypic Ratio
**HH : Hh : hh = 1 : 2 : 1**
---
### (iv) Phenotypic Ratio
Since HH is lethal, among surviving offspring:
**Hairless (Hh) : Hairy (hh) = 2 : 1**
---
### (v) Percentages
Total offspring = 4
- **Mortality (HH):** 1/4 × 100 = **25%**
- **Hairless (Hh):** 2/4 × 100 = **50%**
- **Hairy (hh):** 1/4 × 100 = **25%**
Among surviving offspring (3 total):
- Hairless = 2/3 × 100 = **66.7%**
- Hairy = 1/3 × 100 = **33.3%**
---
## (c) Fill in the Blanks
| Blank | Answer |
|---|---|
| a | **Sebum (oil)** |
| b | **Sweat (water/salts)** |
| c | **Liver** |
| d | **Kidneys** |
| e | **Regulate gaseous exchange / open and close to control air entry** |
| f | **Calcium (Ca)** |
| g | **Phosphorus (P)** |
| h | **Amino acids** |
| i | **Tusks** |
| j | **Reflex action** |
---
# QUESTION 2
## (a) Mammalian Brain — Labeled Diagram Description
*(Draw a sagittal section of the mammalian brain with the following labeled parts and functions)*
**Parts and Functions:**
| Part | Function |
|---|---|
| **Cerebrum** | Controls voluntary movement, memory, reasoning, and conscious thought |
| **Cerebellum** | Coordinates balance, posture, and muscular movement |
| **Medulla Oblongata** | Controls involuntary actions — breathing, heartbeat, swallowing |
| **Hypothalamus** | Regulates body temperature, hunger, thirst, and links nervous system to endocrine system |
| **Thalamus** | Relay center; sorts and relays sensory information to appropriate brain areas |
| **Corpus Callosum** | Connects left and right cerebral hemispheres; coordinates their activities |
| **Pons** | Controls breathing rhythm and relays signals between cerebellum and cerebrum |
| **Pituitary Gland** | Master endocrine gland; controls other hormone-secreting glands |
| **Olfactory Bulb** | Processes sense of smell |
| **Optic Chiasma** | Junction where optic nerves cross; involved in visual processing |
---
## (b) Ten Functions of the Mammalian Liver
1. **Deamination** — Breaks down excess amino acids, removing the amino group to form urea
2. **Urea Formation** — Converts toxic ammonia (from deamination) into less toxic urea for excretion
3. **Glycogen Storage** — Converts excess glucose to glycogen and stores it (glycogenesis)
4. **Glycogenolysis** — Converts stored glycogen back to glucose when blood sugar falls
5. **Bile Production** — Produces bile salts used in the emulsification and digestion of fats
6. **Detoxification** — Neutralizes and breaks down toxic substances including alcohol, drugs, and poisons
7. **Plasma Protein Synthesis** — Produces blood proteins including albumin, fibrinogen, and prothrombin
8. **Fat Metabolism** — Converts excess carbohydrates and proteins into fats for storage
9. **Heat Production** — Generates body heat through its high metabolic activity (thermogenesis)
10. **Vitamin and Mineral Storage** — Stores fat-soluble vitamins (A, D, E, K) and minerals like iron and copper
---
# QUESTION 3
## (a) Cytokinesis in Cell Division
**Definition:** Cytokinesis is the physical division of the cytoplasm of a parent cell into two daughter cells following nuclear division (mitosis or meiosis). It is the final stage of cell division.
### In Animal Cells:
- A cleavage furrow forms at the equator of the cell
- Actin and myosin microfilaments form a contractile ring beneath the plasma membrane
- The ring contracts progressively, pinching the cell inward like a tightening belt
- The plasma membrane is drawn inward until the cytoplasm is divided into two equal daughter cells
- Each daughter cell contains its own nucleus with identical genetic material
### In Plant Cells:
- No cleavage furrow forms because plant cells have rigid cell walls
- Instead, a **cell plate** forms at the center of the cell during telophase
- Vesicles from the Golgi apparatus migrate to the midline and fuse to form the cell plate
- The cell plate grows outward from the center until it reaches the plasma membrane
- The cell plate develops into a new cell wall, separating the two daughter cells
- Plasmodesmata (cytoplasmic channels) are formed in the new cell wall for communication
### Significance:
- Ensures equal distribution of cytoplasm and organelles
- Produces two genetically identical daughter cells in mitosis
- Produces four haploid cells in meiosis
---
## (b) Diploblastic Organization in Hydra
**Definition:** Diploblastic organization refers to a body plan in which the body wall is made up of only **two primary germ layers** — the ectoderm (outer layer) and the endoderm (inner layer), separated by a non-cellular gelatinous layer called the **mesoglea**.
### In Hydra specifically:
**1. Ectoderm (Epidermis) — outer layer:**
- Covers the entire outer surface of the body
- Contains several cell types:
- **Epitheliomuscular cells** — for movement and support
- **Cnidocytes (stinging cells)** — contain nematocysts for defense and prey capture
- **Sensory cells** — detect environmental stimuli
- **Nerve cells** — form a primitive nerve net
- **Interstitial cells** — undifferentiated stem cells for regeneration
**2. Mesoglea — middle layer:**
- A thin, non-cellular, gelatinous matrix between the two layers
- Provides structural support and flexibility
- Not considered a true germ layer
**3. Endoderm (Gastrodermis) — inner layer:**
- Lines the gastrovascular cavity (enteron)
- Contains:
- **Nutritive-muscular cells** — for digestion and movement
- **Gland cells** — secrete digestive enzymes
- **Sensory and nerve cells**
### Significance:
- Diploblastic organization is characteristic of Phylum Cnidaria (coelenterates)
- It represents a relatively simple level of organization compared to triploblastic animals
- The gastrovascular cavity serves as both digestive and circulatory system
---
## (c) Reproduction in Reptiles
Reptiles exhibit several reproductive strategies reflecting their adaptation to terrestrial life.
### 1. Sexual Reproduction
- Reptiles reproduce sexually with **internal fertilization**
- The male uses paired copulatory organs (**hemipenes** in lizards and snakes; a single penis in crocodiles and turtles) to transfer sperm into the female's cloaca
- Internal fertilization is an adaptation to terrestrial life — it protects gametes from desiccation
### 2. Oviparity (Egg-laying)
- Most reptiles are **oviparous** — they lay eggs
- Eggs are amniotic — surrounded by protective membranes (amnion, chorion, allantois) and a leathery or calcareous shell
- The shell prevents water loss and provides physical protection
- Eggs are laid in warm, moist environments (soil, sand, leaf litter) and incubated by environmental heat
- Examples: turtles, most lizards, most snakes, crocodiles
### 3. Viviparity (Live Birth)
- Some reptiles are **viviparous** — the embryo develops inside the mother's body and live young are born
- The embryo receives nourishment from the mother through a placenta-like structure
- Examples: some species of skinks, boas, and vipers
### 4. Ovoviviparity
- Some reptiles retain eggs inside the body until hatching
- The embryo is nourished by the egg yolk (not the mother)
- Examples: some snakes and lizards
### 5. Temperature-Dependent Sex Determination
- In many reptiles (especially crocodiles and turtles), the sex of offspring is determined by the temperature at which eggs are incubated rather than by sex chromosomes
### 6. Parental Care
- Generally limited in reptiles
- Crocodiles show notable parental care — guarding nests and carrying hatchlings to water
---
# QUESTION 4
## Four Main Types of Organic Molecules in a Cell
### 1. Carbohydrates
**Definition:** Organic compounds made of carbon, hydrogen, and oxygen in the ratio Cₙ(H₂O)ₙ.
**Structure:**
- Basic unit (monomer) = **monosaccharide** (e.g., glucose, fructose, galactose)
- Disaccharides = two monosaccharides joined by glycosidic bond (e.g., sucrose, maltose, lactose)
- Polysaccharides = many monosaccharides joined (e.g., starch, glycogen, cellulose, chitin)
**Functions:**
- Primary source of energy (glucose is oxidized in cellular respiration)
- Energy storage (starch in plants; glycogen in animals)
- Structural support (cellulose in plant cell walls; chitin in fungal walls and arthropod exoskeletons)
- Component of nucleic acids (ribose in RNA; deoxyribose in DNA)
- Cell recognition and communication (glycoproteins on cell surfaces)
---
### 2. Proteins
**Definition:** Large, complex organic molecules made of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.
**Structure:**
- Basic unit (monomer) = **amino acid** (20 types)
- Amino acids joined by **peptide bonds** to form polypeptide chains
- Four levels of structure:
- **Primary** — sequence of amino acids
- **Secondary** — alpha helix or beta pleated sheet
- **Tertiary** — 3D folding of polypeptide
- **Quaternary** — multiple polypeptide chains combined
**Functions:**
- Structural support (collagen, keratin)
- Enzymatic catalysis (all enzymes are proteins)
- Transport (hemoglobin transports oxygen)
- Immune defense (antibodies)
- Hormonal regulation (insulin, glucagon)
- Muscle contraction (actin, myosin)
- Cell signaling and receptor functions
---
### 3. Lipids
**Definition:** Organic molecules composed mainly of carbon, hydrogen, and oxygen but with a much lower proportion of oxygen than carbohydrates. They are insoluble in water but soluble in organic solvents.
**Main Types:**
- **Triglycerides** (fats and oils) — glycerol + 3 fatty acid chains
- **Phospholipids** — glycerol + 2 fatty acids + phosphate group (form cell membranes)
- **Steroids** — complex ring structures (e.g., cholesterol, testosterone, estrogen)
- **Waxes** — long-chain fatty acids + alcohols
**Functions:**
- Long-term energy storage (contain more than twice the energy of carbohydrates per gram)
- Structural component of all cell membranes (phospholipid bilayer)
- Thermal insulation (subcutaneous fat)
- Protection of vital organs (adipose tissue)
- Hormone synthesis (steroid hormones)
- Waterproofing (waxes on leaves and skin)
- Fat-soluble vitamins (A, D, E, K) are lipids
---
### 4. Nucleic Acids
**Definition:** Large, complex organic molecules composed of carbon, hydrogen, oxygen, nitrogen, and phosphorus. They are the information molecules of life.
**Basic unit (monomer):** Nucleotide = phosphate group + pentose sugar + nitrogenous base
**Two main types:**
**DNA (Deoxyribonucleic Acid):**
- Double-stranded helix
- Sugar = deoxyribose
- Bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C)
- Found mainly in nucleus
- Stores and transmits genetic information
**RNA (Ribonucleic Acid):**
- Usually single-stranded
- Sugar = ribose
- Bases: Adenine (A), Uracil (U), Guanine (G), Cytosine (C)
- Three types: mRNA, tRNA, rRNA
- Involved in protein synthesis (transcription and translation)
**Functions:**
- Storage and transmission of genetic information (DNA)
- Protein synthesis (mRNA carries code; tRNA brings amino acids; rRNA forms ribosomes)
- ATP (adenosine triphosphate) — a nucleotide that is the universal energy currency of cells
- Coenzymes (NAD, FAD, CoA) are nucleotide derivatives
---
# QUESTION 5
## Mechanism of Perception of Taste in Man
### Introduction
Taste (gustation) is a chemical sense that allows humans to detect dissolved chemical substances in food and drink. The perception of taste involves specialized sensory receptors on the tongue and other oral surfaces.
### Structure of Taste Receptors
**Taste Buds:**
- Located mainly on the tongue within small projections called **papillae**
- Four types of papillae: fungiform, circumvallate (vallate), foliate, and filiform
- Each taste bud contains 50–100 **taste receptor cells** (gustatory cells)
- Taste buds also occur on the soft palate, epiglottis, and upper esophagus
- Taste receptor cells have **microvilli (taste hairs)** that project through a taste pore to the surface
### Five Basic Taste Qualities
1. **Sweet** — sugars, alcohols (tip of tongue)
2. **Salty** — metal ions, especially Na⁺ (sides of tongue)
3. **Sour** — acids/H⁺ ions (sides of tongue)
4. **Bitter** — alkaloids, toxins (back of tongue)
5. **Umami** — glutamate (savory, throughout tongue)
### Mechanism of Taste Perception
**Step 1 — Dissolution:**
- Food enters the mouth and chemicals dissolve in saliva
- Dissolved chemicals are called **tastants**
**Step 2 — Receptor Activation:**
- Tastants diffuse into the taste pore and bind to receptor proteins on the microvilli of taste receptor cells
- Different tastants activate different receptor mechanisms:
- **Salty/Sour:** Ion channels open directly — Na⁺ or H⁺ ions enter the cell
- **Sweet/Bitter/Umami:** G-protein coupled receptors (GPCRs) are activated, triggering second messenger cascades
**Step 3 — Depolarization:**
- Ion entry or second messenger activity causes depolarization of the taste receptor cell
- This triggers release of **neurotransmitters** at the base of the cell
**Step 4 — Nerve Impulse Transmission:**
- Neurotransmitters stimulate sensory nerve fibers
- Three cranial nerves carry taste signals:
- **Facial nerve (VII)** — anterior 2/3 of tongue
- **Glossopharyngeal nerve (IX)** — posterior 1/3 of tongue
- **Vagus nerve (X)** — epiglottis and esophagus
**Step 5 — Brain Processing:**
- Nerve impulses travel to the **medulla oblongata** → **thalamus** → **gustatory cortex** (in the parietal lobe)
- The brain integrates taste signals with smell (olfaction), texture, temperature, and pain to create the complete perception of **flavor**
### Adaptation
- Prolonged exposure to a taste stimulus leads to **taste adaptation** — the receptor cells become less responsive, reducing taste intensity
---
# QUESTION 6
## (a) Completed Vector-Disease Table
| S/No. | Vector | Disease | Pathogen |
|---|---|---|---|
| 1 | **Mosquito (Anopheles/Culex)** | Lymphatic filariasis, Malaria | Parasite |
| 2 | Lice | Typhus, Louse-borne relapsing fever | Parasite |
| 3 | **Sandfly (Phlebotomus)** | Leishmaniasis | Bacteria |
| 4 | Ticks | **Rocky Mountain spotted fever / Lyme disease** | **Bacteria** |
| 5 | Tsetse flies | Sleeping sickness (African trypanosomiasis) | **Parasite (Trypanosoma)** |
---
## (b) Excretion in Protozoa
Protozoa are unicellular organisms and lack specialized excretory organs. Excretion occurs through simple physical and chemical processes:
**1. Diffusion:**
- The main nitrogenous waste product in protozoa is **ammonia** (ammonotelic)
- Ammonia is produced from the breakdown of amino acids
- Being highly soluble, ammonia diffuses directly across the **plasma membrane** down the concentration gradient into the surrounding water
**2. Contractile Vacuole:**
- In freshwater protozoa like *Amoeba* and *Paramecium*, a **contractile vacuole** helps in osmoregulation and excretion
- The contractile vacuole collects excess water and some dissolved waste products
- It periodically contracts and expels its contents to the outside through the plasma membrane
- This prevents the cell from bursting due to osmotic influx of water
**3. Defecation:**
- Undigested food residues are expelled through the **anal pore** (in *Paramecium*) or by rupture of the food vacuole membrane with the plasma membrane (in *Amoeba*)
**Summary:** The simplicity of protozoan excretion reflects their unicellular nature — the large surface area to volume ratio makes diffusion across the plasma membrane sufficient for waste removal.
---
## (c) Five Disadvantages of Asexual Reproduction
1. **No genetic variation** — All offspring are genetically identical clones of the parent. There is no mixing of genetic material, leading to genetic uniformity in the population.
2. **Vulnerability to environmental change** — Because all individuals are genetically identical, a single disease, pathogen, or environmental change can wipe out the entire population. There is no adaptive diversity.
3. **Accumulation of harmful mutations** — Without sexual recombination to purge deleterious mutations, harmful mutations accumulate over generations (known as Muller's ratchet), potentially leading to population decline.
4. **Limited adaptability** — Asexually reproducing populations cannot adapt as rapidly to new environmental conditions, predators, or pathogens as sexually reproducing populations, because they lack the genetic diversity that natural selection requires.
5. **Overcrowding and competition** — Asexual reproduction can produce large numbers of genetically identical offspring rapidly in the same environment, leading to intense competition for the same resources (food, space, light) among individuals with identical needs.
---
## (d) Divergent Evolution
**Definition:** Divergent evolution is the process by which two or more populations or species that share a common ancestor gradually accumulate differences over time, becoming increasingly distinct from one another as they adapt to different environments or ecological niches.
### Key Features:
- Begins with a single ancestral species
- Populations become geographically, ecologically, or reproductively isolated
- Natural selection favors different traits in different environments
- Over time, populations diverge sufficiently to become distinct species (speciation)
### Classic Example — Darwin's Finches:
The finches of the Galápagos Islands all descended from a single ancestral South American finch species. As they colonized different islands with different food sources, natural selection shaped their beaks differently:
- **Ground finches** — large, crushing beaks for seeds
- **Warbler finches** — thin, pointed beaks for insects
- **Cactus finches** — long beaks for cactus flowers
### Another Example — Homologous Structures:
The forelimbs of mammals show divergent evolution from a common pentadactyl (five-fingered) ancestor:
- Human arm — for manipulation
- Horse leg — for running
- Whale flipper — for swimming
- Bat wing — for flying
Despite different functions, all have the same basic bone structure (humerus, radius, ulna, carpals, metacarpals, phalanges), confirming common ancestry.
### Significance:
- Divergent evolution is the primary mechanism of **speciation**
- It is the basis of **adaptive radiation** — the rapid diversification of a lineage into many ecological roles
- It explains the enormous **biodiversity** on Earth
- It is demonstrated by **homologous structures**, **vestigial organs**, and the **fossil record**
---