2019 IJMB Biology Paper 2

1(a) Explain the following terms: - (i) Colour blindness - (ii) Co-dominance - (iii) Co-enzymes - (iv) Heterogamic sex

(b) Assuming uniform colour (C) is dominant over spotted (c) in cattle. When a cross is made between a pure breed (homozygous) black bull (BBCC) with a white spotted cow (bbcc): - (i) Use Punnet diagram to show the result of the F₁ generation - (ii) What will be the phenotype of the calves in the F₁ generation? - (iii) Show the types and ratio of offspring that are possible when two of the F₁ generations are mated. - (iv) Name all the new combinations that have arisen from the cross above (1b iii)

(c) Fill in the blank spaces. Spellings of one word answer and scientific names must be correct to score: - (i) A nucleotide has _, _ and _ components - (ii) Sucrose is digested to _ and _ - (iii) The "bleeders' disease" is known as _ - (v) A condition in which a gene fails to express itself in the presence of dominant allele is _ - (vi) The scientific name of the giant African land Snail is _ - (vii) Urine is approximately 95% _, 2% _, 1% sodium chloride and other smaller amounts of nitrogenous compounds and mineral salts.

2. Give four adaptations of the following vertebrate taxa: - (i) Proboscidea - (ii) Phythonidae - (iii) Chamaeleonidae - (iv) Chiroptera

3. - (a) Outline fifteen (15) characteristics of the phylum Arthropoda - (b) List any five (5) economic importance of Protozoa.

4. - (a) Make a large (8-9cm) diagram of the lateral view of a bony fish - (b) Mention the adaptation of a bony fish for efficient movement in water.

5. Write short notes on any four (4) of the following: - (a) Osmoregulation - (b) Short-sightedness - (c) Involuntary/Reflex action - (d) Economic importance of phylum Annelida - (e) Gene pool

6. - (a) Enumerate any six (6) primary functions of the liver - (b) Write notes on:   - i. Closed circulation   - ii. Open circulation.

# COMPLETE SOLUTIONS ## QUESTION 1(a) — Explain the Following Terms ### (i) Colour Blindness This is a **sex-linked recessive genetic condition** in which an individual is unable to distinguish between certain colours, most commonly **red and green**. It is caused by a defective gene on the **X chromosome**. It is more common in males (XᶜY) than females because males only need one defective X allele to be affected, while females (XᶜXᶜ) need two. Females are mostly **carriers** (XᶜX). ### (ii) Co-dominance This is a type of inheritance in which **both alleles of a gene are equally expressed** in the phenotype of a heterozygous individual — neither allele is dominant or recessive over the other. Both traits appear **simultaneously** in the offspring. Example: ABO blood group — Blood group AB, where both Iᴬ and Iᴮ alleles are fully expressed. ### (iii) Co-enzymes These are **non-protein organic molecules** that bind to an enzyme (apoenzyme) to form an active enzyme complex called a **holoenzyme**. They assist enzymes in catalyzing biochemical reactions by acting as carriers of electrons, atoms, or chemical groups. Examples: **NAD⁺, FAD, Coenzyme A** (many are derived from vitamins, e.g., Vitamin B complex). ### (iv) Heterogamic Sex This refers to the sex that produces **two different types of gametes** — one carrying the X chromosome and one carrying the Y chromosome. In humans and most mammals, the **male (XY)** is the heterogamic sex. In birds and some insects, the **female** is the heterogamic sex. ## QUESTION 1(b) — Genetics Cross **Given:** - Uniform colour (C) is dominant over spotted (c) - Black colour (B) is dominant over white (b) - Pure breed black bull = **BBCC** - White spotted cow = **bbcc** ### (i) Punnet Diagram — F₁ Generation **Parents:** - Black bull: BBCC → gametes: **BC** - White spotted cow: bbcc → gametes: **bc** | | BC | ||| | **bc** | BbCc | **All F₁ offspring = BbCc** ### (ii) Phenotype of F₁ Calves Since B is dominant over b, and C is dominant over c: - All calves are **BbCc** - **Phenotype = Black and Uniform coloured** - All 100% of F₁ calves are **Black Uniform** ### (iii) F₁ × F₁ Cross (BbCc × BbCc) **Gametes of BbCc:** BC, Bc, bC, bc **Punnet Square (4×4):** | | **BC** | **Bc** | **bC** | **bc** | |||||| | **BC** | BBCC | BBCc | BbCC | BbCc | | **Bc** | BBCc | BBcc | BbCc | Bbcc | | **bC** | BbCC | BbCc | bbCC | bbCc | | **bc** | BbCc | Bbcc | bbCc | bbcc | **Phenotype Ratio:** | Phenotype | Genotypes | Number | Ratio | ||||| | Black Uniform | B_C_ | 9 | 9 | | Black Spotted | B_cc | 3 | 3 | | White Uniform | bbC_ | 3 | 3 | | White Spotted | bbcc | 1 | 1 | **Ratio = 9 Black Uniform : 3 Black Spotted : 3 White Uniform : 1 White Spotted** ### (iv) New Combinations from the Cross The **parental combinations** were: Black Uniform (BBCC) and White Spotted (bbcc). The **new combinations** that have arisen are: 1. **Black Spotted** (B_cc) — new combination 2. **White Uniform** (bbC_) — new combination These are recombinants that did not exist in the original parents. ## QUESTION 1(c) — Fill in the Blanks **(i)** A nucleotide has **phosphate group**, **pentose sugar** and **nitrogenous base** components. **(ii)** Sucrose is digested to **glucose** and **fructose** **(iii)** The "bleeders' disease" is known as **Haemophilia** **(v)** A condition in which a gene fails to express itself in the presence of a dominant allele is **epistasis** *(or recessive epistasis / recessiveness)* **(vi)** The scientific name of the giant African land Snail is ***Achatina achatina*** **(vii)** Urine is approximately **95% water**, **2% urea**, **1% sodium chloride** and other smaller amounts of nitrogenous compounds and mineral salts. ## QUESTION 2 — Four Adaptations of Vertebrate Taxa ### (i) Proboscidea (Elephants) 1. **Elongated trunk (proboscis):** A highly muscular and flexible fusion of the nose and upper lip used for grasping food, drinking water, and social interaction. 2. **Large, pillar-like legs:** Support the enormous body weight; bones are dense and nearly vertical. 3. **Large, fan-shaped ears:** Richly supplied with blood vessels; used for thermoregulation — flapping cools the blood. 4. **Tusks (modified upper incisors):** Used for digging for water, stripping bark, and defense against predators. ### (ii) Pythonidae (Pythons) 1. **Highly flexible, ligament-joined jaws:** Allow them to swallow prey much larger than their head diameter. 2. **Vestigial pelvic girdle and hind limb remnants (pelvic spurs):** Evidence of evolutionary origin from limbed ancestors. 3. **Heat-sensitive pit organs (labial pits):** Detect infrared radiation from warm-blooded prey in darkness. 4. **Muscular, scale-covered body:** Allows constriction of prey to cause suffocation; scales reduce water loss and provide grip for movement. ### (iii) Chamaeleonidae (Chameleons) 1. **Zygodactyl feet (toes fused in opposing groups):** Allow firm gripping of branches for arboreal (tree-dwelling) life. 2. **Chromatophore-containing skin:** Allows rapid **colour change** for camouflage, communication, and thermoregulation. 3. **Long, projectile tongue:** Can shoot out to 1.5× body length to capture insects with a sticky tip. 4. **Independently mobile eyes:** Each eye can rotate and focus independently, giving near 360° vision without moving the head. ### (iv) Chiroptera (Bats) 1. **Modified forelimbs (wings):** Elongated finger bones support a thin membrane (patagium) for flight — the only mammals capable of true, sustained flight. 2. **Echolocation (biosonar):** Emit high-frequency ultrasonic sounds and interpret the returning echoes to navigate and locate prey in darkness. 3. **Roosting posture (hanging upside down):** Tendons lock in place with body weight, requiring no muscle energy; facilitates quick take-off. 4. **Nocturnal adaptations:** Large eyes or well-developed auditory systems; reduced body temperature during day (torpor) conserves energy. ## QUESTION 3 ### (a) Fifteen (15) Characteristics of Phylum Arthropoda 1. **Segmented body** divided into distinct regions (head, thorax, abdomen). 2. **Bilaterally symmetrical** body plan. 3. **Exoskeleton** made of **chitin** that provides protection and support. 4. **Periodic moulting (ecdysis):** Shedding of exoskeleton to allow growth. 5. **Jointed appendages** (the name "Arthropoda" means jointed legs) used for locomotion, feeding, and sensory functions. 6. **Triploblastic** — three germ layers (ectoderm, mesoderm, endoderm). 7. **Coelomate** — possess a true body cavity (coelom), though reduced. 8. **Open circulatory system** with a dorsal heart and haemocoel. 9. **Ventral nerve cord** with a dorsal brain (cerebral ganglia). 10. **Compound eyes** and simple eyes (ocelli) for vision. 11. **Specialized mouthparts** adapted for different feeding methods. 12. **Respiration** varies: by gills (crustaceans), tracheae (insects), book lungs (arachnids). 13. **Excretion** by Malpighian tubules (insects) or green glands (crustaceans). 14. **Separate sexes (dioecious)**; mostly sexual reproduction; some parthenogenesis. 15. **Well-developed sensory organs** — antennae, statocysts, proprioceptors. ### (b) Five (5) Economic Importance of Protozoa 1. **Disease causation:** Protozoa cause serious diseases — *Plasmodium* causes **malaria**, *Trypanosoma* causes **sleeping sickness**, *Entamoeba* causes **amoebic dysentery** — leading to economic losses through medical costs and reduced productivity. 2. **Soil fertility:** Free-living soil protozoa feed on bacteria, regulating bacterial populations and releasing nutrients (especially nitrogen), thus improving **soil fertility**. 3. **Food chain:** Protozoa (especially ciliates and flagellates) form a vital part of **aquatic food chains** as primary consumers of bacteria and algae, supporting fish and other organisms. 4. **Indicator organisms:** Certain protozoa serve as **bioindicators** of water quality and pollution levels in environmental monitoring. 5. **Research and medicine:** Protozoa are used as **model organisms** in cell biology and genetic research; study of their biochemistry has aided development of antiparasitic drugs. ## QUESTION 4 ### (a) Diagram — Lateral View of a Bony Fish *(A clearly labeled 8–9cm diagram should be drawn in your answer booklet showing the following structures):*

           Dorsal fin
              |||
    ___________|||__________
   /    Lateral line        \___
  |  o (eye)  Operculum      ===\__  Caudal fin
  |    Mouth                 ===/__
   \__________________________===
        Pectoral  Pelvic  Anal
         fin       fin    fin

**Label the following:** - Mouth - Eye - Operculum (gill cover) - Lateral line - Dorsal fin - Pectoral fin - Pelvic fin - Anal fin - Caudal fin (tail fin) - Scales - Nostril ### (b) Adaptations of a Bony Fish for Efficient Movement in Water 1. **Streamlined (fusiform) body shape:** Reduces water resistance (drag) as the fish moves forward. 2. **Fins:** Dorsal and anal fins provide stability; pectoral and pelvic fins control steering, braking, and vertical movement; caudal fin provides propulsive thrust. 3. **Scales covered with mucus:** Smooth, overlapping scales with a mucous coating reduce friction with water. 4. **Swim bladder (gas bladder):** A gas-filled organ that regulates buoyancy, allowing the fish to remain at any depth without expending energy. 5. **Lateral line system:** Detects pressure changes and water currents, aiding orientation and navigation. 6. **Powerful trunk and tail muscles (myotomes):** Arranged in W-shaped blocks; generate undulating body movements that propel the fish forward. 7. **Flexible vertebral column:** Allows side-to-side body undulation needed for swimming. ## QUESTION 5 — Short Notes on Any Four (4) ### (a) Osmoregulation This is the **physiological process** by which organisms regulate the concentration of water and dissolved solutes in their body fluids to maintain **homeostasis** (internal balance). In humans, it is carried out mainly by the **kidneys**, which filter blood and produce urine of variable concentration depending on the body's water status. The **hypothalamus** monitors blood osmotic pressure and triggers the release of **ADH (antidiuretic hormone)** from the posterior pituitary to increase water reabsorption in the collecting ducts of the kidney when the body is dehydrated. ### (b) Short-sightedness (Myopia) This is a **defect of vision** in which a person can see **near objects clearly but distant objects appear blurred**. It occurs when the eyeball is **too long** or the cornea/lens is too curved, causing light rays from distant objects to converge (focus) **in front of the retina** instead of directly on it. It is corrected using a **concave (diverging) lens**, which diverges light rays before they enter the eye, pushing the focal point back onto the retina. ### (c) Involuntary/Reflex Action This is a **rapid, automatic, and unconscious response** to a stimulus that does not involve the brain directly. It is coordinated through the **spinal cord** via a **reflex arc**. The pathway is: **Receptor → Sensory neuron → Relay neuron (in spinal cord) → Motor neuron → Effector (muscle/gland)** Examples: knee-jerk reflex, withdrawal of hand from a hot object, blinking, salivation. Reflex actions protect the body from harm and allow quick responses without the delay of conscious thought. ### (d) Economic Importance of Phylum Annelida 1. **Soil aeration and fertility:** Earthworms (*Lumbricus*) burrow through soil, improving aeration, drainage, and mixing of organic matter — increasing agricultural productivity. 2. **Food:** Some polychaete worms and earthworms are used as **food** by humans in some cultures and as **fish bait** by anglers. 3. **Indicators of soil health:** Earthworm population density is used as a **bioindicator** of soil quality and health. 4. **Medicine:** Leeches (*Hirudo medicinalis*) are used in **hirudotherapy** — their saliva contains **hirudin** (an anticoagulant) used in microsurgery to restore blood flow to reattached body parts. 5. **Ecological role:** Annelids form part of **food chains** as prey for birds, fish, and other animals. ### (e) Gene Pool This is the **total collection of all alleles** (all forms of all genes) present in a **breeding population** at a given time. It represents the entire genetic diversity available to a population. A **large gene pool** indicates high genetic diversity, making the population more adaptable to environmental changes and less susceptible to extinction. A **small gene pool** (as in inbreeding) leads to reduced genetic variation, increased expression of recessive disorders, and greater risk of extinction. ## QUESTION 6 ### (a) Six (6) Primary Functions of the Liver 1. **Bile production:** Produces **bile** (stored in the gallbladder), which emulsifies fats in the small intestine to aid digestion and absorption. 2. **Detoxification:** Breaks down and neutralizes **toxic substances** such as alcohol, drugs, ammonia, and other metabolic waste products. 3. **Deamination:** Removes the amino group (–NH₂) from excess amino acids, converting it to **ammonia**, then to **urea** (via ornithine cycle), which is excreted by the kidneys. 4. **Glycogen storage and regulation:** Converts excess glucose to **glycogen** for storage (glycogenesis) and breaks it down back to glucose (glycogenolysis) when blood sugar is low — maintaining blood glucose homeostasis. 5. **Plasma protein synthesis:** Synthesizes important blood proteins including **albumin**, **fibrinogen** (clotting), and **globulins**. 6. **Thermoregulation:** The liver is highly metabolically active and generates a large amount of **heat** as a by-product of metabolism, helping to maintain body temperature. *(Other functions: fat metabolism, storage of vitamins A/D/B₁₂, iron storage, red blood cell destruction)* ### (b) Notes on Circulation Types #### i. Closed Circulation This is a type of circulatory system in which **blood is enclosed and flows entirely within blood vessels** (arteries, veins, capillaries) throughout its circuit and **never directly bathes the tissues**. Exchange of materials between blood and tissues occurs through the thin walls of **capillaries** by diffusion. It allows **higher blood pressure**, faster and more efficient delivery of oxygen and nutrients. It is found in **annelids, echinoderms, vertebrates** (fish, amphibians, reptiles, birds, mammals). Example: **Human circulatory system** — blood flows: Heart → Arteries → Capillaries → Veins → Heart. #### ii. Open Circulation This is a type of circulatory system in which **blood (haemolymph) is not always enclosed in vessels** but flows out of the vessels into open body cavities called **haemocoels**, directly bathing the organs and tissues. The heart pumps haemolymph into arteries, which open into the haemocoel; it then slowly returns to the heart through **ostia** (pores). It operates at **lower pressure** and is **less efficient** than closed circulation. It is found in **most arthropods and most molluscs**. Example: **Cockroach (*Periplaneta americana*)** — haemolymph flows: Tubular heart → Arteries → Haemocoel (bathes organs) → Ostia → Heart.