**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.