NECTA BIOLOGY 1 2025 SOLUTION

NECTA Form 4 Biology 2025

Suggested Solutions & Answers

SECTION A (16 Marks)

1. Multiple Choice Questions

(i) Answer: B (Problem identification)
Reasoning: Observing a decrease in yield is the first step of the scientific method where the farmers identify that a problem exists.

(ii) Answer: D (Zebra and giraffe)
Reasoning: Primary consumers are herbivores that feed directly on producers (plants). Zebras and Giraffes eat grasses and shrubs. Lions and Cheetahs are secondary consumers (carnivores).

(iii) Answer: A (Yeasts)
Reasoning: Yeast carries out fermentation (anaerobic respiration) breaking down sugar into alcohol and carbon dioxide. The carbon dioxide gas bubbles get trapped in the dough, causing it to rise.

(iv) Answer: E (Ectopic pregnancy)
Reasoning: An ectopic pregnancy occurs when the fertilized egg (embryo) implants outside the uterus, most commonly in the fallopian tubes.

(v) Answer: B (Vasoconstriction of arterioles)
Reasoning: In response to cold, blood vessels (arterioles) near the skin surface constrict (narrow) to reduce blood flow to the skin, thereby minimizing heat loss.

(vi) Answer: D (AIDS and COVID - 19)
Reasoning: Both AIDS and COVID-19 are pandemics, meaning they have spread across multiple continents or worldwide. Malaria and Bilharzia are typically endemic to specific regions.

(vii) Answer: C (Wipe the floor immediately)
Reasoning: To prevent accidents like slipping and falling, the safety protocol is to remove the hazard (water spill) immediately.

(viii) Answer: B (Tendon)
Reasoning: A typical movable joint consists of bones, cartilage, ligaments, and synovial fluid. Tendons connect muscle to bone and are part of the muscular system's attachment mechanism, not the joint capsule itself.

(ix) Answer: C (Colour blindness and haemophilia)
Reasoning: These are sex-linked traits controlled by genes located on the X-chromosome. Tongue rolling and blood groups are controlled by autosomal genes.

(x) Answer: A (Lizard, crocodile, turtle and snake)
Reasoning: All organisms in this list belong to the Class Reptilia (they have dry scaly skin and are cold-blooded).

2. Matching Items (Hormones)

  • (i) D (Oxytocin): Controls contraction of uterine walls during birth.
  • (ii) F (Insulin): Promotes conversion of excess glucose into glycogen in the blood.
  • (iii) A (Antidiuretic): Regulates amount of water reabsorption in the kidney tubules.
  • (iv) H (Prolactin): Stimulates milk production in lactating mammals.
  • (v) B (Thyroxine): Controls metabolic activities in the body.
  • (vi) G (Oestrogen): Promotes development of secondary sexual characteristics in females.

SECTION B (54 Marks)

3. Traditional Food Preservation

Advantages of traditional methods (e.g., sun-drying, smoking, salting):

  • Prevents Spoilage: Inhibits the growth of bacteria and fungi.
  • Reduces Wastage: Excess harvest can be kept for future use.
  • Food Security: Ensures food availability during seasons of scarcity (droughts/dry season).
  • Cost-Effective: Uses locally available natural resources (sun, smoke) rather than expensive electricity.
  • Ease of Transport: Dried/processed foods are often lighter and less bulky.
  • Flavor Enhancement: Methods like smoking add a distinct, desirable flavor to the food.

4. Mitosis (Prophase Stage)

Events during Prophase:

  • Chromatin Condensation: The thread-like chromatin shortens and thickens to form visible chromosomes.
  • Sister Chromatids: Each chromosome appears as two identical sister chromatids joined at a centromere.
  • Nuclear Disassembly: The nucleolus disappears and the nuclear membrane begins to break down.
  • Spindle Formation: In animal cells, centrioles move to opposite poles and spindle fibers begin to form.
[Image of prophase stage of mitosis]

5. Adaptations of Cardiac Muscles

Structural & Functional Adaptations:

  • Myogenic Nature: Capable of contracting and relaxing rhythmically without external nervous stimulation.
  • Intercalated Discs: These junctions allow electrical impulses to spread rapidly from cell to cell, allowing the heart to beat as a unit.
  • Numerous Mitochondria: Provide a high supply of energy (ATP) to sustain continuous beating.
  • Non-fatiguable: Adapted to work continuously throughout a lifetime without getting tired.
  • Branched Fibers: Ensure a strong, 3-dimensional contraction network.
  • Rich Blood Supply: Ensures constant delivery of oxygen and nutrients.

6. Asexual Reproduction (Bacteria/Amoeba)

Merits:

  • Rapid Multiplication: Populations can grow very quickly in favorable conditions.
  • Single Parent: No need to find a mate, saving energy and time.
  • Certainty: If the parent is well-adapted, offspring are identical clones and will also be well-adapted.

Demerits:

  • No Genetic Variation: Offspring are identical, making the population vulnerable to changing environments.
  • Disease Susceptibility: If one organism is susceptible to a disease, the entire population is at risk.
  • Overcrowding: Rapid growth can lead to competition for resources.

7. Genetic Cross (Blood Groups)

Parents: Male (Heterozygous Group A) x Female (Heterozygous Group B)

Genotypes: IAIO x IBIO

Gametes: (IA), (IO) and (IB), (IO)

Punnett Square Analysis:

IB IO
IA IAIB (AB) IAIO (A)
IO IBIO (B) IOIO (O)

Conclusion: The probability of producing a child with Blood Group O (IOIO) is 1/4 or 25%.

8. Evidence for Organic Evolution

(a) Fossil Records:

  • Missing Links: Fossils like Archaeopteryx show characteristics of both reptiles and birds, proving common ancestry.
  • Chronological Sequence: Fossils in deeper rock layers are simpler, while those in upper layers are more complex, showing change over time.
  • Evolutionary Lineages: Complete fossil series (e.g., of the horse) show gradual structural changes.

(b) Comparative Embryology:

  • Similarity in Early Stages: Vertebrate embryos (fish, bird, human) look very similar in early development (e.g., all have gill slits and tails).
  • Common Ancestry: These similarities suggest that all vertebrates descended from a common aquatic ancestor.
  • Recapitulation: Development of the embryo often mirrors the evolutionary history of the species.

SECTION C (30 Marks)

9. Fighting Drug Abuse

Preventive and Control Measures:

  1. Education/Awareness Campaigns: Teach youth about the severe physical and mental health consequences of drugs.
  2. Law Enforcement: Strict implementation of laws against drug trafficking and supply.
  3. Guidance and Counseling: Establish centers in schools and communities to help at-risk youth.
  4. Positive Peer Groups: Encourage youth to associate with friends who value healthy, drug-free lifestyles.
  5. Recreational Activities: Promote sports, arts, and clubs to keep youth occupied and reduce idleness.
  6. Parental Involvement: Parents should monitor their children's behavior and maintain open communication lines.

10. Gonorrhoea Prevention

Transmission: Sexual intercourse with an infected person; From mother to baby during birth.

Preventive Measures:

  1. Abstinence: Avoiding sexual intercourse is the most effective way to prevent transmission.
  2. Faithfulness: Sticking to one uninfected sexual partner.
  3. Safe Sex: Correct and consistent use of condoms during sexual intercourse.
  4. Early Treatment: Seeking medical attention immediately if symptoms appear to prevent spreading it to others.
  5. Contact Tracing: Informing sexual partners so they can also get tested and treated.

11. Factors Affecting Transpiration

Environmental Factors:

  1. Temperature: Higher temperatures increase the rate of evaporation of water from mesophyll cells, increasing transpiration.
  2. Humidity: High humidity reduces the concentration gradient of water vapor between the leaf and the air, reducing transpiration.
  3. Wind Speed: Wind blows away saturated air around the leaf, maintaining a steep gradient and increasing transpiration.
  4. Light Intensity: Bright light causes stomata to open for photosynthesis, which increases water loss via transpiration.
  5. Soil Water Availability: If soil water is low, plants close their stomata to conserve water, significantly reducing transpiration.

Disclaimer: These solutions are suggested for educational revision.

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