MITIHANI POPOTE EXAMINATION SERIES FORM FOUR BIOLOGY EXAMINATION SERIES 2 (With Marking Scheme)

MITIHANI POPOTE EXAMINATIONS SERIES

FORM FOUR BIOLOGY EXAMINATION SERIES 2

Time: 3 Hours

Instructions:

• Answer all questions in Sections A and B.
• Answer two (2) questions from Section C.
• Write your answers clearly and neatly.

SECTION A (16 Marks)

1. Multiple Choice Questions (10 Marks)

Choose the correct answer for each of the following questions:

(i) Which of the following classes belongs to Phylum Platyhelminthes?
a) Insecta
b) Turbellaria
c) Gastropoda
d) Arachnida

(ii) In genetics, a test cross is used to:
a) Determine the genotype of an individual with a dominant phenotype
b) Identify mutations in DNA
c) Cross two homozygous individuals
d) Determine the number of chromosomes

(iii) The presence of vestigial structures in organisms is evidence for:
a) Artificial selection
b) Convergent evolution
c) Common ancestry
d) Genetic drift

(iv) HIV is classified as a:
a) DNA virus
b) Retrovirus
c) Bacteriophage
d) Prion

(v) Which of the following is an opportunistic infection commonly associated with AIDS?
a) Tuberculosis
b) Influenza
c) Chickenpox
d) Measles

(vi) PLWHA refers to:
a) People Living With Health Awareness
b) Patients Living With Hepatitis A
c) People Living With HIV/AIDS
d) Persons Leading With High Ambition

(vii) Which plant hormone is primarily responsible for cell elongation?
a) Cytokinin
b) Gibberellin
c) Auxin
d) Ethylene

(viii) In Phylum Arthropoda, the class Insecta is characterized by:
a) Two pairs of antennae
b) Three pairs of legs
c) Unsegmented bodies
d) Absence of exoskeleton

(ix) A monohybrid cross between two heterozygous individuals (Aa x Aa) will produce offspring with a genotypic ratio of:
a) 1:2:1
b) 3:1
c) 1:1
d) 2:1

(x) The theory of natural selection was proposed by:
a) Gregor Mendel
b) Jean-Baptiste Lamarck
c) Charles Darwin
d) Louis Pasteur

2. Matching Items (6 Marks)

Match the items in List A with the correct responses in List B:

List A

(i) Fossils

(ii) Comparative anatomy

(iii) Embryology

(iv) Vestigial structures

(v) Molecular biology

(vi) Comparative physiology

List B

A. Presence of similar enzymes and hormones in related species

B. Study of body structures showing common ancestry

C. Preserved remains of ancient organisms in rocks

D. Study of early developmental stages showing similarity among vertebrates

E. DNA and protein sequence similarities between organisms

F. Organs like human appendix with reduced or no function

SECTION B (54 Marks)

3.

a) Describe three distinguishing characteristics of Phylum Arthropoda. (3 marks)

b) Classify the following organisms into their respective classes under Phylum Arthropoda:
i) Housefly
ii) Crab
iii) Spider
iv) Centipede (4 marks)

c) Explain the economic importance of any two classes under Phylum Arthropoda. (3 marks)

4.

a) Define the following genetic terms:
i) Allele
ii) Genotype
iii) Phenotype (3 marks)

b) In a certain plant species, tall stem (T) is dominant over short stem (t). A cross between two heterozygous tall plants is made.
i) What are the possible genotypes and phenotypes of the offspring?
ii) Calculate the phenotypic ratio of the offspring. (7 marks)

5.

a) Explain the concept of adaptive radiation and provide one example. (4 marks)

b) Differentiate between convergent and divergent evolution, giving one example for each. (6 marks)

6.

a) Explain the stages of HIV. (5 marks)

b) Discuss how the destruction of T-helper cells by HIV leads to the development of AIDS. (4 marks)

7.

a) Define opportunistic infections and explain why they are common in individuals with AIDS. (4 marks)

b) List and describe three common opportunistic infections associated with AIDS. (5 marks)

8.

a) Describe the phases of human growth from infancy to adulthood. (5 marks)

b) Explain two internal and two external factors that influence human growth. (4 marks)

SECTION C (30 Marks)

Answer two (2) questions from this section.

9.

Discuss the significance of biological classification, focusing on the criteria used to classify organisms into Kingdom Animalia. Include examples to illustrate your points. (15 marks)

10.

Explain the principles of Mendelian inheritance and how they apply to dihybrid crosses. Use appropriate examples to support your explanation. (15 marks)

11.

What are the seven ways in which you can care for PLWHA. (15 marks)

FORM FOUR BIOLOGY EXAMINATION ANSWERS

SERIES 2

SECTION A ANSWERS (16 Marks)

1. Multiple Choice Answers

1. b) Turbellaria
2. a) Determine the genotype of an individual with a dominant phenotype
3. c) Common ancestry
4. b) Retrovirus
5. a) Tuberculosis
6. c) People Living With HIV/AIDS
7. c) Auxin
8. b) Three pairs of legs
9. a) 1:2:1
10. c) Charles Darwin

2. Matching Items Answers

List A	List B
Fossils	C. Preserved remains of ancient organisms in rocks
Comparative anatomy	B. Study of body structures showing common ancestry
Embryology	D. Study of early developmental stages showing similarity among vertebrates
Vestigial structures	F. Organs like human appendix with reduced or no function
Molecular biology	E. DNA and protein sequence similarities between organisms
Comparative physiology	A. Presence of similar enzymes and hormones in related species

SECTION B ANSWERS (54 Marks)

3a. Distinguishing characteristics of Phylum Arthropoda

1. Jointed appendages
2. Segmented body
3. Chitinous exoskeleton

3b. Classification of organisms

1. Housefly - Class Insecta
2. Crab - Class Crustacea
3. Spider - Class Arachnida
4. Centipede - Class Chilopoda

3c. Economic importance of Arthropoda classes

Class Insecta:

• Pollination of crops (bees)
• Pest control (ladybugs)
• Silk production (silkworms)

Class Crustacea:

• Food source (crabs, lobsters)
• Aquatic ecosystem balance

4a. Genetic terms definitions

1. Allele: Alternative forms of a gene
2. Genotype: Genetic makeup of an organism
3. Phenotype: Observable characteristics

4b. Genetic cross analysis

Cross: Tt × Tt

Possible genotypes: TT, Tt, tt

Possible phenotypes: Tall, short

Phenotypic ratio: 3 tall : 1 short

5a. Adaptive radiation

Adaptive radiation is the rapid evolution of many species from a single ancestor to fill different ecological niches.

Example: Darwin's finches in Galapagos Islands

5b. Convergent vs divergent evolution

Convergent evolution: Unrelated species evolve similar traits (e.g., wings in bats and birds)

Divergent evolution: Related species evolve different traits (e.g., forelimbs of mammals)

6a. Stages of HIV

1. Primary/acute infection (flu-like symptoms)
2. Clinical latency (asymptomatic)
3. Symptomatic HIV infection
4. AIDS (CD4 count < 200 cells/mm³)

6b. T-helper cell destruction and AIDS

HIV destroys CD4+ T-helper cells, weakening the immune system until it can no longer fight infections, leading to AIDS.

7a. Opportunistic infections

Infections that occur more frequently and severely in immunocompromised individuals like PLWHA due to weakened immune systems.

7b. Common opportunistic infections

1. Tuberculosis: Bacterial lung infection
2. Pneumocystis pneumonia: Fungal lung infection
3. Candidiasis: Fungal infection of mouth/throat

8a. Phases of human growth

1. Infancy (0-2 years) - Rapid growth
2. Childhood (2-12) - Steady growth
3. Adolescence (12-18) - Puberty changes
4. Adulthood (18+) - Growth plateaus

8b. Growth influencing factors

Internal:

• Hormones (growth hormone)
• Genetics

External:

• Nutrition
• Disease/illness

SECTION C ANSWERS (30 Marks)

9. Biological classification significance

Significance:

• Organizes biodiversity
• Shows evolutionary relationships
• Facilitates scientific communication

Animalia classification criteria:

1. Body symmetry (radial/bilateral)
2. Germ layers (diploblastic/triploblastic)
3. Body cavity (acoelomate/pseudocoelomate/coelomate)
4. Segmentation
5. Example: Phylum Chordata (vertebrates)

10. Mendelian inheritance principles

Principles:

1. Law of Segregation (allele pairs separate during gamete formation)
2. Law of Independent Assortment (genes for different traits assort independently)

Dihybrid cross example: 9:3:3:1 ratio in F2 generation when crossing double heterozygotes (RrYy × RrYy)

11. Caring for PLWHA

1. Provide emotional support and reduce stigma
2. Ensure medication adherence (ARVs)
3. Maintain proper nutrition
4. Practice good hygiene to prevent infections
5. Encourage regular medical check-ups
6. Offer spiritual/psychological counseling
7. Educate about prevention of transmission