Gobezoch › Past exams › Biology
Grade 12 Biology national exam, 2012 E.C. (2020 G.C.)
30 questions · 120 minutes. The first 5 answers are shown with explanations; sit the whole paper timed in the app to get your score and the textbook page behind every question.
- 1.Which of the following viruses is a RNA virus?
- A. Herpes simplex
- B. H_(1)N_(1)
- C. Bacteriophage
- D. HIV
Answer: B. H1N1 is a strain of the influenza virus, and influenza viruses carry their genetic information as RNA. Herpes simplex is a DNA virus, and the well studied bacteriophages such as the T-even phages also carry DNA. HIV also holds RNA, but it is usually placed in its own group, the retroviruses, because it first copies its RNA into DNA inside the host cell. That is why H1N1 is the expected answer here. Textbook: Biology Grade 12, Unit 2 Microorganisms, section 2.5.3 Classification of Viruses (page 84). Textbook: Grade 12, unit 2 · section 2.5.3. - 2.Which one of the following statements is true regarding the need for recycling nutrients through an ecosystem?
- A. It depletes the resources hence infinite resources become limited By process
- B. It pollutes the environment hence waste products are accumulated During the process
- C. It is energy consuming process hence nutrients are constantly Created and destroyed
- D. It is the key to saving the earth hence nutrients become available
Answer: D. The earth holds a fixed amount of matter. Carbon, nitrogen and other nutrients must be used again and again, so decomposers break down dead bodies and wastes and return the nutrients to the soil, water and air. This keeps nutrients available for new life, which is why recycling matters for the whole planet. Options A, B and C all describe recycling as harmful or wasteful, which is the opposite of its real role. Energy flows one way through an ecosystem, but matter cycles. Textbook: Grade 10, unit 6 · section 6.2. - 3.What is the impact of humans on the sulphur cycle? Production of
- A. Sulphur dioxide through combustion of fossil fuels
- B. Sulphate through weathering and oxidation of rocks
- C. Hydrogen sulphide through oxidation of sulphur
- D. Sulphur through decomposition of dead matter
Answer: A. Human activities affect the sulphur cycle by adding sulphur compounds to the environment. Burning fossil fuels produces sulphur dioxide, $\text{SO}_2$, so A describes a human impact. B is wrong because weathering and oxidation of rocks are natural processes. C is wrong because oxidation of sulphur does not produce hydrogen sulphide, $\text{H}_2\text{S}$. D is wrong because decomposition of dead matter is a natural process, not the human impact asked for. Textbook: Grade 10, unit 6 · section 6.2.2. - 4.As succession progresses, the bare land turns out to be productive Due to the fact that the
- A. environment becomes less stable
- B. abiotic conditions remain unchanged
- C. species diversity and richness falls
- D. amount and depth of the soil increases
Answer: D. The key idea is that succession can make bare land more productive over time. As organisms grow and die, soil builds up and becomes deeper, supporting more plant growth. A is wrong because increasing instability does not explain greater productivity; B is wrong because conditions change during succession; C is wrong because species diversity generally increases rather than falls. Textbook: Grade 10, unit 6 · section 6.2. - 5.What is the economic impact of AIDS?
- A. Enhance of life expectancy and GDP
- B. Increase the resources of public expenditure
- C. Seriously affects the taxable population
- D. Encourage savings for medical treatment
Answer: C. The key idea is that AIDS can harm the economy by affecting people who work and pay taxes. When illness or death reduces the working population, fewer people may contribute tax revenue. A is wrong because AIDS does not enhance life expectancy or gross domestic product; B is wrong because it states an increase in public resources rather than a harmful impact; D is wrong because encouraging savings is not the economic impact described. Textbook: Grade 11, unit 6 · section 6.1.3. - 6.A geographical area with specific climate, soil type, plants and animals with similar adaptation is
- A. habitat
- B. ecosystem
- C. niche
- D. biome
Answer, explanation and textbook page: open in the app. - 7.As energy from the sun, enters the ecosystem in the form of light, one of the following happens to it. It
- A. goes on increasing along the tropic level from primary produces to decomposers
- B. remains much of the time the same but increases as it reaches decomposers
- C. goes on decreasing along the tropic level from primary producers to decomposers
- D. depends on the type of tropic level and changes at each tropic level irregularly
Answer, explanation and textbook page: open in the app. - 8.Suppose a self fertilizing organism has AaBb genotype, how many different types of gametes would it produce if there is no linkage?
- A. 16
- B. 8
- C. 12
- D. 4
Answer, explanation and textbook page: open in the app. - 9.What is the chemical composition of bacterial cell wall?
- A. starch
- B. capsule
- C. Cellulose
- D. Peptidoglycan
Answer, explanation and textbook page: open in the app. - 10.In this biology section, a biology student applied a Gram stain two groups of bacteria named X and Y. At the end, he observed that the bacteria X stained purple while bacteria Y stained pink, which of the following could be the correct conclusion of his experiment? Bacteria
- A. X and Y are both Gram negative
- B. Y are Gram positive and X are Gram negative
- C. X are Gram positive and Y are Gram negative
- D. Y and X are both Gram positive
Answer, explanation and textbook page: open in the app. - 11.As compared to infections diseases, functional diseases
- A. can spread through the bite of insects
- B. are passed from person to person through reservoirs
- C. are Caused by pathogenic microorganisms
- D. can result from malfunction of organs
Answer, explanation and textbook page: open in the app. - 12.Which of the following products does NOT need the role of bacteria?
- A. Enzymes
- B. Insulin
- C. Ethanol
- D. Vaccine
Answer, explanation and textbook page: open in the app. - 13.Bacteria are used in the production of vinegar to
- A. dilute ethanoic acid in to vinegar
- B. produce alcohol in beer
- C. supply oxygen for the fermenter
- D. oxidise alcohol to ethanoic acid
Answer, explanation and textbook page: open in the app. - 14.Among the parts of the cell, which organelles are bounded with Double membrane?
- A. Vacoule, endoplasmic reticulum, and ribosome
- B. Gogibody, chloroplast and lysosome
- C. Lysosome, Vacoule and nucleus
- D. Nucleus, mitochondria and chloroplast
Answer, explanation and textbook page: open in the app. - 15.Why are cells that secrete hormones and enzymes rich in rough endoplasmic reticulum? Because they produce more:
- A. Carbohydrates
- B. Lipids
- C. Proteins
- D. ATP
Answer, explanation and textbook page: open in the app. - 16.What is the role of cholesterol in the cell membrane?
- A. maintain the membrane fluidity
- B. anchor integral proteins with the membrane
- C. serve as signals to other membrane of cells
- D. make the membrane selectively permeable
Answer, explanation and textbook page: open in the app. - 17.If potato cells are immersed in a hypertonic solution, they will
- A. gain water and haemolysed
- B. lose water and plasmolysed
- C. gain water and become larger
- D. lose water and become turgid
Answer, explanation and textbook page: open in the app. - 18.Which molecule of the plasma membrane contains carbohydrate Chains and allows identification of the cell by the immune system?
- A. Peripheral proteins
- B. Integral proteins
- C. Glyco proteins
- D. Channel proteins
Answer, explanation and textbook page: open in the app. - 19.Red - green colour blindness is due to X-Iinked gene and determined By the recessive alleles. Which one of the following is true about this Condition?
- A. Expressed in both sexes equally if the parents arel carriers
- B. Female inherit one sexes allele from each parent and become Affected
- C. It affects males due alleles inherited from the father
- D. It is much more common in females
Answer, explanation and textbook page: open in the app. - 20.Which one of the following statements is true about chromosome? It Is
- A. made up of DNA which is tightly coiled many times around histones
- B. clearly visible in the nucleus when the cell is not dividing
- C. divided in two equal sections by the centromere
- D. Loosely organized throughout the nucleus when the cell is dividing
Answer, explanation and textbook page: open in the app. - 21.24.Consider the following disordered events of transcription l. RNA polymerase crosses a stop sequence in the geme II. RNA polymerase reads the antisense DNA strand and builds mRNA Ill.mRNA molecule detaches from DNA and the DNA rejoin IV.RNA polymerase binds to the promoter which signals the DNA To unwind Which one is the correct sequence of events during transcription?
- A. I -> IV -> III
- B. IV -> I -> II -> III
- C. IV -> II -> I -> III
- D. I -> IV -> III -> II
Answer, explanation and textbook page: open in the app. - 22.Which of the following bases are the triplets of codes in the mRNA That cease translation and the ribosome folds the polypeptide into its Final structure?
- A. UAA, UAG and UGA
- B. TAA, TAG and TGA
- C. ATT, ATCandACT
- D. CCC, UUA and GUU
Answer, explanation and textbook page: open in the app. - 23.By which level of precipitation, temperature and type of plants is the Tagia biome characterized, respectively
- A. Almost none, cold and succulents
- B. Adequate, cool year round and conifers
- C. Humid, days warm, and ferns
- D. Dry, cold and lichens
Answer, explanation and textbook page: open in the app. - 24.In which biome are epiphytes common?
- A. Tundra forest
- B. Tropical rainforest
- C. Temperature forest
- D. Thorn forest
Answer, explanation and textbook page: open in the app. - 25.What makes Ethiopia rich in biodiversity which deserves a global attention?
- A. Uniformity of high lands and low lands
- B. Similar terrestrial and aquatic biomes
- C. Variation in topography and vegetation
- D. Narrow range in altitude and climate
Answer, explanation and textbook page: open in the app. - 26.Why maintaining habitats is the key and fundamental aspect to conserve biodiversity? Because
- A. preserving habitats leads to decreased species richness and abundance
- B. replacing natural habitats by artificial ones increases food security
- C. disturbance of habitats makes the population well adapted
- D. destruction of habitats is the leading cause of extinction
Answer, explanation and textbook page: open in the app. - 27.Among the following statements, which one is correct about mutations? Mutations
- A. are changes in genetic composition of population
- B. that occur in sex cells are completely harmless
- C. are accidents that occur spontaneously and randomly during DNA Replication
- D. that occur in somatic cells can pass on to the next generation
Answer, explanation and textbook page: open in the app. - 28.If the particular triplet of bases in the sense strand of DNA is AGT, Then the corresponding codon for the transcribed mRNA will be
- A. UCA
- B. AGU
- C. ACU
- D. UGA
Answer, explanation and textbook page: open in the app. - 29.What is the theory that states disease is caused by microogranisms?
- A. Endosymbiotic theory
- B. Germ theory
- C. Spontaneous generation
- D. Biogenesis theory
Answer, explanation and textbook page: open in the app. - 30.In the bare bottom of a newly formed pond a biologist observed emergence of new algae. The form of succession he observed can be best described as
- A. secondary succession
- B. primary succession
- C. early succession
- D. late succession
Answer, explanation and textbook page: open in the app.