15 extra multiple-choice questions for Organisms and Populations (12th Standard Zoology, Samacheer Kalvi), beyond the ones printed in the textbook — each with the correct option highlighted and a clear, worked explanation. Free to read in English and Tamil.
Q1
According to Van't Hoff's rule, what is the typical Q10 value for metabolic reactions in living systems?
- A. 1.0
- B. 2.0Correct
- C. 3.0
- D. 4.0
Explanation. Van't Hoff proposed that the rate of metabolic activity doubles with every ten degree Celsius increase. This ratio is represented by the Q10 value, which is typically two in living organisms.
Q2
Which eco-geographic principle states that populations or species of larger body size are found in colder regions, while smaller ones inhabit warmer areas?
- A. Hardy-Weinberg law
- B. Van't Hoff's rule
- C. Bergman's ruleCorrect
- D. Hardin's principle
Explanation. Bergman's rule is an eco-geographic principle. It states that within a broadly distributed taxonomic clade, populations of larger body size are found in colder regions, and smaller sizes are in warmer regions.
Q3
Who was the first ecologist to use the term 'niche' to describe the functional status of an organism in its community?
- A. Charles EltonCorrect
- B. Walter Rosen
- C. Edward Wilson
- D. Paul Ehrlich
Explanation. Charles Elton in 1927 was the first scientist to introduce and use the term niche to describe the functional position and role of an organism within its community.
Q4
Which of the following is an example of amensalism interaction where one species is harmed while the other remains unaffected?
- A. Sucker fish attached to a shark
- B. Barnacles attached to a whale
- C. Small insects disturbed by grazing cattle
- D. Lower organisms destroyed under the feet of elephantsCorrect
Explanation. Amensalism is an interaction where one species is inhibited or harmed, and the other is unaffected. An example is small animals or plants being trampled and destroyed under the feet of elephants.
Q5
What is the short-term physiological adjustment made by an animal to overcome environmental stress, such as plains dwellers increasing their red blood cell count when moving to high altitudes?
- A. AcclimatizationCorrect
- B. Aestivation
- C. Diapause
- D. Homeostasis
Explanation. Acclimatization refers to the process by which organisms modify their physiological responses to environmental changes in a short period. This is seen when plains dwellers show elevated red blood cell counts at high altitudes.
Q6
In a pond ecosystem, which species functions as a column feeder within its ecological niche?
- A. Catla
- B. RohuCorrect
- C. Mrigal
- D. Sucker fish
Explanation. In a pond ecosystem, different species occupy distinct niches to avoid competition. Catla is a surface feeder, Rohu is a column feeder, and Mrigal is a bottom feeder.
Q7
Which of the following characteristics is typically associated with r-selected species?
- A. Large body size
- B. Extended parental care
- C. Production of many small offspringCorrect
- D. Long life expectancy
Explanation. r-selected species are adapted to unstable environments and have high reproductive capacity. They are characterized by smaller body sizes, early maturity, short life expectancy, and producing many small offspring.
Q8
Certain snails and fishes undergo a state of inactivity during summer to avoid heat and desiccation. This phenomenon is known as:
- A. Hibernation
- B. AestivationCorrect
- C. Diapause
- D. Acclimatization
Explanation. Aestivation is a summer sleep or period of inactivity. Snails and some fishes use it to avoid summer-related stress, such as high temperatures and water loss.
Q9
What term is used to describe groups of species that perform comparable functional roles with similar niche dimensions within a single biotic community?
- A. GuildsCorrect
- B. Ecological equivalents
- C. Conformers
- D. Biomes
Explanation. Groups of species that share comparable ecological roles and similar niche dimensions within a community are called guilds, helping categorize functional relationships.
Q10
Which of the following represents a facultative mutualistic relationship where the interacting species can also exist independently of each other?
- A. Cellulose-digesting bacteria in the caeca of herbivores
- B. Cross-pollination of flowers by insects seeking nectarCorrect
- C. The association between a hermit crab and a sea anemone
- D. Lichens formed by fungi and algae
Explanation. Mutualism can be facultative or obligate. The cross-pollination of flowers by insects and birds is a facultative mutualistic relationship, as the species are capable of living independently.
Q11
What is the scientific term used for the study of animal behavior under natural conditions?
- A. Ecology
- B. EthologyCorrect
- C. Pedogenesis
- D. Anthropology
Explanation. Ethology is the formal scientific study of animal behavior in their natural habitats and conditions, helping understand adaptive behavioral traits.
Q12
An organism whose body temperature and osmotic concentration change directly in accordance with the surrounding ambient environment is classified as a:
- A. Regulator
- B. ConformerCorrect
- C. Eurytherm
- D. Stenotherm
Explanation. Conformers are organisms that cannot maintain a constant internal environment. Their body temperature or osmotic pressure fluctuates directly with changes in the ambient environment.
Q13
According to the competitive exclusion principle of Hardin, what occurs when resources in a habitat are inadequate to meet the demands of competing species?
- A. All competing species coexist equally by sharing
- B. The weaker or least adapted individuals are excludedCorrect
- C. Both species undergo rapid genetic mutation
- D. The organisms immediately migrate to different continents
Explanation. Hardin's competitive exclusion principle states that when resources are limiting, the weakest, least adapted, or least aggressive individuals are forced out or excluded by superior competitors.
Q14
Which of the following is classified as an ectoparasite that lives on the outer surface of its host?
- A. Ascaris
- B. Tapeworm
- C. Head louseCorrect
- D. Plasmodium
Explanation. Ectoparasites, like head lice or leeches, attach to or live on the outer surface of the host. Endoparasites, like Ascaris or tapeworms, live inside the host's body.
Q15
Which type of population growth model displays a sigmoid curve and is limited by the carrying capacity of the environment?
- A. J-shaped growth model
- B. S-shaped growth modelCorrect
- C. Exponential growth model
- D. Geometric growth model
Explanation. The S-shaped (sigmoid) growth model shows a population increasing slowly at first, then rapidly, and finally stabilizing as environmental resistance increases near the carrying capacity.
