Which one of the following factors is responsible for the spread of myxomatosis, a severe viral disease among rabbits?
- A.Higher water temperature
- B.Higher soil temperature
- C.High population density of rabbits
- D.Low population density of rabbits
Correct answer
Explanation
The correct answer is C, High population density of rabbits. Myxomatosis passes from rabbit to rabbit through biting insects and contact, so it spreads fastest where rabbits are crowded together.
Myxomatosis is caused by the myxoma virus and is carried mainly by mosquitoes and fleas. In 1950 it was released deliberately in Australia to control the huge European rabbit population, and it killed most of the rabbits in the first outbreaks. Ecologists use it as a classic example of a density-dependent limiting factor: diseases, parasites and competition act more strongly as a population grows, because contact between individuals becomes more frequent. Floods, frost and droughts, by contrast, are density-independent factors that affect a population whatever its size.
A and B are wrong because water and soil temperature are physical conditions that do not decide how often rabbits pass on the virus. D is wrong because at low density rabbits meet less often and the disease spreads slowly.
Exam tip: disease, predation and competition are density-dependent; weather and natural disasters are density-independent.
Practice Questions
View allFor acid rain, the pH of rain water should be less than
- A.7.0
- B.6.6
- C.5.6
- D.8.0
Show answer
Rain is called acid rain when its pH falls below 5.6. Even clean rain is slightly acidic, because carbon dioxide in the air dissolves in it and forms weak carbonic acid, which brings its pH down to about 5.6.
Read the full explanation →Which one of the following statements with regard to ozone is not correct?
- A.Ozone is found mostly at 15-55 km in the atmosphere.
- B.Ozone is produced by gaseous chemical reactions.
- C.16th November is celebrated as the International Day for the Preservation of the Ozone Layer.
- D.Ozone is a form of oxygen in which three oxygen atoms are bounded together.
Show answer
The International Day for the Preservation of the Ozone Layer is observed on 16 September, not 16 November. The date marks the signing of the Montreal Protocol on 16 September 1987, the treaty that phased out chlorofluorocarbons and other ozone-depleting substances.
Read the full explanation →Energy and nutrients flow from one trophic level to another in an ecosystem. Which one of the following statements correctly describes the direction of flow of energy and nutrients in an ecosystem ?
- A.Energy flow is cyclic and nutrient flow is unidirectional.
- B.Energy flow is unidirectional and nutrient flow is cyclic.
- C.Both energy and nutrient flow are unidirectional.
- D.Both energy and nutrient flow are cyclic.
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Energy passes one way from the Sun through the food chain and is lost as heat, while nutrients are used again and again.
Read the full explanation →UNESCO World Heritage site Nanda Devi National Park is located in which one of the following States ?
- A.Arunachal Pradesh
- B.Uttarakhand
- C.Himachal Pradesh
- D.Sikkim
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Nanda Devi National Park lies in the Chamoli district of Uttarakhand, around India's second-highest peak, Nanda Devi. The park is a vast glacial basin ringed by high peaks and was inscribed on the UNESCO World Heritage list in 1988 for its wild, untouched landscape.
Read the full explanation →Which one of the following is related to global dimming?
- A.Fall of atmospheric pressure due to increased particulates
- B.Rise of atmospheric pressure due to increased particulates
- C.Rise of temperature due to increased particulates
- D.Fall of temperature due to increased particulates
Show answer
Global dimming is the drop in sunlight reaching the ground, and the cooling that follows, caused by particles in the air.
Read the full explanation →