Chapter 8, Problem 1TYK

An organism exists for long periods by using only CO₂ and H₂O.

herbivore.

carnivore.

decomposer.

autotroph.

heterotroph.

Summary Introduction

Introduction:

Carbon dioxide (CO₂) is one of the gases in the atmosphere which is essential for maintaining the temperature of the Earth. Like water (H₂O), it causes greenhouse effect, and thus makes the Earth habitable for all life forms.

Answer to Problem 1TYK

Correct answer:

An organism that uses CO₂ and H₂O for a long period of time is categorized under ‘autotroph’.

Explanation of Solution

Justification/Explanation for the correct answer:

Option (d) is autotroph. The green plants and blue-green algae utilize atmospheric CO₂ to prepare food in the form of carbohydrates. It is the carbon atoms of the CO₂ which are ultimately found in glucose, which is the end product of photosynthesis. For this process, H₂ Ois required, which is split with the help of light (photolysis). The electrons generated during photolysis carry the reaction in the forward direction. Water undergoes oxidation to give off oxygen gas as the byproduct of photosynthesis. Hence, option (d) is the correct answer.

Explanation for the incorrect answers:

Option (a) is herbivore. Herbivory is one of the modes of nutrition in animals, where they eat only plants. The food is digested and used to produce energy through respiration, where, the end products are carbon dioxide and water. So, it is an incorrect option.

Option (b) is carnivore. Carnivory is one of the modes of nutrition in animals, where they eat only animals belonging to lower trophic levels. Just like the herbivores, the food is digested and used to produce energy through respiration. Carbon dioxide and water are given off during the process. So, it is an incorrect option.

Option (c) is decomposer. These organisms feed on the dead and decaying matter to obtain their nutrition. Thus, like other animals, they utilize organic carbon instead of inorganic carbon (carbon dioxide). So, it is an incorrect option.

Option (e) is heterotroph. A heterotroph is a broad mode of the nutrition group which includes all the animals that rely on organic carbon as their source of energy. These do not utilize carbon dioxide or water to prepare food. Thus, they are non-photosynthetic. So, it is an incorrect option.

Hence, options (a), (b), (c), and (e) are incorrect.

Conclusion

Thus, the organisms that depend on carbon dioxide and water for a long time to survive are called autotrophs. They use these substances as raw materials to manufacture their own food.