Answer:
ANSWER E. a and c are the answer to this question
The Precambrian era envelopes the major bulk of the history of the Earth, beginning from the creation of the planet approx 4.5 billion years ago and terminating with the origination of composite, multicelled forms of life approximately 4 billion years after.
The Precambrian refers to the earliest of the geologic ages that are signified by the distinct layers of sedimentary rock. The Earth was about more than six hundred million years old when life started. The planet had cooled down from its native molten state, creating a solid crust and oceans formed by water vapor in the atmosphere.
At about three billion years ago, the atmosphere of the Earth was virtually devoid of oxygen. At approximately 2.4 billion years ago, oxygen was discharged from the seas as a waste product of photosynthesis by cyanobacteria. The levels of the gas slowly raised, attaining about 1 percent around two billion years ago.
Approximately 800 million years ago, the levels of oxygen attained about 21 percent and started to breathe life into more composite species. The oxygen-rich ozone layer was also created, protecting the surface of the Earth from the harmful solar radiation.
Answer:
D. Chemoautotrophs
Explanation:
Autotrophs in plain are organisms that synthesize their own food while hetrotrophs are organisms that do not synthesize their own food.
Chemotrophs (Chemoautotrophs and Chemohetrotrophs) are a group of organisms that obtain their energy through the oxidation of inorganic molecules, These organisms require carbon to survive and reproduce.
Chemoautotrophs are able to produce inorganic molecules by the fixation of CO2 from their immediate environment. The energy required for this process is got from Nitrogen, Magnesium, Sulphur etc.
Chemohetrotrophs are a class of chemotrophs that are unable to synthesize their own food but rather ingest complex molecules like carbohydrates from the environment.
Phototrophs are a group of organisms unlike chemotrophs that depend on the source of light or sunlight for synthesizing its food or organic molecules.
Photoautotrophs are basically photosynthetic plants which are able to carry out photosynthesis ie the conversion of CO2 and H2O to give Glucose and Oxygen in the presence of sunlight.
Photohetrotrophs are a class of organisms that do not synthesize their own food but rely on other organisms or already made organic molecules.
Answer:
Option (2).
Explanation:
Ecological succession is the change in the ecological community of the species with respect to time. Two types of the succession are secondary succession and primary succession.
The ecological succession includes various transitional stages before reaching to the climax community. The simple species acquires first and then the climax species is reached at the end of the succession. Different changes are involved in the formation of climax community.
Thus, the correct answer is option (2).
