Quadrat method is used for estimating the number of individuals in an area. In this method, a large square area on the ground or water surface is marked, call it an enclave. The number of animals present in this enclave is counted. Then by assuming that the animals are less migratory and are uniformly distributed, their number for a large area is estimated by the use of unitary method of calculation. Example a 4 square feet area has 2 snails, then a 1000 square feet area will have (1000 x 2)/4, i.e, 500 snails in it. Fishes can be counted using this method only if they are confined in a small water body like a lake or a pond. Rivers are flowing so the fishes may move along its length which can give us an underestimate or an overestimate of their numbers. Sea has its depth and huge area, and fishes can be moving randomly in it. Hence this method will not work for river and sea fishes.
In order for an impulse to cross the synaptic gap between
the neurons, the impulse must be converted into a chemical signal as this will
allow it to exert effects and to be able to travel in distances such as having
to cross the synaptic gap between the neurons.
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The proof that cells only come from other cells
He proved it by his "swan-necked flasks" in which nothing formed in sealed flask whereas many organisms were there in open flask.
So, in short, option D is your final answer!
Hope this helps!
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