Primary tropical rainforest has a canopy 10 metres above the forest floor. The forest floor lacks dense vegetation. The vegetation found on the forest floor consists of
huge tree trunks with a few hanging vines and bushes. The vegetation also consists
of a variety of seedlings and a variety of small ground plants.
Which of the following reasons for the sparse vegetation on the floor of a tropical
forest is incorrect?
a) The nutrients present in the soil are inadequate for the growth of thick
vegetation.
b) The canopy blocks out the sunlight so that very little reaches the forest floor.
c) A proper amount of oxygen cannot reach the plants on the forest floor to ensure
their growth.
d) The canopy prevents most rainwater from reaching the ground.

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explanation:

b r

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cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!