Why can reduction in species biodiversity be a problem for an ecosystem, and what are two things that humans can do to preserve or increase species biodiversity

Aneuron is stimulated with an electric pulse. the action potential is detected at a point 3.70 cm down the axon 0.0052 s later.when the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. what is the speed of the electric pulse along the axon? (why are two measurements needed instead of only one? )

Which of the following is a possible reason for sleep? a) growth b)digestive c)speed d)intelligence

What percentage of light hits earth's surface directly?