What do the plants got from the symbiosis? how could this happen?

In plants, symbionts play significant roles in plant growth, development, and health by providing nutrients and increasing tolerance to biotic and abiotic stress factors. For example, endophytic fungi are very common in plants and many studies have shown that they increase growth and development of colonized plants (Rodriguez, White, Arnold, & Redman, 2009). This is mainly achieved by promoting root growth through the allocation of resources to the expanding root system before stem growth (Rodriguez, Freeman, McArthur, Kim, & Redman, 2009). Indeed, evidence suggests that some of these effects are due to epigenetic effects of plant symbiotic fungi or bacteria on their hosts. Conversely, during the course of the establishment of endosymbiosis, genetic and/or epigenetic changes occur in the interacting microorganisms with plant hosts.

Explanation:

the answer that best describes the relative refractory period in the neuron is the resting membrane potential is restored, but concentrations of sodium and potassium are not restored to their original state.

the refractory period is the time during which another stimulus given to the neuron will not lead to a second potential. thus, because na+ channels are inactivated during this time, additional depolarizing stimuli do not lead to new action potentials.  

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9.9 years

a = p(1 + rt) . . account balance after time t at rate r starting with principal p

3000 = 2500(1 + 0.0202t) . . filling in the given numbers

1.2 = 1 + 0.0202t . . divide by 2500

0.2 = 0.0202t . . . subtract 1

0.2/0.0202 = t ≈ 9.901

it will take about 9.9 years for the account balance to reach $3000.