The food web below represents the interactions between organisms in a salt marsh ecosystem and organisms in an old field ecosystem.

Which of the following is the correct flow of energy?
a. The crab gets energy from eating plants.
b. The heron gets energy from eating plants.
c. The crab gets energy from eating the heron.
d. The heron gets energy from eating the crab.

d. The heron gets energy from eating the crab.

Explanation:

The heron gets energy from eating the crab. The heron primary feeds on small fish but also on shrimp, crabs, small mammals, amphibians, small birds, rodents, and insects when the fish are not available. After shedding of crab's shell, crabs are prey for fish and birds, and eaten by fish and birds like heron whereas, crabs feed primarily on algae, as well as other food, including molluscs, worms, other crustaceans, fungi, bacteria, and detritus.

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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