<span>In marine vertebrates, the gill arches use the external gas exchange. The water holds less oxygen.
The ribs in terrestrial vertebrates have enclosed respiratory surface which is inside the body and comes as paired lungs.
Kidneys are efficient in excretion of regulation of water and nitrogenous wastes. Their reproduction is normally sexual with separate sexes.</span>
Amount of rainfall
I’m not sure if this is right but I think it is because all of the rest are major parts of ecosystems, and although rainfall is too, it’s more of a natural source that happens anywhere whereas the rest of the options may determine the ecosystem
Answer:
The answer is D
Number of motor units recruited
Explanation:
The force a muscle generates is dependent on the length of the muscle and its velocity which is shortened.
A motor unit is the grouping of muscle fibers supplying nerves by the neuron and consists of the motor neuron.
The number of muscle fibers within a motor unit varies, and is a function of the muscle’s ability for accurate and refined motion.
Precision can be determined to be inversely proportional to the size of the motor unit. As a result, small motor units can exercise greater precision of movement compared to larger motor units. For example, thigh muscles which are responsible for large powerful movements, can have a thousand fibers in each unit, while eye muscles which requires small precise movements, might only have about ten.
Groups of motor units are supplied with nerves to coordinate contraction of a whole muscle and generate appropriate movement; all of the motor units within a muscle are referred to as a motor pool.
As a result, the number of motor units with are recruited will facilitate the maximum amount of tension that allows the student keep his arm extended in place under the increasing weight of the books.
