Answer:
D. Calcium ions.
Explanation:
Here we are talking about the mechanism of muscle contraction. The most accepted theory of muscle contraction is sliding filament theory. It was given by Huxley and Huxley. During the process actin filaments slides over myosin filament by forming cross bridges. The sequence of events are as follows:
a. An action potential propagates through the motor nerve and reach the nerve endings on the muscle fiber at neuro-muscular junction.
b. Neurotransmitter called acetylcholine is released by the nerve endings.
c. Acetylcholine binds to the receptors on muscle fiber and opens the gated channels which causes flow of Na+ ions into the muscle fiber.
d. This influx of sodium ions initiates an action potential in the muscle fiber which reaches the T- tubules or transverse tubules. Here it causes the sarcoplasmic reticulum to release large amounts of calcium ion.
e. Calcium ions are responsible for initiating the attractive forces between actin and myosin filaments. Cross bridges are formed, actin slides over myosin causing the contraction of muscle.
When the concentration of a certain solute is low inside the cell with respect to the cell's external environment, then the cell performs active transport of the solute from the cytoplasm with a low concentration of solute within the cell to the cell's external with a high concentration of the solute. This process of active transport requires the need of energy in the form of ATP to drive the pumps that are present on its cell membrane.
The correct answer is descent with modification.
Answer:
acceleration = force / mass
Explanation:
<span>Successive decomposition of dead material and modified organic matter results in the formation
of a more complex organic matter called humus. As they
break down the organic matter, any excess nutrients are
released into the soil in forms that plants can use.</span>
