The answer is d. The solar system used to have a bunch of dust and particles in the air, after a while gravity pulled the particles together and formed the sun and the other planets.
This can be known as trade in some places and kingdoms. But historically, the spread of ideas and culture is know as Trans-cultural diffusion.
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Answer: Here you go
Explanation: nerves (cranial, spinal, and peripheral) and neurons (sensory, motor)
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.
While in photosynthesis carbon dioxide and water yield glucose and oxygen, through the respiration process glucose and oxygen yield carbon dioxide and water.
