Answer:
B. Made of different kinds of tissues
Explanation:
Answer:
Geological events can cause drastic changes over long periods of times
Explanation:
He used these insights and stated that Geological events can cause drastic changes over long periods of time. Such changes can cause entire species to become extinct or cause drastic evolutionary physical changes to other species. This is because the environment changes and the animals living in these environments need to adapt in order to be able to survive. Some changes such as continental drift can even move species to different parts of the world where the climate is drastically different.
Answer:
The source of Calcium (Ca⁺⁺) for the skeletal muscle cells is the sarcoplasmic reticulum, the main store of intracellular Ca⁺⁺.
Explanation:
Calcium (Ca⁺⁺) is an ion that plays an important role in muscle contraction, a process that requires high cytoplasmic concentrations of this ion to promote myofibrillary activity.
The sarcoplasmic reticulum (SR) -equivalent to the endoplasmic smooth reticulum- is an organelle that regulates the contractile activity of skeletal muscle. The two terminal cisterns of the SR attach to the T-tube, forming a triad, which surrounds the myofibrilla.
Once the muscle cell receives the signal to contract, the Ca⁺⁺ channels are opened and allow Ca⁺⁺ to enter the cell, promoting the exit of this cation from the SR and increased its cytoplasmic levels. This stimulates muscle contraction.
