Answer:
by the sarcoplasmic reticulum's calcium ion pumps
Explanation:
Rigor mortis or postmortem rigidity, is a state caused by chemical changes in the muscles that occur post mortem and cause the limbs of the corpse to stiffen.
This occurs because after death, there is no cellular respiration and consequently, no oxygen nor ATP (ATP is required for the muscle relaxation).
Calcium enters the cytosol after death because it is released due to the deterioration of the sarcoplasmic reticulum and due to the breakdown of the sarcolemma. Ca2+ ions activate the formation of actin-myosin cross-bridging necessary for the contraction. Muscles are unable to relax, because myosin heads continue to bind with the active sites of actin and there is no ATP to destabilize the myosin-actin bond.
There are so many examples for that in different areas, like steroidal compounds experiment carried out in our lab recently.
Here's one link: hhttp://www.alfa-chemistry.com/products/steroidal-compounds-8.htm
The outer coverings that are tough but, flexible provided protection to the land plants.
The answer to your problem is question 3 i just took that test i got it right
