Answer:
The correct answer is 3: "<em>High levels of Ca2+ are expected to be found </em><em>within the sarcoplasmic reticulum</em>".
Explanation:
Muscular contraction is a highly regulated process that depends on free calcium concentration in the cytoplasm. Amounts of cytoplasmic calcium are regulated by <u>sarcoplasmic reticulum</u> that functions as a storage of the ion.
When a nerve impulse reaches the membrane of a muscle fiber, through acetylcholine release, the membrane depolarizes producing the entrance of calcium from <u>extracellular space</u>. The impulse is transmitted along the membrane to the sarcoplasmic reticulum, from where calcium is released. At this point, <em>tropomyosin is obstructing binding sites for myosin on the thin filament</em>. The calcium channel in the sarcoplasmic reticulum controls the ion release, that activates and regulates muscle contraction, by increasing its cytoplasmic levels. When <em>calcium binds to the troponin C</em>, <em>the troponin T alters the tropomyosin by moving it and then unblocks the binding sites,</em> making possible the formation of <em>cross-bridges between actin and myosin filaments.</em> When myosin binds to the uncovered actin-binding sites, ATP is transformed into ADP and inorganic phosphate.
Z-bands are then pulled toward each other, thus shortening the sarcomere and the I-band, and producing muscle fiber contraction.
Answer:
1. It secretes a peptide/protein hormone.
Explanation:
The above mentioned answer is more likely true for this question.
Because, rough endoplasmic reticulum is the cytoplasmic organelles which are involved in post-translational modification of peptide chains. After that, peptide chains are further modified (folded) in golgi apparatus. It's means that abundance of rough endoplasmic reticulum and golgi apparatus present in cells ensure the formation and secretion of peptide/protein hormones.
The smooth ER sends the lipids to the golgi which in turn sends them elsewhere in the cell or outside of the cell.
Atmospheric nitrogen fixation<span> is the process in which lightning converts </span>nitrogen<span>gas in the </span>atmosphere<span> into usable compounds. It makes </span>nitrogen<span> available to</span>organisms<span>.</span>
