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:
Hydrophillic head and a hydrophobic tail
Explanation:
Every fatty acid is composed of long chain of hydrocarbon tail. This hydrocarbon tail is nonpolar and insoluble in water. Hence this tail is labeled 'hydrophobic'.
However, the head of the fatty acid contains polar COOH group which is capable of interacting with water, hence the head is hydrophillic.
Hence, a fatty acid is composed of a hydrophillic head and a hydrophobic tail.
<span>Both protexts the organisms' organelles which are inside the cell.
Animal Cell: Cell Membrane
Plant Cell: Cell Wall
Cell
wall is present only in plants, it is not found in all organisms.
Compared to the cell membrane, a cell wall is thick and has a rigid
structure. You can see it in a light microscope, because it is visible.
It serves as the protective cover that surrounds the plasma membrane in a
plant cell. Cell membrane is composed of lipids. Cell walls can be made
up of cellulose or peptidoglycan or chitin.<span> </span></span>
