Answer:
1. CLIMATE CHANGES............easing temperatures have altered migration patterns of humpback whales.
2. NATURAL DISASTERS...........the eruption of mount saint Helens destroyed some populations of conifers.
3. HUMAN EXPLOITATION..........African forest elephants have been hunted to near extinction levels to obtain ivory.
4. DISEASES.........An infection with a fungus reduced population of north American elm trees.........
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Explanation:
Answer:
Cells must divide to perform functions such as growth of the organism, replacement of damaged or old cells, and asexual reproduction in some organisms.
Explanation:
Answer:A. The release of calcium ions causes myosin and actin to attach to each other.
The contraction of skeletal muscles takes place by induction of a nerve impulse, which produces a movement and the interaction of the filaments containing proteins named as actin and myosin. This interaction of filaments is regulated by proteins called tropomyosin and troponin present on the actin filaments. The motor nerve causes the depolarization of the muscle membrane sarcolemma. This triggers the sarcoplasmic reticulum to release calcium ions. This calcium binds to troponin and thus allows the tropomyosine strand on the actin filament to displace so that the part of the actin where myosine head needs to be attached remain uncovered. Binding of the actin myosine filament results in contraction.
Hence, the release of calcium ions causes myosin and actin to attach to each other causes muscle contraction.