As in all animal cells<span>, the </span>cells<span> of the </span>human cheek<span> do not possess a </span>cell<span> wall. A </span>cell<span>membrane that is semi-permeable surrounds the cytoplasm. Unlike plant </span>cells<span>, the cytoplasm in an animal </span>cell is<span> denser, granular and occupies a larger space. The vacuole in an an animal </span>cell is<span> smaller in size, or absent.</span>
The KT boundary marks a mass extinction event. the KT boundary is the time between the Cretaceous and Tertiary periods. An asteroid hit the earth at the end of the Cretaceous and that caused the end of the Cretaceous period. Before the KT boundary, pollen from angiosperms and gymnosperms is high. After the meteor hits the earth, a mass extinction occurs and the amount of pollen from gymnosperms and angiosperms decreases dramatically, while the amount of spores from ferns increases. During the Cretaceous period there were many species of gymnosperms and angiosperms but they disappeared at the KT boundary, when the asteroid hit the earth.
Glucagon
This is a hormone that deals with blood sugar homeostasis. When blood sugar levels are low, glucagon is produced to convert the fats in the reserve back to glucose until normal levels are achieved.
Explanation:
Bone remodeling involves coordinations of osteoclasts and osteoblasts cells in the bone. The former breaks down bone tissue while the latter mineralizes bones. Calcium is the main ion in the body significant in mineralization of bone. Excess Ca2+ is stored in bone while low calcium levels in blood result in bone resorption.
Stress on a bone also causes increased mineralization to strengthen the bone against this stress. This is why astronauts when they go to space, due to less stress from low gravity, bone loses its mass. When they return back to earth, the bone readjusts to the increased stress from higher gravity by increased mineralization.
The hormone responsible for bone homeostasis is parathyroid hormone.
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D.) Both are circumstantial evidence....
Some bones develop within sheet like layers of connective tissue which are called intramembranous bones whereas the bones that are develop from a model of hyaline cartilage and are called endochondral bones.
<h3>Formation of
intramembranous bones and endochondral bones</h3>
Endochondral ossification involves the replacement of hyaline cartilage with bony tissue which leads to the formation of endochondral bones whereas, intramembranous ossification refers to the replacement of sheet-like connective tissue membranes with bony tissue which results in the formation of intramembranous bones.
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