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<span>The brain stem is closest to the spinal cord.</span>
Oxygen is an abiotic factor that is beneficial by-product of primary production.
<u>Explanation:</u>
The non living parts of an ecosystem that mainly affects the living organisms in it are called as an abiotic factor. These can include soil, temperature, water, oxygen and sunlight. The major energy source in earth is Oxygen which is abiotic factor.
It is very essential for the photosynthesis process to take place. Here, the plants converts water and carbon dioxide into oxygen and sugar. This becomes food for plants. Then these plants are eaten by animals. Thus oxygen is an important and beneficial by-product of photosynthesis. Oxygen is also very important for the survival of human beings.
our thyroid glands plays a main role in a human body. It secretes thyroxine and calcitonin. In which thyroxine help in growth and cellular metabolism and calcitonin helps to regulates calcium concentration in blood . If thyroid gland stops working then there is low level of calcium in our blood, which leads to mental and hormonal disorder. In this way a person's blood calcium level would be affected if his/her thyroid gland stops working.