The question is incomplete. The complete question is:
Question: Why do organisms without oxygen need to convert pyruvate to lactate?
A) because pyruvate is toxic to the cells
B) in order to regenerate NAD+
C) in order to use lactate in the citric acid cycle
D) because lactate is needed to produce ATP
Answer:
B) in order to regenerate NAD+
Explanation:
Kreb's cycle and electron transport chain (ETC) are the aerobic stages of cellular respiration. ETC regenerates NAD+ and FAD+ by oxidation of NADH and FADH2 produced during glycolysis and Kreb's cycle. Here, oxygen serves as the terminal electron acceptor.
Glycolytic reactions use NAD+ as an electron acceptor and produce NADH. Therefore, a constant supply of NAD+ is required to sustain glycolysis. In absence of oxygen, ETC cannot occur and organisms convert pyruvate into lactate. Pyruvate is reduced in lactate and NADH serves as the electron donor. Thereby, lactate fermentation regenerates NAD+ to continue the process of glycolysis.
Maybe biosphere and geosphere?
Answer: Air pollution is responsible for seven million deaths each year in the US
Explanation: https://www.who.int/health-topics/air-pollution#:~:text=The%20combined%20effects%20of%20ambient,cancer%20and%20acute%20respiratory%20infections.
<span>Human cells contain 23 chromosomes and has a total of 46
pairs of chromosomes. The answer is letter A. Depending on the length and
morphology, it has seven groups. They are arranged from largest to smallest. It
has 22 pairs of homologus chromosomes known as autosomes and 1 pair of sex chromosomes,
a total of 23 chromosomes. A male karyotype has a total of 46 chromosomes and
gives a pair of XY while a female karyotype has a total of 46 chromosomes and
gives a pair of XX. These pairing are responsible to the gender of the
offspring.</span>
