Two sister chromatids are joined at the centromere prior to meiosis. which statement is correct? a. these chromatids make up a diploid chromosome. b. barring mutation, the two sister chromatids must be identical. c. the cell that contains these sister chromatids must be haploid.

b. Barring mutation, the two sister chromatids must be identical.

Explanation:

Prior to meiosis, the DNA is replicated so cells enter division with all its chromosomes having two sister chromatids united at the centromere.

DNA replication is semiconservative: the original DNA strands are separated and new strands are synthesized using the original ones as templates. As a result, each sister chromatid is made of one original DNA strand and a newly synthesized DNA strand, and both should be identical to each other.

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

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step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.