Correctly order the following key steps in the process of endochondral ossification. a) chondrocytes die. b) osteoblasts build the bone collar on the external surface of the bone. c) perichondrium is invaded by blood vessels. in the primary ossification center, osteoblasts replace calcified cartilage with early spongy bone. d) perichondrial cells differentiate into osteogenic cells then into osteoblasts.

The following key steps in the process of endochondral ossification, in the correct order is:

1. Letter B

2. Letter A

3. Letter C

4. Letter D

Explanation:

1. Osteoblasts build the bone collar on the external surface of the bone (bone collar formation)

2.Cavitation, which means that chondrocytes die. They die because the calcified hyalin cartilage is impermeable to the difusion nutrients, so they cannot receive any nutrients.

3. Periosteal bud invasion, the perichondriume is invaded by blood vessels. It can be compared with a group of robbers who invaded the graves where fallen chondrocytes uesd to rest.

4. Perichondrial cells differentiate into osteogenic cells then into osteoblasts, the bone ends develop (secondary) ossification centers.

as the gila monster consumes the eggs or young of the desert cottontail and gambel's quail, thus its main food supply is only accessible for a restricted time duration every year. however, for this, the gila monsters exhibit three adaptations, which elevate their survival rate in the desert condition.  

first, is that they possess huge bodies, and can consume greater concentrations of food during a small period. secondly, they require to feed infrequently as they can accumulate fat in their tails. ultimately, their rate of metabolism is very low, so that they can burn their reservoirs of fat gradually.  

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.