During the cretaceous period, reptiles were the dominant species, and dinosaurs ruled earth. plants developed flowers and fruits. at the end of the cretaceous period, about 65 million years ago, 50% of the plants and animals on earth became extinct and dinosaurs were never to be seen again. what is thought to have caused the mass extinction at the end of the cretaceous period? a. global warming b. an asteroid hitting earth in mexico c. extensive volcanic activity world-wide d. the start of glaciation and climatic changes

it B very sure

Explanation:

it's     c       this is a cell (b) with a nucleus (c) containing dna (a). the dna is organized into chromosomes (d). a section of the chromosome that codes for a trait is called a gene (e).

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.