A concept that there is a specific time in an organism's development during which external factors have a unique and irreversible impact is:

A. ethology
B. equifinality
C. critical period
D. zone of proximal development

C. Critical period.

Explanation:

Critical period:

In developmental biology, ciritical period is also known as sensitive period which is defined as a period or stage of maturation in the organism's lifespan in which nervous system is more sensitive to various environmental stimulus. Means, brain cell connections are more receptive to influence from surrounding environmental factors. Our body's many cruical functions including behavior are established during critical period with irreversible impact.

the pic attached shows the stages of mitosis. hope it !

you are certainly talking about this picture:

a: is the label of the white square, it is showing the  replication fork, formed by helicase (d) ==> so it is the site of dna separation and replication 

b: is a new dna brand that is following directly the replication fork, so it is continuous ==> built continuously from 5' to 3

c: dna polymerase cannot replicate dna on its own, it needs the of their proteins, and one of them plays the role of a clamp which fixes  the dna with the dna template and increases  the processivity of the enzyme. ==>   stops polymerase from falling off the  template.

d: is the enzyme responsible for forming the replication fork (helicase) ==> unwinds and separates dna into two strands

e: is the delayed strand, it is built  in the opposite sense of the helicase, so dna will be built in fragments ==> built  fragments from 5' to 3 joins

and finally f: is the enzyme that builds  the new dna strand (dna polymerase) ==>   adds nucleotides to make a new dna helix.

credit: gradman555p98x9p

read more on -