Extinctions that occur at a moderate rate and open a limited number of opportunities for the origin of new species are known as background extinctions.
<h3>What are background extinctions?</h3>
Extinction is the physical disappearance of one given species and/or population in an ecosystem.
The term 'background extinctions' makes reference to the extinction that does not generate new niches in an ecosystem.
Background extinctions are well known because they do not contribute to the emergence of biodiversity.
Learn more about background extinctions here:
brainly.com/question/11872946
Answer:
False
Explanation:
The blood brain barrier (BBB) is a selective border that prevents the entry of foreign substances into the brain. It is made up of different components including endothelial cells, astrocytes, and pericytes etc.
Of all these mentioned three, the endothelial cells are directly responsible for the selectivity of the BBB. The endothelial cells are bound together by the tight junctions situated between them, impeding the passage of foreign materials e.g. solutes, pathogens etc.
Astrocytes help to maintain the BBB by surrounding the endothelial cells, providing biochemical strength.
The pericytes are located in the basement membrane, where they communicate with endothelial cells. They help to sustain the BBB by stabilizing and monitoring the maturation of endothelial cells via communicating directly between cell membrane as well as paracrine signalling.
Is less dense than cold water, and has lower salinity than cold water.
Answer:
The correct answer will be option-A
Explanation:
Chromosomal abnormalities are caused when the chromosome pair fails to disintegrate through a process called non-disjunction. The non-disjunction of chromosomes usually takes place at the anaphase I or II of meiosis I which involves the X and Y chromosomes.
The abnormality observed with 45 chromosomes or reduction in one sex chromosome or 45, XO is caused when one X copy of a chromosome is completely absent in the cell.
The cause for the loss of one chromosome is the non-disjunction during meiosis I.
Thus, option-A is the correct answer.
