Cerebrospinal fluid (CSF) is formed by capillary knots called the , which hangs inside the of the brain. Ordinarily, CSF flows from the lateral ventricles into the ventricle and then through the into the fourth ventricle. Some of the fluid continues down the of the spinal cord, but most of it circulates into the by passing through three tiny openings in the walls of the . As a rule, CSF is formed and drained back into the venous blood at the same rate. If its drainage is blocked, a condition called occurs, which results in increased pressure on the brain.

1. Choroid Plexuses

2. Ventricles

3. third

4. Cerebral Aqueduct

5. Central Canal

6. Subarachnoid space

7. Forth Ventricle

8. Hydrocephalus

Explanation:

Cerebrospinal fluid formed by capillary knots called Choroid Plexuses which is hanged inside ventricles. There are four ventricles in which CFS flows from lateral to third and from cerebral aqueduct to forth ventricle. The meninges covers spinal cord which extends more inferiority to form a sac from which cerebrospinal fluid can be withdrawn without damage to spinal chord.

1) gene flow

- it is described as the transfer of genes from one population to another population so that frequency of gene is increased.

-a zebra migrates to join a different herd of zebras.

2) natural selection

- a mechanism of evolutionary change in which individuals with advantageous traits survive and reproduce whereas the others ( those that can not adapt) eliminate from the population.

-competition for sunlight leads to taller trees.

3) mutation

- permanent change in the nucleotide sequence of dna ( genetic material) that could have harmful or useful consequences.

-the dna of a snake changes to make its venom stronger.

4) genetic drift - it is a random phenomenon ( that occurs by chance such as fire) that results in change in the gene frequency in a small population.    

-a grassfire randomly sweeps through a population of buffalo and kills most of the animals.

explanation:

because the light is a great source of energy for the plants to survive. (i hope this )