Answer:
Number of bacteria required 
Explanation:
Given -
Size of each bacterium
micrometers long
These bacteria are arranged end to end.
The size of chain to be formed is equal to
centimetres
Let us say that in forming a chain of
centimetres nearly X number of individual bacterium are required.
hence, number of bacterium required to form
centimetres chain can be represented as

Number of bacteria required 
Answer:
Digestive
Explanation:
The by-products of digestion are solid waste which is removed through egestion.
2. The endosymbiotic theory suggests that a eukaryotic cell is the result of one prokaryotic cell eating another.
Answer:
We know that when substance donate the electron then it from positive charge but when substance take electron then it form negative charge .
The most common ions in blood plasma
1.Cation -Sodium(Na+)
2.Anion -Chloride(Cl-)
The most common ions interstitial fluid
1.Cation -Potassium
2.Anion - Chloride
B: They represent different concepts.