Biology Questions and Answers Part 2


Water and Mineral


1. What is the approximate percentage (in mass) of water

in the human body? Is this percentage expected to be

larger in the adult or in the old individual?

Approximately 65% of the human

individual mass is water. The brain, for

example, has around 90% of water in

mass, the muscles, 85%, and the bones

have between 25% and 40% of water.

Younger adult individuals have

proportionally more water in mass than

older individuals.

2. Water has key participation in organic reactions. What are examples of two types of organic reactions in which

water is respectively incorporated or liberated in

the products of these reactions?

Photosynthesis is a biochemical process

in which water is incorporated into

organic molecules. In the reaction, the

hydrogen atoms from water go to the

produced glucose and the oxygen atoms

from water form the molecular oxygen

liberated: carbon dioxide + water +

light = glucose + molecular oxygen.

Aerobic respiration is an example of

biochemical reaction in which water is

produced: glucose + molecular oxygen

= carbon dioxide + water.

3. Which kind of polarity do water-soluble and fat-soluble

substances respectively have?

Water-soluble substances are polar

molecules, i.e., they have electrically

charged areas. These molecules get the

description “water-soluble” because

they are soluble in water, a polar

molecule too.

Fat-soluble substances are non-polar

molecules, i.e., they are electrically

neutral. They get the description “fat-

soluble” because they dissolve other

non-polar substances.

4. Can the heat capacity of water be considered small or

large? What is the biological significance of that


From Thermology it is known that the

quantity of exchanged heat (Q) is equal

to the mass (m) multiplied by the

specific heat of the substance (c)

multiplied by the variation of

temperature (T), Q = m.c.ΔT., and that

heat capacity is Q/T, hence, m.c. Heat

capacity, however, relates to a specific

body, since it considers mass, whereas

specific heat relates to the general

substance. Therefore it is more correct

to refer to specific heat in this problem.

Water has a specific heat of 1 cal/g.oC

which means that 1 oC per gram is

changed in its temperature with the

addition or subtraction of 1 cal of

energy. This is a very elevated value

(for example, the specific heat of

ethanol is 0,58 cal/g.oC, and mercury, a

metal, has a specific heat of 0,033

cal/g. oC) making water an excellent

thermal protector against variations of

temperature. Even if sudden external

temperature changes occur, the internal

biological conditions are kept stable in

organisms which contain enough water.

High specific heat is one of the most

important water properties.

5. What are the main water properties that make water

special for life?

The water properties that make water

biologically important are molecular

polarity, thermal stability (elevated

specific heat), fusion and ebullition

points that allow water to be liquid in

most environments, acid-base

neutrality, small molecular size and low

chemical reactivity. (Compared to other

substances, like ethanol or hydrogen


6. What are ions? What are the two types of molecules

into which ions are classified?

Ions are atoms or substances

electrically charged by means of loss or

gain of electrons.

The two types of ions are the cations

and the anions. Cations are ions with

positive total electric charge and anions

are ions with negative total electric


7. How do mineral salts participate in osmotic


Osmotic pressure depends on the

number of particles dissolved in a

solution and not on the nature of such

particles. Mineral salts, glucose,

proteins and urea are the main

regulating particles for the osmolarity of

the organism. These molecules along

with other particles inside and outside

the cell generate the larger or smaller

osmotic gradient between the

intracellular and the extracellular space.

8. Why is pH regulation important for living beings?

How do mineral salts

participate in this regulation?

The potential of hydrogen (pH) is a

measure of the amount of hydrogen

ions (H-

) in a solution. The regulation of

the pH according to the necessities of

each organ or tissue is extremely

important for the organism since

enzymes act only under some pH

ranges and many proteins are only

active under some pH ranges. Therefore

biochemical reactions depend on correct

levels of pH to occur.

Neutral pH is one of the water


9. How do mineral salts participate in enzymatic


Many mineral salts are cofactors of

enzymes, i.e., they are substances

without which enzymes do not work.

10. What is hemoglobin? What is the inorganic element that

is fundamental in the composition of hemoglobin?

Hemoglobin is the protein present in the

blood responsible for the transport of

oxygen from the lungs to the tissues

and cells.

The hemoglobin molecule is composed

of four protein chains, each with a heme

group containing an iron atom. The iron

is responsible for the binding of oxygen

in the lungs and also for the red color of

hemoglobin and thus of the blood.

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