CBSE Class X

Question 4:

How are the lungs designed in human beings to maximize the area for exchange of

gases?

Answer

The exchange of gases takes place between the blood of the capillaries that

surround the alveoli and the gases present in the alveoli. Thus, alveoli are the

site for exchange of gases. The lungs get filled up with air during the process of

inhalation as ribs are lifted up and diaphragm is flattened.The air that is rushed

inside the lungs fills the numerous alveoli present in the lungs. 

Each lung contains 300-350 million alveoli. These numerous alveoli increase the

surface area for gaseous exchange making the process of respiration more efficient.

Question 3:

How is oxygen and carbon dioxide transported in human beings?

Answer

Haemoglobin transports oxygen molecule to all the body cells for cellular respiration.

The haemoglobin pigment present in the blood gets attached to four O₂ molecules

that are obtained from breathing. It thus forms oxyhaemoglobin and the blood

becomes oxygenated. This oxygenated blood is then distributed to all the body cells

by the heart. After giving away O₂ to the body cells, blood takes away CO₂ which is

the end product of cellular respiration. Now the blood becomes de-oxygenated.

Since haemoglobin pigment has less affinity for CO₂, CO₂ is mainly transported in

the dissolved form. This de-oxygenated blood gives CO₂ to lung alveoli and takes

O₂ in return.

Question 2:

What are the different ways in which glucose is oxidized to provide energy in various

organisms?

Answer

Glucose is first broken down in the cell cytoplasm into a three carbon molecule

called pyruvate. Pyruvate is further broken down by different ways to provide energy.

The breakdown of glucose by different pathways can be illustrated as follows.

In yeast and human muscle cells, the breakdown of pyruvate occurs in the absence of

oxygen whereas in mitochondria, the breakdown of pyruvate occurs in the presence of

oxygen.

Question 1:

What advantage over an aquatic organism does a terrestrial organism have with

regard to obtaining oxygen for respiration?

Answer

Terrestrial organisms take up oxygen from the atmosphere whereas aquatic animals

need to utilize oxygen present in the water. Air contains more O₂ as compared to

water. Since the content of O₂ in air is high, the terrestrial animals do not have to

breathe faster to get more oxygen. Therefore, unlike aquatic animals, terrestrial

animals do not have to show various adaptations for better gaseous exchange.

Question 5:

How is the small intestine designed to absorb digested food?

Answer

The small intestine has millions of tiny finger-like projections called villi. These villi

increase the surface area for more efficient food absorption. Within these villi, many

blood vessels are present that absorb the digested food and carry it to the blood

stream. From the blood stream, the absorbed food is delivered to each and every cell

of the body.

Question 4:

What is the function of digestive enzymes?

Answer

Digestive enzymes such as amylase, lipase, pepsin, trypsin, etc. help in the breaking

down of complex food particles into simple ones. These simple particles can be easily

absorbed by the blood and thus transported to all the cells of the body.

Question 3:

What is the role of the acid in our stomach?

Answer

The hydrochloric acid present in our stomach dissolves bits of food and creates an

acidic medium. In this acidic medium, enzyme pepsinogen is converted to pepsin,

which is a protein-digesting enzyme.

Question 2:

Where do plants get each of the raw materials required for photosynthesis?

Answer

The following raw materials are required for photosynthesis:

• The raw material CO₂ enters from the atmosphere through stomata.

• Water is absorbed from the soil by the plant roots.

• Sunlight, an important component to manufacture food, is absorbed by the

   chlorophyll and other green parts of the plants.

Question 1:

What are the differences between autotrophic nutrition and heterotrophic nutrition?

Answer

Question 4:

What processes would you consider essential for maintaining life?

Answer

Life processes such as nutrition, respiration, transportation, excretion, etc. are

essential for maintaining life.

Question 3:

What are outside raw materials used for by an organism?

Answer

An organism uses outside raw materials mostly in the form of food and oxygen.

The raw materials required by an organism can be quite varied depending on the

complexity of the organism and its environment.

Question 2:

What criteria do we use to decide whether something is alive?

Answer

Any visible movement such as walking, breathing, or growing is generally used to

decide whether something is alive or not. However, a living organism can also have

movements, which are not visible to the naked eye. Therefore, the presence of life

processes is a fundamental criterion that can be used to decide whether something

is alive or not.

Question 1:

Why is diffusion insufficient to meet the oxygen requirements of multi-cellular

organisms like humans?

Answer

Multicellular organisms such as humans possess complex body designs. They have

specialised cells and tissues for performing various necessary functions of the body

such as intake of food and oxygen. Unlike unicellular organisms, multicellular cells

are not in direct contact with the outside environment. Therefore, diffusion cannot

meet their oxygen requirements

Question 10:

Compare and contrast the arrangement of elements in Mendeleev’s periodic Table and 

the Modern Periodic Table.

Answer:

Question 9:

In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements

with atomic numbers 12, 19, 21, and 38. Which of these have physical and chemical

properties resembling calcium?

Answer:

The element with atomic number 12 has same chemical properties as that of calcium.

This is because both of them have same number of valence electrons (2).

Question 8:

How does the electronic configuration of an atom relate to its position in the Modern

Periodic Table?

Answer:

In the modern periodic table, atoms with similar electronic configurations are placed

in the same column. In a group, the number of valence electrons remains the same.

Elements across a period show an increase in the number of valence electrons.

Question 7:

Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of

the Periodic Table. Write the electronic configuration of these two elements. Which of

these will be more electronegative? Why?

Answer:

Nitrogen is more electronegative than phosphorus. On moving down a group, the

number of shell increases. Therefore, the valence electrons move away from the

nucleus and the effective nuclear charge decreases. This causes the decrease in the

tendency to attract electron and hence electronegativity decreases.

Question 6:

The position of three elements A, B and C in the Periodic Table are shown below −

(a) State whether A is a metal or non-metal.

(b) State whether C is more reactive or less reactive than A.

(c) Will C be larger or smaller in size than B?

(d) Which type of ion, cation or anion, will be formed by element A?

Answer:

(a) A is a non-metal.

(b) C is less reactive than A, as reactivity decreases down the group in halogens.

(c) C will be smaller in size than B as moving across a period, the nuclear charge

increases and therefore, electrons come closer to the nucleus.

(d) A will form an anion as it accepts an electron to complete its octet.

Question 5:

An atom has electronic configuration 2, 8, 7.

(a) What is the atomic number of this element?

(b) To which of the following elements would it be chemically similar? (Atomic

numbers are given in parentheses.)

N(7) F(9) P(15) Ar(18)

Answer:

(a) The atomic number of this element is 17.

(b) It would be chemically similar to F(9) with configuration as 2, 7.

Question 4:

(a) What property do all elements in the same column of the Periodic Table as boron

have in common?

(b) What property do all elements in the same column of the Periodic Table as fluorine

have in common?

Answer:

(a) All the elements in the same column as boron have the same number of valence

electrons (3). Hence, they all have valency equal to 3.

(b) All the elements in the same column as fluorine have the same number of valence

electrons (7). Hence, they all have valency equal to 1.