Give Scientific Reason.

Question 13 Marks

Tobacco smoking causes cancer.

Answer

Tobacco smoke contains harmful chemicals like pyridine, ammonia, aldehyde furfural, carbon monoxide, nicotine, sulphur dioxide etc.
They cause uncontrolled cell division.
Tobacco smoke is full of minute carbon particles which cause normal tissue lining of the lung to transform into thickened black tissue. This leads to cancer.
Therefore, tobacco smoking causes cancer.

Question 23 Marks

Mitochondrial disorders are inherited from the mother only.

Answer

Mitochondrial DNA becomes defective due to mutation.
During fertilization, mitochondria are contributed by the egg cell (ovum) alone.
Hence, mitochondrial disorders are inherited from the mother only.

Question 33 Marks

A carrier or sufferer of sickle-cell anaemia should avoid marriage with another carrier or sufferer.

Answer

Sickle-cell anaemia is a hereditary disease caused due to mutation of a single gene.
It is a monogenic disorder that occurs due to changes in a gene during conception.
If father and mother both are sufferers or carriers of sickle-cell anaemia, their offsprings are likely to suffer from the disease.
Therefore, a carrier or sufferer of sickle-cell anaemia should avoid marriage with another carrier or sufferer.

Question 43 Marks

Answer

Phenotype means external appearance or visible characteristics of organisms whereas the genotype is the pairs of genes responsible for the visible characteristics.
The genes responsible for any particular character are present in pairs.
Though, there are two genes, the phenotype
depends on the presence of the dominant gene, e.g. Genotype for tall height of the plant is TT or Tt.
Therefore, phenotypic and genotypic ratios are different.

Question 53 Marks

DNA molecules are called as ‘Master molecules’.

Answer

Molecules of DNA are present in all organisms from viruses and bacteria to human beings.
These molecules control the functioning, growth and division (reproduction) of the cell.
Genes present in the DNA are also responsible for transfer of hereditary characteristics from parents to offsprings.
Therefore, DNA molecules are called as ‘Master molecules’.

Science Give Scientific Reason.