IGCSE Biology Paper-1: Specimen Questions with Answers 196 - 197 of 208

Question 196

Question

MCQ▾

Haemophilia is more common in males than females, because it is:

Choices

Choice (4)

a.

Dominant autosomal

b.

Recessive X- linked

c.

Y- linked

d.

Dominant X- linked

Answer

b.

Explanation

Haemophilia

This sex-linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied. In this disease, a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non-stop bleeding. The heterozygous female (carrier) for haemophilia may transmit the disease to sons. The possibility of a female becoming a hemophilic is extremely rare because mother of such a female must be at least carrier and the father should be hemophilic (unviable in the later stage of life) .

Question 197

Question

MCQ▾

What is the correct sequence for the stages in a logistic population growth curve?

Choices

Choice (4)

a.

b.

c.

d.

Answer

b.

Explanation

Logistic Growth

  • In nature no species has unlimited resources at its disposal to permit exponential growth.
  • There starts competition between individuals for limited resources. The population growing in a habitat initially shows ‘lag phase’ , followed by phases of acceleration or deceleration (log phase) and finally the stage of asymptote- when population density reaches carrying capacity (plateau phase or stationary phase) .
  • If the population density ‘N’ is plotted against time ‘t,’ the result is ‘S’ shaped growth pattern/curve (Sigmoid curve) .
Population Growth Curve