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

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

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) .

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

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) .