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