IGCSE Biology Paper-1: Specimen Questions with Answers 188 - 189 of 208

The diagram shows part of a genetic diagram for the inheritance of sex in humans.

What are the sex chromosomes in different gametes?

Answer

a.

Explanation

XY and XX system – e. g. Most of the fishes, Amphibians, Reptiles and Mammals.

• In such cases the Y-chromosome is male determining, and the absence of Y-chromosome determines the femaleness. Moreover, the male sex is heterogametic (producing two types of sperms – X-containing and Y-containing) while female is homogametic (producing one type of eggs/ova – all X-containing) . The X-containing sperm and Y-containing sperms can also be called as Gymnosperm and endosperm, respectively.
• In human also, it is the genetic make -up of sperms that determines the sex of the child and it is very unfortunate that women are blamed for producing female children (daughters) and even ill-treated for this false notion.

The diagram shows a single cotyledon.

What is the structures X, Y and Z?

What Are the Structures X, Y and Z?

	X	Y	Z
A	plumule	radicle	cotyledon
B	cotyledon	radicle	plumule
C	cotyledon	plumule	radicle
D	plumule	cotyledon	radicle

Answer

a.

Explanation

• A seed may have one or two coverings called seed coats develops from integuments of oracle. The outer seed coat is called testa, while the inner one is named as tegmen.
• The surface of the seed possesses a fi ne pore at one end is called micropyle.
• The testa ensures survival of seeds. The micropyle of ovule permits the entry of water needed at the time of germination.
• Just behind the micropyle hilum is present. It is a scar left on the seed coat when it is detached from the fruit wall.
• Within the seed coat there is the embryo, consisting of an embryonal axis and two cotyledons. The cotyledons are often fleshy and full of reserve food materials.
• At the micropylar end of the embryonal axis, bears the radicle and the other end contains plumule are present.