IGCSE Biology Paper-4: Specimen Questions with Answers 107 - 108 of 120

Explanation

Bacterial-1. Chancroid (Haemophilus ducreyi)

2. Chlamydia (Chlamydia trachomatis)

Viral-1. Viral hepatitis (Hepatitis B virus)

1. Herpes simplex (Herpes simplex virus 1,2)

Explanation

The sperms are microscopic and motile cells. They remain alive and remain their ability to fertilize an egg. It can be divided into three parts

1. Head
2. Neck
3. Middle piece
4. Tail

1-Head-

• Head is the anterior most part of the spermatozoon. It is often conical but its shape varies considerably
• Acrosome is formed from Golgi body of the spermatid
• It may be long and slender, spheroidal, rod-shaped or lance-shaped, spoon-shaped or short and flat, thin and, cork-screw-shaped or hooked

2-Neck-

• It is very short and present between head and middle piece
• It contains proximal centriole towards the nucleus which plays a role in first cleavage of zygote and distal centriole which gives rise to the axial filament of the sperm

3- Middle piece-

• Middle piece connect to the small neck of sperm. In neck of sperm 2 centrioles are present.
• Proximal centriole form the mitotic spindle after the fertilization process. This centriole arranged longitudinally to the main axis. Distal centriole form the axis of sperm.
• Axial filament of sperm structure as 9 + 2 manner. 2 central fibers and 9 peripheral fibers present

1. Tail

• It is a longest part of sperm. In the tail, the axial filament is covered by a sheet, which is made up of nine singlet fibers.
• Stored food materials absent in the sperm, ribosome endoplasmic reticulum, nucleolus and RNA is absent in the sperm.