Structure of Gametes
Structure of Gametes
Sexual reproduction takes place by the combination of special reproductive cells called 'sex cells'. These sex cells are also known by another name which is gametes'. We can now say that: The cells involved in sexual reproduction are called gametes Gametes are of two types : male gametes, and female gametes. The male gamete in animals is called 'sperm' and the female gamete in animals is called 'egg' (or "ovum'). We will now describe sperms and eggs (or ova) in somewhat detail.
(i) Sperms. The sperms are extremely small cells and we need a microscope to see them. A sperm is about 0.05 mm long. A highly enlarged sketch of sperm is show in Figure 1. A sperm has a head, a middle piece and a tail. A sperm is a single cell with all the usual cell components like nucleus, cytoplasm and cell membrane. The nucleus of sperm cell is tightly packed in its head. The sperm cell has very little cytoplasm. The purpose of tail of sperm is to make it move. The sperm moves by waving its tail from side to side. The term 'sperm' is the short form of the word spermatozoon' (which means male sex cell or male gamete).
(ii) Eggs (or Ova). The eggs (or ova) are also very small and we need a microscope to see them. Eggs (or ova) are, however, much larger than the sperms. The human egg (or ovum) is round and about 0.15 mm in diameter. A highly enlarged sketch of an egg (or ovum) is shown in Figure 2. The egg (or ovum) is also a single cell having a nucleus, cytoplasm and a cell membrane. Outside the cell membrane, an egg (or ovum) has a thin layer of jelly called 'jelly coat' which allows only one sperm to enter into it during fertilisation. Please note that a female gamete (or female sex cell) is known by two names : 'egg' and 'ovum'. So, whether we use the name 'egg' or 'ovum', it will mean the same thing. Another point to be noted is that the plural of ovum is ova. Some of the animals like birds (hen, ostrich, etc.) and reptiles (snakes, crocodiles, etc.) have large eggs.
The nuclei of sperm and egg contain chromosomes which carry genes and transmit the characteristics of parents to the offsprings. The fusion of a male gamete (sperm) with a female gamete (egg) gives rise to a new cell called zygote. Thus, the new cell which is formed by the fusion of a male gamete and a female gamete is called zygote. Zygote is a single cell which contains one nucleus.
Each egg or ovum is a spherical cell much ________________ than the sperm. | |||
| Right Option : B | |||
| View Explanation | |||
Which of the following are correct : (a) Each egg or ovum is a spherical cell much smaller than the sperm. (b) A sperm has a head, a middle piece and a tail. (c) Each egg or ovum is a spherical cell much bigger than the sperm. | |||
| Right Option : B | |||
| View Explanation | |||
The head of the sperm consists of the nucleus and structure called the _______________ at the tip. | |||
| Right Option : A | |||
| View Explanation | |||
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