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HOW DO ORGANISMS REPRODUCE? 1. (i) What is fertilisation? Distinguish between external fertilisation and internal fertilisation. (ii) What is the site of fertilisation in human beings? Answer. (i) Fertilisation is defined as the fusion of a male gamete (sperm) with a female gamete (an ovum or egg) to form a zygote during sexual reproduction. External Fertilisation Internal Fertilisation (i) The fusion of male gamete (sperm) and (i) The fusion of gametes occurs inside fernale gamete (ovum) occurs outside the body. |the body. (ii) Both individuals discharge their gametes (ii) Only the male discharges sperms into loutside the body. female genital tract. (iii) Development occurs outside the body. (ii) Development occurs inside the body. (iv) Example: Frog. (iv) Examples: Human, birds, cattle, etc. (ii) The site of fertilisation in human beings is in the fallopian tube of female reproductive system. 2, Define the terms unisexual and bisexual giving one example of each. Answer. Unisexual is the plant whose flowers contain either stamens or carpels but not both. Example: Papaya, Watermelon. Bisexual is the plant whose flowers contain both stamens and carpels. Example: Hibiscus, Mustard. 3. Differentiate between ‘self-pollination’ and ‘cross-pollination’. Describe double fertilisation in plants. Answer. Self-pollination Cross-pollination (i) Self-pollination occurs within a flower |(i) Cross-pollination occurs between two or between two flowers of the same plant. |flowers borne on different plants of the same species. (ii) Flowers do not depend on other (ii) Agents such as insects, water and wind are agencies for pollination. required for pollination. (iii) Pollen grains are produced insmall _|(iii) Pollen grains are produced in large numbers. numbers. During fertilisation in plants, the following events take place: (i) One of the male gamete fuses with the female gamete present in the embryo sac. (ii) The other male gamete fuses with the two polar nuclei in the embryo sac. The first fusion product gives rise to the zygote while the second one forms the endosperm. The process of two fusions occurring in the embryo sac is called double fertilisation. 4. What is the effect of DNA copying which is not perfectly accurate on the reproduction process? Answer. DNA copying is not perfectly accurate and the resultant errors are a source of variations in populations of organisms. 5. What is ‘reproduction’? Mention the importance of DNA copying inreproduction. Answer. Reproduction is the process of producing new individuals of the same species by existing organisms of a species, i.e. parents. The importance of DNA copying in reproduction are as follows: (i) DNA copying is called DNA replication. In this process, one copy each of replicated DNA will Scanned with CamScanner 
