Chapter 7: How do Organisms Reproduce?
Purpose and Mechanism of Reproduction
Reproduction is not essential for an individual’s survival but is crucial for the continuation of a species. It involves the creation of a DNA copy and the formation of cellular machinery for new cells. While DNA copying ensures that offspring resemble parents, small variations can occur. These variations are important for evolution and allow species to survive environmental changes. Organisms use different reproductive strategies based on their body complexity, ranging from simple cell division to more intricate processes.
Asexual and Sexual Reproduction
Asexual reproduction involves a single parent and includes methods like binary fission in Amoeba, budding in Hydra and yeast, fragmentation in Spirogyra, and spore formation in Rhizopus. Vegetative propagation in plants allows new individuals to grow from roots, stems, or leaves, as seen in Bryophyllum and potato. Sexual reproduction, on the other hand, involves two parents and leads to greater variation. In flowering plants, reproduction occurs through pollination and fertilisation, forming seeds and fruits. In animals, it involves the fusion of male and female gametes, each contributing half of the DNA.
Human Reproductive System and Reproductive Health
Humans reproduce sexually. Males produce sperm in the testes, and females produce eggs in the ovaries. Fertilisation usually occurs in the fallopian tube, and the embryo develops in the uterus. If the egg isn’t fertilised, the uterine lining is shed during menstruation. Puberty marks the onset of reproductive maturity, with noticeable physical and hormonal changes. Reproductive health involves managing pregnancy and preventing sexually transmitted diseases. Contraceptive methods—like condoms, pills, and surgical procedures—help prevent unwanted pregnancies and maintain reproductive well-being.