CLASS X BIOLOGY

Sexual Reproduction When reproduction takes place as a result of fusion of two gametes, one from each parent, it is called sexual reproduction The process of fusion of male and female gametes is called fertilization . ˜ The formation of gametes involves exchange of chromosomal (genetic) fragments between homologous chromosomes causing genetic recombination which leads to variation . Gametes : Special Reproductive cells are different from normal cells as they have half              the  number of chromosomes. e.g Human cells have 46 chromosomes but sperm and egg have 46/2=23 chromosomes. So when sperm and egg fuse, zygote will have 23+23= 46 chromosome. Male gamete : small in size and motile (has tail) Female gamete: big in size ( because of stored food reserve) and non motile. Sexual Reproduction in Plants It occurs mostly in flowering plants. In fact flowers are the reproductive organ of plants. FLOWERS Bisexual Flowers  Unisexual Fl

Class X A, B, C Complete notes of chapter "How do organisms reproduce? "- Asexual reproduction, General features of sexual reproduction. Do NCERT questions based on topics covered so far. Class XA  - Submit your report on dengue emphasising on how it affects our health (body functions affected) and suggesting measures as to how you can prevent its spread by ensuring cleanliness in your surroundings. Establish the relationship between environmental phenomenon of global warming and increase in the population of vector (e.g. mosquito) . Also submit your poster to spread awareness about dengue. HAPPY DUSSEHRA ! Enjoy the holidays and at the same time study for your upcoming Unit test..

HOW DO ORGANISM REPRODUCE ? ˜ Reproduction is the process by which living organisms produce new     individuals similar to themselves. ˜ Reproduction ensured continuity of life on earth. ˜ Reproduction – A bridge to hereditary transmission. ˜ It involves continuation of characters from the parents to daughter cells by Copying of DNA (Deoxyribose Nucleic Acid) molecules present in the chromosomes of the cell. ˜ Copying of DNAs is also not a foolproof exercise, even minute changes bring about Variation in the blue print of the offsprings. ˜ The useful variations are retained while the harmful one does not go beyond. ˜ Actually variations help the species to withstand drastic environmental changes, thus save the species from becoming extinct and promotes its survival for a longer time. ˜ This inbuilt tendency of variation is the ‘‘fuel’’ for Evolution.