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Reproduction Chapter 4 Section 4-2 Reproduction A process by which an organism produces others of the same kind. There are two kinds of reproduction Sexual reproduction – uniting of sperm and egg Asexual reproduction – creating a new life from one parent -lower animals and plants can reproduce in this manner. Humans – sexual reproduction Body cells have 46 chromosomes in every cell Sex cells• Sperm cell – 23 chromosomes - father • Egg cell – 23 chromosomes - mother When sperm and egg unite it produces a child with 46 chromosomes in each body cell. Asexual reproduction - fission New organisms are produced from one parent. DNA or offspring is identical to the DNA of parent. Mitosis is an example of this form of repro. Paramecium- asexual Budding Asexual repro found in invertebrate animals such as hydra, starfish, sponges and worms Hydra – small freshwater tubular organism. Budding Asexual form of repro that allows bud to grow out of the hydra’s side, develop mouth tentacles and finally rip out of the hydra’s side to produce an offspring. Regeneration To grow new body parts from a piece of an animal. Starfish Strawberry plants use runners. Plantlets: These can take the form of runners (eg strawberries) or side branches (busy lizzy). New plant developing from strawberry runner Cuttings of plants Cuttings: We can make cuttings or grafts, which in the right conditions will develop roots and grow into a new plant. Planarian -repro by regeneration Planarian Identification: •Flatworm with prominent eyes and a triangular head. •Size: 5 - 20 mm. •Creeps like a slug on the ground; swims by wriggling in snake-like manner. What it Eats: •Predators that feed on a variety of tiny snails, worms, and protozoans. Interesting Facts: •If you cut a planarian into pieces, each piece will regenerate into a new planarian Bacterial fission Asexual reproduction Bacteria reaches a certain size DNA is copied Splits apart producing two daughter cells Bacterial cell division Sexual Reproduction Production of a new organism when sex cells from two parents combine Male – sperm Small with whiplike tails • Flagella • Used for movement Head – almost all nucleus Contains 23 chromosomes Female - egg Large cell Contains food for the embryo Contains 23 chromosomes Meiosis Production of sex cells Each sex cell must contain half the amount of chromosomes as a body cell Takes place in both plants and animals Importance of Sex Cells In humans there are 23 pairs of chromosomes46 chromosomes Each pair has 2 chromosomes that are alike Diploid – (double) a cell that has 2 of every chromosome Sex cells Haploid – contains one chromosome from each matched pair - (half the number) Fertilization Joining of an egg and a sperm Zygote – fertilized egg Zygote undergoes mitosis to further develop into the offspring. Egg cell surrounded by sperm cells Only one sperm can enter an egg Zygote results Meiosis This is the division of sex cells. There are two divisions of meiosis Return to Top of Page Cell Division Meiosis I Prophase I – doubled chromosomes and spindles appear - nuclear membrane and nucleolus disappear - doubled chromosomes tied Return to Top of Page Cell Division Metaphase I – paired chromosomes line on middle of cell. -centromeres attach to spindles Anaphase I – centromeres detach and move to ends of poles Telophase I – cell divides into 2 daughter cells Return to Top of Page Cell Division Meiosis II Prophase II – spindles and doubled chromosomes reappear Metaphase II – doubled chromosomes move to center of cell Anaphase II – chrom separate and move to ends of cell. Telophase II – spindles fibers disappear and nuclear membrane forms around chrom at ends of cell. Each nucleus is haploid Cell division occurs forming 4 daughter cells Results of meiosis 4 daughter cells with half the number of chromosomes in each (haploid)