Biology lecture 17

Describe mitosis and meiosis to include the terms haploid and diploid.

Mitosis produces two genetically identical daughter cells with the same chromosome number for growth, repair, and replacement. Meiosis involves two divisions, producing four genetically different haploid cells with half the chromosomes. Haploid (n) cells have one set of chromosomes, such as sperm and eggs, while diploid (2n) cells have two sets, one from each parent. Most body cells are diploid.

Describe a typical sexual life cycle in animals and identify the main stages and processes.

Diploid reproductive cells undergo meiosis to produce haploid sperm and eggs. During fertilization, these fuse to form a diploid zygote containing DNA from both parents. The zygote divides by mitosis, developing into a multicellular diploid organism. Once mature, it produces gametes through meiosis, repeating the cycle. In animals, only gametes are haploid; the zygote and developing organism are diploid.

Describe and give examples of the following types of asexual reproduction in animals: (a) budding (b) fragmentation (c) parthenogenesis.

Budding occurs when a new organism grows from the parent and may detach, as in hydra. Fragmentation occurs when an organism breaks into pieces that can regenerate into individuals, as in some sea stars and flatworms. Parthenogenesis occurs when an unfertilized egg develops into offspring, as in aphids, some bees, and certain lizards. All occur without sperm and egg fusion.

Compare and contrast asexual reproduction and sexual reproduction and explain the advantages of each.

Asexual reproduction involves one parent and produces generally identical offspring. It is faster, uses less energy, and requires no mate, making it useful in stable environments. Sexual reproduction involves meiosis and fertilization, producing genetically different offspring. This variation helps populations adapt to environmental changes and diseases, but sexual reproduction requires more time, energy, and mating risks.

Compare and contrast gonochoristic and hermaphroditic species.

Gonochoristic species have separate males and females that produce sperm or eggs, such as humans and birds. Hermaphroditic individuals can produce both gametes. The main difference is separate sexes versus the ability to perform both reproductive roles.

Compare and contrast external fertilization and internal fertilization and explain how they relate to an organisms’ habitat.

External fertilization occurs when sperm and eggs fuse outside the body, usually in water, as in many fish and frogs. Water prevents drying and allows sperm movement, but many gametes may be needed. Internal fertilization occurs inside the reproductive tract, as in mammals, birds, and reptiles. It is useful on land because it protects gametes and increases fertilization success.

Describe and give examples of the following ways in which offspring develop in organisms that carry out internal fertilization: (a) oviparous (b) viviparous (c) ovoviviparous.

Oviparous animals lay eggs that develop outside the body using yolk for nutrients, as in birds and many reptiles. Viviparous animals develop inside the mother and receive nutrients directly from her, often through a placenta, as in humans and most mammals. Ovoviviparous animals retain eggs internally, with embryos nourished mainly by yolk. Eggs hatch internally or around birth, producing live young, as in some sharks and snakes.

Specify the following main structures in male and female reproductive systems and state the function of each:(a) male: (i) testis (ii) vas deferens (iii) seminal vesicle (iv) ejaculatory duct (v) penis (b) female: (i) ovary (ii) oviduct (iii) uterus (iv) vagina. (Ch. 46.)

In males, testes produce sperm and testosterone, the vas deferens transports sperm, and seminal vesicles produce nutrient-rich semen fluid. Ejaculatory ducts carry semen into the urethra, and the penis transfers semen. In females, ovaries produce eggs and hormones, oviducts transport eggs and are the usual fertilization site, the uterus supports embryo and fetal development, and the vagina receives semen and serves as the birth canal.