Asexual vs Sexual Reproduction

UNIT VI REPRODUCTION

• Biology is essentially the story of life, where individual organisms die, but species can last millions of years if not threatened by extinction.
• Reproduction is essential for species to continue, allowing each individual to leave progeny via asexual or sexual means.
• Sexual reproduction introduces variations and enhances survival capabilities.
• This unit will delve into reproductive processes, specifically in flowering plants and humans.
• Human reproductive health and ways to prevent reproductive illnesses is also a topic.

Chapter 1: Reproduction in Organisms

• Every organism has a limited lifespan from birth to natural death and death is certain for all individuals, except single-celled organisms.
• Plant and animal species continuity results from living organisms' reproductive processes.
• The time-span of life may vary being as short as few days to few thousands of years
• Lifespans aren't correlated with size.
• Reproduction: A biological process where organisms create offspring similar to themselves, ensuring the species' continuation through generations and is a cycle of birth, growth, and death.
• Organisms have diverse methods to multiply, influenced by habitat, physiology, and other factors, categorized into asexual and sexual reproduction
• Asexual Reproduction: A single parent produces offspring without gamete formation, creating identical offspring, also called clones.

Asexual Reproduction

• Offspring are genetically similar and morphologically similar to their parents.
• Asexual reproduction occurs in single-celled organisms, plants, and animals with simple organization.
• Protists and Monerans: Organisms or parent cells divide into two to produce new individuals
• Binary fission: a cell divides into two halves that grow into adults (e.g., Amoeba, Paramecium).
• Budding: An unequal division in yeast results in buds which separate and mature (cells).
• Fungi and algae reproduce using special asexual structures such as microscopic motile zoospores. Other structures include conidia (Penicillium), buds (Hydra), and gemmules (sponge).
• Vegetative Reproduction: Plants use vegetative propagules like runners, rhizomes, suckers, tubers, offsets, and bulbs to create new offspring a form of asexual reproduction.
• Asexual reproduction often occurs in organisms with simple organizations (e.g., algae, fungi), while some species shift to sexual reproduction during adverse conditions.

Sexual Reproduction

• Male and female gametes formation by the same or different individuals and fuse and form zygote to create new organism
• Sexual reproduction leads to varied offspring unlike asexual.
• Diverse organisms share a similar pattern in sexual reproduction, regardless of external morphology, internal structure, or physiology.
• Juvenile Phase: All organisms must reach the certain growth and maturity before sexual reproduction. In this stage plants enter the vegetative phase, characterized by differing durations across organisms.
• The end of juvenile/vegetative phase marks reproductive phase, indicated in plants by flowering
• Flowering in some plants happens more than once called inter-flowering juvenile or mature
• In animals, physiological and morphological changes mark the transition to reproductive phase
• Cyclical changes in ovaries, ducts, and hormones characterize the reproductive phase in females
• Oestrus Cycle: Seen in non-primate mammals (cows, sheep, rats, deer, dogs, tigers, etc.) during reproduction.
• Menstrual Cycle: Seen in primates (monkeys, apes, humans).
• Seasonal Breeders: Mammals in natural conditions exhibit reproductive cycles during favorable seasons.
• Continuous Breeders: Other mammals are reproductively active throughout their reproductive phase.
• Senescence: Old age ends reproductive phase with physical changes like slowed metabolism and ultimately leads to death
• Hormones are responsible for transitions between phases, regulated by interactions with environmental factors

Events in Sexual Reproduction

• Involve similarity and differences to ensure successful reproduction.
• Sequence: Pre-fertilization, fertilization, post-fertilization events
• Pre-Fertilization Events: Includes gametogenesis and gamete transfer, before the fusion of gametes
• Gametogenesis: Refers to formation of male and female gametes
• Gametes: Haploid cells that can be similar (homogametes) or different (heterogametes)
• Male gamete called the atherozoid or sperm and female gamete is called the egg or ovum
• Gametes are haploid, produced mitotically in haploid parents or meiotically in diploid parents
• Meiocytes undergo meiosis. At end of meiosis chromosome is incorporated into each gamete, with number of meiocytes and gametes being related to number of chromosomes and genomes.
• Gamete Transfer: Physical transfer of male and female gametes is essential for fusion
• Male gamete is motile while female is stationary, however in fungi and some algae both are motile.
• Medium Needed: Male gametes move and in algae, bryophytes and pteridophytes water is the medium for gamete transport.
• More Male Gametes: Male gametes produced is several thousand times the female gametes, that has egg.
• Pollen Grains: Carriers of male gametes. transfer to stigma for fertilization
• Pollination: Transfer of pollen to the stigma, facilitated by wind or water. In bisexual plants anthers grow close, for cross-pollinating transfer.
• Dioecious animal needs special mechanism for gamtes to transfer to ensure critical for sucessful transfer.

Fertilization and Post-Fertilization Events

• 1.2.2 Fertilization: Syngamy is the fusion of gametes which results in diploidzygote. used often used interchangeably.
• Syngamy doesn't always happen but female gamete develops into new organism without fertilization called parthenogenesis.
• Syngamy In most organism occurs to algae & fishes well as amphibians by external fertilization outside the body,
• Great synchrony in many fishes as a type of external fertilization showing how each sexes great synchrony between them by releasing water.
• External fertilization offspring easy threat so their survive adulthood.
• Inside the body is intemafertilization with the eggs, being non-motile for it pollen tubes are formed seed bearing plants. Large number sperms and small number eges.
• 1.2.3 Post fertilization: zygote formed after set
• 1.2.3.1.Zygote forms both fertilizing organism. With Ext fertilization in external whereas int zygote forms inner body of organism
• Algae & fungi form thick wall in Zygote. For both Haplontific & Diplotife organisms the zygote undergoes this process.
• 1.2.3.2 The word Embryogenests means is development to enbryos of the zygote cell division and the differentiation. Anima

Explore the key differences between asexual and sexual reproduction. Learn about the advantages and disadvantages of each method. Understand the role of genetic variation in species survival.