How do Organisms Reproduce?

7.1 Do Organisms Create Exact Copies of Themselves?

DNA (Deoxyribo Nucleic Acid): The chemical molecule in the chromosomes of a cell nucleus that acts as the information source for making proteins, determining body design.
DNA Copying: A fundamental process of reproduction involving biochemical reactions that create two identical DNA copies in a dividing cell.
Cellular Apparatus: The organized cellular structure created alongside DNA copies to maintain life processes when a cell divides into two.
Variation: Inbuilt biochemical inaccuracies during DNA copying that generate subtle differences in offspring, acting as the foundation for evolution.

Niches: Defined geographical or ecological places in an ecosystem occupied by reproducing species.
Consistency of DNA Copying: Maintains stable body designs suited to specific niches, ensuring the stability of species populations.
Adaptation: Variations allow some individuals of a population to survive sudden environmental disruptions (e.g., global warming, temperature fluctuations).

7.2 Modes of Reproduction Used by Single Organisms

Fission: Unicellular cell division resulting in the creation of new individuals.
Binary Fission: Splitting of a parent cell into two equal halves, which can happen in any plane (e.g., Amoeba) or in a definite orientation (e.g., Leishmania).
Multiple Fission: Simultaneous division of a single-celled organism into many daughter cells (e.g., Plasmodium).

Fragmentation: Simple reproductive method where a multicellular organism with simple organization matures and breaks into smaller fragments that grow into new individuals (e.g., Spirogyra).

Regeneration: The capacity of fully differentiated organisms (e.g., Hydra, Planaria) to grow into complete individuals from cut body fragments using specialized proliferating cells.

Budding: Form of reproduction where a bud develops as an outgrowth from repeated cell division at a specific site, eventually detaching as an independent individual (e.g., Hydra).

Vegetative Propagation: Reproduction in plants where roots, stems, or leaves develop into new plants under appropriate conditions (e.g., Bryophyllum leaves with buds).
Horticultural Techniques: Methods like layering or grafting used to cultivate plants like sugarcane, roses, and seedless varieties (banana, orange).
Tissue Culture: Growing new plants by culturing cells from growing tips in an artificial hormone medium to form a callus.

Sporangia: Tiny blob structures containing spores that are protected by thick walls and develop into new individuals under moist conditions (e.g., Rhizopus).
Asexual Reproduction: Generation of offspring from a single parent without gamete fusion.

7.3 Sexual Reproduction

Sexual Reproduction: Reproductive process combining DNA from two distinct individuals, generating high levels of diversity.
Meiosis: Reduction cell division that halves chromosome numbers in germ-cells (gametes) to maintain a constant DNA volume in subsequent generations.
Male Gamete: A small, highly motile germ-cell.
Female Gamete: A larger, non-motile germ-cell that stores food resources.

Angiosperms: Flowering plants containing reproductive organs in the flower.
Stamen: Male reproductive organ containing pollen grains.
Pistil: Female reproductive organ composed of the ovary (with ovules), style, and sticky stigma.
Pollination: Transfer of pollen from stamen to stigma via self-pollination (same flower) or cross-pollination (different flowers).
Fertilisation: Fusion of male and female gametes to produce a zygote, forming an embryo inside a seed.
Germination: The emergence of a seedling from a seed under favorable conditions.

Puberty: Adolescent phase marked by reproductive tissue maturation and development of secondary sexual traits.
Male Reproductive System: Includes testes located in the scrotum, testosterone hormone, vas deferens, accessory glands (seminal vesicles and prostate), and urethra.
Female Reproductive System: Composed of ovaries, fallopian tubes (oviducts), uterus (womb), and vagina.
Placenta: A specialized disc-like tissue that provides oxygen and nutrient exchange between maternal blood and the growing foetus.
Menstruation: Periodic monthly shedding of the blood-rich uterine lining when fertilization does not occur.
Reproductive Health: Practices focused on safe sexual behavior, contraception, and the prevention of sexually transmitted diseases (STDs) (like syphilis, gonorrhoea, HIV-AIDS).
Contraception: Avoidance of pregnancy using physical barriers (condoms, copper-T), chemical hormonal methods (oral pills), or surgical blocks.

Chapter 7: How do Organisms Reproduce?