Reproduction

  • Definition: The process by which new individuals of the same species are produced.
  • Two types of reproduction:
    • Asexual Reproduction
    • Sexual Reproduction
  • Importance of reproduction: Ensures the survival of species and introduces genetic variation.

Asexual Reproduction

  • Definition: Production of offspring from a single parent.
  • Advantages:
    • Rapid process
    • No need for a mate
    • Efficient in stable environments
  • Examples:
    • Binary Fission
    • Budding
    • Vegetative Propagation

Binary Fission

  • Definition: Division of a single organism into two offspring of identical size.
  • Examples:
    • Bacteria
    • Amoeba
  • Process:
    1. DNA replication
    2. Division of the cell into two equal parts
    3. Formation of two identical daughter cells

Budding

  • Definition: Offspring develops as an outgrowth or bud from the parent organism.
  • Example: Hydra
  • Process:
    1. Bud grows on the parent organism
    2. Bud detaches and develops into a new individual
    3. Parent organism remains intact

Vegetative Propagation

  • Definition: Formation of new individuals from vegetative parts of a plant.
  • Examples:
    • Runners in strawberry plants
    • Rhizomes in ginger plants
    • Tubers in potato plants
  • Process:
    1. Underground stem produces adventitious roots
    2. New plant develops from the stem or root

Sexual Reproduction

  • Definition: Fusion of male and female gametes to produce offspring.
  • Advantages:
    • Generation of genetic variation
    • Formation of hybrids
  • Involves two processes:
    1. Gametogenesis
    2. Fertilization

Gametogenesis

  • Definition: Formation of male and female gametes.
  • Gametes are haploid cells with half the number of chromosomes.
  • Male Gametogenesis: Spermatogenesis
    • Occurs in the testes
    • Results in the formation of sperm cells
  • Female Gametogenesis: Oogenesis
    • Occurs in the ovaries
    • Results in the formation of egg cells (ova)

Spermatogenesis

  • Definition: Process of formation of sperm cells.
  • Occurs in the seminiferous tubules of testes.
  • Process:
    1. Germ cells undergo mitosis to produce spermatogonia.
    2. Spermatogonia undergo meiosis I to form secondary spermatocytes.
    3. Meiosis II results in the formation of spermatids.
    4. Spermatids undergo maturation and develop into sperm cells.

Oogenesis

  • Definition: Process of formation of egg cells.
  • Begins during fetal development and completes during menstrual cycle.
  • Process:
    1. Oogonia undergo mitosis to produce primary oocytes.
    2. Meiosis I starts during fetal development but arrests in prophase I.
    3. After puberty, one primary oocyte completes meiosis I to form secondary oocyte and first polar body.
    4. If fertilized, meiosis II completes to form an egg cell and a second polar body.

Fertilization

  • Definition: Fusion of male and female gametes to form a zygote.
  • Process:
    1. Sperm cells reach the egg cell through the reproductive tract.
    2. Sperm nucleus fuses with egg nucleus to form a zygote.
    3. Zygote undergoes cell division to develop into an embryo.
  1. Sexual Reproduction in Flowering Plants - Flowers
  • Reproductive structure of angiosperms (flowering plants)
  • Consists of:
    • Sepals: Protect the developing flower bud
    • Petals: Attract pollinators with their color and scent
    • Stamens: Male reproductive organ, composed of anther and filament
    • Carpels: Female reproductive organ, composed of stigma, style, and ovary
  • Different types of flowers:
    • Perfect flowers: Bisexual flowers with both stamens and carpels
    • Imperfect flowers: Unisexual flowers with either stamens or carpels
  1. Pollination
  • Transfer of pollen from the anther to the stigma of a flower
  • Agents of pollination:
    • Wind: Anemophily (e.g. grasses, conifers)
    • Animals: Zoophily
      • Insects (entomophily): butterflies, bees, etc.
      • Birds (ornithophily): hummingbirds
      • Bats (chiropterophily)
  • Self-pollination: Pollen from the anther is transferred to the stigma of the same flower or a different flower on the same plant
  • Cross-pollination: Pollen from the anther is transferred to the stigma of a different plant of the same species
  1. Fertilization in Flowering Plants
  • After pollination, pollen grain germinates on the stigma
  • Pollen tube grows through the style and reaches the ovary
  • Double fertilization occurs:
    • One sperm cell fuses with the egg cell to form a zygote (2n)
    • Another sperm cell fuses with the polar nuclei to form endosperm (3n)
  • This process ensures the formation of a zygote and nourishment for the developing embryo
  1. Development of Fruit and Seed
  • After fertilization, the ovary develops into a fruit
  • Fruit protects the developing seeds and aids in seed dispersal
  • Mature fruit may be:
    • Fleshy (e.g. apple, mango)
    • Dry (e.g. bean, wheat)
    • Dehiscent (splits open) or indehiscent (does not split open)
  • Seeds contain the embryo, endosperm (in some cases), and a seed coat
  1. Germination of Seeds
  • Process by which a seed develops into a new plant
  • Conditions required for germination:
    • Water: Activates metabolic processes
    • Oxygen: Required for respiration
    • Suitable temperature: Varies with species
    • Light or darkness: Depends on species
  • Steps of seed germination:
    1. Imbibition: Absorption of water by the seed
    2. Activation: Enzymes become active
    3. Growth of embryo: Radicle (embryonic root) emerges first, followed by the shoot
  1. Asexual Reproduction in Flowering Plants
  • Vegetative propagation: A means of asexual reproduction in plants
  • Methods of vegetative propagation:
    • Stem cuttings: Pieces of stem are planted to grow new plants
    • Bulbs: Underground buds develop into new plants
    • Runners: Long horizontal stems produce new plants at nodes
    • Suckers: New shoots develop from lateral buds
    • Grafting: Union of the stem of one plant with the root system of another
    • Tissue culture: Culturing cells or tissue fragments in a laboratory
  1. Sexual Reproduction in Humans
  • Human reproduction involves the fusion of male and female gametes
  • Male reproductive system:
    • Testes: Produces sperm cells through spermatogenesis
    • Scrotum: External sac that holds the testes
    • Epididymis: Stores and matures sperm cells
    • Penis: Organ of copulation
  • Female reproductive system:
    • Ovaries: Produces egg cells through oogenesis
    • Uterus: Site of fetal development
    • Cervix: Connects the uterus to the vagina
    • Fallopian tubes: Where fertilization occurs
  1. Menstrual Cycle
  • Regular changes occurring in the female reproductive system
  • Phases of the menstrual cycle:
    1. Menstruation: Shedding of the uterine lining
    2. Follicular phase: Development of follicles in the ovary
      • One follicle matures and releases an egg cell
    3. Ovulation: Release of the mature egg cell from the ovary
    4. Luteal phase: Formation of the corpus luteum
      • If fertilization does not occur, the corpus luteum degenerates
    5. Preparing for the next cycle: The uterine lining thickens
  1. Fertilization in Humans
  • In humans, fertilization occurs in the fallopian tubes
  • Sperm cells swim towards the egg cell in the fallopian tube
  • Penetration of the egg:
    1. Acrosomal reaction: Enzymes in the sperm’s acrosome help penetrate the egg’s protective layers
    2. Fusion of sperm and egg nuclei: Fertilization occurs, forming a zygote
  • Implantation: Zygote implants into the uterine wall and develops into an embryo
  1. Pregnancy, Birth, and Lactation
  • Pregnancy: The development of the embryo and fetus in the uterus
  • Developmental stages:
    • Zygote: First two weeks after fertilization
    • Embryo: Weeks 3-8
    • Fetus: Weeks 9-birth
  • Birth: Uterine contractions and cervix dilation lead to the delivery of the baby
  • Lactation: Production and secretion of milk by the mammary glands for breastfeeding the newborn baby Reproduction - Sexual Reproduction in Flowering Plants: Flowers
  • Flowers are the reproductive structures of angiosperms (flowering plants)
  • They play a crucial role in the sexual reproduction of plants
  • Flowers consist of several parts:
    • Sepals: Leaf-like structures that protect the flower bud
    • Petals: Colorful structures that attract pollinators
    • Stamens: Male reproductive organs, composed of anther and filament
    • Carpels: Female reproductive organs, composed of stigma, style, and ovary Reproduction - Sexual Reproduction in Flowering Plants: Perfect and Imperfect Flowers
  • Flowers can be classified as perfect or imperfect
  • Perfect flowers: Also known as bisexual flowers, contain both stamens and carpels
    • Examples: Roses, lilies
  • Imperfect flowers: Complete flowers that have either stamens or carpels, but not both
    • Examples:
      • Staminate (male) flowers: Contain only stamens; e.g., cucumber
      • Pistillate (female) flowers: Contain only carpels; e.g., pumpkin Reproduction - Sexual Reproduction in Flowering Plants: Pollination
  • Pollination is the transfer of pollen from the anther to the stigma of a flower
  • The main agents of pollination are wind, insects, birds, and bats
  • Anemophily: Pollination by wind
    • Examples: Grasses, conifers
  • Zoophily: Pollination by animals
    • Entomophily: Pollination by insects (e.g., bees, butterflies)
    • Ornithophily: Pollination by birds (e.g., hummingbirds)
    • Chiropterophily: Pollination by bats Reproduction - Sexual Reproduction in Flowering Plants: Self-Pollination
  • Self-pollination occurs when the pollen from the anther is transferred to the stigma of the same flower or a different flower on the same plant
  • It can be facilitated by various mechanisms:
    • Homogamy: The maturation of anthers and stigma at the same time
    • Cleistogamy: Flowers that self-pollinate without opening
    • Herkogamy: Physical barriers preventing cross-pollination
  • Self-pollination ensures reproduction in case of a lack of pollinators but limits genetic variation Reproduction - Sexual Reproduction in Flowering Plants: Cross-Pollination
  • Cross-pollination occurs when the pollen from the anther is transferred to the stigma of a different plant of the same species
  • It promotes genetic diversity and leads to the formation of hybrids
  • Cross-pollination is facilitated by various agents, such as insects, birds, and wind
  • To achieve cross-pollination, plants have mechanisms to prevent self-pollination, such as:
    • Dichogamy: The maturation of stamens and carpels at different times
    • Heterostyly: Different arrangements of stamens and carpels in different flowers of the same species Reproduction - Sexual Reproduction in Flowering Plants: Fertilization
  • After pollination, the pollen grain germinates on the stigma
  • A pollen tube grows through the stigma and style, reaching the ovary
  • Double fertilization occurs in flowering plants:
    • One sperm cell fuses with the egg cell to form a diploid zygote (2n)
    • Another sperm cell fuses with the polar nuclei to form the triploid endosperm (3n)
  • The endosperm provides nutrition to the developing embryo
  • This unique process ensures the formation of both the zygote and nourishment for the growing embryo Reproduction - Sexual Reproduction in Flowering Plants: Development of Fruit
  • After fertilization, the ovary develops into a fruit
  • The fruit protects the developing seeds and aids in their dispersal
  • The mature fruit can be classified into different types:
    • Fleshy fruit: Soft, juicy fruit, e.g., apple, mango
    • Dry fruit: Hard or papery fruit, e.g., bean, wheat
    • Dehiscent fruit: Split open when ripe, e.g., pea pod
    • Indehiscent fruit: Do not split open naturally, e.g., acorns
  • The seeds inside the fruit contain the embryo, endosperm (in some cases), and a protective seed coat Reproduction - Sexual Reproduction in Flowering Plants: Germination
  • Germination is the process by which a seed develops into a new plant
  • It requires specific conditions:
    • Water: Activates metabolic processes in the seed
    • Oxygen: Needed for respiration and energy release
    • Suitable temperature: Varies with the plant species
    • Light or darkness: Some seeds require light for germination, others require darkness
  • Seed germination involves several steps:
    1. Imbibition: Absorption of water by the seed, causing it to swell
    2. Activation: Enzymes become activated, initiating metabolic processes
    3. Growth of the embryo: The radicle (embryonic root) emerges first, followed by the shoot Reproduction - Sexual Reproduction in Flowering Plants: Asexual Reproduction
  • Asexual reproduction in flowering plants is known as vegetative propagation
  • It involves the production of new individuals from vegetative parts of a plant, such as stems or roots
  • Methods of vegetative propagation include:
    • Stem cuttings: Planting cuttings from stems to grow new plants
    • Bulbs: Underground buds that develop into new plants
    • Runners: Long horizontal stems that produce new plants at nodes
    • Suckers: New shoots that develop from lateral buds on the roots or stem base
    • Grafting: A stem of one plant is joined with the root system of another plant
    • Tissue culture: Cells or tissue fragments are cultured in a laboratory to produce new plants