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.

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11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. 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