Reproduction
- Definition: The biological process by which new individuals of the same species are produced
- Importance: Ensures the continuation of a species
- Asexual Reproduction
- Definition: Production of offspring from a single parent without involvement of gametes
- Examples: Budding, fission, regeneration
- Advantages: Rapid population growth, no need to find a mate
- Disadvantages: Lack of genetic variation, increased vulnerability to environmental changes
- Sexual Reproduction
- Definition: Reproduction involving the fusion of gametes from two parents
- Examples: Humans, animals, most plants
- Advantages: Genetic variation, adaptability to changing environments
- Disadvantages: Slower population growth, finding a mate can be challenging
Reproduction in Plants
- Plants have a variety of reproductive strategies
- Sexual reproduction is the primary mode of reproduction in flowering plants
Sexual Reproduction in Flowering Plants - Pollination
- Definition: Transfer of pollen grains from anther to stigma
- Types of pollination:
- Self-pollination: Pollen transferred from anther to stigma of the same flower or different flower on the same plant
- Cross-pollination: Pollen transferred from anther to stigma of a different flower on a different plant
Sexual Reproduction in Flowering Plants - Fertilization
- Definition: Fusion of male and female gametes to form a zygote
- Fertilization process:
- Pollen tube growth: Pollen tube extends from pollen grain to reach the ovule
- Entry of male gametes: Male gametes move through the pollen tube to reach the embryo sac
- Fusion: One male gamete fuses with the egg cell to form a zygote
- Formation of endosperm: Another male gamete fuses with the two polar nuclei to form endosperm
Sexual Reproduction in Flowering Plants - Different Types of Ovule
- Ovule: Female reproductive structure in plants
- Types of ovules:
- Anatropous ovule: Ovule with a straight micropyle and a bent embryo-sac
- Campylotropous ovule: Ovule with a curved micropyle and a curved embryo-sac
- Orthotropous ovule: Ovule with a straight micropyle and a straight embryo-sac
Sexual Reproduction in Flowering Plants - Embryo Development
- After fertilization, zygote divides and develops into an embryo
- Embryo development stages:
- Globular stage: Embryo resembles a sphere
- Heart stage: Embryo develops heart-shaped structure
- Torpedo stage: Embryo elongates and acquires a torpedo-like shape
- Mature embryo stage: Embryo matures and is ready to grow into a seedling
- After embryogenesis, seed formation occurs
- Seed components:
- Seed coat: Protective outer covering
- Endosperm: Food reserve for the growing embryo
- Embryo: Developing plant inside the seed
- After fertilization, ovary develops into a fruit
- Fruit characteristics:
- Protects seeds
- Aids in seed dispersal
- Provides nutrition for seed germination
Modes of Sexual Reproduction in Flowering Plants
- Flowering plants have evolved various mechanisms for sexual reproduction
- Examples:
- Self-pollination with self-fertilization
- Self-pollination with cross-fertilization
- Cross-pollination with self-fertilization
- Cross-pollination with cross-fertilization
Slide 11: Reproduction in Flowering Plants - Different Types of Ovule
- Ovule: Female reproductive structure in plants
- Types of ovules:
- Anatropous ovule: Ovule with a straight micropyle and a bent embryo-sac
- Campylotropous ovule: Ovule with a curved micropyle and a curved embryo-sac
- Orthotropous ovule: Ovule with a straight micropyle and a straight embryo-sac
Example: In anatropous ovules, the embryo-sac is bent, allowing for the proper development of the embryo.
Equation: Anatropous ovule arrangement: Micropyle straight, Embryo-sac bent => ovule shape
Slide 12: Reproduction in Flowering Plants - Embryo Development
- After fertilization, zygote divides and develops into an embryo
- Embryo development stages:
- Globular stage: Embryo resembles a sphere
- Heart stage: Embryo develops heart-shaped structure
- Torpedo stage: Embryo elongates and acquires a torpedo-like shape
- Mature embryo stage: Embryo matures and is ready to grow into a seedling
Example: During the torpedo stage, the elongated embryo starts to take on a recognizable plant structure.
Equation: Embryo development stages: Zygote division => Globular stage => Heart stage => Torpedo stage => Mature embryo stage
- After embryogenesis, seed formation occurs
- Seed components:
- Seed coat: Protective outer covering
- Endosperm: Food reserve for the growing embryo
- Embryo: Developing plant inside the seed
Example: In maize plants, the endosperm is rich in starch and provides nourishment for the developing embryo.
Equation: Seed formation: Embryogenesis => Seed coat + Endosperm + Embryo
- After fertilization, ovary develops into a fruit
- Fruit characteristics:
- Protects seeds
- Aids in seed dispersal
- Provides nutrition for seed germination
Example: Apples are a fruit that develops from the ovary and protects the seeds within. The flesh of the apple serves as a source of nutrition for the seeds.
Equation: Fruit formation: Ovary development => Protective covering + Seed dispersal + Seed nutrition
Slide 15: Modes of Sexual Reproduction in Flowering Plants
- Flowering plants have evolved various mechanisms for sexual reproduction
- Examples:
- Self-pollination with self-fertilization: Pollen from the same flower fertilizes the ovule.
- Self-pollination with cross-fertilization: Pollen from one flower of the same plant fertilizes another flower of the same plant.
- Cross-pollination with self-fertilization: Pollen from one flower is transferred to another flower on a different plant of the same species, and self-fertilization occurs.
- Cross-pollination with cross-fertilization: Pollen from one flower is transferred to another flower on a different plant of a different species, and cross-fertilization occurs.
Example: Many plants, such as tomatoes, are capable of self-pollination, enabling them to reproduce even without the presence of other plants.
Equation: Modes of sexual reproduction: Self-pollination + Self-fertilization, Cross-pollination + Cross-fertilization
Reproduction in Flowering Plants - Cross-Pollination Mechanisms
- Cross-pollination can occur through various mechanisms:
- Wind pollination: Pollen grains are carried by wind to reach the stigma of another flower.
- Insect pollination: Insects, such as bees and butterflies, transfer pollen from one flower to another while collecting nectar.
- Bird pollination: Birds, such as hummingbirds, transfer pollen from flower to flower while feeding on nectar.
- Water pollination: Pollen grains are carried through water to reach the ovule of another flower.
Example: Maize plants have separate male and female flowers on the same plant. The tassel produces pollen, which is then transferred by wind to the silk of the ear, where fertilization occurs.
Equation: Cross-pollination mechanisms: Wind pollination + Insect pollination + Bird pollination + Water pollination
Reproduction in Flowering Plants - Flower Adaptations for Pollination
- Flowers have evolved adaptations to attract pollinators:
- Brightly colored petals: Attract insects and birds.
- Sweet-scented nectar: Attracts insects and birds.
- Landing platforms: Provide a stable surface for insects to land.
- Long tubes: Allow for special pollinators, such as hummingbirds, to reach nectar.
- Sticky or feathery stigma: Capture pollen grains brought by pollinators.
Example: Orchids have evolved complex adaptations, such as bright colors, unusual shapes, and long tubes, to attract specific pollinators, such as moths or bees.
Equation: Flower adaptations: Bright petals + Scented nectar + Landing platforms + Long tubes + Sticky stigma
Reproduction in Flowering Plants - Seed Dispersal Mechanisms
- After fruit formation, seeds need to be dispersed away from the parent plant for germination:
- Wind dispersal: Seeds are lightweight and have structures, such as wings or hairs, to catch the wind.
- Animal dispersal: Seeds have adaptations, such as hooks or barbs, to attach to the fur or feathers of animals.
- Water dispersal: Seeds have buoyancy or flotation mechanisms to be carried away by water currents.
- Gravity dispersal: Seeds fall from the parent plant and roll or bounce away.
Example: Maple trees produce samaras or “helicopter” seeds, which have wings that allow them to be carried by the wind.
Equation: Seed dispersal mechanisms: Wind dispersal + Animal dispersal + Water dispersal + Gravity dispersal
Reproduction in Flowering Plants - Germination
- Germination is the process by which a seedling begins to grow from a seed:
- Activation: The seed takes in water and swells, activating biochemical processes.
- Growth: The embryo root (radicle) emerges from the seed and grows downward, seeking water and nutrients.
- Shoot growth: The shoot (plumule) emerges from the seed and grows upward, developing leaves and stems.
- Leaf expansion: The cotyledons or seed leaves unfold and expand, performing photosynthesis.
Example: In pea plants, the radicle emerges first, followed by the plumule, which develops into the stem and leaves. The cotyledons provide nutrition to the growing seedling until it can photosynthesize.
Equation: Germination: Activation + Growth + Shoot growth + Leaf expansion
Reproduction in Animals
- Animals also exhibit various reproductive strategies:
- Oviparous: Animals lay eggs that hatch outside the body.
- Viviparous: Animals give birth to live young after internal development.
- Ovoviviparous: Animals retain eggs inside the body until they hatch, and then give birth to live young.
Example: Birds, such as chickens, are oviparous, as they lay eggs that hatch outside their bodies.
Equation: Animal reproduction: Oviparous + Viviparous + Ovoviviparous
Reproduction in Animals - Sexual Reproduction
- Sexual reproduction in animals involves the fusion of gametes from two parents:
- Male gamete: Sperm produced by testes.
- Female gamete: Egg (ovum or ova) produced by ovaries.
- Fertilization: Fusion of sperm and egg to form a zygote.
Example: In humans, sperm is produced in the testes and released during ejaculation. The egg is produced in the ovaries and released during ovulation. Fertilization occurs in the fallopian tubes.
Equation: Animal sexual reproduction: Male gamete + Female gamete + Fertilization
Reproduction in Humans - Male Reproductive System
- The male reproductive system includes:
- Testes: Produce sperm.
- Epididymis: Stores and matures sperm.
- Vas deferens: Transports sperm from epididymis to urethra.
- Urethra: Passage for both urine and sperm.
- Penis: Organ for copulation.
Example: The testes in the male reproductive system produce millions of sperm cells per day.
Equation: Male reproductive system: Testes + Epididymis + Vas deferens + Urethra + Penis
Reproduction in Humans - Female Reproductive System
- The female reproductive system includes:
- Ovaries: Produce eggs (ova) and female sex hormones.
- Fallopian tubes: Transport eggs from ovaries to uterus.
- Uterus (womb): Site for implantation and development of embryo.
- Cervix: Pathway between uterus and vagina.
- Vagina: Organ for intercourse and childbirth.
Example: The ovaries in the female reproductive system release one mature egg (ovum) per month during ovulation.
Equation: Female reproductive system: Ovaries + Fallopian tubes + Uterus + Cervix + Vagina
Reproduction in Humans - Menstrual Cycle
- The menstrual cycle is a recurring series of physiological changes in females:
- Menstruation: Shedding of the uterine lining (endometrium) if fertilization does not occur.
- Follicular phase: Development of follicles in the ovary, leading to the maturation of an egg.
- Ovulation: Release of a mature egg (ovum) from the ovary.
- Luteal phase: Development of the corpus luteum and preparation of the uterus for implantation.
Example: During the menstrual cycle, the endometrium thickens to create a suitable environment for embryo implantation if fertilization occurs.
Equation: Menstrual cycle: Menstruation + Follicular phase + Ovulation + Luteal phase
Reproduction in Humans - Fertilization and Pregnancy
- Fertilization occurs when a sperm fuses with an egg to form a zygote:
- Embryonic development: The zygote undergoes cell division and implants in the uterus.
- Pregnancy: The period of gestation from fertilization to childbirth.
- Gestational age: The age of the developing fetus measured from the first day of the last menstrual period.
- Trimesters: Pregnancy divided into three-month periods.
Example: Pregnancy lasts approximately 40 weeks from the first day of the last menstrual period (LMP), which is equivalent to 38 weeks from fertilization.
Equation: Fertilization and pregnancy: Fertilization + Embryonic development + Pregnancy + Gestational age + Trimesters