Reproduction

• Floral organs


  • Stamens
  • Carpels
  • Sepals
  • Petals
• Sepal


  • Enclose and protect the floral bud before it opens
  • Usually green and more leaflike in appearance than the other floral organs
• Petal


  More brightly colored than sepals and attract the flower to insects and pollinators
• Stamen


  • Consist of a filament (stalk) and an anther (terminal structure)
  • Within the anther are pollen sacs, chambers which pollen is produced
• Carpel


  • Has an ovary at its base and a long slender neck called style
  • Stigma: sticky structure on top of the style that serves as a landing platform for pollen
  • Within the ovary are one or more ovules, with the number depending on the species
• Pistil


  Sometimes used to refer to a single carpel or to a group of fused carpels
• Flower types


  • Complete - with 4 parts (sepals, petals, pistils, and stamens)
  • Incomplete - integral parts forming a flower are missing (any petals, sepals, pistils, and stamens)
• Flower reproductive structures


  • Perfect - both male and female reproductive structures are present
  • Imperfect/Unisexual - flower that does not have both male and female structures
• Whorls


  Arrangement of sepals, leaves, petals, carpels, or stamen, radiating from specific point and wrapping around the stalk or stem

  
• Gametophyte


  • Stage in the life cycle that is found in all plants and certain species of algae
  • Process includes both Sporophyte (multicellular diploid generation) and gametophyte (multicellular haploid generation)

  
• Diploid


  Two sets of chromosomes in the cells, normally written as '2n'
• Haploid


  Only one set of chromosomes in the cells, written as 'n'
• Development of a male gametophyte (pollen grain)


  1. Microsporangia (pollen sacs) in anthers contain diploid microsporocytes (microspore mother cells)

  2. Each microsporocyte divides to produce 4 haploid microspores, each of which develops into pollen grains

  3. A pollen grain becomes a mature male gametophyte when its generative nucleus divides and forms two sperm

  
• Development of a female gametophyte (embryo sac)


  1. Within the ovule's megasporangium is a large diploid cell called a megasporocyte (megaspore mother cell)

  2. The megasporocyte divides by meiosis and gives rise to 4 haploid cells, but in most species, only one of these survives as the megaspore

  3. 3 mitotic divisions of the megaspore form the embryo sac, a multicellular female gametophyte

  
• Double fertilization


  After landing on a receptive stigma, a pollen grain absorbs moisture and germinates, producing a pollen tube that extends down between the cells of the style toward the ovary
• From ovule to seed


  1. After double fertilization, each ovule develops into a seed, and the overy develops into a fruit enclosing seed(s)

  2. As the embryo develops from the zygote, the seed stockpiles proteins, oils, and starch to varying extents, depending on the species

  3. These nutrients are initially stored in the endosperm, but later in seed development in many species, the storage function of the endosperm is more or less taken over by the swelling
• From ovary to fruit


  1. While the seeds are developing from ovules, the ovary of the flower is developing into a fruit, which protects the enclosed seeds and, when mature, aids in their dispersal by wind or animals

  2. Fertilization triggers hormonal changes that cause the ovary to begin its transformation into a fruit

  3. If the flower has not been pollinated, fruit usually does not develop, and the entire flower withers and falls away

  4. During the fruit development, the ovary wall becomes the pericarp, the thickened wall of the fruit
• Developmental origin of fruits


  • Simple Fruit - Develops from a single carpel (or several fused carpels) of one flower
  • Aggregate fruit - Develops from many separate carpels of one flower
  • Multiple Fruit - Develops from many carpel of the many flowers that form an inflorescence
  • Accessory Fruit - Develops largely from tissues other than the ovary

  
• Asexual reproduction


  Creation of new individuals whose genes all come from one parent without the fusion of egg and sperm
• Sexual reproduction


  • Creation of offspring by the fusion of haploid gametes to form a zygote-(fertilized egg), which is diploid
  • The female gamete, the unfertilized egg (also called an ovum), is a relatively large cell and not motile
  • The male gamete, the sperm, is generally a much smaller, motile cell

  
• Benefits of sexual reproduction

  • Increases genetic variability among offspring by generating unique combinations of genes inherited from two parents
  • May enhance the reproductive success of parents when environmental factors (including pathogens) change relatively rapidly
• Benefits of asexual reproduction


  • Enables animals living in isolation to produce offspring without locating mates
  • Creates numerous offspring in a short amount of time, which is ideal for colonizing a habitat rapidly
  • Perpetuates successful genotypes precisely in stable, favorable environments
• Mechanism of asexual reproduction


  A single parent splits, buds, or fragments to give rise to two or more offspring that have hereditary traits identical with those of the parent
• Types of asexual reproduction


  • Fission - separation of a parent into two or more individuals of approximately equal size
  • Budding - new individuals arise from outgrowths of existing ones
  • Fragmentation - the breaking of the body into several pieces, some or all of which develop into complete adults
  • Regeneration - the regrowth of lost body parts; usually accompanied with fragmentation
• Mechanism of sexual reproduction


  • Involves two parents, each contributing a specialized gamete (an egg or sperm) that fuse to form the fertilized egg, or zygote
  • Fertilization, the fusion of sperm and egg, may take place inside the body (internal fertilization) or outside the body (external fertilization)
• Types of sexual reproduction


  • Internal Fertilization - male generally delivers sperm cells directly into the body of the female
  • External Fertilization - Mating partners usually release eggs and sperms into the water simultaneously
• Male reproductive system


  • Male Gonad (testis) - sperm are produced
  • Sperm duct - used for the transport of sperm to the exterior of the body
  • Penis - terminal part of the sperm duct which opens onto or into a copulatory organ
• Female reproductive system


  • Female gonad (ovary) - eggs are produced
  • Oviduct - a tube for the transport of egg
  • Vagina - terminal portion of the oviduct responsible for the receiving of male copulatory organ
• Many fish, amphibians, and other sexual aquatic animals

  • Use external fertilization
• Exceptions are aquatic mammals, sharks, and some other special types of fish
• MALE REPRODUCTIVE SYSTEM


  • Male Gonad (testis) - sperm are produced
  • Sperm duct - used for the transport of sperm to the exterior of the body
  • Penis - terminal part of the sperm duct which opens onto or into a copulatory organ
• FEMALE REPRODUCTIVE SYSTEM


  • Female gonad (ovary) - eggs are produced
  • Oviduct - a tube for the transport of egg
  • Vagina - terminal portion of the oviduct responsible for the receiving of male copulatory organ
• Metagenesis


  "transformation development", refers to an alternation of asexual and sexual generations
• Both generations consist of diploid organisms
• Parthenogenesis


  "Virgin development", a form of reproduction in which an unfertilized egg develops into an adult animal
• Parthenogenesis occurs for several generations, after which males develop, produce sperm, and mate with females to fertilize their eggs
• Parthenogenesis


  Advantageous in maintaining social order in some species, appears to be an adaptation for survival in times of stress or when there is a serious decrease in population in other species
• Hermaphroditism


  A single organism produces both eggs and sperm
• Although hermaphroditism is still classified as sexual reproduction (since both eggs and sperm are involved), it is an exception to the important generalization that sexual reproduction involves two different individuals</b>
• FEMALE REPRODUCTIVE ORGANS


  • Ovaries - Produce both the egg cell and the sex hormones
  • Oviducts and Uterus - Egg cell is released into the abdominal activity near the opening of the oviduct, or fallopian tube. Uterus is a thick, muscular organ that can expand during pregnancy to accommodate a 4-kg fetus. Endometrium (inner lining of the uterus) is richly supplied with blood vessels. Cervix (neck of the uterus) opens into the vagina.
  • Vagina and Vulva - a thin-walled chamber that is the repository for sperm during copulation and that serves as the birth canal through which a baby is born. Vulva is a collective term for the external female genitalia.
  • Mammary Glands - present in both sexes but normally function only in women. Within the glands, small sacs of epithelial tissue secrete milk which drains into a series of ducts opening at the nipple.