Reproduction and Development

• Reproduction - is an essential characteristic of organisms to perpetuate their kind. Plants and animals can reproduce either sexually or asexually. The table below shows the difference between asexual reproduction and sexual reproduction.
• Asexual Reproduction. number of parents involve:

  • one

  Gametes:

  • No need for gamete union

  Genetic composition of offspring:

  • Genetically identical to parent (Clone)
• Sexual Reproduction

  number of parents involved:

  • Two

  Gametes:

  • Present; sperm has to fertilize the egg

  Genetic composition of offspring

  • Generall, are hybrids of parents
• One strategy of plants reproducing asexually is through - vegetative reproduction
• Vegetative Reproduction - type of reproduction in plants from its vegetative parts or specialized reproductive structures
• The structure in plant that reproduce vegetatively came mostly from modified stems such as,

  • runners
  • rubers
  • corn
  • rhizomes
• Another method used for plants to grow is by means of “artificial plant propagation“ with a little help from the human
• Woody plants are reproduced through “grafting”, which attaches a piece of stem from one plant to the root or root-bearing of another plant.
• The result of combining it to a root-bearing stem host is called “stock”, and the grafted stem part is called the “scion”.
• “Angiosperms” or flowering plants
• Sexual reproduction occurs in the “sexual organ of the flower”.
• Male Organs of the Flower:

  • Stamen -  male reproductive part of a flower.
  • Anther - makes tiny grains called “pollen”, which contains male sex cells
  • Filament – holds up the anther.

  Female Organs of a flower:

  • Carpel - Female Reproductive Part
  • Stigma – top part of the carpel with sticky surface to trap the pollen
  • Style – joins the stigma and the ovary
  • Ovary – Contains the female sex cells called ovules
• Flowering plants may develop and reproduce through “pollination“ wherein the pollen is transfer from the anther to the stigma. This will happen with the help of insects, animals, and wind.
• “Double fertilization“ process is seen in plants that bear fruits which may contain one or many seeds.

   
• Fruits have two purpose:

  (1) to protect the seed from damage against animals and infectious agents

  (2) to aid in seed dispersal
• Seeds protect the future embryo from harm and only grow when favorable conditions exist. Seed can be classified as “monocot” and “dicot”. “Monocot” is a plant with one cotyledon inside its seed, while “dicot” is a plant with two cotyledons inside its seed.
• ANIMAL REPRODUCTION

  Just like this, reproduction is part of a life cycle in which individuals grow, develop, and reproduce according to instructions encoded in DNA. And such is, the most vital function of living organisms.
• Asexual Reproduction in Animals

  The type of reproduction in animals that reproduce asexually are commonly found among lower forms of organisms such as protists, cnidarians, hydra, amoeba, and some complex animals. The resulting offspring are identical to the parent in terms of characteristics.
• Asexual reproduction


  Also called 'clonal reproduction'
• Mechanisms of asexual reproduction in unicellular organisms

  1. Fission

  2. Budding

  3. Fragmentation
• Fission


  • Division of body into two or more equal parts
  • Example: Amoeba and Paramecium
• Budding


  • New individual arises as an outgrowth (bud) from its parent
  • New outgrowth can become an independent animal or may remain attached to parent forming a colony
  • Example: Hydra
• Fragmentation


  • Body breaks into two or more parts
  • Each fragment capable of becoming a complete individual
  • Example: Starfish and Earthworms
• Some species like flatworms, roundworms annelids, crustaceans, insects, fishes, and some reptiles can reproduce through the process known as parthenogenesis (parthenos-virgin; genesis-birth).
• Sexual Reproduction in Animals

   

  Most animals, particularly the higher forms, reproduce sexually (a process in which new individuals are formed from sex cells or gametes) produced by the parents in their sexual organs. The majority of these animals are dioecious (separate sexes).

   

  Sexual reproduction in animals occurs in three fundamental steps:

  1.  Gametogenesis : production of gametes

  2.  Spawning or mating: bringing gametes together

  3.     Fertilization: fusion of gametes (external fertilization or internal fertilization)
• Most numbers of vertebrates, earthworms, and some fishes are hermaphrodites. Few vertebrates, many fishes and some lizards undergo the process of sequential hermaphroditism or sex reversal (can change their sex) in response to social or environmental challenges.
• Animals like cnidarians develop temporary reproductive organ known as gonads during fall (mating season). The rest of the animals in the kingdom has permanent reproductive organs, such as testis (produce sperm) and ovaries (produce eggs). The reproductive systems of animals have accessory ducts and organs that aid the reproductive process of bringing the gametes together.
• The advantages of sexual reproduction: (1) produces genetic variation in the offspring; (2) the species can adapt to new environments due to variation, which gives them a survival advantage, and (3) a disease is less likely to affect all the individuals in a population.
• The only disadvantages of sexual reproduction are time and energy are needed to find a mate and it is not possible for an isolated individual to reproduce.
• Human reproduction consists of two components – main reproductive organs and accessory organs. Similar to other forms of animals, both have a pair of gonads (testis and ovaries) containing germ cells that will later on, give rise to mature sex cells or gametes. Male and female hormones control the maturity of the reproductive systems and the development of secondary sexual characteristics to prepare the body for reproductive processes.

   
• Male Reproductive System


  • Testis - produce sperm cells
  • Scrotum - pouch-like sac that holds the testis
  • Penis - places sperms into the vagina during mating
  • Vas deferens - transports mature sperm to the urethra
  • Glands - provide liquid in which sperm can swim
• Seminal vesicle


  Secretes one of the components of the semen
• Prostate gland


  Secretes a milky fluid that is discharged into the urethra as part of the semen
• Bulbourethral gland


  Mucous secreting glands located at the base of the penis
• Functions of the female reproductive system


  • Production of female sex cells
  • Reception of sperm cells from the male
  • Nurturing the development of, and providing nourishment for, the new individual
• Ovary


  • Produces egg cells
• Oviduct


  • Passageway of eggs from the ovary to the uterus
  • Place where the egg is fertilized
• Uterus


  • Place where fertilized egg develops
• Vagina


  • Receives the penis of male during mating
• The female reproductive organ consists of the ovaries, uterine tubes (fallopian tubes), uterus, vagina, external genitalia, and mammary glands. The internal reproductive organs of the female are located within the pelvis, between the urinary bladder and rectum. The uterus and the vagina are in the middle line, with an ovary on each side of the uterus.