Biology

• Generalized life cycle of plants

  • One of the defining features of land plants is their life cycle
  • The land plant life cycle is known as a sporic (for sporic meiosis), dibiontic, or haplodiplontic life cycle
  • This type of life cycle exhibits alternation of generations
  • To complete a full circuit of its life cycle, a land plant must produce two different types of multicellular organisms
  • These organisms, or generations, are called the sporophyte (spore-producing plant) and the gametophyte (gamete-producing plant)

  
• Spore


  A cell that can grow into a new organism without combining with another cell
• Gametes


  Cells that fuse during fertilization

  
• The plant life cycle

  1. Seed falls on the ground

  2. Germination

  3. Growth

  4. Reproduction

  5. Pollination

  6. Seed spreading

  
• Plant types based on the presence of reproductive structures


  • Monoecious
  • Dioecious

  
• Gametophyte development in flowering plants


  1. Male gametophyte development

  2. Female gametophyte development

  
• Pollination


  1. Transfer of pollen grain from the anther to the stigma

  2. May be animal-aided or wind-aided
• Double fertilization


  1. Pollen tube discharges the sperm cells into the embryo sac

  2. One sperm unites with the egg to form the zygote

  3. The other sperm fuses with the polar nuclei to become the endosperm

  
• Embryo development (embryogenesis)


  1. Zygote divides mitotically to produce the proembryo and suspensor

  2. Cotyledons appear on the proembryo

  3. Proembryo elongates into an embryo

  
• Maturation of ovary and ovule


  1. Ovary matures into fruit

  2. Ovule becomes the seed

  
• Seed germination


  1. Seed undergoes imbibition to break dormancy

  2. Nutrients stored in the endosperm or cotyledons are digested and transferred to the growing regions of the embryo

  3. Primary meristems develop

  4. Radicle emerges

  5. Plumule breaks through the soil surface

  
• Seedling growth to mature plant


  Primary meristems differentiate to become the different plant tissues

  
• Testes


  Male gonads that produce the sperm and male sex hormones

  
• Ovaries


  Female gonads that produce eggs or ova and female sex hormones

  
• Human reproduction employs internal fertilization and involves the integrated action of the endocrine (that is hormones), nervous and reproductive systems
• The gonads are sex organs that produce gametes


  • Male gonads are the testes
  • Female gonads are the ovaries
• Male reproductive system


  • The male external reproductive organs are the scrotum and the penis
  • The internal reproductive organs consist of gonads, accessory sex gland, and ducts

  
• Epididymis


  • A long coiled tube resting on the backside of each testicle
  • Transports and stores sperm cells produced in the testes
  • Brings the sperm to maturity

  
• Vas deferens


  • A long, muscular tube travelling from the epididymis into the pelvic cavity, to just behind the bladder
  • Transports mature sperm to the urethra
• Ejaculatory ducts


  • Formed by the fusion of the vas deferens and the seminal vesicles
  • Empty into the urethra
• Urethra


  • The tube that carries urine from the bladder to outside of the body
  • Has the additional function of ejaculating semen when the man reaches orgasm
• Seminal vesicles


  • Sac-like pouches attached to the vas deferens near the base of the bladder
  • Produce a sugar-rich fluid (fructose) that provides sperm with energy to help them move
• Prostate gland


  • A walnut-sized structure located below the urinary bladder in front of the rectum
  • Contributes additional fluid to the ejaculate
  • Prostate fluids also help to nourish the sperm
• Bulbourethral glands (Cowper's glands)


  • Pea-sized structures located on the sides of the urethra just below the prostate gland
  • Produce a clear, slippery fluid that empties directly into the urethra to lubricate the urethra and neutralize any acidity
• Male reproductive organs and their functions


  • Testis - Produces sperm and sex hormones
  • Epididymis - Site of sperm maturation and some storage of sperm
  • Vas deferens - Conducts and stores sperm
  • Seminal vesicle - Contributes fluid to semen
  • Prostate glands - Contributes fluid to semen
  • Bulbourethral gland - Contributes fluid to semen
  • Urethra - Conducts sperm and urine
  • Penis - Organ of copulation

  
• Unlike the female reproduction system, most of the male reproductive system is located outside the body
• Testes


  • Located in the scrotum which is located outside the abdominal cavity where the temperature is 2oC lower
  • Consist of highly coiled seminiferous tubules, interstitial cells or Leydig cells, blood vessels and extracellular material
  • Sperm are formed in the seminiferous tubules in a process called spermatogenesis
  • Leydig cells produce the androgen testosterone

  
• Sperm cells from the testis

  • Are immature and incapable of fertilization
  • Become motile and gain the ability to fertilize in the epididymis
  • It takes about twenty days for the sperm to pass through the tubules of the epididymis into the vas deferens

  
• Ejaculation

  • Propels sperm from the epididymis to the vas deferens which is connected to the ejaculatory duct and eventually meets the urethra
  • A male usually ejaculates about 2-5 ml of semen which normally contains 50-130 million sperm per milliliter
• How the male reproductive system functions

  • Dependent on hormones like follicle-stimulating hormone, luteinizing hormone, and testosterone
  • Follicle-stimulating hormone is necessary for sperm production (spermatogenesis)
  • Luteinizing hormone stimulates the production of testosterone, which is also needed to make sperm
  • Testosterone is responsible for the development of male characteristics
• Female reproductive system

  • The internal reproductive organs include the vagina, uterus, and cervix
  • The vagina is a canal that joins the cervix to the outside of the body
  • The uterus is a hollow pear-shaped organ that holds the developing fetus
  • The cervix is the lower part of the uterus that opens into the vagina

  
• Key hormones involved in the male reproductive system

  • Follicle-stimulating hormone
  • Luteinizing hormone
  • Testosterone
• Follicle-stimulating hormone

  Necessary for sperm production (spermatogenesis)

  
• Luteinizing hormone


  Stimulates the production of testosterone, which is also needed to make sperm
• Testosterone


  Responsible for the development of male characteristics, including muscle mass and strength, fat distribution, bone mass, facial hair growth, voice change, and sex drive
• Internal female reproductive organs

  • Vagina
  • Uterus
  • Ovaries
  • Fallopian tubes

  
• Vagina


  A canal that joins the cervix (lower part of uterus) to the outside of the body. Also known as the birth canal.
• Uterus (womb)


  A hollow pear-shaped organ that holds the developing fetus. It is divided into 2 parts – the cervix, which is the lower part that opens into the vagina, and the main body of the uterus, called the corpus. The corpus is able to expand to hold a developing baby. A channel through the cervix allows sperms to enter and menstrual blood to exit.

  
• Ovaries


  Small oval-shaped glands that are located on either side of the uterus. The ovaries produce eggs and hormones.
• Fallopian tubes


  Narrow tubes that are attached to the upper part of the uterus and serve as tunnels for the egg cells to travel from the ovaries to the uterus. Fertilization (conception) normally occurs in the fallopian tubes. The fertilized egg then moves to the uterus, where it implants into the lining of the uterine wall.