Biology (Reproduction)

• Asexual Reproduction

  Asexual Reproduction: the process resulting in the production of genetically identical offspring from one parent.

  • Bacteria:
  • Reproduced by binary fission, each bacterium divides into two.
  • The generation time is the time taken for a cell to divide into 2.
• Advantages of Asexual Reproduction-

  • Fast: no need to find a mate, fertilise, etc.
  • Good characteristics are kept
  • Do not need to carry offspring
  • Suitable environments can be easily exploited
• Disadvantages of Asexual Reproduction-

  • No variation/biodiversity
  • Harmful genes transferred
  • Overcrowding- fighting for food
  • Prone to extinction
• Sexual Reproduction

  Sexual reproduction: a process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote and the production of offspring that are genetically different from each other

  • Fertilisation: the fusion of gamete nuclei
  • The nuclei of gametes are haploid, and the nucleus of a zygote is diploid
  • Diploid: Full Set of Chromosomes
  • Haploid: Half Set of Chromosomes
• Advantages of Sexual Reproduction-

  • Produces genetically different offspring
  • Reduced risk of extinction
  • Disease is less likely to affect the whole population
• Disadvantages of Sexual Reproduction-

  • It takes lots of time and energy
  • Mate required
  • Energy on improving appearances or pollen volume for pollination (plants)
• Flowers are the reproductive organ of the plant
• Flowers usually contain both male and female reproductive parts
• Plants produce pollen which contains a nucleus inside that is the male gamete
• Pollen is not capable of locomotion, unlike the male gamete in humans (sperm)
• Plants have mechanisms in place to transfer pollen from the anther to the stigma
• Pollination is the process of transferring pollen from the anther to the stigma
• There are two main mechanisms by which pollination occurs: transferred by insects (or other animals like birds) or transferred by wind
• The structure of insect and wind-pollinated flowers are slightly different as each is adapted for their specific function
• Structures and Descriptions of parts of plants:

  • Sepal- Protects unopened flower
  • Petals- Brightly coloured to attract insects
  • Anther- Releases male sex cell (Pollen Grains)
  • Stigma- Top of the female part of the flower which collects pollen grains
  • Ovary- Produces female sex cell (Ovum)
  • Ovule- Contains female sex cell (Ovum). It is found inside the Ovary.
• This is a Typical General Flower Structure

  
• Insect Pollinated Flower

  
• Wind Pollinated Flower

  
• • The pollen produced by insect and wind-pollinated flowers is also different:
  • Insect pollinated flowers produce smaller amounts of larger, heavier pollen grains that often contain spikes or hooks on the outside so they are better able to stick to insects
  • Wind pollinated flowers produce large amounts of small, lightweight pollen grains that are usually smooth.
• Male Reproductive System

  • Testes: have many coiled tubes that produce sperm, and the cells between tubes produce testosterone.
  • Scrotum: holds testicles
  • Sperm duct: carries sperm from testicles to urethra.
  • Prostate gland: makes seminal fluid
  • Urethra: carries semen from the sperm duct to the tip of the penis
  • Penis: male sex organ used to transfer semen to the female.
• Female Reproductive System

  • Ovary: contains follicles that develop into the ova and produces progesterone and oestrogen
  • Oviduct (fallopian tube): carries the ovum to the uterus
  • Uterus (womb): where the fetus develops.
  • Cervix: neck of the uterus: a robust and rigid muscle, moist by mucus with a small opening
  • Vagina: receives the penis during intercourse and way out for baby at birth. Moist tube of muscle, flexible and secretes mucus
• Testes- They have 2 main functions:

  1. Production of sperm cells (male gamete)
  2. Production of hormone Testosterone

  Sperm cell nuclei diffuse with the ova to form diploid zygotes.

  Testosterone is the main male sex hormone produced during puberty until death. It stimulates:

  • Growth of hair on chest, face, armpits and pubic region
  • Muscle development
  • Broadening of shoulders
  • Deepening if voice
  • Attraction to the opposite sex

  The testes are located inside a scrotum which hangs outside the body. Optimal temperature for sperm production is 35 Degrees Celsius.
• Sperm Duct/ Vas Deferens-

  It is a long tube which conducts sperm from the testes to the prostate gland (which connects to the urethra) during ejaculation
• Epididymis-

  It is a site where sperm matures and develops ability to be mobile (i.e. swim). Mature sperm is stored here until ejaculation.
• Seminal Vesicle-

  Secretes fluid containing fructose (to nourish the sperm), mucus (to protect the sperm) and prostaglandin (triggers uterine contractions).
• Prostate gland-

  Secretes an alkaline fluid to neutralise vaginal acids (necessary to maintain sperm viability).
• Urethra-

  Conducts sperm/ semen from the prostate gland to the outside of the body via penis (also used to convey urine).
• Penis-

  It is a copulatory organ.

  It has erectile tissue, air spaces and blood vessels.

  During coitus, it erects, filled with blood in the air spaces so as to penetrate the vagina.
• Male Reproductive System

  
• Ovaries- They serve three main functions:

  1. Produce ova/ egg cells (female gamete).
  2. Secrete Oestrogen (female sex hormone) which stimulates development of secondary sexual characteristics in girls during puberty.
  3. Secretes Progesterone which stimulates thickening of Uterus so that it is ready to receive and embryo during pregnancy.

  Ovaries are 2 in number, attached to the inside of the abdomen below the kidney.

  After puberty, the egg is released from the ovary about every 28 days. The release of the egg is called Ovulation.
• Oviduct/ Fallopian Tube-

  It has smooth muscles which facilitate the movement of the ovum from the ovary to uterus by peristalsis.

  It has cilia in its inner lining to waft the ovum towards the uterus.

  Has fimbriae to guide ovum into the oviduct.

  Fertilisation occurs at the upper part of the oviduct.
• Uterus-

  It has thick walls made of muscle.

  It is quite small- 10 cm cubed- but it can stretch 500,000 times when a female is pregnant.

  The uterine wall is lined with endometrium (thin lining) for implantation and nourishment of the embryo at its initial state since it's supplied with blood network.

  The muscles of the uterus are important during parturition (birth) because they contract rapidly to expel a fully formed foetus.
• Cervix-

  It is a ring of muscles that separate the uterus from the vagina.

  It secretes a plug of mucus to prevent entry of pathogens into the uterus during pregnancy.
• Vagina-

  It has urinogenital function.

  It is a copulatory canal.

  It is also a birth canal (babies pass through it during child birth).

  It is a muscular tube that opens to the outside of the body.

  Above the vaginal opening is the opening of the urethra through which urine from the bladder passes out.
• Vulva-

  Is the outer opening of the vagina.
• Female Reproductive System

  
• Sperm Cell/ Spermatozoon

  
• Acrosome lytic enzymes which digest the membranes of egg cell to effect fertilisation.
• The sperm nucleus contains haploid number of chromosomes (23) that fuse with haploid number in egg cell nucleus (23) to effect fertilisation.
• The mitochondria provides energy during respiration for sperm cell to swim towards the ovum/ egg cell.