Gametes

• The gametes that make sexual reproduction possible are formed in a process called gametogenesis. For gametogenesis, mitosis provides the precursor cells. Meiosis causes the reduction of genetic material in divisions that result in gametes.
• In females, mitotic divisions occur before birth to form diploid primary oocytes, which remain inactive until after puberty. The second meiotic divisions are only completed if the ovum is fertilised
• 1. Acrosome
  2. Cell membrane
  3. Nucleus
  4. Mid-piece
  5. Cytoplasm
  6. Flagellum
  7. Mitochondria
  8. Head

  
• The nucleus of the sperm contains the highly condensed haploid chromosomes - the condensed state means that less energy is needed to transport it
• The acrosome of the sperm is a membrane bound storage site for enzymes that digest the layers surrounding the ovum
• The microtubles of the sperm produce the whip-like movement of the tail
• The mitochondria in the sperm are tightly packed into the middle section to provide ATP for the movement of the tail.
• The flagellum of the sperm propels the sperm towards the egg
• The sperm is the smallest cell of the human body of around 50 micrometres whereas the ovum is the largest with a size of around 100 micrometres
• 1. Inner follicle cells
  2. Cytoplasm
  3. Nucleus
  4. Zona pellucida
  5. Cell surface membrane

  
• The zona pellucida is a clear protective ’jelly-like’ layer that surrounds the oocyte
• The cytoplasm of the oocyte has many food reserves that provides food when the egg is fertilised until the mother can feed the egg by herself
• The spermatozoa have to carry the genetic information in their nucleus, remain in suspension in the semen and be transported through the female reproductive tract (for this they need a long, beating tail) and they must be able to penetrate the protective barrier around the ovum and deliver the male haploid safely inside.
• Ova usually contain food for the developing embryo. They have a protective layer of jelly around them known as the zona pellucida.
• That main difference between eggs of various species is the quantity of food stored for example in birds and reptiles a lot of development happens before the animal hatches, and so more food reserves are needed
• The formation of gametes in flowering plants is more complex because plants have two phases to their life cycles. The sporophyte generation is diploid and produces spores by meiosis. The resulting gametophyte generation is haploid and produces the gametes by mitosis
• In plants, the haploid gametophytes are reduced to part of the contents of the anther and the ovary. They are produced by meiosis form spore mother cells
• The anthers of flowering plants are the equivalent to the testes of animals. Meiosis occurs here, resulting in vast numbers of pollen grains that carry the make gametes.
• The male gametes in plants are known as microgametes. Each pollen grain contains two haploid nuclei: the tube nucleus and the generative nucleus. The tube nucleus has the function of producing a pollen tube that penetrates through stigma, style and ovary and into the ovule. The generative nucleus them fused with the nucleus of the ovule to form a new individual
• The ovary of the plant is equivalent to the animal ovary. Meiosis resultd in the formation of a relatively small number of ova contained within ovules inside the ovary. The ovule is attached to the wall of the ovary by a pad of special tissue called the placenta. Inside the ovule, the embryo sac forms the gametophyte generation. A combinatoon of meiotic and mitotic cell divisions results in an egg cells, known as the megagamete. It contains two polar nuclei and other small cells, some of which are degenerate