General Biology 4th Quarter

• Growth is a stage of development characterized by an increase in size of an individual.
• Development involves formation of sex cells, zygote formation, subsequent stages in ones life span.
• Development is terminated by death.
• Stages of Animal Development

  1. Gametogenesis

  2. Spermatogenesis

  3. Oogenesis
• Gametogenesis is a process which refers to the biological formation of gametes via a series of cellular division, differentiation, and genetic material reduction to achieve a haploid number of chromosomes.
• The formation and development of sperm cell are via spermatogenesis whereas its female counterpart, egg cell or ovum, is via oogenesis.
• Spermatogenesis

  
• Oogenesis

  
• The precursor cell spermatogonium first divides and differentiates into two primary spermatocytes via mitosis.
• The spermatocyte undergoes first meiotic division giving rise to two secondary spermatocytes.
• Further, each secondary spermatocyte proceeds to second meiotic division giving rise to four spermatids that mature into sperms having an equal number of genetic material and cytoplasm.
• The daughter cells produced from the two meiotic divisions do not receive an equal amount of cytoplasm primarily because almost all of the cytoplasm of the primary oocyte is concentrated only to one of its daughter cells.
• High concentration of cytoplasm in an ovum provides enough nourishment to the developing embryo after fertilization.
• Fertilization- The two gametes fuse together via fertilization which starts the development process. In animals, zygote(fertilized egg) formation occurs once a sperm cell successfully fused to an ovum, which in turn allows embryo development to take place.
• Cleavage - Fertilization initiates embryotic development allowing cleavage to take place. Cleavage is the rapid series of mitotic cell divisions of the developing embryo leading to multicellular ball mass. In mammals, this continuously happens as the embryo transverses the oviduct toward the uterus. Once more than 100 cells are present, the embryo is now a blastocyst, characterized by having a distinct inner cell mass, which eventually forms the fetus.
• Gastrulation - is the formation of three germ layers: ectoderm, mesoderm and endoderm. Each will give rise to specific tissues and organs.
• Organogenesis - is the phase of embryonic development that starts at the end of gastrulation and continues until birth. During organogenesis, the three germ layers formed from gastrulation (the ectoderm, endoderm, and mesoderm) form the internal organs of the organism.
• ECTODERM(Outer layer) - Nervous system (brain and spinal cord), epidermis, sense organs
• MESODERM (Middle layer) - muscles, bones, cartilage, circulatory, excretory, and reproductive organs
• ENDODERM ( Inner layer) - digestive and respiratory organs, endocrine glands, germ cells and gametes
• gametogenesis, fertilization, cleavage, gastrulation, organogenesis, larval stage, maturity.

  
• Spermatogenesis

  Spermatogonium (2N)

  Primary Spermatocyte (2N)

  Secondary Spermatocyte (2N)

  Spermatids (N)

  undergoes differentiation

  Spermatozoa (N)

  
• Plant Development - The mature, multicellular organism is

  a diploid sporophyte.
• Later, some cells undergo meiosis to produce haploid gametes which are then released.
• The life cycle of plants involves the alternation of generations between two distinct phases called the sporophyte generation and the gametophyte generation.
• Gametophytes are usually small and short-lived, while sporophytes are larger and longer lived.
• In flowering plants, the gametophyte phase consists only of the male and female gametophytes within anthers or ovaries respectively.
• gamete's fuse and form the zygote which develops by mitosis to become the multicellular diploid sporophyte.
• In some plants, the dominant part of the life cycle is a multicellular, haploid gametophyte ( all cells have a haploid chromosome number).
• Mitosis releases individual cells that can act like gametes (gamete are produced by mitosis).
• Sporangia produce spores through meiosis.
• Spore germinates into a gametophyte.
• General Life Cycle of Plants

  Zygote (2N) - Mitosis - sporophyte (2N) - sporangium (2N) - Meiosis - spore (N) - Mitosis - gametophyte (N) - Mitosis - Gametes (N) - Fertilization.

  
• The plant body consists of two distinct generations or phases: The Sporophytic Phase and the Gametophytic Phase.
• The sporophytic phase begins with the formation of a zygote from the fusion of male and female gametes.
• The sporophytic phase is dominated by the sporophyte generation while the gametophytic phase is dominated by the gametophyte generation.
• The gametophytic phase includes the haploid gametophyte generation which produces gametes via mitotic division.
• The sporophytic phase includes the diploid sporophyte generation which produces haploid spores via meiosis.
• The sporophytic generation is diploid, meaning it has double the number of chromosomes found in haploid organisms.
• The alternation of generations refers to the succession of one generation followed by another.