Cell Theory: Introduction and Fertilization


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In this video I go over a brief introduction into cell theory, which states that all living things are composed of one or more cells, and in multicellular organisms, every cell is derived from a single cell inside a fertilized egg. More terms and definitions covered are listed below.


  • Cell theory states all living things are composed of one or more cells: 0:00
  • Eukaryotic cells contain a nucleus and can be single-celled or multicellular. Prokaryotic cells are single-celled and do not contain a nucleus: 0:56
  • Every cell in a multicellular organism is derived from a single cell in a fertilized egg: 1:22
  • Fertilization or impregnation is the fusion of gametes to give rise to a new organism: 1:30
  • Sexual reproduction is the cycle of fertilization: 1:54
  • Insemination is the introduction of sperm into a female's reproductive system: 1:59
  • Pollination is the transfer of pollen (which produce gametes) from a male part of a plant to a female part: 2:06
  • Gamete or sex cell is a haploid cell that fuses with another haploid cell during fertilization: 2:23
  • Female is any individual that produces the larger type of gamete (ovum) and a male produces the smaller type (sperm): 2:38
  • Sperm and ovum fusing: 2:57
  • Ploidy is number of complete sets of chromosomes in a cell: 3:00
  • Sets of chromosomes refer to the number of maternal and paternal chromosome copies in each homologous chromosome pair: 3:13
  • Somatic (non-sex) cells, tissues, individual organisms: Ploidy level: monoploid (1 set), diploid (2 sets), triploid (3 set), etc.: 3:48
  • Polyploid refers to 3+ chromosome sets: 4:50
  • Homologous chromosomes or homologs are a set of one maternal and paternal chromosome that pair up during fertilization: 4:59
  • Haploid has 1 complete set of chromosomes for a diploid species; 2 sets for a tetraploid species: 5:27
  • Haploid cells in humans have 23 chromosomes; diploid cells have 46 chromosomes: 6:20
  • Haploid has 2 related definitions: a cell with half the number of chromosomes in somatic cells, and a cell with just 1 set of chromosomes, termed monoploid: 7:08
  • Zygote is a eukaryotic cell formed by a fertilization event between 2 gametes: 7:33
  • Zygote's genome is a combination of the DNA of each gamete: 7:44
  • Egg results from fertilization of an egg cell and contains the zygote from which an embryo develops: 7:53
  • Embryo is the early stage of development of a multicellular organism: 8:10
  • Fetus refers to 9+ weeks after conception in humans: 8:15
  • Male human embryo of 7 weeks old or 9 weeks gestational age: 8:38
  • Gestational age starts from the woman's last menstrual period (LMP): 8:38
  • Menstruation or period is regular discharge of blood and mucosal tissue from the uterus through the vagina: 9:02
  • Mucous membrane or mucosa is a membrane that lines various cavities in the body and covers internal organs: 9:28
  • Uterus or womb is where the fetus develops during gestation: 9:37
  • Gestation is period of development during the carrying of the embryo / fetus: 10:01
  • Hormone is a signaling molecule that regulates physiology and behavior: 10:23
  • Sex organ or reproductive organ is any part involved in sexual reproduction: 10:50
  • Primary sex organs are testis in the male and ovary in the female: 11:04
  • Secondary sex organs include external (genitals) and internal sex organs (genitals): 11:10
  • Uterus and uterine tubes diagram: 11:22
  • Menstrual cycle diagram. Period occurs every 21 to 35 days : 11:37
    • Follicular phase: Eggs mature inside small follicles: 11:52
    • Ovulation: Egg is released from biggest follicle: 12:05
    • Follicle is a small cellular cavity in which other structures grows or other material is contained: 12:32
    • Luteal phase: Endometrium (lining of uterus) is thick to support a pregnancy: 12:59
    • Menstruation: "Period" when the endometrium is shed over 3-7 days if there is no pregnancy: 13:25

Full video below:

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