Biology: Reproduction Modes and Methods

Modes of Asexual Reproduction

• Binary fission: single-celled organisms divide into two identical daughter cells
• Budding: a new individual grows from a parental organism
• Fragmentation: an organism breaks into smaller pieces, each developing into a new individual
• Regeneration: lost or damaged body parts grow back

Advantages and Disadvantages of Asexual and Sexual Reproduction

• Asexual reproduction: rapid population growth, identical offspring, but susceptible to disease and lack genetic variation
• Sexual reproduction: increased genetic variation, but slower population growth and complex process

Hermaphroditism

• An organism that produces both sperm and eggs, self-fertilization possible

Sex Determination

• Humans: determined by presence of X and Y chromosomes (XY for males, XX for females)
• Birds: determined by presence of Z and W chromosomes (ZZ for males, ZW for females)

Environmental Sex Determination

• Temperature-dependent sex determination in turtles and crocodiles
• Social sex determination in some fish and frogs

Semelparous

• Organisms that die after a single reproductive event, e.g., salmon and some insects

External Fertilization

• Occurs outside the body, e.g., fish, amphibians, and some invertebrates
• Examples: coral reefs, sea urchins, and some species of fish

Internal Fertilization

• Occurs inside the body, e.g., humans, mammals, and some invertebrates
• Examples: placental mammals, some species of fish, and some invertebrates

Human Egg Protection and Sperm Penetration

• Egg protection: corona radiata, zona pellucida, and cumulus oophorus
• Sperm penetration: through the corona radiata and zona pellucida

Fertilized Egg Development

• Stages: zygote, morula, blastula, gastrula
• Layers of tissue: ectoderm, endoderm, and mesoderm

Gastrulation

• The process of forming the three primary layers of tissue: ectoderm, endoderm, and mesoderm

Tissue Development

• Ectoderm: nervous system, skin, and senses
• Endoderm: digestive system and respiratory system
• Mesoderm: muscles, bones, and circulatory system

Male Reproductive System

• Penis: delivers semen during ejaculation
• Scrotum: protects and regulates temperature of testes
• Testes: produce sperm
• Semen: seminal fluid containing sperm
• Seminiferous tubules: site of sperm production
• Sertoli cells: support and nourish developing sperm
• Interstitial cells of Leydig: produce testosterone
• Seminal vesicles: produce seminal fluid
• Prostate gland: produces seminal fluid
• Bulbourethral gland: produces seminal fluid
• Vas deferens: muscular tube transporting sperm

Sperm Path

• Epididymis to vas deferens to urethra to outside the body

Sperm Temperature Regulation

• Scrotum regulates temperature, increasing or decreasing as needed

Hormones Influencing Sperm Development

• Testosterone: produced by interstitial cells of Leydig, regulates sperm development
• FSH: stimulates sperm production
• LH: stimulates testosterone production

Female Reproductive System

• Clitoris: sensitive region for sexual stimulation
• Labia majora and minora: protect vulva and vagina
• Ovaries: produce eggs
• Oviducts/Fallopian tubes: site of fertilization
• Fimbriae: finger-like projections guiding eggs into oviducts
• Uterus: supports fetal development
• Vagina: birth canal
• Corpus luteum: produces progesterone, maintains pregnancy
• Follicle: produces eggs

Hormones Influencing Egg Development

• Estrogen: regulates egg development
• Progesterone: maintains pregnancy and prepares uterus for fertilized egg