biology reproduction

• The menstrual cycle is the monthly cycle of changes in the female reproductive system controlled by hormones like estrogen and progesterone, causing the uterus lining to thicken and shed during menstruation if pregnancy doesn't occur

  
• The placenta is an organ connecting the developing fetus to the uterine wall, responsible for nutrient, gas, and waste exchange between mother and fetus

  
• Natural selection is the process where organisms with desirable traits are favored to survive and pass on their traits to offspring
• Evolution is the gradual change in inheritable characteristics of a population over time
• Artificial selection is a deliberate, planned process of selective breeding by humans to identify and use the best progeny for the intended purpose, leading to deliberate genetic change
• Asexual reproduction results in genetically identical offspring from one parent without gamete fusion, while sexual reproduction involves the fusion of gametes to produce genetically dissimilar offspring
• The male reproductive system functions to produce, store, transport sperm and semen, discharge sperm within the female reproductive tract, and produce male sex hormones
• The female reproductive system functions to produce egg cells, transport ova for fertilization, provide a favorable environment for fetal development, and produce female sex hormones
• Ovulation is the release of a mature egg from an ovary into the fallopian tube, with the egg surviving for about 24 hours after release
• Hormones are chemical substances produced in small quantities by endocrine glands, transported in the bloodstream to target organs where they exert their functions
• The menstrual cycle is the monthly cycle of changes in the female reproductive system controlled by hormones like estrogen and progesterone, causing the lining of the uterus to thicken and shed during menstruation if pregnancy does not occur

  
• The placenta is an organ that connects the developing fetus to the uterine wall, responsible for the exchange of nutrients, gases, and waste products between the mother and the fetus

  
• Hormones:

  • Chemical substances produced in minute quantities by an endocrine gland
  • Transported in the bloodstream to target organs where they exert their functions
  • Destroyed by the liver after functions have been performed
• What happens if no fertilization occurs:

  • Degeneration of the corpus luteum causes levels of estrogen and progesterone to fall below a critical level
  • Endometrium begins to shed, starting menstruation on day 1 of the next cycle
• What happens if fertilization occurs:

  • Fertilized egg becomes a zygote and then an embryo
  • Ovary produces estrogen and progesterone to maintain uterine lining
  • Embryo implants into the uterine lining
  • Fertilized egg secretes a hormone called human chorionic gonadotropin (hCG)
  • hCG maintains the corpus luteum which continues to secrete estrogen and progesterone, keeping the endometrium intact
  • Most home pregnancy tests work by detecting hCG in urine
• Anterior pituitary gland release FSH which stimulates growth of follicles in ovary
• Developing follicles secret oestrogen, which stimulate repair and buildup of endometrium/prevents further secretion of FSH & LSH (negative feedback)
• Peak levels of oestrogen occurs about midpoint of cycle. High and sudden peak stimulates secretion of LH (positive feedback)
• Surge in LH stimulates ovulation (day 14)
• LH stimulates conversion of remaining follicle tissue to corpus luteum
• Corpus luteum secretes progesterone, and some oestrogen -> thickening and maintenance of endometrium which becomes filled with blood capillaries is continued + further secretion of LH & FSH is continued
• Falling levels of LH & FSH causes corpus luteum to degenerate -> progesterone & oestrogen decreases + endometrium breaks down ; menstrual cycle restarts
• Fertilisation is the process by which the nucleus of the male gamete fuses with the nucleus of the female gamete to produce a zygote
• Implantation: 1. The zygote slowly moves to the uterus 2. The zygote divides by mitosis to form an embryo 3. Implantation occurs when the embryo (blastocysts) gets embedded in the uterine lining
• • hCG will be produced by the blastocyst to maintain the corpus luteum, which produces progesterone to maintain the thickness of the endometrium
  • once the placenta is fully formed at week 8, hCG level will drop
  • Placenta will start producing progesterone to maintain the endometrium
• Amniotic cavity is filled with amniotic fluid, which protects embryo by:

  • acting as a cushion from external trauma
  • Maintaining a constant temperature
  • allowing for free movement for foetal development (muscle development + lubrication)
  • practice swallowing
• • In the process of implantation, the embryo develops finger-like structures called the chorionic villi
  • the chorionic villi helps the embryo implant itself into the endometrium and are surrounded in tiny pools of blood
  • mother’s blood and embryo’s blood are not in direct contact
  • chorionic villi absorb nutrients and oxygen from mother’s blood and pass the substances to the embryo via chorionic blood vessels
  • embryo’s waste products diffuse to the mother’s bloodstream via the chorionic villi, and is later excreted by the mother’s kidneys
• Pollination is the transfer of pollen grains from the anther to the stigma, with types including self-pollination, cross-pollination, and artificial pollination

  
• Self-pollination advantages: only one parent needed, less genetic variation; disadvantages: weaker offspring, less chance of beneficial qualities
• Cross-pollination advantages: may inherit beneficial qualities from both parents, greater genetic variation; disadvantages: requires two parents, lower probability of successful pollination
• Fertilization process:

  1. Pollen grains on the stigma germinate in response to sugary fluid produced by the mature stigma

  2. A pollen tube grows out from the pollen grain, producing the male gamete

  3. The pollen tube secretes enzymes to digest the tissue of the stigma and style, growing down the style

  4. The pollen tube enters the ovule through an opening in the ovule wall called the micropyle

  5. Within the ovule, the tip of the pollen tube absorbs sap and bursts, releasing the two male gametes

  6. One male gamete nucleus fuses with the ovum nucleus to form the zygote, leading to fertilization

  7. The ovary becomes a fruit and the ovule becomes a seed
• mitosis


  type of cell division giving rise to genetically identical cells in which the chromosome number is maintained
• asexual reproduction


  process that results in the production of genetically identical offspring from one parent, without the fusion of gametes
• when does mitosis occur?

  asexual reproduction

  new cells produced by mitosis for body growth

  and repair of damaged tissues
• Advantages of asexual reproduction

  - only 1 parent needed

  - all beneficial characteristics of parent passed onto offspring

  - no fusion of gametes necessary

  - faster than sexual reproduction
• disadvantages of asexual reproduction

  - no genetic variation in offspring-> not well-adapted to changes in the environment-> whole population vulnerable to the same things, can go extinct easily
• sexual reproduction


  a process involving the fusion of two gametes to form a zygote
• meiosis


  a type of cell division that gives rise to genetically dissimilar cells in which the chromosome number is halves due to the separation of homologous chromosomes (do we even need to know this)
• advantages of sexual reproduction

  offspring may inherit beneficial qualities from both parents

  
  

  there is genetic variation in the offspring that is better adapted to changes in the environment
• disadvantages of sexual reproduction

  two parents required

  slower than asexual reproduction

  fusion of gametes required