Biology

• DNA, or deoxyribonucleic acid, is a polymer made out of lots of similar units stuck together.
• DNA is a double helix, which is a double stranded spiral.
• DNA is found in the nucleus of cells.
• DNA is split into 46 sections, each of our cells has 46 chromosomes in it.
• There are 23 different types of chromosomes, with 2 of each type.
• The 23rd pair of chromosomes are the sex chromosomes, which are the x chromosome and y chromosomes.
• Female has xx chromosome and male has xy chromosomes.
• Chromosomes look like an x shape before they undergo cell division (mitosis & meiosis).
• A gene is a small section of DNA that codes for a protein.
• A gene is a small segment of a chromosome.
• A gene codes for a sequence of amino acids.
• These amino acids combine to make a protein.
• There are 20 different types of amino acids.
• DNA determines which proteins the cell produces, which in turn is going to determine what the cell is going to be.
• The genome is the entire set of genetic material in an organism.
• Identical twins have the same genome.
• Genes may cause diseases, which is called inherited diseases.
• Genes can also increase the risk of a specific disease.
• Menstruation is the process that causes the uterus lining to break down, also known as having a period.
• FSH, or Follicle stimulating hormone, is a hormone released by the pituitary gland that causes an egg to start maturing in the ovary and stimulates the ovaries to start releasing oestrogen.
• Oestrogen levels rise from the first day of the menstrual cycle and peak just before day 14, causing the uterine wall to start thickening and the egg to mature.
• The peak in oestrogen occurs just before the egg is released, which is the process of ovulation.
• LH, or Luteinizing hormones, is a hormone stimulated to be released by the pituitary gland when oestrogen levels have reached their peak.
• LH causes ovulation to occur and stimulates the ovary to produce progesterone.
• Progesterone stays low from day 1-14, and starts to rise once ovulation occurs.
• This increase in levels causes the uterine lining to thicken further.
• When oestrogen levels are high enough, they suppress FSH.
• If the egg has not been fertilised, the corpus luteum dies and progesterone levels drop.
• The follicle produces the hormone oestrogen, which causes growth and repair of the lining of the uterus wall.
• Progesterone maintains the uterus lining, controlling the thickness of the uterus wall.
• A fall in progesterone levels causes the uterine lining to break down, which is menstruation.
• The pituitary gland produces FSH which stimulates the development of a follicle in the ovary, leading to the development of the egg inside the follicle.
• High levels of oestrogen stimulate the release of LH, which then causes the release of the egg.
• The follicle becomes corpus luteum and this produces oestrogen and progesterone which inhibit FSH and LH production by the pituitary.
• This is an example of negative feedback.
• Foetus development during gestation

  1. Gains glucose

  2. Gains amino acids

  3. Gains fatty acids

  4. Gains water

  5. Gains oxygen

  6. Gains mineral ions

  7. Gains vitamins
• Placenta


  Mother's blood comes into very close proximity to the blood of the foetus, but they never mix
• Foetus blood movement


  1. Connects to and from the placenta by the umbilical cord

  2. Mother's blood absorbs waste products from the foetus' blood in the placenta

  3. Waste products include carbon dioxide and urea
• Movement of molecules


  • Occurs by diffusion, due to the difference in concentration gradient
  • Active transport may be needed for some substances
• Placenta


  • Adapted for diffusion by having a large surface area and a thin wall for fast and efficient diffusion