Biology paper 2 edexcel Igsce

• Transcription


  1. Occurs in the nucleus

  2. Part of the DNA unwinds

  3. Bases are exposed along the template strand

  4. Network forms upon which mRNA molecule forms

  5. Building blocks of mRNA: RNA nucleotides

  6. RNA nucleotides pair up with template strand bases according to the complementary base pairing rule

  7. mRNA strand forms, leaves nucleus
• Translation


  1. Takes place in cytoplasm

  2. Ribosome moves along with the mRNA strand

  3. mRNA attaches to the ribosome

  4. tRNA brings amino acids to the ribosome

  5. mRNA codon binds with the complementary anticodon on the tRNA producing an amino acid chain and forms polypeptide bonds

  6. At the end of the chain there will be a stop codon that ends translation
• Mutation


  Random rare change in a DNA
• If addition/deletion of base

  Different sequence of amino acid brought to the ribosome, give a different protein with a different phenotype
• Substitution


  May not be a change in amino acid sequence, may have the same protein with the same phenotype
• Amylase


  Digests starch -> glucose
• Iodine


  • Blue black in the presence of starch
  • Orange in the presence of glucose
• Benedict's


  • Blue
  • Brick red in the presence of glucose
• Nitrogen cycle


  1. Nitrates absorbed by root hair cells by active transport from an area of low concentration -> high concentration against the concentration and uses energy from ATP

  2. Plants use the nitrates to make proteins (amino acids) + growth (assimilation)

  3. Plants eaten by animals (assimilation)

  4. Animal and plants die and the are decayed by decomposers (fungi or bacteria) and this converts nitrates -> ammonia

  5. Nitrifying bacteria converts ammonium ions -> nitrites then nitrates

  6. Denitrifying bacteria converts nitrates -> nitrogen gas

  7. Nitrogen fixing bacteria found in root nodules converts the nitrogen gas -> nitrates. Nitrogen fixation happens with lightning as well.
• Kidney


  Glomerulus -> Bowman's capsule -> PCT -> Loop of Henle -> DCT -> Collecting duct
• Excretion of urea


  1. Ultrafiltration

  2. Occurs in glomerulus

  3. ions, water, glucose, and urea enters the bowman's capsule

  4. Selective reabsorption takes place in PCT where glucose is reabsorbed back into the blood by active transport

  5. Presence of proteins in urine (due to damage to bowman's capsule)

  6. Proteins are too large to enter

  7. Presence of glucose (PCT not working)
• Osmoregulation


  1. Osmoreceptors in the hypothalamus detects low water level

  2. Stimulates pituitary gland to release ADH

  3. ADH acts on the walls of the collecting duct, making them more permeable so more water is reabsorbed back into the blood

  4. Urine is less in volume and more concentrated and yellow
• FSH


  • Matures the egg
  • Stimulates follicle growth
  • Stimulates egg development
  • Stimulates sperm production in males
  • Stimulates estrogen secretion
• LH


  • Stimulates ovulation (egg release) (peaks)
  • Stimulates production of testosterone
  • Stimulates development of corpus luteum
  • Stimulates testosterone production in males
• The kidney is an organ of excretion that removes metabolic waste
• Other organs involved in excretion

  • Lungs (excrete carbon dioxide)
  • Skin (excrete sweat)
  • Kidney (excrete urea)
• Kidneys


  • Two small, fist-sized organs located at the bottom of the back
  • Outermost layer is the cortex
  • Middle layer is the medulla containing nephrons
  • Renal pelvis holds everything in place
  • Renal artery supplies oxygenated blood
  • Renal vein removes deoxygenated blood
  • Ureter leads to bladder
  • Urethra transports urine out of the body
• Ultrafiltration in the nephron

  1. Blood flows into the glomerulus

  2. Pressure forces small molecules out of the glomerulus into the Bowman's capsule

  3. Proteins do not cross the basement membrane
• Ultrafiltration


  The process where small molecules like glucose, urea, ions and water are forced out of the glomerulus and into the Bowman's capsule under pressure
• Selective reabsorption in the proximal convoluted tubule

  1. Glucose and some ions are reabsorbed back into the blood by active transport

  2. Urea remains in the nephron to be excreted
• Selective reabsorption


  The process of the body taking back useful substances like glucose and ions from the nephron and returning them to the blood
• The loop of Henle and distal convoluted tubule further concentrate the contents of the nephron
• The collecting duct flows to the ureter and bladder to excrete urea in urine
• Osmoregulation by the kidney

  • Osmoreceptors in the hypothalamus detect low blood water levels
  • Hypothalamus secretes more ADH (antidiuretic hormone)
  • ADH makes the collecting duct more permeable to water
  • More water is reabsorbed, less urine produced
• Osmoregulation by the kidney (high water intake)

  • Osmoreceptors detect high blood water levels
  • Less ADH secreted
  • Collecting duct less permeable to water
  • More water excreted in urine
• Kidney dialysis removes urea from the blood using a partially permeable membrane and dialysis fluid
• Dialysis is similar to osmosis


  Both involve a partially permeable membrane and movement of water
• Dialysis is similar to diffusion


  Both involve movement of molecules from high to low concentration
• Kidney transplants can treat kidney failure by replacing the failed kidney with a healthy donor kidney
• Kidney transplants have issues like shortage of donors, need for immunosuppressants, and surgical risks
• Processes in the kidney but not in a kidney machine are ultrafiltration and selective reabsorption
• The renal artery carries oxygenated blood to the kidney, the renal vein removes deoxygenated blood, and the ureter connects the kidney to the bladder
• Transplanted kidney is placed in the lower abdomen


  For easier access and proximity to the bladder
• Ultrafiltration occurs in the Bowman's capsule, glucose reabsorption occurs in the proximal convoluted tubule
• A diuretic chemical from a dandelion flower


  Causes less ADH secretion, making the collecting duct less permeable to water, resulting in more urine production
• Reflex arc


  1. Stimulus detected by receptors

  2. Impulses sent along sensory neuron

  3. Impulse passes to relay neuron in CNS

  4. Impulses sent along motor neuron

  5. Impulse reaches effector resulting in response
• Reflex arc


  • Subconscious response to dangerous stimuli
  • Extremely quick response needed, not enough time for conscious brain
• Cornea


  Transparent outer part of the eye that refracts light to reach the retina
• Iris


  Coloured part of the eye that controls how much light enters the eye
• Pupil size control


  1. In bright light, circular muscles contract and radial muscles relax to make pupil smaller

  2. In dim light, circular muscles relax and radial muscles contract to make pupil larger