Excretion

Cards (67)

  • Metabolism
    The chemical reactions that occur inside living cells
  • Metabolic waste products produced by plants
    • Oxygen
    • Carbon dioxide
    • Water/water vapour
  • Photosynthesis produces oxygen as a waste product in plants, not water vapour
  • Light intensity

    Determines which gas accumulates as a waste product in plants
  • At high light intensity more photosynthesis occurs so oxygen accumulates, while at low light intensity more respiration occurs so carbon dioxide accumulates
  • During the day, with sufficient light for photosynthesis, oxygen is produced in excess and is the main waste product in plants
  • Plants respire at night and during the day
  • The majority of water vapour lost from leaves is not a metabolic waste product, but water drawn up from the roots by the transpiration stream
  • Excretion
    The removal from the body of the waste products of metabolism, and any substances present in excess, e.g. excess salts
  • Waste products produced by human metabolic processes
    • Carbon dioxide from respiration
    • Water from respiration
    • Urea from the breakdown of excess amino acids
  • Urea is produced during the breakdown of excess amino acids, not lipids
  • Main excretory organs in humans
    • Kidneys
    • Lungs
    • Skin
  • Waste products of metabolism excreted by the lungs

    Water and carbon dioxide, both produced during respiration
  • A build up of excretory products in the body fluids can cause water to move out of cells
  • How waste products are excreted by the skin
    Waste products are excreted by the skin by the sweat glands when they produce sweat
  • The kidneys excrete urea, excess water and excess salts, not carbon dioxide (which is excreted via the lungs)
  • Main functions of the kidneys
    • Regulating the water content of the blood; this is osmoregulation
    • Excretion of toxic metabolic waste products and excess substances
  • Osmoregulation
    The process of maintaining the balance of water and dissolved substances, e.g. salts, within the body fluids
  • Osmoregulation is important because changes in the osmotic balance between the cells and the body fluids can lead to cells gaining or losing water by osmosis
  • When the solute concentration of body fluids becomes too high, the water concentration is low, so water will move out of the body cells by osmosis down a water concentration gradient
  • What happens if the body cells lose water by osmosis
    Losing water by osmosis causes the cells to shrink, or shrivel; this is known as crenation and can lead to inefficiency of cell activity and potentially cell death
  • Processes that will cause an increase in the water content of the body fluids

    • Aerobic respiration
    • Consumption of water by eating/drinking
  • Organ system responsible for the filtration of blood and the production of urine

    Urinary system
  • The liver is not part of the urinary system, which consists of the kidneys, ureters, bladder and urethra
  • Main structures of the urinary system
    • Kidneys
    • Ureters
    • Bladder
    • Urethra
  • Role of the bladder in the urinary system
    To store urine that is produced by the kidneys. Urine exits the bladder via the urethra which removes it from the body.
  • The urethra carries urine from the bladder to the exterior of the body, not the ureter
  • Nephrons
    Tiny tubes found in the kidney, the role of which is to produce urine
  • Nephrons contain a Bowman's capsule and loop of Henle, but do not contain a renal pelvis (which is the region of the kidney into which the nephrons drain)
  • Sections that make up a kidney nephron

    • Bowman's capsule
    • Convoluted tubules (distal and proximal)
    • Loop of Henle
    • Collecting duct
  • The Bowman's capsule directly surrounds the glomerulus, a ball of blood vessels from which the blood filters into the nephron
  • Ultrafiltration
    The process by which molecules are forced out of the blood and into the Bowman's capsule at high pressure
  • Where ultrafiltration occurs in the kidney

    Between the glomerulus and the Bowman's capsule
  • Ultrafiltration occurs at high blood pressure, not normal blood pressure
  • What determines whether a molecule enters the filtrate or remains in the blood during ultrafiltration

    Whether a molecule enters the filtrate or remains in the blood during ultrafiltration depends on its size; small molecules are filtered and large molecules remain in the blood
  • Substances forced out of the capillaries during ultrafiltration
    • Water
    • Glucose
    • Amino acids
    • Urea
    • Salts
  • Ultrafiltration
    1. Occurs between the glomerulus and the Bowman's capsule
    2. Occurs at high blood pressure
    3. Small molecules are filtered and large molecules remain in the blood
  • Ultrafiltration does not occur at normal blood pressure
  • The narrowing capillaries of the glomerulus increase the blood pressure, forcing small molecules into the filtrate
  • Substances forced out of the capillaries during ultrafiltration
    • Glucose
    • Water
    • Urea
    • Salts