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 removalfrom 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