Excretion Flashcards
(22 cards)
Excretion in Plants
- Oxygen
- CO2
- Water vapour
- other unwanted chemical substances
Excretion in Plants (Oxygen and CO2)
More light means more oxygen in excess as rate of photosynthesis is higher than the rate of respiration (oxygen excreted in day)
When insufficient light, CO2 is in excess as there’s only respiration meaning it’s a waste product (CO2 excreted at night)
Water vapour (plants)
Water vapour lost from a plant isn’t a waste product of metabolism but instead water being drawn up from the roots in the transpiration stream.
(Water vapour gets excreted both day and night)
Chemical substances (plants)
Plant cells can break down molecules into chemical substances no longe required by the plant. These chemical substances can’t be converted into other useful compounds therefore it gets stored in dying tissues of plants.
What is excretion?
the removal of waste products of metabolic reactions
Wastes in human
CO2, Water, Urea, Other substances in excess
The danger of waste products in humans
Toxicity - toxic effects if they are allowed to reach high concentrations
CO2 dissolves in water easily to form an acidic solution that can lower ph of cells. This can reduce the activity of enzymes in the body which is essential for controlling the rate of metabollic reactions
Osmotic effect- body fluids become more concentrated due to higher amounts of waste products.
- This can cause water to move out of cells preventing them from carrying out essential reactions
Organs of excretion
Kidney - excretion of urea, water, and excess salts
(urea comes from the breakdown of excess amino acids in liver)
Lungs - CO2 and water
CO2 leaves the lungs and water in the form of vapour
Skin - excess mineral ions (sodium, water and some urea) via sweating
The Kidney
The regulate the water content of blood (maintaining BP and osmoregulation)
They excrete the toxic waste products of metabolism (such as urea)
Osmoregulation
Process of maintaining water and salt concentrations (osmotic balance) across membranes within the body
Example: homeostasis
The importance of osmoregulation
It is vital to prevent harmful changes occurring to cells of the body as a result of osmosis. If body cells lose or gain too much water, they cannot function properly.
Too much water in the blood results to swelling as water moves into them causing cells to burst (lysis)
Too little water in the blood has a dehydrating effect which could lead to cell death
Types of solutions in the body
Hypertonic:
- Red blood cells have higher water potential than solution
- Net movement of water out
- Shrivelled cells
Isotonic:
- Water potential and red blood cells are equal
- No net movement of water
- Normal cells
Hypotonic:
- Red blood cells have lower water potential than solution
- Net movement of water in
- Cells swell, may burst (lyse)
Water content of the body
Two sources of water in body:
Water produced from aerobic respiration
Water from diet
Water is lost via the lungs through exhalation and from the skin (sweat)
Water lost through the lungs or skin cannot be controlled, but the volume of water in the production of urine can be controlled by the kidneys
The Urinary System
Key functions:
Filter waste products from the blood and remove it from the body as urine
To control the water levels of the body
Main structures of the Urinary System
Kidney: Two bean-shaped organs that filter the blood
Ureter: Tube connecting the kidney to the bladder
Bladder: stores urine (excess water, salts and urea) produced by the kidney
Urethra: tube that connect the bladder to the exterior (where urine is released)
Kidney structure
Cortex - the outermost region
Medulla - the inner section of the kidney
Renal pelvis - the tube linking the kidney to the ureter
The nephron
Glomerulus, Bowman’s capsule, PCT, DCT, Loop of henlé, collecting duct
Step 1 Ultrafiltration (Nephron)
It occurs between the glomerulus and the Bowman’s capsule
High pressure is created by the blood coming from the renal artery which is further increased from the narrowing of the capillaries
The high pressure in the glomerulus forces small molecules out of the blood
These include:
Urea, Glucose, Water, Salts which leads to the formation of the filtrate as it has both useful and wasteful substances
Step 2 Selective Reabsorption (Nephron)
After ultrafiltration, glucose is reabsorbed from the proximal convoluted tubule
Glucose gates are only located in the PCT therefore any glucose that pasts this point will be excreted in the urine
If this is the case it might be because your glucose levels are too high (diabetics)
Reabsorbed by active transport. Since active transport requires energy, there are many mitochondria that provide energy for this
Step 3 Water Reabsorption (Nephron)
Most water are reabsorbed in the Loop of Henlé but some will also get reabsorbed in the collecting duct. Amount depends on the requirement of the body.
In the Loop of Henlé, salts are reabsorbed by diffusion and active transport. Water will follow by osmosis
Fluid now leaving the collecting duct is now called urine as it’s all the waste products that need to be excreted
The Role of ADH
The hormone ADH controls how much water the body must reabsorb depending on the water content of the blood
How much ADH is released depends on how much water the kidneys need to reabsorb from the filtrate
If water content of blood is too high less ADH released meaning less water being reabsorbed causing kidneys to produce diluted urine
If the water content of the blood is too low more ADH is released meaning more water being reabsorbed causing the kidneys to produced small volume of concentrated urine
The Composition of Urine
Contains mixture of:
Urea, excess mineral ions, excess water
Water intake - more fluid drunk means more water will be removed so more dilute urine is produced
Temperature - more concentrated urine when sweating as water is lost in skin instead of bladder (same as exercise)
