Excretion Flashcards
What is excretion?
The removal of metabolic waste products from the body of a living organism.
What are some examples of waste substances?
By-products formed during metabolic processes in the body; excess food substances which cannot be stored in the body; and unwanted materials present in food which are absorbed into the body.
Why do animals need to get rid of carbon dioxide?
If it is allowed to accumulate
Why must excess water be excreted?
Excess water has to be excreted as it will dilute the body fluids.
Why is excess heat harmful?
Excess heat is harmful as it raises the temperature of the body
What is the main function of excretory systems (besides removing waste)?
Helping to maintain a constant internal environment.
What is water balance or osmoregulation?
The mechanism that keeps the osmotic pressure of blood and tissue fluids constant by regulating the amount of water and solutes in the body fluids.
Name 4 types of excretory structures found in organisms
Contractile vacuoles
How does the contractile vacuole in Amoeba work?
It expands as it is filled with water and then empties its contents to the exterior
What is the main problem freshwater organisms face?
Getting rid of excess water.
How do excretory products like ammonia and carbon dioxide leave the Amoeba?
By diffusion through the selectively permeable cell membrane to the exterior.
Describe the flame cells in flatworms
They are special hollow structures with flagella that propel fluid into tubules
What are nephridia?
Excretory organs of earthworms.
Describe the structure of a nephridium
It has a ciliated funnel (nephrostome) at one end that opens into the body cavity
How do nephridia help maintain chemical composition and concentration of body fluid?
Salts and other useful substances are reabsorbed through the walls of the tubes.
What is the main nitrogenous waste excreted by earthworms?
Urea
Why can’t earthworms survive in a dry environment?
They need a moist skin surface for gaseous exchange (carbon dioxide excretion).
What are Malpighian tubules?
The excretory organs of insects.
Where are Malpighian tubules found?
Between the midgut and the rectum.
How do Malpighian tubules conserve water in insects?
Nitrogenous waste is converted to uric acid
What are the excretory organs of humans?
Kidneys
What do kidneys remove from the blood?
Nitrogenous substances like urea and other ammonium compounds.
What other function do kidneys perform?
Maintain the osmotic pressure of the blood by controlling the excretion of water and salts.
Describe the path of urine flow
Kidney → ureter → urinary bladder → urethra → exterior.
What are the two main regions of the kidney?
Outer cortex and inner medulla.
What is the functional unit of the kidney?
The urinary tubule.
Describe the structure of a urinary tubule
Bowman’s capsule → proximal convoluted tubule → loop of Henle → distal convoluted tubule → collecting ducts → pelvis.
What is the glomerulus?
A knot of capillaries in the Bowman’s capsule where blood is filtered.
What are the three processes involved in urine formation?
Ultrafiltration
What happens during ultrafiltration?
Small molecules from the blood pass through the walls of the glomerulus and Bowman’s capsule into the capsular space.
What is glomerular filtrate?
The fluid that filters into the Bowman’s capsule.
What happens during selective reabsorption?
Water and useful substances are reabsorbed from the filtrate into the blood capillaries.
What happens during tubular secretion?
Waste molecules are secreted into the tubules.
What is the fluid that remains in the tubule called?
Urine
Name 4 mechanisms used in urine formation
Active transport
What other organs excrete waste in humans?
Lungs
What do the lungs excrete?
Carbon dioxide and water.
What does the liver excrete?
Bilirubin (in bile).
What does the skin excrete?
Water
Why don’t plants need a special excretory system?
Their metabolic wastes are minimal.
What are the main waste products formed in plants?
Water
How do gases escape from plants?
Through stomata (leaves
How is excess water removed from plants?
As water vapor by transpiration and as liquid droplets by guttation.
What are some examples of waste products stored in plant tissues?
Calcium oxalate
