UNIT 4: EXCRETION AND
WASTE MANAGEMENT
Excretion and Waste Management

What would happen if you never threw out your
garbage or leftover food?
 Be
as detailed and exact as possible
 Specific to your house and family

Why do we sweat?

Why do we urinate?
Waste Removal


One of the 7 life processes = removal of waste
products produced by the cells of our bodies
What are the waste products in the human body?
 Brainstorm
on a piece of paper
 Compile your ideas into the following table on chart
paper:
Waste Product
Origin
Organ of Excretion
Waste Products
Waste Product
Origin
Organ of Excretion
Ammonia
Breakdown of amino acids in
the liver
Kidney
Urea
Conversion of ammonia in the
liver
Kidney
CO2
Cellular respiration
Lungs
Water
Cellular respiration
Kidneys
Mineral Salts
Food and water
Kidneys
Lactic Acid
Anaerobic cellular respiration
Liver
Liver
Kidney
Excretory System

Why is feces not included in the list of metabolic
wastes?
 Feces
is not a product of cellular metabolism. It is a
“leftover” after the body absorbs what nutrients it
needs from the intestines


Brainstorm: the relationships between the excretory
system and the respiratory system, and the
digestive system.
How might the excretory system be involved in
homeostasis?
Waste Products: Cellular Respiration

We obtain energy by converting complex organic
compounds into simpler compounds.


BUT some of these simpler compounds can be harmful
Carbon Dioxide
Humans produce an average of 1kg per day!
 If levels become too high = our blood becomes acidic




Leads to breakdown of enzymes, etc…
Most is converted to bicarbonate ions (less harmful): HCO3-
Lactic Acid
Converted to pyruvate (aerobic respiration)
 OR removed through conversion to glucose


Water
Cellular Respiration
Waste Products
Waste Products: Metabolism


The large intestine removes toxic waste from the
digestive system.
The liver transforms these ingested toxins into
soluble compounds that can be eliminated by the
kidneys
 Alcohol,

heavy metals (Fe, Al, Hg)
The liver also transforms the hazardous products of
protein breakdown to be eliminated by the kidneys
Waste Products: Metabolism
Why are proteins so harmful?
 Fact: The average Canadian consumes more protein
than is required to maintain tissues and promote cell
growth.
 Excess protein is often converted into carbohydrates
 BUT proteins, unlike carbohydrates, contain
nitrogen.
 When amino acids (the protein building blocks) are
broken down we get the by-product: ammonia
Ammonia

Deamination = the breakdown of amino acids
 occurs
in the liver.
 byproduct = ammonia (NH3)


BUT ammonia is extremely toxic - a buildup of as
little as 0.005 mg is lethal!
In the liver, two molecules of ammonia combine with
another waste product, CO2, to form urea
3 Hydrogen atoms (H+) that can
be donated to increase acidity
This acidity makes it a useful
agent for household cleaners
Urea

Urea is 100 000 times less toxic than ammonia.

The blood can dissolve 33 mg of urea per 100 mL of blood.
Excretion: Simple Organisms

For ALL organisms, getting wastes out of the cell is
just as important as bringing in nutrients
 Otherwise
toxins would build up and the cell would
soon die

In unicellular organisms and in primitive multicellular
organisms (e.g. a sponge) every cell is in direct
contact with the external environment
 Therefore,
wastes are released directly from the cell
and water currents carry the waste away
Excretion: Simple Organisms

BUT, unicellular organisms
must regulate their internal
fluids
 More
dissolved solutes then
their freshwater surroundings
 Therefore, these cells should
draw in water, expand, and
eventually burst

Fluid Regulation: a contractile vacuole expels
excess water, preventing this swelling
Excretion: Complex Organisms


Complex multicellular organisms are faced with the
same problem but on a much bigger scale.
Not every cell is in direct contact with the external
environment
 Therefore,
wastes must be collected and temporarily
stored

A secondary problem: our cells are so specialized
that not every cell is designed to remove wastes
 Wastes
must be transported to cells that are capable
of excretion
The earthworm uses a series of tubules to remove wastes from the
blood and body cavity. Cells lined with cilia surround a funnel-like
structure (the nephrostome) and draw fluids from the body cavity into
tiny tubules. The wastes are stored as urine and are released through
small pores (nephridiopores) along the body wall.
Malpighian tubules that run throughout the body cavity of an
insect absorb wastes by diffusion. Wastes are released into
the gut and eliminated with solid wastes from the anus.
Human Excretory System

Major structures:
 Kidneys
 Liver
 Large
 Lungs
 Skin
Intestine
Excretory System Structures
Class Activity
1.
Structure (how is it built, where is it in the body)

2.
3.
4.
5.
Include a simple diagram
Role (in terms of waste removal)
One way in which it is related to one of the other
structures in the excretory system
One way in which it is related to digestive,
respiratory, and circulatory system
How it helps to maintain homeostasis (include one
feedback loop/process)