Download Excretion - JLooby Biology

Excretion
Page 127
SyllabusObjectives

Discuss the importance of excretion in the
living organisms

Give examples of substances excreted by
animals and plants

State the means by which excretory products
are eliminated from the plants and animals
What is Excretion?
Introduction

The production of excretory materials


An excretory product


natural consequence of the metabolic reactions
that take place in the cells of an organisms
a harmful by-product of a chemical reaction taking
place in the cell of an organism.
EXCRETION

The elimination of these substances
Excretion vs Egestion

Excretion must not be confused with
Egestion!

In Animals egestion is the elimination of
undigestible materials e.g. Cellulose


No chemical reactions have taken place
The materials never entered the tissues.
Excretory Products





Potentially poisonous
As they accumulate they slow down
metabolic reaction
If accumulation continues reactions stop all
together
Their build up creates an UNFAVOURABLE
environment for Enzymatic activities
Large quantities of waste products eventually
lead to death
Excretory Products





Carbon Dioxide
Oxygen
Water
Urea
Calcium oxalate
Excretory Products



What are the metabolic processes that
produce these products?
What effect would excess of each of these
products have on the organism?
Do plants and animals excrete ALL these
products? If not which ones apply to Plants
and which ones apply to Animals?
Table: Summary of Excretory Products of Plants and Animals
Plants
Process by which produced
Process by which removed
Excess carbon dioxide
Respiration in cells
Diffusion via stomata
Excess oxygen
Photosynthesis in green cells
Diffusion via stomata
Calcium oxalate
Metabolism in cells
Stored in cells
Others, e.g. tannins, etc.
Metabolism in cells
Stored & lost in old tissues
Carbon Dioxide
Respiration in cells
Lung expiration
Water
Respiration and external intake
Kidney (lungs and skin)
Excess salt
Intake and metabolism
Kidney (skin)
Urea
Deamination of amino acids
Kidney
Animals
Homework (FOR MARKS)
1.
2.
3.
4.
5.
6.
7.
8.
9.
What effect do metabolic wastes have on tissue activities? 3
marks
What sorts of tissue activities produce metabolic wastes? 2 marks
What sort of metabolic wastes do plants and animals produce? 4
What about the effect of a build up of carbon dioxide in the cells?
4 marks
What are the organs that remove excretory products? 10 marks
Draw a summary table to describe where excretory products are
made, and where they are removed in plants and animals. 8
marks
Do plants need special organs for excretion? 1 marks
Draw a nephron 3 marks
TOTAL 35 marks
Carbon Dioxide



By-product of respiration (mainly aerobic) in
plants and animals
In excess it lowers the pH (CO2 forms a weak
acid – carbonic acid which dissolves in water)
Lower pH can affect enzyme activity
Carbon Dioxide removal

In plants



It is used in Photosynthesis during the day
Excess is excreted by diffusion, through leaves
In animals





Amoeba – CO2 lost through diffusion through cell
membrane
As size and complexity increases diffusion is insufficient
Trachea in insects
Gills in fish
Lungs in humans
Lungs


CO2 is transported by the blood from the cells
where it is produced to air sacs.
Here it diffuses from the blood into the airsacs. It is then eliminated from the body
when expiration takes place.
Oxygen


Necessary for the production of energy from
food
In plants




It is produced during the day as a by-product of
photosynthesis
Some is used
Photosynthesis takes place faster than
Respiration therefore O2 is produced in excess
It is lost by diffusion through the stomata in the
leaf
Oxygen

During strenuous muscular exercise muscle
cells anaerobically respire for a while


Lactic acid produced causing muscle fatigue
Lactic acid is removed via oxidation during
continued heavy breathing
Water





A by-product of respiration
Not normally considered a waste product
Concentration of water in cells need to be
kept within narrow limits
Too little or too much changes the osmotic
condition in and around cells
It has to be regulated
Water cont’d





Plant cells are protected from bursting or taking in
excess water by their cell walls
Animal cells do not have cell walls and WILL burst if
they absorb too much water.
Excess water is lost from the respiratory surfaces of
animals
In mammals some is lost through the skin as sweat
Most of the regulation takes place in a highly
sophisticated organ - KIDNEY
Urea

Produced in mammals



Amino acid accumulation is toxic
It is converted to a less toxic in the liver to
UREA


Breakdown of excess amino acids which cannot
be stored
Process called DEAMINATION
Urea is carried by the blood to the kidney
then passed out of the body in urine
Urea cont’d

DEAMINATION


Break up of the amino acid molecule into two
parts
One part to a carbohydrate



used in respiration for energy OR
Converted and stored as fat
One part containing ammonia (toxic)

Further broken down to form UREA
The Kidney also removes….

Other waste products regulated/removed by
the kidney


Salts
Other nitrogenous compounds


Uric acid
water
Bile…

Bile pigments from the breakdown of red
blood cells are formed and released by the
liver into the gut
Excretion in Plants…

Calcium oxalate






Produced by plants
Stored in cells of some plants as insoluble crystals
As crystals it does not affect the metabolic reaction
In general, plant wastes that are not removed by
diffusion are stored
This storage is usually in dying leaves, stems, roots
or flowers, fruits and seeds or the bark of older
plants
The waste is lost when these structures are shed
Excretion in Plants…


Materials to be stored are transported through the
phloem into the tissues of these organs where they
accumulate
These stored materials can serve useful function



E.g. protection from animals
Other such as oils in citrus may assist with dispersal
by attracting animals
Man makes use of some of these substances also

E.g. dyes, rubber
Plants do not need special excretory
organs



They are not very active so they produce
small amounts of wastes
They produce their own food and thus make
only what is needed; there is no excess to
eliminate
Wastes produced are not as toxic as those of
animals
List of Topics for Exams









Classification
Relationships among living organisms
Nutrient cycles
Digestion, Nutrition
Diffusion, osmosis, active transport
Respiration
Photosynthesis
Transport
Excretion