1. Excretion
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2. 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

3. What is Excretion?

5. Introduction The production of excretory materials
natural consequence of the metabolic reactions that take place in the cells of an organisms
An excretory product
a harmful by-product of a chemical reaction taking place in the cell of an organism.
EXCRETION
The elimination of these substances

6. 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.

7. 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

8. Excretory Products
Carbon Dioxide
Oxygen
Water
Urea
Calcium oxalate

9. 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?

10. Table: Summary of Excretory Products of Plants and Animals
Process by which produced
Process by which removed
Excess carbon dioxide
Respiration in cells
Diffusion via stomata
Excess oxygen
Photosynthesis in green cells
Calcium oxalate
Metabolism in cells
Stored in cells
Others, e.g. tannins, etc.
Stored & lost in old tissues
Animals
Carbon Dioxide
Lung expiration
Water
Respiration and external intake
Kidney (lungs and skin)
Excess salt
Intake and metabolism
Kidney (skin)
Urea
Deamination of amino acids
Kidney

11. Homework (FOR MARKS)
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

12. 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

13. 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

14. 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 air-sacs. It is then eliminated from the body when expiration takes place.

15. 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

16. 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

17. 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

18. 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

19. Urea Produced in mammals Amino acid accumulation is toxic
Breakdown of excess amino acids which cannot be stored
Amino acid accumulation is toxic
It is converted to a less toxic in the liver to UREA
Process called DEAMINATION
Urea is carried by the blood to the kidney then passed out of the body in urine

20. 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

21. The Kidney also removes….
Other waste products regulated/removed by the kidney
Salts
Other nitrogenous compounds
Uric acid
water

22. Bile…
Bile pigments from the breakdown of red blood cells are formed and released by the liver into the gut

23. 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

24. 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

25. 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

26. List of Topics for Exams
Classification
Relationships among living organisms
Nutrient cycles
Digestion, Nutrition
Diffusion, osmosis, active transport
Respiration
Photosynthesis
Transport
Excretion