Excretion Page 127. SyllabusObjectives Discuss the importance of excretion in the living organisms...
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Transcript of Excretion Page 127. SyllabusObjectives Discuss the importance of excretion in the living organisms...
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
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
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
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 AnimalsPlants 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
Animals
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
Homework (FOR MARKS)
1. What effect do metabolic wastes have on tissue activities? 3 marks
2. What sorts of tissue activities produce metabolic wastes? 2 marks3. What sort of metabolic wastes do plants and animals produce? 44. What about the effect of a build up of carbon dioxide in the cells?
4 marks5. What are the organs that remove excretory products? 10 marks6. Draw a summary table to describe where excretory products are
made, and where they are removed in plants and animals. 8 marks
7. Do plants need special organs for excretion? 1 marks8. Draw a nephron 3 marks9. 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 air-sacs. 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 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
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