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 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 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 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

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

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 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

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