Excretion

1. Excretion Page 127

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

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 • 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