Excretion

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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 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