Maharashtra Board Class 11 Biology Chapter 15 Excretion and Osmoregulation PDF Download

Excretion And Osmoregulation

Can you recall?

1. Why are various waste products produced in the body of an organism?

2. How are these wastes eliminated?

Array of chemical processes occur in the body of an organism. Sum total of these processes is called metabolism. Metabolism involves catabolic (breaking down) and anabolic (building up) processes. Metabolism produces a variety of by-products, some of which need to be eliminated. Such by-products are called metabolic waste products.

Metabolic waste products might be fluid, gaseous, organic or inorganic. Depending on the type, they are eliminated through various organs of the body of an organism.

15.1 Excretion And Excretory Products

Elimination of metabolic waste products from the body is called excretion. Unlike digestive wastes, which are primarily composed of unabsorbed or undigested substances that have never entered the cells, metabolic wastes are produced inside body cells.

Let us try to enlist various excretory waste products produced in human body. Fluids such as water, gaseous wastes like CO\(_2\), nitrogenous wastes like ammonia, urea and uric acid, creatinine, mineral, salts of sodium, potassium, calcium, etc. which if, are present in body in excess are excreted through urine, faeces and sweat. Pigments formed due to breakdown of haemoglobin are like bilirubin (excreted through faeces) and urochrome (eliminated through urine). Also, the pigments present in foodstuff like beet root consumed by organism, excess of vitamins, hormones and drugs taken are eliminated. Spices we consume contain volatile substances that are excreted through lungs.

Have you ever observed?

1. When does urine appear deeply coloured?

2. If we consume onion and garlic, we get bad breath. Why?

Think about it

1. Do organisms differ in type of metabolic wastes they produce?

2. Do environment or evolution have any effect on type of waste produced by an organism?

3. How do thermoregulation and food habits affect waste production?

Body of an organism can store excess carbohydrates and fats but is unable to store excess amino acids. Hence, excess amino acids are essentially broken down by a process called as deamination. In this process, amino group is separated from the amino acid and ammonia is formed. Toxic ammonia is either excreted as it is or further converted to less toxic forms like urea or uric acid before excretion.

There is no clear correlation between the phylogenetic relationship of organisms and their major excretory products, but it's habitat has. e.g. Tadpole of frog excretes ammonia and adult frogs mostly are ureotelic. Some terrestrial turtles excrete uric acid whereas others excrete urea or ammonia.

Animals can be broadly classified into three types based on nitrogenous wastes they produce. Ammonia is the basic product of deamination process. But it is highly toxic. Hence, it is to be diluted immediately. If there is no or limited access to water, need for conversion of ammonia becomes necessary. Thus, availability of water plays key role in deciding mode of excretion of an organism. These are of mainly three types:

Teacher's Note

Our body makes waste during all activities. Just like we throw garbage from our house, our body throws waste through urine and sweat.

Exam Trick

Remember: More water available = Ammonia is excreted. Less water available = Uric acid is excreted. Think of camel in desert - it makes very concentrated urine.

Points to Remember

Metabolism means all chemical work done in the body.
Waste products are made when body breaks down food.
Different animals excrete different waste based on where they live.
Water availability decides the type of waste excretion.
Ammonia is very toxic and needs lots of water to remove it safely.

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