Chapter 6

Respiration and Excretion in Organisms

Respiration

It is the process in which food is broken down in the cell to release

energy.

It occurs in the cells of all living organisms.

Respiration occurs in two stages – external respiration (breathing) and internal respiration (oxidation of food to release energy)

The energy released is stored in the form of ATP molecule.

Two Types of Respiration 1. Aerobic Respiration – It is the process of breakdown of food

in the presence of oxygen. It occurs in all organisms. It leads to production of carbon dioxide, water, and energy.

oxygen

2Glucose CO Water Energy

2. Anaerobic Respiration – It is the process of breakdown of food in the absence of oxygen. It is observed in some organisms such as yeast. It leads to production of alcohol and carbon dioxide.

without

2oxygenGlucose Alcohol/Lactic acid Energy CO

During heavy exercise, our muscles respire anaerobically to provide energy to muscle cells. This leads to accumulation of

lactic acid that causes muscle cramps and thus, pain in body.

Breathing

It is a continuous process that involves inhalation and exhalation. 1. Inhalation – Process of taking in oxygen-rich air in the body 2. Exhalation – Process of giving out carbon dioxide-rich air into

the atmosphere

Nostril is the opening through which we inhale air. From nostrils, the air

passes into nasal cavity.

Nasal cavity filters and purifies the air that we breathe in.

Rib cage and diaphragm are involved in actual mechanism of breathing.

Rib cage is present around the chest cavity while diaphragm is present at the base of the chest cavity.

During inhalation 1. Diaphragm moves down. 2. Ribs move upwards and downwards increasing the space in the

chest cavity.

During exhalation 1. Diaphragm moves to its original position. 2. Ribs move down and inward reducing the size of chest cavity.

Respiration in Land Animals

A cockroach has small openings on the sides of its body, which are known as spiracles. The oxygen rich-air enters through spiracles.

The spiracles are connected to a network of tubes, called trachea, for gaseous exchange.

Earthworms breathe through the surface of the skin.

Respiration in Aquatic Animals

Frogs respire through both lungs and their skin.

Fishes have special structure called gills for breathing. They do not have

lungs.

Respiration in Plants

Plants respire through tiny pores on their leaves called stomata. Stomata help in gaseous exchange.

Roots of plants respire through air spaces present in the soil.

Respiration in Human Beings

We inhale through nose, then the air enters pharynx which leads to trachea. Trachea divides into two branches called bronchi.

Each bronchus leads to lungs and further divides into bronchioles. At the

end of each bronchiole alveoli are present which are richly supplied with blood vessels.

Diffusion of gases takes place through these blood vessels.

Excretory System

Excretion – It is the process of removing harmful waste products

produced in the cells of living organisms.

The excretory system in humans includes – a pair of kidneys – a pair of ureters – a urinary bladder – a urethra

Kidney is the main excretory organ of the human body.

It plays an important role in the formation of urine. Human kidney produces 1.5 L of urine.

Ureter carries urine to the bladder.

Urinary bladder collects urine.

Urethra carries urine out of the body.

The main excretory product in human body is urea while in aquatic animals, it is ammonia.

In birds, lizards, and snakes, the main excretory product is uric acid.

The process of removing wastes using an artificial kidney is called dialysis.

Transport of Water and Food in Plants

Water and mineral are absorbed by the cells of root hair.

Root hair increases the surface area for absorption of water and minerals.

Xylem and phloem are transport systems in plants.

Xylem transports water and minerals from the soil via root hair to the rest of the plant body.

Phloem transports food materials from leaves to different parts of the plant body.

Excretion in Plants

Plants get rid of the excess of water by transpiration.

Transpiration is the evaporation of water from plants.

The water evaporates through stomata. Stomata help in gaseous exchange and

evaporation of water.

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