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Cellular respiration is the process by which the chemical energy of “food” molecules is released and partially captured in the form of ATP. Carbohydrates, fats, and proteins can all be used as fuels in cellular respiration, but glucose is the most commonly used as an example to examine the reactions and pathways involved.


Types of respiration

Respiration may be of two types,

(a) Aerobic respiration and

(b) Anaerobic respiration.


(a)Aerobic respiration:

  ✦ Respiration which takes place in the presence of oxygen.

                 Glucose + Oxygen -> Carbon dioxide + Water +Energy


(b)Anaerobic respiration

✦ Some micro organisms like yeast and bacteria obtain energy from food in the absence of oxygen. So, the respiration which takes place in the absence of oxygen is called anaerobic Anaerobic respiration takes place in our skeletal muscle

✦ Bacteria and fungi can respire anaerobiaclly , which is useful in convertingsugar into alcohol.  

Absence of oxygen

                          Glucose ->Ethyl alcohol + Carbon dioxide + Energy


Yeast is one-celled fungus and respires anaerobically to produce alcohol. Therefore, they are  used to make wine and beer.


Difference between breathing and respiration




It is a physical process because only the air moves from one place to other

It is a chemical process because the food undergoes chemical changes

During this ,energy is not released

During this energy is released

It involves breathing organs

It takes place in living cells


Cellular Respiration

Cellular respiration is the process of oxidizing food molecules, like glucose, to carbon dioxide and water.

                   C6H12O6 + 6O2 + 6H2O -> 6 CO2

The energy released is trapped in the form of ATP for use by all the energy consuming activities of the cell. This process occurs partially in the cytoplasm, and partially in the mitochondria. The mitochondria are another or ganelle in enukaryotic cells, like the chloroplast, the mitochondria has two lipid bilayers around it, and its own genome. Divide cellular respiration into three metabolic processes: glycolysis, the Krebs cycle, and oxidative phosphorylation. Each of these occurs in a specific region of the cell.

1. Glycolysis occurs in the cytosol.

2. The Krebs cycle takes place in the matrix of the mitochondria.

3. Oxidative phosphorylation via the election transport chain is carried out on the inner mitochondrial membrane.

In the absence of oxygen, respiration consists of two metabolic pathways: glycolysis and fermentation. Both of these occur in the cytosol.





In glycolysis, the 6 – carbon sugar, glucose, is broken down into two molecules of a 3 – carbon molecule called pyruvate. This change is accompanied by a net gain of 2 ATP molecules and 2 NADH molecules.


Krebs cycle

The Krebs cycle occurs in the mitochondrial matrix and generates a pool of chemical energy (ATP, NADH, and FADH2) from the oxidation of pyruvate, the end product of glycolysis. Pyruvate is transported into the mitochondria and loses carbon dioxide to form acetyl – CoA, a 2 – carbon molecule. When acetyl – CoA is oxidized to carbon dioxide in the Krebs cycle, chemical energy is released and captured in the form of NADH, FADH2, and ATP.


Oxidation Phosphorylation via the Election Transport Chain

The electron transport chain allows the release of the large amount of chemical energy stored in reduced NAD+ (NADH) and reduced FAD (FADH2). The energy released is captured in the form of ATP (3 ATP per NADH and 2 ATP per FADH2).

NADH + H+ + 3 ADP + 3 Pi + ½ O2 -> NAD+ + H2O + 3 ATP

FADH2 + 2 ADP + 2 Pi + ½ O2 -> FAD+ + H2O + 2 ATP

The electron transport chain (ETC) consists of a series of molecules, mostly proteins, embedded in the inner mitochondrial membrane.


Glucose and Energy

The chemical energy stored in glucose generates far more ATP in aerobic respiration than in respiration without oxygen (glycolysis and fermentation).



All cells are able to synthesis ATP via the process of glycolysis. In many cells, if oxygen is not present. Pyruvate is metabolished in a process called fermentation.

Respiration – Gaseous Exchange and Energy Production

The main function of the respiratory system is gaseous exchange. This refers to the process of oxygen and carbon dioxide moving between the lungs and blood. It occurs in the lungs between the alveoli and a network of tiny blood vessels called capillaries, which are located in the walls of the alveoli.


Breathing Organs

The organ system which aids in the process of respiration is called the Respiratory system.

The composition of air that we breathe in is

Nitrogen – 78%

Oxygen – 21%

Carbon dioxide – 0.03 – 0.04%

Hydrogen – traces

Noble gases – traces

Name of the animal     Name of the Respiratory organ

1. Unicellulars like amoeba, Euglena    - Body surface

2. Earthworm                                                 - Skin

3. Leech                                                            - Skin

4. Insects                                                         - Trachea

5. Fish                                                               - Gills

6. Prawn                                                          - Gills

7. Frog                                                              - Skin and Lungs

8. Reptiles, Aves and Mammals             - Lungs


Parts of the Respiratory system in man

The primary organism of the respiratory system is lungs, which carry out this exchange of gases as we breathe. Red blood cells collect the oxygen from the lungs and carry it to the parts of the body where it is needed. During the process, the red blood cells collect the carbon dioxide and transport it back to the lungs, where it leaves the body when we exhale.

The respiratory tract is the path of air from the nose to the lungs. It is divided into two sections: Upper Respiratory Tract and the Lower Respiratory Tract. Included in the upper respiratory tract are the Nostrils. Nasal Cavities, Pharynx, Epiglottis, and the Larynx. The lower respiratory tract consists of the Trachea, Bronchi, Bronchioles, and the Lungs. As air moves along the respiratory tract it is warmed, moistened and filtered.



The lungs are the main organs of the respiratory system. In the lungs oxygen is taken into the body and carbon dioxide is breathed out.



The trachea is sometimes called the windpipe. The trachea filters the air we breathe and branches into the bronchi.



The bronchi are two air tubes that branch off of the trachea and carry air directly into the lungs. Only in the alveoli does actual gas exchange takes place.



Breathing starts with a dome – shaped muscle at the bottom of the lungs called the diaphragm. When you breathe in the diaphragm contracts. When it contracts it flattens out and pulls downward.


Gaseous Exchange and Transport

Steps in gas exchange:

1. Oxygen is brought to the surface of an alveolus by inhaling air.

2. Oxygen diffuses across the alveolar membrane via a concentration gradient and into a capillary. Water is needed at the surface between the alveolus and the capillary to facilitate the diffusion of gases (O2 and CO2).

3. At the same time, carbon dioxide (CO2) in the blood diffuses across the membrane and into an alveolus. This happens in the opposite direction to oxygen.

4. The CO2 is then sent back up the airway to be expelled to the outside.


Difference between Respiration and Photosynthesis



It takes place throughout day and night

It takes place during day time

All living organisms do it

Only green plants do it

Food is consumed

Food is synthesized

During this process oxygen is taken in and carbon dioxide is given out


During this process carbon dioxide is taken in and oxygen is given out



      ✦ Horneostasis is the maintenance  of a constant internal environment of thebody.

      ✦ It was first point out by the French physiologist Claude Bernard in 1857. 

      ✦ Behavioural and physiological responses are two important regulatingmechanisms to maintain the stability of Homeostasis.


For example

      ✦ The control of blood glucose 1evel`is a good example of homeostasis andinvolves the secretion of atleast six hormones.



✦ The word metabolism has its root from the Greek work Metabloe which means change means change.

✦ The sum total of biochemical reactions  involved in the release and  utilization of erergy exchange within the organism is termed as metabolism.

✦ Such a chemical reaction in the metabolic process can be divided into two categories.




The simple substances are obtained from the food are converted intocellular substance. This process is called Anabolism.

For example,

Glucose -> Glycogen and other sugars

Amino acids -> Enzymes, hormones, proteins

Fatty acids -> Cholesterol and other steroids.



✦ Organic substances which are obtained from the food are broken down toproduce energy for the purpose of physiological functions of the cells.

✦ This-process is called as catabolism.

✦ Glucose -> CO2, Water and heat

✦ Protein -> amino acid

✦ Fats -> Glycerol, fatty acid, etc.

✦ The repeated anabolism and catabolism in the metabolic process maintains the homeostatic conditions of the body

✦ The metabolic process is responsible for movement growth, development, maintenance and repair of the cell, tissue and body

✦ Pelicans feed on fish, which they scoop up in the flexible pouch that lie under their long beaks.




Integumentary System:

✦ It includes skin, hair, nails, swet glands and oil glands

✦ The skin is the heaviest organ of our body and weighs about 7 kg.

Functions of skin

✦ Protects the inner parts of  the body

✦ It works as an excretory organ by sweating

✦ It acts as a sense organ


Skeletal System

✦ The Skeletal System  is made up of 206 bones.


✦ Skeletal System provides a frame work to the body and helps inmovements.

✦ It protects many internal organs such as brain, heart, lungs etc.

✦ It produces blood cells like Red Blood Cells, White Blood Cells and Platelets.


Muscular System

✦ The Muscular System is made up of three types of muscles. They areskeletal muscles, smooth muscles and cardiac muscles.


✦ Skeletal muscles give shape to the body and makes possible the movementsinour body.

✦ These muscles generate heat required for maintaining our bodytemperature.

✦ Other muscles bring out movement in the internal orgens


Circulatory System

✦ The Circulatory System transports substances from  one part of the body toanother.


✦ Blood transports nutrients oxygen,wastes, hormones.

✦ It regulates water level and body temperature.

✦ Blood vessels are f three types: arteries, veins and capillaries

✦ Nervous System is composed of the brain, spinal cord and nerves.


Endocrine System

✦ A group of ductless glands form a system called Endocrine System in ourbody.

✦ Hormones regulate body functions

Reproductive System

✦ The Reproductive System is composed of mainly testes in males and ovariesin females.

✦ The testes produce male gametes called sperms. The ovaries produce femalegametes called eggs.

Health Care is the prevention and treatment of illness.



The skin is composed of three major tissues.

      ◘ Epidermis

      ◘ Dermis

      ◘ Hypodermis



Epidermis is the upper layer of the skin. The outer most layer consists of flat, thin and scale-like dead cells.



The dermis is the middle layer. It is thick but elastic. The dermis consist of nerves, blood vessels, hair follicles, sweat glands and sebaceous glands(oil glands). The sweat glands separate sweat from blood vessels.

The sebaceous glands secrets sebum which keeps the skin smooth and shiny.



It is the lowest most layer, which contains large amount of adipose tissue.


Functions of the Skin

Skin can prepare vitamin D with help of sunlight.

Skin acts as an excretory organ and excretes sweat.

Skin colour of women is determined by the melanocytes of the basement membrane. The formation of melanocytes is by hereditary. Even then there is some impact of colour by external factors like temperature, sunlight, wind and contumes,



Locomotory Organs








Body satae

Star fish

Tube feet









Skeletal Muscles

✦ The skeletal muscles are attached to the body by tendons.

✦ These muscles are covered by sheets of connective tissues called fascia.



✦ These are connective tissue structure showing slight elasticity. They are like cords or straps strongly attached to bones.



✦ These are assemblages of connective tissue lining skeletal muscles as membranous sheets.

✦ The fascia may be superficial or deep. The Superficial is a layer of loose connective tissue found in between skin and muscles.

✦ of muscles can lift 3.5kg.


Facial Expressions

✦ Facial expression, such as looking, shocked and smiling, are tiny voluntary movements made by more than 30 different muscles.






Upper back and each side of neck

Upper pulling movement



Arm rising



Horizontal pressing and drawing of arm across the body


Wide back muscle

Pulling and rowing movement


Front portion of the upper arm

Arm bending and twisting


Back of upper arm

Pushing and straightening of upper arm


Lower leg between ankle and knee

Raising and lowering of toes.

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