CBSE Class 12 Biology Respiration Notes

Download CBSE Class 12 Biology Respiration Notes in PDF format. All Revision notes for Class 12 Biology have been designed as per the latest syllabus and updated chapters given in your textbook for Biology in Standard 12. Our teachers have designed these concept notes for the benefit of Grade 12 students. You should use these chapter wise notes for revision on daily basis. These study notes can also be used for learning each chapter and its important and difficult topics or revision just before your exams to help you get better scores in upcoming examinations, You can also use Printable notes for Class 12 Biology for faster revision of difficult topics and get higher rank. After reading these notes also refer to MCQ questions for Class 12 Biology given our website

Respiration Class 12 Biology Revision Notes

Class 12 Biology students should refer to the following concepts and notes for Respiration in standard 12. These exam notes for Grade 12 Biology will be very useful for upcoming class tests and examinations and help you to score good marks

Respiration Notes Class 12 Biology

Breathing & Exchange of Gases

 It is a process of oxidation of organic compounds in cell in which energy is released.
 According to scientist G.S. Carter, there are 3 steps in respiration :
1.1 External respiration : Gaseous exchange between environment and lungs.
1.2 Internal respiration : Gaseous exchange between lungs and blood & blood with tissue cells.
1.3 Cellular respiration : Oxidation of organic compounds in cell, in which energy is released.
2. Types of Resplration

     • Respiration is of two types :

2.1 Anerobic Respiration
 Oxygen is not required.
 Process occur in cytoplasm
 Due to incomplete oxidation of organic compounds less energy is released.
 Final products are lactic acid and alcohol. e.g. – RBC, muscles, internal parasites [Tapeworm, Ascaris, parasites of intestine]
Note: Parasites of blood like plasmodium respire by aerobic respiration.
2.2 Aerobic respiration :

 Oxygen is must.
 Process occur in cytoplasm and mitochondria.
 Due to complete oxidation of organic compounds more energy is released.
 Final products are carbon dioxide & water. e.g.– most of Animals & Plants
 Aerobic respiration are of two type :
(a) Direct respiration : In this case environmental oxygen is exchanged with the carbon dioxide of the body cells without special respiratory organs and without the aid of blood. Eg. Aerobic bacteria, protists, plants, sponges, cnidarians, flatworms, and most arthropods.
(b) Indirect respiration : It involves special respiratory organs such as skin, buccopharyngeal lining, lungs and it need the help of blood.
CBSE Class 12 Biology Respiration Notes
CBSE Class 12 Biology Respiration Notes
CBSE Class 12 Biology Respiration Notes

(b) Respiratory region :
 Epithelial lining of maxillo turbinals and inferior turbinals / Ethmoturbinals is composed of PSCGE in which goblet cells are present, which secret mucous, and makes nasal passage
moist.It act as a air conditioning and filtering unit in breathing.

(c) Olfactory region :
  Epithelial linings of nasoturbinals called neurosensory epithelium which receive smell sensation.

4.3 Internal nares = (choanae)
  Nasal chamber open in nasopharynx through internal nares :

CBSE Class 12 Biology Respiration Notes

4.4 Pharynx
  Due to presence of palate in mammals, anterior part of pharynx is divide in two chambers.
(1) On Dorsal surface nasopharynx
(2) On ventral surface oropharynx

  Posteriorly both these chambers open in pharynx, so pharynx is a common chamber for food and air. Therefore mammals can breath through mouth.

  In posterior part of pharynx 2 openings are present :
(1) Upper opening is called Gullet through which pharynx open in oesophagus.
(2) Lower opening is called Glottis through which pharynx open in Larynx/Trachea.

  On glottis leaf shape septum Epiglottis (thin elastic cartilage) is present which close glottis at the time of swallowing. So at this moment breathing stops or breathing rate become zero.

  Pharynx is only body part in which both food and air passage intersect each-other.

4.5 LARYNX (voice box: voice producing organ) :
  It is present in the anterior part of Trachea, so is considered as modification of Trachea.
  It is a bone like str. Which is composed of two cartilage (In structure), Four cartilage (In shape), Nine cartilage (In number)
  These cartilage of larynx attach by ligaments & membranes.

CBSE Class 12 Biology Respiration Notes

(1) Thyroid cartilage :
  Largest cartilage of Larynx.
  Composed of hyaline cartilage.
  It is C-shaped cartilage so incomplete cartilage.
  Ventrally it is broad & laterally it is narrow but absent on dorsal surface.
  So this cartilage complete almost ventral surface and little part of each lateral surface of larynx.
  On anterior part of Thyroid epiglottis is attached which is composed of elastic cartilage.
  In males of human ventral surface of Thyroid makes a process called as Adam’s apple.

(2) Cricoid cartilage :
  Composed of hyaline cartilage.
  It is signet ring shape cartilage. (so complete)
  It is present just below Thyroid cartilage.
  Dorsally it is broad and ventrally it is narrow. So this cartilage complete maximum. Dorsal surface and remaining part of each lateral surface of Larynx.

(3) Arytenoids Cartilage :
  Two in number so paired cartilage.
  Composed of hyaline cartilage.
  These are pyramid shape cartilage which are present just above cricoid cartilage in dorsal surface of Larynx.
• One end of vocal cords is attached with arytenoids and another end is attached with Thyroid cartilage.

(4) Cartilage of Santorini :
  Two in number (paired).
  It is composed of Elastic cartilage.
  They are present in the form of node like structure at the end of arytenoids. So they are considered as Bands of Arytenoids.
  When epiglottis close glottis it fall on cartilage of santorini. So these cartilage protect epiglottis.

(5) Other cartilages :
  Cuneiform and Corniculate are also present.
Vocal cords : In Larynx two pairs of vocal cords are present

(1) Anterior vocal cords : false vocal cord :
  They are composed of membranes.
  They are pink in colour.
  They do not help in Phonation.

(2) Posterior pair : True vocal cord :
  They are composed of yellow fibrous C.T., so they are yellow in colour.
  Usually they are present in relax position, so when air pass through vocal cord, no sound is produced.
  By the contraction in laryngeal muscle vocal cord comes in stretch position, so when air pass through these vocal cords, due to vibration, sound is produced in the form of Laryngeal voice (AA and E) which is converted into true speech by the help of lips and tongue.
  It is due to presence of well developed speech centre.
  This centre was started from ‘Neanderthal man’.

Note :
(i) Sound Production : Sound is produced by true vocal cords. When expired air is passed through the true vocal cords under pressure from the lungs, the vocal cords are set into vibration, which results in the production of sound.
(ii) Pitch of a sound : It is determined by the tension on the vocal cords, greater the tension - higher the pitch.
(iii) Quality of voice : It depends on the resonators above the larynx, namely the pharynx, mouth, bucca cavity and paranasal sinuses.
(iv) Quality of sound : It is controlled by the muscles of the soft palate, tongue, floor of mouth, cheeks, lips and jaws.

4.6 Trachea :
• Its 12 cm long tube with diameter 2.5 cm, which is present in complete length of neck and upto middle part of thoracic cavity (at the level of 5th thoracic vertebra divide into right and left primary bronchi).
 In complete length of Trachea 16-20 ‘C-shaped’ cartilaginous rings are present which are composed of hyaline cartilage.
 These rings are incomplete on dorsal surface of Trachea which prevent trachea to collapse.
 In the absence of cartilage on dorsal surface Trachealis muscles are present which help in dialation of Trachea during forceful breathing.
 In the histology of wall of Trachea there are four layers.
(1) Mucosa : 3 sub layers
           (a) Epithelium             :               PSCGE
           (b) Lamina propria      :                Reticular fibrous C.T.
           (c) Muscularis mucosa :                Longitudinal & circular muscle

(2) Submacosa : Aerolar C.T.

(3) Cartilagenous layer : C shape rings of hyaline cartilage

(4) Tunica Adventia : White fibrous C.T.

4.7 Bronchial Tree (B.T.) and Respiratory Tree (R.T.) :
 When trachea enter into thoracic cavity it divides in two branches called as primary bronchus. Branches of primary bronchus upto Terminal bronchioles make Bronchial Tree.
 Terminal bronchioles divide to form respiratory bronchiole and its branches make Respiratory Tree.

(i) Cartilagenous rings are present in the wall of bronchial tree while absent in respiratory tree.
(ii) Gaseous exchange occur in Respiratory tree while absent in Bronchial Tree.
(iii) Volume of air which is present in bronchial tree is a part of Dead space volume.

CBSE Class 12 Biology Respiration Notes

Please click the link below to download CBSE Class 12 Biology Respiration Notes.

More Study Material