1styear BIOLOGY Notes Chapter-13

Chapter-13
GASEOUS EXCHANGE

RESPIRATORY ORGANS OF COCKROACH TRACHEAL SYSTEM
Cockroach has evolved a special type of invaginated respiratory system called Tracheal system, especially adopted for terrestrial mode of life and high metabolic rate of insects.



STRUCTURAL CONSTITUENTS OF TRACHEAL SYSTEM
1. TRACHEA
2. SPIRACLES
3. TRACHEOLES

1.TRACHEA
Tracheal system consists of number of internal tube called Trachea which are the connection between the spiracles and tracheal fluid.

2. SPIRACLES
Laterally, trachea open outside the body through minute, slit like pores called as spiracles.
• There are 2 pairs of spiracles on lateral side of cockroach.
• 2 lie in thoracic segments and 8 in first abdominal segments.

3. TRACHEOLES
On the other side, trachea ramify throughout the body into fine branches or tracheols.
• Tracheoles, finally end as blind, fluid filled fine branches which are attached with cells of tissue.
• Both the trachea and tracheoles are lined internally by thin layer of cuticle.

MECHANISM OF RESPIRATION “INFLOW OF OXYGEN”
The cockroach takes in air directly from the atmosphere into the trachea through spiracles. This air diffuses directly into fluid filled tracheoles through which diffuses into the cells of tissues. Hence the blood vascular system of cockroach is devoid of haemoglobin.

OUTFLOW OF CARBONDIOXIDE
Removal of CO2 from cells of body is largely depended upon plasma of blood, which takes up CO2 for its ultimate removal through body surface via the cuticle.

RESPIRATORY SYSTEM OF FISH
MAIN RESPIRATORY ORGAN
In fish, main respiratory organs are “Gills”. They are out growth of pharynx and lie internally with in the body so that they are protected from mechanical injuries.

INTERNAL STRUCTURE OF GILLS


Each gill is highly vascularized structure. It is composed of
1. Filaments
2. Gill bar or Gill arch
3. Lamella

1. FILAMENTS
Each gill is composed of two rows of hundreds of filaments, which are arranged in V-shape.

2. GILL BAR OR GILL ARCH
Filaments are supported by a cartilage or a long curved bone the gill bar or gill arch.

3. LAMELLA
Lamella is a plate like structure which is formed by infolding of filaments. Lamella greatly increase the surface area of the gill. Each lamella is provided by a dense network of capillaries.

OPERCULUM (IN BONY FISHES)
Gills are covered on each side by gill cover called “operculum”

MECHANISM OF VENTILATION
In bony fishes, ventilation is brought about by combined effect of mouth and operculum.
• Water is drawn into the mouth. It passes over the gills through pharynx and ultimately exists at the back of operculum through open operculur valve.
• Water is moved over the gills in a continuous unidirectional flow by maintaining a lower pressure in operculur cavity than in buccopharynx cavity.

COUNTER CURRENT FLOW OF WATER AND BLOOD
• Gaseous exchange is facilitated in gills due to counter current flow of H2O and blood.
• In the capillaries of each lamella, blood flows in direction opposite to the movement of water across the gill. Thus the most highly oxygenated blood is brought to water that is just entering the gills and has even high O2 content than the blood. As the H2O flows over the gills, gradually loosing its oxygen to the blood, it encounter the blood that is also increasingly low in oxygen. In this way a gradient is establishment which encourages the oxygen to move from water to blood

IMPORTANCE
Counter current flow is very effective as it enables the fish to extract upto 80–90% of the oxygen from water that flows over the gills.

RESPIRATORY SYSTEM OF MAN
MAIN FUNCTION OF RESPIRATION
The main function of respiratory system is inflow of O2 from the atmosphere to the body and removal of CO2 from body to the atmosphere.

COMPONENTS OF RESPIRATORY SYSTEM
(1) PAIRED LUNGS
The respiratory (gas exchange) organs.

(2) AIR PASSAGE WAYS
Which conduct the air

(3) THORACIC CAVITY
Which lodges the lungs

(4) INTERCOSTAL MUSCLES AND DIAPHRAGM
Which decreases and increase the diameters of thoracic cavity


(5) RESPIRATORY CONTROL CENTRES
Areas in brain which control the respiration.

DETAILS OF COMPONENTS
+ THORACIC CAVITY
Paired lungs with in the pleural sacs are situated in the thoracic cavity. Separating the thoracic cavity from the abdominal cavity is a dome-shaped musculo-tendinuous partition called as Diaphragm.

BOUNDARIES OF CAVITY
Thoracic cavity is supported by bony cage (thoracic cage) which is made up of
• Sternum -> in front
• Vertebral column -> at the back
• 12 pairs of ribs -> on each side
• Ribs are supported by Intercostal muscles

FUNCTION
Increase in thoracic cavity diameter is responsible for inspiration. While decrease in diameter is responsible for expiration.

AIR PASSAGE WAYS
Air is drawn into the lungs by inter-connected system of branching ducts called as “Respiratory tract” or “Respiratory passage ways”
Air passage ways consists of

AIR CONDUCTING ZONE(which only conducts the air)
1. Nostrils
2. Nasal Cavity
3. Pharynx (nasopharynx and oropharynx)
4. Larynx
5. Trachea
6. Bronchi
7. Bronchioles (also called terminal Branchioles)
RESPIRATORY ZONE(Where gaseous exchange takes place)
8. Respiratory Bronchioles
9. Alveolar duct
10. Alveolar sacs or alveoli

GENERAL FUNCTIONS OF CONDUCTING AIR PASSAGES
1. Conduction of air from atmosphere to the lungs
2. Humidification of inhaled dry air.
3. Warming / cooling of air to body temp.
4. The injurious particles are entrapped by mucous and removed by ciliary movements.
5. Lymphoid tissues of pharynx provide immunological functions
6. Cartilages prevent the passages from collapse but are not present in Bronchioles which remains expanded by same pressure that expand the alveoli.

CONDUCTING ZONE
1. NASAL CAVITY
Atmospheric air enters the respiratory tract through a pair of openings called external nares (Nostrils), which lead separately into nasal cavity. Nasal cavity opens into naso pharynx through posterior nares (choanae).
• Nasal cavity is lined internally by Pseudostratified columnar ciliated epithelium containing mucous secreting cells.
• Hairs, sweat and sebaceous glands are also present.

SPECIALIZED FUNCTIONS
• Warming of air
• Humidification or moistening of air
• Filteration of air with the help of hairs
• All these together called as Air conditioning function of upper respiratory passages
• Olfaction ( sense of smell)

2. PHARYNX
Air enters from Nasal cavity into pharynx through internal nostrils. The openings of nostrils are guarded by soft palate. It is internally lined by Pseudostratified ciliated epithelium, mucous glands are also present.
FUNCTION
Pharynx is responsible for conduction of air as well as food

3. LARYNX (VOICE BOX)
Pharynx leads air into larynx through an opening called glottis. Glottis is guarded by flap of tissue called epiglottis. During swallowing, soft palate and epiglottis close the nostrils opening and glottis respectively so that food is prevented to go either into nasal cavity or glottis. Larynx, a small chamber consists of pair of vocal cords
FUNCTION
During speech, vocal cords move medially and their vibration produce sound

4. TRACHEA (WIND PIPE)
Larynx leads the air into a flexible air duct or trachea. It bears C-shaped tracheal cartilages which keep its lumen patent during inspiration. Its internal lining is pseudostratified columnar ciliated epithelium containing mucous secreting goblet cells.
FUNCTION
• Conduction of air
• Due to mucous and upward beating of cilia, any residues of dust and germs are pushed outside the trachea towards the pharynx.

5. BRONCHI
“At its lower end, trachea bifurcates into two smaller branches called Principle Bronchi? which leads the air into lung of its side. They are also supported by C-shaped cartilage rings upto the point where they enter the lungs”.
• In all areas of trachea and bronchi, not occupied by cartilage plates, the walls are composed mainly of smooth muscles.

6. BRONCHIOLES
On entering the lungs, each bronchus divide repeatidly. As the bronchi become smaller, U-shaped bars of cartilage are replaced by irregular plates of cartilages. The smallest bronchi divide and give rise to Bronchioles (less than 1.5 mm in diameter).

7. TERMINAL BRONCHIOLES
Bronchioles divide and give rise to terminal bronchioles (less than 1 mm in diameter). Walls possess no cartilages and are almost entirely the smooth muscles. These are the smalled airways without alveoli.

RESPIRATORY ZONE
In this zone of respiratory tract, gaseous exchange between capillary blood and air takes place.

1. RESPIRATORY BRONCHIOLES
Terminal bronchioles show delicate outpouchings from their walls, which explains the name Respiratory Bronchioles (less than 0.5 mm in diameter). They bear the pulmonary alveoli.

2. ALVEOLAR DUCTS AND SACS
Each respiratory bronchioles terminates at a tiny hollow sac like alveolar duct that lead into tabular passages with numerous thin walled out pouchings called Alveolar sacs.

3. PULMONARY ALVEOLI
The alveolar sacs consists of several alveoli openings into a single chamber. Alveoli are the site of exchange of respiratory gases so they are considered as Respiratory surfaces of lungs. Each alveolus is surrounded by a network of blood capillaries.

INTERNAL STRUCTURE OF ALVEOLI
The alveolar lining cells consists of
1. Type I cells
2. Type II cells
They are also called pneumocytes.
“Bifurcation of trachea is called Carina”.

TYPE I PNEUMOCYTES
Squamous shaped cells which form the epithelial lining of alveoli

TYPE II PNEUMOCYTES
Irregular and cuboidal shaped cells which secretes a substance called Surfactant

SURFACTANT
The internal area of an alveoli is provided with a thin layer of fluid called as Surfactant secreted by type II cells.
FUNCTION OF SURFACTANT
1. It reduces the internal surface tension of alveoli which prevent it collapsing during expiration.
2. It increases the compliance.
3. It stabilize the alveoli.
4. It also helps to keep the alveoli dry.

LUNGS
Lungs are paired, soft, spongy, elastic and highly vascularized structures, which occupy most of thoracic cavity. In child they are pink, but with age they become dark and mottled due to inhalation of dust.

RIGHT LUNG
Partitioned into 3 lobes by two fissures.

LEFT LUNG
Divided into 2 lobes by one fissures.

PLEURAL MEMBRANES
Each lung is enclosed by two thin membranes called as Visceral and parietal pleural membranes.

PLEURAL CAVITY
In between the membranes there is a narrow cavity, the pleural cavity filled with pleural fluid which acts as lubricant.

FUNCTION OF CAVITY
1. Cardinal function is to exchange gases.
2. Phagocytosis of air borne particles
3. Temperature regulation
4. Removal of water
5. Maintainence of acid-base balance (by elemination of CO2)
6. Acts as Reservoir of blood.

BREATHING
DEFINITION
“Breathing is the process of taking in (inspiration or inhalation) and giving out of air (expiration or exhalation) from the atmosphere up to the respiratory surface and vice versa”

TYPES OF BREATHING
There are two types of Breathing
• Negative pressure Breathing
• Positive pressure Breathing

NEGATIVE PRESSURE BREATHING
Normal breathing in man is termed as negative pressure breathing in which air is drawn into the lungs due to negative pressure (decrease in pressure in thoracic cavity in relation to atmospheric pressure).

POSITIVE PRESSURE BREATHING
“In this kind of breathing, lungs are actively inflated during inspiration under positive pressure from cycling valve”.
EXAMPLES
Frog uses positive pressure breathing.

PHASES OF BREATHING
1. INSPIRATION OR INHALATION
2. EXPIRATION OR EXHALATION

(1) INSPIRATION
DEFINITION
“Inspiration is an energy consuming process in which air is drawn into the lungs due to negative pressure in thoracic cavity”

MECHANISM
During inspiration volume of thoracic cavity increases which creates a pressure (intra thoracic) that ****s the air into the lungs.

INCREASE IN VOLUME OF THORACIC CAVITY
Volume of thoracic cavity increases due to
1. Inc. in Anterio-posterior diameter
2. Inc. in Vertical diamter.

INCREASE IN ANTERIO-POSTERIOR DIAMETER During contraction of external intercostals muscle, the ribs as well as the sternum move upward and outward, which causes the increase in anterior-posterior diameter of thoracic cavity.

INCREASE IN VERTICAL DIAMETER
Vertical diameter of thoracic cavity inc. due to Contraction (descent) of Diaphragm which makes it flat.
• As a consequence thoracic cavity enlarges and the pressure is developed inside the thoracic cavity and ultimately in the lungs. So the air through the respiratory tract rushes into the lungs upto the alveoli where gaseous exchange occurs.

(2)EXPIRATION
DEFINITION
“It is reserve of inspiration. The passive process in which air is given out of lung due to increased pressure in thoracic cavity is called “Expiration”

MECHANISM
During expiration, elastic recoil of pulmonary alveoli and of the thoracic wall expels the air from the lungs.


DECREASE IN VOLUME OF THORACIC CAVITY
Volume of thoracic cavity ? due to
1. DECREASE IN ANTERIO-POSTERIOR DIAMETER
2. DECREASE IN VERTICAL DIAMETER

(1) DECREASE IN ANTERIO-POSTERIOR DIAMETER
It is caused by relaxation of external intercostals muscles and contraction of internal intercostals muscles which moves the ribs and sternum inward and downward.

(2) DECREASE IN VERTICAL DIAMETER
It is caused by relaxation of diapharagm which makes it dome shaped thus reducing the volume of thoracic cavity.
• As a consequence, the lungs are compressed so the air along with water vapours is exhaled outside through respiratory passage.

CONTROL OF RATE OF BREATHING
Rate of breathing can be controlled by two modes.
• VOLUNTARY CONTROL
• INVOLUTARY CONTROL

VOLUNTARY CONTROL
Breathing is also under voluntary control by CEREBRAL CORTEX
EXAMPLES
We can hold our breath for short time or can breath faster and deeper at our will.

INVOLUNTARY CONTROL
Mostly, rate of breathing is controlled automatically. This is termed as Involuntary control which is maintained by coordination of respiratory and cardio-vascular system.

TWO MODES OF INVOLUNTARY CONTROL
A. NERVOUS CONTROL (through respiratory centers in brain)
B. CHEMICAL CONTROL (through chemoreceptors)

(A) NERVOUS CONTROL
• Control of rate of breathing by nervous control is through the Respiratory centers in Medulla oblongata which are sensory to the changes in Conc. of CO2 and H+ present in the cerebro-spiral fluid (CSF).

RESPIRATORY CENTRES IN MEDULLA
Two center are present

(1) DORSAL GROUP OF NEURONS
Medulla contains a dorsal group (Inspiratory group) of neurons responsible for inspiration
FUNCTION
In response to increase conc. of CO2 and H+ (decreased pH), it sends impulses to the intercostals muscles to increase the breathing rate

(2) VENTRAL GROUP OF NEURONS
Another area in the medulla is ventral (expiratory) group of neurons.
FUNCTION
It inhibits the dorsal group and mainly responsible for expiration

(B) CHEMICAL CONTROL
Chemical control of rate of breathing is through chemoreceptors.

LOCATION OF CHEMORECEPTORS
• AORTIC BODIES
• CAROTID BODIES

AORTIC BODIES
The peripheral chemoreceptors which are located above and below the arch of aorta are called Aortic bodies. It sends impulses to medulla through Vagus nerve.

CAROTID BODIES
Chemoreceptors which are located at the bifurcation of carotid arteries are called Carotid bodies. It sends impulses to medulla through Glossopharyngeal nerve.
FUNCTION
Inc. in concentration of CO2 and H+ in blood are basic stimuli to increase the rate of breathing which are monitered by these chemoreceptors and then send the impulses to medulla oblongata which produce action potential in inspiratory muscles.

DISORDERS OF RESPIRATORY TRACT
(1) LUNG CANCER (BRONCHIAL CARCINOMA)
CAUSES
• Smoking is a major risk factor either acitively or passively.
• Asbestos, nickel, radioactive gases are associated with increased risk of bronchial cascinoma

PHYSIOLOGICAL EFFECTS
+ LOSS OF CILIA
The toxic contents of smoke such as nicotine and SO2 cause the gradual loss of cilia of epithelical cells so that dust and germ are settled inside the lungs.

+ ABNORMAL GROWTH OF MUCOUS GLANDS
Tumor arises by uncontrolled and abnormal growth of bronchial epithelium mucous glands. The growth enlarges and some times obstruct a large bronchus.
• The tumours cells can spread to other structures causing cancer.

SYMPTOMS
• Cough- due to irritation
• Breath lessness – due to obstruction.

(2) TUBERCLOSIS (KOCH’S DISEASE)(INFECTIOUS DISEASE OF LUNG)
CAUSE
Caused by a Bacterium called as “MYCOBECTERIUM TUBERCLOSIS”

PHYSIOLOGICAL EFFECTS
• Tuber Bacili causes
• Invasion of infected region by macrophages
• Fibrosis of lungs thus reducing the total amount of functional lung tissues
These effects cause
• Increased work during breathing
• Reduced vital and breathing capacity
• Difficulty in diffusion of air from alveolar air into blood.

SYMPTOMS
• Coughing (some time blood in sputum)
• Chest pair
• Shortness of breath
• Fever
• Sweating at night
• Weight loss
• Poor apetite

PREVENTION
A live vaccine (BCG) provides protection against tuberclosis.

3. COPD-(CHRONIC OBSTRUCTIVE PULMONARY DISEASE)
They include
A. Emphysema
B. Asthma

(3-A)EMPHYSEMA
CAUSES
It is a chronic infection caused by inhaling Smoke and other toxic substances such as Nitrogen dioxide and Sulphur dioxide

PHYSIOLOGICAL EFFECTS
• Long infection – Irritants deranges the normal protective mechanisms such as loss of cilia, excess mucus secretion causing obstruction of air ways
• Elasticity of lung is lost
• Residual volume increases while vital capacity decreases.
• Difficulty in expiration due to obstruction
• Entrapment of air in alveoli
• All these together cause the marked destruction of as much as 50-80% of alveolar walls.
• Loss of alveolar walls reduces the ability of lung to oxygenate the blood and remove the CO2
• Oxygen supply to body tissues especially brain decreases.

SYMPTOMS
• Victim’s breathing becomes labored day by day.
• Patient becomes depressed, irritable and sluggish.
• Concentration of CO2 increases which may cause death.

(3-B) ASTHAMA
“Respiratory tract disorder in which there are recurrent attacks of breathlessness, characteristically accompanied by wheezing when breathing out.”
CAUSES
It is usually caused by Allergic hypersensitivity to the plant pollens, dust, animal fur or smoke or in older person may be due to common cough.
Heridity is major factor in development of Asthma.

PHYSIOLOGICAL EFFECTS
• Localized edema in walls of small bronchioles.
• Secretion of thick mucus.
• Spastic Contraction of bronchial smooth muscles (so the resistance in air flow increases).
• Residual volume of lung increases due to difficulty in expiration.
• Thoracic cavity becomes permanently enlarged.

SYMPTOMS
• The asthmatic patient usually can inspire quite adequately but has great difficulty in expiring.

LUNG CAPACITIES
1. TOTAL AVERAGE LUNG CAPACITY
DEFINITION
“It is the maximum volume in which the lung can be expanded with greatest possible inspiratory efforts.”
Or
“Total lung capacity is the combination of residual volume and vital capacity.

VALUE
Total lung capacity = 5000 cm3 or 5 lit of air.

2. TIDAL VOLUME
“The amount of air which a person takes in and gives out during normal breathing is called Tidal Volume.”

VALUE
450cm3 to 500 cm3 (1/2 litre)

3. INSPIRATORY RESERVE VOLUME
DEFINITION
'“Amount of air inspired with a maximum inspiratory effort in excess of tidal volume.”

VALUE
200 cm3 or 2 lit. (Average value)

4. EXPIRATORY RESERVE VOLUME
DEFINITION
“Amount of air expelled by an active expiratory effort after passive expirations.”

VALUE
1000 cm3 or 1 litre.

5. VITAL CAPACITY
DEFINITION
“After an extra deep breath, the maximum volume of air inspired and expired is called Vital capacity.”
Or
“It is the combination of inspiratory reserve volume, expiratory reserve volume and tidal volume.”

VALUE
Averages about 4 litre.

6. RESIDUAL VOLUME
DEFINITION
“Amount of air which remains in lung after maximum expiratory effort is called Residual volume.”

VALUE
Approximately 1 litre or 1000 cm3.

IMPORTANCE OF LUNG CAPACITY
• Residual volume prevent the lung from collapsing completely.
• Responsible for gaseous exchange in between breathing.
• It is not stagnant since inspired air mixes with it each time.
• Aging or Emphysema, etc can increase the residual volume at the expense of vital capacity.

HAEMOGLOBIN
INTRODUCTION
“Haemoglobin is an iron containing respiratory pigment present in the red blood cells of vertebrates and responsible for their red colour.”

STRUCTURE
Haemoglobin consists of
1. Heme
2. Protein (globin like chains)

1. HEME
One Haemoglobin molecule consists of 4 molecules of Heme. Each Heme molecule contains an iron (Fe++) binding pocket. Thus one molecule of Haemoglobin can combine with 4 iron atoms.

2. GLOBIN
Each Hb molecule contains four globin like chains (Two a chains and Two ß chains).

ROLE OF HB DURING RESPIRATION
Two major functions are performed by Hb.
1. Transport of O2 from lung to tissues.
2. Transport of CO2 from tissues to lungs.

1. “TRANSPORT OF O2 FROM LUNGS TO TISSUES”
“Nearly 97% of O2 is transported from the lungs to the tissues in combination with Hb.”

ATTACHMENT OF O2 WITH HB
It is the iron of Hb molecule which reversibly binds with oxygen. One Hb molecule can bind 4 molecules of O2. Thus due to Hb, blood could carry 70 times more oxygen than plasma.

MECHANISM OF TRANSPORT
• Due to high O2 concentration in alveolar air, the O2 moves from air to the venous blood where O2 concentration is low.
• It combines loosely with Hb to form Oxyhemo Globin.
• In this form, O2 is carried to the tissues where due to low oxygen concentration in tissues, oxy Hb dissociates releasing oxygen, which enters in tissues.
Whole process can be represented by following equation.

2. “TRANSPORT OF CO2 FROM TISSUES TO LUNGS”
“Haemoglobin is also involved in 35% of transport of CO2 from tissues to alveolar blood capillaries in alveoli.”

ATTACHMENT OF CO2 WITH HB
CO2 binds reversibly with NH2 group of Hb to form loose compound called “Carboamino Haemoglobin.”

MECHANISM OF TRANSPORT
• Carbon dioxide due to its higher concentration in tissue diffuses out into the blood where it combines with Hb to form Carboamino Hb.
• In the alveoli it breaks and CO2 diffuses out into the Alveoli from where it is expired.

MYOGLOBIN
INTRODUCTION
“Myoglobin is a heme protein, smaller than Hb, found in muscles and giving red colour to them.

STRUCTURE
Myoglobin consists of one heme molecule and one globin chain. It can combine with one iron (Fe++) atom and can carry one molecule of O2.

FUNCTION OF MYOGLOBIN
• Myoglobin has high affinity for O2 as compared to Haemoglobin so it binds more tightly.
• It stores the O2 within the muscles.
• It supplies the O2 to the muscles when there is severe oxygen deficiency (During exercise)
It can be represented as follows:
Mb + O2 ? MbO2

TRANSPORT OF GASES
Oxygen and carbondioxide are exchanged in, Alveoli by Diffusion.

O2 TRANSPORT
Blood returning into the lungs from all parts of body is depleted from oxygen. This deoxygenated blood is dark maroon in colour to appear bluish through skin. It becomes oxygenated in the lungs.

TWO FORMS OF O2 IN BLOOD
O2 is transported in the blood in two forms:
• Dissolved form (3%)
• Combination with Hb (97%) ® Oxyhaemoglobin

MECHANISM OF O2 TRANSPORT
+ DIFFUSION OF O2 FROM ALVEOLUS INTO PULMONARY BLOOD
The air inhaled into the lungs has high concentration of oxygen while venous blood in pulmonary capillaries has low in concentration. Due to this difference in concentration across the respiratory surface, oxygen diffuses into the blood flowing into capillaries around the Alveoli. Now blood becomes oxygenated which is bright red in colour.

+ DIFFUSION OF O2 FROM CAPILLARIES INTO CELLS
Concentration of O2 in the arterial end of capillaries is much more greater than concentration of O2 in the cells. So O2 diffuses from the blood to the body cells. Since the blood takes in oxygen much more rapidly than water. Thus it can transport enough oxygen to the tissues to meet their demand.

CO2 TRANSPORT
Blood returning from tissues contain excess of CO2 as a respiratory by-product, which is eliminated from the body during expiration in the lungs.”

THREE FORMS OF CO2 IN BLOOD
• Dissolved form (in plasma) – 5%
• In form of HCO3- (in RBC’s) – 60%
• In combination with Hb (Carboamino Hb) – 35%

+ DISSOLVED FORM
Only 5% of CO2 is transported in dissolved form in plasma. Here it combines with H2O of plasma to form H2CO3. But this reaction is very slow as plasma does not contain Carbonic Anhydrase to accelerate this reaction.
Reactions can be represented by following equations.
CO2 + H2O ? H2CO3
H2CO3 ?HCO3- + H+
HCO3- + k+ ? KHCO3

+ IN FORM OF HCO3-
60% of CO2 is transported in the blood in form of HCO3- in RBC’s. Here it combines with water to form H2CO3. But this reaction occurs rapidly in RBC’s due to presence of Carbonic Anhydrase.
Reactions can be represented by following equations
CO2 + H2O ? H2CO3
H2CO3 ? HCO3- + H+
HCO3- + Na+ ? NaHCO3

+ IN COMBINATION WITH HB
As discussed previously in role of Hb.

MECHANISM OF CO2 TRANSPORT
+ DIFFUSION OF CO2 FROM CELLS INTO CAPILLARIES
CO2 is continuously synthesizing in the tissues as a result of metabolism. Thus due to its higher concentration. CO2 diffuses from the tissues into blood, which becomes deoxygenated.

+ DIFFUSION OF CO2 FROM PULMONARY BLOOD INTO ALVEOLUS
Blood returning from tissues contain high concentration of CO2. This blood is brought to lungs, where CO2 diffuses from the blood into alveolus where its concentration is lower.

FACTORS EFFECTING THE TRANSPORT OF GASES
Following are some factors, which influence the transport of respiratory gases across the alveolar wall.
1. Concentration Gradient
2. Presence of competitor such as CO
3. Moisture
4. Surfactant
5. pH

1styear BIOLOGY Notes Chapter-12

Chapter-12
NUTRITION

Nutrition in Plants

CLASSIFICATION ON THE BASIS OF MODE OF NUTRITION
Plants can be divided into two groups on the basis of their mode of nutrition.
1. AUTOTROPHIC
2. HETEROTROPHIC

1. AUTOTROPHIC NUTRITION
DEFINITION
“Autotrophic nutrition is the type of nutrition in which organic compounds are manufactured from available inorganic raw material taking from surroundings”.
In autotrophic nutrition, the nutrients do not require to be pretreated or digested before taking them into their cells.

TWO METHODS OF AUTOTROPHIC NUTRITION
On the basis of source of energy, autotrophic nutrition can be sub-divided into following sub-types.
(I) Phototrophic nutrition
(II) Chemotrophic nutrition

I. PHOTOTROPHIC NUTRITION
DEFINITION
“The type of autotrophic nutrition is which organic molecules are manufactured from simple inorganic molecules by using light energy as a source is called Phototrophic Nutrition”.
EXAMPLE
a. Green Plants
b. Photosynthetic Bacteria

(I-A) PHOTOTROPHIC NUTRITION IN GREEN PLANTS
Green plants are very prominent example of phototrophic nutrition. They prepare the food by the process of photosynthesis.

RAW MATERIAL
The raw material needed by these organisms are

(1) CO2 AND H20
They provide carbon, hydrogen and oxygen for the synthesis of organic molecules.

(2) MINERALS
The minerals like Nitrogen, Phosphorus and Sulphur and Magnesium are also required.

(3) GREEN PIGMENTS
The green pigments i.e. Chlorophyll a, b, or others are also required to absorb the energy from universal source of light.

(4) LIGHT
In the presence of sun light nutrients are used to synthesis the energy rich compounded (CHO) This process is called “PHOTOSYNTHESIS”.
This process can be represented by equation as follows.
6CO2 + 12H2O -> C6H12O6 + 6O2 + 6H2O

(I-B) PHOTOTROPHIC NUTRITION IN PHOTOSYNTHETIC BACTERIA
Photosynthetic bacteria are unique because they are the only organisms which are capable of synthesizing the carbohydrate food without chlorophyll “a”.

DIFFERENCES BETWEEN PHOTOSYNTHETIC BACTERIA AND GREEN PLANTS
Photosynthesis in bacteria is different from green plants. Some differences are
• Photosynthetic bacteria usually grow in sulphide spring where H2S is normally present.
• Hydrogen is provided by H2S instead of H2O.
• Free oxygen is not released as a by product in bacterial photosynthesis.
• The process takes place at low expenditure of energy.

TWO TYPES OF PHOTOSYNTHETIC BACTERIA
There are two types of photosynthetic bacteria.

(1) THOSE IN WHICH “S” IS RELEASED AS BY PRODUCT
These bacteria use H2S as donor of hydrogen. Light splits hydrogen sulphide. Hydrogen combines with CO2 to form H2O.
2H2S + CO2 -> (CH2O)n + H2O + 2S
EXAMPLES
Purple Sulphur Bacteria ® which use BACTERIO CHLOROPHIL & CARETENOID as photosynthetic pigments.

(2) THOSE IN WHICH “S” IS NOT RELEASED AS BY PRODUCT
These bacteria use H2S as Hydrogen donor where as sulphur is not the by product in their case.
EXAMPLES
• PURPLE NON-SULPHUR BACTERIA
• BROWN NON-SULPHUR BACTERIA
Both of these contain “BACTERIO CHLORPHYLL” as photosynthetic pigments.

(II) CHEMOTROPHIC NUTRITION
DEFINITION
“The mode of autotrophic nutrition in which organic molecules are manufactured from simple inorganic molecules by using energy produced by the oxidation of certain inorganic substances such as ammonia, nitrates, nitrites, ferrous ions, H2S and etc. This type of nutrition is called CHEMOTROPHIC NUTRITION and process of manufacturing food is called CHEMOSYNTHESIS."
Mainly Bacteria are
AMMONIA USING BACTERIA
They derive their energy by oxidation of Ammonia.
NH4+ + O2 -> 2NO2 + 2H2O + 4H+ + energy
BACTERIA CONVERTING NITRITES TO NITRATES
2NO2 + O2 -> 2NO3- + energy

IMPORTANCE OF CHEMOSYNTHETIC BACTERIA
The chemosynthetic bacteria that act on nitrogen compounds do play an important role in the maintenance of nitrogen balance in the life system.

2. HETEROTROPHIC NUTRITION IN PLANTS
DEFINITION
“Plants which are not capable of manufacturing their own organic molecules entirely or partially depend for these organic molecular are called “HETEROTROPHIC PLANTS”

CLASSIFICATION OF HETEROTROPHIC PLANTS
On the basis of type of organisms on which heterotrophic plants depend, they can be classified into following two classes.
1. PARASITC PLANTS OR PARASITES
2. SAPROPHYTIC PLANTS OR SAPROPHYTES

1. PARASITES
DEFINITION
"Those heterotrophic plants which depend on living plants and animals for their nutritional requirements are known as PARASITES."

TYPES OF PARASITES
Parasitic plants can be divided into following types.
A. Obligate or total parasites.
B. Facultative or partial parasites.

1.A TOTAL PARASITES
DEFINITION
Those parasites which depend for their nutrition entirely on other living organisms

CLASSIFICATION OF TOTAL PARASITIC ANGIOSPERMS
Total or obligate parasitic angiosperms are broadly classified into
• Total stem parasite
• Total root parasite

TOTAL STEM PARASITES
DEFINITION
“Those parasitic plants which depend entirely on the stems of other plants are called “Total stem Parasites”
EXPLANATION
These plants send HAUSTORIA (specialized structures for absorbing nutrients in parasitic plants) inside the tissue of host. The xylem of parasite comes in contact with xylem of host and phloem of parasite to phloem of host. Through xylem it ****s the water and nutrients, through phloem prepared organic material. The host plant eventually dies off due to exhaustion.
EXAMPLE
CUSCUTA (AMER-BAIL)

TOTAL ROOT PARASITES
DEFINITION
"Those parasitic plants which **** their nutritional requirements from the roots of host are called “Total root parasites”.
EXAMPLES
• OROBANCHE -> attacks the roots of the plants belonging to families Cruciferae and Solanaceae
• CISTANCHE -> Parasitizes on the roots of Calatropis.
• STRIGA -> Found as parasite on the roots of sugar cane

(1.B)PARTIAL PARASITES
DEFINITION
“Those parasite plants which depend for their nutritional requirements partially on other living organisms are called Falcultave or partial parasites."

CLASSIFICATION OF PARTIAL PARASITIC ANGIOSPERMS
Partial parasitic angiosperms can be broadly classified into
• PARTIAL STEM PARASITE
• PARTIAL ROOT PARASITE

PARTIAL STEM PARASITES
DEFINITION
Those partial parasites whose haustoria penetrate in the stem of the host and **** their nutrition from vascular tissues of stem are called PARTIAL STEM PARASITE
EXPLANATION
LORANTHUS, is a partial stem parasite. It has thick green leaves, a woody stem and elaborated haustorial system. It can manufacture some of its food with the help of nutrients and water absorbed from host plants. The seeds get stuck upto the stem of host plant and germinates sending its haustoria in the tissues of the host.
EXAMPLES
• LORANTHUS -> found on shrubs, roseaceous tree, Bauhinia and mango
• VISCUM -> produce haustorial branches for an internal ****ling system.
• CASSYTHA FILLIFORMIS -> found in tropics

PARTIAL ROOT PARASITES
EXAMPLE
The examples of this category are rare.
One important example is
• SANDLE WOOD TREE

SAPROPHYTES
DEFINITION
“Those plants which depend for their nutrition on dead or rotten organic remains of plants or animals are called as SAPROPHYTES”
or
“Plants which break up complex dead food material into simple compounds and use them for their growth and development are called as SAPROPHYTES.”

TYPES OF SAPROPHYTES
Saprophytes can be divided into two types:
1. Total Saprophytes
2. Partial Saprophytes

1. TOTAL SAPROPHYTES
DEFINITION
“Those plants which depend entirely for their nutrition on dead organic matter are called Total Saprophytes.

2. PARTIAL SAPROPHYTES
DEFINITION
“Those plants which depend partially on dead organic matter are called Partial Saprophytes.”

EXAMPLES OF SAPROPHYTES
There are some examples of Saprophytes among flowering plants.
1. Neothia (bird’s net or orchid)
2. Monotrapa (Indian Pipe)
In both of these cases, the roots of plant form a Mycorhizzal Association with fungal mycelium to help in absorption process.


SPECIAL MODE OF NUTRITION
CARNIVOROUS OR INSECTIVOROUS PLANTS
DEFINITION
“The plants which have as their prey, insects and small birds are called Carnivorous plants. It is a special mode of nutrition in partially autotrophic and partially heterotrophic plants."
EXPLANATION
Partially autotrophic and partially heterotrophic plants are carnivorous, which possess the green pigments and can manufacture CHO but are not capable of synthesizing nitrogenous compounds and proteins. For their nitrogen requirement, carnivorous plants have to depend on insects, which they catch and digest by specific devices developed in them. J.D. Hooker suggested that the digestion of carnivorous plants is like that of animals.

COMMON AREAS WHERE THESE PLANTS GROW
These plants commonly grow in areas where nitrogen is deficient due to unfavourable atmosphere for nitrifying bacteria but favourable atmosphere for denitrifying bacteria.

SOME COMMON EXAMPLES
1. PITCHER PLANT
In Pitcher plant leaf is modified into pitcher like structure which is insect trapping organ.
EXAMPLES
Common examples are :
• Nepenthes
• Sarracenia
• Cephalotus
• Neliamphora
• Darling tonia

2. DORSERA INTERMEDIA OR SUNDEW
This plant has half a dozen prostrate radiating leaves, which bear hair like tentacles each with gland at its tip. The insects attracted by plant odour are digested.

3. DIONAEA MUSCIPULA OR VENOUS FLY TRAP
Most well known of all carnivorous plants. It has a resette of prostrate radiating leaves with inflorescence in the centre. The petiole of leaf is winged and lamina has two halves, with mid-rib in the centre. Each half has 12-20 teeth. In the centre of dorsal surface of lamina are numerous secretory glands, three hairs projecting out, which are sensitive to touch.

4.ALDROVANDA (WATER FLY TRAP)
It is a root less aquatic plant with floating stem. It has ressettes of modified leaves, which have two lobed mobile lamina having teeth at the margin and sensitive jointed hairs and glands on the surface.

5. UTRICULARIA OR BLADDER WORT
It is a root less plant having branched slender stem. Leaves are also much divided and some leaflets are modified into bladder like traps of about 1/16 to 1/8 inches in diameter. 

1styear BIOLOGY Notes Chapter-11

Chapter-11
BIO-ENERGETICS

DEFINITION
The capturing and conversion of energy from one form to another in the living system and its utilization in metabolic activities is called Bioenergetics.
Bio-energetics is the quantitative study of energy relationships and conversion into biological system. Biological energy transformation always obey the laws of thernodynamic.

ROLE OF ATP AS ENERGY CURRENCY
ATP is adenosine triphosphate. Adenosine is made of adenosine and ribose sugar. Among the three phosphate groups two are energy rich PO4 bonds. So ATP is a high energy compound it gives its PO4 groups easily. When 1 ATP is converted into ADP, 7.3 K cal/mole or 31.81 KJ/mole energy is released. ATP -> ADP + Pi + Energy
Living organisms use organic food for generation of energy. These food usually contain carbohydrates which degrade to produce CO2, H2O and energy. Which is usually in the form of ATPs. ATP plays role in several endergonic and exergonic reactions.

ENDERGONIC REACTIONS
Those chemical reactions which accompanied by the absorption of the energy are known as endergonic reactions. The products have a higher free energy than reactants. Examples of endergonic reaction in human are
1. Synthesis of proteins
2. Synthesis of lipids
3. Synthesis of cholestrol
4. Synthesis of glycogen

EXERGONIC REACTIONS
Those reactions which complete along with the liberation of free energy are known as Exergonic reaction. The products have a lower free energy than the reactants.
EXAMPLE
An aerobic glycolysis, Kreb’s cycle, oxidative phosphoylation.

PIGMENTS
Substances in plants that absorb the visible light are called Pigments. Different pigments absorb light of different wavelength. They are involved in the conversion of light energy to chemical energy. Important plant pigments are chlorophyls, carotenoids, phycobilin, xanthophylls, phaelophytin.

PHOTOSYSTEM
Each photosystem is a highly organized unit consisting of chlorophyll accessory pigment molecules and electron carrier molecules present on the thylakoids of chloroplast. Each thylakoid contains many units of two photosystems the photosystem I and photosystem II. So chloroplast contains thousands of photosystem.
The photosystem consists of chlorophyll “a” and “b” and carotenoids. Chlorophyll having empirical formula of C55H72O5N4Mg is almost identical to “Chlorophyll b” of empirical formula C55H70O6N4Mg. But the slight structural difference between them is enough to give 2 pigments slightly different absorption spectra and hence different colours “Chlorophyll a” is blue green while “b” is yellow green.
Hundreds of chlorophyll a, chlorophyll b and carotenoids cluster together in a photosystem. But only a single molecule of chlorophyll a acts like a reaction centre the rest of others absorbs a photon, the energy is transmitted from pigment, molecules to pigment molecules until it reaches a particular chlorophyll a located in the region of reaction centre, where it gives electrons to primary electron acceptor
FIGURE 11.3 PAGE 260
Hundreds of carotenoids are admixed with 2 types of chlorophyll molecules in photosystem, giving yellow and orange shades. Carotenoids can absorb wavelength of light that chlorophyll cannot transfer to chlorophyll a. Some times excess energy can damage chlorophyll a, so carotenoids accept energy from them, thus providing a function known as Photoreceptor.

ROLE OF LIGHT
Light has a dual nature, can behave like a wave or like a particle. It is composed of packets of energy called photons (hu). Light energy captured in the light harvesting complexes is efficiently and rapidly transferred to the chlorophyll molecules present in the photosynthetic reaction centre. When a photon of light hits these chlorophyll a molecules. The energy of these photons is absorbed and results in the elevation of an e- from the ground state to an excited state, level depends upon the energy and incident photon.
A photon of red light has enough energy to raise an electron to excited state I and this energy is sufficient to carryout all the chemical reactions of photosynthesis.
The energy transferred by blue light raise the electron to excited state –2. However the energy transmitted by red or blue photons to photosynthetic electron transport chain is exactly the same. This is because that extra energy is lost (from absorption of blue photon) by radiationless de-excitation.
The excitation energy can be used in
1. Photochemistry (i.e. it enter the photosynthetic electron transport chain)
2. Lost as heat.
3. Give fluorescence etc.

PHOTOSYNTHESIS
Photosynthesis is an anabolic process in which chloroplast of the plants take up CO2 and H2O and using light energy to synthesize carbohydrates. In photosynthesis, the light energy is converted to chemical energy. It is an oxidation reduction process in which water is oxidized and CO2 is reduced
6CO2 + 12H2O -> C6H12O6 + 6H2O + 6O2 ?
In simple
6CO2 + 6H2O -> C6H12O6 + 6O2 ?
This process divides into
1. Light reaction
2. Dark reaction

1. LIGHT REACTION
In the light dependent reactions, light energy is absorbed by chlorophyll and other photosynthetic pigment molecules. It is then converted into chemical energy. Due to this energy conversion, NADPH+ and ATP are produced.
Components of light reaction
1. Light capturing chlorophyll molecules.
2. Membrane bound protein complexes
3. Mobile electron carriers


CHLOROPHYLL MOLECULES AND PHOTOSYSTEM
Each photosystem consists of a light gathering “antenna complex” and a “reaction centre”. The antenna complex has many molecules of chlorophyll a, chlorophyll b and carotenoids most of them channeling the energy to reaction centre. Reaction centre of photosystem I and II has one or two “chlorophyll a” molecules, primary electron acceptor, associated electron carriers of electron transport system and certain specific proteins known as chlorophyll-bound proteins which differs them from other “chlorophyll a” molecules of the same system. The “chlorophyll a” molecules at the reaction centre of photosystem I (PSI) has a maximum absorbance at 700 nm, while those of PS II absorb at 680 nm. Therefore these reaction centre are called P700 and P680 where P simply stands for pigment.


COMPLEXES
There are 4 major groups of complexes.
1. PS I
2. PS II
3. Cytochrome b/f complex
4. ATPase complex
The PS I and ATPase or ATP synthase complex are present on non-appressed region of thylakoid. While PS II and light harvesting complexes (LHC II) are present on appressed side. The cyt b/f complex is randomly distributed throughout the mambrane.

MOBILE ELECTRON CARRIERS
Transport the excited electrons between the complexes. These are plastoquinone (PQ) plastocyanin (PC), ferredoxin (FD)

ELECTRON TRANSPORT
This process occurs in several steps.

(1) EXCITATION OF PS II
When chlorophyll a of reaction centre of PS II is striked by a photon, the energy of photon absorbs in it. This results in the elevation of an electron from the ground state to an excited state. The excited electrons produced within P680 is rapidly transferred to the primary electrons acceptors phaelophytin. So 2 electrons which are transformed has to be replaced which is done by water.

(2) PHOTOLYSIS OF WATER
In the presence of light a water splitting enzyme complex extracts 4 electrons from two water molecules. Removal of electrons splits the water into two hydrogen ions 2H+ and oxygen atoms. The extracted electrons from water are supplied to PS II (P680) while the oxygen atom immediately combines with another oxygen atom to form O2. Which is released during photosynthesis. The hydrogen ions or proton (H+) are stored in thylakoid space. The overall reaction will be
2H2O -> 4 H+ + 4e- + O2

(3) FLOW OF ELECTRONS FROM PS II TO PS I
Photoexcited electrons accepted by phaelophytin from PS II are transferred to plastoquinone molecules QA and QB which accept two electrons and takes up two protein from the stroma. PQ carries electrons from PS II to cytochrome b/f complex containing FeS protein. This is thought to be the rate limiting step of electron transport. Electrons from PQ are taken up by Cyt b/f complex through FeS and releasing protons (2H+) to the lumen. The second mobile electron carrier plastocyanin (PC) takes the electrons and delivered to the photosystem I.

(4) FLOW OF ELECTRONS FROM PS I TO NADP+ REDUCTASE
A second excitation event within PS I leads to the transfer of electrons to the primary electron acceptor. The primary e- acceptor of PS I passes the photoexcited electrons to a second electron transport chain, which transmit then to ferredoxin, an iron containing protein. An enzyme called NADP reductase then transfer the electrons from Fd to NADP+ (oxidized form)

(5) REDUCTION OF NADP+ TO NADPH+ H+
This is the redox reaction that stores the high energy electrons in NADP+ to reduced it to NADPH + H+.
NADP+ + 2H+ -> NADPH + H+
Hydrogen ions are taken from stroma which is being pumped from thylakoid space to stroma by ATPase.

PHOTOPHOSPHORYLATION
Hydrogen ions are pumped into thylakoid space by cyt b/f and also 2H+ ions are collected there from photolysis of one water molecule. This large no. of H+ ions in thylakoid space compared to stroma, creates an electrochemical gradient, when these hydrogen ions flow out of the thylakoid space by way of a channel protein present in membrane called the ATP synthase complex, energy is prvided to it. The transport of 3 protons (H+ ions) through the ATPase complex are normally required to produce 1 ATP from ADP and inorganic phosphate Pi.
ADP + Pi -> ATP
This is called chemiosmotic ATP synthesis because chemical and osmatic events join to permit ATP synthesis. The linear flow of electrons from H2O to NADP+, coupled to ATP syntheses is non-cyclic photophosphorylation because the electrons pass on to a terminal acceptor.
In cyclic photophosphorylation the electrons are cycled from PS I back to PQ. So only ATP is produced but not NADPH + H+. This occurs under following conditions to meet increased ATP demand for e.g. CO2 fixation
1. Protein synthesis
2. Synthesis of starch

EVENTS OF LIGHT REACTION
1. Photolysis of water.
2. Reduction of NADP+ to NADPH + H+
3. Synthesis of ATP by photophosphorylation.
So during light reaction ATP and NADPH + H+ are produced which are used in Dark reaction, O2 is evolved as a by product.

2. DARK REACTION
The dark reaction consist of a series of light independent reactions which can proceed even in the absence of light. During dark reaction, energy is produced by ATP and NADPH+ H+ and CO2 is fixed in carbohydrates. This cyclic series of enzymatic catalyzed reaction in the stroma of the chloroplasts is called Calvin-Benson Cycle. During this cycle CO2 is reduced to triose-PO4 sugars, therefore this pathway is also known as C3 pathray (reductive pentose phosphate cycle) and the plants undergo this cycle are known as C3 plants. The calvin or C3 cycle is divided into 3 phases.

CARBOXYLATION (CARBON FIXATION)
The calvin cycle begins when a molecule of CO2 reacts with a highly reactive phosphorylated five carbon sugar named ribulase 1.5 bisphosphate (RuBP). This reaction is catalyzed by the enzyme ribulase biphosphate carboxylase or Rubisco (it is the most abundant protein in chloroplast). The product of this reaction is a highly unstable, six carbon intermediate that immediately breakdown into two molecules of three carbon compound called 3-phosphoglycerate (G3P).
3CO2 + 3RuBP -> G3P

REDUCTION
Each molecule of the PGA or G3P receives an additional phosphate from ATP of light reaction, forming 1,3-bisphosphoglycerate (G1,3P) which is then reduced to glyceraldehydes 3-phosphate (GA3P) and Dihydroxyacetone phosphate (DHAP) by NADPH+ H+GA3P and DHAP are intercovertible and the reaction don’t require any energy. These products are also formed during glycolysis and links dark reaction with sugar synthesis pathway.
6G3P + 6ATP + 6NADPH + H+ -> 6GA3P + 6ADP + 6NADP+ + 6Pi

REGENERATION
Three carbon compounds are rearranged to form five carbon units ribulose 1,5-bisphosphate (RuBP), which is the primary carbon acceptors in the cycle.
5 GA3P + 3ATP -> 3 RuBP + 3 ADP + 3Pi
Again more molecules of ATP are used for phosphorylation of RuBP, which then starts the cycle again.

CONCLUSION
For every 3 molecules of CO2 entering the cycle and combining with 3 mole of RuBP (5C), six molecules of three carbon G3P is produced. Out of six G3P only one G3P molecule leaves the cycle and can be used for synthesis of glucose, starch, cellulose, sucrose or other compounds. The other 5 molecules are recycled to regenerate 5C RuBP’s three molecules, the CO2 acceptor.

CONSUMPTION
For the net synthesis of one G3P molecule, the calvin cycle consumes a total of nine ATP’s and six NADPH + H+

PHOTORESPIRATION
In presence of light (photon), oxygen is taken up by RuBP and CO2 is evolved.
RuBP + O2 -> PGA + Phosphoglycolate ® CO2
It occurs when CO2 is deficient, Rubisco works like an oxygenase rather than carboxylase in presence of O2, produce phosphoglycerate (phosphoglyceric acid-PGA) and Phosphoglycolate, where phosphoglycolate rapidly breaks down to release CO2. Alternative mechanisms of carbon fixation in hot, arid climate.
In hot temperature the concentration of CO2 begins to fall in leaves due to closing of stomata, increase yield of photosynthesis etc. These conditions in leaves may cause a wasteful process called photorespiration in which precious products are lost and less energy is generated. In certain plant species alternate mode of CO2 fixation have evolved even in very hot and arid environment.

These two photosynthetic adaptations are

1. C4 PHOTOSYNTHESIS (C4 PATHWAY)
This process occurs in C4 plants. Those which prefer calvin cycle with an alternate mode of carbon fixation are known as C4 plants. CO2 reacts with PEP in presence of PEP carboxylase to produce oxaloacetate, a four carbon compound which converts into malate. Malate transfers from mesophyll cell to bundle sheath cell where it breaks down to pyruvate and releases CO2. This CO2 is fixed in calvin cycle by Rubsico and so the cycle continues.
E.g. Family poaceae especially sugar cane, corn.

2. CAM
Plants of hot, arid environment, open their stomata during the night and close them during the day. Closing stomata during the day helps deserts plants to conserve water but it also prevents CO2 from entering the leaves. During the night, when their stomata are open, these plants take up CO2 and incorporate it into a variety of organic acids because of lack of energy (ATPs and NADPH+ H+). This mode of carbon fixation is called crassulacean acid metabolism (CAM). They store these organic acids in vacuoles. During day time organic acids release CO2 for dark reaction because light reaction can supply ATP and NADPH+ H+ on which the calvin cycle depends.
E.g. Cactus, Pinapple, Succulent plants.

CELLULAR RESPIRATION
Aerobic breakdown of glucose molecules into CO2 and water with synthesis of ATP is called Cellular Respiration.
C6H12O6 +6O2 -> 6CO2 + 6H2O + 673 Kcal/mole
Respiration is an oxidation reduction process because the carbon of substrate, mostly glucose is oxidized to form CO2, while the atmospheric O2 is reduced to form the water.

There are two types of cellular respiration.

(A) AEROBIC RESPIRATION
The breakdown of sugar, in presence of oxygen [molecular O2] and release of carbondioxide and water with sufficient amount of energy. This type of respiration is known as Aerobic respiration, and the organisms performed this are known as Aerobes.

(B) ANAEROBIC RESPIRATION
The break down of sugar in absence of oxygen is known as Anaerobic respiration, and this type of respiration is performed by Anaerobs.
E.g. Yeast, some bacteria, gut parasites (e.g. tapeworm). Some species of annelids, roots of plants growing in water logged area. Anaerobes are of two types. Those which never need of O2 at all are Obligate anaerobes. Those which respire aerobically but can also respire in absence of O2 are known as Facultative aerobes.

CATEGORIES OF AEROBIC RESPIRATION
The process of aerobic respiration is divided into three main categories.
1. Glycolysis
2. Kreb’s cycle
3. ETC

(1) GLYCOLYSIS
Glycolysis is the first and common step in both aerobic and anaerobic respiration. It consists of a complex series of enzymatically catalyzed reactions in which a 6 carbon molecule “Glucose” breaks down into 3 carbon “Pyruvic acid”. These reactions occur in Cytoplasm and doesn’t require oxygen. Following are the different steps of Glycolysis.

(I) PHOSPHORYLATION
Phosphorylation is the addition of phosphate groups to the sugar molecules. Glucose is phosphorylated by a molecule of ATP to form an activated molecule, the glucose 6 phosphate. ATP is converted to ADP.

(II) ISOMERIZATION
Glucose -6-phosphate is converted to fructose -6-phosphate, an isomer of it by an enzyme.

(III) SECOND PHOSPHORYLATION
Another molecules of ATP is invested which transfers its phosphate group to carbon no.1 of fructose –6-phosphate, forming fructose 1,6-bisphosphate and ADP.

(IV) CLEAVAGE
The 6-carbon, fructose 1,6 bisphosphate molecule is break down into 2; three carbon molecules, 3-phosphoglyceraldehyde PGAL and dihydroxyacetone phosphate (DHAP). These two sugar molecules are isomers and are interconvertible. This is the reaction from which glycolysis derives its name. DHAP is converted to its isomer PGAL and then 2 PGAL will be converted to 2 pyruvic acid molecules. Since at this stage 2 ATPs are used, therefore this phase is known as Energy investment phase.
In the subsequent reactions, energy is produced therefore this half is also known as Energy yielding phase

(V) DEHYDROGENATION (OXIDATION)
In the next step, PGAL is acted upon by an enzyme dehydrogenase along with a co-enzyme nicotine amide adenine dinucleotide (NAD+), which convert PGAL into phosphoglyceric acid PGA or phosphoglycerate by the loss of two hydrogen atoms (2e- + 2H+). These H atoms are captured by NAD+. This is a redox reaction in which PGAL oxidized by removal of electrons and NAD is reduced by the gaining of electrons. Now phosphoglyceric acid PGA picks up phosphate group (Pi) present in cytoplasm and becomes 1,3-bisphosphoglyceric acid (DPGA)

(VI) PHOSPHORYL TRANSFER
1,3-bisphosphoglyceric acid loses its phosphate group to ADP forming ATP and 3-phosphoglyceric acid.

(VII) ISOMERIZATION
The PO4 group of PGA, attaches with carbon no,3 changes its position to carbon no.2 forming an isomer 1-phosphoglyceric acid.

(VIII) DEHYDRATION
A water molecule is removed from the substrate and forming phosphoenal pyruvate (PEP)

(IX) PHOSPHORYL TRANSFER
ADP removes the high energy PO4 from PEP producing ATP and Pyruvic acid. OVERALL REACTION of glycolysis can be summarized as Glucose + 2ADP + 2NAD+ -> 2 Pyruvic acid + 2ATP + 2NADH+ H+ + 2H2O

ENERGY YIELD
Since when PGAL is produced, the cycle is counted twice because DHAP also converts into PGAL and enter the same cycle. 4ATP molecules are produced at Substrate level phosphorylation because PO4 groups are transferred directly to ADP from another molecule. 2 ATP are used in the first phase. Thus there is a net gain of 2 ATPs. 2 NADH+ H+ are produced and each gives 2 ATPs (a total of 6 ATPs). Therefore net production of ATP during glycolysis is 8 ATPs

FATE OF PYRUVIC ACID
There are 3 major pathways by which it is further processed under anaerobic conditions, pyruvic acid either forms, ethyl alcohol or lactic acid or produces CO2 and H2O from kreb’s cycle under aerobic conditions.

FERMENTATION
Fermentation the alternative term for Anaerobic respiration was used by W.Pasteur and defined as respiration in absence of oxygen (air). The production of ethyl alcohol from glucose is alcoholic fermentation and that of lactic acid is lactic acid fermentation.

ALCOHOL FERMENTATION
Each pyruvic acid molecule is converted to ethyl alcohol also known as Ethanol in two steps. In the first pyruvic acid is decarboxylated to acetaldehyde under the action of enzyme.
Pyruvic acid CH3.CO.COOH -> CH3CHO + CO2
In the next step NADH+ H+ reduces acetaldehyde to ethyl alcohol
CH3.CHO + NADH+ H+ -> CH3.CH2OH + NAD+
Ethyl alcohol is toxic, plants can never use it because it cannot be converted to carbohydrates or breaks up in presence of O2. When accumulation is more than tolerable limits, plants will be poisoned and subsequently they died.

LACTIC ACID FERMENTATION
When NADH+ H+ transfer its hydrogen directly to pyruvic acid, it results in formation of lactic acid.
Pyruvic acid + NADH + H+ -> CH3.CH.OH. COOH
During extensive exercise such as fast running muscle cells of animals and man respire anaerobically. Due to inadequate supply of O2, pyruvic acid is converted to lactic acid. Blood circulation removes lactic acid from muscle cells. When lactic acid accumulates inside cells, it causes Muscle futigue. This forces person to stop work, until normal O2 levels are restored.

ECONOMIC IMPORTANCE OF FERMENTATION
1. It is the source of ethyl alcohol in wines and beers Wines are produced by fermenting fruits like grapes, dates etc. Beers are produced by fermenting malted cereals such as Barley.
2. Yeast is used to prepare bread from wheat.
3. Milk is converted to curd (yoghurt) by bacteria.
4. Preparation of cheese and other dairy products.
5. Production of lactic acid, propionic acid, and butanol.
6. Flavour of pickles is due to lactic and acetic acid.
7. Addition of lactic and acetic acids prevent foods from spoilage and also give sour flavours to yoghurt and cheese.
8. Acetone is also formed as a by-product.

(2) KREB’S CYCLE
FORMATION OF ACETYL-CO
Before entering the Kreb’s cycle, each molecule of pyruvic acid undergoes oxidative decarboxylation. During this process one of the three carbons of pyruvic acid molecule is removed to form CO2 by enzymatic reactions. Simultaneously pyruvic acid is oxidized and a pair of energy rich Hydrogen atoms are passed on to a H acceptor NAD+ to form NADH+H+. The remaining 2-carbon component is called acetyle which combines with coenzyme A to form an activated two carbon compound called acetyle CoA. “Acetyle CoA connects Kreb’s cycle with glycolysis.” For each molecule of glucose that enters glycoilysis, two molecules of acetyle CoA produced, which enter in a cyclic series of enzymatically catalyzed reactions known as Kreb’s Cycle, which occurs in Mitochondria.
Pyruvic acid (3C) + CoA + NAD+ -> Acetyle CoA + CO2 + NADH+H+

SERIES OF REACTIONS IN KREB’S CYCLE
Sir Hans Kreb was working over these cyclical series of reactions therefore the cycle was given the name as Kreb’s cycle. The first molecule formed during the cycle is citric acid, so it is also called as “Citric Acid cycle.” This cycle is a multi step process and the steps are given below:

1. FORMATION OF CITRIC ACID
In this first step of the Kreb’s cycle, bond between acetyl and CoA is broken by the addition of water molecule. The acetyl (2C) reacts with 4 carbon compound (oxalo acetic) acid to form 6-carbon compound, citric acid, and the CoA is set free. This citric acid possess 3 carboxyl groups, therefore the cycle is also recommended as Tricarboxylic Acid Cycle (TCA cycle).

2. ISOMERIZATION
A molecule of water is removed and another added back so that cirtic acid is isomerized to isocitric acid through an intermediate, Cis-aconitic acid.

3.FIRST OXIDATIVE DECARBOXYLATION
First time the sugar molecules are oxidized, therefore it is also called first oxidation of the cycle. Isocitric acid is oxidized yielding a pair of electrons (2H+) that reduces a molecule of NAD+ to NADH+H+. The reduced sugar molecule is decarboxylated with the removal of CO2. It now converts into a 5 carbon compound a-Ketoglutaric acid (aKG).

4. SECOND OXIDATIVE DECARBOXYLATION
aKG is oxidatively decarboxylated. A CO2 molecule is lost. The remaining 4-C compound is oxidized by transfer of a pair of electrons (2H+) reducing NAD+ to NADH+H+. This 4-C compound accepts CoA forming succinyl CoA.

5. SUBSTRATE LEVEL PHOSPHORYLATION
Bond between succinyl and CoA is broken. CoA is replaced by PO4 group, which is then transferred to Guanosine diphosphate (GDP) to form Guanosine Triphosphate (GTP). GTP then transfers its phosphate group to ADP, forming ATP and with addition of 1 water molecule, succinic acid is formed.

6. THIRD OXIDATION
With loss of two electrons (2H+)succinic acid is oxidized to fumaric acid and FAD+ is reduced to FADH2.

7. HYDRATION
One water molecule is added to fumaric acid to convert it to Malic acid.

8. FOURTH OXIDATION AND REGENERATION OF OXALO-ACETIC ACID
Oxidation of malic acid leads to the production of 1 more NADH+H+ and oxaloacetic acid is regenerated.

ENERGY YIELD
Glucose molecule breaks down into 2 pyruvic acid molecules and each will enter the Kreb’s cycle.

For each pyruvic acid molecule, 3CO2 molecules are produced, four NADH+H+ are produced and 1 FADH2.

Pyruvic Acid + 3H2O + 4NAD+ + FAD+ -> 3CO2 + 4NADH+H+ + 1FADH2

Four calculation of energy (ATPs) we will multiply the products with 2 as 2 acetyle CoA enters the Kreb’s cycle.

Pyruvic Acid to Acetyl CoA..............1NADH2 -> 3ATP x 2 = 6 ATP

Kreb’s Cycle......................................3NADH+H + -> 9ATP x 2 = 18 ATP

.................................................. ....1FADH2 -> 2ATP x 2 = 4 ATP

.................................................S ubstrate Level Phosphorylation -> 1ATP x 2 = 2ATP


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Total..................................... = 30 ATP



OVERALL ENERGY YIELD OF AEROBIC RESPIRATION
Glycolysis..............................8ATP

Pyruvic Acid to Acetyl CoA..............6ATP

Kreb’s Cycle............................24 ATP


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Total...................................38 ATP

But actually 2 ATPs are utilizing in transporting cytoplasmic NADH+H+ to Mitochondria, which are produced during Glycolysis, so overall energy yield is only 36 ATPs.

3. ELECTRON TRANSPORT CHAIN/ ETC OR ET SYSTEM
The last of all steps is ETC. It consists of a series of electron acceptors which are located in the cristae of mitochondria. In respiration there are 6 steps at which hydrogen atoms are released (one in glycolysis, 5 in Kreb’s cycle). A pair of hydrogen atoms are dissociated into a pair of electrons and a pair of protons.
2H -> 2H+ + 2e
These electrons are accepted by Nicotinamide adenine dinucleotide (NAD) and Flavin Adenine Dinucleotide (FAD) from where they are passed along a chain of electron carriers such as cytochrome b, cytochrome c; cytochrome a, cytochrome a3.While passing from one carrier to another, these cytochromes are alternatively reduced and oxidized. During this, the energy released is used in the formation of ATP (adenosine triphosphate) from ADP and Pi. The final electron acceptor is atmospheric oxygen, which also picks up protons, and form the water molecule. The formation of ATP in mitochondria is called Oxidative Phosphorylation.
From every NAD, 3ATPs and from 1 FADH2, 2 ATPs are produced.