BIOLOGY FORM 4 NOTES CHAPTER 7 : RESPIRATION

7.1   THE RESPIRATORY PROCESS

1.    Living organisms require energy to carry out all living processes such as:

(a)  Movement

(b)  Growth

(c)  Reproduction

(d)  Response

(e)  Breathing

(f)   Digestion

(g)  Excretion

2.    Energy is required for the various processes in the cell such as:

(a)  Cell division

(b)  Formation of gamete for reproduction

(c)  Transmission of nerve impulses

(d)  Contraction of muscles

(e)  Synthesis of protein, hormones, lipid and enzymes

3.    Respiration is the oxidation of food substances in the mitochondria of the cells to release energy.

4.    Glucose is the main substrate for energy production. Glucose is obtained from:

(a)  The digestion of carbohydrate in humans and animals

(b)  The process of photosynthesis in plants

7.1.1      Types of respiration

1.    There are two type of respiration:

(a)  Aerobic respiration

-          Aerobic respiration is the breaking down of glucose in the presence of oxygen to release chemical energy

-          Takes place in all living cells of plants, animals and in certain microorganisms

-          Occurs in the mitochondria and cytoplasm

-          Occurs slowly and in stages controlled by enzymes

-          The glucose is completely oxidized to release all the chemical energy in the glucose

-          Some of the energy released is changed into body heat while the rest is stored in the form of adenosine triphosphate (ATP)

When body cells need energy, ATP molecules will be hydrolysed to yield energy, a molecule of ADP and an inorganic phosphate

ATP                ADP + P + energy

-          During aerobic respiration, 38 molecule of ATP or 2898 kJ of energy is released.

-          Aerobic respiration can be represented by the following equation:

Glucose   + Oxygen                             Carbon dioxide + Water + Energy

C₆H₁₂O₆ + 6O₂                                      6CO₂ + 6H₂0 + energy (2898 kJ)     

(a)  Anaerobic respiration

-          Anaerobic respiration is the breakdown of glucose to produce energy in the absence of oxygen

-          Glucose is not completely broken down, only small amount of energy is released

-          Occurs only in the cytoplasm

-          Occurs both in animal cells and plant cells

(i)    Anaerobic respiration in human muscles

·         Occurs in human muscles during vigorous exercise or activities

·         During vigorous exercise,

-          The breathing rate and heart beat are increased to supply oxygen to the muscle for rapid muscular contraction

-          However, the supply of oxygen to the muscles is still insufficient tom provide the sudden energy demand

-          Hence, anaerobic respiration takes place to produce the require energy for muscular contraction in the absence of oxygen

Glucose           Lactic acid + energy (150kJ)

C₆H₁₂O₆                          2 C₃H₆O₃+ energy (150 kJ or two molecules of ATP)

-          Lactic acid accumulates in the muscles causing muscular ache, fatigue and cramps

-          An oxygen debt occurs because the maximum rate of oxygen used is more than the oxygen supplied

-          Oxygen is required to pay off the oxygen debt by rapid breathing after the vigorous exercise

-          Oxygen oxidizes the lactic acid to carbon dioxide, water and energy

(i)    Anaerobic respiration in yeast

·         Anaerobic respiration in yeast is called fermentation

·         During fermentation, yeast secretes the enzyme zymase which hydrolyses glucose in the absence of oxygen to form ethanol, carbon dioxide and energy

Glucose           ethanol + carbon dioxide + energy (150kJ)

C₆H₁₂O₆                          2C₂H₅OH+ 2CO₂ + energy (150 kJ or two molecules of ATP)

·         In the fermentation, only small amount of energy is released. A large amount of energy is still stored in the ethanol as chemical energy. This is because glucose is not completely broken down in anaerobic respiration

1.    Comparison between aerobic respiration and anaerobic respiration

SIMILARITIES
DIFFERENCES
Aerobic respiration	Anaerobic respiration

7.1   RESPIRATORY TRUCTURES AND BREATHING MECHANISMS IN HUMANS AND ANIMALS

1.    Breathing:

-          Is the exchange of gases between the organism and the environment

-          Involves the process of taking oxygen and removing carbon dioxide

2.    The common characteristics of respiratory surface for gaseous exchange:

(a) Large total surface area

-          To enhance the efficiency of gaseous exchange

-          Respiratory surfaces are normally branched, folded or numerous in quantity to increase the total surface area

-          Respiratory surface has large total surface area to volume (TSA / V) ratio to increase the rate of diffusion for gaseous exchange

(b) Moist respiratory surfaces

- The respiratory surfaces has a layer of moisture to facilitate the diffusion of oxygen and carbon dioxide

(a)  Thin wall of respiratory surface

-          The wall of respiratory surface is only one cell thick to facilitate the diffusion of gases across the surface

(b)  Has a network of blood capillaries

-          A network of blood capillaries beneath the respiratory surface (except for protozoa and insects)

7.1.1      Protozao

-          No special respiratory structure

-          Gases exchange by simple diffusion occurs rapidly across the thin plasma membrane

7.1.2      Fish

1.    Respiratory structure: Gills. Gaseous exchange occurs at the gill filaments.

2.    The adaptation of gill filaments for gaseous exchange:

(a)  Many lamella at the gill filaments

-          To increase the TSA / V ratio for the absorption of dissolved oxygen in the water

(b)  Thin epithelial walls of the gill filaments

-          To allow the oxygen to diffuse easily into the blood capillaries of the gill filaments

(c)  A network of capillaries in the gill filaments

-          To increase the rate of gaseous exchange by diffusion

3.    The breathing mechanism

1.    Dissolves oxygen diffuses through the gill epithelium into the blood capillaries at the gill filaments. Carbon dioxide diffuses from the blood capillaries into the surrounding water.

2.    The direction of water flow over the gill lamella is opposite to the flow of blood in order to maximise the rate of diffusion from the water into the blood capillaries

7.1.1      Insects

1.    The respiratory system of insects is called the tracheal system.

2.    For insects, gases are not transported by blood.

3.    Spiracles:

-          Air enters the body through spiracles

-          Spiracles are located on the both sides of thorax and abdomen.

4.    Tracheae and tracheoles:

-          The spiracles lead into a system of large tubes called tracheae, which are kept open by chitin.

-          The tracheae branch into a network of smaller tracheoles.

-          The tracheoles end on the plasma membrane of every body cell in the body cells of insects.

5.    Gases exchange at the respiratory surface:

-          Oxygen enters through the spiracles to tracheae and tracheoles, then  diffuses into muscle cells.

-          Carbon dioxide diffuses from the cells into tracheoles and tracheae, and eliminated through spiracles.

7.1.2      Amphibians

1.    An amphibian exchanges gases in three different ways:

(a)  Cutaneous respiration

(b)  Buccal respiration

(c)  Pulmonary respiration

2.    Cutaneous respiration

·         The amphibian’s skin is thin, moist and is well supplied with blood capillaries.

·         Atmospheric oxygen dissolves into the moist surface of the skin to the blood capillaries.

3.    Buccal respiration

·         The buccal carvity and the pharynx are covered with a thin epithelium, which has an underlying network of blood capillaries.

·         Ventilation of the buccal cavity:

-          The mouth closes, the buccal floor lower to reduce air pressure.

-          Low buccal cavity pressure sucks in the atmospheric air through the nostrils.

-          Oxygen from the buccal air dissolves in the epithelial moisture, and diffuses across the thin epithelium into the underlying blood capillaries.

-          Carbon dioxide from the blood capillaries diffuses into the buccal air.

-          The buccal floor rises, with the glottis closed, increases air pressure in the buccal carvity forces the used air out through the nostrils.

4.    Pulmonary respiration

·         Pulmonary respiration is carried out only when the need of oxygen is great, like when a food is jumping or swimming.

·         The frog has a pair lungs connected to a short bronchus. Each lung is moist and has several hundreds of tiny alveoli. Each alveolus has a network of blood capillaries.

·         Ventilation of the lungs

-          The nostrils close, the glottis opens, the floor of the mouth rises to force air into the lungs.

-          In the lungs, oxygen dissolves in the moisture on the epithelium and diffuses through the thin epithelium into the blood capillaries.

-          Carbon dioxide diffuses out from the blood capillaries into the lungs.

-          The glottis open, air flow out of the lungs. The nostrils open, the used air is eliminated through the nostrils

7.1.3      Human

1.    The human respiratory system consists of:

(a)  Nose and nasal cavity

(b)  Pharynx

(c)  Larynx

(d)  Trachea

(e)  Bronchi and bronchioles

(f)   Lungs

2.    Breathing mechanism

Inspiration	Expiration
1.    The external intercostal muscles ___________, internal intercostal muscles __________, raising the ribs __________ and __________. 2.    At the same time, the diaphragm muscles _________ and ___________. 3.    These ____________ the volume of thoracic cavity, causing the pressure to ___________. 4.    Since atmospheric pressure is ___________, air is _____________ the lungs.	1.    The external intercostal muscles ___________, internal intercostal muscles __________, lowering the ribs __________ and __________. 2.    At the same time, the diaphragm muscles _________ and ___________. 3.    These ____________ the volume of thoracic cavity, causing the pressure to ___________. 4.    Since atmospheric pressure is ____________, air is _____________ the lungs.

1.    Comparison between inspiration and expiration

Changes	Inspiration	Expiration
External intercostal muscles
Internal intercostal muscles
Rid cage
Diaphragm
Volume of thoracic cavity
Pressure in lungs
Movement of air

1.    Models the explain the breathing mechanism in human

(I)            Bell Jar Lung Model

(II)          Rib Cage Model

7.1.1      Comparison between different respiratory system

SIMILARITIES

Characteristics	Protozoa	Insect	Fish	Amphibian	Human
Respiratory system
Respiratory organ
Respiratory structures
High TSA/V ratio achieved by
Respiratory opening
Network of blood capillaries
Passage of respiratory gases
Transport of blood

7.1   GASEOUS EXCHANGE ACROSS THE RESPIRATORY SURFACE AND TRANSPORT OF GASES IN HUMANS

7.1.1      Exchange of oxygen and carbon dioxide between the blood and the alveolus.

1.    In human lungs, there are about 700 million alveoli, giving a total respiratory surface area of 70 – 80m³.

2.    The characteristics of respiratory surface in the alveoli.

(a)  A large surface area for gaseous exchange

(b)  A thin one-cell thick epithelial surface which is moist and permeable to gas.

(c)  An underlying capillary network, which is also one-cell thick, that carries oxygen away and bring carbon dioxide to be eliminated.

3.    The exchange of gases at the respiratory surface is by diffusion from a place of high partial pressure to a place of low partial pressure down its partial pressure gradient.

In the alveoli:

GAS	PASRIAL PRESSURE IN		EFFECTS
	Alveolar Air	Blood Capillaries
OXYGEN
CARBON DIOXIDE

In the body cells:

GAS	PASRIAL PRESSURE IN		EFFECTS
	Alveolar Air	Blood Capillaries
OXYGEN
CARBON DIOXIDE

7.1.1      The transport of respiratory gases and the process of gaseous exchange

7.1.1.1  Transport of Oxygen from the lungs to the body cells and gaseous exchange

1.    Oxygen is transported from the lungs to the body cells in two ways:

(a)  99% of oxygen is transported as oxyhaemoglobin in the red blood cells

(b)  1% of oxygen is transported as dissolved gas molecules in the plasma.

2.    Oxygen diffuses into the blood capillaries will combine with haemoglobin to form oxyhaemoglobin.

3.    Red blood cells transport oxygen as oxyhaemoglobin to respiring body cells where partial pressure of oxygen is low.

4.    At low partial pressure of oxygen, the oxyhaemoglobin dissociates itself to release oxygen molecules.

7.1.1.2  Transport of Carbon dioxide from the body cells to the lungs and gaseous exchange

1.    Respiring body cells produce carbon dioxide.

2.    Carbon dioxide diffuses into the blood capillaries and is carried to the lungs in three ways:

(a)  85% of carbon dioxide is carried as bicarbonate ions (HCO₃^-), dissolved in blood plasma.

(b)  10% of carbon dioxide is combined with amino groups of haemoglobin in red blood cells to form carbaminohaemoglobin.

(c)  5% of carbon dioxide is transported as dissolved gas molecules in the plasma.

3.    When blood carrying carbon dioxide reaches the lungs:

(a)  Hydrogen carbonate ions (HCO₃^-) convert back to carbon dioxide molecule which diffuses into alveolar air.

(b)  Carbaminohaemoglobin breaks down to release carbon dioxide molecule which diffuses into alveolar air.

(c)  Dissolved carbon dioxide molecule in the plasma diffuses from the blood capillaries into alveolar air.

7.1   THE REGULATORY MECHANISM IN RESPIRATION

7.4.1  During a vigorous exercise,

-  muscle cells need more oxygen and glucose to release energy during cellular respiration.

-  Hence

§  The rate of respiration increase   

§  The O₂ content decrease

§  The CO₂ content increase

    -  As a result :

§  The breathing rate increase

-   to supply more O₂ to the muscles and discharge more CO₂ from the lungs.

§  The heartbeat rate increase

-   to pump more blood into the blood circulation.

-   more CO₂ and glucose can be supplied for cellular respiration.

-   more CO₂ can be removed form the cells.

§  The ventilation rate increases

-   the rate of gaseous exchange between alveoli and blood  capillaries becomes faster.

7.4.2  THE REGULAR MECHANISM OF O₂ AND CO₂ CONTENTS IN THE BODY

• Respiratory centre

= a group of cells situated in the medulla ablongata to regulate the rhythm of breathing by controlling the intensity and frequency of contracrion of the intercostal muscles and diaphragm.

• Chemoreceptors

= are sensory receptors in the body that responds to chemical stimuli.

- 2 sets of chemoreceptors

(a) Central chemoreceptors

       - located in the medulla oblongata

 - detect the increase of CO₂ in blood indirectly through the formation of hydrogen ion (H⁺).

(b) Peripheral Chemoreceptors

- consist of the carotid bodies on the carotid arteries ,and the aortic bodies on the aorta

- sensitive to pH levels and the very low level of O₂ in the blood.

Regulation of Respiration by the central Chemoreceptor

7.4.2.2  Regulation of respiration by the peripheral chemoreceptor

.

-          Peripheral chemoreceptors are only activated when oxygen levels drop real low, this can happen at high altitudes where atmosphere oxygen is very thin.

• The O₂ content in the blood usually has little effect on the respiratory centre.
• Usually, a rise in CO₂ concentration is a better indication of a drop in O₂ concentration, because both the CO₂ and O₂ concentrations are affected by cellular respiration.

2.4.3  Human Respiration In Different Situations.

A) RELAXING

            -The rate of breathing : 14 - 20 times/minute

            -The rate of heartbeat : 60 – 70 beats/minute

- Normal, at optimal levels sufficient to maintain all normal body functions.

B) VIGOROUS EXERCISE

§  The rate of breathing : ≈ 30 times/minute

§  The rate of heartbeat : ≈ 120 beats/minute

-           Help to deliver more O₂ and glucose to the respiring cells and remove CO₂ from the cells at a faster rate.

C) FEAR

-The adrenal glands secrete the adrenaline hormone into the bloodstream.

            -The effects of the adrenaline hormone:

§  The rate of breathing increases

             -to increase the supply of O₂

§  The rate of heartbeat increases

-to transport more O₂ to the muscle cells

§  The rate of cellular respiration increases

-to produce sufficient energy for the body to react.

D) AT HIGH ALTITUDE

- The atmosphere pressure is low, this may lead to   difficultly in breathing.

- Above 10,00 feet , the decreased partial pressure of O₂ cause a drop in the O₂ level of the blood.

- A person will experience headaches, nausea and dizziness.

7.5 THE EFFECTS OF SMOKING

• TAR

-          causes lung cancer .

-          deposit in the bronchioles.

• Nicotine

-          is a stimulant which makes the heart beat faster and constrict the blood vessels

-          causes heart disease and strokes

-          causes and addiction to smoking

-          restrict the movement of cilia, making it harder for the lungs to get rid of tar.

• Carbon monoxide

-          competes with O₂ to bind with haemoglobin to  form carboxyhaemoglobin.

-          reduces the supply of O₂ to the cells and thus reduces aerobic respiration.

• 3 , 4 –benzo-pyrene

-          a carcinogenic chemical that can cause cancer.

• Nitrogen dioxide

can dissolve in the mucus to form acific medium  which erodes the lungs tissue.

7.6   RESPIRATION IN PLANTS

7.6.1      Energy requirement  in plants

-          Plants carry out cell respiration to produce energy.

7.6.2      The intake of Oxygen by Plants for Respiration

1.    Gaseous exchange between plant cells and the environment occurs by diffusion , mainly through 

(a) Stomata

                  - Each stoma consists of a pore surrounded by two guard cells.

      - The guard cells contain a large number of chloroplast in which photosynthesis takes place.

- Stomata allow the exchange of gases between atmospheric air and the internal tissues of a leaf.

                  - The stomata open when there is light and the close in the dark.

(b) Lenticels

- Lenticels are raised pores found on the stems and   the roots.

- The cells around the lenticels are arranged loosely to allow the diffusion of gases into and out of the plant tissues.

(a)  Roots

-    Oxygen diffuses from the air spaces between the soil particles into the root tissues by diffusion.

2.    Intake of oxygen during the day

-          During day time, where there is sunlight, photosynthesis takes place.

-          Stomata open. Carbon dioxide diffuses into the leaves and is used in photosynthesis. Oxygen is produced.

-          As the rate of photosynthesis exceeds the rate of respiration, more oxygen is produced that can be used up by the respiring cells.

-          Some oxygen diffuses from the chloroplasts to the mitocondria for cellular respiration the rest diffuses into the substomatal air spaces, and intercellular air spaces.

3.    Intake of oxygen during the night

-          At night, photosynthesis does not occurs. Stomata are closed.

-          Oxygen cannot enter the leaf.

-          Respiration is carried out by using

(i)   oxygen from the air trapped in the substomatal air spaces, and intercellular air spaces.

(ii)  Oxygen taken through the lenticels and root hairs of plants.

7.6.3      Aerobic And Anaerobic Respiration In Plants

• Aerobic respiration

-          is usually carried out by plants throughout the day and night.

C₆ H₁₂ O₆    +        6O₂         →   6CO₂   +   6H₂O   +   energy.

Glucose          Oxygen         

• Anaerobic respiration

-          is carried out under certain conditions for short periods

-          example :- in a flood

    - during the initial stages of seed germination.

C₆ H₁₂ O₆   →   2C₂H₅OH   +    2CO₂

glucose          ethanol           carbon dioxide

7.6.1      Compare and contrast the processes of Photosynthesis and Respiration

SIMILARITIES
DIFFERENCES
Photosynthesis	Respiration

7.6.1      The relationship between the percentage composition of carbon dioxide in the air with photosynthesis and cell respiration

1.    Cell respiration

-          takes place all the time

-          using oxygen and producing carbon dioxide into the air

2.    Photosynthesis

-          takes place only in day light

-          using carbon dioxide and producing oxygen into the air

3.    Percentage composition of carbon dioxide in the air among plants throughout the day

            .

(a)  From morning to noon

            - The rate of photosynthesis increases.

      - Concentration of carbon dioxide in the air drops because more carbon dioxide is used for photosynthesis

(b)  At noon

-    The rate of photosynthesis is the highest.

-    Percentage composition of carbon dioxide reaches the lowest level.

(c)  From noon until sunset

            - The rate of photosynthesis decreases gradually.

- Concentration of carbon dioxide in the air increases because less  carbon dioxide is used for photosynthesis

(d)  At midnight

- No photosynthesis is carried out.

      - Percentage composition of carbon dioxide reaches the peak, of which a large portion of carbon dioxide is contributed by cell respiration.

4.    Compensation point

-          Compensation point is the point of light intensity where there is no net exchange of carbon dioxide and oxygen.

-          This means it is a point where all the released oxygen (by photosynthesis) is used up in the cell respiration and all the released carbon dioxide (by cell respiration) is used up in the photosynthesis.

-          If the rate of photosynthesis and the rate of respiration is remained at the compensation point:

(a)  There will be no growth and development in green plants

Gradually, as the oxygen in the air is used up but not replenished by photosynthesis, all oxygen breathing living organisms would die of suffocation.