Living organisms respire to gain energy from food to power essential functions like movement, growth, and reproduction. Respiration involves the breakdown of food molecules through oxidation, releasing energy that is captured in ATP. There are two types of respiration: aerobic respiration uses oxygen to fully break down glucose, producing much more energy, while anaerobic respiration occurs without oxygen, generating lactic acid and less energy. Respiration takes place in cells across living things to fuel their various energy-requiring processes.

1. Respiration

2. Why do living organisms respire?
• Living organisms needs:
 Energy to move
 Excrete
 Grow
 Reproduce
• In all living cells, including plants and
animals, food molecules are broken
down by a reaction called oxidation
• Respiration is the oxidation of food
substances with the release of energy in
living cells

3. Respiration
• There are two kinds of Respiration:
Aerobic respiration
 It is the oxidation of food substances in the presence of oxygen
with the release of a large amount of energy
Glucose + oxygen → carbon dioxide + water + energy
C6H12O6 + O2 → H2O + CO2 + ATP
Anaerobic respiration
 It is the breakdown of food substances in the absence of oxygen
• The energy that is released by respiration packed as another molecule called ATP
(adenosine triphosphate)
• Anaerobic respiration release less energy than aerobic respiration

4. Some examples of energy consuming process in organisms:
• The synthesis of protein from amino acid
• Building up cells
• Cell division
• Muscular contraction
• respiratory movement
• Active transport
• Transmission of nerve impulses

5. Anaerobic Respiration
• Anaerobic respiration releases less energy than aerobic
respiration
• Yeast needs a little amount of energy to survive
 Yeast release ethanol and carbon dioxide as waste products
 anaerobic respiration in yeast is called alcoholic fermentation
Glucose→ ethanol + carbon dioxide + small amount of energy
C6H12O6 → C2H5OH + CO2 + ATP

6. Energy conversion in muscle cells
• Muscle respire aerobically
• When less oxygen is available, muscles will respire
anaerobically for short time
• During intensive exercise, aerobic respiration is unable
to produce enough energy to meet the demands
 The muscles produce extra energy by anaerobic
respiration
 Lactic acid is produced in this process

7. Energy conversion in muscle cells
 The equation of anaerobic respiration in your muscles is:
Glucose → 2 Lactic acid + small amount of energy
C6H12O6 → 2 C3H6O3 + ATP
 When there is insufficient oxygen to meet the demands of the vigorous muscular
contractions, the muscles are said to incur an oxygen debt
 During the period of rest, the breathing rate continues to be the fast for some
time.
 This is to provide sufficient oxygen to repay the oxygen debt
• Lactic acid builds up in the muscles and cause fatigue and muscular pains
 Lactic acid is transported to the liver and converted back into glucose
Oxygen debt is the amount of oxygen required to oxidize the lactic acid produced in
the muscles during anaerobic respiration

9. Gas exchange system in humans
Nose
• Air usually enters your body through the two
external nares (nostrils).
 The wall of the nostril has a fringe of hairs
• The nostrils leads into two nasal passages
 Which lined with a moist mucous membrane
• Breathing though the nose has the following
advantage:
 Dust, bacteria and foreign particles trapped
by:
1. hairs in the nostrils
2. Mucous in the mucus membrane
 Air is warmed up before entering the lung
 Harmful substances may be detected by
small sensory cells in mucus membrane

10. • The air in the nasal passages enters the
pharynx then larynx and then into the
trachea through an opening known as
glottis.
• Trachea is supported by C-ring shaped
cartilage to keep it open
• Trachea divides into two tubes, the
bronchi, one to each lung
• Each bronchus divides into very fine
bronchioles
• Each bronchiole ends in a cluster of air
sacs

11. The Respiratory Epithelium of the Nasal Cavity
and Conducting System
Figure 23.6a, b
• The thinner wall of the
trachea and bronchi are lined
by cilia
• Gland cells secrete mucus to
trap dust and bacteria
• The cilia sweep these
particles up into the pharynx
• From the pharynx, they are
swallowed into the
esophagus or removed by
coughing

12. The Lung
• Each lung lies inside pleural cavity
 The pleural cavity is lined by two
transparent elastic membranes called
pleural membranes
 The pleural cavity contains lubricating
fluid to reduce friction during breathing
• Thousands of alveoli (air sacs) are
found inside the lung
 Alveoli provide a very large surface area
for gaseous exchange

13. How are the lungs adapted for efficient gaseous
exchange?
1. The numerous alveoli provide a large
surface area
2. The alveoli are richly supplied with
blood capillaries
3. The wall of the alveolus and capillary
is only one cell thick (diffusion of
gases is easy)
4. The wall of alveolus is covered with
thin moist film. This allows oxygen to
dissolve in it

15. The Chest Cavity
• Chest wall is supported by ribs.
• Your ribs are attached dorsally to the
backbone
• And attached ventrally to the chest bone or
sternum
 10 pairs only are attached to the sternum
 2 pairs are free
• External and internal coastal muscles are
found between ribs
 These muscles are antagonistic ( one contract
other relax)
• The thorax is separated from the
abdomen by elastic muscle sheet called
diaphragm
 Diaphragm move down ward and upward
during breathing

16. Inspiration or inhalation

17. Inspiration or Inhalation
Inspiration means breath in.
1. Diaphragm contract and push down
2. External coastal muscles contract
3. Internal coastal muscle relax
4. Ribs move upward and forward
5. Volume of the thoracic cavity increase
6. Pressure in the lungs decrease
7. Air moves into the lung

18. Expiration and exhalation
Inhalation means breath out
1. Diaphragm relax and push up
2. External coastal muscles relax
3. Internal coastal muscle contract
4. Ribs move downward and inward
5. Volume of the thoracic cavity decrease
6. Pressure in the lungs increase
7. Air moves out of the lung

19. Gaseous exchange in alveolus
• Gaseous exchange in the lungs
takes place by diffusion
• The alveolus has:
High concentration of oxygen
Low concentration of carbon dioxide
• Blood entering the lung has:
Low concentration of oxygen
High concentration of carbon
dioxide

22. How is Carbon dioxide removed from your body?
In the tissues:
• Carbon dioxide diffuses to the blood and enter red blood cells
• Carbon dioxide reacts with water to form carbonic acid in the red
blood cells
• This reaction in the presence of enzyme carbonic anhydrase
• The carbonic acid then converted to hydrogencarbonate ions
• Hydrogencarbonate diffuse out of the red blood cell and carried by
plasma to the lungs
In the lungs:
• Hydrogencarbonate ions diffuse back into red blood cells and
converted into carbonic acid
• Then carbonic acid converted to water and carbon dioxide
• The carbon dioxide then diffuses into the alveoli
Also a small amount of CO2 is carried and dissolved in the blood