RESPIRATION AND GAS EXCHANGE

Our cells need energy for:
 Contracting muscles- move parts of the body
 Making protein molecules- linking together amino acids into long
chains
 Cell division- repair damaged tissues and grow
 Active transport- move substances across cell membranes up their
concentration gradient
 Growth- building cells that divide to form new cells
 Transmitting nerve impulses- transfer info quickly from one part of
the body to another
 Producing heat inside the body- keep body temperature constant
(even at cold temp)
Glucose is the main nutrient to provide energy. Glucose contains a lot of
chemical energy. To make this energy work, cells have to break down
glucose molecules and release the energy from them, in a series of
metabolic reactions called respiration. It involves enzyme action.
 Aerobic Respiration In mitochondria
 Uses oxygen to break down glucose and other nutrient molecules to
release energy for the cell to use.
 glucose+oxygen
carbondioxide+water
 C6H12O6+6O2
6CO2+6H2O
 Anaerobic Respiration In cytoplasm
 Cells break down nutrient molecules to release energy w/o oxygen
 Yeast, Plant (short period)= glucose
alcohol+carbondioxide
 C6H12O6
2C2H5OH+2CO2
 Muscle cells= glucose
lactic acid
 C6H12O6
2C3H6O3
 Happens when vigorous exercise is done and the heart& lungs can’t
supply oxygen as quickly as needed, so anaerobic respiration is done to
keep them going until oxygen is available again

Table 11.1
GAS EXCHNGE (FIG 11.3)

Nose and Mouth:
 Inside nose- thin bones covered with a thin layer of cells1. Goblet cells- make a liquid containing water and mucus (11.4); water
evaporates into the air in the nose and moistens it
2. Other cells- tiny hair-like projections called cilia
Cilia- always moving; bacteria or dust gets trapped in them and the
mucus; sweep the mucus containing bacteria and dust particles up to
the back of the throat so that it doesn’t block the lungs
Trachea:
 Nose/ mouth to windpipe (trachea)


has rings of cartilages around; cartiladge helps to prevent the trachea from collapsing when
the air pressure inside is lower than the alr presure outside as air pressure changes while
breathin in and out.

Bronchi:
 The trachea goes down through the neck into the thorax (chest; from
neck to diaphragm)
Trachea
Right Bronchi
Left Bronchi
One bronchus goes to each lung and then branches out into smaller
tubes called bronchioles that take air from the bronchus to every part
of the lung
Alveoli:
 At the end of each bronchiole
 Tiny capillaries are wrapped around the outside of the alveoli
 Gas exchange surface (11.6)1. thin; one cell thick; O2 molecule only has to diffuse across this
small thickness to get to blood
2. excellent transport system; blood is constantly pumped to the
lungs along the pulmonary artery, which branches into
capillaries, which take blood to different parts of the lungs; CO2
can diffuse out into the air spaces in the alveoli and O2 can
diffuse into the blood; blood is taken back to the heart in the
pulmonary vein to be pumped to the rest of the body
3. large surface area; all alveoli- 100m2
4. good supply of oxygen by ventilation (movement of air into and
out of lungs by breathing)




Expired air mixes with normal air in the bronchi and trachea, so that we
breathe out a mixture of the air in the alveoli and the atmospheric air, so
expired air has a significant amount of oxygen
Body cells produce carbon dioxide in aerobic respiration and this carbon
dioxide diffuses out of the blood and into the alveoli, therefore extra
carbon dioxide is present in the air we breathe out
COMPONENT
Oxygen
Carbon dioxide
Water vapour







% IN INSPIRED AIR
21
0.04
Variable
% IN EXPIRED AIR
16
4
Very high
Breathing: Using the muscle in the diaphragm and the intercostal muscles,
to change the volume of the thorax. First- large thorax- air sucked in, thensmall thorax- air squeezed out
Intercostal muscles: Muscle between the ribs, which raise and lower the rib
cage when they contract and relax
Diaphragm: A muscle that separates the chest cavity from the abdominal
cavity in mammals.
Breathing in (11.9):
 Inspiration
 Muscles of the diaphragm contract- pulls diaphragm downwardsincreases the volume of the thorax
 External costal muscles contract- pull rib cage upwards and outwardsincreases the volume of the thorax
 Volume of thorax increases- pressure inside falls below atmospheric
pressure- air flows along the trachea and bronchi into the lungs
Breathing out (11.9):
 Expiration
 Muscle of diaphragm relax, i.e. diaphragm springs back to its dome
shape coz of elastic tissue- decreases the volume of the thorax
 External intercostal muscle relax- rib cage drops down to its original
position- decreases the volume of the thorax
 When you breathe out more forcefully (when coughing- eg)- intercostal
muscle contract strongly making the ribcage drop down further and the
abdomen also contracts, helping to squeeze extra air out of thorax
While exercising, muscles may use aerobic and anaerobic respiration to
supply extra oxygen, therefore oxygen debt (extra oxygen needed after
anaerobic respiration has taken place, in order to break down the lactic
acid produced) is built up. Now, as the lactic acid is combined with oxygen,
the debt is being paid off. Breathing and heart rate will return to normal
only after al the lactic acid has been used up.
Control of breathing rate:
 The rate at which breathing muscle/ breathing rate work, is controlled
by the brain
 The brain constantly monitors the pH of the blood that flows through it
 Lots of CO2 and lactic acid in the blood- pH falls
 When brain senses and sends nerve impulses to the diaphragm and
intercostal muscles, stimulating them to contract higher and more
often- faster breathing rate and deeper breaths.