IGCSE Revision- Biology
Chapter 11- Respiration and gas exchange
11.1 Respiration
USING ENERGY
- Every cell needs energy. In humans our cells need energy for:
- contracting muscles, so that we can move parts of our body, making protein
molecules, cell division so that we can repair damaged tissues, active transport, growth,
transmitting nerve impulses so that we can transfer information quickly, producing heat
inside the body
- Glucose is broken down to glucose molecules and release the energy from them in
a series of metabolic reactions called respiration
AEROBIC RESPIRATION
- Aerobic respiration: chemical reactions that take place in the mitochondria, which
use oxygen to break down glucose and other nutrient molecules to release
energy for the cell to use
- Our cells release energy from glucose by combining it with oxygen (simple
definition)
- Equation: glucose + oxygen → carbon dioxide + water
- C6H12O6 + 6O2 → 6CO2 + 6H2O
ANAEROBIC RESPIRATION
- It is possible to release energy from glucose without using oxygen
- This happens in the cytoplasm not the mitochondria
- Yeast, a single celled fungus often respires anaerobically. It breaks down glucose
to alcohol
- Glucose → alcohol + carbon dioxide
- C6H12O6 → 2C2H5OH + 2CO2
- Some cells in our body, especially muscle cells respire anaerobically
- They make lactic acid instead of alcohol and no carbon dioxide is produced
- Diagram on p218
11.2 Gas exchange
GAS EXCHANGE SURFACES
- Gas exchange: the diffusion of oxygen and carbon dioxide into and out of an
organism’s body
- The gas exchange surfaces have to be permeable, so that oxygen and carbon
dioxide can move easily through them. They have other characteristics which
help the process to be quick and efficient:
- They are thin to allow gases to diffuse across them quickly
, - They are close to an efficient transport system to take gases to and from the
exchange surface
- They have a large surface area, so that a lot of gas can diffuse across at the
same time
- They have good supply of oxygen
THE HUMAN BREATHING SYSTEM
- Each lung is filled with many tiny air spaces called air sacs or alveoli
- It is here that oxygen diffuses into the blood. So the surface of the alveoli is the
gas exchange surface. Because they are so full of air spaces, lungs feel very
light and spongy to touch.
- The lungs are supplied with air through the windpipe or trachea
- Trachea: the tube through which air travels to the lungs; it has rings of cartilage in
its walls, to support it
THE NOSE AND MOUTH
- Inside the nose are some thin bones which are covered with a thin layer of cells,
some of these cells, called goblet cells, make a liquid containing water and
mucus. The water in this liquid eva[orates into the air in the nose and moistens it
- Other cells have very tiny hair-like projections called cilia. The cilia are always
moving, and bacteria or particles of dust get trapped in them and in the mucus.
Cilia are found all along the trachea and bronchi, too.
- They sweep the mucus, containing bacteria and dust particles, up to the back of
the throat, so that it does not block the lungs
THE TRACHEA
- From the nose to the mouth, the air then passes into the windpipe or trachea.
Just below the epiglottis is the voice box or larynx. This contains the vocal cords.
The vocal cords can be tightened by muscles so that they make sounds when air
passes over them
- The trachea has rings of cartilage around it. As you breathe in and out, the
pressure of the air in the trachea increases and decreases. The cartilage helps to
prevent the trachea collapsing at times when the air pressure inside is lower than
the pressure of the air outside it
THE BRONCHI
- The trachea goes down through the neck and into the thorax. The thorax is the
upper part of your body from the neck down to the bottom of the ribs and
diaphragm. In the thorax, the trachea divides into two/ the two branches are
called the right and left bronchi. One bronchus goes to each lung and then
branches out into smaller tubes are called bronchioles
ALVEOLI
- This is where gas exchange takes place
- The walls of the alveoli are the gas exchange surface
, -Tiny capillaries are closely wrapped around the outside of the alveoli
-Oxygen diffuses across the walls of the alveoli into the blood
-Carbon dioxide diffuses the other way
-The walls of the alveoli are very thin. They are only one cell thick. The capillary
walls are also only one cell thick. An oxygen molecule only has to diffuse across
this small thickness to get into the blood
- They have a good transport system. Blood is constantly pumped to the lungs
along the pulmonary artery. This branches into thousands of capillaries which
take blood to all parts of the lungs. Carbon dioxide in the blood can diffuse out
into the air spaces in the alveoli and oxygen can diffuse into the blood. He blood
is then taken back to the heart in the pulmonary vein, ready to be pumped to the
rest of the body
- They have a large surface area. In fact, the surface area is enormous. The total
surface area of all the alveoli in your lungs is over 100,2
- They have a good supply of oxygen. Your breathing movements keep your lungs
well supplied with oxygen. This is called ventilation
- Ventilation: the movement of air into and out of the lungs, by breathing
movements
COMPARING INSPIRING AIR AND EXPIRED AIR
- The air that we breathe in usually has an oxygen content of about 20 to 21%.
There is less oxygen in the air that we breathe out, because cells in the body use
oxygen in respiration. However, expired air does still contain some oxygen,
usually about 16% the main reason for this is that our expired air mixes with
normal air in the bronchi and trachea, so that what we actually breathe out is a
mixture of the air in the alveoli and atmospheric air
- The air that we breathe in contains only a very small percentage of carbon
dioxide, usually about 0.04%. Body cells produce carbon dioxide in aerobic
respiration, and this carbon dioxide diffuses out of the blood and into the alveoli.
Extra carbon dioxide is therefore present in the air that we breathe out at about
4%
BREATHING MOVEMENTS
- First, you make your thorax large so the air is sucked in. then you make it smaller
so the air is squeezed out. This is called breathing.
- Some of the muscles that help you breathe are called the intercostal muscles.
These are between the ribs/ the others are in the diaphragm. The diaphragm is a
large sheet of muscle and elastic tissue which stretches across your body,
underneath the lungs and heart.
BREATHING IN- INSPIRATION
- Muscles in the diaphragm contract
, - This pulls the diaphragm downwards, which increases the volume in the thorax.
At the same time, the external intercostal muscles contract. This pulls the ribcage
upwards and outwards. This also increases the volume of the thorax
- As the volume of the thorax increases, the pressure inside it falls below
atmospheric pressure. Air therefore flows in along the trachea and bronchi into
the lungs
BREATHING OUT- EXPIRATION
- The muscles in the diaphragm relax
- The diaphragm springs back up into its domed shape because it is made of
elastic tissue
- This decreases the volume of the thorax
- The external intercostal muscles also relax
- The rib cage drops down again into its normal position and that decreases also
the volume of the thorax
- When you cough, the internal intercostal muscles contract strongly, making the
rib cage drop down even further. The muscles of the abdomen wall also contract,
helping to squeeze extra air out of the thorax
Chapter 12- Coordination and response
12.1 The Human Nervous System
Stimuli: Changes in the environment that can be detected by organisms
These changes are detected by special cells called receptors. The organism responds using effectors.
Muscles can be effectors by responding with contracting. Glands can be effectors too, by creating saliva if
we smell good food.
Coordination: Ensuring that the actions of different parts of the body work together.
Nerve: A group of neurone axons lying together .
Neurones:
To carry electrical signals neurones have long thin fibers of cytoplasm stretching out of the cell body. The
longest fiber in a neurone is called an axon. The shorter fibers are called dendrites. The dendrites pick up
electrical signals from other neurones nearby. These signals are called nerve impulses.
Chapter 11- Respiration and gas exchange
11.1 Respiration
USING ENERGY
- Every cell needs energy. In humans our cells need energy for:
- contracting muscles, so that we can move parts of our body, making protein
molecules, cell division so that we can repair damaged tissues, active transport, growth,
transmitting nerve impulses so that we can transfer information quickly, producing heat
inside the body
- Glucose is broken down to glucose molecules and release the energy from them in
a series of metabolic reactions called respiration
AEROBIC RESPIRATION
- Aerobic respiration: chemical reactions that take place in the mitochondria, which
use oxygen to break down glucose and other nutrient molecules to release
energy for the cell to use
- Our cells release energy from glucose by combining it with oxygen (simple
definition)
- Equation: glucose + oxygen → carbon dioxide + water
- C6H12O6 + 6O2 → 6CO2 + 6H2O
ANAEROBIC RESPIRATION
- It is possible to release energy from glucose without using oxygen
- This happens in the cytoplasm not the mitochondria
- Yeast, a single celled fungus often respires anaerobically. It breaks down glucose
to alcohol
- Glucose → alcohol + carbon dioxide
- C6H12O6 → 2C2H5OH + 2CO2
- Some cells in our body, especially muscle cells respire anaerobically
- They make lactic acid instead of alcohol and no carbon dioxide is produced
- Diagram on p218
11.2 Gas exchange
GAS EXCHANGE SURFACES
- Gas exchange: the diffusion of oxygen and carbon dioxide into and out of an
organism’s body
- The gas exchange surfaces have to be permeable, so that oxygen and carbon
dioxide can move easily through them. They have other characteristics which
help the process to be quick and efficient:
- They are thin to allow gases to diffuse across them quickly
, - They are close to an efficient transport system to take gases to and from the
exchange surface
- They have a large surface area, so that a lot of gas can diffuse across at the
same time
- They have good supply of oxygen
THE HUMAN BREATHING SYSTEM
- Each lung is filled with many tiny air spaces called air sacs or alveoli
- It is here that oxygen diffuses into the blood. So the surface of the alveoli is the
gas exchange surface. Because they are so full of air spaces, lungs feel very
light and spongy to touch.
- The lungs are supplied with air through the windpipe or trachea
- Trachea: the tube through which air travels to the lungs; it has rings of cartilage in
its walls, to support it
THE NOSE AND MOUTH
- Inside the nose are some thin bones which are covered with a thin layer of cells,
some of these cells, called goblet cells, make a liquid containing water and
mucus. The water in this liquid eva[orates into the air in the nose and moistens it
- Other cells have very tiny hair-like projections called cilia. The cilia are always
moving, and bacteria or particles of dust get trapped in them and in the mucus.
Cilia are found all along the trachea and bronchi, too.
- They sweep the mucus, containing bacteria and dust particles, up to the back of
the throat, so that it does not block the lungs
THE TRACHEA
- From the nose to the mouth, the air then passes into the windpipe or trachea.
Just below the epiglottis is the voice box or larynx. This contains the vocal cords.
The vocal cords can be tightened by muscles so that they make sounds when air
passes over them
- The trachea has rings of cartilage around it. As you breathe in and out, the
pressure of the air in the trachea increases and decreases. The cartilage helps to
prevent the trachea collapsing at times when the air pressure inside is lower than
the pressure of the air outside it
THE BRONCHI
- The trachea goes down through the neck and into the thorax. The thorax is the
upper part of your body from the neck down to the bottom of the ribs and
diaphragm. In the thorax, the trachea divides into two/ the two branches are
called the right and left bronchi. One bronchus goes to each lung and then
branches out into smaller tubes are called bronchioles
ALVEOLI
- This is where gas exchange takes place
- The walls of the alveoli are the gas exchange surface
, -Tiny capillaries are closely wrapped around the outside of the alveoli
-Oxygen diffuses across the walls of the alveoli into the blood
-Carbon dioxide diffuses the other way
-The walls of the alveoli are very thin. They are only one cell thick. The capillary
walls are also only one cell thick. An oxygen molecule only has to diffuse across
this small thickness to get into the blood
- They have a good transport system. Blood is constantly pumped to the lungs
along the pulmonary artery. This branches into thousands of capillaries which
take blood to all parts of the lungs. Carbon dioxide in the blood can diffuse out
into the air spaces in the alveoli and oxygen can diffuse into the blood. He blood
is then taken back to the heart in the pulmonary vein, ready to be pumped to the
rest of the body
- They have a large surface area. In fact, the surface area is enormous. The total
surface area of all the alveoli in your lungs is over 100,2
- They have a good supply of oxygen. Your breathing movements keep your lungs
well supplied with oxygen. This is called ventilation
- Ventilation: the movement of air into and out of the lungs, by breathing
movements
COMPARING INSPIRING AIR AND EXPIRED AIR
- The air that we breathe in usually has an oxygen content of about 20 to 21%.
There is less oxygen in the air that we breathe out, because cells in the body use
oxygen in respiration. However, expired air does still contain some oxygen,
usually about 16% the main reason for this is that our expired air mixes with
normal air in the bronchi and trachea, so that what we actually breathe out is a
mixture of the air in the alveoli and atmospheric air
- The air that we breathe in contains only a very small percentage of carbon
dioxide, usually about 0.04%. Body cells produce carbon dioxide in aerobic
respiration, and this carbon dioxide diffuses out of the blood and into the alveoli.
Extra carbon dioxide is therefore present in the air that we breathe out at about
4%
BREATHING MOVEMENTS
- First, you make your thorax large so the air is sucked in. then you make it smaller
so the air is squeezed out. This is called breathing.
- Some of the muscles that help you breathe are called the intercostal muscles.
These are between the ribs/ the others are in the diaphragm. The diaphragm is a
large sheet of muscle and elastic tissue which stretches across your body,
underneath the lungs and heart.
BREATHING IN- INSPIRATION
- Muscles in the diaphragm contract
, - This pulls the diaphragm downwards, which increases the volume in the thorax.
At the same time, the external intercostal muscles contract. This pulls the ribcage
upwards and outwards. This also increases the volume of the thorax
- As the volume of the thorax increases, the pressure inside it falls below
atmospheric pressure. Air therefore flows in along the trachea and bronchi into
the lungs
BREATHING OUT- EXPIRATION
- The muscles in the diaphragm relax
- The diaphragm springs back up into its domed shape because it is made of
elastic tissue
- This decreases the volume of the thorax
- The external intercostal muscles also relax
- The rib cage drops down again into its normal position and that decreases also
the volume of the thorax
- When you cough, the internal intercostal muscles contract strongly, making the
rib cage drop down even further. The muscles of the abdomen wall also contract,
helping to squeeze extra air out of the thorax
Chapter 12- Coordination and response
12.1 The Human Nervous System
Stimuli: Changes in the environment that can be detected by organisms
These changes are detected by special cells called receptors. The organism responds using effectors.
Muscles can be effectors by responding with contracting. Glands can be effectors too, by creating saliva if
we smell good food.
Coordination: Ensuring that the actions of different parts of the body work together.
Nerve: A group of neurone axons lying together .
Neurones:
To carry electrical signals neurones have long thin fibers of cytoplasm stretching out of the cell body. The
longest fiber in a neurone is called an axon. The shorter fibers are called dendrites. The dendrites pick up
electrical signals from other neurones nearby. These signals are called nerve impulses.
