gas exchange in animals Flashcards
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alveoli
definition
Tiny air sacs in the lungs, where gas is exchanged during breathing.
bronchi
definition
The plural of ‘bronchus’. The bronchi are the two major air tubes in the lungs.
bronchioles
definition
The many small, branching tubules into which the bronchi subdivide.
capillary
definition
Tiny blood vessels with walls one-cell thick where exchange of materials occurs.
carbon dioxide
definition
A gaseous compound of carbon and oxygen, which is a by-product of respiration, and which is needed by plants for photosynthesis.
cartilage
definition
A strong, flexible type of connective tissue. It forms C-shaped rings in the trachea that keep the airway open.
concentration gradient
definition
The difference in the concentration of a chemical across a membrane.
Villi
definition
Finger-like projections in the small intestine that provide a large surface area for the absorption of food.
Ventilation
definition
Breathing in and out.
Trachea
definition
The windpipe, the tube that leads from the mouth towards the lungs.
Respiratory system
definition
The organ system where air is taken into and out the body, and gas exchange happens.
pleural membranes
definition
Thin, moist membranes surrounding the lungs that make an airtight seal.
pleural membranes
definition
Thin, moist membranes surrounding the lungs that make an airtight seal.
oxygen
definition
Gaseous element making up about 20% of the air, which is needed by living organisms for respiration.
intercostal muscles
definition
Sets of muscles between the ribs which raise and lower the rib cage.
human thorax
The ribs and upper backbone, and the organs found in the chest.
diaphragm
definition
A large sheet of muscle that separates the lungs from the abdominal cavity.
epithelial cell
definition
A cell that forms part of an epithelium.
exchange surface
definition
An area of the lungs that is adapted for efficient transfer of gasses.
Diffusion
It is important to remember that the particles:
- will move in both directions, but there will be a net movement from high to low concentration
- will end up evenly spread throughout the liquid or gas, but will continue to move
Unicellular organisms
surface area:volume ratio
Unicellular organisms, such as bacteria, have a very small surface area:volume ratio. Substances can diffuse in and out at a high rate and easily reach all parts of the cell.
Why do larger organisms need transport system s to move substances around the body?
Because of their smaller surface area: volume ratio, larger organisms need transport systems to move substances, such as oxygen, around the body to where they are needed. In many animals, this is the bloodstream. They also need specialised exchange surfaces where substances can enter and leave the transport system by diffusion. An example is the lungs in mammals. Exchange surfaces are adapted to increase their surface area to maximise the rate of diffusion.
Surface area of organisms living in harsh environments
Organisms living in harsh environmental conditions may reduce their surface area, eg cacti, to reduce loss of substances such as water.
The effectiveness of exchange surfaces in plants and animals is increased by having:
- a large surface area
- a short distance required for diffusion
The effectiveness of exchange surfaces in plants and animals is increased by having a large surface area:
- the flattened shape of structures such as leaves
- the alveoli in the respiratory system
- the villi in the digestive system.
The effectiveness of exchange surfaces in plants and animals is increased by having a short distance required for diffusion:
- the membranes of cells
- the flattened shape of structures such as leaves
- the walls of blood capillaries are one cell thick
- the epithelia of alveoli in the respiratory system and the villi in the small intestine are only one cell thick
In animals an efficient blood supply to transport molecules to and from the exchange surface increases effective exchange. Examples of this include:
- the network of blood capillaries that surrounds each alveolus in the lungs
- the network of blood capillaries in each villus in the small intestine
What does the process of ventilation do?
In the lungs, the process of breathing, or ventilation, brings air to, and removes air from the exchange surface - the alveoli.
How can a steep concentration gradient be maintained?
The moving blood and ventilated surfaces mean that a steep concentration gradient can be maintained.
The human lungs provide an exchange surface adapted for:
Absorbing oxygen - needed for respiration - into the blood from the air in the lungs
Transferring carbon dioxide - produced by respiration - from the blood into the lungs (which then goes into the air)
Where are the lungs in the body?
The lungs are enclosed in the thorax, surrounded and protected by 12 pairs of ribs. The ribs are moved by two sets of intercostal muscles. There is a muscular diaphragm below the lungs. The lungs are sealed within two airtight pleural membranes. These wrap around the lungs and line the rib cage.
What is the human respiratory system adapted to do?
The human respiratory system is adapted to allow air to pass in and out of the body, and for efficient gas exchange to happen.
Structure of the trachea
The trachea, or windpipe, branches into two bronchi - one bronchus to each lung. Rings of cartilage in the walls of the trachea help to keep it open as air is drawn in.
structure of the bronchi
The bronchi split into smaller branches and then into smaller tubes called bronchioles. Each bronchiole ends in a cluster of microscopic air sacs called alveoli.
Where does gaseous exchange take place?
The exchange of gases occurs between the alveoli and blood in the capillaries that supply the lungs.
The alveoli are adapted to provide a very large surface area for gaseous exchange:
- small size: each alveolus is a small sphere about 300 μm in diameter, giving it a larger surface area to volume ratio than larger structures
- number: there are around 700 million alveoli - ie 350 million per lung
- the total surface area of the alveoli is around 70 m2 - capillaries cover 70 per cent of the surface of the alveoli
Gaseous exchange
diffusion
There is also a short diffusion path - the walls of blood capillaries and alveoli are just one cell thick. The alveoli are also lined with a thin film of moisture. Gases dissolve in this water, making the diffusion path even smaller.
Gaseous exchange
ventilation
The ventilation of the lungs and the blood flow through the surrounding capillaries mean gases are being removed continually, and steep concentration gradients are set up for gases to diffuse.
The rate of diffusion depends on three factors:
- distance
- concentration gradient
- surface area
How distance effects the rate of diffusion.
If the diffusion distance is small, diffusion happens faster because the particles do not have as far to travel
How concentration difference (concentration gradient) effects the rate of diffusion.
diffusion is faster if there is a big difference in the concentration between the area the substance travels from and the area that it is moving to
How surface area effects the rate of diffusion.
the larger the surface area the higher the number of particles that will be able to move in a given time so the faster the rate
Factors affecting the rate of diffusion
Alveoli
need for fast diffusion in animals
Alveoli in the lungs, fish gills and the villi in the small intestine are adapted so that they have short diffusion distance, big concentration difference and large surface area. This means that they are adapted to have a rapid rate of diffusion. This is important for the survival of animals because they need to obtain as much oxygen, sugar and amino acids to meet the needs of metabolism and they need to expel waste substances such as urea as quickly as possible.
Ficks law
explanation
Fick’s Law describes the relationship between the rate of diffusion and the three factors that affect diffusion. It states that ‘the rate of diffusion is proportional to both the surface area and concentration difference and is inversely proportional to the thickness of the membrane’.
Ficks law
rate of diffusion is directly proportional to :
(surface area x concentration gradient) ÷ thickness of membrane
The rate of diffusion will double if:
1) surface area or concentration difference is doubled or
2) thickness of the exchange membrane is halved.
Why is diffusion very fast across membranes
All of the exchange surfaces consist of cell membranes which are very thin.
Q. The cell membrane has a thickness of 10 nm.
Describe what happens to the rate of diffusion of oxygen into the cell if the thickness changes to 20 nm.
The rate of diffusion will halve.
Gas exchange in animals
topic summary
For an organism to function, substances must move into and out of cells. Three processes contribute to this movement – diffusion, osmosis and active transport.
What happens during gas exchange in the lungs?
Oxygen passes into the blood and carbon dioxide passes out of the blood.
A cube has sides with a length of 4 cm. What is its surface area to volume ratio?
It’s surface area is 96 cm2 and volume is 64 cm3. 96/64 = 1.5:1.
What are the tiny air sacs in the lungs called?
Alveoli
Which features do exchange surfaces have?
Exchange surfaces have a large surface area and short diffusion distance.
How are leaves adapted for effective gas exchange?
Leaves have a thin, flat shape, which increases their surface area.
What is ventilation?
Ventilation is the movement of air into and out of the lungs.
