3.2 Gas exchange Flashcards
Do single-celled organisms have a small or large SA: Vol ratio
Large
In single-celled organisms how is oxygen absorbed
By diffusion across their body surface, which is covered only by a cell-surface membrane
How have insects evolved for gas exchange
Have evolved an internal network of tubes called tracheae
What is the tracheae supported by
Strengthened rings which prevent them from collapsing
What is the name of the smaller dead-end tubes that the tracheae divides into
Tracheoles
Why are tracheoles useful
As they extend throughout all the body tissues of the insect, meaning oxygen and other atmospheric gases are brought directly to the respiring tissues
What are the 3 ways in which respiratory gases move in and out of the tracheal system
- Along a diffusion gradient
- Mass transport
- The ends of the tracheoles are filled with water
How does mass transport help respiratory gases to move in and out of the tracheal system in insects
The contraction of muscles in insects can squeeze the trachea enabling mass movements of air in and out which further speeds up the exchange of respiratory gases
What are the 3 parts of an insect that the body is divided into
- Head
- Thorax
- Abdomen
What type of bodies do insects have
Segmented
How many spiracles does each segment of an insect have
2 spiracles (openings)
What do spiracles contain
Valves
Why are the valves in spiracles useful
As they reduce water loss as they can open and close
What are tracheal tubes lined with
Chitin
What does tracheal tubes being lined with chitin do to the tubes
Provides structural support
What does the tracheal tube branch into
Tracheoles
What do tracheoles provide
A large surface area
What is the site of gas exchange in insects
The tracheoles
What are tracheoles lined with and how it is beneficial
Lined with fluid in the tips so gases can dissolve so can diffuse easier
How is a short diffusion pathway created in insects
As the tracheole tubes contact every single tissue
What don’t insects synthesise since the tracheoles contact every single tissue
Haemoglobin since blood doesn’t transport oxygen
Why do insects have an internal respiratory system
It reduces water loss
What type of ventiliation (tidal or unidirectional) do insects have. And what spiracles does air go in and out of
Unidirectional as the air is sucked into the thorax spiracles and out of the abdomen spiracles
When an insects’ abdomen expands what happens to the internal pressure and volume and what happens to the air
Pressure decreases while the volume increases. Since air flows down a pressure gradient air is sucked in
When an insects’ abdomen contracts what happens to the internal pressure and what happens to the air
Pressure increases which pushes air outwards
What is the SA:Vol ratio like in fish
Relatively small
What does the small SA:Vol ratio in fish mean they can’t do
They can not simply diffusion gases
What is the specialised internal gas exchange surface in fish
The gills
Where are the gills located in fish
Behind the head
What are the gills made up of
Gill filaments
What are positioned at right angles to the gill filaments
Gill plates
How many layers of gills are on either side of the head
4 layers
How are the gill filaments placed together
They are stacked
What increases the surface area in the gills
- Having stacks of gill filaments that are covered in gill plates
What is the gas exchange surface in the fish
The gill plates
What happens once the fish opens its mouth and water is taken in
The water is FORCED over the gills and out through an opening on each side of the body
What does counter-current flow mean
Water flows over the gills in the opposite direction to the flow of blood in the capillaries
Why is a counter-current flow useful
Since a diffusion gradient for oxygen is maintained across the entire width of the gill plate
In relation to fish gills, describe what is meant by counter-current flow
The movement of water and blood in opposite directions across the gill plate
Outline why counter-current flow is an efficient means of exchanging gases across the gills of fish
Because a steady diffusion gradient is maintained over the entire length of the gill plate. Therefore more oxygen diffuses from the water into the blood
Mackerel are active, fast-swimming fish while plaice spend most of their lives moving slowly on the sea bed. There are differences in the gills of these 2 types of fish. Suggest what these differences might be
Mackerel have more gill plates/ gill filaments/ larger SA compared to plaice
Water flow over fish gills is one-way whereas the flow of air in and out of the lungs is 2-way. Suggest why one-way flow is an advantage to fish
Less energy is required because the flow does not have to reversed (important as water is dense and difficult to move)
Name the process by which carbon dioxide is removed from single-celled organism
Diffusion over the body surface
Explain why there is a conflict in terrestrial insects between gas exchange and conserving water
Gas exchange requires a thin permeable surface with a large area. Conserving water requires thick, waterproof surfaces with a small area
Explain how the tracheal system limits the size of insects
Because it relies on diffusion to bring in oxygen to the respiring tissues. If insects were large it would take too long for oxygen to reach the tissues rapidly enough to supply their needs
In mammals, what is their evolved gas exchange organ
Lungs
In humans/ mammals what is the gas exchange surface
Alveoli
In humans what area is classed as the thorax
From the diaphragm to the clavicle
What 3 things protect the lungs
- Ribcage
- Diaphragm
- Sternum
What type of ventilation do mammals have
Tidal
What happens to the air in the nasal cavity
It is warmed and moistened
Why is it beneficial for the air to be warmed and moistened in the nasal cavity before it goes to the lungs
So the gases can dissolve so there’s more efficient gas exchange
Where does the air go after it has entered the nasal cavity
Down the trachea and into the lungs
What is the trachea supported by
C-Shaped cartilage
Why is the cartilage that supports the trachea c-shaped
As it makes the trachea flexible so when we swallow food the food can go down
Why does the trachea need to be supported
So it does not collapse during breathing in
What is the name of the 2 branches at the end of the trachea
Bronchi (left and right bronchus)
What is the trachea lined with
Ciliated epithelial cells
What type of cell lines the trachea and what does it do
Goblet cells and these secrete mucus (mucus is made there and is released there)
What happens to the amount of cartilage as the bronchi get smaller
The amount decreases
What is the name of the branching subdivisions of the bronchi called
Bronchioles
What are the wall of the bronchioles made of
Muscle lined epithelial cells
What does the muscle in the bronchioles do
It allows the bronchioles to constrict so they can control the flow of air in and out of the alveoli
What is the name of the air sacs at the end of the bronchioles
Alveoli
What are the 5 traits of the alveoli
- Moist
- Thin
- Good blood supply- maintains concentration gradient
- Permeable to gas
- Has a large surface area
What is the name of the membrane that lines the chest cavity and surrounds each lung
Pleural membrane
What does the pleural fluid do
It reduces friction when the lungs expand and relax since it acts as a lubricant
What is the difference between adhesive and cohesive
Adhesive- means it sticks to something else
Cohesive- means it sticks to itself
Is the pleural fluid adhesive or cohesive
Both so when the thorax expands and relaxes it pulls the lungs with it
State 2 reasons why humans need to absorb large volumes of oxygen from the lungs
- Humans are very large
- Have a large volume of cells
- Humans have a high metabolic rate
- High body temperature
List in the correct sequence all the structures that air passes through on its journey from the gas-exchange surface of the lungs to the nose
-Alveoli
- Bronchioles
- Bronchus
- Trachea
- Nose
Explain how the cells lining the trachea and bronchus protect the alveoli from damage
The cells produce mucus that traps particles of dirt and bacteria in the air breathed in. The cilia on these cells move this debris up the trachea and into the stomach. The dirt/ bacteria could damage/ cause infection in the alveoli
How does the alveoli provide a short diffusion pathway (3 ways)
- The walls of the capillaries are 1 endothelial, squamous (flattened) cell thick
- The alveoli wall is 1 epithelial, squamous (flattened) cell thick
- Therefore the distance between the alveoli and the capillary is really short about 3 micrometers
How does the alveoli maintain a concentration gradient
- Blood flows away from the site of gas exchange- taking oxygen with it
- Deoxygenated blood flows towards the alveolus
- Inhalation of the air that is rich in oxygen keeps oxygen levels in the alveolus higher than in the capillaries (blood)
How does the alveoli provide a large surface area
- There are many alveolus
- Dense network of capillaries over each alveolus- since there are more places for the oxygen to diffuse into the blood
Why is diffusion of gases between the alveoli and the blood very rapid
- RBC are slowed as they pass through pulmonary capillaries, allowing more time for diffusion
- The distance between the alveolar air and RBC is reduced as the RBC are flattened against the capillary wall
- The walls of both capillaries and alveoli are both very thin
- There is a large SA
- The lungs are constantly being ventilate and the heart is constantly circulating blood around the alveoli
What is the walls of the capillaries called and what are they like
Endothelial and they are squamous (flattened)
What is the walls of the alveoli called and what are they like
Epithelial and they are squamous (flattened)
Explain how the walls of each alveolus not being more the 0.3 micrometers thick contributes to efficient gas exchange
The rate of diffusion is more rapid the shorter the distance across which the gases diffuse
Explain how there being 300 million alveoli in each lung contributes to efficient gas exchange
There is a very large SA in 600 million alveoli (2 lungs) and this makes diffusion more rapid
Explain how each alveolus being covered in a dense network of pulmonary blood capillaries contributes to efficient gas exchange
Diffusion is more rapid the greater the concentration gradient. Pumping of blood through capillaries removes oxygen as it diffuses from the alveoli into the blood. The supply of new carbon dioxide as it diffuses out of the blood into the alveoli helps to maintain a concentration gradient that would otherwise disappear as the concentration equalised
Explain how each pulmonary capillary being very narrow contributes to efficient gas exchange in the alveoli
RBC are flattened against the walls of the capillaries to enable them to pass through. This slows them down, increasing the time for gas exchange and reducing the diffusion pathway, thereby increasing the rate of diffusion
If the number of alveoli in each lung was increases to 600 million and the pulmonary ventilation was doubled, calculate how many times greater the rate of diffusion would be
4 times greater
What is the surfactant
A fluid that prevents the alveoli from collapsing or sticking together so they remain open
Why do alveoli need to be kept open
To increase their surface area
What group of people might need artificial surfactant
Premature babies since their lungs haven’t fully developed
Why do we ventilate (2 reasons)
- To maintain a concentration gradient (by bringing in oxygen rich air)
- To bring the respiratory medium (air in mammals/ insects and water in fish) in contact with the gas exchange surface
In what direction does the respiratory medium always flow
Down a pressure gradient
What happens when the pressure of the atmosphere is greater than the air pressure inside the lungs
Air is forced into the lungs (inhalation)
What happens when the air pressure in the lungs is greater than the atmospheric pressure
Air is forced out of the lungs (exhalation)
When we increase the volume, what happens to the pressure
It decrease
What 2 types of muscles that can change the pressure within the lungs
- Diaphragm
- Intercostal muscles (internal and external)
What does the contraction of the internal intercostal muscles lead to
Exhalation
What does the contraction of the external intercostal muscles lead to
Inhalation
What happens to the intercostal muscles when we inhale
- The internal intercostal muscles relax while the external intercostal muscles contract
What happens to the ribs during inhalation
They are pulled upwards and outwards, increasing the thoracic volume
What happens to the diaphragm during inhalation
It contracts, causing it to flatten, which also increases the thoracic volume
What does the increases volume in the thorax result in
A reduction of the pressure in the lungs, so air is pulled into the lungs
Is breathing in (inhalation) active or passive
Active
Is breathing out (exhalation) active or passive
Passive
What happens to the intercostal muscles during exhalation
The internal intercostal muscles contracts and the external intercostal muscles relax
What happens to the ribs during exhalation
They move downwards and inwards, decreasing the thoracic volume
What happens to the diaphragm during exhalation
It relaxes so it pushed up back to a dome shape, so the thoracic volume is further decreased
What does decreasing the thoracic volume do to the pressure inside the lungs
It increases the pressure, so air is forced out of the lungs
What 2 muscles contract during inhalation
The diaphragm and the external intercostal muscles
During inhalation what 2 things create an increased thoracic volume
- The diaphragm flattens
- The ribcage moves up and out
During inhalation what happens to the pleural membrane to decrease the pleural cavity pressure
The outer pleural membrane gets pulled outwards
What does the inner pleural membrane pulling outwards do to the surface of the lungs
It pulls on the surface of the lungs, causing the alveoli to expand
When the surface of the lungs is pulled outwards, the alveoli expands. What happens to the volume and the pressure of the alveoli. So what process is happening (inhalation or exhalation)
The volume increases and the pressure decrease the below atmospheric pressure. So we inhale
What muscles relax during exhalation
The diaphragm and the external intercostal muscles
During exhalation, what 2 things decreases the thoracic volume
- The diaphragm returning to its dome shape
- The ribcage moves downwards and inwards
During exhalation, what causes the pressure in the pleural cavity to increase
Since there is no pull applied to the outer pleural membrane
During exhalation, why is there no pull on the surface of the lungs
Since there is no pull on the inner pleural membrane as there is also no pull on the outer pleural membrane
What happens to the alveoli when there is no pull on the surface of the lungs
They compress
What happens to the pressure in the alveoli when it compresses, so what happens to the air
It increases to above atmospheric pressure so air is forced out of the lungs
During inhalation what happens to the: intercostal muscles, diaphragm, air pressure in the lungs, lung volume, direction in which the air flows
The external intercostal muscles contract while the inner intercostal muscles relax. The diaphragm contracts which flattens the dome shape so the volume increases. This increase causes a decrease the in pressure in the lungs. Since the respiratory medium (air) always flows down a pressure gradient, the air flows into the lungs
During exhalation, what happens to the: intercostal muscles, diaphragm, air pressure in the lungs, lung volume, and direction in which air moves
The external intercostal muscles relax while the inner intercostal muscles contract so the ribs move downwards and inwards. The diaphragm relaxes back into a dome shape which decreases the volume. This decrease in volume increases the pressure within the lungs so it’s above atmospheric pressure. So, air is forced out of the lungs
Suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide between the blood and the alveol, tidal volume is the volume of air inhaled and exhaled during a single breath when a person is resting
- Less carbon dioxide is exhaled
- A reduced concentration gradient
- So more carbon dioxide stays in blood
Describe and explain the mechanism that causes lungs to fill with air (3 marks )
- Diaphragm contracts and the external intercostal muscles contract
- Causes volume increase and pressure decrease
- Air moves down pressure gradient
If alveolar epithelium cells die inside the human body they are replaced by non-specialised, thickened cells. Explain why death of alveolar epithelium cells reduces gas exchange in human lungs (3 marks)
- Reduced surface area
- Increased distance for diffusion
- Reduced RATE of gas exchange
Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill (3 marks)
- Water and blood flow in opposite directions
- Maintains concentration gradient of oxygen / blood always passing water with higher oxygen concentration
- Diffusion along the entire length of the gill plate
Describe the gross structure of the human gas exchange system and how we breathe in and out (6 marks)
- Named structure : trachea, bronchi, bronchioles, alveoli
- Above stucture named in correct order
- Breathing in : diaphragm and external intercostal muscles contract
- Causes volume increase and pressure decrease in thoracic cavity
- Breathing out: Diaphragm relaxes and internal intercostal muscles contract
- Causes volume decrease and pressure increase in thoracic cavity
Explain 3 ways in which an insect’s tracheal system is adapted for efficient gas exchange (3 marks)
- Tracheoles have thin walls so short diffusion distance to cells
- Large number of tracheoles / highly branched so short diffusion distance to cells
- Large number of tracheoles/ highly branched so large surface area
- Fluid in end of tracheoles that moves out during exercise so larger surface area
Explain 2 ways in which the structure of fish gills is adapted for efficient gas exchange (2 marks)
- Many filaments and gill plates so large surface area
- Thin surface so short diffusion pathway
Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake (2 marks)
- Large(r) organisms have a small(er) surface
area:volume (ratio);
OR
Small(er) organisms have a large(r) surface
area:volume (ratio); - Overcomes long diffusion pathway
OR
Faster diffusion;
Explain how the counter-current principle allows efficient oxygne uptake in the fish gas exchange system (2 marks)
- Blood and water flow in opposite directions;
- Diffusion/concentration gradient (maintained)
along (length of) lamella/filament;
