Unit 7 - Exchange Surfaces and Breathing Flashcards
Why can single-celled organisms rely on diffusion to exchange substances with their environment?
They have low metabolic demands and a high SA:V ratio.
Why do multicellular organisms need exchange surfaces?
- Small SA:V ratio
- Diffusion distance is too short for cells in the centre of the organism to receive materials by diffusion alone
- High metabolic demand
How do you calculate the surface area of a cuboid?
(4 x length x height) + (2 x height x width)
How do you calculate the volume of a cuboid?
length x width x height
How do you calculate the surface area of a cylinder?
(2 x 𝜋 x r x height) + (2 x 𝜋 x r x r)
How do you calculate the volume of a cylinder?
𝜋 x r x r x height
How do you calculate the surface area of a sphere?
4 x 𝜋 x r x r
How do you calculate the volume of a sphere?
4/3 x 𝜋 x r x r x r
What is the surface area to volume ratio?
How much surface area an object has per unit volume.
How does size affect SA:V ratio?
As cells grow, SA:V ratio decreases.
What are the features of efficient exchange surfaces?
- High surface area
- Thin layers
- Good blood supply
- Ventilation
What adaptations does the nasal cavity have?
- large surface area
- good blood supply to warm air
- lined with hairs
- moist surfaces
What adaptations does the trachea have?
- incomplete rings of cartilage
- goblet cells
- ciliated epithelial cells
Why does the trachea have rings of cartilage?
They hold the trachea open to prevent collapse and are incomplete to allow space for food to move down the oesophagus.
How do the cells lining the trachea stop microorganisms from reaching the alveoli?
Goblet cells secrete mucus, which contains mucin and traps particles in the air. Cilia on the surface of ciliated epithelial cells will beat regularly, moving the mucus away from the alveoli.
What are the bronchi?
Extensions of the trachea - one leads to the left lung and one leads to the right lung.
What adaptations do the bronchi have?
- similar structure to the trachea but smaller
- plates of cartilage instead of rings
What adaptations do the bronchioles have?
- diameter approx 1 mm
- smooth muscle instead of cartilage
- thin layer of epithelial tissue
How does the smooth muscle in the bronchioles regulate air flow?
It can contract (making the bronchioles constrict to reduce air flow) and relax (making the bronchioles dilate to increase air flow).
What are the alveoli?
Air sacs at the end of the bronchioles where the majority of gas exchange occurs.
What are the alveoli made of?
Type 1 alveolar cells - a type of flattened epithelial cell which contains collagen and elastin fibres.
How do the collagen and elastin fibres in the alveoli help move air out of the trachea?
They cause elastic recoil by allowing the alveoli to stretch when air moves in and return to their original shape to push air out.
What adaptations do the alveoli have?
- approx 200-200 micrometres in diameter
- large surface area (approx 50-70 metres squared)
- thin layer of alveolar cells to reduce diffusion distance
- extensive capillary network (capillaries are also thin) for a good blood supply
- good ventilation to maintain steep concentration gradient
Why do the alveoli need extra support to prevent collapse of the lungs?
During inhalation, the chest cavity increases in volume. This decreases the pressure of the lungs increasing the likelihood of collapse. Alveoli need extra support to prevent this because they lack cartilage or smooth muscle.
What adaptations do the alveoli have to prevent collapse of the lungs?
The inner layer is covered with a solution of water, salts and lung surfactant. Lung surfactant is a phospholipid that reduces surface tension, keeping the alveoli inflated to prevent lung collapse.
What is the name of the double membrane enclosing the lungs?
The pleural membrane.
What is contained in the pleural cavity and how does this help the lungs expand during breathing?
The pleural cavity (space between the pleural membrane) contains pleural fluid which lubricates the lungs and adheres the outer wall of the lungs to the thoracic (chest) cavity by water cohesion. This means that when the chest expands during inhalation, the lungs will expand as well.
What causes ventilation?
Pressure changes in the thoracic cavity. The ribcage provides a rigid frame allowing the pressure to be changed.
Is inspiration an active or passive process?
Active.
How do the muscles in the lungs change pressure in inspiration?
- diaphragm contracts and flattens
- external intercostal muscles contract and internal intercostal muscles relax to move the ribcage up and out
- thoracic volume increases and thoracic pressure decreases
- air moves into the lungs
Is expiration an active or passive process?
Passive.
How do the muscles in the lungs change the pressure in expiration?
- diaphragm relaxes and moves up
- external intercostal muscles relax and internal intercostal muscles contract to move the ribcage down and in
- thoracic volume decreases and thoracic pressure increases
Define peak flow meter.
peak flow meter = device which measures the rate at which air can be expelled from the lungs
Define vitalograph.
vitalograph = device which produces a graph of the amount of air breathed out and how quickly
How does a spirometer work?
The static lower half of the tank is full of water. The mobile upper half of the tank is full of oxygen. As the patient breathes out into a tube attached to the tank, the upper half will rise. A trace marker is attached to the upper half and produces a graph.
How do you interpret a spirometer trace?
When inspiring, the trace will go down. When expiring, the trace will go up. The peak of expiration to the dip of inspiration shows the volume of a single breath.
Why does the total volume of gas in the upper tank of a spirometer decrease over time?
The spirometer contains soda lime which absorbs carbon dioxide. When breathing, oxygen from the tank is used up and carbon dioxide breathed out is absorbed by the soda lime. As a result, the volume of gas in the tank decreases over time.
Define tidal volume.
tidal volume = volume of air that moves in and out of the lungs with each resting breath
Define vital capacity.
vital capacity = volume of air breathed in when the strongest possible expiration is followed by the deepest possible inspiration
Define inspiratory reserve volume.
inspiratory reserve volume = maximum volume of air you can breathe in (not counting tidal volume)
Define expiratory reserve volume.
expiratory reserve volume = maximum volume of air you can breathe out (not counting tidal volume)
Define residual volume.
residual volume = volume of air left in your lungs after strongest possible expiration
How do you calculate respiratory minute ventilation?
tidal volume x breathing rate
What are the gas exchange surfaces in bony fish?
Gills are the gas exchange surfaces in fish.
What is the structure of gills?
Gills consist of bony gill arches with pairs of gill filaments extending from each arch. Gill lamellae project at right angles from the gill filaments - these are where gas exchange takes place. Gills are protected by the operculum (a flap of skin) which also helps maintain the flow of water over the gills.
How does air move through the respiratory system in bony fish?
Oxygen-rich water enters the fish through the mouth. The water then passes over the gills, flowing between the gill lamellae. Oxygen diffuses from the water into the blood and carbon dioxide diffuses from the blood into the water. Water passes out through the opercular opening.
How are gill lamellae adapted for efficient gas exchange?
- Large surface area
- Short diffusion distance
- Extensive network of capillaries so oxygen is carried away quickly, maintaining a steep concentration gradient
What is the counter-current system in bony fish?
- Blood with a low oxygen concentration passes through the gill lamellae and oxygen diffuses from the water into the blood
- Blood with a high oxygen concentration passes out of the gill lamellae and leaves the gills
- The flow of blood is in the opposite direction to the flow of water - this is called a counter-current system and helps to maintain a steep oxygen concentration gradient
How do bony fish maintain constant water flow?
- When a bony fish opens its mouth, water flows into the mouth space (also called the buccal cavity)
- The floor of the buccal cavity drops down to increase available volume for water
- The fish shuts the operculum and increases the volume of the opercular cavity (where the gills are), lowering the pressure in the opercular cavity
- The floor of the buccal cavity lifts upwards at the same time, increasing the pressure of the water and causing the water to flow over the gills
- Then the fish closes its mouth and opens its operculum, while the sides of the opercular cavity squeeze inwards on the water
- This increases the pressure of the water, which forces it out of the operculum
Why do insects need a specialised gas exchange system?
Insects have a hard exoskeleton made of chitin, which means they can’t carry out gas exchange, and they can’t carry oxygen in the blood.
What is the specialised gas exchange system in insects?
Insects have a tracheal system, which transports gases directly to and from cells.
What do tracheae do in the insect tracheal system?
Tracheae run from the surface of the insect’s body to tissues and transport gases directly to the environment. They branch out into a series of tracheoles, which repeatedly divide until their ends reach individual body cells.
What are spiracles in the insect tracheal system?
Each segment of the insect except the head has a pair of spiracles on the surface of the exoskeleton. Spiracles are pores which are opened and closed by muscles called sphincters to regulate the flow of air and regulate water loss. There is a tracheal tube connected to each spiracle.
How are tracheae adapted in the insect tracheal system?
Tracheae contain rings of chitin - these stop them collapsing.
How are tracheoles adapted in the insect tracheal system?
Tracheoles are open at the end and have fluid which keeps them moist for oxygen and carbon dioxide to dissolve. During increased activity, cells around the tracheoles produce lactic acid through anaerobic respiration - this causes tracheal fluid to diffuse into the cells, drawing air down into the tracheoles and increasing the surface area exposed to air. Tracheoles also contain no chitin so are freely permeable.
How are spiracles adapted in the insect tracheal system?
Spiracles are lined with tiny hairs to trap particles and prevent them entering the tracheal system.
How does air move through the tracheal system?
- Air enters spiracles and passes along tracheae and tracheoles
- Oxygen dissolves in the fluid at the ends of the tracheoles
- The dissolved oxygen diffuses from the tracheole (high concentration) to the cells (low concentration)
- Dissolved carbon dioxide diffuses from the cells (high concentration) to the tracheole (low concentration)
- Carbon dioxide passes into the tracheae
- Air rich in carbon dioxide leaves the tracheal system through spiracles
How have some insects evolved to increase the rate of gas exchange?
- Rhythmic abdominal movements speed up gas exchange by changing the volume of the insect’s thorax and abdomen generating mass movement of air in and out of tracheae
- Some insects have air sacs in the tracheal system - when the volume of the insect’s thorax and abdomen changes, these expand and contract to increase airflow, and when spiracles are closed to conserve water, the oxygen in the air sacs can be used for respiration
- Aquatic insects have tracheal gills along the sides of their abdomen which extract oxygen from the water by diffusion
What are the advantages of the insect tracheal system?
- The impermeable exoskeleton and spiracles that can open and close helps protect the internal gas exchange system and reduce water loss, allowing insects to live in extremely dry areas
- The short diffusion distance in the tracheoles saves energy and space by removing the need for a transport system and speeds up transport of oxygen to respiring cells
- Rhythmic contractions of abdominal muscles increase ventilation by compressing air sacs, which helps the insect maintain a concentration gradient while flying to increase gas exchange and meet increased metabolic demand
What are the disadvantages of the insect tracheal system?
- The system is only effective in smaller organisms because the tracheae would restrict movement and it would take too long for gases to diffuse along the tracheoles
- The system doesn’t work underwater because diffusion of oxygen is slower and water could not be easily ventilated
- Not all air can be forced out of the tracheae, so some oxygen poor air will mix with fresh air, lowering the concentration gradient and making gas exchange less efficient
