Gas Exchange Flashcards
What are the essential features of an exchange surface?
- Large surface area compared to the volume of the
organism (SA:V ratio) - Thin - short diffusion pathways so diffusion is rapid
- Selectively permeable - to allow select materials to cross
- moist
- Efficient transport system/good blood supply to maintain diffusion concentration gradient
What type of circulatory system do insects have?
- open
By which system do insects carry out gas exchange?
- tracheal system
Describe the steps of insect gas exchange
- Gas exchange in insects uses the
tracheal system. - Oxygen diffuses into the insect through
pores called spiracles. - The gas then enters wide tubes called
tracheae (singular: trachea). - The tracheae each branch into narrower
tubes called tracheoles. - Tracheoles allow oxygen to directly e
diffuse to the cells of the insect. - The end of a tracheole is fluid-filled.
- Carbon dioxide diffuses out of the insect in the opposite direction
What are the adaptations of the tracheal system for efficient gas exchange?
- Tracheoles have thin walls so short diffusion distance to cells;
- Highly branched tracheoles so short diffusion distance to cells AND large surface area for gas exchange;
- Tracheae provide tubes full of air so fast diffusion through into insect tissues;
- Fluid in the end of the tracheoles moves out into tissues during exercise so faster diffusion through the air (than through liquid) to the gas exchange surface;
- Body can be moved by muscles to pump air so maintains concentration gradient for oxygen / carbon dioxide (note that this pumping is only needed during vigorous activity);
What are the tracheae made of?
- strengthening rings made of chitin
Draw and label the tracheal system
- includes spiracles, trachea, tracheole and rings of chitin
What are the insect adaptations to prevent water loss?
- insects have small SA:Vol ratio where water can evaporate from
- insects have waterproof exoskeleton due to lipid layer
- spiracles, where gases enter and water can evaporate from, can open and close to reduce water loss
What are the 3 methods of moving gases in the tracheal system?
- Diffusion, when cells respire they use up oxygen and produce carbon dioxide creating a concentration gradient from the tracheoles to the atmosphere
- Mass transport, an insect contracts and relaxes their abdominal muscles to move gases on mass
- When insect in in flight, muscle cells respire anaerobically to produce lactate, lowering water potential of cells and water moves into cells by osmosis, decreasing volume in tracheoles and more air from atmosphere is drawn in
By which system do bony fish carry out gas exchange?
- counter current system
What maintains a steep concentration gradient across the whole gill filament?
- blood in capillaries flows in opposite direction to the water flowing over the surface of the gill filament
Draw and label the counter current system
- gill filament
- gill lamellae
Describe the steps of counter current system
- Blood vessels bring deoxygenated blood to the gill filaments.
- The blood then passes through tiny capillaries present in each of the gill lamallae.
- Oxygen (from water) passes through the gill lamellae into the capillaries and carbon dioxide passes out blood capillaries into the water.
- Blood vessels carry oxygenated blood away.
Give an example of a bony fish
- trout
Give an example of a cartilaginous fish
- shark
By which system does cartilaginous fish carry out gas exchange?
- parallel flow
Describe the steps of parallel flow
- Water is taken into the mouth and is forced out through the gill slits when the floor of the mouth is raised
- Parallel flow - Water and blood in the gills flow in the same direction
- It is a relatively inefficient form of gas exchange
Describe the ventilation of the gills
- Mouth opens
- Operculum closes
- Floor of buccal cavity (mouth) lowered •Volume increases
- Pressure decrease
- Water flows in and over the gills
Why are fish waterproof?
- scales
Why do fish require a gas exchange surface?
- small SA:Vol ratio
What is the gas exchange surface for fish?
- gills
How can rate of diffusion be calculated?
- Ficks law = SA x difference in conc / length of diffusion path
How many layers of gills are there on both sides of head?
- four
What are the gills made up of?
- stacks of gill filaments
What is each gill filament covered in?
- gill lamellae
What are the adaptations for efficient gas exchange in fish?
- large SA:vol ratio created by many gill filaments covered in many gill lamellae
- short diffusion distance due to capillary network in every lamellae and very thin gill lamellae
- maintaining concentration gradient due to countercurrent flow mechanism
What does countercurrent flow ensure and why should equilibrium not be reached?
- that equilibrium is not reached to ensure a diffusion gradient is maintained across the entire length of the gill lamellae
Describe countercurrent flow according the the graph
- when the water, containing oxygen, flows in the opposite direction over the surface of the gill filament, containing gill lamellae to increase the surface area, to the blood in the capillaries, this maintains a concentration gradient across the whole gill filament for diffusion to take place
- water is above blood in the graph as it contains a greater concentration of oxygen than blood
Describe parallel flow according to the graph
- when water, containing oxygen, flows in the same direction over the surface of the gill filament to the blood in the capillaries, there is no concentration gradient for diffusion to occur
- water is over blood in the graph as it has a greater concentration of oxygen but plateaus at the same time as blood as they end up with the same concentration
Draw and label the gas exchange system in mammalian lungs
- trachea
- bronchus
- bronchiole
- alveoli
- external and internal intercostal muscles
- ribs
- diaphragm
Why do mammals require a specialised gas exchange structure?
- smaller SA:Vol ratio
Adaptations for rapid gas exchange in the lungs
- Alveoli create a very large surface area (about 300 million alveoli sacks)
- Surrounding every alveolus is a network of capillaries
- The walls of the alveoli (epithelial cells) and the capillaries (endothelial cells) are very thin (both one cell layer thick) - shorter diffusion pathway
- The capillaries are so narrow - the red blood cells are flattened against the capillary walls to squeeze through - this slows them down allowing time for diffusion AND reduces diffusion pathways even more
- Concentration gradients must be maintained by -
1. Breathing ventilates the lungs - constant movement of oxygen in and carbon dioxide out
2. Heart constantly circulates the blood - moving the blood through the capillaries
What type of cells are walls of alveoli?
- epithelial cells
What type of cells are walls of capillaries?
- endothelial cells
Describe the steps of inspiration (inhalation)
- External intercostal muscles contract, internal intercostal muscles relax
- Ribs pulled upwards and outwards, increasing volume of thorax
- Diaphragm muscles contract, flattens and increases volume of thorax
- Increased volume of thorax results in reduction of pressure in lungs
- Atmospheric pressure is greater than pulmonary pressure, air forced into lungs
Describe steps of expiration (exhalation)
- Internal intercostal muscles contract, external intercostal muscles relax
- Ribs move downwards and inwards, decreasing volume of thorax
- Diaphragm muscles relax and pushed up by contents of abdomen that were compressed during inspiration and volume of thorax further decreased
- Decreased volume of thorax increases pressure in the lungs
- Pulmonary pressure is greater than atmospheric pressure and air is forced out
Define breathing
- movement of air into and out of lungs
Define ventilation
- scientific word for breathing
Define respiration
- chemical reaction to release energy in the form of ATP
Define gaseous exchange
- diffusion of oxygen from air in the alveoli into the blood and of carbon dioxide from the blood into the air in the alveoli
Describe gas exchange in the alveoli
- red blood cells flow into the capillaries (endothelial cells) and when the epithelial cells (alveolus) is reached, oxygen is diffused to the red blood cells
- whilst moving through the capillaries, the carbon dioxide is diffused out of the endothelial cells into the epithelial cells and out of the alveolus
Adaptations of alveoli for efficient gas exchange
- many alveoli in each lung creating a large surface area for gas exchange
- alveoli epithelium cells are very thin to minimise diffusion distance
- each alveolus is surrounded by network of capillaries to remove exchanged gases and maintain a concentration gradient
Draw and label the dicotyledenous leaf structure
- waxy cuticle
- upper epidermis
- palisade mesophyll
- xylem vessel
- spongy mesophyll
- substomatal air space
- lower epidermis, thin cuticle within
- guard cell
- stoma
What are Xerophytic plants?
- are plants adapted to living in environments with little liquid water e.g. deserts; regions covered in snow/ice.
Typical adaptations of xerophytic plant leaves for reducing water loss
- Lower number of stomata per unit area so reduced evaporation;
- Hairs so ‘trap’ water vapour and water potential gradient decreased;
- Stomata in pits/grooves so ‘trap’ water vapour and water potential gradient decreased;
- Thick waxy cuticle layer so increases diffusion distance;
- Rolled leaves so ‘trap’ water vapour and water potential gradient decreased;
- Spine/needle-shaped leaves so reduces surface area to volume ratio;
Describe how a student could use an eyepiece graticule to determine the mean diameter of stomata
- Measure each stoma using eyepiece graticule
- Calibrate eyepiece graticule against stage micrometer
- Take a number of measurements to calculate a mean
Explain how the cuticle reduces water loss
- waxy so is waterproof
Explain how hairs and sunken stomata reduce water loss
- traps layer of air and reduces diffusion gradient
- traps layer of air and stoma can close/reduces area for evaporation or transpiration
Describe and explain the relationship between humidity and transpiration rate
- increased humidity decreases rate of transpiration
- high humidity increases water potential
- reduced water potential gradient
- less evaporation
What is the site of gas exchange in plants?
- stoma / stomata
What does the space in the spongy mesophyll allow?
- maintains concentration gradient
What occurs in the palisade mesophyll?
- photosynthesis
Why do stomata close at night?
- stomata close when photosynthesis isn’t occurring to reduce water loss
Describe gas exchange at a stomata
- oxygen diffuses out of the stomata
- carbon dioxide diffuses in through the stomata
- to reduce water loss by evaporation, stomata close at night when photosynthesis doesn’t occur
Why does carbon dioxide diffuse in the stoma?
- carbon dioxide required for photosynthesis and is constantly in use in the palisade mesophyll, maintaining concentration gradient so lower concentration in spongy mesophyll compared to atmosphere
Why is oxygen diffused out of the stomata?
- a product of photosynthesis so there will be high concentrations of oxygen in spongy mesophyll compared to the atmosphere
