3.3.1 + 3.3.2 SA:V Ratio And Gas Exchange Flashcards
Examples of substances exchanged between organisms and the environment
Respiratory gases eg. Oxygen and carbon dioxide
Nutrients eg. Water, glucose, amino acids
Excretory products eg. Urea, excess amino acids
Heat
What is passive exchange
Requires no energy from ATP eg. Simple and facilitated diffusion, osmosis
What is active exchange?
Requires energy from ATP eg. Active transport
Where does exchange take place?
Exchange surfaces, usually plasma membranes
What is the surface area to volume ratio?
The relationship between the size of an organism and its surface area
What happens to the SA:V ratio as the size of the organism increases?
It decreases (small surface area in comparison to volume), so larger organisms need to have adaptations to make exchange more efficient.
How are large organisms adapted to increase SA:V ratio?
Villi and microvilli to absorb digested food
Alveoli/bronchioles for gas exchange in mammals
Spiracles and tracheoles for gas exchange in terrestrial insects
Gill filaments and lamellae for gas exchange in fish
Thin wide leaves for gas exchange in plants
Many capillaries in the capillary network
Why do large animals especially need to have adaptations?
They have a small surface area to volume ratio and a fast metabolism.
What are the structures in the human gas exchange system?
Trachea
Bronchus
Bronchioles
Alveoli
Diaphragm
Lungs
What are antagonistic pairs of muscles?
One contracts as the other relaxes to enable movement.
What are the muscles involved in ventilation?
Intercostal muscles
Diaphragm
What happens during inspiration?
External intercostal muscles contract
Internal intercostal muscles relax
Rib cage moves up and out
Diaphragm contracts and flattens
Air pressure in lungs initially drops then increases above atmospheric pressure as air moves in
Lung volume increases
Air moves in
What happens during expiration?
External intercostal muscles relax
Internal intercostal muscles contract
Rib cage moves down and in
Diaphragm relaxes and domes
Air pressure in lungs decreases as air moves out
Lung volume decreases
Air moves out
What is pulmonary ventilation?
The total volume of air that is moved into the lungs in one minute.
What is the tidal volume?
Volume of air normally taken in per breath at rest
What is the ventilation rate?
Number of breaths taken in one minute
What is the pulmonary ventilation equation?
Pulmonary ventilation = tidal volume x ventilation rate
How is the alveolar epithelium adapted for efficient gas exchange?
Increase the surface area of the lungs
Walls are very thin/ only one cell thick so creates a short diffusion distance
Many capillaries provide good blood supply to maintain high concentration gradient
How do terrestrial insects limit water loss whilst still maximising gas exchange?
They have a small surface area to volume ratio where water can evaporate from (spiracles)
Have a lipid layer on their exoskeleton, making them waterproof
Spiracles can open and close to reduce water loss and are very small
What is the gas exchange system in insects?
Tracheal system
What are the structures in the tracheal system?
Spiracles
Tracheal
Tracheoles
What are spiracles
Round openings on the surface of the insects body that allow oxygen and carbon dioxide to enter and exit the trachea. They can open and close to reduce water loss.
What are trachea in insects
A network of internal tubes within the insect. They have rings to keep them open and strengthen them.
What are tracheoles
Branches of trachea to extend throughout insect to provide oxygen and remove carbon dioxide from all respiring cells
How is gas exchanged along a diffusion gradient in insects?
When cells are respiring, oxygen is used up and carbon dioxide is produced, creating a concentration gradient from the tracheoles to the atmosphere. Oxygen diffuses into cells from the atmosphere, and carbon dioxide diffuses into the atmosphere from cells, by simple diffusion.
How is gas exchanged by mass transport in insects?
Insects contract and relax abdominal muscles to squeeze trachea and increase mass movement of air.
How is gas exchanged in insects using water-filled tracheoles?
When in flight, the muscle cells respire anaerobically to produce lactate. This lowers water potential of cells so water moves from tracheoles to cells by osmosis. This decreases volume of water in tracheoles, which is replaced by air which is drawn in due to low pressure.
How is the tracheal system adapted for efficient gas exchange?
Large number of highly branched tracheoles provide a large surface area for efficient gas exchange.
Short diffusion distance as walls of tracheoles are thin, and there is a short distance between spiracles and tracheoles.
Oxygen used up in respiring cells sets up a concentration gradient to provide a large concentration gradient for diffusion.
How are single celled organisms adapted for efficient gas exchange?
Have a flattened shape so no part of it is far from the edge of he cell, providing a short diffusion distance, and increases SA:V ratio.
Food vacuole to maintain concentration gradient by lowering concentration of food in the cytoplasm.
Structures in gas exchange system in fish
Gills
Gill filaments
Gill lamellae
How are fish adapted for efficient gas exchange?
Many gill filaments stacked up in a pile that are covered in gill lamellae, all of which provide a large surface area
The walls of the lamellae are one cell thick, which provides a short diffusion distance.
Gills have a rich blood supply due to a capillary network in every lamellae to maintain high concentration gradient.
The countercurrent flow mechanism maintains a high concentration gradient.
Describe what the countercurrent flow mechanism is
Water flows over the gills in the opposite direction to the flow of blood in the capillaries
This means blood is always passing water with a higher oxygen concentration so maintains concentration gradient
Mains diffusion occurs throughout the entire length of the gill lamellae
Ensures that equilibrium is not reached
What are the structures in a leaf?
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Stomata
Lower epidermis
Guard cells
What moves in and out of the stomata?
Oxygen diffuses out of the stomata from photosynthesis
Carbon dioxide diffuses into the stomata for photosynthesis
Water evaporates out of the stomata during transpiration
Why do stomata need to open and close?
To minimise water loss by evaporation from leaves to the environment, so they close at night when photosynthesis is not taking place and gas is not needed.
How are leaves adapted for efficient gas exchange?
Stomata open and close to allow gas to enter and exit the leaf, and no cell is far from stomata as there are a large number of them. This provides a short diffusion distance.
Spongy mesophyll latter has air spaces to allow gas to move around easily to come into contact with photosynthesising mesophyll cells.
Guard cells control opening and closing of stomata to maintain concentration gradient.
Thin and flat leaves to increase surface area to volume ratio.
What is a xerophytic plant?
Adapted to live in environments with limited water, so have structural features to enable efficient gas exchange to occur whilst limiting water loss.
What are the adaptations of xerophytes to reduce water loss?
Curled leaves and hair-covered stomata to trap water to increase humidity and decrease water concentration gradient.
Thicker cuticle to reduce rate of evaporation
Longer root network so bale to reach water at further distance
Less stomata so less water loss
Thick stems so able to store more water
Pointed spines minimise surface area for water loss
Spirometer
Measures lung capacity by patients exhaling into it to produce a spirometer trace.
FEV
Forced expiratory volume- maximum volume of air that can be breathed out in one second
Tidal volume
Volume of air inhaled and exhaled at rest
Forced vital capacity
Maximum volume of air that can be inhaled or exhaled
Total lung capacity
Vital capacity + residual volume
Residual volume
Volume of air left in lungs after expiration
What are the effects of athsma/bronchitis on gas exchange?
Obstruction of the airways that disrupts breathing
Muscle wall of bronchitis and bronchioles contract to secrete more mucus
Diameter of airways reduced so flow of air reduces
Decreased FEV
Low energy as not enough oxygen delivered to alveoli, blood and respiring cells
What are the effects of emphysema/pulmonary fibrosis on gas exchange?
Breakdown of alveoli walls
Alveoli fuse together so reduced SA:V ratio
Walls dilate and thicken which increases diffusion distance
Less oxygen enters the blood
Leads to an increased ventilation rate.
