3.3.2 Gas exchange Flashcards
How are the lungs adapted as an exchange surface?
Large surface area
Thin permeable surface
Steep diffusion gradient
How is a large surface area achieved in the lungs?
Has a large number of alveoli per lung
Each alveolus is folded to form a set of interconnected spaces
How is a thin permeable surface achieved by walls found in the lungs?
Alveolus wall is a single layer of flattened epithelial cells
Capillary wall is a single layer of flattened endothelial cells
How is a steep diffusion gradient maintained in the lungs
Blood in capillaries is circulated
Lungs are ventilated and air inside is replaced by breathing
What happens during inspiration - breathing in?
- External intercostal muscles and the diaphragm muscles contract, this uses energy from ATP - active process (internal intercostal muscles relaxes)
- Ribs are pulled upwards, diaphragm is pulled flatter - volume of thorax increases
- Volume of lungs increases, pressure inside becomes lower than atmospheric pressure
- Air is forced into alveoli via the trachea, bronchi and bronchioles due to pressure difference
What happens during expiration - breathing out?
- External intercostal muscles and the diaphragm muscles relaxes, this does not use energy from ATP - passive process (internal intercostal muscles contracts)
- Ribs are pulled downwards by the thorax walls due to elastic recoil of the lungs, diaphragm returns to its original domed position - volume of thorax decreases
- Volume of lungs decreases, pressure inside becomes greater than atmospheric pressure
- Air is forced out of the alveoli via the bronchioles, bronchi and trachea due to pressure difference
Why does the movement of the ribs and the diaphragm influence the movement of the lungs - thus pressure is altered?
Lungs are attached to the inside of the rib cage by the pleural membranes - has a slightly sticky quality due to water’s surface tension (permeable)
What happens during forced expiration - e.g. breathing out during exercise?
- Internal intercostal muscles and muscles of abdominal wall contracts, this uses energy from ATP - active process
- Ribs are pulled downwards, diaphragm is forced into its domed position - volume of thorax decreases
- Volume of lungs decreases, pressure inside becomes greater atmospheric pressure
- Air is forced out of alveoli vis bronchioles, bronchi and trachea
How is a large surface area archived by the gills?
Many pairs of gills filament per gill
Filaments have many flattened gill plates - secondary lamellae projecting from surface
How is a thin permeable membrane achieved by the gills?
Surface of gill plates are made up of flattened epithelial cells
Capillary walls are flattened endothelial cells
Short diffusion pathway between pair of gills - surfaces next to each other
How is a steep diffusion gradient maintained by the gills?
Blood circulation: oxygenated blood carried away from gill plates to the rest of the body and deoxygenated blood are brought back to the gill plates from the rest of the body
Ventilation: water with high oxygen concentration brought to the gills, water with high carbon dioxide concentration brought away from the gills, leaving through operculum
Countercurrent flow ensures diffusion across entire surface of gill plate
What happens during inspiration in a fish?
Mouth opens, tongue drops, buckle cavity increases, volume increases, pressure decreases, water is forced into the mouth
What happens during expiration in a fish?
Mouth closes, tongue drops, buckle cavity decreases, volume decreases, pressure increases, water is forced out through operculum
Where are gill plates located in fish?
Under the operculum
Why is non-tidal ventilation beneficial for fish?
Water flows in one direction only across gills
Less energy needed, only need to inspire water - harder to inspire and expire water (tidal)
Constant flow means oxygen intake is maximised (lower oxygen level in water)
What is the function of gill rakers?
Keep gills clean - filter food
What is the function of gill bars?
Support gill filaments and keep them separated
Carries blood for capillaries
What is the difference between countercurrent flow and parallel flow?
Countercurrent:
Water and blood flow in opposite directions
Concentration gradient maintained - constant flow of blood
Diffusion across entire gill plate
Parallel:
Water and blood flow in the same direction
Concentration gradient not maintained - eventually reaches equilibrium
Fast rate of diffusion at first - reaches equilibrium before reaching the end of gill plate
How is a large surface area achieved by the leaf
Flat and spread out to cover a large area
Mesophyll cells are separated - large air space between them to allow gas to move - air around most surface of each cell
How is a thin permeable membrane achieved by the leaf?
Leaf is less than 10 cells thick
Gases only need to cross a cell wall and cell membrane to enter epithelial cells
How does light intensity affects gas exchange
Bright:
Rate of photosynthesis > aerobic respiration
Conc. of CO2 in leaf < atmospheric CO2 conc.
Dim:
Rate of photosynthesis < aerobic respiration
Conc. of CO2 in leaf > atmospheric CO2 conc.
What leads to the opening of stomata?
- Guard cells contain chloroplasts which photosynthesise and produce glucose
- Water potential inside guard cell decreases. Water from cells of lower epidermis moves into guard cells via osmosis
- Guard cells swell up and curves - creating an opening - stoma
How are insects adapted to gas exchange?
Have internal network of tubes called tracheae which are supported by strengthened rings to prevent collapse
Tracheae divides into smaller tracheoles which extend through the body tissue of the insect
Ends of tracheoles are fluid-filled with water (dissolved with O2) and have permeable walls
Atmospheric air are brought directly to respiring tissues
What is the process of gas exchange in tracheoles of insects?
- Respiratory gas move through tracheal system along diffusion gradient
- High CO2 and low O2 conc. in respiratory tissues, gases diffuse down conc. gradient in opposite directions
- Muscular contraction squeeze trachea which creates mass movement of air in and out - ventilation further increases exchange of gas
- Lactic acid produced from anaerobic respiration lowers water potential of tissue cells
- Water from tracheoles move into tissue cells by osmosis, drawing in more air
- Final diffusion pathway is in gas (faster) instead of in water (fluid-filled end)
How do evolved mechanism of terrestrial organisms limit water loss whilst optimising gas exchange?
Exoskeleton of insects is composed of chitin and covered with a waterproof cuticle
Spiracles on the abdominal surface can open and close to suit the needs of insect
Spiracles only close when insect is at rest as gas exchange would’ve been prevented
What are the adaptations of xerophytic plants in order to conserve water?
Decrease in S.A. to Volume ratio
Thicker waxy cuticle
Rolling up of leaves - lower epidermis on the inside (trap water vapour)
Hairy leaves - trap moisture
Stomata located in pits
What are xerophytes?
Plants with adaptations to limit water loss
