Gas exchange Flashcards
Explain the surface area to volume ratio
- When an organism doubles in size, its volume (and O2 needs) is cubed, but is surface area is only squared
- As organism’s size increases, specialised gas exchange surface is needed to increase area available
Characteristics of efficient gas exchange surface
- Large SA:Vol ratio
- Moist (allow gas to dissolve)
- Thin (short diffusion pathway)
- Gas permeable
How does the size of unicellular organisms affect its gas exchange?
- Surface area is large enough to meet the organism’s needs so materials exchanged across thin permeable membrane
- Cytoplasm always moving=concentration gradient maintained
How does the size of multicellular organisms affect its gas exchange?
- Surface area of body surface (for gas exchange) is insufficient for the organisms needs => evolved adaptations solve problems
- Active animals with fast metabolisms need more O2 than just the body surface would provide
- Have specialized gas exchange surface with ventilation system (ensuring constant conc. gradient is maintained)
What’s the problem with terrestrial animals maintaining a moist respiratory surface, and how is it minimised?
Water loss: minimised by having internal gas exchange surfaces (lungs)
How is a flatworm adapted for gas exchange?
Flattened body - reduce diffusion distance between surface and inside cells + increase surface area
How is a earthworm adapted for gas exchange?
- Secrete mucus (maintain moist surface) + well developed capillary network under skin
- Low metabolic rate (reduce O2 needs)
- Network of blood vessels, transporting O2 via haemoglobin in blood (CO2 in blood plasma)
How are amphibians adapted for gas exchange?
- Moist permeable skin with well developed capillary network under skin
- Lungs for when more active
How are reptiles adapted for gas exchange?
Internal lungs - like amphibians but more complex with larger surface area
How are birds adapted for gas exchange?
- High metabolic rate from flying=large O2 requirement
- Efficient ventilation system to increase concentration gradient across lung surface
Describe the structure of a fish’s internal gas exchange surface? How is this an adaptation for gas exchange?
-Gills: vertical gill arches/bars have layers of filaments coming off them horizontally
Filaments contain lamellae at right angles to them
-Greatly increase the surface area for O2 and CO2 gas exchange
What are the 2 ways fish ventilate their gills?
- Parallel flow: Cartilaginous fish (e.g. sharks)
- Counter-current flow: Bony fish (e.g. salmon)
Describe Parallel flow
- Blood flows in same direction as water over gills
- Gas exchange only over part of filament surface (equilibrium is reached - reducing O2 absorption)
- Simple ventilation: open mouth while swimming allows water to pass over gills
Describe Counter-current flow
- Blood flows in opposite direction to water over gills
- Diffusion maintained along entire length of filament (always higher O2 concentration in water than in meeting blood - no equilibrium)
- More efficient than parallel as higher O2 absorption
- Advanced ventilation
Describe ventilation in bony fish
- As mouth opens floor of buccal cavity lowers (increased volume decreases the pressure, causing water to rush in + opercular valve to close)
- As mouth closes floor of buccal cavity rises (decreased volume increases the pressure, forcing the rush of water over gills + opercular valve to open
Describe the parts of the human ventilation system
- Trachea branches into 2 bronchi (each entering a lung)
- These branch into finer bronchioles, further ending as alveoli (site of gas exchange)
Describe human inspiration (active)
- External intercostal muscles and diaphragm contract, moving ribs up and out (pulling pleural membranes out) and diaphragm flat
- Pressure in pleural cavity reduces (from volume increase) => pulling of lung surface causes alveoli to expand
- Alveolar pressure below ATM=air sucked in
Describe human expiration (passive)
- External intercostal muscles and diaphragm relax, moving ribs down and in (pushing pleural membranes in) and diaphragm up
- Pressure in pleural cavity increases (from volume decrease) => pushing on lung surface causes alveoli to contract
- Alveolar pressure above ATM=air forced out
How are alveoli adapted for gas exchange?
- Large surface area + thin walls (1 cell thick)
- Short diffusion pathway+good blood supply (capillaries surround)
- Moist lining + permeable to gases)
- Collagen and elastic fibres allow expansion/recoil
Describe gas exchange in insects
- Branched tracheae system with spiracle openings, lined with chitin (arranged in rings - allowing tracheae to expand/relax)
- Spiracles (on surface of organism) can close during inactivity+chitin helps to reduce water loss
- Tracheoles touch all tissue with fluid for (C)O2 exchange=no haemoglobin needed
Describe the ventilation system in insects for gas exchange
- Muscles in thorax/abdomen contract and relax
- Rhythmic movements ventilate the tracheole tubes (keeping concentration gradient)
Describe gas exchange in plants
- Need O2 for respiration + CO2 for photosynthesis (diffusion through leaves)
- Waxy cuticle (covering leaf surface) reduces water loss and diffusion of gases
- Stomata on most leaves’ underside open for gas exchange in day and close at night/drought to reduce water loss
What is transpiration?
Evaporation of H2O (from leaves/any above ground parts) through stomata into the atmosphere
-Controlled by size of pore between guard cells
Explain the stomatal opening mechanism
Guard cells produce ATP via photosynthesis (energy released used to actively transport potassium ions into guard cells)
- This triggers starch to convert into malate ions (soluble), so H2O diffuses in guard cells (lower ψ)
- Pore created between cells by outer wall stretching more than inner
- Reverse happens at night
