3.1 - adaptations for gas exchange Flashcards
how does an organisms size relate to its SA:V ratio
larger organism = lower SA:V
how does SA:V affect transport of molecules
lower SA:V = further distance molecules must travel to reach all parts of organism
diffusion alone not sufficient in organisms w/ small SA:V
why do larger organisms require mass transport + specialised gas exchange surfaces
- small SA:V
- diffusion insufficient to provide all cells w/ required O2 + to remove all CO2
- large organisms more active than smaller organisms
four features of an efficient gas exchange surface
- large SA
- short diffusion distance
- steep diffusion gradient
- ventilation mechanism
describe the gas exchange mechanism in amoeba
- unicellular organism w/ large SA:V
- thin cell membrane providing short diffusion distance
- simple diffusion across cell surface membrane sufficient to meet demands of respiratory processes
describe the gas exchange mechanism in flatworms
- multicellular organisms w/ relatively small SA:V (in comparison to amoeba)
- flat surface provides large SA + reduces diffusion distance
- simple diffusion sufficient to meet demands of respiratory processes
describe the gas exchange mechanism in earthworms
- cylindrical, multicellular organisms w/ relatively small SA:V (in comparison to flatworms)
- slow moving + low metabolic rate (require little O2)
- rely on external surface for gas exchange
- circulatory system transports O2 to tissues + removes CO2, maintaining steep diffusion gradient
define ventilation
movement of fresh air into a space + stale air out of a space to maintain a steep conc gradient of O2 + CO2
name the organ of gaseous exchange in fish
gills
what are gill filaments
- main site of gaseous exchange in fish, over which water flows
- overlap to increase resistance to flowing water, slowing it down + maximising gaseous exchange
- found in large stacks (gill plates) + have gill lamellae which provide large SA + good blood supply for exchange
explain the process of ventilation in bony fish
- buccal cavity volume increases + pressure decreases to enable water to flow in
- contraction of buccal cavity forces water across gills
- pressure in gill cavity rises, opening operculum
- water leaves
how is a steep diffusion gradient maintained across the entire gas exchange surface in bony fish
due to counter current flow
define counter current flow
blood + water flow in opposite direction across gill plate
how does counter current flow maintain a steep diffusion gradient
what’s the advantage of this
- water always next to blood of lower O2 conc
- keeps rate of diffusion constant + enable 80% of available O2 to be absorbed
what type of flow is exhibited in cartilaginous fish
parallel flow
define parallel flow
water + blood flow in same direction across gill plate
compare counter current + parallel flow
counter current:
- blood + water flow in opposite directions
- steep diffusion gradient maintained, allowing diffusion of O2 across whole gill plate
- high rate of diffusion
- more efficient, more O2 absorbed into blood
- found in bony fish
parallel flow:
- water + blood flow in same direction across gill plate
- diffusion gradient not maintained, diffusion of O2 doesn’t occur across whole plate
- lower rate of diffusion
- less efficient, less O2 absorbed into blood
- found in cartilaginous fish, e.g: sharks
name + describe the main features of an insects gas transport system
spiracles - small external openings along thorax + abdomen through which air enters, + air and water leave gas exchange system
tracheae - large tubes extending through all body tissues, supported by rings of chitin to prevent collapse
tracheoles - smaller branches dividing off tracheae
what’s the main site of gas exchange in insects
tracheoles
describe the adaptations of the insect tracheal system to a terrestrial environment
- spiracles can open + close to regulate diffusion
- bodily contractions speed up movement of air through spiracles
- highly branched tracheoles provide large SA
- impermeable cuticle reduces water loss by evaporation
describe ventilation of the tracheal system in insects
- expansion of abdomen opens thorax spiracles (air enters) + closes abdominal spiracles
- compression of abdomen closes thorax spiracles + opens abdominal spiracles (air expelled)
compare gas exchange surface of an active + inactive amphibian
active - has simple lungs
inactive - relies on moist external surface
how are mammals adapted for gas exchange
- alveoli provide large SA + thin diffusion pathway, maximising volume of O2 absorbed from one breath
- have plentiful supply of deoxygenated blood, maintaining step conc gradient
describe the structure of + function of larynx
hollow, tubular structure located at top of trachea involved in breathing + phonation
describe the trachea + its function in the mammalian gaseous exchange system
- primary airway. carries air from nasal cavity down into chest
- wide tube supported by C-shaped cartilage to keep air passage open in pressure changes
- lined by ciliated epithelial cells which move mucus (produced by goblet cells) towards back of throat to be swallowed, preventing lung infections
describe the structure of the bronchi
- divisions of trachea leading to lungs
- narrower than trachea
- supported by rings of cartilage + lined by ciliated epithelial + goblet cells
describe the structure of+ function of bronchioles
- many small divisions of bronchi that allow passage of air into alveoli
- contain smooth muscle to restrict airflow to lungs but dont have cartilage
- lined w/ thin layer of ciliated epithelial cells
what’s the primary gaseous exchange surface in humans
alveoli
describe the alveoli in the mammalian gaseous exchange system
- mini air sacs, lined w/ epithelial cells
- walls one cell thick
- good blood supply to maintain steep diffusion gradient
- 300 million in each lung
what are pleural membranes
thin, moist layers of tissue surrounding pleural cavity that reduce friction between lungs + inner chest wall
define pleural cavity
space between pleural membranes of lungs + inner chest wall
describe ventilation in humans
- movement of fresh air into lungs + stale air out of lungs via inspiration + expiration
- via negative pressure breathing
what are internal intercostal muscle
set of muscles found between ribs on inside involved in forced exhalation
what are external intercostal muscles
set of muscles found between ribs on outside involved in forced + quiet inhalation
explain the process of inspiration + the changes occurring throughout the thorax
- external intercostal muscles contract (internal relax), raising ribcage
- diaphragm contracts + flattens
- outer pleural membrane moves out, reducing pleural cavity pressure + pulling inner membrane out
- alveoli expand, alveolar pressure falls below air pressure so air moves into trachea
what’s surfactant
fluid lining the surface of alveoli that reduces surface tension + prevents collapse of alveoli in exhalation
describe the function of the waxy cuticle
reduces water loss from leaf surface
describe how the upper epidermis is adapted for photosynthesis
- layer of transparent cells allow light to strike mesophyll tissue
- epidermal cells synthesise waxy cuticle, reducing water loss
where’s the palisade mesophyll layer located
directly below upper epidermis
how is the palisade mesophyll layer adapted for photosynthesis
receives most light so contains greatest conc of chloroplasts
how is the spongy mesophyll layer adapted for photosynthesis
- contains air spaces reducing diffusion distance for CO2 to reach chloroplasts in palisade layer
- contains some chloroplasts
what’s the vascular bundle
vascular system in dicotyledonous plants consisting of 2 transport vessels, xylem + phloem
why are vascular bundles important in photosynthesis
form large network to deliver water + nutrients to photosynthetic tissues + remove glucose
describe how the lower epidermis is adapted for photosynthesis
contains many stomata enabling evaporation of water + inward diffusion of CO2
what are stomata
small holes found on leaves that can be opened + closed by guard cells to control gas exchange + water loss
summarise the malade theory
states that the accumulation or loss of malade + K+ ions by guard cells results in changes in turgor pressure that open or close stomata
by what mechanism do K+ ions enter guard cells
active transport
how does accumulation of K+ + malade ions affect guard cells
- lowers water potential of guard cells
- water moves in by osmosis
- guard cells become turgid, opening stomata
why is starch important for stomatal opening
starch converted to a late ions
