gas exchange Flashcards
unicellular organisms
enough surface membrane available for gas exchange, and uptake of mineral ions
eg bacteria, archaea
high SA:V ratio
plant structure
waxy cuticle - reduces water loss
upper epidermis - may contain a few stomata
palisade mesophyll cells - contain many chloroplasts - major region of photosynthesis
spongy mesophyll cells - short term store of CO2
lower epidermis
guard cells - regulate opening and closing of stomata
- stomata usually. kept closed to reduce water loss
- light is the stimulus to open the stomata
mechanism of stomatal opening
thicker cellulose cell wall causing uneven curvature of cells
opening
- K+ pumped into guard cells by active transport
- water potential of guard cells decreases
- water diffuses in to guard cells by osmosis
- guard cells become turgid
- stomata open
closing
- K+ move out of guard cells by facilitated diffusion
- water potential of guard cells increases
- water diffuses out of guard cells by osmosis
- guard cells become flaccid
- stomata close
features of leaves
leaves are flat and thin - short diffusion distance and large SA:V ratio
- air enters the stomata - Co2 diffuses into cells down the concentration gradient - photosynthesis
- air leaves the stomata
- opening of stomata also leads to loss of water vapour - transpiration
LOSS OF WATER IS AN UNAVOIDABLE CONSEQUENCE OF GAS EXCHANGE
plant adaptations - dry conditions
xerophytes = have adaptations
efficient water gathering
- long roots - deep water
- branched roots - water near surface
efficient water storage
- water is stored in stems and leaves (thorns and spines to protect against grazing animals)
reduction of water loss
- sunken stomata
- high-like structures around stomata
- curled leaves
water vapour is trapped near the stomata so small diffusion gradient
- no stomata on upper epidermis
- waxy cuticle
- stomata closed during the day - CAM photosynthesis
- fewer stomata
small animals
- small volume so require less O2 and release less Co2
high SA:V ration
short diffusion distance especially in flat worms
- enough to supply O2 and remove Co2 to the animal
no need for specialised gas exchange surfaces
insects
head
thorax
abdomen
specialised gas exchange system - air tubules (trachea and tracheoles) thoughout the body open to the environment via spiracles
- each spiracle is connected to a tube called trachea which are interconnected to form the tracheal system
- the tracheal branch into tracheoles which terminate on the respiring muscle
o2 diffuses out of tracheole into the muscle down the concentration gradient
gets used in respiration
Co2 produced which diffuses out of muscle into the tracheole down the concentration gradient
adaptations common to ALL insects
thin wall - short diffusion distance
branched - short diffusion distance - delivers O2 straight to the muscle, large surface area - delivers O2 to all parts of the muscle
tubes only contain air - fast movement / fast diffusion
fluid at the end of the tracheoles get pushed into the respiring muscles - easier for gas exchange to occur because larger moist surface available
larger insects
eg cockroaches
these mechanisms are not enough, as they have a lower SA:V ratio
they have a ventilation (ie like breathing in and out) mechanism
- mass flow is movement of air/liquid down a pressure gradient which enables movement over a large distance quickly
insects do mass flow ventilation by abdominal pumping
- air enters through abdominal spiracles
- abdomen contracts by muscle contraction
- volume decreases, pressure increases
- pushes air into the thorax
- air leaves through thoracic spiracles
fish
lower concentration of oxygen in water than in air so require specialised gas exchange system - internal gills and circulation system (blood) to transport gases to other parts of the body
fish - structural
gill filament - several lamella to increase surface area for gas exchange
one layer of epithelial cells surrounding the capillary and one layer of epithelial cells in the lamella so short diffusion distance
fish - RAM ventilation
mostly in cartilaginous fish
fills exposed to water (as not covered)
mouth open and water flows in because constantly swimming forward
water flows over the gills and out
- only works if the fish is constantly swimming forward
fish - buccal pumping
mainly bony fish - gills covered by operculum
ONENOTE FOR STRUCTURE
mass flow - movement of water down a pressure gradient
- only one of the 2 opercular cavities is open at any time to create the pressure difference ??
- mouth opens by lowering the jaw
- volume of mouth cavity increases
- pressure inside the mouth decreases
- water flows in from outside
- mouth closed - opercular value opened
- pressure increases in mouth and decreases in operculum
- water is forced over the gills
- so flows out through the open opercular valve
by these two processes - water is brought to the gas exchange surface ie the lamellae
fish - counter-current exchange system
blood and water flow in opposite directions
blood - less O2 and more Co2
water - more O2 and less Co2
efficient because the concentration gradient is maintained along the entire length of the lamella
so diffusion can occur along the entire length of lamella
vs parallel/concurrent system (less efficient)
- as concentration gradient reaches equilibrium - so max concentration achieved in blood is limited to lower than counter-current system
human gas exchange system - alveolus
layer of epithelial cells - very thin cell with only nucleus - short diffusion distance - concentration
humans - inhalation
• External intercostal muscles contract & internal intercostal muscles relax. This pulls the rib cage up and out.
• At the same time, diaphragm contracts. This flattens the diaphragm.
• Together, these two processes increase the volume of the thorax.
• Therefore, pressure in the thorax (lungs) decreases to less than the atmospheric pressure.
• Therefore, air enters the lungs, inflating the alveoli until air pressure in the lungs = atmospheric pressure.
humans - exhalation
• External intercostal muscles relax & internal intercostal muscles contract. The rib cage drops mainly because of its own weight.
• At the same time, diaphragm relaxes. The dropping of the rib cage forces the diaphragm into a dome shape, pushing it into the thorax.
• Together, these two processes decrease the volume of the thorax. Therefore, pressure in the thorax (lungs) increases above atmospheric pressure.
• Therefore, air is forced out of the lungs.
humans - gas exchange
capillary transports oxygenated blood to the heart - pumped to all over the body - gas exchange at the respiring tissues
humans - role of water
- because the gas exchange surface is moist - water vapour is released into the alveolus
- therefore water vapour concentration in exhaled air is greater than in inhaled air
- some water vapour is retained in the trachea - helps prevent excessive water loss (decrease in concentration gradient)
humans - lung volume
tidal volume = volume inhaled or exhaled in a breath
exercise increases tidal volume
breathing rate = number of breaths per minute
pulmonary ventilation rate (volume of air breathed in/out per minute) = tidal volume (volume per breath) x breathing rate
three features of an efficient gas exchange surface
large surface area eg folded membranes in mitochondria
thin/short distance eg wall of capillaries
steep concentration gradient, maintained by blood supply or ventilation eg alveoli
why cant insects use their bodies as an exchange surface
they have a waterproof chitin exoskeleton and a small surface area to volume ratio to conserve water
name and describe the three main features of an insect’s gas transport system
spiracles = holes on the body’s surface which may be opened or closed by a valve for gas or water exchange
tracheae = large tubes extending through all body tissues, supported by rings to prevent collapse
tracheoles = smaller branches dividing off the tracheae
why cant fish use their bodies as an exchange surface
they have a waterproof, impermeable outer membrane and a small area to volume ratio
name and describe the two main features of a fish’s gas transport system
gills = located within the body, supported by arches, along which are multiple projections of gill filaments, which are stacked up in piles
lamellae = at right angles to the fill filaments, give an increased surface area - blood and water flow across them in opposite directions
describe the trachea and its function in mammalian gaseous exchange system
wide tube supported by C-shaped cartilage to keep the air passage open during pressure changes
lined by ciliated epithelium cells which move mucus towards the throat to be swallowed, preventing lung infections
carries air to the bronchi
describe the bronchi and their function in mammalian gaseous exchange system
like trachea - supported by rings of cartilage and are lined by ciliated epithelium cells
they are narrower and there are two of them - one for each lung
allow passage of air into the bronchioles
describe the bronchioles and their function in the mammalian gaseous exchange system
narrower than the bronchi
do not need to be kept open by cartilage - therefore mostly have only muscle and elastic fibres so that they can contract and relax easily during ventilation
allow passage of air into the alveoli
describe the alveoli and their function in the mammalian gaseous exchange system
mini air sacs, lined with epithelium cells, site of gas exchange
walls only one cell thick, covered with a network of capillaries, 300 million in each lung, all of which facilitates gas diffusion
explain the process of inspiration
external intercostal muscles contract
internal relax
pulling the ribs up and out
diaphragm contracts and flattens
volume of the thorax increases
air pressure outside the lungs is therefore higher than the air pressure inside, air moves in to rebalance
explain the process of expiration
external intercostal muscles relax
bringing the ribs down and in
diaphragm relaxes and domes upwards
volume of the thorax decreases
air pressure inside the lungs is therefore higher than the air pressure outside, so air moves out to rebalance
how do you calculate pulmonary ventilation rate
tidal volume x breathing rate
can be measured using a spirometer - a device which records volume changes onto a graph as a person breathes
