gas exchange Flashcards
as size increases, internal and external stems are…?
needed to facilitate exchange of substances and heat.
small organisms have a large..?
surface ares to volume ratio
why do small animals loose heat more quickly?
also have a high..?
because of their large area to volume ratio
metabolism
larger organisms have a smaller…?
surface area to volume ratio
why do larger organisms have a higher demand for oxygen and glucose?
because they have more respiring cells
extra respiration means..?
extra waste products e.h co2 and heat
gas exchange in plants
what are dictyledonous plants?
plants that have mesophyl and stomata
what are the structures in a leaf and explain their roles?
waxy cuticle layer - prevents water loss by evaporation
upper epidermis - transparent to let light through
palisade mesophyll - main site of photosynthesis
spongy mesophyll - contain holes for gases to diffuse here, maintains conc gradient
stomata - holes formed by two gurad cells, main site of gas exchange
lower epidermis
xylem and phloem - transport sugar and water
why do plants need to go through photosynthesis?
so plants can use o2 for respiration to produce co2
where does oxygen and carbon dioxide come from during photosynthesis?
some carbon dioxide comes from respiration however most of it comes from the external air. in the same way some oxygen from photosynthesis is used in respiration but most of it diffuses out of the plant
explain what happens before photosynthesis when it’s dark?
oxygen diffuses into the lead
explain why plants have a fast, short diffusion pathway?
no living cell is far from the external air an therefore a source of oxygen and carbon dioxide
diffusion takes place in the gas phase which makes it more rapid than if it was in water
adaptions in a leaf?
large surface area - so absorbs as much sunlight as possible
thin - for light absorbtion , shorter diffusion pathway
transparent cuticle and epidermis - allows light to pass through for photosynthesis
long, narrow upper mesophyll cells and chloroplast - so collect sunlight
numerous stomata - for gas exchange, short diffusion pathway from one
stomata - opens and closes in changes to light intensity
may air spaces in lower mesophyll layer - allows rapid diffusion of co2 and o2
xylem and phloem - brings water and carries away sugar (glucose)
draw and label the stomata
- chloroplast
- nucleus
- cell wall
- vacoule
Explain why how oxygen and carbon dioxide enter and leave the stomata?
oxygen diffuses out of the stomata because there is a high concentration in the spongy mesophyll compared to the atmosphere, carbon dioxide diffuses into the stomata as its being constantly used in the palisade mesophyll, maintaining the conc gradient.
what causes stomata to open and close?
when carbon dioxide levels are low inside the plant, the guard cells gain water and become turgid, they curve out opening the stomata and allowing gases to diffuse in and out, water then evaporates through the stomata
high carbon dioxide levels cause guard cells to loose water, closing the stomata becoming flaccid.
what are xerophytic plants?
are plants which are adapted to survive in environments with limited water
how do plants limit water loss? what adaptions?
curled leaves - trap moisture to increase local humidity
hairs trap moisture- to increase local humidity
stomata sunken in - to trap moisture, more humid , less evaporation
thicker cuticle - to stop evaporation
longer root network - to reach more water
stomata - have ability to open and close when necessary to prevent water loss
smaller surface ares to volume ratio - slow rate of diffusion
the rate of water uptake by a plant might not e the same as the rate of transpiration because..?
- water is used for support/ turgidity
- water used in photosynthesis
- water used in hydrolysis
- water produced during respiration
gas exchange in insects
why do insects have a high demand for oxygen?
because they are very active
what is an insects exoskeleton made of?
a hard fibrous material for protection and a lipid layer to prevent water loss/ dehydration
what is an insects system made up of?
trachea
tracheoles
spiracles
what are spiracles?
What gases leave and enter?
round, valve like openings, running along the length of abdomen. oxygen and carbon dioxide enter and leave via the spiracles. trachea attaches to these openings
role of spiracles?
controls water loss
what is the trachea?
a network of internal tubes. the trachea tubes have rings within them to strengthen the tubes and keep them open
what are the tracheoles?
the trachea branch into smaller tubes, deeper into the abdomen of the insect. these extend throughout all tissue in the insect to deliver oxygen to all respiring tissue
there are three methods of moving gases in the tracheal system
1. gases moving by diffusion?
along a concentration gradient. when cells are respiring, oxygen is used up and so its concentration towards end of the tracheoles falls. this creates a concentration gradient that causes gaseous oxygen to diffuse from the atmosphere along the trachea and tracheoles to the cells.
carbon dioxide is produced by cells during respiration which creates a diffusion gradient in the opposite direction. this causes gaseous carbon dioxide to diffuse along the tracheoles and trachea from the cells to the atmosphere.
as diffusion in air is much more rapid than water, respiratory gases are exchanged quickly by this method
second method of gas exchange?
mass transport. the contraction of muscles in insects can squeeze the trachea enabling mass movements of air in and out. this further speeds up the exchange of respiratory gases
third method of gas exchange?
the end of the tracheoles are filled with water.
during periods of major activity, the muscle cells around the tracheoles respire and cary out anaerobic respiration. this produces lactate, which is soluble and lowers the water potential of the muscle cells.
water therefore moves into the cells from the tracheoles by osmosis. the water in the ends of the tracheoles decrease in volume and doing so draws water further into them.
this means that the final diffusion pathway is in a gas rather than a liquid phase and therefore diffusion is more rapid.
this increases the rate at which air is moved into the tracheoles but leads to greater water evaporation
Terrestrial insects live on land. explain one problem for them?
water easily evaporates from the surface of their bodies and they can become easily dehydrated
describe how some terrestial insects are adapted to limit water loss?
small SA to volume ratio to minimise the area over which water is lost
waterproof covering around their body surfaces. rigid outer skeleton of chitin that is covered with a waterproof cuticle
spiracles can be closed to reduce water loss. this conflicts with the need for oxygen so occurs largely when the insect is at rest.
how are insects adapted for efficient diffusion?
- large number of tracheoles - increases the surface area
- walls of tracheoles are thin and short - distance between spiracles and tracheoles- short diffusion pathway
- use of oxygen and production of carbon dioxide sets up steep diffusion gradients
gas exchange in fish
where do fish get their oxygen from?
from the surrounding water. this is because oxygen dissolves in water.
why do fish need to be specially adapted to maintain diffusion?
because there is 30x less oxygen in water than in air
fick’s law?
diffusion ∝ SA x difference in conc.
/length of diffusion path
what is the operculum?
a protective, bony flap
describe the structure of the gills
- four layers of gills on both sides of their head - bony arch- v- shape
- the gills are made up of a stack of gill filaments
- each gill filament is covered in gill lamellae positioned at right angles to the filament
which increases the surface area of the gills.
how is water passed along fish gills?
water is taken in through the mouth and forced over the gills and out through an opening on each side of the body
Describe fully the ventilation process in a bony fish
- Mouth opens (operculum is closed)
- The buccal cavity floor is lowered
- This increases the volume and decreases the pressure of the buccal cavity compared to outside
- Water rushes into the mouth down a pressure gradient
- Opercular cavity expands
- The buccal cavity floor is raised
- The pressure inside the buccal cavity is now higher than in the opercular cavity
- Water moves from buccal cavity over the gills into the opercular cavity
- The mouth is now closed and the operculum opens
- The sides of the opercular cavity move inwards, increasing the pressure
- Water rushes out of the fish through the operculum
what is Countercurrent flow?
the flow of water in the gill lamellae and the flow of blood within them are in opposite directions - ensures more gas exchange takes place
the arrangement of the counter current flow mean that…?
- blood is already well loaded with oxygen, meets water which has its maximum concentration of oxygen. therefore diffusion of oxygen from the water to the blood takes place
- blood with little oxygen in it meets the water, which has had most, but not all, of its oxygen removed. Again, diffusion of oxygen from the water to the blood takes place
what does the Countercurrent system ensure?
ensures equilibrium is not reached
ensures that a diffusion gradient is maintained across the entire length of the gill filament
DONE!!
