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3.2 Gas exchange - Coggle Diagram
3.2 Gas exchange
Insects
Breathing movements
Expiration- abdomen contracts, increasing pressure and squeezing air out, air leaves through spiracles
Inspiration- abdomen expands, decreasing pressure to draw air in, air enters through spiracles in the thorax
Spiracles
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Closing- muscle contracts, pulling valves together
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Tracheoles
Structure
Insects have an internal network of tubes, tracheae, strengthened by rings to prevent collapse. The tracheae extend into smaller tubes called tracheoles (insect exchange surface). They extend through all the body tissue and carry oxygen.
Adaptations
Usually filled with water as a result of respiration, reducing the water potential gradient between cell cytoplasm and tracheoles.
During flight, high respiration rates mean energy demand can be greater than oxygen supply. This leads the cells to carry out anaerobic respiration, building lactic acid up in the cells. This reduces the water potential in the cells and causes water to enter by osmosis, exposing more of the tracheole's surface to the air, increasing SA for gas exchange.
How are a large SA, conc. gradient, and short diffusion distance achieved
Steep concentration gradient: high metabolic rate, abdominal pumping
Short diffusion distance: tracheoles in direct contact with cells, tracheoles have no chitin
SA: many highly branched tracheoles, removing water from tracheole endings using lactic acid
Single-celled organisms
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How are a large SA, conc. gradient, and short diffusion distance achieved
SA: extensions make structure long and thin (increases SA:V), small size gives large SA:V
Concentration difference: high metabolic rate i.e reactions use up reactants to produce product very quickly
Short diffusion distance: exchange surface is just one membrane thick, one cell means short distance from exchange surface to centre of volume
Fish
Gill structure
The gills are behind the head, and are made up of gill filaments which branch off the main gill bar (the gill with branching filaments looks like a feather). At right angles to the filaments are the lamellae, which increase SA.
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How are a large SA, conc. gradient, and short diffusion distance achieved
Short diffusion distance: gill filaments and lamellae are very thin, capillaries on lamellae are close to its surface.
Steep concentration gradient: large blood supply to carry oxygen away from gills and bring CO2 to gills. Flow of water over gills brings fresh supply of O2 and take away CO2, countercurrent principle.
SA: many gill filaments, each filament has many lamellae, flow of water keeps filaments separated.
Dicotyledonous plants
Gas exchange takes place in the leaf, the gas exchange surface is the plasma membrane of the mesophyll tissue.
How are a large SA, conc. gradient, and short diffusion distance achieved in leaves
SA: leaf is flat, air spaces inside leaf have large SA compared to tissue volume, large SA of mesophyll for rapid diffusion.
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Short diffusion distance: many small pores (stomata) mean no cell is far from a stomata and therefore makes a short pathway. Mesophyll has interconnecting air spaces so air only has to cross the membrane, leaf is thin.
Limiting water loss
Stomata- guard cells open and close a stoma, they can control rate of gas exchange and close stomata when the water loss would be very high
Example: Maram grass
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Water potential gradient: rolling up leaves shields lower epidermis, where lots of stomata are found. It traps a region of air in the roll which gets saturated and gains a high water potential, reducing gradient.
Unicellular hairs trap humid air. Sunken stomata trap water around pores
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