Mass transport

describe the structures involved in the gas exchange of insects: (4)

1. exoskeleton: made of chitin, co2 and o2 cannot easily pass through

2. spiracles: openings in exoskeleton that let gas diffuse into insect body

3. spiracles lead to trachea, extending down and along insect body. reinforced with chitin, preventing trachea from collapsing during movement

4. tracheoles: fine tubes extending from tracheae, single cell lengthened to form tube. extend down between cells, not supported by chitin

why are tracheooles important for gas exchange (5)

1. tracheoles extend between cell, so very short diffusion distance for gases moving between cells and tracheoles

2. oxygen can diffuse rapidly into cells, and co2 can rapidly diffuse back into tracheole

3. huge number of tracheoles means very large surface area for gas exchange

4. ends of tracheoles filled with tracheal fluid, which moves by osmosis to anareobically respiring cells that have produce lactic acid

5. decreases volume of tracheal fluid, drawing oxygen into tracheole and increasing tracheole SA, and increasing steepness of O2 gradient

Describe and explain sphincters (2)

1. walls of tracheoles are moist and ends contain tracheal fluid, so water can be lost as vapour through spiracles

2. so each spiracle is surrounded by muscular sphincter, insects can reduce water loss by closing spiracles eg. when o2 need is relatively low

describe the operculum and its purpose (2)

1. operculum: flap thats in front of opercular cavity, which houses the gills

2. water enters through mouth and passes through gills, and passes through the opercular opening

describe and explain the structure of gills and gill filaments

1. gills inside of opercular cavity

2. gills consist of several bony gill arches

3. extending from each gill arch is many gill filaments, covered in gill lamellae / plates

4. water flows between gill lamellae, o2 difuses from water into bloodstream, co2 diffuses from bloodstream to water

how are gill lamellae adapted to specialised gas exchange (3)

1. massive surface area, from many being on gill filaments increasing surface to voulme ratio

2. very short diffusion pathway / distance between gill lamellae walls and into bloodstreams

3. gill lamellae have extensive network capillaries, which carry o2 away, keeping steep concentration gradient for oxygen

explain the counter current system (4)

1. blood with low O2 conc pass through gill lamellae, oxygen diffuses from water into blood

2. oxygen rich blood now passes out of gill lamellae and leaves gills

3. flow of blood is in opposite direction to flow of water, therefore called counter-current system

4. maintains steep concentration gradient for oxygen

describe and explain the trachea (4)

1. walls contain the firm yet flexible cartilage, which prevents the trachea from collapsing, cartilage forms a c shape so food easily passes down oesophagus

2. goblet cells secretes mucus which traps dust particles and pathogens

3. ciliated epithelial cells have cilia extending from cell membrane, beating of cilia moves mucus to throat

4. mucus is swallowed and dust / pathogens are digested by stomach enzymes

which parts of the gas exchange system contain ciliated epithelia and goblet cells

trachea, bronchi

describe the pathway of o2 from nose to blood

1. nose cavity

2. trachea

3. bronchi

4. bronchioles

5. aveoli

describe and explain bronchioles (4)

1. extend from bronchi

2. larger bronchioles contain cartilage

3. contain smooth muscles. when smooth muscles contract, bronchioles widen, so air coan pass into deeper parts of the lungs

4. deeper, narrower, leading to aveoli

describe and explain the structure of aveoli (4)

1. extend from broncohioles

2. internal walls are covered in thin layer of moisture which o2 dissolves in

3. covered in extensive blood capillaries, which o2 diffuses into the red blood cells within, combining with Hb. Co2 diffuses from blood to aveolar air space

4. between aveoli are elastic fibres which stretch and recoil while breathing

Describe and explain how the aveoli is adapted for gas exchange

1. millions of aveoli - very large surface area for gas exchange

2. aveolar wall is 1 cell thick, so very short diffusion distance between air in aveoli and red blood cells in capillary. capillary wall is also narrow to decrease diffusion distance

3. extensive capillary network: O2 is rapidly carried away after diffusing int oblood, therefore O2 gradient remains steep

How is steep concentration gradient maintained in lungs (2)

1. extensive capillary netwrok around aveoli rapidly transports O2 away once diffused into blood

2. breathing brings fresh air into aveoli

Inspiration (7)

1. external intercostal muscles contract / shorten

2. pulls ribs upwards and outwards

3. diaphragm contracts, causing it to flatten

4. increases volume of thorax cavity / lungs, decreasing air pressure

5. air moves in through diffusion

6. air moves into aveoli and elastic fibres between aveoli stretch

7. muscle contraction - active process, requires energy

explain exhalation (5)

1. during regular breathing, exhalation is passive because muscles relax

2. external intercostal muscles relax, returning to original length

3. diaphragm relaxes, to dome

4. reduces volume of thorax and lungs. increasing pressure, so air is pushed out

5. elastic fibres between aveoli recoil, helping to push air out (elastic recoil)

explain pleural membranes and fluid

1. lungs are surrounded by pleural membranes,

2. between pleural membranes is pleural fluid

3. which acts as a lubricant as lung volume changes

explain exhalation during exercise

1. in active exercise, exhale strongly means internal intercostal muscles contract

2. pulls ribs down and inwards, forcing air out of lungs

3. external intercostal muscles relax

4. internal and external intercostal muscles are antagonistic

explain the roles of the elasitc fibres between aveoli (2)

1. inspiration: when air moves into aveoli, elastic fibres stretch

2. exhalation: elastic fibres recoil helping to push air out (elastic recoil)