6: Gas Exchange in Insects and Fish

• large surface area to volume ratio which increases the rate of exchange

• thin so short diffusion distance for rapid exchange
  -selectively permeable to allow selected materials to cross

• movement of external medium-diffusion gradient maintained

• movement of internal medium- diffusion gradient maintained

• small surface area to volume ratio where water can evaporate from

• waterproof exoskeleton

• spiracles where gases enter and water can evaporate from. Open and close to control water loss

• spiracles- round openings running along the length of the abdomen. Oxygen and CO2 enter and leave via spiracles. Trachea attach to these

• trachea- network of internal tubes that have rings within them to strengthen them and keep them open

• tracheoles- trachea branch into tracheoles which extend throughout all the tissues to deliver oxygen to respiring cells

1. Gas exchange by diffusion as when cells respire, they use up oxygen and produce carbon dioxide, creating a concentration gradient from the tracheoles to the atmosphere

2. Insect contracts and relaxes abdominal muscles to move gases

3. When the insect is in flight the muscles start to respire anaerobically to produce lactate. This lowers the water potential of the cells and therefore water moves from the tracheoles into the cells by osmosis. This decreases the volume in the tracheoles and as a result, more air from the atmosphere is drawn in

• large number of tracheoles- large surface area

• walls of tracheoles are thin and short distance between spiracles and tracheoles- short diffusion pathway

• use of oxygen and production of CO2 sets up steep diffusion gradients

• four layers of gills on both sides of the head

• made up of stacks of gill filaments

• each gill filament is covered in gill lamellae, positioned at right angles to the filament

• this creates a large surface area

• when fish open their mouth water rushes in over the gills and then out through a hole in the sides of their head

• large surface area to volume ratio created by many gill filaments covered in many gill lamellae

• short diffusion distance due to a capillary network in every lamellae and very thin gill lamellae

• countercurrent flow mechanism to maintain conc gradient

• 
  water flows over the gills in the opposite direction to blood flow in the capillaries

• ensures that equilibrium is not reached

• ensures that a diffusion gradient is maintained across the entire width of the gill lamellae

• oxygen diffuses and CO2 diffuses out

• to reduce water loses by evaporation stomata close at night as photosynthesis is not occurring

• adapted to survive in environments with limited water

• structural features to enable efficient gas exchange while also limiting water loss

• curled leaves and hairs which trap moisture to increase local humidity. Increases water potential outside leaf so smaller water potential gradient so less water diffuses out of the leaf

• thicker cuticle to reduce evaporation

• longer root network to reach more water

• lungs
  -trachea- airway that is supported by rings of cartilage to prevent it collapsing.

• bronchi- two divisions of the trachea each leading to one lung. Produce mucus to trap dirt and particles and have cilia to move mucus to throat

• bronchioles- series of branching subdivisions of the bronchi. Walls are muscle lined so can constrict to control air flow in and out of the alveoli

• alveoli- minute air sacs lined with epithelium. Have elastic fibres which allow the alveoli to stretch as they fill with air when breathing in. Spring back during breathing out to expel CO2 rich air

1. 
   external intercostal muscles contract while internal intercostal muscles relax

2. ribs are pulled upwards and outwards, increasing the volume of the thorax

3. diaphragm muscles contract causing it to flatten and volume in thorax increases

4. Pressure is reduced in the lungs below atmospheric pressure

5. air is forced into the lungs

1. external intercostal muscles relax and internal intercostal muscles contract

2. ribs move downwards and inwards, decreasing the volume of the thorax

3. diaphragm muscles relax so it is pushed up again

4. pressure increased in the lungs to greater than atmospheric pressure

5. air forced out lungs

tidal volume x breathing rate

• red blood cells are slowed as they pass through pulmonary capillaries, allowing more time for diffusion

• red blood cells flattened against capillary wall to reduce diffusion distance

• walls of alveoli and capillary are very thin- short diffusion distance

• alveoli and capillaries have a large total surface area

• blood flow through the capillaries maintains a concentration gradient

evidence that one event directly influences or causes another event

when a change in one or two variables is reflected by a change in the other variable

volume of air that enters and leaves lungs at normal resting breath

max volume of air we can inhale and exhale

volume of air left in the lungs after the strongest exhalation

large biological molecules are hydrolysed into smaller molecules that can be absorbed across cell membranes

salivary glands and pancreas

hydrolyses polysaccharides into maltose

hydrolyses single glycosidic bond in sucrose to produce glucose and fructose

hydrolyses single glycosidic bond in lactose to produce glucose and galactose

1. saliva mixed with food during chewing

2. salivary amylase hydrolyses starch to maltose

3. food enters stomach. acid denatures amylase to prevent further hydrolysis of starch

4. passed into small intestine and mixed with pancreatic amylase

5. hydrolyses starch to maltose. Alkaline salts produced by pancreas and small intestine to maintain optimum pH

6. muscles in intestine wall push food along ileum.

7. membrane bound disaccharidase maltase hydrolyses maltose into alpha glucose

1. Lipids are emulsified by bile salts to form micelles. This increases the surface area of lipids so rate of lipase action increases
   2.lipases are produced in the pancreas and hydrolyse the ester bond in lipids to form a monoglyceride and fatty acids

hydrolyse the peptide bonds between amino acids in the central region of a protein molecule

hydrolyse peptide bonds on the terminal amino acids of peptide molecules formed by endopeptidases.

hydrolyse the peptide bonds between dipeptides to produce single amino acids
they are membrane bound

• increase the surface area for diffusion
  -thin walled- reduced diffusion distance

• contain muscles so can move and mix the content of the ileum which help to maintain diffusion gradients

• well supplied with blood vessels that can carry away absorbed molecules-maintains diffusion gradient

• contain microvilli which are fingerlike projections that further increase the surface area

1. micelles contan bile salts/ monoglycerides and fatty acids

2. which make monoglycerides/fatty acids more soluble in water and bring fatty acids/monoglycerides to the lining of the ileum

3. fatty acids/monoglycerides absorbed by diffusion

4. triglycerides reformed in epithelial cells

5. vesicles move to cell membrane

Micelles are important because they transport insoluble lipid molecules (like monoglycerides and fatty acids) across the intestinal lumen to the epithelial cells for absorption during digestion.