3.3.2 - Gas Exchange

What is the definition of breathing (ventilation)?

The movement of air in and out of the lungs

What is the definition of respiration?

A chemical reaction that releases energy in the form of ATP

What is the definition of gaseous exchange?

• The diffusion of oxygen from the air into the blood in the alveoli

• The diffusion of carbon dioxide from the blood into the air in the alveoli

What 3 features do gas exchange surfaces have?

• Large surface area : volume ratio

• Short diffusion distance

• A maintained concentration gradient

What is Fick’s Law

How is the alveoli adapted for gas exchange?

• 300 million alveoli in each lung which increases surface area

• The alveoli epithelial cells are very thin to minimise diffusion distance

• Surrounded by capillaries therefore maintains a concentration gradient

Where does gas exchange take place in fish?

The lamella in the gills

a) What adaptation have fish produced to enable diffusion to occur?

Countercurrent flow

b) What is this adaptation?

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

What is the anatomy of the fish gills?

• There are 4 layers of gills made up of stacks of gill filaments

• Each gill filament is covered in gill lamellae, perpendicular to the filaments

How is a short diffusion distance maintained in gills?

• Because the gill lamellae are very thin

• Every gill lamellae has a capillary network which comes into contact with the water therefore a short diffusion distance

How does countercurrent flow maintain a diffusion gradient across the entire length of the gill lamellae?

Insects have a hard exoskeleton, how is this an advantage? (2 points)

• For protection

• Prevents water loss

What does the tracheal system consist of? (3 points)

• Trachea

• Tracheoles

• Spiracles

What are spiracles and what are their function?

Round openings running along the abdomen. Oxygen and carbon dioxide enter and leave via the spiracles

What is the trachea?

The network of internal tubes in the body which have rings within them to keep them open

What are tracheoles and what function do they serve?

Smaller tubes attached to the trachea that go deeper into the abdomen extending throughout all tissues to deliver oxygen to all respiring cells

How are the tracheoles adapted for gas exchange? (3 points)

• Thin walls so short diffusion distance to cells

• Highly branched providing a short diffusion distance

• Highly branched providing a large surface area

At rest, how does gas exchange take place in an insect?

Diffusion is the main method of gas exchange - a steep concentration gradient is created when the cells respire using up oxygen and producing carbon dioxide

During periods of high activity, how does gas exchange take place?

The insect will undergo rhythmic abdominal movements, which actively moves air in and out of the tracheal system maintaining the diffusion gradient for oxygen and carbon dioxide

During periods of very intense activity, how does gas exchange take place?

Anaerobic respiration takes place producing lactic acid. This lowers the water potential of muscle cells causing water at the end of the tracheoles to move into the cells via osmosis. This reduces the volume of fluid in the tracheoles so gases diffuse quicker.

What is digestion?

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

How are carbohydrates hydrolysed in the mouth?

Amylase is secreted by the salivary glands and hydrolyses polysaccharides into disaccharides

Where does the pancreas secrete more amylase and why?

• In the duodenum (top of the small intestine)

• Because the stomach acid denatures the amylase that is present

Once the carbohydrates have been hydrolysed into disaccharides and travelled through the stomach, where are they hydrolysed again?

The ileum

What enzymes hydrolyse disaccharides?

Membrane-bound disaccharidases

eg:

Sucrase - Sucrose

Maltase - Maltose

Lactase - Lactose

How many enzymes are capable of hydrolysing a protein?

3 - Exopeptidase, Endopeptidase, Dipeptidase

What does endopeptidase hydrolyse?

Peptide bonds in the middle of a polymer chain producing smaller chains

What does exopeptidase hydrolyse?

Peptide bonds at the end of a polymer chain - terminal peptide bonds

Why does endopeptidase increase rate of hydrolysis for exopeptidase?

Because endopeptidase increases the number of exposed ends for exopeptidase to hydrolyse terminal peptide bonds

What do dipeptidases hydrolyse?

Any remaining dipeptides into amino acids

Where are the 3 types of enzymes for proteins found?

• Endopeptidase - Stomach/Duodenum

• Exopeptidase - Stomach/Duodenum

• Dipeptidase - Ileum

What 2 things hydrolyse lipids?

• Lipase

• Bile Salts

Where is lipase produced and secreted?

Produced - Pancreas

Secreted - Duodenum

What does lipase hydrolyse triglycerides into?

It hydrolyses the ester bond in triglycerides into monoglycerides, glycerol and fatty acids

Where are bile salts produced and released?

• Produced - liver

• Released - gall bladder then duodenum

What are the function of bile salts? (2 points)

• They emulsify lipids to form lipid droplets to increase the surface area for lipase to hydrolyse lipids

• They make micelles water-soluble

What are micelles?

Water-soluble vesicles

How do micelles help with lipid absorption?

• Makes fatty acids more soluble in water which allows the micelles to move them towards the surface membrane

• They carry and then release fatty acids to the ileum lining helping maintain a high concentration gradient so fatty acids diffuse down the concentration gradient into the epithelial cell via simple diffusion

Once fatty acids are absorbed into the ileum what do they reform into?

Triglycerides

Where are triglycerides reformed?

In the golgi body

Once triglycerides are reformed, what happens?

They are packaged into vesicles, allowing them to move to the opposite cell membrane. Then the vesicle releases the triglyceride where it then enters a lacteal

How are glucose and amino acids absorbed into the blood?

Via co-transport