Adaptations for gas exchange in animals

Counter-current flow

• blood + water flow in opposite directions across the gill plate

• steep diffusion gradient maintained, allowing diffusion of oxygen across the whole gill plate

• high rate of diffusion

• more efficient as more oxygen absorbed into the blood

• found in bony fish

Parallel flow

• water + blood flow in the same direction across the gill plate

• diffusion gradient not maintained so diffusion of oxygen doesn’t occur across the whole plate

• lower rate of diffusion

• less efficient as less oxygen absorbed into the blood

• found in cartilaginous fish

Gas exchange mechanism in Amoeba

• unicellular organism with a large SA to V ratio

• thin cell membrane provides short diffusion distance

• simple diffusion across the cell surface membrane is sufficient to meet the demands of respiratory processes

Gas exchange mechanism in flatworms

• multicellular organisms with a relatively small SA to V ratio

• flat structure provides a large SA and reduces the diffusion distance

• simple diffusion is sufficient to meet the demands of respiratory processes

Gas exchange mechanism in earthworms

• cylindrical, multicellular organisms with a relatively small SA to volume ratio

• slow moving and low metabolic rate so require little oxygen

• rely on external surface for gas exchange

• circulatory system transports oxygen to the tissues and removes CO2, maintaining a steep diffusion gradient

Name and describe the main features of an insect’s gas transport system

• spiracles - small, external openings along the thorax + abdomen through which air enters, and air and water leave the gas exchange system

• tracheae - large tubes extending through all body tissues, supported by rings of chitin to prevent collapse

• tracheoles - smaller branches dividing off the tracheae

Describe the adaptations of the insect tracheal system to a terrestrial environment

• spiracles can be opened or closed to regulate diffusion

• bodily contractions speed up the movement of air through the spiracles

• highly branched tracheoles provide a large surface area

• impermeable cuticle reduces water loss by evaporation

Describe the ventilation of the tracheal system in insects

• expansion of the abdomen opens the thorax spiracles and closes the abdominal spiracles

• compression of the abdomen closes the thorax spiracles and opens the abdominal spiracles

Compare the gas exchange surface of an active and inactive amphibian

• active amphibian has simple lungs

• inactive amphibian relies on its moist external surface for gas exchange

Ventilation

the movement of fresh air into a space and stale air out of a space to maintain a steep concentration gradient of oxygen and carbon dioxide

Gas exchange in fish

occurs in the gills between oxygenated water and deoxygenated blood

Gill filaments

• main sites of gaseous exchange in fish, over which water flows

• overlap to increase resistance to flowing water - slowing it down and maximising gaseous exchange

• found in large stacks, gill plates, and have gill lamellae which provide a large SA and good blood supply for exchange

Ventilation in bony fish

• buccal cavity volume increases and pressure decreases to enable water to flow in

• contraction of the buccal cavity forces water across the gills

• pressure in the gill cavity rises, opening the operculum

• water leaves

Inspiration in mammals

• external intercostal muscles contract, raising the ribcage

• diaphragm muscles contract so it flattens

• outer pleural membrane moves out, reducing pleural

Expiration in mammals

external intercostal muscles relax, ribs move downwards and inwards, diaphragm muscles relax so it domes upwards, thorax volume decreases, pressure in lungs increases, air pressure in lungs greater than atmospheric pressure so air forced out of the lungs.

How are mammals adapted for gas exchange

alveoli provide a large SA + thin diffusion pathway, maximising the volume of oxygen absorbed from one breath. They also have a plentiful supply of deoxygenated blood, maintaining a steep concentration gradient

Describe the structure + function of the larynx

a hollow, tubular structure located at the top of the trachea involved in breathing and phonation

Describe the trachea and its function in the mammalian gaseous exchange system

• primary airway, carries air from the nasal cavity down into the chest

• wide tube supported by C-shaped cartilage to keep the air passage open during pressure changes

• lined by ciliated epithelial cells which move mucus, produced by goblet cells, towards the back of the throat to be swallowed - preventing lung infections

Describe the structure of the bronchi

• divisions of the trachea that lead into the lungs

• narrower than the trachea

• supported by rings of cartilage and lined by ciliated epithelial cells and goblet cells

Describe the structure and function of the bronchioles

• many small divisions of the bronchi that allow the passage of air into the alveoli

• contain smooth muscle to restrict airflow to the lungs but don’t have cartilage

• lined with a thin layer of ciliated epithelial cells

Describe the alveoli in the mammalian gaseous exchange system

• mini air sacs, lined with epithelial cells

• walls 1 cell thick

• good blood supply to maintain a steep diffusion gradient

• 300 million in each lung

What are the pleural membranes and what do they do

thin, moist layers of tissue surrounding the pleural cavity that reduce friction between the lungs and the inner chest wall

What are internal intercostal muscles

a set of muscles found between the ribs on the inside that are involved in forced exhalation

What are external intercostal muscles

a set of muscles found between the ribs on the outside that are involved in forced and quiet inhalation

How does an organism’s size relate to its surface area to volume ratio

the larger the organism, the lower the surface area to volume ratio

How does SA to V ratio affect transport of molecules

the lower the SA to V ratio, the further the distance molecules must travel to reach all parts of the organism. Diffusion alone is not sufficient in organisms with small SA to V ratios.

Why do larger organisms require mass transport + specialised gas exchange surfaces

• small SA to V ratio

• diffusion insufficient to provide all cells with the required oxygen and to remove all CO2

• Large organisms more active than smaller organisms

4 features of an efficient gas exchange surface

• large SA

• short diffusion distance

• steep diffusion gradient

• ventilation mechanism