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 surface area to volume (SA/V) ratio affect transport of molecules?
The lower the SA/V ratio, the further the distance molecules must travel to reach all part of the organism. Diffusion alone is not sufficient in organisms with small SA/V ratios.
Why do larger organisms require mass transport and specialised gas exchange surfaces?
- Small SA/V ratio.
- Diffusion insufficient to provide all cells with the required oxygen and to remove all carbon dioxide.
- Large organisms more active than smaller organisms.
Name four features of an efficient gas exchange surface.
- Large surface area
- Short diffusion distance
- Steep diffusion gradient
- Ventilation mechanism
Describe the gas exchange mechanism in Amoeba.
- Unicellular organism with a large SA/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.
Describe the gas exchange mechanism in flatworms.
- Multicellular organisms with a relatively small SA/V ratio (in comparison to Amoeba).
- However, flat structure provides a large surface area and reduces the diffusion distance.
- Simple diffusion is sufficient to meet the demands of respiratory processes.
Describe the gas exchange mechanism in earthworms.
- Cylindrical, multicellular organisms with a relatively small SA/V ratio (in comparison to the flatworm).
- 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 carbon dioxide, maintaining a steep diffusion gradient.
Define 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.
Name the organ of gaseous exchange in fish.
Gills.
What are gill filaments?
- Main site of gaseous exchange in fish, over which water flows.
- They overlap to increase resistance to flowing water (slowing it down and maximizing gaseous exchange).
- Found in large sacks, know as gill plates, and have a gill lamellae which provide a large surface area and good blood supply for exchange.
Explain the process of 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.
How is a steep diffusion gradient maintained across the entire gas exchange surface in bony fish?
Due to counter current flow.
Define counter current flow.
Blood and water flow in opposite directions across the gill plate.
How does countercurrent flow maintain a steep diffusion gradient? What is the advantage of this?
- Water is always next to blood of a lower oxygen concentration.
- Keeps rate of diffusion constant and enables 80% of available oxygen to be absorbed.
What type of flow is exhibited in cartilaginous fish?
Parallel flow.
Define parallel flow.
Water and blood flow in the same direction across the gill plate.
Name and describe the main features of an insect’s gas transport system.
- Spiracles: small, external openings along the thorax and 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.
What is the main site of gas exchange in insects?
Tracheoles.
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 branches 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 (through which air enters) and closes the abdominal spiracles.
- Compression of the abdomen closes the thorax spricales and opens the abdominal spiracles (through which air is expelled).
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.
How are mammals adapted for gas exchange?
Alveoli provide a large surface area and thin diffusion pathways, 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 and 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 with ciliated epithelial cells which move mucus, produced by goblet cells, towards the back of the throat to be swallowed, this prevents lung infections.
