Gas exchange Flashcards
Describe the relationship between SA:VOL and what does this mean for organisms?
Smaller organisms have a larger SA:VOL for sufficient exchange across outer surface by simple diffusion, for example: amoeba bacteria. Larger organisms have a smaller SA:VOL. As organisms get larger, SA:VOL decreases- the volume increases more than the surface area, so simple diffusion across outer surface can only meet needs of inactive organisms with a low metabolic rate. Larger organisms are more metabolically active, which requires oxygen to be up taken at a faster rate. Larger organisms therefore require one of the following: a flattened shape and/or specialised gas exchange surfaces with large surface areas, plus a transport system.
What are the 5 characteristics of exchange surfaces?
- Large surface area to increase rate of exchange.
- Very thin so diffusion distance is short.
- Selectively permeable to only allow selected materials across.
- Movement of externalmedium to maintain diffusion gradient.
- Movement of internal medium to maintain diffusion gradient.
Describe the pathway for gas exchange in a leaf.
Oxygen will diffuse from the palisade mesophyll through the spongy mesophyll into the air space through the stomata down a diffusion gradient.
Describe and explain how the movement of external medium improves gas exchange in plants
Air movements around the leaf help to maintain concentration gradients. CO2 enters through the stomata by diffusion (down a concentration gradient). Diffuses through air spaces, which allows faster diffusion.
Describe and explain how a short diffusion pathway improves gas exchange in plants
Leaves and cell walls are very thin to provide short diffusion pathway.
Describe and explain how selectively permeability improves gas exchange in plants.
Cell surface membrane is selectively permeable allowinh CO2 and O2 diffuse freely across the membrane.
Describe and explain how a large SA:VOL ratio improves gas exchange in plants.
Leaves have a large internal surface area to volume ratio. They have a broad and flat shape. Large number of stomata provides a large surface area. Guard cells open stomata.
Describe and explain how movement of internal medium improves gas exchange in plants
CO2 is used for photosynthesis which keeps concentration of CO2 in the cell low, maintaining the concentration gradient.
Describe and explain the adaptation in xerophytes that provides a bigger diffusion pathway, a small surface area and selective permeability.
Thicker, waxy cuticle: waterproof to reduce evaporation as impermeable / increase in diffusion distance.
Describe and explain the adaptations in xerophytes that provide a small surface area (4 points)
- Guard cells can close the stomata which prevents diffusion of water vapour out of the leaf.
- Reduced number of stomata, which reduces surface area that water can be lost through, so reduced evaporation/transpiration.
- Leaves are reduced to spine which reduces surface area of leaf.
- Shallow roots to absorb surface water, and deep roots ro reach the water.
- Reduced
Describe and explain the adaptation of xerophytes for movement of the external medium (3 points).
- Sunken stomata and hairs: traps water vapour, increases humidity, reduces water vapour potential gradient.
- Exchange surface is inside the leaf and the mesophyll cell walls are moist, evaporated into air spaces which are now saturated with water vapour: high water vapour potential, reducing concentration gradients so less water evaporates/diffuses out of cell.
- Curled leaves: traps moist air, increases humidity, reduces water vapour potential gradient.
Describe and explain how the movement of external medium improves gase xchange in insects (2 points).
- Abdominal pumping- muscular contractions in the abdomen helps with ventilation so more oxygen enters, maintaining a diffusion gradient.
- Air movements around the opening of the tracheoles help to maintain concentration gradient. Oxygen diffuses in down a concentration gradient, lower in the tissues where it is used in aerobic respiration.
Describe and explain how a short diffusion pathway improves gas exchange in insects.
Tracheoles branch deep into tissue so no cell is far from source of oxygen, short diffusion pathway as diffusion through muscle is slow. trachea/tracheoles filled with air so fast diffusion.
Describe and explain how selective permeability improves gas exchange in insects.
Cell surface membrane is selectively permeable allowing CO2 and O2 to diffuse freely across the mmebrane.
Describe and explain how a large surace area improves gas exchange in insects.
There are multiple spiracles located along the abdomen (opening to the trachea). Tracheoles heavily branched to increase surface area. Ends of tracheoles are filled with fluid. In flight, lactic acid produced in the muscles, draws the fluid out by osmosis, increases the surface area for exchange and speeding up diffusion as it is through a gaseous medium.
Describe and explain how the movement of internal medium improves gas exchange in insects.
Respiring cells use up oxygen, resulting in there being a higher concetrtion of crabon dioc=xide in the cytoplasm (internal medium) than in the air (external medium). This helps to maintain concentration gradients between the air and cells.
Describe the structures and explain the functions of these structures within insects that reduce water loss (4 points).
- Exoskeleton is waxy so is waterproof.
- Spiracles to prevent water loss.
- Spiracles only open when CO2 reaches a critical level and can open independently.
- Spiracles can be sunken, and/or surrounded by hair, traps a layer of moisture, reducing air movements, and reducing the water potential gradient.
