3A - Gas exchange Flashcards
What are the main adaptations of gas exchange surfaces?
Large SA.
Thin - short diffusion pathway.
Steep concentration gradient.
Where do single-celled organisms exchange gases?
Across their body.
How do single-celled organisms absorb and release gases?
By diffusion through their outer surface.
Why is there no need for a gas exchange system in single-celled organisms?
Large SA.
Thin - short diffusion pathway.
(Oxygen can take part in biochemical reactions as soon as it diffuses into the cell).
Why system do fish use for exchange?
Counter-current.
Is there a lower concentration of oxygen in air or water?
Water.
Where does water containing oxygen enter and leave a fish?
Enters through the mouth and leaves through the gills.
What is each gill made out of?
Lots of thin plates called gill filaments.
What are the adaptations of gill filaments?
Large SA for gas exchange.
What are gill filaments covered in?
Lamellae.
What do lamellae do?
Increase SA.
What do lamellae have that increases gas exchange?
Lots of blood capillaries and a thin surface layer of cells to speed up diffusion.
What is the counter-current flow system in fish?
Blood flows through the lamellae in one direction and water flows in the opposite direction.
What does the counter-current system help to do?
Maintain a large concentration gradient between the water and the blood. The concentration of oxygen in the water is always higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood.
What do insects use to exchange gases?
Tracheae
What are tracheae?
Microscopic air-filled pipes that insects have.
What is the pathway of air in terrestrial insects?
Spiracles - tracheae - tracheoles
What are spiracles?
Pores on the surface of terrestrial insects.
How does air move into terrestrial insects?
Through pores on the surface called spiracles.
What are the features of the tracheoles?
They have thin permeable walls and go to individual cells meaning that oxygen diffuses directly into the respiring cells.
What aids gas exchange in terrestrial insects?
Mass transport - Rhythmic abdominal movements by flexing body by muscle contraction expanding and compressing system - pressure - valves.
Diffusion gradients along the length of the tracheal system.
What are the problems for multicellular organisms size?
The distance between the exterior and the interior environment are too great for substances to simply diffuse therefore they have had to involve increasingly more intricate systems for exchanging substances with their environment.
How do terrestrial insects respond to high intensity exercise and oxygen debt?
Tracheole ends are filled with water and as lactic acid is soluble, it dissolves in the water, reducing water potential so that water moves into the cells which therefore reduces water potential in the tracheole ends so extends reach of air into the tissues.
How do terrestrial insects conserve water?
Close spiracles.
Why do terrestrial insects need to regulate water content?
So that they don’t become dessicated.
What doesn’t the skin of fish allow?
Diffusion of gases as it acts as a watertight barrier.
Do fish have a high or low SA:V?
Low as they are bigger than insects.
Where do fish obtain their oxygen from?
The water
What covers the opercular cavity in fish?
The operculum.
What is the operculum?
Covers the opercular cavity in fish.
How does a partially permeable membrane aid exchange?
Allows selected materials to diffuse easily.
How does the movement of external medium (air) aid exchange?
To maintain a diffusion gradient.
How does the movement of internal medium (blood) aid exchange?
To maintain a diffusion gradient.
What gases do leaves need to exchange?
Carbon dioxide and oxygen.
Where do dicotyledonous plants exchange gases?
At the surface of the mesophyll cells.
What do plants need oxygen for?
Respiration
What do plants need carbon dioxide for?
Photosynthesis
What is the main gas exchange surface in plants?
Spongy mesophyll.
How do gases move into a leaf?
Via stomata
What are the features of a leaf that make them good for gas exchange?
Large SA:V - air spaces in leaf, numerous cells.
Very thin - short diffusion pathway.
Partially permeable cell membrane.
Moist inside leaf - dissolve gases.
Steep concentration gradient of carbon dioxide.
What phase does gas exchange occur in in plants?
Gas phase as it is faster than in other phases such as the water phase.
What adaptations do leaves have for gas exchange?
Stomata, interconnecting airspaces throughout the mesophyll layer, large SA of mesophyll cells.
What is the function of the waxy cuticle?
Controls water loss as it is made of lipids which are insoluble.
What is the function of the upper epidermis?
Protection
What is the function of the palisade mesophyll?
Site of photosynthesis (has lots of chloroplasts).
What is the function of the spongy mesophyll?
Increases SA and is the site of gas circulation in air spaces (gas exchange).
What is the function of the lower epidermis?
Protection and has stomata for air to enter.
What is the function of the stomata?
Where air enters for gas exchange.
What is the function of the guard cells?
Control the opening/closing of the stomata.
What are stomata?
Each stomata is a minute pore surrounded by 2 guard cells.
Where are most of the stomata on a leaf?
Lower epidermis.
How do stomata close to reduce water loss?
- Potassium ions pumped out of guard cell.
- Solute potential outside of guard cell increases.
- Water potential outside of guard cell decreases.
- Water moves by osmosis out of the guard cell.
- Guard cell becomes flaccid and less curved.
- The stomatal pore closes reducing air flow in and out of the leaf, reducing transpiration.
How do stomata open?
- Potassium ions pumped into guard cell.
- Solute potential outside of guard cell decreases.
- Water potential outside of guard cell increases.
- Water moves by osmosis into the guard cell.
- Guard cell becomes turgid and more curved.
- The stomatal pore opens increasing air flow in and out of the leaf, increasing transpiration.
What happens to gas exchange when photosynthesis is happening?
Carbon dioxide mostly from external air moves into the plant.
Oxygen produced is used in respiration but most diffuses out of the plant.
What happens to gas exchange when photosynthesis is not happening?
In the dark, oxygen diffuses into the leaf as it is constantly being used by cells in respiration.
Carbon dioxide produced by respiration diffuses out.
What are xerophytes?
Plants adapted to a dry habitat E.g. cacti or marram grass.
What are adaptations of xerophytes?
Stomata sunk in pits that trap moist air reducing the concentration gradient of water.
Layer of ‘hairs’ on the epidermis trap moist air.
Curled leaves with the stomata inside protecting them from the wind (wind increases diffusion and evaporation).
Reduced number of stomata so fewer places for water to escape.
Waxy, waterproof cuticles on leaves and stems to reduce evaporation.
Reduced SA:V ratio of the leaves.
