6.1 - 6.8 Exchange Flashcards
List the two ways exchange can take place
- Passively (No energy required e.g osmosis and diffusion)
- Actively (Energy required e.g active transport)
List some adaptations of an exchange surface and their purposes
- A large SA:vol, increase rate of exchange
- Very thin, shorter diffusion distance
- Selectively permeable, to allow selected materials to cross
- Movement of environmental medium, maintain concentration gradient
- A transport system, ensure movement of internal medium and maintain concentration gradient
Explain how gas exchange in single-celled organisms works
- Large SA:Volume ratio
- O₂ is moved in and CO₂ moved out by diffusion
Explain how gas exchange takes place in an insect
- Gases enter trachea through spiracles on the body surface
- Gases travel through trachea as they divide into smaller tubes called tracheoles which extend throughout all body tissue
- Gases diffuse into and out of tissue cells
Explain why gas exchange can take place in an insect
- Along a diffusion gradient
- Mass transport, the contraction of muscles can squeeze the trachea to force the movement of respiratory gases
- Ends of tracheoles filled with water
Explain why the end of tracheoles being filled with water assists with gas exchange
- When there is a lot of activity, cells carry out some anaerobic respiration
- This produces lactic acid which lowers the water potential of the cells
- Water moves out from ends of tracheoles and into cells
- Decreases volume of water in ends of tracheoles and draws air into them
Explain why the opening and closing of spiracles is important
- Opening is necessary for gas exchange
- Closing is necessary to reduce water loss
Describe the counter-current exchange principle of gas exchange in fish
- Blood and water flow over the gill lamellae in opposite direction
- Blood that is already well loaded with oxygen meets water, which has its maximum concentration of oxygen. Therefore diffusion of oxygen from water to blood takes place.
- Blood with little oxygen meets water which has most of its oxygen removed. Therefore diffusion of oxygen from water to blood takes place.
- This system allows diffusion gradient to be maintained the full length of the gill lamellae
Describe how leaves are adapted for gas exchange
- Thin leaf for short diffusion distance
- Diffusion takes place in gas phase (air), which is more rapid than if it were in water
- Stomata allow gases in and out of leaf
- Plenty of stomata so short diffusion pathway
- Many interconnecting air spaces in mesophyll so larger SA for gases to come into contact with mesophyll cells
- Large SA of mesophyll cells
List the 5 adaptations leaves use to conserve water
- Thick cuticle
- Hairy leaves
- Stomata in pits or grooves
- Reduced SA:Vol
- Rolling up of leaves
Describe how a leaf’s thick cuticle helps it conserve water
- Waterproof barrier
- Thicker cuticle, less water escapes
Describe how a plant’s hairy leaves helps it conserve water
- Traps moist air next to leaf
- Reduces water potential gradient so less water is lost via evaporation
Describe how a leaf’s stomata in pits and grooves helps it conserve water
- Traps moist air next to leaf
- Reduces water potential gradient so less water is lost via evaporation
Describe how a leaf’s reduced SA:Volume helps it conserve water
- Reduced water loss via evaporation
- Does have to be balanced with the need for SA for photosynthesis
Describe how a leaf rolling up helps it conserve water
- Traps a region of still air inside next lower epidermis (where most stomata are)
- This area becomes saturated with water and so has a very high water potential
- This means there is no water potential gradient between inside and out so no water is lost
