Gaseous Exchange Flashcards
Define gaseous exchange
Uptake of molecular oxygen from the environment and discharge of carbon dioxide to the environment by cells
What is a respiratory medium?
The source of oxygen
(Air for land animals, water for aquatic)
What is a respiratory surface?
The boundary between the external environment and body interior
Define ventilation
Movement of air between the gas exchange medium and respiratory system to maintain appropriate concentrations of oxygen and carbon dioxide in the body.
Define respiration
Chemical reactions by which food is broken down to release energy in cells
Compare the suitability of air and water as a gas exchange media in animals
- Air is richer than water in oxygen
- Air has a lower density and is less viscous than water
- Air has a dehydrating effect on surfaces
- Slight temperature increase causes oxygen to diffuse out of water while oxygen in air remains relatively stable
- Water’s high density prevents collapse of respiratory structures such as gill filaments while in absence of lung surfactants alveolar sacs collapse
- Unidirectional water flow during ventilation in aquatic animals is energetically less costly than tidal ventilation in lungs
- Countercurrent flow of water with respect to blood flow over gill lamellae improves oxygen extraction efficiency
- Carbon dioxide is highly soluble in water making it easier to eliminate than in air
Why does a fish placed out of water soon suffocate?
- The gill lamellae lack structural strength and rely on water for their support thus in air its gills collapse into a mass of tissue reducing the diffusion surface area of the gills
- Gill lamellae surface dries and oxygen in air fails to dissolve and diffuse into blood
State Fick’s law
The rate of diffusion is proportional to the surface area across which diffusion occurs and inversely proportional to the square of the distance through which molecules must move
Give the significance of large organisms having a small surface area to volume ratio
- Small SA/V ratio decreases the rate of gaining unwanted substances eg toxic substances
- Enables slow heat loss during cold weather
- Causes slow entry of useful substances eg oxygen
-Causes slow heat loss during hot weather
How do organisms minimize the limitations of body sizes?
Small organisms:
- Live in habitats where harmful substances easily get diluted before harming the body
- Allowing body enzyme systems function at varying temperatures
Large organisms:
-Development of an efficient transport system
- Improved oxygen carriage by pigments
- Development of ventilation mechanisms
- High metabolic rate
Give characteristics of effective gaseous exchange surfaces
- Large SA/V ratio
- Thin
- Moist
- Permeable to respiratory gases
- Operated in a way that maintains a high concentration gradient
Define non-directional ventilation
Passive process by which respiratory medium flows past gas exchange surface in an unpredictable pattern.
Passive ventilation relies on water and air currents
Eg skin breathers like toads, earthworms
Define bi-directional (tidal) ventilation
Active mechanism by which external medium moves in and out of respiratory system in a back and forth movement.
For example tidal ventilation
Occurs in;
Lung breathers like mammals, amphibians, etc
Define unidirectional ventilation
Active mechanism by which respiratory medium flows in at one point, and exits via another.
[Blood flow relative to medium flow]
(1) Same Direction- Concurrent eg dogfish, shark
(2) Opposite Direction- Countercurrent eg bony fish
(3) At an angle- Crosscurrent eg bird lungs
Why do Air breathers use bi-directional ventilation while water breathers use unidirectional ventilation?
Air breathers use bi-directional ventilation since air has low density and is less viscous while water breathers use unidirectional flow to save respiratory energy.
Give adaptations of the cell surface membrane as the gas exchange surface of unicellular organisms like amoeba
• The cell surface membrane has a sufficiently large surface area to volume ratio enables efficient diffusion of gases.
• Being aquatic, the cell membrane is always moist to dissolve respiratory gases to enable their diffusion.
• The cell surface membrane is permeable to respiratory gases
What adaptations does the earthworm have to using its entire body surface (skin) as a gas exchange surface?
• Skin surface is moist to enable dissolving of respiratory gases for efficient diffusion.
• Skin is thin to reduce the diffusion distance such that there is increased rate of diffusion of respiratory gases.
• The epidermal tissue is highly vascular to deliver and carry respiratory gases such that a high concentration gradient for the gases is maintained
Give the advantages and disadvantages of external gills in tadpoles and lugworms
- Increased surface area for diffusion
- They offer great resistance because they are highly branched, hence external gills are ineffective except in smaller animals.
- Easily get damaged since the thin epithelium required for gas exchange is thin and delicate.
Adaptations of the gas exchange site in insects include?
• Tracheae are kept open by circular bands of chitin to enable continual air movement to reach and leave tracheoles.
• Tracheae highly branch to form tracheoles that reach every cell to ventilate respiring cells directly.
• Tracheoles are moist to enable dissolution of respiratory gases for increasing their diffusion.
• Tracheae are impermeable to gases to maintain a high diffusion gradient in the air that reaches the tracheoles.
State the adaptations of gill filaments in bony fish to their functions
• Gill filaments have folds called secondary lamellae that increase the surface area for gas exchange.
• The gill lamellae contain a network of capillaries for carrying away oxygen or bringing in Carbon dioxide for expulsion.
• There is counter current flow i.e. water and blood in the gills flow in opposite directions to maintain a favourable concentration gradient for diffusion of respiratory gases.
• Gill filaments are moist to enable dissolution of respiratory gases for efficient diffusion.
• Gills filaments are thin-walled to provide a short distance for diffusion of respiratory gases.
• Tips of adjacent gill filaments overlap = increases the resistance to the flow of water over gill surfaces and slows down the movement of water= more time for gaseous exchange to take place
Give adaptations of the lungs to gas exchange
• Lungs have many saccular alveoli which provide a large surface area for gas exchange.
• Diffusion of respiratory gases is made faster by the shortened distance due to (1) alveoli and capillary walls being only one cell thick
(2) epithelial cells are flattened so are very thin
(3) capillaries are pressed against alveoli.
• The moistened alveolar surface enables dissolution of respiratory gases to increase the rate of diffusion.
• Alveolar surface is internal to reduce water evaporation.
• High concentration gradients of the gases, maintained by ventilation and flow of blood in the extensive capillary network.
• Air is warmed as it passes through the nostrils, to increase diffusion rate.
What are the adaptations of the gas exchange structures of plants to their function?
• When the stomata open, production and consumption of oxygen and carbon dioxide in the leaf is sufficient to maintain a concentration gradient steep enough to facilitate gas exchange with the atmosphere.
• Large intercellular air filled spaces in the spongy mesophyll act as a reservoir for gaseous exchange.
• The cortical air spaces of roots and stems are continuous up and down and also in a sideways direction, thus allowing gas transport throughout the stem and root tissues.
• Root hairs lack a waxy cuticle and have moist surfaces to facilitate rapid diffusion of gases through the cell wall.
• Mangrove species that grow in water logged soils with less air content develop breathing roots above the ground level to increase gas exchange.
• Root hairs are numerous to increase the surface area for gas exchange.
• In the stem, lenticels consist of loosely packed cells at the opening to enable diffusion of respiratory gases.
Describe gaseous exchange in unicellular organisms such as protozoa e.g. amoeba
The medium of gas exchange is fresh water and the gas exchange surface is the plasma membrane.
Along their concentration gradients, dissolved oxygen diffuses from the water across the permeable plasma membrane into the cytoplasm while dissolved carbon dioxide diffuses into water.
Describe gaseous exchange in Spirogyra
In filamentous algae, the medium of gas exchange is fresh water and gas exchange occurs across the plasma membrane by diffusion.
(i) In the dark, no photosynthesis occurs in the chloroplast, no oxygen is made. Dissolved oxygen diffuses from the water across the cell membrane into the mitochondria while dissolved carbon dioxide diffuses into water, along their concentration gradients.
(ii) In the light, photosynthesis in chloroplasts releases oxygen, some of which diffuses into the mitochondria, the excess diffuses out.
Describe gas exchange in plants
In plants, different structures (roots, stems, leaves, flowers, fruits) care for their own gas exchange needs; therefore the medium of gas exchange varies depending on environmental location of each plant part.
Plants respire all the time, but photosynthesis only occurs when there is light.
This means that the net gas exchange from a leaf depends on the light intensity.
What is net gas exchange in plants dependent on?
Light intensity
In darkness no photosynthesis occurs, hence in the absence of photosynthesis there is a net release of carbon dioxide and a net uptake of oxygen.
In bright light during the day, the rate of photosynthesis is much higher than the rate of respiration hence there is a net release of oxygen and a net uptake of carbon dioxide
In Dim light during early morning and evening, photosynthesis greatly decreases hence the release of oxygen also decreases while respiration occurs normally hence the release of carbon dioxide increases causing compensation point.