U2T1ab - Principles of Exchange & Transport Flashcards
What 2 things do cells need to be able to do?
Obtain essential substances and remove waste.
Where does exchange take place in unicellular organisms?
Through the cell surface membrane.
How does exchange take place in multicellular organisms?
They have specialised exchange surfaces. More complex have a transport system which links the exchange surface to the cells throughout the organism. e.g. gills. This increases rate of substance exchange to meet greater metabolic need. Metabolites supplied by surrounding environment.
What does rate of exchange of substances depend on?
Surface area.
What does the requirement of metabolites depend on?
The volume of metabolically active tissue in an organism.
Describe how surface area and volume are related as an organism increases in size.
As an organism gets bigger, so does surface area and volume. However, volume increases much more than SA.
As an organism increases in size, how does their surface area to volume ratio change? What does this mean?
SA/V ratio decreases. Small organisms can get all requirements + remove waste through body surface. (CSM) Larger organisms don’t have a big enough SA to meet metabolic needs of larger num of cells in larger volume. Larger num cells aren’t in direct contact with surrounding environment. Rate of diffusion will be too slow. Smaller = higher ratio. Larger = lower ratio. Cube illustration.
What are 5 key features of exchange surfaces?
Large surface area relative to volume so gas exchange occurs rapidly, thin membrane to allow for short diffusion pathway for rapid diffusion, large concentration gradient + moist surface so gases can dissolve first + permeable to O2 + CO2.
How do some smaller organisms increase surface area and what are the benefits of this?
Flattened shape. (flatworm) Increase SA/V ratio. Allows more diffusion of respiratory gases more quickly so don’t need a specialised respiratory exchange surface. Also decreases diffusion distance.
What is required for the diffusion of gases?
A moist surface.
What are the 2 types of specialised exchange surfaces? (e.g.s) How do they increase SA?
External (folded external membrane of external gills in tadpoles or internal (alveoli in lungs + fish gills). Large SA as they are folded.
How does a thin exchange surface help?
Short diffusion pathway. e.g. Alveoli + blood capillary walls are 1 cell thick so oxygen only has to diffuse through 2 layers. Max diffusion rate.
How does a large concentration gradient help?
Diffusion only happens where a concentration gradient exists. Larger organisms have a ventilation system to maintain a high O2 conc in lungs so O2 blood constantly moving away from alveoli. Low O2 in cells + high in atmosphere gives conc gradient.
How are root hair cells adapted to increase SA?
Hair like extensions from epidermis. Required because O2 is necessary for respiration to provide ATP for active transport of mineral ions into root hair cells. Ions can also go in by facilitated diffusion.
How are erythrocytes adapted for exchange?
Biconcave to increase SA/V ratio for O2 uptake + also ensures short diffusion distance to haem. No nucleus, tightly packed haemoglobin. Conc gradient between alveolus + capillary maintained as transported in blood away from lungs. Increase SA.
How are fish gills adapted for exchange?
Extensively folded internal membranes + feathery filaments with secondary lamellae which are 1 cell thick. Rich blood supply + water pumped over to counter-current blood.
How is the leaf mesophyll adapted for exchange?
Loosely arranged cells with air spaces, thin, stoma open + close. Stomatal pores allow diffusion of CO2, as do air spaces.
How are blood capillaries adapted for exchange?
Very narrow, sit tight against alveolar walls + flow of blood through capillaries maintains conc gradient. RBCs squeeze through so on contact with wall, reducing diffusion pathway.
How does the transport of substances within large organisms happen?
Mass Flow
What 5 factors affect the rate of gas exchange?
Large surface area, moist surface, diffusion gradients for O2 + CO2, permeable to O2 + CO2 + short diffusion pathway (thin).
Finish these sentences:
As surface area increases, rate of diffusion —-.
As conc gradient increases, ROD ___.
As membrane thickness increases, ROD —-.
Increases, increases, decreases.
In plants, what is the dominant process during these times:
Midday, midnight.
Photosynthesis, respiration.
At what kind of light intensity might you find the compensation point?
Low light.
What is necessary for a plant to grow?
Carb being produced by plant in photosynthesis must be more than carb loss in respiration. Over 24 hours, net intake of CO2 must be greater than net produced of CO2.
How does the leaf minimise the diffusion pathway for gases?
Being thin, cells in spongy mesophyll are loosely arranged creating air spaces and large surface area. SM cells are large + moist. Stomata + guard cells open + close.
What forms the gaseous exchange surface in the leaf?
Cell-surface membrane of spongy mesophyll layer.
What is the purpose of closing stomata at night?
Reduces water loss by transpiration. Guard cells change shape depending on whether cells are turgid or not. Guard cells contain chloroplasts.
What does the mammalian respiratory system allow?
Mass flow of gases into an organism and maintaining diffusion gradient. Exchange surface is the alveolar wall.
What are some of the features of a gaseous exchange surface in animals?
Large surface area (700 million alveoli), thin respiratory membrane, alveoli lined with 1 layer of simple squamous epithelium + capillaries right next to them with 1 layer endothelial cells, creating short diffusion pathway. Inner alveoli surface is moist to aid gaseous diffusion, in moisture layer there’s a lung surfactant, phospholipid rich substance which helps reduce surface tension of alveoli so they can flex easily as lungs inflate + deflate. Vast capillary system surrounds alveoli, each is fed by branch of pulmonary artery + drained by branch of pulmonary vein. Constant flow of blood past alveoli helps maintain diffusion gradient coupled with good ventilation (breathing). Bronchi divide into bronchioles.
Describe the alveolus.
Lined with squamous epithelial cells + lung surfactant secreting cells, also contains macrophages. Surfactant stops them collapsing which would reduce SA.
How is air drawn into the lungs?
When air pressure in lungs is lower than atmospheric pressure. Forced out when it’s higher than atmospheric pressure. Since thorax is an air tight chamber, pressure changes when thorax volume changes.
How are alveoli adapted to ensure these properties:
Large Surface Area
Short Diffusion Distance
Concentration Gradient
600,000,000 alveoli.
Each alveolus is 1 cell thick.
Constant ventilation (Breathing)
How are fish gills adapted to ensure these properties:
Large Surface Area
Short Diffusion Distance
Concentration Gradient
Extensively folded internal membranes + feathery filaments with secondary lamellae.
Lamellae are 2 cells thick.
Rich blood supply + water constantly pumped over gills.
How is the leaf mesophyll adapted to ensure these properties:
Large Surface Area
Short Diffusion Distance
Concentration Gradient
Loosely arranged cells with air spaces in spongy layer. Very thin (flattened structure). Stoma open + close + cells constantly respire.
How are erythrocytes adapted to ensure these properties:
Large Surface Area
Short Diffusion Distance
Concentration Gradient
Biconcave shape.
RBC bigger than capillary + so close to capillary sides.
Haemoglobin has differential affinity for oxygen.
How are the blood capillaries adapted to ensure these properties:
Large Surface Area
Short Diffusion Distance
Concentration Gradient
Capillary beds.
Thin walls.
Flow of blood through capillaries.
Describe how inspiration occurs.
External intercostal muscles contract, ribcage moves up + out, diaphragm muscles contract, diaphragm flattens, thorax volume increases, thorax pressure decreases, air flows into lungs down pressure gradient.
Describe expiration.
External intercostal muscles relax, ribcage moves down + in, diaphragm muscles relax, diaphragm bulges upwards, thorax volume decreases, thorax pressure increases, air flows out of lungs down pressure gradient. Occurs passively by elastic recoil but can be assisted by contraction of internal intercostal muscles.
What toxic chemicals are in tobacco smoke? What can it do and what diseases might it cause?
Tar, many being carcinogens. Can damage DNA in epithelial cells lining lungs. Lung cancer, emphysema, bronchitis.
What correlates with number of years as a smoker and cigarettes per day?
Lung cancer
What is xylem tissue made up of?
Cells which have no end walls (disintegrate, forming continuous column), no cell contents (as cell matures, cytoplasm disappears), become dead cells when fully formed, become strengthened by lignin which waterproofs it, column of vessels which produce long, continuous tube up plant for water transport.
