3.3- Organisms exchange substances with their environment Flashcards
Why do small organisms have a good SA:V ratio?
They have a SA that is large enough compared with their volume to allow efficient exchange across their body surface.
What happens to SA:V ratio when organisms get bigger?
Their volume increases at a faster rate than their SA.
So SA:V ratio decreases.
Therefore, simple diffusion at the outer surface is not sufficient for activity levels/ to diffuse to inner layers.
How have organisms evolved to deal with their SA:V ratio changes?
- A flattened shape so no cell is far from the surface increases SA:V ( eg leaf)
- Specialised exchange surfaces with a large SA: increases internal SA:V ratio and maintains a conc gradient for diffusion eg by ventilation- ( eg lungs)
What is metabolic rate?
The amount of energy used up by an organism within a given period of time.
Explain the link between SA:V and metabolic rate.
As SA:V ratio increases in smaller organisms, metabolic rate increases as:
-Rate of heat loss per unit body mass increases so organisms need higher rate of respiration to release enough heat to maintain constant body temp.
How to calculate SA of a cube?
area of one side x number of sides
Work out the SA of a cube with length of one side 5cm?
5x5 = 25cm2
25 x 6 = 150cm2
How to calculate volume of a cube?
length x width x height
Work out the volume of a cube with length of one side 4cm?
l x w x h
4 x 4 x 4 = 64cm3
How to work out SA:V ratio?
SĄ of whole cube/ volume of cube
Work out SA:V ratio of a cube with SA 96 and V 64?
96/64 = 1.5:1
What are the specialised adaptations of exchange surfaces?
Large SA compared to V increasing rate of exchange.
Very thin so diffusion distance is short and materials cross exchange surface faster.
Selectively permeable.
Movement of environmental medium (air) to maintain a diffusion gradient.
Transport system to ensure movement of internal medium (eg blood) to maintain a diffusion gradient.
What is Ficks law regarding diffusion?
Diffusion = surface area x diff in concentration/ length of diffusion path
What are the adaptations of single- called organisms?
Small so have a large SA:V ratio. Oxygen absorbed by diffusion across their body surface, covered only by a cell- surface membrane.
Carbon dioxide from respiration diffuses out.
Cell walls don’t affect diffusion of gases.
Describe 3 sections of the tracheal system of an insect.
1) Spiracles- pores on surface that open/close to allow diffusion
2) Tracheae- large tubes of air that allow diffusion
3) Tracheoles- smaller branches form tracheae, permeable to allow gas exchange within cells.
What are the 3 ways respiratory gases move in and out the tracheal system?
-Along a diffusion gradient
-Mass transport
-By the ends of the tracheoles filling with water.
How is an insect’s tracheal system adapted for gas exchange?
1) Tracheoles have thin walls: short diffusion distance to cells.
2) High number of branched tracheoles so short diffusion distance to cells and large SA.
3) Tracheae provide tubes of air for fast diffusion.
4) Contraction of abdominal muscles changing pressure in body causing air to move in/out.
5) Fluid in end of tracheoles drawn into tissues by osmosis during exercise (lactate produced in anaerobic respiration lowers water potential of cells), diffusion faster through air than liquid.
Is diffusion more rapid in air or water?
Air as the particles in a gas are closer together so vibrate more= more kinetic energy so move faster.
4 key facts about fish?
-Waterproof, airtight external surface.
-Large so have a small SA:V ratio
-Body surface not sufficient to allow respiratory demands
-Internal gas exchange system (gills)
What is the function of gills?
Water enters fish’s mouth and is forced over gills, out through openings on each side.
Gills are the exchange surface for O2 into blood CO2 out of blood.
What is the structure/ adaptations of gills?
Made of many gill filaments covered with many lamellae which stack on top of eachother increasing SA for diffusion.
Thin lamellae wall/ epithelium so short diffusion distance between water and blood.
Lamellae have many capillaries to remove O2 and bring CO2 quickly for concentration gradient.
What is the counter current principle regarding fish?
Blood and water flow in opposite directions.
Blood always passes water with a higher oxygen concentration.
For diffusion along whole length of lamellae.
Why is parallel flow worse for exchange in fish?
A diffusion gradient is only maintained half the distance of the lamellae as equilibrium would not be reached.
50% O2 diffuses into blood as equilibrium wouldn’t be reached.
Why is countercurrent flow better for exchange in fish?
A steep diffusion gradient is maintained all the way across the gill lamellae- almost all O2 diffuses into blood.
How may active, fast swimming fish have different gills?
Require more oxygen so may have more gill lamellae on each gill filament for increased SA for gas exchange.
Increased gill size as there would be less time the water would pass through the gills.
What are 3 key pieces of information regarding plants?
-Plants respire all the time.
-Plants photosynthesise when conditions are right.
-Volumes and types of gases that are being exchanged in a plant leaf change depending on balance of respiration and photosynthesis.
What are the adaptations of leaves of dicotyledonous plants for rapid diffusion?
Short diffusion path with many small pores (stomata).
Large surface area of mesophyll cells for rapid diffusion.
Air spaces interconnect throughout the mesophyll.
No specific transport system for gases, they move simply by diffusion.
Describe the cross-section of a leaf from top to bottom
Waxy cuticle
Upper epidermis
Palisade mesophyll
Spongy mesophyll
Lower epidermis
What are stomata?
Small holes/ pores on the underside of leaves, single hole= stoma.
Each stoma surrounded by 2 guard cells which control opening and closing of stoma so rate of gas exchange.
How do stomata control the rate of gas exchange?
When CO2 levels are low inside the plant, the guard cells gain water and become turgid- they curve out, opening the stoma allowing gases in/out. Water evaporates through stoma.
High CO2 levels in the plant cause the guard cells to lose water, closing the stoma.
How do insects limit water loss?
-Small SA:V ratio to minimise the area from which water can be lost from.
-Waterproof covering: rigid outer skeleton of chitin covered by waterproof coat.
-Spiracles: openings to the tracheae at the surface of the body which can close when insect is at rest, stopping water evaporating out.
How does a thick cuticle limit water loss in xerophytic plants (living in dry conditions)?
The waxy cuticle forms a waterproof barrier, the thicker the cuticle, the less water can escape.
How does rolling up of leaves limit water loss in xerophytic plants?
Most leaves have stomata confined to lower epidermis- rolling of leaves in a way that protects lower epidermis from outside helps trap region of still air in rolled leaf.
Region of air becomes saturated with water vapour so has very high water potential- no water potential gradient between inside and outside leaf= no water loss.
How do hairy leaves limit water loss in xerophytic plants?
Thick layer of hairs trap still moist air next to leaf surface: water potential between inside and outside is reduced= less water lost by evaporation.
How do stomata in pits/grooves limit water loss in xerophytic plants?
They trap still moist air next to the leaf surface and reduce the water potential gradient between the inside and outside.
How does reduced SA:V ratio of leaves limit water loss in plants?
Leaves that are small and roughly circular in cross-section rather than broad and flat have a rate of water loss that can be reduced.
Describe how carbon dioxide in the air outside the leaf reaches mesophyll cells inside the leaf.
Carbon dioxide enters via the stomata.
The stomata are opened by the guard cells.
CO2 diffuses through the air spaces down a diffusion gradient.
Why is gas exchange needed in the lungs? (CO2 and O2)
O2: aerobic respiration requires constant supply of O2 in order to release energy in the form of ATP.
CO2: respiration produces CO2 which needs to be removed from the lungs as a build up is toxic to the body and can change pH.
Why do we need a high volume of exchange regarding the lungs?
1) To maintain a high body temperature (37C) in order to have high metabolic and respiratory rates.
2) Relatively large volume of living cells.
Draw the structure of the lungs
Trachea- thin tube in the middle splits into 2 bronchi.
Bronchi split into bronchioles which have alveoli on the ends.
Intercostal muscles on sides of lungs, diaphragm at bottom.
Which part is the thorax and which is the abdomen?
The thorax includes the upper half, with the lungs.
Diaphragm splits thorax from abdomen.
The abdomen refers to the lower half.
Describe the structure of the lungs?
Lobed structures made of highly branched tubules called bronchioles that end in tiny air sacs called alveoli.
Describe the structure and function of the trachea?
Flexible airway surrounded by rings of cartilage that prevent trachea collapsing as the air pressure falls when breathing in.
Trachea walls are made of muscle lined with ciliated epithelial cells and goblet cells.
Describe the structure and function of the bronchi?
2 divisions of the trachea: each leading to a lung.
They secrete mucus (goblet) and have cilia to move mucus towards throat.
Larger bronchi have cartilage, reducing as bronchi get smaller.
Describe the structure and function of bronchioles?
Series of branching subdivisions of bronchi.
Walls are made of muscle lined epithelial cells to allow them to constrict to control the flow in/out the alveoli.
Describe the structure and function of the alveoli?
Minute air sacs (diameter 100-300 micrometres) found at end of bronchioles.
Between alveoli there is collagen and elastic fibres which allow alveoli to stretch as they fill with air and spring back to expel CO2 rich air.
What is the gas-exchange surface in the alveoli/lungs?
The alveolar membrane.
Explain features of alveolar epithelium that make it adapted for gas exchange.
1) Flattened cells (1 cell thick) so short diffusion distance.
2) Folded so large SA
3) Permeable to allow diffusion of 02/CO2
4) Moist so gases can dissolve for diffusion
5) Good blood supply from capillaries to maintain conc gradient.
How does gas exchange occur in the lungs?
O2 diffuses from alveolar air space into blood down its concentration gradient across alveolar epithelium then across capillary endothelium.
