3.3.1 Exchange Surfaces and 3.3.2 Gas Exchange Flashcards
What is the rate of exchange affected by?
- Size of organism (SA:V ratio)
- Metabolic rate
What is diffusion directly proportional to?
surface area x diff in concentration / length of diffusion pathway
What are the 5 features of an exchange surface?
- Large Surface Area
- Thin
- Selectively Permeable
- Movement of external medium
- Movement of internal medium
Why is a large SA:V ratio beneficial?
Increases the rate of exchange
Why is a thin exchange surface beneficial?
Decreases diffusion distance, allowing quicker diffusion
Why is the movement of internal and external medium beneficial?
maintains concentration gradient
Explain the process of gas exchange in insects (2)
- Gases enter and leave the tracheae through the spiracles via diffusion
- Spiracles are opened and closed through valves
Why might it be a problem to have the spiracles open for a long time?
water loss
What are spiracles?
tiny pores in which gases leave and enter.
Can be opened and closed through valves
What is tracheae?
internal network of tubes in insects
What are tracheoles?
tracheae divided into smaller dead-end tubes
What 3 ways do respiratory gases move in and out of the tracheae?
- Along a diffusion gradient (insect at rest)
- By mass transport (high activity)
- Ends of tracheoles are filed with water (high activity)
How do respiratory gases move in out the tracheae along a diffusion gradient?
Muscle cells use up oxygen in aerobic respiration
Muscle cells produce carbon dioxide
This creates a diffusion gradient
So ocygen diffuses in via spiracles
How do respiratory gases move in out the tracheae by mass transport?
The contraction of muscles in insects can squeeze the trachea allowing large amounts of gas to move in and out. (abdominal pumping)
How do respiratory gases move in out the tracheae through the ends of tracheoles (5)
- Muscle cells at the end of tracheoles respire anaerobically during major activity
- This produces lactic acid (lactate)
- Lactic acid is soluble and so dissolves in cells, lowering their water potential
- Water moves into the cells by osmosis (from the tracheoles)
- There is now a lower volume of water in the tracheoles, and so space for more air to be drawn further into the tracheal system
Why is simple diffusion not suitable for gas exchange in fish? (3)
- multicellular organism, so diffusion would take too long
- small SA:V ratio
- Waterproof outer covering
What is a gill arch?
rigid curved structure made from cartilage which supports one or two rows of gill filaments
What are gill filaments?
threadlike projections covered by lamellae
Each filament contains two blood vessels, one carrying deoxygenated blood, the other oxygenated
What is lamellae?
a thin piece of tissue covered by capillary network
Explain the process of exchange in fish(3)
- Water is taken in through the mouth
- Water is forced over the gills and out through the opening on each side of the body
- The flow of blood is opposite to the flow of water (counter current flow)
What is meant by counter current flow?
blood and water that flow over the lamella flow in opposite directions
Why is a counter current flow system beneficial?
it maintains a diffusion gradient across the whole length of the lamellae
What exchange features does a fish have?
- Many filaments and lamellae = a large surface area
- Lamellae are very thin = short diffusion pathway
- Endothelial cells of the capillary walls are selectively permeable to oxygen and carbon dioxide
- Movement of blood (internal medium) and movement of water (external medium) = maintains a steep concentration gradient
Another name for gill cover is..
Operculum
What factors affect the rate of transpiration? (4)
Temperature
Wind
Light Intensity
Humidity ( conc. of water vapour)
What is the site of gas exchange in plants?
Leaves
Why do leaves have no specific transport system and are reliant on passive diffusion? (2)
Thin - short distance between phosynthesising cells and air spaces
Large surface area due to the many air spaces
What are stomata?
many small pores that have guard cells which control the rate of gaseous exchange
How does the stomata open? (3)
- Water moves into guard cell via osmosis, down a water potential gradient
- Causes cell to become turgid
- Due to their inner cell wall being thicker and more rigid, the guard cells bend away from each other when they fill with water, opening the stomatal pore.
How does the stomata close? (3)
- Water moves out of guard cell by osmosis, down a water potential gradient
- This causes the cell to become flaccid
- The guard cells no longer bend away from each other causing the stoma to close
What is meant by transpiration?
the movement of water through a plant from roots to leaves, caused by the evaporation of water out of the leaf.
What are plants that are adapted for very dry /extreme conditions called?
xerophytes
What adaptations do plants have to prevent water loss? (5)
- Thick waxy cuticle – waterproof layer
- Rolling up leaves – traps air (containing water vapour)
- Hairy leaves – traps air (containing water vapour)
- Stomata in pits or grooves – traps air (containing water vapour)
- Reduced SA:V for some leaves – e.g. pine needles,
How are the lungs adapted for efficient gas exchange? (4)
- Many alveoli and many capillaries provide a large surface area, which increases the SA:V = fast diffusion
- Alveolar epithelium and capillary walls are only one cell thick so short diffusion gradient between alveoli and blood = fast diffusion
3. Alveolar wall made of squamous (flattened) epithelial cells
4. Ventilation and circulation maintain a diffusion gradient = fast diffusion
What tissues allow the alveoli to stretch and recoil?
collagen and elastic
List the correct sequence of all the structures that are part of the journey of mammalian gas exchange.
trachea, bronchus, bronchioles, alveoli, alveolus
Describe how gas exchange occurs in the alveolus (5)
- Oxygen diffuses from a high concentration through the alveolar epithelium and capillary endothelium into the blood.
- This is because there is higher concentration of oxygen inside the alveoli.
- Carbon dioxide diffuses through the capillary endothelium and alveolar epithelium into the alveoli.
- This is because there is higher concentration of carbon dioxide in the blood.
Explain the adaptations of the alveolus for rapid diffusion (5)
Hint: constant ventilation and circulation (1)
- Constant ventilation and circulation, maintaining a diffusion gradient
- Thin alveolar epithelium and capillary endothelium are only one cell thick so diffusion pathway is short
- Many alveoli and capillaries = large SA = increasing SA: V
- Alveolar surface is moist so gases dissolve
- RBC’s are compressed against capillary wall so reduces diffusion pathway
Describe how oxygen in the air reaches surrounding capillaries surrounding the alveoli in the lungs (4)
- Trachea and bronchi and bronchioles
- Down pressure gradient
- Down diffusion gradient
- Across alveolar epithelium
- Across capillary endothelium
Limiting water loss in insects (3)
- Small SA:V ratio
- Waterproof coverings
- Spiracles
Breathing in =
inspiration
Breathing out =
expiration
Explain the Process of Inspiration (5)
- External intercostal muscles contract, internal intercostals relax
- Ribs are pulled up and out which increases volume
- Diaphragm contracts (flattens) which further increases volume
- Increased volume in thorax leads to decreased pressure.
- Atmospheric pressure > pulmonary pressure, so air is forced into lungs down a pressure gradient
Explain the process of Expiration (5)
- Internal intercostal muscles contract, external intercostals relax
- Ribs move down and in which decreases volume
- Diaphragm relaxes (pushed up) which further decreases volume
- Decreased volume leads to increased pressure
- Pulmonary pressure > atmospheric pressure, so air is forced out of lungs down a pressure gradient
pulmonary ventilation rate =
tidal volume x breathing rate
Tidal volume
volume of air taken in each breath (at rest)
Breathing rate
number of breaths per minute
What does a spirometer do?
measures tidal volume and breathing rate.
The top of the chamber of air is attached to a position sensor, which records movement of the chamber and displays the results on a computer screen.
Diffusion of gases between the alveoli and
the blood will be very rapid because:
- the distance between the alveolar air and red blood cells is reduced as the red blood cells are flattened against the capillary walls
- the walls of both alveoli and capillaries are very thin = short diffusion pathway
