3.1.1 Exhange Surfaces Flashcards
Why do some organisms need specialised exchange surfaces
In multi-cellular organisms
Metabolic activity/ demand is too high for diffusion alone
SA:V is smaller in larger organisms, gases can’t be exchanged fast enough/in large enough amounts to keep organism alive
Features of effective specialised exchange surfaces
Increased SA
Thin layers
Good blood supply
Ventilation to maintain diffusion gradient
How does SA help exchange surfaces be efficient
Increases SA provides area needed for exchange, overcomes limitations of larger organism’s SA:V
Eg root hair cells and villi
How do thin layers help exchange surfaces be efficient
Short diffusion distance for substances, makes process faster
Eg alveoli and villi
How does a good blood supply help exchange surfaces be efficient
Steeper concentration gradient means diffusion takes place faster
Ensures gas exchange takes place constantly and maintains steep concentration gradient
Eg alveoli, gills, villi
How does ventilation help exchange surfaces be efficient
Helps maintain concentration gradient, makes process more efficient
Eg alveoli, gills
Structure of trachea
Wide tube supported by c-shaped rings of cartilage, stops it from collapsing, c-shaped so food can move down oesophagus behind trachea
Lined with ciliated epithelium with goblet cells between and below
Secrete mucus to trap dust and microorganisms
Structure of bronchus
Trachea divides to form left and right bronchus
C-shaped rings of cartilage
Structure of bronchioles
Bronchi divide to form many bronchioles
No cartilage
Smooth muscle in the walls, contract and relax to constrict and dilate the bronchioles which alters amount of air reaching the lungs
Lined with thin layer of flattened epithelium
Structure of alveoli
Small air sacs, main gas exchange surfaces
Layer of thin, flattened epithelial cells
Contain collagen and elastic fibres which allow them to stretch as air is drawn in
Recoil to squeeze air out, elastic recoil
Adaptations of the alveoli
Large SA
Thin layers, one cell thick
Good blood supply, alveoli surrounded by many capillaries, maintains steep concentration gradient
Ventilation, steep concentration gradient due to air moving in and out
Inner surface lined with surfactant, makes it possible for alveoli to remain inflated, oxygen dissolves in water before diffusing into blood
Describe the mechanism of inspiration
Active process
Diaphragm contracts and flattens
External intercostal muscles contract, forces ribs up and out
Volume of thorax increases so pressure is reduced
Pressure is lower than atmospheric pressure, air is drawn in to equalise pressures
Describe the mechanism of expiration
Passive process
Diaphragm relaxes into dome shape
External intercostal muscles relax, ribs move down and in
Elastic fibres in alveoli return to normal length
Volume of thorax decreases, pressure in the thorax is higher than atmospheric pressure
Air is forced out to equalise pressure
What’s tidal volume
Volume of air that moves into and out of the lungs with each resting breath
Around 500cm3, 15% of vital capacity
What’s vital capacity
Maximum volume of air that can be breathed in/out
What’s breathing rate
How many breaths taken in a minute
What’s oxygen uptake
Rate at which an organism uses up oxygen
How are spirometers used to investigate breathing
Oxygen chamber with moveable lid
Person breathes through tube connected to chamber
Lid moves up and down and movements are recorded by a pen attached to the lid, writes on a rotating drum
Creates a spirometer trace
Soda lime in the exhaled tube to absorb CO2
Valve ensures inhaled and exhaled air goes in different directions
Volume decreases as oxygen is used up
Mechanism of gas exchange in insects
Air moves into tracheae through pores on insect’s surface called spiracles
Oxygen travels down conc gradient towards cells
CO2 travels down conc gradient towards spiracles
Tracheae branch into tracheoles, thin permeable walls, contain fluid for oxygen to dissolve in
Oxygen diffuses into body cells, CO2 diffuses out
Use rhythmic abdominal movements to change volume of the body and move air in/out of spiracles
Mechanism of gas exchange in bony fish (counter-current system)
Water enters fish through mouth and passes out through gills
Gills made of thin branches, gill filaments, big SA for exchange of gases
Filaments covered in gill plates, increase SA
Gill supported by gill arch
Plates have lots of capillaries and thin surface layer, speeds up diffusion
Blood flows through gill plates in one direction and water flows in opposite direction (counter-current system)
Maintains steep conc gradient
How are fish gills ventilated
Fish opens mouth, buccal cavity floor lowered
Volume of buccal cavity increases, pressure decreases
Water sucked into cavity
When fish closes its mouth, floor of buccal cavity is raised
Volume decreased, pressure increases
Water forced out across gill filaments
Each gill covered by bony flap (operculum), increase in pressure forces operculum to open and allows water to leave the gills
How to dissect fish gills
Wear lab coat and gloves
Place fish in dissection tray
Push back operculum and use scissors to remove gills
Cut each gill arch through bone at the top and bottom
Filaments should be visible
Draw gill and label it
How to dissect gaseous exchange system in insects
Cockroach/grasshopper
Fix insect to dissecting board, use dissecting pins through legs to hold in place
Cut and remove piece of exoskeleton along length of abdomen
Fill abdomen with saline solution with syringe
Observe network of thin, silver-grey tubes (tracheae)
Examine under wet mount slide with light microscope, rings of chitin can be seen
