3.3.2 (gas exchange) Flashcards
Ficks law
Rate of diffusion is proportional to (surface area x conc gradient) / distance which diffusion occurs
How are single celled organisms adapted for gas exchange?
Can exchange gases with environment using cell surface membrane
May have adaptations to increase surface area to volume ratio eg making themselves wide, flat or having many folds
Increases rate of gas exchange and diffusion
What is the diffusion rate of a single celled organism?
Rapid as substances only have to move across one cell membrane
How are diffusion distance and time taken related?
If you double distance for diffusion time taken is squared
What is the gas exchange system of an insect called?
Tracheal system
How does gas enter/exit the tracheal system of an insect?
Holes in exoskeleton along thorax and abdomen called spiracles
Can open and close to allow gas to enter tubes called trachea
Subdivide into tubes of smaller diameter called tracheoles which end at the body cells
How is an insects tracheal system adapted to maximise the rate of diffusion?
Tracheoles have thin walls so short diffusion distance to cells
Highly branched/many tracheoles so short diffusion distance to cells
Highly branched/many tracheoles so high surface area
Fluid in tracheoles moves out during exercise so shorter diffusion distance
Muscles can contract to move air to maintain concentration gradient
Describe gas exchange in a resting insect
Oxygen diffuses down concentration gradient into spiracles then through trachea and tracheoles
Oxygen diffuses into cells to be used up in aerobic respiration
Describe gas exchange in an active insect
Lack of oxygen increases rate of anaerobic respiration in cells increasing lactic acid concentration which decreases water potential of cells causing water to move by osmosis from tracheoles into cells down water potential gradient which decreases diffusion distance increasing rate of diffusion
Describe methods used to prevent water loss in insects
Water in tracheoles to prevent water moving out of cells by osmosis
Spiracles surrounded by small hairs which trap humid air decreasing difference in water potential and reduces air movement
Have a waxy cuticle to prevent water loss
Summarise gas exchange in fish
Oxygenated water enters through mouth
Water passes over gills
Deoxygenated water leaves
Describe how water is moved over the gills
Mouth opens
Lowers floor of mouth, increasing volume and decreasing pressure
Causes oxygenated water to flow in
Mouth shuts
Raises floor of mouth, decreasing volume and increasing pressure
Forces water over gills and out through operculum
Describe how the gills are adapted to have a high surface area
Contain gill filaments which are highly branched and folded thin tissue covered in lamella
Describe the counter current system in gills
Flow of blood and water in lamella are in opposite directions
Blood is always passing water with a higher oxygen concentration
Diffusion gradient is maintained for full length of gill
What is breathing?
The mechanical process of moving air in and out of the lungs
Describe the movement of air when breathing
Air enters mouth -> pharynx -> larynx -> trachea -> left/right bronchi -> bronchioles -> alveoli
Describe the nasal cavity
Large SA with rich blood supply which warms the air
Hairy lining which secretes mucus to trap dust and bacteria
Moist surfaces to increase the humidity of incoming air to reduce water loss at the alveoli
Describe the trachea
Carries the now humid air to lungs
Supported by layer of cartilage that holds the trachea open- prevents collapsing in on itself
Incomplete c-shaped cartilage rings allow it to bend when food is swallowed down oesophagus behind
Lined with ciliated epithelial and goblet cells that prevent dust and bacteria entering
Describe the bronchi
Extensions of trachea that split into two- one in left lung, one in right
Similar structure to trachea but smaller
Describe the bronchioles
Bronchus divide to form bronchioles
Diameter of less than a mm
No cartilage- smooth muscle which can contract causing them to constrict
Lined with thin layer of epithelium facilitating gas exchange
Describe the alveoli
Mini air sacs lined with epithelium
Gas exchange surface
Covered with a network of capilaries
Millions in each lung
Provide large surface area for gas exchange
Describe the intercostal muscles
External and internal muscles work antagonistically
External muscles contract and internal intercostal muscles relax causing inhalation
Internal intercostal muscles contract and external inter costal muscles relax causing exhalation
Muscular contraction causes pressure changes within thoracic cavity
Describe inhalation
Diaphragm contracts and flattens
External intercostal muscles contract
Internal intercostal muscles relax
Ribcage moves up and out
Increases thoracic cavity volume
Decreases pulmonary pressure
Atmospheric pressure greater than pulmonary pressure so air forced into lungs
Describe exhalation
Diaphragm relaxes
External intercostal muscles relax
Internal intercostal muscles contract
Ribcage moves downward and inward
Causes decrease in thoracic cavity volume
Increases pulmonary pressure
Pulmonary pressure greater than atmospheric pressure so air forced out of lungs
Pulmonary ventilation
Total volume of air moved into the lungs in one minute - cm³/min
pulmonary ventilation rate(PVR) = tidal volume x breathing rate
Tidal volume
Volume of air inspired per breath when at rest
Residual volume
The amount of air left in the lungs after breathing out
Total lung capacity
Maximum volume of air the lungs can hold
=vital capacity+residual capacity
Vital capacity
Maximum volume of air we can inhale and exhale
Name 5 essential features of exchange surfaces
Partially permeable
Thin exchange surface (1/2 cells)
Movement of external medium
Movement of internal medium
Large SA:volume ratio
Describe the epidermis
Outer layer on upper and lower surface of leaf
Closely fitting cells
Outer walls contain lipids and waxes that make up the cuticle
Stops water evaporating from surface of leaf
Describe the stomata
Pores in epidermis- site of gas exchange
Found mainly in lower epidermis
Each is surrounded by guard cells which change shape to open and close stomata
Stomata close when guard cells lose water and become flaccid
Stomata open when guard cells gain water by osmosis and become turgid
Describe the mesophyll
Central tissue of the leaf
Spongy layer has extensive network of air spaces to allow gases to easily circulate by diffusion
Cells contain few chloroplasts
No ventilation system so this layer must be thin
Upper layer- palisade- contains elongated palisade cells packed with chloroplasts- main site of photosynthesis
Describe the vascular tissue
Xylem vessels transport water and mineral ions to the leaves from the roots (one way)
Phloem tubes transport sucrose from the photosynthesising leaf cells to other cells in the plant (dual movement)
Describe how plants are adapted to increase the rate of the diffusion of carbon dioxide
Many palisade cells with many chloroplasts to use carbon dioxide in photosynthesis to maintain concentration gradient
Elongated palisade cells to increase SA
Many air pockets in spongy mesophyll to decrease diffusion distance
Describe how plants are adapted to reduce water loss
Replace lost water via uptake in roots
Close stomata during hottest parts of day
Close stomata at night
What is a xerophyte?
A plant that is adapted to reduce water loss to enable it to survive in very dry conditions
Describe how each xerophyte adaptation allows it to survive in arid conditions
Smaller leaves to reduce SA so less water lost through transpiration
Succulent tissue to increase storage of water
Thicker waxy cuticle to seal water in
Hairs on surface of leaf trap humid air reducing difference in concentration reducing evaporation through stomata
CAM photosynthesis to prevent water loss from stomata in day
Rolling leaves so traps moist air increasing humidity slowing evaporation from stomata
Deep root system to reach underground water
Shallow root system to collect rainfall
Low stomata density to reduce transpiration
