B3.1 gas exchange (year 6) Flashcards
Why does direct gas exchange get harder for larger organisms?
Increase in size > SA:V ratio decreases (SA is square unit, V is cubed function), active tissues are further away from exterior = an organisms ability to take in an release substances is limited by outer surface area
Properties of gas exchange surfaces
- thin to keep diffusion distance short
- moist to encourage gas diffusion
- large SA for maximum diffusion
- permeable to respiratory gases
Adaptations of mammalian lungs
- alveolus is at the terminal end of one of the branches of tubes that started as the trachea
- Surfactant on inner surface of each alveolus to reduce surface tension, prevent alveolus from collapsing when air is expired
- Bronchioles connect the millions of alveoli to the trachea for access to inspired/expired air
- alveoli spherical shape to provide vast SA for more diffusion of CO2 and O2
- dense network of capillaries surrounding each alveoli for high conc gradient = faster disunion
- capillaries and alveolus are one cell thick = gases only need to diffuse through 2 cells to enter/exit blood stream
Describe process of inspiration
Inspiration
1. diaphragm contracts, increasing volume of thoracic cavity
2. external intercostal muscles + one set of abdominal muscles contract to raise rib cage, increase vol. of thoracic cavity
3. pressure inside thoracic cavity decreases = lung tissue increases volume, responding to the lower pressure
4. decreased pressure in lungs creates a partial vacuum, air comes in through mouth/nasal passages to counter the partial vacuum within the lungs and fills the alveoli.
Describe process of expiration
- Diaphragm relaxes, decreasing vol. of thoracic cavity
- internal intercostal muscles + one set of abdominal muscles relax to lower rib cage, decrease vol. of thoracic cavity
- pressure inside thoracic cavity increases = lung tissue decreases volume, responding to higher pressure
- increased pressure in lungs forces air out
What instrument is used to measure lung volume (optional)
spirometer
Adaptations for gas exchange in leaves
- usually thin (a few cell layers) for quick efficient gas diffusion
- large SA:V ratio for efficient diffusion
- waxy cuticle, a waxy lipid layer that covers the surface of leaves, prevents water loss by evaporation
- Palisade mesophyll, a densely packed region of cylindrical cells in upper portion of leaf, which contain chloroplasts and are located to receive max sunlight
- spongy mesophyll, loosly packed cells below the palisade layer and above stomata, hv few choloplasts and many air spaces = large SA for gas exchange
- veins - enclose xylem and phloem to distribute water, dissolved sugars to the leaf
- stomata - composed of 2 guard cells, allowing CO2, water vapour and O2 to enter/exit leaf by diffusion down conc. gradient. Locared on lower surface of leaves to prevent transpiration
Draw and label the distribution of tissue in a transverse section of a dicotyledonous leaf
Pearson pg 278
Factors affecting rate of transpiration (4)
Increased light increases Transpiration (stimulates guard cells to open stomata, increases rate of photosynthesis, stomata opens to diffuse co2 in and o2 out)
Increased temp increases Transpiration (incresed molecular movement = increased evaporation of water)
Increased wind speed increases Transpiration (wind removes water vapour at the entrance of stomata, increasing water conc. gradient btwn inside, outside of leaf)
Increased humidity decreases transpiration (lessens the water conc. gradient btwn inside, outside of leaf)
Adaptations of foetal and adult haemoglobin for transport of oxygen
Haemoglobin - a protein molecule found within RBC/erythrocytes
- each RVC has no nuclei, few organelles = increased carrying capacity
- when haemoglobin binds to o2, the IRON atom is bonding with o2 = as there are four iron atoms within haemoglobin, can transport 4 oxygen molecules (4o2), and is saturated
- COOPERATIVE BINDING - each o2 molecule that binds to haemoglobin INCREASES its affinity for another o2 molecule.
- co2 binds to the polypeptide chains of haemoglobin, the allosteric site.
- ALLOSTERIC BINDING - each binding of co2 to haemoglobin increases the release of o2 molecules (bohr shift)
- foetal haemoglobin have higher affinity for o2 than mother as molecular structure is different
- in the placenta, mothers capillaries are very close to capillaries of foetus, allowing molecular exchanges including o2 and co2
- conc gradient btwn mother and foetus, aided by the foetal haemoglobin greater affinity for o2 = encourages diffusion of the mothers o2 to foetus
Describe the Bohr shift
When haemoglobin bonds to co2, its affinity for o2 decreases
- this is as binding to co2 is more likely to occur when co2 conc is high as a product of cell respiration
- this is also when o2 is most needed
- in the alveolar the inverse is true, with low co2 conc and high o2 conc, so haemoglobin loses co2 to the expired air and renews its bonding affinity for oxygen (cooperative binding)
Explain the S-shaped form of the oxygen dissociation curve in terms of cooperative binding
y-axis = % haemoglobin saturation
x-axis = partial pressure of oxygen (can be thought of, but is not, oxygen conc. in blood)
the s-shape where rate of increase for y-axis is increasing at a decreasing rate is the result the cooperatively of oxygen molecules as hamoglobin is loaded with o2 to become saturated.
- without cooperativity the graph would be linear
- To calculate % oxygen released to tissues, take % haemoglobin saturation from the partial pressure that corresponds to oxygen partial pressure in lungs - %haemoglobin saturation from the partial pressure in body tissues where cell respiration is utilizing oxygen
explain the difference in oxygen dissociation curves when foetal haemoglobin and haemoglobin binded to co2 is used compared to normal haemoglobin
- comparing foetal vs maternal haemoglobin, the foetal hamoglobin curve will be shifted to the left of the mothers, indicating a greater affinity of o2 for almost every partial pressure of o2
- when haemoglobin binds to 1 or more co2 molecules, its affinity for o2 is reduced (bohr effect). So its curve will shift to the right.
