topic 3A - exchange Flashcards
what is surface area?
the total area of the organism that is exposed to the external environment
what is volume?
total amount of space inside the organism
the larger the animal, the _____ the surface area-to-volume ratio
smaller
do surface area and volume increase at the same rate?
no, volume increases much more rapidly than surface area as size increases
adaptations of single-celled organisms for exchange:
-the large surface area allows for maximum absorption
-the small volume means the diffusion distance is short
disadvantages of surface area and volume as the size of an organism increases (for exchange)
-less surface area for the absorption of nutrients and secretion of waste products
-greater volume results in a longer diffusion distance to the cells and tissues of the organism
why is a specialised system needed for gas exchange?
supply of oxygen:
-organisms need ATP to carry out biochemical processes
-most ATP is produced through aerobic respiration which requires oxygen
removal of carbon dioxide:
-carbon dioxide is a toxic waste product of aerobic respiration
-if it accumulates in cells/tissues it alters the pH
why isn’t diffusion viable for large multicellular organisms but it is for single called organisms?
-in single celled organisms, oxygen can diffuse across the cell wall and membrane of the organisms
-reaching the centre of the organisms would be a quick process
-if the cell was larger, diffusion time would increase
-the time taken for oxygen to diffuse from the cell-surface membrane to the tissues would be too long for a multicellular organism
what is metabolic rate?
the amount of energy expended by that organism within a given period of time
what is basal metabolic rate (BMR)?
the metabolic rate of an organism when at rest
what does the body need energy for during rest periods?
the functioning of vital organs
(heart, lungs)
how can metabolic rate be measured?
-oxygen consumption
-carbon dioxide production
-heat production
metabolic rate & body mass:
the greater the mass of an organism, the higher the metabolic rate
(eg: a single rhino consumes more oxygen within a given period of time compared to a single mouse)
BMR & animal sizes:
BMR is higher in smaller animals than in larger animals
why is BMR higher in smaller animals than larger animals?
-smaller animals have a greater SA:V ratio → they lose more heat
-they have to use up more energy to maintain their body temperature
what apparatus can be used to investigate metabolic rates in organisms?
-respirometers
-oxygen/carbon dioxide probes
-calorimeters
effective exchange surfaces in organisms have:
-a large surface area
-short diffusion distance
-concentration gradient (maintained)
how does a thin diffusion distance contribute to a good exchange surface?
more molecules can cross the surface per unit time
how does a steep diffusion gradient contribute to a good exchange surface?
-greater difference in concentration increases rate of diffusion
-more molecules can cross the surface per unit time
how much contact do multicellular organisms have with the environment?
-outer cells in contact with environment
-inner cells have no contact with environment
how much contact do unicellular organisms have with the environment?
-whole cell surface is in contact with environment
-they exchange molecules over their whole outer surface
define metabolic demand
how much oxygen and nutrients an organism needs to take in daily to
respire enough to maintain the metabolic rate
heat transfer & animals with a large surface area:
transfer heat to their surroundings more quickly than those with a smaller surface area
heat transfer & animals with a small surface area:
-molecules & heat have to pass across layers of cells → heat is lost & gained slower
what is gas exchange?
the process by which oxygen is acquired
and carbon dioxide is removed
what do exchange surfaces provide?
the means for gases to enter or leave the body
exterior of an insect
-rigid exoskeleton
-waxy coating that is impermeable to gases
what have insects developed for gas exchange?
a breathing system that delivers oxygen directly to all the organs and tissues of their bodies
what is a spiracle?
an opening in the exoskeleton of an insect which has valves
what does a spiracle do?
it allows air to enter the insect and flow into the system of tracheae
are spiracles open or closed most of the time?
most of the time, the spiracle is closed to reduce water loss
what are tracheae?
tubes within the insect breathing system which lead to tracheoles (narrower tubes)
contents of the walls of the tracheae:
the walls have reinforcement that keeps them open as the air pressure inside them fluctuates
where do tracheoles run?
between cells and into the muscle fibres
what is the site of gas exchange in insects?
the muscle fibres
how is a concentration gradient created in insects?
oxygen is used by respiring tissues allowing more to move in through the spiracles by diffusion
movement of carbon dioxide in an insect:
carbon dioxide produced by the respiring tissues moves out through the spiracles down a concentration gradient
which insects is the tracheae and tracheole system sufficient for?
for smaller insects, this system provides sufficient oxygen via diffusion
what do very active/flying insects need?
a more rapid intake of oxygen
how do very active insects create a mass flow of air into the tracheal system?
-closing the spiracles
-using muscles to create a pumping movement for ventilation
what is produced when insects fly and what does this do?
-lactate is produced in the respiring muscles
-the water potential of muscle cells lowers
-water found at ends of the tracheoles is then drawn into the respiring muscle by osmosis
-this allows gases to diffuse across more quickly
exterior of fish:
waterproof
oxygen and water:
-oxygen dissolves less readily in water
-a set volume of water contains much less oxygen than the same volume of air
how do fish adjust to the lack of oxygen in water?
fish are adapted to directly extract oxygen from water (gills)
structure of fish gills in bony fish:
-series of gills on each side of the head
-each gill arch is attached to two stacks of filaments
-on the surface of each filament, there are rows of lamellae
-the lamellae surface consists of a single layer of flattened cells that cover a vast network of capillaries
fish mechanisms: capillary system purpose
ensures that the blood flow is in the opposite direction to the flow of water
(counter-current system)
what does the counter current system ensure?
-a concentration gradient is maintained along the whole length of the capillary
-oxygen continually moves from the water into the blood
what is it called when water and blood flow in opposite directions?
countercurrent flow
what would happen if parallel flow occurred in fish?
equilibrium would be reached and no oxygen would pass into the blood via diffusion
how are the gills of a fish are adapted for efficient gas exchange?
lamellae/filaments → increase surface area
large number of capillaries → maintains a diffusion gradient
thin epithelium / lamellae wall →
short diffusion pathway
what happens when water enters the mouth of a fish?
it passes over the gills
describe how fish maintain a flow of water over their gills
1) mouth opens, operculum shuts
2) floor of mouth is lowered
3) water enters due to decreased pressure & increased volume of the mouth (pressure is higher outside the mouth of the fish and so water flows in)
4) mouth closes, operculum opens
5) floor is raised which results in increased pressure/ decreased volume
6) increased pressure pushes water over the gills
what do plants need to carry out photosynthesis?
an adequate supply of carbon dioxide
mechanisms of dicotyledonous plants for gas exchange:
1) when the guard cells are turgid, the stoma remains open allowing air to enter the leaf
2) the air spaces within the spongy mesophyll layer allows carbon dioxide to rapidly diffuse into cells
3) the carbon dioxide is quickly used up in photosynthesis by cells containing chloroplasts - maintaining the concentration gradient
4) no active ventilation is required as the thinness of the plant tissues and the presence of stomata helps to create a short diffusion pathway
why is the exchange of gases from the atmosphere essential for the survival of oranganisms?
-oxygen is required for respiration
-carbon dioxide is required for photosynthesis
examples of vital functions of water within plants :
-solvent that facilitates the transport of essential nutrients
-extreme water loss can lead to death
the relationships between water loss & gas exchange
scientists have observed in organisms that adaptations that reduce water loss negatively affect gas exchange and vice versa
the balance between water loss & gas exchange:
(+ examples)
-compromises have been made in organisms to ensure that there is a sufficient supply of both water and gases
(eg: terrestrial insects and xerophytic plants)
habitats of terrestrial insects:
small insects living on the ground are surrounded by air and prone to drying out
exoskeleton of terrestrial insects:
-possess a waterproof exoskeleton that prevents water loss
-the waterproof waxy coating of the exoskeleton makes gas exchange by diffusion very difficult
what do terrestrial insects have in order to combat issues with the exoskeleton?
-insects have evolved a tracheal system which consists of many tubes that carry oxygen directly to all tissues and cells of the body
-spiracles are connected to the tracheal system
what are xerophytes?
plants that can tolerate dry/arid conditions due to the presence of a number of adaptations
adaptations of xerophytes:
-very few stomata / sunken stomata
-stomata in pits, with hairs surrounding
-thick, waxy cuticle
-reduced or rolled leaves
-low growth
-CAM physiology
how having less stomata helps xerophytes:
less water loss as fewer pores
how having sunken stomata helps xerophytes:
water loss is minimised as moist air is trapped and diffusion gradient reduced
how having stomata in pits, with hairs surrounding helps xerophytes:
traps water vapour and reduces transpiration
how having a thick, waxy cuticle helps xerophytes:
prevents water loss from the leaf surface
how having reduced or rolled leaves helps xerophytes:
reduced leaves:
lesser & smaller leaves reduces the surface area available for water loss
rolled leaves:
reduces the exposure of stomata to the air
how having low growth helps xerophytes:
low growing plants are less exposed to wind and more likely to be shaded, reducing water loss
how having CAM physiology helps xerophytes:
(close in light, open at night)
plants with CAM physiology open their stomata at night, reducing water loss via evaporation
-daytime water loss minimised
-open their stomata at night to take in carbon dioxide and store it for use during the day when stomata are closed to reduce water loss
examples of xerophytes
cacti, marram grass
cacti adaptations:
-spines
-both shallow and deep, widespread roots
-very thick, waxy cuticle
-reduced stomata
-thick stem
cacti adaptations: spines
-modified leaves that minimise the surface area and so reduce water loss
-spines also protects the cacti from animals that might eat them
disadvantages of spines
can’t photosynthesise
solution to the issue with spines
photosynthesis occurs in the green stem which possesses chloroplasts
cacti adaptations: both shallow and deep, widespread roots
allow it to access all available water
deep, widespread roots:
can collect water from a large area or from very deep underground
cacti adaptations: thick, waxy cuticle
reduce water loss by evaporation
cacti adaptations: reduced
stomata
reduce water loss by transpiration
cacti adaptations: thick stem
the stem has a thick cuticle and is very large in diameter which allows it to store water
where is marram grass usually found?
sand dunes
leaves of marram grass:
-leaves can roll up to reduce the exposure of surfaces to the wind
-the rolling of the leaf provides deep grooves which protect the stomata
-the exposed surface has no stomata and a thick cuticle
-the inner surface of the leaf possesses a large number of hairs
hinge cells of marram grass
hinge cells shrink when flaccid:
-causes leaves to roll, exposing thick cuticle to the air and creating a humid space in the middle of the rolled leaf
where does gas exchange occur in humans?
lungs
which structures are in the thorax?
-trachea
-lungs
-bronchi
-bronchioles
-alveoli
-capillary network
what is the trachea?
-the airway that leads from the mouth and nose to the bronchi
-the trachea is lined with mucus-secreting goblet cells and cilia
-have tracheal rings
what are the lungs?
the organ where gas exchange takes place
what are the bronchi?
-at the bottom of the trachea
-they are similar in structure to the trachea but narrower
-the bronchi lead to bronchioles
what are bronchioles?
-narrow tubes which carry air from the bronchi to the alveoli
-they have no supporting cartilage and so can collapse
what are alveoli?
-the main site of gas exchange in the lungs
-tiny sacs with many structural adaptations to enable efficient gas exchange
what is the capillary network?
-an extensive network of capillaries surrounds the alveoli
-an exchange surface between the lungs and the blood
how do gases move from the air to the blood?
(gases in the air)
trachea
→
bronchi
→
bronchioles
→
alveoli
→
alveolar epithelium
→
capillary endothelium
→
blood
(gases in the blood)
role of the tracheal rings:
-they help to support the trachea and ensure it stays open
-allow it to move while we breathe
what is ciliated epithelium & where is it found?
a specialised tissue found along the trachea down to the bronchi
role of the ciliated epithelium:
each cell has small projections of cilia which sweep mucus, dust and bacteria upwards and away from the lungs
where are goblet cells found?
scattered throughout the ciliated epithelium in the trachea
the role of goblet cells:
-mucus-producing cells
-mucus which traps dust, bacteria and other microorganisms & stops them from reaching the lungs
-the mucus is then swept along by the cilia of the ciliated epithelium upwards and is swallowed
-the mucus and any microorganisms will then be destroyed by the acid in the stomach
where is squamous epithelium found?
alveoli have a lining of squamous epithelium
the role of the squamous epithelium:
very thin and permeable for the easy diffusion of gases
where is smooth muscle found?
throughout the walls of the bronchi and bronchioles
the role of smooth muscle:
helps to regulate the flow of air into the lungs by dilating when more air is needed and constricting when less air is needed
what is each alveolus surrounded by?
an extensive network of capillaries
the role of the capillary network:
-carbon dioxide diffuses out of the capillaries and into the alveoli to be exhaled
-oxygen diffuses from alveoli and into the capillaries to be carried around the body for aerobic respiration
what process is used to exchange oxygen and carbon dioxide?
simple diffusion
what does the air in the alveoli contain?
a high concentration of oxygen
what does the blood in the capillaries contain?
-relatively low concentration of oxygen
-high concentration of carbon dioxide
features of the alveoli:
-large number of alveoli
-thin walls
-extensive capillary network
alveoli features: large number of alveoli
-the average human adult has around 480 - 500 million alveoli in their lungs
-the large number of alveoli increases the surface area available for oxygen and carbon dioxide to diffuse across
alveoli features: thin walls
-the walls of the alveoli are only one cell thick and these cells are flattened
-this means that gases have a very short diffusion distance so gas exchange is quick and efficient
alveoli features: extensive capillary network
-diffusion distance for gases is short
-the constant flow of blood through the capillaries means that oxygenated blood is brought away from the alveoli and deoxygenated blood is brought to them
-this maintains the concentration gradient necessary for gas exchange to occur
where is surfactant?
coats surface of lungs
role of surfactant:
-maintains moisture
-reduces surface tension to stop alveoli collapsing when air pressure falls
what does gas exchange in the lungs require?
a concentration gradient
how is a concentration gradient maintained in the lungs?
-through ventilation
-the continuous flow of blood in the capillaries
what is ventilation?
the movement of air into and out of the lungs to supply oxygen to the body and remove carbon dioxide
what does the continuous flow of blood in the capillaries ensure?
that there is always a higher concentration of oxygen in the alveoli than in the blood
exercising & ventilation
exercise causes oxygen demands to increase which can be facilitated by an increased rate of ventilation
steps of inhilation/inspiration:
1) diaphragm contracts (moves down)
2) external intercostal muscles contract, so ribcage moves up and out
3) the volume of the thoraxic cavity increases, which reduces the air pressure (compared to atmospheric pressure) because there is more space (concentration gradient)
4) air moves into the lungs down the pressure gradient
is inhilation an active process?
yes, it requires energy
steps of exhalation/expiration:
1) diaphragm relaxes (moves up)
2) external intercostal muscles relax, ribcage moves in and down
3) volume of the thoraxic cavity decreases, so air pressure increases because there is less space
4) air moves out of the trachea
is exhalation active or passive?
normal expiration is passive
how does air get to the alveoli?
-air flows in through the mouth and nose then down the trachea
-the trachea then splits into two bronchi which branch off further into smaller tubes (bronchioles)
-bronchioles end in small air sacs known as alveoli
what is each lung surrounded by?
-each lung is surrounded by a membrane and the space (pleural cavity) is filled with pleural fluid
-this lubricates the lungs and helps the lungs adhere to the walls of the thoracic cavity by water cohesion
-this allows the lungs to expand with the chest during inhalation
what is tidal volume?
the volume of air inspired per breath when at rest
what is breathing rate?
the number of breaths taken per minute
what is PVR?
the volume of air breathed (in or out) in one minute
how is PVR calculated?
tidal volume x breathing rate
when does cancer occur?
if mutations affect mitosis in cells
when do tumours develop? (long cancer)
-tumours develop if mutations occur in oncogenes
-this causes uncontrolled mitosis which develops into a mass of cells in the lumen of the airways
why do tumours get larger? (lung cancer)
it has no method of programmed cell death and survives because it develops its own blood supply (vascularisation)
what does the tumour do after getting larger?
-the tumour then starts to interfere with the normal working of the lungs, such as by squeezing against blood vessels
symptoms of lung cancer:
-coughing up blood
-a persistent cough
-wheezing and breathing difficulties
-sudden weight loss
what does COPD stand for?
chronic obstructive pulmonary disease
what is COPD?
includes a range of lung-based diseases, such as chronic bronchitis and emphysema
symptoms of COPD:
-shortness of breath,
-a chronic or persistent cough
-chest tightness
risk factors of lung disease:
-pollution
-smoking
environmental pollution sources:
-burning of fossil fuels
-car exhaust fumes
studies on the effects of smoking on lung disease…
-more studies have been carried out investigating the effect of smoking on the incidence of lung disease than pollution
-exposure to smoking is a much easier variable to control and measure than pollution (eg: number of cigs per day and for how many years)
studies on the effects of pollution on lung disease…
usually draw comparisons between different urban and rural locations and the incidence of lung disease in those populations
which chemicals are in cigarettes?
-tar
-nicotine
-carbon monoxide
what is tar?
a carcinogen
what is nicotine?
an addictive substance which narrows blood vessels
what is carbon monoxide?
reduces the oxygen-carrying capacity of the blood
effects of smoking on air passages:
-tar destroys the cilia
-this causes the buildup of mucus and potentially leads to bronchitis as the lining of the bronchi become irritated
effects of smoking on alveoli:
1)
-tar contributes to the break down of the walls of the alveoli, causing them to merge together
-this creates an insufficient surface area to volume ratio, allowing less gas exchange
-this reduces the efficiency of gas exchange, causing emphysema where less oxygen is carried in blood (making exercise difficult)
2)
-tar can also build up and form a layer on top of the alveolar cells which can increase the diffusion distance for gas exchange
smoking in the past:
-it wasn’t until the 1930s that doctors started to suggest that smoking could be negatively impacting people’s lung health
-they were seeing a large number of lung cancer patients who were heavy smokers
doll and hill study results (1951)
-smoking greatly increases the mortality from lung cancer and lung disease
-the greater the intensity of smoking, the higher the increased mortality
-smoking increases the mortality rate from other cancers
what is a risk factor?
a factor that increases the likelihood of a person developing a disease
what is the incidence of disease?
the number of cases of a disease that occur in within a particular group of people within a given time
different types of studies that can be done to collect data:
-prospective studies
-retrospective studies
what are prospective studies?
collecting data as it becomes available
advantage & disadvantage of prospective studies:
advantage:
-more accurate data can be obtained
disadvantage:
-it can be highly time-consuming
what are retrospective studies?
collecting data from the past
advantages and disadvantages of retrospective studies:
advantages:
results can be obtained more rapidly
disadvantages:
the data collected may be unreliable as people forget details or alter them
why can collecting data for studies from the population be difficult?
-controlled experiments where only one variable is investigated can’t be carried out on humans due to ethical implications (eg: it would be immoral to ask a random group of people to smoke exactly 10 cigarettes every day for 10 years, while the control group is banned from smoking)
-finding people with sufficiently similar lifestyles can be difficult
-long term studies with multiple follow-ups take a lot of time and money
which things should be taken into consideration when analysing data from studies on health risk factors?
-sample size
-individuals in the sample
-levels of exposure
-control group
-statistical significance
-the influence of other factors/variables
considerations: sample size
a study with a large sample size will have more reliable results
considerations: individuals in the sample
-if the study only has women aged 20-40 this data is not able to suggest the effect on a male or an older woman
-it is therefore important to state the who the data is referring to when evaluating it
considerations: control group
-identify if the control group matches the other groups closely enough
-the people in the control group should be of a similar age and background to those in the other groups
considerations: the influence of other factors/variables
-there are many variables that have not been controlled due to moral reason
-this means there may be a combination of factors that are interacting with each other to influence the results
(genetics, secondary exposure to smoking)
disease development speed:
-some diseases develop slowly so there may be a delay between exposure to a risk factor and the disease becoming visible in the population
what is correlation?
a relationship between two variables
what is causation?
when one variable influenced by another
what are scattergrams used for?
to identify correlations between two variables to determine if a factor does increase the risk of developing a disease
what 2 things can correlation be?
positive: as one variable increases, the other one does
negative: as one variable increases, the other decreases
risk factors can ____ with eachother?
interact
correlation doesn’t equal….
causation
