Exchange Between Organisms And Their Environment Flashcards
The external environments is different from the internal environment found within an organism and within its cells. In order to survive organisms transfer
Materials between the two environments; this transfer takes place at exchange surfaces and always involve crossing cell plasma membranes
What role does tissue fluid play in organisms for exchange?
Tissue fluid is the environment around the cells of multicellular organisms. The majority of cells are too far from exchange surfaces for diffusion alone to supply or remove their tissue fluid with the various materials needed to keep its composition relatively constant. Therefore, once absorbed materials are rapidly distributed to the tissue fluid and the waste products returned to exchange surface for removal- this involves a mass transport system
What’s the importance of the mass transport system?
Maintains the diffusion gradient that brings materials to and from the cell-surface membranes
What are some examples of things that need be interchanged between an organism and its environment?
- respiratory gases e.g. oxygen and carbon dioxide
- nutrients (glucose, fatty acids, amino acids, vitamins, minerals
- excretory (urea and carbon dioxide)
- heat (most organisms need to stay roughly at the same temperature)
Except for heat substances that need to be interchanged between an organism and it’s environment can occur in 2 ways:
1- passively (no metabolic energy is required) by diffusion and osmosis
2- actively (metabolic energy is required) by active transport
Define diffusion
The movement of molecules or ions from a region were they are highly concentrated to one where their concentration is lower until equilibrium is reach
Define osmosis
The passage of water from a region of high water potential to a region where its water potential is lower through a partially (selectively) permeable membrane
Exchange takes place at the surface of an organism, but the materials absorbed are used by cells that mostly make up its volume. What is needed for the exchange to be effective?
Exchange surface of the organism must be large compared to its volume
Small organisms have a surface area that is large enough, compared with their volume to allow efficient exchange across their body surface. However, as organisms become larger
Their volume increases at a faster rate than their surface area. Because of this, simple diffusion of substances across the outer surface can only meet the needs of relatively inactive organisms. Even if the outer surface could supply enough of a substance, it would still take too long for it to reach the middle of the organism if diffusion alone was the method of transport
Organisms have evolved one or more of the following features:
- a flattened shape so that no cell is ever far from the surface e.g. flatworm or a leaf
- specialised exchange surfaces with large areas to increase the surface area e.g. lungs in a mammal or gills in a fish
How do you calculate surface area of a cube?
1- area of cross section X number of faces
2- e.g. 4X4 = 16
16X6= 96cm
How do you calculate the volume?
BXWXH
Larger cells have a smaller surface area for exchange across plasma membrane so
Diffusion across plasma membrane is insufficient to meet metabolic needs
Describe the effect of SA:V ratio on the rate of diffusion
As SA:V ratio decreases the rate of diffusion also decreases
Explain the importance of SA:V ratio to living organisms
- Larger animals have a smaller SA:V ratio
- Are unable to obtain enough nutrients and oxygen by diffusion across outer surface
- Require specialised exchange surfaces (to increase SA)
- Require a transport system to transport nutrients / oxygen larger distances to cells deep within body
All cells and organisms must exchange substances with their environment and so, many organisms have specialised
exchange surfaces adapted to make it easier for substances to cross from one side of the surface to another
Some organisms can exchange nutrients and gases across their outer surface if:
- Large SA:V ratio
- Short diffusion distance
- Less metabolically active
Single-celled organisms like Amoeba do not require specialised exchange surfaces Why?
- Large SA:V ratio
- Exchange gases (e.g. oxygen / carbon dioxide) by simple diffusion across plasma membrane
- Short diffusion distance to centre of organism
- No transport system required
Some multicellular organisms
e.g. tapeworm also do not require specialised exchange surfaces Why?
- Some multicellular organisms are very thin and flat
- Large SA:V ratio
- Short distance for diffusion of gases e.g. oxygen
- Not very metabolically active
- Also do not require a transport system
More complex multicellular organisms do require specialised exchange surfaces Why?
- Small SA:V ratio
- Outer surface is too small to allow sufficient gas exchange to meet metabolic needs of the large volume of organism
- So require a specialised exchange surface
Complex multicellular organisms may also need a transport system Why?
- In larger organisms some cells are deep within the body
- Increases the diffusion distance for gases
- More metabolically active
- Must supply cells with oxygen and glucose more rapidly for aerobic respiration
- Diffusion is therefore too slow to meet metabolic needs so also require a transport system
Factors that determine the need for a transport system:
- SA:V ratio
- Size (determines diffusion distance)
- Metabolic rate
Some multicellular organisms do not require a transport system if:
- Large SA:V ratio (easy enough to exchange enough substances to a small volume of animal but large outer surface for gas exchange across cell-surface membrane)
- Short diffusion distance
- Low level of activity
More complex multicellular organisms do require a transport system if:
- Smaller SA:V ratio
- Larger diffusion distance
- More metabolically active
- Must supply cells with oxygen and glucose more rapidly for aerobic respiration
What are the features of exchange surfaces?
•Large surface area often achieved by folding
•Thin so short diffusion distance
•Steep concentration gradient
•Maintained by a fresh supply of substances on one side (to maintain high concentration)
•Rapid removal of substance on the other side (to maintain low concentration)
- selectively permeable to allow selected materials to cross
What are some examples of exchange surfaces?
-Alveoli in lungs: gas exchange (oxygen in / carbon dioxide out) •Gills in fish •Villi in small intestine •Hepatocytes in liver •Mesophyll tissue in leaf •Root hair cells
Villi in small intestine increase
surface area for absorption of the products of digestion- microvilli further increase surface area of epithelial cells in small intestine and of hepatocytes in liver
What are the functions of the liver?
- Removes excess glucose from blood to store as glycogen
- Releases glucose back into blood when blood glucose levels are low
- Removes excess amino acids from blood
How is a plant root adapted
for the uptake of water and
mineral ions?
Root hairs increase surface area for:
•Uptake of water by osmosis
•Uptake of mineral ions by active transport
Single-celled organisms are small and therefore have a large SA:Vol ratio. Oxygen is absorbed by diffusion across their body surface which is covered only by
A cell-surface membrane (in the same way,carbon dioxide from respiration diffuses out across their body surface- where a living cell is surrounded by a cell wall, this is no additional barrier to the diffusion of gases)
If a cell has the shape of a sphere, and is 10 micrometers in diameter, work out the SA: Vol ratio
1- surface area of a sphere= 4X pi X r squared
2- surface area of the cell = 4 X 3.14 X (5X5) = 314 micrometers squared
3- volume of a sphere= 4/3 X pi X r cubed
4- volume of the cell = 4/3 X 3.14 X (5X5X5)= 523.33 micrometers cubed
5- SA: V ratio = 3.14/ 523.33= 0.6:1
Name some factors that affect the rate of diffusion of substances into cells:
- surface area/ thickness of cell-surface membrane
- permeability of cell-surface membrane to particular substance
- concentration gradient of substance inside/outside of cell
- temperature
What is Fick’s Law?
Rate of diffusion =
area of diffusion surface X difference in conc
———————————————————
Thickness of surface over which diffusion takes place
Insects and some other terrestrial invertebrates exchange gases with their surroundings via a system of air filled tubes called tracheae- the insect breathing system is therefore known as the
Tracheal system
Describe and explain the tracheal system
- insects have evolved an internal network of tubes called tracheae
- the trachea are supported by strengthened rings to prevent them from collapsing
- the trachea divide into smaller dead-end tubes called tracheoles
- the tracheoles extend throughout all the body tissues of the insect
- in this way, atmospheric air with the oxygen it contains is brought directly to the respiring tissues as there is a short diffusion pathway from a tracheole to any body cell
Respiratory gases move in and out of the tracheal system in 3 ways:
1- along a diffusion gradient
2- mass transport
3- the ends of tracheoles are filled with water
Explain how respiratory gases move in and out of the tracheal system along a diffusion gradient
When cells are respiring, oxygen is used up and so its concentration towards the end of the tracheoles falls. This creates a diffusion gradient that causes gaseous oxygen to diffuse from the atmosphere along the trachea and tracheoles to the cells. Carbon dioxide is produced by cells during respiration; this creates a diffusion gradient in the opposite direction. This causes gaseous carbon dioxide to diffuse along the tracheoles and trachea from the cells to the atmosphere
What is a benefit of respiratory gases moving in and out of the tracheal system along a diffusion gradient?
Diffusion in air much faster than in water, respiratory gases are exchanged quickly by this method
Explain how respiratory gases move in and out of the tracheal system by mass transport?
The contraction of muscles in insects can squeeze the trachea enabling mass movements of air in and out. This further speeds up the exchange of respiratory gases
Explain how respiratory gases move in and out of the tracheal system from the ends of tracheoles being filled with water
- During periods of major activity, the muscle cells around the tracheoles respire and carry out anaerobic respiration, producing lactate which is soluble and lowers the water potential of the muscle cells. Water therefore moves into the cells from the tracheoles by osmosis
- the water in the ends of the tracheoles decreases in volume and in doing so draws air further into them
- this means the final diffusion pathway is in a gas rather than a liquid phase and therefore diffusion is more rapid = increases the rate at which air is moved into the tracheoles but leads to greater water evaporation
Gases enter and leave the trachea through tiny pores called
Spiracles
Where are spiracles located?
On the body surface
The spiracles may be opened or closed by
A valve
When the spiracles are open
Water vapour can evaporate from insect; so most of the time, insects keep their spiracles closed to prevent this water loss. But periodically they do open the spiracles to allow gas exchange
Explain how the tracheal system limits the size of insects?
- because it relies on diffusion to bring oxygen to the respiring tissues
- if insects were large it would take too long for oxygen to reach the tissues rapidly enough to supply their needs
Explain why there is a conflict in terrestrial insects between gas exchange and conserving water?
Gas exchange requires a thin, permeable surface with a large area and conserving water requires thick, waterproof surfaces with a small area
Why are fish body surfaces not adequate to supply and remove their respiratory gases?
Fish have a waterproof (and therefore gas-tight) outer covering; being relatively large they have a small SA:vol ratio= like humans and insects they have evolved a specialised internal gas exchange- the gills
Describe the structure of the gills
- The gills are located within the body of the fish, behind the head
- they are made up of stacked gill filaments
- perpendicular to the gill filaments are gill lamellae which increase the surface area of the gills
- water is taken in through their mouth and forced over the gills out through an opening on each side of the body
- the flow of water over the gill lamellae and the flow of blood within them are in opposite directions = counter-current flow
Explain the countercurrent exchange principle
- the essential feature of the countercurrent exchange system is that blood and water flow over the gill lamellae in opposite directions meaning that:
- blood that is already well loaded with oxygen meets water that has its maximum concentration of oxygen therefore diffusion of oxygen from water to the blood takes place
- blood with little oxygen in it meets water which has had most, but not all of its oxygen removed. Again, diffusion of oxygen from the water to the blood takes place
What is the result of the countercurrent exchange system?
A diffusion gradient for oxygen is maintained across the ENTIRE WIDTH of the gill lamellae. In this way, about 80% of the oxygen available in the water is absorbed into the blood of the fish
What would be the result if fish didn’t have a countercurrent exchange system?
If the flow of water and blood was in the same direction (parallel flow) the diffusion gradient would only be maintained across part of the length of the gill lamellae and only about 50% of the available oxygen would be absorbed
How are gills adapted for gaseous exchange?
- gill filaments and lamellae increase the surface area increasing rate of exchange of gases
- lamella have lots of blood capillaries and thin epithelium increasing rate of diffusion- thin layer of cells= short diffusion pathway
Water flow over fish gills is one-way whereas the flow of air in and out of the lungs is two-way. Suggest why one-way flow is an advantage
Less energy is required because the flow does not have to be reversed (important as water is dense and difficult to move)
If an organism has a large volume is it easier or harder to lose heat from its body?
If an organism has a large volume e.g. hippo, its surface area is relatively small making it harder to lose heat from its body
If an organism is small (has a small volume) is it easier or harder to lose heat from its body?
If an organism is small e.g. mouse its relative surface area is large, so heat is lost more easily meaning smaller organisms need a relatively high metabolic rate in order to generate enough heat to stay warm
Will animals with a compact shape lose or conserve more heat?
Animals with a compact shape have a small surface area relative to their volume, minimising heat loss from their surface- animals with a less compact shape (those that are a bit gangly or have sticky outy bits) have a larger surface area relative to their volume, increasing heat loss from their surface
Organisms have behavioural and physiological adaptions to aid exchange (not all organisms have a body size or shape to suit their climate, some have other adaptive instead) give some examples
1- animals with a high SA: volume ratio tend to lose more water as it evaporates from their surface. Some small desert mammals have kidney structure adaptions so that they produce less urine to compensate
2- to support their high metabolic rates, small malls living in cold regions need to eat large amounts of high energy goods such as seeds and nuts
3- smaller mammals may have thick layers of fur or hibernate when the weather gets very cold
4- larger organisms living in hot regions e.g. elephants and hippos find it hard to keep cool as their heat loss is relatively slow. Elephants have developed large flat ears to increase their surface area, allowing them to lose more heat
- hippos spend much of their day in the water- behavioural adaption to help them lose heat
When it comes to gas exchange, plants show one major difference from animals:
Some plant cells (plant cells with chloroplasts) photosynthesis
During photosynthesis plant cells take in carbon dioxide and release oxygen; at times the gases produced in photosynthesis can be used
In respiration and vice versa- reducing gas exchange with the external air
Volumes and types of gases that are being exchanged by a leaf change depending on
The balance between rates of photosynthesis and respiration
The diffusion gradients in and out of the leaf are maintained by
mitochondria carrying out respiration and chloroplasts carrying out photosynthesis
When photosynthesis is taking place, although some carbon dioxide comes from respiration of cells, most of it is obtained from
The external air
some oxygen from photosynthesis is used for respiration but most of it
Diffuses out of the cell
When photosynthesis is not occurring e.g. in the dark, what happens to oxygen?
Oxygen diffuses into the leaf because it is constantly being used by cells during respiration; in the same way, carbon dioxide produced from respiration diffuses out
In what ways is plant is gas exchange in plants similar to insects?
- no living cell is far from the external air and therefore, a source of oxygen and carbon dioxide
- diffusion takes place in the gas phase (air) which makes it more rapid than if it were in water
There is no specific transport system for gases in plants
Which simply diffuse in and out the leaves
Dicotyledonous plants exchange gases at
The surface of the mesophyll cells in the leaf. Gases move in and out through special pores in the epidermis called stomata (occur mainly on underside of leaf) which can open to allow exchange of gases and close if the plant is losing too much water
What controls the opening and closing of stomata?
Guard cells
How are leaves adapted for rapid diffusion?
1- many stomata (small pores), so no cell is far from a stomata and therefore the diffusion pathway is short
2- numerous interconnecting air spaces that occur throughout the mesophyll so that gases can readily come into contact with mesophyll cells
3- Large surface area of mesophyll cells for rapid diffusion
State some differences between gaseous exchange in a plant leaf in a terrestrial insect
- insects may create mass air flow whereas plants never do
- insects have a smaller SA: vol ratio than plants
- insects have special structures (trachea) along which gases can diffuse, whereas plants do not
- insects do not interchange gases between respiration and photosynthesis whereas plants do
Explain the advantage of a plant being able to control the opening and closing of stomata
Helps to control water loss by evaporation/ transpiration
The features that make a good gas-exchange system are the same features that increase water loss so in order to survive terrestrial organisms must limit their water loss without
Compromising the efficiency of their gas-exchange systems
What adaptions have insects evolved to limit water loss?
- small SA: vol ratio to minimise the area over which water is lost
- waterproof coverings over their body surfaces: a rigid outer skeleton of chitin that is covered with a waterproof cuticle
- spiracles: if losing too much water they close their spiracles using their muscles
- tiny hairs around spiracles to reduce evaporation
An insect’s adaptions to minimise water loss means that insects cannot use their body surface to diffuse respiratory gases in the way a single-celled organism does. Instead they have
An internal network of tubes called tracheae that carry air containing oxygen directly to the tissues
Why can’t plants have a small SA: vol ratio like insects do to minimise water loss?
Plants photosynthesis which requires a large SA for the capture of light
How do terrestrial plants limit water loss?
- waterproof waxy cuticle over parts of the leaves
- stomata: stomata are usually kept open in the dah to allow gaseous exchange. Water enters the guard cells, making them turgid which opens the stomata pore. If the plant starts to become dehydrated, the guard cells lose water and become flaccid which closes the pore
Some plants are specially adapted for life in warm, dry or windy habitats where water loss is a more significant problem- what are these plants called?
Xerophytes
Xerophytes have evolved a range of adaptions to limit water loss through evapotranspiration - give some examples:
- thick waxy cuticles on leaves and stems to reduce evaporation
- rolling up of leaves: protects the lower epidermis from the outside helps trap a region of still air within the rolled leaf. This region becomes saturated with water vapour and so has a very high water potential. There is no water potential gradient between the inside and outside of the leaf and therefore no water loss e.g. Marram grass
- layer of ‘hairs’ on epidermis traps still,moist air next to the leaf surface. The water potential gradient between the inside and the outside of the leaves is reduced and therefore less water is lost through evaporation e.g. species of heather plant
- reduced number of stomata = fewer pores for water to escape
- reduced SA:volume ratio of the leaves e.g. pine needles as opposed to broad flat leaves considerably reduces rate of water loss (reduced evaporation)- this reduction in SA is balanced against the need for a sufficient area for photosynthesis to meet the requirements of the plant
Insects and plants face the same problems when it comes to living on land- what is the main problem they share?
Efficient gas exchange requires a thin, permeable surface with a large area. On land these features can lead to a considerable loss of water by evaporation
State one modification to reduce water loss that is shared by plants and insects
- Waterproof covering to the body
- Ability to close the openings of the gas exchange system (stomata and spiracles)
Plants such as marram grass roll up their leaves with the lower epidermis on the inside to reduce water loss. Why would rolling the epidermis the other way not be effective n reducing water loss?
Almost all stomata are on the lower epidermis. This would be exposed to air currents that would reduce the water potential immediately outside the leaf. The water potential gradient would be increased and a lot of water vapour would be lost
In humans where does gaseous exchange take place?
Epithelium of the alveoli in the lungs
The volume of oxygen that has to be absorbed and the volume of carbon dioxide that must be removed in mammals are large because:
- relatively large organisms with a larger volume of living cells
- they maintain a high body temperature which is related to them having metabolic and respiratory rates
As a result, mammals have evolved specialised surfaces called lungs to ensure efficient has exchange between the air and their blood
The lungs are the site of gas exchange in mammals. Why are they located inside the body?
- air is not dense enough to support and protect these delicate structures
- the body as a whole would otherwise be a great deal of water and dry out
The lungs are supported and protected by a bony box called
The ribcage
The ribs can be moved by
The muscles between them
The lungs are ventilated by
A tidal stream of air, thereby ensuring that the air within them is constantly replenished
What are the main parts of the human gas-exchange system?
- lungs
- trachea
- bronchi
- bronchioles
- trachea
Describe the structure and function of the lungs
Pair of lobed structures made up of a series of highly branched tubules called bronchioles, which end in tiny air sacs called alveoli
Describe the structure and function of the trachea
Flexible airway supported by rings of cartilage that prevent the trachea collapsing as the air pressure inside falls when breathing in. The tracheal walls are made up of muscle lined with ciliated epithelium and goblet cells
Describe the structure and function of the bronchi
Two divisions of the trachea, each leading to one lung. They are similar in structure to the trachea and, like the trachea, they also produce mucus to trap dirt particles and have cilia that move the dirt-laden mucus towards the throat. The larger bronchi are supported by cartilage but the amount of cartilage is reduced as the bronchi get smaller
Describe the structure and function of the bronchioles
Series of branching subdivisions of the bronchi. Their walls are made of muscle lined with epithelial cells. This muscle allows them to constrict so that they can control the flow of air in and out of the alveoli
Describe the structure and function of the alveoli
Minute air-sacs with a diameter between 100-300 micrometers, at the end of the bronchioles. Between the alveoli there are some elastic and collagen fibres and the alveoli are lined with epithelium. The elastic fibres allow the alveoli to stretch as they fill with air when breathing in. They then spring back during breathing out in order to expel the carbon dioxide rich-air. The alveoli membrane is the gas exchange surface.
List in the correct sequence all the structures that air passes through on its journey to the alveoli and the capillary
Oxygen in air moves through the nose, the trachea, the bronchi and bronchioles into the alveoli down a pressure gradient. Once in the alveoli, the oxygen diffuses across alveolar epithelium, then the capillary endothelium down a diffusion gradient ending up in the capillary itself
Explain how the cells lining the trachea protect the alveoli from damage
ciliated epithelium and goblet cells- goblet cells produce mucus that ‘traps’ particles of dirt and bacteria in the air breathed in. The cilia on these cells moves the debris up the trachea and into the stomach. The dirt/bacteria could possibly cause damage to the alveoli
The ribcage, intercostal muscles and diaphragm all work together to
Move air in and out
What is the process of ventilation (breathing)?
To maintain diffusion of gases across the alveolar epithelium, air is constantly moved in and out the lungs= ventilation
What is inhalation?
When the air pressure of the atmosphere is grater than the air pressure inside the lungs air is forced into the lungs
What is exhalation?
When the air pressure inside the lungs is greater than that of the atmosphere, air is forced out the lungs
The pressure changes within the lungs are brought about by the movement of what muscles?
- the diaphragm (sheet of muscle that separates the the thorax from the abdomen)
- the intercostal muscles which lie between the ribs. There are 2 types of intercostal muscles:
- internal intercostal muscles= whose contraction leads to exhalation
- external intercostal muscles= whose contraction leads to inhalation
Describe the process of inhalation
- the external intercostal muscles and diaphragm contract while the internal intercostal muscles relax
- causes the ribcage to move upwards and outwards and the diaphragm to flatten, increasing the volume of the thoracic cavity (space where lungs are)
- as the volume of the thoracic cavity increases the lung pressure decreases (to below atmospheric pressure)
- as air moves down a pressure gradient, the air flows down the trachea into the lungs
- inhalation is an active process so requires energy
Describe the process of exhalation
1- the external intercostal muscles and diaphragm relax
2- the ribcage moves downwards and inwards and the diaphragm becomes curved again
3- the volume of the thoracic cavity decreases causing the air pressure to increase (above atmospheric pressure)
4- air is forced down the pressure gradient and out of the lungs
5- normal exhalation is a passive process so doesn’t require energy
Describe how forced exhalation works e.g blowing out candles
The external intercostal muscles relax and the internal intercostal muscles contract, pulling the ribcage further down and inwards- during this time, the movement of the two sets of intercostal muscles is said to be antagonistic
How do you work out pulmonary ventilation rate? (Total volume of air that is moved into the lungs in 1 minute)
Pulmonary ventilation= tidal volume X breathing rate
Check camera roll for units
To maintain a diffusion gradient there has to be movement of both the environmental medium (e.g. air)
And the internal medium (e.g. blood)
Each alveolus is made from a single layer of
Thin, flat cells called the alveolar epithelium
Describe the process of gaseous exchange via the alveoli
1- there’s a huge number of alveoli in the lungs which means there’s a big surface area for exchanging oxygen and carbon dioxide
2- the alveolar are surrounded by a network of capillaries
3- oxygen diffuses out of the alveoli across the alveolar epithelium and the capillary endothelium (type of epithelium that forms the capillary wall) and into the haemoglobin in the blood
4- Carbon dioxide diffuses into the alveoli from the blood and is exhaled out
Diffusion of gases between the alveoli and the blood will be very rapid because:
- red blood cells (erythrocytes) are slowed as they pass through pulmonary capillaries allowing more time for diffusion
- the distance between the alveolar air and the erythrocytes is reduced as the erythrocytes are flattened against the capillary walls
- alveoli have only a single layer of epithelial cells and the blood capillaries have only a single layer of endothelium cells therefore short diffusion pathway
- alveoli and pulmonary capillaries have a very large total surface area
- breathing movements constantly ventilate the lungs and the action of the heart constantly, circulates blood around the alveoli. Together, these ensure that a steep concentration gradient of gases to be exchanged is maintained
How are the alveoli alone adapted to gas exchange?
- thin surface exchange- alveolar epithelium single layer of epithelial cells = short diffusion pathway which speeds up diffusion
- large surface area= the large number of alveoli means there’s a large surface area for gas exchange
- each alveolus is covered by a dense network of pulmonary blood capillaries= steep concentration gradient of oxygen and carbon dioxide between alveoli and capillaries which increases rate of diffusion- this is constantly maintained by the flow of blood and ventilation (blood capillaries have only a single layer of endothelial cells)
What is tidal volume?
Volume of air in each breath- usually between 0.4dm^3 and 0.5dm^3 for adults
What is ventilation rate?
Number of breaths per minute- for a healthy person it’s about 15 breaths
What is forced expiratory volume?
Maximum volume of air that can be breathed out in 1 second
What is forced vital capacity?
Maximum volume of air it is possible to breathe forcefully out of the lungs after a really deep breath in
You can figure out tidal volume, ventilation rate and other measures of breathing from a graph produced from a
Spirometer
What are the different lung diseases we need to know about?
- pulmonary tuberculosis (TB)
- fibrosis
- asthma
- emphysema
What is TB and what are its effects?
- when someone becomes infected with TB, immune system cells build a wall around the bacteria in the lungs forming small, hard lumps known as tubercles
- infected tissue within the tubercles dies and gaseous exchange surface is damaged so tidal volume is decreased
- tuberculosis also causes fibrosis which further reduces the tidal volume
- a reduced tidal volume means less air can be inhaled with each breath. In order to take in enough oxygen, patients have to breathe faster I.e. ventilation rate is increased
- common symptoms include a persistent cough, coughing up blood and mucus, chest pains and shortness of breath and fatigue
What is fibrosis and what are its effects?
- fibrosis is the formation of scar tissue in the lungs; this can be the result of an infection of exposure to substances like asbestos or dust
- scar tissue is thicker and less elastic than normal lung tissue = lungs less able to expand so can’t hold as much air as normal = tidal volume decreased and so is forced vital capacity (FVC)
- there’s a reduction in the rate of gaseous exchange- diffusion is slower across a thicker scarred membrane
- symptoms of fibrosis in our shortness of breath, a dry cough, chest pain, fatigue and the weakness
- fibrosis sufferers have a fast ventilation rate than normal (to get sufficient air into their lungs to oxygenate their blood)
What is asthma and what are its effects?
- asthma is a respiratory condition where the airways become inflamed and irritated- the causes vary from case to case but it’s usually because of an allergic reaction to substances such as pollen and dust
- during an asthma attack, the smooth muscle lining the bronchioles contracts and a large amount of mucus is produced = constriction of the airways making it difficult for the sufferer to breathe properly. Air flow in and out of the lungs is severely reduced,so less oxygen enters the alveoli and moves into the blood. Reduced air flow means that forced expiratory volume is severely reduced I.e. less air can be breathed out in 1 second
- symptoms include wheezing, a tight chest and shortness of breath. During an attack, the symptoms come on very suddenly- they can be relived by drugs (often in inhalers) which cause the muscle in the bronchioles to relax, opening up the airways
What is emphysema and what are its effects?
- emphysema is a lung disease caused by smoking or long-term exposure to air pollution- foreign particles in the smoke (or air) become trapped in the alveoli = causes inflammation which attracts phagocytes to the area- the phagocytes produces an enzyme that breaks down elastin (a protein found in the walls of the alveoli). Elastin is elastic and helps the alveoli to return to their normal shape after inhaling and exhaling air.loss of elastin means the alveoli can’t recoil to expel air as well (it remains trapped in the alveoli)
- emphysema also leads to the destruction of the alveoli walls which reduces the surface area of the alveoli, so the rate of gaseous exchange decreases
- symptoms of emphysema include shortness of breath and wheezing. People with emphysema have an increased ventilation rate as they try to increase the amount of air (containing oxygen) reaching their lungs
Why do sufferers of TB, fibrosis, asthma and emphysema often feel tired and weak?
All of those lung diseases reduce the rate of gaseous exchange in the alveoli. Less oxygen is able to diffuse into the bloodstream, so the body cells receive less oxygen and the rate of aerobic respiration is reduced = less energy released and so sufferers often feel tired and weak
Why is the human digestive system referred to as an exchange surface through which food substances are absorbed?
The human digestive system is made up of a long muscular tube and its associated glands- the glands produce enzymes that hydrolyse larger molecules into smaller ones ready for absorption. The digestive system is therefore an exchange surface through which food substances are absorbed
What is digestion?
Process in which large molecules are hydrolysed by enzymes into small molecules which can be absorbed and assimilated
What is the role of the oesophagus in the digestive system?
Carries food from the mouth to the stomach
What is the role of the stomach in the digestive system?
Muscular sac with an inner layer that produces enzymes- its role is to store and digest food, especially proteins. It has glands that produce enzymes that digest proteins
What is the role of the ileum in the digestive system?
The ileum is a long muscular tube- food is further digested in the ileum by enzymes that are produced by its walls and by glands that pour their secretions into it. The inner walls of the ileum are folded into villi which gives them a large surface area- the surface area of these villi is further increased by millions of tiny projections called microvilli on the epithelial cell of each villus = adapts ileum for its purpose of absorbing the products of digestion into the bloodstream
What is the role of the large intestine in the digestive system?
Absorbs water- most of the water that is absorbed is water from the secretion of the many digestive glands
What is the role of the rectum in the digestive system?
Final section of the intestines- the faeces are stored here before being periodically being removed via the anus in a process called egestion
Where are the salivary glands located and what is their function?
Situated near the mouth- they pass their secretions via a duct into the mouth. These secretions contain the enzyme amylase which hydrolyses starch into maltose
Where is the pancreas located and what is its function?
Large gland situated below the stomach and produces a secretion called pancreatic juice- this secretion contains proteases to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch
In humans, digestion takes place in 2 stages
1- physical breakdown
2- chemical digestion
The contents of the intestines are not inside the body- molecules and ions only truly enter the body when they cross
The cells and cell-surface membranes of the epithelial lining of the intestines
Describe the process of physical breakdown
If the food is large, it is broken down into smaller pieces by means of structures such as the teeth; this not only makes it possible to ingest the food but provides a large surface area for chemical digestion. Food is churned up by muscles in the stomach wall and this also physically breaks it up
Large biological molecules e.g. starch and proteins in food are too to cross cell membranes =
Can’t be absorbed from the gut into the blood
Describe the process of chemical digestion
Chemical digestion hydrolyses large, insoluble molecules into smaller, soluble ones carried out by enzymes- enzymes are specific and so it follows that more than one enzyme is needed hydrolyse a large molecule. Usually, one enzyme hydrolyses a large molecule into sections and these sections are then hydrolysed into smaller molecules by one or more additional enzymes
What are 3 important digestive enzymes and their function
1- carbohydrases hydrolyse carbohydrates ultimately to monosaccharides
2- lipases hydrolyse lipids to fatty acids and glycerol
3- proteases hydrolyse proteins, ultimately to amino acids
Describe the steps of carbohydrate digestion
1- saliva enters the mouth from the salivary glands and is thoroughly mixed with food during chewing. Saliva contains the enzyme salivary amylase which hydrolyses any starch present in the food into maltose by hydrolysing the alternate glycosidic bonds. It also contains mineral salts that help to maintain the PH at around neutral, as this is the optimum PH for amylase to work
2- the food is swallowed and enters the stomach, where the conditions are acidic, denaturing the amylase, preventing further hydrolysis of starch.
3- after a time,the food is passed to the small intestine where it mixes with the secretion from the pancreas, pancreatic juice. This pancreatic juice contains pancreatic amylase, which continues the hydrolysis of any remaining starch to maltose. Alkaline salts are produced by both the pancreas and the intestinal wall, to maintain the PH at around neutral, so that amylase can function.
4- muscles in the intestinal wall push the food along the ileum; its epithelial tissue produces the disaccharide maltase. Maltase is part of the cell-surface membranes of the epithelial cells, that line the ileum, so it is therefore referred to as a membrane-bound disaccharide. The maltase hydrolysis the maltose from the starch breakdown to a-glucose
Aside from maltose, 2 other common disaccharides in the diet are hydrolysed
1- sucrase (in lots of fruits) hydrolyses the single glycosidic bond in sucrose to give glucose and fructose
2- lactase hydrolyses the single glycosidic bond in the lactose molecule to give glucose and galactose
Describe the process of lipid digestion
- Lipids are hydrolysed by enzymes called lipases
- lipases are enzymes produced in the pancreas that hydrolyse the ester bond found in the triglycerides to form fatty acids and monoglycerides (glycerol molecule with a single fatty acid attached)
- lipids are firstly split up into tiny droplets called micelles, by bile salts, which are produced by the liver- emulsification and increases the surface area of lipids, so that the action of lipases is speeded up
Describe the process of protein digestion
- Proteins (polypeptides) are large, molecules that are hydrolysed by a group of enzymes called peptidases (proteases)
- endopeptidases: hydrolyse the amino acids in the central region of a protein molecule, forming a series of peptide molecules
- exopeptidases: hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases
- dipeptidases: hydrolyse the bond between the two amino acids of a dipeptide- dipeptidases are membrane-bound, being part of the cell-surface membrane of the epithelial cells lining the ileum
Suggest why the stomach does not have villi or microvilli
Villi and microvilli increase surface area to speed up absorption of soluble molecules. As the food in the stomach has not yet been hydrolysed into soluble molecules they cannot be absorbed so villi and microvilli are unnecessary
Explain how lowering of water potential in the colon can cause diarrhoea
Low water potential in the colon causes water to move from epithelial cells in the lumen of the colon creating watery stools
Describe the structure of the ileum
- ileum adapted to the function of absorbing the products of digestion
- the wall of the ileum is folded and possess finger-like projections called villi- they have thin walls lined with epithelial cells on the other side of which is a rich network of blood capillaries
- the villi considerably increase the surface area of the ileum and therefore accelerate the rate of absorption
Villi of the ileum are situated
At the interface between the lumen of the intestines (in effect the outside of the body)
Villi are part of a specialised exchange surface adapted for the absorption of the products of digestion. Their properties increase the efficiency of absorption in the following ways:
- they increase surface area for diffusion
- they are very thin walled, thus reducing the distance over which diffusion takes place
- they contain muscle so are able to move. This helps to maintain diffusion gradients because their movement mixes the contents of the ileum; this ensures that as the products of digestion are absorbed from the food adjacent to the villi, new material rich in the products of digestion replaces it
- well supplied with blood vessels so blood can carry away absorbed molecules and hence maintain a diffusion gradient
- epithelial cells lining the villi possess microvilli- finger-like projections of the cell-surface membrane that further increase the surface area for absorption
The products of digestion are absorbed across the
Ileum epithelium into the bloodstream
How are monosaccharides absorbed?
- glucose is absorbed by active transport with sodium ions via a co-transporter protein; galactose is absorbed in the same way using the same co-transporter protein
- fructose is absorbed via facilitated diffusion through a different transporter protein
How are monoglycerides and fatty acids absorbed?
- once formed during digestion, monoglycerides and fatty acids remain in association with the bile salts that initially emulsified the lipids droplets- structures formed called micelles
- through the movement of material within the lumen of the ileum, the micelles come into contact with the epithelial cells lining the villi of the ileum
- here the micelles break down, releasing the monoglycerides and fatty acids (as these are non-polar molecules they can easily diffuse across the cell-surface membrane into the epithelial cells
- once inside the epithelial cells monoglycerides and fatty acids are transported to the ER where they are recombined to form triglycerides. Starting in the ER and continuing into the Golgi apparatus, the triglycerides associate with cholesterol and lipoproteins to form structures called chylomicrons (specialised particles adapted for the transport of lipids)
- chylomicrons move out of the epithelial cells by exocytosis and they enter lymphatic capillaries called lacteals that are found at the centre of each villus. From here, the chylomicrons pass via lymphatic vessels into the blood system. The triglycerides in the chylomicrons are hydrolysed by an enzyme in the endothelial cells of the blood capillaries from where they diffuse into cells
What are 3 organelles that you would expect to be numerous and/or developed in an epithelial cell of the ileum
- ER to re-synthesise triglycerides from monosaccharides and fatty acids
- Golgi apparatus to form chylomicrons from triglycerides, cholesterol and lipoproteins
- mitochondria to provide ATP required for co-transport of glucose and amino acid molecules
What are haemoglobin molecules?
Globular protein in erythrocytes that readily combines with oxygen to transport it around the body- it comprises 4 polypeptide chains each containing an iron-containing haem group
Haemoglobin are highly adapted molecules for transporting
Oxygen
Haemoglobins are protein molecules with a quaternary structure that has evolved to make it efficient at loading oxygen under one set of conditions and
unloading it under a different set of conditions
Describe the structure of haemoglobin in terms of primary structure etc
- primary structure= sequence of amino acids in the 4 polypeptide chains
- secondary structure= in which each of these polypeptide chains is coiled into a helix
- tertiary structure= in which each polypeptide chain is folded into a precise shape- an important factor in its ability to carry oxygen
- quaternary structure= in which all 4 polypeptides are linked together to form an almost spherical molecule. Each polypeptide is associated with a haem group, which contains a ferrous ion; each ferrous ion can combine with a single oxygen molecule making a total of 4 oxygen molecules that can be carried by a single haemoglobin molecule in humans
The process by which haemoglobin binds with oxygen is called
Loading or associating; in humans this takes place in the lungs = oxyheamoglobin
- haemoglobin saturation depends on partial pressure of oxygen. Oxygen loads onto haemoglobin to form oxyhaemoglobin where there’s a high partial pressure of oxygen (oxygen enters blood capillaries at alveoli in lungs so alveoli have high partial pressure of oxygen)
The process by which haemoglobin releases its oxygen is called
Unloading or dissociating; in humans this takes place in the tissues
Haemoglobin with a high affinity for oxygen e.g in lungs
Take up oxygen more easily, but release it less easily
Haemoglobin with a low affinity for oxygen e.g. respiring tissue
Take up oxygen less easily, but release it more easily
The role of haemoglobin is to transport oxygen; to be efficient at transporting oxygen, haemoglobin must
- readily associate with oxygen at the surface where gas exchange occurs
- readily dissociate from oxygen at tissues requiring it
- these two requirements may appear to contradict each other, but they are achieved by a remarkable property of haemoglobin- it changes its affinity (chemical attraction) for oxygen under certain conditions. It achieves this because its shape changes in the presence of certain chemicals, like carbon dioxide- in the presence of carbon dioxide, the new shape of the haemoglobin molecule binds more loosely to oxygen = haemoglobin releases its oxygen
Why do different haemoglobins have different affinities for oxygen?
- each species produces a haemoglobin with a slightly different amino acid sequence
- haemoglobin of each species therefore has a slightly different tertiary and quaternary structure and hence different oxygen binding properties
- depending on its structure, haemoglobin molecules range from those that have a high affinity for oxygen to those that have a low affinity for oxygen
Explain how DNA leads to different haemoglobin molecules having different affinities for oxygen
- different base sequences in DNA
- different amino acid sequences
- different tertiary/quaternary structure and shape
- different affinities for oxygen
When the body is at rest, only one of the four oxygen molecules carried by haemoglobin is normally released into tissues. Suggest why this could be an advantage when the organism becomes more active
If all oxygen molecules were released, there would be none in reserve to supply tissues when they were more active
Carbon monoxide occurs in car exhaust fumes. It binds permanently to haemoglobin in preference to oxygen. Suggest a reason why a person breathing in car-exhaust fumes might lose consciousness
Carbon monoxide will gradually occupy all the binding sites on haemoglobin instead of oxygen. No oxygen will be carried to tissues such as the brain. These will cease to respire and to function, making the person lose consciousness
What is the oxygen dissociation curve?
When haemoglobin is exposed to different partial pressures of oxygen, it does not bind the oxygen evenly. The graph of the relationship between between the saturation of haemoglobin with oxygen and the partial pressure of oxygen = oxygen dissociation curve
Draw the oxygen dissociation curve
Check camera roll
Explain the shape of the oxygen dissociation curve
1- shape of the haemoglobin molecule makes it difficult for the first oxygen molecule to bid to one of the sites on its four polypeptide subunits because they’re closely united. Therefore, at low oxygen concentrations, little oxygen binds to haemoglobin = gradient of curve is shallow initially
2- however, binding of this first oxygen molecule changes the quaternary structure of the haemoglobin molecule causing it to change shape; this change makes it easier for the other subunits to bind to an oxygen molecule I.e. binding of first oxygen molecule induces the other subunits to bind to an oxygen molecule
3- it therefore takes a smaller increase in partial pressure of oxygen to bind to the second oxygen molecule than it did the first = positive cooperativity as binding of the first oxygen molecule makes binding of the second easier and so on= gradient of curve steepens
4- situation changes however after binding of the third oxygen molecule simply due to probability- with the majority of binding sites occupied, it is less likely that a single oxygen molecule will find an empty site to bind to = gradient of curve reduces and graph flattens off
The many different oxygen oxygen dissociation curves are better understood if two facts are always kept in mind:
1- the further to the left the curve, the greater is the affinity of haemoglobin for oxygen (so it loads oxygen readily but unloads it less easily)
2- the further to the right the curve, the lower is the affinity of haemoglobin for oxygen (so it loads oxygen less readily but unloads it more easily)
What is the Bohr effect?
Haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide- the greater the concentration of carbon dioxide (higher the partial pressure of carbon dioxide) the more readily haemoglobin releases its oxygen = Bohr effect
Explain how carbon dioxide concentration affects oxygen unloading (Bohr effect)
(To complicate matters, haemoglobin gives up its oxygen more readily at higher partial pressures of carbon dioxide= cunning way of getting more oxygen to cells during activity)
1- when cells respire they produce carbon dioxide which raises the partial pressure of carbon dioxide
2- this increases the rate of oxygen unloading (I.e the rate at which oxyhaemoglobin dissociates to form haemoglobin and oxygen) = dissociation curve ‘shifts’ to the right. The saturation of blood with oxygen is lower for a given partial pressure of oxygen meaning more oxygen is being released = BOHR EFFECT
How does the Bohr effect explains why behaviour of haemoglobin changes in different regions of the body ( contrast gas-exchange surface to respiring tissue)?
- at the gas exchange-surface e.g. lungs, the concentration of carbon dioxide is low because it diffuses across the exchange surface and is excreted from the organism. The affinity of haemoglobin for oxygen is increased, which coupled with high concentrations of oxygen in the lungs, means that oxygen is readily loaded by haemoglobin. The reduced carbon dioxide concentration has ‘shifted’ the oxygen dissociation curve to the left
- in rapidly respiring tissues e.g. muscles, the concentration of carbon dioxide is high= the affinity of haemoglobin for oxygen is reduced, which coupled with low concentrations of oxygen in the muscles means that oxygen is readily unloaded from the haemoglobin into the muscle cells = increased carbon dioxide concentration has shifted the oxygen dissociation curve to the right
Haemoglobin is different in various organisms- different organisms have different types of haemoglobin with different oxygen transporting capacities; having a particular type of haemoglobin is an adaption that helps the organism to survive- give examples
1- organisms that live in environments with a low concentration of oxygen have haemoglobin with a higher affinity for oxygen than our human haemoglobin = dissociation curve to the left of ours e.g animals living in depleted oxygen environment such as a lugworm (higher affinity for oxygen)- haemoglobin of the lugworm is fully loaded with oxygen even when there is little available in their environment
2- organisms that are very active and have a high oxygen demand have haemoglobin with a lower affinity for oxygen than human haemoglobin = curve to the right of a human one e.g. active animal with a high respiratory rate living where there’s plenty of oxygen available such as a hawk
In order of left to right of human dissociation curve draw
- A= animal living in environment with depleted oxygen e.g. lugworm
- B= animal living at high altitude where the partial pressure of oxygen is lower e.g. llama in Andes
- C= human dissociation curve
- D= active animal with a high respiratory rate living where there’s plenty of oxygen available e.g. hawk
Check camera roll
A rise in temperature ‘shifts’ the oxygen dissociation curve to the right. Suggest how this enables an exercising muscle to work more efficiently
Exercising muscles release heat, ‘shifting’ the curve to the right causing the haemoglobin to release more oxygen to fuel the muscular activity
Haemoglobin usually loads oxygen less readily when the concentration of carbon dioxide is high (Bohr effect). The haemoglobin of lugworms does not exhibit this effect. Explain why to do so could be harmful
Respiration produces carbon dioxide and this builds up in the burrows when the tide is out. If lungworm haemoglobin exhibited the Bohr effect, it would not be able to absorb oxygen when it was present in only very low concentrations in the burrow
Suggest whether the oxygen dissociation curve of a pigeon is shifted to the right or left of the curve of a human
Shifted to the right because this means that oxygen is more readily released to the tissues and so the haemoglobin supplies more oxygen to enable the muscles to respire rapidly
The oxygen dissociation curve of the mouse is shifted to the right of that of a human.
A) explain what difference this makes to the way oxygen is unloaded from mouse haemoglobin compared to human haemoglobin
B) suggest an advantage this has for the maintenance of body temperature in mice
A- unloads more easily
B- oxygen is more easily released from haemoglobin to the tissues = helps tissues respire more and so produce more heat which helps to maintain the body temperature of the mouse
The greater the concentration of carbon dioxide, the more readily haemoglobin releases its oxygen. This is because dissolved
Carbon dioxide is acidic and lowers PH causing haemoglobin to change shape
Explain why large organisms have a transport system?
- all organisms exchange materials between themselves and their environment
- in small organisms, this exchange takes laces over the surface of the body
- but with increasing size, the SA:Vol ratio decreases to a point where the needs of an organism cannot be met by body surface alone = specialist exchange surface required (to absorb nutrients snd respiratory gases and remove excretory products)
- transport system required to take materials from cells to exchange surfaces and from exchange surfaces to cells
- as organisms have evolved into larger and more complex structures, the tissues and organs of which they are made have become more specialised and dependent upon one another
= transport system all more essential
In a nutshell, why do large organisms have a transport system?
Large organisms require a transport system to take materials from exchange surfaces to cells that require them
Whether or not there is a specialised transport medium, and whether or not it is circulated by a pump depends on 2 factors:
1- SA:Vol ratio
2- how active the organism is
lower the SA:vol ratio and more active the organism, the greater is the need for a specialised transport system with a pump
Any large organism encounters the same problems in transporting materials within itself= not surprisingly, the transport systems of many organisms have many common features:
- suitable medium in which to carry materials e.g blood (this is normally a liquid based on water because water readily dissolves substances and can be moved around easily, but can be a gas such as aid breathed in and out of the lungs
- form of mass transport in which the transport medium is moved around in bulk over large distances= more rapid than diffusion
- a closed system of tubular vessels that contain transport medium and forms a branching network to distribute it to all parts of the organism
- a mechanism for moving the transport medium within vessels- this requires a pressure difference between one part of the system and another
- a mechanism to maintain the mass flow movement in one direction e.g. valves
- a means of controlling the flow of the transport medium to suit the changing needs of different parts of the organism
- a mechanism for the mass flow of water or gases, for example intercostal muscles and diaphragm during breathing in animals
Regarding common features of transport systems, a mechanism for moving the transport medium within vessels which requires a pressure difference between one part of the system and another can be achieved in 2 ways:
1- animals use muscular contraction, either of the body muscles or of a specialised pumping organ, such as the heart
2- plants rely on natural, passive processes such as the evaporation of water
Mammals have a closed, double circulatory system in which blood is confined to vessels and passes twice through the heart for each complete circuit of the body- why is this?
- because when the blood is passed through the lungs, its pressure is reduced
- if it were to pass immediately to the rest of the body, its low pressure would make circulation very slow
- blood is therefore returned to the heart to boost its pressure before being circulated to the rest of the tissues
- as a result, substances are delivered to the rest of the body quickly, which is necessary as mammals have a high body temperature and hence a high metabolic rate
The vessels that make up the circulatory system of a mammal are divided into 3 types:
Arteries, veins and capillaries (blood circulates through heart to arteries, arterioles, capillaries, venules, to veins, back to heart)
What is a double circulatory system?
Two ‘loops’ in our body in which blood circulates-pulmonary circulation I.e. blood flow between heart and lungs is separate from systematic circulation- I.e. movement of blood from the heart through the rest of the body (excluding the lungs) then back to heart
- pulmonary circulation= oxygenated blood
- systemic circulation= deoxygenated blood
Many small multicellular organisms such as anthropods, insects, spiders, crabs etc and molluscs (snails,slugs etc) have what kind of circulatory system?
- open circulatory system
- these systems include a pump (heart) and open-ended vessels
- hemolymph is pumped out of the vessels into the body cavity where it bathes the tissues
How do active insects maintain maintain a high metabolic rate with an open circulatory system?
- have a system of air tubes (trachea) that respiratory gases diffuse through to reach every cell in the body
- BUT this limits the maximum body size of insects
State the main advantage of double circulation found in mammals
Increases blood pressure and therefore the rate of blood flow to tissues
Draw a plan of the mammalian circulatory system
Check camera roll
Explain how fish have a closed single circulatory system?
Blood flows through the heart once in a complete circuit around the body
Heart-> gills-> body-> heart
Summarise mammalian circulatory system
- closed double circulatory system
- made up of 2 parts: pulmonary circulation and systemic circulation
- blood travels twice through heart in one complete circuit around the body
Contrast blood pressure regarding circulatory systems of fish and mammals
- circulatory system in fish:
- blood pressure reduced as blood passed through capillaries of gills
- therefore flow is reduced through the rest of the body
- oxygen and glucose not delivered as quickly to respiring tissues for aerobic respiration
- fish however are less active than mammals and do not maintain their body temp = require less energy
IN CONTRAST
- double circulatory system in mammals:
- lower blood pressure in pulmonary circulation to avoid damage to capillaries in lungs
- heart increases blood pressure in systemic circulation so blood flows more quickly through body tissues
- oxygen and glucose delivered quickly to respiring tissues for aerobic respiration
- mammal more active than fish and maintain their body temp = require more energy from respiration
The heart has its own blood supply-
Left and right coronary arteries
Meganeuropsis is related to modern dragon flies but had a wing span up to 65cm, and lived in Carboniferous period 300 million years ago. How did it grow so large?
Thought atmosphere contained more oxygen than today
Blood vessels is an umbrella term for
Arteries (arterioles) capillaries (venules) and veins
What are function and structure of arteries?
- carry blood away from heart at high pressure
- narrow lumen to maintain pressure
- thick wall containing:
- collagen (provide strength to withstand pressure)
- elastic tissue (allows wall to stretch and recoil to maintain pressure)
- smooth muscle (contract to constrict lumen to maintain pressure)
- folded endothelium (squamous epithelium provide a smooth surface to reduce friction and folded to allow wall to stretch)
What’s main artery of the body?
Aorta- distributes oxygenated blood to all parts of the body through systemic circulation
All arteries carry oxygenated blood except for
Pulmonary arteries, which take deoxygenated blood to the lungs
Arteries divide into smaller vessels called
Arterioles- these form a network throughout the body. Blood is directed to different areas of demand in the body by muscles inside the arterioles, which contract to restrict the blood flow or relax to allow full blood flow
What are the function and structure of veins?
- carry blood back to heart at low pressure
- wide lumen to aid blood flow
- very little elastic or muscle tissue (no need to stretch, recoil, restrict blood flow)
- veins contain valves to prevent backflow of blood
- blood flow through veins is aided by contraction of skeletal muscles surrounding them
All veins carry deoxygenated blood except for
Pulmonary veins which carry oxygenated blood to the heart from the lungs
How is blood flow through the veins helped by skeletal muscle contraction?
1- pressure falls behind valves. Pockets fill and close the valve
2- pressure builds from the blood JG
What is the function and structure of capillaries?
- arterioles branch into capillaries, which are smallest of blood vessels
- site of exchange (e.g. glucose,oxygen, carbon dioxide) between blood and cells via tissue fluid so they’re adapted for efficient diffusion
- always found very near cells in exchange tissues e.g. alveoli in lungs = short diffusion pathway
- walls consist of single layer of endothelium (squamous epithelium) = shortens diffusion pathway
- large number of capillaries = increases SA for exchange- networks of capillaries in tissues called capillary beds
Blood pressure reduces as blood pressure divides into more blood vessels= due to
Increase in cross sectional area in arterioles and capillaries
What is blood?
- specialised tissue composed of:
Cells including erythrocytes, leukocytes, and platelets suspended in a liquid called plasma
Plasma contains many dissolved substances:
- salts
- nutrients e.g. glucose, amino acids, fatty acids
- carbon dioxide (mainly as hydrogencarbonate ions)
- waste products e.g. urea
- plasma proteins e.g. immunoglobulins and albumin
- hormones e.g. insulin
What is tissue fluid?
- fluid that bathes the cells formed from blood plasma
- cells exchange materials with tissue fluid by diffusion or facilitated diffusion (take in oxygen and nutrients from it and release metabolic waste into it)
- provides stable environment with the conditions cells need to function
- composition of tissue fluid maintained as part of homeostasis (by maintaining composition of the blood)
- unlike blood, does not contain erythrocytes or large proteins (too large to be pushed out of capillary walls)
Exchange takes place between the blood and tissue fluid by simple/ facilitated diffusion- how is the efficiency of exchange increased?
- thin capillary walls composed of squamous epithelium= short diffusion distance
- steep concentration gradient (cells use nutrients and produces waste, also blood flow)
- capillary bed has large surface area for which exchange can occur= increases diffusion rate
In a capillary bed, substances move out of the capillaries into tissue fluid by
Pressure filtration = formation of tissue fluid
Explain the formation of tissue fluid
1- due to high hydrostatic pressure (due to contraction of the muscle in the ventricle) at the artery end of the capillary bed
2- plasma containing dissolved substances is forced out of the capillary
3- through gaps (pores) in the capillary wall by ultrafiltration
4- forms tissue fluid
What’s 3 differences between blood and tissue fluid?
1- tissue fluid = no large proteins blood= contains large proteins
2- tissue fluid= some leukocytes but not erythrocytes or platelets blood= contains erythrocytes
3- tissue fluid= always low pressure blood= pressure variable
How is tissue fluid returned to circulatory system?
-once tissue fluid has exchanged metabolic materials with the cells it bathes, it is returned to circulatory system-most tissue fluid returns to blood plasma directly via capillaries and occurs as follows:
1- loss of tissue fluid from capillaries reduces hydrostatic pressure inside them
2- as a result, by the time the blood has reached the venous end of the capillary network, its hydrostatic pressure is usually lower than that of the tissue fluid outside of it
3- therefore tissue fluid forced back into capillaries by the higher hydrostatic pressure outside them
4- in addition, the plasma has lost water and still contains proteins = therefore has a lower water potential than tissue fluid
5- as a result, water leaves the tissues by osmosis down a water gradient
- the tissue fluid has lost much of its oxygen and nutrients by diffusion into the cells that it bathed, but has gained carbon dioxide and waste materials to return
If 90% of tissue fluid returns to the blood, what remaining percentage drains into the lymphatic system? (Network of tube that acts a bit like a drain, which transports this excess fluid from the tissues and dumps it back into circulatory system)
10%
What is lymph and describe lymph flow
- a colourless fluid containing white blood cells, which bathes the tissues and drains through the lymphatic system into the bloodstream
- lymph flows very slowly
- lymph vessels contain semilunar valves and rely on contraction of skeletal muscles to ensure flow
- lymph nodes are also found at intervals which contain macrophages (phagocytes) and lymphocytes
- eventually returns to the blood in the subclavian veins
Lymph is similar in composition to tissue fluid except
Less oxygen, more carbon dioxide and fewer nutrients
Why do we have tissue fluid?
Capillaries cannot serve every single cell directly, so metabolic materials travel in tissue fluid which bathes the tissues
The heart is a muscular organ that lies
In the thoracic cavity behind the sternum (breastbone)
The heart is divided laterally into 2 sides by the septum and this division creates 4 chambers:
- left atrium
- left ventricle
- right atrium
- right ventricle
The left side of the heart deals with what kind of blood?
Oxygenated = oxygenated blood-> body = systemic circuit
The right side of the heart deals with what kind of blood?
Deoxygenated = de-oxygenated blood-> lungs = pulmonary circuit
The atrium is ____-walled and elastic as it collects blood
Thin
The ventricle has a much ______ muscular wall as it has to contract strongly to pump blood some distance (either lungs or rest of body)
Thicker
Why is the blood not just pumped through the lungs to collect oxygen and then straight to the body before returning to the heart?
- problem with such a system is that blood has to pass through tiny capillaries in the lungs in order to present a large surface area for the exchange of gases
- in doing so, there is a very large drop in pressure and so the blood flow to the rest of the body would be very slow
- mammals therefore have a system in which the blood is returned to the heart to increase its pressure before it is distributed to the rest of the body
Heart essentially powers the entire
Circulatory system transporting nutrients, oxygen, waste materials, hormones and immune cells throughout the body continuously
The heart generates high hydrostatic pressure to pump blood
Out of the heart, while also creating low pressure to bring it back in
Draw structure of the heart
Check camera roll
Where does oxygenated blood enter the heart?
Pulmonary vein
What valve links the left atrium from ventricle?
Left atrioventricular valve
What artery carries oxygenated blood from the heart to the rest of the body?
Aorta ❤️
What valve links the left ventricle to the aorta?
Semi-lunar valve
Where does de-oxygenated blood enter the heart?
Through the vena cava
What valve links the right atrium from ventricle?
Right atrioventricular valve
What valve links the right ventricle to the pulmonary artery?
Semi-lunar valve
Why does the left ventricle have a thicker wall than the right ventricle?
- right ventricle pumps deoxygenated blood only to the lungs
- whereas left ventricle has a thick muscular wall enabling it to contract to create enough pressure to pump oxygenated blood to the rest of the body
Both atria contract together and then
Both ventricles contract together, pumping the same volume of blood
What is the function of the AV and semi-lunar valves?
- blood always moves from a region of higher pressure to one of lower pressure
- valves used to prevent any unwanted back-flow of blood
- AV valves= between atria and ventricles
- closure of these valves ensures that when the ventricles contract(ventricle pressure exceeds atrial pressure) blood within them moves to the aorta and pulmonary artery and aorta rather than back to the atria
- semi-lunar valves= prevent back-flow of blood into the ventricles when the pressure within these vessels exceeds that in the ventricles
- this arises when the elastic walls of the vessels recoil increasing the pressure within them and when ventricle walls relax reducing the pressure within the ventricles
Suggest why it is important to prevent mixing of the blood in the two sides of the heart
- mixing of oxygenated and deoxygenated blood would result in only partially oxygenated blood reaching the tissues and lungs
- this would mean the supply of oxygen to the tissues would be inadequate and there would be a reduced diffusion gradient in the lungs
- limiting the rate of oxygen uptake
The valves only open one way- whether they’re open or closer depends on
- the relative pressure of the heart chambers
- if there’s higher pressure behind a valve, it’s forced open
- but if pressure is higher in front of the valve, it’s forced shut
- this means blood only flows one way through the heart
Although oxygenated blood passes through the left side of the heart, the heart does not use this oxygen to meet its own greater respiratory needs. Instead, the heart muscle is supplied by its own blood vessels called
The coronary arteries, which branch off the aorta shortly after it leaves the heart
What is the cardiac cycle?
Ongoing sequence of contraction (systole) and relaxation (diastole) of the atria and the ventricles that keeps blood continuously circulating around the body
What are the stages of the cardiac cycle?
1- relaxation of the heart (diastole)
2- atrial systole
3- ventricular systole
Explain 1- relaxation of the heart (diastole)
- blood returns to the atria of the heart through the pulmonary vein (from the lungs) and the vena cava (from the body)
- as the atria fill, the pressure in them rises
- when this pressure exceeds that in the ventricles the AV valves open allowing the blood to pass into the ventricles
- passage of blood aided by gravity
- muscular walls of both atria and ventricles are relaxed at this stage
- the relaxation of the ventricle walls causes them to recoil and reduces the pressure within the ventricle
- this causes pressure to be lower than that in the aorta and pulmonary artery
- so the semi-lunar valves in the aorta and pulmonary artery close
- accompanied by the ‘dub’ sound of the heart
Explain 2- atrial systole
- contraction of atrial walls forces the remaining blood into the ventricles from the atria
- throughout this stage, the muscles of the ventricle walls remain relaxed
Explain 3- ventricular systole
- after a short delay to allow the ventricles to fill with blood, their walls contract simultaneously
- this increases the blood pressure within them and forces shut the AV valves preventing back-flow of blood into the atria
- the ‘lub’ sound of these valves closing is a characteristic of the heartbeat
- with the AV valves closed, the pressure in the ventricles rises further
- once it exceeds that in the aorta and the pulmonary artery, blood is forced from the ventricles into these vessels = semi-lunar valves open
Where are pocket valves found?
In veins that occur throughout venous system
What is the role of pocket valves?
Ensure that when veins are squeezed during skeletal muscle contraction blood flows back towards the heart rather than away from it
What is cardiac output?
Volume of blood pumped by one ventricle of the heart in one minute
What is the equation for cardiac output?
Cardiac output= heart rate X stroke volume (volume of blood pumped out at each beat)
Explain how most cardiovascular diseases start with atheroma formation
- the wall of an artery is made up of several layers
- the endothelium (inner lining) is usually smooth and unbroken
- if damage occurs to the endothelium e.g by high blood pressure, white blood cells and lipids (fat) from the blood clump together under the lining to form fatty streaks
- over time, more white blood cells, lipids and connective tissue build up and harden to form a fibrous plaque called an atheroma
- this plaque partially blocks the lumen of the artery and restricts blood flow which causes blood pressure to increase
Coronary heart disease (CHD) is a type of cardiovascular disease that occurs when
The arteries have lots of atheroma in them which restricts blood flow to the heart muscle and can lead to myocardial infarction
Atheromas increase the risk of
Aneurysm and thrombosis (diseases that affect the arteries)
What is an aneurysm?
- atheroma plaques damage and weaken arteries and also narrow the arteries increasing blood pressure
- when blood travels though a weakened artery at high pressure, it may push the inner layer of the artery through the outer elastic layer to form a balloon-like swelling (aneurysm)
- this aneurysm may burst, causing a haemorrhage (bleeding)
What is thrombosis?
- an atheroma plaque can rupture (burst through) the endothelium (inner lining of an artery)
- this damages the artery wall and leaves a rough surface
What is a myocardial infarction?
A heart attack
Explain how interrupted blood flow to the heart can cause a myocardial infection?
- the heart is a muscle supplied with blood from the coronary arteries
- this blood contains the oxygen needed by the heart muscle cells to carry out respiration
- if a coronary artery becomes completely blocked e.g. by a blood clot, an area of the heart muscle will be totally cut off from its blood supply, receiving no oxygen
- causing a myocardial infarction
- heart attack can cause damage and death of the heart muscle
- symptoms include pain in the chest and upper body, shortness of breath and sweating
- if large areas of the heart are affected then complete heart failure can occur which is often fatal
What are 3 factors that increase the risk of cardiovascular disease?
- high blood cholesterol and poor diet
- cigarette smoking
- high blood pressure
Explain how high blood cholesterol and poor diet is a risk factor associated with cardiovascular disease
- high blood cholesterol increases risk of cardiovascular disease
- this is because cholesterol is one of the main constituents of the fatty deposits that form atheromas
- atheromas can lead to increased blood pressure and blood clots
- this could block the flow of blood to coronary arteries which could cause a myocardinal infarction
- a diet in high saturated fat is associated with high blood cholesterol levels
- a diet high in salt also increases the risk of cardiovascular disease because it increases the risk of high blood pressure
Explain how cigarette smoking is a risk factor associated with cardiovascular disease
- both nicotine and carbon monoxide found in cigarette smoke increase the risk of cardiovascular disease
- nicotine increases the risk of high blood pressure
- carbon monoxide combines with haemoglobin and reduces the amount of oxygen available to the tissue
- if heart muscle doesn’t receive sufficient oxygen it can lead to a myocardial infarction
Explain how high blood pressure is a risk factor associated with cardiovascular disease
- high blood pressure increases the risk of damage to the artery walls
- damaged walls have an increased risk of atheroma formation causing a further increase in blood pressure
- atheromas can also cause blood clots to form
- a blood clot could block flow of blood to the heart muscle, possibly resulting in a myocardial infarction
- so anything that increases blood pressure also increases the risk of cardiovascular disease e.g. being overweight, not exercising and excessive alcohol consumption
Most of risk factors are under our control e.g. a person can choose to smoke, eat fatty foods etc, however some risk factors can’t be controlled such as
Having a genetic predisposition to coronary heart disease or having high blood pressure as a result of another condition
Draw out the cross section of a leaf
Check camera roll
Why do plants need a transport system?
- oxygen for respiration
- carbon dioxide for photosynthesis
- mineral ions and water
- organic nutrients for respiration and growth
Explain how the demand of oxygen and carbon dioxide is met by diffusion in plants
- large SA: V ratio due to many leaves
- leaves are thin= short diffusion pathway
- large SA for gaseous exchange
- demand for energy from respiration in plants is typically lower than in animal cells
Explain why plants require a mass flow transport system
To transport water and products of photosynthesis large distances
State the movement of water and sugars in a plant?
- water absorbed in soils= needed all over plant
- water and mineral ions= up stem in xylem
- water lost= leaves
- sugars= synthesised in leaves (source)
- sugars move = down stem in phloem
What is responsible for transport in plants?
Vascular tissues
What are the two types of vascular tissue responsible for the transport in plants?
- xylem tissue transports water and mineral ions in solution (these substances move up the plant from the roots to the leaves)
- phloem tissue (and sieve tubes) transports organic substances like sugars (products of photosynthesis) also in solution both up and down the plant
What is a tissue?
A group of similar cells working together to perform a particular function
Xylem vessels are the part of the xylem tissue that actually
Transports the water and ions
What are the elements of the xylem vessels?
- composed of elongated cells arranged end-to-end
- dead cells that lack cytoplasm and nucleus
- lignin deposited in cell walls to become impermeable (waterproof) and cell contents die
- end walls break down to form a continuous narrow, hollow tube for the transport of water
- contains pits (non-lignified areas of cellulose cell wall) to allow movement of water in/out of vessels
Explain the movement of water out of the stomata (transpiration)
- humidity of atmosphere usually less than that of their air spaces next to the stomata
- as a result there is a water potential gradient from the air spaces through the stomata to the air
- provided the stomata are open, water vapour molecules diffuse out of the air spaces into the surrounding air
- water lost by diffusion from the air spaces is replaced by water evaporating from the cell walls of the surrounding mesophyll cells
What is transpiration?
Evaporation of water from a plant’s surface, especially the leaves
Why are the stomata open during the day?
Allow gaseous exchange for photosynthesis
What is a consequence of stomata being open during day?
Water also lost via transpiration
If water uptake from the soil is sufficient what happens to the guard cells?
Go turgid
What happens when the guard cells go turgid?
They open
What happens to the guard cells if water loss in transpiration is greater than the uptake in roots?
Guard cells go flaccid
What happens when the guard cells are flaccid?
Stomata close reducing water loss
The main factor that is responsible for the movement of water up the xylem from the roots to the leaves is
Cohesion-tension
Explain stages of cohesion-tension theory
- water evaporates from mesophyll cells due to heat from the sun leading to transpiration
- water molecules from hydrogen bonds between one another hence tend to stick together = cohesion
- water forms a continuous, unbroken column across the mesophyll cells and down the xylem
- as water evaporates from the mesophyll cells in the leaf into the air spaces beneath the stomata, more molecules of water are drawn up behind it as a result of this cohesion
- a column of water is therefore pulled up the xylem as a result of this cohesion = transpiration pull
- transpiration pull puts the xylem under tension, that is, there is a negative pressure within the xylem hence name cohesion-tension theory
Transpiration is really a side effect of
Photosynthesis- plant needs to open its stomata to let in carbon dioxide so that it can synthesis glucose, but this also lets water out
What are the 4 main factors that affect transpiration rate?
- light
- temperature
- humidity
- wind
Explain how light effects transpiration rate
The lighter it is the faster the transpiration rate I.e positive correlation between light intensity and transpiration rate because stomata open when it gets light to let in carbon dioxide for photosynthesis and when it’s dark stomata sure usually close so there’s little transpiration
Explain how temperature effects transpiration rate
- higher the temp the faster the transpiration rate
- increased evaporation and diffusion due to increased kinetic energy so increased water movement
Explain how humidity effects transpiration rate
- higher humidity will decrease rate of water loss as there will be a smaller water vapour potential gradient between the air spaces in the leaf and the air outside
Explain how wind effects transpiration rate
Air moving outside the leaf will carry away water and maintain a high water vapour gradient so winder it is, the faster the transpiration rate
What evidence is there for cohesive tension theory?
- change in diameter of tree trunks according to rate of transpiration- during the day when transpiration is at its greatest, there is more tension (negative pressure) in the xylem pulling the walls of the xylem vessels inwards and causes the trunk to shrink in diameter. At night, when transpiration is at its lowest, there is less tension in the xylem and so the diameter of the trunk increases
- if a xylem vessel is broken and air enters it, the tree can no longer draw up water; the continuous column of water is broken and so the water molecules can no longer stick together
- when a xylem vessel is broken, water does not leak out, as would be the case if it were under pressure. Instead, air is drawn in which is consistent with it being under tension
Explain how phloem tissue is adapted for transporting solutes
- solutes are dissolved substances which the phloem tissue transports round plants. Like xylem, phloem is formed from cells arranged in tubes
- sieve tube elements and companion cells are important cell types in phloem tissue
- sieve tube elements are living cells that form the tube for transporting solutes- they have no nucleus and few organelles so…
- there’s a companion cell for each sieve tube element that carry out living functions for sieve cells e.g. providing the energy needed for active transport of solutes
What is translocation?
Movement of solutes e.g sugars like sucrose from sources (e.g leaves where sugars synthesised so is at a high concentration) to sinks where they’re used up (e.g. other parts of the plants especially food storage organs so at lower concentration)
- enzymes maintain a concentration gradient from the source to the sink by changing the solutes at the sink e.g. by breaking them down ensuring there’s always a lower concentration at the sink than the source e.g. in potatoes, sucrose is converted to starch in the sink areas
Scientists still aren’t certain exactly how the solutes are transported from source to sink by translocation but the best supported theory is the mass flow hypothesis:
1- sugars are actively transported into the phloem from sources in the plant via companion cells
2- lowering the water potential in the siege tubes
3- so water moves by osmosis from the xylem into siege tubes
4- this increase in pressure causes mass movement towards the sinks e.g. the roots where sugars are stored
While mass flow is a passive process it occurs as the result of
Active transport of sugars
What is evidence supporting mass flow hypothesis?
- if a ring of bark (which includes the phloem, but not the xylem) is removed from a woody stem, a bulge forms above the ring. The fluid from the bulge has a higher concentration of sugars than the fluid from below the ring = evidence that there’s a downward flow of sugars
- radioactive tracer such as radioactive carbon ^14C can be used to track the movement of organic substances in a plant
- pressure in phloem can be investigated using aphids- they pierce the phloem, then their bodies are removed leaving the mouthparts behind, which allows the sap to flow out. The sap flows out quicker nearer the leaves than further down the stem = evidence there’s a pressure gradient
- if a metabolic inhibitor (which stops ATP production) is put into the phloem, then translocation stops = evidence that active transport is involved
What are examples of objections to mass flow hypothesis?
- sugar travels to many different sinks, not just the one with the highest water potential as the model suggests
- the sieve plates would create a barrier to mass flow- a lot of pressure would be needed for the solutes to get through at a reasonable rate
Explain how the translocation of solutes in plants can be modelled in an experiment using radioactive tracers
1- can be done by supplying part of a plant (often a leaf) with an organic substance that has a radioactive label
2- radioactive carbon will then be incorporated into organic substances produced by leaf e.g. sugars produced by photosynthesis, which will then be moved around the plant by translocation
3- the movement of these substances can be tracked using a technique called autoradiography. To reveal where the radioactive tracer has spread to in the plant, the plant is killed e.g. by freezing it using liquid nitrogen and then the whole plant, or sections of it, is placed on photographic film- the radioactive substance is present wherever the film turns black
- results demonstrate translocation of substances from source to sink over time e.g. autoradiography of plants killed at different times shows an overall movement of solutes e.g. products of photosynthesis from leaves towards roots
Squirrels sometimes strip sections of bark from around branches. Explain why these branches may die
If squirrel strips away phloem around whole circumference of the branch it may not have sufficient sugars for its respiration to release enough energy for survival as none can reach it from other parts of the plant
Suggest how a branch with a complete ring of phloem stripped from it by squirrels may still survive
If the branch has sufficient leaves to supply its own sugar needs from photosynthesis, rather than depending on supplies from elsewhere, it might survive for a little while at least
Explain why squirrels are unlikely to cause the death of a large mature tree by stripping some bark from its trunk
Unlikely that squirrels would strip bark from around a whole circumference of a large tree trunk and any intact phloem could still supply sufficient sugars to its roots to allow it to survive
List the 3 features of a phylogenetic system of classification
- based on evolutionary relationships between organisms and their ancestors
- classifies species into groups using shared characteristics derived from their ancestors
- arranged in a hierarchy in which groups are contained within larger composite groups with no overlap
Mackerel are active, fast-swimming fish whilst plaice spend most of their lives moving slowly on the sea bed. There are differences in the gills of these two types of fish- suggest what these differences may be
Mackerel have increased number of gill lamellae = larger surface area compared to plaice
