AS - Unit 1 - Exchange and transport Flashcards
What substances do all living cells need to survive?
Oxygen for aerobic respiration
Glucose as a source of energy
Proteins for growth and repair
Fats to make membranes and to be a store of energy
Water
Minerals to maintain their water potential and to help enzyme action and other aspects of metabolism
What waste products do living cells need to remove?
CO2 (in animals and microorganisms, and also from plant cells that are not actively carrying out photosynthesis)
Oxygen (from photosynthesis in some plant cells and some protoctists)
Other waste products such as ammonia or urea, which contain excess nitrogen
What features should all good transport systems have in common?
Large surface area to provide more space for molecules to pass through - often achieved by folding the walls and membranes
Thin barrier to reduce the diffusion distance
Fresh supply of molecules on one side to keep the concentration high
Removal of required molecules on the other side to keep the concentration low
Give 4 exchange surfaces in living organisms.
Small intestine - where nutrients are absorbed
Liver - where levels of sugars in the blood are adjusted
Root hairs of plants - where water and minerals are absorbed
Hyphae of fungi - where nutrients are absorbed
Which way does oxygen move in the alveoli?
From the air in the alveoli to the blood in the capillaries
And vice versa for carbon dioxide
Give 4 ways the lungs are adapted for exchange
Large surface area
Barrier permeable to oxygen and carbon dioxide
Thin barrier to reduce diffusion distance
Maintaining a steep diffusion gradient
How does a large surface area help the lungs to work efficiently?
It provides more space for molecules to pass through. There are so many alveoli that the total surface area is larger than that of our skin.
How does an oxygen and CO2 permeable barrier helpful to the proper function of the lungs?
The plasma membranes that surround the thin cytoplasm of the cells form the barrier to exchange. These readily allow the diffusion of oxygen and carbon dioxide
How are alveoli adapted to have a short diffusion distance?
Alveolus wall is one cell thick
Capillary wall is one cell thick
Both walls consist of squamous cells
Capillaries are in close contact with the alveolus walls
Capillaries are so narrow the RBC’s are squeezed against the capillary wall reducing the rate at which they flow past in the blood
Total barrier to diffusion is only two flattened cells thick (less than 1um thick)
How can you keep oxygen diffusing into the lungs?
Having a high concentration of molecules on the supply side and a low concentration on the demand side. To keep the demand side low there needs to be a constant flow of blood to carry off the oxygen as it diffuses over. To keep the supply side high oxygen needs to move in often e.g constant breathing
What happens during inspiration?
Diaphragm contracts to become flatter and pushes digestive organs down
External intercostal muscles contract to raise ribs
Volume of chest cavity increases
Pressure in chest cavity drops below atmospheric pressure
Air moves into lungs
What happens during expiration?
Diaphragm relaxes and is pushed up by displaced organs underneath
External intercostal muscles relax and ribs fall
Volume of chest cavity decreases
Pressure in lungs increases and rises above atmospheric pressure
Air moves out of lungs
What properties must airways have to be effective?
The larger airways must be large enough to allow sufficient air to flow without obstruction
They must also divide into smaller airways to deliver air to all the alveoli
The airways must be strong enough to prevent them collapsing when the air pressure inside is low (during inhilation)
Must be flexible to allow movement
Must be able to stretch and recoil
Give 4 properties of the trachea and the bronchi
Much of the wall consists of cartilage
Cartilage in the form of C-rings in the trachea, but less regular in the bronchi
Inside surface of the cartilage is a layer of glandular tissue, connective tissue, elastic fibres, smooth muscle and blood vessels (called the loose tissue)
Inner lining in an epithelium later with two types of cells. Most have cillia cal lied ciliated epithelium cells, these are among goblet cells
Describe some properties of the bronchioles
Much narrower than the bronchi
Larger ones may have some cartilage but smaller ones have no cartilage
Wall is made of mostly smooth muscle and elastic fibres
The smallest bronchioles have alveoli at their ends
What is the role of cartilage in the gas exchange system?
Plays a structural role
Supports trachea and bronchi, holding them open
Prevents collapse when air pressure is low during inhalation
Not a complete ring so some flexibility, allows movement of neck without constructing the airways. Also allows the oesophagus to expand during swallowing
What is the role of the smooth muscle in the gas exchange system?
Smooth muscle can contract, when contracts makes the lumen of the airway narrower
Controlling the flow of air to the alveoli may be important if there are harmful substances in the air
Contraction of smooth muscle and control of airflow is not a voluntary act
Someone may have an allergic reaction to certain substances in the air and their bronchioles constrict
One of the causes of asthma
What is the role of the elastic fibres in the gas exchange system?
When smooth muscle contacts it deforms the elastic fibres, the SM can’t reverse this effect so the elastic fibres once deformed, recoil into their original shape and size, this widens the airway again
What role do goblet cells and glandular tissue play in the gas exchange system?
Secrete mucus, the mucus traps tiny particles from the air so they can be removed to reduce the risk of infection
That role does ciliated epithelium play in the gas exchange system?
Cilia move in synchronised pattern to waft the mucus up the airway to the back of the throat, once there the mucus is swallowed and the stomach acid will kill any bacteria
What is tidal volume?
The volume of air that moves in and out of the lungs with each breath when you are at rest
Approx 0.5dm^3
What is vital capacity?
The largest volume of air that can be moved into and out of the lungs in any one breath
Approx 5dm^3
What is residual volume?
The volume of air that always remains in our lungs even after the biggest possible exhalation
Approx 1.5dm^3
What is dead space?
The air in the bronchioles, bronchi and trachea. There is no gas exchange between this air and the blood
What is the inspiratory reserve volume?
How much more air can be breathed in (inspired) over and above the normal tidal volume when you take a big breath
What is expiratory reserve volume?
How much more air can be breathed out (expired) over and above the amount that is breathed in a tidal volume breath
What does a spirometer consist of?
A chamber filled with oxygen that floats on a tank of water
How does a spirometer work?
A person breathes from a disposable mouthpiece attached to a tube connected to the chamber of (medical-grade) oxygen. Breathing in takes oxygen from the chamber, which then sinks down. Breathing out pushes air into the chamber, which then floats up
Effectively a pen is attached to the top of the chamber lid and tracks the movement of the chamber, which records the breaths
Why is soda lime used in a spirometer?
When breathing in a spirometer for a period of time the carbon dioxide levels are increased dangerously.
The soda lime absorbs the carbon dioxide exhaled.
Why do the spirometer traces gradually decrease down the page?
As air is exhaled the soda lime absorbs the carbon dioxide which decreases the amount of air in the chamber
How do you know the volume of oxygen used up by someone breathing by a spirometer?
You measure the difference between the lowest point of the first wave and the lowest point of the last wave and divide it by how long the person was breathing into the spirometer
What is the definition of transport regarding the body?
The movement of oxygen, nutrients, hormones, waste and heat around the body
What three main factors affect the need for a transport system?
Size
Surface-area-to-volume ratio
Level of activity
Why does the size of an organism affect the need for a transport system?
Any oxygen or nutrients only diffuses to the outer layers of the organism and is used up, the middle cells don’t get anything
Why does surface-area-to-volume ratio affect the need for a transport system?
As an organism grows the size of it grows a lot faster than the surface area, this means the surface area is not large enough to supply all the oxygen and nutrients needed by the internal cells. Therefore the larger the organism the more urgent the need is for a transport system!
Why does level of activity affect the need for a transport system?
Animals need energy from food so that they can move around. Releasing energy from food by respiration requires oxygen. If an animal is very active the cells need a ready supply of energy for movement. And animals such as mammals who keep themselves warm need even more energy
Give three aspects of an effective transport system
Fluid or medium to carry nutrients and oxygen around the body - blood
A pump to create pressure that will push the fluid around the body - heart
Exchange surfaces that enable oxygen and nutrients to enter the blood and to leave it again where they are needed
Give two aspects of an efficient transport system
Tubes or vessels to carry blood
Two circuits - one to pick up oxygen and another to deliver oxygen to the tissues
What route does the blood take in a single circulatory system?
Heart –> gills –> body –> heart
What is the name of the circuit that carries blood to the lungs to pick up oxygen?
Pulmonary circulation
What is the name of the circuit that carries oxygen and nutrients around the body to the tissues?
Systematic circulation
How many times does blood flow through the heart for each circulation of the body?
twice
What route does blood take around the mammalian body?
Heart –> body –> heart –> lungs –> heart
Give three features of the fish single circulatory system
Blood pressure is reduced as blood passes through the tiny capillaries of the gills
Blood doesn’t flow very quickly through the rest of the body
The rate at which oxygen and nutrients are delivered to respiring tissues is limited
Why is a single circulatory system ideal for a fish?
They are not as active as mammals
They do not maintain their body temperature
Need less energy
Give three features of the mammal double circulatory system
Heart can increase the pressure of the blood after it has passed through the lungs so blood flows more quickly to the body tissue
Systematic circulation can carry blood at a higher pressure than the pulmonary circulation
Blood pressure must not be too high in the pulmonary circulation, otherwise it may damage the delicate capillaries in the lungs
Why is the double circulatory system idea for mammals?
Mammals are active
Maintain their body temp
All energy used in living is required from food
Energy is released from food in the process of respiration
To release a lot of energy the cells need good supplies of both nutrients and oxygen
A double circulatory system is ideal for all of these things
What kind of blood does the right side of the heart pump?
Deoxygenated blood to the lungs to be oxygenated
What does the left side of the heart do?
Pumps oxygenated blood to the rest of the body
What is the name of the vessels that lay over the surface of the heart?
Coronary arteries
What do the coronary arteries do?
Carry oxygenated blood to the heart muscle itself
How does deoxygenated bloody flow through the heart?
From the vena cava into the right atrium, through the atrioventricular valves into the ventricles. Flows into the pulmonary artery through the semilunar valve leading to the lungs
How does oxygenated blood travel through the heart?
From the lungs flows from the pulmonary vein into the left atrium. From the atria flows down through the atrioventricular valves into the ventricles. Flows up into the aorta as carries blood through semilunar valve to a number of arteries that’s supply all parts of the body
What is the significance of the septum?
Separates ventricles from each other, so oxygenated and deoxygenated blood doesn’t mix together
Why is the muscles of the atria very thin?
Because these chambers do not need to create much pressure, function is to push blood into ventricles
Why are the walls of the right ventricles thicker than the atria walls?
Enables the right ventricle to pump blood out of the heart
Why are the walls of the left ventricle thicker than the walls of the right ventricles?
Right ventricle –> blood to lungs, the lungs are in the chest cavity, therefore blood doesn’t need much pressure to go as far, pressure needs to be kept down to prevent capillaries in the lungs from bursting easily
Left ventricle –> blood to rest of body, needs lots of pressure to go all round the body and overcome resistance of the systematic circulation
Why are the capillaries in the lungs delicate?
Alveoli walls are very thin, very little or no tissue fluid so capillaries are not supported and could easily burst
What kind of blood does the right side of the heart pump?
Deoxygenated blood to the lungs to be oxygenated
What does the left side of the heart do?
Pumps oxygenated blood to the rest of the body
What is the name of the vessels that lay over the surface of the heart?
Coronary arteries
What do the coronary arteries do?
Carry oxygenated blood to the heart muscle itself
How does deoxygenated bloody flow through the heart?
From the vena cava into the right atrium, through the atrioventricular valves into the ventricles. Flows into the pulmonary artery through the semilunar valve leading to the lungs
How does oxygenated blood travel through the heart?
From the lungs flows from the pulmonary vein into the left atrium. From the atria flows down through the atrioventricular valves into the ventricles. Flows up into the aorta as carries blood through semilunar valve to a number of arteries that’s supply all parts of the body
What is the significance of the septum?
Separates ventricles from each other, so oxygenated and deoxygenated blood doesn’t mix together
Why is the muscles of the atria very thin?
Because these chambers do not need to create much pressure, function is to push blood into ventricles
Why are the walls of the right ventricles thicker than the atria walls?
Enables the right ventricle to pump blood out of the heart
Why are the walls of the left ventricle thicker than the walls of the right ventricles?
Right ventricle –> blood to lungs, the lungs are in the chest cavity, therefore blood doesn’t need much pressure to go as far, pressure needs to be kept down to prevent capillaries in the lungs from bursting easily
Left ventricle –> blood to rest of body, needs lots of pressure to go all round the body and overcome resistance of the systematic circulation
Why are the capillaries in the lungs delicate?
Alveoli walls are very thin, very little or no tissue fluid so capillaries are not supported and could easily burst
What is the cardiac cycle?
The sequence of events in one heartbeat
What happens in the filling phase of the cardiac cycle?
While the atria and ventricles are relaxing the internal volume increases and blood flows into the heart from the major veins.
Blood flows into the atria, through the atrioventricular valves and into the ventricles. This phase is called diastole
What happens during atrial contraction
Left and right atria contract together
Small increase in pressure created by this contraction pushes blood into the ventricles (atrial systole)
Ventricles fill
Blood fills the atrioventricular valve flaps making them snap shut
Prevent blood flowing back into the ventricles
What happens during ventricular contraction?
Short period where all four heart valves are closed
Ventricle walls contract (ventricular systole)
Contraction starts at base of heart and pushes blood upwards
Semilunar valves open and blood is pushed out of the heart
What is the purpose of valves in the heart?
Valves ensure that blood flows in the right direction
They are opened and closed by changes in the blood pressure in the various chambers of the heart
How do the atrioventricular valves work?
When ventricle walls relax the pressure in the ventricles dips below the pressure in the atria
This causes AV valves to open
Blood enters heart goes through atria into ventricles
Pressure in both raises as fill with blood
Valves remain open as atria contract
As ventricles contract, pressure rises above pressure in atria
Blood starts to move upwards
Movement fills valves pockets
They snap shut
Prevents back flow of blood
How do the semilunar valves work?
Ventricles begin to contract
Pressure in major arteries higher than pressure in ventricles
So semilunar valves are closed
ventricles contract
Pressure rises very quickly
Once pressure in ventricles above pressure in aorta and pulmonary arteries SL valves are pushed open
How do the semilunar valves close
Once ventricles finish contracting, heart muscles start to relax
Elastic tissue in walls of ventricles recoil to stretch muscle out again
This causes pressure in ventricle to drop quickly
Drops below pressure in major arteries
Semilunar valves are pushed closed by blood starting to back flow towards ventricles and collecting in pockets of the valves
Prevents blood returning to the ventricles
What is the written sound of the heart beating
Lub-dub
What happens during the ‘lub’ sound of the hearts ‘lub-dup’ sound
The atrioventricular valves closing as the ventricles start to contract
What happens during the ‘dup’ sound of the hearts ‘lub-dup’ sound
Semilunar valves closing as the ventricles start to relax
Which valve makes the loudest sound in the heart and why?
The AV valves closing because they snap shut so the noise is louder than the closing of the semilunar valves
What is the heart muscle described as?
Myogenic
Which muscles in the heart contract at a higher frequency?
The atrial muscles contract at a higher frequency than the ventricular muscle
Why does the heart need a mechanism to coordinate it?
Because the chambers contract at different frequencies so therefore need to be kept in sync in order to prevent fibrillation
Where is the SAN located in the heart?
At the top of the right atrium, near the point where the vena cava empties blood into the atrium.
What is the SAN (sinoatrial node)?
A small patch of tissue that generates electrical activity.
How does the SAN work?
It initiates a wave of excitation at regular intervals. In a human it occurs approx 55-80 times a minute. It is also known as the pace maker
What happens during atrial systole?
The wave of excitation from the SAN spreads over the walls of both atria. It travels along the membranes of the muscle tissue. As the wave of excitation passes, it makes the cardiac muscles contract.
How is atrial systole contained to only the atria?
At the base of the atria is a disc of tissue that cannot conduct the wave of excitation into the ventricular muscle walls.
How can ventricular contraction occur?
In the septum of the heart there is another node. The atrioventricular node (AVN).
How does the wave of excitation reach the AVN?
The wave of excitation from the SAN passes down the septum of the heart (the only route that conducts the wave) to the AVN.
How do the SAN and AVN work together in the heart to make it beat in time?
The wave of excitation is passed from the SAN through the atrial walls. It then reaches the AVN where it is delayed to ensure the atria have finished contracting and the blood has passed into the ventricles. Once the atria have finished contracting the AVN releases the wave of excitation down specialised conducting tissue called Purkyne tissue.
How does ventricular contraction occur?
Once the wave of excitation has travelled through the Purkyne tissue down the ventricular septum. At the base of the septum the wave spreads out over the walls of the ventricles. The wave spreads upwards from the base of the ventricles and it causes the muscles to contract. This causes the ventricles to contract from the base upwards, pushing blood up to the major arteries at the top of the heart.
What does ECG stand for?
electrocardiogram
In the trace of an ECG what does wave P show?
Excitation of the atria
In the trace of an ECG what does the QRS area indicate?
the excitation of the ventricles
What does T show in an ECG trace?
Diastole
What can you pick up from an ECG?
Parts of the heart which might not be working correctly
What is the name for a condition where your heart beats irregularly?
Arrhythmia
What causes a heart attack?
Heart muscle cells respire fatty acids and must have a continuous supply of oxygen as it can only respire aerobically. So a blood clot in the coronary artery starves part of the heart muscle of oxygen and those cells die, causing a heart attack.
In an ECG trace what change in wave indicates a heart attack?
Elevation of the ST section
What change in the ECG trace indicates atrial fibrillation?
Small and unclear P wave
What change in ECG trace indicates abnormal ventricular hypertrophy (increase in muscle thickness)?
A deep S wave
What do muscles need in order to be active?
Supply of oxygen and nutrients (such as glucose, amino acids and fatty acids) and the rapid removal of CO2
What is an open circulatory system?
Blood fluid circulates through the body cavity, so the tissues and cells of the animal are bathed directly in blood. NO BLOOD VESSELS)
How does blood get around an insects body?
There is a muscular pumping organ, much like a heart. It is a long muscular tube that lies under the upper surface of the insect. blood from the body enters the heart through pores called ostia. The heart then pumps the blood towards the head by peristalsis. At the front end of the head the blood pours out into the body cavity.
What single layer of cells do all blood vessels have?
the endothelium
What is the blood pressure like inside arteries?
High
Why is the lumen of an artery small?
To maintain high pressure
What is the use of the elastic tissue in the arteries?
Allows the wall to stretch and then recoil when the heart pumps.
This is felt as a pulse in areas there the arteries lie close to the surface of the skin.
The recoil maintains the high pressure while the heart relaxes
What is the use of the smooth muscle in arteries?
contract and constrict the artery. Constriction narrows the lumen of the artery
How does the endothelium work in the arteries?
It is folded and unfolds when the artery stretches
What is the pressure like in the veins?
low
Why can the walls of the veins be thin without them bursting?
Because the pressure is so low
how large is the lumen in veins?
relatively large
What three things do veins have which are thicker in arteries? and why is this?
Collagen, smooth muscle and elastic tissue
Because they do not need to stretch and recoil and so not need to be actively constricted to reduce blood flow
What do veins and the heart have in common?
They contain valves which help to move/keep blood in a certain place.
What do capillaries consist of?
A single layer of flattened endothelial cells
Why are capillaries so thin?
So they have a short diffusion distance for oxygen to diffuse in and carbon dioxide to diffuse out easily and quickly
Why is the lumen of a capillary so small?
It causes the red blood cell to be squeezed through the capillary.
This helps them give up their oxygen because it presses them close to the capillary wall, reducing the diffusion path to the tissues
What 11 things can be found in blood?
Red blood cells, white blood cells, platelets, oxygen, carbon dioxide, salts, glucose, fatty acids, amino acids, hormones and plasma proteins.
What is the different between blood and tissue fluid?
Tissue fluid is very similar to blood however it does not contain most cells found in blood or plasma proteins.
What is the role of tissue fluid?
to transport oxygen and nutrients from the blood to the cells, and to carry carbon dioxide and other wastes back to the blood.
what is the pressure like at the arteriole end of a capillary?
High hydrostatic pressure
What are arterioles and venules?
Blood vessels that break off from arteries and veins which then lead into/from capillaries
How does blood fluid leave the capillaries?
Blood entering the capillaries from the arterial end has a high hydrostatic pressure, this high pressure pushes the blood fluid out of the capillaries through tiny gaps in the capillary wall.
Why aren’t the blood cells and plasma proteins in tissue fluid?
Because they are too large to exit the tiny gaps in the capillary wall which the dissolved substances can escape through
How do cells get the oxygen that is carried in tissue fluid?
The tissue fluid that leaves the capillaries surrounds the body cells so the exchange of gases can occur across the cell surface membranes.
What type of transport occurs during gas exchange?
Either normal diffusion or facilitated diffusion
What is exchanged at the cell surface membrane?
Oxygen and nutrients enter the cells and carbon dioxide and other wastes leave the cells.
How does tissue fluid return back to the blood?
- The tissue fluid itself has some hydrostatic pressure which will tend to push the fluid back into the capillaries.
- Water potential of the fluid is less negative than the blood, meaning water tends to move back into the blood from the tissue by osmosis, down the potential gradient
- venous end of the capillary has lost its hydrostatic pressure, combined effect of hydrostatic pressure in tissue fluid and osmotic force of plasma proteins moves fluid back into capillary dragging with it anything left by the cells e.g. CO2
How is lymph similar to and different from tissue fluid?
It is the fluid that has been drained off from the tissue fluid, so it contains the same solutes.
It contains less oxygen as that has been absorbed by the body cells, it has more carbon dioxide as that was produced by the body cells, and it will contain more fatty material which has been absorbed from the intestine
What are lymphocytes?
Cells which are produced in the lymph nodes where any filtered off bacteria and foreign material is sent from the lymph fluid. They engulf and destroy these bacteria and foreign particles to protect the body against infection
What cells are present in blood?
Erythrocytes, leucocytes and platelets
What proteins are present in blood?
Hormones and plasma proteins
What fat are present in blood?
Some are transported as lipoproteins
How much glucose is present in blood?
80-120mg per 100cm3
How much oxygen, carbon dioxide and amino acids are present in blood?
Lots of oxygen and amino acids
Not a lot of carbon dioxide
Which cells are present in tissue fluid?
Some phagocytic white blood cells
What proteins are present in tissue fluid?
Some hormones, and proteins secreted by body cells
Is there any fat present in tissue fluid?
No
How much glucose, amino acid, oxygen and carbon dioxide is present in tissue fluid?
Not much glucose (absorbed by body cells)
Not many amino acids (absorbed by body cells)
Not much oxygen (absorbed by body cells)
Lots of carbon dioxide (released by body cells)
Which cells are found in the lymph?
Lymphocytes
Are any proteins found in the lymph?
Some
Is there fat found in the lymph?
More than in the blood (absorbed from lacteals in intestine)
How much glucose, amino acid, oxygen and carbon dioxide is there in the my lymph?
Not a lot of glucose, amino acid or oxygen however there is more carbon dioxide
How is oxygen transported around the body?
In the erythrocytes (red blood cells). These cells contain the protein haemoglobin. When haemoglobin takes up oxygen it becomes oxyhaemoglobin.
Briefly describe the structure of haemoglobin
Complex protein
Four subunits
Each subunit contains a polypeptide chain and a haem group (non protein group)
Each haem group contains an Fe2+ ion
Each iron ion can attract and hold one oxygen molecule
The haem group has an affinity for oxygen
so haemoglobin can carry four oxygen molecules
How is oxygen taken from the lungs?
Oxygen absorbed into the blood in the lungs
O2 molecules enter the red blood cells
taken up by the haemoglobin (Hb)
which takes the oxygen molecules out of the solution mainting a high diffusion gradient
this gradient allows more oxygen to enter the cells
What is dissociation in the body tissues?
The body tissues need oxygen for aerobic respiration. Therefore the oxyhaemoglobin needs to be able to release the oxygen. this release of the oxygen is called dissociation
What does the ability of haemoglobin to take up and release oxygen depend on?
The amount of oxygen in the surround tissues
When plotting haemoglobin’s affinity to oxygen on a graph, what is the curve called?
oxyhaemoglobin dissociation curve
When oxygen tension is low, how does haemoglobin react to that?
It doesn’t readily take up oxygen molecules
Why does haemoglobin not readily take up oxygen at low oxygen tension???
Because the haem groups that attract the oxygen are in the centre of the haemoglobin molecule, this make it difficult for the oxygen molecule to reach the haem group to associate with it
Why is it easier to associate oxygen with haemoglobin when one oxygen has already associated with it?
When one oxygen molecule associates with the haemoglobin, it changes the shape of the molecule (known as conformational change) this allows more oxygen to diffuse into the haemoglobin and associate with the other haem group relatively easily
What is conformational change?
The ability for the second and third oxygen molecules to associate with a molecule of haemoglobin after one oxygen has already associated. This is because the first molecule joining has changed the shape of the Hb molecule making it easier for the other O2 molecules to join
How can haemoglobin lose oxygen to release it into the body tissue?
The oxygen tension in respiring body tissues is sufficiently low which helps the oxygen to dissociate readily form the oxyhaemoglobin
Does fetal haemoglobin have a higher or lower affinity to oxygen than adult haemoglobin?
Higher affinity
Which way does the graph shift for oxyhaemoglobin in the oxyhaemoglobin dissociation curve?
It shifts to the left
How does the fetal haemoglobin get more oxygen?
it absorbs oxygen from the fluid in the mothers blood, this reduces the oxygen within the blood fluid, which in turn makes the maternal haemoglobin release oxygen.
What is the Bohr effect?
A change in the shape of the oxyhaemoglobin curve when carbon dioxide is present - this causes the oxyhaemoglobin to release oxygen more readily
What are the three ways in which carbon dioxide can be transported around the body?
5% is dissolved directly into the plasma
10% is combined directly with haemoglobin to form a compound called carbaminohaemoglobin
85% is transported in the form of hydrogencarbonate ions HCO3-
How are hydrogen carbonate ions formed?
CO2 + H20 –> H2CO3 catalysed by the enzyme, carbonic anhydrase
Carbonic acid H2CO3 dissociates to release H+ ions and hydrogen carbonate ions HCO3-
HCO3- diffuse out of RBC and into plasma
Charge inside the RBC maintained by the movement of Cl- ions from the plasma into the red blood cell
This is called chloride shift
What is chloride shift?
The movement of Cl- ions into red blood cells to maintain the charge after the exit of HCO3- ions from the red blood cells to the plasma during the transport of CO2 round the body
How is pH managed inside the RBC?
H+ ions are given off by H2CO3 which can cause the RBC’s to become very acidic
However the H+ ions are taken up by haemoglobin to produce haemoglobinic acid. The haemoglobin acts as a buffer to try to maintain a constant pH
How does haemoglobin release oxygen?
As blood enters the respiring tissues the Hb is carrying oxygen in the form of oxyhaemoglobin. The oxygen tension is lower in the respiring tissues than in the blood as oxygen is being used up in respiration in the tissues. So oxyhaemoglobin begins to dissociate and releases oxygen to the tissues down the concentration gradient
Which way does the oxyhaemoglobin dissociation curve shift in the presence of carbon dioxide?
Down and to the right
What is the role of the xylem?
To transport water and soluble minerals up the plant
What is the role of the phloem?
Transports sugars and other assimilates up and down the plant
In a plant root how are the xylem and phloem situated?
The xylem is in the shape of an X in the centre
The phloem is found between the arms of the xylem
How does the arrangement of the xylem and phloem benefit the root of a plant?
It provides strength to withstand the pulling forces the roots are exposed to
What is the sheath of cells around the vascular bundles called?
The endodermis
Just inside the endodermis there is a layer of cells, what are the cells called and what is the layer itself called?
Meristem cells
Pericycle
In non-woody plants how are the vascular bundles arranged?
They are separate and discrete
In woody plants how are the vascular bundles arranged?
They are separate in young stems but become continuous in older stems
How does the arrangement of vascular bundles inside a tree help to aid its survival?
There is a complete ring of vascular tissue under the bark of the tree, provides strength and flexibility to withstand the bending forces to which stems and branches are exposed
How are the xylem and phloem arranged within a vascular bundle?
The xylem is on the inside and the phloem is on the outside
What is between the xylem and the phloem in a vascular bundle? and what is its function?
The cambium
A layer of meristem cells that divide to produce new xylem and phloem
What is the phloem?
A plant transport tissue that carries the products of the photosynthesis (e.g. sugars) to the rest of the plant.
It consists of sieve tube elements and companion cells
What is the xylem?
A plant transport tissue that carries water from the roots to the rest of the plant. It consists of hollow columns to dead cells lined end-to-end and reinforced lignin. It provides imprtant support for the plant
Explain the structure of the xylem vessel
long cells with thick walls which have been impregnated with lignin, lignin waterproofs the walls of the cells
the cells die and their end walls and cell contents decay
leaves a long column of dead cells with no contents
lignin strengthens the vessel walls and prevents the vessel from collapsing
keeps the vessels open even in times of low water supply
How is lignin helpful in the xylem vessel?
It forms patterns in the cell wall, these may be spiral, rings or broken rings. This prevents the vessel from being too rigid and allows flexibility of the stem or branch
Explain the role of pits or bordered pits?
Some places in the xylem contain areas where lignification is not complete and leaves pores in the wall of the vessel. These are the pits. They allow water to leave one vessel and pass into another adjacent vessel or pass into the living part of the plant
How is the flow of water not impeded in the xylem vessel?
There are no end walls
There are no cell contents
There is no nucleus or cytoplasm
Lignin thickening prevents the walls from collapsing
What are the cells that are attached to the phloem called?
Companion cells
Describe the structure of the phloem
Long cells called sieve tube elements, lined up end to end to form a tube, containing sieve plates at intervals.
Sieve tubes also contain very little cytoplasm
next to the sieve tube are companion cells, these have a large nucleus, dense cytoplasm and lots of mitochondria which help to carry out processes needed for the phloem to survive
Why do companion cells need lots of mitochondria?
To produce ATP needed for active processes in the cell.
Including loading sucrose into the sieve tubes
communication and flow of minerals
What is the plasmodesmata?
Gaps in the cell wall between the sieve tube element and the companion cell. They allow communication and flow of minerals between the cells
What is water potential?
The total potential energy of the water molecules in a system. It is a measure of how likely it is that water will be lost from the system by diffusion down its water potential gradient
Explain how a cell becomes turgid
When the water potential outside the plant cell is higher than inside the plant cell, water will diffuse in by osmosis. The cell will NOT continue to absorb water until it bursts because the plant has a strong cellulose cell wall
When the cell is full of water it is described as being turgid
Explain plasmolysis
If a plant cell is placed in a solution with very low water potential, the cell will lose water by osmosis
The water diffuses down its potential gradient out of the cell
It loses its turgidity, the cytoplasm and vacuole shrink and pulling the cytoplasm away from the cell wall
List three main points about water potential
Pure water has a water potential of zero
Cells have a negative water potential because they contain dissolved salts and sugars
Water molecules move from less negative regions to more negative regions
What are the three routes taken by water through cells?
Apoplast
Symplast
Vacuolar
Explain which way water travels when taking the apoplast route
Water moves through the spaces in the cell wall and spaces between the cells
In this pathway water does not pass through any plasma membranes, this means that the dissolved mineral ions and salts can be carried with the water
Explain which way water travels when taking the symplast route
Water enters the cell cytoplasm through the plasma membrane. It then passes through the plasmodesmata from one cell to the next.
the plasmodesmata contain a thin strand of cytoplasm so the cytoplasm of adjacent cells is linked. Once inside the cytoplasm water can move through the continuous cytoplasm from cell to cell
Explain which way water travels when taking the vacuolar route
Similar to the symplast route but the water is not confined to the cytoplasm of the cells
It is able to enter and pass through the vacuoles as well
What is the plasmodesma?
A fine strand of cytoplasm that links the contents of adjacent cells
What are plasmodesmata?
Gaps in the cell wall that contain a thin strand of cytoplasm to allow the movement of water between cells
What is cohesion?
The attraction of water molecules for one another
What is adhesion?
The attraction of water molecules to the walls of the xylem
How do the root hair cells help the plant to absorb water?
Root hair cells absorb minerals by active transport
Minerals lower the water potential
Meaning water is taken up across the plasma membrane by osmosis
How is water moved across the root?
The endodermis contains specialist cells which have a waterproof strip in some of their walls, this is called the Casparian Strip
The Casparian strip blocks the apoplast pathway forcing water through the symplast pathway
Endodermis cells move minerals by active transport from the cortex into the xylem
decreases the water potential in the xylem
as a result water moves from the cortex through the endodermal cells to the xylem by osmosis
What is the role of the casparian strip?
Block the apoplast pathway between the cortex and the xylem
Ensures that water and dissolved nitrate ions have to pass into the cell
Transporter proteins in cells membranes
Active transport of nitrate ions
Lowers the water potential in the xylem so water can travel by osmosis from the cortex
Water in xylem cannot pass back into cortex
Name three factors which help water to move up the stem
Root pressure
Transpiration pull
Capillary action
Explain how root pressure helps water to move up the stem
Action of moving minerals into the xylem by AT drives water into the xylem by osmosis
Forces water into the xylem and pushes the water up the xylem
Root pressure can push water a few metres up a stem but cannot account for water getting to the top of tall trees
Explain how transpiration pull helps water to move up the stem
the loss of water from the leaves must be replaced by
water coming up from the xylem
Water molecules attached to each other by cohesion, these forces are really strong and hold the H2O molecules together in a long chain
Pull from above creates tension on the column of water
Explain how capillary action helps water to move up the stem
The same forces that hold water molecules together also attract the water molecules to the sides of the xylem vessel
This is called adhesion
Xylem vessels are very narrow, these forces of attraction can pull the water up the sides of the vessel
Explain how water leaving the leaf of a plant help water to move up the stem
Water leaves leaf through stomata, tiny pores in the epidermis
Water evaporates from the cells lining the cavity immediately below the guard cells
Lowers the water potential in these cells causing water to re-enter them by osmosis from neighbouring cells
and water is constantly being pulled up to make up for that loss, like a chain
What is transpiration?
The loss of water by evaporation from the aerial parts of a plant
What three processes does transpiration involve?
Osmosis from the xylem to mesophyll cells
Evaporation from the surface of the mesophyll cells into the intercellular spaces
Diffusion of water vapour from the intercellular spaces out through the stomata
How can you measure the rate of transpiration?
Using a potometer, it measures the rate of water loss.
actually measures the rate of water uptake by a cut shoot, however as about 99% of water taken up is lost in transpiration it does give an reasonable estimate of water loss
What 6 factors affect the rate of water loss from a plant?
No. of leaves Number, size and position of stomata Presence of cuticle Light Temperature Relative humidity Air movement or wind Water availability
How does No of leaves affect the rate of water loss from the plant?
A plant with more leaves has a larger surface area over which water vapour can be lost
How does number, size and position of stomata affect the rate of water loss from the plant?
If the leaves have many large stomata, then water vapour is lost more quickly. If the stomata are on the lower surface water vapour is lost slower
How does the presence of a cuticle affect the rate of water loss from the plant?
A waxy cuticle reduces evaporation from the leaf surface
How does the presence of light affect the rate of water loss from the plant?
In light, the stomata open to allow gaseous exchange for photosynthesis
How does temperature affect the rate of water loss form the plant?
A higher temperature will increase the rate of water loss in three ways:
Increase evaporation from the cell surfaces so that the water vapour potential in the leaf rises
Increase diffusion through the stomata because the water molecules have more kinetic energy
Decrease relative water vapour potential in the air, allowing more rapid diffusion of molecules out of the leaf
How does relative humidity affect the rate of water loss from the plant?
Higher relative humidity in the air will decrease the rate of water loss. Because there is a smaller water vapour gradient between the air spaces in the leaf and the air outside
How does air movement or wind affect the rate of water loss from the plant?
Air moving outside the leaf will carry away water vapour that has just diffused out of the leaf. The will maintain a high water vapour potential
How does water availability affect the rate of water loss from the plant?
If there is little water in the soil, then the plant cannot replace the water that is lost. Water loss in plants is reduced when stomata are closed or when the plants shed leaves in winter
What happens if a plant loses too much water?
The cells will lose turgidity. Non woody plants will eventually die, the leaves of woody plants will also wilt and the plant will eventually die
What is a xerophyte?
A plant that is adapted to reduce water loss so that it can survive in very dry conditions
Which ways do plants reduce their water loss by structural and behavioural adaptations?
A waxy cuticle on the leaf will reduce water loss due to evaporation through the epidermis
The stomata are often found on the undersurface of the leaves, not in the top surface, reduces evaporation due to direct heating from the sun
Most stomata are closed at night, when there is no light for photosynthesis
Deciduous plants lose their leaves in winter, when the ground may be frozen which reduces available water uptake
What 8 adaptations do xerophytes have to increase their chances of survival
Smaller leaves
Dense spongy mesophyll layer
Thick waxy cuticle
Closing the stomata
Hairs on the surface of the leaf trap a layer of air close to the surface
Pits containing stomata to trap with water vapour
Rolling the leaves so lower epidermis is not exposed
Some plants have a low water potential inside their leaf cells
How do smaller leaves help the survival of xerophytes?
It reduces the total surface area of the leaves. The total leaf surface area is also reduced, so that less water is lost by transpiration. A typical example is the pine tree
How does a dense spongy mesophyll layer ensure the survival of xerophytes?
Reduces the cell surface area that is exposed to the air inside the leaves. Less water will evaporate into the leaf air spaces, reducing the rate of water loss
How does a thick waxy cuticle ensure the survival of xerophytes?
Reduces further evaporation
How does closing of the stomata ensure the survival of xerophytes?
Reduce water loss and so reduce the need to take up water
How do hairs on the surface of the leaf ensure the survival of xerophytes?
Trap a layer of air close to the surface. This air can become saturated with moisture and will reduce the diffusion of water vapour out through the stomata. This is because the gradient of the water vapour potential between the inside of the leaf and the outside has been reduced
How do pits on the base of a leaf ensure the survival of xerophytes?
They trap air that can become saturated with water vapour. Reduce the gradient in the water vapour potential between inside and outside the leaf so reducing loss by diffusion
How does rolled leaves ensure the survival of xerophytes?
So the lower epidermis is not exposed to the atmosphere can trap air that can become saturated. This is another way to reduce or even eliminate the water vapour potential gradient
How does plants having a low water potential inside their leaf cells ensure the survival of xerophytes?
Achieved by maintaining a high salt concentration in the cells, the low water potential reduces the evaporation of water from the cell surfaces as the water potential gradient between the cells and the leaf air spaces is reduced
What 5 adaptations does marram grass have?
Leaf rolled up Thick waxy cuticle Trapped air in the centre Hairs on lower surface Stomata in pits
What is translocation?
The transport of assimilates throughout the plant, in the phloem tissue
What is a source?
Part of the plant which releases sucrose into the phloem
What is a sink?
A part of the plant which removes sucrose from the phloem
How does sucrose enter the phloem?
Sucrose is loaded into the phloem by active transport
ATP is used by the companion cells to actively transport H+ ions into the surrounding cytoplasm
Sets up diffusion gradient
and the H+ ions diffuse back into companion cells
diffusion occurs through co transporter protein
Proteins enable the hydrogen ions to bring sucrose molecules into the companion cells
As the conc of sucrose molecules builds up inside the companion cells, they diffuse into the sieve tube elements through the numerous plasmodesmata
Explain 5 steps of mass flow in the phloem
- Sucrose is actively loaded into the sieve tube element and reduces the water potential
- Water follows by osmosis and increases the hydrostatic pressure in the sieve tube element
- Water moves down the sieve tube from higher hydrostatic pressure at source to lower hydrostatic pressure at sink
- Sucrose is removed from the sieve tube by the surrounding cells and increases the water potential in the sieve tube
- Water moves out of sieve tube and reduces the hydrostatic pressure
How does sucrose move along the phloem at the source?
Sucrose enters the sieve tube element reduces the water potential inside the sieve tube. As a result water molecules move into the sieve tube element by osmosis from the surrounding tissues
Increases the hydrostatic pressure in the sieve tube at the source
How does sucrose move along the phloem at the sink?
Sucrose is used in the cells surrounding the phloem. Sucrose may be converted to starch for storage, or may be used in metabolic processes such as respiration
Reduces sucrose conc in these cells
Sucrose molecules move by diffusion or active transport from the sieve tube element in the surrounding cells
Increases water potential in the sieve tube element so water molecules move into the surrounding cells by osmosis. This reduces the hydrostatic pressure in the phloem at the sink
How does sucrose move along the phloem?
Water entering phloem at the source
moving down the hydrostatic pressure gradient and leaving the phloem at the sink
produces a flow of water along the phloem
flow carries sucrose and other assimilates along the phloem
called mass flow
can occur in either direction up or down the plant depending on where sugars are needed
