3.3 Chapter 7- Mass Transport Flashcards
1
Q
Give the key features of haemoglobin.
A
Many organisms have haemoglobin to transport oxygen and the type varies depending on their needs. Haemoglobin is highly adapted for transporting oxygen.
2
Q
Describe the structure of haemoglobin.
A
- Group of chemically similar molecules found in many different organisms.
- Large proteins with a quanternary structure of four polypeptide chains
- Evolved to be efficient at loading oxygen in certain conditions and unloading it in others.
- Primary structure- the sequence of amino acids in the 4 polypeptide chains.
- Secondary structure- polypeptide chains coiled into a helix.
- Tertiary structure- haemoglobin folded into a precise shape to carry oxygen.
- Quanternary structure- four peptide chains linked together- each one associated with a haem group - iron ion of Fe2+- gives the haemoglobin its red colour- can combine with oxygen to form Fe3+ so 4 oxygen can be carried by a single human haemoglobin.
3
Q
Describe briefly how oxygen and haemoglobin interact.
A
- Oxygen joins to haemoglobin in red blood cells to form oxyhemoglobin.
- Reversible reaction.
- Oxygen leaves near body cells.
4
Q
Describe the key terms surrounding the action of haemoglobin and where these terms occur.
A
- Binding oxygen= loading/ association- occurs in human lungs
- Releasing oxygen= dissociation/ unloading- occurs in human tissue.
5
Q
Why is haemoglobin important for the circulatory system?
A
- An important part of the circulatory system.
- Found in human red blood cells.
- Red blood cells and haemoglobin have a role of transporting oxygen around the body.
6
Q
What is important about haemoglobin in different organisms?
A
- Many chemically similar types of haemoglobin in different organisms carry out the same function.
- Haemoglobin is found in many organisms from vertebrates to humans.
7
Q
What does affinity mean in terms of haemoglobin (define affinity)?
A
- Affinity is the tendency for a molecule to bind with oxygen.
- Haemoglobin’s affinity varies depending on its conditions.
- Haemoglobin with a higher affinity for oxygen takes it up more easily, but releases it less easily and vice versa.
8
Q
What role does haemoglobin have and what features mechanics does it have to achieve this?
A
- To be efficient at transporting oxygen haemoglobin has to readily associate with oxygen where gas exchange occurs and readily dissociate from oxygen at tissues.
- Does this by changing its affinity for oxygen at different conditions.
- Shape changes in the presence of e.g. CO2- binds more loosely with oxygen and releases oxygen more easily.
9
Q
What is the oxygen disassociation curve? Draw it and explain.
A
- The graph of the saturation of haemoglobin with the partial pressure of oxygen.
- Affinity affects how saturated haemoglobin is.
- pO2 is high- e.g. the lungs- oxygen affinity increases- oxygen saturation increases.
- pO2 is low- e.g. respiring tissues- oxygen affinity decreases- oxygen saturation decreases.
- Saturation of haemoglobin affects affinity and shape, so the graph is S-shaped not a straight line.
10
Q
How does hemoglobin’s affinity vary with regards to pO2?
A
- Haemoglobin’s affinity varies depending on the partial pressure of oxygen- pO2= measure of oxygen concentration.
- More oxygen = more pO2 = more affinity for oxygen.
- Areas of high pO2- oxygen loads onto haemoglobin to form oxyhaemoglobin
- Areas of low pO2- oxyhemoglobin unloads oxygen.
- Oxygen enters the blood at the alveoli in the lungs with a high pO2 so oxyhemoglobin is formed.
- Cells aerobically respire- use up oxygen- lower the pO2- oxyhaemoglobin in red blood cells unloads oxygen and haemoglobin returns to the lungs.
11
Q
What happens at different partial pressures with haemoglobin?
A
At different partial pressures of oxygen haemoglobin loads, transports and unloads oxygen.
12
Q
Describe step by step the oxyhaemoglobin dissociation curve and draw it.
Hint: 3 Steps
A
- The first haemoglobin finds it more difficult to bind as its 4 sites are close together. At a low PO2 (oxygen concentration) little oxygen binds.
- First O2 molecule associating- changes the quanternary structure of the haemoglobin- shape change uncovers second binding site- easier for oxygen to bind. Binding of the 1st molecule helps other molecules- takes a smaller pO2 increase to bind to the 2nd oxygen- positive cooperativity/ cooperative binding- makes it easier to bind to the 2nd molecule- steeper curve- small change in pO2 = more oxygen loading.
- Third molecule binds to haemoglobin- harder for oxygen to bind- less likely to find an empty site- gradient of the graph reduces and flattens.
13
Q
Why does the shape of oxygen dissociation curves vary?
A
- Shape of the haemoglobin can change under certain conditions and/or between species.
- A wide variety of oxygen dissociation curves
14
Q
What does an oxyhemoglobin curve moving left or right mean?
A
- Further to the left= greater affinity- haemoglobin loads oxygen easily but doesn’t find it easily easy to unload.
- Further to right = lower affinity.
15
Q
Describe and name the effect of CO2 on haemoglobin include. the effect on the oxygen dissociation curve.
A
- The partial pressure of carbon dioxide- pCO2- a measure of CO2 concentration.
- Greater pCO2 produces acid due to the dissolving of CO2- decreases the pH- causes haemoglobin to change shape and release oxygen- dissociate.
- Haemoglobin- reduced affinity for oxygen in the presence of high pCO2= increased oxygen- the Bohr effect.
- Helps haemoglobin release more oxygen at times of high activity
- Increases oxygen association at the lungs- CO2 concentration low as it diffuses across the exchange surface and is excreted- affinity of oxygen increases- the loading of oxygen increases- oxygen dissociation curves shifts to the left.
- Respiring tissues- increased pCO2 decreases oxygen affinity- low pO2 and high pCO2- oxygen is readily unloaded to muscle cells- the oxygen dissociation curve is shifted to the right.
16
Q
Why is the effect of CO2 on haemoglobin in organisms important?
A
- The effects of CO2 on haemoglobin helps haemoglobin release more oxygen in times of high activity.
- The Bohr effect increases dissociation of oxygen for aerobic respiration at the tissues in times of high activity.
17
Q
Why might pCO2 per breath not change during intense exercise?
A
During periods of high exercise, pCO2 may not change per breath as breathing rate or tidal volume may increase instead.
18
Q
Describe the gas exchange process of haemoglobin.
(Hint: 5 steps)
A
- At gas exchange surfaces CO2 is constantly removed.
- pH increases due to low concentration of CO2.
- Increased pH causes haemoglobin to change shape, making it have a higher affinity and more easily load oxygen.
- High affinity means the oxygen isn’t released while it’s being transported. CO2 is produced in the tissues and is acidic in solution- the pH in the blood around the tissues decreases.
- Changes the shape- quanternary structure- of the haemoglobin to have a lower affinity- increases oxygen dissociation.
- Haemoglobin releases oxygen into respiring tissues.
19
Q
How does the gas exchange process change? And why is this important?
A
- Process is flexible to ensure there is always sufficient oxygen for respiring tissues.
- The more active the organism= more respiration occurs= higher pCO2 = lower pH= more haemoglobins shape changes= more oxygen is unloaded = more O2 is released for respiration.
- This ensures in times of high activity more oxygen reaches respiring cells for aerobic respiration to produce ATP.
20
Q
Why is not all haemoglobin saturated and describe the saturation of haemoglobin at different stages?
A
- In humans haemoglobin is a saturated the lungs
- Not all is saturated as atmospheric pressure is usually 97%.
- When haemoglobin reaches a tissue with a low respiratory rate- 1 oxygen molecule is released, but blood is still 75% saturated with oxygen when it reaches the lungs.
- In high respiratory rates- 3 oxygen molecules are released.
21
Q
What are the features of different haemoglobins in different organisms
A
- All haemoglobins are chemically similar and found in many different organisms.
- Slight differences between different organisms.
- Different types of haemoglobin within/ between species have different dissociation curves.
- Found in some vertebrates, worms, some insects and some bacteria.
22
Q
Why are there different types of haemoglobin?
A
- Different types of haemoglobin with different oxygen transporting capacities and properties relating to the different organisms living conditions
23
Q
What causes haemoglobin to have different properties and what are these properties?
A
- Different carrying capacity is related to the shape of the haemoglobin.
- Each organism has a haemoglobin with a slightly different amino acid sequence, so a different quanternary structure, binding capacity and affinity.
24
Q
What determines the type of haemoglobin and organism has?
A
- The different types of haemoglobin are evolved adaptions related to an organism’s habitat, environment, size and activity to help it survive.
- e.g. A low pO2 environment= higher affinity haemoglobin.
25
Describe haemoglobin in low oxygen environments. Give examples and draw the dissociation curve relative to humans.
* Low oxygen environments- low pO2.
* Haemoglobin has a higher affinity for O2 than a human haemoglobin as little oxygen means more loading is needed to maintain oxygen for aerobic respiration.
* The oxyhaemoglobin dissociation curve shifts to the left.
* e.g. lug worms- live in burrows- get O2 from seawater- have to hold oxygen until the tide comes in again- they fully load their haemoglobin with oxygen despite little in environment.
* e.g. llamas live in higher altitudes- low oxygen environment- need specialised haemoglobin.
26
Describe the features of myoglobin.
Myoglobin has a **higher affinity for O2** and h**olds oxygen for longer than normal haemoglobin** to **provide O2 when haemoglobin is unloaded** in low oxygen environments.
27
Describe haemoglobin in high activity level organisms give examples and draw the dissociation curve relative to humans.
* High activity levels- high oxygen demand- low affinity is needed to unload oxygen so more is available to use for aerobic respiration.
* Oxyhaemoglobin dissociation curve shifts to the right.
* e.g. hawks- high activity so haemoglobin has to unload oxygen quickly to meet demand.
28
Describe haemoglobin in small organisms, give examples, draw the dissociation curve relative to humans and explain why it has its features.
* Smaller sized animals- increased SA:V- increased heat loss- need increased metabolic rate for warmth- increased oxygen demand.
* Need a lower affinity for oxygen as they need easier unloading
* Oxyhaemoglobin dissociation curve shifts to the right.
29
Describe foetal haemoglobin why it has its features and draw the dissociation curve relative to humans.
* **Foetal haemoglobin has a higher affinity** for oxygen than adult haemoglobin so it is **better at loading oxygen.**
* Important because the foetus has to **unload oxygen from the mother from the mother for aerobic respiration- makes it easier**, so it has to be better at binding to oxygen.
* The oxyhaemoglobin dissociation curve shifts to the right.
30
Why is mass transport important to certain organisms and name the specific organisms?
* Large multicellular organisms i.e. mammals have small SA:V, meaning not enough exchange occurs on their outer surfaces.
* All organisms need to exchange materials between outside and inside environments so mammals use specialised exchange systems and specialised mass transport systems to carry materials from exchange surfaces to cells and vice versa.
31
How have mammals evolved with regards to exchange?
Mammals have evolved to have more specialised organs and tissues making transport essential.
32
What are mammals mass transport systems called and what are their features?
* Mammelian specialised mass transport systems are circulatory systems.
* They may have a specialised transport medium and may have a pump.
33
What determines whether a mammals mass transport system has a pump?
* The surface area to volume ratio and the activity of the organism.
* Decreased SA:V and increased activity means the organism is likely to have a pump.
34
Why do some organisms not need mass transport?
Have **short diffusion pathways** and as mass transport is only needed if diffusion is not fast enough these organisms may not need mass transport.
35
What are the common features of mass transport systems?
| (Hint: 8 features)
* A medium to carry materials- usually water based- because soluble and easy to move e.g. the blood, could also be a gas.
* Mass transport is more rapid than diffusion- the medium is moved in bulk over large distances.
* Usually a closed system in tubular vessels that contain the transport medium and branch out to all parts of organisms.
* Mechanism for moving the transport museum in vessels- usually pressure differences- maintained by animals using muscular contraction of body muscles or specialised organs such as the heart/ plants using passive processes such as evaporation
* Mechanisms that keep one direction of flow e..g. valves.
* Mechanisms to control the flow of transport mediums to different parts of the organism.
* Mechanisms for mass flow of water and gases e.g. intercostal muscles.
36
What type of circulatory system do mammals have and why?
* Closed double circulatory system.
* Blood is confined to vessels
* Passes twice through the heart in each circulation.
* Pressure after the lungs is low, so blood circulation would be very slow without the system.
* The heart boosts the pressure- important to speed up movement of blood- important due to high oxygen demand due to high aerobic resipration due to high body temperature and metabolism of mammals.
37
What is the circulatory system made up of and what are their roles?
* The circulatory system is the heart and blood vessels.
* Heart- pumps blood through the blood vessels to reach parts of the body.
* Blood vessels- arteries and arterioles, veins and capillaries.
* Pulmonary artery- heart to lungs.
* Pulmonary vein- lungs to heart.
* Aorta- heart to body.
* Vena Cava- body to heart.
* Renal artery- body to kidneys.
* Renal vein- kidneys to vena cava.
38
How does the mass transport system ensure swift transport?
* Transport systems move substances longer distances.
* Final exchange is by diffusion.
* Diffusion is rapid because of the large surface area, short distances and steep diffusion gradients maintained by the transport system.
39
What does blood transport?
* Respiratory gases
* Digestion products
* Wastes
* Hormones.
40
What does a double circulatory system mean?
The blood goes from the heart to the lungs, to the heart to the body, and passes through the heart twice.
41
Draw the cycle of the blood around the body to the kidneys, naming the specific vessels.
Blood moves from:
* the right atrium
* the right ventricle
* the pulmonary artery
* the lungs
* the pulmonary vein
* the left atrium
* the left ventricle
* the aorta
* Renal artery/ other arteries.
* Kidney/ body
* Renal veins/ other veins
* Vena Cava
* the right atrium.
42
How many pumps does the human heart have? What do they do and what do they contain?
* Two pumps.
* Left pumps- contain oxygenated blood- move it from the lungs to the body.
* Right pumps- contain deoxygenated blood- move it from the body to the lungs.
* Each pump contains an atria and a ventricle.
43
How many pumps does the heart have and why does it need them?
* The heart needs two pumps
* Make the pressure around the body stronger than in the lungs
* Ensures that oxygenated and deoxygenated bloods don't mix.
44
How are the hearts pumps adapted to suit their function?
* Atria- elastic walls allow to stretch as they collect blood and thin walled as they only need to pump to the ventricles.
* Ventricles- thick and muscly- can pump blood along distance.
* Left ventricle- thicker than the right ventricle- powerful- enough pressure to pump blood around the body.
* Right ventricle- thick enough to get blood to the lungs.
45
What must you be careful of in heart diagrams?
The left and right sides are reversed.
46
What is the pattern of the heart pumps?
* The pumps pump in time with each other- the atria and then the ventricles.
* The same volume of blood each time.
47
What do the pumps ensure with regards to blood?
The oxygenated and deoxygenated blood do not mix after birth.
48
What do valves ensure, what types of valves are there and what are their features?
* Valves prevent backflow.
* Atroventricular valves- in the left and right atria and ventricles- link the atria and ventricles and stop backflow- chords attatch the atrioventricular valves to the ventricles to stop them being forced up the atria when ventricles contract.
* Semi-lunar valves- link ventricles to pulmonary arteries and aorta- stop backflow.
49
How many chambers are there in the heart and how are they connected?
The four chambers of the heart are connected by large blood vessels carrying blood towards and away from the heart.
50
Describe the chambers of the hearts.
* Atria- receive blood from the veins.
* Ventricles- pump blood away from the heart and into the arteries.
51
Name and describe the blood vessels in the hearts.
* Aorta- connect to left ventricle- carries oxygenated blood to all the body parts except the lungs.
* Vena Cava- connected to right atrium- carries deoxygenated blood from the tissue of the body except from lungs- **lowest blood pressure.**
* Pulmonary artery- connects to right ventricle- carries deoxygenated blood to the lungs- O2 is replenished and CO2 is removed- only artery that carries deoxygenated blood.
* Pulmonary vein- connects to left atria- carry oxygenated blood from the lungs to the heart- only vein that carries oxygenated blood.
* Coronary arteries (left and right)-
52
What are the roles of the coronary arteries and what is dangerous about issues with them?
* Branch off aorta- supply oxygen and blood to the heart.
* Blockage in these arteries can lead to a myocardial infaction or heart attack- heart muscles are deprived of oxygen and blood so can't aerobically respire and die.
53
Draw and label the heart
Answer on revision card
54
Describe the movement of blood and how valves aid this.
* The pressure created by the heart keeps blood flowing in one direction.
* Blood always moves from a region of high pressure to a region of low pressure.
* Sometimes pressure differences cause blood to flow the wrong way, so valves are used to prevent backflow and maintain **a unidirectional flow** of blood from the heart, around the body and back to the heart again.
55
Describe what makes valves open and close and what this enables.
* Valves only open one way depending on pressure.
* High pressure behind valves causes them to open in the required direction.
* High pressure in front of valves causes them to close as the direction of blood isn't desirable.
* Convex pressure> concave- valves open.
* Concave pressure > convex pressure- the blood collects in the 'bowl' to prevent the passage of blood.
56
Name and describe the different types of valves, their position, role and what causes them to open and close.
* Atroventricular valves- between the atria and the ventricles- prevent backflow when ventricles contract meaning their prressure is greater than atrial pressure- ensures blood moves into the aorta **Atrial pressure > ventricles= open. Atrial pressure < ventricles =close.**
* Semi-lunar Valves- between aorta, pulmonary arteries and the ventricles- prevent backflow into the ventricles when elastic walls of the vessels recoil, causing the aorta and pulmonary arteries to have a greater pressure than the relaxed ventricle walls.
* Pocket valves- in veins- veins are squeezed by muscle contraction- blood flows towards the heart and not away.
57
Describe the structure of the valves and draw a diagram.
* Made of tough but flexible fibrous tissue.
* Cusp shape- one side convex one side concave.
* Chords attached the atroventricular. valves to the ventricles to stop them moving during ventricle contractions.
58
What must you remember when sketching a dissection?
* Only use **single continuous lines.**
* **Add labels**/annotations/ a title.
* Add the **magnification** and scale.
* **Draw all parts to the same scale**/ relative size.
* **Don't shade.**
59
What safety must you remember when performing a heart dissection?
* **Use sharp clean tools.**
* **Disinfect tools, hands and work surfaces.**
* **Wash sharp instruments pointing away from the body.**
60
Describe the steps of a heart dissection.
| Hint: 11 steps
1. Wear a labcoat and gloves
2. Put the heart on the dissection tray.
3. Identify the main vessels on the heart, feel them to feel the difference between the veins and arteries as the arteries are thicker.
4. Identify the left and right atria, ventricles and coronary arteries.
5. Draw a sketch of the label.
6. Using a clean scalpel, cut the heart to see the right and left ventricles.
7. Measure the thickness and note the differences.
8. Cut open the atria to look at the size and look at the difference to the ventricles.
9. Find the atrio ventricular and semi lunar valves ant test opening.
10. Sketch the ventricles, valves and atria.
11. Wash and disinfect hand tools and work surfaces.
61
Where are the atroventricular valves positioned in a heart dissection?
**Quite high in the heart.**
62
What is the cardiac cycle and how does it work?
* Relaxation and contraction of the heart muscles.
* Ongoing to keep blood flowing around the body.
* Volume of the atria and ventricles change as they contract and relax changing the pressure.
63
What are the main processes of the cardiac cycle?
* Two main phases
* Contraction-systole- two stages.
* Relaxation- diastole- one stage.
64
What regulates the cardiac cycle's pressure and volume changes in mammals?
* Mammals have a closed circulatory system
* Blood is confined to the vessels so the pressure and volume are regulated.
65
What is the cardic output?
* Cardiac output is the volume of blood pumped by one ventricle of the heart per minute in dm3/min-1
* Cardiac output = heart rate x stroke volume.
* Heart rate= beats per minute- the rate at which the heart beats
* Stroke volume= the volume of blood at each heartbeat in dm3.
66
Give the cardiac output equation?
Cardiac output = heart rate x stroke volume.
67
Annotate the graph of the cardiac cycle.
| 4 points
* Ventricular pressure- first low- increases gradually as fill with blood as the atria contract. Left AV valve closes and pressure rises dramatically as thick muscular walls of ventricle contract. Pressure rises above aorta- blood forced into the aorta through semi lunar valves. Pressure falls as the ventricles empty in and the walls relax. Both ventricles **contract at the same time, but the left has a higher pressure** than the right.
* Atrial pressure- always relatively low- thin walls of the atria Can't create much force. Highest when contracting. Drops when the left atroventricular valve closes and the walls relax. Atria fill up with blood- gradual build up of pressure until slight drop when left AV valve opens and some blood moves into the ventricles.
* Aortic pressure- rises when the ventricles contract- blood is forced into the aorta. Gradually falls, but never very low because of the elasticity of its walls-creates a **recoil action**- which is **essential to constantly deliver blood to the tissues** by **maintaining the rate of blood flow**. Produces a **temporary rise in pressure at the start of the relaxation phase.**
* Ventricular volume- rises as the atria contract and the ventricles fill with blood- drops suddenly as SL valves open and the blood is forced into the aorta. Volume increases again as the ventricles feel with blood.
68
Describe and draw the cardiac cycle.
| Hint: 3 steps
1. Diastole- relaxation- atria and ventrices both relax. Higher pressure in the pulmonary artery and aorta than in the ventricles as the ventricle walls recoil. The semi lunar valves close to prevent backflow into the ventricles. Blood fills the atria due to the higher pressure in the vena carva and pulmonary vein than in the atria- increases the pressure in the atria. Relaxed ventricles have a less pressure than the atria- atrioventricular valves open- blood flows passively into the ventricles aided by gravity.
2. Atrial systole- **atria contract, the ventricles relax, and the arteries recoil**. **Decreased volume of the atria** due to the contraction of the walls increases the pressure in the atria and the **increased volume** and decreased pressure **of the ventricles** as the walls recoil **pushes remaining blood into the ventricles**. The **semi lunar valves remain closed.**
3. Ventricular systole- ventricle walls contract and atria relax. Decreased volume in the ventricles increases pressure in the ventricles. Pressure more than in the atria- **atrioventricular valves shut** to prevent backflow. Pressure in the ventricles- higher than in the aorta and pulmonary artery- blood is forced into these vessels as the **semi lunar valve opens**. The ventricles thick muscles especially in the left ventricle create high pressure to pump blood around the body.
69
What must you remember when analysing graphs of the cardiac cycle?
* You may be asked to analyse data about pressure and volume in the cardiac cycle using a graph or diagram.
* Remember to **compare pressure- one is greater than the other.**
* Make **note of whether the valves are shut or open depending on the position.**
* Be careful as the graph may be **mid stage so the pressure may not match the stages for a diagram as the valves may not be open yet.**
* You may have to work out from a diagram which valves are open and which chambers are contracted.
* e.g. Atrioventricular valves open- pressure hgh in atria- atria contracting.
70
What do small pressure changes in the cardiac cycle cause?
**A small pressure change causes elastic recoil.**
71
What are the functions of the arteries?
* Arteries carry blood from heart to the arterioles to the body.
* Transport blood rapidly under high pressure from the heart to tissues.
* Carry oxygenated blood apart from the pulmonary artery, which carries deoxygenated blood from the heart to the lungs.
72
Describe the structure of the arteries related to their function.
| Hint: 5 points
* Have a thicker muscle layer than veins- constricts and dilates to control the volumes of blood.
* Thicker elastic layer than veins- stretches and recoils as heart beats to cope with high blood pressure. Stretch during systole. Recoil during diastole to maintain a high blood pressure and reduce pressure surges.
* The inner layers are folded to allow stretching and maintain high pressure
* Thicker walls stop bursting.
* No valves except at the heart as the constant high pressure stops backflow.
73
Describe the function of arterioles.
* Smaller arteries
* Form a network in the body
* Direct blood to different areas of demand.
* Carry and control blood flows from arteries to capillaries
* Carry blood at lower pressure than the arteries.
74
Describe the structure of arterioles related to function.
* Similar to arteries in structure but some differences.
* **Thicker muscle layer** than arteries- **contraction**/ constriction resist/aid the flow of blood to control the movement into the capillaries- controls direction to meet demand in the body- **narrows lumen.**
* Thinner elastic layer than arteries as blood pressure is lower
* Smaller with a bigger lumen.
75
Describe the function of veins
* Carry blood from capillaries in the tissues back to the heart.
* Transport blood slowly under low pressure to the heart.
* Carry deoxygenated blood except the pulmonary vein which carries oxygenated blood from the heart to the lungs
76
Describe the structure of veins related to their function.
* **Thinner muscle layer** than arteries as carry blood away from tissues- constriction and dilation can’t control the flow of blood
* Elastic layer- thinner than arteries- low blood pressure in veins means not enough to burst or create recoil action.
* Thin walls- no need for thick walls- pressure too low to create any risk for bursting- allows them to be flattened to help blood flow.
* Lots of valves- ensures no backflow due to low pressure. Have pocket valves. Body muscles contract- veins compressed- puts pressure on blood- valves ensure the pressure directs blood only towards the heart.
* **Wider lumen** than arteries
77
What layers do all blood vessels have?
* Tough fibrous outer layer- resists pressure changes
* Muscle layer- contracts to control blood flow
* Elastic layer- maintains blood pressure by recoiling.
* Thin inner lining (endothelium)- smooth to reduce friction and thin to allow diffusion.
* Lumen- central cavity which blood flows through.
78
What are the functions of the capilleries?
* Vessels that link arterioles to veins.
* Exchange metabolic materials e.g. oxygen, glucose, between blood and the cells of the body.
* Aided the final distance by tissue fluid.
* Branch from arterioles.
* Networks of capillaries in tissues- called capillary beds.
79
What are the stuctures of the capilaries related to their function?
| Hint: 8 points
* Adapted for efficient diffusion.
* Blood flow slower for exchange.
* Near cells in exchange tissues e.g. alveoli for a short diffusion pathway- aided the final distance by tissue fluid.
* Walls- one cell thick and mostly a lining layer- endothelium- extremely thin- diffusion distance short- rapid diffusion between blood and cells.
* Numerous and highly branched- large surface area for exchange.
* Narrow diameter- permeate tissue- no cell far from capillary- short diffusion pathway.
* Small and lumen is narrow- red blood cells squeezed flat against sides- closer to the cells to supply oxygen- reduced diffusion distance.
* Spaces between lining (endothelial cells)- allow white blood cells to escape to deal with infections.
80
Sketch the different blood vessels and note what you must remember when identifying them.
* Answer on revision card
* Need to **look at lumen/ wall size to identify vessels.**
81
What is tissue fluid and what does it contain?
* Surrounds cells in tissues
* Made of small molecules that leave the blood plasma.
* Water
* Glucose
* Amino acid
* Fatty acids
* Ions
* Oxygen.
* Supply cells with these and receive CO2 and waste.
* Doesn't contain red blood cells or large proteins- too large to leave the capillaries.
82
What is the role of tissue fluid and where is it found?
* Exchange medium between blood and cells
* Surrounds all cells.
83
How is tissue fluid made/ maintained (brief explainanion.
* Made from blood plasma
* Composition controlled by homeostasis to maintain a constant environment.
* In capilary beds (networks of capillaries in tissue) substances move out of the capillaires to tissue fluid by by pressure filtration.
84
How is tissue fluid formed
| Hint: 4 steps
1. **Ventricular contraction** causes **high hydrostatic pressure** at the arterial end of the capillary. making it easier for tissue fluid to move out of the plasma.
2. The outward pressure is opposed by the hydrostatic pressure of tissue fluid outside the capillaries and the lower water potential of the blood plasma proteins causing water to move black into the blood.
3. However, near the arteries, hydrostatic pressure in the capillaries is greater than in tissue fluid- overall outward pressure **forces small molecules** e.g. **water**, dissolved substances **out**, creating tissue fluid. This pressure is not enough to move large molecules e.g.cells, large proteins so these are filtered by pressure filtration/ ultrafiltration.
4. The tissue fluid returns to the circulatory system.
85
When does tissue fluid return and where does it return to?
Once tissue fluid has exchanged materials with cells, it returns the circulatory system especially to blood plasma in the capillaries.
86
How does tissue fluid return to the circulatory system?
| Hint: 5 steps
1. Fluid leaves- hydrostatic pressure reduces in the capillaries- at the venule end of the capillary bed- hydrostatic pressure is lower than the tissue fluid.
2. The higher hydrostatic pressure of the tissue fluid forces it back into the capillaries.
3. Plasma in the venule end has lost water but it's plasma proteins remain so the blood in the capillaries has a lower water potential than the tissue fluid. Water leaves the tissue fluid by osmosis down the water potential gradient into the blood.
4. Not all tissue fluid returns to the capillaries. The rest is carried away by the lymphatic system- network of tube like capillaries beginning in the tissues with dead ends- merge into larger vessels, forming a network through the body.
5. Larger vessels in the lymphatic system drain excess fluid back into the bloodstream by two ducts in the veins close in the heart. Movement occurs through the hydrostatic pressure of the tissue fluid leaving the capillaries and the contraction of body muscle squeezing the lymph vessels combined with valves ensuring fluid moves towards the heart.
87
What does returning tissue fluid contain
* Lost nutrients and oxygen.
* Gained CO2 and water.
88
Draw diagram representing tissue fluid transfer.
Answer on revision card.
89
What is cardiovascular disease (CVD)?
* The general term for diseases to do with heart and blood vessels.
* Includes aneurysms, thrombosis and myocardial infactions
* Start with atheroma formation.
90
What is coronary heart disease and how does it escalate?
* Type of CVD when coronary arteries have atheromas.
* Restricts blood flow leading to a myocardial infaction (heart attack).
* No blood = no oxygen = no respiration = heart muscles die.
91
How are atheroma formed?
* Artery- made up of layers.
* If damage occurs to the endothelium- usually smooth and unbroken- clumps of white blood cells and lipids form under the lining in fatty streaks.
* Builds up and hardens into fibrous plaque- atheroma.
* Blocks the lumen, restricts blood flow and increases blood pressure.
92
What are aneurysms, how do they form and how do they escalate?
* Aneurysms are balloon like swellings of an artery.
* Formation of atheromas- weakens, damages and narrows the arteries- increases the blood pressure.
* High blood pressure and weak arteries pushes the inner layer (epithelium) through the outer elastic layer forming an aneurysms.
* The aneurysm can burst, causing a haemorrhage- internal bleeding.
93
What is thrombosis, how does it form, and how does it escalate?
* Thrombosis is a blood clot.
* The athoroma ruptures the endothelium forming a rough surface.
* Platelets and fibrin proteins accumulate and form blood clots which block the arteries sometimes completely or become dislodged and block other vessels or split of and cause more clots.
* Thrombosis in coronary arteries can lead to mycardial infarction.
94
What is a myocardial infaction, what causes it and why is it dangerous?
* A myocardial infaction is a heart attack
* If coronary arteries become completely blocked, e.g. through a blood clot, not enough oxygen reaches the heart muscle cells for aerobic respiration.
* No blood = no oxygen = no aerobic respiration = heart muscles die/ become damaged.
* Heart attacks involve shortness of breath and chest pain.
* If large areas of the heart muscles are affected, this can lead to complete heart failure which can be fatal.
95
Why is thickened blood dangerous?
**Thickened blood, e.g. through drugs can cause clots to form causing thrombosis potentially leading to myocardial infaction.**
96
What factors increase the risk of atheromas?
| Hint: 7 factors
* High blood cholesterol e.g. due to poor diet.
* High blood pressure e.g. due to poor diet
* Diet high in saturated fat- increases low density lipoprotein and therefore blood cholesterol.
* Diet high in salt can increase blood pressure.
* Diet high in antioxidants e.g. vitamin C can reduce the risk of heart disease.
* Thickened blood, e.g. through drugs
* Smoking is the highest cause of cvd in lower life expectancy due to carbon monoxide, nicotine, and reduced antioxidants.
97
How does high blood pressure increase the risk of atheromas?
* The heart has to work harder to pump blood - more prone to failure.
* Increased risk of damage to the artery wall- atheromas- increase blood pressure further and cause various forms of CVD.
* The walls of the arteries harden and thicken to resist high blood pressure- restricts blood flow.
98
How does high blood cholesterol increase the risk of atheromas?
* Cholestorol- important component of membranes transported by the blood as spheres of lipoproteins.
* High density lipoproteins remove cholesterol from tissues and transport them to the liver to protect against heart disease.
* Low density lipoproteins transport cholesterol from the liver to tissue and can cross artery walls causing atoromas.
* Cholesterol is the main component of a atheromas causing high blood pressure and other CVDs.
99
How does smoking increase the risk of atheromas?
* Carbon monoxide- combines with haemoglobin permanently- forms carboxyhemoglobin- reduces the oxygen carrying capacity of the blood. Reduces the amount of oxygen available to the heart muscles causing myocardial infaction. Heart has to work harder to supply oxygen- increases the blood pressure- increases the risk of CVD.
* Nicotine- stimulates adrenaline- increases the heart rate and blood pressure- increases the risk of CVD. Also makes platelets more sticky- increases the risk of thrombosis.
* Decreased antioxidants protecting cells from damage- leads to more cell damage to the epithelium- more atheromas.
100
How do you combined factors affect risk?
* Factors separately increase the risk of CVD.
* Combinations create disproportionate greater risk.
101
How can risk be reduced and how is this limited?
* Reduced risk means removing risk factors.
* Reduced by factors in control e.g. not smoking, better diet.
* Cannot control genetic risks e.g. predisposition to higher blood pressure/ diabetes.
102
How should you interpret data on risks?
| Hint: 5 points
* Describe the data using values to back up description. e.g., the relative risk of... increases as...
* Draw conclusions- positive and negative correlations
* Check the conclusions are valid- remember correlation doesn't equal causation.
* Think about limitations of the data. Remember risk factors increase probability but not do not mean that the person will get the disease. Remember other risk factors may also be at play.
* Think about the sample size.
103
How do you evaluate conflicting evidence?
* You may have to evaluate conflicting evidence with regards to risk factors.
* One study may say the factor is a risk factor, while another studies may say it's not.
* Think about why they conflict- method, sample size, control factors, demographic of subjects, other factors.
* Check the data is reproducible.
* The problem may be resolved by further study to prove that the data is reproducible.
104
What is xylems role?
Xylem transports water and mineral ions absorbed from the root hairs in the soil through xylem vessels in the stem to evaporate through the leaves in transpiration.
105
What should be noted about what xylem transports with regards to phloem?
Xylem transports mineral ions, but some are transported by the phloem, **especially in younger plants**.
106
What is required to drive the process of transpiration?
* Evaporation of water drives transpiration.
* Passive process- energy supplied by the sun to evaporate water from the surface of cells in the leaves.
107
How is xylem formed?
| Hint: 3 steps
1. Xylem cells form end to end.
2. Cell walls become impregnated with lignin in different patterns as the cells age. Lignin is impermeable to water and gives strength to the vessels.
3. The cell contents die due to lignification and the end walls break down, so the xylem consists of continuous columns.
108
Describe xylems structure and how it facilitates transpiration.
| Hint: 6 points
* No cell contents or cytoplasm, so water can move easily in a continuous column through the lumen.
* Lignin and thick walls give strength and flexibility so the walls don't collapse but can bend slightly so they don't break if the plant moves slightly.
* Long contuous unbroken hollow tubes of dead cells with no end walls from the roots to the leaves called vessel elements enable a continuous uninterupted column of water which is essential for cohesion tension theory.
* The xylem are bundled together for mechanical support.
* Bordered pits or gaps in the lignin for water to diffuse outside of the xylem into the phloem or into other branches in the plant.
* Xylem vessels are dead- don't actively move water- transpiration is a passive process and doesn't need metabolic energy.
109
How does water move in plants?
Water moves up the plant against gravity through the xylem from the roots to the leaves by transpiration due to cohesion tension theory.
110
How does water enter the xylem?
| Hint: 3 steps
1. Water is absorbed by root hair cells- specialised to have a large surface area- maximises the rate of osmosis anduptake of mineral ions by facilitated diffusion and active transport.
2. Water has to travel from the roots through a number of layers of cells in the cortex before it reaches the xylem to be transported. It does this through osmosis through either the cell walls or the cytoplasm of adjacent cells in the cortex surrounding the xylem.
3. Once water reaches the xylem, it travels up the xylem by mass transport through transpiration.
111
Describe cohesion tension theory.
| Hint: 5 steps
1. **Water evaporates** from the mesophyll cells into the air spaces by the stomata due to the suns heat causing **transpiration**. This **lowers the water potential of the mesophyll.**
2. **Water molecules have hydrogen bonds** and **stick together** as they are cohesive. This **forms a continuous,** unbroken **column of water** across the mesophyll and down the xylem as **water sticks to the xylem walls.**
3. **Water** evaporation **creates tension** or suction as more **water molecules are drawn up** the xylem due to the cohesion of water.
4. The whole column of water is pulled upwards through transpirtation pull- pulls from the roots into the stem.
5. Transpiration pull creates tension, creating a negative pressure within the xylem that sucks up water.
112
Where does water travel in plants?
Roots, to xylem vessels in the stem, to leaves, to evaporation.
113
When does transpiration only occur?
* Transpiration only occurs when the stomata are open.
* Changing the size of the stomatal pores can change the rate of transpiration.
114
What can transpiration also be described as?
Transpiration pull
Cohesion tension theory
115
Describe the process of transpiration.
| Hint: 5 steps
1. Water in the airspaces under the stomata causes them to have a higher humidity than the atmosphere. If the stomata are open, a water potential gradient forms between the air spaces by the stomata and the air- diffusion occurs as **water evaporates.**
2. The water in the airspaces is replaced by water evaporating from the moist mesophyll cell walls due to the suns heat.
3. **Mesophyll cells now have a lower water potential.** Water enters by osmosis from neighbouring cells.
4. Loss of water from neighbouring cells decreases their water potential, so there's movement of water by osmosis.
5. **A water potential gradient is established**, **pulling water from the xylem** into the mesophyll, either via the cell walls or the cytoplasm, due to the **tension of** osmosis (**the water potential gradient**) and the **cohesion of water due to hydrogen bonds** maintaining a column of water.
116
What does cohesion tension create and how powerful is it?
* The cohesion of water and tension from transpiration pull creates a negative pressure.
* Transpiration pull is so strong that it can raise water over 100 metres.
117
What evidence is there for cohesion tension theory?
| Hint: 3 points
* Diameter of tree trunks changes according to the rate of transpiration. In the day- increased transpiration increases tension and negative pressure- pulls the xylem inwards- causes trunk to shrink. Reverse happens at night.
* If xylem vessels are broken and air added- the plant can't draw up water as the continuous column of water is broken- water can't be cohesive and stick.
* If xylem are broke- water won't leak out like in positive pressure- air is drawn up, suggesting tension and negative pressure.
118
How do you perform a plant dissection?
| Hint: 6 steps
1. Cut a cross section of the stem thinly using a scalpel.
2. Place cut sections into water until use to prevent them from drying out.
3. Add a drop of water to the microscope, add the plant section, stain and (Toluidine Blue O) leave a minute.
4. Add a cover slip.
5. View under the microscope- xylem should be blue-green and the rest of the vessels pink slash purple.
6. Draw your findings.
119
Draw the arrangement of xylem and phloem in the roots and stem.
Answer on revision card.
120
What safety measures should be taken during plant dissections?
* **Cut away from the body.**
* **Use a sharp scalpel.**
* **Use a hard or flat surface.**
121
What factors affect the transpiration rate?
| Hint: 4 points
* Light intensity- increased light increases the transpiration rate- positive correlation. Stomata open with light to get CO2 for photosynthesis, but close when dark. Transpiration only occurs when the stomata are open. Light changes the size of stomatal pores. Changing the size of the stomatal pores can change their rate of respiration.
* Temperature- increased temperature= increased transpiration rate- positive correlation. Water has more energy, so evaporates faster- increased water potential inside and outside the leaf- increased diffusion.
* Lower humidity- increases the transpiration rate- negative correlation. Dryer air- increases the water potential gradient between the leaf and air- increases the transpiration rate.
* Wind/ airflow- increased wind/ air flow= increased transpiration rate. Air blows water molecules away- increases the water potential gradient and transpiration.
122
What do protometers do?
* Potometers estimate the transpiration rate.
* Measure water uptake.
123
What assumptions are made with potometers?
* Assumes water uptake linked to transpiration rate, but other factors may be at play- leakages, photosynthesis, water storage.
* **Not reflective of whole plant as only used the shoot, not the root.**
124
What methods other than a potometer can be used to measure water intake?
* Using a change in mass.
* Counting the numbers of xylum.
* Measuring how much dye moves up the stem.
125
How do you use a potometer?
| Hint: 8 steps
1. Cut the shoot underwater to prevent air from entering the xylem to increase the surface area
2. Assemble the potometer underwater and insert the shoot to avoid air.
3. Remove the potometer from the water, but keep the capillary tube in the beaker of water.
4. Check the potometer is airtight.
5. Dry the leaves and let the shoot acclimatise then close the tap.
6. Remove the tube from the capillary to form 1 air bubble, then put the tube back.
7. Record the start position of the air bubble. Start the stopwatch and record the distance per e.g. hour to find the rate of movement as an estimate for transpiration rate.
8. Change one variable at a time to see the effects.
126
What do the phloem transport and where do they transport them?
* Transport organic molecules- sugars and some mineral ions in solution.
* Mass transport the products of photosynthesis from the leaves to other parts of the plant.
* Transport up and down the plant through translocation.
* Mostly in flowering plants.
127
Describe the structure of the phloem.
* Cells arranged in tubes.
* Made of sieve tube elements and companion cells.
* Sieve tube elements are living cells that join end-to-end and are long and thin.
* Sieve tube end walls are perforated, forming sieve plates- form a tube for transporting solutes.
* Sieve tubes have no nucleus and few organelles to stop them from interupting flow.
* Companion cells- for each sieve tube element- carry out the living functions of the cell- possess mitochondria and perform respiration to produce ATP for active transport. Required as mass transport requires active transport.
128
What is translocation?
* Movement of solutes (amino acids and sugars) to where they're needed.
* Solutes are also known as assimilates.
129
What are solutes also known as?
Assimilates
130
What does translocation require?
Energy from respiration for active transport.
131
Where does translocation move things?
* Occurs in the phloem.
* Moves solutes from sources (sites of production) to sinks (where they're stored or used directly).
* Sinks can be above or below the sources so translocation occurs in both directions.
* There is a high concentration of assimilates at the source, but a low concentration at the sinks.
* The sources are usually leaves and the sinks are usually food storage organs or meristems.
132
What maintains the concentration gradient at the sink?
* Enzymes maintain the concentration gradients at sinks by changing solutes into storage form, or using them in reactions, maintaining the low concentration.
* e.g. conversion of sucrose into starch.
133
Why isn't translocation just diffusion and what causes it?
* Translocation isn't just diffusion because the concentration gradients aren't steep enough.
* Scientists aren't sure of the mechanism of diffusion, but mass flows theory is most supported.
134
Describe mass flow.
1. **Source**- sucrose is made from photosynthesis in cells with chloroplasts- diffuses down the concentration gradient by facilitated diffusion from the photosynthesising cells into companion cells. Hydrogen ions are actively transported from companion cells into spaces within the cell walls and then diffuse down the concentration along with sucrose through co-transporter carrier proteins into sieve tube elements/ **Sucrose is actively transported into the phloem by companion cells.**
2. Mass flow- **sieve tubes have a lower water potential** due to the increased solute. **Water moves from the xylem**/ companion cells **by osmosis into the phloem**. Increased water potential **creates high hydrostatic pressure** at the source end.
3. Sink- solutes actively transported by companion cells out of the sieve tubes and into the sink. **Sucrose** is either **used up in respiration or converted for storage into starch**. The movement of solutes into the cells lowers their water potential- water moves by osmosis into the sink cells from the sieve tubes lowering the hydrostatic pressure in the sieve tubes.
4. Mass transport- There is a high hydrostatic pressure at the source, but a lower hydrostatic pressure at the stink creating a **hydrostatic pressure gradient** forcing solutes towards the sink, **causing mass movement.**
135
What affects the amount of mass flow?
* Low photosynthesis- there is less sucrose in the phloem- increasing the water potential- less water movement from the xylem into the phloem by osmosis as gradient less steep- less pressure created.
* High water loss means less mass flow- less water movement from the **xylem into the phloem to create pressure due to lower water potential in the xylem.**
* The higher the concentration of sucrose at the source, the more the rate of translocation.
* Mass flow- passive, but requires the active transport of sugars- active processes affected by temperature or metabolism affect mass flow.
136
Define mass flow
Mass flow is the bulk movement of a material through a given channel or area in a specific time frame.
137
Describe the experiments that prove mass flow theory.
| Hint: 3 experiments
* Ringing experiments- Ringing bark of woody plants, therefore removing the phloem- causes a bulge to form around the ring with a higher concentration of sugar than below. The sugar can't move past the bark, so it shows sugar moves downwards with the source of sugar above the sink- suggesting mass flow.
* Aphids- pierce phloem with mouthpiece. If it's cut off while they're sucking, the sap flows out quicker near the leaves than further a down stem-, suggesting a pressure gradient.
* Radioactor tracer- CO2 with radioactive 14C is used as a tracer- incorporated into the sugars- produced and moved by translocation. Audioradiographs show traces after the plant is killed. The results show source to sink translocation as killing and taking an audioradiograph at different times shows movement of solute from leaves to roots.
138
What is the evidence for mass flow?
| Hint: 7 1/2 points
* Ringing, radioactive tracer and aphid experiments- **bulge could be proof of mass flow as it suggests sucrose moves downwards.**
* Evidence the phloem is involved.
* Pressure in the sieve tubes positive- sap leaks out when cut.
* Sucrose concentration is higher in the leaves (source) tahn in the roots (sink)
* Downward flow in phloem hapopens in the light but not the dark- only occurs when photosynthesis is happening.
* Increase in sucrose levels in the leaf- followed by increases in sucrose in the phloem.
* Companion cells possess mitochondria and produce ATP- implies active transport.
* **Metabolic inhibitors/ lack of oxygen (lack of ATP) inhibit translocation and respiration- active transport involved.**
139
What is the evidence against mass flow?
| Hint: 6 points
* **Bulge could be due to gravity.**
* Sieve plates- role unclear- create a barrier to mass flow- high pressure needed to get solutes through- but may have a structural funtion to stop bursting under pressure.
* Not all solutes move at the same speed- mass flow suggests they do.
* Sucrose is delivered at the same rate to all regions- not just the lowerest concentration ones.
* Sucrose travels to many sinks not just the one with the lowerest water potential.
140
What is the evidence phloem carries sugars/ amino acids?
| Hint: 4 points including 3 experiments
* When phloem are cut- organic molecule solution flows out.
* Aphid's mouthparts penetrate phloem and are cut to extract the sieve tube contents. Variation of sucrose concentrations in the leaves identical to later concentration in the phloem.
* Ringing stems- bark around woody stems containing phloem is removed- region above swells with liquid rich in organic substances. Non-photosynthetic tissue below withers and dies, but above still grows. Sugars above accumulate, and sugars below are blocked by removing the phloem- shows phloem is the translocator. Xylem is still there- suggests that if they were the translocator tissue, the parts of the plant wouldn't die.
* Tracer experiments- radioactive isotope 14C makes radioactive CO2. The plant **converts this into sugars made during photosynthesis**- traced using audioradiography. The plant is killed. placed on flim or X rayed- the film is blackened where it is exposed to radioactive ubstances. The film only blackens in regions with phloem- no other regions in blacken so they don't carry sugars only the phloem.
141
What must you consider with correlations causation?
* Data especially proving mass flow and must be considered carefully.
* You can conclude causation if there is a plausible mechanism but be careful of data limitations.
* Limitations include other evidence, a small dataset or a method error. Eg, damaged bark or different species.
* When a lot of experiments are done, correlation can show a relationship to causation.
