3B - More Exchange And Transport Systems Flashcards
What is digestion?
The process by which large food molecules are broken down into smaller molecules so that they can be absorbed into the from the gut into blood.
Why must digestion happen?
Large food molecules are too big to cross cell membranes, so they cannot be absorbed from the gut into the blood.
What type of reaction is digestion?
Usually hydrolysis.
What are carbohydrates broken down into in hydrolysis?
Disaccharides (and then monosaccharides)
What are fats broken down into in hydrolysis?
Fatty acids and monoglycerides
What are proteins broken down into in hydrolysis?
Amino acids
Why are there many different digestive enzymes?
Enzymes only work with a specific substrate and so different enzymes are needed to catalyse the breakdown of different food molecules.
Describe the digestion of starch in terms of products, bonds and enzymes.
- Starch broken down into maltose by amylase
- Glycosidic bond is hydrolysed
- Maltose broken down into two glucose molecules by maltase (a membrane-bound disaccharidase)
- Glycosidic bond is hydrolysed
Describe the digestion of carbohydrates in terms of products, bonds and enzymes.
STARCH
• Starch broken down into maltose by amylase
• Glycosidic bond is hydrolysed
DISACCHARIDES
• Disaccharides broken down into two monosaccharides by membrane-bound disaccharidases (e.g. sucrose by sucrase)
• Glycosidic bond is hydrolysed
What enzyme catalyses the breakdown of starch?
Amylase
Where is amylase produced and released?
- Salivary glands -> Released into mouth
* Pancreas -> Released into small intestine
What is the name for enzymes that catalyse the breakdown of disaccharides?
Membrane-bound disaccharidases
What are membrane-bound disaccharidases?
- Enzymes that are attached to the cell membranes of epithelial cells lining the ileum (small intestine).
- Break down disaccharides into monosaccharides.
Where are membrane-bound disaccharidases found?
Attached to the cell membranes of epithelial cells lining the ileum.
Describe the breakdown of maltose in terms of enzymes and products.
- Enzyme: Maltase
* Products: Glucose + Glucose
Describe the breakdown of sucrose in terms of enzymes and products.
- Enzyme: Sucrase
* Products: Glucose + Fructose
Describe the breakdown of lactose in terms of enzymes and products.
- Enzyme: Lactase
* Products: Glucose + Galactose
Describe the digestion of lipids in terms of products, bonds and enzymes (+ other substances).
- Bile salts emulsify lipid droplets to make smaller lipid droplets
- Lipids now broken down into monoglycerides and fatty acids by lipase
- Ester bond hydrolysed
- Monoglycerides and fatty acids stick with bile salts to form micelles
What enzyme catalyses the breakdown of lipids?
Lipase
Where is lipase produced and released?
• Pancreas -> Released into small intestine
What is a monoglyceride?
A glycerol molecule with one fatty acid attached.
Where are bile salts produced?
Liver
What do bile salts do and why?
- Emulsify lipids -> Several small lipid droplets have a bigger surface area than a single large droplet (for a given volume).
- This increases the SA for lipase to work on.
- Digestion happens faster.
Describe the digestion of proteins in terms of products, bonds and enzymes.
- Proteins are broken down into amino acids by proteases.
- Endopeptidases -> Hydrolyse peptide bonds within a protein.
- Exopeptidases -> Hydrolyse peptide bonds at the ends of a protein.
What is another name for a protease?
Peptidase
What are the two types of protease?
- Endopeptidases
* Exopeptidases
What enzyme catalyses the breakdown of proteins?
Proteases -> Endopeptidases and exopeptidases
What are endopeptidases?
Enzymes (proteases) that act to hydrolyse peptide bonds within a protein.
What are exopeptidases?
Enzymes (proteases) that act to hydrolyse peptide bonds at the end of a protein. They remove a single amino acids from proteins.
Give 3 examples of endopeptidases and where they are produced and released.
- Trypsin + chymotrypsin -> Produced in pancreas and released into small intestine.
- Pepsin -> Produced in stomach lining and released into the stomach
What type of enzyme is trypsin and where is it produced and secreted?
- Endopeptidase
- Produced: Pancreas
- Secreted: Small intestine
What type of enzyme is chymotrypsin and where is it produced and secreted?
- Endopeptidase
- Produced: Pancreas
- Secreted: Small intestine
What type of enzyme is pepsin and where is it produced and secreted?
- Endopeptidase
- Produced: Stomach lining
- Secreted: Stomach
In what conditions does pepsin work and why?
Acidic, because it is in the stomach with hydrochloric acid.
Give an example of exopeptidases and where it is found.
- Dipepeptidases
* Found: In the cell-surface membrane of epithelial cells in small intestine
What are dipeptidases?
- Exopeptidases that work specifically on dipeptides -> Separate two amino acids.
- Often located in the cell-surface membrane of epithelial cells in small intestine.
Where are the products of digestion absorbed?
Across the ileum epithelium into the bloodstream.
Describe how monosaccharides are absorbed into the epithelial cells from the ileum lumen.
- Glucose + galactose -> Active transport with sodium ions via a co-transporter (see pg 43)
- Fructose -> Facilitated diffusion through a different transporter protein
Describe how monoglycerides and fatty acids are absorbed into the epithelial cells from the ileum lumen.
- Micelles constantly break up and reform, so they can “release” monoglycerides and fatty acids
- Monoglycerides and fatty acids are lipid-soluble, so they DIFFUSE across the epithelial cell membrane
- Micelles are NOT taken across the membrane
Are micelles taken across cell membranes?
No, they simply release their contents so that they can be absorbed.
Describe how amino acids are absorbed into the epithelial cells from the ileum lumen.
- Sodium ions are actively transported out of the epithelial cells into the ileum
- They then diffuse back through sodium-dependent transporter proteins, carrying amino acids with them
Through what type of transport protein are amino acids absorbed into epithelial cells from the ileum lumen?
Sodium-dependent transporter proteins
Describe how glucose is absorbed into epithelial cells from the ileum lumen.
Via a sodium-glucose co-transporter protein.
See pg 43
Describe how galactose is absorbed into epithelial cells from the ileum lumen.
Via a co-transporter protein with sodium.
Like glucose - see pg 43
Describe how fructose is absorbed into epithelial cells from the ileum lumen.
Facilitated diffusion via a (different) transporter protein.
Note: Check if the absorption of glucose vis co-transporter proteins is active transport.
Do it.
What carries oxygen around the body?
Haemoglobin in RBCs
What is the symbol for haemoglobin?
Hb
What is haemoglobin?
A large protein with a quaternary structure that carries oxygen around the body.
Describe the structure of haemoglobin.
- 4 polypeptide chains -> Quaternary structure
* Each chain has a haem group, which contains an iron ion
What gives haemoglobin its colour?
The iron ion in each chain
What does “affinity for oxygen” mean?
Tendency to combine with oxygen.
In general, what is the affinity for oxygen of haemoglobin?
High - it can carry 4 oxygen molecules.
What happens in the lungs to haemoglobin?
4 oxygens join onto each haemoglobin molecule to form oxyhaemoglobin.
Give the equation for haemoglobin joining with oxygen.
Hb + 4O2 HbO8
Haemoglobin + Oxygen Oxyhaemoglobin
What is the name for oxygen leaving oxyhaemoglobin?
Dissociation
In what organisms is haemoglobin found?
- All vertebrates
- Earthworms
- Starfish
- Some insects
- Some plants
- Some bacteria
Is haemoglobin the same in all organisms?
- There are many chemically similar types of haemoglobin
* All carry out same function
What determines the saturation of haemoglobin with oxygen?
The partial pressure of oxygen.
What is partial pressure of oxygen?
- A measure of oxygen concentration.
* The greater the concentration of dissolved oxygen in cells, the higher the partial pressure.
What is the symbol for partial pressure of oxygen?
pO2
What is the partial pressure of carbon dioxide?
A measure of concentration of CO2 in a cell.
Describe how haemoglobin’s affinity for oxygen changes with partial pressure of oxygen.
- High pO2 -> High affinity -> Oxyhaemoglobin formed
* Low pO2 -> Low affinity -> Oxyhaemoglobin dissociates
What happens to haemoglobin in the lungs and why?
- High pO2 in the alveoli
* So oxygen binds to haemoglobin to form oxyhaemoglobin
What happens to haemoglobin near cells and why?
- Cells respire, using up oxygen
- This lowers the pO2
- Oxyhaemoglobin dissociates into haemoglobin and oxygen
What graph can be used to show how haemoglobin’s affinity for oxygen changes with partial pressure of oxygen?
Dissociation curve
What does a dissociation curve for haemoglobin show?
How saturated the haemoglobin is with oxygen at any given partial pressure of oxygen.
What does 100% saturation of haemoglobin mean?
Each haemoglobin molecule is carrying the maximum of 4 molecules of oxygen.
What does 0% saturation of haemoglobin mean?
None of the haemoglobin molecules are carrying any oxygen.
Describe the shape of a dissociation curve for haemoglobin.
S-shaped from the origin to the top-right corner.
See diagram pg 68 of revision guide
Explain the shape of the dissociation curve for haemoglobin.
- Difficult for first O2 to join to haemoglobin -> Shallow gradient -> First part of “S”
- When haemoglobin combines with the first O2 molecule, it’s shape changes so that it’s easier for their molecules to join too -> Increasing gradient -> Middle part of “S”
- As haemoglobin becomes more saturated, it’s harder for more oxygen molecules to join -> Decreasing gradient
At which part of the dissociation curve is a small change in partial pressure most significant?
- Steep part
* Small change in partial pressure causes a big change in the amount of O2 carried by the Hb
What is the symbol for partial pressure of carbon dioxide?
pCO2
What factors affect the affinity of haemoglobin for oxygen?
- Oxygen partial pressure
* Carbon dioxide pressure
How does the partial pressure of carbon dioxide affect the affinity of haemoglobin for oxygen?
- High partial pressure of CO2 -> Low affinity for O2
* Low partial pressure of CO2 -> High affinity for O2
Explain how a high partial pressure of carbon dioxide affects the dissociation curve of haemoglobin and explain the implications of this.
Shifts it to the right -> For a given pO2, the saturation of haemoglobin with oxygen is lower -> More O2 released to cells
(See diagram pg 69 of revision guide)
Explain how the affinity of haemoglobin for oxygen changes during exercise.
- Cells respire -> Produce carbon dioxide and raise the pCO2.
- The affinity of haemoglobin for oxygen decreases so the rate of oxygen unloading increases
- O2 is released for cells
- Dissociation curve shifts to the right
What is the Bohr effect?
The way in which partial pressure of carbon dioxide affects the affinity of haemoglobin for oxygen and causes the dissociation curve to shift.
Compare the dissociation curve of the same haemoglobin at:
• 2.5 kPa CO2
• 11.5 kPa CO2
- 2.5 kPa CO2 -> More to the left
* 11.5 kPa CO2 -> More to the right
Which way does a high CO2 concentration shift the dissociation curve of haemoglobin?
Right
Why do different organisms have different types of haemoglobin?
As an adaptation to help the organism survive in a particular environment.
How many oxygen molecules can each haemoglobin molecule carry?
4 x O2 molecules
Explain the dissociation curve of an animal living in low oxygen conditions.
- To the left
- For a given pO2, the haemoglobin has a high affinity for oxygen and so the saturation is higher
- This allows the haemoglobin to pick up oxygen at low pO2 values (but is not good for efficient respiration)
Explain the dissociation curve of an active animal with high oxygen demand.
- To the right
- For a given pO2, the haemoglobin has a low affinity for oxygen and so the saturation is lower
- This allows the haemoglobin to release more oxygen at low pO2 values, so that more is supplied for respiration (but this is disadvantageous in low oxygen conditions)
Describe the affinity of haemoglobin for oxygen in an animal living in a low-oxygen environment.
High affinity
Describe the affinity of haemoglobin for oxygen in an active animal (in a high-oxygen environment).
Lower affinity
How can you remember what is favoured by shifting the dissociation curve shape each way?
- Left = Lungs
* Right = Respiration
What does a far-left dissociation curve suggest about an organism?
It lives in a low-oxygen environment.
What does a far-right dissociation curve suggest about an organism?
It has a high respiratory rate (i.e. it is active) and lives in an oxygen-rich environment.
Remember to practice labelling the 4 dissociation curves on the bottom graph of pg 69.
Do it.
What is the circulatory system?
A mass transport system consisting of the heart and blood vessels used to carry materials between the exchange organs and body cells.
Why do multicellular organisms, like mammals, require a circulatory system?
They have a low surface area to volume ratio, so a specialist transport system is needed to carry raw materials from exchange organs to body cells.
What is the circulatory system made of?
- Heart
* Blood vessels
What are the types of blood vessel?
- Arteries
- Arterioles
- Veins
- Capillaries
What does blood transport around the body?
- Respiratory gases
- Products of digestion
- Metabolic wastes
- Hormones
Describe the two circulatory circuits.
1) From the heart to the lungs and back
2) From the heart to the rest of the body and back
What are the 4 vessels entering and leaving the heart?
- Vena cava
- Aorta
- Pulmonary artery
- Pulmonary vein
What vessel enters the right side of the heart?
Vena cava
What vessel leaves the right side of the heart?
Pulmonary artery
What vessel enters the left side of the heart?
Pulmonary vein
What vessel leaves the left side of the heart?
Aorta
What vessel enters the lungs?
Pulmonary artery
What vessel leaves the lungs?
Pulmonary vein
What vessel enters the kidneys?
Renal artery
What vessel leaves the kidneys?
Renal vein
What vessel enters the liver?
- Hepatic artery (from heart)
* Hepatic portal vein (from gut)
What vessel leaves the liver?
Hepatic vein
Which side of the heart pumps oxygenated blood?
Left
Which side of the heart pumps deoxygenated blood?
Right
What type of blood does the aorta carry and where?
Oxygenated blood from the heart to the body.
What type of blood does the vena cava carry and where?
Deoxygenated blood from the body to the heart.
What type of blood does the pulmonary vein carry and where?
Oxygenated blood from the lungs to the heart.
What type of blood does the pulmonary artery carry and where?
Deoxygenated blood from the heart to the lungs.
What type of blood does the renal artery carry and where?
Oxygenated blood to the kidneys.
What type of blood does the renal vein carry and where?
Deoxygenated blood away from the kidneys.
What type of blood does the hepatic artery carry and where?
Oxygenated blood to the liver.
What type of blood does the hepatic portal vein carry and where?
Oxygenated blood from the gut to the liver.
What type of blood does the hepatic vein carry and where?
Deoxygenated blood away from the liver.
Describe the path of blood through the heart, lungs and kidneys, starting in the right atrium.
Right atrium -> Right ventricle -> Pulmonary artery -> Lungs -> Pulmonary vein -> Left atrium -> Left ventricle -> Aorta -> Renal artery -> Kidneys -> Renal vein -> Vena cava -> Right atrium
Remember to practise labelling the diagram of the circulatory system on pg 70.
Do it.
How does the heart supply itself with blood?
Through the coronary arteries.
How many coronary arteries are there?
2 -> The left and right coronary arteries.
Where do arteries carry blood?
Away from the heart.
What type of blood do arteries carry?
Oxygenated, except the pulmonary artery.
Explain the structure of an artery.
- Thick, muscular walls -> Withstand high pressure
- Elastic tissue in walls -> Stretch and recoil to maintain high pressure
- Endothelium (inner lining) is folded -> Allows artery to stretch
- Narrower lumen than veins -> Maintain high pressure
(See diagram pg 70 of revision guide)
What is the endothelium of a blood vessel?
The inner lining of the walls.
How do arteries maintain a high pressure as the heart beats?
- Elastic tissue in walls -> Recoils after heartbeat
* Folded endothelium
What are arterioles and what is their role?
- Arteries divide into smaller vessels called arterioles, which form a network throughout the body
- Muscles in the arterioles allow them to constrict or relax and direct blood to areas of need
What allows arterioles to direct blood?
They have muscles inside which can contract or relax.
Where do veins carry blood?
Back to the heart.
What type of blood do veins carry?
Deoxygenated, except the pulmonary vein.
Explain the structure of a vein.
- Thin walls with little elastic tissue -> Low pressure
- Valves -> Prevent backflow
- Wider lumen than arteries -> More blood can pass
(See diagram pg 70 of revision guide)
What keeps blood flowing through veins?
Contraction of body muscles surrounding them.
Compare the structure of veins and arteries.
ARTERIES • Smaller lumen • Folded endothelium • Thick muscle wall • Lots of elastic tissue VEIN • Larger lumen • Smooth endothelium • Thinner muscle walk • Little elastic tissue
Compare the pressure in veins and arteries.
Vein: Low
Arteries: High
What are capillaries?
- Arterioles branch off into capillaries
* Capillaries are the smallest of blood vessels
Where are substances exchanged between the blood and tissues?
In the capillaries.
What are capillaries adapted for?
Efficient diffusion.
Explain the structure of capillaries.
- Thin wall (1 cell thick) -> Efficient diffusion
* Small lumen
How are capillaries adapted for efficient diffusion? (3)
1) Found very near cells in exchange tissues (e.g. alveoli) -> Short diffusion pathway
2) Walls are one cell thick -> Short diffusion pathway
3) Large number of capillaries -> Increased SA for diffusion
What are capillary beds?
Networks of capillaries in tissue.
See diagram pg 71 of revision guide
What is tissue fluid?
- The fluid that surrounds cells in tissues.
- Made from small molecules that leave the blood plasma.
- Cells exchange oxygen, nutrients and metabolic waste with the tissue fluid.
What is tissue fluid made of?
- Small molecules that leave the blood plasma
* NOT large proteins or RBCs
Why isn’t tissue fluid made of RBCs or large proteins?
They are too large to be pushed out through the capillary walls.
What is the function of tissue fluid?
- Cells take in oxygen and nutrients from the tissue fluid
- Cells release metabolic waste into the tissue fluid
(i.e. It is like the in-between of blood and cells.)
By what process do substances move from capillaries into the tissue fluid?
Pressure filtration
Describe the exchange of substances in tissue fluid along a capillary bed.
- At start of capillary bed, near arteries, hydrostatic (liquid) pressure in capillaries is higher than in the tissue fluid
- So an overall outward pressure forces fluid out of capillaries and into the spaces around cells -> Forms tissue fluid
- As fluid leaves, hydrostatic pressure in capillaries is reduced -> Pressure at venule end of capillary bed
- Due to fluid loss and increasing concentration of plasma proteins in capillaries, the water potential at venule end of capillary bed is lower than in tissue fluid
- Some water re-enters the capillaries from tissue fluid by osmosis
What is hydrostatic pressure?
Liquid pressure
Remember to revise the diagram of tissue fluid exchange on of 71 of revision guide.
Do it.
What happens to excess tissue fluid?
It is drained into the lymphatic system, which transports it away and releases it back into the circulatory system.
When looking at a diagram of the heart, what is it important to remember?
The left and right sides of the heart are reversed.
How many pumps does the heart consist of?
2
The right side of the heart pumps…
Deoxygenated blood to the lungs.
The left side of the heart pumps…
Oxygenated blood to the whole body.
Remember to practise labelling a diagram of the heart.
Pg 72 of revision guide
What are the 4 chambers of the heart?
- Right atrium
- Right ventricle
- Left atrium
- Left ventricle
Describe the positions of the atria and ventricles.
The atria are above the ventricles.
What are the two vessels that make up the vena cava and what is the difference?
- Superior vena cava -> Brings blood from above
* Inferior vena cava -> Brings blood from below
What is the valve between the atrium and ventricle called?
Atrioventricular valve
How many atrioventricular valves are there?
2 -> A left and a right valve
In which direction does an atrioventricular valve allow blood to flow?
From atrium to ventricle.
What is the valve between the ventricle and aorta / pulmonary artery called?
Semi-lunar valve
How many semi-lunar valves are there?
2 -> A left and right valve.
In which direction does a semi-lunar valve allow blood to flow?
From ventricle to aorta / pulmonary artery.
What are the string-like pieces attached to the atrioventricular valves in the heart?
Cords (valve tendons) that prevent the valves being forced open the wrong way.
Where are the cords (valve tendons) in the heart?
In the ventricles, attached to the atrioventricular valves.
Compare and explain the structure of the left and right ventricles.
- The left ventricle has thicker, more muscular walls than the right ventricle.
- Because it needs to contract more powerfully to pump blood all the way around the body, not just to the lungs.
Compare and explain the structure of the ventricles and atria.
- Ventricles have thicker, more muscular walls than the atria.
- Because they have to push the blood out of the heart, whereas atria just need to push blood a short distance into the ventricles.
What is the shorthand for atrioventricular valves?
AV
What is the shorthand for semi-lunar valves?
SL
What is the function of the atrioventricular valves?
Stop blood flowing back into the atria from the ventricles when the ventricles contract.
What is the function of the semi-lunar valves?
Stop blood flowing back into the ventricles from the aorta / pulmonary artery after the ventricles have contracted.
What is the function of the cords in the heart?
- Are attached to the atrioventricular valves and are in the ventricles.
- Stop the AV valves from being forced up into the atria when the ventricles contract.
Do valves open both ways?
No, they open only one way.
What determines whether a valve is open or closed?
- Higher pressure behind valve than in front -> Open
* Higher pressure in front of valve than behind -> Closed
What is the cardiac cycle?
- Ongoing sequence of contraction and relaxation of atria and ventricles.
- Keeps blood continuously circulating around the body.
How does the volume and pressure of a chamber change when it contracts?
- Volume decreases
* Pressure increases
Name the 3 stages of the cardiac cycle.
1) Ventricles relax, atria contract
2) Ventricles contract, atria relax
3) Ventricles relax, atria relax
Describe the first stage of the cardiac cycle.
- Ventricles are relaxed
- Atria contract -> Decreasing volume + increasing pressure
- Blood is pushed into ventricles -> Slight increase in ventricular pressure and chamber volume
(VENTRICLES RELAX, ATRIA CONTRACT)
Describe the second stage of the cardiac cycle.
- Atria relax
- Ventricles contract -> Decreasing volume + increasing pressure
- Pressure higher in ventricles than atria -> AV valves shut to prevent back-flow
- Pressure higher in ventricles than aorta / pulmonary artery -> SL valves forced open + blood moves in
(VENTRICLES CONTRACT, ATRIA RELAX)
Describe the third stage of the cardiac cycle.
- Ventricles and atria both relax
- Higher pressure in aorta / pulmonary artery than ventricles -> SL valves close to prevent backflow
- Blood returns to heart -> Atria fill again due to higher pressure in the vena cava / pulmonary vein -> Pressure in atria increases
- Ventricles continue to relax -> Pressure falls below atria -> AV opens
- Blood flows passively from atria to ventricles (without contractions)
- Atria contract + process starts again
(VENTRICLES RELAX, ATRIA RELAX)
Describe the entire cardiac cycle in detail.
1:
• Ventricles are relaxed
• Atria contract -> Decreasing volume + increasing pressure
• Blood is pushed into ventricles -> Slight increase in ventricular pressure and chamber volume
2:
• Atria relax
• Ventricles contract -> Decreasing volume + increasing pressure
• Pressure higher in ventricles than atria -> AV valves shut to prevent back-flow
• Pressure higher in ventricles than aorta / pulmonary artery -> SL valves forced open + blood moves in
3:
• Ventricles and atria both relax
• Higher pressure in aorta / pulmonary artery than ventricles -> SL valves close to prevent backflow
• Blood returns to heart -> Atria fill again due to higher pressure in the vena cava / pulmonary vein -> Pressure in atria increases
• Ventricles continue to relax -> Pressure falls below atria -> AV opens
• Blood flows passively from atria to ventricles (without contractions)
• Atria contract + process starts again
What are different names for cardiac contraction and relaxation?
- Cardiac contraction = Systole
* Cardiac relaxation = Diastole
Remember to practise describing and identifying different stages of the cardiac cycle.
Pg 73 of revision guide
What are the two types of question you might be asked about analysing data on the cardiac cycle?
- Graph of pressure or volume against time
* Heart diagram
Remember to practise drawing out a pressure-time and volume-time graph for ventricles and atria.
See diagram pg 74 of revision guide.
Explain the line for an atrium on a pressure-time graph starting with stage 1 of the cardiac cycle (ventricles relaxed, atria contracting).
STAGE 1
• Pressure increases steadily until start of stage 2 -> Atria contracting
STAGE 2
• Pressure decreases at a decreasing rate until start of stage 3 -> Atria relaxing + AV valves are shut near start
STAGE 3
• Pressure increases to peak -> Atria fill until AV valve opens
• Pressure decreases slightly -> AV valve opens and blood passively moves into ventricle
• Pressure increases gradually -> Atria continue to fill passively
Explain the line for a ventricle on a pressure-time graph starting with stage 1 of the cardiac cycle (ventricles relaxed, atria contracting).
STAGE 1
• Pressure increases gradually -> Filling from atrium
• Slight drop before start of stage 2
STAGE 2
• Pressure increases rapidly at a decreasing rate to peak at start of stage 3 -> Ventricles contracting + AV valves close near start
STAGE 3
• Pressure falls at an increasing rate to a trough halfway through stage 3 -> Ventricles relax
• Pressure increases slowly and gradually -> Ventricles fill passively after AV opens
Explain the line for an atrium on a volume-time graph starting with stage 1 of the cardiac cycle (ventricles relaxed, atria contracting).
STAGE 1
• Volume decreases gradually -> Atria contracting
STAGE 2
• Volume increases gradually -> Atria expanding as they fill with blood
STAGE 3
• Volume continues increasing at same rate -> Atria expanding as they fill with blood
• Volume decreases slightly -> AV valves open and blood flows into the ventricles
• Volume continues to increase as before -> Atria expanding as they fill with blood
Explain the line for a ventricle on a volume-time graph starting with stage 1 of the cardiac cycle (ventricles relaxed, atria contracting).
STAGE 1
• Volume increases gradually to peak at start of stage 2 -> Stretch while filling from atria contractions
STAGE 2
• Volume decreases quickly but gradually to trough at start of stage 3 -> Ventricles contract
STAGE 3
• Volume increases gradually -> Ventricles relax + fill with blood from the atria
Which sees the greatest variation in pressure and volume, the atria or the ventricles?
The ventricles.
Compare the pressure in the left and right ventricle.
Higher in the left ventricle due to more powerful contractions.
From a pressure-time graph of the cardiac cycle, when can you tell when valves open or close?
- They open when the pressure in the area behind gets higher than in the area in front of the valve
- So when the lines for the ventricle and atrium pressure cross, the AV valve either opens or closes
Remember to practise answering the questions about the pressure-time graph on pg 74.
Do it.
What is the unit for pressure on a cardiac cycle pressure-time graph?
mmHg
What is the unit for volume on a cardiac cycle volume-time graph?
ml
Remember to practise looking at a diagram of the heart and describing the changes in pressure and volume.
See diagram pg 74 of revision guide.
When told to describe the changes in pressure and volume shown by a diagram, how can you know what is happening?
- Look at open/closed valves to determine relative pressures
- Think about what causes these pressures
- Determine the stage of the cardiac cycle and therefore the contractions occurring
Describe the structure of an artery from the centre outwards.
- Lumen
- Endothelium
- Muscle layer
- Elastic tissue
How does most cardiovascular disease start?
With an atheroma formation.
Describe the formation of an atheroma.
- Damage occurs to the artery endothelium
- White blood cells and lipids from the blood clump together under the lining -> Form fatty streaks
- More WBCs, lipids and connective tissue build up and harden
- Forms a fibrous plaque called an atheroma -> Partially blocks blood flow
What is an atheroma?
A fibrous plaque formed when WBCs, lipid and connective tissue build up under a part of damaged endothelium.
Where does an atheroma form?
UNDER the endothelium, when it is damaged.
What does CHD stand for?
Coronary heart disease
What is coronary heart disease and what is its effect?
- When the coronary arteries have lots of atheromas.
* Restricts blood flow to the heart muscle -> Can lead to a heart attack
What are the dangers of an atheroma?
- Coronary heart disease + heart attacks (myocardial infarction)
- Aneurysms
- Thrombosis
What is an aneurysm?
A balloon-like outwards swelling of the artery.
What is thrombosis?
Formation of a blood clot after an atheroma plaque ruptures.
How does an atheroma affect blood pressure?
Increases it - by restricting blood flow.
What is a haemorrhage?
Bleeding when an aneurysm bursts.
Describe the formation of an aneurysm.
- Atheroma plaques damage and weaken arteries
- Also narrow arteries, increasing blood pressure
- Blood at high pressure may push the inner layers through the outer elastic layer -> This is an aneurysm
- If this bursts, it is a haemorrhage
Describe how thrombosis happens.
- Atheroma ruptures through the endothelium
- This smashes the artery and leaves a rough surface
- Platelets and fibrin accumulate at the site of damage -> Form a blood clot (thrombus)
- This can cause a blockage or dislodge and block a vessel elsewhere
What is the danger of an aneurysm?
May burst, causing a haemorrhage (bleeding).
What is the danger of thrombosis?
• Can block the vessel
• Can dislodge and block a vessel elsewhere
• Debris can cause another blood clot further down the artery
These can lead to a heart attack.
What is a blood clot in an artery called?
A thrombus.
What is fibrin?
A protein that accumulates at the site of a ruptured atheroma to form a blood clot (thrombus).
What supplies the heart muscle with blood?
Coronary arteries
What is the technical term for a heart attack?
Myocardial infarction
Describe what causes a heart attack.
- Coronary artery becomes completely blocked by a thrombus or atheroma
- Area of heart muscle is cut off from receiving oxygen -> Can’t respire
- This can caused damage and death of heart muscle (or complete heart failure)
What are the symptoms of a heart attack?
- Chest pain
- Shortness of breath
- Sweating
What is complete heart failure?
In a heart attack, if large areas of the heart are affected, the heart can stop working which is usually fatal.
What are cardiovascular diseases?
Diseases associated with the heart and blood vessels.
Name the different cardiovascular problems that one can experience.
• Atheroma
• Aneurysm
• Thrombosis
These can lead to myocardial infarction.
Remember to revise cardiovascular disease.
Pg 75 of revision guide.
What are some risk factors of cardiovascular disease?
- High blood cholesterol -> High saturated fat diet
- Cigarette smoking
- High blood pressure -> High salt diet, Obesity, Lack of exercise, Alcohol
- Sex
- Age
How does a high blood cholesterol level increase the risk of cardiovascular disease?
- Cholesterol is one of the main constituents of the fatty deposits that form atheromas
- This leads to high blood pressure and blood clots -> Can cause myocardial infarction
Why is a diet high in salt a risk factor of cardiovascular disease?
- Increases the risk of high blood pressure
* Which weakens artery walls and increases the risk of atheroma and blood clot formation.
What is classed as a high blood cholesterol level?
Above 240mg per 100cm³
How does cigarette smoking increase the risk of cardiovascular disease?
- Cigarette smile contains nicotine and carbon monoxide
- Nicotine -> Increases the risk of high blood pressure -> Weakens artery walls and increases the risk of atheroma and blood clot formation.
- Carbon monoxide -> Combines with haemoglobin and reduces the amount of oxygen transported in the blood -> Less oxygen supplied to heart muscle can lead to myocardial infarction.
- Decreases amount of antioxidants in blood -> Weakens cells in artery walls, which can cause atheroma formation.
How do antioxidants affect the risk of cardiovascular disease?
- Antioxidants protect cells from damage
* A lack of antioxidants makes cells in coronary artery walls more susceptible to damage -> Atheroma formation
How does a high blood pressure increase the risk of cardiovascular disease?
- Increases the risk of damage to artery walls
- Which increases the risk of atheroma and blood clot formation
- This can lead to myocardial infarction
Why is being overweight a risk factor for cardiovascular disease?
- Increases the risk of high blood pressure
* Which weakens artery walls and increases the risk of atheroma and blood clot formation.
Why is not exercising a risk factor for cardiovascular disease?
- Increases the risk of high blood pressure
* Which weakens artery walls and increases the risk of atheroma and blood clot formation.
Why is a diet high in saturated fat a risk factor of cardiovascular disease?
It is associated with high cholesterol levels, which contribute to the fatty deposits in atheromas, etc.
Why is excessive alcohol consumption a risk factor for cardiovascular disease?
- Increases the risk of high blood pressure
* Which weakens artery walls and increases the risk of atheroma and blood clot formation.
How can the risk of cardiovascular disease be reduced?
Removing as many risk factors as possible.
Are all risk factors of cardiovascular disease under our control?
Most are, but some may be as a result of a genetic predisposition or as a result of another condition.
What are some things that can cause high blood pressure?
- High salt diet
- Being overweight
- Not exercising
- Excessive alcohol consumption
- Nicotine
Looking at the study on pg 77, describe the data.
The relative risk of a cardiovascular event increases as the level of LDL cholesterol in the blood increases.
Looking at the study on pg 77, draw conclusions from the data.
- The graph shows a positive correlation between the relative risk of a cardiovascular event and the level of LDL cholesterol in the blood.
- BUT you can’t say that one caused the the other (there may be another reason for the trend).
Looking at the study on pg 77, how can you ensure that any conclusions are valid?
Any conclusions must match the data exactly!
e.g.
• Data boy looked at women -> Can’t say the trend is true for everyone
• Can’t claim a correlation between LDL levels and risk of heart attacks, because the data looks at all cardiovascular events
• Can’t claim that high LDL levels caused the increased relative risk -> There may be other reasons for this trend
Looking at the study on pg 77, what is the significance of the sample size?
Large sample size -> Representative of whole population
Remember to practise evaluating the study on pg 77 of the revision guide.
Do it.
What can be done when two studies about risk factors of cardiovascular disease present conflicting evidence?
- Think about what could cause that conflicting evidence -> Sample size? Other risk factors accounted for? Similar groups studied?
- Carry out more studies
What things could cause conflicting results in two studies looking at risk factors of cardiovascular disease?
- Sample size
- Other risk factors accounted for
- Groups studied
- Method of study
What are the two types of tissue involved in transport in plants?
- Xylem
* Phloem
What does the xylem transport and where?
- Water and mineral ions
* Up the plant
What does the phloem transport and where?
- Organic substances in solution (e.g. sugars)
* Up and down the plant
What are the xylem and phloem?
Mass transport systems that move substances over large distances in plants.
Describe the general structure of the xylem and phloem.
Cells arranged in long tubes.
Describe the structure of the xylem.
- Dead cells (vessel elements) are joined end to end to form xylem vessels
- No end walls
- Pores in side walls
- Lignin forms rings or spirals in the xylem vessel, which provides strength
Is the xylem dead or alive?
Dead
What is the function of lignin in the xylem?
Strengthen and support the vessel
Why are there no end walls in the xylem?
Allows water to pass up easily.
What is the name for long stacks of dead cells in the xylem?
Xylem vessel
What are the individual components in the xylem vessel called?
Xylem elements (these are just dead cells).
Remember to practise drawing out the xylem vessel structure.
See diagram pg 78 + lignin
Describe how water moves up a plant through the xylem.
1) Water evaporates form the leaves at the top of the xylem (transpiration).
2) This creates tension (suction), which pulls more water into the leaf.
3) Cohesion in water means that the whole column of water in the xylem moves upwards.
4) Water enters through the roots.
What two features of water allow it to be moved upwards through the xylem?
- Cohesion
* Tension
What is the name for the process by which water is moved upwards through the xylem?
The cohesion-tension theory of water transport.
What is transpiration?
Evaporation of water from a plant’s surfaces, especially the leaves.
Describe transpiration.
1) Water evaporates from the moist cell walls
2) Accumulates between cells in the leaf
3) When stomata open, water moves out down the concentration gradient
What factors affect the rate of transpiration?
- Light
- Temperature
- Humidity
- Wind
How does light affect the rate of transpiration?
- The lighter it is, the higher the transpiration rate
* Because stomata open in response to light in order to let in CO2 for photosynthesis
How does temperature affect the rate of transpiration?
- The higher the temperature, the higher the transpiration rate
- Because warmer water molecules have more energy, so they evaporate from the cells in leaves faster
- This increases the concentration gradient between inside and outside the leaf -> Faster transpiration
How does humidity affect the rate of transpiration?
- The lower the humidity, the higher the transpiration rate
- Because dry air around the leaf creates a steeper concentration gradient between inside and outside the leaf -> Faster transpiration
How does wind affect the rate of transpiration?
- The windier it is, the higher the transpiration rate
- Because the wind blows water molecules away from around the leaf
- This increases the concentration gradient between inside and outside the leaf -> Faster transpiration
What device can be used to estimate the rate of transpiration?
Potometer
What is a potometer?
- A piece of equipment used to estimate transpiration rates.
* Measures water uptake by a plant.
What is an assumption of a potometer?
The water uptake of a plant is directly related to water loss by the leaves.
(This is unlikely to be the case)
Describe the structure of a potometer.
- Plant placed through a bung on a tube containing water -> Plant touching water
- Capillary tube connects tube to a beaker of water
- Bubble in the capillary tube next to a scale to measure movement
- Reservoir of water with a tap (between plant and bubble) -> Used to return bubble to start for repeats
(See diagram pg 79 of revision guide)
Remember to practise drawing out a potometer.
Pg 79 of revision guide.
What is the reservoir of water and tap used for in a potometer?
Returning bubble to the start position for repeats.
Describe how you can investigate the rate of transpiration in a plant.
1) Cut a shoot underwater to prevent air from entering the xylem + cut at a slant to increase surface area for water uptake
2) Assemble potometer underwater and insert shoot underwater so no air can enter
3) Remove the apparatus from the water (but keep end of capillary tube submerged) -> Check if watertight and airtight
4) Dry the leaves and allow time for the shoot to acclimatise, then shut the tap
5) Remove the end of the capillary tube from the beaker until one air bubble has formed, then put the end back into the water
6) Record the starting position of the air bubble
7) Start a stopwatch and record the distance moved by the air bubble per unit time
8) The rate of air bubble movement is an estimate for the rate of transpiration.
9) Remember to change only one variable at a time.
When preparing a shoot for a potometer experiment, what is it important to remember?
- Cut it underwater -> Prevents air from entering the xylem
* Cut at slant -> Increases surface area for water uptake
Remember to revise the potometer setup.
Pg 79 of revision guide
What things must you remember before starting a potometer experiment?
- Dry the leaves
- Allow time for shoot to acclimatise
- Shut the tap
In the potometer experiment, what is the air bubble sometimes called?
Air-water meniscus
Describe how to dissect a plant for observation of the xylem and phloem.
1) Cut a thin cross-sections of the stem using a scalpel.
2) Use tweezers to place these in water, which stops them drying out.
3) Transfer each section to a dish containing stain (e.g. toluidine blue O) and leave for a minute -> TBO stains the lignin in the xylem walls blue-green.
4) Rinse off the sections in water and mount each one on a slide.
Which stain is commonly used to colour the xylem for observation under a microscope and what does it do?
- Toluidine blue O (TBO)
* Stains the lignin in the xylem walls blue-green -> So you can see the position and structure of the xylem vessels
What are the two types of cell that make up phloem tissue?
- Sieve tube elements
* Companion cells
Describe the structure of the phloem.
- Living sieve tube elements are joined end to end to form a long tube
- Sieve plates between these
- Companion cell next to each sieve tube element
(See diagram pg 80 of revision guide)
Is the phloem dead or alive?
Alive
What are sieve tube elements?
Living cells that form the tube in the phloem for transporting solutes.
Describe sieve tube elements.
- No nucleus
- Few organelles
- Thin layer of cytoplasm on inner sides of each cell
What are companion cells and why are they needed?
- Cells that are next to the sieve tube elements in the phloem
- Carry out living functions for sieve tube elements -> Since these have few organelles themselves
How many companion cells are there?
One per sieve tube element.
Give an example of the functions that companion cells carry out for sieve tube elements.
Providing energy for active transport of solutes
What is the term for the movement of solutes around a plant?
Translocation
What is translocation?
The movement of solutes to where they’re needed in a plant.
What is another name for solutes in the phloem?
Assimilates
Where does translocation happen?
In the phloem.
Does translocation require energy?
Yes
From where to where does translocation move solutes?
From sources to sinks.
What are sources and sinks?
- Sources -> Where a solute is made
* Sink -> Where a solute is used up.
Compare the concentration of a solute at the source and sink.
- Source -> High concentration
* Sink -> Low concentration
What are the sources and sinks of sucrose?
- Sources -> Leaves
* Sinks -> Other parts of the plant, especially food storage organs and meristems
What are meristems?
Areas of growth, in the roots, stems and leaves.
How is a concentration gradient maintained between the source and sinks of a solute?
- Enzymes break down or convert solutes at the sink
* This ensures there’s always a lower concentration at the sink than at the source
Describe how a concentration gradient between the source and sink of sucrose is maintained in potatoes.
- Sucrose is converted to starch in sink areas -> Always a lower concentration at the sink
- So there’s a constant supply of sucrose from the source
What is the name for the theory that explains how solutes are moved around a plant in the phloem?
Mass flow hypothesis
Are scientists sure how solutes are transported around the plant by translocation?
No, but the best supported theory is the mass flow hypothesis.
Describe the mass flow hypothesis (how the phloem transports solutes around a plant).
AT SOURCE:
1) Active transport is used to move solutes from companion cells into sieve tube elements near the source.
2) This lowers the water potential in the sieve tubes, so water enters by osmosis from the xylem and companion cells.
3) This creates a high pressure in the sieve tubes near the source.
AT SINK:
1) Solutes are removed from the phloem into companion cells (ADD PROCESS).
2) This increases the water potential in the sieve tubes, so water moves into the xylem by osmosis.
3) This lowers the pressure in the sieve tubes.
SO:
1) This results in a pressure gradient from the source to the sink end of the phloem.
2) This pushes solutes along the sieve tubes towards the sink.
3) When they reach the sink, the solutes are used or stored.
(See diagram pg 80 of revision guide)
Remember to revise the mass flow hypothesis diagram.
Pg 80 of revision guide
What determines the rate of translocation?
The concentration of sucrose at the source.
What two things can happen to a translocated solute once it reaches the sink?
- Used up (e.g. in respiration)
* Stored (e.g. as starch)
What are some pieces of evidence supporting the mass flow hypothesis?
1) Removing a ring of bark -> Bulge forms above the ring
2) Radioactive tracers used to track the movement of organic substances
3) Aphid mouthparts used to pierce the phloem -> Sap leaks out faster near the leaves
4) Metabolic inhibitor is put into the phloem -> Stops translocation
How is removing a ring of bark evidence for the mass flow hypothesis?
- Bark contains the phloem, but not the xylem
- Bulge forms above removed ring of bark, with higher sugar concentration than below
- Shows a downwards flow of sugars
How can the use of radioactive tracers be used as evidence for the mass flow hypothesis?
- Radioactive tracers, such as C-14 can be used to track the movement of organic substances
- This shows the direction that solutes move
How can aphids be used as evidence for the mass flow hypothesis?
- Aphids pierce the phloem -> Then their bodies are removed, leaving just the mouthparts
- This allows sap to flow out
- Sap flows out faster near the leaves than further down the stem -> Shows pressure gradient
How can metabolic inhibitors be used as evidence for the mass flow hypothesis?
- Metabolic inhibitor our into phloem and stops ATP production
- This stops translocation -> Shows that active transport is involved
What are some pieces of evidence against the mass flow hypothesis?
1) Sugar travels to many different sinks, not just to the one with the highest water potential
2) Sieve plates create a barrier to mass flow -> Would require a lot of pressure to allow solutes through at a reasonable rate
How can the movement of sugar be used as evidence against the mass flow hypothesis?
- Sugar travels to many different sinks
* But the mass flow hypothesis appears to suggest that it would travel to just one
How can sieve plates be used as evidence for against the mass flow hypothesis?
- Sieve plates would create a barrier to mass flow
* A lot of pressure would be needed for solutes to get through at a reasonable rate
Remember to revise evidence for and against the mass flow hypothesis.
Pg 81 of revision guide
How can translocation of solutes be demonstrated?
1) Part of a plant is supplied with an organic substance with a radioactive label (e.g. Leaves supplied with CO2 containing C-14).
2) Radioactive tracer is incorporated into organic substances produced by the source (e.g. sugars)
3) The translocation of these substances can be tracked using autoradiography -> Plant is killed and the whole plant is placed on photographic film. The radioactive substance is present wherever the film turns black.
4) Results demonstrate translocation of substances over time.
What is the name of the process used to see the spread of a radioactive tracer?
Autoradiography
Describe autoradiography with plants.
- Part of plant is given radioactive tracer
- Tracer spreads
- Plant is killed (e.g. by freezing it using liquid nitrogen)
- Plant is placed on photographic film
- Radioactive substance is present wherever the film turns black
