Mass transport Flashcards by Muminah Hussain

Describe the role of red blood cells & haemoglobin (Hb) in oxygen transport

Red blood cells:
○ No nucleus & biconcave → more space for Hb, high SA:V & short diffusion distance

● Hb loads oxygen where partial pressure of oxygen is high

● This forms oxyhaemoglobin which transports oxygen
○ Each can carry four oxygen molecule, one at each Haem group

● Hb dissociates from / unloads oxygen near cells / tissues where pO2 is low

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Describe the structure of haemoglobin

Protein with a quaternary structure
● Made of 4 polypeptide chains
● Each chain contains a Haem group containing an iron ion (Fe2+)

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Describe the loading, transport and unloading of oxygen in relation to the
oxyhaemoglobin dissociation curve

low PO2:
- Hb has a low affinity for oxygen
● So oxygen readily dissociates with Hb
● So % saturation is low

High PO2:
Hb has a high affinity for oxygen
● So oxygen readily loads Hb
● So % saturation is high

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Explain S shaped curve

1.Binding of first oxygen changes tertiary / quaternary structure of haemoglobin
2. This uncovers Haem group binding sites, making further binding of oxygens easier

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What is the Bohr effect?

Effect of CO2 concentration on dissociation of oxyhaemoglobin → curve shifts to right

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Explain effect of CO2 concentration on the dissociation of oxyhaemoglobin

1.Increasing blood CO2 eg. due to increased rate of respiration

Lowers blood pH
Reducing Hb’s affinity for oxygen tertiary changes slightly
So more unloading of oxygen to respiring cells at a given pO2

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Explain the advantage of the Bohr effect (eg. during exercise)

More dissociation of oxygen → faster aerobic respiration / less anaerobic respiration → more ATP produced

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Explain why different types of haemoglobin can have different oxygen transport properties

Different types of Hb are made of polypeptide chains with slightly different amino acid sequences
● Resulting in different tertiary / quaternary structures / shape
● So they have different affinities for oxygen

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Explain curve shifts in terms of affinity

Curve shift left
Hb has higher affinity for O2
More O2 associates with Hb more readily
At gas exchange surfaces where pO2 is lower
Eg. organisms in low O2 environments - high
altitudes, underground, or foetuses

Curve shift right
Hb has lower affinity for O2
More O2 dissociates from Hb more readily
At respiring tissues where more O2 is needed
Eg. organisms with high rates of respiration /
metabolic rate

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Describe the general pattern of blood circulation in a mammal

Deoxygenated blood in right side of heart pumped to lungs; oxygenated returns to left side
2. Oxygenated blood in left side of heart pumped to rest of body; deoxygenated returns to right

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Suggest the importance of a double circulatory system

Prevents mixing of oxygenated / deoxygenated blood

Blood can be pumped to body at a higher pressure

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Name the blood vessels entering and leaving the heart and lungs

Vena cava – transports deoxygenated blood from respiring body tissues → heart

Pulmonary artery – transports deoxygenated blood from heart → lungs

Pulmonary vein – transports oxygenated blood from lungs → heart

Aorta – transports oxygenated blood from heart → respiring body tissues

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Name the blood vessels entering and leaving the kidneys

Renal arteries – oxygenated blood → kidneys

Renal veins – deoxygenated blood to vena cava from kidneys

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Name the the blood vessels that carry oxygenated blood to the heart muscle

Coronary arteries - located on surface of the heart, branching from aorta

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Suggest why the wall of the left ventricle is thicker than that of the right

Thicker muscle to contract with greater force
To generate higher pressure to pump blood around entire body

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Explain what happens at the atrial systole

Atria contract- so their volume decreases,
pressure increases

Atrioventricular valves open - when pressure in atria exceeds pressure in ventricles

Semilunar valves remain shut -as pressure in arteries exceeds pressure in ventricles

blood pushed into ventricles

Explain what happens at ventricular systole

Ventricles contract - so their volume decreases,
pressure increases
Atrioventricular valves shut - when pressure in ventricles exceeds pressure in atria

Semilunar valves open - when
pressure in ventricles exceeds pressure in arteries

So blood pushed out of heart through arteries

What happens at diastole

Atria & ventricles relax - so their volume increases,
pressure decreases

SL shut, AV open

So blood fills atria via veins

How can heart rate be calculated from cardiac cycle data?

Heart rate = 60s/ length of one cardiac cycle

Describe the equation for cardiac output

Cardiac output = stroke volume x heart rate

Explain how the structure of arteries relates to their function

Function - carry blood away from heart at high pressure

Thick smooth muscle tissue - Can contract and withstand blood flow

Thick elastic tissue -
Can stretch as ventricles contract and recoil as ventricles relax - maintain high pressure

Thick wall - Withstands high pressure

Narrow lumen -
maintains high pressure

Explain how the structure of arterioles relates to their function

Function - direct blood to different capillaries / tissues

Thicker smooth muscle layer than arteries
○ Contracts → narrows lumen → reduces blood flow to capillaries

○ Relaxes → widens lumen → increases blood flow to capillaries

● Thinner elastic layer → pressure surges are lower (as further from heart / ventricles)

Explain how the structure of capillaries relates to their function

Function - allow efficient exchange of substances between blood and tissue fluid

One cell thick -
Reduces diffusion distance

Capillary bed - large network of branched capillaries - Increases surface area for diffusion

Small diameter / narrow lumen - Reduces blood flow rate so more time for diffusion

Explain how the structure of veins relates to their function

Wider lumen than arteries → less resistance to blood flow

● Very little elastic and muscle tissue → blood pressure lower

● Valves → prevent backflow of blood

Explain the formation of tissue fluid

Higher blood / hydrostatic pressure inside capillaries than tissue fluid Forcing water out of capillaries Large plasma proteins remain in capillary

Suggest and explain causes of excess tissue fluid accumulation

Low concentration of protein in blood plasma - lymph system can't drain excess fast enough High blood pressure increases outward pressure from arteriole so more tissue fluid formed

Explain the return of tissue fluid to the circulatory system

Hydrostatic pressure reduces as fluid leaves capillary Lowers water potential in capillary below that of tissue fluid Water enters capillaries from tissue fluid by osmosis down a water potential gradient

Describe the function of xylem tissue

Transports water (and mineral ions) through the stem, up the plant to leaves of plants

Suggest how xylem tissue is adapted for its function

Cells joined with no end walls forming a long continuous tube → water flows as a continuous column ● Cells contain no nucleus → easier water flow / no obstructions ● Thick cell walls with lignin → provides support

Explain the cohesion-tension theory of water transport in the xylem

Explain effect of light on transpiration

Light intensity Increases rate of transpiration ● Stomata open in light to let in CO2 for photosynthesis ● Allowing more water to evaporate faster ● Stomata close when it’s dark so there is a low transpiration rate

Explain effect of temp on transpiration

Temperature Increases rate of transpiration ● Water molecules gain kinetic energy as temperature increases ● So water evaporates faster

Explain effect of wind on transpiration

Wind intensity Increases rate of transpiration ● Wind blows away water molecules from around stomata ● Decreasing water potential of air around stomata ● Increasing water potential gradient so water evaporates faster

Effect of humidity on transpiration

Decreases rate of transpiration ● More water in air so it has a higher water potential ● Decreasing water potential gradient from leaf to air ● Water evaporates slower

Describe the function of phloem tissue

Transports organic substances eg. sucrose in plants

Sieve tube elements ○ No nucleus / few organelles → maximise space for / easier flow of organic substances Companion cells ○ Many mitochondria → high rate of respiration to make ATP for active transport of solutes

What is translocation?

Movement of solutes from sink to source

Explain the mass flow hypothesis for translocation in plants

1.At source, sucrose is actively transported into phloem sieve tubes / cells 2. By companion cells 3. This lowers water potential in sieve tubes so water enters (from xylem) by osmosis 4. This increases hydrostatic pressure in sieve tubes (at source) / creates a hydrostatic pressure gradient 5. So mass flow occurs - movement from source to sink 6. At sink, sucrose is removed by active transport to be used by respiring cells or stored in storage organs

Arguments for and against mass flow

For - a radioactive tracer can track movement of organic substances If you remove a ring of bark from a woody stem a bulge forms above the ring and the fluid has a high conc of sugar than the fluid below the ring - shows there is a downward flow of sugars Against - Sugars travel to many different sinks not just to highest WP