3.3.4 Mass transport

Question 1

What is haemoglobin?

Answer 1

A large protein with quaternary stricture

Question 2

What is haemoglobin made up of?

Answer 2

4 polypeptide chains - 2 alpha and 2 beta

Each chain has a haem unit (total of 4) which contains Fe2+

Question 3

How do haemoglobin differ in crustaceans

Answer 3

In the form of haemocyanin which is made up of copper units

Question 4

Which organisms are haemogoblin found in?

Answer 4

All vertebrates

Question 5

What is association or loading?

Answer 5

When oxygen molecule joins to haemoglobin by binding to Fe2+

Question 6

What is dissociation or unloading?

Answer 6

When oxygen molecule leaves oxyhaemoglobin

Question 7

What is the affinity for oxyegn?

Answer 7

The tendency a molecule has to bind with oxygen

Question 8

How is haemoglobin’s affinity for oxygen varied and in what way?

Answer 8

By partial pressure (concentration of dissolved oxygen in cells) of oxygen - pO2

Higher PP, affinity for oxygen increases, more association of oxygen - load onto haemoglobin

Lower PP, affinity for oxygen decreases, more dissociation of oxygen - unload from oxyhaemoglobin

Question 9

Where in the body is pO2 high or low?

Answer 9

High in alveoli in lungs

Low in respiring tissues

Question 10

What is the Bohr effect?

Answer 10

When oxygen dissociation curve ‘shifts’ to the right due to an increase of pCO2

Question 11

Why does an increase in CO2 decrease affinity for oxygen

Answer 11

1. CO2 and H2O released from aerobic respiration is joined together by carbonic anhydrase (catalyst) to form carbonic acid (H2CO3)
2. H2CO3 then dissociates into H+ and HCO3-
3. H+ is acidic which causes a conformational change (change in shape of macromolecule due to environmental factors) of haemoglobin
4. Quaternary structure changes -affinity for oxygen decreases
5. Oxygen is unloaded from oxyhaemoglobin and will then enters cell

Question 12

How would oxygen dissociation curve look at different conditions?

Answer 12

High activity level / metabolism:
Graph shifts to the right- lower affinity for oxygen (more unloading of oxygen) at lower pO2

High altitude:
Graph shifts to the left - higher affinity for oxygen (more loading of oxygen) at lower pO2

Question 13

What does oxygen dissociation graph show?

Answer 13

A sigmoid curve - S shaped

At lower pO2, affinity of oxygen is lower - less oxygen bound to haem unit (shallower)

As haemoglobin combine with the first O2 (more partial pressure needed), its shape alters which makes it easier for other O2 to join afterwards (steeper curve in the middle) due to positive cooperative binding

Curve gets shallower towards the end as it is now harder for more oxygen molecules to join

Question 14

What valves separate the atria and ventricle

Answer 14

atrioventricular valves

Tricuspid on the right
Bicuspid on the left

Question 15

Which are the only arteries that contains valves (semi-lunar)?

Answer 15

Pulmonary artery contains semi-lunar pulmonary valve

Aorta contains semi-lunar aortic valve

Question 16

What is the septum and its function?

Answer 16

A wall of tissue that separates the left and right ventricle - keeping oxygenated and deoxygenated blood separate

Question 17

What is the general structure of a blood vessel (artery/vein)?

Answer 17

Outside to inside:

Three tunica layers:
Tunica intima (thin layer of elastic tissues)
Tunica media (thick layer of smooth muscle)
Tunica externa (thick layer of fibrous protein, collogen - withstand pressure and elastic tissue)

A single layer of endothelial cells

Lumen

Question 18

How does structure of artery and vein differ?

Answer 18

Lumen:
A: small/narrow
V: large/wider

Thickness of layers in walls:
A: thicker
V: thinner

Valves in lumen:
A: absent
V: present

Question 19

How are structure of artery and vein similar?

Answer 19

Both have a single layer of endothelial cells surrounding the lumen

Both have elastic tissue, smooth muscle and collogen in their walls

Question 20

What are tissue fluids?

Answer 20

Fluid that surrounds cells in tissue

Question 21

What causes tissue fluid to move in and out of capillary?

Answer 21

Water and other small molecules (ions, glucose, amino acids) move out of capillary at the arteriole end due to higher hydrostatic kPa at arteriole end

Hydrostatic pressure decreases along capillary and water potential becomes more negative as fluid has been lost and proteins remain in capillary

When hydrostatic pressure / water potential in capillary is lower than in surrounding cells, water will move back into capillary from surrounding cells due to pressure difference and down the water potential gradient

Excess tissue fluid will be drained into the lymphatic system to be drained back into circulatory system

Question 22

What is cardiac output?

Answer 22

stroke volume x heart rate

Question 23

What are the four stages of cardiac cycle?

Answer 23

Atrial systole
Isovolumetric contraction
Ejection phase
Isovolumetric relaxation

Question 24

What happens in “Atrial systole” of cardiac cycle?

Answer 24

Atria contracts, Ventricle is relaxed

Pressure inside atria increases due to blood filling it (kPa in atria > ventricle) and this forces atrioventricular valves to open

Blood now flows from atria to ventricle through opened valve into the ventricle

Question 25

What happens in “Ventricular systole” of cardiac cycle?

Answer 25

Ventricle contracts, Atria is relaxed, pressure in ventricle increases due to blood entering(kPa in ventricle > atria), this forces atrioventricular valves to shut to prevent back-flow Ventricle's high pressure forces semi-lunar valves to open (kPa in ventricle > arteries) Blood is ejected from the ventricles into arteries Volume of blood in ventricle decreases, pressure in ventricles deceases

Question 26

What happens in “Diastole” of cardiac cycle?

Answer 26

Atria and Ventricle both relaxes Semi-lunar valves are shut due to higher pressure in arteries as blood flows from ventricle into arteries (kPa in arteries > ventricle) When blood returns to heart again, atria will be filled, volume deceases and pressure increases

Question 27

How has the structure of arteries adapted to its function?

Answer 27

Contains a thick layer of elastic fibre to stretch to accommodate high blood pressure from heart Contains thick outer wall to withstand high blood pressure Narrow lumen to keep blood under high pressure

Question 28

How has the structure of veins adapted to its function?

Answer 28

Contains thinner muscular and elastic outer walls due to a decrease in blood pressure - does not have to withstand as high pressure Contains valves to prevent blood from flowing backwards due to lower blood pressure Wider lumen as blood pressure is lower

Question 29

How has the structure of capillaries adapted to its function?

Answer 29

Contain walls that are one cell thick, allowing a shorter diffusion pathway as they are exchange surfaces Very narrow lumen (slightly larger than a RBC) to ensure slow blood flow - efficient exchange

Question 30

What does the xylem tissue transport in plants?

Answer 30

Water and mineral ions in solution

Question 31

What direction are substances transported in the xylem tissue?

Answer 31

Move up from roots to leaves - unidirectional

Question 32

What are the features of the xylem tissue?

Answer 32

Long and hollow Formed from dead cells No end walls - continuous tube Cell wall made of cellulose

Question 33

How does water move up the xylem against the force of gravity?

Answer 33

Through water adhesion and cohesion: 1. Transpiration occurs at the top of the xylem in the leaves 2. Water cohesion meant water molecules will be pulled into leaf as previous water molecules leaf through their ‘stickiness’ due to hydrogen bonds between water molecules 3. Whole column of water in the xylem will be pulled upwards from the roots 4. Water adhesion meant water molecules will bind to cellulose found in the cell wall - this pull on the cell wall creates tension

Question 34

What is the process of transpiration?

Answer 34

Evaporation of water from plant’s surface, especially leaves Water move out of xylem into spongy mesophyll layer via osmosis Water is evaporated from the moisture cell walls into the air space Water molecule moves out of leaf via diffusion through the stomata down the water potential gradient

Question 35

What factors affect transpiration rate?

Answer 35

1. Light intensity - positive correlation High: Stomata open to allow CO2 in for photosynthesis (more) Low: Stomata close (less) 2. Temperature - positive correlation High: molecules have more energy - rate of evaporation increases - concentration gradient between inside and outside increases (more) 3. Humidity - negative correlation Low: Dry air around leaves give a larger water potential gradient between inside of leaf and air (more) 4. Wind speed - positive correlation High: Lots of air movement blows away water molecules around the stomata - increase in water potential gradient (more)

Question 36

What direction are substances transported in the phloem tissue?

Answer 36

Bi-directional

Question 37

What are the features of the phloem tissue?

Answer 37

Formed from living cells which are separated from phloem tube by companion cells Have sieve plates - allow for plasmodesmata - cytoplasm move across cells

Question 38

Why are companion cells needed by phloem cells?

Answer 38

Phloem cells do not contain nucleus - cannot control cell's activity Nucleus found in companion cell controls itself and its phloem cell

Question 39

How are sugar/amino acids loaded from source (photosynthesising cells) to the phloem tissue?

Answer 39

1. There's a high conc. of sugar/amino acids in the source, they will move across to its companion cell via facilitated diffusion 2. H+ ions are pumped out of companion cells via active transport into the gap between companion cell and the phloem tube 3. There's an increase of H+ conc. in gap, H+ diffuse back into companion cells down the concentration gradient, co-transporting sugar/amino acid out (antiport - opposite directions) 4. Sugar/amino acids have diffused into the phloem tube

Question 40

How are sugar/amino acids transported in the phloem?

Answer 40

1. Conc. of sugar and amino acids is increased due to diffusion, water potential in phloem tissue becomes more negative 2. Water moves into the phloem from the xylem down the water potential gradient via osmosis 3. Hydrostatic pressure increases - build up in phloem, this causes mass flow of water - pushing molecules away from the source towards the sink through sieve plates (with holes)

Question 41

How are sugar/amino acids unloaded from phloem tissue to the sink?

Answer 41

1. Sugar/amino acids move into the sink through companion cells via active transport/ diffusion, then diffuse into the sink 2. Water potential in phloem tissue increases (less negative), water moves out of phloem tissue into the xylem tissue via osmosis

Question 42

What evidence are there to support the mass flow hypothesis?

Answer 42

Sugar conc. at source is higher and lower at sink Sap flows out of phloem when cut open - under pressure Companion cells have lots of mitochondria (for active transport of H+) When O2 conc. is lower (inhibit with poison/at night) - rate of mass flow hypothesis decreases as respiration rate decrease - less ATP produced)

Question 43

What evidence are there to be against the mass flow hypothesis?

Answer 43

Speed of flow isn't the same everywhere between molecules Rate of delivery is not effected by concentration gradient between source and sink, but rather the type of molecule Presence of sieve plates are non-essential - have no clear function

Question 44

What are the effects of carbon monoxide binding with haemoglobin?

Answer 44

Haemoglobin has a higher affinity of carbon monoxide than oxygen - will bind instead of oxygen Binding of carbon monoxide with haemoglobin is irreversible

Question 45

What is the function of valve tendons/ cords?

Answer 45

To prevent valves from being forced back up into the atrium when the ventricle contracts (high pressure) - maximise cardiac output as all blood will now only flow out through the aorta/pulmonary artery