Mass transport

Question 1

What is haemoglobin and describe the structure

Answer 1

a globular protein with 4 polypeptide chains

it has a quaternary structure

each polypeptide has a haem group with an Fe2+ ion

it has 4 oxygen binding sites so it carries oxygen through the blood to respiring cells

Question 2

describe the shape of a standard oxyhaemoglobin dissociation curve

Answer 2

graph begins shallow at low partial pressures of oxygen until the first O2 molecule binds

upon the binding of the first oxygen molecule a conformational shape change of haemoglobin is causes so the 2nd and 3rd binding oxygen is much easier, this causes the curve to become very steep very quickly

the graph then begins to plateau as there is a decrease in binding site availability so it is harder for oxygen to bind

Question 3

What is the Bohr effect

Answer 3

During exercise, rate of respiration increases which increases blood concentration of carbon dioxide

CO2 dissolves in blood to form carbonic acid which lowers blood pH

this causes a change in haemoglobins tertiary structure, lowering oxygen affinity

this means more oxygen is dissociated from haemoglobin at respiring tissues which will compensate for the increased rate of respiration

Question 4

How does haemoglobin differ in different organisms

Answer 4

Organisms that live in low partial pressures of oxygen have a higher affinity so haemoglobin is more readily loaded at these low partial pressure

Organisms that live in high partial pressures have myoglobin, which has a lower affinity for oxygen, so oxygen can be more readily dissociated

Question 5

3 Blood vessels surrounding the liver

Answer 5

Hepatic artery
Hepatic vein
Hepatic portal vein

Question 6

2 Blood vessels surrounding the kidneys

Answer 6

Renal artery
Renal vein

Question 7

4 blood vessels surround heart

Answer 7

vena cava
aorta
pulmonary artery and vein

Question 8

Flow of blood through the heart to lungs

Answer 8

through vena cava into right atrium

through tricuspid valve into right ventricle

through semilunar valve to pulmonary artery to lungs

Question 9

Flow of blood through heart to body

Answer 9

Through pulmonary vein into left atrium

through bicuspid valve into left ventricle

through semilunar valve into aorta and out to the whole body

Question 10

Adaptations of the heart

Answer 10

left ventricle walls are much thicker than the right ventricle walls as blood has to be pumped much further

Aorta is much thicker than any other artery as has to withstand the highest pressure of blood

valves to prevent backflow

septum to prevent mixing of oxygenated and deoxygenated blood

Question 11

1st Step of cardiac cycle

Answer 11

Cardiac diastole
- both atria and ventricles are relaxed and blood enters the atria
- As pressure rises atrioventricular valves will open and blood moves down pressure gradient

Question 12

2nd step of cardiac cycle

Answer 12

Ventricular diastole and atrial systole

• atria contract to ensure all blood enters ventricles
• as pressure increases in ventricles, atrioventricular valves shut to prevent backflow

Question 13

3rd step of cardiac cycle

Answer 13

Ventricular systole

• ventricles contract, increasing pressure further so semilunar valves open
  -blood flows into pulmonary artery and aorta

Question 14

Why is double circulatory system a good adaptation and why would a single system not work

Answer 14

it allows a high pressure to be maintained

Large surface area of lung capillaries would decrease pressure so less oxygenated blood will be delivered to tissues

Question 15

Structure of artery

Answer 15

Thick muscular layer so constriction and dilation can control blood volume

Thick elastic layer to allow to stretch and recoil

Thick wall to withstand high pressures

Question 16

Structure of arterioles

Answer 16

thick muscular layer to restrict blood flow into capillaries

thinner elastic wall to arteries

Question 17

Structure of veins

Answer 17

thin muscular layer

thin elastic layer due to lower pressure

valves to prevent backflow at lower pressure

Question 18

Capillary structure

Answer 18

1 cell thick wall for short diffusion pathway

no muscle or elastic layer

form capillary beds which have narrow diameter

Question 19

Formation and return of tissue fluid

Answer 19

• Blood enters capillaries from arterioles resulting in a high hydrostatic pressure at arteriole end
• molecules like glucose, amino acids, fatty acids, ions, water and oxygen are forced out to form tissue fluid
• larger molecules such as proteins will remain in capillaries, which lower water potential at venule end
• at venule end, low hydrostatic pressure and water potential means that water re - enters by osmosis ( NOT ALL OF IT )
• REMAINING TISSUE FLUID ABSORBED INTO LYMPHATIC SYSTEM

Question 20

How is water moved through the plant

Answer 20

Water absorbed via root hair cells by osmosis

water reaches xylem and travels against gravity in continuous columns

transpiration occurs so water vapour evaporates through stomata

Question 21

Describe the cohesion tension theory

Answer 21

Water is dipolar so hydrogen bonds form between molecules (cohesion)

results in a continuous water column created in the xylem

water evaporates out of stomata, so the column is pulled up the xylem (transpiration pull)

Tension on the xylem is created, causing its diameter to decrease

Question 22

Adaptations of the xylem to form a column

Answer 22

Made of dead cells so are hollow

have no end walls so a column can form

Question 23

Function of the phloem

Answer 23

transport of organic substance by translocation by mass flow

Question 24

Structure of the phloem

Answer 24

sieve tube element

sieve tube plates

companion cells

Question 25

Steps of mass flow hypothesis

Answer 25

• organic molecules such as sucrose are made via photosynthesis at the SOURCE and transported to companion cells by facilitated diffusion
• sucrose is actively transported into sieve tube element by co transport with H+ ions
• this decreases water potential so water enters phloem from xylem by osmosis
• this causes an increase in hydrostatic pressure at the source
• as sugars are used in respiring cells, water potential is decreased so water exits by osmosis, decreasing hydrostatic pressure
• mass flow occurs as water moves down the created hydrostatic pressure gradient to the SINK

Question 26

What is the ringing experiment

Answer 26

ring of bark and phloem are removed from tree trunk

trunk swells above the removed ring and the liquid was found to contain sugars

This shows that the phloem transports the sugars as they are not transported when phloem is removed

Question 27

What is the tracing experiment

Answer 27

plants were supplied with radioactively labelled CO2

this is absorbed during photosynthesis and the sugars produced were therefore labelled

samples of the plant were cut out and viewed through an x ray which detects radioactive material

this highlighted the location of the sugars and therefore showed us where the phloem is located