Biology - MASS TRANSPORT

Describe the simple structure of haemoglobin

globular protein made from 4 polypeptides - 2 alpha and 2 beta subunits. Each subunit has a haem group containing an iron ion and space for 1 molecule of oxygen to bind.

Why can haemoglobin be described as having a quaternary structure?

It is made from more than 1 polypeptide

What is formed when haemoglobin and oxygen associate?

oxyhaemoglobin

What is the name for oxyhaemoglobin releasing its oxygen to respiring cells?

dissociation

What is partial pressure a measure of?

the concentration of gas in a mixture

Where in the body would have the largest pO2 ?

lungs

As pH decreases, what happens to the oxygen affinity of haemoglobin ?

it decreases

How does increased respiration affect blood pH ?

lowers blood pH due to lactic acid and CO2 forming carbonic acid

Explain how saturation of haemoglobin affects its affinity for oxygen

Increased saturation increases the affinity of haemoglobin for oxygen (positive cooperativity)

With reference to protein structure, explain how lowering blood pH levels affects haemoglobin

lowering blood pH levels can affect tertiary and quaternary structure of haemoglobin reducing its affinity for oxygen

What is the net result of the Bohr effect?

more oxygen is unloaded at tissues that are respiring rapidly

What is the main difference between foetal and adult haemoglobin?

foetal haemoglobin has a higher affinity for oxygen

explain why it is an advantage for foetal haemoglobin to have a higher affinity than adult haemoglobin

it can take oxygen from the mother’s blood supply in the placenta

Give 3 examples of environments with low oxygen concentrations

high altitude

under mud/sand

under still water

Explain why it is an advantage to have haemoglobin with a higher affinity for oxygen if you live in high altitude

pO2 is lower at high altitude as total air pressure is lower

Explain why it is an advantage to have haemoglobin with a lower affinity for oxygen if you are a mammal with a larger SA:V

Organisms with a large SA:V often have high metabolic rates and need to use oxygen at a faster rate. Having haemoglobin with a lower affinity for oxygen makes it better at delivering oxygen to the tissues.

What is mass transport?

efficient movement of substances to and from exchange surfaces over large distances

Why does oxygen loading increase after the first haem group binds to an oxygen molecule?

the rest of the haem groups change shape and increase affinity for binding with oxygen

What is the shape of the oxygen dissociation curve and why is it shaped this way?

s shaped. Steep part occurs where there is rapid loading/dissociating of oxygen from haemoglobin. As partial pressure of oxygen changes in different parts of the body, oxygen will load/dissociate

How is the heart supplied with blood?

via coronary arteries

Which 2 veins enter the heart and where from?

pulmonary vein (receiving oxygenated blood from lungs) and vena cava (receiving deoxygenated blood from body)

Which 2 arteries leave heart and where do they take blood?

pulmonary artery (taking deoxygenated blood to lungs) and aorta (sending oxygenated blood to body)

Which blood vessels supply and remove blood from kidneys ?

renal artery and vein

Name the 4 chambers of the heart

L Ventricle

L Atrium

R Ventricle

R Atrium

How does blood pressure compare between the pulmonary system and the systemic (body) system?

pulmonary system has lower pressure than systemic system

How does structure of arteries and veins compare?

arteries have thicker walls, more elastic tissue and smoother muscle tissue than veins

veins have a larger lumen and contain valves

What is the purpose of valves in the heart?

prevent backflow of blood

How is tissue fluid formed?

at capillaries, fluid passes from the capillaries into the spaces around cells, bathing them in nutrients

What is the role of xylem?

transports water from the roots to the stem and leaves in 1 direction only

How do xylem and phloem compare?

xylem transport water in 1 direction; phloem transport sugars in all directions

xylem often dead tissue; phloem living tissue and has companion cells

What is translocation in plants?

transport of sugars and other substances from sources (eg leaf cells) to sinks (cells that use/store substances)

What apparatus would you use to measure transpiration rates?

potometer

How to calculate cardiac output

CO = SV x HR

What is cardiac output?

Volume of blood pumped from the left ventricle of the heart in 1 minute

What is stroke volume?

the volume of blood pumped by the left ventricle in 1 heartbeat

Why do mammals have a double circulatory system ?

blood pressure reduces through lungs ; if it passed immediately to the body circulation would be very slow ; therefore blood returns to heart first to boost pressure before its circulated to the rest of the tissues

Why does the R ventricle have a thinner muscular wall than the L ventricle?

it only pumps blood to the lungs whereas the L ventricle pumps blood to the body

Where are the atrioventricular valves located?

between the atrium and ventricle

Blockage of which arteries leads to myocardial infarction

coronary

What is diastole?

relaxation of the heart

What happens during diastole?

blood returns to atria through pulmonary vein and vena cava. As atria fill pressure rises. When pressure in atria exceeds pressure in ventricles, AV valves open. Muscular walls of atria and ventricle are relaxed.Pressure lower in ventricle than in aorta/pulmonary artery so semi lunar valves close (dub sound)

What is atrial systole?

contraction of the atria

What happens during atrial systole?

contraction of atria walls forces remaining blood from atria into ventricles

What is ventricular systole?

contraction of the ventricles

What happens during ventricular systole?

ventricle walls contract simulltaneously after filling with blood. This increases blood pressure in them , forcing AV valves shut (lub sound). Once pressure in exceeds that in aorta and pulmonary artery, blood forced from ventricles into these vessels.

What is tissue fluid?

watery liquid containing glucose, AAs, fatty acids, ions in solution and oxygen. Tissue fluid supplies these substances to the tissues and in return getsCO2 and other waste material from tissues.

Outline movement of water up xylem (cohesion tension theory)

• water evaporates from mesophyll cells

• water molecules form H bonds between one another and tend to stick together (cohesion)

• water forms continuous unbroken column down xylem

• as water evaporates more water molecules drawn up behind it as a result of cohesion

• column of water pulled up xylem (transpiration pull)

Evidence to support cohesion-tension theory

• change in diameter of tree trunks according to rate of transpiration

• if a xylem vessel is broken and air enters it the tree can no longer draw up water

• when a xylem vessel is broken water does not leak out (as it would if it was underpressure) but draws air in (as it is under tension)

What are the 3 phases of the mass flow theory (translocation)

1. transfer of sucrose into sieve elements from photosynthesising tissue

2. mass flow of sucrose through sieve tube elements

3. transfer of sucrose from sieve tube elements into sink cells

What happens in stage 1 of the mass flow theory

• sucrose made from products of photosynthesis in cells with chloroplasts

• sucrose diffuses down conc gradient by facilitated diffusion from photosynthesising cells into companion cells

• H+ ions actively transported from companion cells into spaces within cell walls using ATP

• H+ ions diffuse down conc gradient through carrier proteins into sieve tube elements

• sucrose molecules co transported with H +.

What happens in stage 2 of mass flow theory

• sucrose produced by photosynthesising cells (source) is actively transported into sieve tubes as per step 1.

• this causes sieve tubes to have a lower (more negative) WP

• as xylem has much higher WP ,water moves from xylem into sieve tubes by osmosis, creating high hydrostatic pressure in them

• at respiring cells (sink) , sucrose either used up during respiration or converted to starch for storage

• these cells have low sucrose content and so sucrose actively transported into them from sieve tubes, lowering their WP

• due to lowered WP, water also moves from sieve tubes into respiring cells by osmosis

• hydrostatic pressure of sieve tubes in this region therefore lowered

• due to water entering sieve tubes at source and leaving at sink, there is high hydrostatic pressure at source and low one at sink

• theres therefore a mass flow of sucrose solution down this hydrostatic gradient in the sieve tubes

What happens in step 3 of the mass flow theory

• sucrose actively transported by companion cells out of sieve tubes into sink cells

Experiments showing that phloem transports organic substances and xylem transports water

tree ringing

tracer experiments