3.3 organisms exchange substances with their environment

what is haemoglobin and structure

protein with a quaternary structure
made of 4 polypeptide chains
each contains a Haem group containing an iron ion

role of haemoglobin

associates with oxygen at gas exchange surfaces where the partial pressure of oxygen is high
forming oxyhemoglobin which transports oxygen
dissociates from oxygen near tissue where partial pressure of oxygen is low

what is meant by the partial pressure of oxygen

the pressure exerted by oxygen within a mixture of gases; a measure of oxygen concentration

areas of low partial pressure - respiring tissues

• haemoglobin has a low affinity for oxygen

• so oxygen readily dissociates with haemoglobin

• so % saturation is low

areas of high partial pressure - gas exchange surfaces

• haemoglobin has a high affinity for oxygen

• so oxygen readily associates with haemoglobin

• so % saturation is high

explain this dissociation curve

• the oxyhemoglobin curve shows how saturation of haemoglobin with oxygen changes as partial pressure of oxygen changes

• at areas of low partial pressure of oxygen such as respiring tissues the oxygen dissociates as there is a low affinity for oxygen

• at areas of high partial pressure of oxygen such as gas exchange surfaces the oxygen readily associates as there is a high affinity for oxygen

explain this sigmoid curve oxyhemoglobin dissociation curve

• binding of the first oxygen causes haemoglobin to change quaternary structure

• uncovering haem group binding sites

• making further binding of oxygen easier

  evidence

  • at low partial pressure of oxygen, as oxygen increases there is a slow increase in % saturation of haemoglobin with oxygen when first oxygen binds

  • at a higher partial pressure of oxygen as oxygen increases there is a rapid increase in % saturation of haemoglobin with oxygen showing it has got easier for oxygen to bind

BOHR EFFECT: oxygen dissociation curve for oxyhemoglobin shifts to the right

• increasing blood CO2 levels (e.g., due to increased rate of respiration)

• lowers blood ph (more acidic)

• reducing haemoglobin’s affinity for oxygen as quaternary structure changes

• faster dissociation of oxygen to respiring cells at a given partial pressure of oxygen

  evidence:

  • at a given partial pressure for oxygen the % saturation of haemoglobin is low

  advantage:

  • more oxygen for tissue for aerobic respiration > produce more ATP for muscle contraction

different haemoglobins for different organisms

• different transport properties

• made of different polypeptide chains with different amino acid sequences > different shapes > different affinities for oxygen

curves shift to the LEFT

• haemoglobin has a higher affinity for oxygen

• more oxygen associates with haemoglobin more readily

• at gas exchange surfaces where partial pressure of oxygen is lower

• example: organisms in low oxygen environments (high altitudes, underground, foetuses)

curve shifts to the RIGHT

• haemoglobin has a lower affinity for oxygen

• more oxygen dissociates from haemoglobin more readily

• at respiring tissues where more oxygen is needed

• example: with high rates of respiration/ metabolic rates (rats/birds)

loading tension

the oxygen tension at which 95% of the haemoglobin molecules are saturated

unloading tension

the oxygen tension at which 50% of the haemoglobin molecules are saturated

effect of carbon dioxide

CO2 can bind to haemoglobin and change the shape pf the molecule so it has a lower affinity for oxygen

CO2 also dissolves in water (alot of water in the blood plasma) to form carbonic acid

H+ ions change the shape of haemoglobin so it has a lower affinity for oxygen

in respiring tissue:

• more CO2 produced

• HB has lower affinity for oxygen

• more oxygen dissociation

in the lungs:

• less CO2 present

• HB has higher affinity for oxygen

• more oxygen binding

xylem

transports water and ions up through the stem to the leaves of the plant

how is xylem tissue adapted for its function

• cells joined with no end walls to form a long continuous tube

• cells contain no cytoplasm/ nucleus - easier for water to flow

• thick cell walls with lignin - provide support as withstands tension and prevents water loss

• pits in side walls - allow lateral water movements

cohesion-tension theory in the xylem

LEAF

• water lost from leaf by transpiration; water evaporates from mesophyll cells into air spaces and water vapour diffuses through open stomata

• reducing water potential of mesophyll cells

• so water drawn out of xylem down a water potential gradient

XYLEM

• creating tension in xylem

• hydrogen bonds result in cohesion between water molecules

• so water is pulled up as a continuous column

• water also adheres to walls of xylem

ROOT

• water lost enters the roots via osmosis

cohesion-tension theory

how water moves up the xylem against gravity via the transpiration stream

transpiration

loss of water vapour from plant leaves by evaporation through stomata

phloem tissue

transports organic substances e.g., sucrose in plants

sieve tube elements

• no nucleus/ few organelles - easier flow of organic substances

• end walls between cells perforated = sieve plate

companion cells

many mitochondria - high rate of respiration to make ATP for active transport of solutes

translocation

movement of solutes (assimilates) from sources to sinks (where used/ stored) by mass flow

translocation

1. at the source

   1. active transport loads solutes from companion cells to phloem sieve tubes - high conc

   2. lowering water potential in sieve tubes

   3. so water enter phloem by osmosis from xylem/ companion cells

   4. increasing hydrostatic pressure in sieve tubes near source

2. at the sink

   1. solutes removed to be used up or stored - low conc

   2. increasing water potential in sieve tubes

   3. so water leaves phloem by osmosis

   4. lowering hydrostatic pressure in sieve tubes near sink

3. mass flow

   1. pressure gradient from source to sink pushes solutes from source to sink

tracer experiments

1. leaf supplied with radioactive tracer (eg, CO2 containing radioactive isotope 14C

2. radioactive carbon incorporated into organic substances during photosynthesis

3. these move around plant by translocation

4. movement traced using autoradiography or a geiger counter

ringing experiment

1. remove all phloem (eg, remove a ring of bark)

2. bulge from on source side of ring

3. fluid from bulge has a higher conc. of sugars than below - shows sugar is transported in phloem

4. tissues below ring die as cannot get organic substances

how does light intensity affect transpiration rate

TRANSPIRATION INCREASE

• stomata open in light to let in CO2 for photosynthesis

• allowing more water to evaporate faster

• stomata close when its dark so there is a low transpiration rate

how does temperature affect transpiration rate

TRANSPIRATION INCREASES

• water molecules gain kinetic energy as temperature increase

• so water evaporated faster

how does wind intensity affect transpiration

TRANSPIRATION INCREASE

• wind blows away water molecules from around stomata

• decreasing water potential of air around stomata

• increasing water potential gradient so water evaporates faster

how does humidity affect transpiration

TRANSPIRATION DECREASES

• more water in air so it has a higher water potential

• decreasing water potential gradient from leaf to air

• water evaporates slower

POTOMETERS - investigating transpiration

arteries

carry blood away from the heart at high pressure
a narrower lumen than a vein
thick muscular wall
elastic tissue and a folded endothelium

veins

carries blood back to the heart at lower pressure
wide lumen, thin muscular wall, smooth endothelium
pocket valves that prevent the back flow of blood

capillaries

thin blood vessels that surround all cells for exchange of substances
the endothelium is one cell thick and they have a large surface area

renal artery and vein

blood vessels carrying blood to and from the kidneys

pulmonary artery

carries deoxygenated blood from the right ventricle of the heart to the lungs

pulmonary vein

carries oxygenated blood from the lungs to the left atrium of the heart

vena cava

vein that carries deoxygenated blood from the body to the right atrium of the heart

aorta

the largest artery in the body which carries oxygenated blood from the heart to the rest of the body

right atrium

contracts to push blood into the right ventricle

right ventricle

contracts to push deoxygenated blood into the pulmonary artery

left atrium

contracts to push blood into the left ventricle

left ventricle

has a much thicker muscular wall and contracts to push oxygenated blood to the rest of the body

tissue fluid formation

arteriole: hydrostatic pressure > water potential

venule: hydrostatic pressure < water potential

remaining fluid returns to circulation via the lymphatics system

pattern of circulation

oxygenated blood leaves the heart through the aorta (artery) to supply oxygen to the respiring tissue for respiration.

deoxygenated blood enters the heart through the vena cava, the blood leaves to the lungs via the pulmonary artery, picks up oxygen from the lungs, then enters the left side of the heart via the pulmonary vein, to be pumped out through the aorta

the renal artery takes blood to the kidneys, where it leaves by the renal vein

the coronary arteries take oxygenated blood to the heart cells

what are the two types of valves:

atrioventricular valves between the atria and the ventricles on either side

semi-lunar valves between the ventricle chamber and opening of the aorta

how is the direction of blood in one way maintained

• valves open in way oly

• whether they open or close depends upon the pressure that builds up in the heart chambers (atria and ventricles)

• if the pressure in the atrium is higher than the ventricles , the atrioventiruclar valve opens, then as the pressure decreases the valve closes again

• if the pressure in the ventricles increases too much (a pressure higher than the aorta), the semi-lunar vlave opens, then as the pressure decrease the valve closes again

systole def

contraction

diastole def

relaxation

1. cardiac diastole (both atria and ventricles are relaxed)

passive filling of blood (in through the vena cava) into the atria

the pressure behind the AV valves increases, so the AV valves open and blood enters the ventricles from the atria and the SL valves remain closed

2. atrial systole (atria contract and ventricles are relaxed)

the atria contract to push any remained blood into the ventricles, SL valves remain closed

3. ventricular systole (atria relax and the ventricles contract)

the ventricles contract after the pressure builds, increasing the pressure, closing the AV valves. Due to the pressure the SL valves open (so the blood flows through the arteries out the heart). Pressure in the ventricles decrease the SL valves close.

late diastole & atrial systole

AV valves = open

SL valves = closed

passive filling of the ventricles, then atrial systole

ventricular systole (isometric phase)

AV valves = closed (at the end of atrial systole)

all valves closed as the ventricle muscles contract without shortening, pressure builds up in the ventricles

ventricular systole (isotonic phase)

SL valves = open

blood is ejected into the aorta and pulmonary artery

muscles shorten as they contract

ventricular diastole (relaxation)

SL valves = close as the ventricles begin to relax

pressure falls in the ventricles and the AV valves = open

valve movementt during the cardiac cycle

what enzyme digests carbohydrates

amylases and membrane-bound disaccharidases

what enzyme digests lipids

lipase, and action of bile salts

what enzyme digests proteins

endopeptidases, exopeptidase and membrane-bound dipeptidases

mechanisms for the absorbtion of the products of digestion by cells lining the ileum of mammals include:

• co-transport of amino acids and monosaccharides

• micelles in the absorption of lipids

digestions of carbohydrates

• takes place in the mouth as well as the small intestine

• digestion in the mouth takes place with the help of salivary amylase at an alkaline pH of 7.5-8

digestions of lipids

• digestions of lipids takes place in duodenum of small intestine

• fats are broken down into small droplet to increase the surface area

• emulsification of fats: breaking down of fats into small droplets in presence of bile salts

5 steps of digesting lipids

1. lipids are emulsifies by the bile

2. lipase break down triglycerides into fatty acids and monoglyerides

3. fatty acids and monoglycerides are packaged into micelles that are absorbed by microvilli

4. fatty acids and monoglyceriedes are converted back into triglycerides, the triglycerides aggregate with cholesterol, proteins and phospholipids to form chylomicrons

5. the chylomicrons move into a lymph capillary, which transports them to the rest of the body

digestions of proteins

• takes place in the stomach and duodenum of small intestine

• when entering the stomach the food has an alkaline pH, which then turns acidic (when mixing with HCL and enzymes etc.)

• HCL maintains acidic pH of 1-2, optimum for pepsine action

digestions in the small intestine

• dipeptidases: hydrolyses the peptide bond between two amino acids, creating single amino acids

• endopeptidases: hydrolyse the peptide bond in the middle of the peptide chain

• exopeptidase: hydrolyse the peptide bond at the end of the peptide chain

  • advantage: expose more ends, for more surface area

how is the tracheal system adapted

• tracheoles have thin walls so short diffusion distance to cells

• high branched so short diffusion distance to cells, large surface area for exchange

• tracheae provide tubes full of air so fast diffusion

types of diffusion

• simple diffusion: from a high to low concentration gradient where small nonpolar lipid soluble molecules pass via the phospholipid bilayer

  • large polar water soluble molecules go through the proteins (carrier or channel)

• water modifies via osmosis from a high water potential to a low water potential

• facilitated diffusion: active transport is the movement from a high to a low concentration against the concentration gradient - involved carrier proteins

• active transport required energy in the form of ATP

• co transport can also occur with sodium and glucose