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3.3 Organisms exchange substances with their environment - Coggle Diagram
3.3 Organisms exchange substances with their environment
3.1 Surface area to volume ratio
Brush up on maths skills! Be able to work out sa : vol
See 'gel block' doc for practical application
3.2 Gas Exchange
RP 5 - See document for details
SINGLE CELLED ORGANISMS
No specialised gas exchange structures needed, as their surface area to volume ratio is large.
PROBLEMS - Organisms with a large surface area to volume ratio are prone to dessication (drying out).
Eg. Unicellular algae, e. coli, S. cerevisiae - unicellular fungus
(baker’s / brewer’s yeast), plasmodium
NO specialised gas exchange surfaces.
Still achieve high rate of diffusion because of a...
High sa : vol ratio -> more space to enter / leave
Small diffusion -> substance has less space to travel
Cell surface membrane is thin, reduces diffusion distance
Steep conc gradient (see FICKS LAW)
INSECTS
The tracheal system of an insect contains -
tracheae
tracheoles
spiracles
The gas exchange surface is the tracheole, not the spiracle!
This is the surface in direct contact with the insect’s cells.
How do they achieve ->
Large surface area
Many branching tracheoles
(Lactic acid is a solute which lowers water potential of the cytoplasm.) So....
Lactic acid is used to draw water out of the ends of the tracheoles, exposing more surface for gas exchange
Short diffusion distance
Tracheole do not have
chitin
so walls are permeable
Direct contact between tracheoles and the cells
^^ Tracheole wall is very thin.
Steep concentration gradient
Very fast metabolic rate (once oxygen comes in it is used up)
Abdominal pumping (in bigger insects)
Abdominal pumping ->
Inspiration
(air in) - abdomen expands, decreasing pressure and drawing the air inward.
Expiration
(air out) - abdomen contracts, increasing pressure and squeezing air out.
See 'gas exchange in insects' handout! :)
HUMANS
See folder for diagrams!
Intercostal Muscles
Intercostal muscles are in
antagonistic
pairs.
Muscles can only exert a force when they contract.
When muscles contract, they get shorter.
When one muscle contracts and shortens, the other relaxes and lengthens.
INSPIRATION -> full description
Muscles -
The
external
intercostal muscles
contract
, pulling the ribcage up and out.
The diaphragm
muscle contracts,
causing it to
flatten
.
Volume -
The
volume
in the thoracic cavity
increases
.
Pressure -
The
pressure
in the thoracic cavity
decreases
.
Air movement -
Air moves
into
the thoracic cavity (because thoracic pressure is less than external / environmental pressure)
EXPIRATION -> full description
Muscles-
The
external
intercostal
muscles
relax
, so the ribcage moves down and in.- The diaphragm
muscle relaxes,
returning
it to a
domed shape.
Volume -
The
volume
in the thoracic cavity
decreases
.
Pressure -
The
pressure
in the thoracic cavity
increases
.
Air movement -
Air moves
out
of the thoracic cavity (because thoracic pressure is greater than external / environmental pressure)
The only time we speak about the internal intercostal muscles contracting is to pull the ribcage down and in during times of forced expiration.
Eg. during exercise when breathing rate needs to be faster than normal
Make sure to use words in
BOLD
PVR = tidal volume * breathing rate
Alveoli
Lined with
epithelial cells
- very thin, thinner than their own nucleus!. Specifically
SQUAMOUS
epithelial.
A specific adaptation for the alveoli
Epithelium is avascular. Cells obtain nutrients from vessels within connective tissue.
Epithelial cells form the covering of all body surfaces, line body cavities and hollow organs, and are the major tissue in glands.
Elastic connective tissue
- aids recoil during expiration.
Surfactant -
maintains fluidity of alveoli since as the walls of the alveoli touch they have a tendency to get stuck together.
By preventing walls from being stuck together.
Aids inspiration
Produced by epithelial cells.
90-95% of the alveolar surface is covered by capillaries. Maintains
blood flow
past alveoli.
See table in folder for details on structure & how they link to
FICKS LAW
LUNG DISEASE
and its impact on gas exchange
Eg. Emphysema results in alveoli losing their elasticity and becoming ruptured.
You do NOT need to know
specific
lung diseases. But know HOW they affect gas exchange.
OR Eg. Chronic Obstructive Pulmonary Disease results in narrowed bronchioles and ruptured alveoli.
FOR EXAMS, you must know how this (eg. ruptured alveoli) impacts gas exchange.
FOR EXAMPLE -
(Rate of exchange decreases) because....
Reduced elasticity, alevoli are less able to stretch and
recoil
so they conc. graident is less steep.
Narrowed bronchioles - smaller vol of air passes through so conc. gradient is less steep.
Ruptured alveoli - reduced surface area.
Less
diffusion
of gases.
LINK TO FICKS LAW!
SMOKING -
In addition scientists have gathered experimental evidence to show a causal link between smoking and lung disease.
Between smoking and lung disease there is a clear correlation.
Therefore, we can say smoking causes cancer
Smoking causes cancer in multiple ways. The main way is by damaging the DNA in our cells.
DNA controls how our cells grow and behave. Damage to DNA causes cells to behave in ways that they’re not supposed to. And the build-up of DNA damage over time can lead to cancer.
See 3.2 lung disease in drive for notes on data, correlation vs causation & smoking.
IMPORTANT!! - FICKS LAW -
Large surface area
Short diffusion distance
(Maintaisn) steep conc. gradient
DICTOTYLEDONOUS PLANTS
LEAF GAS EXCHANGE - Gas exchange takes place within the leaf.
The gas exchange surface is the plasma membrane of the mesophyll tissue.
All plant cells carry out respiration, however the mesophyll cells also carry out photosynthesis (only in daytime.)
Large surface area -
Large SA of mesophyll, because of
air spaces
which enable contact between cell surface & gases.
Short diffusion distance -
Leaf is very thin (physically makes short distance)
Air spaces
enable direct gas to surface contact (doesn't need to cross other cells to get there after entering in stomata)
Cells are always in close proximity to a stomata so gas entering doesn't travel far to get to exchange surface.
Steep concentration gradient -
The rate of the metabolic reactions. (Mesophyll) cells are always producing oxygen to exchange with carbon dioxide.
ie. speed of photosynthesis varies, respiration is more constant.
Dicotyledonous plants have a pair of leaves in the embryo.
Eg. oak trees, daisies, sunflowers, roses, maple
During daylight hours :
Photosynthesis -
carbon dioxide + water (light) -> glucose + oxygen (<- out)
All the time :
Aerobic respiration -
glucose + oxygen -> carbon dioxide (<- out) + water
LIMITING WATER LOSS -
The features that makes a good gas-exchange system are the same features that increase water loss.
How do plants prevent this?
A waxy cuticle to reduce evaporation on the upper surface
Guard cells becomes flaccid and close the stomata when water loss occurs too much (they lose their shape with keeps the stomata open)
XEROPHYTES -
Plants that are adapted to living in very dry habitats eg. marram grass and cacti
MARRAM GRASS
Reduced surface area
Curled leaf
- reduces the amount of exchange surface in contact with the air around it.
Increased diffusion distance
ThickER waxy cuticle
- Increases the diffusion distances so reduces the rate of evaporation.
Reduced water potential gradient
Curled leavers
- Reduces the water potential gradient (by trapping humid air) and reduces surface area.
Unicellular hairs
- trap humid air to reduce the water potential gradient
Sunken stomata
– reduce the water potential gradient as water is trapped around pores
CACTI
Reduced surface area
Leaves reduced to spines
Small surface area to vol ratio
Increased diffusion distance
ThickER cuticle
Reduced water potential gradient
Sunken stomata
Hairs / spines
3.3 Digestion & Absorption
See Qs in google drive for Carb (chemical) test stuff.
See folder for carb info and enzyme chem digestion info.
See folder for human digestion info.
Triglyceride
! Ester bond is broken (hydrolysed) during digestion.
LIPID DIGESTION - Lipase
- Hydrolyses the triglyceride into...
TWO fatty acids
& A monoglyceride
Produced in ->
Pancreas
NOT SPEC mouth and stomach, but on a smaller scale (can ignore for A level)
BILE ->
Aids the digestion of fat globules by lipase.
Lipid globules are
Emulsified
by bile salts into smaller droplets. (one big globule becomes many smaller ones)
This increases the surface area for chem digestion of lipids by lipase. (It has more SA to reach since broken up)
Stored in the galbladder, made in the liver. Released into the duodenum (first part of the small intestine)
Lipid biochem test ->
Mix sample with ethanol & shake.
Decant mixture into distilled water.
If milky white emulsion appears then lipids present.
PROTEIN DIGESTION
See 3.1.4 for details on protein structure and chemical tests for proteins. Plus additional details on amino acids.
Proteases / peptidases -
Digests proteins (polypeptides) to (ultimately) amino acids.
Endo
peptidases hydrolyse
internal
peptide bonds within the polypeptide to break the chain into shorter peptides.
Exo
peptidases hydrolyse the
penultimate / terminal
peptide bonds, forming dipeptides or single amino acids.
Di
peptidases diest
dipeptides
by hydrolysing the bond between pairs of amino acids to release induvidual amino acids.
Stomach produces ENDOpeptidase
Pancreas produces EXO and ENDO
Small intestine produces ENDO, EXO and DI (all three)
3.4 Mass Transport
IN ANIMALS
HEART & CIRCULATION
Double circulatory system ->
When the blood passes through the heart twice during each circuit around the body. The 'pulmonary' circuit and the 'systemic' circuit.
ADVANTAGES
?
Low pressure
and speed of blood to the lungs allows time for gas exchange.
But, back to heart to then pump it to a
high pressure t
o enable blood to travel longer distances quickly eg. to extermeties.
Vein
-> blood
into
heart.
Veins will occasionally have valves to prevent blood from flowing backwards. Mostly in the bottom (below the heart) of the body since above the heart gravity will prevent this.
Artery
-> blood
away
from the heart.
ARTERIOLES -
Arterioles have proportionally the greatest quantity of muscle.
This is to regulate how much blood is able to pass to tissues via
vasoconstriction
(vessel narrowing) and
vasodilation
(vessel widening), enabling blood to be diverted towards or away from specific organs when necessary.
ARTERY & VEIN STRUCTURE
-
Lining layer -
endothelium (smooth to reduce friction resulting from blood flow)
Only thing present in capillaries.
Elastic layer -
stretches
(to accommodate the volume of blood) &
recoils** (to push the blood along, therefore maintaining blood pressure and speed)
Muscle layer -
withstands high pressure. Also
contracts
and
relaxes
to alter the rate of blood flow, particularly in arterioles.
Tough outer layer -
to withstand pressure of blood (resulting from ventricular systole.)
See handout for details on capillary structure and tissue fluid formation.
HAEMOGLOBIN
Please see haemoglobin handout for details & photos.
Quaternary structure
4 Polypeptide chains (2 alpha and 2 beta in humans)
Conjugated protein
Each polypeptide chain is associated with a non-protein (haem) group.
One haemoglobin molecule can carry 4 molecules of oxygen
One per haem group.
Sigmoid shape
as a result of cooperative binding.
Each molecule of oxygen that attaches makes it easier to attach the next molecule.
Oxyhaemoglobin dissociation curve
These two things are both due to the cooperative binding nature.
In
high pO2,
oxygen
associates
(loads) more readily than we might expect.
As blood approaches the
lungs
, a small increase in pO2 causes a large increase in affinity.
More rapid uptake of oxygen.
In
low pO2
oxygen
dissasocates
(unloads) more readily than we might expect.
At
respiring tissues,
a small decrease in partial pressure results in a large decrease in affinity.
More rapid release of oxygen
Curve shift to the left ->
At each pO2 the % saturation is
higher
Haemoglobin has a
higher
affinity for oxygen
More
oxygen binds to haemoglobin
Curve shift to the right ->
At each pO2 the percentage saturation is lower.
The haemoglobin has a lower affinity for oxygen
More oxygen dissociates / is unloaded to the tissues.
More aerobic respiration / energy release.
Effect of carbon dioxide -
Bohr shift
Same effect is true of an increase in temperature (results from increased respitory rate)
Dissolved carbon dioxide is acidic.
As the partial pressure of carbon dioxide increases, the percentage saturation of haemoglobin decreases
Haemoglobin’s affinity for oxygen decreases
More oxygen dissociates / is unloaded
This effect occurs as respiratory rates increase, enabling oxygen supply to the cells to increase
IN PLANTS
XYLEM
Transports
water and mineral ions
up the plant via transpiration.
Made up of...
Xylem vessels
-> long hollow tubes with no end walls, forms a continuous column for water transport.
Lignin strengthens the wall, provides structural support.
Pits
-> non-lignified regions, allows lateral movement of water between adjacent xylem vessels.
Lignification patterns -> Arranged in spiral to provide flexibility.
No cytoplasm / organelles -> Avoids obstructing water flow
COHESION-TENSION THEORY
- Model explaining how water is pulled up the xylem due to cohesion between water molecules and tension created by
transpiration
.
See folder for details on this process.
Energy from the sun causes...
Water to evaporate from the cells into the air spaces of the leaf
This causes the water potential to lower in these cells.
This causes water to enter the cells from neighbouring cells via osmosis.
This creates
tension
(negative pressure) at the top of the xylem.
(6.) Transpiration puts the xylem under
tension
due to the adhesion of water molecules to the walls of the xylem vessels.
Adhesion stops the column of water from falling.
Water is pulled up the xylem in a continuous column, known as the transpiration stream.
This is maintained by
cohesion
(hydrogen bonds) between water molecules.
PHLOEM
Transports sucrose and amino acids up and down the plant via
translocation
TRANSLOCATION -
See HW doc in drive for more details.
Translocation is the transport of organic substances, such as sucrose and amino acids, from source to sink, through phloem tissue.
Source -
Cell producing assimilates, eg. mesophyll cell.
Sink
- Cell using assimilates, eg. cell in meristem of short / root
SUMMER -
Most movement of sucrose is from the leaves to the roots.
For respiration and conversion to starch for storage.
Some sucrose will be moving from the leaves to growing tip of plant / flower / fruit.
For respiration.
WINTER / SPRING -
Most movement of sucrose is from roots up the plant to branches / growing leaves / flowers.
For respiration
MASS FLOW HYPOTHESIS - See diagram in folder for more info
Sucrose is actively transported into the sieve tube element via the companion cells.
The sucrose lowers the water potential in the sieve tube element, so water enters by osmosis.
A high hydrostatic pressure in the sieve tube element pushes sucrose towards the sink.
At the sink, sucrose is transported out (varies how) of the sieve tube element.
The water potential in the sieve tube element increases, which causes water to diffuse out by osmosis (into xylem). The loss of water lowers the hydrostatic pressure, which maintains the pressure gradient through the sieve tube element.
COMPANION CELLS -
Contains (most of) the organelles for the tissue to be alive.
SIEVE TUBES -
Place in which the transport takes place. Contains a few organelles.
MASS FLOW HYPOTHESIS -
Explains how organic compounds (sugars like sucrose) move through a plant's phloem.
It says that sugars are passively transported down a hydrostatic pressure gradient created by osmotic water movement between a "source" and a "sink".
Ringing Experiments -
A ring of bark and phloem is removed from stem (sieve tube seals themselves to limit loss of sap.)
It proves that sugars are transported downwards exclusively through the phloem.
The accumulation of sucrose above the ring causes swelling,
While the area below the ring dies due to a lack of sugars.
Tracing Experiments (Radioactivity) -
When exposed to radioactive CO2 it produces radioactively labelled sucrose.
X-ray imaging shows that the radioactive sucrose moves through the phloem following a source to sink pattern.
Only the phloem vessels show up as radioactive.
Aphids (Greenfly) -
When aphids piece the phloem, the sap continues to flow out even after the aphid is removed.
Showing that translocation occurs under pressure. Supporting that movement is due to hydrostatic pressure gradients in the phloem.
Respiratory Inhibitors -
Respiratory inhibitors stops respiration from occurring, ATP release therefore stops.
Translocation also stops, therefore proving it must require ATP and is an active process.
Mass flow then makes sure of active transport.
