Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

(a) The need for specialised exchange surfaces
To include surface area to volume ratio, metabolic activity, single-celled and
multicellular organisms
Organisms need to absorb certain substances, (e
...
oxygen, glucose, proteins, fats, water and
minerals) from the surrounding environment and remove waste products (carbon dioxide,
oxygen and other wastes)
...

Multicellular organisms not only need more supplies as they have more cells, but they also
have a smaller surface-area-to-volume ratio, meaning that the outer surface is not large
enough to enable gases and nutrients to enter the body fast enough to keep all of the cells
alive
...

So, larger organisms need a large area to exchange more substances, so often they combine
this with a transport system to move substances around the body
...
This can only occur through its surface area
...
Unfortunately, its surface
area does not increase as quickly as its volume, so the larger an organism gets, the more
difficult it becomes to absorb enough substances over its surface
...
6:1

Surface area: length x width x number of sides
Volume: length x width x height
Small organism – high SA:V
Sphere
Surface area: 4 pie r(squared)
Volume: 4/3(pie)r(cubed)
Radius
2
4
6
8

Surface Area (mm2)
2xpiex2(squared) = 50
...
062
4xpiex6(squared)=452
...
248

Volume (mm3)
4/3xpiex2(cubed) = 33
...
083

SA:V
1
...
75:1

4/3xpiex6(cubed)=904
...
5:1
4/3xpiex8(cubed)=2144
...
375:1

We can see that as size increases:




Surface area increases
Volume increases, but more quickly than surface area
Surface area to volume ratio decreases

The SA:V ratio is the surface area of an organism divided by its volume
...

The significance of surface area to volume ratio
Single-celled organisms are small and have a large surface area to volume ratio
...

Multicellular organisms have a smaller SA:V
...
The surface area is no longer large enough to
supply all the needs of the larger volume
...
Being multicellular and
metabolically active also increases the need for a specialised exchange surface
...

(b) The features of an efficient exchange surface
To include: increased surface area (root hair cells), thin layer (alveoli), good blood
supply/ventilation to maintain gradient (gills/alveolus)
All good exchange surfaces have certain features in common:
Feature
Large surface area

Thin layer

Steep concentration gradient

Reason
To provide for molecules of
oxygen and carbon dioxide to
pass
To provide a short diffusion
pathway
To ensure molecules diffuse
rapidly in the correct
direction

In the lungs
Lung epithelium folded to
form numerous alveoli
Lung epithelium and
capillary endothelium are
made from squamous cells
Good supply of blood on one
side and ventilation of the air
sacs on the other side

A steep concentration gradient is maintained by increasing the concentration of molecules on
the supply side and reducing the concentration on the demand side
...
Blood flow brings carbon dioxide
to the lungs and removes oxygen; ventilation brings oxygen to the lung surface and removes

carbon dioxide
...

A concentration gradient is the difference in the concentration between two points
...
In alveolus
this helps to expel air
To produce and release
mucus
Contracts to constrict or
narrow the airways
To provide a thin barrier to
exchange – a short
diffusion pathway
To provide a thin barrier to
exchange – a short
diffusion pathway

The gaseous exchange system in mammals consists of the lungs and associated airways that
carry air into and out of the lungs
...
Finally, it reaches tiny air-filled sacs called
alveoli
...

The lungs are protected by the ribcage
...

The action of these muscles and the diaphragm helps to produce breathing movements
(ventilation)
...
Oxygen passes from the air in
the alveoli to the blood in the capillaries
...
The lungs must maintain a steep concentration gradient in each direction in order
to ensure that diffusion can continue
...
However, they’re so numerous that the total surface area of the lung is
much larger than that of our skin
...
The lungs must produce a surfactant that coats the
internal surface of the alveoli to reduce the cohesive forces between the water molecules, as
these forces tend to make the alveoli collapse
...
The cells and their plasma membranes readily allow the diffusion of oxygen and
carbon dioxide, as the molecules are small and non-polar
...





The blood system transports carbon dioxide from the tissues to the lungs
...
Therefore, carbon dioxide diffuses into the alveoli
...
This ensures that the
concentration of oxygen in the blood is kept lower than that in the alveoli – so that
oxygen diffuses into the blood

Describe the features off the mammalian lung that adapt it to efficient gaseous exchange:


Many, many alveoli meaning that the total surface area is about 70m2
...
It refreshes the air in the alveoli
...
The processes that take
place during inspiration and expiration are summarised below:
Structure/feature
Diaphragm

Intercostal muscles
Pressure in chest cavity

Pressure change

Air movement
Diaphragm muscle
Rib cage
Volume of thorax

Inspiration (inhaling)
Contracts and moves
downwards, pushing organs
down
Contract to raise the rib cage
up and outwards
Chest cavity increases in
volume
...
It
resumes to dome shape
...
Increases above
atmospheric pressure
Pressure inside chest cavity
rises about atmospheric
pressure
Air is pushed out of lungs by
higher pressure in alveoli
Relaxes
Moves down and in
decreases

The breathing movements ventilate the lungs
...
Ventilation ensures that:


The concentration of oxygen in the air of the alveolus remains higher than that in the
blood



The concentration of carbon dioxide in the alveoli remains lower than that in the
blood

(e) The relationship between vital capacity, tidal volume, breathing rate and oxygen
uptake
To include analysis and interpretation of primary and secondary data e
...
from a data
logger or spirometer
Tidal volume - The volume of air moved in and out of the lungs during breathing when at
rest
Vital capacity - The largest volume of air that can be moved into and out of the lungs in any
one breath
A spirometer consists of a chamber filled with oxygen floating on a tank of water
...
Breathing in
takes oxygen from the chamber so it sinks down, and breathing out pushing air back into the
chamber which floats up
...

Vital capacity - Asking a person to breathe in and out as much as they can
Tidal volume - Asking a person to breathe normally
Breathing rate - Asking a person to breathe normally, and then dividing the number of
breathes by the time in minutes to calculate the number of breaths per minute
Oxygen uptake - Divide (the amount of oxygen (dm3) times 60) by the time taken in
seconds
...

Insects – spiracles, trachea, thoracic and abdominal movement to change body
volume, exchange with tracheal fluid
...
They use gills to absorb oxygen
dissolved in the water and release carbon dioxide into the water
...
The filaments are very thin
and their surface is folded into many gill lamellae (gill plates)
...
Blood capillaries carry deoxygenated blood close to the surface of the secondary
lamellae where exchange takes place
...
Ventilation is achieved by movements of the floor of the
mouth (buccal cavity) and operculum (the bony flap over the gills)
...
They have an air-filled tracheal system that supplies
air directly to all the respiring tissues
...
The air
passes through the body in a series of tubes called tracheae
...
The ends of the tracheoles open into tracheal fluid
...

Larger insects can also ventilate their tracheal system by movements of the body
...
This is often coordinated with opening and closing the spiracles, inhaling
at the front end and exhaling at the rear end
...

Level of activity- If an animal is very active then it will need a good supply of nutrients and
oxygen to supply the energy for movement
...
Their volume increases as the body
gets thicker, but the surface area does not increase as much
...
Larger animals do not have a large enough surface
area to supply all of the oxygen and nutrients that they need
...
Diffusion will supply enough oxygen and
nutrient to keep the cell alive
...
The diffusion distance becomes too long and diffusion alone
will be too slow to supply all the requirements
...


Single and double circulatory systems
Fish have a single circulatory system
...
The blood takes the following route:
Heart  gills  body heart
Mammals have a double circulatory system
...
One circuit
carries blood to the lungs to pick up oxygen
...
The other circuit
carries the oxygen and nutrients around the body to the tissues
...

Blood flows through the heart twice for each circuit of the body
...
The blood is at high
pressure, so the artery wall must be thick in order to
withstand that pressure
...

The walls consist of 3 layers:





Inner layer (tunica intima) consists of a thin layer of
elastic tissue which allows the wall to stretch and
then recoil to help maintain blood pressure
Middle layer (tunica media) consists of a thick layer of
smooth muscle
Outer layer (tunica adventitia) is a relatively thick
layer of collagen and elastic tissue
...

Arteriole walls contain a layer of smooth muscle
...
This increases resistance to flow and reduced the rate of flow of
blood
...

Capillaries
Capillaries have very thin walls
...






The lumen is very narrow – its diameter is about the same as that of a red blood cell
...
It also increases resistance and reduces rate of flow
...
This reduces the
diffusion distance for the materials being exchanged
...
They allow blood plasma and dissolved substances to leave the
blood
...
These collect the blood
from the capillary bed and lead into the veins
...


Veins
Veins carry blood back to the heart
...






The lumen is relatively large, in order to ease the flow of blood
The walls have thinner layers of collagen, smooth muscle and elastic tissue than in
artery walls
...
As the walls are thin, the
vein can be flattened by the action of the surrounding skeletal muscle
...


(d) The formation of tissue fluid from plasma
To include reference to hydrostatic pressure, oncotic pressure and an explanation of
the differences in the composition of blood, tissue fluid and lymph
...
It consists of:






Water – based plasma containing dissolved substances – oxygen, nutrients such as
glucose and amino acids, lipoproteins, carbon dioxide (most transported as
bicarbonate ions), other wastes such as urea, hormones, antibodies and plasma
proteins
Erythrocytes (red blood cells), probably carrying oxygen
Phagocytes (white blood cells), such as neutrophils and lymphocytes
Platelets

Tissue fluid
Tissue fluid surrounds the body cells
...
These are too large to pass out of the blood vessels
...

Hydrostatic pressure if the pressure a fluid exerts on the sides of a vessel
Oncotic pressure is the osmotic pressure created by dissolved substances such as proteins
The walls of the capillaries are a single layer of endothelium cells
...
The fluid is acted upon
by 2 factors forces:




The hydrostatic pressure gradient between the blood and the tissue fluid, which
tends to push fluid out of the capillary
The oncotic pressure gradient between the blood and tissue fluid, which tends to
move fluid into the flood because the water potential of the blood is lower than water
potential of the tissue fluid

Remember that tissue fluid is blood that does not contain blood cells or plasma proteins, but
it does contain the dissolved components
...
Therefore, there is a steep pressure gradient pushing fluid out of the capillary
...
This overcomes
the oncotic pressure gradient and fluid moves out of the capillary to become tissue fluid
...

At the venous end of the capillary, the hydrostatic pressure is lower
...

Carbon dioxide and other wastes are carried back into the blood as tissue fluid moves back
into the capillary
...

Lymph
Lymph is excess tissue fluid that is not returned to the blood vessel
...
These carry the fluid back to the circulatory system by a different route
...
Lymphocytes produced to the lymph nodes may also be
present
...
The SAN initiates a wave of
excitation at regular intervals
...
As it
passes, it causes the muscle cells to contract
...
The excitation is delayed here to allow for the atria to finish contracting and
for the blood to flow into the ventricles
...
At the base of the septum, the wave of
excitation spreads out over the walls of the ventricles
...

(h) The use and interpretation of electrocardiogram (ECG) traces
To include normal and abnormal heart activity e
...
tachycardia, bradycardia, fibrillation and
ectopic heartbeat
...

Transports of oxygen
Oxygen enters the blood in the lungs
...
Here, they associate with the haemoglobin to form oxyhaemoglobin
...
Each subunit contains a haem group that
contains a single iron ion (FE2+)
...
The harm group is said
to have an affinity for (an attraction to) oxygen – the haemoglobin attracts and holds the oxygen
...


Oxygen dissociation curves
Haemoglobin has a high affinity for oxygen
...

At a low pO2, haemoglobin does not readily take up oxygen molecules
...
This difficulty is combining the first oxygen molecule accounts for the low saturation level
of haemoglobin at low pO2
...
This
causes a conformational change in the shape of the haemoglobin molecule, which allows more
oxygen molecules to associate with the other three haem groups more easily
...
In the body tissues, cells need oxygen for aerobic respiration, so
oxyhaemoglobin releases the oxygen
...

Dissociation is the release of oxygen from oxyhaemoglobin
...

Oxyhaemoglobin is the product that is formed when oxygen from the lungs combines with
haemoglobin in the blood
...
Carbon dioxide in the blood is transported in 3 ways:




As hydrocarbonate ions (HCO3-) in the plasma (85%)
...
Its
haemoglobin must be able to take up oxygen from an environment that makes the adult haemoglobin release
oxygen
...
This reduces the oxygen tension near the
blood, making the maternal haemoglobin release oxygen
...

Fetal haemoglobin is a modified form of haemoglobin found in the mammalian fetus
...
However, in very active tissues a lot of carbon
dioxide is release and, therefore, a lot of hydrogen ions are created
...
The change in pH alters the structure of the haemoglobin,
reducing its affinity for oxygen
...
The haemoglobin dissociation curve shifts
to the right (the Bohr Effect)
...

The Bohr Effect is the shift to the right of the position of the haemoglobin dissociation curve in the presence of
extra carbon dioxide
...

Transpiration is the loss of water vapour from the upper parts of a plant, mainly the leaves
...
Transpiration involves three stages:
1) Water moves by osmosis from the xylem to the mesophyll cells in the leaf

2) Water evaporates from the surfaces of the spongy mesophyll cells into the air spaces inside
the leaves
3) Water vapour diffuses out of the lead via the stomata
The stomata open during the day to allow gaseous exchange – carbon dioxide enters the leaf
and oxygen is released
...
As the stomata are open,
water vapour is lost
...

Factors that affect the rate of transpiration
There must be a water potential gradient between the air spaces in the leaf and the surrounding
air to make water vapour leave the leaf
...
Factors that increase transpiration rate include:





Higher temperatures – this increases evaporation so there will be a higher water potential
inside the lead
More wind – this blows water vapour away from the leaf, reducing the water potential in the
surrounding air
Lower relative humidity – this increases the water potential gradient between the air inside
the leaf and outside
Higher light intensity – this causes the stomata to open wider

(ii) Practical investigations to estimate transpiration rates
To include the use of a photometer
Transpiration can be estimated using a bubble photometer
...
Care must be taken when setting up the photometer to ensure that there are no leaks and no
air in the system, except the bubble used for measuring
...
Transpiration rate is calculated by dividing the distance moved by a set time
...
Cut healthy shoot underwater to stop air entering xylem
2
...
Ensure apparatus is full of water and that there is only the desired air bubble
4
...
Remove potometer form water and ensure it is airtight around the shoot
6
...
Keep conditions constant to allow shoot to acclimatise
8
...
Keep scale fixed and record position of air bubble
10
...


(d) The transport of water into the plant, through the plant and to the air surrounding the
leaves
To include details of the pathways taken by water AND the mechanisms of movement, in terms of
water potential, adhesion, cohesion and the transpiration stream
Water uptake and movement across the root
The outermost layer of cells (the epidermis) of a root contains root hair cells
...
These cells absorb mineral ions
and water from the soil
...
Water may also travel through the apoplast
pathway as far as the endodermis, but must then enter the symplast pathway as the apoplast
pathway is blocked by the casparian strip
...
The cell-surface membrane is selectively
permeable
...
The more concentrated the mineral ions, the lower the water potential
...
Similarly, water can
enter a cell from its environment if the water potential in the cell is lower than the water potential in
the environment
...


Pathways
Once in the plant, water can move across a tissue such as the root cortex by different pathways
...

Water often passes through plasmodesmata linking the cytoplasm of adjacent cells
3) The vacuolar pathway carries water through the cytoplasm and vacuole of each cell
...
The transpiration stream is
the flow of water from the roots to the leaves to replace the water lost in transpiration
The transpiration stream
Water movement from the roots up to the leaves in the xylem is known as the transpiration stream
...
Root pressure and capillary action combined can only raise water by a few
meters
...
Movement of water up through the xylem is by mass flow – a flow of water and mineral
ions in the same direction
...
Pressure in the root medulla builds up and forces water into the
xylem, pushing the water up the xylem
...

Transpiration pull
The loss of water by evaporation from the leaves must be replaced by water coming up from the
xylem
...
These cohesion forces are
strong enough to hold the molecules together in a long chain or column
...
The pull from above creates tension

in the column of water
...
The lignin
prevents the vessel from collapsing under tension
...
It relies on the plant maintaining an unbroken
column of water all the way up the xylem
...

Capillary action
The same forces that hold water molecules together also attract the water molecules to the walls of
the xylem vessel
...
Because the xylem vessels are very narrow, these forces of
attraction can pull the water up the sides of the vessel
...

Adhesion is the attraction between water molecules and the walls of the xylem
...

Cohesion is the attraction between water molecules caused by hydrogen bonds
...
The following adaptations help them
to reduce loss of water vapour:






Thick, waxy cuticle on the leaves
Smaller leaf area
Automata in pits
Hairy leaves
Rolled leaves

Hydrophytes
Hydrophytes are plants that are adapted to living in water, such as water lilies
...
The
following adaptations help them to do this:
1) Leaves and leaf stems have large air spaces (to help them float so that they are in the air and
can absorb sunlight)
2) The stomata may be on the upper epidermis (to gain carbon dioxide from the air and to
allow gaseous exchange)

3) The leaf stem has many large air spaces (this helps with buoyancy, but also allows oxygen to
diffuse quickly to the roots for aerobic respiration)

Marram grass
Marram grass specialises in living on sand dunes
...
Marram grass is a xerophyte – adapted to living in arid
conditions
...

These adaptations help to reduce air movement and therefore loss of water vapour
The spongy mesophyll is very dense, with few air spaces – so there is less surface area for
evaporation of water

Cacti
Cacti show other features to overcome arid conditions:





Cacti are succulents – they store water in their stems which become fleshy and swollen
...

The leaves are reduced to spines
...
When the total
leaf surface area is reduced, less water is lost by transpiration
...
This is achieved by maintaining
a high salt concentration in the cells
...
g
...
g
...
Sugar is made in the
leaves, so they are the source, and transported to the roots, so they are the sink
...




---