Transport in Animals: Right Atrium Left Atrium Pump Blood

Transport In Animals
1.Humanheart:
consistsof4chambers:rightatrium,rightventricle,leftatriumandleftventricle.
pumpbloodtoallpartsofthebody.
madeupofcardiacmuscle.
Front/venrtral view of heart
2. Superior vena cava

--> carries deoxygenated blood
--> from the head + arms
--> into right atrium.
3. Inferior vena cava
--> from the lower body + legs
--> into right atrium
4. Right atrium
--> receives deoxygenated blood
--> from vena cava
--> to right ventricle.
5. Tricuspid (antrioventricular) valves
--> prevent blood (from right ventricle) flowing backwards
--> to the right atrium.
6. Right ventricle
--> pumps blood
--> to lungs
--> via pulmonary arteries.
7. Semilunar valves
--> prevent blood (from pulmonary arteries)
--> from flowing backwards
--> into right ventricle.
Cross-section of heart
8. Pulmonary artery branches

--> from right ventricle
--> to lungs.
9. Pulmonary vein
--> carrying oxygenated blood
--> from lungs
--> to left atrium.
10. Left atrium
--> receives oxygenated blood
--> from lungs
--> to left ventricle.
11. Bicuspid (atrioventicular) valves
-- > prevent blood (from left ventricle) flow backwards to left atrium
12. Left ventricle
--> pumps oxygenated blood
--> to body tissue (via aorta).
13. Semilunar/aortic valves
--> prevent blood (from aorta) flowing backwards (into left ventricle).
14. Aorta
--> carries oxygenated blood
--> from left ventricle
--> to the rest of the body.
15. Septum separates the right and left side of the heart.
Mammals:
Plants:
Specialised tubes - arteries, capillaries and veins.
Specialised tubes xylem vessels and

tracheids and
phloem sieve
tubes.
All tubes are composed of living cells.
Some tubes are

composed of
living cells, e.g.
phloem. Others
are composed of
dead cells, e.g.
xylem.
The concentration of substances transported is controlled

(see homeostasis).
The concentration
of the substances
being transported
is not controlled.
The heart controls the circulatory system. The heart is
There is no such
controlled by the nervous system.
control in plants.
The rate of flow is moderate and is regulated by

vasoconstriction and vasodilation.
The rate of flow in

the xylem and
phloem is quite
slow. The rate of
flow in the xylem
is controlled by
external factors
via the stomata
(e.g. temperature,
wind, humidity).
Uses water as a medium in which to transport substances (it

is a good solvent, it has a high specific heat capacity, has good
surface tension but is not viscous, and is unreactive).
Uses water as a
medium in which
to transport
substances.
The substances being transported are: respiratory gases,

glucose, amino acids, fatty acids, glycerol, vitamins, minerals,
hormones.
Substances being
transported are:
sucrose, amino
acids, fatty acids,
glycerol, vitamins,
hormones (in the
phloem) and
minerals and
water (in the
xylem).
Respiratory gases
are not
transported by
this system but
move via a series
of interconnecting air
spaces.
Two main types of plant tissue are used in transport - xylem and
phloem. Xylem transports water and minerals. Phloem transports organic
molecules such as the products of photosynthesis.
Xylem
There are four types of xylem cells:
Xylem vessels: Consist of dead hollow cells because the walls are lignified
and the cell contents disintegrate. The lignin makes the cell wall impermeable so
they are in effect waterproof. It also makes the vessels extremely strong and
prevents them from collapsing. They have a wide lumen and are linked end to end to
create a long, hollow tube since the end cell walls have one or many perforations in
them. This allows the transport of large volumes of water. The sidewalls have
bordered pits (unlignified areas) to allow lateral movement of water. Xylem vessels
are found in angiosperms.
Tracheids: Similar to vessels but with narrower lumens and connected by

pits. They have tapered ends so that they dovetail together. Tracheids are found in
conifers.
Parenchyma: Living cells with thin cellulose walls. They can store water,
which makes them turgid and so gives them a supporting role.
Fibres: They provide strength because their walls are lignified (and therefore,
dead).
Movement in the root

Water enters through the root hair cells and then moves across into the xylem
tissue in the centre of the root. Water moves in this direction because the soil water
has higher water potential, than the solution inside the root hair cells.
This is because the cell sap has organic and inorganic molecules dissolved in it. The
root hairs provide a large surface area over which water can be absorbed.
Minerals are also absorbed but, as you should be able to work out, their absorption
requires energy in the form of ATP because they are absorbed by active transport.
They have to be pumped against the concentration gradient.
Water taken up by the root hairs moves across the cortex of the root either via the
cytoplasm of the cells in between the root hair cell and the xylem (the symplast
pathway) or through the cell walls of these cells (the apoplast pathway). The root
hair cell will have higher water potential than the cell next to it. As always, water
moves by osmosis to where the water potential is lower. In this way, as water is
always being absorbed by the root hairs, water will always move towards the centre
of the root.
When the water reaches a part of the root called the endodermis, it encounters a
thick, waxy band of suberin in the cell walls. This is the Casparian strip and it
is impenetrable. In order to cross the endodermis, the water that has been moving
through the cell walls must now move into the cytoplasm.
Once it has moved across the endodermis, it continues down the water potential
gradient until it reaches a pit in the xylem vessel. It enters the vessel and then moves
up towards the leaves.
Movement in the xylem

Water evaporates from the mesophyll cells into air spaces in the leaf. If the air
surrounding the leaf has less water vapour than the air in the intercellular spaces,
water vapour will leave the leaf through stomata.
This process is called transpiration and will continue as long as the stomata are
open and the air outside is not too humid. On dry, windy days when water vapour is
continually diffusing out and being removed, transpiration will increase in rate.
Although this loss of water can cool the plant, it is essential that the plant does not
lose too much water. Therefore water must be continuously supplied to the leaves.
The xylem ensures that this happens. Xerophytes are plants which are well adapted
to living where conditions are very dry. They may have rolled up leaves - for example,
Marram grass which exposes the waterproof cuticle on the outside and means the
stomata open into an inner humid space. Other Xerophytes store water in their
stems and reduce the surface area of their leaves, which become spines - for
example, Cactus.
Water is removed from the top of xylem vessels into the mesophyll cells down the
water potential gradient. This removal of water from the xylem reduces
the hydrostatic pressureexerted by the liquid so the pressure at the top is less than
at the bottom. This pushes the water up the tube. The surface tension of the water
molecules, the thin lumen of the xylem vessels and the attraction of the water
molecules for the xylem vessel wall (adhesion), helps to keep the water flowing all
the time and to keep the water column intact.
Pressure to push water up can also be increased from the bottom. By actively
pumping minerals from cells surrounding the xylem into the xylem itself, more water
is drawn into the xylem by osmosis.
This increase in water pressure, called root pressure, certainly helps in the process
but is less important than the simple movement of water down the water potential
gradient, ultimately from the soil at the bottom, to the air at the top. This is because
moving water this way does not require energy (it is passive).
Phloem
There are four types of phloem cells:
Sieve tube elements: These are living, tubular cells that are connected end
to end. The end cell walls have perforations in them to make sieve plates. The
cytoplasm is present but in small amounts and in a layer next to the cell wall. It lacks
a nucleus and most organelles so there is more space for solutes to move. The cell
walls are made of cellulose so solutes can move laterally a well as vertically. Next to
each sieve tube element is a companion cell.
Companion cell: Since the sieve tube element lacks organelles, the
companion cell with its nucleus, mitochondria, ribosomes, enzymes etc., controls the
movement of solutes and provides ATP for active transport in the sieve tube
element. Strands of cytoplasm called plasmodesmata connect the sieve tube
element and companion cell.
Parenchyma: Provides support through turgidity.
Fibres: Provides support for the sieve tube elements.
Movement in the phloem

This process is called translocation and involves the movement of organic
substances around the plant. It requires energy to create a pressure difference and
so is considered an active process.
Sucrose is loaded into the phloem at a source, usually a photosynthesizing leaf. For
this to occur, hydrogen ions are pumped out of the companion cell using ATP. This
creates a high concentration of hydrogen ions outside the companion cell. Sucrose is
loaded (moved into companion cells) by active transport, against the concentration
gradient.
However, the protein carrier involved in the loading, has two sites, one for sucrose
and one for a hydrogen ion. When it is used to pump sucrose into the companion
cell, hydrogen will move in the opposite direction, back down its concentration
gradient. This is why a high concentration of ions is needed outside the cell.
The sucrose can then diffuse down the concentration gradient into the sieve tube
element via the plasmodesmata that connects the companion cell with the sieve
tube element. This lowers the water potential of the sieve element so water enters
by osmosis.
At another point sucrose will be unloaded from the phloem into a sink (e.g. root). It
is likely that the sucrose moves out by diffusion and is then converted into another
substance to maintain a concentration gradient. Again, water will follow by osmosis.
This loading and unloading results in the mass flow of substances in the phloem.
There is evidence to support this theory; the rate of flow in the phloem is about
10,000 times faster than it would be if it was due only to diffusion, the pH of the
phloem sap is around 8 (it is alkaline due to loss of hydrogen ions), and there is an
electrical potential difference across the cell surface (negative inside due presumably
to the loss of positively charged ions).

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Transport In Animals

Front/venrtral view of heart

2. Superior vena cava

8. Pulmonary artery branches

Specialised tubes - arteries, capillaries and veins.

Specialised tubes xylem vessels and

All tubes are composed of living cells.

Some tubes are

The concentration of substances transported is controlled

The heart controls the circulatory system. The heart is

controlled by the nervous system.

The rate of flow is moderate and is regulated by

The rate of flow in

Uses water as a medium in which to transport substances (it

The substances being transported are: respiratory gases,

Tracheids: Similar to vessels but with narrower lumens and connected by

Movement in the root

Movement in the xylem

Parenchyma: Provides support through turgidity.

Fibres: Provides support for the sieve tube elements.

Movement in the phloem

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