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Transport
Transport in plants
XYLEM AND PHOLEM
Plants have tissues to transport water, nutrients and minerals
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TISSUE
Xylem
Phloem

WHATS MOVED
Water and minerals
Sucrose and amino acids

PROCESS
Transpiration system
Translocation

Xylem; Mature xylem consists of elongated dead cells, arranged end to end to form continuous vessels (tubes)
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Unlike xylem, phloem vessels contain cytoplasm, and
this goes through holes from one cell to the next
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This is called translocation
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This means, for example, that sucrose is transported:
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from sources in the root to sinks in the leaves in spring time
from sources in the leaves to sinks in the root in the summer

Applied chemicals, such as pesticides, also move through the plant by translocation
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The position of these bundles varies in
different parts of the plant
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Root; Xylem vessels are tough and strong, so the vascular bundles are in the centre of the root to resist forces that
could pull the plant out of the ground
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The vascular bundles are arranged near the edge of the stem, with the phloem on the outside and the xylem
on the inside
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Water moves through the xylem vessels in a continuous transpiration stream:
root → stem → leaf
Transpiration produces a tension or ‘pull’ on the water in the
xylem vessels by the leaves
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Transpiration produces a tension or ‘pull’ on the water in the
xylem vessels by the leaves
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The transpiration stream has several functions
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They are long and thin so they can penetrate between soil
particles, and they have a large surface area for absorption of water
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This happens because the soil water has a higher water potential than the root hair
cell cytoplasm

RATE OF TRANSPIRATION
If the rate of transpiration increases, the rate of absorption of water by the root increases too
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If water is scarce, or the roots are damaged, a plant
may wilt
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LEAF ADAPTATIONS
The leaves in hot or dry environments may be adapted to reduce transpiration
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This is the reverse of what usually happens, and it means that the stomata are
closed when the rate of transpiration would be greatest
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It contains:
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plasma
red blood cells

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white blood cells
platelets

Plasma is a straw-colored liquid that makes up just over half the volume of blood
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They must be able to absorb oxygen in the lungs, pass
through narrow blood vessels, and release oxygen to respiring cells
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The cells themselves are
thin, so there is only a short distance for the oxygen to diffuse to reach the centre of the cell
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THE NEED FOR TRANSPORT SYSTEMS
A simple, unicellular organism (consisting of one cell) can rely on diffusion to move substances into and out of the
cell
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However, the surface area of a multicellular organism, such as a plant or animal, is small compared to its volume
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Common features of exchange surfaces:
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thin - for a short diffusion distance
large area - achieved by being long and thin, flat, or folded
moist - so that substances can be dissolved for diffusion to happen
Common features of transport systems:
tubes or ‘vessels’ that carry materials from one part of the organism to another
close contact with cells, such as those of exchange surfaces

The circulatory system in humans has a pump, the heart
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LYMPHOCYTES
About 25 per cent of the white blood cells are lymphocytes
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Antibodies
Antibodies attach to antigens
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Different antibodies attach to different antigens
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Antibodies can neutralise toxins produced by pathogens
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They are part of the body’s immune system, but they do
not produce antibodies
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This is what happens:
1
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enzymes are secreted into the vacuole to
destroy the bacterial cell

The process of ingesting the pathogen is called phagocytosis
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Different vaccines are needed for different
pathogens
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Vaccination involves putting a small amount of an inactive form of a pathogen into the body
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When injected into the body, they stimulate lymphocytes to produce antibodies that can
recognise the pathogen
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If the vaccinated person later becomes
infected with the same pathogen, the immune system is prepared, and the required lymphocytes are able to
reproduce rapidly and destroy it
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Compared to the primary immune response, this secondary immune response:
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happens sooner after infection
produces antibodies faster and in greater quantities

The Circulatory System
GENERAL STUCTURE
The circulatory system consists of:
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a system of tubes (arteries, capillaries and veins)
a pump (the heart)
valves to ensure a one-way flow of blood

ARTERIES AND VEINS
Arteries carry blood away from the heart towards an organ,
while veins carry blood from an organ towards the heart
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ORGAN
Lung
Liver
Kidney

TOWARDS ORGAN
Pulmonary artery
Hepatic artery
Renal artery

AWAY FROM ORGAN
Pulmonary vein
Hepatic vein
Renal vein

DOUBLE CIRCULATION
The human circulatory system is a double circulatory system
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The blood is oxygenated there and then
carried back to the heart
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Systemic Circuit; The systemic circuit transports blood around the body
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BLOOD VESSELS
Arteries;

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Carry blood away from the heart (always oxygenated apart from the pulmonary artery which goes from the
heart to the lungs)
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Have small passageways for blood (internal lumen)
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Have thin walls
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Contain blood under low pressure
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Capillaries;
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Found in the muscles and lungs
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Very low blood pressure
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THE HEART
The heart is a muscular organ
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The right side pumps blood through the pulmonary
circuit, while the left side pumps blood through the systemic circuit
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The left side has thicker walls because it needs to put the blood under
higher pressure than the right side
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The heart contains valves to prevent the blood flowing backwards:
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the right side has a tricuspid valve (a valve with three flaps)
the left side has a bicuspid valve (a valve with two flaps)
Both sides have semi-lunar valves (at the entrances to the pulmonary artery and aorta)
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They therefore need to respire more and, as a
consequence, need more oxygen and glucose, and they produce more waste carbon dioxide
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The hormone adrenaline is secreted when we are afraid, stressed or angry
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