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3.3 Nutrition and Transport
Plant Nutrition and Transport
3.3 Nutrition and Transport
Nutrition in the Flowering Plant
• Plants are autotrophic – they make their own food.
• Plants need to be able to transport water, carbon
dioxide, oxygen and certain minerals around their
body as they need them for metabolism, growth and
reproduction
3.3 Nutrition and Transport
Water
Uptake of water
1. Water moves into the root
hair cells from the soil by
osmosis
2.The water then diffuses from
cell to cell across the ground
tissue
When it reaches the vascular
tissue and goes into the
xylem cells.
Xylem vessels – a continuous
pipeline through the plant
3.3 Nutrition and Transport
3.3 Nutrition and Transport
Water
Transport of Water
1.root pressure –
the water entering the root
cells by osmosis pushes the
water up the xylem – a
pushing force
3.3 Nutrition and Transport
2. Water evaporates from the cells in the leaf and they
become less turgid.
This creates an osmotic gradient that causes water to
move from the xylem cells out to these leaf cells – a pulling
force
3.3 Nutrition and Transport
3.3 Nutrition and Transport
Control of transpiration
The loss of water from the leaves is
reduced by:
a waxy cuticle on the leaf
and
the closing of the stomata at night
3.3 Nutrition and Transport
H 3.3.7
Cohesion – Tension Model of Xylem Transport
3.3 Nutrition and Transport
A confusing problem…
How water can travel up from the
soil to the leaves of a tree,
which could be up to 136 m tall,
AGAINST THE FORCE OF
GRAVITY?
An explanation of this mechanism
was first proposed by Two Irish
Scientists from Trinity College
in 1895.
- Henry Dixon and John Joly
Dixon and Joly’s
Cohesion – Tension Model
3.3 Nutrition and Transport
The cohesion – tension model explains how water can be transported
in plants to extreme heights against the force of gravity
3.3 Nutrition and Transport
1. Transpiration causes water tension
Transpiration causes water to move from the xylem cells out to
leaf cells.
•Water molecules stick together
(cohesion) and stick to the sides
of the thin xylem tubes
(adhesion).
•As each water molecule is
pulled out of the xylem the next
water molecule is pulled with it.
The water in the xylem is put in a
state of tension.
3.3 Nutrition and Transport
3.3 Nutrition and Transport
3.3 Nutrition and Transport
3.3 Nutrition and Transport
3.3 Nutrition and Transport
3.3 Nutrition and Transport
3.3 Nutrition and Transport
3.3 Nutrition and Transport
2. Cohesive forces hold water molecules in
a column
The water is under great tension BUT the cohesion between the
water molecules is strong enough to hold the water molecules
in a column without breaking.
3.3 Nutrition and Transport
3. The transpiration stream
The continuous water tension in the
xylem pulls molecules upwards from
the roots to replace the water
molecules that have been lost at the
leaves from transpiration.
The flow of water upwards through
the plant is called the transpiration
stream.
3.3 Nutrition and Transport
Minerals
Uptake
they are dissolved in the water
that comes into the plant at
the roots.
Transport
by the xylem cells
3.3 Nutrition and Transport
Carbon dioxide
Uptake
directly from the respiring cells
inside the plant
or
enter the leaves through open
stomata.
3.3 Nutrition and Transport
Oxygen
Uptake
Oxygen can be obtained from
photosynthetic cells
or
enter the leaves through open stomata
or
Can enter the bark through lenticels
3.3 Nutrition and Transport
Photosynthetic products
The glucose product of photosynthesis is :
stored as starch in the leaves
or
Transported from the leaves to
other plant cells through
phloem sieve tubes
3.3 Nutrition and Transport
Modified Plant Storage Organs
• Plants can store the food that they make in
organs
• Modified Plant Storage Organs include roots,
stems and leaves
3.3 Nutrition and Transport
3.3 Nutrition and Transport
Root modification
The first root grows straight down to form the main
root of the plant. It may then become fleshy and
modified to store food. example: carrot
3.3 Nutrition and Transport
Stem modification
stems become modified to store food.
known as “tubers” e.g. Potatoes
3.3 Nutrition and Transport
Leaf modification
In some plants leaves are modified to store
food e.g. onion
3.3 Nutrition and Transport