Transport in Plants

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How do plants get what they need?
Like all organisms, plants have to get materials for growth
from their environment. Plants must then get these
nutrients to the part of the plant that needs them.
What do plants need for
healthy growth?
 minerals
 carbon dioxide for
photosynthesis
 water
 oxygen for respiration
 sunlight
Where do plants get these nutrients?

Moving materials
How do plants transport materials to where they are needed?

How are plants adapted for transport?
The structures of cells and tissue in different parts of the
plant are adapted to allow transportation of essential
materials.
Leaves are entry and exit
points for the gases
needed by plants.
Roots absorb water and
minerals from the soil.
Stems connect the roots to
the leaves, flowers and fruits.
They contain cells specially
adapted for transportation of
water, minerals and sugars.

What are the functions of plant parts?

Which cells transport nutrients?
The cells are arranged in plants as vascular bundles.
Plants contain two types of cell adapted for transportation.
Phloem cells transport sugars
produced in the leaves up
and down the stem to growing
and storage tissues.
Xylem cells transport water
and minerals up the stem from
the roots to the shoots and
leaves. This transport occurs
in one direction only.
Both phloem and xylem form continuous systems
connecting roots, stems and leaves.

Inside a plant stem

What are vascular bundles?

How is xylem adapted for transportation?
Xylem vessels have thick cellulose
cell walls, strengthened by lignin.
The inside of the cell is hollow.
Xylem vessels are dead cells.
The thick walls of xylem cells also
help support plants.
Water and minerals travel in xylem
vessels.
Xylem vessels transport water and
minerals from the roots to the shoot
and leaves. This transport only
occurs in one direction.

Sugars are carried from the
leaves to the growing and
storage parts of the plants.
This movement takes place in
both directions.
How is phloem adapted to transportation?
Phloem is made of columns of
living cells. They transport food,
in the form of sugars.
Phloem cells are also called
sieve tubes. Cells are joined by
small holes in the cell wall at the
end of each cell, forming a
continuous system. The end cell
walls are called sieve plates.

Cells in the vascular bundles

Do plants produce waste?
All animals eat food to survive.
Does this mean they do not produce
any waste?
Not all of the food can be used by
the body, so eventually some will
exit the body as waste.
Oxygen is made during photosynthesis
but not all of it is used by the plant. It is
a waste product.
Plants are different from animals
because they produce their own food
through the process of photosynthesis.
How is it removed from the plant?

How do gases move in and out of plants?
When the concentration of
carbon dioxide inside the
plant is low, it will diffuse in
from the air, through pores in
the leaves into the plant cells.
Plants use carbon dioxide during photosynthesis and
produce oxygen. These gases move in and out of the plant
through the leaves by diffusion.
If the concentration of
oxygen is high inside the
plant, it will diffuse from the
plant cells through the pores
and into the air.

How are leaves adapted for diffusion?
The diffusion of gases occurs in the leaves. They are
adapted for this function in the following ways:
 Leaves are thin. This decreases the distance gases have
to travel between the air and cells.
 There are air spaces
between cells. This
increases the speed of
diffusion from the air to
the cells inside the leaf.
 There are lots of
stomata (pores) on the
undersides of leaves.
These let gases in and out.

What are stomata?
On the underside of leaves are small holes, or pores, called
stomata. A single hole is called a stoma.
Each stoma is surrounded by two guard cells, which control
the opening and closing of the stoma.
When carbon dioxide levels are low inside
the plant, the guard cells gain water and
become turgid. They curve out, opening the
stoma and allowing gases in and out. Water
also evaporates through stomata.
High carbon dioxide levels cause the guard
cells to lose water, closing the stoma.
What would happen if the stomata
were permanently open?

Opening and closing of stoma

Diffusion of gases

How do tall trees get enough water?
Redwoods are the tallest
species of tree in the world.
How does a plant this size
get water from its roots to
the branches at the top?
What experiment could show
that water travels up stems?
The tallest redwood ever
measured was 120 metres tall.
That is six times the height of
the Angel of the North!
The water will travel up the
stem, or trunk, of the tree.

Movement of water up a stem

What is transpiration?
Although it may seem bad for plants, transpiration actually
moves water from the roots to the top of the plant, without
using energy. How does this work?
Water always moves from an area of
high concentration to an area of low
concentration. This movement of water
is a type of diffusion called osmosis.
Transpiration is the loss of water by evaporation from plants.
Plants lose water when they open the
stomata in the leaves to let in carbon dioxide.
Air around the plant usually contains
less water than the cells of the plant,
so water evaporates into the air.

Transpiration

 humidity (amount of moisture in the
air)
Is the rate of transpiration constant?
The speed at which a plant loses water is
called the rate of transpiration. This varies
depending on the plant’s environment.
Transpiration is a bit like a straw, pulling water
up the plant. Sometimes the pulling force will
be stronger and the plant will lose more water.
What environmental factors will
affect the rate of transpiration?
 light intensity
 temperature
 air movement (wind).

Why does transpiration vary?

How is the rate of transpiration measured?
Transpiration can be measured using a potometer.
A cut plant stem is sealed into the
potometer using a rubber bung.
This gives an indirect measurement of the rate of
transpiration.
An air bubble is introduced
to the capillary tube.
The distance the bubble
travels shows how much
water the stem has taken up.

Transpiration – true or false?

How are roots adapted to their function?
Roots contain thousands of tiny
root hair cells, which project out
into the soil.
The roots of this hyacinth bulb are long
and thin. They have formed a fine
network, filling the available space.
How do these features make roots
suitable for absorbing water and
minerals?
 high surface area to volume ratio
 maximum contact with the soil
 firm anchorage.

How do minerals enter plants?
Like water, minerals enter plants through the roots.
However, they do this by different methods.
Water passively diffuses with a
concentration gradient from the
soil into the roots and up the stem.
Diffusion cannot take place
against a concentration gradient.
Minerals are usually found in the
soil in lower concentrations than
they occur in the plant.
Why can they not be
transported by diffusion?
Instead, minerals enter the roots by active transport.

Active transport uses energy from respiration to move
substances against a concentration gradient.
What is active transport?
Specific minerals from
the soil enter through
channels in the cell walls
of the root hair cells.
The minerals then travel
around the plant in the
xylem vessels.
soil
mineral
root hair cell
Plants may take up some
minerals in the soil but not
others. Why is it important
that plants select which
minerals to transport?

Active transport

Transporting minerals – activity

Glossary (1/2)
active transport – The movement of a substance from
an area of low concentration to high concentration.
concentration gradient – A change in the
concentration of a substance from one area to another.
cellulose – The main component of cell walls.
diffusion – The movement of a substance from an area
of high concentration to low concentration.
guard cells – A pair of cells that control the opening and
closing of a stoma (single hole).
humidity – The amount of water vapour in the air.
lignin – A substance found in some xylem cells, which
strengthens the cell wall.
osmosis – The movement of water from an area of high
concentration to low concentration.

Glossary (1/2)
phloem – Plant tissue that transports food.
potometer – A piece of equipment that can be used to
indirectly measure the rate of transpiration.
root hair cell – A thin, hair-like outgrowth on roots.
transpiration – The evaporation and diffusion of water
from leaves into the air.
sieve tube – A series of joined phloem cells.
stoma (singular) – A single hole on the lower surface of
the leaf that allows gases in and out.
stomata (plural) – Small holes in the lower surface of a
leaf that allow gases in and out.
vascular bundle – A grouping of transport tissues.
xylem – Plant tissue that transports water and minerals.

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Transport in Plants

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