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FIND OUT MORE. Flowering Plants 92–93 • Non-Flowering Plants 90–91 • Trees 94–95

Nature^89

Stiff prongs stop

the damselfly

from escaping

WHY DO PLANTS HAVE ROOTS?

Plants have roots for two main reasons. Roots

anchor the plant in the soil, and prevent it being

blown away by strong winds. They also take up water

and minerals, such as nitrogen and sulphur, from

the soil. Plants need water to replace that lost by

. TRANSPIRATION, and minerals to make substances

essential for life.

HOW DO PLANTS DEFEND THEMSELVES?

Plants cannot escape from hungry plant-eaters, but

they have evolved a wide range of defences. Some

have thorns or spines that cut into an animal’s skin,

and will pierce its mouth if eaten. Others produce

chemicals that taste terrible and may be very

poisonous. Some have tiny hairs on their leaves that

stop leaf-eating insects reaching the leaf’s surface.

WHAT IS THE VASCULAR SYSTEM?

Water and nutrients are moved through a plant by its

vascular system. This consists of two types of

microscopic tubes – xylem and phloem. Xylem carries

water and minerals from the roots to the rest of the

plant. Phloem carries nutrients, such as glucose, from

where they are made to other parts of the plant.

1 STOMA IN DAYLIGHT

During the day, the guard cells

open the stoma. This lets carbon

dioxide enter the leaf and water

vapour escape during

transpiration.

1 STOMA AT NIGHT

Seen in microscopic view, this

stoma (pore) in the leaf’s surface

is surrounded by two guard cells.

At night, these guard cells close

the stoma.

Water is

drawn up

xylem vessels

in the stem

1 TRANSPIRATION STREAM

Water lost from leaves by

transpiration is replaced by water

from the roots. An unbroken

column of water flows from the

roots up to the leaves.

1 ROOT HAIRS
Magnified 200 times here, root hairs are tiny projections from a plant’s
root. They provide a massive surface area through which the root can
quickly and efficiently absorb essential water and minerals.

4 VENUS FLYTRAP

The carnivorous Venus flytrap,

which grows in very poor soils, takes

essential minerals from insects. The

ends of the plant’s leaves form a trap

of two pads. If an insect lands on the

pads, the trap snaps shut. The plant digests

the insect and absorbs its minerals.

Roots

absorb

water from

the soil

Damselfly lands on

pad and touches

sensory hair

Inside of pad

has sensory hairs that

trigger trap to close

when moved

1 CHLOROPLASTS

The green structures seen in

this microscopic view of leaf cells

are chloroplasts. They contain

chlorophyll, a green pigment

that traps sunlight energy.

Water enters

via the stem

from the

roots

Oxygen

escapes

into the air

Glucose is

carried

away

Carbon

dioxide

enters

from

the air

PINEAPPLE SAGE

Water

escapes from

the leaves

WHAT HAPPENS IN PHOTOSYNTHESIS?

The leaves of plants trap sunlight energy, which

changes carbon dioxide gas and water into an

energy-rich food called glucose. Glucose provides

the plant with energy, and is also used to make

substances such as cellulose, which builds the

plant’s cell walls.

PHOTOSYNTHESIS

Animals have to find and eat food, but

plants are able to make their own by using

sunlight energy. This process, called

photosynthesis, provides plants with the

energy and raw materials for growth.

TRANSPIRATION

Leaves constantly lose water by evaporation

through tiny pores, or stomata, that also let

carbon dioxide into, and oxygen out of, the

leaf. This water loss, called transpiration,

creates a force that helps draw up more

water from the roots.

Leaf absorbs

sunlight

MAKING GLUCOSE 3

Leaf cells absorb sunlight

energy during photosynthesis.

They use it to turn carbon dioxide

from the air, and water, absorbed

by the roots, into glucose

molecules. Oxygen is released

as a waste product.

Leaf stalk

carries water

into the

leaf

plants