Download World of Plants

World of Plants
Making Food
G Davidson
Food Webs and Plants
• Animals get their food by eating other
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living things.
They either eat plants, or eat animals which
have eaten plants.
Plants have to make their own food.
When energy in the form of food passes
from a plant to an animal and then on to
another animal, it forms a food chain.
When we link up all the food chains in an
environment we form a food web, e.g.
Woodland web
HAWK
FOX
BLACKBIRDS
SQUIRREL
BLUETIT
RABBITS
INSECTS
BEETLES
WOODLICE
FRUITS & SEEDS
GRASS
TREE BARK
ROOTS
If some of the plants in this web were to disappear it would
have a major effect on other organisms.
Plants and Light
• Plants manufacture their own food in a
process called PHOTOSYNTHESIS.
• When a plant carries out photosynthesis it
combines simple substances to make more
complex substances like glucose and starch.
• Photosynthesis is carried out in the leaves of
a plant.
PHOTO
SYNTHESIS
(Light)
(To build)
Photosynthesis
Light energy
Carbon + Water
Dioxide
CO2
H2O
Raw Materials
Glucose + Oxygen
C6H12O6
Products
O2
Photosynthesis
Photosynthesis CANNOT work without:
• Carbon dioxide
• Water
• Chlorophyll
• sunlight
If any of the above are in short supply they
are said to be “Limiting Factors”.
Photosynthesis
We can check for evidence of photosynthesis by
testing a leaf for starch.
1. Boil the leaf in water (kills cells)
2. Boil the leaf in alcohol (removes chlorophyll)
3. Dip leaf in hot water (softens the leaf)
4. Put leaf in iodine solution (test for starch)
Photosynthesis
So what happens to the sugar made in the leaves?
It can be used in a number of ways
Used as building
Material
(e.g. cellulose
in cell walls
Sugar
Used immediately
For energy
Stored as starch
And Converted
back when Sugar
is needed by
Plant.
Photosynthesis
If a plant is converting carbon dioxide and water to
carbohydrate, then it’s weight should increase.
If a plant is dried out and weighed, it’s weight
increases during a day.
This is done by taking discs from a leaf at different
times of the day, drying them and weighing them.
Leaf Surfaces
• Leaves take in carbon dioxide from the air.
• In exchange they give out oxygen produced
during photosynthesis.
• These gases must be able to get in and out
of a leaf.
• Leaves have special structures which allow
gas exchange.
• These structures are called STOMATA.
Stomata
• Tiny pores on the
surface of a leaf which
allow gases in and out.
• They also allow water
to escape.
• Each pore is a
STOMA and is
surrounded by 2
GUARD CELLS.
Stomata
Leaf Surfaces
• A leaf is very thin and flat.
• We know it has stomata on it’s surface.
• Since it’s job is photosynthesis, there must
be reasons for it’s design.
• Inside the leaf there are a number of layers,
all with different jobs.
• However, they all help to make
photosynthesis as quick and efficient as
possible.
Leaf Surface
Leaf Surface
Water Transport in Plants
• The transport system of a plant does 2 jobs.
• One is to carry materials needed for
photosynthesis.
• The other is to carry materials produced by
photosynthesis.
Water Transport in Plants
• Water and minerals have to be carried from
the roots to the leaves.
• In the leaves water is used in
photosynthesis.
• Tubes, in the stem, called XYLEM vessels
carry the water and minerals.
• If a plant is cut and placed in red dye, it is
easy to see where the xylem vessels are.
Transport in Plants
• The other job of the plant’s transport system is to
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carry food from the leaves to every part of the
plant.
Tubes called the PHLOEM carry the food.
The xylem and phloem are usually found close
together in bundles called VASCULAR
BUNDLES.
The position of the vascular bundles in roots and
stems is not the same.
In most plants the xylem and phloem are found in
the centre of the root, whereas in a stem they are
found round the outside.
Transport in Plants
Root – Cross Section
Epidermis
Cortex
Xylem
Phloem
Transport in Plants
Stem – Cross section
Phloem
Xylem
Epidermis
Structure of the Xylem
• Xylem cells are dead and have no cell contents.
• The end walls have disintegrated
• The side walls have become inlaid with a tough
waterproof substance called LIGNIN
• Lignin is arranged in the side walls usually as
rings or spirals.
• A number of these cells laid end to end forms a
rigid pipe.
• This adds considerable support to the plant
Structure of Xylem
In this case the
lignin is spiral
Structure of the Phloem
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Phloem contains 2 types of cell
Sieve tubes
Companion cells
In sieve tubes the end walls are perforated
(sieve plates)
• Strands of cytoplasm pass through the pores
and allow contact with the next cell.
• The companion cells lie next to the sieve
tubes.
Structure of the Phloem
Elodea Bubbler
• When green plants photosynthesise they produce
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oxygen.
In aquatic plants, this oxygen is given off as bubbles
which are easily seen.
The Canadian pondweed, Elodea, has large spaces in
its stem.
When the stem is cut, and the plant is placed in strong
light, bubbles of oxygen can be seen coming from the
cut end.
The number of bubbles produced every minute, i.e. the
rate, gives us an idea of how fast the plant is
photosynthesising.
Elodea bubbler
Elodea Bubbler
Typical Set of Results
Light Intensity
10
20
30
40
50
60
70
No. of Bubbles / 3 minutes
0
6
15
26
35
38
38
Elodea Bubbler
Number of bubbles/3minutes
Elodea Bubbler
40
35
30
25
20
15
10
5
0
10
20
30
40
Light intensity
50
60
70
Limiting Factors
• Photosynthesis does not just depend on
light, carbon dioxide and a suitable
temperature, but also the amounts of each
available.
• If they are in short supply, they cut down or
LIMIT the rate of photosynthesis.
• Light, water, carbon dioxide and
temperature can act as “Limiting Factors”.