Transcript Unit: Leaves

Unit: Leaves
The Energy Powerhouse
of the
Plant
Leaves are diverse and are adapted for their needs and growth
• “…tubular, needlelike, feathery, cupped, sticky,
fragrant, smooth or waxy…”
Some Leaf statistics…
• A maple tree with
100,000 leaves has a
combined surface area
greater than the size of 6
basketball courts
• Globally, leaves produce
more than 200 billion
tons of sugar a year;
that’s 2200 lbs X
1,000,000,000…WOW!
Structure & function of leaves
• Leaf Structure – the wide, flat plant organ designed to
absorb as much sunlight as possible
• Leaf Function - to absorb light and produce sugar
through photosynthesis
Photosynthesis = “light” and “putting together”
• Plants use light energy to put carbon dioxide (from the
air) and water (gathered from the roots) to make sugar
• Oxygen is also given off
• The sugar produced by photosynthesis is used for
energy to make other plant tissues
• Photosynthesis is a series of biochemical reactions that
occurs in the presence of chlorophyll, the green pigment
that makes leaves green!
Chloroplasts - the plant cell organelle
that is the location for photosynthesis
“ Energy –capturing solar cells and sugar
factories”
The “raw materials” for photosynthesis
enter the plant through these locations:
• Stomates – tiny holes on
the underside of leaves
that let carbon dioxide
enter and water exit
• Stems – the site where
water and minerals travel
from the roots to the
leaves via
• Roots – the site of water
absorption
• Xylem – ‘tubes’ that
bring water and minerals
from the roots to the
leaves
• Phloem – ‘tubes’ that
bring food (sugar) from
the leaves to all plant
parts
How does Photosynthesis work?
…remembering the Visible
Spectrum… (ROYGBJ)
• Color is seen because it
is reflected by a pigment,
any substance that
absorbs light
• So, green leaves absorb
all the other colors, but
reflects the green
wavelength we are able
to see
Leaf Transpiration
• “the loss of water vapor” from the plant
• Water lost contributes to the Water Cycle
• Plants wilt when too much water is lost by transpiration
or when there is not enough water absorbed by the
roots
• During transpiration, water moves out of the plant
through its stomates (plural: stomata)
Why leaves change color in the Fall…
Spectacular autumn foliage is not all
about “leaf peeping”!
• Chlorophyll, the pigment needed for photosynthesis that
gives leaves their green color, stops being produced
• The withdrawal of nitrogen and phosphorus, needed for
photosynthesis, are taken from the leaves and used for
winter storage in twigs and branches while they are
dormant
• Colors seen in the fall are no longer hidden by the
chlorophyll’s green color
Bright and beautiful colors
are the result of chlorophyll
production“shutdown”
• Carotenoid pigments – yellow + orange,
seen in maples
• Anthocyanin pigments – pink, red and
purple, seen in sugar and red maples,
sassafras, sumac trees
• Tannins – brown, seen in oaks, beech, and
other trees
Weather conditions affect fall colors
• Warm and sunny days with cool nights promote red
autumn colors
• Freezing, rainy, cloudy weather conditions reduce leaf
color intensity
• “leaf peepers” look for “peak” colors and foliage reports
to plan trips to the New England States
• Check out http://www.vtonly.com/foliage.htm for a look
at the foliage travel report!
Leaf Abscission means leaves fall in
Deciduous Trees
• Enzymes in leaves cause
cell death at the base of
leaf petioles
• The xylem still brings
water to the leaf, but…
• The abscission zone
forms a protective layer
called suberin, which
protects the tree from
insects, disease, and
dehydration
• The phloem pathway for
sugar flow is blocked as
photosynthesis stops for
the winter
• The abscission zone is
the site of leaf “fall”, and
the leaf’s petiole
separates from the stem
Falling leaves leave “Sleeping trees” Senescence
• Senescence is the breakdown of cell contents and
membranes – for trees, this happens at the abscission
zone
• Leaves falling let trees enter a winter dormant period
while the trees rest
• Fallen leaves on the forest floor decompose
• The soil is “restocked with nutrients” and becomes food
for soil organisms like worms and bacteria
Strange, beautiful and functional leaves
• Tendrils are string-like
leaves that “help the
plant climb or support
weak stems”
• Thorns and spines keep
plants from losing water
and protects them from
hungry animals (except
Eeyore, the thistle eater)
• Succulent leaves store
water
• Reproductive leaves have
“babies” – plantlets with
roots and leaves
• Insect-Trapping leaves
include the popular
Venus Fly Traps and
Pitcher Plants