Transcript Roots, Stems & Leaves

Roots, Stems & Leaves
“Principal organs of seed plants”
3 Tissue Types:
Dermal Tissue
- outer covering, epidermal cells
Vascular Tissue
- xylem / phloem, transport system
Ground Tissue
(between dermal / vascular)
- parenchyma, collenchyma and
sclerenchyma cells
Seed Plant Structure
23-2 Roots – Try This:
http://www.virted.org/Plants/RootsQuiz.html
• Absorbs water and dissolved
nutrients
• Anchors plants to ground
• Prevents erosion
• Protection from soil bacteria and
fungus
• Transports water & nutrients
• Holds plants upright against forces
such as wind and rain
Roots – Two main types:
Plants have taproots, fibrous roots or both
#1 Taproots - Characterized by having one main
root (the taproot) from which smaller branch
roots emerge.
• When a seed germinates, the first root to
emerge is the radicle, or primary root. In
conifers and most dicots, this radicle
develops into the taproot.
• Taproots can be modified for use in storage
(usually carbohydrates) such as those found in
sugar beet or carrot or radishes or turnips ….
• Taproots are also important adaptations for
searching for water, as those long taproots
found in mesquite and poison ivy.
Taproot
#2. Fibrous Roots –
• Characterized by having a mass of
similarly sized roots.
• In this case the radicle from a
germinating seed is short lived and is
replaced by adventitious roots.
Adventitious roots are roots that form on
plant organs other than roots.
• Most monocots have fibrous root
systems.
• Some fibrous roots are used as storage;
for example sweet potatoes form on
fibrous roots.
• Plants with fibrous roots systems are
excellent for erosion control, because the
mass of roots cling to soil particles.
Fibrous Roots - A cabbage seedling with
white, fibrous roots snaking through the soil
Root Overview
(new cells produced here)
(undifferentiated)
Meristematic tissue
- only plant tissue that produces new cells by
mitosis
Root Cap
- protects the meristematic tissue, thick cells
to push through soil
Apical meristem
- near the tip of roots and stems
- cells increase the length of roots and stems
- undifferentiated
Zone of elongation
- where new cells are enlarging
23-3 Stems
Stems have 3 important functions:
1. Produce leaves, branches, flowers
2. Hold leaves up to sunlight
3. Transport substances between
roots and leaves
23-4 Leaves
• The leaves of a plant are its main
organs of photosynthesis.(plant
leaves are the world’s most
important manufacturers of food)
• The structure of a leaf is
optimized for absorbing light and
carrying out photosynthesis.
More about leaves…
• The vascular tissues of leaves are
connected directly to the vascular of
stems, making them part of the
plant’s transport system. The
vascular bundle (xylem and
phloem) appear as “veins” in the
leaves.
Leaf cross-section
Leaf Cross section cont…
• Cuticle – (together with epidermal cells) form a
waterproof barrier that protects tissue and limits
water loss.
• Epidermis – the top and bottom layer of leaves
made of tough, irregularly shaped cells.
• Mesophyll – (palisade/spongy) bulk of most
leaves. Where photosynthesis occurs. Sugars
are produced and move into the phloem vessels
to be carried to the rest of plant
Palisade – rich in plastids (chloro/chromoplasts)
Spongy – rich in plastids/spaces for gas exchange
Leaf cross-section cont…
• Stomata (stoma) – porelike
openings in the underside of the leaf
that allow CO2 and O2 to diffuse in
and out of the leaf.
• Guard cells – each stoma consist
of 2 of these that control the
opening and closing of stomata by
responding to changes in water
pressure.
Leaves
• Photosynthetic organ of the plant,
used to convert sunlight into food
• Photosynthesis Equation:
Notes:
•
•
•
cuticle - top / bottom (thicker on top most of the time)
epidermis - top/bottom
air spaces in spongy mesophyll
•
•
stoma surrounded by guard cells
generally more stoma on the bottom than on the top (stomata is
both stoma and guard cells)
•
when the plant has lots of water, the guard cells are full and they
move apart opening the stoma; when the plant is lacking in water,
the guard cells close
•
•
finally, stoma are open in the day; its needed for photosynthesis
Most plants, stoma are closed at night when plant doesn't need
CO2 (go to link)
plants gain CO2 while losing water
http://www.ftexploring.com/photosyn/chloroplast.html
•
•