Transcript Structures and Functions in Plants

Structures and
Functions in Plants
Roots, Stems, and Leaves
Specialized Plant Cells
There are three types of cell found
in plants that are arranged
differently in roots, stems, and
leaves.
– Parenchyma
– Collenchyma
– Sclerenchyma
Parenchyma
 Loosely packed,
cube-shaped or
elongated cells with
large central
vacuoles
 Involved with many
metabolic functions
including
photosynthesis
 Usually form the
bulk of nonwoody
plants
 Alive at maturity
Collenchyma
 Thicker cell walls
 Provide support
for the plant
 Usually in founds
in strands
 Celery has a lot of
collenchyma cells
 Alive at maturity
Sclerenchyma
 Thick,even,rigid
cell walls
 Support and
strengthen in
areas of plant no
longer growing
 Dead at maturity
 This is FIBER!
The gritty texture of the pear fruit is due to
sclerenchyma cells!
Plants Also Have Tissue Systems
Plants cells work together to form
three tissue systems: dermal,
ground, and vascular.
These tissue systems organize to
produce the three organs of a plant:
roots, stems and leaves.
Dermal Tissue
– Primary function is absorption and
protection.
– Parenchyma cells.
– Forms the outside covering of plants
– Epidermis and cuticle
Ground Tissue
– This consists of all three types of cells.
• Mostly parenchyma, some collenchyma and few
sclerenchyma
– Primary function is storage and support.
Vascular Tissue
– Primary function is transport and support.
– Xylem and phloem
Growth Occurs in Meristem
 Apical
– Tips of roots and
shoots
– Growth in length
 Lateral
– Occurs in
gymnosperms and
most dicots
– Growth in diameter
 Intercalary
– Located above the
bases of leaves and
stems
Roots
Tap
Fibrous
Adventitious
Primary Growth in Roots
Roots increase in length
through cell division,
elongation, and
maturation in the root
tip. A root cap covers
the apical meristem. It
produces a slimy
substance allowing the
root to move easily
through the soil. Root
hairs are extensions of
the epidermis that
increase surface area.
Secondary Growth in Roots
This occurs in gymnosperms and
dicots.
The vascular core of a primary root
is surrounded by the pericycle.
The pericycle produces lateral
roots.
Root Functions
 Anchor the plant in the soil
 Absorb water and minerals
– 13 minerals are required for normal growth
 Adapted to store carbohydrates
– Usually stored as starch and stored in
parenchyma cells
– Potatoes, sweet potatoes,
carrots, turnips
Modified Roots
Monocot vs Dicots Roots
epidermis
endodermis
xylem
phloem
Vascular tissue matures to form the innermost cylinder of the root.
In the dicot, the xylem forms an X and the monocot has a prominent
endodermis. The cortex is between the epidermis and endodermis.
The cortex and the endodermis compose the GROUND TISSUE.
Stems
There are many differences in
stem shape and growth that are
the results of adaptations to the
environment.
Stems have a more complex
structure than roots.
Stems grow in length at the
tips and grow in circumference
through lateral meristem.
Stem Structures
Stems are divided into segments
called internodes.
A node is at the end of each
internode.
At the point of attachment, each
leaf has bud.
A bud is capable of developing into
a new shoot. The bud has apical
meristem enclosed in special
leaves called bud scales.
At the tip of each stem there is
usually a terminal bud. Each spring
when growth resumes, the terminal
bud opens.
Primary Growth in Stems
Apical meristem gives rise to all
three types of tissue.
In gymnosperms and dicots,
ground tissue forms the cortex
and pith. Pith is located in the
center of the stem. In
monocots, the ground tissue
does not separate into pith and
cortex.
Monocot / Dicot Stems
Monkey faces
Secondary Growth in Stems
is Called Wood
Summerwood
Sapwood (light)
Springwood
Annual ring
Heartwood
Bark-protective outer covering
composed of cork, cork cambium and
phloem
Functions of Stems
Function in transport and
storage of nutrients.
Translocation is the movement
of food in the phloem.
– Pressure-flow hypothesis
(carbohydrates are actively
transported and water moves by
osmosis)
Transpiration is water loss
(cohesion-tension theory)
Storage of Water and
Nutrients
Abundant parenchyma cells in
the cortex provide plants with
ample storage.
Cactus stems are specialized
for storing water.
Sugar-cane stores large
amounts of sucrose.
Potatoes store starch.
Leaves
Most leaves are thin and flat, an
adaptation that helps a plant
capture sunlight for
photosynthesis.
Leaves exist in many variations
that reflect adaptations to
environmental conditions.
Leaf Adaptations
Tendrils – coiled specialized leaves
to aid a climbing vine ( some may
be modified stems – grapes)
Carnivorous plants – pitcher plant
and venus fly trap – leaves function
as food traps
Spines- modified leaves that
protect the plant. Spines are small
and nonphotosynthetic. In a cactus,
spines reduce transpiration.
Leaf Structures
– blade
– stipules
– petiole
– vein
– midrib
Leaves are Either Simple or
Compound
Simple leaves
A compound leaf consists of several, separated segments
called leaflets. The leaflets are usually grouped in pairs
around the elongated rhachis
that corresponds to the midrib of a normal leaf.
Leaf Arrangement
Vein Patterns
 In parallel - veined leaves, the veins run
parallel to each other. This condition is
characteristic of the monocotyledoneae.
 Pinnately netted - veined leaves have a
single primary vein or midrib, from
which smaller veins branch off, like the
divisions of a feather.
 Palmately netted- veined leaves have
several principal veins radiating from the
base of the leaf blade, as in Acer rubrum
(red maple).
Parts of a leaf
Stomata
palisade lay
spongy layer
veins
chloroplast
thylakoid
grana
stroma
Leaf Functions
Photosynthesis
– Limitations –
insufficient water
due to
transpiration. A
corn plant losses
98% of water
absorbed by roots
through
transpiration.
Benefits of Photosynthesis
–1. The oxygen in the air comes from
photosynthesis. The plants continue to
replenish the oxygen in the air.
–2. All of our food comes directly or
indirectly from photosynthesis.