Download Parenchyma cells

Objectives:
• List and describe the major plant organs their structure and
function
• List and describe the major types of plant cells and their
functions
• List and describe the major types of plant tissues, identify their
locations and describe their functions.
• Identify and describe the external parts of a monocot and
eudicot plant.
• Identify and describe the distribution of tissues in the stem, root,
and leaf of a monocot and eudicot plant.
• Identify, describe, and explain the changes that occur in a
eudicot stem as it matures.
• Explain the relationship between the distribution of tissues in the
leaf and the functions of these tissues.
Plant Tissues and Organs
Major Plant Organs
• Flowering plants possess three kinds of vegetative (nonreproductive) organs: roots, stems, and leaves. The flower is
the reproductive organ of the Angiosperms.
Shoots consist
of stems and
leaves.
Functions are
photosynthesis,
support and
transport
Roots anchor
and absorb
water and
minerals and
provides
nutrients for
the shoot and
can be an area
of storage
Organ Functions
• The shoot system of a plant consists of the stems and the
leaves, as well as flowers.
• Leaves are the main sites of photosynthesis in plants.
• Stems hold and display the leaves to the sun and provide
connections for the transport of materials between roots and
leaves. It may also serves as an area of storage.
• A node is the point where a leaf attaches to a stem.
• Regions of stem between nodes are the internodes.
• Flowers are modified leaves structure which support the
microsporangia and megasporangia gametophyte
generations and are involved in plant sexual reproduction.
Flowers are usually located apically or a the end of a stem.
• The root system provides support, storage and nutrition.
Plant Cell Types (Support and Storage)

Parenchyma cells:
o
numerous
o
thin walls and large central vacuoles
o
the photosynthetic cells in leaves
•
filled with chloroplasts
•
mesophyll cells.
o
Some store lipids or starch
(potatoes)

Collenchyma cells:
o
supporting cells that lay down
primary cell walls that are thick in
the corners
o
provide support to leaf petioles,
nonwoody stems, and growing
organs
o
compose the cortex and pith tissues
of the root and stems
Plant Cell Types (Support)

Sclerenchyma cells:

main supporting cells of a plant
•
thick secondary cell wall
•
contains lignin -a component of
wood

two types:

elongated fibers

variously shaped sclereids

Fibers often organize
into bundles.
Plant Cell Types Vascular (Transport)
Xylem

contains conducting cells called tracheary elements.

Tracheids are evolutionarily more ancient tracheary elements found in
gymnosperms.

tracheary elements and tracheids undergo apoptosis(die) leaving only their cell
walls to become functional

Vessel elements: similar to tracheids (tracheary elements) but larger and are laid
end to end - also formed from dead cells - Flowering plants have both!
Phloem

Conducting cells called seive tube members

are alive

are arranged end-to-end and form long sieve tubes, which transport
carbohydrates and other materials.

The plasmodesmata in sieve tube members enlarge as they mature

filled with sieve tube sap (water, sugars, and other solutes).

The sieve tube members have adjacent companion cells

Companion cells retain all their organelles and regulate the performance of and
support the sieve tube members
Xylem and Phloem Cell Types
Plant Tissues

A tissue is an organization of cells that work together as a functional unit.

Parenchyma cells make up parenchyma tissue, which is a simple tissue.
Xylem and phloem are complex tissues; they are composed of a number of
different cell types.


Tissues are grouped into tissue systems that extend throughout the body of the
plant from to form the various organs of the plant.

There are four plant tissue systems: vascular, dermal, ground and meristemic.
Plant Tissues
Vascular Tissue



xylem and phloem
phloem transports carbohydrates from sites of
production (sources such as leaves) to sites of
utilization for energy or where it is being stored
(sinks) elsewhere in the plant.
xylem distributes water and mineral ions taken up
by the roots to the stem and leaves.
Dermal Tissue



outer covering of the plant.
All parts of the young plant body are covered by an
epidermis, which is a single layer or multiple layers
of cells.
 epidermal cells and other specialized cells
such as guard cells.
The shoot epidermis secretes a layer of wax-covered
cutin, the cuticle, which helps retard water loss
from stems and leaves.
Ground Tissue


primarily parenchyma tissue
storage, support, photosynthesis, and the
production of defensive and attractant
substances (oils and toxins)
Meristems (Plant Stem Cells)

The localized regions of cell division in plants, called meristems, are forever
embryonic. They have the ability to produce new cells indefinitely.

When a meristem cell divides, one daughter cell develops into another meristem
cell, and the other differentiates into a more specialized cell. The meristem gives
rise to all plant cell and tissue types.
There are two types of meristems in Angiosperms:

1.
2.
Apical meristems give rise to the primary plant body, which is the entire
body of many plants.
•
Shoot and Root
•
Apical meristems are responsible for primary growth, which leads to
elongation and organ formation.
Lateral meristems give rise to the secondary plant body.
•

Lateral meristems t give rise to the tissues responsible for this
thickening.
Intercalary – found in grasses
Location of Meristematic Tissues
Growing Eudicot Stem Structure
These
tissues form
a vascular
bundle. In
woody plants
they grow
together and
fuse to form a
continuous ring
creating annual
growth rings.
Mature Eudicot Stem








Secondary growth increases the
diameter of stems and roots.
Secondary growth results from the
activity of vascular and cork cambia.
Vascular rays connect storage
parenchyma to the sieve tubes of the
phloem.
Only eudicots have a vascular cambium
and a cork cambium and thus undergo
secondary growth.
Cross sections of most tree trunks in
temperate zone forests have annual
rings.
Annual rings form due to differential
rates of growth in spring (when water
is plentiful) and in summer.
Wood that is no longer conducting
water is known as heartwood.
Sapwood is wood that is actively
conducting water and minerals in the
tree.
Root Tip Structure
Root Structure (Monocot vs Eudicot)
Root Structure (Monocot vs Eudicot)
Eudicots have their
xylem centrally located
usually in an X formation.
no pith is present!
Monocots have pith
tissue that is centrally
located. Xylem cells
arranged in a ring.
Leaf Structure

Leaf anatomy is adapted to carry out photosynthesis, limit evaporative water loss,
and transport the products of photosynthesis to the rest of the plant.

The two zones in leaf parenchyma that photosynthesize are the palisade
mesophyll and the spongy mesophyll.

Within the mesophyll is air space through which CO2 can diffuse to the
photosynthesizing cells.

Veins supply mesophyll cells with water and minerals, and they transport the
products of photosynthesis to the rest of the plant.

The epidermis of the leaf is the outermost cell layer, which is covered by a waxy
cuticle. The epidermis functions to keep water and photosynthetic products in the
leaf.

Guard cells allow controlled gas exchange through pores in the leaf (the stomata).
Leaf Structure