Transcript CB098-008.38_Plant_Structure_A

Plant
Structure:
Cells, Tissues,
Organs, Meristems
& Growth
Organization of the
Plant Body
Organ – several types of tissues that
together carry out particular functions. A
typical plant body contains basic organs:
roots, stems, and leaves, and flowers.
Organ systems in plants are the shoot
system and Root System.
Shoot System (Mostly Above Ground) –
Stems, leaves, buds, flowers, and fruit.
The shoot system develops from the shoot
apical meristem (SAM). Function of the
shoot system is photosynthesis,
reproduction, seed dispersal, support, and
gas exchange.
Root System (Mostly Below Ground) –
Main root (primary) and branch roots.
The root system develops from the
root apical meristem (RAM). Function
of the root system is anchorage,
absorbs and transports minerals and
water, and stores food.
Plant Cells & Tissues
Meristems – sites in the plant body where cells divide and where differentiation into
specialized cells and tissues are initiated. Meristematic areas are the source of new
cells and tissues.
Tissues – a group of cells of similar structure that performs a special function. Tissues
make up plant organs. Plant tissues are made up of living and dead cells.
Three Tissue Systems Make Up the Plant Body
1) Ground Tissue System
- Responsible for housekeeping functions (photosynthesis, storage and support).
- Most extensive tissue type.
- Simple tissues make up this tissue system.
- Tissue Types: Sclerenchyma, Collenchyma, and Parenchyma.
- Ground Tissue System is found in the mesophyll of leaves & pith (often internal
to vascular tissue) & cortex (often external to vascular tissue) of young
green stems.
- Ground Tissue System is found throughout the plant.
Note: On the below cross sections, only ground tissues are circled with red dots.
Leaf Cross Section
Stem Cross Section
Root Cross Section
The Simple Tissues of the Ground Tissue System
A) Parenchyma Tissue (Cells)
- Most common type of plant cell.
- Primary cell walls that are thin and flexible.
Secondary cell walls are often absent
but not all the time. If secondary wall
is present, lignin makes up the
secondary cell wall.
Celery Parenchyma
Pine _____________________
- Parenchyma cells perform most of
the metabolic functions of a plant.
This include photosynthesis,
cellular respiration, and food
storage.
- Mesophyll (Parenchyma) cells make
up the bulk of leaf tissue and these
cells have chloroplasts and
photosynthesize and store water.
- In roots, parenchyma cells (in the
cortex) contain plastids and store
starch.
Parenchyma Tissue (Cells) continued.
- When parenchyma cells are turgid, they give support to the plant.
- Most parenchyma cells can divide and differentiate into other types
of plant cells under certain conditions, such as during the repair of
an injury. In the laboratory, an entire plant can be regenerated
from a single parenchyma cell.
Impatiens sp.
The Simple Tissues of the Ground Tissue System
B) Collenchyma Tissue (Cells)
- Supports “Strengthening tissue” young
stems and leaf petioles. These cells are
right below the surface.
 Collenchyma cell walls are thickened at the
corners.
- Collenchyma cells have
primary cell walls only.
- Mature collenchyma cells are
alive and they elongate as
stems and leaves grow.
- The “strings” of a stalk of
celery consists of
collenchyma cells.
Celery Collenchyma
The Simple Tissues of the Ground Tissue System
C) Sclerenchyma Tissue (Cells)
- Main function of sclerenchyma cells is to support the weight of the plant and
plant organs.
- Cells have rigid, thick primary and secondary cells walls.
- Secondary cells walls are thick with lignin providing strength.
- Sclerenchyma cells are dead at maturity.
Sclerenchyma Cells from Geranium
Sclerenchyma Tissue (Cells) continued.
- There are two types of sclerenchyma cells.
FIBERS
Fibers are long, thin and fibrous-like and they
usually occur in bundles. They are used
commercially to make rope and clothing
(hemp) and flax fibers are used to make
linen.
SCLEREIDS
Sclereids look like sheets. They are short and
irregular in shape but very hard. They
make up tough seed coats, nutshells and
pits. They give the pear its gritty texture.
Impatiens sp.
Pear Sclereids
Three Tissue Systems Make Up the Plant Body
2) Vascular Tissue System
- These are the conducting tissues, which transport water, nutrients and sugar.
- Complex tissues make up this tissue system.
- Vascular tissue is often found in vascular bundles in a plant.
- Main Tissue Types: Xylem (Primary & Secondary), Phloem (Primary &
Secondary), (Note: Primary is early growth and secondary is
later growth.)
- Vascular Tissue System is found throughout the plant.
Note: On the below cross sections, only vascular tissues are circled with red dots.
Leaf Cross Section
Stem Cross Section
Root Cross Section
The Complex Tissues of the Vascular Tissue System
A) Xylem Tissue (Cells)
- Xylem tissue transports water and minerals upwards from the roots.
- Xylem makes up wood and is not living at maturity. It needs to be dead and hollow for
transport.
Primary Vascular Bundle of Sunflower
Secondary Growth of Basswood Stem
Xylem Tissue (Cells) continued.
Xylem is made up of 4 cells types: Tracheids, Vessel Members (Vessel
Elements), Fibers (Sclerenchyma cells) and Parenchyma cells.
Fibers (Sclerenchyma Cells), a simple tissue we discussed before from the
ground tissue system, is present in the vascular tissue system helping in
the support of xylem.
Parenchyma, a simple tissue we discussed before from the ground tissue
system, is present in the vascular tissue system helping tracheids and
vessel members with transport. Parenchyma cells are the only living
cells in xylem tissue.
Tracheids and Vessel members are the cells that actually do the transport.
Tracheids are long, thin cells that overlap and are tapered at the ends. Water
passes from one cell to another through pits, areas with no secondary
cell wall. Because their secondary cell walls are hardened with lignin,
tracheids function to support the plant as well as to transport nutrients
and water.
Vessel Members are aligned end to end and differ from tracheids in that the
ends are perforated to allow free flow through the vessel member. In
other words, these cells are in a line and have openings at the ends of the
cells to allow water transfer.
Seedless vascular plants (Ferns) and most gymnosperms (pine trees and relatives) have
only tracheids; most angiosperms (flowering plants) have both tracheids and
vessel members.
Xylem Tissue (Cells) continued.
Water
Flowing
Upwards
Vessel Members (Note: Aligned end to
end but they digest out end walls
forming a tube called a vessel)
Tracheids (Note: Overlapping and are
tapered at the ends and are
connected by bordered pits)
The Complex Tissues of the Vascular Tissue System
B) Phloem Tissue (Cells)
- Phloem transports sugar (food) down through the plant originally from
photosynthesizing cells (often the leaves) by active transport.
Primary Vascular Bundle of Sunflower
Secondary Growth of Basswood Stem
Phloem Tissue (Cells) continued.
In flowering plants (angiosperms), the following cells make up phloem: Sieve
Tube Members (Sieve Tube Elements), Companion Cells, Parenchyma
Cells, Fibers and Sclereids.
Fibers & Sclereids (Sclerenchyma Cells), a simple tissue we discussed before
from the ground tissue system, may present in the vascular tissue
system helping in the support of phloem.
Parenchyma, a simple tissue we discussed before from the ground tissue
system, is present in the vascular tissue system helping phloem tissue in
“unloading and loading” and also involved in storage.
Sieve tube members are the cells that actually do the transport.
Sieve Tube Members are the food-conducting cells. These cells are joined at
their ends to form long sieve tubes (conducting elements of phloem). In
contrast to conducting elements of xylem, these cells are alive at maturity
but they lose organelles as they age in order to function as a tube. The
end walls of sieve-tube members contain sieve plates (which have pores)
to facilitate the flow of fluid from one cell to the next.
Companion Cells are connected by plasmodesmata to sieve tube members.
Companion cells retain their organelles and they nurture sieve tube
members by producing proteins and transporting these proteins to sieve
tube members.
Phloem Tissue (Cells) continued.
Sugar Flowing Down
Stem Phloem Tissue
(Shown from side view)
Phloem Tissue (Cells) continued.
Primary phloem in
cucumber stem
shown in cross
section.
Phloem Tissue (Cells) continued.
In seedless vascular plants (Ferns) and gymnosperms (pine trees and
relatives), sieve cells rather than sieve-tube members are the conducting
elements in phloem. Albuminous cells (parenchymna-like cells) act as
companion cells to these sieve cells.
Pine Phloem
(Shown from side view)
BIO 141 Botany with Laboratory
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