Angiosperms III
Plant Cell Types
Plant Cell Types
• Most angiosperm plants are composed of
10 fundamental cell types
• Many more specialized cell types do
occur in some plants
• These 10 cell types are differentiate from
the dividing cells found in meristems and
cambia (meristematic cells)
Meristematic cells
• Found in meristems
(root and shoot), the
cambial layers, and buds
• Function is cell division
(cell cycle)
• Small (about 10 m)
with a large nucleus (the
cells you saw in the
squashed root tip in the
mitosis lab)
Parenchyma Cells
•
•
•
•
Large (100m) cells
Thin cellulose cell walls
Usually with a large vacuole
Function as storage or
“packing” cells
• Common in the pith and
cortical layers, the wood
rays, petals, etc…
• A “generalist” cell type
Chlorenchyma Cells
• Large parenchyma
cells with
chloroplasts
• Found in the leaves
and in some stems
• Major function is
photosynthesis
Collenchyma Cells
• Cells used for temporary support,
primarily in herbaceous stems
• Cells walls have extra cellulose
thickenings in the corners (strong
but flexible)
• Often found in bundles as
“collenchyma tissue” just under the
epidermis
• Best experienced in celery (or
rhubarb) as the “ribs” that get stuck
in your teeth
Sclerenchyma Cell Types
• “Sclerenchyma cells” are four cell types
which all share these features in
common:
– all have thick secondary cell walls of
LIGNIN (and stain red in prepared slides)
– all are DEAD at maturity
– include: fibers, sclereids, tracheids, and
vessels elements
Fibers
• Long, narrow cells with
thick walls and a small
lumen
• Used for support in woody
tissues (secondary xylem) or
for support in vascular
bundles and herbaceous
stems
• Not found in conifer wood
(thus the wood is “soft”)
Fibers
(longitudinal
section)
Sclereids
• Irregular cells with thick walls
• Function primarily for protection
(surfaces often look like jigsaw puzzles)
• Found in dry fruits (nuts etc.), seed
coats, some leaves
Sclereids
• A special form of
a sclereid, the
stone cell, gives
pears their
“gritty” texture
Tracheids
• Water conducting cells of the
xylem in gymnosperms, ferns,
and fern allies
• Cells have closed end walls
• Found along with vessels in
angiosperms
• May have complex “pits”
through which water moves
from cell to cell
• Secondary wall may be
deposited in rings or spiral
shapes
Vessels Elements
• Water conducting cells
of the xylem in
angiosperms; also found
in gnetophytes
• Have open end walls
• May have spiral or ringlike secondary cell wall
patterns
Vessel Elements
• Are short and
squat cells,
one on top of
another,
forming vessel
“tubes” for
conduction
Sieve Tube Members
• Tall, thin cells with
only primary cellulose
cell walls
• Living cells but lack a
nucleus at maturity
• Similar to sieve cells
of gymnosperms
Sieve Tube Members
• Part of the phloem
tissue which
conducts sugars and
hormones
throughout the
plant
Sieve Tube Members
• End walls
have a
“sieve plate”
Companion Cells
• Long, thin cells with a nucleus directly
adjacent to each sieve tube members
• Sieve tube member and its companion
cell are derived from the same initial
• Responsible for the loading and
unloading of substances from the sieve
tube members in the phloem
• Similar to albuminous cells in
gymnosperms
Development of Sieve Tubes and
Companion Cells
Summary of Cell Types
•
•
•
•
Meristematic
Parenchyma
Chlorenchyma
Collenchyma
• Fibers
•
•
•
•
Sclereids
Tracheids
Vessel Elements
Sieve Tube
Members
• Companion
Cells