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Distinguishing
features of plants
1. Photosynthetic
2. Chlorophyll is photoactive pigment
– typically Chl A and chl B
3. Chloroplasts – membrane bound
organelle where chlorophyll is
concentrated
4. Cell wall – predominantly made of
polysaccharide cellulose
5. Vacuole – storage and metabolism;
bounded by tonoplast membrane
Plant Cells
 Cell wall – distinguishes plant cells
from animal cells; metabolically
active and/or structural
 Plasma membrane - surrounding the
protoplast (cytoplasm)
 Organelles of metabolism – including,
among the standard others, a variety
of plastids
 Membrane system – synthesis and
transport (ER, golgi)
 Nucleus – hereditary info
Plant Cell Size and
Longevity
Cell longevity – varies from hours to
millenia
 reproductive cells – a few hours
 functional dead xylem (water
conducting cells) ~7000 years
Cell size – minute to large
 cells in a region of cell division ~10
um
 Trachieds in pines ~10 mm
 Cotton fiber ~5 – 6 inches
STORAGE
VACUOLES
 Vacuoles may be the dominant
feature of many cells
 occupying the majority of the cell volume
(up to ~90%).
 Can be one large one or many small ones
 Tonoplast – single membrane
enclosing vacuole
 Maintains homeostasis
 Transport proteins for nutrients and
other products
 Mature vacuoles – contain molecules
such as inorganic sugars, sugars,
enzymes, organic acids, secondary
compounds, etc.
PLASTIDS
 All are maternally inherited
 Have their own DNA and ribosomes
 Divide by binary fission (like
bacteria)
 Three typical types
 Chloroplast – tertiary membrane system
for photosynthesis
 Amyloplasts – store starch
 Claioplasts – store oils
Features of the
Cell Wall
1.
2.
3.
Found in all plant cells except
sperm and some eggs
Middle lamella – mostly pectin,
cements adjacent cells together
Primary cell wall



Found in all plant cells
Cellulose matrix with hemicellulose,
proteins, pectin, lignin, cutin, and wax
Characteristic of undifferentiated
cells or ones that still are gorwing
4. Secondary cell wall




Just inside primary cell wall
Characteristic of mature cells
Comprised of hemicellulose and lignin
3 layers thick
• Middle lamella
surrounded by
primary walls
• Appearance of
plasmodesmata
Primary
Cell Walls
Note the darkly stained
primary wall CW1 with
indistinguishable middle
lamella ML. Warts W
which are cell wall
irregularities are
observed in a crosssectional view on the
inner surface of the S3
layer.
• Tracheids have
three layered
walls
• Warts may also
appear
• Wood of conifers
consists of
tracheids with
three-layered
secondary cell
walls as shown
here for ground
hemlock (Taxus
canadensis).
They are
designated as
S1, S2 and S3.