exam 1 slides 7 and 8 Flashcards
Meristems
Actively dividing cells or cells that
retain the ability to divide
Cells in meristems
“anatomy”
-primary walls only (no secondary walls)
–lack a large central vacuole
»small vacuoles instead
Apical meristem at
stem tip
function of it
– Contributes to increase
in stem length
– Dormant before growing
season begins
– Protected by bud scales
and by leaf primordia
-Leaf primordia
Leaf primordia
Tiny
embryonic leaves that develop
into mature leaves
Apical Meristems
-Found at the tips of roots and shoots
* Roots and shoots increase in length as the apical meristems
produce new cells
Roots and shoots increase in length as the apical meristems
produce new cells
primary growth
Apical meristems give rise to 3 primary meristems that also
cause primary growth and produce primary tissues
-Protoderm
* Ground meristem
* Procambium
Protoderm - Gives rise to
epidermis
Procambium - Produces
primary xylem and phloem
Ground Meristem -
Produces
pith and cortex,
both composed of
parenchyma cells
(produces fundamental or
ground tissue in monocot
stem)
Lateral Meristems =
Secondary Meristems
- Produce secondary tissues that increase the girth of
roots and stems (= secondary growth) - For thickening growth
- Include the vascular cambium and the cork cambium.
- Found in dicots and gymnosperms
- Monocots lack typical secondary growth
Vascular Cambium
– A secondary meristem
– Composed of a thin cylinder of brick-shaped cells
that extends the length of stems and roots
– Causes thickening growth
– Produces secondary xylem and secondary phloem
– Forms true wood
Cork Cambium =
=Phellogen
– A secondary or lateral meristem.
– A thin cylinder that runs the length of roots and
stems of woody plants
– Is to the outside of the vascular cambium
within the outer bark (periderm)
* Produces secondary tissues:
– Produces cork to the outside
– Produces phelloderm to the inside
Intercalary Meristems
- Grasses and related plants do not have a vascular
cambium or a cork cambium. - They have apical meristems.
- Intercalary meristems are present.
- Occur in vicinity of nodes (leaf attachment area)
along stems - Add to stem length
- When you cut the grass the intercalary meristems
remain to regrow the grass.
Tissues Produced by Meristems
(what do they look like)
-After they arise from the meristems, maturing cells
assume various shapes and sizes.
* Shape is related to function.
* Simple tissues and complex tissues are produced
Fibrous root system what type of stem
typical monocot
what type of stem have taproots
typical dicot
Root cap
- The root cap protects the sensitive apical
meristem as the root grows through the soil. - It secretes a slimy sheath to help the root
grow through the soil. - It is the site of gravity perception.
Region of Cell Division composed of
apical meristem in
the center of root tip
Root apical meristem gives rise
to 3 primary meristems
Protoderm
ground meristem
procambium
Protoderm gives rise to
epidermis
Ground meristem - Gives rise to
cortex and pith (if present
procambium gives rise to
primary
xylem and primary phloem
Region of Elongation
Cells become several times their
original length
how does The Region of Elongation work
– Vacuoles merge
– No further increase in cell size takes place above the
region of elongation.
– Increases in girth may occur if vascular cambium is
present
The Region of Maturation
- Sometimes called the root hair zone
– Root hairs are extensions of epidermal cells - Cells differentiate and tissues form
Casparian Strips
- Named after Robert Caspary
- Consist of fatty suberin
- Impermeable to water
- Found on 4 out of the 6 walls of endodermis
cells
– Passage cells do not have Casparian strips - Force water and dissolved substances through
selectively permeable plasma membranes - Enable control over what enters the vascular
transport system within the vascular cylinder
Typical Dicot Root
things in it
- Epidermis
- Cortex
- Vascular cylinder
- No pith, just cortex
- Secondary growth occurs in some species
epidermis in Typical Dicot Root
-Site of root hair origin
Cortex in typical dicot root
– Parenchyma cells between epidermis and vascular
cylinder
– Main function is storage
– Endodermis with Casparian strips is inner
boundary between cortex and vascular cylinder
Vascular cylinder (stele) in the center of root in typical dicot root
– Surrounded by endodermis with Casparian Strips
– Pericycle site of origin of branch roots
– Solid core of xylem with “arms”
– Phloem in between “arms” of xylem
Secondary growth occurs in some species in a typical dicot root
Wood formation and bark formation
Typical Monocot Root
- Has epidermis with root hairs
- Has pith and cortex
- Has endodermis with Casparian strips
- Has pericycle beneath endodermis
– Site of origin of lateral (branch) roots - Xylem alternates with phloem in a circle
(cylinder) surrounding the pith - No secondary growth
Monocot roots
summary
- Pith and cortex
Dicot roots summary
Cortex, no pith
Monocot shoots summary
Fundamental tissue
(ground tissue)
Dicot shoots summary
Pith and cortex
Specialized Roots: used for
- Food storage
- water storage
3.propagative roots
4.pneumatophores
5.aerial roots - parasitic roots
7.mycorrhizae
8.root nodules
food storage
A combination of root and stem:
– Carrots
– Beets
– Turnips
– Radishes
- Propagative Roots
- Buds on roots develop into suckers (aerial
stems) - Some plants can spread this way
– Fruit trees - Cherries, apples, pears
– Some invasives - Canada thistle
- Tree-of-heaven
Invasive Canada Thistle, Invasive Tree of Heaven with Propagative Roots
- Not from Canada, not native to N. America
- Can extend up to 15 feet by propagative roots
- Pneumatophores
- In some species with
roots growing in water - Spongy roots that
extend above the
water’s surface and
enhance gas exchange
between atmosphere
and subsurface roots - Found in mangroves
- Aerial Roots
- Corn prop roots
- Orchid velamen roots
-banyan trees
- Parasitic Roots
- Dodder plant with haustoria
– Haustoria tap into host to absorb water and nutrients
-Mistletoe (partial parasite) has haustoria to
absorb water and minerals
