Cellular Structure in Plants Flashcards
5 types of cells in plants
Parenchyma Collenchyma Sclerenchyma Water-conducting cells of the xylem Sugar-conducting cells of the phloem
What is ground tissue composed of
Parenchyma
Collenchyma
Sclerenchyma
Parenchyma cells in ground tissue
have thin and flexible primary walls Large central vacuole Lack secondary walls Are the least specialized Perform the most metabolic functions Retain the ability to divide and differentiate
Metabolic functions of parenchyma ground tissue cells
store nutrients
Photosynthesize
Collenchyma ground tissue cells
grouped in strands and help support young parts of the plant shoot
Have thicker and uneven cell walls
They lack secondary walls
These cells provide flexible support without restraining growth
Strings in a celery stalk
Sclerenchyma ground tissue cells
rigid because of thick secondary walls strengthened with lignin
dead at functional maturity
Two types of sclerenchyma cells
sclereids and fibers
sclereids
short and irregular in shape and have thick lignified secondary walls
source of hardness in nutshells and seed coats
Fibers
long and slender and arranged in threads
Vascular Tissue cells
Xylem and Phloem
Tracheids
Found in all vascular plants
Tubular, elongated and dead
Water transfers via pits in the tracheids
Vessel elements
large diameter and shorter
Aligned end-to-end to form vessels
End walls have perforation plates
Phloem cells
Sieve-tube elements
Sieve plates
Companion cell
Sieve-tube elements
Alive at functional maturity
They lack organelles, including nucleus
Allows sugars to flow more easily
Sieve plates
The porous end walls that allow fluid to flow between cells along the sieve tube
Companion cell
One for each sieve-tube element
Nucleus and ribosomes serve both cell
Cell Growth
Indeterminate growth, Determinate growth, Annuals, Biennials, and Perennials
Indeterminate growth
growing throughout and organism’s life
Determinate growth
some plant organs cease to grow at a certain size
Annuals
Complete their life cycle in a year or less
Biennials
Require two growing seasons
Perennials
Live for many years
Meristems
Perpetually embryonic tissue
Maintains indeterminate growth
Functionally similar to animal stem cells
Apical meristems
located at the tips of roots and shoots and at the axillary buds of shoots
Primary growth
occurs when apical meristems elongate shoots and roots
Secondary growth
lateral meristems add thickness to woody plants. Involves two lateral meristems
Two kinds of lateral meristems
vascular cambium and cork cambium
vascular cambium
adds layers of vascular tissue called secondary xylem (wood) and secondary phloem
Cork cambium
replaces the epidermis with periderm, which is thicker and tougher
Tree rings
visible where late and early wood meet, and can be used to estimate a tree’s age
Dendrochronology
the analysis of tree ring growth patterns, and can be used to study past climate change
What is the vascular cambium made of
a cylinder of meristematic cells one cell layer thick
what does the vascular cambium develop from
undifferentiated parenchyma cells
what does the secondary xylem accumulate as
wood, and consists of tracheas, vessel elements (only in angiosperms), and fibers
Early wood
formed in the spring, has thin cell walls to maximize water delivery
late wood
formed in late summer, has thick-walled cells and contributes more to stem support
As a tree or woody shrub ages,
the older layers of secondary xylem, the heartwood, no longer transport water and minerals
Outer layers, known as sapwood, still transport materials through the xylem
Older secondary phloem sloughs off and does not accumulate
Xylem Cells
Tracheids and Vessel elements
