Chapter 35 Flashcards
How are plants organized?
Plants have organs composed of different tissues,
which in turn are composed of different cell types
A cell…
is the fundamental unit of life
A tissue
is a group of cells consisting of one or more
cell types that together perform a specialized function
An organ…
onsists of several types of tissues that
together carry out particular functions
Basic Vascular Plant Organs:
Roots, stems, and leaves
How are the three basic organs organized?
They are organized into a root system and a shoot
system
Roots rely on…
sugar produced
by photosynthesis
in the shoot
system
Shoots rely on…
water and minerals absorbed by the root system Basic
A root is an organ with important functions:
- Anchoring the plant
- Absorbing minerals and water
- Storing carbohydrates
The primary root
branches to form
lateral roots for
anchorage and water
absorption occurs
Tall plants with large shoot masses generally have
a taproot system
The taproot generally develops from
the primary root
and functions in anchoring the plant in the soil
Small or trailing plants generally have a
fibrous root system that spreads out like a thick
mat below the soil surface
Root hairs…
are finger-like extensions of epidermal cells, form near the root tip and increase the absorptive surface of the root
Most root systems form
mycorrhizal associations
A stem is a plant organ
consisting of
an alternating system of nodes and internodes
nodes..
the points of leaves attachment
internodes…
the stem segments between nodes
The growing shoot tip, or apical bud causes
elongation of a young shoot
An axillary bud is a structure that
has the potential
to form a lateral branch, thorn, or flower
The primary function of
the stem is to
elongate and orient the shoot to maximize
photosynthesis
Many plants have
modified stems that
perform alternate
functions, for example…
rhizomes, stolons, tubers
The leaf is the
main photosynthetic organ of most vascular plants
Leaves functions:
intercept light, exchange gases, dissipate
heat, and defend the plant from herbivores and
pathogens
Leaves generally consist of
a flattened blade and a stalk called the petiole
a petiole…
which joins the leaf to a
node of the stem
Some plant species have evolved modified leaves that serve various functions, for example...
spines, tendrils, storage leaves, and reproductive leaves
Roots, stems, and leaves are composed of three tissue types:
dermal, vascular, and ground tissues
In nonwoody plants, the dermal
tissue system consists
of a epidermis and a cuticle
epidermis
covered in a waxy coating
cuticle
that helps
prevent water loss
In woody plants, protective tissues
called periderm
replace the epidermis in older regions of stems
and roots
Tissues that are neither
dermal nor vascular are the
ground tissue system
Ground tissue internal to the
vascular tissue
is pith
ground tissue external to the vascular tissue
is cortex
Ground tissue includes cells
specialized for
storage, photosynthesis, support, and
transport
The two vascular tissues are
xylem and phloem
Xylem
conducts water and dissolved minerals upward
from roots into the shoots
Phloem
transports sugars from where they are made
(primarily leaves) to storage or growth sites
The vascular tissue of a root or stem is collectively
called
the stele
In angiosperms, the stele of the root is a
solid central vascular cylinder divided into vascular bundles, strands of xylem and phloem
The two types of water-conducting cells
tracheids and vessel elements are dead and
lignified at maturity
Cells of the phloem are
alive at maturity, but lack
organelles
In seedless vascular plants and gymnosperms, sugars are
transported through sieve cells
In angiosperms, sugars are
transported in sieve tubes, chains of cells called sieve-tube elements
Sieve plates are
the porous end walls between sieve
-tube elements that allow fluid to flow between cells
along the sieve tube
Each sieve-tube element is connected to a
companion cell by
plasmodesmata whose nucleus
and ribosomes also serve the adjacent sieve-tube
element
indeterminate growth
A plant can grow throughout its life due to the activity of meristems, unspecialized tissues composed of dividing cells
determinate growth
Most animals and some plant organs cease to grow at a certain size
There are two main types of meristems:
apical meristems and lateral meristems
Apical meristems
ocated at the tips of roots and
shoots, lengthens them; called primary growth
Lateral meristems add
thickness to woody plants
secondary growth
There are two lateral
meristems:
the vascular
cambium and the cork cambium
The vascular cambium adds
layers of vascular tissue
called secondary xylem
(wood) and secondary phloem
The cork cambium replaces
the epidermis with periderm,
which is thicker and tougher
The root tip is covered by a root
cap, which
protects the root apical
meristem as the root pushes
through soil
Growth occurs just behind the root
tip, in three zones of cells:
Zone of cell division
Zone of elongation
Zone of differentiation (maturation)
The primary growth of roots
produces
the epidermis, ground
tissue, and vascular tissue
In most eudicots, the xylem is
starlike in appearance with
phloem between the “arms”
In many monocots, a core of ground tissue is
surrounded by alternating rings of xylem and phloem
A shoot apical
meristem is a
dome-shaped mass of dividing cells at the
shoot tip
The leaves of the
apical bud protect
the meristem
Axillary buds
develop from
meristematic cells
left at the bases of
leaf primordia
In most eudicots, the vascular tissue consists
of vascular
bundles arranged in a ring
In most monocot stems, the vascular bundles are
scattered
throughout the ground tissue
Leaves develop from
leaf primordia along the sides
of the shoot apical meristem
stomata
pores that allow CO2 and O2 exchange between the air and the photosynthetic cells in a leaf
Each stomatal pore is flanked
by two guard cells, which regulate the pore’s opening and closing and
control water loss
The ground tissue in a leaf, called mesophyll, is
between the upper and lower epidermis
The mesophyll of eudicots has two layers:
palisade and spongy
Veins are the leaf’s vascular bundles, function as
the leaf’s skeleton, and are protected by bundle sheaths
Secondary growth, the growth in thickness produced by
lateral meristems
Secondary growth occurs
in gymnosperms and many eudicots, but is rare in monocots
Secondary growth occurs in
stems and roots of woody plants but rarely in leaves
Primary growth and secondary growth occur
simultaneously
In a woody stem, the vascular cambium is located
outside the pith and primary xylem and to the inside of the primary phloem and the cortex
In a woody root, the vascular cambium forms
exterior to the primary xylem and interior to the primary phloem
Secondary xylem accumulates as
wood and consists of tracheids, vessel elements (only in angiosperms), and fibers
Early wood
formed in the spring in temperate regions,
has thin cell walls to maximize water delivery
Late wood
formed in the summer, has thick-walled
cells and contributes more to stem support
Thick rings
indicate a year
with warm or wet
growing
conditions
thin rings
indicate a
cold or dry year
The outer layers, known as sapwood, still
transport materials through the xylem
Older secondary phloem sloughs off as
part of the bark and does not accumulate
