Chapter 27 13-03-03 1:59 PM
Photosynthetic autotroph: a photosynthetic organism that uses light as
it’s energy source and carbon dioxide as its carbon source.
Organ: two or more different tissues integrated into a structure that carries
out a specific function.
Tissue: a group of cells and intercellular substances with the same structure
that function as a unit to carry out one or more specialized tasks.
Totipotency: the ability to develop into any type of cells.
Indeterminate Growth: growth that is not limited by the organism’s
genetic program, so that the organism grows for as long as it lives; typical
of many plants.
Meristem: an undifferentiated permanently embryonic plant tissue that
gives rise to new cells forming tissues and organs.
Xylem: the plant vascular tissue that distributes water and nutrients.
Phloem: the food conducting tissue of the vascular plant.
Tracheid: a conducting cell of xylem, usually elongated and tapered.
Vessel Members/Elements: any of the short cells joined end to end in
tube-like columns in the xylem.
Monocot: a plant belonging to the Monocotyledones, one of the two major
classes of angiosperms; monocot embryos have a single seed leaf
(cotyledon) and pollen grains with a single groove.
Eudicot: a plant belonging to the Eudicotyledones, one of the two major
classes of angiosperms; their embryo’s usually have two seed leaves
(cotyledons), and their pollen grains have three grooves.
Vascular cambium: a lateral meristem that produces secondary vascular
tissues in plants.
Since plants are sessile (non-motile), they must obtain water and nutrients
from the soil around them…
nutrients and water are patchily distributed in the soil, (not even and gets
used up by the plant) so the best solution for the plant is to INCREASE
• Both above and below ground.. not compact like animals, plants
spread out in a dendritic form (tree-like/branched).
o Large and spread out root and shoot system allows for
greater access to water and nutrients in the soil, greater and more dominant access to sunlight, and stronger root systems
keep plants in place.
• Chloroplasts: function in photosynthesis; unique to plant cells.
• Vacuole: may occupy majority of the volume in mature cells–
important in cell elongation and maintenance of ridged tissues, also
• Primary Cell Wall: surrounds the plasma membrane and cell
o Are the skeleton of the plant; serve as support
o Made largely of microfibrils of cellulose, embedded into a
matrix of other polysaccharides.
The combination of cellulose and other polysaccharides
gives the cell wall strength and flexibility
Also contains proteins (add to strength).. not a solid
barrier–> like a mesh or filter.
• Plasmodesmata: cytoplasmic connections between adjacent cells
o Allows solutes (ie. amino acids and sugars) to move from one
cell to the next.
• Middle lamella: the polysaccharide layer filling the space in between
adjacent cells primary walls
• Secondary wall: additional cellulose and other materials are
deposited inside the primary wall to forma a strong secondary wall.
o Often contain lignin–complex water insoluble polymer– which
makes cell walls very strong, ridged and impermeable to
Plants have a general growth pattern of indeterminate growth
• Individual plant parts (leaves, flowers, fruits) exhibit determinate
growth • Indeterminate growth gives plants a great deal of flexibility
(plasticity) in their possible changes to an ever changing
environment (changes in light, water and nutrient supply and
• Allows plants to adapt: to a change in direction of light, to a
depletion of water or nutrients in the soil.
• Plants grow by two mechanisms:
o 1. An increase in the number of cells by mitosis
o 2. An increase in size of the individual cells
Meristems are responsible for growth in both girth and height
Apical meristem: in all plants– clusters of self-perpetuating tissue at the
tips of their buds, stems and roots.
• Tissues that develop from apical meristems are called primary
tissues–make up the primary plant body.
• Called PRIMARY GROWTH
o herbaceous plants (grass) only have primary growth.
SECONDARY GROWTH: originate at cylinders of tissue called lateral
meristems–increases the diameter of older roots and stems (secondary
• Woody plants (trees and shrubs) have secondary tissues.
Primary and secondary growth can occur simultaneously….
• Shoot apical meristem: dividing cells at all shoot tips are
responsible for a shoot’s primary tissues and growth
• Root apical meristem: dividing cells at root tips behind the root
caps are responsible for a root’s primary tissues and growth.
• Vascular cambium: secondary growth around the middle vascular
• Cork cambium: secondary growth just inside the woody bark. Annuals: are herbaceous plants in which the life cycle is completed in one
• Minimal or no secondary growth (only apical meristems)
Biennials: complete their life cycle in two growing seasons
• Limited secondary growth
• 1 season: roots stems and leaves form
• 2 season: the plant flowers, forms seeds and dies
Perennials: vegetative growth and reproduction continue year after year
• Many have secondary tissues.
monocot root system is branching and fibrous
eudicot root system has a main taproot with smaller lateral roots.
27.2 Tissue System Name of Tissue Types of Cells in Tissue Function
Ground Tissue Parenchyma Parenchyma cells Photosynthesis,
Colenchyma Colenchyma cells Flexible strength
for growing plant
Sclerenchyma Fibres or Rigid support,
Vascular Tissue Xylem Conducting cells Transport water
(tracheids, vessel and dissolved
Phloem Conducting cells Sugar transport
Dermal Tissue Epidermis Undifferentiated Control of gas
cells, guard cells,exchange, water
other specialized loss and
Periderm Cork, cork Protection.
Xylem: Conducts water and dissolved minerals absorbed from the soil upward from
a plant’s roots to the shoot.
Was a key adaptation for plants to make the transfer to land.
Contains two types of conducting cells: tracheids and vessel members.
• Both develop thick, lignified secondary walls and die at maturity…
the now empty cell walls (cytoplasm not longer exists after death)
serve as pipelines for water and minerals
• Tracheids: are elongated with tapered, overlapping ends… keep
plants from collapsing in dry conditions
o Water moves from cell to cell in pits… water seeps laterally
from tracheid to tracheid.
• Vessel members: shorter and wider cells joined end to end in a
o Several centimeters long… in vines and trees they may be
o Adaptation that increases water flow: as vessel members
mature, enzymes breakdown portions of their end walls,
producing perforations.. holes in the ends
o Water moves more efficiently through vessels than tracheids
due to their greater diameter and perforated ends.
Problem is air bubbles– potentially lethal to a plant
• Air bubbles can get stuck in vessels, and prevent water flow… killing
• But the air bubbles in tracheids stay where they are and to not
affect the water flow
o Even though tracheids may be slower at transporting water,
their pits are impermeable to air bubbles.
Transports solutes (sugars made in photosynthesis and other organic
molecules) throughout the plant body.
Sieve Tube Members: main conducting cells, connected end to end
• Their end walls are called sieve plates– are studded with pores
• Fibres and sclereids (often in the phloem as well) strengthen stems.
• As the cells mature they loose the nucleus and most organelles, but
continue to live • Companion cells are connected to the mature sieve cells by
plasmodesmata (companion cells retain their nuclei)
o Assist the sieve cells with the uptake and unloading of sugars
o Help regulate the metabolism of mature sieve cells.
There are four key functions of stems:
1. Stems provide mechanical support, generally along a vertical axis, for
body parts involved in growth, photosynthesis, and reproduction. These
parts include meristematic tissues, leaves and flowers.
2. Stems house the vascular tissues (xylem and phloem), which transport
products of photosynthesis, water and dissolved minerals, hormones and
other substances throughout the plant.
3. Stems are often modified to store water and food
4. Buds and specific stem regions contain meristematic tissue that gives rise
to new cells of the shoot.
The Modular Organization of a Stem
A plant stem develops in a pattern that divides the stem into modules, each
consisting of a node and internode
• Node is a place on the stem where one or more leaves are
attached; the region between the two nodes is the internode.
New primary growth occurs in buds– a terminal bud at the apex of the
main shoot, and axillary buds which produce branches (lateral shoots) at
the point where leaves meet the stem.
Meristematic tissue in buds give rise to leaves, flowers or both.
• We usually think that flowering plants grow from the base of their
stems, but shoot grow actually occurs from the apical meristem
(the tip of the plant, not the base)
In eudicots, most of the growth occurs just below the apical meristem, as
internode cells divide and elongate–internode cells nearest the apex are the
most active Meristems in grass