Download Plant tissues and organs

Plant Anatomy:
roots, stems and leaves
The plant body has a hierarchy of
organs, tissues and cells
•
Plants, like animals, have
organs composed of different
tissues,
which are composed of cells.
•
Tissue is group of cells with a
common function and
structure
•
Organ consists of several
types of tissues that carry out
a particular function
Plant cells
• Plant cells have 3 unique parts:
- Chloroplasts: the sites of photosynthesis
- Central vacuole: containing fluid that helps maintain firmness
- Cell wall: made from the structural carbohydrate cellulose
(types: primary and secondary walls)
•
Major types of cells:
Parenchyma
Collenchyma
Sclerenchyma
Water conducting cells of xylem
Sugar conducting cells of phloem
Parenchyma cells perform most of the metabolic
functions of a plant
They are in charge of photosynthesis, cellular respiration, and food
storage.
They remain alive when mature and usually have only primary cell walls,
which are thin and flexible.
Most parenchyma cells can divide and differentiate into other types of
plant cells under certain conditions, such as during the repair of an
injury.
Collenchyma cells provide flexible support
Support for still growing parts like young stems
the “string” of a celery stalk
Resemble parenchyma cells in lacking secondary walls, but they have
unevenly thickened primary walls.
These living cells elongate as stems and leaves grow
Sclerenchyma cells provide support for non-growing regions
They have thick secondary cell walls, usually strengthened with lignin, which
is the main chemical component of wood.
Mature sclerenchyma cells cannot elongate, and they occur in regions of the
plant that have stopped growing in length.
When mature, most sclerenchyma cells are dead, their cell walls form a rigid
“skeleton” that supports the plant.
Hemp fibers
Give nutshells its hardness
Water conducting cells of xylem
FUNCTION:
Water transport
Support
They have rigid,
lignin- containing secondary cell walls.
The tubes are hollow because the cells are dead when mature,
with only their cell walls remaining.
Water passes through pits in the walls and
through openings in the end walls of vessel elements.
There are two kinds of cells
Tracheids are long, thin cells with tapered ends.
Vessel elements are wider, shorter, and less tapered.
Cross section of dicot stem
Sugar conducting cells of phloem
Food-conducting cells called sieve-tube members,
are also arranged end to end, forming tubes as part of phloem
Unlike water-conducting cells
sieve-tube members remain alive at maturity,
though they lose most organelles,
The reduction in cell contents allows
for nutrients
to pass more easily through the cell.
The end walls between sieve-tube members,
called sieve plates, have pores that
allow fluid to flow from cell to cell along the sieve tube.
Each sieve-tube member has at least one companion cell,
Helps sieve cells by producing and transporting proteins
Cross section of moncot stem
These cells are grouped into tissues…..
….These tissues are organized
into the plants organs
The three types of tissues: dermal, vascular and ground
•
Each tissue is continuous
throughout the plant
From root to stem to leaf
•
But,
Are there differences in the tissue
arrangement between stems and roots?
Are there differences in the tissue
arrangement between monocots
And dicots?
Dermal tissue covers the outside of the plant
• Non woody plants:
One single layer called epidermis
•
Woody plants:
several layers form the cork
•
Main function is protection
Specializations of dermal tissue:
Stems and leaves: waxy coating (cuticle)
and trichomes,
Many functions:
catch water, reduce airflow, produce wax
Leaves have special cells: guard cells
Regulate the size of the stomata
Roots: epidermis forms root hairs
Function?
Vascular tissue transports materials and supports
• Xylem:
Transports water and dissolved minerals
• Phloem:
Transports organic nutrients (sugars)
The arrangement of the vascular tissue
varies depending on the organ
And between monocots and dicots.
Root:
Stems:
leaves:
Ground tissue fills the area between epidermis and
vascular tissue
Ground tissue in leaves
is called the mesophyll
Function?
Ground tissue in stem
Called pith or cortex
Function?
Ground tissue in roots
also called cortex
Function?
The three basic plant organs: roots, stems and leaves
•
The solution to the separation of resources on land,
was the development of the 3 basic organs
•
The are organized into:
Shoot system:
Which organs? ____________
Function: ________________
Root system
Which organs? ___________
Function: _______________
Monocots and Dicots
vary in the structure of these organs
Roots
•
Function:
Anchors plant in the soil,
absorbs and transports minerals and water,
stores food.
•
Monocot roots
consists of a mat of generally thin roots
spread out shallowly in the soil.
• Dicots have one main vertical taproot
with many small secondary lateral roots
growing outward.
•
Near the root tips are root hairs
Each root hair is an extension of an epidermal cell
Dicot roots have phloem
between arms of xylem in the
center
Monocots have xylem and phloem in a
ring with pith in the center
Stems
•
Function:
Support the leaves and flowers.
Green stems also perform photosynthesis
.
In the case of a tree, the stems are:
the trunk
and all the branches,
including the smallest twigs.
A stem has nodes,
the points at which leaves are attached,
internodes,
the portions of the stem between nodes.
The buds are undeveloped shoots.
Stem’s internal structure
Leaves
•
Function: photosynthesis
It is has a large surface area to maximize light harvesting
They are thin so that light will penetrate through to the bottom cells
Composed of the lamina (blade) and the petiole (stalk)
Monocots have parallel venation
Dicots have branched venation
Internal structure of a leaf
Upper and Lower Epidermis:
protective function
lower epidermis generally contains
more stomata
Epidermal cells lack chloroplasts
Palisade Mesophyll : tightly packed cells on the upper surface
Contain three to five times as many chloroplasts as
those of the spongy parenchyma.
Chloroplasts remain usually near the cell wall,
since this adjustment guarantees optimal use of light
Spongy Mesophyll : loosely arranged cells
Creates air spaces to facilitate gas exchange