BIOL 100C:
Introductory Biology III
Plant Cell Types
Dr. P. Narguizian
Fall 2012
Principles of Biology
Plants (Anatomy & Physiology)
1) What are the differences between Nonvascular vs. Vascular plants (examples)?
2) Gymnosperms vs. Angiosperms?
3) Monocots vs. Eudicots (Dicots)?
4) What are the 3 basic plant organs
(components & functions)?
5) What are the 3 plant tissue systems
(components & functions)?
6) Roots vs. Shoots (components &
functions)?
Plant Anatomy
BIOSKILL
Plants have three basic organs: roots,
stems, and leaves.
• Vascular plants exist in two distinct terrestrial environments at
the same time-above ground (leaves and stems) and below
ground (roots).
• Each part of a vascular plant contains cells grouped into
tissues, which are collections of cells of one or more type that
perform specific functions.
• A collection of tissues used for a particular process is called an
organ. A plant's organs are its roots, stems, and leaves.
• A root anchors a plant in the ground and absorbs water and
other nutrients from the soil. A plant's roots comprise its root
system, which generally exists below ground.
Principles of Biology
Plant Anatomy
Figure 2 Root systems that grow above ground.
Not all roots are underground. When the
roots of the tidal-growing red mangrove
(a) are not standing in air, they are
immersed in water.
Some scientists think the exposed roots
help the trees take in oxygen. The
buttress roots of the fig tree (b) add
additional support to the tree. These
types of roots are most common among
trees that are grow in shallow soil, so
cannot penetrate the ground deeply.
Much like they do for the mass of a
stone cathedral building, they provide
additional support to the tree structure
by attaching high on the tree trunk and
extending in a tapered shape toward the
ground..
Principles of Biology
Plant Anatomy
BIOSKILL
Plants have three basic organs: roots,
stems, and leaves.
• There are two main types of root systems: taproot and fibrous
root.
• The taproot system consists of a main root, the taproot, running
vertically into the ground, with lateral roots growing out of the
taproot.
• Taproots tend to be thick and sturdy, whereas the lateral roots
that grow from them are often stringy and thin.
Principles of Biology
Plant Anatomy
Figure 3 Root systems: taproots and fibrous roots.
Taproot systems are structured with a single, thick
main root, growing vertically down from the plant stem.
A carrot (left) is a eudicot taproot that is also a
common vegetable. In contrast, fibrous root systems
are a collection of many smaller adventitious roots, all
similar in size. Small green onions (right) are monocot
plants with fibrous root systems.
Principles of Biology
Plant Anatomy
BIOSKILL
Plants have three basic organs: roots,
stems, and leaves.
•Roots developing from the stem or from other
unusual locations (such as leaves) are
known as adventitious roots.
•In most monocots, the taproot dies early and
many smaller roots of similar size emerge
directly from the stem, developing into a
fibrous root system.
Principles of Biology
Plant Anatomy
BIOSKILL
Interpret Micrographs
•Root hairs are extensions of epidermal cells that lie
just beyond the tip of the root.
•Root hairs infiltrate the spaces between soil particles
and absorb the water by osmosis.
•Root hairs pump positive hydrogen ions into the soil
and exchange them for the positive mineral ions.
Principles of Biology
Plant Anatomy
Figure 4 Root hairs.
Plants absorb water
mostly through root
hairs, which are
extensions of epidermal
cells.
Root hairs are tiny —
only 80 to 1,500
micrometers in length.
Principles of Biology
Plant Anatomy
The stems and leaves of a plant are the shoot system.
• The main function of the leaves and stems-which together constitute
a plant's shoot system-is harvesting sunlight.
• The stem of a vascular plant supports the plant, stores nutrients,
generates new tissue, and makes and supports leaves.
• The stem of a vascular plant makes leaves at special sites called
nodes. Between two nodes is a segment called an internode.
Together, they make up the majority of the stem.
• In eudicots, the very tip of a stem, where most growth occurs, is
called the apical bud.
• Branches develop from lateral buds called axillary buds, which grow
at the upper angle between leaves and the stem.
• In most plants, the apical bud is dominant over the axillary buds. This
phenomenon is called apical dominance.
Principles of Biology
Plant Anatomy
Figure 5 Shoot system.
The shoot system
contains the stem
and leaves.
Principles of Biology
Plant Anatomy
The stems and leaves of a plant are the shoot system.
• Leaves are the organs primarily responsible for photosynthesis, the process
whereby plants use energy from sunlight, carbon dioxide, and water to
make sugars.
• The blade is the part of the leaf that contains chloroplasts for
photosynthesis and is usually flat and thin to maximize exposure to sunlight.
• The blade contains the stomata, which enable the plant to transpire and
exchange gases with the atmosphere.
• The petiole is the part of the leaf near the node where the blade joins the
stem.
• A simple leaf consists of a single blade, whereas a compound leaf has
many divisions, known as leaflets.
Principles of Biology
Plant Anatomy
Figure 6 Leaf morphology.
A simple leaf possesses a single,
undivided blade. The blade of a
compound leaf has leaflets,
arranged either singly or doubly.
Note that axillary buds form only
where the petiole meets the stem,
not in the leaflets.
Principles of Biology
Plant Anatomy
Exceptions to the rule.
•Leaves are not always used for photosynthesis, like
in cacti, in which the stems do photosynthesis.
•The spines of cacti likely evolved from leaves, but
they are nothing like the leaves of any other plant;
mature spines are not even alive.
Principles of Biology
Plant Anatomy
Figure 7 Cacti spines.
In cacti, leaves have evolved into sharp
spines. Notice that the stems display the
characteristic green of photosynthetic
tissue.
Principles of Biology
Plant Anatomy
Plant Tissues
All of the tissue in vascular plants consists of just three typesdermal, vascular, and ground.
Principles of Biology
Plant Anatomy
Figure 8 Plants are composed of three types of tissues.
Dermal tissues primarily protect
a plant. Vascular tissues
transport water, nutrients, and
minerals.
Ground tissues are responsible
for every other function in a
plant, including metabolic
processes, protection, and
transport.
Principles of Biology
Plant Anatomy
Plant Tissues
• Ground tissue comprises the bulk of the plant and generally
makes up the structures in between the dermal and vascular
tissues.
• Ground tissue carries out most of the plant's metabolic
processes, e.g., photosynthesis.
• Dermal tissue provides a protective covering for the roots,
stems, and leaves, so it is found on the outside of plant organs.
• Vascular tissue serves to transport food, water, hormones, and
minerals, so it is usually found in a plant's interior.
Principles of Biology
Plant Anatomy
Dermal tissues surround and protect plant organs.
• In nonwoody plants, epidermal cells form a single, tightly packed layer
called the epidermis.
• Epidermal cells in leaves and stems secrete a waxy material called the
cuticle, which coats the epidermis and prevents excessive water loss.
• In woody plants, a thicker, multilayered protective tissue called the
periderm commonly replaces the epidermis in mature regions of roots
and stems.
• Root hairs are extensions of epidermal cells in roots. Hair-like
structures called trichomes are extensions of epidermal cells in leaves
and stems.
Principles of Biology
Plant Anatomy
Figure 9 Trichomes.
In this SEM of a Nicotania benthamiana leaf, the trichomes extend
from the tough epidermal cell layer on either side. Sandwiched in the
middle are the photosynthetic cells.
At the far left is part of a vein (mv), which contains vascular tissue.
Principles of Biology
Plant Anatomy
Vascular tissue transports water, minerals, and sugars.
• The two main vascular tissues are xylem and phloem.
• Xylem tissue transports water and minerals from the roots to the shoots of a
plant, moving from bottom to top, against gravity.
• Phloem tissue moves sugars from the leaves to the rest of the plant.
• Together, xylem and phloem tissues form cylindrically shaped bundles
called vascular bundles, or stele.
Principles of Biology
Plant Anatomy
Figure 10 Vascular bundles in stem tissue.
This micrograph shows a cross
section of a grape plant stem,
with vascular bundles aligned
side by side. Each vascular
bundle contains adjacent xylem
and phloem tissue.
Xylem tissue is the innermost
red-stained layer, and phloem
tissue is the thinner bluestained layer. Vascular bundles
are the main transport system
of the plant stem. (Magnification
= 116x).
Principles of Biology
Plant Anatomy
Figure 11 Xylem tissue.
Tracheids and vessel elements differ in shape. Tracheids are narrower,
have tapered ends, and transport water and minerals between cells
through bordered pits. Vessel elements (SEM at right) transport water
and minerals vertically through pores.
Principles of Biology
Plant Anatomy
Ground tissue has multiple roles and contains diverse cells.
• The great majority of tissue in plants is ground tissue.
• In eudicots, ground tissue inside the ring of vascular bundles is commonly
called the pith. Ground tissue exterior to the vascular bundles is called the
cortex.
• The three types of ground tissue cells are parenchyma, collenchyma,
and sclerenchyma.
• Parenchyma cells are the most common and versatile ground tissue cells.
They have thin primary cell walls and usually lack secondary walls.
Principles of Biology
Plant Anatomy
Figure 12 Parenchymal cells.
Photosynthesis takes place
in parenchymal cells. The
green structures in these
Arabidopsis cells are
chloroplasts.
Principles of Biology
Plant Anatomy
Ground tissue has multiple roles and contains diverse cells.
• Collenchyma cells are thin, elongated cells with unevenly thickened walls that provide
support and flexibility to growing regions of the plant, particularly in the stems and
leaves.
• Sclerenchyma cells are the principle structural support in tissue that has ceased to
grow in length.
• Many sclerenchyma cells are dead but retain their functionality because of their hard,
thick secondary walls, which contain high amounts of lignin.
• Sclereids are short sclerenchyma cells that contain the most lignin and so are the
hardest. These are the cells that form the outer covering of nuts and many fruit seeds.
• Fibers tend to be longer and more tapered in appearance than sclereids. They are
often used commercially in the production of ropes and linen.
Principles of Biology