Download Unit 4 - Lesson 6 - Monocot and Dicot

Grade 11 College Biology – Unit 4
Plant Structure – Monocot versus Dicot
What is the difference between HERBACEOUS and WOODY?
Herbaceous
Woody
•
Stems are usually soft, green. The stems typically do NOT contain woody tissue.
The stems die back to the ground every year.
•
Plants usually die each year
•
Most annuals and perennial flowers, as well as vegetables and house plants
•
Stems are hard and stiff. The stems do NOT die back to the ground in the winter.
One classification of angiosperm plants is MONOCOT and DICOT. The table lists the major
morphological differences between the classes. Additional information is provided below. NOTE: As
with all things in nature, there are exceptions to these characteristics.
Monocot
Dicot
Embryo with single cotyledon
Embryo with two cotyledons
Pollen with single furrow or pore
Pollen with three furrows or pores
Flower parts in multiple of three
Flower parts in multiple of four or five
Major leaf veins are parallel
Major leaf veins are reticulated
Stem vascular bundles are scattered
Stem vascular bundles are in a ring
Secondary growth is absent
Secondary growth is often present
Roots are adventitious
Roots develop from radicle
Number of cotyledons
• The number of cotyledons in the embryo is the basis for defining the two classes of angiosperms.
“Mono” is one and “di” is two. The cotyledons are the “seed leaves” produced by the embryo. The
cotyledons absorb nutrients packaged in the seed until the seedling is able to produce its first true
leave and photosynthesis to make more nutrients.
Pollen structure
• The first angiosperms had pollen with a single furrow or pore through the outer layer. The feature is
retained in monocots. Dicots are descended from plants which developed three furrows or pores.
Number of flowers
• If you count the number of petals, stamens or other floral parts, you will find the monocot flowers tend
to have a number of parts divisible by three. Dicot flowers tend to have multiples of four or five (e.g.,
four, five, eight, ten…)
Leaf veins
• In moncots, the major leaf veins run parallel the length of the leaf. In dicots, there are often
numerous auxillary veins which reticulate between the major ones (i.e., resemble a net).
Stem vascular arrangement
• Vascular tissue occurs in long strands called VASCULAR BUNDLES. In dicot stems, the bundles are
arranged to form a cylinder, appearing as ring of spots in a cross-section. In moncots, the bundles
are randomly distributed throughout the stem with many bundles located toward the stem periphery
(i.e., outer edge).
Root development
• In most dicots, the root develops from the lower end of the embryo from a region called the RADICLE.
The radicle gives rise to the APICAL MERISTEM which produces new root tissue throughout the
plant’s life. In monocots, the radicle stops growing and new roots grow ADVENTIOUSLY from nodes
in the stem. Since these new roots are clustered at the base of the stem, they are called PROP
ROOTS.
Secondary growth
• Most seed plants increase their diameter by secondary growth – adding wood and bark. Monocots
do not produce wood or bark.
Common Questions about Monocots and Dicots
1. Are pine trees monocots or dicots?
• Pines are CONIFERS. They are NEITHER monocot or dicot. Only flowering plants are grouped
in these two classes.
2. Do all dicots produce flowers?
• Sort of. All dicots are flowering plants. However, the flowers may not be large or “showy.”
Maples and oaks are dicot trees. They do not produce obvious flowers. Grasses and cattails are
monocots. Their flowers are overlooked because they do not have petals or sepals.
3. In monocots do not have wood, what supports a palm tree?
• Palm trees rely on overlapping leaf bases, prop roots and thickened, enlarged cells for support.