BSCI 124 Lecture Notes
Undergraduate Program in Plant Biology, University of Maryland
LECTURE 20 - KINDS OF PLANTS: FLOWERING PLANTS
Three recently discovered new kinds of flowering plants found in the
Sierra Madre del Sur, Guerrero, Mexico, by Maryland botanists
I.
General
information about flowering plants (angiosperms = covered seed)
-
Possess
flowers
and
fruits
with
seeds
-
Habitat- everywhere; dominant plants of earth's flora
II. Significance of flowering plants
-
Extent of flowering plant success
-
Area
-
Dominant plants in almost every terrestrial environment
-
Exception - northern coniferous forests where dominant plants are conifers
-
Number of species
-
Estimated at 260,000
-
This is 88 percent of the species estimated to be in the Plant Kingdom (295,000)
-
Evolutionary significance of flowering plants
-
Most advanced plants on earth
-
Advancements over gymnosperms
-
Flowers-
many use animal pollinators- assures greater reproductive success
-
Fruits and seeds adapted for dispersal
-
Double fertilization -> endosperm in seed
-
Other structural advancements that will be discussed in later lectures
-
Ecological roles of flowering plants
-
Food, shelter, and concealment for animals
-
Help form and improve soil; prevent soil erosion
--
© Ross Konig at Eastern Connecticut State University
III. Sexual reproduction in flowering plants
-
Floral
structure
-
Male sex organs
-
The
stamens
are the male sex organs composed of
-
The stamens may have
derived
from a leaf blade with a sporangia near its tip (apex) or from slender branch
systems bearing terminal sporangia.
-
Female sex organs
-
The carpel is the
evolutionary female structure (a modified leaf).
-
One or more carpels forms a pistil (the central organ of flowers that is
composed of an ovary, style, and stigma)
-
1) The ovary is the enlarged basal portion of a carpel or fused carpels that
contain the ovules. A mature ovary, sometimes with other adherent parts,
is a fruit.
2) The ovules are structures within the ovary containing the female gametophyte
with egg cell. When mature, the ovule becomes a seed.
3) The stigma is the region of a carpel that serves as a receptive surface
for pollen grains and on which they germinate to form pollen tubes. The movement
of pollen to the stigma is termed
pollination
4) The style is a slender column of tissue that arises from the top of the
ovary. Pollen tubes grow through the style.
5) An example of a pistil composed of several carpels is the orange (each
section in the fruit is derived from a single carpel)
6)
Ovaries
may be "superior" (located above the sepals and petals) or "inferior" (located
below the sepals and petals)
Non-reproductive whorls in flowers
-
Consist of an outer whorl of leaf-like bracts called sepals
-
And an inner whorl of leaf-like bracts called petals
-
Sepals tend to be green while petals tend to be variously colored and usually
much less leaf-like
-
The sepals and petals can be
variously
shaped such as free and simply arranged (actinomorphic) or variously
fused and of dissimilar shaped and size (zygomorphic)
IV.
Life
cycle of flowering plants
-
Heterosporous
-
male - diploid sporophyte anther with microsporangium containing microspore
mother cells; through meiosis they produce haploid microspores which germinate
within the anther sac to produce immature male gametophytes
(pollen
grains) containing tube nucleus and generative cell (2 sperm nuclei)
-
female - diploid sporophyte ovule within ovary has megasporangium containing
megaspore mother cells; through meiosis they produce megaspores which germinate
into female gametophyte containing egg and 2 polar nuclei
-
Double fertilization
-
pollen grain germinates on stigma forming pollen tube growing to the ovary;
the two haploid sperm travel down the tube to the ovary where one sperm nucleus
fertilizes the haploid egg forming a diploid zygote and the other sperm nucleus
unites with the two polar nuclei forming a triploid endosperm nucleus which
grows into the endosperm
-
Seeds
-
the fertilized
egg becomes a zygote that grows into a plant embryo.
-
the endosperm nucleus grows into the endosperm, a tissue containing stored
food that will be used by the growing embryo (most of these storage tissues
are absorbed by the developing embryo before the seed becomes dormant)
-
the mature ovule becomes a seed coat
-
Flowering plants (technically called Magnoliophyta) are divided into two
groups, dicotyledons (Magnoliopsida) and monocotyledons (Liliopsida); each
of these is divided further into additional smaller, technical groups - see
examples
of each group of dicots and
each
of the smaller monocots groups
-
As the zygote grows into the embryo, the first leaves of the young sporophyte
develop and are referred to as
cotyledons
(seed leaves).
-
These fleshy modified leaves store food materials that are used by the
germinating seed (include carbohydrates, proteins, and lipids).
-
The origin of the stored food is provided, at least initially, by the endosperm.
-
There are two groups of flowering plants that are differentiated by the number
of cotyledons that develop in the young embryo: those with one cotyledon
(monocots) and those with two (dicots).
Monocots
(monocotyledons)- corn, lily
-
Dicots (dicotyledons)- bean, oak
-
Comparison
of monocots and dicots
FEATURE MONOCOTS DICOTS
cotyledons 1 2
leaf venation parallel net
woody or herbaceous herbaceous either
vascular bundles in stem scattered arranged in circle
root system fibrous tap
number of floral parts in 3's in 4's or 5's
endosperm in mature seed yes seldom
Other sites of interest:
All about
flowers
Review
of flower parts with definition of terms: from Texas A&M
Review
Glossary
Review of the
life cycles of a flower - 1
Review of the
life cycles of a flower - 2
Review of the
life cycles of a flower - 3
Review of the
life cycles of a flower - 4
Review of the
life cycles of a flower - 5
Pollen
allergy
Seeds of life:
A good review of seeds
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Last revised: 23 Aug 1998 - Reveal