Lab 1. Plant Diversity Plants are autotrophic organisms

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Section #__________________________
Lab 1. Plant Diversity
Plants are autotrophic organisms with cellulose cells walls and a true nucleus. The
approximately 300,000 species of plants described, run the gamut from simple nonvascular plants such as mosses and liverworts to the highly derived flowering plants such
as most ornamental and crop plant species. The classification of plants is based on a
number of morphological, cellular and molecular criteria and the relationship of the
different diverse groups of plants is constantly being fine tuned as new information
develops and as new scientific advances are applied to plant biology.
The classification of plants got its start with Aristotle (384-322 B.C.) and his pupil
Theophrastus (372-287 B.C.) who first grouped plants into trees, shrubs and herbs.
Gradually, the realization that
obvious vegetative features were 1a)
Animal Kingdom
not the most important in
Plant Kingdom
classifying plants led to natural
Flowering p
classifications schemes, which
lants
Gymnospe
rms
featured sexual reproductive
systems as the fundamental basis
Green alga
e
for plant classification. In
Red algae
the1700s, the Swedish botanist
Carolus Linnaeus classified
organisms into two great
Brown Al
Fungi
gae
kingdoms of life (the plant and
animal kingdoms) and plants
Blue‚Äźgreen algae
were grouped with many
organisms that are no longer
considered plants (figure 1a).
???
Today modern
classification schemes group life
1b)
into three major Domains
(Bacteria, Archaea and Eukarya)
and plants make up one diverse,
but distinctive branch on the tree
of life (figure 1b). Most plant
biology texts still include a
discussion of the groups of
organisms that were historically
included in the plant kingdom
although not now considered as
Figure1. a) Linnaean 2-Kingdom classification system with
members of the plant kingdom.
plants, algae, fungi and cyanobacteria included in one super
These include algae, fungi and
kingdom. b) Modern classification scheme that groups organisms
cyanobacteria, which are all now into three domains and showing plants, fungi, algae and
considered members of their
cyanobacteria as branch tips on a complex tree of life
own distinct and unique
lineages.
Today’s lab will be an introduction to the diversity of plants and other groups that
were historically grouped with the plants.
1) Cyanobacteria (Domain Bacteria)
The Cyanobacteria is an ancient group of photosynthetic prokaryotes with fossil
records dating back 3.5 billion years. They can
occupy extreme habitats and are known for their
ability to fix nitrogen. The cyanobacteria are
ecologically important in binding and enriching soils
and can form toxic blooms in both freshwater and
marine ecosystems. Recently, several species have
been studied as a potential source for medicinally
important compounds.
Observe under the microscope, the specimens of
cyanobacteria available in today’s lab. Look for the
green photosynthetic cells as well as any specialized
cells such as heterocysts or akinetes. Heterocysts
Cyanobacteria with akinete
are round clear cells that are responsible for nitrogen (upper picture) and heterocysts
(bottom picture)
fixation. Akinetes are large cigar shaped cells that
serve as asexual reproductive structures.
Draw and label a cyanobacterium in the space below.
2) Algae (Domain Eukarya, Kingdom Protista)
The Algae is a very diverse heterogeneous group of photosynthetic organisms. They
can be found in both freshwater and marine ecosystems and can play dominant ecological
roles in their communities.
Algae are often separated into
green, red and brown groups
based on their photosynthetic
pigments, which often give them
a distinctive color. The algae is
considered to be an artificial
grouping because, although they share many of the same characteristics, they are also
quite distinct lineages. In fact the green, red and brown algae are no more closely related
to each other than they are to other members in the kingdom Protista.
Observe the specimens of algae on display in lab today. Which species are green, red
and brown algae? What is the range in body construction? Can you find any evidence of
sexual reproductive structures?
3) Fungi (Domain Eukarya; K. Fungi)
The Fungi is the only group in today’s lab that is not photosynthetic. Fungi secrete
enzymes to breakdown organic matter into simpler products, which they then absorb for
their nutrition. They were included in the plant kingdom by earlier classification schemes
because they have cell walls (like plants) and do not move around (like animals).
Ironically, recent evidence from molecular biology indicates that fungi are more closely
related to animal lineages than they are to green plants. Structurally, the fungi are quite
different from
plants in that their
bodies are made up
of many thread-like
filaments called
hyphae. The
mushrooms,
toadstools and bird
cup fungi that we
commonly see are
actually the sexual
reproductive
structures designed
to disseminate spores. The vast majority of the fungal body occurs as hyphae growing
throughout the soil. Fungi are important ecologically as decomposers and are also
important disease causing agents in plants. Fungi can form symbiotic relationships with
the roots of plants, which greatly enhances a plant’s ability to harvest both water and
nutrients from the soil. These symbiotic fungi are called mycorrhizae, which literally
translates into “fungus root”
.
Observe the various fungal fruiting bodies on display in lab. Where are the spore
produced in these reproductive structures? Tease apart a small piece of a mushroom in
a drop of water on a glass slide. Place a coverslip over specimen and observe under the
scope. Can you distinguish individual hyphae?
Use the space below to record your observations and sketches of fungi.
4) Lichens – symbiosis between fungus and algae
Lichens are formed from the symbiosis between a fungus and an alga. A symbiosis
refers the intimate association of two unrelated organisms often to their mutual benefit.
Symbioses are prevalent
throughout nature and lichens
were the first true symbioses
described. In a lichen
symbiosis the fugal partner
makes up the bulk of the body
whereas the alga provides
nutrition through
photosynthesis. Lichens take
on a great variety of shapes and
colors and are found in just
about every habitat.
Look at the lichens on
display today in lab. Can you
distinguish different body
forms (crustose – crusts,
thallose – ribbon like, fruticose
- branching)? Look at a
prepared slide of a lichen body. Can you determine the algae and fungal components?
Draw a cross section of a lichen in the space below.
5) Green Plants (Domain Eukarya, Kingdom Plantae)
The green plants are photosynthetic and
multi-cellular. They are distinguished from
other photosynthetic groups (i.e. the algae) by
producing embryos. Plants are very diverse in
shape, size, color and physiology. They have
tremendous ecological and cultural
importance because they are the source of
oxygen, food, fiber, dyes, drugs and poisons.
There are currently 10 different phyla of
plants recognized, which are separated in part
on their body construction and reproductive
characteristics. The simplest plants, called
Moss Life Cycle
bryophytes, do not produce seed and have no root or specialized tissues (vascular
tissue) for the transport of water and sugars. Consequently these species must absorb
water with their whole bodies and are tied to moist habitats. Mosses and liverworts
are both example of bryophytes.
Ferns and related plants do produce roots and vascular tissue. They, however,
disseminate via spores and do not produce seed. Unlike seed plants, which deliver
their sperm nuclei in pollen, ferns still
Fern Life Cycle
retain flagellated sperm that must
swim through a film of water to
complete fertilization. Sexual
reproduction in both ferns and
bryophytes is tied to water because of
this critical step in their life history. It
is not surprising that the highest
diversity of these seedless plants
occurs in moist habitats
There are two general groups of
seed bearing plants: the gymnosperms
and the angiosperms. The seed habit
involved both the development of a
structure to protect the new embryo
(the seed) but also the advancement of
pollen and ovules. These reproductive
advancements led to the successful
establishment in drier habitats, which
are now dominated by seed bearing
species. The gymnosperms include common species such
as firs, pines, redwood and gingko. The angiosperms, the
most diverse of the plant phyla, include all the flowering
plants. The diversity of all these plant groups is on display
in the laboratory today.
6) Species Concept
Individual plants within a population, like most other organisms, can show
significant variation in size, color and chemical composition. Because many plant
species are of particular importance to humans as sources
of food, fiber and medicines, humans have been selecting
and breeding individual plants for centuries to accentuate
their most desirable characteristics. Consequently,
humans have created many different races and cultivars of
plant species through artificial selection. These cultivars
may have been selected for superior yield, color, flower
color, disease resistance among many other
characteristics.
In today’s lab we have two agriculturally important
plants, which have several cultivars: Brassica oleracea –
cole crops and Triticum aestivum -wheat. Note the
differences between the cultivars. Can you tell for which
characteristics each cultivar has been bred?
Use the table below to indicate the selected characteristic(s) each cultivar on
display.
Cultivar
Wheat
Brassica
Selected Characteristic (s)
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