Download Lab 08: Plant Diversity

Biol 160: Lab 8
Name: __________________________
Exploring Plant Diversity
OBJECTIVES
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Become familiar with the diversity of plants.
Observe fruits, how they are formed and how they are dispersed.
Observe conifer seed and pollen cones and pollen.
General Procedures
Read the following information to help you understand the nature of plant diversity. Then start
the flowers to fruits lab set up in stations around the room.
Part 1: Plant Diversity
A) Nonvascular plants “Bryophytes” (mosses)
The Bryophytes, or nonvascular plants, represent the earliest group of terrestrial plants. The most
familiar species in this group are the mosses. They do not have vascular tissue (some mosses
have simple tubular structures). Vascular tissues serve two main purposes in plants: 1) as a
transport system (tubes) for moving water, sugars and minerals throughout the plant, and 2) it
provides structural support. Because Bryophytes do not have vascular
tissue, they do not have true leaves, stems and roots. The lack of vascular
tissue limits the Bryophytes morphologically and ecologically. Without
vascular tissue to transport water, a Bryophyte must be low lying or matlike, so that all of its body can be in contact with the moist environment,
and also be fairly thin in structure (only a few cells thick). Since water is
moving via osmosis through cells (a relatively slow process), the plant
cannot be very thick. Most Bryophytes need to live in moist environments,
although they have many adaptations for living in dryer environments.
Additionally, the lack of vascular tissue means that Bryophytes do not have
the structural support to grow tall. Since the Bryophytes are all fairly short
plants, this leads to strong competition for sunlight and space.
B) Seedless vascular plants (ferns & horsetails)
Vascular tissue is composed of cells joined into tubes transporting water and nutrients
throughout the plant body. Xylem tissue is the water-transport tissue
carrying water and minerals from the roots up the plant body, and
phloem tissue is the food-transport tissue carrying phloem sap (food
nutrients) from food sources (leaves or food storage organs) to food
sinks (growing non-photosynthetic structures or food storage organs).
The bodies of the vascular plants are divided into an aerial shoot
system (stems, leaves, and reproductive structures), and an
underground root system. True leaves, stems, and roots all contain true
vascular transport tissue.
The development of vascular tissue allowed the vascular plants to
grow much taller than the non-vascular plants for two reasons: 1)
plants with vascular tissue no longer had to have most of their body in
contact with a moist environment, and 2) vascular tissue provided
structural strength within stems. Growing taller meant that they could intercept the light before
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Biol 160: Lab 8
low-growing plants could. This allowed the seedless vascular plants to become dominant during
the Carboniferous period. The most familiar seedless vascular plants are ferns. Both seedless
vascular plants and Bryophytes use spores to disperse (move the next generation further away
from the parent generation). Ferns have special spore producing structures, called sori, that are
typically visible underneath their leaves, which often look like rows of brown, green or whitish
dots.
C) Seed bearing vascular plants: Gymnosperms
Seed bearing vascular plants developed two structures that helped this
group be successful in dryer environments: 1) pollen, and 2) the seed.
These structures are found in both gymnosperms and angiosperms.
Pollen is the male gametophyte (which will produce the sperm),
wrapped in a protective coating. Pollen allowed for the dispersal of the
male gamete (sperm) over longer distances and without the need for
water. In Bryophytes and seedless vascular plants the sperm must swim
to the egg, so they require a moist environment. In seed bearing
vascular plants, the zygote develops into an embryo within the ovary.
The embryo, its food supply and a seed coat are packaged together
by the plant as a seed. The seed can be released from the plant
to germinate in appropriate environmental conditions. Seeds provide
several reproductive advantages for these plants. First, they can
increase dispersal of the next diploid generation as the seed can be carried by the wind, water,
or another organism. Second, the food supply gives the developing embryo an energy boost
early in its life. With this energy boost, the embryo will produce leaves that allow for
photosynthesis and metabolic independence. Third, the seed coat provides protection for the
embryo while it waits to germinate until conditions are suitable.
The most familiar gymnosperms are members of the conifer, or “cone-bearing”, group
which includes pine, fir, cedar and spruce trees. Gymnosperm means “naked seed”. The seeds
of gymnosperms are not enclosed. In conifers they develop on the scales of the cone.
Gymnosperms can be quite tall and can be found both in moist and dry environments. Almost
all the conifers are “evergreen”, holding their needle-like or scale-like leaves year round. This
allows for growth year round, although this growth is reduced in the seasons of least sunlight.
The reduced leaves are adapted to colder, drier climates with a thick cuticle (waxy layer that
prevents water loss). Commercially, most of our lumber and paper pulp comes from the wood
of conifers.
D) Seed bearing vascular plants: Angiosperms
The angiosperms are recognized as the “flowering
plants.” In addition to pollen and seeds, the
angiosperms developed two other distinctive traits: 1)
flowers, and 2) fruits. Flowers are made up of four
main parts: 1) sepals, 2) petals, 3) stamen, and 4)
carpels. Many flowers have
been modified to attract insect, bird or mammal
pollinators. Modifications include bright colors, scents
or nectar rewards.
Angiosperm means “container seed”, and the
seeds are found within fruit. Fruit is a development of
the ovary tissue that surrounds the seed. Fruit evolved
to aid in dispersal of the seeds. We will be looking at types of fruits and dispersal mechanisms in
Part II of this lab.
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Biol 160: Lab 8
Part 2: Flowers, Fruits and Cones Lab
There will be several demonstration stations set up around the room. Go to each station and
examine the specimens. For each specimen answer the questions indicated at the station.
Make whatever drawings and notes necessary for you to remember the material and to be
able to answer the questions.
Station 1: Flowers to Fruits
This area contains a variety of specimens demonstrating the transition from flower to fruit.
After finishing with this station you should be familiar with:
• Identifying floral structures (sepals, petals, stamens, ovary, style, stigma) on developing and
mature fruits.
• Tell the difference between an inferior or superior ovary.
Station 2 A and B: Fruit Type & Dispersal
This area contains a variety of fruits and is divided into two parts: fruit type and fruit dispersal.
After finishing with this station you should be familiar with:
• Identifying different types of fruit.
• Determining how a fruit may be dispersed and describing the structural adaptations that
support your determination.
Station 3: Gymnosperm Reproduction
This area contains seed cones and pollen (staminate) cones of various conifer species.
After finishing with this station you should be familiar with:
• Determining the difference between a mature seed cone and a mature pollen cone.
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