Download Lab #9: Plant Diversity

Lab #9: Plant Diversity
Objectives:
• Become familiar with the diversity of plants.
• Understand how each group of plants is defined by one or more evolved traits.
• Become familiar with the alternation of generations.
• Describe the life cycle of a typical fern and a typical angiosperm; distinguish between the
gametophyte and sporophyte generations.
• Understand the changes in the alternation of generation that occurred over time, moving from
the bryophytes to the vascular plants.
• Observe the parts of the flower and their variations
• Observe fruits, how they are formed and how they are dispersed
• Observe conifer seed and pollen cones and pollen
General Procedures
This lab will be broken into three parts:
Part 1: Plant diversity scavenger hunt & comparison of plant diversity
Part 2: Flowers, fruits and cones lab
Part 3: Group activities reviewing alternation of generations and major plant traits.
Part 1: The assignment - Plant diversity scavenger hunt at home
In order to help you become more familiar with common members of the major plant groups you
will be collecting specimens from each group. You will later use these specimens to help you visualize
how the alternation of generations have changed between the different plant groups. While collecting,
pay attention to the overall size of the plants you are collecting from, and in what environment type you
found them. Each lab group of 4-5 people should collect one specimen from each of the following
groups (you may decide how to divide and conquer):
• Bryophytes or non-vascular plants (mosses)
• Seedless vascular plants (ferns and horsetail)
• Gymnosperms (conifers or cone-bearing trees)
• Angiosperms (flowering plants)
On the computer or through reference books, find out more about the plants that you found. Include the
name of the plant, the major plant group that it belongs to, where it normally grows (and where you
found it), how big the plant grows, and any other interesting information that you find about it. Since
this is the fall, you may not be able to find awesome specimens of each type. You can go to grocery and
plant stores if you can’t find anything around town and just take a picture of it. Bring the picture in with
your description.
**On Monday, your lab group of four-five people will present your findings to the class. Be prepared to
share your specimen, the information you found out about it on the web or in books, the resource that
you used to find this information, and whether you think this resource was reliable. Feel free to e-mail
me pictures of your plants that you find in your reference material, and I will have them on hand for you
to show to the class if you would like a few points of extra credit.
Information to help you in your search:
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 serves 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 mat-like, 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 nonvascular 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 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.
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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.
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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