Download Biology 160 Laboratory: Plant Lab

Biology 160 Laboratory: Plant Lab
What obstacles to plants have to overcome for survival on land? What are the relationships that exist
between plants and organisms from other domains and kingdoms?
The movement of plants onto terrestrial surfaces created challenges (selective pressures) that had to be
overcome. Over hundreds of millions of years, plants have successfully radiated into terrestrial
ecosystems due to four major developments. The first major development was an enclosed
reproductive structure called gametangia. This development appeared first in a group of nonvascular
plants called generally called bryophytes (mosses, liverworts and hornworts). These plants are generally
small, low growing, and lacking roots. The second huge evolutionary step was the development of
vascular tissues. Tracheophytes are plants that have vascular tissue to transport water and nutrients
throughout the root and stem system. This development allowed plants to grow vertically and become
large. These plants still have gametangia and have flagellated sperm (must swim in water to fertilize
egg). The third developmental step was the evolution of reproductive structures that moved away from
requiring water. Seed plants produce pollen which can be transported by animals or wind to the egg
which is located inside ovules… fertilize the ovule with pollen and presto – you have a seed! The seed is
multifunctional as it is not only the developing embryo, but it also includes a protective coat and an
internal food source. Seed plants fall into two categories: gymnosperms and angiosperms.
Gymnosperms include conifers (cone producing trees) ancient cycads and ginkgos, these plants produce
their seeds on modified leaves. Angiosperms introduce the fourth major evolutionary development –
the flower. All plants that produce flowers are angiosperms. The flower is a complex structure that
produces both pollen and ovules.
The movement onto land also meant that there would be interactions between plants and other living
organisms. Not only are plants stems, leaves, roots used for food sources (and as a result have evolved
many different forms of defenses) for many creatures, plants also provide habitats for a multitude of
organisms. Relationships exist between plants and animals to help with fertilization, protection and
distribution or dispersion of seeds. There are also relationships between different domains and
kingdoms! Nitrogen fixing bacteria and symbiotic fungi are just two examples of symbiotic relationships
found between plants and other living organisms.
Pre-Lab Questions
1. What benefit do you think gametangia provided the earliest plants?
2. What major development allowed plants to move away from water sources?
3. What major plant development enabled plants to become larger, and why?
4. What is the difference between a seed and a gamete?
Plant Lab Learning Outcomes
Upon completion of this lab you will be able to
1. state the major developmental steps in plant evolution, and
2. describe the form and adaptations of plants
1. Plant Diversity and Evolution
In this activity you will observe representatives from the major groups of land plants and answer
questions. The plant life cycle is different from animal life cycles that we are slightly familiar with.
Understanding the life cycle of plants will help make sense of the different structures that we see in
plants.
The life cycle of plants includes alternating between haploid (n) and diploid (2n) stages. This is called an
alternation of generation cycle. In each generation multicellular forms exist. If the form is diploid that
means that it will produce spores and is aptly called the sporophyte. The sporophyte produces spores
through meiosis. The spores then develop into a haploid multicellular structure called the
gametophyte. The gametophyte produces gametes via mitosis (as it is already a haploid structure).
Fertilization occurs between the gametes and produces the diploid sporophyte again. There is a
generalized plant life cycle diagrammed below. Each different group of plants will have their own small
differences, but the plan remains the same.
1.A. Non-vascular plants (mosses and relatives)
The ancestors to non-vascular plants are green algae. Green algae reproduces by releasing sperm into
water which obviously won’t work on land. To get around this, land plants evolved structures called
gametangia. Gametangia protect gametes during development, however in the non-vascular plants
sperm must still swim to the egg. This limits the development of bryophytes to environments with high
levels of moisture. Combine this with the fact that they have no vascular tissues and nutrients must
diffuse and water must move via osmosis, these non-vascular plants are therefore not only limited to
moist environments, they are also limited as to how large they can be.
Materials:
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slides of moss
chart of moss life cycle
chart of non-vascular plants
compound Microscope & Dissecting Microscope
Procedure:
1.
Observe the chart of non-vascular plants, and living specimens on the back counter.
What is the general size and height of mosses and why?
2. Obtain a slide of a moss sporangium from the slide tray. After you are done, please return it to
the same tray you picked it up from.
Sketch your moss sporangium here:
What is inside the moss sporangium? Which generation do the spores become?
Plants have two types of gametangia: the archegonium and the antheridium. The archegonium is the
gametangia that produces eggs, while the antheridium is the gametangia that produces sperm. In the
case of the non-vascular plants, the gametophyte is the dominant multicellular generation. The sperm
from the antheridium must swim to the archegonium to fertilize the eggs and create the sporophyte.
3. Use your microscope to observe the moss archegonia and antheridia
What are the differences you observe between the two different gametangia?
1.B. Tracheophytes: Seedless Vascular Plants (ferns and relatives)
The Tracheophytes include all vascular plants and are divided into seedless and seed plants. The earliest
plants with vascular tissues are the ferns and their relatives. With vascular tissue, these plants can grow
extremely tall, some over one hundred feet! The vascular tissue includes two different fluid
transporting tissues. Xylem transports water and soil materials dissolved in water throughout the plant.
Phloem transports the products of photosynthesis as well as plant hormones.
Materials:
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chart of fern life cycle
chart of vascular seedless plants
fern specimen (with sori)
Procedure:
1. Observe the fern specimen and the charts of seedless vascular plants and answer the following
questions.
What are the common plants that are in this group?
What is the general size and height of the seedless vascular plants compared to the nonvascular plants?
2.
Examine the underside of a fern frond (leaf – but it’s called a frond). The spots that you see are
called sori – these are fern sporangia (spore forming structures).
Based on your observations of the fern, what do you think the dominant multicellular
generation is in seedless vascular plants?
1.C. Tracheophytes: Vascular Seed Plants (gymnosperms and angiosperms)
The other group of tracheophytes are the vascular seed plants, and are the dominant plant form on land
today. The combined adaptations of vascular tissue, gametangia and seeds allowed them to thrive in an
environment that was becoming warmer and drier. Remember, seeds provide both nutrition and
protection for the developing embryo, and this has proved to be a large reproductive advantage,
resulting in seed plants being the dominant plant form today. Within this dominant group of plants
there are two different reproductive strategies. One is to produce pollen and seeds on cones – these
are the gymnosperms. This strategy requires wind for both fertilization and seed dispersal. The second
group are the angiosperms and these are the flowering plants. The flowering plants have an ovary that
encloses ovules. When fertilized and the ovule becomes a seed, the ovary matures into a fruit. When
you eat an apple… you are eating an ovary, and usually throwing away the developing embryo when you
toss the core away. Similar to flowers, fruits have evolved to attract animals. Animals eat the fruit,
move and deposit the seeds some distance from the parent. Fruits come in all shapes and sizes, from
soft and fleshy like a tomato to hard and dry like a peanut.
Materials:
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chart of life cycle of gymnosperm
chart of life cycle of angiosperm
chart of vascular seed plant diversity
specimens (availability depends on season)
Slide of cross section of plant stem showing vascular tissue
Procedure:
1. Observe the life cycles and charts of vascular seed plants and answer the following questions
List examples of each type of vascular seed plants.
What is the relative size of the plants in this group compared to other plant groups we
have observed in this lab?
2. Obtain a slide of a stem cross-section (it may be either a monocot or dicot stem). Vascular
tissue is arranged differently in angiosperms and gymnosperms. The diagram below shows the
types of tissue in a dicot plant and how that tissue changes in the different parts of a plant.
Dicots are angiosperms that seed leaves (cotyledons) in the seed and monocots only have one
cotyledon. Gymnosperms have more than two and are sometimes classified as polycots.
Cotyledons are difficult to see, so there are other phenotypic characteristics that are used to
distinguish between the two major groups of angiosperms. These are shown in the chart below.
Other characteristic differences are found in the root structure as well the pollen grains.
Monocots typically have a fibrous spreading root system, while dicots generally have a main or
tap root system that penetrates deeper into the soil. Monocot pollen grains have a single pore
or groove, while dicot pollen grains have three holes or grooves on the surface.
Is a palm tree a monocot or dicot?
If you notice a flower that has 15 petals, what else would you need to see or examine to
determine if it is a monocot or dicot?
Why do you think dandelions tend to stay green longer than the grass lawns they are
growing in?
3.
Besides the xylem and phloem which make up the vascular tissue, tracheophytes also have
ground tissue and dermal tissue. The ground tissue contains photosynthetic tissue and the
dermal tissue is the outer protective covering of plants. These tissues are illustrated below.
One critical need for vascular plants is the ability to have flow between cells. Remember, plants
have cell walls, and that would prevent plants from allowing fluids to transfer between them.
The solution to this are small pits called plasmodesmata linking cell walls and allowing fluid to
flow from one cell to the next.
Within the vascular tubes groupings
of plasmodesmata on the ends of the
tubular cells form sieve plates. This
allows products of photosynthesis to
flow from the ground tissues into the
vascular tissue and then through the
phloem, and likewise allows for
water to be transported through
dermal and ground tissue into and
through the xylem.
Looking and thinking about the location of the vascular tissue in the stem of plants, what would
happen if someone cut a slice around the entire circumference of a stem of a small plant or even
the trunk of a tree?
4.
Flower Structure – The diagram below shows the typical structure of a flower. A flower
contains both male and female components and represents the gametophytes of angiosperms.
The flower structure also includes the petals – whose main purpose is to attract and direct
pollinators. Sepals are the protective covering that encloses the flower as it is developing. The
male structures are called stamen and are composed of a filament and the anther. The female
structure is called the carpel and is composed of the stigma, style and ovary. Review the
structures on the typical flower illustrated below.
Why do you think there is such a range of flower types?
Having both male and female reproductive structures could allow for self-pollination… what
would this do to genetic diversity, and how could a plant prevent this?
The sporophyte (2n) is the dominant generational form in seed plants. It actually houses the
gametophytes which are small and reduced in seed plants. You may have guessed it already,
the female gametophyte is inside the ovule and the male gametophyte is inside the anther.
Below is the life cycle of an angiosperm indicating both stages and the location of the
gametophytes.
What do you think the benefit is to having the sporophyte stage house the gametophyte
stage?
Summary question: Describe the major structural adaptations found in land plants and explain
how these adaptations allowed plants to radiate dramatically on dry land.