Download Flower Structure

BIOLOGY 103 – LABORATORY EXERCISE
5
Name:
Day & Time of Assigned Lab:
Seat Number:
Flower Structure
Introduction:
The Angiosperms, or flowering plants, represent the most successful and most
diverse Division within the Plant Kingdom. The estimated number of species of
flowering plants is in excess of 250,000 named species; about 90% of all plants
are angiosperms. It is not surprising that the plants that we are most familiar with,
and most dependent on are flowering plants. Flowers are reproductive structures.
It is interesting that to show a sentiment of love we send our intended a bunch of
plant sexual organs. Flowers evolved about 125 million years ago. The early
flowers were probably beetle pollinated as beetles unintentionally transferred
pollen from flower to flower as they ate pollen. Following this discovery the
number of species of flowering plant, and insects that pollinate flowers, such as
butterflies, rapidly increased.
Fertilization of female ovules by male sperm cells carried inside pollen, leads to
the development of another structure unique to the angiosperms; fruit, the
subject of next weeks lab.
Learning Outcomes:
After completing this laboratory, you should be able to:
1. Learn terminology used to describe floral structures of plants
2. Making careful observations and drawings of floral structures
3. Review the differences between monocot and dicot flowers
4. Use dissecting microscopes to examine plant ovaries
5. Review different modes of pollination
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Flowering Plants
Not all plants have flowers, and there was a time in history when no plants at all
had flowers. Conifers for example have cones, which produce pollen or seeds,
they function as structures for sexual reproduction but they are not flowers.
About 125 million years ago, primitive flowers appeared in the fossil record. In
addition to producing pollen and eggs, the sex cells of plants, they had
adaptations which encouraged other species to carry pollen from the flowers of
one plant to another of the same species. Originally beetles were attracted to eat
the pollen and inadvertently transferred some of the pollen they had failed to eat
to other flowers of the same species, thus achieving pollination. As time
progressed flowering plants formed numerous and intricate relationships with a
variety of insects including moths, butterflies, flies, and bees, that drove
diversification of both plants and insects. In addition to flowers, flowering plants,
(Angiosperms) had one more trick up their sleeves; fruit. Following fertilization
the ovules develop into seeds, and the ovary grows into a structure with
adaptations to facilitate seed dispersal. Various contrivances have evolved,
including dehiscent seed pods that rupture scattering seeds around the parent
plant, feather-like plumes to catch air currents, barbs and hooks to snag passing
hairy beasts, or edible, juicy, and seed packed fruit, eaten and dispersed by a
variety of animals. Today flowering plants dominate the world.
Floral Structure
Most simple flowers consist of four basic whorls of modified leaves: sepals,
petals, stamens that produce pollen, and the innermost carpel, the female
reproductive organs consisting of the ovary and the stigma, the site of pollination.
Following fertilization (an event occurring after pollination) ovules form seeds,
while the ovary develops into some form of fruiting structure.
Fusion of Floral Parts
While some flowers have free petals, many familiar flowers have their petals
partially fused to form a tube. The term corolla is used to refer collectively to the
petals of a flower be they free or fused.
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Activity 1: Virtual Herbarium Flower Anatomy
Introduction- We will make use of the online illustrated Herbarium to help to
learn and visualize key terms used to describe plant floral structures.
http://www.vplants.org/plants/glossary/
FLORAL
ARRANGEMENT
DESCRIPTION
Inflorescence
catkin
corymb
Panicle
Head/Capitulum
Raceme
Umbel
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Floral Symmetry
Simple flowers are symmetrical in all directions so that if you draw a line through
the flower in any direction one side of the line is a mirror image of the other side,
much like a pie. Such flowers are radially symmetrical; lillies and sunflowers and
California poppies are examples of this form of symmetry, and are also termed
actinomorphic (actin = ray) flowers. Other flowers, often regarded as more
advanced in their design, have petals which are dissimilar to each other in
structure, and are arranged so that it is only possible to draw one line through the
flower (often from top to bottom) and still have two mirror images. Such blooms
have bilateral symmetry, and are termed zygomorphic flowers. Plant families
with zygomorphic flowers include the Orchidaceae, Lamiaceae (mints),
Fabaceae (Beans), and Scrophulariaceae (Figworts)
SYMMETRY
DESCRIPTION
actinomorphic
zygomorphic
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EXAMPLE
Actinomorphic Flowers
Zygomorphic Flowers
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.
FLORAL
STRUCTURE
DESCRIPTION
Sepal
Petal
Stamen
Stigma
Pistil
Anther
Ovary
Corolla
Calyx
Style
Filament
Receptacle
Bract
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Ovary Position
The position of the ovary relative to the petals is an important characteristic often
distinguishing different families of flowering plants. In epigynous flowers the
ovary is inferior, or below where the petals attach. In hypogynous flowers, the
ovary is above, or superior with respect to the petals. In perigynous flowers a
hypanthium, which consists of the fused bases of the sepals, the petals, and the
stamens is present, with the sepal and petal lobes separating at the mid-position
of the ovary.
OVARY
DESCRIPTION
POSITION
Epigynous
Perigynous
Hypogynous
Superior
Inferior
Locule
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PLANT TYPES
DESCRIPTION
Moneocious
Dioecious
Staminate
Flowers
Pistilate flowers
Unisexual
Procedure: Use the definitions above to label the
following diagram
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Composite Flowers.
Members of the Sunflower family, the Asteraceae have a dense flower head
(also called a capitulum) which consists of either disk florets, ray florets, or both.
What appear to be the ‘petals’ radiating out from the edge of the flower are
themselves miniature flowers. The individual florets lack peduncles and all attach
to a shared receptacle. Many bracts form an involucre under the capitulum. Thes
are termed phyllaries, or involucral bacts, and these bear the spines of thistles.
ASTERACEAE
FLOWERS
DESCRIPTION
Ray Floret
Disk Floret
Pappus
involucre
recepticle
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Activity 2 : Drawing Specimens
In this activity you will examine and draw some flowers. Using the
terms you defined in Activity 1 label your diagrams, note down the
species name using both the Common name and the latin name
using Genus species format. Also record the family name. Provide
drawings of each specimen in the spaces provided for each question.
For each drawing provide a scale.
Monocotyledon flower
Common Name
Family
Genus
species
Scale __________
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Dicotyledon Flower
Common Name
Family
Genus
species
Scale __________
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Composite Flower
Common Name
Family
Genus
species
Scale __________
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Activity 3: Monocots v Dicots
Referring to your drawings in Activity 2 complete the following table.
Monocotyledon
Dicotyledon
Number of sepals
Number of petals
Number of stamen
Activity 4: Dissecting Scope
In this activity we will make use of the dissecting microscope to
examine characteristics of our representative plant specimens.
Ovary
Procedure: Obtain a flower and locate the ovary. Determine the ovary
position, then using the razor blade make a cut across the ovary
(transverse section. The ovary may contain a number of internal
chambers or locules. Make cross sections of two more ovaries and
record your observations in the table below.
Inside the ovary are the ovules. These correspond to the eggs of
animals and, following fertilization, these will develop into the seeds.
The ovary will play some part in the formation of the fruit.
Genus
Number of Locules
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Activity 5: Pollination
Questions
1.a. List three different ways that pollen could get from the anther to the female
part (stigma) of a flower.
When the pollen reaches the stigma, it germinates into a pollen tube that grows
down the style to the ovary and ovules. Concurrently, two sperm cells are
formed by mitosis. The sperm cells move down the pollen tube to the ovule,
fertilize the egg and form the endosperm (food) for the new plant.
1.b. How could a plant prevent its sperm from fertilizing its own eggs?
1.c. What advantage is there to preventing self-fertilization?
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