SEED PLANT REPRODUCTION
LABORATORY OBJECTIVES
Upon completion of this laboratory, the student will be able to:
1. Describe the life cycle of the typical flowering plant.
2. Identify and give the functions of the parts of a typical flower.
3. Name and give the characteristics of various types of fruits.
4. Distinguish between the structure and function of male and female pine cones.
5. Recognize and give the functions of the structural parts of seeds.
6. Distinguish between monocot and dicot angiosperms by examination of flowers or fruits.
7. Recognize various modes of pollination by examination of flowers.
8. Recognize various modes of seed dissemination by examination of fruits.
MATERIALS NEEDED
large frozen corn grain thawed
large frozen Lima bean (butterbean) thawed
Small knife
A gladiolus flower and geranium flower from the florist or flower bed
One each of the following fruits
plum or peach
tomato
blackberry (frozen is OK)
string bean (green bean); whole peanut including pod
acorn, walnut, or hickory nut
whole grain (such as corn "seed)
samara (ash or maple "seed")
apple
iodine
razor blade
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PREPARATION
Read the pages 14-15 and in the text.
INTRODUCTION
Some plants, especially the aquatic ones, do not bear cones nor flowers and do not produce seeds. Seaweeds, mosses and
ferns are examples. But, most of the plants you are familiar with have either cones or flowers and DO produce
seeds. Gymnosperms, like pines; and angiosperms, the flowering plants, are the seed bearers.
Reproduction in the seed plants has been profoundly influenced by the requirements necessitated by living on land. For the
most part, swimming sperm are not involved; consequently, water is not required for fertilization. Rather, the wind or some
animal moves the pollen from the male parts to the female. Not only is the sporophyte (2n body) of the plant dominant, but
the gametophyte (1n body) has been reduced to a tiny cluster of cells which is totally dependent upon the sporophyte for its
survival. Additionally, the embryo is surrounded by a layer of nourishing tissue and a protective covering to form the
seed. Since the seed is typically too large to be disseminated by the wind, other methods of dispersal have evolved in the
seed plants.
Angiosperm Reproduction
Reproduction in angiosperms involves special structures called flowers. While the flowers of the various species differ sometimes radically - a "typical" flower is made up of several whorls of parts, all emanating from the receptacle, the swollen
tip of the flower stem. Examine the flower on page 406 in Starr as you read the following description. The outermost whorl
is made up of the sepals. In some flowers the sepals are brightly colored, but in others they are green and serve to protect the
flower before the "bud" opens. Interior to the sepals are the petals. These are often brightly-colored and "showy".
The next whorl of flower parts are the male reproductive organs. These are termed stamens and are formed of a stalk, the
filament, and the pollen-producing portion or anther.
The central portion of the flower is occupied by the female organ. This is termed the pistil and is composed of the swollen
base or ovary, in which the seeds develop, a slender extension of the ovary termed the style, and the sticky tip of the style
(stigma).
Flowers which have all of the above parts are termed perfect flowers. Many flowers lack some organs and are therefore
imperfect. Some imperfect flowers may be of one sex only, others have brightly colored sepals and no petals. Often wind
pollinated flowers have no colorful parts at all! In still other cases, flower parts of the same or different whorls may be
fused. On close inspection the pistil, for example, may prove to be compound, indicating a fusion of several simple pistils.
Angiosperms are divided into two groups, monocots and dicots. Monocot have floral parts in threes or multiples of
three. Since the fruit comes from the mature ovary, and the ovary may be compound, it may have one, three or six
compartments. Dicots have floral parts in fours or fives, or multiples of four or five. Their fruits may have one, four, or five
(or a multiple of four or five) compartments.
The development of fruit begins with the distribution of pollen, the male gametophyte, which formed by meiosis of some
diploid cells in the anthers. Although it is possible for some flowers to pollinate themselves, cross-pollination is generally
the rule. In plants which lack brightly-colored and/or "smelly" flowers, pollen is distributed by the wind. Bright colors,
sweet nectars and strong odors in flowers indicate that their pollen is distributed by insects or other animals.
However it is transferred, when the pollen reaches the stigma of the pistil, it adheres and germinates. The pollen tube grows
down the style to the ovary and eventually reaches the ovule into which two sperm nuclei are discharged.
Meanwhile, within the ovule, meiosis of a megaspore mother cell and subsequent mitotic divisions lead to the development of
a female gametophyte, the tissues of which enclose three special nuclei, and egg nucleus and two polar nuclei.
For an ovule to develop into a seed, an event unique to the angiosperms must occur. This is termed double fertilization. As
in all sexual organisms, the egg fuses with a sperm nucleus to form a diploid (2n) zygote which will grow and differentiate to
form the embryo. At the same time, the remaining sperm nucleus fuses with both polar nuclei and for a triploid (3n)
primary endosperm nucleus. From this nucleus is derived the endosperm, a body composed mostly of starch which
furnishes the nutritional material necessary to sustain the embryo until it germinates and puts its photosynthetic machinery to
work. The seed, then, is composed of the embryo, the endosperm and the seed coat.
All seeds of the angiosperm are retained within the protective confines of the ovary as they develop. The ovary itself grows
larger and thicker and often differentiates specialized tissues to become a fruit. Biologically, a fruit is simply a ripened
ovary (sometimes with other mature floral parts like the receptacle). Fruits protect the seed and/or aid in distributing
them. Biologically, a vegetable is an edible part of a plant NOT associated with the ovary. Students are then often surprised
to find that tomatoes, cucumbers and squash are technically fruits and not vegetables! Page 370 describe the most common
types of fruits.
ACTIVITIES:
B.
Flowers
1. Obtain one daffodil (monocot flower) for dissection. Examine your flower carefully. How can you tell
that it is a monocot? Use the photographs on page 366, 369 and 396 in your text to assist you in identifying the
various
parts of a flower.
a. Carefully remove the sepals (these are colored in the daffodil and are at the base of.flower).
How many are there?
b. Then remove the fused petals.
c. Next, carefully take off the stamens. How many are there? Can you identify the filament and the anther?
d. You are now left with the pistil on the receptacle. You should use a razor blade to
carefully dissect the ovary. Cut across the ovary. How many
compartments to you see inside the ovary? Can you see the ovules which will become the seed inside the
fruit?
e. Are the leaves net-veined or do they run parallel in the leaves?
2. Obtain a pansy (dicot) flower. Remember, dicot flowers have floral parts in fours or fives, or
multiples of four or five.
a. Identify and count the sepals and petals.
b. Identify the remaining floral parts.
c. Are the leaves net-veined or do they run parallel in the leaves?
Answer the follow-up questions and report your work
C.
Fruits
For this activity, you will need the fruits identified in the materials needed section. You will dissect and examine each one,
identify its characteristics and determine what fruit type it is. To assist you, you will access the following web address:
http://arnica.csustan.edu/key/key.html
Read the sections pertaining to seeds and fruits. Especially note section V: Illustrations of various fruits and fruit types; you
are to access the images of examples of each fruit type. Also, from "Other Sites", access: Test Yourself -- Use the Fruit
Key. With this key you can "key out" any fruit to identify the fruit type.
1. Dry fruits are those which are dry at maturity. Included among the various types of dry fruits are:
a. The legume consists of an elongate simple pistil (pistil with one compartment) which splits
open along two seams when dry. Beans and peas are legumes. Remember to use the
aforementioned web site to help you and to give you experience identifying characteristics
and fruit types.
b. Nuts are dry fruits in which special basal leaves termed bracts partially or totally enclose
the ovary. The bracts may form a husk. The ovary wall is hard or woody. Acorns, hickory
nuts, and walnuts are examples.
c. In a grain, the wall of the simple ovary is fused with the single seed within it . Corn,
wheat, rice, grass, etc. are grains.
d. The winged fruits of the maple are called samaras. The wings "helicopter" the single seed
away from the parent plant. The ovary wall is papery thin.
e. The achene is much like a samara, except without the wing. Sunflower "seeds"
are actually sunflower fruits.
f. The capsule splits along several seams to free its seeds. Examples include
milkweed, and cotton.
2. In fleshy fruits, the ovary wall is thick and generally nutritious. Its function is apparently to entice
animals into eating the fruit and its enclosed seeds. The seeds pass through the animal undamaged and
are therefore disseminated some distance from the parent plant (along with a tidy package of natures best
fertilizer). Common fleshy fruits include:
a. The berry is derived from a compound pistil. It is a fleshy fruit containing many seeds (grapes for ex.)
It is surprising to students that tomatoes, cucumbers, melons, and many vegetables are technically berries.
b. The pome, of which apple is an example, is termed an accessory fruit because the bulk of the fruit is not
made of the ovary wall, but of an accessory structure. In the case of the apple, the receptacle over grows
the ovary, which we call the core. So the fleshy part that you eat actually develops from the receptacle of
the flower. Look at the apple from both the longitudinal section (lengthwise down the middle) and the
cross-section. Identify the core (ovary) and the fleshy receptacle. Look at the cross-section and determine
if the apple is a monocot or a dicot. What other fruit is similar to an apple and is a pome?
c. In a drupe, the outer part of the fruit wall is soft and fleshy, and the inner part is hard and
stony. Inside this "pit" is a single seed. The peach, and the plum are examples.
d. An aggregate fruit develops from one flower with many ovaries. Which of your
fruits is an aggregate fruit? Notice that many "fruitlets" sit on one receptacle and share
one set of sepals. (hint this fruit makes good pies)
e. The multiple fruit develops from the ovaries of several flowers borne together on the
same stalk. Pineapple is a multiple fruit.
Answer all follow-up questions and report this exercise.
D.
Seeds
1. The lima bean will be examined as a representative dicot seed. When these seeds are mature, the nutritional
material of the endosperm has been absorbed and incorporated into two thick cotyledons or seed leaves. Hence the
name monocotyledonae, or monocot. When we eat legumes, of which the bean is one, we are consuming mostly
cotyledons. Select a frozen lima bean which you have let soak overnight and carefully separate it into two halves by
slicing the seed coat with your razor blade. In the interior of the seed, and along one edge, you will be able to find
the tiny embryo, complete with its leaves and future stem and root Refer to pages 362, 369, and 401 in text to see
photos of bean and corn seeds and their germination.
2. The grasses are monocots (one seed leaf) and we will use the seed of a large grass, corn, to illustrate the monocot
seed. Thaw out a fairly large frozen corn grain; use a razor blade or sharp knife to cut it in half using a lengthwise cut,
and note the presence of the embryo or "germ". Most of the corn seed is endosperm and when we buy corn meal it
has usually been "degermed". Now add a drop of iodine stain to the cut portion, then blot off the excess, and observe
what happens. Iodine reacts with starch to create a dark blue to black color. It is the endosperm of the corn seed that
becomes blue-black in color. In corn seeds and other monocot seeds, the seed has just one cotyledon (seed leaf).
Answer the follow-up questions and report your work
Please E-mail the completed report by the due date--see
calendar.
SEED PLANT REPRODUCTION
A.
Report Sheet
Name:
Seed Plants
1. What are the differences between the gymnosperms and the angiosperms (see pages 14-15).
B.
Flowers
1. Describe the vein pattern in the leaves of monocots.
2. In the daffodil, how many colored sepals? fused petals? stamens? pistils?
3. Describe the interior of the ovary of the daffodil flower.
4. Describe the vein pattern in the leaves of dicots such as a pansy.
5. In the pansy, how many sepals? petals? stamens? pistils?
C.
Fruits
1. Is the "peanut" a true nut?
If not, what type fruit is it?
2. How are walnut and hickory seed usually dispersed?
4. Look closely at the apex of an apple fruit; you should see how many dried up sepals?
(The petals fell off but the little sepals should still be there.)
5. On this chart give some of the characteristics for each fruit and the fruit type (as
determined from the fruit key--- http://arnica.csustan.edu/key/key.html
FRUIT
plum or peach
tomato
blackberry
bean pod
CHARACTERISTICS
FRUIT TYPE
acorn, walnut, hickory nut
corn
ash or maple fruit
apple
D.
Seeds
1. When the bean seed first germinates, two _______________(seed leaves) will be the first
noticeable leaves; in time the true leaves will grow and the seed leaves will wither and fall
off. (see page 401)
2. What part of the corn seed is rich in starch?