Lab 5 Manual - Flowers & Fruits PDF

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Lab 5 Manual...

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BIO SCI 152 LABORATORY 5 (SPRING 2021): FLOWERS, FRUITS, AND PLANT REPRODUCTION OBJECTIVES OF LABORATORY: 1. Become familiar with flower structure and functions of the flower parts 2. Learn to relate flower and fruit structure to the angiosperm life cycle 3. Gain an understanding of pollen dispersal and seed dispersal and the plant adaptations associated with different dispersal vectors MAKE SURE YOU VIEW THE INTRODUCTION VIDEO BEFORE COMING TO CLASS LINK: https://youtu.be/iaa74-Mipzg (today’s quiz has questions relating to that video) Angiosperms (flowering plants) are characterized by two unique reproductive structures, flowers and fruits. Within the angiosperms, there are two dominant groups, the monocots and the eudicots. In this exercise, you will be studying the angiosperm life cycle and the characteristics of flowers and fruits in both groups. In this lab, you will be introduced to many new terms. Because flower and fruit structures are highly variable, precise terminology is especially important to allow for consistent reference to structures with quite different appearances but from a common developmental origin. Part 1: Inflorescences, Floral Parts. Video Link: https://youtu.be/g5g3M6UsSqM I. INFLORESCENCES Flowers are attached to plants in various distinct arrangements, which are important for differentiating and identifying different plant types. If a plant has only one flower (like a tulip), the flower is solitary and is attached to the stem by a stalk, the peduncle. A solitary flower develops from a single shoot tip. Flowers may occur in clusters of flowers or inflorescences. In this case, the stalk to the cluster of flowers is called the peduncle and the stalks of each individual flower is called a pedicel. Inflorescences are categorized by their pattern of growth (determinate or indeterminate), their overall shape (elongate, flat-topped, etc.), and whether individual flowers are stalked or stalk-less. Below are some common types of inflorescences.

spike

corym

raceme

simple umbel

panicle

compound umbel

cyme

head

1) Examine the flowering plants 1-4 shown in the video clips and photographs. Determine the type of each inflorescence by referring to the diagram of inflorescence types above and insert the plant name and inflorescence type in the table below.

1

Number

Name of plant

Inflorescence Type

1 2 3 4 II. FLOWER TERMINOLOGY AND STRUCTURE Floral parts An angiosperms flower’s basic design has four whorls of floral organs. In reality, there is tremendous diversity in this basic plan. The four whorls consist of the following: a) The outermost floral appendages are sepals (collectively, the calyx) and are usually green in appearance but can be colored (e.g. lily flower). If green, they can be mistaken for leaves. b) Next inward are the petals (collectively, the corolla). Petals are usually brightly colored to attract pollinators. c) Next inside the petals, are the stamens (collectively, the androecium), consisting of a filament (the stalk) and an anther. The anther contains the microsporangia in which pollen cells are produced by meiosis. Stamens carry out the “male” function in the flower. d) Lastly, in the center, is the gynoecium, the “female” part of the flower consisting of carpels. A carpel contains a terminal stigma that is receptive to pollen, an elongated style through which the pollen tubes will grow, and an expanded basal ovary containing ovules. Ovules contain the megasporangia in which the female gametophyte develops; they are attached to the ovary wall by a stalk (the funiculus). The ovary will mature into the fruit, the ovule into seeds. 2)

A diagram of a typical angiosperm flower is provided below. Place the correct letter next to the label in the textbox to the right (see example for petal). e.g. Petal - a sepal calyx corolla stamen anther filament carpel stigma style ovary

Carpels are modified ovule-bearing leaves (sporophylls) that are folded and fused to enclose the ovules (fused carpels are sometimes called pistils). This feature of enclosing the ovules is the basis of the term “angiosperm” (which translates into seed vessel”). 2

3) What are the advantages to this enclosed seed for plant survival?

Flowers possessing all four whorls (see floral parts above) are called complete flowers. If one or more of the whorls is absent, then the flower is incomplete. If both sexes are present in a flower, it is bisexual; if one sex is absent, the flower is unisexual. A plant species that possesses both male and female flowers on the same individual plant is termed a monoecious plant, while a species in which male and female flowers occur on different individual plants is a dioecious plant. Note: The terms monoecious and dioecious apply to an individual plant, not a flower. 4)

Examine the plants shown in the video materials. For each, check in the columns which accurately describe the flowers as complete/incomplete, bisexual/unisexual and monoecious/dioecious. Plant Name

Complete

Bisexual

Incomplete

Unisexual

Monoecious

Dioecious

Hibiscus rosa-sinensis Begonia ‘Richmondensis’ Pennisetum nigra ? 5)

Check in with your TA for a Discussion question:

Floral symmetry Flowers have a characteristic symmetry when viewed from above, due mainly to the shape of the calyx and corolla. Flowers with one plane of symmetry (i.e. one mirror-image plane) are called bilateral, zygomorphic, or irregular. Those with two planes of symmetry are isobilateral, and those with three or more planes of symmetry are radial, actinomorphic, or regular.

Bilateral

Isobilateral

3

Radial

6)

Refer to the diagram of floral symmetry types above. Observe the plants shown in the video and determine their floral symmetry, inserting plant name and symmetry in the table below.

Plant Name

III.

Symmetry

ANGIOSPERM LIFE CYCLE

Flowers and fruits are the reproductive structures of the angiosperms. To appreciate plant reproduction, it is important to develop an understanding of the life cycle. The flowering plant life cycle is characterized by a small, reduced haploid gametophyte generation and a much larger dominant diploid sporophyte generation. The angiosperm sporophyte is the familiar “plant” with roots, stems, and leaves. Angiosperms have distinct male and female gametophytes that result from meiosis in specialized cells within the sporophyte plant, followed by several mitotic cell division events. The male gametophyte (microgametophyte) is called the pollen grain, and the female gametophyte (megagametophyte) is called the embryo sac. Flowers are the sporophyte organs that produce these gametophytes. Note: Syngamy is also called fertilization.

Below is a diagram of the Angiosperm life cycle. In the textbox below, insert the correct labels missing from the diagram

Blue box – Red box – Green oval -

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Male gametophyte development: In angiosperms, both gametophyte plants are structurally reduced in comparison to other plant groups. The male gametophyte begins its development in the anther. In the anther, diploid cells undergo meiosis to form masses of haploid microspores. These microspores occur in tetrads (groups of four). Nourished by the surrounding layer of cells, each microspore will develop into a pollen grain, containing the immature male gametophyte plant. The outer wall of angiosperm pollen is made up of sporopollenin, one of the most chemically inert biological polymers on the planet. It is chemically very stable and is usually well preserved in soils and sediments. Each microspore divides to form two cells, the tube cell and the generative cell, both within the original spore wall. The generative cell is mostly a nucleus that will divide to produce two sperm, the male gametes. The tube cell is a nucleus surrounded by cytoplasm and will produce the pollen tube, after the pollen has landed on a receptive stigma surface. This simple arrangement of cells comprises the entire mature male gametophyte plant! 6)

Observe the scanning electron micrographs of angiosperm pollen. What is a possible function of the highly sculptured outer wall of a pollen grain?

7)

Examine the images in the video of the prepared slide of a mature lily anther cross section showing low power then higher power magnification. Notice the two large chambers on either side of the anther. These are the pollen sacs where microspores arise by meiosis. Each microspore develops into a pollen grain. Examine these microspores under higher power. On the drawing of the anther cross-section below, label the filament, pollen sacs, and microspores.

5

8) View the images of pollen in the anther. On the drawing below, label the pollen wall, the tube nucleus which is larger and the and the smaller generative nucleus on the side of the pollen on the diagram of a pollen grain in cross section to the right of the box.

9)

Examine the microscope image of a pollen grain germinating. Sketch and label your observations below, if you wish.

10) Is the germinated pollen with its pollen tube gametophyte or sporophyte tissue?

Female gametophyte development The ovule of an angiosperm contains the megasporangium is surrounded by two layers of cells called the integuments. An opening in the integuments, the micropyle, provides access to the megasporangium inside. In the ovule, diploid cells within the megasporangium undergo meiosis to produce four haploid megaspores. Usually only one of the four megaspores will continue to develop into the embryo sac, the mature female gametophyte plant. At maturity, the female gametophyte will usually have seven cells. Most important are the egg cell (the female gamete situated near the micropyle) and the central cell (containing two polar nuclei). The egg cell is usually surrounded by two synergids (these three cells collectively are referred to as the egg apparatus). The three cells opposite the egg apparatus referred to as the antipodal cells. 11) Examine the image of a prepared slide of a lily ovary cross section using low power. The three chambers within the ovary contain ovules. Examine the video images showing the ovules under higher power. 12)

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13) On the drawing of the mature female gametophyte to the right, label: egg cell, synergids, polar nuclei, antipodal cells, central cell, micropyle, and integuments.

14) Label the following structures in the diagram of the angiosperm life cycle below: Using your lecture notes and lab materials, make sure you can lab the following on the diagram below: carpel, stigma, megaspore mother cell, megaspores (three usually abort), female gametophyte (megagametophyte or embryo sac), anther, microspores, germinating pollen grain, male gametophyte (microgametophyte), pollen tube, egg, endosperm, embryo, seed. Indicate which stage is haploid (N) and which stage is diploid (2N) and where meiosis occurs in the life cycle. For the six textboxes on the diagram, choose and insert which of the labels above are correct for those.

(a process)

(a process) 7

Part 2: Flower Dissection, Pollination, Fruits. Video Link: https://youtu.be/hyQAKErxsZg IV. FLOWER STRUCTURE OF MONOCOTS AND EUDICOTS See the dissection videos and pictures on the video of the monocot and dicot flower. These were done using a dissection procedure provided below, identify all the structures you can which are indicated and answer all relevant questions on the next two pages. Make rough sketches of the dissections as you watch the video. Pause the video whenever you need to get all the information. Dissection Procedure: Before dissecting a flower, observe the type of inflorescence from which your flowers come. A dissection microscope is an important aid in your dissection below. a. Obtain an entire open or partially open flower by breaking it off at its attachment point to the stem. b. The outermost structures on the flower are the sepals. In monocots, the sepals may be green or colorful like the petals. In eudicots, they are usually green. Identify the colorful petals to the inside of the sepals. c. Use a razor blade to cut off, one at a time, the sepals and petals at their point of attachment to the flower. The remaining structures left are the true reproductive structures. d. Locate the stamens surrounding the carpel. Each stamen consists of a long slender filament and an anther. Draw a stamen in the space provided and label the filament and anther. e. Pollen (the male gametophyte) is produced in the anther. Remove the stamens. Slice across the anther to expose the pollen. Draw the cross section of the anther in the space provided. f. Centermost in the flower is the carpel or carpels (also known as pistil). It consists of the ovary toward the base of the flower, the style, and the stigma. Draw this structure and label the ovary, style and stigma. g. The stigma is the receptive part of the carpel, where the pollen will land and germinate. Look at the stigma under the microscope and observe its morphology. h. Use a razor blade to cut a very thin cross section from the center of the ovary. Place the section flat and examine under the microscope. Note the small, whitish ovules (immature seeds) within the ovary. Draw this section in the space provided on the following pages, labeling the ovary and ovules. For each line below, click your cursor after the colon : and type in your answers, and use the text boxes. 15)

MONOCOT FLOWER DISSECTION For more detailed images and video, also see here

a. Name of species (Insert from lab video provided): b. Inflorescence type: c. Floral symmetry : d. # of sepals: e. # of petals: f.

# of anthers: 8

g. When you slice across ovary, what do you find inside?

h. Flower type (highlight all that apply): complete, incomplete, bisexual, unisexual i.

Which structure contains the female gametophyte with egg?

j.

In eudicots, floral parts typically occur in multiples of 2 (4) or 5, while in monocots, parts are in multiples of 3. How many do you see and in which parts? Does the flower follow this rule?

16) EUDICOT FLOWER DISSECTION For additional video of a different eudicot flower dissection, see here a. Name of species: b. Inflorescence type: c. Floral symmetry : d. # of sepals: e. # of petals: f. # of anthers: g. When you slice across the ovary, what do you find inside?

h. Flower type (highlight all that apply): complete, incomplete, unisexual, bisexual i. Which structure contains the female gametophyte with egg? j. In eudicots, floral parts typically occur in multiples of 2 (4) or 5, while in monocots, parts are in multiples of 3. How many do you see and in which parts? Does the flowers follow this rule?

Scanning electron micrograph showing germinating pollen on a style. Photo: Rebecca Flanagan.

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V. POLLINATION, FERTILIZATION AND EMBRYOGENESIS Pollination is the transfer of pollen grains from the stamen to the stigma. In angiosperms, this transfer can be accomplished by wind, by water, or by pollinator organisms such as insects, birds, mammals, frogs, etc. The structure of the flower is typically fashioned to maximize pollination efficiency. Some general observations are that bilateral flowers are commonly pollinated by insects that use the fused flattened petals as a “landing platform” for their bodies. Red-colored flowers with long, tubular corollas and copious nectar indicate bird pollination. 17) Why do you think red coloration works to attract birds and butterflies but not other pollinators?

18)

“Beetle pollinated flowers” are often spicy-scented and have inferior ovaries (an ovary which is situated or “buried” below other floral organs, such as petals and sepals). What might be the advantage of these features (hint: beetles eat flower parts)?

19)

Check in with your TA for a Discussion question and answer below:

20) Study the four flowers shown in the video and photos in the lab materials. Based on the lecture materials and what you know about pollinators, list what you think is the most likely pollinator for each of the plant flower structures presented? (if you get stuck, there is a key at the end of this document which might help) Plant name

Pollinator

Once pollen lands on a receptive stigma, the grains germinate and the pollen tube grows into the style through the tissue of the style. The pollen tube eventually reaches the micropyle and enters the embryo sac. The tube bursts and releases the two sperm nuclei. One sperm fuses with the egg to form a zygote. The other fuses with the polar nuclei to form the triploid endosperm nucleus. This double fusion of sperm has been referred to as “double fertilization”, a feature characteristic of angiosperms (the term is a misnomer because only one sperm fertilizes the egg). The zygote divides mitotically to produce a miniature plant, the embryo. During embryonic 10

development, the endosperm nucleus also undergoes repeated divisions to form endosperm, a tissue unique to the angiosperms. 21) Are embryo cells haploid or diploid?

22)

What is the purpose of the endosperm? What advantages does this confer?

Eventually the embryo will stop developing, become dormant, and the integuments will become hard and impervious. The fully-ripened and mature ovule is the seed. The integuments form the seed coat and enclose the dormant embryo and endosperm. The presence of two seed coat layers is found only in the angiosperms. When mature, seeds eventually detach from the ovary wall, sometimes aiding in their dispersal. 23)

24)

Observe the image of the Capsella seeds on the video. Can you tell whether the embryo will become a monocot or eudicot? How do you know?

Sketch your observations of an angiosperm embryo here, if you wish.

VI. FRUITS AND SEEDS During maturation of the ovules into seeds, the ovary wall undergoes many changes and becomes a protective structure called the fruit . Because only angiosperms have carpels, the ovary and resultant fruit are structures unique to this group. Fruits are categorized by their texture (fleshy or dry), number of carpels, and whether they open up to release seeds (dehiscent) or not (indehiscent). In the case of many fleshy fruits, the outer layers of the fruit are called the pericarp. Fruits are important not only for their function in reproduction, but for their role in plant dispersal. Some plants have evolved seeds that use wind as the mechanism for dispersal. Wind-dispersed seeds are usually lighter and smaller than other seeds and have special structures that catch the air, such as wings or fluff. This increases the seed’s hang time in the air, allowing them to travel great distances. Article on ‘The magic of seed dispersal from our local Schlitz Audubon center. Another strategy for seed dispersal is to use animals to carry seeds to suitable locations. There are several methods plants use to get animals to carry their seeds. Some embed their seeds in fruits. Fruits have bright 11

colors and nutrient rich flesh that attract animals such as birds and mammals to eat them. The animals then disperse the seeds when they defecate or spit them out. The seed itself can also become an attractive food item for an animal that likes to cash food for the winter. Any seed the animal forgets has the opportunity to germinate into a new plant. Seeds can also take advantage of animals by becoming hitch hikers. Seeds can develop special structures such as burs or hooks that allow them to get tangled in an animal’s feathers or fur and be carried ...