FLOWER DISSECTION

AUTHOR’S NAME: Elizabeth Morrison

LENGTH OF LESSON: 50 minutes

NAME OF COURSE: Biology

GRADE LEVEL: 9

SOURCE OF THE LESSON: http://www.shenet.org/high/hsacaddept/science/gaugust/gadissectionpages/gaflowerdissectionlab.htm

Shenendehowa Central Schools, NY

TEKS ADDRESSED:

(1.A)  Scientific processes. The student, for at least 40% of instructional time, conducts field and laboratory investigations using safe, environmentally appropriate, and ethical practices. The student is expected to demonstrate safe practices during field and laboratory investigations;

(2.B) Scientific processes. The student uses scientific methods during field and laboratory investigations. The student is expected to: collect data and make measurements with precision;

(10.A)  Science concepts. The student knows that, at all levels of nature, living systems are found within other living systems, each with its own boundary and limits. The student is expected to interpret the functions of systems in organisms including circulatory, digestive, nervous, endocrine, reproductive, integumentary, skeletal, respiratory, muscular, excretory, and immune;

(10.C) Science concepts. The student knows that, at all levels of nature, living systems are found within other living systems, each with its own boundary and limits. The student is expected to analyze and identify characteristics of plant systems and subsystems.

(13.B)  Science concepts. The student knows the significance of plants in the environment. The student is expected to survey and identify methods of reproduction, growth, and development of various types of plant

CONCEPT(S):

Plants have both male and female reproductive organs, made up of identifiable parts. Pollen grains from the stamen land on the stigma of a pistil. A pollen tube grows through the style into an ovule, and two sperm nuclei move through the tube to fuse with egg nuclei to form an embryo.

PERFORMANCE OBJECTIVES:

Day 1: Students will be able to:

Explain the process of reproduction in plants

Identify flower structures and relate them to their function.

Distinguish between pollination and fertilization.

Day 2:

Identify Relate the reproductive parts of a flower to their function

Dissect an organism carefully

Explain the process of reproduction in plantsCompare reproductive structures in representative plants.

Classify plants based on reproductive structures.

RESOURCES (for each group):

Fresh flowers (monocot and dicot varieties)

Dissecting needle

Hand lens

Microscope scalpel or razor blade

Plain paper

Forceps

Clear tape

Metric ruler

Slides and coverslips

Dropper

microscope

SAFETY CONSIDERATIONS:

Be very careful with the scalpel or razor blade. It is very sharp and can cut you easily.

SUPPLEMENTARY MATERIALS, HANDOUTS:

Lab worksheets

Five-E Template

Teacher Does Probing Questions Student responses

Misconceptions

Engage: Fresh flowers will be on lab tables when students come in.

What are these? What is that part of the plant’s function?

Flowers. Reproduction.

Day 1.

Engage: Hold up a flower and an apple and ask students what the relationship is between them. Bite into the apple. Hold up a grass flower and ask why it is different from the first flower.	What is the relationship between a flower and an apple? What part of the flower am I eating? Why is this grass flower different from the petalled flower I just showed you?	Flowers produce apples. Answers will vary. Grass flowers lack petals (ask why).
Explore: Today you will dissect flowers and examine the reproductive organs that make them up. They’ve done this before so make the purpose a little more complex like, “Today we will be using plant reproductive structures to study plant evolution” or “Today we will be comparing reproduction in different plants.” Before you start, lets review how flowering plants reproduce. (Students will have covered this already. Background info follows.) If you review all of this background, there will not be time to do anything with the flowers in a 50 minute period. The stamen is the male reproductive organ and consists of two parts: the anther and the filament.  The anther is the enlarged structure at the top of the stamen.  Inside the anther are pollen sacs.  Special cells within the pollen sacs undergo meiosis to form pollen grains.  Each pollen grain contains two sperm nuclei.  When the pollen grains mature, the pollen sacs split open to release the dust-like pollen. The pollen of each plant species has a specific shape. This allows it to stick to the female reproductive organ of the same species and not other plant species. Today you will have the opportunity to make slides of pollen and compare the pollen from different flowers. The filament is a thin stalk that supports the anther. The pistil is the female reproductive organ and consists of three parts: the stigma, style, and ovary.  The stigma is an enlarged portion at the top of the pistil that becomes moist and sticky when mature.  The style is the middle portion of the pistil.  It can be long and slender, short, or even absent, depending upon the species.  The ovary is the enlarged structure at the bottom of the pistil.   The ovary contains one or more hollow compartments called locules.  Each locule containsThe ovary contains one or more ovules.  Special cells within the ovule undergo meiosis to form ova (eggs) containing egg nuclei. Pollination occurs when pollen grains land on the sticky surface of the stigma and are trapped there.  The pollen grain germinates and a pollen tube emerges from the grain.  It releases special enzymes that digest a cell the wall on the surface of the stigma.  The pollen tube grows down through the style to the ovary and enters the ovule, making a continuous passageway for the two sperm nuclei to enter the ovum.  Fertilization occurs when the sperm nuclei join the egg nuclei.  The fertilized egg becomes an embryo.  The wall of the ovule thickens and forms a seed, thus enclosing and protecting the embryo.  The ovary wall also thickens and develops into a fruit.  In some plants such as apples, the ovary walls become fleshy and contain stored sugars and starches.  In other plants such as walnuts, the ovary walls become dry and hard..  Follow the directions on your data sheets and dissect the flowers, labeling the parts as directed. Answer the observation questions, and write the function of each part in the appropriate column.	What is the male part of the flower? What is the female part? What does the stamen produce? What is pollen in terms of reproduction? What part of the stamen produces the pollen? What is the function of the filament? What are the parts of the pistil? What does the ovary do? What does the stigma do? Where will pollen bind when it lands on the pistil? What does the style do? How is it similar to the filament? Which part of the pistil will develop into a seed? Which part will develop into a fruit? (So when you eat an apple or pear, you’re really eating a fat juicy plant ovary!) What is pollination? How do plants pollinate? Are animals always involved in pollination? Why doesn’t the pollen from one type of plant fertilize another type of plant? What is the difference between pollination and fertilization?	The stamen The pistil Pollen Plant sperm Anther To hold the anther up. Ovary (should remember), stigma and style (might not remember) Make eggs. Catch pollen, stigma. Hold the stigma up. Both hold up part of the reproductive organ. Ovule Ovary Process of transferring pollen from one flower to another or from the anther to the stigma. Bees transfer pollen. No wind can pollinate plants. The pollen has a specific shape that allows it to stick to only one type of stigma. Pollination gets the pollen to the pistil. Fertilization is the union of sperm and egg.
Extend / Elaborate:	Sometimes, pollen from a different species lands on the stigma of a flower.  Based on your knowledge of cell communication, suggest a mechanism that would ensure that only the correct species of pollen germinates on the stigma of a particular type of flower.	Difference in flowering time, self-incompatibility, stigma chemically recognizes pollen as same species..

Engage: Fresh flowers will be on lab tables when students come in. So, when you smell a flower, you’re really sticking your nose in its private parts! :-> NOTE: Students dissect flowers in elementary school and junior high (not that they learn anything from it but it would be good to probe to see what they already know).	What are these? What do they do for the plant? What is their function?	Flowers. Reproduction.
Explore: Follow the directions on your data sheets and dissect the flowers, labeling the parts as directed. Answer the observation questions, and write the function of each part in the appropriate column. Compare the flowers in terms of complexity. Which flowers are monocots and which are dicots? How many seeds will each flower produce? Prepare a slide of the pollen from your flower and examine it. Compare it with the pollen from your neighbor’s flower. How do they differ?
Explain:	How many petals did your flower have? Sepals? Stamens? Does this make your flower a monocot or a dicot? Were your stamens or pistils mature? How do you know? What did your petals look like? How could this attract insects? Summarize how reproduction occurs.	If parts of 3, monocot, if parts of 4 or 5, dicot. Yes if stamens opened pollen sacs and pistils are enlarged and sticky. Colorful, aromatic, lines pointing toward stamens, etc. Pollen is released from the stamen. It lands on a pistil and grows a tube down toward the egg to release sperm to form an embryo. Then the ovary wall develops into a seed and a fruit.

Extend / Elaborate: Here discuss why flowers have different adaptations. For example, why do conifer flowers and grasses lack petals? Which flower is more primitive based on structure? How do flowering plants compare with more primitive plants such as ferns and algae? Which structures evolved first? Get students to move beyond relating structure and function to conjecturing about why the same structure might be shaped differently and how that affects function.

Sometimes, pollen from a different species lands on the stigma of a flower.  Based on your knowledge of cell communication, suggest a mechanism that would ensure that only the correct species of pollen germinates on the stigma of a particular type of flower.

Difference in flowering time, self-incompatibility, stigma chemically recognizes pollen as same species..

Evaluate: Write a brief outline in your lab manual summarizing the information covered in this lab. Include info about all flower parts, their appearance, and their functions.

Evaluate students’ answers to lab questions.

Plant Reproduction Lab

Procedure

1.  Obtain a single flower and observe its parts carefully.  Flower parts are arranged in a circular pattern.  Each circle is called a whorl.  The whorls are attached at the enlarged receptacle located at the base of the flower. 

Please read this overview before you begin your flower dissection:

As you examine your flower, you will be carefully removing parts beginning with the outer whorl and working your way in towards the pistil.  You will arrange each whorl in a circle on the plain paper, beginning with the sepals as the largest outermost circle.  As you proceed with your dissection, you will carefully tape each whorl of flower parts into position and label them.

2.  The sepals form the outermost whorl of the flower.  The sepals are leaf-like structures that are usually green in color.  Sometimes, the sepals are the same color as the petals, or appear to be another set of petals of a different color.  The function of the sepals is to protect the inner part of the flower before it blossoms.  Gently remove the sepals, tape them into position onto the paper, and label them.  On the chart, record the following observations:

a) How many sepals does your flower have?

b) Describe the appearance of the sepals (color, markings, etc.).

3.  The petals are found directly under the sepals.  The color and odor of the petals help to attract birds and insects to the flower for pollination.What is the purpose of petals?Why do some flowers lack petals? How might grass flowers be pollinated? Gently remove the petals, tape them into position onto the paper, and label them. 

On the chart, record the following observations:

a) How many petals does your flower have?

b) Describe the appearance of the petals (color, markings, etc.).

4.  The stalk-like structures inside the petals are the stamens, the male reproductive organs.  Depending on the species, the stamens may be attached  to the receptacle, to the petals, or to the pistil.  The enlarged portion at the top of the stamen is the anther.  Inside the anther are pollen sacs, which produce pollen grains.  When the pollen grains mature, the pollen sacs split open, releasing the dust like pollen grains. Place a drop of water on your slide and shake some pollen on it. Place a cover slip on the slide and observe the pollen under the microscope. Draw your pollen under 400x magnification in your lab book. Observe and draw pollen from a different flower. How do they differ? If the pollen sacs on your flower have not matured, obtain a prepared slide of pollen from the front and draw that. The filament is the thin structure that supports the anther.  Gently remove the stamens, tape them into position onto the paper, and label them.  On the chart, record the following observations:

a) How many stamens does your flower have?

b) To which structure(s) were the filaments attached?

c) Have the pollen sacs opened?  How can you tell?

d) If pollen grains are visible, describe their appearance.

5.  The central structure of the flower is the female reproductive organ, the pistil.  The top of the pistil is the stigma.  When mature the stigma is enlarged, and its surface is moist and sticky.  The style is the middle portion of the pistil.  It supports the sigma.  Some flowers lack a style.  The ovary is the enlarged structure at the bottom of the pistil.  The ovary contains one or more hollow compartments known as locules.  The loculesThe ovaries contain ovules, which in turn, contain the egg nuclei.  Carefully remove the pistil by cutting it from the stem just under the ovary.  Make a life-sized sketch of the entire pistil (just the outline) in the center of the plain paper and label it.  Cut the style just at the top of the ovary, tape it next to your sketch, and label the stigma and style.  Using the ruler, measure the length of the style in 

millimeters.  Cut a thin cross-wise section of the ovary and tape it under the stigma and style.  Label the ovary wall, locules and ovules.   Using the dissecting needle, carefully pick the ovules out of one of the loculesthe ovary.  Try to estimate how many ovules are contained in one loculethere are.   On the chart, record the following observations:

a) What color is the pistil?

b) Describe the appearance of the stigma.  Is the stigma mature?  How can you tell?

If you could put the top of the stigma under a microscope, what shape indentations might be present based on the pollen you observed?

c) How long is the style (in mm)?

d) Describe the appearance of the ovary.

e) How many locules does the ovary contain?

f) Approximately how many ovules are contained in one loculein the ovary?

How many seeds would this flower produce if all the ovules are fertilized?

Draw the path of the sperm nucleus from the stigma to the ovule.

Structure	Observations	Function
Sepals
Petals
Stamen
Filament
Anther

Pollen grains

Pistil

Stigma

Style

Ovary

Summary questions: Have some questions that summarize and are higher level than recall.

Which plants had the most complex flowers? (if you have them compare flowers).