Plant Dissection Lab Part 1: Non-germinated Seed Lab Introduction: One of the basics for classifying flowering plants is the number of cotyledons



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Plant Dissection Lab

Part 1: Non-germinated Seed Lab
Introduction:

One of the basics for classifying flowering plants is the number of cotyledons or seed leaves with the seed. Whether there are one or two cotyledons, the seed is a mature ovule and is the final product of angiosperm reproduction. The new plant within the seed is provided with stored food and special coverings. The seeds of some plants are consumed by humans and many others are planted to grow into consumable products. In natural situations, animals, wind, and water are the agents by which seeds are dispersed. Many seeds are adapted for dispersal by theses agents. All seeds, however large or small, are the products of flowers.


Purpose:

To study the structure of dicot and monocot seeds and to understand seed dispersal.


Materials:

Kidney Bean (dry and soaked), Corn seeds, Paper towels, Dissecting needle, Hand lens


Kidney Seed

Beans are produced in a pod, the fruit of the bean plant. Each seed is covered by a hard, protective, seed coat, or a testa, and is attached to the pod at the hilum. At one end of the hilum, is a small pore called the micropyle, where the pollen tube enters the flower. The micropyle is the only place where water can enter the seed.



  1. Examine the soaked kidney bean using a dissecting microscope. Locate the hilum (a scar on one side of the seed) and the micropyle.


Does the micropyle seem to extend all the way through the seed coat?


  1. Draw the seed and label the hilum, seed coat, and the micropyle.




  1. Peel the seed coat from the seed very carefully. Near the hilum and micropyle a part of the inner seed may break easily. If the two halves of the seed seem to be coming apart, hold the two halves together. Place the inner seed on a paper towel.

The seed coat can prevent the drying out of the seed for years. It can also withstand the digestive juices of birds, allowing the seed to pass through their digestive tracts without change. In fact, many seeds are dispersed by birds. Birds eat the seed, carry it a distance and drop it with their digestive wastes. The seed can then grow in a new environment.




  1. Examine the seed coat. Hold it up to the light to see the tissue structure.

There is no endosperm in a mature bean seed. The embryo develops to such an advanced stage before germinating that it uses up all of the endosperm in the process.




  1. Look at the plant embryo on the paper towel.

What are the two halves of the plant embryo?



  1. Slowly and gently separate the cotyledons until you feel their point of attachment break. Lay the two sides flat on the paper towel like an open book, and examine them.

Are the two halves alike? If so, in what way? If not, how are they different?

The plummule consists of tiny leaves that will grow to become the first true leaves of the plant and the stem above the cotyledons. Below the plummule is the hypocotyl, the embryonic stem. Located at the base of the hypocotyl is the radicle. The radical is the embryonic root.




  1. Use the hand lens to locate the epicotyls and the plummule lying against the cotyledons.

How many leaves are in the plummule?
Do they have a leaf structure?
Can you see the veins?



  1. Half close the two halves to try to determine the positions of the embryo structures in a whole seed. The epicotyl was completely enclosed by the cotyledons. The epicotyl, hypocotyl, and cotyledons were all attached at one point. Below this attachment, the hypocotyl was free of the cotyledons, and the radical extended toward the micropyle.

  2. Draw and label the internal structures of the kidney bean. Label the epicotyls, plummule, cotyledon, hypocotyls, radicle, and point of attachment.



Corn Seed

The corn seed contains one cotyledon. In corn, the seed makes up most of the fruit, which is the grain. The seed coat is completely joined to the outer covering of the grain. This outer covering is the ovary wall of the corn flower. At the base of the grain is a pointed projection, where the grain was attached to the corn cob, called the pedicel. Another projection at the top of the grain is called the silk scar, where corn silk (a long flexible style) extended from the ovule to the outside of the corn husks that cover the cob.




  1. Examine the soaked corn grain. Observe its tough outer coat. Find the pointed pedicel. Also note a shield- shaped structure on one broad side of the corn grain. This is an outline of the plant embryo.

  2. Lay the corn grain on a paper towel, pedicel toward you and embryo-side up. Examine the embryo outline with a dissecting microscope.

  3. At the end of the embryo opposite the pedicel, feel for a tiny raised point. This is the silk scar.

  4. Draw and label the corn grain. Label the ovary wall, pedicel, silk scar, and embryo outline.




  1. With a scalpel, cut lengthwise through the center of your grain.

The plant embryo is surrounded by stored food called endosperm. Endosperm from the corn is the source of corn starch, commonly used for thickening sauces and puddings.


A plant embryo consists of three parts --- the cotyledon, the epicotyls, and the hypocotyls. The cotyledon, or seed leaf absorbs food from the endosperm and transfers it to the embryo during the early growth of the seedling. The epicotyl and hypocotyl are both attached to the cotyledon. The epicotyl grows up from the cotyledon and is the first part of the new plant to sprout above the ground. It gives rise to the stem and the first leaves of the plant. The tip of the epicotyl is called the plummule. The hypocotyl grows down from the cotyledon. The very tip of the hypocotyl, which becomes the primary root, is the radicle.


  1. Examine the cut surfaces of the corn grain with a dissecting microscope. You can see the tissues of the embryo plant and above the embryo, is the endosperm.

  2. Examine the surface of the one-half of the corn grain with the hand lens. Hold the grain with the pedicel down. On the embryo, find two tips of tissue, one pointing upward and one pointing downward.

Which is the epicotyl and which is the hypocotyl?



  1. With a dissecting needle, try to separate the epicotyl from the tissue behind it. It will bend outward.

What parts of the plant will develop from the epicotyl?


  1. Gently separate the tip of the hypocotyl from the cotyledon with the dissecting needle. Be careful not to break off the tip. Note that the hypocotyl is embedded in the cotyledon.

What parts of the plant develop from the hypocotyl?


  1. Draw and label the cut corn grain. Label the ovary wall, endosperm, cotyledon,

epicotyl, hypocotyl, and radicle.

Conclusions and Applications:been? Explain.

____________________________________________



  1. Name the parts of the monocot seed and the dicot seed.

Monocot Parts

Dicot Parts









  1. What is the function of the micropyle?




  1. What are 2 functions of a seed coat?




  1. What is the function of the cotyledons of a dicot seed?




  1. What is a silk scar?




  1. If an ear of corn had 205 grains, how many silks would there have been? Explain.


Part 2: Seed Germination Lab
Purpose:

To compare and contrast dicot and monocot seeds AFTER germination.


Materials:

Germinating lima beans and corn seeds (1-2 days old), Ruler, Paper towels.


Procedure:

  1. Place each seed on a paper towel.

  2. Measure the distance from the tip of the root to the top of the developing plant in centimeters (cm).

  3. Make a drawing of each type of germinating seed in the proper block.

  4. Label the following on the drawings:

Lima Bean: radicle, hypocotyl, cotyledon, seed coat, epicotyl, root hairs

Corn Seed: primary root, branch roots, epicotyl, coleoptiles.





Corn Seed

Bean

Length






Drawings








Analysis Questions:

Lima Bean:



  1. Is the lima bean an example of a monocot seed or a dicot seed?




  1. What develops from the radicle?




  1. What serves as the source of food for the developing embryo?




  1. What purpose do the root hairs serve?



  1. Once planted, what part emerges from the soil first?




  1. Will the cotyledon emerge from the soil?

Corn Seed:



  1. Is the corn seed an example of a monocot seed or a dicot seed?




  1. What develops from the primary root?




  1. What emerges from the soil first?




  1. Does the endosperm of the corn seed emerge from the soil?




  1. What develops into the leaves of a corn plant?




  1. What serves as the source of food for the developing embryo?




  1. What is the purpose of the coleoptile?



Conclusions:

  1. List at least 5 differences in monocot and dicot plants.




Monocot

Dicot






















Part 3: Leaf Stomata
Materials:

Plant leaves, clear fingernail polish, clear package sealing tape, microscope slides, microscope


Procedure:

  1. Paint a thick patch of clear nail polish on the surface of the leaf being studied. Make a patch at least one square centimeter.

  2. Allow the nail polish to dry completely.

  3. Tape a piece of clear tape to the dried nail polish patch.

  4. Gently peel the nail polish patch from the leaf by pulling on a corner of the tape and ‘peeling’ the fingernail polish off the leaf. This is the leaf impression you will examine.

  5. Tape your peeled impression to a very clean microscope slide. Use scissors to trim away any excess tape.

  6. Scan the slide, using a microsope, until you find a good area where you can see the stomata. Each stoma is bordered by two cells that are usually smaller than surrounding epidermal cells. These small cells are called guard cells and, unlike other cells in the epidermis, contain chloroplasts.

  7. Sketch your sample. Label the Stoma, Guard Cells, Epidermal Cells, and Chloroplasts.



  1. About how many stomata are on your sample (the whole slide)? Put your answer in the table below for light plant.


Experiment:

Guard cells are responsible for opening and closing the stoma. When water concentration is high, the guard cells will bulge, and cause the stoma to open. When the water concentration is low, the stoma will close. Stoma are generally open when plants are photosynthesizing.


Question: Will plants have more stoma open during the day than during the night?


  1. Make a hypothesis about the number of open stomata found in a plant kept in the dark compared to a plant kept in the light.


  1. Repeat the procedure above for preparing your slide. You will make another impression, from a ‘Dark Plant’. You will compare the two impressions.

Data Table:



Plant

Number of Stomata

Light





Dark






Conclusions:

  1. Write a short paragraph that answers the question- use your data to support your

conclusion.
Part 4: Flower Dissection
Purpose:

To investigate the structure and function of a flower.


Materials:

Lily, Dissecting microscope, dissecting supplies, paper towel.


Procedure:

  1. Place a flower on the paper towel.

  2. How many sepals and petals does your flower have? (If you cannot distinguish petals from sepals, then your flower has what are called tepals)




  1. Find the androecium (male flower parts). How how many stamens does your flower have?




  1. Find the gynoecium (female flower parts). How many carpels does your flower have? This may be tricky. Flowers may have only one carpel, two to numerous distinct carpels, or fused carpels. When in doubt, you can determine the number of carpels a flower has by counting the lobes of the stigma or by cutting a cross section of an ovary and counting the chambers inside.




  1. Now we will look more closely at the flowers parts: Peel away several petals, in order to reveal the reproductive parts of the flower.

  2. Draw and label the parts of the flower. Label: anther, stamen, filament, petals, stigma, sepal, style and ovary. Next to each label, say whether it is a male or female part.



  1. Scrape some pollen off of the anther and put it on the dissecting microscope. Examine it as closely as you can. Describe the appearance of the pollen (color, texture, size, shape, etc)

Conclusion Questions:

  1. Is the lily a monocot or dicot? How can you tell?


  1. Which does your flower produce in greater numbers: ovules or pollen grains? Explain why this would be important in terms of reproductive success.


  1. What are some adaptations (at least two) of flower petals to help attract pollinators? Explain how they give the flower an advantage in survival.




  1. 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.


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