Lab Topic 17
Investigating Plant Phylogeny: Seed Plants

 

Angiosperms

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How to study for the practical

Learn the language:
For this topic a vocabulary list is given in your lab manual. You need to know the definitions of the terms. Make flashcards for those that you do not know and work to learn the definitions.

Seek the big picture:
In lab manual a list of Key Concepts and Objectives are given. Be sure that you can explain how the lab addresses or illustrates each.
You will probably find it helpful to outline the background section at the beginning of each lab topic in the manual as it attempts to give you a “big picture” overview.

Apply your knowledge of terms and concepts to reality:
Review the images on this www site for each lab topic in the practical.

You need to develop visual memory so that you can recognize images similar to these in the lab practical questions.

As you look at the images, answer any questions that given with the image. Use you lab notebook and lab manual to check your answers.

Synthesize and consolidate you knowledge:
Draw life cycle diagrams where you can. For each organism, know when mitosis and meiosis occur in the life cycle. Be able to describe the ploidy levels as well as the names of different life cycle stages. If there are special organs involved in sexual or asexual reproduction, know the names, functions and what they look like.

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Images in order of study in lab manual

Gymnosperms

Phylum (Division) Ginkgophyta, Ginkgoes

Phylum (Division) Coniferophyta (Conifers)

Pine: staminate cones, young and old ovulate cones

• What is the dominant generation of this plant?
• To what phylum does this organism belong?
• List two adaptive developments which prevent water loss from this plant allowing it survive in terrestrial environments.
• Name the type of cones visible here.

Cross section of pine needle (stained)	Resin duct in stained pine needle at 400X	Stomata on upper surface of pine needle at 400X
What is the ploidy level of cells in the needles and stem? Do the needles and stem represent the sporophyte or gametophyte stage? Name one adaptation to land that is present in this structure   What is the major function of mesophyll cells in pine needles? (A) transport system; (B) sexual reproduction; (C) cuticle secretion; (D) photosynthesis.  Is this slide a cross section of an organ found in the sporophyte or gametophyte generation of the Coniferophyta?	What is the function of resin?	The purpose of the small gaps in the surface of this tissue is: A. release of spores   B. exchange of gases  C. penetration of symbiotic fungi   D. fertilization What is the structure and  function of the cuticle?

Stem Histology

Stained cross section of pine stem at 35X	Cross section of pine stem at 100X	Cross section of pine stem at 400X
The woody rings that you see in the center of this slide are what kind of tissue?  What two functions do these cells perform?  In conifer stems, where do cells divide actively to form new secondary xylem inwardly and second phloem outwardly? (A) vascular cambium; (B) periderm; (C) cork cambium; (D) pith.	Which is the function of the xylem:  A. Transport of carbohydrates   B. Transport of water and nutrients  C. Support   D. Protection from fire damage  What types of cells compose the rings of this stem (that are used to determine age) ?	What are the functions of xylem in pines? Find both xylem and phloem in the above sections. What specific material in the xylem cell wall cause it to be stained as red color? A. Starch, B. Cellulose, C. Glycogen, D. Lignin

 

Isolated xylem tracheid showing shape of cell and pits in walls.

Male Gametophyte System 

• Indicate which cone contains the microsporangium when it matures.

Staminate cones T/F The cones on this branch are female. T /F   The cones on the end of this branch will, as they mature in a year or two, look like the cones found on  lower  the branches.	Staminate cone longitudinal section at 35X T/F--This slide is of the female reproductive cone which contains ovules situated in an ovary. Microspore mother cells are (A) haploid; (B) diploid; (C) triploid.

Longitudinal section of staminate cone  at 100X	Pollen at 400X
Where does meiosis occur in their life cycle of pine? What is the difference between pollen and spores? What's the name of the cell like structures here and what's their ploidy? A. Microsporangia, 1N; B. Microsporangia, 2N; C. Pollen, 1N; D. Pollen, 2N Is this structure involved in the production of male gametophytes or female gametophytes?	Which of the above structures is the male gametophyte: the cone or pollen? What is the ploidy level of a nucleus in pollen? Explain how pollen represents a reproductive adaptation to terrestrial living. What is the name and ploidy level of this structure? Which phase of the life cycle does this structure represent? What is the advantage to pines of having the male gametophyte be a microscopic pollen grain? How does the occurrence of pollen  in a plant's life cycle increase the chances of genetic outcrossing?

Female Gametophyte System

  Ovulate cones that are one two and three years old.

• T/F The cones on this branch are female
•  Which of the following could be found within an ovulate cone? A) microspores B) megaspores C) male gametophyte D) all of the above
•  What reproductive structure do you see here?
•  Name the division to which this plant belongs.
•  In the life cycle of conifers, which stage is the dominant one? (A) sporophyte; (B) gametophyte.

Longitudinal section of ovulate cone at 35X	Ovulate cone section at 100X	Ovulate cone section at 400X
Is the cone itself composed of sporophyte or gametophyte tissue? Is most of the cone composed of haploid or diploid tissue? True or False--This slide is of the female reproductive cone which contains ovules situated in an ovary.	Compare this to the previous photo and find the ovules. How many ovules are found on each scale of the cone? Where does meiosis occur in the ovulate cone to produce eggs?  What occurs in this round structure? A) fertilization B) formation of a gametophyte C) formation of a sporophyte D) formation of spores E) all of the above	Indicate the location of the integument, nucellus and micropyle in the above photo. What is the function of each?

• Indicate the megasporangium in the above photo. Why is it  important?
• Describe how fertilization occurs in pine.
• This is a section of an ovulate cone in a conifer. Clearly visible is the entire ovule, its integument, micropyle, nucellus, and the lyoung female gametophyte.
• What does the identified tissue become in the mature seed? A. endosperm.  B. gametophyte  C. seed coat   D. flesh of fruit
• What is the name and ploidy level of cells in this structure?
• Is this structure involved in the production of male gametophytes or female gametophyte?

Mature seeds and cones
 

Mature ovulate cones and seeds. Seeds are found on bottom surface of scales when cones are hanging from a branch. What structure  in the conifer seed helps in dispersal? A. Air bladder, B. Foot, C. Bract, D. Wing Which of the following Divisions produce seeds:  Byophyta, Sphenophyta, Coniferophyta, Hepatophyta, Pterophyta, Lycophyta, Anthophyta? Compare and contrast a spore and a seed.

Common Yew-A comparative system to pine
Not all gymnosperms have hard cones. Some have a fleshy fruit like structure instead. The common yew that is used as an ornamental planting around houses is one example. Note the prominent exposed (naked) seed in the bright red "fruit "(actually the integment, i.e., a fleshy seed coat).  What possible purpose could this bright color serve? How could it be an advantage to the yew?

Fleshy cones of yew showing characteristic naked seed of gymnosperms	Staminate "cones" of yew that produce pollen

Juniper cones

 General and Comparative Questions

• List 1 major similarity and 1 difference between non-vascular and vascular plants other than vascular plants have vascular tissues.
• Briefly discuss how the life cycle and reproductive structures of seedless plants differ from those of plants with seeds.
• How are Pteridophytes similar to seed plants in their terrestrial adaptation ?
• What are the two  generations of the plant life cycle called and what are their ploidy levels?
• Name at least four adaptations of conifers to a terrestrial existence.
• Give the common names of several species that are gymnosperms.
• How does pollination differ from fertilization?
• How is pollen transferred from male organs to female organs in conifers?
• What is the difference between a spore and a seed?
• If a species of pine has a diploid number of chromosomes equal to 40, how many chromosomes will be found in: a pine needle epidermal cell: a cell differentiating to become xylem; a root cell; in cell in the embryo inside the seed; in a microspore mother cell; a microspore; a megaspore mother cell; a megaspore? a sperm? a zygote?
• Explain why pollen is an important adaptation to a terrestrial environment.
• Explain why a seed is an imporant adaptation to living in a terrestrial environment.
• Explain where you would look for the male gametophyte generation in a pine. Do the same for a female gametophyte.
• In addition to reproductive structures/processes, conifers show other adaptations to terrestrial environments. What are they and why are they  important?
• If you wanted to study the gametophyte generation of a pine, sprecifically describe where would you have to look to find male and female representatives.
• Are sperm and eggs produced directly by meiosis in pines? If not ,what form of cell division in involved?

 

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Credits
    Photos by Maria Oehler, Allison Hall, Linda Westgate, W.D. Dolphin  and Botanical Society of America
    Text and layout by W. D. Dolphin