Wednesday, March 18, 2015

Student Blog Post Assignment #10: Anthers and Stigmas and Styles, Oh My!

How do flowering plants (angiosperms) like our Brassica oleracea plants reproduce? That is the basic question we will address with this post.

Begin by reading section 24-1 in your text (Reproduction with Cones and Flowers) to get a basic idea of how flowering plants reproduce. Pay particular attention to Figure 24-7.

When you have finished your reading, get permission to visit the garden and harvest two or three yellow flowers from one of the Brassica oleracea flower stalks. Bring them back to the classroom and, with a partner, get a dissecting microscope. If you have never used a dissecting microscope before, read this brief tutorial on dissecting microscopes first.

Study Figure 24-5 on page 612. Now, follow the procedure below to complete the Brassica flower dissection.
  1. Lay your flowers on the table and take a closeup picture of one of them. In the next step, looking through the dissecting microscope, you will examine all of the flower's parts that are directly involved in reproduction.
  2. Now, using the forceps and/or your fingers, very carefully remove the sepals and petals of one of the flowers. Do you see the anthers?
  3. This step can be tricky: take a picture of the image of the anthers coming out of the eyepiece of the microscope.
  4. Now pull back the filaments and anthers to reveal the carpel (the entire female reproductive structure). Take a photograph of the carpel, focusing on the stigma.
  5. Take the ovary and use very sharp scissors or your fingernails to cut the ovary open lengthwise. Do you see the ovules inside? They look a bit like shiny green jelly beans attached to a central stem. Take a picture of the ovules inside the ovary.
  6. For extra points, take one of the anthers and tap some of its pollen onto a glass slide to prepare a wet mount slide of pollen. Ask the teacher for a compound light microscope and set it up on the lab station at which you are working. Get the pollen grains in focus at high power and try to capture a photo from the eyepiece of the microscope with your camera.
Using the photos you took to illustrate, write a paragraph explaining how fertilization occurs in flowering plant species like Brassica oleracea. Each picture you post should also include a detailed caption explaining what is shown in the photograph and how it functions in angiosperm reproduction.

Take a look at the example images below to get an idea of what you should capture in your photographs.

This image shows anthers surrounding a stigma. They are all part of the same flower. When both male and female parts appear in the same flower, the flower is said to be perfect. In some species of flowering plant, the male and female parts are located in separate flowers (some flowers are male, some are female), and yet another situation is when the male and female flowers are on entirely separate individuals (some plants are male, some are female).

Here is a view (40x) of the male reproductive anatomy of a flower, known as the stamen. It has a stalk called the filament coming up from the base of the flower and at the end of this stalk is a part called the anther. This portion of the stamen produces and releases pollen grains, which contain the plant's male gametes (sperm cells).

This is a view (40x) of the female anatomy of a flower called the carpel. The carpel consists of a stalk called a style with a sticky tip called a stigma. It is this sticky tip to which pollen grains adhere (get stuck).

This is a picture of a flower that has had all of the parts stripped away (sepals, petals, stamens, and the top of the carpel) EXCEPT the ovary (the large green tube on the right), which has been sliced open and has tiny ovules (immature, unfertilized seeds) spilling out--one of these ovules can be seen to the left of the ovary.


Monday, January 12, 2015

Student Blog Post Assignment #9: A Matter of Selection

Now that you have been watching many varieties of Brassica oleracea in the WGHS GOLD Main Garden for several stages of their life cycle, you have had the opportunity to see these organisms develop into bodies with quite a wide range of characteristics. Some have pink or purple stems and leaf veins, while others have a light green or yellowish color in the same parts of their anatomy. Some have short stems with many very round leaves packed tightly together, while others have longer stems with fewer more angular leaves, and others still have even taller stems with relatively long, dentate leaves. However, if we were to analyze the DNA of all of these varieties, we would see that the base sequences in most of their genes are more than 99% identical. Moreover, upon close inspection, these plants all still look, smell, and taste basically the same as each other, and they are all capable of mating with one another and producing fertile offspring. Finally, they all share key characteristics with an ancient type of Brassica oleracea called wild cabbage.

All of these observations (of the differences as well as the similarities) could be considered and interpreted as evidence of a natural process that shapes all life: evolution. Using your knowledge of basic principles of biological evolution and data collected from measurements made in the garden, respond to the questions below in a TSOTS blog post titled, "A Matter of Selection."
  1. Which part (anatomy) or characteristic of the Brassica oleracea plants seems to exhibit the most variation (greatest number of different forms)? Which part or characteristic of the Brassica oleracea plants seems to show the greatest range of variation (biggest difference between one extreme and its opposite)? Use and include data collected from multiple measurements to support your answer.
  2. Using the terms that follow, explain why you think there is so much variability in the domestic forms of Brassica oleraceatraits, selective breeding, artificial selection, genes, descent with modification, natural variations, mutations
  3. Which part (anatomy) of the Brassica oleracea plants seems to be most consistently the same in all of the examples in our garden, regardless of how extreme the differences between other parts of the same plants may be? Why do think this is so? Again, use and include data collected from multiple measurements to support your answer.
  4. What would plant breeders have to do in order to get the body part or characteristic you described above (in your response to question #3) to become much different than it is presently?


Wednesday, December 10, 2014

Student Blog Post Assignment #8: Seed Stories, Semester 1

Now it's time to sit back for a few moments and ruminate on what you have done and experienced this year through doing The Story of the Seed project. What have you learned? What surprised or amazed you? What made you laugh? What made you pause and think a little deeper? Take five minutes to talk about it with your teammates. Listen carefully to each person's reflections on what the project has been like for him or her. What questions do you have about things you observed or experienced in the garden? OK, now, guess what? You are going to write about the experiences of one of your teammates! Work closely with one other person in your group and summarize that person's  answers to the questions above in a short paragraph that you will post under your name. Your post title should include your teammate's name (e.g., "John's Seed Story").


Thursday, December 4, 2014

Student Blog Post Assignment #7: One of a Kind: The Wonders of Biodiversity

Compose and publish a post in which you answer the following questions in detail using terminology and ideas we have studied so far in the Genetics Unit.

The website below may be of some help to you as you search for information on Brassica olercea, the species of plant we have all been growing during The Story of the Seed project.

What kind of plant are you experimenting with? Describe it and include at least one recent photo of your actual plant. What (if anything) can you tell about the organisms (parent plants) from which your plant is descended? How could you predict what kinds of traits the offspring (baby plants grown from seeds) of your plant(s) will have? How would they acquire (get) these traits (talk about meiosis/gamete formation)? How will your plant pass its genetic information on to the next generation? Will your plant’s offspring look just like it? Why or why not? If all of the varieties of Brassica oleracea being grown by you and your classmates are so closely related, why do they look so different from each other in some ways? Find a picture of the wild-type (land race) Brassica oleracea (the ancestral plant for your green baby). How did so many different forms (polymorphisms) come to be from just this one ancestral species?

Monday, December 1, 2014

A Meiosis Model

The following sequence of images illustrates how the sperm and ova our plants use to procreate are formed through the cellular process known as meiosis.

Before meiosis begins, there is only a single copy of each of the organism's chromosomes from its two parents. These chromosomes are duplicated by DNA replication to form sister chromatids during the S phase of Interphase.

During Prophase I of meiosis, the nuclear membrane dissolves and the homologous chromosomes begin to move together.

Homologous chromosomes pair up and form tetrads (tetra- means 4).

At this point, homologous chromosomes may cross over and exchange segments of their chromatids.

In metaphase I spindle fibers attach to the chromosomes.
The two photos above show two different ways the tetrads could be arranged. This is possible because chromosomes can assort independently--just because the maternal chromosome #1 is on the right does not mean maternal chromosome #2 will line up on the right, for example.

The chromosomes are then pulled apart during anaphase I and the cell divides into 2 genetically different daughter cells.

Both of these two cells then go on to divide one more time to create four genetically unique daughter cells.

Here are the four haploid (only a single copy of each chromosome) daughter cells. If this was happening in the male reproductive structures (testis), then these would go on to become sperm cells. If this process was occurring in a female reproductive structure (ovary), the final products would be one large egg cell and 3 smaller structures called polar bodies.

Thursday, November 6, 2014

Student Blog Post Assignment #6: How Does Your Garden Grow?

Now it's time to put some of your recently acquired skills and knowledge into practice.

Your first step today should be to visit your plants in the garden. Try to find your group's plants. If you can't, don't worry--the most important thing to do is to notice the changes all of the plants have experienced. Snap a few pictures with your phone's camera (or an actual camera) and then return to the classroom. Briefly discuss your observations with your group and then proceed to answer the following questions in a post titled How Does Your Garden Grow.
  1. How is your plant getting bigger and adding biomass? Discuss in terms of cell division (mitosis)photosynthesis, and respiration.
  2. Phosphoenolpyruvate carboxylase (PEPC) and ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) are two important enzymes used in photosynthesis. Describe how your plants would make these enzymes if a signal was sent to the nucleus to produce more of them. (Hint: enzymes belong to which category of biomolecule?)
Be sure to talk with your group members about the questions as you attempt to compose your responses--together you should be able to come up with some very thoughtful explanations.

If you finish this post assignment with time remaining, work on any previous post assignments. If you have completed all post assignments, revisit them and make sure they all have detailed titles


Monday, October 20, 2014

Student Blog Post Assignment #5: Living or Not

Considering the characteristics of living things that we discussed in class, create a new blog post on your team's Blogger site to let us know how your plants are doing and to convince your audience that your plant is in fact a living thing. Tell us how the appearance has changed since you first put your seeds in a resealable plastic bag with water. What other things could we measure (in addition to growth in size and mass) to convince us that this little green thing is actually alive?