Lab 5: Seed-bearing Plants
Materials needed
Sharp knife
Cutting board
Large pine cone with open “scales”
Fascicle (bundle) of pine needles
2 household cups (may be disposable)
Measuring cup
Red food coloring
Blue food coloring
Salt
Celery stalk
Pea pod: sugar snap pea or snow pea
Dry lima beans (3)
Activity: anatomy of pine
1. Obtain a pine cone and a fascicle (bundle) of pine needles. Refer to Figure 5.1 as you perform this activity.
2. Examine the fascicle of pine needles (Figure 5.1). A pine needle is actually a leaf. It has green pigmentation for photosynthesis. It is skinny, leathery, and coated with a sticky resin to help retain water. Pine needles are bound together in a bundle (fascicle). Different species have different numbers of needles per fascicle. For example, white pines (Pinus strobus) have five needles per fascicle, while red pines (Pinus resinosa) have two needles per fascicle.
3. Examine the large pine cone (Figure 5.1). It should be large enough to fit into your palm, andits woody “scales” should be open. Pine trees produce two kinds of cones: pollen cones and seed cones (or ovulate cones). Pollen cones are small – they often are not much bigger than the last digit of your pinky finger. These cones produce pollen grains, which contain sperm. You should have a larger cone, the seed cone. Each woody “scale” of the seed cone typically produces two eggs at its base. Before the eggs are fertilized, the seed cone is closed up. Pollen grains blow into the cracks between the closed scales, and fertilize the eggs. The fertilized egg then develops into a seed, and the scale opens. The scales are called sporophylls (“spore” + “leaf”).
4. Break off a few scales near the top of the cone. Examine the base. You should see two indentations where the seeds used to be. Examine or break off a few scales near the bottom of the cone. There may be seeds present (Figure 5.1). The pine seed has a “wing.” This enables the seed to disperse away from the parent plant via the wind. This is why the scales open up once the seed develops.
5. A seed cone usually does not release all of its seeds at once. Thus, part of the cone, usually the top, is often more “open” than other parts. Because pine cones rely on the wind to disperse seeds, it is important that the “wing” of the seed stays dry. Pine cones protect developing seeds from becoming waterlogged through a passive reaction.
a. Place your open seed cone into a cup of tap water.
b. Record: Time into water _________
Describe your observations and any changes in the cone appearance
c. Let the cone sit in the water for at least 30 minutes.
d. Record: Time out of water _______
Describe your observations and any changes in the cone appearance
Fig 5.1
Lab Report
This is an experimental variation on the celery food dye activity of Lab 5.
Activity
1. Obtain four cups (two of which could have been used in Lab 5). As in Lab 5, fill each cup with 400 ml of tap water. Use red dye to darkly stain two cups, and use blue dye to darkly stain the other two cups. Be sure that each red cup gets the same amount of dye and that each blue cup gets the same amount of dye. Record the drops in each. Add a spoonful of salt into each cup.
2. Label one red dye cup and one blue dye cup with an S (high salt). Add 4 spoonfuls of salt to each of these cups. Stir the solutions thoroughly.
3. Obtain two similar stalks of celery, each with some leaves at the top. Cut a 1-cm piece (about one-half inch) off the bottom of each stalk. Keep the relative lengths of the two stalks as similar as possible.15
4. Carefully, split the stalks up the middle about half-way. The stalks should each now have two “legs.” Be sure that the legs of each stock are similar sized (i.e., the left leg and right leg are the nearly the same length and width).
5. Place the red S cup and the blue S cup together. Gently place one “leg” of one stalk into the red S cup, and the other “leg” of the stock into the blue S cup. The celery should now be “straddling” the two S cups (Figure 5.2.B). Place the red non-S cup and blue non-S cup together and situate the legs of the other celery stalk into each cup (i.e., the celery "straddles" these two non-S cups).
6. Record the time at which you place each celery into the pairs of cups as "Start time."
Start time
Stop time
a. S cups (high salt)
b.Non-S cups (low salt)
7. Let the celery sit in the cups for 6 hours, or until you can see color in the leaves of one of the stalks. In Step 6 above, record the time when you remove the stalks as "Stop time."
8. Examine the top of the celery stalks. Are there differences between the celery in the high salt (S) and low salt (non-S) water conditions? Record your observations in Question 1 of Lab Report 6.
9. Remove the celery from the cups (be sure to keep it clear which came from the high salt solution (S) and which came from the low salt (non-S) condition). Lay each stalk out flat. Starting at the top, move down the stalk, making cross-sectional cuts. Stop when you first see evidence of dye. Measure how far up each stalk the red and blue dyes climbed. In Table 6.1 in Lab Report 6, record the distance (cm) traveled by the red dye in high salt conditions (S), the blue dye in high salt conditions (S), the red dye in low salt conditions (non-S) and the blue dye in low salt conditions (non-S).
10. Tear apart the celery stalk. Notice the feel of the vascular tissue, and how the food coloring lies within it.
Lab 6A: Water transport and salinity
1. Examine the top of the celery stalks. Are there differences between the celery in the high salt and low salt water conditions? Describe your observations.
2. Record the distance (cm) traveled by the red dye in high salt conditions (S), the blue dye in high salt conditions (S), the red dye in low salt conditions (non-S) and the blue dye in low salt conditions (non-S).
Table 6.1
Distance (cm)
Red dye (S)
Blue dye (S)
Red dye (non-S)
Blue dye (non-S)
3. From Question 2 above, did the dyes travel at the same rate? What can you conclude about the effect of salinity on water transport in celery from this experiment? Propose a biological or physical explanation for your conclusion.
Activity: seeds
1. Obtain a sugar snap pea pod, or a snow pea pod. This is the fruit that develops from the pea flower (Figure 5.4). In this case, the fruit is not as sweet or as juicy as an apple. Cut along the curve of the pod. This exposes the seeds (peas) on the inside. You should be able to crack the peas in half. This reveals that the seed is composed of two cotyledons (seed “leaves”). The cotyledon becomes the main food source as the seed starts sprouting.
2. Angiosperm plants are divided into dicots (Class Dicotyledonae) and monocots (ClassMonocotyledonae). There are 180,000 species of dicots, including many flowers, shrubs,and trees. Dicots are distinguished by seeds with two cotyledons (e.g., bean, peanut, pea),leaves with veins having a branching pattern (e.g., maple, oak), and flower parts in multiples of four or five (e.g., four petals of poppies, five petals of wild roses). There are 80,000 species of monocots, including grasses and important crops (e.g., wheat, corn, rice), palms, and orchids. Monocot seeds have one cotyledon (e.g., corn kernel), leaves with parallel veins (e.g., blade of grass), and flower parts in multiples of three (e.g., six petals on lilies).
3. Obtain a few dry lima beans. Soak them in a cup of tap water for at least 8 hours.
4. Gently dry the beans on a paper towel. With your finger, you should be able to gently peel off the outer seed coat (if you cannot, soak the bean for 1-2 more hours).
5. Using a knife, carefully cut along the curvature of the bean. You should then be able to break the bean in half. Each half is a cotyledon, which has become swollen with nutrients from the endosperm.
