Download LAB 3

LAB 4
NONSEED PLANTS, GYMNOSPERMS,
AND THE GENERAL STRUCTURE OF ANGIOSPERMS
Answers to questions in the lab exercise:
Examine fern sporophytes.
 Are these structures (fonds, rhizomes, and roots) haploid or diploid?
Diploid.
 Are the walls (of the sporangia) uniformly thickened?
No. The annulus is much thicker than the lip cells. As the sporangium matures
and dries the annulus contracts. This pulls on the thin lip cells, eventually
rupturing them and releasing the spores.
Examine a male cone.
 Female cones usually occur on higher branches and, and male cones are usually
located farther from the trunk than the female cones. Why would this be so?
The positioning of the male cones below the female cone reduces the chance of
self-fertilization occurring from pollen falling straight down.
The pollen released by the male cones is wind dispersed. Therefore, positioning
the male cones on the outside of the tree facilitates the pick up and dispersal of
pollen to areas beyond that tree.
Examine Brassica.
 At what level is the main root thickest in diameter?
It is thickest at the top, then tapers off downwards.
 Can you identify a level on the main axis of the plant where the root “joins” the stem
or is there a “transition” zone that is not recognizable as root or shoot?
There is a thin transition zone.
 Can you see any significance in the positioning of the passage cells?
The endodermis controls the movement of water in and out of the vascular
bundle with passage cells allowing water to leave the xylem at specific points.
 Are the internodes variable in length?
They can be as the distances reflect growing conditions. Low light levels would
result is greater distances between nodes (etiolation). Also, near the tip,
distances might be short if cell elongation is not complete.
 Do you find stem branches in the axils of your plant? If not, what do you find there
instead?
There are no branches but leaf buds can be found instead. These will develop
further is apical dominance is suppressed.
 Do the leaves appear to be arranged in any particular manner on the stem, i.e., is there
more than one leaf at a node?
The cotyledons are opposite but later leaves are alternate, i.e., with a single leaf
at each node. The alternation becomes more pronounced as the inflorescence
develops.
 In what way do the cotyledons differ from the other leaves on the plant? Note the
difference in size and texture between the older (lower) leaves and the younger
leaves.
The cotyledons are thicker and tougher in texture than the leaves that appear
later and further above. A cotyledon’s function is primarily food storage and
not photosynthesis.
 Is there a prominent midrib (central vein) or are there several main veins?
Brassica is a eudicot and so it has netlike venation with one prominent midrib.
 Are the veins more prominent on the upper or lower side of the blade? Note that the
veins form a netted pattern
They are more prominent on the lower surface of the blade.
 Do the veins go completely to the margin or merely approach it closely? Use a
magnifier or dissecting microscope to determine this.
The veins merely approach it closely. They are supplying the cells with water
and nutrients and therefore need not go right to the leaf margin.
Examine a eudicot stem.
 Is the center of the stem hollow?
No. There are pith cells in the center of the stem. However, as the plant ages
and begins to senescence, the stem may dry and get hollow then.
 Which cell types have lignified cell walls?
Xylem cells and bundle sheath (sclerenchyma) cells.
Examine a leaf.
 Phloem is composed of thinner welled cells than xylem. How are the two tissue
types oriented with respect to the upper and lower surfaces of the leaf?
Xylem is closer to the upper surface of the leaf, above phloem
 Are there greater numbers of stomata in the upper or the lower epidermis?
In the lower epidermis away from direct sunlight (less evapo-transpiration).
 Are there chloroplasts in the upper or the lower epidermis?
No. The epidermis is nonphotosynthetic.
 What structural features of the leaf could be of particular importance in making it an
efficient organ for carrying on the process of photosynthesis?
Leaf shape. There is a broad flat surface for intercepting light for
photosynthesis to occur yet the leaf is thin so gases are never far from the
epidermis and therefore never far from stomata. Also, leaf density. The air
spaces within the spongy mesophyll are crucial in permitting the circulation of
gases.
Stomata
 How does the salt solution affect turgor?
The salt solution causes water to move out of the guard cells, lowering turgor
pressure. With lower pressure, the guard cells collapse and the stomata closes.
Examine leaf adaptations.
 Compare the two numbers in the final column of the table and examine the graph.
Notice how the two different leaves reacted to desiccation. Which type of leaf was
most vulnerable to drying?
The succulent is more resistant to desiccation, Oxalis wilts.
 What is the significance of these reactions? What do these results imply for the
survival of these two species under differing environmental conditions?
These results indicate whether the plants can survive hot, xeric conditions and
therefore within which kind of habitat the plants might grow. The succulent
retained more of its water and therefore seems better suited to hot, dry areas.
Oxalis wilted and showed an inability to tolerate heat and drought.
Examine the results of the first week’s experiment on light availability.
 A technician will place one of your bean seeds in complete darkness in the
greenhouse. How will the germinating plant respond to darkness? What will the bean
seedling look like in three weeks time?
The plant will be etiolated, that is, tall, spindly, and yellow in colour.