Answer Key for Second Midterm

The BAC will meet Wednesday at noon in room 204 in McClellan Hall. Please attend if you can, but don't miss a class to come to the BAC meeting.

Multiple Choice Answers

Form 1 and Form 2

1. a
2. b
3. b
4. a or e
5. d
6. c
7. d
8. b
9. a
10. b
11. d
12. a
13. d
14. b
15. b
16. c
17. d
18. a
19. b
20. e
21. b
22. c
23. a
24. d
25. d
26. a
27. d
28. c
29. b
30. a

Essay Questions

Photosynthesis Question

The rate of photosynthesis can be limited directly, or indirectly, by a variety of environmental factors. Agriculture provides us food and fiber and is a major component of the economy in many parts of the world. Farmers attempt to increase the production of their crops by fertilizing and irrigating.
Discuss how fertilization and irrigation can increase agricultural production by increasing rates of photosynthesis. An excellent answer will indicate how these activities affect the physiology of plants in a way that increases the rate of photosynthesis.

The rate of photosynthesis can be limited by a variety of environmental factors including temperature, light level, carbon dioxide, soil fertility, and water availability. Some of these factors (e.g., soil fertility and soil moisture level) can be manipulated by farmers in a way that can increase photosynthetic rates production whereas other factors (e.g., temperature and atmospheric carbon dioxide concentration) are harder to manipulate on a large scale. Thus, most large scale agriculture involves increasing soil nutrients by adding fertilizers and increasing soil moisture availability by irrigation.

Water can indirectly regulate the rate of photosynthesis. Irrigating crops increases the soil moisture content. When plants are water stressed they respond by closing their stomata which blocks carbon dioxide from entering the leaf by diffusion. Carbon dioxide is required in the light independent reactions of photosynthesis. The ultimate purpose of the light independent reactions is to use energy from ATP and NADPH to convert carbon dioxide to glucose which contains chemical energy stored in its chemical bonds. Specifically, carbon dioxide is involved in the following reaction-
CO2 + RuBP  PGA
Irrigating crops increases the soil moisture content which allows plants to keep their stomata open longer which allows them to take up carbon dioxide for a longer period of time which allows photosynthesis to occur longer.

Fertilizing can add a number of potentially limiting resources to the soil. An important nutrient in all fertilizers is nitrogen. Because nitrogen is an important element in amino acids, increasing soil nitrogen content can increase the rate of nitrogen uptake which allows plants to make more proteins. By far the most protein in plants is RuBP carboxylase, the enzyme that catalyzes the reaction between carbon dioxide and RuBP. Fertilizing with nitrogen increases the amount of RuBP carboxylase in the plant which speeds up carbon fixation and allows more carbon to be produced in the Calvin Cycle.

Life Cycle Question
 
Diagram the life cycle of a fern. Discuss the characteristics of ferns that makes them advanced relative to the mosses and primitive relative to the gymnosperms. Be sure to discuss the evolutionary advantage of the advanced traits relative to the primitive traits.
(I am sorry that this doesn't look right when it is posted)

zygote (2N) ==> sporophyte (2N) ==> sporangia (2n)
fertilization
meiosis
archegonia => (egg N) <== gametophyte <== spores
angtheridia=> (sperm N) mitosis


Ferns appeared at an intermediate step of the evolution of plants. Thus, they are advanced relative to the bryophytes but primitive relative to the gymnosperms. Ferns are considered to be advanced relative to the bryophytes because they are diploid dominant and have a vascular system and they are considered to be primitive to the gymnosperms because they are homosporous rather than heterosporous and they reproduce by spores rather than seeds.

Diploid dominance is advantageous relative to haploid dominance because individuals are not as adversely affected by lethal alleles. If an organism is haploid then they will die if they get a lethal mutation. However, if that lethal mutation is recessive, then that allele can be masked in the heterozygote state in a diploid organisms. Thus, dipoloid dominant species should have higher survival levels than homozygous dominant species.

The evolution of the vascular system (xylem, phloem, roots, stems, leaves) which occurred for the first time in ferns is a major adaptation for terrestrial plants. Plants with a vascular system produce true roots that can take up water and nutrients from the soil. They have xylem, the tissues that carry water and nutrients from the roots to the leaves, and phloem that carries sugar around the plant. Having a vascular system is a huge advantage because it allows plants to achieve a much larger size and allows them to inhabit more arid regions.

Heterospory, the production of two types of spores to produce two types of gametophytes, is an advantage over homospory, the production of one type of spore to produce one type of gametophyte because heterosporous plants no longer have to rely on swimming sperm. Thus, heterosporous plants have the potential to live in environments that are arid year around.

Reproducing by seeds is a major advantage relative to reproducing by spores because an individual seed has a much larger probability of survival. Seeds contain an embryo, seed coat and nutritive tissues. The resources held in the seed are used to nourish the germinating seedling until it is has established its roots and leaves well enough to collect its own food.