First Midterm Examination
MULTIPLE CHOICE [4 points/question]
Correct answers are marked in bold.
1. Which of the following tissues is primarily responsible for photosynthesis?
A. epidermis
B. ground tissue
C. phloem
D. xylem
2. Which of the following evolutionary innovations distinguished the pteridophytes from the bryophytes that preceded them?
A. vascular tissue
B. flowers
C. seeds
D. gametophytes
3. The veins of a plant leaf are composed of
A. spongy parenchyma
B. palisade parenchyma
C. xylem (only)
D. xylem and phloem
4. In a complete flower, meiosis occurs in two different organs. Which of the following accurately describes both sites of meiosis?
A. stigma and stamen
B. ovary and petal
C. sepal and stigma
D. ovule and anther
5. A mineral ion in the ground water must enter the symplast before it can reach the vascular tissue of a root. The ion can potentially enter the symplast in any of the following tissues except
A. endodermis
B. root hair
C. xylem vessel
D. cortex
6. During transpiration, water travels from root to shoot against the pull of gravity. What sort of force is being generated in the leaves to draw water up from the roots?
A. negative hydrostatic pressure
B. positive hydrostatic pressure
C. negative osmotic pressure
D. positive osmotic pressure
7. An increase in the volume of the guard cells causes the stoma to open. This change in cell volume is accompanied by what other changes in the guard cell's cytoplasm?
A. cytoplasm becomes more positively charged and hypertonic
B. cytoplasm becomes more positively charged and hypotonic
C. cytoplasm becomes more negatively charged and hypertonic
D. cytoplasm becomes more negatively charged and hypotonic
8. Which of the following statements is not true of a turgid cell at equilibrium?
A. osmotic pressure of the cytoplasm is lower than that of the extracellular fluid
B. hydrostatic pressure of the cytoplasm is greater than that of the extracellular fluid
C. cytoplasm is hypoosmotic to the extracellular fluid
D. cell wall stretched by expansion of the cell (= protoplast) within
9. The annual rings in a tree trunk reflect the yearly cycle of mitotic activity in which cell population?
A. primary meristem
B. secondary phloem
C. vascular cambium
D. cork cambium
10. Which of the following statements is not true of a shoot experiencing phototropism?
A. shoot bends towards side exposed to light
B. proton pumps hyperactivated on side exposed to light
C. auxin concentration higher on dark side
D. cellulose microfibrils have fewer crosslinks on dark side
SHORT ANSWER QUESTIONS
Each question is worth a total of 20 points. Correct answers are shown in italics.
11. Alternation of generations
Fill in the blanks.
A. [4 pts]
The reproductive cycle of plants involves an alternation of generations. To produce the next generation, the gametophyte gives rise to reproductive cells that are called __gametes __.
B. [3 pts]
The gametophyte generates these reproductive cells through what type of cell division? ___mitosis__
C. [3 pts]
To produce a sporophyte, the reproductive cells in Part A must undergo what cellular event?
___fertilization_____
D. [3 pts]
Are the tissues of the developing sporophyte embryo haploid, diploid, or triploid?
____diploid_______
E. [3 pts]
Once it has grown to maturity, the sporophyte will generate reproductive cells called ___spores___.
F. [4 pts]
In seed plants, what is the name of the process by which male and female gametophytes are brought together for the purpose of reproduction? ___pollination_____
12. Active transport
Azide is a poison that blocks the synthesis of ATP, and treatment with azide slowly inactivates active transport proteins which require ATP to function. Given what you know about active transport in plants, use this information to answer the following questions.
A. [4 pts]
What if any effect would prolonged azide poisoning have on a plant cell's membrane potential?
Correct answer marked in bold.
No effect.
Less negative inside.
More negative inside.
B. [4 pts]
What if any effect would prolonged azide poisoning have on the pH of a plant cell's cytoplasm?
Azide poisoning inactivates the proton pump - which transports H+ ions from inside the cell to outside - so there would be an increase in the concentration of H+ ions in the cytoplasm. This would decrease the cytoplasmic pH, i.e. the cytoplasm would become more acidic.
C. [4 pts]
If a living leaf were poisoned with azide, would its stomata be paralyzed in the open position or the closed position?
Hyperactivation of the proton pump is required for guard cells to swell and stomata to open. Inactivation of the proton pump by azide poisoning would paralyze the stomata in the closed position.
D. [8 pts]
In a healthy plant, a phloem sieve-tube member located at a sugar source takes up sucrose from the extracellular fluid into its cytoplasm. However, the sieve-tube slowly loses this ability if poisoned with azide. Explain in detail why azide poisoning has this effect .
A phloem sieve-tube takes up sucrose from the extracellular fluid by means of a membrane protein called the sucrose-H+ co-transporter. This co-transporter does not require ATP directly; rather, it relies on the normally steep concentration gradient of H+ ions to transport sucrose into the cell.
However, azide poisoning would inactivate the cell's proton pump, and the normally steep H+ gradient - as well as the ability to internalize sucrose - would slowly disappear.
13. Structure and function of plant cells
A. [5 pts]
Describe 2 structural features that differ between the epidermis of the root and the epidermis of the shoot.
There are several correct answers:
- Shoot epidermis has a cuticle. Root epidermis does not.
- Leaf epidermis (part of the shoot) has guard cells and stomata. Root epidermis does not.
- Root epidermis bears fine root hairs. Shoot epidermis does not.
- Root epidermis is coated with mycorrhizae (symbiotic fungi). Shoot epidermis does not.
B. [6 pts]
Give 2 different reasons why plasmodesmata are essential for the survival and function of the cells (= protoplasts) within a phloem sieve-tube.
1. The individual cells or members of the sieve-tube are connected to one another by plasmodesmata. These plasmodesmata permit the flow of phloem sap from one cell to the next.
2. The sieve-tube members are also connected by plasmodesmata to their companion cells. The sieve-tube members can not synthesize their own gene products, and for survival they rely on gene products synthesized in the companion cell and transported through the plasmodesmata.
C. [9 pts]
All cell walls contain cellulose, but the following 3 compounds are only found in certain cell walls. For each compound [1] name a cell or tissue with which it is normally associated and [2] explain its primary function.
suberin
Suberin is associated with the endodermis, where it is a part of the Casparian strip. The function of suberin is to prohibit water flow through the extracellular space, i.e. it blocks the apoplastic pathway for water and minerals crossing the endodermis.
____________________________________________________________________________
lignin
Lignin is associated with the wood of trees, and also hard nutshells. Its primary function is mechanical support and protection.
____________________________________________________________________________
sporopollenin
Sporopollenin is found in the external coats of both pollen and spores. The primary function of sporopollenin is to protect the cells inside from desiccation when exposed to air.
14. Primary Growth
A. [4 pts]
What change(s) do cells experience as they move from an apical meristem to a primary meristem?
Cells become committed to the production of a particular tissue type (e.g. epidermis; ground tissue; vascular tissue).
B. [6 pts]
What change(s) do cells experience as they move from a primary meristem to the zone of elongation?
These cells cease to undergo mitosis (i.e. become postmitotic), and differentiate into a particular tissue type. They also experience a growth in size or elongation.
C. [6 pts]
A hungry rabbit completely devours the top half of a plant's shoot, but is scared away by the gardener before it can finish off the lower leaves [see picture]. What pattern of primary growth should the gardener expect from this partially eaten shoot?
The axillary bud at the base of each leaf will transform into a new apical meristem, and grow out as a secondary branch.
There will be no growth at the bitten end of the stem, where this is no longer any meristem.
D. [4 pts]
The same rascally rabbit comes back later, and begins to nibble on a second plant. But this time the gardener chases the rabbit off quickly, and only half of one leaf is consumed [see picture]. What pattern of growth should the gardener expect from this partially eaten leaf?
The half-eaten leaf will experience no growth. It does not have any meristematic tissue, and the axillary bud at its base will remain dormant because the terminal bud is still intact.