1.  Which of the following affect the availability of nutrients for plants?
a.  Soil pH
b.  Soil salinity
c.  Soil composition
d.  All of the above

The correct answer is d—
A.  Answer a is incorrect. Acidic or basic conditions in the soil can affect the availability of ions and anions.  However, it not the only correct answer.

The correct answer is d—
B.  Answer b is incorrect. Salinity will affect water uptake, which will influence nutrient uptake.  However, it is not the only correct answer.

The correct answer is d—
C.  Answer c is incorrect. The soil composition determines the soil organic matter, water-holding capacity and nutrient-holding capacity.  However, it is not the only correct answer.

The correct answer is d—All of the above
D.  Answer d is correct. A, b, and c are all correct.

2.  If you wanted to conduct an experiment to determine the effects of varying levels of macronutrients on plant growth and did so in your small greenhouse at home, which of the following macronutrients would be the most difficult to regulate?
a.  Carbon
b.  Nitrogen
c.  Potassium
d.  Phosphorus

The correct answer is a—Carbon
A.  Answer a is correct. The source of carbon is the atmosphere.  It would be impossible for someone to control the amount of carbon in their greenhouse at home.

The correct answer is a—
B.  Answer b is incorrect. One could vary the amount of nitrogen.

The correct answer is a—
C.  Answer c is incorrect. One could vary the amount of potassium.

The correct answer is a—
D.  Answer d is incorrect. One could vary the amount of phosphorus.

3.  You are performing an experiment to determine the nutrient requirements for a newly discovered plant and find that for some reason your plants die if you leave boron out of the growth medium but do fine with as low as 5 parts per million in solution.  This suggests that boron is—
a.   an essential macronutrient
b.   a nonessential micronutrient
c.   an essential micronutrient
d.   a nonessential macronutrient

The correct answer is c—
A.  Answer a is incorrect. Although boron is essential, it is only required in small amounts.

The correct answer is c—
B.  Answer b is incorrect. Boron is required for the plant to live and therefore is an essential nutrient.

The correct answer is c—an essential micronutrient
C.  Answer c is correct. Boron is required in small amounts for the plant to live.

The correct answer is c—
D.  Answer d is incorrect. Boron is required for the plant to live and therefore is an essential nutrient.

4.  Which of the following might you do to increase nutrient uptake by crop plants?
a.  Decrease the solubility of nutrients
b.  Create nutrients as positive ions
c.  Frequently plow the soil
d.  Genetically modify plants to increase the density of plasma membrane transporters in root cells

The correct answer is d—
A.  Answer a is incorrect. Decreasing the solubility of nutrients would decrease their availability as the nutrients need to be in soil solution.

The correct answer is d—
B.  Answer b is incorrect. Nutrients in positive ion form would allow them to stick to the negatively charged soil particle surfaces, thereby being less available to plants.

The correct answer is d—
C.  Answer c is incorrect. Plowing the soil often decreases nutrient availability for crop plants.

The correct answer is d—Genetically modify plants to increase the density of plasma membrane transporters in root cells
D.  Answer d is correct. Membrane transporters are important in actively bringing minerals into the root, so increasing their numbers would increase uptake by plants.

5.  Which of the following would decrease nitrogen availability for a pea plant?
a.  Inability of the plant to produce flavonoids
b.  Formation of Nod factors
c.  Presence of oxygen in the soil
d.  Production of leghemoglobin

The correct answer is a—Inability of the plant to produce flavonoids
A.  Answer a is correct. It is the production of flavonoids and secretion into the soil initiates the mutualistic relationship with nitrogen-fixing bacteria.

The correct answer is a—
B.  Answer b is incorrect. The formation of Nod factors is required for the mutualistic relationship to occur.

The correct answer is a—
C.  Answer c is incorrect. Although oxygen inhibits nitrogenase, it is required by the bacteria and plant for survival.

The correct answer is a—
D.  Answer d is incorrect. Leghemoglobin is essential for tying up oxygen so nitrogenase can function properly.

6.  Different soils contain varying amounts of space between the soil particles.  Which of the following statements is correct?
a.  Some of the space in soils must be filled by air in order for plants to survive.
b.  The amount of water a soil can hold is the same amount of water a plant can extract.
c.  Even though sandy soils have a lot of space between particles, a lot of water is lost because of drainage due to gravity.
d.  All of these statements are correct.

The correct answer is a and c—Some of the space in soils must be filled by air in order for plants to survive.  Even though sandy soils have a lot of space between particles, a lot of water is lost because of drainage due to gravity.
A.  Answer a is correct. Roots require oxygen to perform respiration in order to survive.

The correct answer is a and c—
B.  Answer b is incorrect.  This statement is incorrect because plants are not able to remove all of the water in a soil.  Water will remain in the soil even as a plant wilts, because some water is unavailable. 

The correct answer is a and c—Some of the space in soils must be filled by air in order for plants to survive.  Even though sandy soils have a lot of space between particles, a lot of water is lost because of drainage due to gravity.
C.  Answer c is correct. Sandy soils tend to lose a lot of water because of gravity. 

The correct answer is a and c—
D.  Answer d is incorrect. Answer b is not a correct response.

7.  Some plants, such as the Venus flytrap, have evolved the ability to digest insects.  This benefits the plants because—
a.  they gain energy from the digested insect and can therefore photosynthesize less
b.  they live in nutrient-poor environments and can gain valuable macronutrients such as nitrogen
c.  they are prone to herbivory from insects and thus can defend themselves from insects
d.   they gain carbon from the insects, enabling them to increase photosynthetic rates

The correct answer is b—
A.  Answer a is incorrect. There are no energy gains from consuming the insects.  The plants must still photosynthesize.

The correct answer is b—they live in nutrient-poor environments and can gain valuable macronutrients such as nitrogen
B.  Answer b is correct.  Carnivorous plants tend to live in nitrogen-poor environments like bogs.  Insects provide a means to gain valuable nutrients.

The correct answer is b—
C.  Answer c is incorrect.  Herbivory is not the concern of these plants.

The correct answer is b—
D.  Answer d is incorrect.  Carnivorous plants still take carbon from the atmosphere to perform photosynthesis.

8.  There is concern about increased atmospheric carbon dioxide levels as it may relate to global warming.  However, increasing atmospheric carbon dioxide should theoretically help plant growth.  Which of the following could be drawbacks for plants from increased carbon dioxide?
a.  Increased protein to carbohydrate ratios in plants
b.  Increased herbivory
c.   Increased photorespiration
d.  All of the above

The correct answer is b—
A.  Answer a is incorrect. Increasing carbon dioxide will actually decrease the protein-to-carbohydrate ratio of plants as nitrogen becomes the limiting factor.

The correct answer is b—Increased herbivory
B.  Answer b is correct. If protein levels decrease, herbivores will need to consume more vegetation to acquire enough protein.  Thus, increased herbivory would likely result.

The correct answer is b—
C.  Answer c is incorrect. Photorespiration would actually decrease.  Increased carbon dioxide would reduce the likelihood that oxygen would be taken up by Rubisco.

The correct answer is b—
D.  Answer d is incorrect. Only b is correct.

9.  If you were asked how to clean up a trichloroethylene (TCE) spill without having to resort to burning or other chemical methods, how would you do it?
a.   Plant poplar trees to phytoremediate the soil.
b.   Plant bean plants to replace the TCE with fixed nitrogen.
c.   Plant Brassica plants to phytoaccumulate the TCE.
d.   Plant Indian pipe because it is not adversely affected by TCE in the soil.

The correct answer is a—Plant poplar trees to phytoremediate the soil
A.  Answer a is correct. Poplar trees are able to take up TCE and break it down to produce CO2 and Cl–.

The correct answer is a—
B.  Answer b is incorrect. Fixing nitrogen from the atmosphere will not get rid of TCE in the environment.

The correct answer is a—
C.  Answer c is incorrect. Brassica can phytoaccumulate heavy metals, but not TCE.

The correct answer is a—
D.  Answer d is incorrect. Although Indian pipe may not be affected by the TCE, it cannot remove TCE from the environment.  Furthermore, Indian pipe is a parasitic plant that would require another plant in order to acquire nutrients. 

10.  Which of the following is most common among plants as nutritional adaptations?
a.  Forming symbiotic relationships with nitrogen-fixing bacteria
b.  Becoming carnivorous
c.  Becoming parasitic
d.  Forming symbiotic relationships with mycorrhizae

The correct answer is d—
A.  Answer a is incorrect. Mutualistic associations with nitrogen-fixing bacteria are generally limited to the legume family.

The correct answer is d—
B.  Answer b is incorrect. Very few plant species have evolved the ability to become carnivorous.

The correct answer is d—
C.  Answer c is incorrect. Parasitic plants are quite rare.

The correct answer is d—Forming symbiotic relationships with mycorrhizae
D.  Answer D is correct. Mycorrhizae are found in about 90% of vascular plants.

11.  Why must plants actively transport positive ions into their roots?
a.  It is the positive ions in the roots that allow water to be drawn from the soil.
b.  The soil solution contains primarily negatively charged ions, so positive ions are continually drawn out of the root.
c.  Negative ions in the plant root must be balanced by positive ions.
d.  None of the above.

The correct answer is b—
A.  Answer a is incorrect. Solute potential can be generated by other molecules, including negatively charged ions and molecules with no charge.

The correct answer is b—The soil solution contains primarily negatively charged ions, so positive ions are continually drawn out of the root.
B.  Answer b is correct. Most of the molecules in the soil solution are negatively charged because the positively charged molecules are often attracted to soil particles, owing to their negative charge.  Thus, the soil solution tends to be negatively charged, thus pulling positively charged molecules out of the plant root to balance the charge in the soil solution.

The correct answer is b—
C.  Answer c is incorrect. Balanced charge in the roots isn’t imperative.

The correct answer is b—
D.  Answer d is incorrect. Answer b is correct.

12.  Saline soils are detrimental to plant growth for which of the following reasons?
a.  Salt in soils does not allow active transport of mineral nutrients into the plant.
b.  Salt in soils prevents water from moving into the plant via osmosis.
c.  Salt is toxic to plants.
d.  None of the above.

The correct answer is b—
A.  Answer a is incorrect. Plants could still actively transport mineral nutrients in salty soils.

The correct answer is b—Salt in soils prevents water from moving into the plant via osmosis.
B.  Answer b is correct. Salt in the soil can give the soil a lower water potential than the plant, thereby moving water from the plant into the soil.

The correct answer is b—
C.  Answer c is incorrect. Salt is not toxic per se.

The correct answer is b—
D.  Answer d is incorrect. Answer b is correct.

13. Most plants are limited in their growth because nitrogen is often limiting in the environment, yet plants are bathed in an atmosphere that is full of nitrogen.  Why can’t plants utilize this nitrogen source?
a.  Nitrogen gas (N2) is held together by very strong bonds, which plants cannot break.
b.  N2 is not soluble.
c.  N2 cannot be broken down by any organisms.
d.  All of the above.

The correct answer is a—Nitrogen gas (N2) is held together by very strong bonds, which plants cannot break.
A.  Answer a is correct. Nitrogen gas is held together by a triple bond, which plants cannot break.

The correct answer is a—
B.  Answer b is incorrect. Solubility doesn’t really matter if the bonds can’t be broken.

The correct answer is a—
C.  Answer c is incorrect. Nitrogen-fixing bacteria are indeed capable of breaking these bonds, though at very high energetic costs.

The correct answer is a—
D.  Answer d is incorrect. Answers b and c are incorrect.

Challenge Questions

1.  Match each of the following nutrients with its appropriate function in plants, and discuss whether it is a macro- or micronutrient.

2.  If you were to eat one ton (1000 kg) of potatoes, approximately how much of the following minerals would you eat?
a.   Copper between 0.4 and 3 g
b.   Zinc between 1.5 and 10 g
c.   Potassium between 0.5 and 6%
d.   Iron between 2.5 and 30 g

Answer—Here is how you solve the problems:
The macronutrient potassium constitutes 0.5–6% of the dry weight. Let’s assume that the potato is 90% water. The dry weight would be 10% of 1000 kg, or 100 kg. Next you calculate 0.5% of 100, which is 0.5 kg. You would do the same type of calculation for 6%.
The micronutrient problems would also use the estimate of 100 kg dry weight. The conversion you need to use is that 1 ppm is the same as 1 mg/kg. So, 4 ppm of copper is the same as 4 mg/kg. Multiply this by 100 kg of dry weight potato and you have 400 mg of copper. Since there are 1000 mg in a gram, 400 mg X 1 g/1000 mg = 0.4 g of copper in a ton of potato. The other micronutrient problems would be calculated in a similar manner.