Question 1

Nitrogen fixation is a process that ________.

Accepted Answer

Nitrogen fixation is the conversion of atmospheric nitrogen gas into a usable form by organisms, such as ammonia. This process is important because nitrogen gas cannot be directly used by most living organisms.

Question 2

You are weeding your garden when you accidentally expose some roots of your pea plants. You notice swellings (root nodules)on the roots, and there is a reddish tinge to the ones you accidentally damaged. Most likely your pea plants ________.

Accepted Answer

The presence of root nodules and a reddish tinge on the roots suggest that the pea plants have a mutualistic relationship with nitrogen-fixing bacteria. The bacteria provide the plant with usable nitrogen in exchange for carbohydrates produced by the plant. This symbiotic relationship benefits both the plant and the bacteria, as the plant receives an important nutrient and the bacteria gain access to a carbohydrate energy source.

Question 3

Soil leaching can cause nutrient deficiencies in the soil. Which of the following are symptoms of nutrient deficiency in plants?
I chlorosis
II death of meristems
III excess storage of chlorophyll
IV small internodes

Accepted Answer

Chlorosis (yellowing of leaves) is a symptom of nutrient deficiency, as well as death of meristems (the growing tips of plants) and small internodes (the space between leaves on a stem). Excess storage of chlorophyll is not a symptom of nutrient deficiency.

Question 4

Hyphae form a covering over roots. These hyphae create a large surface area that helps to do which of the following?

Accepted Answer

The large surface area created by the hyphae allows for increased absorption of minerals and ions, which can then be transported to the plant.

Question 5

Rhizobia, actinomycetes, and cyanobacteria all share the common feature that they can ________.

Accepted Answer

Rhizobia, actinomycetes, and cyanobacteria are all known for their ability to fix atmospheric nitrogen, meaning they convert unusable nitrogen gas in the air into a usable form that plants can absorb. This is a mutualistic relationship where the bacteria provide the plants with nitrogen and in return, the plant provides the bacteria with carbohydrates. Although these microorganisms may have other beneficial characteristics such as improving soil quality or surviving in extreme environments, the shared feature mentioned in the question is their ability to fix nitrogen.

Question 6

The earliest vascular plants on land had underground stems (rhizomes), but no roots. Water and mineral nutrients were most likely obtained by ________.

Accepted Answer

The earliest vascular plants likely formed a mutualistic relationship with mycorrhizal fungi, which helped the plants absorb water and minerals from the soil. This allowed the plants to grow taller than non-vascular plants and paved the way for the evolution of roots. Diffusion through stomata and the cuticle of the rhizome, as well as osmosis through root hairs, are mechanisms used by later-evolving plants with roots.

Question 7

A plant developed a mineral deficiency after being treated with a fungicide. What is the most probable cause of the deficiency?

Accepted Answer

The answer of A plant developed a mineral deficiency after...

Question 8

Which of the following is a primary difference between ectomycorrhizae and endomycorrhizae?

Accepted Answer

Ectomycorrhizae form a sheath around the outside of the root cells and do not penetrate them, while endomycorrhizae grow into invaginations of the root cell membranes called arbuscules. This is a significant difference between the two types of mycorrhizae. A is incorrect because it describes the opposite of the actual difference - ectomycorrhizae have thicker, longer hyphae than endomycorrhizae. C and D are both incorrect; while endomycorrhizae may be more common in some ecosystems, there is no general trend that makes one type of mycorrhizae more common than the other, and there are significant physiological and ecological differences between the two types.

Question 9

A major function of magnesium in plants is to be ________.

Accepted Answer

Magnesium is an essential component of chlorophyll, which is responsible for capturing light energy during photosynthesis. Without magnesium, plants cannot produce chlorophyll and will not be able to carry out photosynthesis efficiently.

Question 10

Nitrogen-fixing bacteria and nitrifying bacteria convert atmospheric nitrogen into different compounds of nitrogen such as: (a)ammonium ion, (b)ammonia, (c)nitrate ion, and (d)nitrite ion. Which of the following is the correct sequence of formation of the nitrogen compounds?

Accepted Answer

The answer of Nitrogen-fixing bacteria and nitrifying bacteria convert atmospheric...

Question 11

The specific relationship between a legume and its mutualistic Rhizobium strain probably depends on ________.

Accepted Answer

The specific relationship between a legume and its mutualistic Rhizobium strain is based on specific recognition between the chemical signals and signal receptors of the Rhizobium strain and the legume species. This recognition allows for the formation of a successful symbiotic relationship where the Rhizobium provides the legume with nitrogen and the legume provides the Rhizobium with a carbon source. Therefore, choice D is the correct answer.

Question 12

What major benefits do plants and mycorrhizal fungi receive from their symbiotic relationship?

Accepted Answer

Plants receive nitrogen and phosphorus, which are essential for their growth and development, from the mycorrhizal fungi. In exchange, the fungi receive photosynthetic products such as sugars from the plants, which they use as a source of energy to grow and colonize more roots. This mutualistic relationship benefits both organisms and is essential for the nutrient cycling in terrestrial ecosystems.

Question 13

Which one of the following micronutrients plays a critical role as a component of chlorophyll?

Accepted Answer

Magnesium is a critical component of chlorophyll, the pigment that gives plants their green color and facilitates the process of photosynthesis. Chlorophyll contains a magnesium atom in the center of a ringed structure, which allows it to absorb sunlight and convert it into energy that can be used by the plant.

Question 14

Synthesis of which of the following compounds in a mature leaf would be least impacted by a temporary soil nitrogen deficiency?

Accepted Answer

Cellulose synthesis in mature leaves is primarily dependent on carbon fixation through photosynthesis, whereas DNA, RNA, and amino acid synthesis require nitrogen as a key component. Therefore, a temporary soil nitrogen deficiency would have the least impact on cellulose synthesis compared to the synthesis of other compounds.

Question 15

Micronutrients are needed in very small amounts because ________.

Accepted Answer

Micronutrients are needed in very small quantities because they serve mainly as cofactors of enzymes, which are proteins that catalyze chemical reactions. Enzymes require specific micronutrients to function properly, and without them, the plant cannot carry out essential metabolic processes.

Question 16

Two groups of tomatoes were grown under laboratory conditions, one with humus added to the soil, and one a control without humus. The leaves of the plants grown without humus were yellowish (less green)compared with those of the plants grown in the humus-enriched soil. The best explanation for this difference is that ________.

Accepted Answer

The yellowing of leaves is often a sign of chlorophyll deficiency, which can be caused by a lack of essential nutrients such as magnesium and iron. The humus likely contained these minerals and therefore provided the necessary nutrients for chlorophyll synthesis, resulting in the greener leaves observed in the plants grown in humus-enriched soil.

Question 17

Why is nitrogen fixation an essential process?

Accepted Answer

Fixed nitrogen is often the limiting factor in plant growth, which means that it is necessary for plant growth and productivity. Without enough fixed nitrogen, plants would not be able to produce enough proteins and nucleic acids necessary for their growth and development.

Question 18

If an African violet has chlorosis, which of the following elements might be a useful addition to the soil?

Accepted Answer

Chlorosis in African violets is often caused by a lack of magnesium in the soil. Therefore, adding magnesium to the soil would be a useful addition in correcting this issue.

Question 19

We would expect the greatest difference in plant health between two groups of plants of the same species, one group with mycorrhizae and one group without mycorrhizae, in an environment ________.

Accepted Answer

Mycorrhizae form mutualistic associations with plant roots, providing them with mineral nutrients such as phosphorus and access to water in exchange for carbohydrates produced by the plant through photosynthesis. In an environment where the soil is relatively deficient in mineral nutrients, the difference in plant health between a group of plants with mycorrhizae and a group without mycorrhizae would be greatest as the mycorrhizae would provide an important source of nutrients for the plants. In contrast, in environments where nitrogen-fixing bacteria are abundant or there is poor soil drainage or the presence of water, the difference in plant health between the two groups would not be as great as the plants may have other sources of nutrients or waste build up issues with water.

Question 20

Which of the following plants is classified as an epiphyte?

Accepted Answer

Epiphytes are plants that grow on the surface of other plants, typically trees, without drawing nutrients from their host. The staghorn fern is commonly found growing in this way. The Venus flytrap and pitcher plant are carnivorous and obtain their nutrients by trapping and digesting insects. Mistletoe is a parasitic plant that does draw nutrients from its host.

Quiz 37: Soil and Plant Nutrition