35. Soil

Nitrogen Fixation

Science of Nitrogen Fixation

 provide a steady supply of sugar to the host plant 

 No. Plants manufacture their own organic compounds. 

 produce antibiotics that protect the plant from soil bacteria 

 No. This is accomplished by the fungal component of mycorrhizae. 

 increase the surface area for water uptake 

 No. This is accomplished by both root hairs and mycorrhizae. 

This is a mutualistic endosymbiosis.

Legumes (members of the pea family) have roots with swellings called nodules that __________.

 as stored nutrients to support the plant when necessary 

 No. Mycorrhizae are not nutrients, though they play a role in the acquisition of nutrients. 

 only in plants such as mistletoe that parasitize other plants 

 No. Mycorrhizal associations are not restricted to parasitic plants. 

 when soil is too compact and lacks sufficient air spaces 

 No. Mycorrhizal associations are not stimulated by anaerobic conditions. 

 to control the evaporation of water from leaves 

 No. Guard cells regulate the opening of the stomata through which water evaporates. 

Consider the mutualistic relationship in which mycorrhizae are involved.

Mycorrhizae develop __________.

Mycorrhizae enhance plant nutrition mainly by
a. absorbing water and minerals through the fungal hyphae.
b. providing sugar to root cells, which have no chloroplasts.
c. converting atmospheric nitrogen to ammonia.
d. enabling the roots to parasitize neighboring plants.

 the use of nitrogen to build molecules such as proteins and nucleic acids 

 No. Nitrogen fixation is not the incorporation of nitrogen into proteins and nucleic acids. 

 the recycling of nitrogen from organic matter in the soil 

No. Recycling organic nitrogen in the soil into ammonia is called ammonification.

the absorption of N2 from the soil

 No. Nitrogen fixation is the conversion of nitrogen from one form to another. 

 performed by fungi inhabiting root nodules 

 No. It is performed by nitrogen-fixing bacteria. 

 the conversion of nitrogen gas in the air to a form usable by plants 

Consider the organisms that accomplish this process.

Nitrogen fixation is __________.

 No. These plants live in habitats such as bogs, where water is not in limited supply. 

 No. The amino acids of which proteins are made do not contain phosphorus. 

 sugars; because they can't make enough in photosynthesis 

 No. Photosynthesis produces sufficient sugar to meet the needs of a carnivorous plant. 

Consider the nutritional quality of insects.

By trapping insects, carnivorous plants obtain __________, which they need __________.

 Epiphytes are
a. fungi that attack plants.
b. fungi that form mutualistic associations with roots.
c. nonphotosynthetic parasitic plants.
d. plants that grow on other plants.

Nitrogen & Phosphorus Cycles: Always Recycle! Part 2 - Crash Course Ecology #9

No. Rhizobium is a genus of nitrogen-fixing bacteria.

 No. Leghemoglobin is an iron-containing protein that helps to provide an anaerobic environment for nitrogen fixation, but it is not the enzyme that catalyzes the reaction. 

No. This enzyme is responsible for the incorporation of CO2 into the Calvin cycle.

 No. Hydrogenation replaces a double bond between two carbon atoms with a single bond and an additional hydrogen atom bonded to each carbon. 

Enzyme names are fairly predictable. What would you name an enzyme that fixed nitrogen?

The enzyme complex that catalyzes the conversion of atmospheric nitrogen to ammonia is __________.

The specific relationship between a legume and its mutualistic Rhizobium strain probably depends on
a. each legume having a chemical dialogue with a fungus.
b. each Rhizobium strain having a form of nitrogenase that works only in the appropriate legume host.
c. each legume being found where the soil has only the Rhizobium specific to that legume.
d. specific recognition between chemical signals and signal receptors of the Rhizobium strain and legume species.

Understanding Our Soil: The Nitrogen Cycle, Fixers, and Fertilizer

Nitrogen Cycle

 No. Plants obtain carbon dioxide from the atmosphere. 

 No. Plants obtain oxygen from the atmosphere. 

 No. Iron is a micronutrient that plants obtain from the soil. 

The correct answer is often a limiting nutrient to plants.

The most abundant gas in our atmosphere cannot be used by plants directly in its atmospheric form. Fortunately, this gas is made available to some plants by certain bacteria that live symbiotically in their roots. What is this gas?

The carnivorous plant Nepenthes bicalcarata (“fanged pitcher plant”) has a unique relationship with a species of ant—Camponotus schmitzi (“diving ant”). The diving ants are not digested by the pitcher plants, but instead live on the plants and consume nectar. Diving ants also dive into the digestive juices in the pitcher, swim to the bottom, and capture and consume trapped insects, leaving uneaten body parts and ant feces behind. What nutritional impact do the ants have on fanged pitcher plants? Do the pitcher plants derive any nutritional benefit from this relationship?

Nitrogen is a key nutrient often obtained by carnivorous plants from the insects they digest. Are the results presented here what would be expected if nitrogen is a limiting nutrient? Explain.

 Vesicles containing bacteria bud into cortical cells. 

 No. Vesicles do not form until after the production of the infection thread. 

 No. This is one of the last stages in the formation of a root nodule. 

 An infection thread is initiated in the root hair of the legume. 

No. Signals from Rhizobium are necessary to initiate the infection thread.

There is nodule growth in response to secretions from Rhizobium.

 No. Nodule growth does not begin until the infection thread reaches the cortex. 

Soybeans secrete chemical signals that are detected by Rhizobium.

Is this symbiosis initiated by the bacterium or by the plant?

Which of these describes the initial interaction between Rhizobium and a soybean root?

The greatest difference in health between two groups of plants of the same species, one group with mycorrhizae and one group without mycorrhizae, would be in an environment
a. where nitrogen-fixing bacteria are abundant.
b. that has soil with poor drainage.
c. that has hot summers and cold winters.
d. in which the soil is relatively deficient in mineral nutrients.

 No. Plants actually provide an anaerobic environment, which is required for nitrogen fixation. 

 No. The plants rely on the nitrogen-fixing bacteria to provide fixed nitrogen to use for the synthesis of amino acids, among other things. 

 No. The atmosphere is full of nitrogen gas. The bacteria fix the nitrogen into a form that the plants can assimilate and use. 

In a mutualistic symbiosis, both organisms gain something.

In root nodules, the plants provide __________, and the bacteria provide __________.

 No. Mycorrhizal fungi associate with plant roots to increase absorptive surface area. 

 No. Lichens are symbiotic associations between protists and algae. 

No. Azolla are aquatic ferns that form symbiotic relationships with nitrogen-fixing cyanobacteria.

 No. Legumes form root nodules within which nitrogen-fixing bacteria are housed. 

If you think all bacteria are bad, think again.

Which of the following organisms can fix nitrogen?

Nitrogen Fixation - Seven Wonders of the Microbe World (4/7)

The Nitrogen Cycle

NITROGEN CYCLE: A level biology AQA.   Saprobionts, nitrogen-fixing, ammonification & nitrification

 Arbuscular mycorrhizae penetrate the cytoplasm of root cells. 

 No. In arbuscular mycorrhizae, hyphae penetrate root cell walls but not cytoplasm. 

 Ectomycorrhizae are found in many crop plants, such as wheat and maize. 

 No. Arbuscular mycorrhizae are found in over 85% of plant species, including crop plants, such as wheat and maize; in contrast, ectomycorrhizae are only found in about 10% of plant families, and these generally contain woody plants. 

 The fungal hyphae of ectomycorrhizae form arbuscules. 

 No. The fungal hyphae of arbuscular mycorrhizae form arbuscules. 

 None of the listed responses is correct. 

 No. One of the other answers is correct. 

 Arbuscular mycorrhizae do not have a dense mantle ensheathing roots. 

Review the two types of mycorrhizae.

Which of the following is true of mycorrhizae?

Nodules

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