Biology Chapter on Nitrogen Cycle

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Questions and Answers

What primarily provides energy in a grazing food chain?

Microbial biomass

Carnivores

Plant energy (correct)

Dead organic matter

What is a characteristic of food webs?

They connect different types of organisms at various trophic levels. (correct)

They consist of only one food chain.

They are simple linear sequences.

They are unstable compared to food chains.

Why do ecosystems with complex food webs have greater stability?

Each species relies solely on one other species for survival.

They are composed only of carnivorous organisms.

They operate as isolated linear sequences.

They have numerous options available at each trophic level. (correct)

Which statement is true regarding detritus food chains?

They obtain energy primarily from plant biomass. Signup and view all the answers

What is the main feature of ecosystems in tropical regions compared to Antarctic ecosystems?

They contain a greater diversity of species and complex food webs. Signup and view all the answers

What is the primary way nitrogen is fixed in the atmosphere?

By lightning and certain bacteria Signup and view all the answers

Which of the following compounds is produced as a result of ammonification?

Ammonia Signup and view all the answers

Which process involves the conversion of nitrates back into molecular nitrogen?

Denitrification Signup and view all the answers

What percentage of the atmosphere is composed of nitrogen in its molecular form (N2)?

78% Signup and view all the answers

During the decomposition of organic matter, which group of bacteria converts organic nitrogen into ammonia?

Ammonifying bacteria Signup and view all the answers

What is the significance of nitrification in the nitrogen cycle?

It converts ammonia into nitrites and nitrates. Signup and view all the answers

Which of the following processes can lead to eutrophication?

Excess nitrogen runoff from fertilizers Signup and view all the answers

What role do plants play in the nitrogen cycle?

They absorb nitrates and participate in metabolism. Signup and view all the answers

Which type of desert has cold winters and warm summers?

Cold Desert Signup and view all the answers

What adaptation helps desert plants reduce water loss during transpiration?

Scaly leaves Signup and view all the answers

What is a characteristic feature of pond ecosystems?

They are usually seasonal and may be shallow. Signup and view all the answers

Which zone in a lake ecosystem is known for effective penetration of solar light?

Limnetic zone Signup and view all the answers

Why do desert animals typically have thick outer coverings?

To minimize loss of water Signup and view all the answers

What is a common anthropogenic pressure that affects pond ecosystems?

Pollution from washing clothes Signup and view all the answers

What type of plant adaptation involves the flattening of stems to perform photosynthesis?

Flattened stems Signup and view all the answers

Which of the following describes the nutrient status of desert soil?

Rich in nutrients but deficient in water Signup and view all the answers

Which trophic level has the largest population in a forest ecosystem?

Herbivores Signup and view all the answers

What does the pyramid of numbers in a grassland ecosystem imply?

Fewer producers than herbivores Signup and view all the answers

What type of pyramid is formed in a parasitic food chain?

Inverted pyramid of numbers Signup and view all the answers

Which of the following represents secondary consumers in a forest ecosystem?

Frogs and birds Signup and view all the answers

How is the pyramid of biomass different from the pyramid of numbers?

It is based on dry matter at each trophic level. Signup and view all the answers

Which organisms act as hyperparasites in the described food chain?

Fleas and microbes Signup and view all the answers

What is the primary role of big trees in a forest ecosystem?

To serve as producers Signup and view all the answers

Why does the pyramid of biomass in a forest likely appear upright?

Due to the large number of producers Signup and view all the answers

What does the 'I' in the universal energy flow model represent?

Energy input Signup and view all the answers

In a single channel energy flow model, energy flows in what manner?

Unidirectional Signup and view all the answers

What phenomenon results in the gradual decline of energy levels at each trophic level in a grazing food chain?

Heat loss Signup and view all the answers

In which ecosystem is the grazing food chain likely to predominate?

Marine ecosystem Signup and view all the answers

What does the 'R' in the one-way energy flow model signify?

Respiratory loss Signup and view all the answers

Which model represents two pathways of energy flow operating simultaneously?

Y-shaped model Signup and view all the answers

What does the term 'detritus' refer to in ecological energy models?

Dead organic matter in an ecosystem Signup and view all the answers

Which component is NOT part of the universal energy flow model?

Energy exported Signup and view all the answers

Study Notes

Nitrogen Cycle

Nitrogen constitutes 78% of the atmosphere primarily in the form of N2.
Nitrogen fixation occurs through lightning or bacteria/cyanobacteria.
Plants absorb nitrogen for amino acids, proteins, and vitamins, passing it up the food chain.
Decomposition of dead organisms releases organic nitrogen, converted by ammonifying and nitrifying bacteria into ammonia, nitrites, and nitrates.
Some bacteria return nitrates to the atmosphere as N2, continuing the nitrogen cycle.

Energy Flow Models

Single Channel Model:
- Energy flows unidirectionally from producers to herbivores to carnivores.
- Energy loss occurs at each trophic level, contributing to heat loss.
- Measurements include Gross Primary Production (GPP) and Net Primary Production (NPP).
Double Channel Model:
- Recognizes both grazing and detritus food chains, which coexist in ecosystems.
- Grazing chains dominate in marine ecosystems; detritus chains are significant in forest ecosystems.
- Energy in grazing food chains primarily comes from plant energy, while in detritus chains, it derives from plant biomass decomposed by fungi and bacteria.

Food Webs

Food webs consist of interconnected food chains, providing greater ecosystem stability than linear food chains.
They offer multiple feeding options, reducing impact if one species declines.
Antarctic ecosystems demonstrate simple food webs compared to the complex diversity found in tropical regions.

Pyramids of Numbers and Biomass

Pyramid of Numbers: Shows the quantity of organisms at each level; forests have narrow bases with fewer producers and wider middle levels of herbivores.
Pyramid of Biomass: Represents the total dry matter at each trophic level; can be upright (like forests) or inverted (like parasitic chains).

Desert Ecosystems

Deserts exhibit adaptations for water conservation, such as reduced scaly leaves and deep root systems.
Desert soils are nutrient-rich but water-deficient, resulting in low plant diversity and slower recovery from stress.

Aquatic Ecosystems

Freshwater Ecosystems: Divided into lentic (standing water, e.g., ponds) and lotic (flowing water, e.g., rivers).
Pond Ecosystem: Small, stagnant water bodies often subjected to pollution from human activity.
Lake Ecosystem: Larger bodies of standing water with zones defined by light penetration:
- Littoral zone (shallow, near shore),
- Limnetic zone (open, light-penetrated area),
- Profundal zone (deep, light-deprived area).

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Test your knowledge on the nitrogen cycle with this quiz. Explore how nitrogen is fixed, its role in plant metabolism, and the process of decomposition. Understand the importance of nitrogen for life and its movement through ecosystems.