Nutrition (B4.2 Ecological Niches, C4.2 Transfer of Energy and Matter

What is an ecological niche?

It is the role of a species in an ecosystem, including all the biotic and abiotic interactions (like how it obtains food) that influence its growth, survival, and reproduction.

What is the difference between obligate aerobes, facultative anaerobes, and obligate anaerobes?

Obligate aerobes require oxygen to survive. Facultative anaerobes can survive with or without oxygen. Obligate anaerobes can only live in oxygen-deficient environments.

What is the mode of nutrition for plants, algae, and cyanobacteria?

Photosynthesis, a form of autotrophic nutrition where they produce their own food using light energy.

What is holozoic nutrition, and what are its four main stages?

It is a type of heterotrophic nutrition used by animals. The four stages are: 1. Ingestion (intake of food), 2. Digestion (internal breakdown), 3. Absorption (transport of small molecules into the body), and 4. Assimilation (incorporation into metabolism).

What is mixotrophic nutrition? Give an example.

Mixotrophic nutrition is when an organism can switch between or combine autotrophic and heterotrophic modes. For example, the protist Euglena can perform photosynthesis in the light and consume food in the dark.

What is saprotrophic nutrition, and what organisms use it?

It is a mode of heterotrophic nutrition that involves the extracellular digestion of decayed organic matter, followed by the absorption of the resulting small molecules. Organisms that use it, like some fungi and bacteria, are called decomposers.

What are the different ways that organisms in the domain Archaea can produce ATP?

Archaea are metabolically very diverse and can produce ATP using one of three energy sources: light, the oxidation of inorganic chemicals, or the oxidation of carbon compounds.

How does the dentition (teeth structure) of omnivores and herbivores in the family Hominidae relate to their diet?

Herbivores (e.g., Paranthropus robustus) have large, flat molars for grinding fibrous plant tissue. Omnivores (e.g., Homo sapiens) have a combination of modified sharp canines/incisors for tearing meat and large molars for grinding plants.

What is an example of an adaptation of a herbivorous insect for feeding, and a plant for resisting herbivory?

A herbivorous insect like a beetle has chewing mouthparts (mandibles) to cut leaves. A plant may have physical defenses like thorns or produce toxic secondary compounds in its leaves and seeds to deter herbivores.

What is one chemical, physical, and behavioral adaptation of a predator?

Chemical: Using venom to kill prey. Physical: Enhanced senses like sharp vision to find prey. Behavioral: Hunting in packs to catch larger prey.

What is one chemical, physical, and behavioral adaptation of a prey animal?

Chemical: Releasing toxins or irritant sprays. Physical: Using camouflage to hide. Behavioral: Making warning calls to alert others to danger.

Describe two different strategies that plants in a forest use to harvest light.

1. Canopy trees grow tall with dominant vertical shoots to reach direct sunlight. 2. Lianas are climbing plants that use other trees for support to reach the canopy without investing energy in thick stems.

What is the difference between a fundamental niche and a realized niche?

A fundamental niche is the full range of environmental conditions and resources a species could potentially occupy and use. A realized niche is the actual part of the fundamental niche that a species occupies due to limiting factors like competition with other species.

What is the competitive exclusion principle, and what are two possible outcomes of competition between two species?

The principle states that two species competing for the same limited resource cannot coexist indefinitely. Possible outcomes are: 1. The elimination of the inferior competitor. 2. Niche partitioning, where both species restrict their use of the resource to a part of their fundamental niche, leading to the formation of realized niches.

Why is an ecosystem considered an open system?

An ecosystem is an open system because it interacts with its surroundings by exchanging both energy (e.g., sunlight entering, heat leaving) and matter (e.g., water or organisms entering and leaving).

What is the principal source of energy that sustains most ecosystems, and what are two exceptions?

Sunlight is the principal source of energy. Exceptions include ecosystems in deep-sea hydrothermal vents and caves, where the primary energy source is chemical energy from oxidation reactions (chemosynthesis).

How does chemical energy flow through a food chain?

Chemical energy, stored in the carbon compounds of an organism, passes to a consumer when it feeds on an organism from the previous stage (trophic level) in the food chain.

In food chain and food web diagrams, what do the arrows represent?

The arrows indicate the direction of the transfer of both energy and biomass.

What are three sources of dead organic matter that supply energy to decomposers?

1. Dead whole organisms (corpses). 2. Faeces from organisms. 3. Dead parts of organisms (e.g., shed leaves, skin, hair).

What defines an autotroph, and why is energy required for this process?

An autotroph is an organism that uses an external energy source to synthesize its own carbon compounds from simple inorganic substances. Energy is required for the initial carbon fixation and for the subsequent anabolic reactions that build macromolecules.

What is the difference between the external energy source used by photoautotrophs and chemoautotrophs?

Photoautotrophs use light as their external energy source (photosynthesis). Chemoautotrophs use the energy released from oxidation reactions of inorganic chemicals as their energy source (chemosynthesis).

What defines a heterotroph?

A heterotroph is an organism that obtains the carbon compounds it requires by consuming other organisms.

How do both autotrophs and heterotrophs release the energy stored in carbon compounds?

Both autotrophs and heterotrophs release the chemical energy stored in carbon compounds through the process of cellular respiration.

What are the first four trophic levels in an ecosystem?

1. Producer (autotrophs). 2. Primary consumer (herbivores that feed on producers). 3. Secondary consumer (carnivores or omnivores that feed on primary consumers). 4. Tertiary consumer (carnivores or omnivores that feed on secondary consumers).

What does a pyramid of energy represent, and what are its units?

A pyramid of energy illustrates the rate at which energy is contained within the biomass of each trophic level. The units are typically kilojoules per square meter per year (kJ m⁻² yr⁻¹).

What are two major causes of energy loss between successive trophic levels in a food chain?

1. Energy is lost as heat during cellular respiration at each trophic level. 2. Not all biomass from one trophic level is consumed or assimilated by the next; some is uneaten, and some is lost as waste (faeces, urea).

Why is heat continuously lost from an ecosystem?

Energy transfers are not 100% efficient. When chemical energy is converted to ATP during cell respiration, and when ATP is used for life processes, a significant portion of that energy is converted to thermal energy (heat) and lost to the environment.

Why is the number of trophic levels in an ecosystem limited?

Due to the large energy losses at each successive stage, there is progressively less energy available at higher trophic levels. Eventually, there is not enough energy remaining to support another level.

What is primary production, and what are its standard units?

Primary production is the accumulation of carbon compounds in the biomass by autotrophs (producers). Its rate is typically measured in mass of carbon per unit area per unit time (e.g., g C m⁻² yr⁻¹).

What is secondary production, and why is its rate always lower than primary production in an ecosystem?

Secondary production is the accumulation of carbon compounds in the biomass of heterotrophs. It is always lower than primary production because a large amount of biomass (carbon) is lost as carbon dioxide during cellular respiration by consumers at each trophic level.

How is carbon recycled in ecosystems through the processes of photosynthesis, feeding, and respiration?

Photosynthesis removes CO₂ from the atmosphere and converts it into organic compounds. Feeding transfers these carbon compounds between organisms. Respiration, by all organisms (producers, consumers, decomposers), releases the carbon back into the atmosphere as CO₂.

What is the difference between a carbon sink and a carbon source?

An ecosystem acts as a carbon sink when the rate of photosynthesis is greater than the rate of respiration, resulting in a net uptake of CO₂. It acts as a carbon source when the rate of respiration is greater than photosynthesis, resulting in a net release of CO₂.

What are three carbon sinks that can release carbon dioxide into the atmosphere through combustion?

1. Biomass (e.g., forests). 2. Peat (partially decomposed organic matter). 3. Fossil fuels (coal, oil, and natural gas).

What do the annual fluctuations and the long-term trend of the Keeling Curve show?

The annual fluctuations show a decrease in atmospheric CO₂ during the Northern Hemisphere's summer (due to photosynthesis) and an increase in winter (due to respiration). The long-term trend shows a consistent and accelerating increase in the overall concentration of atmospheric CO₂.

How are photosynthesis and aerobic respiration interdependent regarding atmospheric gases?

Photosynthesis is dependent on the carbon dioxide produced by respiration. Aerobic respiration is dependent on the oxygen produced by photosynthesis. The fluxes of these gases between autotrophs and heterotrophs are huge.

What is the essential role of decomposers in an ecosystem?

Decomposers break down dead organic matter and in doing so, they release all the chemical elements that were locked within it back into the ecosystem as inorganic nutrients. This recycling makes these essential elements available for producers to use again.