Ecosystems - IB Biology

Define what an ecological niche is, and state what kinds of interactions it includes.

The role a species plays in an ecosystem, including biotic and abiotic interactions affecting its growth, survival, reproduction, and food acquisition.

What kinds of factors determine the niche of a species?

Biotic interactions (competition, predation, food source) and abiotic interactions (temperature, water, pH, etc.).

How do niche generalists differ from niche specialists?

Generalists survive under a wide range of conditions/resources; specialists need narrow, specific conditions/resources.

Fill in the blank: an organism that cannot survive in the presence of oxygen is called an obligate _____.

anaerobe

What is a facultative anaerobe?

An organism that can grow with or without oxygen.

What is an obligate aerobe?

An organism that requires oxygen to survive and grow.

Multiple choice: which nutrition mode uses light energy and CO2 to build carbon compounds, occurring in plants, algae, and some prokaryotes? A) Holozoic B) Saprotrophic C) Photosynthesis D) Mixotrophic

C) Photosynthesis

In photosynthesis, what are the energy source and the carbon source?

Energy source: light. Carbon source: CO2.

Name three groups of photosynthetic autotrophs.

Plants, algae, and photosynthetic prokaryotes (e.g. cyanobacteria).

What is holozoic nutrition, and which organisms use it?

Heterotrophic nutrition via ingestion, internal digestion, absorption, and assimilation of food; used by animals.

Put these steps of holozoic nutrition in order: absorption, digestion, ingestion, assimilation.

Ingestion, digestion, absorption, assimilation.

What happens during assimilation in holozoic nutrition?

Absorbed nutrients are incorporated into the body's own cells and tissues.

What is mixotrophic nutrition, and what is a common example organism?

A combination of autotrophic and heterotrophic nutrition; example: Euglena, a protist.

What's the difference between an obligate and a facultative mixotroph?

Obligate mixotrophs must use both modes; facultative mixotrophs can switch between them depending on conditions.

What is saprotrophic nutrition, and which organisms typically use it?

External digestion of organic matter by secreting enzymes onto it, then absorbing the products; used by some fungi and bacteria (decomposers).

Why are all saprotrophs decomposers, but not all decomposers saprotrophs?

Saprotrophs digest externally; other decomposers like detritivores ingest food and digest it internally.

Name the three domains of life.

Bacteria, Archaea, and Eukarya.

How do archaea obtain energy to make ATP?

By using light, oxidation of inorganic chemicals, or oxidation of carbon compounds.

How do chemoautotrophs and photoautotrophs differ in their energy and carbon sources?

Chemoautotrophs: energy from oxidizing chemicals, carbon from CO2. Photoautotrophs: energy from light, carbon from CO2.

How can dentition (tooth shape) be used to study the diet of extinct Hominidae species like Paranthropus robustus?

Comparing their teeth to living mammals lets scientists deduce whether the diet was herbivorous, omnivorous, or carnivorous.

What adaptations let leaf-eating insects feed on plants, and how do plants resist this herbivory?

Insects: piercing/chewing mouthparts. Plants: thorns, physical structures, and toxic secondary compounds in leaves/seeds.

How can some herbivores safely eat toxic plants?

They have metabolic adaptations that let them detoxify the plant's toxic compounds.

Multiple choice: a cheetah's speed and a snake's venom are examples of which kinds of predator adaptation? A) Physical B) Chemical C) Behavioral D) Both A and B

D) Both A and B

Give an example of a behavioral adaptation predators use to catch prey.

Hunting in coordinated packs or groups.

List the plant adaptations for harvesting light in a forest, from tallest to lowest.

Tall canopy trees, lianas (climbing vines), epiphytes/strangler epiphytes on branches, shade-tolerant shrubs and herbs on the forest floor.

What is an epiphyte?

A plant that grows on another tree's branches to reach more light, without being rooted in soil.

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

Fundamental niche: full potential niche based on adaptations/tolerance limits. Realized niche: smaller, actual niche occupied due to competition.

What is competitive exclusion, and when does it happen?

If two species share an identical niche, competition leads to one being eliminated or both being restricted to parts of their niche; occurs because no two species can share the same niche indefinitely.

Why do organisms adapted to extreme niches face less competition and predation?

Fewer other species can tolerate those extreme conditions.

Scenario: a graph shows Species A's niche as a large circle when alone, but shrinking between Species B and C when they're added. What does the larger circle represent versus the smaller one?

Larger circle: A's fundamental niche. Smaller circle: A's realized niche once in competition.

Define obligate anaerobe in one exam-style sentence.

An organism that cannot survive/grow in the presence of oxygen.

Distinguish between holozoic and mixotrophic nutrition.

Holozoic: purely heterotrophic (ingestion, digestion, absorption, assimilation). Mixotrophic: combines autotrophic and heterotrophic nutrition.

What is the definition of ecology?

The study of the distribution and abundance of organisms, interactions between organisms and their environment, and the structure/function of ecosystems.

What does the "abiotic" component of a niche include?

The habitat an organism lives in and the resources available in it, e.g. light and temperature.

What does the "biotic" component of a niche include?

The organism's activity patterns and its interactions with other species, e.g. competition and predation.

Fill in the blank: an autotroph is an organism that produces its own organic food using an external energy source, most commonly _____.

light (photosynthesis)

What is a facultative aerobe?

An organism that can tolerate oxygen and normally uses it for aerobic respiration, but can also do anaerobic respiration if oxygen is absent.

What is a facultative mixotroph?

An organism that can optionally use either autotrophic or heterotrophic nutrition, depending on which resources are available.

Why do autotrophs like phytoplankton typically have plenty of carbon but limited nitrogen?

They get carbon easily via photosynthesis (CO2), but don't consume protein-rich prey, so nitrogen for making proteins is scarce.

Why do heterotrophs like zooplankton typically have plenty of nitrogen but limited carbon?

They get nitrogen-rich protein from eating prey, but respire away much of their carbon, so carbon runs short.

How does mixotrophic nutrition solve the carbon/nitrogen imbalance that pure autotrophs and heterotrophs each face?

It combines photosynthesis (extra carbon) with feeding on prey (extra nitrogen), giving more balanced, efficient resource acquisition.

Name the three ways archaea can generate energy for ATP production.

Phototrophy (using light), chemolithotrophy (oxidizing inorganic compounds), and organotrophy (oxidizing organic compounds).

True or false: archaea phototrophs produce oxygen during their light-driven energy process, just like plant photosynthesis.

False — it's a different process and no oxygen is produced.

What kinds of inorganic compounds do chemolithotrophic archaea oxidize for energy?

Compounds like ammonia, nitrites, or sulfur compounds.

What kinds of organic compounds do organotrophic archaea oxidize for energy?

Organic compounds such as sugars and fatty acids.

What is a lithotroph?

An autotroph that gets energy from chemical bonds in minerals rather than from light.

In a microbial food chain, what do single-celled protozoans typically eat?

Autotrophs (primary producers), and sometimes other protozoans or small metazoans.

Why are primary producers considered the starting point of energy flow in an ecosystem?

They convert inorganic materials like CO2 and light into food; the energy in every other organism traces back to them.

What critical role do decomposers play in nutrient cycling?

They break down dead organisms and release nutrients back into the environment, making them available again for primary producers.

According to the video, what is an ecological niche?

The unique role a species fulfills in an ecosystem, including biotic and abiotic interactions that influence its growth, survival, and reproduction.

What is a "zone of tolerance," using the bluebird's prey size as an example?

The range of a variable (e.g. prey length) a species can handle; the bluebird prefers about 4mm prey but can manage anywhere from 1mm to 13mm.

Besides prey size, what other factor shapes the bluebird's niche within a tree?

The height above the ground at which it hunts.

Can two different species occupy the exact same niche in an ecosystem at the same time?

No — species can differ by prey type, hunting height, etc., but no two species share the identical niche simultaneously.

Give three examples of services a species' niche can provide to the wider ecosystem.

Recycling mineral elements, pollinating flowers, and dispersing seeds.

What is a heterotroph?

An organism that obtains its energy and carbon by consuming other organisms, rather than making its own food.

What is a detritivore?

An animal that feeds on dead organic matter (detritus) by ingesting it and digesting it internally, unlike saprotrophs which digest externally.

List the types of evidence found in the teeth of fossil skulls that scientists use to deduce diet.

Jaw thickness, enamel thickness, gap between teeth, size/shape of canines, size/shape of premolars and molars, microscopic wear patterns, and jaw muscle strength.

Complete the table: what canine size/shape, incisor size/shape, and molar shape are typical of a carnivore vs. a herbivore?

Carnivore: large pointed canines, small incisors, pointed molars/premolars. Herbivore: small diamond-shaped canines, flattened incisors, flat molars for grinding.

What kind of teeth does an omnivore typically have, and why?

A mix: medium blunt canines, larger sharper incisors, and molars with cusps (bumps) — allowing it to both tear meat and crush plant material.

Why do herbivores need strong jaw muscles, while carnivores need strong jaws for a different reason?

Herbivores: strong jaw muscles for chewing tough, fibrous foods. Carnivores: strong jaws for overpowering and biting into large prey.

What do the teeth of a Homo sapiens skull suggest about its diet?

Large sharp incisors, small blunt canines, and flattened molars — consistent with an omnivorous diet.

What do Paranthropus robustus's teeth and jaw suggest about its diet?

Bigger jaw and teeth than other Homo species, thicker enamel, and evidence of large jaw muscles — suggests a herbivorous diet of hard, tough foods like tubers and seeds.

What do Homo floresiensis's teeth suggest about its diet?

Relatively large molars and premolars for its small body size, with incisors not much reduced — suggests a diet of tough plant food, possibly with some small animals (omnivorous).

A fossil tooth is found with a worn, wide, flattened appearance. What can be deduced about that animal's diet?

The flattened, worn shape suggests repeated grinding of tough plant material, indicating a herbivorous diet.

Why do herbivores and carnivores typically differ in the position of their eye sockets (orbits) on the skull?

Carnivores usually have forward-facing eyes for depth perception to judge distance when hunting prey; herbivores often have eyes positioned more to the sides for a wider field of view to detect approaching predators.

Multiple choice: which two dentition features are especially adapted in carnivore predators for their diet? A) Flat molars and small canines B) Large pointed canines and strong jaws C) Diamond-shaped canines and flattened incisors D) Cusped molars and blunt canines

B) Large pointed canines and strong jaws

Suggest two ways an Acacia tree defends itself against herbivores like giraffes in the savanna.

Physical thorns/spines to deter feeding, and chemical defenses such as toxic or bitter compounds in the leaves.

What is lignin, and how does it help protect tree bark from herbivores and pathogens?

A rigid compound in bark that's tough to chew and highly impermeable to pathogens.

What is the function of a plant's waxy cuticle as a defense?

It deters insects and microbes from accessing and damaging the leaf surface.

What are trichomes, and how do some plants use them for defense?

Sharp, hair-like structures on leaves/stems; some also release chemical irritants (e.g. stinging nettles release histamine, causing pain on contact).

What are raphides, and how do they defend plants like spinach and rhubarb?

Microscopic needle-shaped crystals that cause tiny wounds in an herbivore's mouth, creating entry points for toxins.

How does the mimosa plant physically defend itself from being eaten?

Touch-sensitive cells trigger an electrical signal that makes the leaflet lose water and fold shut rapidly, startling insects and making the plant look less appealing.

When a plant's outer defenses are breached, what internal immune responses can it trigger?

Thickening the cuticle, strengthening cell walls, sealing leaf pores, self-destructing infected cells to quarantine damage, and producing toxic compounds targeted at the invader.

How can an attacked plant warn other plants nearby, and what's an example of recruiting outside help?

It releases hormones, airborne chemical signals, or electrical signals; cotton plants under caterpillar attack release chemicals that attract parasitic wasps to attack the caterpillars.

Give an example of a physical/structural predator adaptation, using the vampire bat.

Sharp, razor-like incisors and canines adapted for piercing prey to feed on blood.

Give an example of a chemical predator adaptation, using the black mamba.

Venom containing neurotoxins that block nerve signals to muscles, paralyzing prey so it can be swallowed without resisting.

Give an example of a behavioral predator adaptation, using grizzly bears catching salmon.

Learned ambush strategies (e.g. waiting at waterfalls) developed through trial and error or by copying other bears.

Give an example of a structural prey defense, using the buff-tip moth.

Camouflage that makes it resemble a broken birch twig, hiding it from predators while at rest.

Give an example of a chemical prey defense, using cinnabar moth caterpillars.

They accumulate toxic alkaloids from the ragwort plants they eat, paired with warning coloration (black and yellow stripes) to deter predators.

Give an example of a behavioral prey defense, using schooling fish like blue-striped snappers.

Swimming in a tight group with sudden direction changes, making it harder for predators to detect or catch a single individual.

How does the horned lizard defend itself against a coyote if hiding fails?

It increases blood pressure until it can shoot a jet of foul-tasting blood up to 3 feet from its eye, deterring the predator.

Rank predator/prey adaptation types from fastest to slowest to evolve/change, and explain why.

Behavioral (can be learned within an individual's lifetime) is fastest; structural is slower (requires genetic change via natural selection); chemical is usually slowest (new enzymes may take much longer to evolve).

What's the difference between an epiphyte and a liana as light-harvesting strategies?

Epiphytes grow rooted on tree branches themselves; lianas root in the ground and climb up a tree trunk for support.

Real-world scenario: the Eurasian red squirrel and Eastern grey squirrel share very similar niches. What ecological outcome does competition theory predict?

Competitive exclusion — one species (commonly the grey squirrel, due to its competitive advantages) is expected to outcompete and displace the other over time.

Is an ecosystem an open or closed system in terms of energy and matter?

Open — both energy and matter can enter and exit.

What is a closed system, using Earth itself as the example?

A system where only energy can enter/exit, not matter (Earth is essentially closed to new matter but constantly receives solar energy).

What is the principal source of energy that sustains most ecosystems?

The sun.

How do producers (autotrophs) capture the sun's energy to start the flow of energy through an ecosystem?

They use photosynthesis to convert light energy, CO2, and water into chemical energy stored in organic (carbon) compounds.

Name an example of an ecosystem that does NOT rely on sunlight for energy, and explain how it gets energy instead.

Deep cave ecosystems (e.g. Movile Cave, Romania); energy comes from chemoautotrophic archaea/bacteria that get energy from chemical reactions with substances like sulfides or methane.

What is a producer, and how does it differ from a consumer?

A producer makes its own organic food from inorganic materials (via photosynthesis or chemosynthesis); a consumer must eat other organisms to obtain energy and matter.

What is a primary consumer, and what is another name for it?

An organism that feeds directly on producers; also called a herbivore.

What is a secondary consumer, and what is another name for it?

An organism that eats primary consumers; also called a carnivore (predator of herbivores).

What is a tertiary consumer?

An organism that eats secondary consumers (a third-level consumer).

What is an apex predator?

A top consumer with no natural predators of its own in that food chain.

Why don't omnivores (like bears) fit neatly into a single trophic level?

Because they eat both producers and other consumers, so they're generally placed at trophic level 3 but don't cleanly match one category.

What role do decomposers and detritivores play in an ecosystem's energy flow?

They break down dead organic matter and waste, releasing simple inorganic compounds (nutrients) back into the environment for producers to reuse.

In what chemical form does energy pass along a food chain?

Chemical energy (stored in organic/carbon compounds).

Approximately what percentage of energy is transferred from one trophic level to the next?

About 10%.

List at least three reasons why so much energy is lost between trophic levels rather than passed on.

Incomplete consumption (uneaten parts), energy lost as waste/feces during inefficient digestion, energy used for the organism's own metabolism (respiration, movement, growth), and heat lost during cellular respiration.

Why is heat loss during cell respiration considered "lost" energy from an ecosystem?

Because living organisms can't use heat itself as a usable energy source, so once it dissipates it leaves the food chain.