Ecological niches

Question 1

Define an ecological niche.

Answer 1

An ecological niche describes the functional position and role of an organism within its environment.

It consists of all biotic and abiotic interactions that influence growth, survival and reproduction, including how a species obtains food.

Question 2

State factors that determine the niche of a species.

Answer 2

1. Zones of Tolerance for Abiotic Variables
The range of abiotic conditions a species can withstand.
2. Food Source and Nutrition Specialization
3. Interactions with Other Species:

Question 3

Compare abiotic and biotic components of niches.

Answer 3

An ecological niche will be comprised of various components, including:

Abiotic: The habitat in which an organism lives and the resources within the environment (light, temperature, etc.)

Biotic: The activity patterns of the organism and its interactions with other species (competition, predation, etc.)

Question 4

Compare the different oxygen requirements of obligate anaerobes, facultative anaerobes and obligate aerobes.

Answer 4

Obligate Aerobes:
* Require oxygen to survive
* Aerobic respiration
* Oxygen-rich environments
* eg. humans

Obligate Anaerobes:
* Killed or inhibited by oxygen
* Anaerobic respiration or fermentation
* Oxygen-depleted environments

Facultative Anaerobes:
* Can survive with or without oxygen
* Prefer aerobic respiration but can use anaerobic pathways
* Diverse environments

Question 5

Define the process of photosynthesis.

Answer 5

Photosynthesis is the process where energy from sunlight is harnessed to fix carbon dioxide into organic compounds.

Question 6

List three groups of photosynthetic autotrophs.

Answer 6

Plants
* Includes mosses, ferns, conifers, and flowering plants.
* Plants are the dominant terrestrial photosynthesizers, playing a crucial role in capturing solar energy and converting it into chemical energy.
Eukaryotic Algae
* Includes seaweeds that grow along rocky shores and unicellular algae like Chlorella.
* These photosynthesizers dominate aquatic environments, producing significant amounts of oxygen and forming the base of marine ecosystems.
Photosynthetic Bacteria
* Includes cyanobacteria (commonly called blue-green bacteria) and purple bacteria.
* Cyanobacteria are especially important because they are believed to be responsible for the Great Oxygenation Event, which made Earth’s atmosphere habitable for aerobic organisms.

Question 7

Define holozoic nutrition.

Answer 7

Holozoic nutrition is the process by which animals obtain energy and nutrients by consuming other organisms or organic matter.

Question 8

Outline how animals are distinguished according to their feeding patterns.

Answer 8

All animals undertake holozoic nutrition but may be distinguished according to their feeding patterns:

Consumers feed on living or recently killed organisms (includes herbivores, carnivores and omnivores)

Scavengers feed on dead and decaying carcasses rather than hunting live prey (e.g. hyenas, carrion birds)

Detritivores feed on non-living organic matter – such as detritus and leaf litter (e.g. beetles, crabs, earthworms)

Question 9

Explain how heterotrophs obtain their organic molecules.

Answer 9

Heterotrophs obtain their organic molecules from other organisms – this mode of nutrition can be holozoic or saprotrophic

In holozoic nutrition, organic matter is ingested and then digested internally, before being absorbed and assimilated

All animals are heterotrophic.

Question 10

Outline the stages of holozoic nutrition.

Answer 10

1. Ingestion: the first step in holozoic nutrition, where animals take food into their bodies.
2. Digestion: the process of breaking down food into smaller, absorbable molecules.
3. Absorption: the process by which digested nutrients are transported into the body, primarily occurring in the small intestine.
4. Assimilation: the process by which absorbed nutrients are transported to cells and used for growth, repair, and energy production.

Question 11

Outline the adaptations in herbivoers for nutrition.

Answer 11

Long Digestive Tracts: Cows have complex stomachs (rumen, reticulum, omasum, abomasum) for fermenting cellulose.

Specialized Enzymes: Break down tough plant fibers.
* Detoxification Enzymes: Herbivores can neutralize toxic compounds produced by plants.

Specialized Feeding Habits: Many herbivores feed on specific plants, leading to plant-herbivore specificity. This results in a co-evolutionary relationship where both plants and herbivores develop traits to outcompete each other.

Question 12

Outline the adaptations in carnivores for nutrition.

Answer 12

Sharp Teeth: Lions have canines for tearing meat.
Short Intestines: Efficient for rapid digestion of protein-rich diets.

Question 13

Outline the adaptations of omnivores for nutrition.

Answer 13

Versatile Mouth Structures: Combination of incisors, canines, and molars to handle both plant and animal-based foods.
Flexible Digestive Systems: Adapt to a wide range of dietary inputs.

Question 14

Describe mixotrophs.

Answer 14

Mixotrophs are organisms that can obtain energy and carbon through both autotrophic and heterotrophic modes of nutrition.
* Autotrophy: The ability to create organic compounds (like glucose) from inorganic substances (like carbon dioxide and water), typically through photosynthesis.
* Heterotrophy: The consumption of organic compounds produced by other organisms, either by ingesting them or absorbing them.

Question 15

State an example of a mixotrophic protist.

Answer 15

Unicellular organisms such as Euglena (fresh-water protist):
* In Bright, Nutrient-Scarce Environments: Euglena uses its chloroplasts to photosynthesize, behaving like a plant.
* In Low-Light or Nutrient-Rich Environments: It switches to heterotrophy, engulfing detritus or smaller organisms through endocytosis.

Question 16

Distinguish between obligate and facultative mixotrophs.

Answer 16

Facultative mixotrophs can function as either autotrophs or heterotrophs, depending on environmental conditions.
Obligate mixotrophs require both autotrophic and heterotrophic modes of nutrition to survive.

Question 17

Outline the evolutionary advantages of mixotrophs.

Answer 17

Flexibility: Organisms can adapt to nutrient availability, surviving in both nutrient-rich and nutrient-poor environments.
Energy Efficiency: Mixotrophs maximize energy intake by switching between modes as conditions change.

Question 18

Define saprotrophic nutrition.

Answer 18

Saprotrophic nutrition is a mode of heterotrophic nutrition where organisms derive energy and nutrients by feeding on dead or decaying organic material.

Question 19

Outline the key characteristics of saprotrophic nutrition.

Answer 19

External Digestion: Saprotrophs release enzymes like proteases, lipases, and cellulases into their environment to break down complex organic molecules such as proteins, lipids, and cellulose.
Nutrient Absorption: Once the organic matter is broken down into simpler compounds (e.g., amino acids, sugars, fatty acids), these are absorbed through the saprotroph’s cell membrane.

Question 20

List two example saprotrophic organisms.

Answer 20

1. Fungi
Fungi are among the most well-known saprotrophs, playing a critical role in decomposition.
Eg. Mushrooms: Grow on decaying wood, breaking down cellulose and lignin with secreted enzymes.
2. Bacteria
Soil Decomposers: Bacillus and Pseudomonas decompose plant material, enriching soil fertility.
Aquatic Saprotrophs: Some bacteria specialize in breaking down organic material in aquatic environments, such as dead algae or marine organisms.

Question 21

Outline saprotrophs contributions to ecosystems.

Answer 21

1. Nutrient Recycling
* Saprotrophs release essential elements like carbon, nitrogen, and phosphorus from organic matter back into the environment.
* These elements are then available for uptake by plants, supporting nutrient cycles such as the carbon and nitrogen cycles.

2. Soil Fertility: by decomposing organic matter, saprotrophs produce humus— a dark, nutrient-rich material that enhances soil structure and fertility.

3. Energy Flow in Ecosystems
* Saprotrophs form a critical link in the food web.
* By breaking down complex organic matter into simpler compounds, they make nutrients available to primary producers, ensuring the continuous flow of energy through ecosystems.

Question 22

Outline the process of saprotrophic nutrition.

Answer 22

1. Enzyme Secretion: saprotrophs secrete digestive enzymes into their surroundings. These enzymes catalyze the breakdown of complex macromolecules

2. External Digestion: enzymes act on the organic matter, breaking down complex molecules into smaller, soluble molecules that can diffuse through cell membranes.

3. Absorption: saprotroph absorbs the digested nutrients across its cell membrane and uses them for energy, growth, and reproduction.

Question 23

List the three domains of life.

Answer 23

The three domains of life are Archaea, Bacteria, and Eukarya.

Question 24

Outline the characteristics of archaea.

Answer 24

Archaea are a metabolically diverse group of organisms capable of performing a variety of modes of nutrition.
Phototrophs use light as an energy source to produce ATP (however they do not undergo photosynthesis or produce oxygen gas)

**Lithotrophs **use a variety of inorganic compounds to produce ATP (such as ammonia, hydrogen gas, hydrogen sulfide or iron oxide)

Organotrophs use organic compounds to produce ATP (these compounds may be obtained via heterotrophic nutrition)

Question 25

Outline the adaptations of mammalian teeth for different diet types.

Answer 25

**Herbivores:** Species like gorillas consume fibrous plant material, such as leaves and stems. Their teeth are optimized for grinding and crushing tough vegetation. **Omnivores:** Humans and chimpanzees eat a mix of plant and animal matter. Their dentition is more versatile, with teeth adapted for both cutting meat and grinding plant material.

Question 26

Define hominidaes.

Answer 26

Hominidae are a family of greater apes that include gorillas and chimpanzees, as well as modern and ancestral humans. Hominids that feed predominantly on plant matter have broader jaw muscles, larger premolars and thicker tooth enamel for grinding tough vegetation. Hominids that eat more meat have narrower jaws and smaller teeth for chewing softer animal tissue, while incisor teeth and canines are tightly packed to enable cutting and tearing.

Question 27

State the two main groups of herbivores.

Answer 27

**Chewing Herbivores** Examples: Beetles and other insects with jaw-like mouthparts. Feeding Mechanism: These insects bite off, chew, and ingest pieces of leaf material. **Sap-Feeding Herbivores** Examples: Aphids and other insects with tubular mouthparts. Feeding Mechanism: They pierce plant tissues to reach phloem sieve tubes and feed on nutrient-rich sap.

Question 28

Outline the adaptations of plants for resisting herbivory.

Answer 28

**1. Physical Defenses:** eg. thorns: sharp structures that can injure herbivores **2. Chemical Defenses:** Plants produce secondary metabolites, which are toxic or deterrent compounds.

Question 29

Outline the adaptations of predators for finding, catching and killing prey.

Answer 29

Physical structures – sensory organs to better detect prey and physical features such as sharp teeth and claws Appearances – predators may be camouflaged or have a streamlined body shape to increase speed Chemical compounds – neurotoxins and venoms can be used to paralyse or subdue their prey Behaviours – predators may act in certain ways to successfuly capture prey (e.g. lay in ambush, hunt in packs)

Question 30

Outline the adaptations of prey animals for resisting predation.

Answer 30

Physical structures – tough exoskeletons and shells provide a level of protection against predators Appearances – prey may be camouflaged, mimic predator structures or possess bright warning colours Chemical compounds – toxins and scents may deter predators or cause harm to the predator when consumed Behaviours – prey may act in certain ways to avoid predation (e.g. feigning death, puffing up, grouping together)

Question 31

Outline the adaptations of plant form for harvesting light.

Answer 31

Lianas: Woody vines that are rooted in the soil and use the trunks of trees to reach the canopy Overstory: Emergent trees can grow above the canopy to gain the most sunlight for photosynthesis Understory: Low-growing herbs and shrubs possess large leaves to maximise their surface area Shade tolerant plants: Contain different photosynthetic pigments to absorb more wavelengths of light Epiphytes: Plants that grow on the branches of other plants, with no direct contact with the soil Canopy Trees: Grow tall to reach direct sunlight

Question 32

Distinguish between the fundamental and realized niche.

Answer 32

A **fundamental niche** is the entire set of conditions under which an organism can survive and reproduce (where it could live) * It is the theoretical habitat and may not be fully occupied due to the presence of competing species A **realised niche** is the set of conditions used by an organism after including interactions with other species (where it does live) * It is the actual habitat that is completely occupied by an organism in the presence of competing species

Question 33

Explain the competitive exclusion principle.

Answer 33

In every ecosystem, species compete for limited resources such as food, water, space, and light. If two species depend on the same resource in the same way, one will eventually outcompete the other.

Question 34

Explain why two species cannot survive indefinitely in the same habitat if their niches are identical.

Answer 34

No two species can share the exact same niche, as this would lead to direct competition for space and resources This competition will reduce the biological fitness of the organisms – leading to a struggle for survival