Ecology: Organisms and Populations Study Notes

Difference Between Predation and Parasitism

Question: State the difference between predation and parasitism.

Answer:

• Predation: One organism (predator) kills and eats another organism (prey). The prey is immediately killed. Example: Lion and deer.
• Parasitism: One organism (parasite) lives on or inside another organism (host) and harms it, but usually does not kill it immediately. Example: Tapeworm in humans, lice on humans.

Gause's Competitive Exclusion Principle

Question: Explain the Gause competitive exclusion principle.

Answer: The Gause competitive exclusion principle states that two species competing for the same limited resources cannot coexist indefinitely in the same habitat. One species will outcompete the other, leading to the elimination or migration of the weaker species.

Commensalism vs Mutualism

Question: Write the difference between commensalism and mutualism.

Answer:

• Commensalism: One organism benefits, and the other is neither harmed nor benefited. Example: Epiphytes growing on trees, remora fish with sharks.
• Mutualism: Both organisms benefit from the relationship. Example: Lichen (algae + fungus), bees and flowering plants.

How Light Influences Plant Growth

Question: How does light influence the growth and development in plants?

Answer: Light affects plants by controlling photosynthesis, photoperiodism, and phototropism. It influences flowering, stem growth, leaf formation, and germination. Without light, plants become weak and etiolated.

Characteristics of Parasitic Plants

Question: What are the special characteristics of parasitic plants?

Answer: Parasitic plants:

• Live on or inside host plants.
• Obtain food, water, and minerals from the host.
• Have special sucking organs called haustoria.
• Usually have reduced roots, stems, or leaves.

Example: Cuscuta, Viscum.

Mutualism and Its Examples

Question: What is mutualism? Explain mutualism with suitable examples.

Answer: Mutualism is a relationship where both organisms benefit from each other.

Examples:

• Lichen (algae + fungus).
• Bees and flowering plants (pollination).
• Rhizobium bacteria and leguminous plants.

Plant Adaptations to Water Scarcity

Question: Write a note on the adaptation of plants to water scarcity.

Answer: Plants in dry areas (xerophytes) show:

• Thick cuticle and waxy leaves.
• Reduced leaves (spines).
• Deep or extensive roots.
• Water storage tissues (succulents).

Example: Cactus, Opuntia.

Understanding the Age Pyramid

Question: What is an age pyramid? Draw the expanding age pyramid.

Answer: An age pyramid is a graphical representation showing the age structure of a population.

Expanding age pyramid:

• Broad base (more young individuals).
• Narrow top (few old individuals).
• It indicates rapid population growth.

Key Factors of Population Growth

Question: What are the factors of population growth?

Answer: The main factors are:

• Birth rate (Natality).
• Death rate (Mortality).
• Immigration.
• Emigration.

Main Characteristics of a Population

Question: Write the characteristics of a population.

Answer: Population characteristics include:

• Population size and density.
• Age structure.
• Sex ratio.
• Birth and death rates.
• Growth rate and dispersion pattern.

Types of Age Pyramids

Question: Describe pre-reproductive, reproductive, and post-reproductive pyramids.

Answer: An age pyramid is a graphical representation showing the distribution of different age groups (young, adult, old) in a population.

1. Pre-reproductive Age Group (0–14 years)

• This group includes young individuals who cannot reproduce.
• A large number indicates future population growth.

2. Reproductive Age Group (15–49 years)

• This group includes sexually mature individuals capable of reproduction.
• This group directly determines population increase.

3. Post-reproductive Age Group (50 years and above)

• This group includes old individuals who cannot reproduce.
• A large number indicates a declining population.

Abiotic Factors Affecting Plant Development

Question: Write a note on abiotic factors influencing plant growth.

Answer: Abiotic factors are non-living environmental factors that affect plant growth and development.

• Light: Essential for photosynthesis; controls flowering and phototropism.
• Temperature: Affects enzyme activity and metabolic processes.
• Water: Required for photosynthesis, transpiration, and nutrient transport.
• Soil: Provides minerals, water, and anchorage; pH and texture influence growth.
• Air and Humidity: CO₂ is needed for photosynthesis; humidity affects transpiration.

The Exponential Population Growth Model

Question: Write an account on the exponential growth model.

Answer: Population growth refers to the increase in the number of individuals in a population over time due to births, deaths, immigration, and emigration.

When resources are unlimited, population increases rapidly and follows an exponential growth pattern.

• Population size increases very fast.
• Growth rate remains constant.
• The curve formed is J-shaped.
• Occurs in ideal conditions (no competition, no predators, enough food and space).

Mathematical Expression: dN / dt = rN

Where: N = Population size, r = Intrinsic rate of increase, t = Time.

Describe Various Population Growth Factors

Answer: Population growth depends on several biotic and abiotic factors:

• Natality (Birth Rate): Number of individuals born per unit time; increases population.
• Mortality (Death Rate): Number of individuals dying per unit time; decreases population.
• Immigration: Movement of individuals into a population; increases size.
• Emigration: Movement of individuals out of a population; decreases size.
• Environmental Factors: Availability of food, water, shelter, climate, and diseases.

Concept of Carrying Capacity

Question: What is carrying capacity?

Answer: Carrying capacity (K) is the maximum number of individuals of a species that an environment can support permanently with available resources like food, water, space, and shelter.

• Represented by K.
• Population growth slows when it reaches carrying capacity (logistic growth).

Verhulst–Pearl Logistic Growth Equation: dN / dt = rN ((K - N) / K)

Allelopathy vs Antibiotics

Answer:

Allelopathy

• The chemical inhibition of one plant by another plant.
• Occurs between plants.
• Chemicals released are called allelochemicals.
• Example: Eucalyptus releasing chemicals that inhibit the growth of other plants.

Antibiotics

• Chemical substances produced by microorganisms to inhibit or kill other microorganisms.
• Occurs between microorganisms (like bacteria and fungi).
• Chemicals released are called antibiotics.
• Example: Penicillin produced by the Penicillium fungus.

The Logistic Growth Curve

Answer: The logistic growth curve describes how a population grows when resources are limited. It is also called the S-shaped (sigmoid) growth curve.

1. Lag Phase: Slow growth; population is small and adjusting.
2. Exponential (Log Phase): Rapid increase; birth rate is high and resources are abundant.
3. Stationary Phase: Population becomes stable at carrying capacity (K) as resources become limited.

Types of Population Interactions

Answer: Population interaction is the relationship between different populations (species) living together in a community, where one or both species are affected either positively, negatively, or neutrally.