🌸Chapter 11
Organisms & Populations
(5 Marks)
1.
Define
population and discuss its characteristics.
Answer:
- Population: A group of individuals of the same
species living in a particular area at a given time.
- Characteristics:
- Size (N): Total number of individuals.
- Density (D): Number of individuals per
unit area or volume.
- Dispersion: Spatial arrangement –
clumped, uniform, random.
- Age structure: Distribution among
pre-reproductive, reproductive, post-reproductive age groups.
- Growth rate: Change in population size
over time.
2.
Explain
the three types of population dispersion with examples and reasons.
Answer:
- Clumped: Individuals occur in groups;
e.g., elephants, fishes. Reason: Protection, social behavior,
patchy resources.
- Uniform: Even spacing; e.g., penguins,
territorial plants. Reason: Territoriality, competition for
resources.
- Random: Unpredictable; e.g.,
dandelions, plants in homogeneous environment. Reason: No strong
attraction or repulsion among individuals.
3.
Explain
the concept of natality and mortality and their role in population dynamics.
Answer:
- Natality (birth rate): Number of births per 1000
individuals per year.
- Mortality (death rate): Number of deaths per 1000
individuals per year.
- Role in dynamics:
- High natality → population
growth
- High mortality → population
decline
- Population growth depends on difference
between natality and mortality
4.
Explain
age structure in populations and its significance. Draw an example of
triangular age pyramid.
Answer:
- Age structure: Proportion of individuals in
pre-reproductive, reproductive, and post-reproductive groups.
- Significance:
- Predicts population growth
- Helps in planning resources
(food, education, health)
- Triangular pyramid: Broad base → many young →
expanding population
5.
Explain
the difference between exponential and logistic growth curves.
Answer:
| Feature | Exponential (J-shaped) | Logistic (S-shaped) |
|------------------------|---------------------------|---------------------------|
| Resources | Unlimited | Limited |
| Growth rate | Rapid | Slows near carrying capacity |
| Population size | Increases indefinitely | Stabilizes at K |
- Examples: Bacteria (exponential), deer
in forest (logistic)
6.
Explain
the phases of population growth with a graph.
Answer:
- Lag phase: Slow growth, population
adjusting
- Log/exponential phase: Rapid increase, abundant
resources
- Stationary phase: Growth stabilizes near
carrying capacity
- Graph: J-shaped for exponential,
S-shaped for logistic
7.
Explain
carrying capacity and factors affecting it.
Answer:
- Carrying capacity (K): Maximum population an
environment can support indefinitely.
- Factors:
- Food, water, space
- Predation, disease
- Environmental conditions
(temperature, climate)
- Populations stabilize around K
due to density-dependent factors
8.
Explain
intraspecific and interspecific competition with examples and significance.
Answer:
- Intraspecific: Same species; e.g., male deer
fighting for mates. Significance: Maintains population balance.
- Interspecific: Different species; e.g., lion
and hyena competing for prey. Significance: Determines species
distribution and abundance
9.
Explain
mutualism, commensalism, parasitism, amensalism, and predation with examples.
Answer:
- Mutualism: Both benefit; e.g., lichen
(alga + fungus), oxpecker and rhinoceros
- Commensalism: One benefits, other
unaffected; e.g., epiphytic orchids, cattle egret and cattle
- Parasitism: One benefits at host’s
expense; e.g., Cuscuta on plants, tick on dog
- Amensalism: One harmed, other unaffected;
e.g., Penicillium secreting antibiotic, elephant stepping on ants
- Predation: Predator-prey; e.g., lion
hunts deer; regulates prey population
10.
Explain
the concept of ecological niche with examples.
Answer:
- Ecological niche: Role of a species in its
ecosystem (habitat, food, interactions).
- Examples:
- Honeybee: pollinator, nectar
feeder
- Wolf: predator, controls prey
population
- Significance: Reduces competition, maintains
balance
11.
Explain
the effects of immigration and emigration on population dynamics.
Answer:
- Immigration: Increases population size,
adds genetic diversity
- Emigration: Reduces population size, may
reduce competition
- Net effect: Alters density, growth rate,
and structure of population
12.
Explain
density-dependent and density-independent factors with examples.
Answer:
- Density-dependent: Effects increase with
population size; e.g., competition, predation, disease
- Density-independent: Effects independent of
population size; e.g., floods, fires, earthquakes
- Both regulate population size
and growth
13.
Explain
the role of predation in regulating prey populations and ecosystem stability.
Answer:
- Reduces prey overpopulation
- Prevents overgrazing or
depletion of resources
- Drives natural selection and
co-evolution
- Maintains food chain and
ecosystem balance
14.
Explain
the significance of studying age pyramids in human population.
Answer:
- Predict population growth
trends
- Identify pre-reproductive, reproductive,
post-reproductive proportions
- Plan resources (education,
employment, healthcare)
- Anticipate social and economic
challenges
15.
Explain
morphological, physiological, and behavioral adaptations with examples.
Answer:
- Morphological: Physical features; thorns of
cactus, spines of porcupine
- Physiological: Internal functions; camel hump
stores fat
- Behavioral: Activity patterns; nocturnal
desert animals, migration
16.
Explain
the importance of population ecology in conservation biology.
Answer:
- Helps maintain biodiversity
- Predicts growth trends
- Guides management of endangered
species
- Helps in habitat restoration
and sustainable resource use
17.
Explain
the relationship between carrying capacity and population size.
Answer:
- Population < K → growth is
positive
- Population = K → growth
stabilizes
- Population > K → resources
insufficient → population declines
- Ensures balance between
resources and population
18.
Explain
the concept of zero population growth and its significance.
Answer:
- Birth rate = Death rate
- Population size remains
constant
- Significance: Prevents
overpopulation, maintains sustainable resources
19.
Explain
the effect of density-independent factors on populations.
Answer:
- Independent of population size
- Example: Flood, fire,
earthquakes
- Can suddenly reduce population
and affect species survival
20.
Explain
the effect of density-dependent factors on populations.
Answer:
- Effect increases with
population density
- Examples: Disease spreads
faster, competition for food, predation
- Maintains population within
carrying capacity
21.
Explain
the role of limiting factors in population regulation.
Answer:
- Resources, predation,
competition, disease limit growth
- Prevents population from
exceeding carrying capacity
- Ensures ecosystem stability
22.
Explain
the significance of studying population growth curves.
Answer:
- Helps predict population trends
- Guides resource allocation and
conservation
- Understands impact of
environmental factors on growth
23.
Explain
the difference between population density and population size with examples.
Answer:
- Density: Individuals per unit area;
e.g., 10 trees/m²
- Size: Total number of individuals in
area; e.g., 500 trees in a forest
- Both used in ecology and
management
24.
Explain
the role of competition in natural selection.
Answer:
- Reduces overpopulation
- Favors survival of best-adapted
individuals
- Drives evolution and adaptation
- Maintains ecosystem balance
25.
Explain
how predation influences prey adaptations.
Answer:
- Drives evolution of defense
mechanisms: camouflage, speed, warning colors
- Example: Peppered moth color
variation
- Maintains predator-prey
co-evolution
26.
Explain
the importance of studying population dispersion patterns.
Answer:
- Helps understand social
behavior
- Indicates resource distribution
and competition
- Guides conservation strategies
27.
Explain
how reproductive strategies affect population growth.
Answer:
- r-strategists: High
reproduction, low parental care → rapid growth (e.g., bacteria, insects)
- K-strategists: Low
reproduction, high parental care → stable population (e.g., elephants,
humans)
28.
Explain
the differences between r- and K-strategists.
Answer:
| Feature | r-strategist | K-strategist |
|-----------------|-----------------------|-----------------------|
| Reproduction | High, early | Low, delayed |
| Parental care | Minimal | High |
| Population growth| Exponential | Logistic |
| Example | Bacteria, insects | Elephants, humans |
29.
Explain
the ecological significance of parasitism.
Answer:
- Regulates host population
- Drives evolution of host
defenses
- Maintains ecosystem balance
- Example: Cuscuta on host plants
30.
Explain
the ecological significance of mutualism.
Answer:
- Supports survival of both
species
- Enhances nutrient cycling
- Promotes biodiversity
- Example: Lichen (alga + fungus)
31.
Explain
the concept of population regulation by feedback mechanisms.
Answer:
- Negative feedback: Density-dependent factors
reduce growth as population approaches K
- Positive feedback: Rarely occurs, can cause
population explosion
- Ensures population remains
within carrying capacity
32.
Explain
how human activities affect population dynamics.
Answer:
- Habitat destruction, pollution,
hunting
- Alters carrying capacity, age
structure, growth trends
- Impacts biodiversity and
ecosystem stability
33.
Explain
the role of ecological niche in species coexistence.
Answer:
- Reduces interspecific
competition
- Allows species to occupy
different roles
- Example: Two bird species
feeding at different tree heights
34.
Explain
the importance of studying reproductive age group in population.
Answer:
- Determines potential population
growth
- Helps in predicting future
population trends
- Guides resource allocation
35.
Explain
how stationary phase in population growth is achieved.
Answer:
- Population reaches carrying
capacity
- Resource limitation, disease,
predation reduce growth rate
- Birth rate = Death rate
36.
Explain
the adaptive significance of behavioral adaptations in population survival.
Answer:
- Reduces predation risk
(nocturnal activity)
- Optimizes resource use
(migration)
- Enhances reproductive success
(mating rituals)
37.
Explain
the significance of studying population ecology for sustainable development.
Answer:
- Helps maintain biodiversity
- Guides resource management
- Predicts human population
trends and ecological impact
38.
Explain
how age pyramids can be used to predict social and economic needs.
Answer:
- Broad base → need for schools,
employment
- Narrow base → aging population
→ healthcare, pensions
- Assists in planning and
policy-making
39.
Explain
the significance of logistic growth in natural populations.
Answer:
- Reflects resource limitation
- Maintains population stability
- Prevents over-exploitation of
resources
40.
Explain
the effect of predation on natural selection.
Answer:
- Predators remove weak/unfit
individuals
- Favors survival of well-adapted
prey
- Drives evolutionary changes in
both predator and prey
41.
Explain
the significance of dispersion patterns in plant populations.
Answer:
- Indicates resource distribution
- Helps understand competition
and social behavior
- Guides conservation and
management
42.
Explain
the role of disease as a density-dependent factor.
Answer:
- Spreads faster in crowded
populations
- Reduces population growth
- Example: Rabbit populations
affected by myxomatosis
43.
Explain
the role of environmental resistance in population regulation.
Answer:
- Includes predation, disease,
competition, limiting resources
- Prevents population from
exceeding carrying capacity
44.
Explain
the adaptive significance of morphological adaptations in plants.
Answer:
- Protection from herbivores
(thorns)
- Water conservation (succulent
leaves)
- Survival in specific habitats
45.
Explain
the importance of studying human population ecology.
Answer:
- Predicts growth trends and
challenges
- Helps in sustainable resource
management
- Guides health, education, and
employment planning
46.
Explain
how reproductive strategies affect population structure.
Answer:
- r-strategists → many young,
rapid growth
- K-strategists → few young,
stable population
- Determines age structure and
growth rate
47.
Explain
the significance of studying predator-prey interactions.
Answer:
- Maintains ecosystem balance
- Influences adaptations of both
species
- Drives co-evolution
48.
Explain
the difference between carrying capacity and population size with example.
Answer:
- Population size: Number of individuals (e.g.,
500 deer in a forest)
- Carrying capacity: Maximum sustainable (e.g.,
forest can support 400 deer)
- Population > K → decline due
to resource limitation
49.
Explain
how limiting factors determine the population growth curve.
Answer:
- Abundant resources →
exponential growth
- Limited resources → growth
slows → logistic curve
- Density-dependent and independent
factors shape population trajectory
50.
Explain
the ecological significance of age structure, dispersion, and interactions in
maintaining biodiversity.
Answer:
- Age structure → predicts growth
and resource needs
- Dispersion → indicates social
behavior and resource use
- Interactions → competition,
predation, mutualism regulate populations
- Together, maintain ecosystem
stability and biodiversity
