🌸Chapter 11
Organisms & Populations
(3 Marks)
1.
Differentiate
between natality and mortality.
Answer:
- Natality: Birth rate of a population;
number of individuals born per 1000 per year.
- Mortality: Death rate; number of
individuals dying per 1000 per year.
2.
Explain
the three types of population dispersion with examples.
Answer:
- Clumped: Individuals occur in groups;
e.g., elephants in herds.
- Uniform: Evenly spaced; e.g., penguins
maintaining territories.
- Random: Individuals scattered
unpredictably; e.g., dandelions in a field.
3.
Describe
intraspecific and interspecific competition with examples.
Answer:
- Intraspecific: Competition among same
species; e.g., male deer fighting for mates.
- Interspecific: Competition among different
species; e.g., lion and hyena competing for prey.
4.
Define
carrying capacity and explain its importance.
Answer:
- Definition: Maximum population size an
environment can support indefinitely.
- Importance: Prevents overpopulation,
depletion of resources, and ecosystem collapse.
5.
What
are the three main age groups in a population? Explain their significance.
Answer:
- Pre-reproductive: Not capable of reproduction;
indicates future growth potential.
- Reproductive: Contribute directly to
population growth.
- Post-reproductive: Beyond reproduction; affect
resource consumption but not growth.
6.
Draw
and explain a triangular age pyramid.
Answer:
- Triangular: Broad base → many young
individuals → expanding population.
- Significance: Indicates high
growth rate, common in developing countries.
7.
Explain
the difference between exponential and logistic growth.
Answer:
- Exponential: Unlimited resources → rapid
growth → J-shaped curve.
- Logistic: Growth slows near carrying
capacity → S-shaped curve → density-dependent regulation.
8.
Explain
the formula ΔN = (B–D) + (I–E).
Answer:
- ΔN = Change in population size
- B = Births, D = Deaths, I =
Immigration, E = Emigration
- Used to calculate net change
in population over time.
9.
Give
examples of density-dependent and density-independent factors.
Answer:
- Density-dependent: Disease, competition,
predation (effects increase with density).
- Density-independent: Flood, fire, earthquake
(effects independent of density).
10.
Describe
mutualism with one plant and one animal example.
Answer:
- Definition: Both species benefit.
- Plant example: Lichen (alga + fungus)
- Animal example: Oxpecker and rhinoceros
11.
Define
commensalism and give two examples.
Answer:
- One species benefits, the other
unaffected.
- Examples: Cattle egret and
cattle; epiphytic orchids on tree branches.
12.
Define
parasitism and give one example each in plants and animals.
Answer:
- One species benefits at the
expense of the host.
- Plant: Cuscuta on host plants
- Animal: Tick on dog
13.
Define
amensalism and give one example.
Answer:
- One species is harmed, the
other unaffected.
- Example: Penicillium secreting
antibiotic affecting bacteria.
14.
Explain
predation and its ecological significance.
Answer:
- Predator feeds on prey.
- Example: Lion hunting deer.
- Significance: Regulates prey population,
prevents overpopulation, maintains balance.
15.
Differentiate
between density-dependent and density-independent regulation.
Answer:
- Density-dependent: Effect increases with
population size (e.g., disease).
- Density-independent: Effect independent of
population size (e.g., flood).
16.
Explain
lag, log, and stationary phases of population growth.
Answer:
- Lag phase: Slow growth, population
adjusting.
- Log phase: Rapid exponential growth.
- Stationary phase: Growth stabilizes near
carrying capacity.
17.
Describe
clumped dispersion in animals and its adaptive significance.
Answer:
- Individuals form groups.
- Example: Elephants in herds.
- Significance: Protection, social
interactions, better resource access.
18.
Explain
uniform dispersion with an example.
Answer:
- Individuals evenly spaced due
to competition/territoriality.
- Example: Penguins in breeding
grounds.
19.
Explain
random dispersion with an example.
Answer:
- Individuals distributed
unpredictably.
- Example: Dandelions in a field;
occurs when resources are uniform.
20.
Explain
the role of immigration and emigration in population dynamics.
Answer:
- Immigration: Increases population size.
- Emigration: Decreases population size.
- Both influence density and
growth rate.
21.
How
does age structure influence population growth?
Answer:
- Broad pre-reproductive → rapid
growth.
- Broad post-reproductive →
declining population.
- Helps predict future trends.
22.
Give
an example of morphological, physiological, and behavioral adaptations.
Answer:
- Morphological: Thorns of cactus
- Physiological: Camel hump
storing fat
- Behavioral: Nocturnal desert
activity
23.
Explain
why population growth cannot continue indefinitely.
Answer:
- Limited resources (food, space,
water)
- Predation, disease, competition
- Population stabilizes near
carrying capacity.
24.
Explain
the ecological niche with an example.
Answer:
- Niche: Role of species in
ecosystem (habitat, food, interactions).
- Example: Honeybee – pollinator,
feeds on nectar.
25.
Explain
pre-reproductive, reproductive, and post-reproductive age groups with examples.
Answer:
- Pre-reproductive: Children →
future growth
- Reproductive: Adults →
contribute to growth
- Post-reproductive: Elderly →
consume resources, no reproduction
26.
Explain
the concept of carrying capacity with an example.
Answer:
- Maximum sustainable population.
- Example: Deer population in a
forest limited by food and space.
27.
What
is the role of predation in regulating populations?
Answer:
- Maintains prey population
balance
- Prevents overpopulation
- Promotes natural selection
28.
Explain
the significance of age pyramids in human population studies.
Answer:
- Helps predict growth trends
- Identify potential social and
economic pressures
29.
Differentiate
between J-shaped and S-shaped growth curves.
Answer:
- J-shaped: Exponential,
unlimited growth
- S-shaped: Logistic, stabilizes
near carrying capacity
30.
Give
an example of intraspecific competition in plants.
Answer:
- Trees of same species competing
for sunlight or nutrients
31.
Give
an example of interspecific competition in animals.
Answer:
- Lion and hyena competing for
prey
32.
Explain
the effect of density-independent factors on populations.
Answer:
- Natural disasters like floods,
fire
- Can reduce population
suddenly regardless of density
33.
Explain
the effect of density-dependent factors on populations.
Answer:
- Disease, competition, predation
- Impact increases with
population density
34.
Explain
the ecological significance of parasitism.
Answer:
- Controls host population
- Influences natural selection
- Maintains ecosystem balance
35.
Give
two examples each of mutualism in plants and animals.
Answer:
- Plants: Lichen (alga + fungus),
Mycorrhizal association
- Animals: Oxpecker and
rhinoceros, Ants and aphids
36.
Explain
the adaptive significance of nocturnal behavior in desert animals.
Answer:
- Reduces water loss
- Avoids heat stress
- Enhances survival in harsh
conditions
37.
Explain
why broad-based age pyramids indicate expanding populations.
Answer:
- Many young individuals → high
reproductive potential → population growth
38.
Explain
why narrow-based age pyramids indicate declining populations.
Answer:
- Fewer young → low reproductive
potential → population declines
39.
Explain
the difference between immigration and emigration with examples.
Answer:
- Immigration: Individuals
entering population → increases size (e.g., birds migrating in)
- Emigration: Individuals leaving
→ decreases size (e.g., birds migrating out)
40.
Define
population and community.
Answer:
- Population: Same species, same
area
- Community: Different species,
same area
41.
Give
an example of commensalism in plants and animals.
Answer:
- Plants: Epiphytic orchids
- Animals: Cattle egret and
cattle
42.
Give
an example of amensalism in plants and animals.
Answer:
- Plants: Penicillium affecting
bacteria
- Animals: Elephant stepping on
ants
43.
Explain
the role of competition in population regulation.
Answer:
- Reduces overpopulation
- Ensures survival of fittest
- Maintains ecosystem balance
44.
Give
an example of logistic growth in any population.
Answer:
- Deer in a forest stabilizing
due to limited food
45.
Give
an example of exponential growth in any population.
Answer:
- Bacteria in nutrient-rich lab
medium
46.
Explain
why population growth curves are important in ecology.
Answer:
- Predict population trends
- Plan conservation strategies
- Study effects of limiting
factors
47.
Explain
the difference between density and population size.
Answer:
- Density: Number of individuals
per unit area
- Population size: Total number
of individuals in an area
48.
Define
ecological niche and habitat.
Answer:
- Niche: Functional role of
species
- Habitat: Physical place where
species lives
49.
Explain
the effect of predation on prey adaptations.
Answer:
- Prey evolve defense mechanisms
(camouflage, speed, warning colors)
- Predator-prey interactions
drive co-evolution
50.
Explain
the difference between morphological, physiological, and behavioral
adaptations.
Answer:
- Morphological: Physical
structure (thorns)
- Physiological: Internal
function (camel hump)
- Behavioral: Activity patterns
(nocturnal behavior)
