🌸Chapter 11
Organisms & Populations
(Summary Notes)
Organisms
& Populations – Revision Sheet
1. Key Definitions
|
Term |
Definition |
|
Population |
Group of individuals of the same species living in a
particular area at a given time. |
|
Population size (N) |
Total number of individuals in a population. |
|
Population density (D) |
Number of individuals per unit area or volume. |
|
Dispersion |
Spatial distribution of individuals in a population
(clumped, uniform, random). |
|
Natality (Birth rate) |
Number of births per 1000 individuals per year. |
|
Mortality (Death rate) |
Number of deaths per 1000 individuals per year. |
|
Immigration |
Movement of individuals into a population. |
|
Emigration |
Movement of individuals out of a population. |
|
Age structure |
Distribution of individuals among pre-reproductive,
reproductive, and post-reproductive age groups. |
|
Carrying capacity (K) |
Maximum population size an environment can sustain
indefinitely. |
|
Population growth |
Change in population size over time. |
|
Exponential growth (J-shaped curve) |
Population grows rapidly under unlimited resources. |
|
Logistic growth (S-shaped curve) |
Population growth slows and stabilizes near carrying
capacity. |
|
Ecological niche |
Functional role of a species in an ecosystem, including
habitat, food, and interactions. |
2. Population Characteristics
1.
Size
(N) – total individuals.
2.
Density
(D) – individuals per unit area/volume.
3.
Dispersion
patterns:
o Clumped – group formation (elephants,
fishes).
o Uniform – evenly spaced (penguins,
territorial plants).
o Random – unpredictable (dandelions).
4.
Age
structure –
pre-reproductive, reproductive, post-reproductive groups.
5.
Population
growth rate
– change over time (ΔN = (B–D) + (I–E)).
3. Population Growth
Growth Curves
1.
Exponential
(J-shaped)
o Unlimited resources, rapid growth
o Example: Bacteria
2.
Logistic
(S-shaped)
o Growth slows near carrying capacity
o Example: Deer in forest
Phases of Logistic Growth
- Lag phase – slow adjustment
- Exponential/log phase – rapid growth
- Stationary phase – population stabilizes at K
4. Factors Affecting Population
Density-dependent
- Effects increase with
population size
- Examples: Disease, predation,
competition
Density-independent
- Effects independent of
population size
- Examples: Flood, fire,
earthquake
Limiting factors
- Resources, predation, disease,
environmental conditions limit growth
5. Population Regulation
- Carrying capacity (K) – limits population size
- Negative feedback mechanisms – density-dependent factors
reduce growth as population approaches K
- Zero population growth – birth rate = death rate
6. Age Structure & Population
Pyramid
Age Groups:
- Pre-reproductive → future
growth
- Reproductive → contributes to
growth
- Post-reproductive → consumes
resources
Pyramids:
- Expanding: Broad base → rapid growth
- Stable: Uniform width → slow growth
- Declining: Narrow base → declining
population
Diagram:
Expanding Pyramid:
Post-reproductive
Reproductive
Pre-reproductive (broad base)
7. Species Interactions
|
Interaction |
Effect |
Examples |
|
Mutualism |
Both benefit |
Lichen, oxpecker & rhino |
|
Commensalism |
One benefits, other unaffected |
Epiphytic orchids, cattle egret & cattle |
|
Parasitism |
One benefits at host's expense |
Cuscuta on plants, tick on dog |
|
Amensalism |
One harmed, other unaffected |
Penicillium secreting antibiotics, elephant stepping on
ants |
|
Predation |
Predator feeds on prey |
Lion hunts deer |
8. Ecological Niche
- Role of a species in an
ecosystem
- Includes habitat, food,
interactions
- Reduces interspecific
competition
- Example: Honeybee – nectar
feeder, pollinator
9. Adaptations
|
Type |
Definition |
Examples |
|
Morphological |
Physical features |
Thorns of cactus, porcupine spines |
|
Physiological |
Internal function |
Camel hump stores fat, osmoregulation in fishes |
|
Behavioral |
Activity patterns |
Nocturnal desert animals, bird migration |
10. Reproductive Strategies
|
Strategy |
Features |
Examples |
|
r-strategists |
High reproduction, low parental care, rapid growth |
Bacteria, insects |
|
K-strategists |
Low reproduction, high parental care, stable population |
Elephants, humans |
11. NCERT Keywords & Important
Points
- Population, density,
dispersion, natality, mortality, immigration, emigration
- Carrying capacity (K), limiting
factors, exponential growth, logistic growth, feedback mechanisms
- Age structure, population
pyramid, pre-reproductive, reproductive, post-reproductive
- Ecological interactions:
mutualism, commensalism, parasitism, amensalism, predation
- Adaptations: morphological,
physiological, behavioral
- r-strategists, K-strategists,
ecological niche
12. Important Diagrams to Draw
1.
Population
growth curves
– J-shaped and S-shaped
2.
Population
pyramid –
expanding, stable, declining
3.
Dispersion
patterns –
clumped, uniform, random
4.
Species
interactions
– simple diagrams showing mutualism, parasitism, predation
Quick Tips for Exam
- Always mention examples
from NCERT.
- Draw simple labeled diagrams
wherever possible.
- Highlight key terms in
answers.
- Use ΔN = (B–D) + (I–E)
for numerical questions.
- For population pyramids,
identify expanding, stable, or declining clearly.
