Chapter 13: Organisms and Populations

Q1. What are the different types of interactions between organisms?

Solution

1. Mutualism: Both benefit (+/+)
2. Commensalism: One benefits, other unaffected (+/0)
3. Parasitism: One benefits, other harmed (+/-)
4. Predation: One kills and eats other
5. Competition: Both harmed (-/-)

Q2. What is an ecological niche?

Solution

Ecological niche is the unique functional role and position of a species in its environment, including its habitat, food, interactions, and tolerances. Gause's principle states that two species cannot occupy the same niche indefinitely.

Q3. What are the attributes of a population?

Solution

1. Birth rate (natality)
2. Death rate (mortality)
3. Immigration rate
4. Emigration rate
5. Age distribution
6. Population density

Q4. What are the types of ecological adaptations in plants?

Solution

Hydrophytes: Water plants (e.g., Lotus) - no cuticle, floating leaves
Xerophytes: Desert plants (e.g., Cactus) - thick cuticle, sunken stomata
Mesophytes: Moderate water (e.g., Mango)
Halophytes: Salty soil (e.g., Rhizophora) - pneumatophores

Q5. What are the types of population growth models?

Solution

J-shaped: dN/dt = rN (exponential growth)
S-shaped: dN/dt = rN((K-N)/K) (logistic growth)
Where: r = intrinsic rate, K = carrying capacity, N = population size

Q6. What is predation? Give examples.

Solution

Examples: (1) Tiger and deer (2) Starfish (Pisaster) and mussel (keystone predator) (3) Lynx and snowshoe hare (cyclic changes)

Q7. What is the difference between r-strategists and K-strategists?

Solution

r-strategists: High reproductive rate, small body, short life, unstable environment (insects, bacteria)
K-strategists: Low reproductive rate, large body, long life, stable environment (elephants, whales)

Q8. What are the types of parasitism?

Solution

Ectoparasitism: On body surface (lice, ticks)
Endoparasitism: Inside body (tapeworm, Plasmodium)
Brood parasitism: Laying eggs in another's nest (Cuckoo)

Q9. What is an age pyramid? What are its three types?

Solution

Expanding (triangular): More young, growing population
Stable (bell-shaped): Equal proportion, stationary
Declining (urn-shaped): More older, declining population

Q10. What are the adaptations of desert animals?

Solution

1. Nocturnal behavior
2. Concentrated urine
3. Burrowing habits
4. Thick skin
5. Estivation
Example: Kangaroo rat - gets water from metabolic water

Q11. What is the difference between competition and predation?

Solution

Competition: Two organisms compete for same resource, both harmed
Predation: One kills and eats another, predator benefits

Q12. What is commensalism? Give three examples.

Solution

Examples: (1) Orchid on tree (2) Remora fish on shark (3) Barnacles on whale

Q13. What is the carrying capacity of an environment?

Solution

Maximum population size environment can sustain
Factors: Food, water, space, predation, disease
In logistic growth, population stabilizes at K

Q14. What is mutualism? Give three examples.

Solution

Examples: (1) Mycorrhiza (2) Lichen (3) Fig and fig wasp (4) Clownfish and sea anemone (5) Leguminous plants and Rhizobium

Q15. What is the difference between habitat and niche?

Solution

Habitat: Where organism lives (physical address)
Niche: Functional role in habitat (profession)
Two species can share habitat but have different niches

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