Question 6.
Name Important defence mechanisms in plants against herbivory.
Answer:
Plants cannot escape from herbivores, so they have developed several defence mechanisms to protect themselves. These defences can be structural or chemical:

1. Structural (Morphological) Defences

• Thorns and spines: Example – Bougainvillea, Acacia. These prevent animals from eating the plant.
• Sharp, silicate leaf edges: Example – grasses with silica deposits that make leaves hard and difficult to chew.
• Hairy (trichome-covered) leaves: These irritate or discourage herbivores.

2. Chemical Defences

Plants produce toxic, repellent, or distasteful chemicals such as:

• Morphine – produced by Papaver somniferum (opium poppy)
• Nicotine – produced by Nicotiana tabacum (tobacco plant)
• Strychnine – produced by Strychnos nux-vomica
• Cardiac glycosides, tannins, latex, resins, alkaloids – harmful or bitter to herbivores

These adaptations reduce herbivore attacks and increase the plant’s chances of survival.

Question 7.
An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree?
Answer:
An orchid growing on the branch of a mango tree is an epiphyte. Epiphytes are plants that grow on other plants but do not obtain nutrients from them. Therefore, the relationship between the orchid and the mango tree is an example of commensalism, where one species benefits while the other is neither harmed nor benefited.

In this interaction:

• The orchid is benefited as it gets support and better access to light.
• The mango tree remains unaffected.

Question 8.
What is the ecological principle behind the biological control method of managing with pest insects?
Answer:
The ecological principle behind the biological control of pest insects is the predator–prey relationship. Biological control depends on the ability of natural predators, parasites, or pathogens to regulate and reduce the population of pest insects.
By introducing or enhancing these natural enemies, pest populations are controlled in an eco-friendly and sustainable manner.

Question 9.
Distinguish between the following:
(a) Hibernation and Aestivation
(b) Ectotherms and Endotherms
Answer:
(a) Hibernation and Aestivation

(b) Ectotherms and Endotherms

Question 10.
Write a short note on
(a) Adaptations of desert plants and animals
(b) Adaptations of plants to water scarcity
(c) Behavioural adaptations in animals
(d) Importance of light to plants
(e) Effect of temperature or water scarcity and the adaptations of animals.
Answer:
(a) Adaptations of desert plants and animals

Desert plants show several adaptations to reduce water loss and survive extreme heat:

• Deep and extensive root systems to absorb maximum water.
• Thick, waxy cuticle on leaves and stems to prevent transpiration.
• Leaves reduced to spines (e.g., cactus) to minimize water loss.
• Green, fleshy stems to store water and perform photosynthesis.
• Presence of mucilage in tissues to retain moisture.

Desert animals also exhibit special adaptations:

• They remain burrowed during daytime to avoid heat.
• Produce dry faces and concentrated urine to conserve water.
• Kangaroo rat meets 90% of its water requirement from metabolic water obtained by oxidation of fats and never drinks water.
• Camel avoids sweating until body temperature reaches 55–66°C and tolerates 40% dehydration.

(b) Adaptations of plants to water scarcity

Xerophytes exhibit four types of adaptations:

1. Ephemerals (Drought escapers):

• Complete life cycle quickly during rains.
• Example: Euphorbia prostrate, Tribulus terrestris.

2. Annuals (Drought evaders):

• Survive for a few months even after rains.
• Have modifications to reduce transpiration.
• Example: Echinus echinates.

3. Succulents (Drought resistant’s):

• Store water in fleshy leaves/stems.
• Stems are green and photosynthetic.
• Examples: Opuntia, Euphorbia, Asparagus.

4. Non-succulent perennials (Drought endures):

• Extensive deep root systems.
• Waxy coating, hairs, sunken stomata, reduced leaves.
• Examples: Acacia nilotica, Calotropis proceri.

(c) Behavioural adaptations in animals

Some animals use behaviour to survive environmental extremes:

• Desert lizards regulate body temperature by basking in the sun when cold and moving into shade when hot.
• They lack physiological thermoregulation like mammals but maintain comfort temperature through movement.
• Many species also burrow into soil to avoid high temperatures.

(d) Importance of light to plants

Light affects several physiological activities in plants:

1. Photosynthesis:

• Depends on light intensity, quality, and duration.

        2. Growth:

• Red light promotes growth; blue light regulates normal development.
• UV light induces rosette habit.

        3. Transpiration:

• Light opens stomata and enhances transpiration.

        4. Seed germination:

• Some seeds are photoblastic (require light), e.g., Viscum, Lactuca.

        5. Movements:

• Phototaxis in Chlamydomonas, Euglena.
• Shoots show positive phototropism.

        6. Photoperiodism:

Flowering depends on light duration (short-day, long-day, day-neutral plants).

(e) Effect of temperature or water scarcity and adaptations of animals

Animals adopt structural, physiological, and behavioural adaptations:

1. Kangaroo rat:

• Never drinks water.

1. • 90% of its water comes from metabolic oxidation of fats.
   • Produces solid urine and faces.
   • Nocturnal and remains in burrows during daytime.
   • Thick fur reduces evaporative water loss.
2. Camel:
   • Body temperature fluctuates widely; avoids sweating until 55–66°C.
   • Can tolerate up to 40% dehydration.
   • Produces dry faces and concentrated urine.
   • Stores urea during extreme water scarcity.

Question 11.
List the various abiotic environmental factors.
Answer:
Abiotic environmental factors are the non-living components that influence organisms. They include:

1. Atmospheric Factors

• Light
• Temperature
• Wind
• Water (humidity, rainfall)

2. Lithosphere

• Rocks
• Soil

3. Hydrosphere

• Pond
• River
• Lake
• Ocean

4. Edaphic Factors (soil-related)

• Soil texture
• Soil water
• Soil air
• Soil microorganisms
• Soil pH
• Mineral content

5. Topographic Factors

• Slope
• Altitude
• Valley

Question 12.
Give an example for:
(a) An endothermic animal
(b) An ectothermic animal
(c) An organism of benthic zone
Answer:
(a) An endothermic animal – Monkey (mammal)
(b) An endothermic animal Frog (amphibian), snake (reptile)
(c) An organism of the benthic zone – Angle Fish

Question 13.
Define population and community.
Answer:
Population:
A population is a group of individuals of the same species living in a specific geographical area at a given time and capable of interbreeding.
Community:
A community is a group of different populations of various species living and interacting in the same habitat.

Question 14.
Define the following terms and give one example for each:
(a) Commensalism
(b) Parasitism
(c) Camouflage
(d) Mutualism
(e) Interspecific competition
Answer:
(a) Commensalism

Definition:
Commensalism is an interaction between two individuals of different species in which one organism benefits, while the other is neither harmed nor benefited to any significant extent.

Example:
The pilot fish (Naucratis) accompanies a shark and feeds on pieces of food left over when the shark eats, without affecting the shark.

(b) Parasitism

Definition:
Parasitism is an interaction in which one organism (parasite) derives food and shelter directly from another living organism (host). The parasite spends part or whole of its life in or on the host’s body and benefits at the host’s expense.

Example:
Lice living on the human scalp.

(c) Camouflage

Definition:
Camouflage (cryptic appearance) is the ability of an organism to blend with its surroundings so that it remains unnoticed. It is a common protective adaptation used either to escape predators or to catch prey.

Example:
Praying mantis (Mantis religiosa) is green and resembles plant stems, allowing it to remain hidden till prey approaches.

(d) Mutualism

Definition:
Mutualism is an interaction between two species in which both organisms’ benefit. (The word symbiosis is often used in the same sense.)

Example:
Termites and protozoans in their gut. Protozoans digest cellulose from wood and release sugars for termites; termites provide food and shelter to protozoans.

(e) Interspecific competition

Definition:
Interspecific competition occurs when individuals of different species compete for the same natural resources, such as light, nutrients, water, pollinators, or space.

Example:
In a forest, trees, shrubs, herbs, and vines compete with each other for sunlight, nutrients, and water.

Question 15.
With the help of suitable diagram describe the logistic population growth curve.
Answer: