Chapter 29: NATURAL ENVIRONMENT

Chapter 29: Natural Environment Class 10 Science and Technology (212) NIOS Textbook Solutions

Chapter 29. NATURAL ENVIRONMENT

INTEXT QUESTIONS 29.1

1. Sunlight forms the abiotic component of ecosystem, name one biotic component.

Answer: A biotic component of an ecosystem is plants (animals and microorganisms).

2. Why are plants called producers? Which trophic level do they occupy in an ecosystem?

Answer: Plants are called producers because they are the only organisms that can convert inorganic substances like carbon dioxide, water, and minerals into organic food such as carbohydrates, using sunlight energy through the process of photosynthesis. They produce food for all other living organisms in the ecosystem.
Plants occupy the first trophic level in an ecosystem.

3. Give one reason in support of the statement that “food web is a jumble of food chains”.

Answer: A food web is a jumble of food chains because an organism occupies more than one trophic level and feeds on multiple sources. Since animals eat varied food to meet energy needs, interconnected food chains form a complex, tangled web rather than a simple linear path.

4. Construct one food chain and one food web from the following :

Tiger, grains, vulture, frog, snake, grass, cat, sheep, peacock, wolf, rabbit, phytoplankton, small fish, rat, large fish.

Answer: Food chain : Grass → Rabbit → Tiger  

Food Web: Grass → Rabbit → Tiger

Grass → Sheep → Wolf

Grains → Rat → Snake → Peacock

Grains → Rat → Cat

Phytoplankton → Small Fish → Large Fish → Vulture.

INTEXT QUESTIONS 29.2

1. Name any two ways which are responsible for adding carbon dioxide in the atmosphere.

Answer: Two ways responsible for adding carbon dioxide to the atmosphere are:

(i) Factories  (ii) Vehicles

2. Name the bacteria which live in the roots of the leguminous plants and are responsible for nitrogen fixation.

Answer: The bacteria that live in the roots of leguminous plants and are responsible for nitrogen fixation are called rhizobium .

3. What is the process of conversion of free atmospheric nitrogen into nitrites and nitrates called?

Answer: The conversion of free atmospheric nitrogen into nitrites and nitrates is called nitrogen fixation.

4. What is the role played by denitrifying bacteria and nitrifying bacteria in the nitrogen cycle? Give the name of one denitrifying bacteria and one for nitrifying bacteria.

Answer: Role of denitrifying bacteria: Reduces nitrate to nitrogen .

Examples:

Denitrifying bacteria – Pseudomonas (or Clostridium)
Role of nitrifying bacteria: Converts ammonia to nitrate .

Examples:

Nitrifying bacteria – Nitrosomonas (or Nitrobacter)

5. Mention any one role that you play in the (i) nitrogen cycle and (ii) carbon cycle.

Answer: i) Role in the nitrogen cycle: We release nitrogen compounds into the soil through our urine and excreta.

(ii) Role in the carbon cycle: We release carbon dioxide (CO₂) into the atmosphere through respiration.

6. Nitrogen is an essential component of the proteins and nucleic acids in living beings. Mention any one way by which you obtain nitrogen for your growth.

Answer: We obtain nitrogen from the food we eat, such as vegetables, pulses, milk, eggs, or meat, which contain proteins.

7. Mention one way in which increasing deforestation by humans is influencing the carbon cycle.

Answer: Increasing deforestation increases the level of carbon dioxide (CO₂) in the atmosphere, as fewer trees are available to absorb CO₂ during photosynthesis.

INTEXT QUESTIONS 29.3

1. Why are leaves of water lily coated with wax on the upper surface?

Answer: The upper surface of water lily leaves is coated with wax because the wax acts as a water repellent, preventing water from staying on the leaf.

2. Name two tree dwellers.

Answer: Two tree dwellers are monkeys and tree frogs.

3. Enumerate the adaptations of birds that enable them to fly so easily (Any two).

Answer: Any two adaptations of birds that help them fly are streamlined body and hollow bones.

4. How are penguins able to survive in the extreme cold conditions?(Any two adaptations)

Answer: Penguins survive in extreme cold conditions because they have:

(i) A thick layer of densely packed feathers

(ii) Flippers and legs adapted to reduce heat loss .

5. Why do the desert plants have fewer stomata?

Answer: Desert plants have fewer stomata to reduce water loss through transpiration, helping them conserve water.

6. Humans are not adapted for aquatic life. List any two challenges that you would face when you go for swimming in a pond/lake and the ways by which you would overcome them and become an effective swimmer.

Answer: Challenges :

(i) Difficulty in keeping afloat     (ii) Difficulty in breathing

Ways to overcome :

(i) Move hands and feet to stay afloat and swim.   (ii) Keep the nose above water to breathe air.

INTEXT QUESTIONS 29.4

1. How is the sucker fish benefitted by attaching itself to the shark’s body? What type of association is it?

Answer: The sucker fish benefits by getting protection from predators and being carried to different places by the shark. This type of association is commensalism.

2. If alga provides food to the fungus that lives on it, what does the fungus do for the alga?

Answer: The fungus provides water, minerals, and protection to the alga. This is a mutualistic association.

INTEXT QUESTIONS 29.5

1. When does the population density increase?

Answer: Population density increases when the birth rate is higher than the death rate.

2. What is the difference between Emigration and Immigration?

Answer: The difference between Emigration and Immigration is :

Emigration	Immigration
(i) It is the permanent outward movement of the organisms from a given population.	(i) It is the permanent inward movement of the organisms from outside into a given population.
(ii) Decrease the size of the population.	(ii) Increases the size of the local population.

3. What is lag phase?

Answer: Lag phase is the initial stage of population growth in which the growth is slow because the individuals are adapting to the new environment and establishing themselves.

TERMINAL EXERCISES

1. What is an ecosystem? Name the various components of an ecosystem.

Answer: An ecosystem is a functionally independent unit of biotic and abiotic components of an ecosystem.

Components of an ecosystem:

(i) Biotic components .

(ii) Abiotic components .

2. Is detritus a biotic component or is it an abiotic component of an ecosystem?

Answer: Detritus is a biotic component of an ecosystem because it consists of dead and decaying organic matter from plants and animals.

3. What is the function of Nitrosomonas in nitrogen cycle?

Answer: Nitrosomonas converts ammonia into nitrites during the nitrogen cycle. This process is called nitrification.

4. With the help of suitable examples differentiate between the detritus and grazing food chain.

Answer:

Detritus Food Chain	Grazing Food Chain
Starts with dead and decaying organic matter (detritus).	Starts with green plants (producers).
Example: Dead leaves → Earthworm → Frog → Snake	Example: Grass → Grasshopper → Frog → Snake

5. What is the significance of food chain and food web?

Answer: The significance of food chain and food web is :

(i) They help to maintain ecological balance.

(ii) They help in understanding the feeding relations among organisms.

(iii) Energy flow and nutrient cycle takes place through them.

6. Why does the energy decrease as we go along the food chain from producers to tertiary consumers?

Answer: Energy decreases along the food chain because organisms use most of the energy they obtain for life processes such as growth, movement and respiration. Only a small amount of energy is passed to the next trophic level. Therefore, producers have the maximum energy, while tertiary consumers have the least.

7. What will happen if all the animals are removed from a pond?

Answer: If all the animals are removed from a pond, the food chain will be disturbed and the ecosystem will become imbalanced. Producers may increase excessively, while decomposers will have less organic matter. The natural flow of energy and nutrients in the pond will also be affected.

8. Why is the number of trophic level restricted to four or five in a food chain?

Answer: The number of trophic levels is restricted to four or five because only about 10% of the energy is transferred from one level to the next. As we move up, the energy available keeps decreasing. After four or five levels, the remaining energy is too little to support another trophic level, so the food chain cannot continue further.

9. What is the difference between energy flow and biogeochemical cycle in an ecosystem?

Answer:

Energy Flow	Biogeochemical Cycle
(i) Energy flows in one direction through the ecosystem.	(i) Nutrients are recycled between living organisms and the environment.
(ii) Energy is not reused after being lost as heat.	(ii) Elements like carbon, nitrogen and water are used repeatedly through natural cycles.

10. How are camels able to survive in extreme heat?

Answer: Camels are able to survive in extreme heat because they can drink very large amounts of water at one time and survive for a long period without drinking water. They also excrete highly concentrated urine during water scarcity, which reduces water loss and helps conserve water.

11. Why do polar bear have thick fur over their body?

Answer: Polar bears have thick fur over their body to reduce heat loss and keep their body warm in the extremely cold polar regions.

12. Compare the S-shaped pattern of population growth with the J-shaped pattern of population growth.

Answer: The comparison between the S-shaped pattern of population growth and the J-shaped pattern of population growth :

S-shaped (Sigmoid) Population Growth	J-shaped Population Growth
Population grows slowly at first, then rapidly, and finally slows down and becomes stable.	Population grows slowly at first and then increases rapidly without slowing down.
Occurs when resources are limited and the population reaches the carrying capacity of the environment.	Occurs when resources are abundant and there are no limiting factors.
Population size remains stable after reaching carrying capacity.	Population may crash suddenly after rapid growth due to depletion of resources.

13. What is population dispersal? What are the two types of population dispersal?

Answer: Population dispersal is the movement of individuals from one place to another.

The two types of population dispersal are:

(i) Immigration: The movement of individuals into a population.

(ii) Emigration: The movement of individuals out of a population.

14. What is the main cause of population explosion?

Answer: Answer: The main cause of population explosion is the rapid decline in the death rate while the birth rate remains high. This results in a rapid increase in population.

15. Do you think population remains static? Support your answer with suitable explanation.

Answer: No, population does not remain static. It changes continuously due to births, deaths, immigration, and emigration. When the birth rate is higher than the death rate, the population increases. When the death rate is higher than the birth rate, the population decreases. Immigration and emigration also affect the population size.

16. Try to complete the table given below

	Feature	How is the feature advantageous to the organism?	Name of the plant/animal if is found
1.	Nostrils positioned near the top of the head of animals
2.		To store water	Cacti
3.	Loss of water by excreting uric acid in water
4.	Hollow bone		Birds
5.		Trap air to keep the body warm and help the bird to fly	Birds
6.	Presence of flippers and legs
7.	Thin, bread leaves with a large number of stomata on the underside of leaves
8.		Acts as a water repellent and allows them to remain afloat on the surface of water	Water lily

Answer:

Feature	How is the feature advantageous to the organism?	Name of the plant/animal if found
1. Nostrils positioned near the top of the head of animals	Allows the animal to breathe while keeping most of its body submerged underwater (helps in respiration without fully surfacing).	Crocodile / Hippopotamus (or any aquatic mammal)
2. Succulent/Spongy stem (fleshy tissue)	To store water	Cacti
3. Loss of water by excreting uric acid	Conserves water in the body (as uric acid is less toxic and requires very little water to excrete).	Birds / Reptiles (e.g., lizards, snakes)
4. Hollow bones	Makes the body lightweight, helping in easy flight.	Birds
5. Feathers (or air sacs)	Trap air to keep the body warm and help the bird to fly.	Birds
6. Presence of flippers and legs	Helps in swimming and moving on land (flippers for swimming, legs for walking on land/ice).	Seal / Turtle / Penguin (any aquatic animal with both)
7. Thin, broad leaves with a large number of stomata on the underside of leaves	Allows maximum absorption of sunlight and efficient gaseous exchange for photosynthesis in aquatic plants.	Water lily / Lotus (any aquatic floating plant)
8. Waxy coating/cuticle on leaves	Acts as a water repellent and allows them to remain afloat on the surface of water.	Water lily

17. Extensive poaching and hunting has reduced the tiger population in Asia to a dangerous level.

(a) What are they hunted for (2 points)

(b) Draw a food web with tiger as the top level carnivore (At least 2 food chain to be shown)

(c) What effect will removal of the tiger have on (i) the herbivore (ii) producer?

(You can answer this question by making a food chain)

Answer: (a) (i) For their skin/fur (used in trade and decoration).

(ii) For their bones and other body parts (used in traditional medicines).

(b) Food web with tiger as the top level carnivore:

Photo

(Two food chains shown in the web:)

Food Chain 1: Plants → Deer → Tiger

Food Chain 2: Plants → Wild Boar → Tiger

(c) Effect of removal of the tiger:

(i) Effect on Herbivores	(ii) Effect on Producers
Herbivore population will increase dramatically because there is no natural predator to control their numbers.	Producers (plants) will decrease because the increased herbivore population will overgraze and consume more vegetation, leading to depletion.

Food chain showing the effect:
Plants → Herbivores (increase) → (no tiger to control) → Plants (decrease due to overgrazing

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