12th Bio - Botany - Book Back Answers - Chapter 7 - English Medium Guides

 

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Tamil Nadu Board 12th Standard Bio-Botany - Chapter 7: Book Back Answers and Solutions

    This post covers the book back answers and solutions for Chapter 7 – Bio-Botany from the Tamil Nadu State Board 12th Standard Bio-Botany textbook. These detailed answers have been carefully prepared by our expert teachers at KalviTips.com.

    We have explained each answer in a simple, easy-to-understand format, highlighting important points step by step under the relevant subtopics. Students are advised to read and memorize these subtopics thoroughly. Once you understand the main concepts, you’ll be able to connect other related points with real-life examples and confidently present them in your tests and exams.

    By going through this material, you’ll gain a strong understanding of Bio-Botany Chapter 7 along with the corresponding book back questions and answers (PDF format).

Question Types Covered:

• 1 Mark Questions: Choose the correct answer, Fill in the blanks, Identify the correct statement, Match the following 
• 2 Mark Questions: Answer briefly 
• 3, 4, and 5 Mark Questions: Answer in detail

All answers are presented in a clear and student-friendly manner, focusing on key points to help you score full marks.

All the best, Class 12 students! Prepare well and aim for top scores. Thank you!

Unit 7 - Ecosystem

I. Multiple Choice Questions

1. Which of the following is not a abiotic component of the ecosystem? 
a) Bacteria 
b) Humus 
c) Organic compounds 
d) Inorganic compounds
Answer Key:
a) Bacteria 
 
2. Which of the following is / are not a natural ecosystem? 
a) Forest ecosystem 
b) Rice field 
c) Grassland ecosystem 
d) Desert ecosystem 
Answer Key:
b) Rice field 

3. Pond is a type of 
a) forest ecosystem
b) grassland ecosystem 
c) marine ecosystem 
d) fresh water ecosystem 
Answer Key:
d) fresh water ecosystem 

4. Pond ecosystem is 
a) not self sufficient and self regulating 
b) partially self sufficient and self regulating 
c) self sufficient and not self regulating 
d) self sufficient and self regulating 
Answer Key:
d) self sufficient and self regulating 

5. Profundal zone is predominated by heterotrophs in a pond ecosystem, because of 
a) with effective light penetration 
b) no effective light penetration 
c) complete absence of light 
d) a and b 
Answer Key:
b) no effective light penetration 

6. Solar energy used by green plants for photosynthesis is only 
a) 2 – 8% 
b) 2 – 10% 
c) 3 – 10% 
d) 2 – 9% 
Answer Key:
b) 2 – 10% 

7. Which of the following ecosystem has the highest primary productivity? 
a) Pond ecosystem 
b) Lake ecosystem 
c) Grassland ecosystem 
d) Forest ecosystem 
Answer Key:
d) Forest ecosystem 

8. Ecosystem consists of 
a) decomposers 
b) producers 
c) consumers 
d) all of the above
Answer Key:
d) all of the above
 
9. Which one is in descending order of a food chain 
a) Producers → Secondary consumers → Primary consumers → Tertiary consumers 
b) Tertiary consumers → Primary consumers → Secondary consumers → Producers 
c) Tertiary consumers → Secondary consumers → Primary consumers → Producers 
d) Tertiary consumers → Producers → Primary consumers → Secondary consumers 
Answer Key:
c) Tertiary consumers → Secondary consumers → Primary consumers → Producers 

10. Significance of food web is / are
a) it does not maintain stability in nature 
b) it shows patterns of energy transfer 
c) it explains species interaction 
d) b and c
Answer Key:
d) b and c
 
11. The following diagram represents 

 a) pyramid of number in a grassland ecosystem 
b) pyramid of number in a pond ecosystem 
c) pyramid of number in a forest ecosystem 
d) pyramid of biomass in a pond ecosystem 
Answer Key:
c) pyramid of number in a forest ecosystem 

12. Which of the following is / are not the mechanism of decomposition 
a) Eluviation 
b) Catabolism 
c) Anabolism 
d) Fragmentation 
Answer Key:
c) Anabolism 

13. Which of the following is not a sedimentary cycle 
a) Nitrogen cycle 
b) Phosphorous cycle 
c) Sulphur cycle 
d) Calcium cycle 
Answer Key:
a) Nitrogen cycle

14. Which of the following are not regulating services of ecosystem services 
i) Genetic resources 
ii) Recreation and aesthetic values 
iii) Invasion resistance 
iv) Climatic regulation 
a) i and iii 
b) ii and iv 
c) i and ii 
d) i and iv 
Answer Key:
c) i and ii 

II. Short Answer Questions

1. The productivity of profundal zone will be low. Why?

• The productivity of profundal zone will be low because of less penetration of light.

 
2. Discuss the gross primary productivity is more efficient Wthan net primary productivity.

• Gross primary productivity (GGP)is the total amount of organic matter produced in an ecosystem by photosynthesis.
• But net primary productivity (NPP) is the proportion of energy which remains after respiration loss in the plant.
• So the gross primary productivity is more efficient than net primary productivity

 
3. Pyramid of energy is always upright. Give reasons

• A graphical representation of energy flow at each successive trophic level in an ecosystem is called pyramids of energy.
• The bottom of the pyramid of energy is occupied by the producers.
• There is a gradual decrease in energy transfer at successive tropic levels from producers to the upper levels.
• Therefore, the pyramid of energy is always upright. 

 

4. What will happen if all producers are removed from ecosystem?

• If all producers are removed from the ecosystem, there is no consumers. So the ecosystem is imbalance.

 
5. Construct the food chain with the following data. Hawk, plants, frog, snake, grasshopper.
Plants→ grasshopper→ frog→ snake→ Hawk
 
6. Name of the food chain which is generally present in all
type of ecosystem. Explain and write their significance.
Detritus food chain type of food chain is present in all ecosystems.
The transfer of energy from the dead organic matter, is transferred through a series of organisms called detritus food chain.
Detritus consumers (detritivores)→Small carnivores→  
→Large (top) carnivores with repeated eating

Significance: Dead organic matter of plant and animals is broken down by decomposer and then carnivores.   

  
7. Shape of pyramid in a particular ecosystem is always different in shape. Explain with example.
1. pyramid of number in grassland and pond ecosystem are always upright.

• There is a gradual decrease in the numberWS of organisms in each trophic level
• From producers to primary consumers and then to secondary consumers, and finally to tertiary consumers.
• Therefore pyramid of number in grassland and pond ecosystem are always upright.

2. The pyramid of number in forest ecosystem looks spindle shaped

• In a forest ecosystem the pyramid of number is somewhat different in shape.
• (T1) of the pyramid occupies large sized trees (producer) which are lesser in number.
• herbivores (T2) (Fruit eating birds, elephant, deer) occupying second trophic level, are more in number.
• In final trophic level (T4), tertiary consumers (lion) are lesser in number than the secondary consumer (T3) fox and snake.
• Therefore the pyramid of number in forest ecosystem looks spindle shaped.

3. The pyramid of number in a parasite ecosystem is always Inverted

• It starts with a single tree.
• There is gradual increase in the number of organisms in successive tropic levels from producer to tertiary consumers.
• So the pyramid of number in a parasite ecosystem is always inverted

 

8. Generally human activities are against to the ecosystem, where as you a student how will you help to protect ecosystem?

• If i am a student I will help to protect ecosystem by following methods
• we have to practice the following in our day today life.
• Buy and use only eco-friendly products and recycle them.
• Grow more trees
• Choose sustained farm products (vegetables, fruits, greens)
• Reduce the use of natural resources.
• Recycle the waste & reduce the amount of waste you produce.
• Reduce consumption of water and electricity.
• Reduce the use of house-hold chemicals and pesticides.
• Maintain your cars and vehicles properly, (to reduce carbon emission)
• Create awareness and educate your friends and family members. 

   
9. Generally in summer the forest are affected by natural fire. Over a period of time it recovers Itself by the process of successions. Find out the types of succession and explain.

• This types of succession is secondary succession.
• The development of a plant community in an area where an already developed community has been destroyed by fire is known as secondary succession.
• Generally, This succession takes less time than the time taken for primary succession.
• Example: The forest destroyed by fire and excessive lumbering may be re-occupied by herbs over period of times.

 
10. Draw a pyramid from following details and explain in brief. Quantities of organisms are given-Hawks-50, plants-1000.rabbit and mouse-250+250, pythons and lizard-100+ 50 respectively. 

• There is a gradual decrease in the number of organisms each trophic level.
• From producers to primary consumers and then to secondary consumers, and finally to tertiary consumers.
• Therefore pyramid of number in grassland ecosystem is always upright.

 
11. Various stages of succession are given bellow. From that rearrange them accordingly. Find out the type of succession and explain in detall. Reed-swamp stage, phytoplankton stage, shrub stage, submerged plant stage, forest stage, submerged free floating stage, marsh medow stage.

• 1. Phytoplankton stage
• 2. Submerged plant stage
• 3. Submerged free floating stage
• 4. Reed-swamp stage
• 5. Marsh meadow stage
• 6. Shrub stage
• 7. Forest stage

• Hydrosere
• The succession in a freshwater ecosystem is also referred to as hydrosere.
• It begins with colonization of the pioneers like phytoplankton.
• Finally ends with the formation of climax .community like forest stage.
• 1. Phytoplankton stage
• It consisting of the pioneer community like blue green algae, green algae, diatoms, bacteria, etc.,
• The colonization of these organisms enrich the amount of organic matter and nutrients of pond due to their life activities and death.
• This favours the development of the next seral stages.
• 2. Submerged plant stage
• As the result of death and decomposition of planktons.
• Silt brought from land by rain water.
• It leads to a loose mud formation at the bottom of the pond.
• Hence, the rooted submerged hydrophytes begin to appear on the new substratum.
• Example: Chara, Utricularia, Vallisneria and Hydrilla etc.
• The death and decay of these plants will build up the substratum of pond to become shallow.
• Therefore, this habitat now replaces another group of plants which are of floating type.
• 3. Submerged free floating stage
• During this stage, the depth of the pond will become almost 2-5 feet.
• Hence, the rooted hydrophytic plants and with floating large leaves start colonising the pond.
• Example: Rooted floating plants like Nelumbo, Nymphaea and Trapa.
• Some free floating species like Azolla, Lemna, Wolffia and Pistia are also present in this stage.
• By death and decomposition of these plants, further the pond becomes more shallow.
• Due to this reason, floating plant species is gradually replaced by another species which makes new seral stage.
• 4. Reed-swamp stage-
• It is also called an amphibious stage.
• Rooted floating plants are replaced by plants
• It can live successfully in aquatic as well as aerial.
• Example: Typha, Phragmites, Sagittario and Scirpus etc.
• At the end, water level is very much reduced,
• making it unsuitable for the continuous growth of amphibious plants.
• 5. Marsh meadow stage
• The pond becomes swallowed due to decreasing water level.
• The species of Cyperaceae and Poaceae such as Corex, Juncus, Cyperus and Eleocharis colonise the area.
• They form a mat-like vegetation with the help of their much branched root system.
• This leads to an absorption & loss of large quantity of water.
• At the end of this stage, the soil becomes dry and the marshy vegetation disappears gradually and leads to shurb stage.
• 6. Shrub stage
• As the disappearance of marshy vegetation continues, soil becomes dry.
• These areas are now Invaded by terrestrial plants like shrubs (Salix and Cornus) and trees (Populus and Alnus).
• These plants absorb large quantity of water and make the habitat dry.
• Further, the accumulation of humus with a rich flora of microorganisms produce minerals in the soil, ultimately favouring the arrival of new tree species in the area.
• 7. Forest stage
• It is the climax community of hydrosere.
• A variety of trees Invade the area and develop any one of the diverse type of vegetation.
• Example: Temperate mixed forest (Ulmus, Acer and Quercus),
• Tropical rain forest (Artocarpus and Cinnamomum) and Tropical deciduous forest (Bamboo and Tectona).
• In the 7 stages of hydrosere succession,
• stage is occupied by pioneer community,
• while the stage 7 is occupied by the climax community.
• The stages 2 to 6 are occupied by seral communities.

 

 

III. Long Answer Questions

12th bio botany

IV. Exercise

12thbio botany