12th Bio - Botany - Book Back Answers - Chapter 6 - English Medium Guides

 

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Tamil Nadu Board 12th Standard Bio-Botany - Chapter 6: Book Back Answers and Solutions

    This post covers the book back answers and solutions for Chapter 6 – 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 6 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 6 - Principles of Ecology

I. Multiple Choice Questions

1. Arrange the correct sequence of ecological hierarchy starting from lower to higher level. 
a) Individual organism → Population Landscape → Ecosystem 
b) Landscape → Ecosystem → Biome → Biosphere 
c) community → Ecosystem → Landscape → Biome 
d) Population → organism → Biome → Landscape
Answer Key:
c) community → Ecosystem → Landscape → Biome 

2. Ecology is the study of an individual species is called 
i) Community ecology 
ii) Autecology 
iii) Species ecology
iv) Synecology 
a) i only 
b) ii only 
c) i and iv only 
d) ii and iii only
Answer Key:
d) ii and iii only

3. A specific place in an ecosystem, where an organism lives and performs its functions is 
a) habitat 
b) niche 
c) landscape 
d) biome
Answer Key:
b) niche 

4. Read the given statements and select the correct option. 
i) Hydrophytes possess aerenchyma to support themselves in water. 
ii) Seeds of Viscum are positively photoblastic as they germinate only in presence of light. 
iii) Hygroscopic water is the only soil water available to roots of plant growing in soil as it is present inside the micropores. 
iv) High temperature reduces use of water and solute absorption by roots.
a) i, ii, and iii only 
b) ii, iii and iv 
c) ii and iii only 
d) i and ii only
Answer Key:
d) i and ii only

5. Which of the given plant produces cardiac glycosides? 
a) Calotropis 
b) Acacia 
c) Nepenthes 
d) Utricularia
Answer Key:
a) Calotropis 

6. Read the given statements and select the correct option. 
i) Loamy soil is best suited for plant growth as it contains a mixture of silt, sand and clay. 
ii) The process of humification is slow in case of organic remains containing a large amount of lignin and cellulose. 
iii) Capillary water is the only water available to plant roots as it is present inside the micropores. 
iv) Leaves of shade plant have more total chlorophyll per reaction centre, low ratio of chl a and chl b are usually thinner leaves. 
a) i, ii and iii only 
b) ii, iii and iv only 
c) i, ii and iv only 
d) ii and iii only
Answer Key:
c) i, ii and iv only 

7. Read the given statements and select the correct option. 
Statement A : Cattle do not graze on weeds of Calotropis. 
Statement B : Calotropis have thorns and spines, as defense against herbivores. 
a) Both statements A and B are incorrect. 
b) Statement A is correct but statement B is incorrect. 
c) Both statements A and B are correct but statement B is not the correct explanation of statement A. 
d) Both statements A and B are correct and statement B is the correct explanation of statement A.
Answer Key:
b) Statement A is correct but statement B is incorrect. 

8. In soil water available for plants is 
a) gravitational water 
b) chemically bound water 
c) capillary water 
d) hygroscopic water
Answer Key:
c) capillary water 

9. Read the following statements and fill up the blanks with correct option. 
i) Total soil water content in soil is called _________________ 
ii) Soil water not available to plants is called _________________ 
iii) Soil water available to plants is called _________________

	(i)	(ii)	(iii)
(a)	Holard	Echard	Chresard
(b)	Echard	Holard	Chresard
(c)	Chresard	Echard	Holard
(d)	Holard	Chresard	Echard

Answer Key:
(a)    Holard    Echard    Chresard

10. Column I represent the size of the soil particles and Column II represents type of soil components. Which of the following is correct match for the Column I and Column IL 
Column - I                                     Column - II 
I). 0.2 to 2.00 mm                            i) Slit soil 
II) Less than 0.002 mm                   ii) Clayey soil 
III) 0.002 to 0.02 mm                     iii) Sandy soil 
IV) 0.002 to 0.2 mm                       iv) Loamy soil

	I	II	III	IV
a)	ii	iii	iv	i
b)	iv	i	iii	ii
c)	iii	ii	i	iv
d)	None of the above

Answer Key:
c)    iii    ii    i    iv

11. The plant of this group are adapted to live partly in water and partly above substratum and free from water 
a) Xerophytes 
b) Mesophytes 
c) Hydrophytes 
d) Halophytes
Answer Key:
d) Halophytes

12 . Identify the A, B, C and D in the given table

Interaction	Effects on species X	Effects on species Y
Mutualism	A	(+)
A	(+)	(-)
Competition	(-)	C
D	(-)	0

	A	B	C	D
a)	(+)	Parasitism	(-)	Amensalism
b)	(-)	Mutalism	(+)	Competition
c)	(+)	Competition	0	Mutalism
d)	0	Amensalism	(+)	Parasitism

Answer Key:
a)    (+)    Parasitism    (-)    Amensalism

13. Ophrys an orchid resembling the female of an insect so as to able to get pollinated is due to phenomenon of 
a) Myrmecophily 
b) Ecological equivalents 
c) Mimicry 
d) None of these
Answer Key:
c) Mimicry 

14. A free living nitrogen fixing cyanobacterium which can also form symbiotic association with the water fern Azolla 
a) Nostoc 
b) Anabaena 
c) chlorella 
d) Rhizobium
Answer Key:
b) Anabaena 

15. Pedogenesis refers to 
a) Fossils 
b) Water 
c) Population 
d) Soil
Answer Key:
d) Soil

16. Mycorrhiza promotes plant growth by 
a) Serving as a plant growth regulators 
b) Absorbing inorganic ions from soil 
c) Helping the plant in utilizing atmospheric nitrogen 
d) Protecting the plant from infection
Answer Key:
b) Absorbing inorganic ions from soil 

17. In a fresh water environment like pond, rooted autotrophs are 
a) Nymphaea and typha 
b) Ceratophyllum and Utricularia 
c) Wolffia and pistia 
d) Azolla and lemna
Answer Key:
a) Nymphaea and typha 

18. Match the following and choose the correct combination from the options given below:

Column I (Interaction)	Column II (Examples)
I. Mutualism II. Commensalism III. Parasitism IV. Predation	i). Trichoderma and Penicillium ii). Balanophora, Orobanche iii). Orchids and Ferns iv). Lichen and

	I	II	III	IV	V
a)	i	ii	iii	iv	v
b)	ii	iii	iv	v	i
c)	iii	iv	v	i	ii
d)	iv	iii	ii	v	i

Answer Key:

d)            iv           iii        ii        v            i 

19. Sticky glands of Boerhaavia and Cleome support 
a) Anemochory 
b) Zoochory 
c) Autochory 
d) Hydrochory
Answer Key:
b) Zoochory 

II. Short Answer Questions

1.Define ecology.

• Biology which deals with the study of environment in relation to organisms is called Ecology.

 
2.What is ecological hierarchy? Name the levels of ecological hierarchy.

• The Interaction of organisms with their environment results In the establishment of grouping of organisms is called ecological hierarchy.
• The levels of ecological hierarchy are as follows
• Individual organism→Population→Community→Ecosystem→landscape→Biome→Biosphere 

 
3. What are ecological equivalents? Give one example

• Taxonomically different species occupying similar habitats (Niches) in different geographical regions are called ecological equivalents.
• Examples:
• Certain species of epiphytic orchids of Western Ghats of India differ from the epiphytic orchids of South America.But they are epiphytes.

 
4. Distinguish habitat and niche

	Habitat	Niche
1	A specific physical space occupied by an organism (species)	A functional space occupied by an organism in the same eco-system
2	Same habitat may be shared by many organisms (species)	A single niche is occupied by a single species
3	Habitat specificity is exhibited by organism.	Organisms may change their niche with time and season.

 
5. Why are some organisms called as eurythermals and some others as stenohaline ?

• Eurythermals: organisms can live in a wide range of temperature
• Stenohaline: Can withstand only small range of salinity

 
6. 'Green algae are not likely to be found in the deepest strata of the ocean'. Give at least one reason.

• Green algae or plants are not found beyond a certain depth, as light (not all colour components of visible spectrum) can reach only till a certain depth in sea and oceans.

 
7. What is Phytoremediation?

• The plants soya bean, tomato, rice and Eichhornia can be used to remove cadmium from contaminated soil, and this make suitable for cultivation is known as Phytoremediation.

 
8. What is Albedo effect and write their effects?

• Aerosols with small particles is reflecting the solar radiation entering the atmosphere is called albedo effect.
• It reduces the temperature (cooling) limits, photosynthesis and respiration

 
9. The organic horizon is generally absent from agricultural soils because tilling, e.g., plowing, buries organic matter. Why is an organic horizon generally absent in desert soils?

• A desert has little or no plants.
• Without plants, there is no organic material in the soil.
• So there is no organic horizon.

 
10. Soil formation can be initiated by biological organisms.
Explain how?

• The organisms like bacteria, fungi, lichens and plants acids produce certain chemical substances. It helps in the breakdown of rocks and originates the soil.

 
11. Sandy soil is not suitable for cultivation. Explain why?

• Sandy soil contains 85% sand and 15% of clay and stilt. The soil particles are larger, low water holding capacity and poor organic content. So this soil is not suitable for cultivation.

 
12. Describe the mutual relationship between the fig and wasp and comment on the phenomenon that operates in this relationship.

• The relationship between fig tree and wasp shows mutualism.
• The wasp while searching for sits to lay its egg, pollinates the fig's inflorescence.
• On the other hand, the fig not only provides shelter (fruit) for ovi position but allows wasp's larva to feed on its seeds.

 
13.Lichen is considered as a good example of obligate mutualism. Explain.

• It is an interaction between two species of organisms in which both are benefitted from the obligate association.
• The algae and fungi closely associate to form lichen where algae performs photosynthesis and provide food to fungi and fungi helps algae to absorb water and minerals.

 
14. What is mutualism? Mention any two example where the organisms Involved are commercially exploited in modern agriculture.

• It is an interaction between two species of organisms in which both are benefitted from the obligate association.
• Examples of the organisms involved are commercially exploited in modern agriculture are as follows.
• Rhizobium:
• It is a mutual relationship between bacteria and leguminous plant is used as a bio fertilizer.
• These enrich the nutrients quality of the soil by fixing atmospheric nitrogen into organic forms.

• Mycorhiza:
• It is an association of the fungus, and the roots of higher plants
• It improves the soil quality,plant growth and development reduce the soil erosion and helps to absorb minerals from the soil.

  
15.List any two adaptive features evolved In parasites enabling them to live successfully on their host?

• Presence of adhesive organs to cling onto the host.
• Produce houstorial roots to absorbs nutrients from the vascular tissues of host plants.

 
16. Mention any two significant roles of predation plays in nature. Defense mechanisms are evolved by plants. (Any two)

• Calotropis produces highly poisonous cardiac glycosides.
• Tobacco produces nicotine,
• Coffee plants produce caffeine,
• Cinchona plant produces quinine,
• Thorns of Bougainvillea, spines of Opuntia, and
• latex of cacti.

 
17.How does an orchid ophrys ensures its pollination by bees?

• Ophrys an orchid, the flower looks like a female insect to attract the male insect to get pollinated by the male insect and it is otherwise called 'floral mimicry'.

  
18. Water is very essential for life. Write any three features for plants which enable them to survive in water scarce environment.

• The adaptations of plants to water scarcity are as follows.
• Xenopytic plants have hick cutile on their leaf surface.
• Stomata is small shaped, it minimize water loss through transpiration.
• Leaves re reduced to spines.

 
19. Why do submerged plants receive weak illumination than exposed floating plants in a lake?

• Because all colours of the visible components of the spectrum of light does not enter or penetrate in the depth of water in a lake.

 
20. What is vivipary? Name a plant group which exhibits vivipary.

• Seeds germinate in the fruits of mother plant itself are called vivipary. It is exhibited in halophytes.

 
21. What is thermal stratification? Mention their types.

• It is usually found in aquatic habitat.
• The change in the temperature profile with increasing depth in a water body is called thermal stratification.
• The three kinds of thermal stratifications are
• 1. Epilimniotn - The upper layer of warmer water.
• 2. Metalimnion - The middle layer with a zone of gradual decrease in temperature.
• 3. Hypolimnion - The bottom layer of colder water.

 
22. How is rhytidome act as the structural defence by plants against fire?

• Rhytidome is the structural defense by plants against fire.
• The outer bark of trees which extends to the last formed periderm is called Rhytidome.
• it is composed of multiple layers of suberized periderm, cortical and phloem tissues.
• it protects the stem against fire, water loss, invasion of insects and prevents infections by microorganisms.

 
23. What is myrmecophily?

• Sometimes, ants take their shelter on some trees such as Mango, Litchi, Jamun, Acacia etc.
• These ants act as body guards of the plants against any disturbing agent.
• The plants in turn provide food and shelter to these ants.
• This phenomenon is known as Myrmecophily.
• Example: Acacia and acacia ants.

  
24. What is seed ball?

• Seed ball is on ancient Japanese technique.
• Encasing seeds in a mixture of clay and soil humus (also in cow dung).
• These are scattering on to suitable ground, not planting of trees manually.

• This method is suitable for barren and degraded lands for tree regeneration.
• This vegetation before monsoon period where the suitable dispersal agents become rare.

 

25. How is anemochory differ from zoochory?

Anemochary	Zoochory
The dispersal fruit or seed by wind.	The dispersal fruit or seed by animals.
Minute seeds, wings, feathery appendages and censor mechanisms are devices found	Hooked fruit, sticky fruits and seeds and fleshy fruits are devices found
Ex. Gyrocarpus, Vemonio,Asclepias and Aristolochia	Ex. Xanthium, Andropogon, Cleome and Alangium

26. What is co evolution?

• The interaction between organisms, when continues for generations, involves reciprocal changes in genetic and morphological characters of both organisms.
• This type of evolution is called Co-evolution.

 
27. Explain Raunkiaer classification in the world's vegetation
based on the temperature.

• Raunkiaer classification in the world's vegetation based on the temperature are four types.

• 1. Megatherms, 
• 2. Mesotherms,
• 3. Microtherms and
• 4. Hekistotherms.

 
28. List out the effects of fire to plants.

• Fire has a direct lethal effect on plants
• Burning scars are the suitable places for the entry of parasitic fungi and insects
• It brings out the alteration of light, rainfall, nutrient cycle, fertility of soil, pH, soil flora and fauna
• Some fungi which grow in soil of burnt areas called pyrophilous.
• Example: Pyronema confluens.

29. What is soil profile? Explain the characters of different soil horizons.

 30.Give an account of various types of parasitism with examples.

• An interaction between two different species in which the smaller partner (parasite) obtains food from the larger partner (host or plant).
• So the parasitic species is benefited while the host species is harmed.
• Prasitism is classified into two types. They are holoparasite and hemiparasite.
• Holoparasites
• The organisms which are dependent upon the host plants for their entire nutrition are called Holoparasites. 
• They are also called total parasites.
• Examples:
• Cuscuta is a total stem parasite of the host plant Acacia, Duranta.
• Balanophora, orobanche and Refflesia are the total root parasites on higher plants.
• Hemiparasites
• The organisms which derive only water and minerals from their host plant
• The organisms synthesizing their own food by photosynthesis are called Hemiparasites.
• They are also called partial parasites.
• Examples:
• Viscum and Loranthus are partial stem parasites.
• Santalum (Sandal Wood) i a partial root parasite.

31. Explain different types of hydrophytes with examples.
i. Free floating

hydrophytes:

• These plants float freely on the surface of water.
• They remain in contact with water and air, but not with soil.
• Examples: Eichhornia, Pistia and Wolffio (smallest flowering plant).

ii. Rooted floating hydrophytes:

• In these plants, the roots are fixed in mud, but their leaves and flowers are floating on the surface of water.
• These plants are in contact with soil, water and air.
• Examples: Nelumbo, Nymphaea, Potomogeton and Marsilea.

iii. Submerged floating hydrophytes:

These plants are completely submerged in water and not in contact with soil and air.
Examples: Ceratophyllum and Utricularia.

submerged hydrophytes:
These plants are completely submerged in water and rooted in soil and not in contact with air.
Examples: Hydrilla, Vallisneria and Isoetes.

iv. Amphibious hydrophytes (Rooted emergent hydrophytes):
These plants are adapted to both aquatic and terrestrial
modes of life.
They grow in shallow water.
Examples: Ranunculus,Typha and Sagittaria.

32. Enumerate the anatomical adaptations of xerophytes.

• Presence of multilayered epidermis with heavy cuticle to prevent water loss due to transpiration.
• Hypodermis is well developed with sclerenchymatous tissues.
• Sunken shaped stomata are present only in the lower epidermis with hairs in the sunken pits.
• Scotoactive type of stomata found in succulent plants.
• Vascular bundles are well developed with several layered bundle sheath.
• Mesophyll is well differentiated into palisade and spongy parenchyma.
• In succulents the stem possesses a water storage region

 33. List out any five morphological adaptations of halophytes.

• The temperate halophytes are herbaceous but the tropical halophytes are mostly bushy
• In addition to the normal roots, many stilt roots are developed
• A special type of negatively geotropic roots called pneumatophores with pneumathodes to get sufficient aeration.
• They are called breathing roots. 
• Example: Avicennia
• Presence of thick cuticle on the aerial parts of the plant body
• Leaves are thick, entire, succulent and glossy. Some species are aphyllous (without leaves).
• Vivipary mode of seed germination is found in halophytes

34. What are the advantages of seed dispersal?

• Seeds escape from mortality near the parent plants due to predation by animals and getting diseases and also avoiding competition.
• Dispersal also gives a chance to occupy favourable sites for growth.
• This is the only method available for self-fertilized flowers and maternally transmitted genes in out crossing plants.
• Seed dispersal by animals help in conservation of many species even in human altered ecosystems.
• It acts as a key for proper functioning and establishment of many ecosystems from deserts to evergreen forests
• The maintenance of biodiversity conservation and restoration of ecosystems.

 
35. Describe dispersal of fruit and seeds by animals.

• Birds and mammals, including human beings play an efficient and important role in the dispersal of fruit and seeds.
• They have the following devices.
• Hooked fruit:
• The surface of the fruit or seeds have hooks, (Xanthium), barbs (Andropogon), soines (Aristida) by means of which they adhere to the body of animals or clothes of human beings and get dispersed.
• Sticky fruits and seeds:
• Some fruits have sticky glandular hairs by which they adhere to the fur of grazing animals. Example: Boerhaavia and Cleome.
• Some fruits have viscid laver which adhere to the beak of the bird which eat them and when they rub them on to the branch of the tree, they disperse and germinate. Example: Cordia and Alangium
• Fleshy fruits:
• Some fleshy fruits with conspicuous colours are dispersed by human beings to distant places after consumption. 
• Example: Mango and Diplocyclos

 

III. Long Answer Questions

12th bio botany

IV. Exercise

12thbio botany