CBSE Class 12 Biology Reproduction In Organisms Notes

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Reproduction In Organisms Class 12 Biology Revision Notes

Class 12 Biology students should refer to the following concepts and notes for Reproduction In Organisms in standard 12. These exam notes for Grade 12 Biology will be very useful for upcoming class tests and examinations and help you to score good marks

Reproduction In Organisms Notes Class 12 Biology

INTRODUCTION

•The period from birth to the natural death of an organism represent, its life span.

 Reproduction is a biological process in which an organism gives rise to young ones. It enables the continuities of the species.

 Reproduction

a) Asexual

b) Sexual

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SEXUAL REPRODUCTION

Juvenile Phase in Animals

Vegetative Phase in Plants

Plants – Reproductive phase (Flowering)

Annual and biennial – Vegetative and Reproductive phases are distinct.

Animals -                             Reproductive phase

Egg laying animals -           Birds

Placental animals -             Non-primates- OestrousCycle(Seasonal Breeders)

Primates-                           Menstrual cycle(Continuous Breeders)

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CBSE Class 12 Biology - Reproduction In Organisms notes

CBSE Class 12 Biology - Reproduction In Organisms notes

 

CBSE Class 12 Biology - Reproduction In Organisms notes

CBSE Class 12 Biology - Reproduction In Organisms notes

 

Bisexual – self Pollination

Ex: Pea

Unisexual – Cross Pollination Pollen Stigma Pollen tube formation Discharge of male gametes

Fertilization
Male gametes (n) + female gametes (n) Syngamy Zygote

Parthenogenesis
Female gametes develop into an organism without fertilization.
Ex: Rotifers, honey bees, some lizards and birds (turkey)

""CBSE Class 12 Biology Reproduction In Organisms

Post- fertilization events

Zygote (2n) – First cell of the organism

Universal in all sexually reproducing organisms

Zygote------- > Meiosis -------------> Haploid organism

Zygote -------->Mitosis -------------->Diploid organism 

Embryogenesis

Zygote -------------------- Mitotic division ------------------->Cell differentiation  increase in number of cells specialized tissue and organs 

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Chances of survival is greater in viviparous because of proper embryonic care and protection provided to the young ones.

POST FERTILISATION EVENTS IN PLANTS

Sepals, petals, stamens ----------------------- -wither and fall off

Zygote ---------------------------------------------- embryo

Ovule-----------------------------------------------------seeds

Ovary------------------------------- fruit ---------------Pericarp (wall- protective in function) 

 

 

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Definitions:

CLONE :- Offspring from single parent, Morphology and genetically similar individuals.

CYST :- Hard covering around the organism protecting from anti environment.

DIOECIOUS :- It is the condition in which either male or female reproductive organs are found in the same body of an organism.

EMBRYOGENESIS :- It is the process of development of embryo from the zygote..

FERTILIZATION :- The union of two opposite types of gametes, spermatozoa and ova to produce single diploid zygote.

FISSION :- Division of nucleus with cytoplasm.

FRAGMENTATION :- Division of breaking into distinct pieces each of which can produce an offspring.

GEMMULE :- The parent individual releases a specialized mass of cells enclosed in a common opaque envelope called the gemmule.

HERMAPHRODITE :- Organisms which have both male and female reproductive organs in the same individual.

HOMOGAMETES :- When the two gametes of male and female are so similar in appearance that it is not possible to categorize them into male and female gametes.

JUVENILE PHASE :-Juvenile Phase represents the period of an organism from birth upto reaching reproductive maturity.

LIFE SPAN :-The period from birth to the natural birth of an organism.

MEIOCYTE ;- The cell which undergoes meiosis is called a meiocyte .

MONOECIOUS :- It is the condition in which male and female reproductive organs are found in the same body of an organism.

PARTHENOGENESIS :-The female gamete undergoes development to form new organisms without fertilization.

REPRODUCTION :-Biological process in which an organism gives rise to young ones of its own kind.

SYNGAMY :- Syngamy refers to the fusion of two (male and female) gametes.

VEGETATIVE PROPAGATION :-It is the process of formation or regeneration of new plants from a portion of a vegetative part of the plant .

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REPRODUCTION IN ORGANISMS
 
Briefing of Concept
 
Life Span: Period from birth till natural death. Every organism lives only for certain period of time
Reproduction –Producing young-ones of their kind, generation after generation.
 
Types of reproduction:
 
1. Asexual reproduction: single parent capable of producing offsprings.Somatogenic reproduction.
2. Sexual reproduction : two parents are involved in producing offspring.
 
Modes of asexual reproduction
 
1. Binary fission: parent body divides into two halves, genetically identical to parent. Organisms considered immortal Amoeba: It is simple or irregular. Paramecium: Transverse binary fission.
 
2. Multiple fission: parent body divides into many daughter organisms e.g., Plasmodium.
 
3. Budding: daughter organisms grow from small buds arising in parent body. Exogenous budding: out side the body eg. Hydra, Yeast.Endogenous budding: inside the body eg. Gemmule in sponge.
 
4. Spore Formation: Exogenous spores Conidia: non-motile eg. Fungi. Zoospores: microscopic motile structures eg. Algae.
 
5. Vegetative reproduction: In plants term vegetative reproduction frequently used instead of asexual reproduction, units of vegetative propagation called vegetative propagules. Eg runner, rhizome, sucker, tuber offset, bulb give rise to new plant
 
PHASES OF LIFE SPAN.
i. Juvenile phase: The phase of growth before reproductive maturity.
ii. Reproductive phase: Reproductive maturity.
iii. Senescent phase: Phase between reproductive maturity and death.
 
The main events of sexual cycle are:
 
1. PRE-FERTILISATION EVENTS:
a. Gametogenesis :
The process of formation of male and female gametes by meiosis (cell-division).
√ Homogamete (Isogamete): - gametes similar eg. Algae
√ Heterogamete(an-isogamete): - morphologically dissimilar gamete ,male gamete (antherozoid or sperm) ,female gamete (egg or ovum) eg. Human.
 
→ Sexuality in organisms:
• In plants
 
Bisexual term is used for Homothallic and Monoecious plants: Both male and female reproductive structures in same plant eg. Higher plants, cucurbits and coconut.
Unisexual term used for Heterothallic and Dioecious plants: Male and female reproductivestructure on different plants. Male flower–staminate flower and female flower–pistillate flower eg. papaya and date-palm.
 
 In Animals
Bisexual term is used for Hermaphrodite animals-eg. Earth-worm, Tape-worm, Leech,Sponge.Unisexual animals have male & female sexes in separate individuals-e.g. insects, frogs,human beings
 
→  Cell division during gamete formation:
•  Haploid-parent (n) produces haploid gametes (n) by mitotic division, eg. Monera, fungi, algae and bryophytes.
• Diploid parent (2n) produces haploid gametes(n) by meiosis division (possess only one set of chromosomes)and such specialized parent cell is called meiocyte or gamete mother cell.
 
b) Gamete transfer:- to facilitate fusion. Male gametes mostly motile and female non-motile,exception few fungi and in algae both gametes are motile in some cases.Water medium for gamete transfer- in lower plants. Large number of male gametes are produced to compensate loss. Higher plants, pollen-grains are transferred by pollination.
 
2. FERTILIZATION: Fusion of male and female gametes to produce diploid zygote.
 
Two types- external and internal
 
→ External fertilisation- outside the body of organism in external- medium (water) eg. majority of algae, fishes, amphibians.
 
Advantage-
1. Show great synchrony between the sexes
2. Release of large number of gametes into surrounding medium
2. Large number of off springs produced.
 
Disadvantage- offspring vulnerable to predators, natural disasters.
 
→ Internal fertilisation- fusion occurs inside female body eg. majority of plants and animals. Egg non-motile and formed inside female body. Male gamete motile, produced in large numbers to reach egg and fuse with it. In seed plants, non- motile male gamete carried to female gamete by pollen-tube.
 
3. POST -FERTILISATION EVENTS
 
Formation of zygote. Zygote. One celled, diploid, vital link between two generations.
 
√ Haplontic life cycle- zygote (2n) divides by meiosis to form haploid (n) spores.
√  Diplontic life-cycle- zygote (2n) divides mitotically, develops into embryo (2n).
UNDERGO MEIOSIS –HAPLOID SPORES----HPLONTIC LIFE CYCLE ZYGOTE UNDERGO MITOSIS ---DIPLONTIC LIFE CYCLE

CBSE Class 12 Biology Reproduction in Organisms Notes 1

Embryogenesis: development of embryo from zygote by cell division (mitosis) and cell differentiation. Cell- division increases the number of cells in the developing embryo
Parthenogenesis.-development into new organism without fertilisation eg. Rotifers, honey-bees,some lizard, bird(turkey).
Parthenogenesis: Female gamete develops into new organism.
 
√ Seedless fruits formed by parthenogenesis
√ Clone: A group of individuals of the same species that are morphologically and genetically similar to each other & their parents
√ Turion : Fleshy overwintering buds in aquatic plants help in perrenation Eg potomegaton, utricularia
√Bulbil : Fleshy buds that produce new plant Eg Agave and Oxalis

Q1. If chromosomes number in meiocyte in rat, elephant and rice is 42, 56, 24 what will be the chromosomes number in their gamete?
Answer : Rat 21, elephant 28, rice 12

Q2. Arrange the following w.r.t. increasing life span : Rose, Fruit fly, Rice
(a) Fruit fly, Rice, Rose (b) Rose, Rice, Fruit fly (c) Rice, Rose, Fruit fly (d) Fruit fly, Rose, Rice 
Answer : A Fruit fly = 2 Weeks
Rice = 3-4 Months
Rose =5-7 Years
Fruit fly < Rice < Rose

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• REPRODUCTION IN ORGANISMS 

  Life Span 
  Period from birth till natural death.Every organism lives only for certain period of time Eg Elephant 60 -90 years, Fruit fly 4-5 weeks. Every organism live only for a certain period of time. 
• Reproduction –Producing young-ones of their kind, generation after generation. 

Types of reproduction: 
Asexual reproduction :single parent capable of producing offspring. Somatogenic reproduction 
Sexual reproduction :two parents are invovled in producing offspring. 

Modes of asexual reproduction 
 Binary fission: parent body divides into two halves, genetically identical to parent. 
• Amoeba: It is simple or irregular. Paramoecium: Transverse binary fission. Organisms considered immortal 
 Multiple fission: parent body divides into many daughter organisms : Plasmodium. 
 Budding: daughter organisms grow from small buds arising in parent body. Exogenous budding: out side the body eg. Hydra, Yeast. 

Budding in Yeast Endogenous budding : inside the body eg. Gemmule in sponge. 
 Conidia: non-motile, exogenous spores in chains eg. Fungi. 
 Zoospores: microscopic motile structures eg. Algae.
In plants : term vegetative reproduction 
frequently used instead of asexual reproduction, units of vegetative propagation called vegetative propagules.Eg runner, rhizome, sucker, tuber offset, bulb give rise to new plant 

  All organisms show remarkable similarity. Vast difference in their reproductive structure. Similar pattern or phases in their life cycles 

  PHASES OF LIFE SPAN. 
  Juvenile phase: The phase of growth before reproductive maturity. 
  Reproductive phase: Reproductive maturity. 
 Senescent phase: Phase between reproductive maturity and death. 

• The main events of sexual cycle are: 
i. Prefertilisation events: 

a.Gametogenesis : 
  The process of formation of male and female gametes by meiosis (cell-division). 
  Homogamete(Isogamete): - gametes similar eg. Algae 
  Heterogamete(an-isogamete): - morphologically dissimilar gamete ,male gamete (antherozoid or sperm) ,female gamete (egg or ovum) eg. Human. 

 Sexuality in organisms : In plants Bisexual term is used for Homothallic and Monoecious plants
Both male and female reproductive structures in same plant eg. Higher plants, cucurbits and coconut.

♦ Unisexual term used for Heterothallic and Dioecious plants Male and female reproductive-structure on different plants.
Flowering plants – male flower–staminate flower and female flower–pistillate flower eg. papaya and date-palm.

 Animals – Bisexual term is used for Hermaphrodite animals-eg. Earth-worm, Tape-worm, Leech, Sponge.

• Unisexual animals have male & female sexes in separate individuals-e.g. insects, frogs, humanbeings 

Cell division during gamete formation:

Haploid-parent (n) produces haploid gametes (n) by mitotic division, eg. Monera,fungi, algae and bryophytes.

Diploid parent (2n) produces haploid gametes(n) by meiosis division (possess only one set of chromosomes)and such specialized parent cell is called meiocyte or gamete mother cell.

CBSE Class 12 Biology - Reproduction In Organisms

b) Gamete transfer:- to facilitate fusion.
 Male gametes mostly motile and female non-motile, exception few fungi and in algae both gametes are motile in some cases
 Water medium for gamete transfer- in lower plants. Large number of male gametes produced to compensate loss
 Higher plants, pollen-grains are transferred by pollination.
 Fertilization: Fusion of male and female gametes diploid zygote.
 Parthenogenesis.-development into new organism without fertilisation eg. Rotifers, honey-bees, some lizard, bird(turkey).

Fertilization Two types- external and internal .
1. Release of large number of gametes into surounding medium
2. Large number of offsprings produced.

 Disadvantage- offspring vulnerable to predators, natural disasters.
 Internal fertilisation- fusion occurs inside female body eg. majority of plants and animals. Egg non-motile and formed inside female body. Male gamete motile, produced in large numbers to reach egg and fuse with it. In seed plants, non- motile male gamete carried to female gamete by pollen-tube. 

Post -fertilisation events- formation of zygote.
a. Zygote. One celled , diploid, vital link between two generations.

• External fertilization –zygote formed in external medium water eg. Frog,
• Internal fertilization –zygote formed inside the body eg. Humanbeings. Development of zygote depends on type of life cycle and environment. Some develop thick wall ( prevent damage and desiccation) & undergo period of rest eg. Algae, fungi.
• Haplontic life cycle- zygote (2n) divides by meiosis to form haploid (n) spores.
• Diplontic life-cycle- zygote (2n) divides mitotically, develops into embryo (2n).
• Oviparous animals lay eggs out-side the female body.Eggs can be fertilized/ unfertilized. Fertilized eggs covered which hard calcareous shell, laid in safe place in the environment. Unfertilised eggs laid in water. Example- fishes, frogs, reptiles, birds.
• Viviparous animals bear and rear the embryo inside female body, give birth to youngones.

Advantage- proper embryonic care, protection, survival chances of young-ones greater.Example- cows, whales, humanbeings
• Embryogenesis: development of embryo from zygote by cell division (mitosis) and cell differentiation.
♦ Cell- division increases the number of cells in the developing embryo Cell differentiation - groups of cells undergo certain modifications for the formation of different kinds of tissues and organs.

• In flowering plants- zygote formed inside ovule
♦ Changes occur in flowering plants:

CBSE Class 12 Biology - Reproduction In Organisms

• Parthenogenesis: Female gamete develops into new organism.
• Seedless fruits formed by parthenogenesis
• Clone: A group of individuals of the same species that are morphologically and genetically similar to each other & their parents
• Turion :Fleshy overwintering buds in aqatic plants help in perrenation Eg potomegaton, utricularia
• Bulbil :Fleshy buds that produce new plant EgAgave and Oxalis

 

Very Short Answer Type Questions

Question. Mention two inherent characteristics of Amoeba and yeast that enable them to reproduce asexually.
Answer : The characteristics that enable Amoeba and yeast to reproduce asexually, are as follows
(i) Unicellularity (ii) Simple body organisation
(iii) Uniparental condition

Question. What is meiocyte?
Answer : It is the gamete mother cells which undergoes meiosis.

Question. Why is date palm referred to as dioecious?
Answer : In date palm the male and female flowers are present in different plants.

Question. What is special in flowering in bamboo?
Answer : Bamboo flowers only once in their life time generally after 50‐100 years .

Question. Define clone?
Answer : It is a group of individual of the same species that are morphologically and genetically similar.

Question. What is vegetative propagule?
Answer : The units of vegetative propargations that gives rise to a new plant is called vegetative propagule. Examples: Runner and rhizome.

Question. Digramatically represents asexually reproduction in yeast?
Answer : See Figure 1.2 (page‐5)

Question. Cucur bit are called monoecious. Justify?
Answer : They have male and female reproductive structures in different flowers.

Question. If chromosomes number in meiocyte in rat, elephant and rice is 42,56,24
what will be the chromosomes number in theier gamet?
Answer : Rat 21, elephant 28,rice 12

Question. Why do we refer to offspring formed by asexual method of reproduction as clones?
Answer : The reproduction is called asexual, when offspring is produced by a single parent with or without the involvement of gamete formation.
As a result, the offspring that are produced are not only similar to one another, but are also exact copies of their parent. Such a group of morphologically and genetically similar individuals is called clone.

Question. Although potato tuber is an underground part, it is considered as a stem. Give two reasons.
Answer : Potato tuber is considered as a stem because of the following reasons
(i) The tuber has nodes and internodes.
(ii) Leafy shoots appear from the nodes.

Question. Between an annual and a perennial plant, which one has a shorter juvenile phase? Give one reason.
Answer : In a lifespan, the organism has to grow and develop (the juvenile phase). After that the organism mature sexually and enter into the reproductive phase, before it undergoes
senescence followed by death.
Since, the entire life cycle of an annual plant is shorter and has to be completed in one growing season, its juvenile phase is shorter than that of a perennial plant.

Question. Rearrange the following events of sexual reproduction in the sequence in which they occur in a flowering plant embryogenesis, fertilisation, gametogenesis, pollination.
Answer : The correct sequence of events of sexual reproduction in a flowering plant are as follows gametogenesis, pollination, fertilisation, embryogenesis.

Question. The probability of fruit set in a self-pollinated bisexual flower of a plant is far greater than a dioecious plant. Explain.
Answer : The probability of fruit set in a self-pollinated bisexual flower of a plant is far greater than a dioecious plant.
In self-pollinated bisexual plants transfer of pollen to stigma of flowers is easier than the dioecious plants. It is so because the anther and stigma lie close to each other and pollination
is not effected even in the absence of pollinator. But in dioecious plants pollinator is necessary to bring about effective pollination as the anther and stigma lie away from each other.

Question. Is the presence of large number of chromosomes in an organism a hindrance to sexual reproduction? Justify your answer by giving suitable reasons.
Answer : No, presence of large number of chromosomes in an organism is not a hindrance to sexual reproduction. Ophioglossum (a fern) has chromosome number 1260, still it can reproduce sexually.
In higher organisms, the chromosomes are present in a compartment called nucleus, within the cell. Whether the number is small or large, the chromosomes are duplicated and then segregated inside this compartment, during cell division. The basis of sexual reproduction is generation of haploid gametes.

Question. Is there a relationship between the size of an organism and its life span?
Give two examples in support of your answer.
Answer : There is no relationship between the size and life span of an organism. e.g.,
(i) The mango tree has a shorter life span as compared to a peepal tree though both are of the same size.
(ii) The size of crow and parrot is almost same but the life span is 15 years and 150 years respectively.

Question. In the figure given below the plant bears two different types of flowers marked ‘A’ and ‘B’. Identify the types of flowers and state the type of pollination that will occur in them.
Answer : In the figure given below the plant bears folllowing two types of flowers A—Chasmogamous flower (the flowers remain open, exposing anthers and stigmas).
B—Cleistogamous flowers (the flowers remain closed, so that anthers and stigmas are
never exposed) following are the types of pollination that will occur in these flowers.
(i) Autogamy (within same flower)
(ii) Geitonogamy (different flowers of same plant)
(iii) Xenogamy (different plants)
It is a case of cleistogamy (a type of autogamy) in which some plants, like, Commelina bengalensis possess both chasmogamous and cleistogamous flowers.
In chasmogamous flowers, the flowers may undergo self-pollination or cross-pollination, while in cleistogamous flowers, the flowers undergo only self-pollination.

Question. Give reasons as to why cell division cannot be a type of reproduction in multicellular organisms.
Answer : In unicellular animals, cell division is the means of reproduction to increase their number while, in case of multicellular organisms, they have well developed reproductive organs
which help in reproduction.
Their whole body does not participate in reproduction like unicellular organisms.

Question. In the figure given below, mark the ovule and pericarp.
Answer : In flowering plants, the zygote is formed inside the ovule. After fertilisation the sepals, petals and stamens of the flower wither and fall off. The pistil however, remains attached to
the plant.
The zygote develops into the embryo and the ovules develop into the seed. The ovary develops into the fruit which develops a thick wall called pericarp that is protective in function.

Question. Why do gametes produced in large numbers in organisms exhibit external fertilisation?
In most aquatic organisms, such as a majority of algae and fishes as well as amphibians, syngamy (fusion of gametes in sexual reproduction) occurs in the external medium (water) , i.e., outside the body of the organism. This type of genetic fusion is called external fertilisation.
Answer : Organisms that take part in such process produce large number of gametes because (i) In external fertilisation, there is a great chance that the sperm and the eggs released by the organisms can be affected by factors present in the environment like dessication, predators, etc. So, to make up for the high fatality rate of the gametes, the organism produces a lot of gametes.
(ii) Producing large number of gametes increase the chance for at least some eggs and sperms to meet in the environment ensuring that atleast a stable number of offspring
are able to survive and carry on.

Question. Which of the following are monoecious and dioecious organisms?
(a) Earthworm ............. (b) Chara ..........
(c) Marchantia ........... (d) Cockroach ...........
Answer : (a) Earthworm- Monoecious animal
(b) Chara- Monoecious plant
(c) Marchantia-Dioecious plant
(d) Cockroach- Dioecious animal
Note In several fungi and plants, terms such as homothallic and monoecious are used to denote the bisexual condition (male and female reproductive structures in the same plant) and heterothallic and dioecious are the terms used to describe unisexual condition (male and female reproductive structures on different plants).
But in animals, individuals are either male or female (unisexual) or possess both the reproductive organs (bisexual).

Question. What do the following parts of a flower develop into after fertilisation?
(a) Ovary ....... (b) Ovules ......
Answer : (a) Ovary ........... fruit (b) Ovules .......... seed
After fertilisation, the zygote develops into the embryo and the ovules develop into the seed. 
The ovary develops into the fruit which develops a thick, protective wall called pericarp.

Question. Amoeba is immortal. Explain?
Answer : Amobea has no natural death. It undergoes binary fission and forms two new daughter cells.

Question. Which is the first diploid single cell which begins life?
Answer : Zygote.

Q What is the fate of zygote in organism which show
1 Haplontic life cycle
2 Diplontic life cycle
Answer : In haplontic life cycle zygote undergoes meiosis during its generation In diplontic life cycle zygote divides mitotically during embryogenesis

Question. What type gamete are formed in staminate and pistillate flowers?
Answer : Pollen grains and egg cell respectively.

Question. Name the organisms with respect to their sexuality?
i) Monoecious animal
ii) Dioecious animal
iii) Monoecious plant
iv) Dioecious plant
Answer : i) Earthworm ii) Cockroach iii) Chara iv) Marchantia.

 

Short Answer Type Questions

Question. In haploid organisms that undergo sexual reproduction, name the stage in the life cycle when meiosis occurs. Give reasons for your answer. 
Answer : Meiosis can take place only in a diploid stage (post-zygotic stage) because the zygote is the only diploid cell in the life cycle of such organisms. This meiosis an case of haploid organisms will occur of the fertilisation.

Question. Why higher organisms have resorted to sexual reproduction in spite of its complexcity?
Answer : 1. It brings about variations.
2. Variation helps in better adaptation in nature.
3. Variation is the basis of evolution.

Question. What is parthenogenesis. Give Example?
Answer : Development of a new individual from an unfertilized egg is called parthenogenesis. It is simpler easier and rapid mode of replication. But there is no chance of any variation. So it does not play any role in evolution. Eg.‐ Honey bee and some lizards

Question. Mention the reason for difference in ploidy of zygote and primary endosperm nucleus in angiosperm
Answer : Zygote is formed by fusion of haploid male gamete and haploid egg so it is diploid.
Whereas the PEN is formed by fusion of haploid male gamete with two haploid polar nuclei so it is triploid.

Question. The number of taxa exhibiting asexual reproduction is drastically reduced in higher plants (angiosperms) and higher animals (vertebrates) as compared with lower groups of plants and animals. Analyse the possible reasons for this situation.
Answer : Higher plants (angiosperms) and higher animals (vertebrates) have a more complex structural organisation as compared to the lower groups of plants and animals. They have evolved very efficient mechanism of sexual reproduction. These groups have resorted to reproduction by the sexual method for the following reasons (i) To ensure healthy progeny (ii) To produce genetically varied offsprings that adapt to changes in environment and surviveal in all climatic conditions. (iii) It ensures the genetic recombination that results in variation which gives rise to evolution.

Question. Honeybees produce their young ones only by sexual reproduction. Inspite of this, in a colony of bees we find both haploid and diploid individuals. Name the haploid and diploid individuals in the colony and analyse the reasons behind their formation.
Answer : (i) Sterile diploid females as workers (ii) One fertile diploid female as queen (iii) Fertile haploid males as drones. In case of honeybees, both haploid and diploid individuals formad as a result of incomplete (cyclic) parthenogenesis, i.e., both sexual reproduction and parthenogenesis. Fertilised eggs (zygote) give rise to queen and workers (both are females) by the process of sexual reproduction and unfertilised eggs (ova) develop into drones (males) by the process of parthenogenesis.

Question. With which type of reproduction do we associate the reduction division? Analyse the reasons for it.
Answer : Reduction division (meiosis) is associated with sexual reproduction. The reasons are (i) Since, sexual reproduction involves the fusion of two types of gametes male and female), they must have haploid number of chromosomes. (ii) The cell (meiocyte) which gives rise to gametes often has diploid number of chromosomes and it is only by reducing the number by half that we can get haploid gametes. (iii) Reduction division also ensures maintenance of constancy of chromosome number from generation to generation.

Question. Is it possible to consider vegetative propagation observed in certain plants like Bryophyllum, water hyacinth, ginger, etc., as a type of asexual reproduction? Give two/three reasons.
Answer : The formation of new plants from vegetative units (vegetative propagules) such as buds, tubers, rhizomes. etc., is called vegetative propagation (vegetative reproduction). It can be considered as a type of asexual reproduction as it involves the production of new individuals. (i) by a single parent (ii) without the formation and fusion of gametes (iii) without resulting in any genetic or morphological variations.

Question. ‘Fertilisation is not an obligatory event for fruit production in certain plants’. Explain the statement.
Answer : Fertilisation is not an obligatory event for fruit production in certain plants. Some fruits are developed from unfertilised ovary called parthenocarpic fruits. These are seedless fruits, such as pomegranate, grapes, etc. Flowers of these plants are sprayed by a growth hormone that induces fruit development even though fertilisation has not occurred. The ovules of such fruits, however, fail to develop into seeds.

Question. In a developing embryo, analyse the consequences if cell divisions are not followed by cell differentiation.
Answer : Cell divisions increase the number of cells in the developing embryo, while cell differentiation helps group of cells to undergo certain modifications to form specialised tissues and organs to form an organism. At many stages of embryogenesis, if cell differentiation does not occur, the embryo cannot develop into a new organism. It will only remain as a mass of cells.

Question. List the changes observed in an angiosperm flower subsequent to pollination and fertilisation.
Answer : In an angiosperm flower, the post-fertilisation changes occur as follows
Sepal                      Fall off
Petal                       Fall off
Stamen                   Fall off
Zygote                    Embryo
Primary endosperm  Endosperm (3n) 
nucleus
Synergid                   Disintegrate
Antipodals                 Disintegrate
Ovary                        Fruit
Ovule                        Seed

Question. Suggest a possible explanation why the seeds in a pea pod are arranged in a row, whereas those in tomato are scattered in the juicy pulp.
Answer : In pea, fruit is legume. The pea pod is developed from monocarpellary, unilocular and half superior ovary. At maturity, the fruit splits along the dorsal and ventral sutures and discharge its seeds. In gynoecium with single carpel, ovules are always attached to the ventral suture. This results in the fruit with marginal placentation. Thus, the seeds are arranged in a row in legume (pea) pod. (Image 21) In tomato, the fruit is berry. It is fleshy fruit develop from superior or inferior ovary. In this, the margins of the carpels grow inward to the centre of the ovary dividing the central chamber into compartments called locules. So that, the ovules are arranged radially on the axis, attached by placenta that is called axial placentation. That’s the reason the seeds are embedded in the juicy pulp.

Question. Draw the sketches of a zoospore and a conidium. Mention two dissimilarities between them and atleast one feature common to both structures.
Answer : The feature common to zoospores and conidia is that both of these are the asexual reproductive structures, which facilitate the process of reproduction in asexually reproducing organisms.

The two dissimilarities between these (zoospore and conidium) are as follows 
          Zoospore                           Conidium
(Found usually in Algae)      (Found usually in Fungi)
Flagellated                                Non-flagellated
Formed inside a sporangium    Formed at the tip of conidiophores
(endogenously)                             (exogenously)

Question. Justify the statement ‘vegetative reproduction is also a type of asexual reproduction’.
Answer : In flowering plants, the units of vegetative reproduction such as runners, stolons, suckers, offsets, rhizome, corm, tuber, etc., are capable of giving rise to new offsprings. These structures are called vegetative propagules. In all these plants the formation of these structures does not involve two parents, the process involved is asexual. So, it can be said that vegetative reproduction is also a type of asexual reproduction.

 

Long Answer Type Questions

Question. Enumerate the differences between asexual and sexual reproduction. 
Describe the types of asexual reproduction exhibited by unicellular organisms.
Answer : The differences between asexual and sexual reproduction are mentioned below.  (Image 23)  
Asexual reproduction occurs usually in unicellular organisms, such as monerans and protists and in plants and certain animals. It takes place in the following ways
(i) Binary Fission In this type of asexual reproduction, the parent organism divides into two halves, each half forming an independent daughter organism. e.g., Amoeba, Euglena, Paramecium.
(ii) Budding In this type of asexual reproduction, a daughter individual is formed from a small projection, the bud, arising from the parent body. e.g.,yeast, Hydra.
(iii) Fragmentation In this type of asexual reproduction, the parent body breaks into two or more fragment. Each body fragment develops into an organism. e.g., sponges, Selaginella.
(iv) Gemmule In this type of asexual reproduction, internal buds, called gemmules are involved. Gemmules are asexually reproduced mass of cells, that is capable of developing into a new organism. e.g., sponges.
(v) Sporulation In this type of asexual reproduction, dispersive structures called spores are released from the parent body that germinate under favourable conditions form new individuals.
(a) Motile spores are called zoospores and are found in aquatic animals. e.g., Albugo, Chlamydomonas.
(b) Non-motile spores are named as sporangiospores (e.g., Rhizopus, Mucor) and conidia e.g., Penicillium.

Question. Do all the gametes formed from a parent organism have the same genetic composition (identical DNA copies of the parental genome)? Analyse the situation with the background of gametogenesis and provide or give suitable explanation.
Answer : No, all the gametes formed from a parent organism do not have the same genetic composition.
It can be better understand with the help of the explanation given below Sexual reproduction in organisms generally involves the fusion of gametes from two different individuals. These gametes form by the process of gametogenesis. In the heterogametic species, gametes are of two types namely male and female. Gametes are haploid though the parent body from which they arise may be either haploid or diploid.
(a) A haploid parent like Monera, fungi, algae and bryophytes produce gametes by mitotic division. The number of chromosomes, i.e., the genetic composition remain same after such type of division.
(b) The diploid parent like pteridophytes, gymnosperms, angiosperms and most of the animals including human beings produces gametes by meiosis. In such organisms (diploid), specialised cells called meiocytes (gamete mother cell) undergo meiosis. At the end of meiosis only one set of chromosomes gets incorporated into each gamete. It means the gametes formed contain a haploid number of chromosomes in contrast to the number of chromosomes in mother cells.

Question. Although sexual reproduction is a long drawn, energy-intensive complex form of reproduction, many groups of organisms in kingdom–Animalia and Plantae prefer this mode of reproduction. Give atleast three reasons for this.
Answer : Follwing are the three reasons for the mode of sexual reproduction in higher group of organisms
(i) The sexual mode of reproduction ensures creation of new variants.
(ii) Genetically varied offsprings are produced that adapt to changes in environment and survive in all climatic conditions. (iii) Sexual reproduction ensures the genetic recombination that results in variation which gives rise to evolution.

Question. Rose plants produce large, attractive bisexual flowers, but they seldom produce fruits. On the other hand a tomato plant produces plenty of fruits though they have small flowers. Analyse the reasons for failure of fruit formation in rose.
Answer : Rose plants produce large, attractive bisexual flowers, but they seldom produce fruits. The reasons for failure of fruit formation in rose are as follows
(i) Rose plants may not produce viable pollens, hence, no fertilisation can take place.
(ii) Rose plants may not have functional eggs.
(iii) Rose plants may have defective and non-functional ovule ,which is the female gametophyte generator.
(iv) There may be self-incompatibility.
(v) There may be internal barriers for pollen tube growth or fertilisation.
(vi) As rose plants are hybrids and reproduce vegetatively, there are chances for them to be sterile.

Multiple Choice Questions

Question. Which of the following factor is/are responsible for how organism reproduces?
(a) Organisms habitat
(b) Internal physiology
(c) Environmental factors
(d) More than one option is correct

Answer : D

Question. Cell division itself is a mode of reproduction in
(a) Amoeba, Penicillium
(b) Chara, Bacteria
(c) Chlamydomonas, Penicillium
(d) Amoeba, Bacteria

Answer : D

Question. During budding in yeast
(a) Cytokinesis is unequal
(b) Identity of parent is lost
(c) Clones are produced
(d) More than one option is correct

Answer : D

Question. Most common asexual structure produced in algae is
(a) Thick walled
(b) Multicellular
(c) Flagellated
(d) Produced in chains

Answer : C

Question. In which of the following plants root bud is involved in vegetative propagation?
(a) Sugarcane
(b) Banana
(c) Ginger
(d) Dahlia

Answer : D

Question. Offsprings produced through which of the following processes/structures represent clone?
(a) Gametic fusion
(b) Syngamy
(c) Vegetative propagule
(d) More than one option is correct

Answer : C

Question. In all the sexually reproducing organisms, events involved are
(a) Same, sequential
(b) Same, non-sequential
(c) Different, sequential
(d) Different, non-sequential

Answer : A

Question. Majority of sexually reproducing organisms form
(a) Isogametes
(b) Homogametes
(c) Heterogametes
(d) More than one option is correct

Answer : C

Question. In flowering plants, zygote is formed
(a) Inside ovule
(b) Inside archegonium
(c) In water
(d) More than one option is correct

Answer : A

Question. Self fertilisation is seen in
(a) Unisexual flower of papaya
(b) Bisexual flower of pea
(c) Unisexual flower of date palm
(d) Bisexual flower of coconut

Answer : B

Question. Define external fertilization? Mention its disadvantages?
Answer : ➢ Syngamy occurs in the external medium. i.e. water outside the body of the organism.
Disadvantage- offspring are extremely vulnerable to predators. Threatening there development up to adulthood.

Question. Compare monoecious & dioecious plants?
Answer : ➢ Monoecious-Bisexual condition- having both male and female reproductive organs.
Dioecious -Unisexual condition- having either of the reproductive organs.

Question. Distinguish between.
1) Oviparous & viviparous.
Answer : ➢ Oviparous: Lay eggs. Development of zygote takes place outside the body of female parent
➢ Viviparous: Give birth to young one. Development takes place inside the body of female parent
2) External & internal fertilization.
➢ External Fertilization: Syngamy occurs outside body, Danger of predation is always there
➢ Internal Fertilization: Syngamy occurs inside the body of the organism, No danger of predator to offspring because they are protected inside the body of female.

Question. Define: a) Juvenile Phase b) Senescent Phase.
Answer : ➢ Juvenile phase:- The period of growth involving an increase in the body dimensions before attaining sexual maturity is called juvenile phase.
➢ Senescence phase:- The part of life involving an increase in degenerative changes rather than repair.

Question. What are staminate and pistillate flowers? Name the types of gametes that are formed in staminate and pistillate flowers?
Answer : ➢ Staminate – unisexual male flower bearing stamen is called staminate flower.
➢ Pistillate - the unisexual female flower bearing pistils .
i) Staminate flower – male gamete, ii) Pistillate flower – female gamete.

Question. Give two examples of animals in which oestrus cycle occurs?
Answer : ➢ Non – Primate mammals like cows, sheep.

Question. Name the two stages that a zygote undergoes during embryogenesis?
Answer : ➢ Zygote undergoes cell division (mitosis) and cell differentiation

Question. Describe major events of sexual reproduction?
Answer : The major events are:
 Pre fertilization: Gametogenesis & gamete transfer.
 Fertilization: Syngamy resulting in diploid zygote.
 Post fertilization: Embryogenesis after the formation of zygote.

Question. Describe vegetative reproduction in plants?
Answer : ➢ In plants different plant parts which are modified into structures like runner, rhizome, sucker, tuber, etc. are capable of giving rise to new plants, such a method of reproduction is called vegetative propagation. For e.g., Offset in Water hyacinth, Tuber in Potato.etc.

Question. Which are the vegative propagules found in the following angiosperms?
a)__________ of ginger. b) __________ of Agave.
c) __________ of water hyacinth. d) __________ of potato
e)__________ of onion.
Answer : ➢ Rhizome, bulbil, offset, tuber and bulb.

Question. Describe with suitable diagrams.
Answer : a) Budding in yeast
b) Binary fission in amoebae.

Question. a) Differentiate between gametogenesis and embryogenesis.
b) Differentiate between zoospore and Zygote.
Answer : ➢ Gametogenesis: The process of formation of two types of gametes male and female.
➢ Embryogenesis: The process of development of embryo from the zygote

Question. Why higher organisms have resorted to sexual reproduction in spite of its complexcity?
Answer : 1. It brings about variations.
2. Variation helps in better adaptation in nature.
3. Variation is the basis of evolution.

Question .What is parthenogenesis. Give Example?
Answer : ➢ Parthenogenesis: Female gamete develops into new organism.
➢ Seedless fruits are formed by parthenogenesis
➢ Occurs naturally in some plants and invertebrate animals

Question. Mention the reason for difference in ploidy of zygote and primary endosperm nucleus in angiosperm.
Answer : ➢ Zygote is diploid due to the fusion of two haploid gametes
➢ Endopserm nucleus is triploid formed by triple fusion

 

 

CBSE Class 12 Biology Reproduction in Organisms Mind Map

 

Very Short Answer Questions

Question. In yeast and Amoeba the parent cell divides to give rise to two new individual cells. How does the cell division differ in these two organisms? 
Answer. In Amoeba, binary fission takes place whereas in yeast cell division occurs by budding.

Question. Explain why meiosis and gametogenesis are always interlinked.
Answer. Gametogenesis (formation of male and female gametes) is associated with reduction in  chromosome number thus, the gamete formed contains half the chromosome set of the parental cell. So, gametogenesis is interlinked with meiosis because meiosis reduces the chromosome number to half, i.e., from 2n to ‘n’.

Question. Name the phenomenon and one bird where the female gamete directly develops into a new organism.
Answer. The phenomenon is called parthenogenesis. Turkey is the name of the bird.

Question. Meiosis is an essential event in the sexual life cycle of any organism. Give two reasons.
Answer. (i) Meiosis helps in the formation of gametes by reductional division and maintains constant number of chromosomes.
(ii) Meiosis brings variation in offsprings by recombination of genes.

Question. What is a bisexual flower? Collect five bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names.
Answer. A flower which possess both the male and female reproductive structures, i.e., both stamen and carpel is called a bisexual flower.

Question. At what state does the meiosis occur in an organism exhibiting haploidic life cycle and mention the fate of the products thus produced. 
Answer. Organisms exhibiting haploidic life cycle undergo meiosis during zygote formation. The products thus formed are haploid gametophyte.

Short Answer Questions

Question. Out of many papaya plants growing in your garden, only a few bear fruits. Give reason.
Answer. Papaya plant is dioecious, i.e., male and female flowers are borne on separate plants. Only plants bearing female flowers will bear fruits.

Question. Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).
(i) Ovary (ii) Anther (iii) Egg
(iv) Pollen (v) Male gamete (vi) Zygote.
Answer. (i) Diploid (2n) (ii) Diploid (2n) (iii) Haploid (n)
(iv) Haploid (n) (v) Haploid (n) (vi) Diploid (2n)

Question. It is said apomixis is a type of asexual reproduction. Justify. 
Answer. Apomixis is a type of asexual reproduction because :
(i) Apomixis is the formation of seeds or embryo without fusion of gametes or fertilisation.
(ii) Diploid egg cell is formed without reductional division and develops into the embryo without fertilisation.
(iii) Some cells of the nucellus start dividing and develop into embryo.

Question. Which of the following are monoecious and dioecious organisms:
(a) Earthworm (b) Chawra
(c) Marchantia (d) Cockroach. 
Answer. (a) Monoecious (b) Monoecious
(c) Dioecious (d) Dioecious.

Question. Explain the importance of syngamy and meiosis in a sexual life cycle of an organism.
Answer. In the sexual life cycle of an organism, meiosis results in formation of haploid gametes which fuse together by syngamy and the diploid nature of the organism is restored in the zygote.

Question. What is vegetative propagation? Give two suitable examples.
Answer. In plants, the vegetative propagules (runner, rhizome, sucker, etc.) are capable of producing new offsprings by the process called vegetative propagation. As the formation of these vegetative propagules does not involve both the parents, the process involved is asexual.
Examples: (i) Adventitious buds in the notches along the leaf margins of Bryophyllum grow to form new plants.
(ii) Potato tuber having buds when grown, develops into a new plant.

Question. A moss plant produces a large number of antherozoids but relatively only a few egg cells. Why?
OR 
Why do moss plants produce very large number of male gametes? Provide one reason. What are these gametes called? 
Answer. Antherozoids are motile male gametes which have to swim on the water surface to fertilise the immotile female gametes, i.e., egg. Since, during its transfer many antherozoids get destroyed, a large number of them are produced.

Question. Name any two organisms and the phenomenon involved where the female gamete undergoes development to form new organisms without fertilisation. 
Answer. The phenomenon of development of female gamete directly into an individual without fertilisation is called parthenogenesis, e.g., rotifers, honeybees, lizards and birds.

Long Answer Questions

Question. Pollen banks are playing a very important role in promoting plant breeding programme the world over. How are pollens preserved in the pollen banks? Explain. How are such banks benefitting our farmer? Write any two ways. 
Answer. Cryopreservation/preserved in liquid nitrogen (–196°C).
(i) Availability of pollen of different genetic strains (for wider use).
(ii) Cryopreservation increases viability of pollens (which can be used in crop breeding programmes).
(iii) Can be preserved/stored for longer duration.
(iv) Conserve large number of species.
(v) To prevent complete extinction of any species.
(vi) Maintain biodiversity.

Question. What are vegetative propagules? Name any four of them along with an example for each.
Answer. The units of asexual vegetative structures of plants which are capable of giving rise to new individuals/plants are called vegetative propagules.
Example:
(i) Rhizome of ginger,
(ii) bulbil of Agave,
(iii) leaf buds of Bryophyllum,
(iv) bulbs of onion.

Question. Offspring formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
Answer. Offspring formed due to sexual reproduction have better chances of survival because:
(i) the offspring retains its hybrid vigour which may adapt better with the changing environment.
(ii) genetic variation is introduced among the offspring, which increases the range of tolerance or biological tolerance.
(iii) sexual reproduction occurs in adverse conditions in lower plant kingdom, so sexual spores survive in adverse conditions.
Sexual reproduction may not always show better chances of survival because the offspring may be inferior to the parents.

Very Short Answer Questions

Question. Is Marchantia monoecious or dioecious? Where are the sex organs borne in this plant? 
Answer. Marchantia is dioecious. The male sex organs, antheridia, are borne on the antheridiophores and female sex organs, called as archegonia are borne on archegoniophores.

Question. Write the two pre-fertilisation events from the list given below: Syngamy, Gametogenesis, Embryogenesis, Pollination
Answer. Gametogenesis, Embryogenesis, Pollination.

Question. Which is a better mode of reproduction: sexual or asexual? Why?
Answer. Sexual mode of reproduction is better because it is biparental reproduction and introduces variation among offsprings and their parents (in a population) due to crossing over and recombination during gamete formation by meiosis and thus helps in better adaptation to changing environment.

Question. How is it possible in Oxalis and Viola plants to produce assured seed-sets even in the absence of pollinators?
Answer. By presence of cleistogamous flowers, hence anthers and stigma lie close to each other ensuring self-pollination.

Question. Mention the unique feature with respect to flowering and fruiting in bamboo species.
Answer. Bamboo species flower once in its life time generally after 50–100 years of vegetative growth. It produces large number of fruits and then dies.

Short Answer Questions

Question. A liverwort plant is unable to complete its lifecycle in a dry environment. State two reasons. 
Answer. For sexual reproduction to take place in mosses and liverworts the motile male gametes,antherozoids, have to swim on the water surface to fertilise the immotile female gametes, egg.
In dry conditions, the antherozoids do not reach the egg and hence fertilisation cannot occur. So, the life cycle remains incomplete.

Question. Name the relationship between the first two words and suggest a suitable word (a) Doob grass : Runner : : Potato : ………… (b) Endogamy : Self-fertilisation : : Exogamy : …………
Answer. (a) Tuber (b) Cross-fertilisation.

Question. Mosses and frogs both need water as a medium for fertilisation. Where does syngamy occur and how is it ensured in both these organisms?
                                                                                      OR
Write the basis of categorising animals as oviparous or viviparous, giving one example of each.
Answer. In frogs, external fertilisation takes place in water. The frogs release large number of motile gametes. There is synchronised maturation of ova and sperms. In moss, internal fertilisation takes place. The male gametes are motile and are produced in large numbers.
                                                                                      OR
Oviparous animals are egg laying (fertilised or unfertilised). For example, reptiles, birds.
Viviparous animals give birth to young ones. For example, majority of mammals; humans.

Question. Why dogs and cats have oestrus cycle but human beings have menstrual cycle, though all are mammals? 
Answer. Dogs and cats are seasonal breeders . They have heat period during which ovulation takes place.
Humans, on the other hand, have this cycle monthly.

Question. A single pea plant in your kitchen garden produces pods with viable seeds, but the individual papaya plant does not. Explain. 
Answer. Flowers of pea plants are bisexual, hence can be self pollinated and produce pods with viable seeds.
Papaya is a dioecious plant bearing male and female flower on separate plants. It is unable to produce viable seeds as there is no cross-pollination. It could be a male plant which is unable to produce fruit and seeds.

Question. With which type of reproduction do we associate the reduction division? Analyse the reasons for it. 
Answer. Reduction division is associated with sexual reproduction because the diploid organisms undergo meiosis to form haploid gametes.

Long Answer Questions

Question. Differentiate between an annual and a biennial plant. Provide one example of each.
Answer.

S.No. Annual plants Biennial plants
(i)These plants require a single season to complete their whole life cycle.These plants require two seasons to complete their whole life cycle.
(ii)They grow, set seeds and die within one year.In the first year, they grow a healthy root system and short stem, i.e., show vegetative growth and become dormant in winters. In second year, they grow quickly, flower, set seeds and die.
(iii)For example, rice, wheat, etc.For example, onion, carrot, etc.

Question. Although sexual reproduction is a long drawn, energy-intensive complex form of reproduction, many groups of organism in Kingdom Animalia and Plantae prefer this mode of reproduction. Give at least three reasons for this. 
Answer. (a) Sexual reproduction brings about variation in the offspring.
(b) Since gamete formation is preceded by meiosis, genetic recombination occurring during crossing over (meiosis-I), leads to a great deal of variation in the DNA of gametes.
(c) The organism has better chance of survival in a changing environment.

Question. Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
Answer. In viviparous animals, the young one develops inside the body of the female organism. As a
result of this, the young one gets better protection and nourishment for proper development. In case of oviparous animals, they lay eggs and the young ones develop inside the calcareous shell, outside the body of the female. So, the young ones are not effectively protected and nourished and are vulnerable to predators. So, they are at a greater risk as compared to the offsprings of the viviparous animals.

Chapter 10 Microbes In Human Welfare
CBSE Class 12 Biology Microbes In Human Welfare Notes
Chapter 11 Biotechnology Principles and Processes
CBSE Class 12 Biology Biotechnology Principles And Processes Notes
Chapter 12 Biotechnology and Its Application
CBSE Class 12 Biology Biotechnology And Its Application Notes
Chapter 13 Organisms and Populations
CBSE Class 12 Biology Organisms And Populations Notes
Chapter 15 Biodiversity and Conservation
CBSE Class 12 Biology Biodiversity And Conservation Notes
Chapter 16 Environmental Issues
CBSE Class 12 Biology Environmental Issues Notes

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