Samacheer Kalvi Class 12 Bio Zoology Solutions Chapter 1 Reproduction in Organisms

Question 1. In which type of parthenogenesis are only males produced?
(a) Arrhenotoky
(c) Amphitoky
(d) Both a and b
Answer: (a) Arrhenotoky
In simple words: Arrhenotoky is a special way of reproduction where only male offspring are born from eggs that are not fertilized. This means the mother does not need a father to have sons.

🎯 Exam Tip: Remember Arrhenotoky is for males only, Thelytoky for females, and Amphitoky for both sexes.

Question 2. Animals giving birth to young ones:
(a) Oviparous
(b) Ovoviviparous
(c) Viviparous
(d) Both a and b
Answer: (c) Viviparous
In simple words: Viviparous animals give birth to live babies, much like humans do. The young ones grow inside the mother's body before they are born.

🎯 Exam Tip: Distinguish between viviparous (live birth), oviparous (egg-laying), and ovoviviparous (eggs hatch inside mother, then live birth).

Question 3. The mode of reproduction in bacteria is by ............
(a) Formation of gametes
(b) Endospore formation
(c) Conjugation
(d) Zoospore formation
Answer: (c) Conjugation
In simple words: Bacteria often reproduce by conjugation, where two bacteria temporarily join and swap some genetic material. This helps them get new traits and adapt better.

🎯 Exam Tip: Conjugation is a form of sexual reproduction in bacteria, involving direct transfer of genetic material.

Question 4. In which mode of reproduction variations are seen?
(a) Asexual
(b) Parthenogenesis
(c) Sexual
(d) Both a and b
Answer: (c) Sexual
In simple words: In sexual reproduction, genes from two parents mix, which leads to offspring that are a little different from each other and their parents. This difference is called variation and it helps species change over time.

🎯 Exam Tip: Sexual reproduction creates genetic variation, while asexual reproduction typically produces identical clones.

Question 5. Assertion and reasoning questions:

In each of the following questions there are two statements. One is assertion (A) and other is reasoning (R). Mark the correct answer as
A. If both A and R are true and R is correct explanation for A
B. If both A and R are true but R is not the correct explanation for A
C. If A is true but R is false
D. If both A and R are false

Question 5. I. Assertion: In bee society, all the members are diploid except drones. Reason: Drones are produced by parthenogenesis.
Answer: (A) If both A and R are true and R is correct explanation for A
In simple words: In bee colonies, male bees (drones) hatch from unfertilized eggs, a process called parthenogenesis, which makes them haploid. All other bees (queens and workers) come from fertilized eggs, making them diploid. This means the reason correctly explains why drones are different.

🎯 Exam Tip: Understand the genetic makeup (haploid/diploid) of different castes in social insects like honeybees and how their development links to fertilization and parthenogenesis.

Question 5. II. Assertion: Offsprings produced by asexual reproduction are genetically identical to the parent. Reason: Asexual reproduction involves only mitosis and no meiosis.
Answer: (A) If both A and R are true and R is correct explanation for A
In simple words: Asexual reproduction makes new individuals that are exact copies of the parent because it only uses mitosis, a cell division process that creates identical cells. Meiosis, which shuffles genes, is not involved.

🎯 Exam Tip: Clones are formed in asexual reproduction because mitosis ensures genetic sameness between parent and offspring.

Question 5. III. Assertion: Viviparous animals give better protection to their offsprings. Reason: They lay their eggs in the safe places of the environment.
Answer: (C) If A is true but R is false
In simple words: Viviparous animals, which give birth to live young, offer good protection because the offspring grow inside the mother's body. However, the reason given is false because viviparous animals do not lay eggs; egg-laying is characteristic of oviparous animals.

🎯 Exam Tip: Always analyze both the assertion and reason separately for truthfulness, then determine if the reason actually explains the assertion.

Question 6. Name an organism where cell division is itself a mode of reproduction.
Answer: Amoeba
In simple words: In simple organisms like amoeba, the cell just divides into two, and each new part becomes a whole new organism. This is their way of making more of themselves.

🎯 Exam Tip: Binary fission, a type of cell division, is a common asexual reproduction method for single-celled organisms.

Question 7. Name the phenomenon where the female gamete directly develops into a new organism with an avian example.
Answer: Parthenogenesis is the phenomenon where the unfertilized female gamete (egg) develops into a new individual. For example, Turkey.
In simple words: Parthenogenesis is when an egg grows into a baby without needing to be fertilized by sperm. In some birds like turkeys, this can happen naturally.

🎯 Exam Tip: Parthenogenesis means "virgin birth" and can occur in various animal groups, including some insects, fish, reptiles, and birds.

Question 8. What is parthenogenesis? Give two examples from animals.
Answer: Development of an egg into a complete individual without fertilization is known as parthenogenesis. It was first discovered by Charles Bonnet in 1745. For example, Honey bees, Aphis.
In simple words: Parthenogenesis is when an egg develops into a full organism without being fertilized by sperm. It's like a single parent creating offspring without needing a partner, as seen in honey bees and aphids.

🎯 Exam Tip: Remember the key characteristic of parthenogenesis is the absence of fertilization and the development of an unfertilized egg.

Question 9. Which type of reproduction is effective – Asexual or sexual and why?
Answer: Sexual reproduction is highly effective than asexual reproduction since the offspring are genetically different from parents causing variations. This variation leads to evolution.
In simple words: Sexual reproduction is more effective because it mixes genes from two parents, creating unique offspring. These differences help a species adapt and change over time, which is important for survival.

🎯 Exam Tip: Highlight genetic variation as the primary advantage of sexual reproduction, as it drives evolution and species adaptation.

Question 10. The unicellular organisms which reproduce by binary fission are considered immortal. Justify.
Answer: In unicellular organisms during binary fission, the entire cell (organism) divides completely to form two daughter cells which later on develop into adults. This process goes on repeatedly during each division, leading to the immortality of the cell (organism). Hence, unicellular organisms like amoeba are 'biologically immortal'.
In simple words: Single-celled creatures like amoeba never truly die of old age because they simply split into two new identical cells. They keep dividing and living on through their offspring, making them seem immortal.

🎯 Exam Tip: When discussing immortality in unicellular organisms, emphasize that the parent cell simply becomes the daughter cells, without leaving behind a "dead" parent body.

Question 11. Why is the offspring formed by asexual reproduction referred as a clone?
Answer: Offspring developed by asexual reproduction are referred to as clones since they are genetically and morphologically similar to their parent. They are exact copies because they get all their genetic material from one parent.
In simple words: Offspring from asexual reproduction are called clones because they are exact genetic copies of their single parent. They look and act just like the parent.

🎯 Exam Tip: The key characteristic of a clone is its identical genetic makeup to the parent, resulting from asexual reproduction.

Question 12. Why are the offsprings of oviparous animal at a greater risk as compared to offsprings of viviparous organisms?
Answer: Oviparous animals are egg-layers. The eggs containing the embryo are laid outside their body and are highly susceptible to environmental factors (temperature, moisture etc.) and predators. In contrast, in viviparous animals, the embryo develops inside the body of the female and comes out as young ones. This internal development offers more protection from outside dangers. Hence, offsprings of oviparous animals are at risk compared to viviparous animals.
In simple words: Babies that grow inside the mother (viviparous) are safer than those in eggs laid outside (oviparous). Eggs can get too hot or cold, dry out, or be eaten by other animals, while babies inside the mother are protected from these dangers.

🎯 Exam Tip: Focus on the comparative protection levels: external development (eggs) exposes offspring to more risks than internal development (live birth).

Question 13. Give reasons for the following:
1. Some organisms like honey bees are called parthenogenetic animals
2. A male honey bee has 16 chromosomes whereas its female has 32 chromosomes
Answer:
1. Among honey bees, the queen bee and worker bees develop from fertilized eggs, but the drones (males) develop from unfertilized eggs. This process, where unfertilized eggs develop into individuals, is called parthenogenesis. Honey bees show incomplete parthenogenesis because both sexual and asexual reproduction happen.
2. Female honey bees (queen or worker bees) are diploid, meaning they have 32 chromosomes, as they develop from fertilized eggs with contributions from both parents. On the other hand, male honey bees (drones) develop from unfertilized eggs, so they have only 16 chromosomes (they are haploid). This difference in chromosome number is a unique feature in honey bees.
In simple words: Honey bees use a special trick where male bees are born from eggs that are not fertilized, which is called parthenogenesis. This also means male bees have half the number of chromosomes (16) compared to female bees (32), who are born from fertilized eggs.

🎯 Exam Tip: For honeybees, remember that drones are haploid (from unfertilized eggs) and queens/workers are diploid (from fertilized eggs), illustrating a unique form of sex determination.

Question 14. Differentiate between the following:
(a) Binary fission in amoeba and multiple fission in Plasmodium
(b) Budding in yeast and budding in Hydra
(c) Regeneration in lizard and Planaria
Answer:
(a) Binary fission in amoeba and multiple fission in Plasmodium

🎯 Exam Tip: When differentiating, always focus on distinct features like number of offspring, cell division type, and the extent of regeneration.

Question 15. Differentiate between juvenile phase and reproductive phase.
Answer:

🎯 Exam Tip: Clearly define the start and end points of each phase in terms of growth and reproductive capability.

Question 16. What is the difference between syngamy and fertilization?
Answer: Syngamy and fertilization are similar terms, but there is a slight difference. Syngamy refers to the process of fusion of two gametes (sperm and egg) forming a zygote. Fertilization refers to the broader process of being fertile, which includes syngamy and other events like gamete transport and activation. So, syngamy is a specific event within fertilization.
In simple words: Syngamy is when the sperm and egg cell directly join together to make a new cell. Fertilization is a bigger process that includes syngamy, but also all the other steps like the sperm reaching the egg and getting ready to join.

🎯 Exam Tip: Remember that syngamy is the critical fusion event, while fertilization is a more encompassing term for the entire reproductive process.

12th Bio Zoology Guide Reproduction in Organisms Additional Important Questions and Answers

I. Choose the Correct Answer:

Question 1. Transverse binary fission is noticed in....
(a) Amoeba
(b) Planaria
(c) Ceratium
(d) Vorticella
Answer: (b) Planaria
In simple words: Transverse binary fission is a way of splitting where the organism divides across its shorter side. This can be seen in creatures like Planaria.

🎯 Exam Tip: Note the distinction between transverse (across the width), longitudinal (along the length), and irregular fission, and recall examples for each.

Question 2. Multiple fission occurring in the oocyte of Plasmodium is called..............
(a) Schizogony
(b) Merogamy
(c) Syngamy
(d) Sporogony
Answer: (d) Sporogony
In simple words: In the life cycle of Plasmodium, when the oocyte divides many times to make new cells, this specific process is known as sporogony. It is an important part of how malaria spreads.

🎯 Exam Tip: Familiarize yourself with the different stages of Plasmodium reproduction and the specific terms used for each type of fission.

Question 3. Taenia solium requires ............as a secondary host to complete its life cycle.
(a) Mosquito
(b) pig
(c) dog
(d) human
Answer: (b) pig
In simple words: The tapeworm Taenia solium needs a pig as its second host to finish its life cycle. Humans usually get infected by eating undercooked pork.

🎯 Exam Tip: Remember that tapeworms like Taenia solium have complex life cycles involving primary (human) and secondary (pig) hosts.

Question 4. Which type of parthenogenesis only females are produced?
(a) Arrhenotoky
(b) Amphitoky
(c) Thelytoky
Answer: (c) Thelytoky
In simple words: Thelytoky is a special type of reproduction where only female offspring are born from eggs that have not been fertilized. This means the mother can have only daughters without a male partner.

🎯 Exam Tip: Differentiate between thelytoky (females only), arrhenotoky (males only), and amphitoky (both sexes) in parthenogenesis.

Question 5. Which among the following animal is not a continuous breeder?
(a) Hen
(b) Rabbit
(c) Honey bees
(d) Frogs
Answer: (d) Frogs
In simple words: Frogs are not continuous breeders; they reproduce only at certain times of the year, usually during specific seasons. Animals like hens, rabbits, and honey bees can reproduce throughout their reproductive lives.

🎯 Exam Tip: Continuous breeders reproduce year-round, while seasonal breeders have specific periods for reproduction, often linked to environmental conditions.

Question 6. Match the following.

🎯 Exam Tip: Memorize examples for each type of asexual reproduction to accurately match them with the correct organisms.

Question 7. Identify the incorrect statement regarding parthenogenesis.
(a) Development of sperm without fertilization.
(b) It was first discovered by Charles Bonnet.
(c) Honey bees exhibit incomplete parthenogenesis.
(d) Amphitoky is a type of natural parthenogenesis.
Answer: (a) Development of sperm without fertilization.
In simple words: The wrong statement is that parthenogenesis is the development of sperm without fertilization. Parthenogenesis is actually about the development of an *egg* without fertilization, not sperm.

🎯 Exam Tip: Understand that parthenogenesis always involves the development of an unfertilized ovum (egg), not a sperm.

Question 8. Oblique binary fission is seen in....
Answer: Dinoflagellates
In simple words: Oblique binary fission is a type of splitting where a cell divides at an angle. This kind of division is found in small marine organisms called Dinoflagellates.

🎯 Exam Tip: Binary fission can occur in different planes (transverse, longitudinal, oblique), and each is characteristic of certain organisms.

Question 9. The process by which gravid proglottids of tapeworm get cut off is called.............
Answer: Apolysis
In simple words: Apolysis is when the mature, egg-filled segments (gravid proglottids) of a tapeworm break off from its body. This is how the tapeworm spreads its eggs.

🎯 Exam Tip: Apolysis is crucial for the dispersal of tapeworm eggs, ensuring the continuation of its life cycle.

Question 10. The concept of regeneration was first noticed in.......
Answer: Hydra
In simple words: The idea that a creature can regrow lost body parts, called regeneration, was first observed in a small water animal named Hydra.

🎯 Exam Tip: Associate Hydra with early discoveries in regeneration due to its remarkable ability to regrow from small fragments.

Question 11. Fusion of small sized, morphologically different gametes is called.............
Answer: Merogamy
In simple words: Merogamy is when two reproductive cells (gametes) join together, where these cells are small and look a bit different from each other.

🎯 Exam Tip: Note the nuances between different types of gamete fusion: isogamy (similar), anisogamy (dissimilar size), and merogamy (small, different-looking gametes).

Question 12. Identify the wrong statement.
(a) Oviparous animals lays eggs.
(b) Viviparous animals give rise to young ones.
(c) Ovoviviparous animals lays eggs and then hatch it to young ones.
(d) Amphibians are oviparous animals.
Answer: (c) Ovoviviparous animals lays eggs and then hatch it to young ones.
In simple words: The wrong statement is about ovoviviparous animals. They do have eggs, but these eggs stay inside the mother's body and hatch there, so the mother gives birth to live young. They don't lay the eggs for them to hatch outside.

🎯 Exam Tip: Clearly differentiate ovoviviparous from oviparous; the key is internal hatching of eggs, leading to live birth, rather than laying eggs externally.

Question 13. Assertion (A): Organisms show three phases in their life cycle. Reason (R): Juvenile phase is a degenerative phase.
(a) A is correct R but is incorrect.
(b) Both A and R are correct
(c) R is the correct explanation for A
(d) A is not correct but R is correct
Answer: (a) A is correct R but is incorrect.
In simple words: The assertion is true because living things do go through three stages: juvenile, reproductive, and senescent. However, the reason is false because the juvenile phase is a time of growth and development, not a time of getting weaker or breaking down.

🎯 Exam Tip: Remember the three phases of a life cycle and their characteristics; the juvenile phase is for growth and development, not degeneration.

Question 14. Match the statements.

🎯 Exam Tip: For matching questions, correctly identifying the key process or structure described on one side and its corresponding organism or related concept on the other is essential.

Question 15. The ploidy of males produced by arrhenotoky parthenogenesis is
Answer: haploid
In simple words: When males are produced by arrhenotoky, a type of parthenogenesis, they only get genetic material from one parent (the mother) because the egg is not fertilized. This means they have half the usual number of chromosomes, making them haploid.

🎯 Exam Tip: Remember that in arrhenotoky, males are typically haploid because they develop from unfertilized eggs.

Question 16. Identify the mismatched pair.
(a) Paedogenesis- Liver fluke
(b) Strobilation- Aurelia
(c) Amphitoky- Honey bee
(d) Encystment- Amoeba
Answer: (c) Amphitoky – Honey bee
In simple words: The mismatched pair is Amphitoky-Honey bee. Honey bees typically show arrhenotoky (producing males) or thelytoky (producing females), but not amphitoky (producing both sexes). All other pairs are correctly matched examples of biological processes.

🎯 Exam Tip: Review examples for different reproductive strategies and life cycle stages to correctly identify mismatched pairs.

Question 17. Identify the proper sequence.
(a) juvenile phase, senescent phase, vegetative phase
(b) juvenile phase, maturity phase, senescent phase
Answer: (b) juvenile phase, maturity phase, senescent phase
In simple words: The correct order of phases in a living organism's life cycle is juvenile (growth), then maturity (reproduction), and finally senescent (aging and decline).

🎯 Exam Tip: The life cycle sequence generally follows growth, reproduction, and then aging. "Vegetative phase" is typically used for plants, not animals.

Question 18. Match the following:

🎯 Exam Tip: Understand the characteristics of each syngamy type (e.g., source of gametes, appearance of gametes) and recall representative organisms.

Question 19. Which of the following types of asexual reproduction is noticed in Amoeba?
(a) Sporulation
(b) Encystment
(c) Binary fission
(d) All of the options
Answer:
In simple words: Amoeba can reproduce in many ways without a partner, like splitting into two (binary fission), forming a protective cyst (encystment) during bad times, and then releasing spores (sporulation) from that cyst. So, it can do all these.

🎯 Exam Tip: Amoeba exhibits multiple forms of asexual reproduction, including binary fission during favorable conditions and encystment/sporulation during unfavorable conditions.

Question 20. Pick out the organism whose fertilization occurs internally.
(a) reptiles
(b) sponges
(c) pisces
(d) amphibians
Answer: (a) reptiles
In simple words: Reptiles are animals where the male and female reproductive cells join together inside the female's body. This process is called internal fertilization.

🎯 Exam Tip: When asked about internal or external fertilization, remember to link it to the environment where the process happens: inside the body for internal, outside for external.

Question 21. Assertion (A): Asexual reproduction is called blastogenic reproduction Reason (R): It is accomplished by mitotic and meiotic divisions.
(a) A and R are correct
(b) A is correct but R is incorrect
(c) Both A and R are incorrect
(d) R is the correct explanation for A
Answer: (b) A is correct but R is incorrect
In simple words: The first statement (assertion) is true because asexual reproduction is known as blastogenic reproduction. However, the reason given is false because asexual reproduction only uses mitotic cell division, not both mitotic and meiotic.

🎯 Exam Tip: Understand the core processes of asexual reproduction: it typically involves mitotic divisions, leading to genetically identical offspring.

Question 22. Egg laying hen is an example for
(a) Thelytoky
(b) Ovovivipary
(c) Vivipary
(d) Ovipary
Answer: (d) Ovipary
In simple words: A hen that lays eggs is an example of ovipary. This term describes animals that lay eggs, and the embryo develops outside the mother's body.

🎯 Exam Tip: Remember that oviparous animals lay eggs outside their body, viviparous animals give birth to live young, and ovoviviparous animals keep eggs inside until they hatch.

Question 23. Assertion (A): Syngamy refers to the fusion of two haploid gametes. Reason (R): Syngamy leads to zygote formation.
(a) A and R are correct.
(b) A and R are incorrect.
(c) R is not the right explanation for A
(d) A is correct but R is incorrect.
Answer: (a) A and R are correct.
In simple words: Both statements are true and the reason explains the assertion. Syngamy is the joining of two single-chromosome cells, and this joining creates a new cell called a zygote.

🎯 Exam Tip: When analyzing Assertion-Reason questions, first check if each statement is true individually, then check if the Reason actually explains the Assertion.

Question 24. Human beings are an example for ................. breeders.
Answer: continuous
In simple words: Human beings are an example of continuous breeders. This means they can reproduce throughout their sexual maturity, not just during specific seasons.

🎯 Exam Tip: Differentiate between seasonal breeders (reproduce only at specific times) and continuous breeders (reproduce throughout their adult life).

12th Bio Zoology Guide Reproduction In Organisms Two Marks Questions And Answers

Question 1. Why asexual reproduction is called somatogenic reproduction?
Answer: Asexual reproduction is called somatogenic reproduction because it happens through cell division (either amitotic or mitotic) of the body cells, which are also called somatic cells. This is how new individuals are formed without sex cells, making it a direct copy from the parent's body.
In simple words: Asexual reproduction uses body cells to make new life. So, it is called somatogenic because 'soma' means 'body'.

🎯 Exam Tip: The term 'somatogenic' highlights that asexual reproduction involves body cells (somatic cells), not reproductive cells.

Question 2. Name the four types of fission seen in animals.
Answer: The four types of fission seen in animals are: Binary fission, Multiple fission, Sporulation, and Strobilation. Each of these methods involves a single parent organism dividing to produce new individuals.
In simple words: Animals can make new copies of themselves by splitting in four ways: binary, multiple, sporulation, and strobilation.

🎯 Exam Tip: When listing types of reproduction, be precise with the names and spellings, as they are key terms.

Question 3. Define fission.
Answer: Fission is a biological process where a single parent organism divides into two or more identical daughter individuals. It is a common form of asexual reproduction.
In simple words: Fission means one parent body splits into two or more identical new bodies.

🎯 Exam Tip: A clear definition of fission should include both the division of the parent body and the resulting identical daughter individuals.

Question 4. Differentiate between transverse binary fission and longitudinal binary fission.
Answer:
**Transverse binary fission:**
1. The organism splits across its middle, with the plane of division running along the transverse axis.
2. An example of an organism that does this is Paramecium.

**Longitudinal binary fission:**
1. The organism splits lengthwise, from top to bottom, with the plane of division running along the longitudinal axis.
2. An example of an organism that does this is Euglena.
In both cases, a single organism divides to form two new, similar organisms.
In simple words: In transverse fission, an organism splits across its width (like Paramecium). In longitudinal fission, it splits down its length (like Euglena).

🎯 Exam Tip: When differentiating, clearly state the key difference (e.g., plane of division) for each type and provide a relevant example.

Question 5. Define Plasmotomy with example.
Answer: Plasmotomy is a special type of cell division where a parent cell with many nuclei divides directly into several smaller cells, each also having multiple nuclei. The nuclei then divide later to keep the correct number in each new cell. This process happens in organisms like Opalina and Pelomyxa (which is a large amoeba), allowing for quick multiplication.
In simple words: Plasmotomy is when a cell with many nuclei splits into smaller cells, each still having many nuclei. Opalina is an example.

🎯 Exam Tip: Highlight that plasmotomy involves a multinucleated parent and results in multinucleated daughter individuals, with nuclear division occurring later.

Question 6. What is regeneration in living organisms? Mention its types.
Answer: Regeneration is when a living organism can regrow a lost or damaged body part. This amazing ability is seen in many animals. There are two main types of regeneration:
1. **Morphallaxis:** This is when a whole new organism can grow from a small piece of the old one, often with some restructuring of the remaining parts.
2. **Epimorphosis:** This type involves the regrowth of specific lost body parts, like a lizard regrowing its tail, without forming a whole new organism from a small piece.
The capability of regeneration helps organisms recover from injuries.
In simple words: Regeneration is the body's power to regrow a hurt part. It has two types: morphallaxis (like growing a whole new body from a piece) and epimorphosis (like growing a lost tail).

🎯 Exam Tip: When asked about regeneration, define it clearly and name its two main types, briefly explaining what each type involves.

Question 7. How is the fertilization of amphibians differs from aves based on site?
Answer: In amphibians, fertilization is external. This means the male and female reproductive cells join outside the female's body, usually in water. However, in birds (aves), fertilization is internal, meaning the joining of these cells happens inside the female's body. This difference is linked to their different environments.
In simple words: Amphibians' eggs join outside their body. Birds' eggs join inside their body.

🎯 Exam Tip: The key difference between amphibian and avian fertilization is the location: external for amphibians (usually water) and internal for birds (inside the female).

Question 8. What is Paedogamy?
Answer: Paedogamy is a form of sexual reproduction where young individuals, which have just been formed right after an adult parent cell divides using mitosis, come together to reproduce. These young cells mature quickly to participate in fusion.
In simple words: Paedogamy is when young cells that just divided, join together to make new life.

🎯 Exam Tip: Remember that paedogamy is a type of sexual union specifically involving young individuals formed by mitotic division.

Question 9. Write a brief note on conjugation.
Answer: Conjugation is a temporary process where two individuals of the same species join together. During this time, they exchange some of their genetic material (DNA). After sharing genetic information, the two individuals separate. This process is common in tiny organisms like Paramecium, Vorticella, and also in bacteria (prokaryotes), allowing for genetic variation.
In simple words: Conjugation is when two same-type organisms briefly join to swap some genetic material, then separate. It is common in small creatures like Paramecium.

🎯 Exam Tip: When describing conjugation, emphasize the temporary union, exchange of genetic material (DNA), and the fact that it occurs between individuals of the same species.

Question 10. Explain the types of breeding animals based on the time of breeding, giving examples.
Answer: Based on the time they reproduce, breeding animals are mainly of two types:
1. **Seasonal breeders:** These animals reproduce only during specific times or seasons of the year, usually when environmental conditions are favorable. Examples include frogs, lizards, most birds, and deer.
2. **Continuous breeders:** These animals can reproduce throughout their entire period of sexual maturity, not restricted to certain seasons. Examples of continuous breeders are honey bees, poultry, and rabbits.
The timing of breeding is an important factor in their survival and population dynamics.
In simple words: Animals can breed at certain times (seasonal breeders, like frogs) or all the time once they are grown up (continuous breeders, like honey bees).

🎯 Exam Tip: Clearly distinguish between seasonal and continuous breeders by explaining their reproductive timing and providing distinct examples for each type.

Question 11. Define Vivipary.
Answer: Vivipary is a biological condition where animals give birth to live young ones that have developed inside the mother's body. These young ones are nourished by the mother, often through a special organ called the placenta, during their development in the uterus. Humans are an example of viviparous animals.
In simple words: Vivipary means animals give birth to live babies that grew inside their mother, like humans.

🎯 Exam Tip: When defining vivipary, key points are 'live young,' 'development inside the mother,' and 'nourishment via placenta' (if applicable).

Question 12. List out the four types of binary fission.
Answer: The four main types of binary fission are:
1. Simple irregular binary fission
2. Transverse binary fission
3. Longitudinal binary fission
4. Oblique binary fission
Each type is named based on how the organism divides its body into two new parts.
In simple words: The four ways an organism can split into two are simple irregular, transverse, longitudinal, and oblique binary fission.

🎯 Exam Tip: When listing types, ensure all items are included and correctly named. Binary fission is a common asexual reproduction method.

Question 13. Repeated fission is a type of multiple fission. Yes or No? Why?
Answer: Yes, repeated fission is indeed a type of multiple fission. In this process, multiple fission happens where an organism produces many daughter individuals through equal cell division. The important point is that these new individuals do not separate from each other until the entire process is finished. Vorticella is an example of an organism that undergoes repeated fission, allowing for numerous offspring.
In simple words: Yes, repeated fission is a kind of multiple fission. It's when many new cells are made but stay together until the splitting is fully done, like in Vorticella.

🎯 Exam Tip: For Yes/No questions, always provide a clear 'Yes' or 'No' and then fully explain the reasoning to score maximum marks.

Question 14. Define apolysis.
Answer: Apolysis is the process where mature, egg-filled segments (called gravid proglottids) of a tapeworm detach from its body. These segments can break off either one by one or in groups, to release the eggs into the environment and continue the tapeworm's life cycle.
In simple words: Apolysis is when the egg-filled parts of a tapeworm break off its body, one by one or in bunches.

🎯 Exam Tip: Apolysis is a specific term for tapeworms; ensure you mention 'gravid proglottids' and 'tapeworm' in your definition.

12th Bio Zoology Guide Reproduction In Organisms Three Marks Questions And Answers

Question 15. Compare schizogony with sporogony of plasmodium.
Answer: Here's a comparison between schizogony and sporogony in Plasmodium:
**Schizogony:**
1. Multiple fission in schizogony takes place inside a cell called the schizont.
2. This process leads to the formation of many new cells called merozoites.
**Sporogony:**
1. Multiple fission in sporogony occurs inside a different type of cell known as the oocyte.
2. This process results in the creation of sporozoites.
Both are types of multiple fission but happen in different stages and produce different infectious forms, crucial for the parasite's life cycle.
In simple words: Schizogony is when Plasmodium splits many times inside a schizont cell to make merozoites. Sporogony is when it splits many times inside an oocyte cell to make sporozoites.

🎯 Exam Tip: When comparing, use clear headings or bullet points for each term and focus on distinct differences like the location of fission and the resulting cells.

Question 16. Write a short note on encystment in amoeba.
Answer: Encystment is a survival method used by amoeba. When conditions are not good (like very hot or cold temperatures, or not enough food), the amoeba pulls in its false feet (pseudopodia). It then creates a thick, three-layered protective wall around itself, which makes it inactive. This protective covering is called a cyst. When conditions improve, the amoeba inside the cyst divides many times through multiple fission, making many tiny amoebae called pseudopodiospores or amoebulae. The cyst wall then breaks open, letting these young amoebae go free to live on their own.
In simple words: When conditions are bad, an amoeba forms a hard, protective cover called a cyst and becomes inactive. When conditions get better, it breaks out and makes many tiny new amoebae.

🎯 Exam Tip: Describe the conditions that trigger encystment, the formation of the cyst, and what happens when favorable conditions return, including the term 'pseudopodiospore'.

Question 17. How exogenous buds are developed by Hydra?
Answer: Exogenous budding in Hydra happens when new buds grow on the outer surface of the parent's body. When Hydra has plenty of food, its outer cells (ectoderm) increase and form a small bump on its body. Both the outer (ectoderm) and inner (endoderm) cell layers push outwards to form this bud. This bud has an internal space that connects to the parent's main body cavity. As the bud grows, it gets bigger, forms a mouth, and develops tentacles at its tip. Once it is fully grown, the bud pinches off from the parent at its base and lives independently. This allows for rapid population growth.
In simple words: In Hydra, new small Hydras grow on the outside of the parent's body. They get bigger, make a mouth and tentacles, and then break off to live on their own.

🎯 Exam Tip: Explain exogenous budding in Hydra step-by-step, including the role of ectoderm/endoderm, formation of mouth/tentacles, and final separation.

Question 18. Apolysis favours Taenia solium. How?
Answer: Apolysis helps the tapeworm *Taenia solium* in its life cycle. The oldest and mature segments filled with eggs (gravid proglottids) are at the very end of the tapeworm's body. These segments regularly break off from the tapeworm, either one by one or in clusters. This process of detachment is called apolysis. It is very important because it helps to release the eggs, which contain developing embryos, from the primary host (humans). These eggs can then be picked up by a secondary host (like a pig), allowing the tapeworm's life cycle to continue.
In simple words: Apolysis helps the tapeworm by dropping off its egg-filled body parts. These parts carry the baby tapeworms from humans to pigs, so the tapeworm can keep growing.

🎯 Exam Tip: Connect apolysis directly to the tapeworm's life cycle, explaining how the detachment of gravid proglottids facilitates the transfer of embryos to a new host.

Question 19. What is autogamy?
Answer: Autogamy is a type of self-fertilization where the male and female reproductive cells (gametes) are produced by the same cell or the same individual organism. Both these gametes then fuse together within that same individual to form a zygote. Examples of organisms that show autogamy include Actinosphaerium and Paramecium.
In simple words: Autogamy is when an organism makes both male and female cells, and they join inside the same body to make a new cell. Actinosphaerium is one example.

🎯 Exam Tip: When defining autogamy, emphasize that gametes are produced and fuse within the *same* cell or organism, making it a form of self-fertilization.

Question 20. What is exogamy?
Answer: Exogamy is a type of sexual reproduction where the male and female reproductive cells (gametes) come from two different parents. These two gametes then join together to form a zygote. Because two different parents are involved, it is considered biparental. Humans are an example of organisms that reproduce through exogamy, as they are dioecious (meaning separate male and female individuals).
In simple words: Exogamy is when male and female cells from two different parents join to make a baby, like in humans.

🎯 Exam Tip: Contrast exogamy with autogamy by highlighting that it involves gametes from *different* parents, making it biparental.

Question 21. Give the definition for
1. Arrhenotoky
2. Thelytoky
3. Amphitoky
Answer:
1. **Arrhenotoky:** This is a type of parthenogenesis (reproduction without fertilization) where only male offspring are produced. A common example is honey bees, where drones (males) develop from unfertilized eggs.
2. **Thelytoky:** In this type of parthenogenesis, only female offspring are produced. Solenobia, a type of moth, is an example.
3. **Amphitoky:** This is a type of parthenogenesis where the unfertilized egg can develop into individuals of either sex (male or female). Aphis (aphids) are known to exhibit amphitoky.
These are all fascinating variations of reproduction in nature.
In simple words: 1. Arrhenotoky makes only males (like honey bees). 2. Thelytoky makes only females (like Solenobia). 3. Amphitoky can make either males or females (like Aphis).

🎯 Exam Tip: When defining types of parthenogenesis, clearly state which sex (male, female, or both) is produced and give a specific example for each.

Question 22. What is Incomplete parthenogenesis? Explain with example.
Answer: Incomplete parthenogenesis is a form of reproduction where both sexual reproduction and parthenogenesis (development of an egg without fertilization) happen within the same species. A great example is honey bees. In honey bees, fertilized eggs develop into female queen bees and worker bees (which are sterile females). However, unfertilized eggs develop through parthenogenesis into male drones. This shows a mix of both reproductive methods, leading to different roles in the colony.
In simple words: Incomplete parthenogenesis is when an animal uses both normal reproduction and parthenogenesis. Honey bees do this: fertilized eggs make queens and workers, while unfertilized eggs make male drones.

🎯 Exam Tip: For incomplete parthenogenesis, the key is to explain that both sexual reproduction and parthenogenesis occur, and honey bees are the classic example to illustrate this.

Question 23. Explain briefly the nature of Ovovivipary.
Answer: Ovovivipary is a type of reproduction where the embryos develop inside eggs, but these eggs stay inside the mother's body. The young ones hatch from the eggs while still inside the mother, or immediately after the eggs are laid. Unlike viviparous animals, the embryos in ovoviviparous animals do not get nourishment directly from the mother through a placenta; instead, they are fed by the yolk stored in their egg. This method is similar to giving live birth but without a direct maternal connection for food. Some fishes, like sharks, exhibit ovovivipary.
In simple words: Ovovivipary means babies grow in eggs inside the mother. They get food from the egg, not the mother's body. Then they hatch and come out live, like some sharks.

🎯 Exam Tip: Distinguish ovovivipary from vivipary by emphasizing that embryos get nourishment from the egg yolk, not a placenta, even though they are born live.

Question 24. Point out any six modes of asexual reproduction seen in animals.
Answer: Here are six common ways animals reproduce asexually:
1. **Fission:** The parent organism splits into two or more new individuals.
2. **Budding:** A new organism grows out from the body of the parent, eventually detaching.
3. **Fragmentation:** The parent's body breaks into pieces, and each piece develops into a new individual.
4. **Sporulation:** Spores are formed which then develop into new organisms.
5. **Regeneration:** The ability of an organism to regrow lost or damaged body parts, sometimes forming a whole new individual.
6. **Gemmule formation:** In sponges, internal buds (gemmules) are formed which can survive harsh conditions and later develop into new sponges.
These methods allow for rapid reproduction without needing a partner.
In simple words: Six ways animals make babies without a partner are by splitting (fission), growing a small copy (budding), breaking into parts (fragmentation), making spores (sporulation), regrowing body parts (regeneration), and making tiny buds inside (gemmule formation).

🎯 Exam Tip: When listing modes of asexual reproduction, ensure you provide six distinct methods. Briefly defining each helps in clarity.

Question 25. Enumerate the types of syngamy.
Answer: Here are the various types of syngamy and related sexual fusions:
1. **Autogamy:** Self-fertilization where gametes are produced and fuse within the same individual.
2. **Exogamy:** Fertilization involving gametes from two different individuals.
3. **Hologamy:** Fusion of two adult individuals directly, where they act as gametes.
4. **Paedogamy:** Fusion of young individuals or cells immediately after they are formed.
5. **Merogamy:** Fusion of small, specialized reproductive cells (merogametes).
6. **Isogamy:** Fusion of gametes that are identical in size and shape.
7. **Anisogamy:** Fusion of gametes that differ in size or shape (one usually larger, one smaller).
8. **Conjugation:** Temporary union of two individuals to exchange genetic material, as seen in some ciliates and bacteria.
These different types demonstrate the diverse strategies organisms use for sexual reproduction.
In simple words: There are many types of how living things combine their cells: autogamy (self-joining), exogamy (joining from two different ones), hologamy (whole bodies join), paedogamy (young cells join), merogamy (small cells join), isogamy (same-size cells join), anisogamy (different-size cells join), and conjugation (swapping parts).

🎯 Exam Tip: When enumerating types of syngamy, provide a concise definition or a key characteristic for each type to demonstrate understanding.

Question 26. Name the types of animals based on embryonic development with an example for each.
Answer: Based on how their embryos develop and are born, animals are grouped into three main types:
1. **Oviparous animals:** These animals lay eggs, and the embryo develops and hatches outside the mother's body. Birds are a common example.
2. **Viviparous animals:** These animals give birth to live young that have developed inside the mother's body, receiving nourishment directly from her. Humans are a good example.
3. **Ovoviviparous animals:** In these animals, the embryos develop inside eggs that are kept within the mother's body. The young hatch from these eggs inside the mother and are born live, but they get their nourishment from the egg yolk, not directly from the mother. Sharks are an example of ovoviviparous animals.
This classification helps us understand the different reproductive strategies in the animal kingdom.
In simple words: Animals can be grouped by how babies grow: oviparous (lay eggs, like birds), viviparous (live birth, like humans), and ovoviviparous (eggs grow inside, then live birth, like sharks).

🎯 Exam Tip: Ensure you accurately define each type of embryonic development and provide a distinct, correct example for each category.

Question 27. Write a short note on the phases of the life cycle.
Answer: The life cycle of an organism generally consists of three main phases:
1. **Juvenile phase:** This is the period of growth that starts from the birth or hatching of an individual and continues until it becomes capable of reproduction. During this time, the organism focuses on growing bigger and stronger.
2. **Reproductive phase:** After the juvenile phase, the organism enters this phase where it reaches reproductive maturity. During this stage, it is able to produce offspring, ensuring the continuation of its species.
3. **Senescent phase:** This is the final phase of life, often referred to as aging. In this period, the body's structures and functions begin to decline and degenerate, leading towards the end of its life.
Each phase plays a critical role in the organism's development and survival.
In simple words: An organism's life has three parts: juvenile (growing up), reproductive (having babies), and senescent (getting old and body slowing down).

🎯 Exam Tip: Clearly define each life cycle phase (juvenile, reproductive, senescent) by outlining its start, end, and main biological characteristic.

Question 28. What is paedogenetic parthenogenesis? Explain with an example.
Answer: Paedogenetic parthenogenesis, also known as paedogenesis, is a unique type of reproduction where the larval stage of an organism can produce new larvae through parthenogenesis (without fertilization). This means the young forms (larvae) themselves can reproduce. This process is observed in the sporocysts and Redia larvae stages of liver flukes. It is also found in the larvae of some insects, such as the Gall fly. This is a fascinating way to quickly increase numbers without reaching adulthood.
In simple words: Paedogenesis is when baby forms (larvae) of an animal can have their own babies without a partner. Liver fluke larvae and Gall fly larvae do this.

🎯 Exam Tip: When explaining paedogenetic parthenogenesis, highlight that it's the *larval stage* that reproduces asexually, and provide examples like liver fluke or gall fly.

Question 29. Draw and label a gemmule of sponge.
Answer: Below is a diagram showing the structure of a gemmule from a sponge. A gemmule is a tough, survival capsule that sponges produce to withstand harsh conditions. It contains unspecialized cells called archaeocytes, protected by spicules and a double membrane, with a small opening called a micropyle, allowing new sponges to emerge when conditions improve.
In simple words: This is a picture of a sponge's gemmule. It's like a tough little seed that holds special cells (archaeocytes) so the sponge can survive bad times and grow later.