CBSE Class 12 Biology Reproduction in Organisms Worksheet Set A

Very Short Answer

Question. What is clone?
Answer. Clone is used to describe such morphologically and genetically similar individuals.

Question. In organisms what is the mode of reproduction?
Answer. In organisms cell division itself a mode of reproduction.

Question. How single celled organisms reproduce?
Answer. Single-celled organisms reproduce by binary fission

Question. What is life span?
Answer. The period from birth to the natural death of an organism represent its life span

Question. Which reproduction is common among single-celled organisms?
Answer. Asexual reproduction is common among single celled organisms.

Short Answer

Question. What do you mean by vegetative propagules?
Answer. The units or structures of vegetative propagation which are capable of giving rise to new offspring are called vegetative propagules, for example: vegetative propagules are runner and sucker, the end tip of the runner can produce buds that develop into new plants that are clones.

Question. What do you understand by fragmentation?
Answer. Fragmentation in multicellular organisms is a form of asexual reproduction in which an organism is split into fragments. Each of these fragments develops into matured, full grown individuals that are identical to their parents.

Question. What is the necessity of reproduction?
Answer. Reproduction prevents all kinds of organisms from becoming extinct. Reproduction is not necessary for carrying out life processes of an individual but helps in increasing the individuals in a population. Reproduction is essential in creating variations in species through genetic recombination.

Question. How encystation is different from sporulation?
Answer. Encystation is a process of becoming enclosed or withdrawn by the organism in a cyst in response to adverse environmental conditions whereas sporulation is a developmental process adopted by organism such as bacteria and fungus into endospores in response to adverse environmental conditions

Question. Define reproduction?
Answer. Reproduction is the biological process by which new individual organisms’ offspring are produced from their parents. The cloning of an organism is a form of asexual reproduction, by asexual reproduction an organism creates a genetically similar or identical copy of itself.

Long Answer

Question. State the difference between homothallic and heterothallic?
Answer. 1. Homothallic is the condition of having a haploid phase that produces two kinds of gametes capable of fusing to form a zygote whereas heterothallic is the condition of having two or more morphologically similar haploid phase or types of which individuals from the same type.
2. In homothallic a mating partner is not required whereas in heterothallic two compatible mating partners are required.
3. In homothallic it undergoes with the bisexual reproduction whereas in heterothallic it undergoes with unisexual reproduction.
4. In homothallic it undergoes with self-fertilization whereas in heterothallic it undergoes with cross-fertilization.
5. Homothallic is a mutational event whereas in heterothallic mutations occur in heterothallism.

Question. Explain the pre-fertilisation events?
Answer. Pre-fertilisation is the process that occurs before the actual fertilization, i.e., the process before the fusion of gametes. There are two events that occur before the fertilization.
The two main pre-fertilisation events are:
1. Gametogenesis: Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. The existence of a multicellular, haploid phase in the life cycle between meiosis and gametogenesis is also referred to as alternation of generations. Gametogenesis is important because it is the process that produces your functional gametes (egg and sperm cell) either through meiosis from a diploid cell or mitosis from a haploid cell (plants). These gametes are important because this allows genetically varied organisms (offspring) to be formed.
2. Gamete transfer: The process of bringing together of male and female gamete for fertilization is called gamete transfer. Male and female gametes need to be physically brought together to facilitate fertilization. In most of the organisms, male gamete is motile and female gamete is stationary. In a few fungi and algae both types of gametes are motile. The pollen tube grows to reach the ovary and the ovule. When the pollen tube reaches the ovule, it pushes the male gametes into the egg cell. So, the fusion of the male and the female gamete occurs.

Question. Difference between sexual reproduction and asexual reproduction?
Answer. 1. Sexual reproduction is found in almost all the animals, plants and other life forms including fungi, bacteria, and protists whereas asexual reproduction is found in lower animals and plants, fungi, protozoans, and bacteria.
2. Sexual reproduction is a bi-parental process whereas asexual reproduction is a uni-parental process.
3. Sexual reproduction produces their offspring less rapidly whereas asexual reproduction is involved in the rapid production of offspring in a short time period.
4. The cells undergoing sexual reproduction are mortal whereas the cells undergoing asexual reproduction are considered immortal.
5. Male and female gametes are formed during sexual reproduction whereas gametes are not formed during asexual reproduction.
6. Meiosis, syngamy, and conjugation are involved in the sexual reproduction whereas budding, vegetative reproduction, fragmentation and spore production are the types of asexual reproduction.

Question. Explain the post-fertilisation events?
Answer. The events in sexual reproduction after the formation of the zygote are called post fertilization events. There are two types of post fertilization events:
1. The Zygote: fertilization is defined as the fusion of the male and the female gamete to develop into a diploid zygote. After fertilization, a series of the event occurs in the zygote to develop into a seed. Let us take an overview of the process of post fertilization, endosperm and embryo formation. Development of the zygote depends on the type of the life cycle of the organism. Zygote is the vital link that ensures continuity of the species between the organisms of one generation and the next. Every sexually reproducing organism including the human beings begins life as a single cell the zygote.
2. Embryogenesis: Embryogenesis is defined by a sequential series of dynamic processes that include cell division and growth, and the elaboration of differentiation programs leading to cell fate specification. Embryogenesis is the development of a fertilized egg that occurs early on in pregnancy. After a sperm fuses with an egg, many changes occur in a specific order. The cells divide, reorganize and form layers of tissue that will eventually develop into specific organs, together they form a zygote.

Question. Write short note on fertilisation?
Answer. In sexual reproduction, two parents donate genes to their offspring through a process called fertilization. The resulting young receive a combination of inherited genes. In fertilization, male and female sex cells or gametes fuse to form a single cell called a zygote. The stages of fertilization can be divided into four processes: 1) sperm preparation, 2) sperm-egg recognition and binding, 3) sperm-egg fusion and 4) fusion of sperm and egg pronuclei and activation of the zygote. External fertilization is a mode of reproduction in which a male organism's sperm fertilizes a female organism's egg outside of the female's body. It is contrasted with internal fertilization, in which sperm are introduced via insemination and then combine with an egg inside the body of a female organism. Parthenogenesis is defined as reproduction without fertilization and occurs when the female gamete develops into a new individual without being fertilized by a male gamete.

Question. Cucurbits and papaya plants bear staminate and pistillate flowers. Mention the categories they are put under separately on the basis of the type of flowers they bear. 
Answer. Cucurbits are monoecious plants i.e., they bear both male and female flower on the same plant. On the otherhand, papaya plants are dioecious i.e., both male and female flowers are present on separate plant.

Question. Mention the unique flowering phenomenon exhibited by Strobilanthus kunthiana(neelakuranji). 
Answer. Strobilanthus kunthiana produce flowers once in twelve years.

Question. Name the mode of reproduction that ensures the creation of new variants. 
Answer. Sexual reproduction ensures creation of new variants. It involves, fusion of gametes from different parents which results in genetic recombination that cause variations.

Question. Name the phase all organisms have to pass through before they can reproduce sexually.
Answer. All organisms have to pass through the period of growth known as juvenile or vegetative phase before they start reproducing sexually. The period of growth is between the birth of an individual upto reproductive maturity.

Question. Name the phenomenon and the cell responsible for the development of a new individual without fertilisation as seen in honey bees.
Answer. Female gamete undergoes development to form new individual without fertilisation. This phenomenon is known as parthenogenesis.

Question. Mention the site where syngamy occurs inamphibians and reptiles respectively.
Answer. In amphibians, syngamy takes place outside the body of the organism in water and in reptiles syngamy takes place inside the body of the female organism. Thus, in amphibians external fertilisation takes place and in reptiles internal fertilisation takes place.

Question. Write the difference between staminate and pistillate.
Answer. In flowering plants, staminate is a unisexual male flower which bears stamens only while pistillate is a female flower which bears pistils only.

Question. Why do algae and fungi shift to sexual mode of reproduction just before the onset of adverse conditions? 
Answer. Organisms, such as fungi and algae, switch to sexual mode of reproduction just before the onset of adverse conditions because sexual reproduction brings variation into the individuals, some of which might help the individuals to adapt to the changed environmental condition

Question. Coconut palm is monoecious, while date palm is dioecious. Why are they so called?
Answer. Coconut palm is monoecious because it bears both male and female flowers on the same plant,whereas date palm is said to be dioecious as it bears male and female flowers on separate plants.

Question. The cell division involved in gamete formation is not of the same type in different organisms. Justify. 
Answer. Gametes in all heterogametic species are of two types, male and female. Gametes are haploid though the parent body from which they arise may be either haploid or diploid. Several organisms belonging to monera, fungi, algae and bryophytes have haploid plant body, but organisms belonging to pteridophytes, gymnosperms, angiosperms and most of the animals including human beings, have diploid parental body. Meiosis will take place, if the diploid body has to produce haploid gametes. In diploid organisms, specialised cells called meiocytes undergo meiosis, at the end only one set of chromosome gets incorporated into each gamete.

Question. A list of three flowering plants is given below.
List - Datepalm, cucurbits and pea.
Which ones out them are
(a) monoecious and
(b) bearing pistillate flowers? 
Answer. (a) Cucurbits and pea plants are monoecious bearing both staminate and pistillate flowers on the same plant.
(b) Date palm, cucurbits and pea, all three bear pistillate flowers.

Question. Name any two organisms and the phenomenon involved where the female gamete undergoes development to form new organisms without fertilisation.
Answer. The phenomenon where female gamete undergoes development to form new organism without fertilisation is called parthenogenesis. It occurs in honeybees and rotifers. 

Please click on below link to download CBSE Class 12 Biology Reproduction in Organisms Worksheet Set A