Ch. 8 How do Organisms Reproduce?

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Q. Why is reproduction important in animals?

A. Reproduction is not vital for survival but it is necessary for maintaing the continuity of species.A basic event in reproduction is copying of DNA (source of hereditary information).

Q. What is Niche?

A. These are well defined places in the ecosystem filled in by population of organisms using their ability to reproduce.

Q. What are the different types of asexual reproduction?

A. i) Fission-Binary & Multiple
ii) Budding
iii) Fragmentation
iv) Regeneration
v) Vegetative Propogation
vi) Spore formation

Q. What is regeneration? 

A. It is the ability of many fully differentiated organisms to give rise to new individual organisms from their body parts.

Q. Differentiate between Fragmentation and Regeneration.

A. 
Fragmentation
Regeneration
Occurs in organisms with relatively simple body design Occurs in fully differentiated, relatively complex organisms
Does not involve any organised sequence of events Takes place in an organised sequence referred to as development
There are no specialised cells involved
Involves specialised cells. The specialised cells proliferate (rapidly divide), making a large number of cells and from this mass of undifferentiated cells, different cells differentiate to form cell types and tissues.

Q. What is vegetative propogation?

A. It is a method where new plants develop from plant parts like roots, stems and leaves under appropriate conditions.

Q. What is Grafting?

A. A cut stem of one plant, known as scion is taken and firmly attached to the root stock of another plant in such a manner, that the cambium of both is in contact with each other.

Q. Differentiate between Binary and Multiple Fission. 

A. 
Binary Fission
Multiple Fission
Nucleus divides into two parts Nucleus divides into many parts
Gives rise to two individuals Gives rise to many individuals
Cytoplasm divides after each nuclear division.
Eg. Amoeba		 Cytoplasm does not divide after every nuclear division. Eg. Plasmodium

Q. Differentiate between Mitosis and Meiosis.

A. 
Mitosis
Meiosis
Number of Chromosome remains the same Number of Chromosome gets halved
2 cells are formed 4 cells are formed

Q. What is the information source for making proteins in a cell and what will happen if this information is changed?

A. DNA is the information source for making proteins and if it is changed, it results in variation. Different proteins will be made leading to altered body design.

Q. What event accompanies DNA copying and why?

A. DNA copying is accompanied by the creation of an additional cellular apparatus, and then the DNA copies separate, each with its own cellular apparatus. Thus a cell divides. This is because when cell is copied, additional DNA is carried which becomes difficult for the  cell to carry leading to cell division.

Q. The two daughter cells formed at the cell division, are they similar or identical?

A. No bio- chemical reaction is absolutely reliable. Thus, it is only expected that the process of copying the DNA will have some variations each time. As a result, the DNA copies generated will be similar, but may be identical to the original. Some of these variations may be so drastic that the new DNA copy cant work with cellular apparatus it inherits.

Q. How can variations be drastic or beneficial to organisms?

A. Some variations can be so drastic that new DNA copy cannot work with the cellular apparatus it inherits. Such a newborn cell will simply die. On the other hand, there could still be many other variations in the DNA copies that would not lead to such a drastic outcome.

Q. Reproduction is linked to stability of population of species. Justify.

A. The consistency of DNA copying during reproduction is important for the maintenance of body design features that allow the organism to use that particular niche. Therefore, reproduction is linked to the stability of population of species.

Q. Why cant all multicellular organisms reproduce through fragmentation? What is the alternative strategy used by them?

A. In multicellular organisms with relatively simple body organisation, simple reproductive methods can still work.  Though, tis is not true for all multicellular organisms. They cannot simply divide cell by cell. The reason is that many multicellular organisms have specialised cells which are organised into tissues and tissues are organised into organs that then have to be placec at definite positions in the body. In such a cell division, cell by cell division would be impractical. In such cases, the basic strategy used is that different cell types perform different specialised functions. Here, a single cell type in the organism is capable of growing, proliferating and making other cell types under the right circumstances.

Q. Differentiate between Asexual Reproduction and Sexual Reproduction.

A. 
Asexual Reproduction Sexual Reproduction
Only one parent is involved Two parents are involved
Does not involve fusion of gametes Involves fusion of male and female gametes
Involves only miotic division Involves meiosis during gamete formation
Does not have high variation since they are genetically similar to their parents Involves greater variation since they are genetically different from their parents

Q. Enlist main events in sexual reproduction.

A. i) Formation of gametes and gamete transfer

ii) Fertilisation

iii) Embryo development

Q. How is pollination achieved?

A. Pollination is achieved through pollinating agents.
Pollinating Agents
Biotic Abiotic
Insects
Birds
Bats		 Wind
Water


Q. Explain types of Pollination.

A. 
Types of Pollination
Self Pollination
Cross-Pollination
Transfer of pollen grains from an anther of a flower to the stigma of the same flower Transfer of pollen grains from an anther of a flower to the stigma of another flower present on the same plant or another plant of the same species

Q. Why is regeneration not the same as reproduction?

A. It is not the same as reproduction, as most organisms would not depend on being cut up to be able to reproduce, whereas regeneration is when the individual is somehow cut up into many pieces and many of these grow into separate individuals.

Q. How can the following plants be propagated vegetatively?

A.  Rose- Cutting and Grafting
      Jasmine- Cutting
      Orange- Layering
      Grapes- Grafting
      Banana- Rhizome
      Sugarcane- Grafting, Cutting
      Strawberry- Layering (Runners)

Q. Illustrate budding in yeast and hydra.

A. Hydra- In hydra, a bud develops as an outgrowth due to repeated cell division at one specific site.

These buds develop into tiny individuals and when fully mature, these detach from the parent body and become new independent individuals.


Yeast- In yeast, a small protuberance is produced on the parent cell that grows to a full size and forms a bud.

The nucleus of the parent cell splits into a daughter nucleus and migrates into the new cell.

The bud detaches from the mother's body by forming a constriction at the base.

Q. Give the steps of fertilisation in plants.

A. Pollen grain lands on the stigma and germinate to form the pollen tube.


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