Class 10 chapter 8 how do organisms reproduce notes with diagrams
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BIOLOGY NOTES: CLASS X:
CHAPTER:8: HOW DO ORGANISMS REPRODUCE
Q.1 What is reproduction?
Ans. It is the process by which new individuals of the same kind are proudced from
pre-existing organisms (parents).
a.2 What is the significance of reproduction?
Ans. Reproduction is important for ;
a) existence and continuity ofspecies (maintenance of species on the earth).
b) bringing about evolution by transmitting favourable variations of the
organisms from one generation to the next.
c) increasingthe population of a species.
Q.3 What is the basic event in reproduction at the cellular level ?
Ans The basic event in reproduction at the cellular level is the creation ofa DNA copy.
What does Nucleus of a cell contains chromosomes which carry imformation for inheritance of
DNA stand characters from the parents to the offsprings in the form of DNA (deoxyribonucleic
for ? acid). This information is required for synthesis of proteins. During the process of
reproduction a new copy of the existing DNA molecule is created. In addition to it, an
additional cellular apparatus is also formed. These events take place when a parent cell
divides to form new cells. The division could be
a) mitotic division
b) meiotic division
Q.4 How is the type of cell division associated with the type of reproduction?
Ans. Organisms showing asexual reproduction, divide by mitosis. The new individuals
How do (offspring) are exact copies of parents and showverylitle variation which could
asexually be due to faulty DNA copying. The number ofchromosomes is also same as the
reproducing parent.
organisms Organisms showing sexual reproduction have special cells that divide by
divide ? meiosis which give rise to gametes. Gametes have half the number of
chromosomes than the parent cell. The new individuals are formed as a
result of recombination of DNA from two different cells of two different
individuals (combination of gametes. Therefore, they show considerable
variations)
Q.5 What is the significance of variation ?
Ans. () Variations allow organisms to exist in diverse habitats or niches
() During unfavourable conditions, individuals showing variations are able to
survive while the rest of the species may perish.
() Variations are useful for survival of species and formation of new species.
Q.6 Enlist the characteristics of asexual reproduction. Also state the advantages and
disadvantages of this method of reproduction.
Ans. Characteristics of asexual reproduction
(1) Only one parent is involved.
(2) Cells divide by mitosis.
(3) No gametes required.
(4) New individuals are genetically identical to parents.
, (5) hese methods are usually seen in unicellular organisms and some plants and
lower multicellular organisms like hydra and sponges.
Advantages
Methods are simple and fast.
large number of organisms having desired characters can be obtained
gene pool is conserved/helps in maintenance of species.
Disadvantages
Because identical organisms are produced generation after generation, so
defects of parents are also inherited.
Evolutionary change is not possible as no variations are produced.
Q.7 What are the, different methods of asexual reproduction ?
Ans The different methods of asexual reproduction are
Binary
Fission
Multiple
) Budding
IID) Fragmentation
Regeneration
V Spore formation
VI) Vegetative opagation
Fission
Fission means 'to divide'
Itcould be a) Binary Fission
b) Multiple Fission
a)a) Binary Fission
1 The nucleus divides into two.
2 The cytoplasm divides into two.
3 Two daughter organisms are formed. Eg. Amoeba, Leishmania (binary
fission is along a definite orientation).
b) Multiple Fission
Seen in unicellular organisms during unfavourable conditions within the cyst.
1. Nucleus divides into many daughter nuclei.
2. They arrange along the periphery of parent cell.
The cytoplasm divides into corresponding number of bits.
4 Each nucleus is surrounded by cytoplasm.
5. The parental cell burst and many daughter cells are formed; on return of
favourable conditions eg. Plasmodium
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