CBSE Textbook of Biology XII Solution :
CHAPTER 1
REPRODUCTION IN ORGANISMS
SYLLABUS
Reproduction
By: Mr CBSE Solition,
Reproduction in organisms: Reproduction, a characteristic feature of all organisms for continuation of species; Asexual reproduction Modes of reproduction-Asexual and sexual reproduction; Modes-Binary fission, sporulation, budding, gemmule, fragmentation; vegetative propagation in plants.
1.1 Life Span
1. Important facts about life span
2. Main stages during life span
1.2 Reproduction
1.3 .Asexual Reproduction
1. Fission (Binary andMultiple)
2. Budding
3. Spore formation
4. Fragmentation
5. Vegetative propagation
1.4.Vegetative Propagation
1. Characteristics
2. Natural methods of vegetative propagation
3. Artificial methods of vegetative propagation
4. Advantages and disadvantages of vegetative propagation
1.5 Sexual Reproduction
◆Features common to all sexually - reproducing organisms
1.6.Events in Sexual Reproduction
1. Pre-fertilisation events
2. Fertilisation (External and Internal)
3. Post-fertilisation events (zygote and embryogenesis)
1.7 Special Modes of Reproduction
1.8 Some Deviations in Sexually Reproducing Animals
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A Textbook of Biology XII
1.1.LIFE SPAN
Life span may be defined as a period from birth to natural death of an organism.
Each organism has a certain length of time for which it will survive. Even if an organism does not meet an accident, does not suffer from a disease, does not fall prey to predators, death is a certainty, it still comes as a last event of ageing. Life span is different for all the existing species.
1. Important facts about life span
Observed and examined life spans of a few common plants and animals are represented in Table 1.1. You will notice some of the following interesting facts about life spans. (1) Life span can be as short as a few days or as long as several thousand years.
◆ Mayfly - 24 hours or 1 day
◆ Banyan tree 200-300 years
◆ Sequoia - 3000-4000 years
Life span of most of the living organisms are between the two extremes- animals have life spans ranging from a few days to 100 years while plants have life most
spans ranging from a few months to 2000-3000 years.
Whatever be the life span, death of every individual is certainty, i.e., no individual is immortal, except single-celled organisms like Amoeba and Paramecium. These protozoans keep dividing by binary fission producing two organisms which grow further and again divide into two by binary fission and the process goes on.
(ii) Life spans are not correlated with the sizes of organisms.
Mango and peepal trees have almost the same size but differ markedly in their life spans.
Mango tree - 100-200 years
Peepal tree - 2000-3000 years
Crow and eagle have almost the same sizes but their life spans are markedly different.
Crow - 15 years app.
Eagle- 90 years app.
(iii) The plants generally have greater life spans as compared to animals.
Some perennial plants (remember, annual plants live for one year, biennials for two years and perennials for many years) like Sequoia, the Redwood tree, may live for more than 3,000 years.
Table 1.1: Approximate life spans of some organisms
Animals App life span
1. Mayfly 1 day
2. Cicada 1 day
3. Butterfly 1-2 weeks
4. Fruit fly 30 days
5. Rat 4 years
6. Rabbit 13 years
7. Crow 15 years
8. Cow 20-25 years
9. Monkey 26 years
10.Dog 14-20 years
11. Cat 35-40 years
12. Horse 60 years
13. Crocodile 60 years
14. Elephant 60-90 years
15. Eagle 90 years
16. Man 100 years
17.Parrot. 140 years
18. Tortoise 100-250 years
Reproduction in Organisms
Plants App. life span
1. Rice plant 3-4 months
2. Wheat plant 5 months
3. Rose bush 5-7 years
4. Banana tree 25 years
5. Banyan tree 200 years
6. White Oak tree 500 years
7. Peepal 2000-3000 years
8. Sequoia 3000-4000 years
(Redwood tree)
