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Q.1 What do you know about reproduction? What are its different types?
Ans Reproduction
The biological process by which living organisms produce young ones of their own kind to maintain their species is known as reproduction
Explanation: Every species of organisms can reproduce new individuals of that species. Different organism has different methods of reproduction. Some methods are quite complex. The process of reproduction differs from all other functions of animals. Reproduction is not necessary for the well being of the individual. It has nothing to do with the survival of the individual but it is very important for the survival of a species or a population Reproduction is the mechanisms that produces new generation and maintains a species.
Types of reproduction
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Reproduction is of two types
(a) Axexual Reproduction
b Sexual Reproduction
(a) A sexual reproduction Asexual reproduction requires only a single parental organism which gives rise to offspring by mitotic cell division, during which the complete adult number of chromosomes is exactly replicated and passes on, so that the offspring arc genetically identical to the parent
Method of asexual reproduction
These are given below
Fission
(i) Sporulation
(ii) Budding
iv) Vegetative Propagation
(iii) Artificial propagation i Parthenogenesis
(vii) Apomixis
(B) Sexual Reproduction
Sexual reproduction usually involves two parents. A fertilized egg is produced through the union of meiotically produced specialized sex cells (egg and sperm) from cach parent. Meiosis or reduction division gives rise to (gametogenesis) in which not only the chromosome number is halved (haploid) but reshuffling of genes lead to new recombination of genes This not only maintains the chromosomes number in a species but also produces genetic vanations. The genetic variation is an important factor in the survival and adaptation of a species ora population
Q. 2. How do plants reproduce asexually?
Aus Asexual reproduction in plants.
By spore formation: Plants reproduce asexually by means of spores. In plants with alteration of generations between a diploid sporophyte and a haploid gametophyte, the meiosis occurs during spore formation (sporogenesis). Spores (n) give rise to haploid gametophytes.
Disadvantages of asexual reproduction
In asexual reproduction, although Increase in number of genetically alike individuals from a parent is very rapid but this is not an adaptive method and may at some stage jeopardise the survival of a species valuable characteristics
Man has favoured this type of reproduction for his own necds. commonly in plants but now tissue culture in plants and cloning in animals are being adapted for producing organisms of valuable characteristics.
without a change in their genetic make up
Disadvantages of Cloning
Cloning has been practiced successfully but ts disadvantage like rapid aging and low resistance to environmental stress and disease are still the limitations in commercial ventures Also it is still not being accepted socially and morally in general
Methods of Asexual Reproduction
In asexual reproduction. layering grafting, budding to an artificial methods.
Q. 4. What is the significance of evolution of pollen tube?
Ans Significance of evolution of pollen tube
(a) The evolution of pollen tube was an important step in land adaptation by seed plants,
(b) Pollen tube acts as a vehicle for sperms for their safe transport to cgg in ovule in hostile land environment.
(c) The evolution of pollen tube is parallel to the evolution of seed
(d) Pollen tube is a tool of success for seed plants
Q. 5. Write a short note on Parthenocarpy?
Ans. Parthenocarpy
In some cases, fruit development proceeds without fertilization and thus no seed formation occurs Such development is called parthenocarpy
Examples: Banana, pineapples and some varieties of oranges and grapes show parthenocarpy.
Te is due to hormonal imbalance, usually high auxin levels occur in these ovaries. Benefits Parthenocarpy is some time artificially induced for commercial purposes, by adding auxins as in tomato, peepers etc
Q.9. What is seed dormancy? What is its importance?
And. Seed Dormancy
"It is the special condition of rest, which enables an embryo to survive the Song periods of unfavourable environmental conditions like water shortage, or low temperature"
Advantages
During seed dormancy, the embryo ceases or limits its growth. This is of great survival importance to plants in that it prevents the dormant seed from germinating in response to conditions like a warm spell in winter. Which is temporary favourable
Breakdown of dormancy
Germination or resumption of normal growth by a dormant embryo requires certain, very precise combinations of environmental cues, to avoid any accidental stimulus which may prove fatal later on.
10. Write a note on fruit set and fruit ripening?
Ans Fruit set and fruit ripening
Germinating pollen grain is not only an important structure for safe transfer of gametes and insurance for fertilization but also a rich source of auxins as well as commonly stimulating the tissues of the style and ovary to produce more auxin. This auxin is necessary for fruit set", ie. retention of the ovary, which becomes the fruit after fertilization. Without it abscission of flowers normally occurs leading to low fruit: yields
Fruit Ripening
After fertilization, the ovary and the npe seeds continue to produce auxins which stimulate fruit development. Developing seeds are not only a nich source of auxins and gibberellins, but also on cytokinins These growth substances are mainly associated with development of the embryo and accumulation of food reserves in the seed and some times in the pericarp (fruit wall).
Fruit opening is often accompanied by a burst respiratory activity called the climacteric. This is associated with ethane production, which helps in ripening of the fruit
Q. 11. Define photoperiodism. Explain with examples
Ans. Photoperiodism
"The response of plants to produce flower to relative length of day and night is called photoperiodism"
Apart from photosynthesis and phototropic responses, another very important way in which light exerts its effect on plants is through vanations in day length called photoperiod.
Effect of photoperiod and temperature
In plants, photoperiod and temperature affect
(1) flowering,
(ii) fruit and seed production,
(iii) bud and seed dormancy,
(iv)bud and seed dormancy,
v) leaf fall and germination, Photoperiod affects flowering.
when shoot meristems starts producing floral buds instead of leaves and lateral buds Photoperiodism in tobacco plants
The phenomenon of photoperiodism was first of all observed in 1920 by Garner and Allard. They studied that tobacco plant produces flowers only after exposure to a series of short days Tobacco plant naturally produces flowers under same conditions, in autumn, but flowering could induced artificially to short days exposing. With further studies they ere able to classify flowering plants in long-day plants, which require long days for flowering and day-neutral plants that lower without being influenced by photoperiod
Length of Dark Period is critical Later on, further studies indicated that it is really the length of the dark period which is critical. Thus short-day plants are really long-night plants. If they are grown in shon days, but the long night is interrupted by a short light period, flowening is presented. Long-day plants will flower in short days if the long night period is interrupted
Effect of quality of Bight on phototropism
Further experimentation also revealed that quantity of light is also influenced by the quality of light.
Cocklebur a short day plant, will not flower if its long night is interrupted but experiments revealed that red light was effective in preventing flowering but fol-reel light reversed the effect of red light. It was also demonstrated that the last light treatment always determines the response. This response to light intensity and quality leads to the discovery of a blue light sensitive protein pigments, the phytochromes.
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