NCERT Solutions for Class 10 Science Chapter 9
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Important Questions with answers
Heredity and Evolution
Difference between Inherited and Acquired traits.
1. The traits which are inherited by the parents (father and mother) by the off springs (progeny) are called inherited traits.
2. These traits cannot be acquired in the life time but are inherited from parent to the progeny.
3. These traits are due to genetic make-up of the progeny.
1. The traits which an individual does not inherit from its parent.
2. These traits are acquired by the individuals due to life time experiences. They are not transmitted
3. These traits are not inherited over generations. Because these traits or experiences are not incorporated in the germ cells (genome or DNA make up) of the individual.
How is the equal genetic contribution of male and female parents ensured in the progeny?
Genetic material in most organisms is present in pair of chromosomes. Gametes in sexually reproducing organisms are formed by the process of meiosis (a type of cell division occurring mainly in reproductive cells for the formation of gametes) during which half of the genetic material goes into each gamete. When the gametes from male and female parents fuse with each other during sexual reproduction, the normal complement is restored. Half of the genetic material comes from female and half from the male. Thus, process of meiosis is necessary to ensure equal genetic contribution of male and female parents through gametes.
Experiences of an individual during its lifetime cannot be passed on to its progeny and cannot direct evolution. Justify this statement giving an example.
Experiences of an individual during its life time are in the somatic cells of the body. That is, in non-reproductive tissues that cannot be passed to the next generation. Thus, they cannot contribute directly in evolution.
For inheritance of traits over generations and involvement in direct evolution, they must be passed to the DNA of the germ cells (reproductive tissues). The characteristics of DNA are passed to the progeny and also can play direct role in evolution.
Differentiate between Homologous Organs and Analogous Organs.
1. Organs with similar basic plan of origin but different in function.
2. Fundamental plan of structure is similar e.g., fore-limb of man, horse and whale.
1. Organs with similar function but different in origin.
2. Fundamental plan of structure is different e.g., wings of butterfly and bat.
More Questions for Exams
What are fossils? State their importance in the study of evolution with the help of a suitable example.
Fossil: A fossil is the record of an organism that lived in the geologic past. Remains, impressions, cast , mould and traces of organisms of past have been preserved in the earth’s crust as fossils. Fossils help us to build up broad historical sequence of biological evolution. For example, the study of fossils of Equidae (horse) family provides reliable records of evolution. The dawn horse-five-toed Echippus, gave rise to Mesohippus which in turn developed into several lines of evolution. The modern Equus (one-toed horse) evolved from Pliohippus.
What is organic evolution?
Evolution can be defined as the changes in the genetic composition of a population with the passage of each generation. Evolution can be defined as the gradual unfolding of the organism from pre-existing organism through change since the beginning of life. The origin of life is very much associated with evolution. Evolution or organic evolution is the study of how complex organisms of today evolved (formed) from the simpler forms of the past.
How are fossils formed? State two methods of determining the age of fossils.
Fossil: Remains, impression, casts or traces of organisms of past geologic ages have been preserved in earth’s crust called fossils.
Determining age of a fossil: There are two methods:
(i) This is relative, the fossils we find closer to the surface are more recent than the fossils we find in deeper layers of earth’s crust.
(ii) The second way of dating fossils is by the ratios of different isotopes of same element in the fossil material.
Define the following: (a) Analogous Organs (b) Evolution (c) Genetic Drift
(a) Analogous: Organs which look similar because they have common use but differ in their structure and components are called analogous organs
(b) Evolution: The gradual unfolding of events by which new organisms evolved from pre-existing organisms through changes since the beginning of life, is said to be evolution.
(c) Genetic Drift: The random change in gene frequency and gene number by chance only, irrespective of its being advantageous or not in a population is called genetic drift. The effect of genetic drift is very small in a large if population is small.