Long Answer -Class 10 -Science-Biology-Chapter 8 :Heredity and Evolution

Class 10 -Science-Long Answer -Biology-Chapter 8 :Heredity and Evolution

Q1. During evolution some changes may have occurred for a reason but proved to be useful for some other purpose. Cite one such example.

b. Has the evolutionary changes took place all of sudden. Elaborate.

Ans : Evolutions of feathers: Functional Advantage: A change that is useful for one property to start with can become useful later for quite a different function. Feathers, for example, can start out as providing insulation in cold weather. But later, they might become useful for flight. In fact, some dinosaurs had feathers, although they could not fly using the feathers. Birds seem to have later adapted the feathers to flight. This, means that birds are very closely related to reptiles, since dinosaurs were reptiles. Birds have evolved from reptile.

Evolution changes has not took place all of sudden. Evolution takes place in stages, i.e., bit by bit over generations. Even an intermediate stage, such as a rudimentary eye, can be useful to some extent. This might be enough to give a fitness advantage. In fact, the eye seems to be a very popular adaptation. Insects have them, so does an octopus, and so do vertebrates. And the structure of the eye in each of these organisms is different – enough for them to have separate evolutionary origins.

Q2. Define evolution. How does it occur? Describe how fossils provide us evidences in support of evolution.

Ans: Evolution is the formation of more complex organisms from pre-existing simpler organisms over a certain period. Accumulation of variation in genetic material forms the basis of evolutionary processes. Fossils provide a unique view into the history of life by showing the forms and features of life in the past. Fossils tell us how species have changed across long periods of the Earth’s history. Importance of fossils in the evolutionary process:

a. Some invertebrates living on the sea bed died and were buried in the sand.

 b. More sand was accumulated and formed , sandstone under pressure.

c. After millions of years, dinosaurs living in the area died and their bodies were buried in the mud.

d. The mud got compressed into the rock, just above the rock containing earlier invertebrate fossils.

e. Again millions of years later, the bodies of horselike creatures dying in the area were fossilised in the rocks above the earlier rocks.

f. Much later, because of erosion and water flow, some rocks wore out and exposed the horse-like fossils.

Q3. Woman are often blamed for bearing daughters. As a student with knowledge in science how will you explain it to your fellow students that the sex of the child is not determined by mother’s genetic contribution?

 Ans : Sex of the child is not determined by mother’s genetic contribution. The sex is determined by a specific pair of 7 chromosomes called sex-chromosomes. In female, this pair consists of two similar (homologous) chromosomes denoted as XX. Hence, females produce only one type of gametes (Ova/eggs) each having an ‘X’ chromosome.

Whereas male human being has two different types of sex chromosomes i.e., X, Y (heterologous) having different sizes and shapes. Hence male produces two different kinds of gametes (sperms). Half of them have “X’ chromosome and half have ‘Y’ chromosome.

If a sperm with ‘X’ fuses with the ovum, female child is born and if a sperm with ‘Y’ chromosome fuses with the ovum, male child is bom as shown below in the cross. Therefore, the father’s genes is responsible for the determination of the sex of the child. 

Q4. Give differences between: a. Heredity and variations.

 b. Dominant and recessive traits,

c. Natural and artificial selection.

Ans : a. Heredity: It is the transmission of characters from parents to the next generation. Variations: The changes that occur in the DNA of an organism because of mutations, or by chance.

b. Dominant: The trait which is able to express itself even in the presence of contrasting trait. It appears in all the progenies in Fj generation. Recessive: The trait which can express itself only in homozygous condition. It doesn’t appear in Fj generation.

 c. Natural selection: Is the gradual natural process by which any biological traits become either more or less common in a population. Example, red beetle eaten up by crow, leading to increase in the population of green beetle. Artificial selection: It is the artificial mechanism of selecting the breeds having desirable characters to bring about major changes in plant and animals. Example, different vegetables generated from wild variety of cabbage.

Q5. What are fossils? How are they formed? Describe in brief two methods of determining the age of fossils. State any one role of fossils in the study of the process of evolution.

 Ans : Fossils are preserved remains or impressions of prehistoric organisms in the different strata of the earth’s crust.

Fossils are dead remains of animals and plants from remote past.

Fossils are formed when dead organisms are not completely decomposed. The organisms may get trapped in resins of tree, lava of volcanoes or hot mud which when hardens, retains the animal’s parts thus, forming fossils.

Two methods of determining the age of fossils:

a. Relative method:

By estimating the age of the layer of earth’s crust where the fossil is found. Fossils near the surface are recent and those in the deeper layers are more ancient.

 b. Radio-carbon dating method: By detecting the ratios of different isotopes of carbon in the fossils. Fossils help in determining the connecting links between various groups and their origin from their primitive ones, e.g., Archaeoptyrx.