Bihar Board - Class 12 Biology - Chapter 7: Evolution Plants Long Answer Question

Q.1.What are the types of evolution?

A.1. The different types of evolution are:

1. Convergent evolution– It is the process, which evolves independently, under similar selection pressures. For example, flying insects, birds and other flying species have all evolved the ability to fly, but independently of each other.

2. Coevolution evolution–It is the process in which two or more species evolve in tandem by exerting selection pressures on each other. For example, host and parasites, predators and prey,  flowering plants and pollinating insects and mutualistic or symbiotic interactions.

3. Adaptive radiation–It is the process in which a species splits into a number of new forms when a change in the environment makes new resources available or creates new environmental challenges. For example, finches on the Galapagos Islands have developed different shaped beaks to take advantage of the different kinds of food available on different islands.

Q.2.By taking industrial melanism as an example, explain the concept of natural selection by evolution?

Ans: Natural selection is a mechanism through which populations of living creatures adapt to changes to survive. It claims that because of the survival of the fittest, species evolve rapidly. Minimal differences are preserved and transmitted, giving rise to new forms over time.

A collection of moths was discovered in the year 1850. White-winged moths outnumbered dark-winged moths in this collection. The population of dark-winged moths rose with industrialization. The explanation for this is because, throughout the post-industrial period, tree trunks became darkened by industrial smoke, preventing the white-winged moth from surviving. However, it is also known that before industrialization, trees were coated with thick growths of off-white-colored lichens, allowing white-winged moths to thrive while dark-colored moths were easily identified by predators. As a result, it may be argued that nature chooses the best species for the job.

Q.3.What is Biogenetic law? How comparative embryology does provide evidence for evolution?

Ans: It has become evident from embryological studies that there was one developmental pattern. In all organisms, life begins with a unicellular structure. The embryos of fish, frog, turtle, bird, and man resemble one another so closely that it becomes difficult to distinguish them.

Mammalian embryos pass through fish–like, amphibian-like, reptile- like and bird-like stages during the development of an organism (ontogeny), some of the evolutionary steps (phylogeny) are repeated in different groups of organisms. This leads Ernst Haeckel to formulate a famous theory – “Recapitulation Theory / Biogenetic Law which states that “Ontogeny recapitulates phylogeny” The sequence of embryonic development shows striking similarity e.g. appearance of gill cleft and notochord in embryonic development of all vertebrates from fish to man.

Q.4.What are the facts that support Darwin’s theory of Natural selection?

Ans: The following facts that support Darwin’s theory of Natural selection

1. Overproduction: - All organisms tend to multiply at a high rate but all organisms can’t survive.

2. Struggle for Existence: - Because of limitation of space and food all the offspring resulting in overproduction will not survive and they will compete with one another to grow. This develops a struggle for existence not only among individuals of different species but also among the same species.

3. Variations:  No two individuals of the same species are exactly alike even coming out from the same parental stock.

4. Survival of fittest:  The individuals with useful variation will survive during the struggle of existence while those with less fortunate variation would perish.

Q.5. Trace the important events or stages of human development?

Ans: The common ancestor of apes and man is the primate Dryopithecus that lived about 15 million years ago the human evolution is as follows : 

1. Australopithecus:  They are 4ft, with a brain capacity – 500 to 650 cc. They have bipedal locomotion, are omnivorous, and have an erect posture. They used stone weapons for hunting and lived in caves.

2. Homo Erectus:  They showed an increase in brain size. They are good hunters, ate meat, domesticated animals, and discovered fire.

3. Netherlands man:  They were short with heavy brows retreating forehead large jaws and stooped postures They wore clothes, good hunters, and tool makers.

4. Cromagnonman:  They were completely erect and 6 ft tall. He used bones as tools and was a cave dweller. They are excellent tool makers and fine artists.

5. Homo sapiens:  They have a brain capacity of 1450cc. and skull much thicker. His intelligence has enabled him to adapt and control the environment. He started agriculture.

Q.6.What does Hardy Weinberg’s principle state? What are the factors which affect Hardy Weinberg’s equilibrium?

Ans: A. to Hardy Weinberg’s principle, allele frequency in a population is stable and is constant from generation to generation i.e. total gene pool remains constant. This is called genetic equilibrium e.g. In a diploid organism, suppose ‘p’ represents the frequency of allele ‘A’ and ‘q’ represents the frequency of allele ‘q’. 

p2+2pq+q2=1

Factors affecting Hardy – Weinberg Equilibrium : 

(i) Gene flow: When the migration of a section of a population to another place starts, gene frequency changes in both the original as well as in the new population.

(ii) Genetic drift: If by chance a particular allele frequency decreases or increases in a population.

(iii) Mutations: They are sudden changes in the genotype which are carried over a generation. 

(iv) Genetic recombination: Sometimes changes in the frequency of an allele are different in a new sample of the population as they become new species.

(v) Natural selection: Process by which individuals with particular heritable characteristics survive and reproduce at a higher rate than other individuals favored by natural selection tend to be more common in the next generation than in the parent generation.

Q.7. What is biogeny?

Ans. Biogeny or biological evolution is a stage that consists of

i) Formation of nucleic acids by polymerization of nucleotides.

ii) Giant molecules of nucleoproteins tend to be aggregated in various combinations to form large colloidal particles called coacervates.

iii) The development of the plasma membrane resulted in the accumulation of different substances inside coacervates and the occurrence of certain internal reactions leading to the development of the cell.

Q. 8.How does the study of fossils help to understand evolution?

A.8.The fossils are the remains of past organisms preserved in sedimentary rocks.
Paleontology is the study of fossils.

• Rocks form sediments and a cross-section of earth’s crust indicate the arrangement of sediments one over the other during the long history of earth.

• Different aged rock sediments contain fossils of different life forms, who died during the formation of the particular sediment.
  Fossils which were present in a specific area explain the presence of that organism in that area only.

• Some organisms appear similar to modern organisms. They represent extinct organisms like dinosaurs.

• A study of fossils in different sedimentary layers indicates the geological period in which they existed.
  Fossils which are obtained from old rocks are of simple type, while those which were obtained from new rocks are of complex type.

• The study showed that life forms varied over time and certain life forms are restricted to certain geological time scales. Hence, new forms of life have evolved at different times in the history of earth. Thus, palaeontological evidence helps in detailed study of progress of evolution from old to new forms.