(a) Define ‘natural selection’.
(b) “Only variations that confer an advantage to an individual organism will survive in a population”. Do you agree with this statement ? Give reason for your answer.
(a) Natural selection is the process of evolution of a species whereby characteristics which help individual organisms to survive and reproduce are passed on to their offspring, and those characteristics which do not help are not passed on.
(b) Yes, only those variations that confer advantage to an individual organism will survive in a population. This will become clear from the following example. Suppose there is a population of red beetles in the green bushes and a colour variation arises during reproduction so that one beetle is now green in colour (instead of red). This variation offers advantage of survival because the green beetle can mix up with green bushes, it cannot be spotted and eaten up by a crow and hence its population will increase. If, however, the variation had produced a blue coloured beetle, then this colour could not offer any survival advantage because blue beetle in green bushes could be easily spotted by a crow and eaten by it.
(a) Explain the terms ‘analogous organs’ and ‘homologous organs’ with examples.
(b) In what way are analogous organs evidence for evolution ?
Can the wing of butterfly and the wing of a bat be considered homologous organs ? Why or why not ?
How is the equal genetic contribution of male and female parents ensured in the progeny? [Delhi]
Name the various tools of tracing evolutionary relationships which have been used for studying human evolution.
What evidence do we have for the origin of life from inanimate matter (lifeless matter) ?
Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species ?
Describe briefly four ways in which individuals with a particular trait may increase in a population. [Foreign]
How are fossils formed? Describe, in brief, two methods of determining the age of fossils. [All India]
(a) State one advantage of variation to a species.
(b) What are sex chromosomes ? How many sex chromosomes are there ? Name them.
(a)What is meant by ‘heredity’ ? What are the units of heredity.
(b) State Mendel’s first law of inheritance.
Match the terms given in column I with those given in column II :
How does the creation of variations in a species promote survival ?
During which stage can the chromosomes be seen clearly? Write the features of the eukaryotic and prokaryotic chromosomes.
Who provided the evidence of DNA as the genetic material? Write the names of the components of the DNA molecule.
Define ‘evolution’. Describe Darwin’s theory of evolution.
With the help of suitable examples explain natural selection. [Foreign]
Name one variation in humans connected with ears.
Which of the two, sperm or ovum, decides the sex of the child ?
Which of the following combinations of sex chromosomes produce a male child : XX or XY ?
(a) If a normal human cell has 46 chromosomes, how many chromosomes will be there in a human (;) sperm cell, and (ii) zygote ?
(b) What sizes of plants are produced if both parents have genes Tt ?
(a) What do you understand by the term ‘variation’ ?
(b) Name two human traits which show variation.
What name is given to the sequence of gradual changes over millions of years in which new species are produced ?
State one characteristic which shows that the birds are very closely related to dinosaurs.
Where did life originate on the earth ?
Name the famous book written by Charles Robert Darwin.
What is meant by acquired and inherited traits ? Explain with one example each.
Will geographical isolation be a major factor in the speciation of a self-pollinating plant species ? Why or why not ?
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better body design’ why or why not ?
How is the equal genetic contribution of male and female parents ensured in the progeny?
How do embryological studies provide evidence for evolution?
Define evolution. Describe the contribution of Lamarck.
How do homologous organs provide evidence in support of evolution?
Explain the terms: (i) Speciation (ii) Natural selection [Delhi]
What are homologous organs? Can the wing of a butterfly and the wing of a bat be regarded as homologous? Why? [All India]
What is meant by the term speciation? List four factors which could lead to speciation. [Delhi]
State the meaning of inherited traits and acquired traits. Which of the two is not passed on to the next generation? Explain with the help of an example.
Which of the processes, sexual reproduction or asexual reproduction, brings about maximum variations in the offsprings ?
Mendel said that the characteristics or traits of organisms are carried from one generation to the next by internal factors which occur in pairs. What is the modern name for these factors ?
What are the chromosomes XY and XX known as ?
A man having blood group O marries a woman having blood group B and they have a daughter. What will be the blood group of the daughter ?
a) Name the scientist who gave the laws of inheritance.
(b) Name an animal in which individuals can change sex. What does this indicate ?
(a) What will you get in the F1 and F2 generations in the following cross ?
Pure tall pea plant x Pure dwarf pea plant
(b) Is it an example of monohybrid cross or dihybrid cross ?
In the F2 generation of a cross, progeny having different traits are produced in the ratio 3:1. State whether it is a monohybrid cross or a dihybrid cross ? Give one example of such a cross.
(a) What is the genotype of dwarf plants which always produced dwarf offspring ?
(b) What is the genotype of tall plants which always produced tall offspring ?
(c) What is the genotype of
Does genetic combination of mother play a significant role in determining the sex of a new born baby ?
(a) Why did Mendel choose pea plants for conducting his experiments on inheritance ?
(b) State Mendel’s second law of inheritance.
(a) What are genes ? Where are they located in our body ?(a) What are genes ? Where are they located in our body ?
(b) What is meant by dominant genes and recessive genes ? Give one example of each.
(c) Explain how, characteristics (or traits) are inherited through genes.
Name the scientist who gave the theory of evolution.