PHOTOSYNTHESIS FOR CLASS 11

Question of plant reproduction

HAPPY DIWALI TO ALL LEARNERS

Board Based Questions from heredity and Evolution

Q. Why did Mendel chosen pea plant for his experiments?

Answer:   Mendel chose pea plant for his experiments because it is:

(a) Easy to grow (b) Short lifespan (c) Easily distinguishable characters (d) Larger size of flower  (e) Self-pollinated.


Q. What is heredity?

Ans:- Heredity refers to the transmission of characters or traits from the parents to their offspring.

Q. What do you understand by evolution?

Ans:-Evolution is the sequence of gradual changes which takes place in the primitive organisms over million of years in which new species are produced.

Q. What is  a gene?

Ans:- Gene is a small segment of DNA on a chromosome occupying specific position in which is a hereditary determinant or unit of a biological function.

Q. With the help of suitable examples, explain why certain traits cannot be passed on to the next generation. What are such traits called? 

Solution:      The traits which are acquired during the lifetime of a person are called acquired traits. These traits involve changes in non reproductive cells (somatic cells) which are not transferred to germ cells. So, these traits cannot be passed on to the next generation. For example: Learning skills like swimming, dancing, cooking, body building, etc are acquired traits and cannot be passed on to the next generation.

Q. "A trait may be inherited, but may not be expressed." Justify this statement with the help of a suitable example.

Ans: When a tall plant was crossed with a short plant, the first (F1) generation plants were all tall. But when the F1 generation plants were crossed, the second (F2) generation plants were not all tall: there were both tall and short plants. 

 This shows that the F1 plants had inherited their trait from the short plants but did not express it in the presence of the tallness, and had transferred it to the next generation.

Q. 'It is a matter of chance whether a couple will give birth to a male child or a female child." Justify this statement with the help of a flow chart showing the fusion of sex chromosomes.

 Ans: Sex is determined at the time of fertilization and the two sexes are produced in approximately equal numbers. A human male has XY sex-chromosomes and produces two types of sperms (heterogametic). Either with X-chromosome or with Y-chromosome.

A human female has XX sex-chromosomes and produce ova of one type (homogametic) all with X-chromosomes.

Parents Male                                   Female

Gametes         X Y                                X

Progeny          XX                                XY

                     Female (50%)           Male (50%)
Q.What are homologous organs? How do they provide evidence in support of evolution?

Ans:- Homologous organs are those organs which have the same basic structure and developmental origin but have different functions and appearance.

Homologous organs support evolution:

(i) The similarities of structure and origin of organs indicate that all vertebrates had common ancestors. For example, the forelimbs of humans, whale and bat show structural similarities but functional dissimilarities. Forelimbs in humans used for grasping or holding the things, in whale for swimming and in bat for flying.
(ii) All the organs and systems of the vertebrates show fundamental similarities i.e. homology, which indicate towards common ancestry. Thus, homologous point that organic evolution has taken place.  

Q. What is a retrovirus?

Ans:- A virus having RNA (Ribonucleic acid) as genetic (heredity) material is called Retrovirus. For example, Human immunodeficiency virus (HIV) is a retrovirus.

Q. Who provided the evidence of DNA as a genetic material? Write the names of components of DNA?

Ans:- Griffith, Avery , McLeod and McCarty established that DNA is the genetic material.
Components of DNA: A DNA molecule consists of two polynucleotide chains. Each nucleotide consists of (a) nitrogenous base (Adenine/guanine/Thymine or Cytosine) ,a pentose sugar(deoxyribose) and a phosphate group.

Q.How many types of nitrogenous bases are present in DNA?Name them.

6
Ans:-In DNA two types of nitrogenous bases are present. These are 
(i)PURINES which are adenine and guanine (ii)PYRIMIDINES which are Thymine and cytosine.


Q.How do embryological studies provide evidence for evolution?

Ans:- The similarities in embryonic development reinforce the idea of evolution from common ancestors. The sequence of embryonic development in different vertebrates shows striking similarities. Notochord and gill clefts appear in the embryos of all vertebrates.

Q.Define evolution. And Describe the contribution of Lamarck?

Ans:- Evolution is the sequence of gradual changes which takes place in the primitive organisms over millions of years in which new species are produced.

Contribution of Lamarck:
(i) Lamarck proposed a theory called “The Theory of inheritance of Acquired Characters” to explain the origin and evolution of species.
(ii) The theory was explained in his book ‘Philosophic Zoologique.

Q. What are transgenic organisms? Which property of DNA is used as a tool in genetic engineering?

Ans:-The organisms that contain a segment of foreign DNA are known as transgenic organisms.The complimentary property of the nucleotides of DNA.is the most powerful tool in genetic engineering.

Q.Name the two homologous structures in vertebrates. Why are they so called? How do such organs help in understanding an evolutionary relationship?

Ans:  Limbs of birds, reptiles and humans are all the examples of homologous structures in the vertebrates.  They are called so as the basic structure of the limbs is similar. Though it has been modified to perform different functions in various vertebrates.

These are organs which are inherited from a common ancestor. Such a homologous characteristic helps to identify an evolutionary relationship between apparently different species.

Q. What are the different ways in which individuals with a particular trait may increase in a population? 

Ans : The different ways in which individuals with a particular trait may increase in a population, are :

Genetic drift ; Geographical isolation ; Natural selection and Artificial selection

Q.  Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics? 

Ans : If they all die out became extinct, tiger gene will be lost forever and the coming generation will not be able to see tiger at all.

Q. Will geographical isolation be a major factor in the speciation of a self-pollination plant species? Why or why not?

Ans: No, In asexually reproducing organisms pass on the parent DNA to offspring that leaves no chance of speciation

Q. What is the evolutionary significance of the fossil archaeopteryx?

Ans: Archaeopteryx serves as a connecting link between birds and reptiles. It is the fossil evidence to show that birds have evolved from reptiles.

Q. Give the evidence that bird have been evolved from reptile?

Ans: They both lay eggs, have scales on feet and soft anatomy such as musculature, brain, heart.  

Q. What are vestigial organs? Name any two vestigial organs in man and name organ which is vestigial in man but not in birds.
Ans: Organs that are well developed and functional in many organisms and are very much reduced and functionless in other organisms is called vestigial organs. Nictitating membrane in the eye and vermiform appendix attached to the intestine are two such examples of vestigial organs in man.
Nictitating membrane provides protection of eyes in birds, but in humans it remains as a small fold of skin.

Q.Variation is useful for the survival of species overtime but the variants have unequal chances of survival. Explain the statement.

Ans: If organisms are suited to a particular environment there is chances of survival but  drastic changes in environment could wipe out that population
(i) If some variations are there, few individuals might survive  
(ii) Depending on whether the variations are useful to the change in the environment some variants survive whereas others do not

Q. a) Why do we see different variety of organisms around us?  b) In which type of reproduction   
(i) Off springs are identical? (ii) Exact similar offspring‘s are not produced?    

Ans: (a) Due to inaccuracies in DNA copying (i) asexual (ii)sexual reproduction

Q. How do species of two isolated sub populations become two different species?

Ans: Together, the processes of genetic drift and natural selection will result in these two isolated sub-populations and thus species of two isolated sub populations become two different species

Q. How does sexual reproduction leads to similarities as well as variations ? 

Ans: Similarities and variations are dependent on the type of allele combination an offspring will get from their parents. If a child get dominant alleles from  father then he will look quite similar to his  father and quit different from his mother. If he got a combination of dominant alleles from both the parents then he will be quite different from both the parents.  

Q.All dead organisms do not leave their fossil records, but in some cases their fossils are formed. How do these fossils records form a direct evidence of past happenings?

Ans:  There are two components to this estimation. One is relative. If we dig into the earth and start finding fossils, it is reasonable to suppose that the fossils we find closer to the surface are more recent than the fossils we find in deeper layers. The second way of dating fossils is by detecting the ratios of different isotopes of the same element in the fossil material.

Q. Evolution is a process in which simple life forms change into complex life forms by gradual changes. But, there is a difference between chemical and organic evolution. Differentiate by giving three points.

Ans: The formation of organic molecules from inorganic molecules is known as chemical evolution. Around four billion years ago, earth’s atmosphere consisted of chemicals such as water vapour, methane, ammonia, hydrogen,  Sunlight, heat from volcanoes and lightning caused these molecules to combine in the shallow seas and produce various organic molecules such as sugars. Slowly, these organic molecules combined to form big molecules which include proteins and simple RNA and DNA molecules.
The enzymes, proteins, RNA and DNA once formed constituted a self-replicating system enclosed in a selectively
Permeable, protective lipid sphere which further evolved into membrane bound proto cells and finally into living
Cells. This is known as organic evolution. It includes the changes from the simplest unicellular forms of life to the most complex multicellular forms.

Q. There are a number of ways by which the genes enter a population. Explain briefly the three ways
Ans: Gene flow refers to the transfer of alleles from one population to another as a result of interbreeding between members of two populations.
Mutation: are the sudden changes that take place in the DNA sequence of an organism.
Migration: Migration will change gene frequencies by bringing in more copies of an allele already in the population or by bringing in a new allele that has arisen by mutation.  

Q. why more complex organisms cannot give rise to new individuals through regeneration? 
Ans:   Complex organisms have highly differentiated tissues and organs. In this case regeneration of complex individual organism is difficult from a small piece. 

Q.Why are the small number of surviving tigers a cause of worry from the point of view of genetics?
Ans: Decrease in population; decreases the chances of recombination and variation which impacts the gene pool. As a result, there is a loss of genes. Thus they become extinctQ: shibu's father is a wrestler and has a robust body. His son was thin

(a) Is it true that a wrestles son should also have heavy muscles

(b) What type of character is it - acquired or inherited?

(c) If you are shibu's friend how will you convinced him that he is normal

​

Answer: (a) It is not true that wrestlers son also have heavy muscles.

(b) Having heavy muscles is an acquired trait. Heavy muscles can be made by regular exercising.

(c) As Shibu's friend can convince him by telling him that traits like heavy muscles are not inherited but are acquired in the lifetime. So he can start exercising on a regular basis to be like his father. If he is not as strong as his father, there is also a possibility that he may have more traits from her mother .

Board based question from reproduction

Reproduction for class 10 solved questions from previous year board Exam 

1. Give and advantage of vegetative propagation. 
Ans: Propagation of plants which have lost the capacity to produce seeds
          Plants raised by this method can bear fruits earlier
          Produce genetically similar plants

2. Variation is useful for the survival of species over time. But the variants have unequal chances of survival. Explain this statements 

Ans: - If organisms are suited to a particular niche, drastic changes in the niche could wipe out that population
=>  If some variations are there, few individuals might survive
=> Depending on whether the variations are useful to the change in the environment some variants survive whereas others do not

3. Explain happens when :
(a) Testosterone is released in males              (b) Pollen grain falls on the stigma of the flower. 
(c) Egg fuses with sperm cell.                            (d) Planaria is cut into many pieces.
(e) Buds are formed on the notches of the Bryophyllum leaf.     

Ans: (a) Secondary sexual characters                                        (b) Pollen tube formed for fertilization
         (c) Fertilization                                                                          (d) Each part grows into a new organism
        (e) Fall on the soil and forms new plants              

4. Some flowers contain either stamens or carpel’s whereas some flowers contain both categorise the two types of flowers and give one example of each. 

 Ans: Either stamens/carpels – Unisexual,             e.g. – papaya/watermelon
         Both – Bisexual,       e.g. – Hibiscus/mustard               

5. Compare the processes of binary fission and multiple fission using diagrams. 

 Ans: Binary fission-division into two equal halves
         Multiple fission – division into many daughter cells                            Diagram [yourself]

6. Differentiate between the following :
(a) Pollen tube and Style                                                      (b) Fission in Amoeba and Plasmodium 
(c) Fragmentation and Regeneration                               (d) Bud of Hydra and bud of Bryophyllum 
(e) Vegetative propagation and Spore formation 

Ans: (a) Pollen tube – Carries male germs cell
               Style – Carries pollen tube
(b) Fission in Amoeba – Binary fission
      Plasmodium – Multiple fission
(c) Fragmentation – Simple multicellular organisms
     Regeneration – Complex multicellular organisms
(d) Budding
     Vegetative propagation
(e) Vegetative propagation – Formation of new plants from leaves, root and stem
      Spore formation – reproduction by spores

7. What is the effect of DNA copying which is not perfectly accurate on the reproduction process?

Ans. During the process of DNA copying, some mutations are produced which give rise to useful, harmful or neutral variations in the offspring.

8. Why do testes lie outside the abdominal cavity?

Ans. Testes are present inside a fibrous covering called scrotum or scrotal sac. The scrotum helps in maintaining 1–3 degree Centigrade lower temperature than the body temperature. This is necessary for the development of sperms.

9. The organisms formed by asexual reproduction are considered as clones. Why?

Ans:  This is because In asexual reproduction, the young ones formed are genetically identical to the parents.

 10. Draw the diagrams to explain the process of regeneration in Planaria. Name any other organism in which a similar process occur. 

Ans:  Regeneration in Planaria — Planaria have the ability to give rise to new individuals from their body parts. This process is called regeneration. If the body of Planaria is somehow cut or broken up into many pieces, each piece grows into a complete organism                    .
Figure 8.3 Regeneration in Planaria NCERT
Other organism in which a similar process occur are: Hydra, Lizard etc

 11. List any four method of contraception used by humans? How does their use have direct effect on the health and prosperity of a family?

Ans:  Following are the four method of contraception used by humans :- 
Barriers: Here a mechanical barrier is created so that the sperms cannot penetrate the egg. It Include condoms, diaphragms, cervical caps and vaults.
Intra uterine devices (IUDs) : They release hormones to cause phagocytosis of sperms, or they release copper ions to decrease sperm motility.
Oral contraceptive pills: They contain hormones—either progesterone or progesterone- oestrogen combination, which causes hormonal imbalance of the body.

Surgical methods : Include vasectomy (removal of a part of the vas deferens) in males and tubectomy (removal of a part of the fallopian tubes) in females.

 Use of these contraceptive devices helps in preventing unwanted pregnancies. They can prevent the chances of frequent pregnancies which otherwise affect the health of a mother. They help in family planning by controlling the number of children in a family. So, that proper care is provided to the children and that also reduces the chances of poverty.

Use of contraceptive devices also reduces the chances of getting sexually transmitted diseases such As AIDS. In this way, the birth control methods play important roles in the health and prosperity of the family.

 12. Answer these Questions

(a) Give one examples of each unisexual and bisexual flower
(b) Mention the changes a flower under goes after fertilization
(c) How does the amount of DNA remain constant though each new generation is combination of DNA copes of two individuals?

Ans: (a) The flowers in which either the male or the female reproducative organs are present only, are called unisexual flowers. They are called incomplete flowers. They undergo cross-pollination in order to reproduce.
Example - Papaya, Watermelon, Corn, etc.

The flowers in which both the male and female reproductive organs are present, are known as complete or bisexual flowers. They are capable of self-pollination.
Example - Mustard, rose, lily, hibiscus, etc.

(b) After fertilization the petals,stamen and carpel fall off and only sepal,ovary and ovule remain. This is because after fertilization the ovary develops into fruit and protect the seeds, these seeds are actually fertilized ovule. But, carpels and petals do not have any role after fertilization so they fall off. After fertilization, the outer layers of the ovule become impervious, hard and function as a seed coat. An ovule with an embryo inside is called a  seed  .

(c) In sexual reproduction the gametes usually contain half number of chromosomes compared to the chrome gametes and some numbers present in the body cells. These haploid gametes when fuse produce a new cell with double number of chromosomes than the gametes and same as the body cells. In this way organisms restrict doubling of DNA and maintain the chromosome number.

13. Answer these Questions        
(a) Name the reproductive part of humane female reproductive system:
(i) That produce egg
(ii) where fussion of egg and sperm takes place
(iii) where zygot get implanted

(b) Describe what happen to the zygote after it get implanted

Ans: (a)    (i) ovaries           (ii) oviduct[Fallopian tube]       (iii) In the lining of the uterus
(b) The fertilized egg, the zygote, gets implanted in the lining of the uterus, and starts dividing . The lining thickens and is richly supplied with blood to nourish the growing embryo

14. Q. Name the information sources making protein in the cell? What is the basic event in reproduction?

 Ans: The information source for making proteins in the cells: gene specific for that protein
Basic event of reproduction: replication of DNA

 15. (a)Write the name of those parts of a flower which serve the same functional as the following do in the animals:
(i) Testis (ii) sperm (iii) ovary (iv) egg   (b) State the function of flower in the flowering plants 

Ans:  (a) (i) Testis : Anther
In animals, testis is the male reproductive organ that produces sperms. Similarly, in plants, anther is the male reproductive part that produces pollen grains.
(ii) Sperm : Pollen grains
Sperm is a male gamete in animals. In plants, pollens are male gametes. The generative cell of pollen divides to produce two nuclei called male gametes.

(iii) Ovary : Ovary
In animals, ovary is the female reproductive organ that produces eggs. Similarly, in plants, ovary is the female reproductive organ that contains ovules.

(iv) Egg : Ova/Ovum
Eggs in animals are also called ova. In plants, eggs are present inside the female gametophyte, i.e., ovule.

(b) The function of flowers in flowering plants is to assist in sexual reproduction. Flower is the most important part in angiosperms because the reproductive parts are located inside it.

 16. What is the main difference between sperms and eggs of humans? Write the importance of this difference. 

Ans:
Difference between sperms and eggs of humans:
The major genetic differences lies in the difference in sex chromosome of sperm (male gamete) and egg( female gamete). Sperm has Y chromosome as sex chromosome, while egg has X chromosome as sex chromosome. There is a marked difference in  size, shape, metabolic activity, cytoplasm content, motility, etc in the sperms and eggs.


Human eggs are much larger than sperms and are highly metabolically active cells. They contain more amount of cytoplasm.

Importance of the difference:

The difference in the sperm and egg cells maintains the continuity of the species generation after generation by the process of reproduction.

 17. How is the process of regeneration in Planariadifferent from reproduction? 

Ans: Different from asexual reproduction:

The reproduction in planaria is different from the asexual reproduction because in the asexual reproduction, a complete individual is formed while in planariathe body parts are regenerated.

Different from sexual reproduction:

 It is entirely different from the sexual reproduction because in sexual reproduction male and female gamete fuses and zygote is formed.

18. What is placenta? State its function in human female. 

Ans: Placenta is a special umbilical cord develops in the fourth week which establishes an intimate connection between the foetal membrane and he uterine wall.

Function of Placenta:
The exchange of materials between the mother’s blood and the blood of foetus takes place through placenta. It serves as a nutritive, respiratory and excretory organ of the foetus.

19.Name the part where    
(i) eggs develop.   (ii) fertilisation take place.   (iii) fertilised egg gets implanted.
(b) Describe, in brief, the changes the uterus undergoes.  
(i) to receive the zygote.   (ii) if zygote is not formed.

Ans:
(a) (i) The development of egg occurs in the ovary.
(ii) Fertilisation takes place in the fallopian tubes.
(iii) The fertilised egg gets implanted in the uterus.
 (b) (i) The uterus prepares itself every month to receive a fertilised egg/zygote. The inner uterus lining (endometrium) becomes thick and is supplied with blood to nourish the embryo.
(ii) If the egg is not fertilised, then the uterus lining is not required. Hence, it breaks down and gets released in the form of blood and mucous through the vagina. This process lasts for 2–8 days. This cycle occurs every month and is known as menstruation.

20. (a) What is pollination? State its significance.
(b) How does fertilisation occur in flowers? Name the parts of the flower that develop into (i) seed, and (ii) fruit after fertilisation.
Ans:
(a) The transfer of pollen grains from the anther to the stigma of a flower is known as pollination. It is of two types:
(i) Self-pollination
It is the transfer of pollen grains from the anther to the stigma of the same flower or another flower on the same plant.
(ii) Cross-pollination
It is the transfer of pollen grains from the anther to the stigma of the flower present on two different plants.

Significance of pollination:
(i) It is a significant event because it precedes fertilisation.
(ii) It brings the male and female gametes closer for the process of fertilisation.
(iii) Cross-pollination introduces variations in plants because of the mixing of different genes. These variations further increase the adaptability of plants towards the environment or surroundings.

(b) Double fertilisation is a characteristic feature of flowering plants. In this process, out of the two sperm nuclei, one sperm nucleus fuses with the egg nucleus to form an embryo (process is called syngamy) and another fuses with the polar nucleus to form an endosperm (process is called triple fusion). Because two kinds of fusion—syngamy and triple fusion—take place, the process is known as double fertilisation.
After fertilisation,
(i) the ovule develops into a seed
(ii) the ovary develops into a fruit

21.Q. (a) Name the following parts:
(i) Part that produces pollen grain                  (ii) Part that transfers male gametes to the female gametes
(iii) Part that is sticky to trap the pollen grain     (iv) Part the develops into a fruit
(b) Differentiate between pollination and fertilization.

Ans: (a) (i) Part that produces pollen grain: anther              (ii) Part that transfers male gamete to the female gamete: style
(iii) sticky part to trap pollen grain: stigma                               (iv) Part that develops into fruit: Ovary     
(b) Pollination
1. Pollination is the process of transfer of pollen grains from anther to the stigma of the same or different flower.
2. It takes place with the help of pollinations like wind, water insects etc.
Fertilization
1. Fertilization is the process of fusion of male gamete with the female gamete.
2. It takes place by the growth of pollen tube towards the ovary.

 22. Q. a) Explain the role of placenta in the development of human embryo.
(b) Give example of two bacterial and two viral sexually transmitted diseases. Name the most effective contraceptive which prevents spread of such disease.      
Ans: (a) Placenta is a temporary organ which is formed from the tissues derived from the foetus and the mother. The placenta contains villi on the embryo’s side of tissue and blood spaces on the mother side of tissue. The blood space surrounds the villi. The villi provides a large surface area for glucose and oxygen to pass from the mother to the embryo. Thus, through placenta, the maternal blood passes food (glucose, amino acids, lipids and proteins), oxygen, hormones, water, antibodies to the foetal blood and the foetal metabolic wastes (carbon dioxide, urea) pass into the maternal blood.

(b) BACTERIAL INFECTION – which includes gonorrhoea (inflammation of mucus membrane of urinogenital tract) and syphilis (lesions in the mucus membrane of urinogential tract).
VIRAL INFECTION – which includes warts, HIV-AIDS, Hepatitis-B.                              
Use of condoms can prevent the spread of these diseases to a great extent

23. What is the role of the seminal vesicles and the prostate gland?
Ans: Seminal Vesicle:  Its secretion form a major part of the semen (60%). Its secretion is alkaline in nature which neutralizes the effect of acid in the female genital tract. It has fructose sugar which provides nutrition and energy to the sperm.
Prostate gland: Its secretion form 13-33% of semen. It helps in sperm motility and viability(chances of striking the ovum).
Cowper 's gland: Its secretion lubricates the end of male reproductive part during copulation.

HEREDITY AND EVOLUTIOM

1. Heredity : It refers to the transmission of characters or traits from the parents to their offspring. Heredity is the continuity of features from one generation to another which are present in fertilised egg or zygote. The zygote develops into an organism of a particular type only.

2. Genetics : It is the branch of biology which deals with heredity and variation. Genetics is to help our understanding of heredity by knowing how offspring inherit characteristics from their parents.

3. Variation : It means the differences in the characters or traits among the individuals of a species. Variations occur during reproduction both because of error in DNA copying and as a result of sexual reproduction. Variations contribute to evolution.
Causes of variations:

1. Different combinations of genetic material.
2. Some positive gene mutations.
3. Interaction of genes with environmental changes (adaptations).

Importance of variations:

1. It forms, the. basis of heredity.
2. It causes adaptations due to which organism can easily adjust to its changing environment.
3. Accumulation of variations forms the basis of evolution.

Remember!

Variations are produced both in sexual and asexual reproduction but amount of variations produced in asexual reproduction are subtle (so little) that they are hardly noticeable as compared to variations caused due to sexual reproduction.

4. Genotype : The genetic constitution of an organism e.g., Genotype of human male is 44 + XY and

genotype of human female is 44 + XX

5. Phenotype : The appearance of the organism, i.e., the way in which genotype is expressed. Phenotype is the result of interaction of genes with the environment.

e.g., Red colour may be controlled by a pair of genes RR. Now if genotype is RR phenotype will be red only but if genotype is Rr then also phenotype will be red since R is a dominant gene.

6. Gene : It is the basic unit of inheritance by which characters are transferred from parents to their offspring. Gene consists of a specific length of DNA on a chromosome. A specific Segment of DNA that provides the information for one protein is called gene for that protein.

According to Mendel, both parents must contribute equally to the DNA of the progeny during sexual reproduction. As both parents determine the trait in the progeny, so both parents must be contributing a copy of the same gene.

7. Chromosomes : These are the long threads present in the nucleus of every cell. Chromosomes are made- up of DNA and protein. Each chromosome contains very long molecule of DNA.
Remember!

Each gene set is present as separate independent pieces each called a chromosome. Each cell have two copies of each chromosome, one each from male and female parents. Every germ cell will take one chromosome from each pair and these may be of either maternal or paternal origin. When two germ cells combine, they will restore the normal number of chromosomes in the progeny, ensuring the stability of the DNA of the species. Such mechanism of inheritance is used by all sexually and asexually reproducing organisms.

8. Allele : It is a alternative form of a gene occupying the same position on a chromosome and affecting the same characteristic but in two alternative ways, e.g., the free and attached ear lobe are the alleles of ear lobe character.
Expressing allele of a gene :

1. Homozygous dominant in capital letters, e.g., tallness(TT)
2. Homozygous recessive in smalMetters, e.g., shortness or dwarfness (tt)
3. Heterozygous (Tt)-lt will be called hybrid tall.

9. Dominant allele: An allele that affects the phenotype of an organism both in heterozygous and homozygous condition. It is denoted by a capital letter, e.g., tallness in pea plant is denoted by ‘T.

10. Recessive allele: An allele that affects the phenotype of the organism in absence of a dominant allele, i.e., in homozygous recessive individuals. It is denoted by a small alphabet, e.g., dwarfness in pea plant is denoted by’t’.

11. Homozygous: When both alleles of a particular gene are the same, e.g., TT

12. Heterozygous : When both alleles of a particular gene are different, e.g., Tt

13. Diploid : Cells or organism containing two sets of genes, e.g., human body cells. Diploid cells have genetic constitution of 2n.

14. Haploid : Cells or organism containing one set of genes, e.g., human reproductive cells (sperms and ova). Haploid cells have genetic constitution of n.

15. Monohybrid cross : A cross between two parents taking the alternative traits of one single character, e.g., A cross between tall and dwarf pea plants.
Monohybrid Ratio :

1. In F1 generation : 100% hybrid
2. In F2 generation : phenotypic ratio is 3 : 1 and genotypic ratio is 1 : 2 : 1

16. Dihybrid cross: A cross between two parents taking into consideration alternative traits of two different characters, e.g., A cross between two pea plants one having round, green seeds and the other having wrinkled, yellow seeds.
Dihybrid Ratio :

1. F1 ratio is 100% Hybrid type.
2. F2 ratio : Phenotypic is 9 : 3 : 3 : 1 and Genotypic . ratio is very complex.

17. Human Blood Groups: There are four types of blood groups A, B, AB or O. These are controlled by a gene which is denoted by symbols IA, IB and IO(sometimes also denoted as i). The genes IA and IB show no dominance over each other (they are codominant, i.e., both expresses themselves independently). But these both genes are dominant over the gene IO. Therefore, blood group of a person depends on the type of genes present, e.g., (i) Blood group A has the following gene types :

18. Determining sex of a newborn individual genetically:

(a) In human beings the sex of the individual is ” determined genetically.

(b) There are 23 pairs of chromosomes of which 22 are similar in male and female and are known as autosomes.

(c) The remaining one is sex chromosome which is XY in males and XX in females.

(d) Males produce two types of sperms X and Y, while female produces one type of egg X.

(e) If a X type of sperm fertilizers the egg then the sex of baby will be female (XX).

(f) If Y type of sperm fertilizers the egg then the sex of the baby will be male (XY).

19. Mendel’s experiment to show that traits may be dominant or recessive:

(a) Mendel conducted breeding experiments in garden pea.

(b) selected pure plant of a tall/short plant.

(c) produced first generation plants by crossing them.

(d) found that all plants were tall.

(e) produced second generation by self fertilization of hybrids.

(f) found that three quarter of the plants were tall and one quarter was short.

20. Homologous chromosomes: A pair of corresponding chromosomes of the same shape and size, one from each parent.

21. Autosomes and Sex chromosomes :The identical » chromosome pairs are called autosomes. The

chromosome pair which is different are called sex chromosomes. Humans have 23 pairs of chromosomes. 1-22 pairs are autosomes while 23rd pair (XX in females and XY in males) which are designated as X and Y are sex chromosomes.

22. Molecular Phylogeny: It is the study of evolutionary relationships by comparing DNA of different species.

23. Natural selection : Natural selection is one of the basic mechanisms of evolution, along with mutation, migration and genetic drift. Natural selection means the environmental conditions prevailing around an organism against which organism adapts itself, grows – and reproduces further. This leads to a change in the composition of genes within a population further causing evolution. Thus, it can be said that,

Natural selection results in adaptation in population to fit their environment better. Thus, natural selection direct evolution in the population of a particular species.

24. Fossils of the information which they provide regarding evolution:Fossils are the remains of ancient life forms, which got preserved somehow in the layers of earth, snow or oil.

Information given by fossils:

1. They reveal that the life forms which existed earlier do not exist today
   
   which indicate that the living forms are ever changing (evolving).
2. They are used to guess the time when a particular organism existed on earth. It is done through carbon dating.

25. Genetic drift: The change in the frequency of some genes in a population which provides diversity without any survival advantage is called genetic drift.

26. The various ways in which individuals with a particular trait may increase in a population : Differences in population are responsible for the diversity such as, colour of eyes, hair, shape of ear lobes. This occurs due to : (i) Sexual reproduction (ii) Inaccuracies during DNA replication (iii) Due to environmental changes. This diversity will increase with time as these variations can be passed on only through DNA/genes during reproduction through reproductive tissue (germ cells or gametes).

(i) If these variations give survival advantage, then such traits are selected in nature and such traits increase in a population.

(ii) Due to genetic drift. This occurs due to geographical or reproductive isolation. It results in the change in gene frequency in a particular : population.

(iii) Migration which leads to gene flow in and out of the population.

(v) Mutation caused due to particular type of environment. ,

(v) Acquired traits due to particular type of environment.

27.Evidence of evolution : Errors in DNA copying (mutation) and sexual reproduction lead to variations which form the basis of evolution. Characteristics that

are common in different kinds of living organisms provide evidence in favour of evolution.

28.Evolution : Evolution can be defined as a naturally occurring slow, continuous and irreversible process of change. The gradual change of living organisms from pre-existing organisms since the beginning of life is called organic evolution. Whereas, gradual change in elements from one form to another with time is termed as inorganic evolution, i.

29.Inherited traits : are those traits which are passed from one generation to another through specific genes. Any change in DNA of the germ cells will be passed.

30. Acquired traits : are those traits which are acquired by the organism in its lifetime, e.g., removal of tail cannot change the genes of the germ cells of the mice thus cannot be passed to next generation.

31. Speciation : It means the origin of new species from the existing ones. It happens when different populations of the same species evolve along different lines.
How speciation occurs ?

1. It occurs when two populations are isolated (both geographically and reproductively) leading to almost no gene flow between the two populations.
2. Over generations, genetic drift will accumulate different changes in each sub-population.
3. Natural selection may also operate differently in these different locations.
4. Together natural selection and genetic drift will cause such changes (severe changes in the DNA) that these two groups will not be able to reproduce with each other even if they happen to meet.
5. When DNA changes occur to larger extent, it may lead to change in the number of chromosomes or gene expression, eventually the germ cells of the two groups cannot fuse with each other. This leads to emergence of new species.

32. Estimating Age of Fossil: There are 2 methods :

1. Relative method : On digging, the fossils which are closer to the surface are more recent than the fossils found in deeper layers.
2. Dating fossils (carbon dating method):It is done by detecting the ratios of different isotopes of the same element (i.e., isotope of C-14 which is radioactive) in the fossil material.

33. Evolution by stages :

1. Complex organs like eye has evolved from rudimentary organs, (e.g., rudimentary eye in flatworm might be useful enough to give only a fitness advantage and the structure of eye in different organisms is different indicating them to have different evolutionary origins) not by a single DNA change but created bit-by-bit over generations.
2. A change that is useful for one property to start with can become useful later for quite a different
   
   function (e.g., Feathers might start as providing insulation in cold weather. But later, they might be useful for flight. Some heavy birds and reptiles also have feathers but they do not fly.
3.  Some very dissimilar looking structures evolve from a common ancestral design, e.g., wild cabbage was cultivated as a food plant and many different vegetables were generated by selection over last two thousand years, (a) Selection of very small distances between the leaves gave rise to cabbage we eat. (b) Selection for arrested flower development gave rise to broccoli, (c) Selection for sterile flowers gave rise to cauliflower (d) Selection for swollen parts gave rise to kohlrabi.(e) Selection for larger leaves gave rise to leafy vegetable kale. It suggests that, if these selections were not done then there would have been only wild cabbage.

34. Homologous organs are organshaving same origin and basic structure but they appear different and perform different functions in various organisms, e.g., (a) Fore limbs of horse and arms of man.

(b) Wings of birds and flippers of whale.

Similarities in basic structure of (homologous) organs in different organisms, indifferent groups indicate common ancestry.

35. Analogous organs are organs, which look similar because they perform same function, but they do not have same origin and basic structure.

e.g.,(a) Wings of birds and wings of insects. (b) Fins of fish and flippers of whale.

HOW DO ORGANISMS REPRODUCE

MINERAL NUTRITION

Transportation in plants

Types of immune system

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