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Tuesday, February 2, 2016

10th Our Environment CBSE Board solved Questions

Class 10 our environment board solved Questions 2016
1. What is the function of ozone in upper atmosphere?

Ans: It shields the surface of the earth from ultraviolet rays from the Sun.

2. Why should biodegradable and non biodegradable waste be discarded in two separate dustbins?

Ans: So that the time and energy required in segregation may be saved and waste may be disposed off quickly

3. The following organisms form a food chain. Which of these will have the highest concentration of non-biodegradable chemicals ? Name the phenomenon associated with it. Insects, Hawk, Grass, Snake, Frog.
Ans: Hawk ; Biomagnifications

4.. Write the full name of the group of compounds mainly responsible for the depletion of ozone layer.

Ans: Chloroflurocarbons

5. List two examples of natural ecosystem.
Ans: Forests ,Ponds,Lakes

6. Differentiate between biodegradable and non-biodegradable substances with the help of one example each.
List two changes in habit that people must adopt to dispose non-biodegradable waste, for saving the environment.

Ans: Biodegradable substances – Any substance that can be broken down into simpler substances by biological process is called biodegradable. Ex. – Human Excreta/ Vegetable peels, etc.

Non-biodegradable substances – Any substance that can can’t be broken down into simpler substances by nature or decomposers. Ex. – Plastic/ glass (or any other) (any one)

Habits that people must adopt to dispose non-biodegradable waste, for saving the environment:

- Use of separate dustbins for biodegradable and non biodegradable waste,

- Reuse of things such as poly-bags, etc.,

- Recycle of waste

- Use of cotton /jute bags for carrying vegetables

7. What will be the amount of energy available to the organisms of the 2nd trophic level of a food chain, if the energy available at the first tropic level is 10,000 joules?

Ans: 10% of 10,000 joules = 1000 J

8. ‘‘Energy flow in food chains is always unidirectional.’’ Justify this statement.
Explain how the pesticides enter a food chain and subsequently get into our body.
Ans: The flow of energy is unidirectional. The energy that is captured by the autotrophs does not revert back to the solar input and the energy which passes to the herbivores does not come back to autotrophs.

Therefore, in food chain the energy moves progressively through the various trophic levels it is no longer available to the previous level. Thus, The flow of energy in food chain is unidirectional.

The pesticides enter a food chain and subsequently get into our body in following way:

(i) Pesticides used for crop protection when washed away into the soil or water bodies absorbed by plants.

(ii) On consumption they enter our food chain and being non – biodegradable these chemicals get accumulated progressively and enter our body.

9. What is ozone ? How and where is it formed in the atmosphere? Explain how does it affect an ecosystem.

Ans: Ozone (O3) is a molecule formed by three atoms of oxygen.

Ozone is formed at at the higher levels of the atmosphere by action of UV radiation on oxygen (O2) molecule.

The higher energy UV radiations split apart some moleculer oxygen (O2) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone as shown—

O2 ⎯⎯UV⎯→ O + O then, O + O2 ⎯⎯⎯→ O3 (Ozone)

Ozone shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.

10. Construct an aquatic food chain showing four trophic levels.

Ans: Hydrilla →Scorpio→ Fish → Crane

11. To protect the food plants from insects, an insecticide was sprayed in small amounts but it was detected in high concentration in human beings. How did it happen?
Ans: As insecticides are not degradable, these get accumulated progressively at each tropic level. As human beings occupy the top level in any food chain, the high concentration of insecticide gets accumulated in their bodies. This phenomenon is known as biological magnification

12. Why do most food chains have 3- 4 steps only?

Ans: The loss of energy at each step is so great that very little usable energy remains after four trophic levels. Therefore, food chains generally consist of only three or four steps.

13. What will be impact on ecosystem if bacteria and fungi are removed from the Environment?
Ans: The decomposers bacteria and fungi secrete enzymes that breakdown organic remains into simpler soluble substances that are absorbed by saprophytes. They clean the earth from organic matter hence Environmental pollutioncreated and food chain disturbed if bacteria and fungi are removed from the Environment.

14. Why is a pond self sustaining unit while an aquarium may not be?

Ans: A pond contains microorganisms that break-down the dead remains and waste products of organisms into simple inorganic substances that are used by other organism.

Since, pond is a natural ecosystem while an aquarium is created by man and is artificial, thus a pond self sustaining while an aquarium may not be.

15. Which level shows the maximum biological magnification? Why?

Ans: The top tropic level in any food chain has the maximum concentration of chemicals. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up by plants and animals.

10th Science – Chapter: Our Environment
10th Science - Our Environment: Summative assignments
10th Chapter: Our Environment Questions Paper for FA-III
10th Science: Chapter: Our Environment HOTS Questions
10th Chapter: Our Environment: Gist of Lesson

Tuesday, January 5, 2016

CBSE E-Notes-Heredity and evolution - X Biology

Class 10 Heredity and Evolution – Gist of lesson
Genetics : Branch of science that deals with Heredity and variation.
Heredity : It means the transmission of features / characters/ traits from one generation to the next generation.
Variation : The differences among the individuals of a species/population are called variations.
Mendel and His Work on Inheritance
Gregor Johann Mendel started his experiments on plant breeding and hybridization. He proposed the laws of inheritance in living organisms. Mendel was known as Father of Genetics
Plant selected by Mendel : Pisum sativum (garden pea). Mendel used a number of contrasting characters for garden pea.
Following are the seven pairs of contrasting characters in Garden Pea
Flower colour
Flower position
Seed colour
Seed shape
Pod shape
Pod colour
Height of plant   

Mendels Experiments : Mendel conducted a series of experiments in which he crossed the pollinated plants to study one character (at a time)

Monohybrid Cross : Cross between two pea plants with one pair of contrasting characters is called a monohybrid cross. Example : Cross between a tall and a draft plant (short).
Observations of Monohybrid Cross
1. All F1 progeny were tall (no medium height plant (half way characteristic)
2. F2 progeny ¼ were short, ¾ were tall
3. Phenotypic ratio F2 – 3:1 (3 tall : 1 short)
Genotypic ratio F2 – 1 : 2 :1  = TT : Tt : tt
1. TT and Tt both are tall plants while tt is a short plant.
2. A single copy of T is enough to make the plant tall, while both copies have to be ‘t’ for the plant to be short.
3. Characters/Traits like 'T' are called dominant trait (because it express itself) and ‘t’ are recessive trait (because it remains suppressed)
Dihybrid Cross : A cross macle between two plants having two pairs of contrasting characters is called dihybrid cross.

Phenotypic Ratio
1. When RRyy was crossed with rrYY in F1 generation all were Rr Yy round and yellow seeds.
2. Self pollination of F1 plants gave parental phenotype and two mixtures (recombinants round yellow & wrinkled green) seeds plants in the ratio of 9:3:3:1
1. Round and yellow seeds are DOMINANT characters
2. Occurrence of new phenotypic combinations show that genes for round and yellow seeds are inherited independently of each other
SEX DETERMINATION : Phenomenon of decision or determination of sex of an offspring
FACTORS Responsible for Sex Determination
1. Environmental : In some animals the temperature at which the fertilised eggs are kept decides the gender. eg. in Turtle                                                                                  2. Genetic : In some animals like humans gender or individual is determined by a pair of chromosome called sex chromosome  XX – Female and XY – Male
This shows that half the children will be boys and half will be girls. All children will inherit an X chromosome from their mother regardless whether they are boys or girls. Thus sex of children will be determined by what they inherit from their father, and not from their mother.
Evaluation is the sequence of gradual changes which takes place in the primitive organisms, over millions of years, in which new species are produced.

Group of red beetles

Colour variation arises during reproduction

All beetles red except one that is green
One beetle Green Reproduction
Crows feed on red beetle
Progeny beetles green
No. of beetles reduces
Crow could not feed on green beetles as they got camouflaged in green bushes

Number of green beetles increases

Situation 1 : Green beetles got the survival advantage or they were naturally selected as they were not visible in green bushes. This natural selection is exerted by crows resulting in adaptations in the beetles to fit better in their environment  
Situation 2 : Blue beetles did not get survivals advantage. Elephant suddenly caused major havoc in beetle population otherwise their number would have been considerably large.
From this we can conclude that accidents can change the frequency of some genes even if they do not get survival advantage: This is called genetic drift and it leads to variation.
Characters or traits of an organism are controlled by the genes
A Section of DNA (cellular)


   Provides information

  For synthesis of Proteins

 Proteins controls a character
Example :
Gene T
responsible for synthesis of efficient enzyme (Protein)
More production
of growth hormone

Results in Tall Plants

Gene t
responsible for synthesis of less  efficient enzyme

Less production
of growth hormone

Results in short Plants

Genetic drift. It leads to diversity without any adaptation
Group of red beetles
Habitat of beetles (bushes)
Suffer from plant disease
Average weight of beetles
decreases due to poor nourishment
Number of beetles kept on reducing
Later plant disease gets eliminated
Number and average weight of the beetles increases again

Situation 3 : No genetic change has occurred in the population of beetle. The population gets affected for a short duration only due to environmental changes.

Acquired Traits
Inherited Traits
1. These are the traits which are developed in an individual due to special conditions
1. These are the traits which are passed from one generation to the next.
2. They cannot be transferred to the progeny
2. They get transferred to the progeny.
3. They cannot direct evolution eg. Low weight of starving beetles.
3. They are helpful in evolution. eg. Colour of eyes and hair

Micro evolution : It is the evolution which is on a small scale. eg. change in body colour of beetles.
The process by which new species develop from the existing species is known as speciation.
Speciation : it is the process of formation of new species. 
Species : A group of similar individuals within a population that can interbreed and produce fertile offspring.
Geneflow : It is exchange of genetic material by interbreeding between populations of same species or individuals
Speciation takes place when variation is combined with geographical isolation.
Gene flow : occurs between population that are partly but not completely separated
It is the random change in the frequency of alleles (gene pair) in a population over successive generations.
*Natural Selection : The process by which nature selects and consolidate those organisms which are more suitably adapted and possesses favorable variations 
Genetic drift takes place due to 
(a) Severe changes in the DNA  (b) Change in number of chromosomes
Evolution and classification
Both evolution and classification are interlinked.
1. Classification of species is reflection of their evolutionary relationship.
2. The more characteristic two species have in common the more closely they are related.
3. The more closely they are related, the more recently they have a common ancestor.

4. Similarities among organisms allow us to group them together and to study their characteristic.
(Evidences of Evolution)
I. Homologous Organs : (Morphological and anatomical evidences. These are the organs that have same basic structural plan and origin but different functions.
Homologous organs provides evidence for evolution by telling us that they are derived from the same ancestor.
Example :
Forelimb of Horse
Same basic structural but different functions perform.
Winds of bat
(flying) plan,
Paw of a cat
II. Analogous Organs : These are the organs that have different origin and structural plan but same function example :
Example : Analogous organs provide mechanism for evolution.
Wings of bat       elongated fingers with skin folds

Wings of bird     Feathery covering along the arm

Different basic structure, but perform similar function i.e., flight

III. Fossils : (Palaeontological evidences) : The remains and relics of dead organisms of the past.

Fossil Archaeopteryx possess features of reptiles as well as birds. This suggests that birds have evolved from reptiles. Examples of Fossils

AMMONITE - Fossil-invertebrate                
TRILOBITE - Fossil-invertebrate
KNIGHTIA - Fossil-fish                                 
RAJASAURUS - Fossil dinosaur skull


I. Deeper the fossil, older it is.                                                                                                           
II. Detecting the ratios of difference of the same element in the fossil material i.e. Radio-carbon dating [C-(14) dating)
Evolution by stages : Evolution takes place in stages ie bit by bit over generations.
I. Fitness advantage
Evolution of Eyes
Evolution of complex organs is not sudden it occurs due to minor changes in DNA, however takes place bit by bit over generations.

Flat worm has rudimentary eyes
Insects have compound eyes                 enough to give fitness advantage
Humans have binocular eyes

II. Functional Advantage
Evolutions of feathers :
Feathers provide insulation in cold weather but later they might become useful for flight.
Example : Dinosaurs had feathers, but could not fly using feathers. Birds seem to have later adapted the feathers to flight.
Evolution by Artificial Selection :
Humans have been a powerful agent in modifying wild species to suit their own requirement throughout ages by using artificial selection. eg
(i) From wild cabbage many varieties like broccoli, cauliflower, red cabbage, kale, cabbage and kohlrabi were obtained by artificial selection.
(ii) Wheat (many varieties obtained due to artificial selection).
Molecular Phylogeny
Þ  It is based on the idea that changes in DNA during reproduction are the basic events in evolution

Þ Organisms which are more distantly related will accumulate greater differences in their DNA

                                         HUMAN EVOLUTION

Tools to Study Human Evolutionary Relationship
Excavating         Time dating        Fossils    Determining DNA Sequences

Although there is great diversity of human forms all over the world get all humans are a single species.

Chapter - 9: Heredity and Evolution
Assignment  for practice before  exam
CBSE Notes-Heredity & evolution
Point to remember- To revise before exam
NCERT Solutions Heredity & evolution
CBSE Notes-Heredity & evolution
Heredity and Evolution Questions for practice
Heredity and Evolution  Guess questions 
Heredity and Evolution  Notes
Heredity and Evolution[Solved Questions]-1
Heredity and Evolution[Solved Questions]-2
Heredity and Evolution[Solved Questions]-3