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Biology X | How do Organisms Reproduce?

November 23rd, 2014

How do Organisms Reproduce?

Reproduction is the process by which living organism produce new individuals similar to themselves.

Reproduction ensured continuity of life on earth.

 

It involves continuation of characters from the parents to daughter cells by copying of DNA (deoxyribose Nucleic Acid) molecules present in the chromosomes of the cell.

 

The DNA in the cell nucleus is the information source for making proteins. If the information is changed, different proteins will be made. Different proteins will eventually lead to altered body designs.

 

Therefore, a basic event in reproduction is the creation of a DNA copy. Cells use chemical reactions to build copies of their DNA. This creates two copies of the DNA in a reproducing cell, and they will need to be separated from each other.

 

Copying of DNA is also not a foolproof exercise, even a minute changes bring about Variation in the blue print of the offsprings.

 

The useful variations are retained while the harmful one does not go beyond.

 

REPRODUCTION


Asexual Reproduction:

Asexual Reproduction is extremely useful as a mean of rapid multiplication. It is common in lower plants and animals.

Asexual reproduction can be divided in following parts:

  1. FISSION : When parent cell divides/split into two or more individuals.
    1. Binary Fission: when parent cell divides into two individuals it is termed as binary fission. e.g. Amoeba, Paramecium.

     


 

 

2. BUDDING : Some individual develops a small outgrowth from its body part known as bud, as the bud grows it detaches from the parent body and develops into a whole new individual.


 

Budding in yeast

 

  1. Spore Formation : Spores are small, bulb like structure develops at the top of the erect hyphae of the fungus plant. They a light weight and produce numerous spores at same time, released into the air and germinate, into new individuals after landing into food or soil.


Spore formation in Bread Mould

4. FRAGMENTATION : It is the accidental process when the broken pieces of an organism (fragments) grows into a complete organism. eg. fragmentation in spirogyra

 


Fragmentation in Spirogyra

 

 

 

 

5. REGENERATION : When the simple animals like Hydra, Planaria develop a new individual from their broken older part it is known as regeneration. It is carried out by specialised cells which grow large numbers of cells.


VEGETATIVE PROPAGATION :

A mode of reproduction in which part like the stem, root, leaves develop into new plant under favourable conditions.

e.g.
Sugarcane, roses, Bougain-villea, Chrysanthemum etc

Vegetative propagation are of following types:

  • Layering : The adventitious roots are produced in the branch of the stem before the plant is detached from the parent plant. The branch of stem is called a layer. This process is utilized in the propagation of plant and the phenomenon is called layering. Layering is used in the propagation of plants like Lemon, Guava, Hibiscus, Bougainvillea, Jasmine, Raspberry, Strawberry and many ornamental plants.
  • Grafting : In this method of reproduction, two plants of closely related varieties are joined together so that they leave as one plant.
  1. The portion of a plant that is grafted on the other plant is called scion, and the plant in which grafting is performed is called the stock.
  2. This method is applied to improve variety of fruits like mango, apple, peas, citrus and guava.


 

Benefits

1. Plants can bear flowers, fruits earlier than those produced from seeds.

2. Growing Banana, orange, rose, jasmine that have lost the capacity to produce seeds.

3. Genetical similarity is maintained in the plants.

eg. Sugarcane, rose, grapes by layering or grafting.

 

Assignment

  1. Which life process ensure that a plant or animal species will not disappear from the earth?                                        (1)

  2. Define Asexual reproduction?                            (1)

  3. Why is DNA copying an essential part of the reproduction?            (1)

  4. Can you consider cell division as a typr of reproduction in unicellular organism? Give one reason.                                    (1)

  5. What are the advantages of sexual reproduction over asexual reproduction?    (2)

  6. Why more complex organisms cannot give rise to new individuals through regeneration?                                    (2)

  7. How does reproduction help in providing stability to population of species?    (2)

  8. Why does bread mould grow profusely on a moist slice of bread rather than on dry slice of bread?                                    (2)

  9. (i) Which are the two main types of reproduction in lioving organisms?    (3)

    (ii) classify the following under these two types: Amoeba, frog, Earthworm. Yeast.

  10. Explain vegetative propagation with the help of two examples. List two advantages of vegetative propagation.                            (3)

  11. What is a sexual reproduction? How do potato and bryophyllum plants reproduce vegetatively?

  12. Write three differences between asexual and sexual reproduction.        (3)

  13. What are the various artificial methods of vegetative propagation in plants?    (5)

  14. Define asexual mode of reproduction. What are the different methods of asexual mode of reproduction? Define regeneration with the help of diagram.        (5)

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CBSE Sample Paper for Class X Science

November 23rd, 2014

                                            Time: 3hrs

                                            MM: 90

General instructions:

  1.     The question paper comprises of two sections, A & B. you are to attempted both the sections.
  2. All the questions are compulsory.
  3. There is no overall choice. However, internal choice has been provided in all the five questions of five marks category. Only one option in each question is to be attempted.
  4. All the questions of sections A and all sections of section B are to be attempted separately.
  5. Question numbers 1 to 3 in section A are 1 mark questions. These are to be answered in one word or one sentence.
  6. Question number 4 to 7 are 2 mark questions, to be answered in about 30 words.
  7. Question numbers 8 to 19 are 3 mark questions, to be answered in about 50 words.
  8. Question numbers 20 to 24 are 5 mark questions, to be answered in about 70 words.
  9. Question numbers 25 to 42 is section B are multiple choice question on practical skills. Each question is 1 mark question. You are to choose one most appropriate response of the options provided to you.

Section – A

  1. List the three phenomenon of light responsible for formation of rainbow in the sky.
  2. Why is DNA copying an essential part of the process of reproduction?
  3. List any two common methods by which solid wastes of urban areas are disposed off.
  4. Why do we see stars twinkling whereas planets do not twinkle?
    1. i)     What is meant by power of accommodation of eyes?

          ii)     How does the focal length of the eye lens change when we shift looking from a distant object to a nearby object?

      1. i)     Why are coal and petroleum called as fossil fuel?

            ii)    Name the two elements which are present both in CNG and petroleum?

      2. i)     What is the position of hydrogen in the modern periodic table?
    2. Where are isotopes of the same element having different atomic masses placed in the periodic table?
      1. Pure breed pea plants A are crossed with pure breed pea plant B. it is found that the plants who look

    like A do not appear in F1 generation but B re-emerge in F2 generation. Which of the plants A and

    B (i) tall (ii) dwarf ? Give reason for your answer.

  1. A student sitting in the last row of the classroom is not able to read clearly the writing on the

    blackboard :

  1.     Name the type of defect vision he is suffering from
  2. How can this defect be corrected?
  3. a)     Name the compound CH3COOH and identify its functional group.
  1. Give a chemical test to identify this compound.
    1.     Name the gas evolved when this compound acts on solid carbonate. How would you identify this gas.
    2. a)     Explain the terms (i) implantation (ii) placenta

          b)     What is the average duration of human pregnancy?

          c)     What happen when the egg is not fertilized?

    12.     a)     A spherical mirror A forms an erect image of an object, a spherical mirror B forms erect as well as inverted image of an object. Name the types of the spherical mirror A and B.

        b)     What is the relation between the focal length and radius of curvature of a spherical mirror? If the radius of a curvature of a spherical mirror is 25cm, what is focal length?

13.     An organic compound A is an essential constituent of wine and beer. Oxidation of A yield an organic acid B which is present in vinegar. Name the compounds A and B and write their structural formula. What happens when A and B react in the presence of an acid Catalyst? Write the chemical equation for the reaction.

  1. Which of the following are homologous and which are the analogous? Give reasons

    (i)     Trunk of the elephant and hand of a chimpanzee

    (ii)     Wing of a bird and wing of a bat.

    (iii) Scales of fishes and shell of mollusks

  2. Lit is desired to obtain an erect image of an object, using an concave mirror of focal length 20cm.

    (i)     What should be the range of the distance of object from the mirror?

    (ii)     Will the image be bigger or smaller than the object?

    (iii) Draw a ray diagram to show the image formation in this case.

    16.     a) Why does carbon form largest number of compounds?

    (b) Why are some of these called saturated and other unsaturated compounds?

    (c) Which of these is more reactive?

    17.    Write three advantages of constructing dams across the rivers?

    18.     (a) State two effects produced by scattering of light by the atmosphere?

    (b) Why are danger signal lights red in colour?

    (c) What would the sky look like if the earth had no atmosphere?

    19.     The electronic configuration of these elements X, Y and Z are given below?                         X         2

    Y             2,6

    Z         2,8,2

    1.     Which element belongs to second period ?
    2. Which element belongs to second group?

      iii) Which element belongs to 18th group?

    20.     (a) What are the main reasons why human beings are over-exploiting the forests?

    (b) What are the effects of damages?

    (c) Names the different measures taken up for the conservation of forests?

    21.     a)     Why do we classify elements ?

    b) What were the two criteria used by Mendeleev in creating his periodic table?

    c) In Mendeleev’s periodic table, why was there no mention of noble gasses like helium, neon and argon?

    d) Why did Mendeleev leave some gaps in his periodic table?

    e) Would you place the two isotopes of chlorine, CI-35 in different slot because of their different atomic masses or in the same slot because their chemical properties are the same ? Justify your answer.

    22.     Names the type of mirror(s) that should be used to obtain:

    (a) A magnified and virtual image            (b) A diminished and virtual image of an object.

    (c) Draw labeled ray diagrams to show the formation of the required image in each of the above two cases .Which of these mirrors could also form a magnified and real image of the object? State the position of object for which this could happen.

    23     a) Define homologous series of organic compounds. Mention any two characteristics of homologous series.

        b)     Name the compound formed on heating ethanol at 443k with excess of conc.H2S04.

        c)     Describe a chemical test to distinguish between ethanol and ethanoic acid.

    24.     (a)     Give an example of bisexual flower. What is its female reproductive part known as?

        (b) Draw a diagram of its longitudinal section showing the process of germination of pollen on stigma and label the following on it.

        (c) Pollination may occur without fertilization but fertilization will not take place without pollination. Give reason.

    SECTION -B

    25.     “An iron nail was suspended in copper sulphate solution and kept for a while”. The solution

        a)     remained blue and a coating was formed on the nail

        b) turned green and a coating was formed on the nail

        c) remained blue and ho coating was formed on the nail

        d) turned green and no coating was formed on the nail

    26.     A student put a big iron nail each in 4 test-tube containing solutions of zinc sulphate, aluminum sulphate, copper sulphate, and iron sulphate. A reddish brown coating was observed only on the surface of iron nail which was put in the solution

    a) Zinc sulphate b) iron sulphate        c) Copper sulphate    d) aluminum sulphate

    27.     Four test tubes were taken and marked as A, B, C & D respectively. 2mLod solution of Al2(S04)3 in water was filled in each of the test tubes. Clean piece of metal zinc was placed in A, clean iron nail in B, clean copper wire in C & a clean aluminium wire in D. It was observed that no change occurred in any of the test tubes. The correct inference drawn is:

    (a) Zinc is more reactive than Aluminium

    (b) Zinc is more reactive than Copper

    (c) Copper is more reactive than Aluminium

    (d) Zinc, Iron & copper is more reactive than Aluminium

    28.     Which of the following reagents gives brisk effervescence with EthanoicAcid?

    (a) Calcium Hydroxide                (b) Sodium Chloride

    (c) Sodium Bicarbonate                (d) Ammonium Chloride

    29.     A student soaked 5g of raisins in beaker A containing 25ml of ice chilled water and another 5g of raisins in beaker B containing 25ml of tap water at room temperature. After one hour, the student observed that

    (a) water absorbed by raisins in beaker A was more than that absorbed by raisins in beakerB

    (b) water absorbed by raisins in beaker B was more than that absorbed by raisins in beakerA

    (c) the amount of water absorbed by the raisins of both beakers A and B was equal.

    (d) No water was absorbed by raisins in either of the beakers A and B

    30.     When a stopper of a bottle containing a colourless liquid was removed, the bottle gave out a smell like that of vinegar. The liquid in the bottle could be

    a) Hydrochloric acid solution            b) sodium hydroxide.solution

    c) Acetic acid                     d) saturated sodium bicarbonate

    31.     In amoeba, asexual reproduction by multiple fission

    a) never take place                b) sometimes takes place

    c) take place when amoeba wishes

    d) take place during unfavorable environment conditions

    32.     For determining the percentage of water absorbed by raisins in a given time, apart from water, raisins and a watch, we shall also require ,

    (a)     a beaker, a graduated cylinder, a thermometer ,a filter paper.

    (b) a watch glass, a graduated cylinder, a thermometer, a weighing balance.

    (c) a beaker, a thermometer, a filter paper, a weighing balance.

    (d) a graduated cylinder, a thermometer, a weighing balance.

    33.     The inner surface of a stainless steel spoon behaves as__________.

    (a) concave mirror.                (b) convex mirror.

    (c) plane mirror                    (d) neither concave nor convex

    34.     A student obtains a blurred image of an object on a screen by using a concave mirror. In order to obtain a sharp image on the screen, he will have to shift the mirror

    (a) towards the screen

    (b) away from screen

    (c) either towards or away from screen, depending upon the position of the object

    (d) to a position very far away from the screen

    35.     In an experiment to determine the focal length of a convex lens, a student obtained a sharp inverted image of a distant tree on the screen behind the lens. She then removed the screen and looked through the lens in the direction of the object. She will see

    (a) an inverted image of the tree at the focus of the lens

    (b) no image as the screen has been removed

    (c) a blurred image on the wall of the lab

    (d) an erect image of the tree on the lens

    36.     A student is to find the focal length of a (i) concave mirror, (ii) convex lens by using a distant object. We will observe that the screen is on the same side as the object

    (a) in both cases                    (b) in neither of the two cases

    (c) in case (i) but not in case(ii)            (d) in case (ii) but not in case (i)

    37.     A student suggested the following Guidelines to his friend for doing the experiment on dressing the path of a ray of a light, passing through a rectangular slab, for three different angles of incidence:

    A) Draw outline of the glass slab at three positions on the drawing sheet.

    B) Draw normal on the top side of these outlines near their left end

    C) Draw the incident rays on the three outlines in direction, making angles of 30o, 45c 60o with the normal drawn

    D) Fix two pins vertically on each of these incident rays at two points nearly 1 cm apart.

    E) Look for the images of the feet of these pins while fixing two pins, from other side, to get the refracted ray

    When he showed these guidelines to his teacher, the teacher told him that two of them need to be corrected and modified. These two Guidelines are

    (a) B & C            (b) C & D        (c) D&E        (d) B&D

    38.     If you find the focal length of a concave and convex mirror respectively which appears to be the same say 20 cm. If you face the mirror to distant object, then the size of the image will be

    (a) same in both the mirrors.            (b) smaller in concave mirror

    (c) bigger in convex mirror            (d) bigger in concave mirror

    39.     Which one of the following is depicted in the sketch of a slide shown below?


    (a) Binary fission in yeast            (b) Budding in yeast

    (c) Binary fission in amoeba            (d) Budding in amoeba

    40.     Which one out of the following diagrams correctly depicts an amoeba undergoing binary fission?


    (a) I          (b) II          (c) III (d) IV

    41.     Acetic acid is:

    (a) Colourless, pungent smelling liquid        (b) Colourless, sweet smelling liquid

    (c) Green coloured liquid having pungent smell     (d) none of the above

    42.     If the object is at 2F of a convex lens, and then the image is at:

    (a) 2F             (b) F            (c) infinity      (d) Between F and 2F

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