Micro organisms CBSE Class 8 Basic Science solved questions
Questions: What are diatoms? How they are helpful to us?
Ans: Diatoms are a single-celled alga which has a cell wall of silica called frustule. When diatoms die, they slowly sink to the sea floor and build up siliceous earths that are used to make glass, porcelain and ceramics. It is also used to make polishes and toothpaste.
Questions: Why diatoms are called chief producers in oceans?
Ans: Diatoms are autographs and synthesize food by photosynthesis.
(i) All the other creatures depend on the planktons in the ocean for food, as it completes the food chain. They play the vital role of primary producers.
(ii) They also maintain the ecological balance.
Questions: Why diatoms are called the jewels of plant kingdom?
Ans: The cell walls of diatoms are silicified i.e. impregnated with silica. On account of their delicately arranged ornamentation of cell walls diatoms have been regarded as jewels of plant kingdom.
Questions: How does the growth of algae harm water bodies?
Ans: some of the algae became poisonous after the die. Thus pollute water bodies. Bacteria feed on algae to multiply rapidly using up a lot of dissolve oxygen and prevent aquatic organism of their oxygen
Questions: Viruses are considered as being on the border line between living and non-living organisms, Why?
Ans: Viruses is nonliving outside living cells but grows and multiplies inside living cell so, viruses are considered as being on the border line between living and non-living organisms. The study of viruses is called Virology.
Questions: How are protozoan help in the bodies of termites and bacteria live in the intestine of human body?
Ans: Termites have protozoans living in their bodies that digest the cellulose in the wood eaten by termites and convert it into carbohydrates that the termites can use.
Bacteria live in the intestine of human body help absorption of food and prevent from many diseases. It helps with the production of some vitamins (B and K).
Questions: What we call the study of fungi?
Questions: What we call the study of virus?
Questions: What we call the study of bacteria and algae ?
Ans: The study of bacteria is called Bacteriology and the study of algae is called Phycology
Questions: How do viruses multiply within host cell?
Ans: Viruses when enters into the cell of host living body destroy the nuclear material and finely host cell burst out to release the viruses.
Questions: How do paramecium move and feed?
Ans: Paramecium swim in water by beating hair like structure called cilia against the water. The movement of cilia also direct food and water into gullet
Questions: Mention two ways in which fungi harm us?
Ans: Mould a kind of fungi spoil cooked food. Moulds and mildew grow on leather goods and cloths and furniture in monsoon and spoil them. Fungi cause diseases in plants and animals.
Questions: Mention three ways in which we use fungi?
Ans: Following are the three ways in which we use fungi
(i) Mushroom a kind of fungi eaten as a food.
(ii) Yeast is a kind of fungi used to prepare alcoholic drink, bakery product,
(iii) Penicillin and some other antibiotics are made from certain moulds
Questions: What does Sargasso Sea woe its name to?
Ans: Sargasso Sea woe its name to Sargassum, a particular sea weeds that grow abundantly in sea. Sailor avoids this sea as their boat stuck in the tangled mass of seaweeds.
Questions: What are the difference between the cell of bacteria and the cell of other living body?
Ans: The difference between the cell of bacteria and the cell of other living body are
(i) Cell wall is not made up of cell wall
(ii) Do not have nucleus
(iii)Does not have membrane bound organelles
Questions: Do red and brown algae have chlorophyll?
Ans: Yes, red and brown algae have pigment of colour which cover the colour of chlorophyll and make them appear red brown or yellowish
ï»¿Questions: Name a protozoon which can photosynthesize?
Ans: Euglena contain chlorophyll and can photosynthesise, lack of cell wall
Questions: How do bacteria reproduce?
Ans: Bacteria reproduce by binary fission
Download text material for Open Text-based Assessment (OTBA) for classes IX & XI, 2015
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9th physics Thrust and Pressure, Archimedes’ Principle, Relative Density key points
The total force acting perpendicular on a given surface is called thrust.
Thrust acting upon a unit area is called pressure. Its S.I. unit is Pascal denoted by ‘P’
Thus, pressure =Thrust/Area of contact
Archimedes’ principle states that when a body is immersed partially or fully in a fluid, it experiences an upward force that is equal to the weight of the fluid displaced by it.
Archimedes' Principle is used in designing ships and submarines. The Lacto meters and hydrometers used for measuring the purity of a sample of milk and for determining the density of the liquids are based on this principle.
Buoyancy can be defined as the tendency of the fluid to exert an upward force on an object, which is wholly or partially immersed in a fluid.
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Problem Solving Assessment (PSA) Question Papers: Class IX
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Reproduction for class 10 solved question from Board Exam
1. Give and advantage of vegetative propagation.
Ans: Any one:
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
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
(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.
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?
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?
(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
(ii) oviduct[Fallopian tube]
(iii) In the lining of the uterus
(b) The fertilised 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
(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 Planaria different 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.
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.
(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.
(a) The transfer of pollen grains from the anther to the stigma of a flower is known as pollination. It is of two types:
It is the transfer of pollen grains from the anther to the stigma of the same flower or another flower on the same plant.
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.
(i) the ovule develops into a seed
(ii) the ovary develops into a fruit
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