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851.

Question : What is neurotransmitters?

Answer»

Solution :Neurotransmitters are chemicals, which allow the transmission of NERVE impulse from the axon terminal of ONE neuron to the dendron of another neuron or to an effector organ. Acetylcholine is the NEUROTRANSMITTER released by neurons.
Discussion
852.

Question : What are nastic and curvature movements ? Give one example of each.

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Solution :Nastic Movement : They AR non-directional curvature movements of turgor or growth, when the movements are determined by the structure of the responding organ irrespective of the DIRECTION of structure which is generally diffused. e.g., Drooping and folding of leaves in SENSITIVE plant in response to shock (seimonasty).
Curvature Movement : They are CHANGES in orientation of some plant parts in relation to others movement or nyctinasty of lagume leaves, bending of stem towards light.
Discussion
853.

Question : What are mycorrhizae?

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The fruiting bodies of basidiomycetes
Mutualistic ASSOCIATIONS of PLANT roots and fungi 
The HORIZONTAL hyphae that spread out over food
Asexual structures formed by deuteromy cetes 

ANSWER :B
Discussion
854.

Question : What are Motor or efferent neuron?

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Solution :Motor or efferent neuron CARRY impulses from the Central Nervous System to effector organ such as MUSCLE FIBRE or GLAND.
Discussion
855.

Question : A 4cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 24 cm. the distance of the object from the lens is 16 cm. Find the position, size and nature of the image formed using the lens formula.

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Solution :The ray which stricks the mirror surface ncar the periphery are called marginal rays for comer LENS. f = -24 cm. U= 16 cm using lens formula
`(1)/(f)= (1)/(v) =(1)/(u)`
`(1)/(24)= (1)/(v)- (1)/(-16)= (2-3)/(48)= (-1)/(48)`
V= -48 now `h_(1)= 4 cm`
so magnitication.`m= (h_(2))/(h_(1))= (v)/(u)`
`h_(2)= (v)/(u) xx h_(1)= (-48)/(-16) xx 4= 12 cm`
The image is formed at a distance of 48 cm from the optical focus of the lens on the same side of the object. This is indicated by the negative sign. Size of image is three times the size of objec i.e 12 cm.
Nature of image: Positive sign in the image height indicates that image is virtual and ERECT.
Discussion
856.

Question : What are magnetic field lines : Justify the following statements. (a) Two magnetic field lines never interesect each other. (b) Magnetic field lines are closedcurves.

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Solution :MAGNETIC field lines. It is defined as the path along which the unit North pole (imaginary) tends to move in a magnectic field if free to do so .
(a) The magnetic lines of FORCE do not intersect (or cross ) one another . If they do so then at the point of intersection, two tangents can be drawn at that point which indicates that there will be two different directions of the same magnetic field. i.e. the compassneed points in two different directions which is not possible .
Magnetic field lines CLOSED continuous curves. They diverge from the north pole of a bar magnet and converge is south pole. Inside the MAGENT they move from south pole to north pole.
Discussion
857.

Question : What are magnetic field lines ? How is the direction of a magnetic field at a point determined ?

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Solution :The space surrounding a magnet in which magnetic force is exerted is called a magnetic filed. Magnetic field lines are the lines that are drawn at every point indicating the direction in which a north pole would MOVE if PLACED at that point. Thcy are determined by placing an imaginary hypothetical north pole at that point and finding the direction in which it would move due to the magnetic filed at that point of a compass needle gets deflected when placed ear a magnet due to the magnetic force exerted by the magnet on it.
Some important properties of magnetic field lines are:
The tangent drawn at any point on the field line indicates the dircction in which a north pole would move if placed at that point
The relative strength of the ficld is proportional to the degree of closeness of IHE lines. The mure elustered they are the stronger thc ficld in the region.
The magnetic field lines never intersect This is bccause a pole can move only in ZONE direction and if the LINCS interseet they wourld have to move in two direction aimultaneously which is npossible.
Discussion
858.

Question : What are locomotory organs of paramecium?

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FLAGELLA
CILIA
TENTACLES
Pseudopodia

Answer :B
Discussion
859.

Question :What are Lymph nodes?

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SOLUTION :Lymph nodes are small OVAL or fean shaped structures, LOCATED along the LENGTH of lymphatic vessels.
Discussion
860.

Question : What are living fossils ?

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SOLUTION :Living fossils are living organisms that are similar in APPEARANCE to their FOSSILIZED distant ANCESTORS usually have no extinct close FEATURES. Eg. Ginko biloba.
Discussion
861.

Question : What is Kinetochore?

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SOLUTION :SMALL disc-shaped STRUCTURE at the SURFACE of the CENTROMERES.
Discussion
862.

Question : What are isomers? Give example.

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Solution :Compound with IDENTICAL molecular formula but DIFFERENT structures are CALLED structural ISOMERS.
Discussion
863.

Question : What are ionic compounds?

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Solution :The compounds which have BONDS formed by loss and gain of electrons are called ionic compounds or ELECTROVALENT compounds.
Two properties of Ionic compounds
i) Ionic compounds are hard and BRITTLE. ii) Tonic compounds have HIGH MELTING and boiling points.
Discussion
864.

Question : What are indicated by (i) and (ii) in the illustration of DNA molecule given below?

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<P>

ANSWER :i) G (GUANINE)II) P ( Phospate )
Discussion
865.

Question : What are homologous organs ? Give examples.

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Solution :Homologous organs. The organs of different classes have different forms because they have to perform different functions but their structures basically REMAINS similar. Such organs are CALLED homologous organs.

Examples of homologous organs. 1. The wings of bird and bat, flipper (fin) of whale, structure of human forearm are different in forms because these have to perform different functions. STUDIES of the BONES forming the skeleton of these organs, would reveal SIMILARITY in construction. In fact, these are the forms of fore-arms which have originated from pentadactyl forms and due to the different functions they are performing hence transformed into different forms.
2.In plants, the homologous organs may be a thorn of Bougainvillea or a tendril of cucurbita both arising in axillary position.
Discussion
866.

Question : What isareheatsounds? Howaretheyproduced?

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Solution :The RHYTHMIC closure and OPENING of the valves CAUSE the sound of the heart. When the closure of the tricuspid and bicuspid valves after the BEGINNING of ventricular systole, the sound ‘LUBB’is PRODUCED. When the closure of semilunar valve at the end of ventricular systole, the sound ‘DUPP. is produced.
Discussion
867.

Question : What are fossils ? What do they tell us about the processof evolution.

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Solution :Fossils are the preserved traces of organisms that LIVED in the PAST. Fossils
•give us the idea about the STRUCTURE of organs/organisms
• the period of their existence
• the geographic location of the organisms
• the evolutionary RELATIONSHIP between the existing and the EXTINCT species of the organism.
Discussion
868.

Question : What are fossils ? What do they tell us about the process of evolution ?

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SOLUTION :Out of SYLLABUS.
Discussion
869.

Question : What are fossils? How are they formed? List two methods of determining the age of fossils. Explain in brief the importance of fossils in deciding the evolutionary relationships.

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Solution :Fossils are dead remains of ANIMALS and plants from remote past.
Fossils are formed when dead organisms are not completely decomposed. The organisms may GET trapped in resins of tree, lava of volcanoes or hot mud, which when hardens RETAINS the animal.s parts thus forming fossils.
Two methods of determining the age of fossils are:
(a) Relative method: By estimating the age of the layer of earth.s crust where the fossil is found. Fossils near the surface are recent and those in the deeper layers are more ancient.
(b) Radio-carbon DATING method: By detecting the ratios of different isotopes of carbon in the fossils.
Fossils play the following roles:
(i) By determining the age of fossils we come to know the type of earth strata present at that time.
(II) We can also know the type of animals and plants present on the earth at that time.
(iii) They help in establishing evolutionary relationship by providing connecting links.
Discussion
870.

Question : What are fossils ? How do they form ? Give example of various kind of fossils ? How do we know how old the fossils are ?

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Solution :The fossils are the remains or impressions of the dead animals and plants that lived in the past.
Usually, when organisms DIE, their bodies are decomposed and lost. However if the body or some of its parts remain in an environment that does not let it decompose completely, the body or its parts will eventually be preserved or alternately leave the impressions.
If a dead INSECT GETS caught in mud, it will not decompose QUICKLY, and the mud will eventually harden and retain the impression of the body parts of the insect.
There are two METHODS to estimate the age of a fossil.
(1) Relative method : This method depends on the depth at which fossil is found. If we dig the earth to locate fossils, the fossils we find closer to the surface are more recent than the fossils we find in deeper layers.
(2) Carbon dating method : The dating of rocks or fossils is done by working out the ratio of different isotopes mainly `C^(14)` of the same element in the fossil material.
Discussion
871.

Question : What are fossils? How are they formed? Describe in brief two methods of determining the age of fossils. State any one role of fossils in the study of the process of evolution.

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Solution :Fossils are dead remains of animals and plants from REMOTE past.
Fossils are formed when dead organisms are not completely decomposed. The organisms may get trapped in resins of tree, lava of VOLCANOES or hot mud, which when hardens RETAINS the animal.s PARTS thus forming fossils.
Two methods of determining the age of fossils are:
(a) Relative method: By estimating the age of the layer of earth.s crust where the fossil is found. Fossils near the surface are recent and those in the deeper layers are more ancient.
(b) Radio-carbon dating method: By detecting the ratios of different isotopes of carbon in the fossils.
Fossils play the following roles:
(i) By determining the age of fossils we come to know the type of earth strata present at that time.
(ii) We can also know the type of animals and plants present on the earth at that time.
(iii) They help in ESTABLISHING evolutionary relationship by providing connecting links.
Discussion
872.

Question : What are fossils? What do they tell us about the process of evolution?

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Solution : FOSSILS are preserved REMAINS of living ORGANISMS from REMOTE past. Mainly preserves only a portion of the dead organism (e.g., skeleton, bone, teeth etc..)
Fossils may vary from microscopic (single bacterial cell) to dinosaurs.
Layers of fossils are formed one after another over years. Deeper the layer where the fossil is found, older it is.
Discussion
873.

Question : What are fossils?

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Solution :Fossils are the REMAINS or IMPRESSIONS of the DEAD animals and PLANTS that lived in the PAST.
Discussion
874.

Question : What are fossil fuels ? State its disadvantages.

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Solution :Fossil fuels are the major energy source at present day because we continue to be largely DEPENDENT on fossil fuels for most of our energy REQUIREMENTS.
Plants and animals which got buried deep under the earth surface millions of YEARS ago was converted into fuel due to excess heat and pressure. These are called fossil fuels.

The growing demand for energy was largely met by the fossil fuels - coal and PETROLEUM.
Disadvantages : (1) Fossil fuels were formed over millions of years and they are only limited reserves.
(2) The fossil fuels are non-renewable sources of energy.
(3) Air pollution is caused by burning of coal or petroleum products. The oxides of carbon, nitrogen and sulphur that are released on burning fossil fuels are acidic oxides. These can lead to acid RAIN.
( 4) Carbon dioxide produced by burning of fossil fuels leads to greenhouse effects.
Discussion
875.

Question : What are fossil fuels? How are they formed?

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Solution :The fossil fuels are petroleum, COAL and natural gas. Due to the anaerobic decomposition of buried DEAD organisms, by natural process over millions of YEARS, energy rich substances are formed. As the accumulating sediment LAYERS PRODUCE heat and pressure, the remains of the organisms are gradually transformed into hydrocarbons.
Discussion
876.

Question : What are five R's used to save environment ?

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Solution :The five R.s to SAVE environment are : REFUSE, Reduce, Reuse, Repurpose and RECYCLE.
Discussion
877.

Question : What are extremophiles?

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Solution :The organisms which live in extreme environmental conditions on Earth are called extremophiles WITHIN our own solar SYSTEM. There are many areas that are DIFFERENT from the Earth. We may find the presence of life similar to EXTREMOPHILE BACTERIA.
Discussion
878.

Question : What are Ductless glands? Why are they called so?

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Solution :ENDOCRINE glands are called DUCTLESS glands because their secretions are diffused into the blood STREAM, and are carried to the different parts of BODY. They do not have specific DUCTS to carry the hormones.
Discussion
879.

Question : What are diphyodont dentition and Heterodont dentition?

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Solution :The existence of two sets of teeth in the life of an animal is called diphyodont DENTITION. The two types of teeth are Milk teeth (Young ONES) and Permanent teeth (in adults).
The different types of dentition is called Heterodont. There are four kinds of teeth in mammals.
The incisors (I), Canines (C), PREMOLARS (PM) and Molars (M).
Discussion
880.

Question : What are different ways in which individual with a particular trait may increase in population ?

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Solution :The different WAYS in which individuals with a particular trait may increase in a population are :
(i) By natural selection-Organisms with a particular trait may be naturally SELECTED because it provided a survival advantage. That particular trait may thus increase in, the population. It may direct evolution of SPECIES population by ADAPTATIONS to fit their environment better.
(ii) Genetic drift and inheritance - An accident in small population may result in surviving of organisms with a particular variant only. This can increase the FREQUENCY of some gene in that population, even if they give no survival advantage. This is the notion of genetic drift, which provides diversity without any adaptations.
Discussion
881.

Question : What are different conterceptive methods How are they important for reproductive health ?

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Solution :Use of condom, copper T are common methods. Contraceptives are used to control the UNWANTED CHILD birth. These are also used to prevent CERTAIN sexually transmitted diseases like AIDS, syphilis, etc.
Discussion
882.

Question : What are decomposers ? Write the role of decomposers in the environment.

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Solution :DECOMPOSERS are microorganisms that derive their nutrition from dead remains and waste products of organisms.
They play a vital role in our environment by breaking down the complex organic substance into simple INORGANIC substance which is made available for plants and other organisms. HENCE they act as SCAVENGERS and not only keep the environment clean but also replenish the minerals.
Discussion
883.

Question : What are coliforms ?

Answer»

a GROUP of BACTERIA found in HUMAN intestine.
a group of bacteria found in animal dung.
a group of bacteria found in root nodules of lagumes.
None of these

Solution :a group of bacteria found in human intestine.
Discussion
884.

Question : What are chromosomes made up of?

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Solution :Chromosomes are made up of DNA, RNA, chromosomal proteins (histones and non-histones) and certain metallic ions. These proteins PROVIDE structural SUPPORT to the CHROMOSOME.
Discussion
885.

Question : What are chromosomes ? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained.

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Solution :Chromosomes are carriers of GENETIC information which is inherited from generation to generation. Number of chromosomes in sexually REPRODUCING organisms is maintained. This has been achieved by having special lineages of cells in specialised organs which have only half the number of chromosomes and thus half the amount of DNA. Thus, when these germ-cells from TWO individuals combine during SEXUAL reproduction to form a new individual, it results in re-establishment of the number of chromosomes and DNA CONTENT in the new generation.
Discussion
886.

Question : What are chromonema and chromomeres?

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Solution :Each chromatid is MADE up of SPIRALLY coiled thin structure CALLED chromonema. The chromonema has a number of bead-like structure along its LENGTH which are called chromomeres.
Discussion
887.

Question : What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained.

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Solution :Chromosomes are thread-like structures, made of proteins and DNA, found in the nucleus at the time of CELL division.
In sexually REPRODUCING organisms, the gametes undergo meiosis, and hence, each GAMETE contains only half a set of chromosomes. When TWO gametes fuse, the zygote formed contains the full set of chromosomes. Hence, the formation of gametes by meiosis HELPS to maintain the number of chromosomes in the progeny.
Discussion
888.

Question : What are chemical messengers?

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SOLUTION :A chemical messenger is any compound that SERVES to TRANSMIT a MESSAGE. A chemical messenger refers to hormones
Discussion
889.

Question : What are cerebrospinal fluid? What are it's functions?

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Solution :The brain is suspended in a special fluid environment CALLED cerebrospinal fluid (CSF).
FUNCTIONS:
(i) It acts as a shock absorbing fluid and protects the brain from damage, when it is subjected to sudden jerk.
(ii) It SUPPLIES NUTRIENTS to the brain.
(iii) It collects and removes wastes from the brain.
(IV) It is responsible for maintaining a constant pressure inside the cranium.
Discussion
890.

Question : What are cerebral lobes?

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Solution :Each cerebral HEMISPHERE is DIVISIBLE into a frontal LOBE, a partietal lobe, a temporal lobe and an OCCIPITAL lobe. These lobes are CALLED cerebral lobes.
Discussion
891.

Question : What are catabolic reactions ?

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SOLUTION :Catabolic reactions or destructive reactions are those in which complex organic molecules are broken down into twoor more simple INORGANIC molecules. Example : RESPIRATION.
`C_(6) H_(12) O_(6)to 6 CO_(2) _ 6 H_(2) O + "Energy" uarr`
Discussion
892.

Question : What are capillaries ? Write their function

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Solution :The smallest vessels having WALLS which are one-cell thick and these called capillaries. These join together to form veins that convey the blood from the organ or tissues. Exchange of material between the blood and surrounding CELLS take PLACE ACROSS these.
Discussion
893.

Question : What are capillaries?

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Solution :Capillaries are NARROW tubes FORMED by branching of arterioles which then unite to FORM the venules and VEINS. Capillaries are formed of SINGLE layer of endothelial cells.
Discussion
894.

Question : What are bulk genomic DNA and satellite DNA?

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Solution :In human BEINGS. 99% of the DNA BASE sequences are the same and this is called a BULK genomic DNA. The remaining 1% of DNA sequence DIFFERS from one individual to another. This 1% DNA sequence is present as small stretch of repeated sequences, which is called SATELLITE DNA
Discussion
895.

Question : What are bulliform cells?

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SOLUTION :Some of the upper EPIDERMAL cells of monocot leaves are LARGE and thin walled. So they are CALLED BULLIFORM cells.
Discussion
896.

Question : What are brain injuries? Give examples.

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Solution :The damage of BRAIN tissue, neurons and nerves. This damage affects our brain.s abilityto COMMUNICATE with the REST of our blody.
Example of Brain INJURIES include blood clots, hematomas, SWELLING inside the skull, strokes and etc.
Discussion
897.

Question : What are analogous organs ? Give examples.

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Solution :ANALOGOUS organs. The organs which are similar in appearance and perform the same function but DIFFER in their fundamental structure and ORIGIN are called analogous organs.
Examples. 1. Wings of birds and insects.
2. LEAVES of a PLANT and cladodes of Ruscus are also analogous organs.
Discussion
898.

Question : What are allosomes?

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Solution :Out of 23 PAIRS of CHROMOSOMES, 22 pairs autosomes and the `23^(rd)` pair is the ALLOSOME or SEX chromosome.
Discussion
899.

Question : What are advantages of sexual reproduction over asexual reproduction ?

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SOLUTION :Advantages of sexual reproduction :
Sexual reproduction has a dual significance for the species.
1. It results in multiplication and perpetuation of the species.
2. It contributes to evolution of the species by INTRODUCING VARIATIONS in a population MUCH more rapidly than asexual reproduction.
Discussion
900.

Question : What are addition reaction? What are catalysts? Illustrate with an example.

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Solution :Reactions which involve ADDITION of two reactants to form a SINGLE product aren CALLED addition reactions. Catalysts are the substanceswhich can change, usually increase the speed of a chemical reaction without being used up in that reaction.
For example, vegetable oils having long UNSATURATED carbon chains are converted into vegetable ghee by heating them in presence of Nickel, PLATINUM or palladium metals used as catalysts.
`underset("(Liquid)")("Vegetable oil"+ H_2) overset("Nickel 48 K")to underset("Solid")("Vegetable Ghee")`
Discussion