Ques 24: Answer the following questions
(a) What is division of labour with reference to multicellular organisms?
(b) Why striated muscles are also knownas skeletal muscles?
(c) Which structure takes impulse a way from a neuron.
Ans: (a) In multicellular organisms, different functions of the body are assigned to different group of cells, i.e., these organisms show division of labour.
(b) It is because these muscles are attached to bones. (c) Axon of neuron carries impulse away from neuron.
Ques 25: Answer the following questions (a) Heart pumps blood all through the body. Can you explain the reason behind this peculiar ability of heart? (b) Animals of colder regions and fishesof cold water have thicker layer of subcutaneous fat. Why?
Ans: (a) Heart is made up of cardiac muscles. These cardiac muscles are involuntary muscle (not under the control of our will). These muscles show continuous rhythmic contraction and relaxation throughout life; which there by, helps the heart to pump blood.
(b) Fat is a type of connective tissue (adipose tissue). It acts as a subcutaneous insulation of body for thermoregulation.
Ques 26: An object covers a distance S1, with a constant speed v1 and then covers a further distance s2 with a constant speed v2. Find an expression for his average speed.
Ans: Here total distance covered by the moving object S = S1 + S2 Now time taken by theobject to cover a distance, S1 with a constant speed, v1 t1 = S1/v1 and time taken by the object to cover a distance, S2 with a constant speed, v2 t2 = S2/v2 Total time taken, t = t1 + t2Average speed,
Ques 27:A girl of mass 40 kg jumps with a horizontal velocity of 5ms-1 onto a stationary cart with friction less wheels. The mass of the cart is 3 kg. What is her velocity as the cart starts moving? Assume that there is no external unbalanced force working in the horizontal direction?
Ans: Here, mass of the girl, m1 = 40kg Mass of cart, m2 = 3kg Horizontal velocity of girl when the cart is stationary u1 = 5ms-1
∴ Initial momentum of system p1 = m1u1 + m2u2 = 40 * 5 + 3 * 0 = 200kg ms-1
Let the final velocity of girl when the cart also starts moving with= v
∴ Final momentum of the system pf = (m1 +m2) v = (40 + 3) v = 43v
As there is no horizontal unbalanced force on the system. Total final momentum = Total initial momentum 43v = 200 v = 200/43 = 4.65ms-1.
Ques 28: A 30 kg shell is flying at 48 ms-1,suddenly it explodes and one of its partof 18 kg comes to rest while the remaining part flies off. Find the velocity of the latter.
Ans: Here, mass of shell = 30 kg Initial velocity of shell u = 48 ms-1 Total initial momentum = m * u = 30*48. On exploding, mass of one part = 18 kg, Hence, mass of other part = 30 -18 = 12kg (1) The first part comes to rest, i.e.,v1 = 0 Let the velocity of other part = v2 Then total final momentum = m1v1 + m2v2 = 18 * 0 + 12 * v2 = 12v2 Applying law of conservation of momentum, we have Total final momentum = Total initial momentum
∴ 12v2 = 30*48
Ques 29: Humans and all other animals dependon plants for their food. Hard work of several years have resulted in the development of tissue culture technology by scientists. What can be the application of such technology inour present society?
Name the following
(a) Tissue that forms the inner lining of our mouth.
(b) Tissue that connects muscle to bonein humans.
(c) Tissue that transport food in plants.
(d) Tissue that stores fat in our body.
(e) Connective tissue with a fluid matrix.
(f) Tissue present in the brain.
Ans: Plant tissue culture has wide spread use in scientific research. It has commercial as well as agriculturaluse. Some of its uses are (i) It is widely used in forestry and in floriculture. Rare and end angered species of plants can alsobe conserved by this technology.
(ii) Large scale growth of plant cells is done by this technology. Large production of plant cells are used for production of valuable compounds, biopharmaceuticals, etc.
(iii) Interspecific hybrids can be made by this technique. The product so formed is more useful and contain advantageous characters of both.
(iv) Clean plant materials can be achieved from diseased stock, which can be harmful for the human population.
(v) Large number of identical individuals can be made for commercial advantages.
(a) Simple squamous epithelium
(d) Adipose tissue
(f) Nervous tissue
Ques 30: Answer the following questions
(a) Farmer 'X' planted soyabean + maize+ cowpea (lobia) in the same field simultaneously in a set row pattern. Farmer 'Y' planted cereal crop in one season and leguminous plant in next season on the same piece of land inpreplanned succession. Name the cropping pattern used by the farmers'X' and 'Y'.
(b) What are the advantages of different cropping patterns followed by the farmers 'X' and 'Y'?
(c) Differentiate between mixed cropping and mixed farming. Or One of your family friend is thinking toopen a dairy farm for economic purpose. He wants to earn profits by selling milk. While he was discussing this with your father, what additional information can you give based on your knowledge for maintenance of catties
Ans: (a) X- Inter cropping, Y-Crop rotation.
(b) These cropping systems are beneficial in insect, pest and weed control, besides providing nutrients. They reduce the risk and give some insurance against failure of one of the crops. They give maximum benefit. They ensure maximum utilisation of the nutrients supplied.
(c) Mixed cropping is growing of two or more crops simultaneously on the same piece of land. Mixed farming is a system of farming on a particular farm which includes crop production, raising of livestock, etc.
The following points can be given in accordance withdairy farm
(i) Exotic breeds can be selected for long lactation period (e.g., Jersey and Brown Swiss).
(ii) Necessary Maintenance
(a) Proper cleaning of the sheds should be done regularly.
(b) They should be sheltered under well-ventilated roofed sheds that will protect them against rain, heat and cold.
(c) The floor should be kept sloping, so as to stay dry and to facilitate cleaning.
(d) Animals should be brushed regularly toclear dirt and loose hair.
(iii) Food Requirements Catties need a balanced ration having all the nutrients in proportional amount. Along with feeds, feed additives should also be given containing micro nutrients that would promote good health and milk production of catties.
(a) Roughage Largely fibrous.
(b) Concentrates Low in fibre but contain higher levels of proteins and other nutrients.
(iv) Protection Against diseases the parasites of catties are of two types
(a) External parasites living on the skin.
(b) Internal parasites Affect stomach and intestine or liver. Bacteria and viruses also cause infectious disease. Vaccinations and proper medical treatment should be done at regular intervals against disease if occurs respectively.
Ques 31: Give reasons
(a) A gas fills completely the vessel in which it is kept.
(b) A gas exerts pressure on the walls of the container.
(c) A wooden table should be called asolid. (d) We can easily move our hand in air, but to do the same through a solid block of wood, we need a karate expert.
(a) You want to wear your favorite shirtto a party, but the problem is that it isstill wet after a wash. What steps would you take to dry it faster?
(b) It is a hot summer day, Priyanshi and Ali are wearing cotton and nylonclothes respectively. Who do you think would be more comfortable and why?
Ans: (a) There is little attraction between particles of gas. Thus, gas particles move freely in all directions. Therefore, gas completely fills the vessel in which it is kept.
(b) Particles of gas move randomly in all directions, at high speed. As a result, the particles hit each other and also hit the walls of the container witha force. Therefore, gas exerts pressure on the walls of the container.
(c) A wooden table has a definite shape and volume. It is very rigid and cannot be compressed i.e., it has the characteristics of a solid. Hence, awooden table should be called a solid.
(d) Particles of air have large spaces between them. On the other hand, wood has little space between its particles. Also, it is rigid. For this reason, we can easily move our hands in air, butto do the same through a solid block of wood, we need a karate expert.
(a) We can take (any one or more) the following steps
(i) Dry it under the fan.
(ii) Use hanger for exposing its larger surface toair.
(iii) Dry in sun.
(iv) Use iron.
(b) Priyanshi would be more comfortable. The reason is that cotton absorbs sweat from the body and provides it a larger surface area for evaporation. Increased evaporation causes more, cooling effect. Nylon does not absorb sweat so the sweat doesnot evaporate and Ali would feel uncomfortable.
Ques 32: Explain the following giving examples
(a) Saturated solution
(b) Pure substance
A group of students took an old shoe box and covered it with a black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the light. They placed a milk sample containedin a beaker/tumbler in the box as shown in the figure. They were amazed to see that milk taken in the tumbler was illuminated. They tried the sameactivity by taking a salt solution but found that light simply passed throughit?
(a) Explain why the milk sample was illuminated. Name the phenomenon involved.
(b) Same results were not observed witha salt solution. Explain.
(c) Can you suggest two more solutions which would show the same effect as shown by the milk solution?
Ans: (a) Saturated Solution A solution in which no more of the solid (solute) can be dissolved at agiven temperature is called a saturated solution. Suppose 50 g of a solute is the maximum amount that can be dissolved in 100 g water at 298 K.Then 150 g of solution so obtained is the saturated solution at 298 K.
(b) Pure Substance It consists of a single of matter or particles and cannot be separated into other kind of matter by any physical process. Pure substances always have the same colour, taste and texture at a given temperature and pressure. For example, pure water is always colorless, odorless and tasteless and boils at 373 K at normal atmospheric pressure.
(c) Colloids They are heterogeneous mixtures. The particlesize is too small to be seen with a naked eye, but it is big enough to scatter light. The particles are called the dispersed phase and the medium in which they are distributed is called the dispersion medium. Colloids are useful in industry and daily life. The particles of colloid cannot be separated from the mixture by filtration. The process of separation of colloidal particles is known as 'centrifugation'. They do not settle down when left undisturbed. In other words, colloids are quite stable. e.g., smoke, milk, fog, cloud, etc.
(d) Suspension It is a heterogeneous mixture in which thesolute particles do not dissolve but remain suspended throughout the bulk of the medium. The particles of suspension can scatter a beam of light passing through it. The particles of a suspension settle down when left undisturbed. The particles of a suspension can be separated from its mixture by filtration.
(a) The milk sample was illuminated because milk is a colloidal solution and hence, scatter the light passing through it. The phenomenon observed is called 'Tyndall effect'.
(b) As salt solution is a true solution i.e., solute particle size istoo small to scatter the light, so it does not show "Tyndall effect'.
(c) Examples of colloid are gold (Au) sol and arsenius sulphide (As2S3 sol.