Current Affairs 7th Class

Learning Objectives

Different types of nutrition

Nutrition in amoeba-digestion is intracellular,

Nutrition in humans

Nutrition in ruminants- has four chambered stomach

Different types of teeth in relation to food habits.

Humans have two sets of teeth- milk teeth and permanent teeth.

   INTRODUCTION Plants make their food by the process of photosynthesis, but animals cannot make their food themselves. Animals get their food from plants. Some animals eat plants directly while some animals eat plant eating animals. Thus, animals get their food from plants either directly or indirectly. All organisms require food for survival and growth. Requirement of nutrients, mode of intake of food and its utilization in body are collectively known as nutrition. Animals are heterotrophic in nutrition as they cannot make their own food. Euglena is an exception. It has chlorophyll and is capable of synthesizing food. But in the absence of light it feeds on dead organic matter and is a saprophyte. Animals are also holozoic because they swallow or ingest food. Examples of some holozoic method of intake of food by heterotrophic animals:

Herbivores- These animals feed on plants and plant products, e.g cow, goat, horse, deer.

Carnivores- These are also called meat eaters, e.g snakes, lions, tigers, eagle, frog etc.

Omnivores- They feed on both plants and animal flesh. Man is an omnivore. e.g pigs, bears, crow, etc.

 

Parasites- These live on or inside the body of ether living organisms

(a) Ectoparasite- These live on the body of the host. These are blood Slicking parasites, e.g lice, bedbugs, ticks, leeches etc (b) Endoparasite- These live inside the body of the host. e.p tapeworm, liook v/orm, malaria parasite lives inside mosquito and man.

Saprotroph- These feed on dead organic matter, e.g earthworm.

Scavengers- They feed on flesh of dead matter, e.g vulture.

  Nutrition in complex animals involves following steps: Ingestion Digestion. Absorption. Assimilation Egestion. Ingestion - The intake of food is called ingestion Method of ingestion, i.e., taking of food, varies from one animal to another.   Digestion- The process of breaking down of complex component of food into simpler substances is called digestion. The process of digestion is different in human, grass eating animations, amoeba, etc. Absorption- The process of passing of digested food into blood vessels in the intestine is called the absorption. Assimilation- The Conversion of absorbed food in complex substances such as proteins and vitamins required by body is called assimilation. In other words, assimilation is the conversion of absorbed food (Nutrients) into living tissues. Through the process of assimilation our cells are supplied with oxygen and nutrients. more...

Learning Objectives

Introduction

All living things need food.

The process of utilization of food by an animal to obtain energy for growth and development is known as nutrition.

Autotrophic mode of nutrition

Heterotrophic mode of nutrition

Some plants are parasites, saprophytes and symbiotic.

    INTRODUCTION Food is the most important and basic thing for life. Carbohydrates, proteins, fats, vitamins and minerals are the components of food. These components are necessary for all living beings. All plants and animals require food for their growth and to get energy. The process of utilization of food by an animal to obtain energy for growth and development is known as nutrition, Plants make their food themselves but animals cannot. Hence, animals depend directly or indirectly on the plant.   MODE OF NUTRITION IN PLANTS Plants obtain their nutrition by various modes. The mode of nutrition can be divided into two distinct types. Broadly speaking, plants can be divided into autotrophs and heterotrophs. Autotrophic Nutrition Auto means self and trophos means nourishment. Plants are called autotrophs because they make their food themselves. The making of food for themselves is called the Autotrophic nutrition. Autotrophic nutrition is found in green plants. If the autotrophs prepare their own food by utilizing chemical energy they are called chemoautotrophs.   Heterotrophic Nutrition The word Heterotrophic is the combination of two words i.e. Hetero + Trophos. Hetero means 'others' and 'trophos' means nourishment. If organisms depend on others for their food, it is called the Hetetrophic Nutrition. Animals cannot make their food themselves. They depend for food upon plants. Therefore, nutrition in animals is called Hetetrophic Nutrition. Animals are known as Heterotrophs. Heterotrophic plants can be further divided into parasites, saprophytes and symbiotic plants.     Photosynthesis - Food Making Process in Plants The process of making of food by green plants in the presence of sunlight and chlorophyll is known as photosynthesis. Photosynthesis is the combination of two words- Photo + Synthesis. 'Photo' means light and 'Synthesis' means to make.   Process of Food Making in Green Plants Green plants make their food themselves. Green leaves make food from Carbon dioxide and water in the presence of sunlight and chlorophyll. Hence, for taking place of photosynthesis carbon dioxide, water and sunlight must be reached at the green leaves in addition to presence of chlorophyll.   Leaves have several tiny pores more...

Learning Objectives

To understand concept of soil formation

To understand soil profile and composition of soil

To learn about different types of soil

To study soil erosion-its causes and preventions

To learn about soil pollution –its sources and control.

Soil is a precious gift from nature. Soil supports life on earth. Most people think soil as a layer of dirt and mud. However this layer of mud and dirt is actually filled with life. Food we eat, fibre we use to make fabric, habitat for various organism etc. is provided by soil. If you closely observe a freshly dug pit you may see various creatures like earthworm, ants, beetles etc. Soil provides nutrients to the plants and support their growth. All living organisms depend directly or indirectly on soil. Let’s learn more about soil. SOIL The mixture of rock particles and humus is called soil. Soil is an important natural resource. It contains water, dissolved substances, mineral salts and living organisms. Soil forms a very thin layer on the surface of the earth ranging from a few m to 3 to 4 m. Note: Humus is a brown or black organic substance formed from decaying plant remains or animal matter. It determines the fertility of soil. It is porous in nature and increases the ability of soil to retain water.   SOIL FORMATION Soil is formed from parent rock material over millions of years by a process of weathering. Weathering is the process of breaking down of rock present on the surface of earth into fine particles. Weathering Occurs by Two Main Processes (a) Physical weathering, which is caused by physical phenomena like atmospheric changes (heating, cooling, wetting-drying etc). (b) Biological weathering, which involves breaking down of rocks by the action of living organisms. Do you know? Earthworm’s burrows act as tunnels which allow water to moves quickly and provide pathways for roots to grow. They also decompose dead plants and animal matter. Their castings are valuable as fertilizer.   SOIL PROFILES Soil profile is a vertical section of different layers of the soil. Various layers are called horizons. Each layer diners in colour, depth, chemical composition. Generally we see the top surface of the soil, not layers below it. Soil profile can be seen while digging a we'l or laying the foundation of a building. Soil profile i.e. various layers of soil can also be observed in a deep cut through the soil. Typically, four distinct soil layers can be seen. It can also be seen at the sides of a mad on a hill or at steep river bank. A-Horizon more...

Learning Objectives  

To learn about physical and chemical changes

To understand characteristics of physical and chemical changes

To understand the process of rusting of iron and methods of its prevention

To study crystallization process and its applications

  We have learnt in previous class about different changes around us like periodic and non-periodic, slow and fast changes, reversible and irreversible changes around us and their causes. Every change has a cause for example days change tonight because of rotation of earth around the sun, melting of ice is due to heat supplied. There are changes in everything. When we eat, breathe, talk or sleep changes take place in our body Changes can be in shape, size, temperature, state of substance etc. In this section we will learn about the classification of the changes around us into two main categories- Physical and chemical changes.   PHYSICAL PROPERTIES The properties which describe the look or feel of a substance e.g., colour, hardness, density, texture and phase of matter, etc. Every substance has its own characteristic physical properties that we use to identify the substance.   PHYSICAL CHANGES A change in which physical properties of substance such as, size, appearance or state, may alter, but its chemical composition remains the same and no new substance is formed are called physical changes. A physical change is a reversible change. For example dissolving sugar in water, cutting of wood etc.   Characteristics of Physical Changes

To bring about a physical change some external force or energy has to be applied. For example for opening a door we push the door or we kick the ball for changing its position.

The molecules of the substance remain same after and before the change. For example on dissolving sugar in water properties of sugar and water remain the same.

Physical change is a temporary change .On removing the cause of the change the substance regains its original form. For example electric bulb glow on supplying current and comes to its original state on switching off the current.

Note:- By using a piece of gold, a goldsmith can make a large variety of ornaments. But all of them consist of the same substance, namely gold.   Some Other Examples of Physical Changes 1. Change of state- On heating water evaporates and ice melts, but on cooling water vapours changes to water and water freezes to form ice. Therefore change in state of water is a physical change.   Note: A mixture consist of two or more substances simply mixed together but not chemically combined. For example air is a mixture of various gases.

Formation of mixture- When we dissolve salt in water or mix different vegetables and fruits to make salad they form a mixture Properties of the salt in water and vegetable and fruits in salad remain the same, no new substance is formed. Hence formation of mixture is a physical change.

more...

Learning Objectives

To study the concept of acids, bases and salts

To study different indicators and their color changes on different substances

To understand neutralization reaction and formation of salts

To study neutralization by taking some examples from everyday life.

To study uses of acids, bases and salts.

  We have learnt in previous class about the classification of substances based on their physical properties like appearance, solubility, hardness etc. Substances can also be grouped on the basis of their taste as sweet, salty, sour or bitter. Have you ever tasted lemon without adding water and salt? Or have you noticed the slippery touch of soap? Lemon juice, tamarind, raw mango etc. taste sour, some substances like baking powder tastes bitter. Common salt tastes salty These tastes are the characteristics of three different types of compounds that are acids, bases and salts. In this section we will learn why some substances are sour or bitter to taste. Note:- Although all acids taste sour and all bases taste bitter, a taste test is not the best general-purpose way to determine whether a substance is an acid or a base. Some acids and bases are poisonous, and some are quite corrosive. Never taste laboratory chemicals. Too many of them are toxic, and others might be contaminated.   ACIDS Taste of substances containing acids is sour e.g. curd, lemon juice, orange juice, vinegar, etc. The acids in these substances are natural acids. Lemonade contains citric acid, grapes and tamarind contains tartaric acid. Synthetic substance such as vinegar contains acetic acid and cold drinks contain carbonic acid. The chemical nature of acids is acidic. The word acid comes from Latin word acere which means sour.   Do you know? Robert boyle was the first to study the properties of acids and described them as sour, corrosive and turning blue litmus red.   Type of Acids Acids are of two types

Mineral acids

Organic acids

Organic acids: These acids contain carbon as a constituent and are present in organic matter i.e, animals and plants. For example Citric acid, acetic acid, tartaric acid etc. Organic acids are weak acids. Mineral acids: These acids are prepared from minerals present in the Earth's crust. For example sulphuric acid\[\text{(}{{\text{H}}_{\text{2}}}\text{S}{{\text{O}}_{\text{4}}}\text{)}\], hydrochloric acid (HC1), nitric acid (HNO^) etc. These are also called laboratory acids. Mineral acids are strong acids.   Do you know? Sulphuric acid is known as the king of chemicals.   Do you know? The earlier name for sulphuric acid was oil of vitriol due more...

Learning Objectives

To study natural fibers obtained from animals-Wool and silk

To learn about animals giving wool

To study each step involved in making wool from fiber

To understand life cycle of silkworm

To study the process of formation of silk from cocoons

To understand the health hazards of wool and silk industry

  Fibre are hair-like material that form the building blocks from which yam and fabric are made. Fibres obtained from plants and animals are called natural fibres. The history of fibres is as old as human civilization. Most clothing worn in the Stone Age was probably made from the skins of animals. It is also likely that some clothing was made by weaving grasses and other plant life. You have leamt in previous class about type of clothing material, their development and types of fibres obtained from plants which includes Fabric like cotton, jute, coir etc. In this chapter you will leam about animal fibres. Wool and silk are two important fibres obtained from animals. These natural fibres are used to make a variety of fabrics. Wool is hair of animals like sheep, goat, rabbit, camel etc. Sweaters, socks, gloves, scarves, shawls and coats etc., are made from these hairs/fibres. Stuffing for furniture can be done from wool, and recycled wool can be utilized to make insulation and sound proofing. Wool also has a long history of being used in carpets and carpet padding. Silk is obtained from salivary secretion of silkworm. Besides clothing silk is also used in wall hangings, paintings, religious ornamentation, interior decoration, and to maintain religious records. Now lets leam more about these animal fibres and how these are converted into fabrics. Do you know? Natural fibres of animal origin are mostly protein fibres while those of plant source like cotton and jute are starch based. WOOL Wool is obtained from fleece of sheep and goat .It is also obtained from llama, alpaca, angora rabbit, yak etc. It is used in various ways to make woolen clothing, carpets, rugs and shelters. Do you know? Australia is the biggest grower of wool in the world.   Characteristics of Wool

It is light, soft, thick, durable, elastic and wrinkle resistant.

Wool fibres are complex animal proteins. If wool samples are burnt, they emit strong smell of burning hair.

It traps air and so it has insulating properties because air is a bad conductor of heat. Thus wool has the property of retaining heat.

Wool is reusable and biodegradable.

  Do you know? Bharat Merino a breed of sheep was more...

Learning Objective

Introduction

Winds and sir pressure

Wind currents and Manson

Storms

Cyclones

Damages caused by cyclones

Safety measures for cyclones

  INTRODUCTION We have heard many times about the natural disasters. The natural disaster include storms, cyclones, earthquakes, etc. which can cause   lot of damage to human life, animals and property. In this chapter we shall study about what are winds, storms, cyclones and hurricanes? How are they formed and why are they so destructive?   WINDS AND AIR PRESSURE Moving air is called wind. The difference in the air pressure which is caused by the unequal heating of different parts of the earth causes wind. Now let us see how wind blows? Do you know? It is thought that wind energy was first used to propel sailing boats. The air in certain regions becomes hot due to the heat from the sun. The hot air is lighter and so it rises up. As a result there is a drop of air pressure in that region. The cooler air from the colder regions being heavier starts flowing towards the low pressure regions. This air moving from the high pressure regions to the low pressure regions is called wind.   Do you know? The movements of air toward the equator are called trade wind.   Air Pressure Earth is surrounded by an envelope of air. The force exerted by air per unit surface area is called air pressure. If a can half-filled with water is heated till all the air is expelled out, and then covered with a lid. Thereafter cold water is poured over the can then it is found that the can gets crushed. It happens because on pouring cold water, the steam convert into water, thereby, reducing the pressure inside the can. The large air pressure outside the can crushes it. Air pressure is measured by barometer. It is important to note that air pressure is exerted in all directions.   Consequences of Air Pressure

Though air exerts large pressure on us but we don't feel that pressure. It is because our blood contains dissolved oxygen at a higher pressure than the air pressure. So the air pressure is counter-balanced.

The nose starts bleeding at higher altitudes. Actually the air pressure falls at higher altitudes. This creates a difference between the internal pressure of the body and the external air pressure. As a result the fine capillaries inside the nose burst, and hence the nose starts bleeding.

sucking of lemonade with the help of straw is also based on the air pressure. As on sucking through the more...

Learning Objectives

Introduction

Heat and temperature

Temperature measuring scales

Temperature measuring instrument thermometers

Heat transfer

• Conduction
• Convection
• Radiation

Conductors and insulators

  Introduction We wear woolen clothes during winters when it is cold outside. Woolen clothes keep us warm. In summers we feel hot inside the house as well. How do we know whether an object is hot or cold? We find some objects are hotter than others while some are colder than others. We often decide it by touching the objects, in the case of a hot body, heat flows into our body while in case of a cold body heat flows out of our body.   HEAT AND TEMPERATURE Heat is a form of energy which causes sensation of hotness and coldness. Heat always flows from the hot object to the cold object. Temperature is the degree of hotness or coldness of. a body. Temperature determines the direction of flow of heat. Heat energy flows from a body at higher temperature to the body at lower temperature. The transfer of heat continues till the temperature of both the bodies become same. i.e., the bodies are said to be in equilibrium. Heat is a cause while temperature is an effect. The S.I. unit of heat is joule (j) because heat is a form of energy. Conventionally, heat is measured in calories (Cal). The amount of heat energy required to raise the temperature of 1 g of water by 1°C is called 1 calorie. \[\text{1calorie}=\text{4}.\text{2 joule}\]   Do you know? \[100c{{m}^{3}}\] of water and the \[10c{{m}^{3}}\]of water are equally hot. But \[10c{{m}^{3}}\]of water contains \[1/10\]heat than the  \[100c{{m}^{3}}\] of water.   TEMPERATURE MEASURING SCALES Temperature is measured by an instrument called thermometer. The three scales of temperature are (i) Celsius scale (ii) Fahrenheit scale and (iii) Kelvin scale (i)   Celsius Scale: Introduced by Swedish astronomer Celsius. It has 100 divisions, where each division measures one degree celsius (°C). The lower fixed point is marked as 0°C which gives the freezing point of water and upper fixed point is marked as 100°C and measures the boiling point of water. (ii) Fahrenheit Scale: This scale was introduced by Fahrenheit. This scale has 180 divisions with each division measuring 1°F on this scale. 32°F gives the melting point of ice and 212°F gives the steam point. Fahrenheit scale is used for meterological and clinical purposes. (iii) Kelvin Scale: It is known as absolute scale of temperature. It was introduced by Lord Kelvin. The lowest limit of temperature is absolute zero. Zero kelvin corresponds to -273°C. Conversion of Temperature Scales more...

Learning objectives

Introduction

Slow and fast motion

Relation between distance and time: speed

Types of speed

• Uniform speed
• Non-uniform/variable speed
• Average speed

Time

Time measuring devices

• Sundial
• Sand clock/hour glass
• Water clock

Measuring of time using periodic motion: simple pendulum

Unit of time

Graph: Distance versus time

  INTRODUCTION The famous scientist Albert Einstein said "Nothing in the universe can be at absolute rest". This means that all objects are executing some types of motion. A body is said to be in motion whenever it changes its position with respect to its surroundings. When a body is in motion there is often a need to measure the quality of this motion with respect to time. Measuring time is of great importance to each one of us. How often in a day we check the time on a watch or clock? We need to know when it is time to attend a dance class, to catch the school bus, and many other such daily life activities.   SLOW AND FAST MOTION The distance moved by objects in a given interval of time can help us to decide which object moves faster or slower than the other. Speed is refered to decide when object is slower or faster than the other. When two bodies move through same distance the faster one will take less time. When this distance is given in a particular direction it is known as displacement. The S.I. unit of distance or displacement is metre (m).   Do you know? Cheetah is the fastest animal on the earth. It can accelerate from 0to 72 km/h in 3 seconds.   RELATION BETWEEN DISTANCE AND TIME: SPEED In everyday life we see many objects which are moving like vehicles on the road, boats in the river, aero planes in the sky, etc. We need to measure their speeds. You would have seen that some vehicles have speedometer, which tells you how fast the vehicle is travelling.   Do you Know? The maximum recorded speed ever is the speed of light which is 3   Speed is defined as the distance travelled per unit time. When the quality of direction is added to the speed of moving object, then the body is said to have velocity. Mathematically speed can be written as,                 Speed is a scalar quality while velocity is a vector quantity. The S.I. unit of speed or velocity is meter/second or m/s. The other units are km/h, km/min etc. The rate of change of velocity is called acceleration. more...

Learning Objectives  

Introduction

Work

Types of work

Energy

Mechanical energy-Kinetic and Potential

Law of conservation of energy

Different forms of energy and their inter conversion

  Introduction In everyday language, we often term 'work' and 'energy'. A child sitting and doing his/her homework, a laborer breaking a wall, a man making a presentation on PC, a farmer plugging his fields, all are said to be doing some work. A person who can do more work is said to have more energy. In this chapter we study the actual meaning of work and energy and how they are related to each other.   WORK When a force is applied on a body, and it displaces the body through some distance, then work is said to be done. But if there is no displacement even when a force is applied, then no work is said to be done. Thus work depends on the applied force and the displacement made by the body due to that force. \[Work(\text{W})=Force(\text{F})\times displacement(\text{d})\] i.e., work is the product of force and displacement.   Do you know? If nothing is actually moving, no work is done no matter how great the force involved.   Units of Work The S.I. unit of work is joule (J) From the equation W = F d \[\text{1J=1N }\!\!\times\!\!\text{ 1m}\] i.e. If 1N force displaces a body through 1m in the direction of force, then work done is one joule (1 J). The C.G.S unit of work is erg. Again, from the equation \[\text{W=F}\times \text{d}\] \[\text{1erg=1dyne }\!\!\times\!\!\text{ 1cm}\] Work done is said to be one erg, when one dyne of force, displaces a body through 1 cm in the direction of applied force. \[W=F\times d\] \[1erg=1dyne\times 1cm\]   Do you know? The rate at which work is done by a force is called the power delivered by that force   Relation between joule and erg \[\text{1J=1N}\times \text{1m}\] \[\text{=1}{{\text{0}}^{\text{5}}}\text{dyne}\times \text{1}{{\text{0}}^{\text{2}}}\text{cm}\] \[\text{=1}{{\text{0}}^{\text{7}}}\text{dyne cm}\] \[\therefore 1\,\text{joule=1}{{\text{0}}^{\text{7}}}\text{erg}\]   TYPES OF WORK Work done can he positive, negative or zero as per the direction of displacement with respect to the force applied. (1) Positive Work: if displacement occurs in the same direction as that of force applied, then work done is positive For example: (a) When a ball falls down due to gravity, the work done is positive .Because force of gravity pulls ball down and it moves also down wards. So the direction of displacement of ball and action of gravity are more...