# Current Affairs 4th Class

#### Geometry

Geometry   Synopsis   Closed plane figures:
• The geometrical figures triangle, square, rectangle and circle are all closed plane figures or closed curves. They are bounded by line segments or curved lines.
• Closed plane figures, bounded by line segments are called polygons.
• A triangle is a polygon with 3 sides.
• Square and rectangle are polygons with four sides.
• All four sided polygons are named as quadrilaterals.
• Square, rectangle, parallelogram, rhombus and trapezium are all quadrilaterals.
(a)                (b)             (c)           (d)             (e)           (f)       Circle:
• A circle is a closed geometrical figure formed by points equidistant from a fixed point.
Circle
• Every circle has a fixed point in it called the centre of the circle, from which all the points on the circle are at the same distance.
• A line segment drawn from the centre of the circle to any point on the circle is called the radius of the circle. We can draw many radii (plural of radius) in a circle.
• A chord is a line segment whose end points always lie on the circle.
• A diameter is a chord that passes through the centre of the circle. We can draw many diameters to a circle. All the diameters of a circle are of the same length.

• The diameter is the biggest chord of a circle.
• Circumference of a circle is the total length of the boundary of the circle.
• Any part of a circle is called an arc.

• If an arc represents half of the circle, it is a semicircle or half-circle.
• A line which divides the given figure exactly into two identical figures is called the line of symmetry or axis of symmetry.

• A reflection is like a mirror image.

• Some shapes of tiles can fit in such a way that there are no gaps and overlaps. This tiling is called tessellation.

#### Time

Time   Synopsis
• 4 Time is measured using a clock.
• A clock has two hand, a long hand and a short hand. The long hand is called minute hand and the short hand is called hour hand.
• Some clocks have a third hand called second hand. Generally second hand is the thinnest hand. It moves much faster than the other two hands.
Some Conversions:
• hour $=\text{6}0$ minutes; 1 minute $=\text{6}0$ seconds
$\therefore$ 1 hour $=\text{6}0\times \text{6}0=\text{36}00$ seconds; 1 day $=\text{24}$ hours; 7 days $=\text{1}$ week;        12 months $=\text{1}$ year; 10 years $=\text{1}$ decade; 10 decades$=\text{1}$ century         $\therefore$ 100 years = 1 century   Time Notations:
• The time 12 o'clock in the midnight is written as 12 midnight. The time 12 o'clock in the noon is written as 12 noon.
• The time from 12 midnight to 12 noon is noted as a.m. (ante meridiem) and the time from 12 noon to 12 midnight as p.m. (post meridiem).
• In a 24 hour clock, the hours from each midnight to the next one are numbered from 0 to 24.
• Railway and airlines time tables are based on 24 hour clock.
• We write the 24 hour time in 4 digits. The first two digits represent hours and the last two digits represent minutes.
e.g., 14:20 hours   Time Calculations:
• 12 midnight is written as 24: 00 hours or 00: 00 hours. 12 noon is written as 12:00 hours.
• When we change p.m.to 24 hour clock time we add 12 to the hours and then write hours and minutes together without separating them.
• If the first two digits of 24 hour clock time show more than 12, the time will be in p.m. of 12 hour clock. To get time hours in p.m., we subtract 12 from first two digits.

#### Perimeter and Area

Perimeter and Area   Synopsis   Closed Curve:
• A curve which begins and ends at the same point is called a closed curve.
Perimeter:
• The length of the boundary or edge of a figure is called its perimeter.
• Perimeter of a triangle is the sum of the lengths of its three sides.
Perimeter of triangle
• The perimeter of a square is four times the length of its side.
Perimeter $=(\text{4}\times \text{S})$ units
• The perimeter of a rectangle is twice the sum of its length and breadth.
• Perimeter = 2x (Z + b) units
• Perimeter is expressed in units of length.
• Area:
• The amount of surface covered by a plane figure is its area.
• Area of an enclosed plane is the number of square units that fit into it.
• Area is always expressed in square units.

#### Handling data

Handling Data   Synopsis
• A collection of numbers or facts gathered for some specific purpose is called data.
• Interpreting the collected data gives us information.
• The data collected is organised and represented in pictorial form such as tables and graphs.
• A graph is a pictorial representation of data that gives a lot of information clearly.

• Some kinds of graphs:
(i) Bar graph                (ii) Pictograph   (iii) Pie chart etc.
• A pictograph has pictures or symbols to represent information.
• A pictograph has a title and gives the definition of the symbol.
• Pictographs enable us to compare information and understand facts better.
• A bar graph also helps us compare the information and understand it better. It is also called a column graph.
• Every bar graph must have,
(i) a title that explains the information given in the graph. (ii) the scales on the horizontal and vertical axes. (iii) labels on the axes.
• Circle charts are also used to represent data and compare information.
• In a circle graph, information is represented in different parts of the circle depending on the size of information.
(1-5): The graph shows the number of rubber bands each child has.

#### Plant Life-I (Adaptations in Plants)

Plant Life - I (Adaptations in Plants)     Synopsis
 Tit Bits The bull's horn, acacia tree not only has spines to protect it from grazing animals, but also has swarming ants on it. The ants live in spines and feed on sugar produced by the tree. Any animal which disturbs the ants are vigorously attacked and cannot feed on the tree.

• The process of adjusting to different types of environment is called adaptation.

• The regions in which a living organism lives and dwells is called its habitat.

• The different conditions like type of soil, availability of water, temperature of the place, amount of rain and availability of light.

• Plants of plains have lots of branches and leaves. These can bear heat in the summer. In temperate countries trees shed their leaves in autumn, This helps mem to survive me severe cola in winter.
e.g., Maple tree and Oak tree.
• The plants of hilly areas are tall and straight with needle shaped leaves. These trees bear cones instead of flowers.
e.g., Pine, cedar, spruce, etc.
• Plants growing in hot and damp places have large number of leaves. They remain evergreen and do not shed their leaves.
e.g., Pepper, mango, coconut, neem etc.
• Plants growing in deserts have leaves in the form of spines. These plants synthesise food and store water in their fleshy stem.
e.g., Cactus
• Plants which grow in marshy areas include mangroves. Since the roots are always underwater, there is not enough air for the roots. Breathing roots which grow above the ground help them to take in air.

• Plants which grow in water are called aquatic plants. They can be divided into
(a) Floating plants (b) Fixed Plants (c) Submerged or underwater plants.
• Floating plants are small or light with spongy or swollen parts and float freely in water.
e.g., Duckweed, water hyacinth, etc.
• Fixed plants remain fixed to the bottom of more...

#### Plant Life-II (How Plants Make Food)

Plant Life - II (How Plants Make Food)     Synopsis
 Tit Bits The atmosphere contains very, very little carbon dioxide, plant get most of it from, animals who breathe it out. It from animals who breathe it out. Photosynthesis is the only process by which carbon dioxide is removed from the air and oxygen is added to it.

• Plants can make food on their own. Food is manufactured in the leaves. Hence, leaves are also called food factories of the plant.

• The roots of the plant take in water and mineral salts from the soil and the stem carries them to leaves. The leaves have tiny openings called stomata, through which the exchange of gases takes place.

• The green leaves contain a green pigment called Plants take in water from the soil and carbon dioxide from the air and combine them to form sugar and oxygen in the presence of chlorophyll and sunlight. $carbon\,dioxide+water~\xrightarrow[Chlorophyll]{Sun\,\,light}+\text{ }oxygen$ Chlorophyll

• The reaction takes place only in the presence of light. 'Photo' means light and synthesis means to put together.

• Water, food and minerals are distributed through a network of veins.

• The plant uses some of its food for daily activities and stores the extra food as starch in the roots, stems, leaves, fruits, seeds or sometimes even flowers of the plant.

• When a food material rich in starch is treated with iodine solution, the solution is turned blue-black. This test indicates the presence of starch.

• Some non-green plants get their food from dead and decaying plants.

• In some plants like cactus the leaves are reduced to spines. Hence, the stem performs photosynthesis. Cacti are adapted to survive in deserts.

#### Animal Life-I (Adaptations in Animals)

Animal Life - I (Adaptations in Animals)   Synopsis
 Tit Bits Spiders produce silk to make their webs. They trap prey in the web, but do not get caught in their own webs because the tips of their legs are oily.

• Animals which live on land or in the burrows or below the surface of the ground are called terrestrial animals. Most of these have legs, lungs to breathe and well developed sensory organs like eyes, ears, skin and nose.
e.g. Human beings, lions, rabbits, etc.
• Animals which spend most of their time on trees are called arboreal animals. They have strong arms, legs and claws to hold the branches firmly and support their body weight when they sit on trees.
e.g. Monkey, lizard, chameleon, etc.
• Animals which fly in air are aerial animals. Aerial animals, like birds and bats, have wings to fly.

• Animals which live in water are called aquatic animals. These have modified limbs like fins and flippers which help them to swim. They breathe through gills and lungs.
e.g. Fish, crabs, whales etc.
• Animals which can live in water as well as on the land are called amphibians. These have limbs which help them to swim in water and walk on land.
• Animals which live by eating plants are called plant eating animals or herbivores. They have sharp cutting teeth and strong grinding teeth.
e.g. Buffaloes, goats and sheep.
• Animals which live by eating other animals are called flesh eating animals or carnivores. They have strong tearing teeth.
e.g. Tiger, lion and dog.
• Animals which eat both plants as well as other animals are called omnivores.
e.g. Bear, crow and human beings.
• Animals which live inside or on the bodies of other animals are called parasites.
Some of them have sucking tubes to suck food from hosts. They cause damage to the host.
• Animals adapt their body structure to survive in their surroundings. The following are some examples.
Animals like polar bear, silver fox and himalayan rabbit have brown coats and white thick more...

#### Animal Life-II (Reproduction in Animals)

Animal Life-II (Reproduction in Animals)   Synopsis
 Tit Bits The ostrich is the largest living bird, and lays the biggest egg, weighing almost 1400 gm.

• The process by which new living beings resembling their parents are produced is called reproduction.

• Animals reproduce by giving birth to young ones or by laying eggs.

• The animals which reproduce by giving birth to young ones are called mammals. Human oeings, cows, lions, etc., are some examples or mammals.

• Mammals take care of their young ones by giving milk, cleaning them and protecting them from enemies.

• Birds lay eggs and keep them warm. After some days, eggs hatch and young ones come out.

• Eggs are either oval shaped or round shaped with a thick outer protective shell which protects the growing chick inside. Inside the egg, there is a white thick liquid called egg-white (albumen) and a yellow liquid (yolk) at the centre the chick forms and grows inside the yolk. The growing chick is called embryo.

• Fish lay eggs in water and reptiles like crocodiles, snakes and turtles lay their eggs on land.

• Frogs lay eggs in water which hatch into tadpoles. Tadpoles look like fish. They undergo metamorphosis and grow into frogs.

• Some insects like grasshopper and cockroach pass through three stages in their life cycle. Eggs laid by cockroach develop into small 'baby' insects called nymphs. These look mostly like fully grown insect. Caterpillars are the larvae of butterflies and moths. They go through several changes from the egg stage to the adult stage. This kind of changes in growing is called metamorphosis. The youn gone of cockroach shed their skin several times to become an adult cockroach. This process is called moulting.

• Other insects like housefly and butterfly pass through four stages. The youngones hatched from the eggs are called caterpillars.

• After growing for sometime the larva covers itself more...

#### Food & Digestion, Health & Hygiene

Food & Digestion, Health & Hygiene   Synopsis
 Tit Bits Milk is a called complete food. It is rich in calcium and other minerals, vitamins, proteins and has fat too. Hence drinking milk is very important.

• The food we eat gives us energy to live. Food contains substances that are useful to our body.
These are called nutrients.
• Carbohydrates, fats, proteins, vitamins and minerals are different nutrients required by our body.

• Carbohydrates are the main energy giving foods. Sugar and starch are the important carbohydrates. Wheat, rice, potato, etc. are the important sources of carbohydrates.

• Fats give us heat and energy. Fats give more energy than carbohydrates. Butter, ghee and creams are some sources of fats. Excess fats make us fat and lead to many diseases, Proteins are body building foods. They help our body to grow and repair the damaged parts. Egg, fish, meat, pulses, milk and soyabeans are some important sources of proteins.

• Vitamins keep us healthy and protect us from many diseases. Fruits, vegetables and fish are rich in vitamins. The food items rich in vitamins are called protective foods.

• Vitamins are named A, B, C, D, E and Vitamin D can be prepared in our body with the help of sunlight.

• Minerals help us to make our bones and teeth strong. They help to prepare blood. We get minerals from fruits, vegetables, milk and liver.

• The food we eat is chewed in the mouth. Mouth secretes saliva, saliva makes the food like a paste. It also changes starch into sugar with the help of an enzyme. Later, food is passed into the stomach through food pipe.

• Several digestive juices produced from the walls of stomach break down proteins in the food into smaller substances. Then the food is pushed into small intestine.

• More juices secreted in the small intestine make the food into liquid form and it is absorbed by the blood.

• The undigested food goes into large intestine where some water is more...

#### Teeth & Microbes

Teeth & Microbes   Synopsis
 Tit Bits The enamel is the hard white part on the outside of tooth. It is the hardest substances in the human body.

• Teeth help us to chew food and to break it into smaller pieces. Without the teeth we would not be able to enjoy food.

• A newborn baby has no teeth. Teeth begin to (appear when the baby is six to seven months old. By the age of three years children have 20 teeth. These are called temporary teeth or milk teeth.

• By the age of six years milk teeth begin to fall off and new teeth appear in their place. These are called permanent teeth. At the age of 12 to 13 years, 28 permanent teeth grow. Four more teeth, called wisdom teeth grow between the age of 20 to 25 years. So, an adult has 32 teeth.

• The portion of the tooth above the gum is called the crown. The portion inside the gum is called the root.

• The upper layer of the tooth which is hard is called enamel. The next layer inside is called dentine. The soft material inside the dentine is called pulp and it has blood vessels and nerves.

• There are four kinds of teeth namely, incisors, canines, premolars and molars. Incisors are also called cutting teeth. These are four in number, present in the front side and have sharp edges. These are used for cutting and biting.

• There are four canines on either side and are called tearing teeth. They are very sharp and pointed.

• Premolars are called cracking teeth. They are broad and flat and are next to the canines.

• Molars are broader than premolar teeth and are used for grinding food. So, they are also called grinding teeth.

• The food stuck between the teeth is converted to plaque by the action of germs and cause tooth decay. Plaque reacts with sugar and produces acids which destroy the enamel of the teeth.

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