CHAPTER 6 REACHING THE AGE OF ADOLESCENCE
When the body undergoes changes that lead to reproductive maturity, it is called adolescence. When the human body undergoes these changes, it is called the beginning of puberty and it ends when the adolescent reaches the reproductive maturity.
CHANGES AT PUBERTY
Increase in height: Puberty leads to an increase in height as the bones of the arms and the legs elongate to make the person tall.
Change in body shape: For girls, the region below the waist becomes wider and for boys, shoulders broaden and body muscles grow.
Voice change: At puberty, the voice box (or larynx) begins to grow. Boys develop a larger voice box than girls. As a result, the voice box protrudes out and can be seen as Adam’s Apple Girls develop an high pitched voice whereas boys develop a deep voice.
Increased activity of sweat and sebaceous glands: The secretion of sweat glands and oil glands increases during puberty and this causes acne and pimples on the face.
Development of sex organs: In boys, the testes and penis develop completely and testes start to produce sperms. In girls, ovaries enlarge and eggs begin to mature.
Reaching mental, emotional, intellectual maturity: A lot of changes happen in an adolescent’s body and these changes lead to a mental, intellectual and emotional maturity to develop in them.
SECONDARY SEXUAL CHARACTERS
The additional features that help to differentiate between the male and female are called secondary sexual characters. For boys, the chest hair, facial hair, etc. are secondary sexual characters. For girls, the development of breasts is secondary sexual characters. The common changes for both genders are hair growth under arms and pubic region.
WHY DO THESE CHANGES OCCUR?
An endocrine gland secretes hormones. Hormones are chemical substances which control the physical changes that occur at puberty. The male hormone is called testosterone which is released by the testes. The female hormone is called estrogen and is produced by the ovaries. The estrogen is responsible for the development of the breasts. The milk secreting glands or the mammary glands develop inside the breasts.
All these hormones are controlled by a hormone that is secreted by the pituitary gland.
REPRODUCTIVE PHASE OF LIFE IN HUMANS
For females, the reproductive age begins from 10-12 years of age till about 45-50 years of age. The ovum, once matured, is released by one of the ovaries once in about 28 to 30 days. The wall of the uterus thickens so that it can receive the egg. If fertilization occurs, it result in pregnancy but if fertilization does not occur the thickened lining and the blood vessels are shed of and this cause bleeding in women. This is known as menstruation. The beginning of menstrual flow is called menarche and when it stops ate the age of 45-50, it is called menopause. This monthly cycle of bleeding is called menstrual cycle.
SEX OF THE CHILD
If the child has the XY set of chromosomes, it is a boy and if the child has XX set of chromosome, it is a girl. The egg has the X and the 2nd chromosome is given by the sperm. It can be X or Y.
Adolescence can be a tough time, both physically and mentally. It is important to take care of your body during adolescence. Eating good food, exercising and maintaining personal hygiene is very important.
CHAPTER 5 REPRODUCTION IN ANIMALS
The process of reproduction is producing young ones of the species. Reproducing is important for the continuation of a species.
MODES OF REPRODUCTION
(i) Sexual reproduction
When reproduction occurs from the fusion of male and female gametes is called sexual reproduction.
Male reproductive organs:
Male reproductive organs include a pair of testes, two sperm ducts and a penis. The male gametes are called sperms and are produced by testes. A sperm is a single cell. It has a head, a middle piece and a tail.
Female reproductive organs:
Female reproductive organs are a pair of ovaries, oviducts (fallopian tubes) and uterus. The female gametes are called ova or eggs. Eggs are also single celled.
When sperms come in contact with an egg, one of the sperms fuses with the egg and this process is called fertilization during which the nuclei of both the egg and the sperm fuse together to form a single nucleus. This fertilized egg is called a zygote. Since the fertilization takes place inside the body of a female, it is called internal fertilization.
Sometimes fertilization may take place outside the female body. This is called external fertilization.
Development of embryo:
When the zygote divides repeatedly, it gives rise to a ball of cells which then begin to form group of cells which develop into different tissues and organs of the body. This structure is called an embryo.
When the embryo matures a little more, its body parts can be identified. This stage is called the foetus.
Viviparous and oviparous animal:
The animals which give birth to their young ones are called viviparous animals and the animals which lay eggs are called oviparous animals.
(ii) Asexual reproduction
The type of reproduction that involves only one parent is called asexual reproduction. In this type of reproduction, an animal divides into two individuals. This process is called binary fission.
In hydra, new individuals develop from buds and this process is called budding.
CHAPTER 4 CELL
The basic structural unit of a living organism is called a cell.
VARIETY OF CELLS
There are a number of varieties when it comes to cells. Some of them are:
CELL STRUCTURE AND FUNCTION
Similar cells performing similar functions form a tissue.
Tissues combine to form an organ.
And every organism is made up of organs.
This goes out to show the cell is the basic structure of every living organism.
PARTS OF A CELL
CHAPTER 3 CONSERVATION OF PLANTS AND ANIMALS
Deforestation is the clearing of forests to use the land for other purposes.
EFFECTS OF DEFORESTATION
CONSERVATION OF FOREST AND WILDLIFE
Sanctuary: These are areas where the biodiversity of the area is protected from any outer disturbance
National Park: These are areas reserved for wild life they can freely the habitats and natural resources.
Biosphere reserve: These are large areas of protected land for not just conserving wildlife and plants but also the traditional life of the tribal people living in the area.
FLORA AND FAUNA
The plants found in a particular area are called flora of that area.
The animals found in a particular area are called fauna of that area.
The species of plants and animals which are found exclusively in a particular area are called endemic species.
The species whose numbers are becoming diminished to a level at which they might face extinction are called endangered species.
RED DATA BOOK
Red Data Book contains the list of all the endangered species across the globe.
Migration is when animals, generally birds, move to far away areas during a particular time because of climatic changes.
RECYCLING OF PAPER
To reduce deforestation, paper must be recycled and wasted less.
To increase the forest cover, reforestation has to be done. Reforestation is the planting of new tres in the deforested areas.
CHAPTER 2 MICROORGANISMS
Living organisms that we cannot see with our eyes alone are called microorganisms or microbes. They are classified into four major groups: bacteria, fungi, protozoa and some algae.
Viruses are also microorganisms but they reproduce only inside the host organism.
Disease causing microorganisms are called pathogens. Some common diseases caused by microorganisms are:
Chicken Pox: Virus
Hepatitis B: Virus
PRESERVATION OF FOOD
(i) Chemical method: By using preservatives
(ii) By common salt
(iii) By sugar
(iv) In oil and vinegar
(v) Heat and cold treatment: Pasteurization
(vi) Storage and packing
Certain bacteria present in the soil take nitrogen from the air and convert it into nitrogenous compounds. Certain bacteria convert nitrogenous compounds present in the soil into nitrogen gas which is then released into the atmosphere.
CHAPTER 1 CROP PRODUCTION AND MANAGEMENT
Plants of the same kind grown at one place on a large scale are called a crop.
The tasks performed in order to grow a crop are called agricultural practices or activities. These are as follows:
(i) Preparation of soil
The soil is loosened and turned. This process is called ploughing or tilling. Sometimes manure can be added before tilling so that it gets mixed with the soil properly.
Seeds are scattered over the field. Good quality seeds are selected for good crop. This can be done using traditional tools such as funnels or by modern methods such as drilling.
(iii) Adding manure and fertilisers
Manure and fertilisers are added to the soil to make it rich in nutrients. Manure is organic while fertiliser is chemical in nature.
Irrigation is the process of supplying water to the crops. Water can be drawn from ponds, lakes, rivers, dams, canals, wells, tubewells, etc.
(v) Protection from weeds
The undesirable plants which grow along with the crop are called weeds. Removing weeds is called weeding. They can be manually uprooted or sprayed with weedicides which kill the weeds.
When the crop matures, it is finally cut. This is called harvesting.
It is important to store the crop grains in a proper manner to keep them safe from insects and rodents. Large scale storage of grains is done in granaries.
FOOD FROM ANIMALS
When animals are reared for food, it is known as animal husbandry.
CHAPTER 5 POLLUTION OF AIR AND WATER
When unwanted substances enter the air and contaminate it causing harmful effects on both living and non-living, it is called air pollution.
These unwanted substances are called air pollutants.
Major air pollutants: Carbon monoxide, carbon dioxide, nitrogen oxides, smoke.
Effects of air pollution: Respiratory problems, smog (smoke+ fog), global warming, reduced air quality, acid rain
When unwanted substances enter the water and contaminate it causing harmful effects on both living and non-living, it is called water pollution.
These unwanted substances are called water pollutants.
Major water pollutants: Sewage, industrial wastes, pesticides that wash off into water bodies.
Effects of water pollution: Water related diseases, danger to aquatic life forms
Potable water: Water that is suitable for drinking is called potable water.
Ways to purify water: Filtering, boiling, chlorination
CHAPTER 4 COMBUSTION AND FLAME
When a substance reacts with oxygen to give off heat, the process is called combustion. The substance is called combustible substance or a fuel.
The lowest temperature required for a substance to catch fire is called its ignition temperature.
The substances which have low ignition point are called inflammable substances.
Controlling fire: To control fire, the oxygen supply to the fire has to be cut off.
Types of combustion:
When a substance burns and a sudden evolution of heat, light and sound takes place, it is called an explosion.
The different zones of a candle flame are:
A fuel is a substance which is a source of energy. The properties of a good fuel are:
The amount of heat energy produced on complete combustion of 1 kg of a fuel is known as its calorific value. Unit of calorific value is kilojoule per kg (kJ/kg).
HARMFUL EFFECTS OF BURNING FUELS
CHAPTER 3 COAL AND PETROLEUM
INEXHAUSTIBLE NATURAL RESOURCES
The resources present in unlimited quantity and will not be exhausted by human use are called inexhaustible natural resources. E.g. Air
EXHAUSTIBLE NATURAL RESOURCES
The resources present in limited quantity and will be eventually exhausted by human use are called exhaustible human resources. E.g. Crude oil
Formation of coal:
When plant matter got buried under the soil a long time ago, it got converted into coal under high temperature and pressure. Coal is black, stone-hard and mainly contains carbon and therefore the formation of coal is called carbonisation. Coal is a fossil fuel.
Processing of coal:
Processing of coal gives many useful products like:
Formation of petroleum:
As the organisms under the sea died they got buried under layers of sand and clay. Over millions of years, under high temperature and pressure and in the absence of air, these dead organisms transformed into petroleum and natural gas.
Refining of petroleum:
Petroleum is a dark oily liquid having an unpleasant odour. Various constituents of petroleum are separated in petroleum refinery. The following are the constituents of petroleum:
Natural gas is a major fossil fuel. It is stored under high pressure as Compressed Natural Gas (CNG). It is used for power generation and as fuel in vehicles. Compared to other fuels available, natural gas is a cleaner fuel as it is less polluting.
Coal and petroleum are exhaustible resources. The rate at which these fuels are being consumed, we will run out if them in a few hundred years. Therefore, these fuels must be conserved.
CHAPTER 2 MATERIALS: METALS AND NON-METALS
PHYSICAL PROPERTIES OF METALS
PHYSICAL PROPERTIES OF NON-METALS
CHEMICAL PROPERTIES OF METALS ANDS NON-METALS
USE OF METALS
USE OF NON-METALS
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