Category: Science

Introduction

The widely recognized nebular theory postulated that a massive cloud of dust including hydrogen and other gases created the solar system, including the planet earth. Small earthly particles like iron and nickel were created as a result of the earth’s contraction, rotation, and lowering of temperatures. The planet was created approximately 4.5 billion years ago after millions of years of precipitation and accumulation. Since then, the earth’s temperature has decreased, causing the crust to become more fragile. However, the earth’s interior core is still hot and igneous.

A short note on Prehistoric Earth’s Origin of Life

There were numerous theories about the origins of life on Earth. 

• According to the Panspermia theory, some scientists thought life originated from spores that came from outer space, while others hypothesized that it originated from decomposing materials like dirt, straw, etc (Spontaneous generation theory). Different experiments were carried out by various scientists, and they all disproved the hypothesis of spontaneous generation. 
• Later in 1953, Oparin and Haldane advanced the theory that life emerged from pre-existing non-living organic molecules like RNA, DNA, and other similar molecules because of abiotic chemical reactions.
• Numerous studies have suggested that RNA came before DNA, even though it is still unclear what replicating molecule was the earliest. Because RNA molecules can self-replicate and are simpler than DNA, they are considered autocatalytic.

Precambrian Life

The Precambrian period includes the Archean and the Proterozoic eons from 4.6 billion years to 542 million years. Most of the life that existed during the Precambrian period were prokaryotic organisms. Microfossils that looked like stromatolites and cyanobacteria from the Precambrian epoch first revealed the presence of life about 3.8 billion years ago (layered mounds). Additionally, the absence of oxygen in the early atmosphere rendered primitive organisms anaerobic. However, when cyanobacteria developed photosynthesis, it added oxygen to the atmosphere.

Eukaryotes, which have a nucleus, cytoskeleton, organelles, and mitotic spindle, first evolved around two billion years ago. It was once thought that endosymbionts like mitochondria and chloroplasts descended from bacteria. The evolution of eukaryotes benefited greatly from these endosymbiotic relationships.

Cambrian Explosion- Origin of Animal Diversity

The surge in the diversity of multicellular organisms during the early Cambrian epoch, which began 540 million years ago, is known as the Cambrian explosion. Tens of millions of years before the early Cambrian epoch, the first multicellular living forms began to appear as fossils. These ancient animals have diverse body designs from those of living creatures today. They vanished and were replaced by modern-day animal body types in the Cambrian fauna.

Evolution of Land Plants

The evolution of land plants from a green algal ancestor is a significant event in the history of life since it caused profound changes in the earth’s environment and the formation of the entire terrestrial ecosystem. The formation of land plants and the divergence of the four main surviving clades (liverworts, hornworts, mosses, and vascular plants) may have taken place during the late Ordovician and Silurian periods, according to evidence from fossil spores found in the mid-Ordovician.

Formation 

The majority of researchers concluded that the earliest life form and subsequent other life forms on earth appeared as a result of chemical evolution, or the production of molecules. The Nebular theory, developed by Immanuel Kant and Pierre Laplace, postulates that planets are formed by a cloud of hydrogen and helium. Clouds were created by tiny particle collisions, and the planet itself was created through accretion.

Evolutionary Milestones

• Life’s history is represented by several milestones. For instance, unicellular organisms first appeared on Earth, and ever since then, diversification has led to the emergence of complex living forms. These living forms will eventually go extinct and be replaced by other creatures. 
• Complex living forms evolve as a result of this evolution. According to some fossil research, numerous species began to independently become multicellular around 1 billion years ago, and animals started to grow hard portions in their bodies to survive on the earth. 
• Dinosaurs were the most prevalent class of creatures on the planet for millions of years. For a considerable amount of time, they dominated the prehistoric landscape before a disaster led to the extinction of dinosaurs.
• The Great Apes, from which humans emerged, was the next significant event. Human evolution is still clearly visible, although it has not yet reached its conclusion.

Presence of Humans

• The most well-known species, Homo sapiens, is a descendant of hominids, the first creatures that resembled humans. 
• According to several fossil records, archaeological findings, and embryological research hominids are thought to have diverged from other primate species in the southern and eastern African areas 2.5–4 million years ago. 
• As a result, they have bipedalism in common (the ability to walk on two legs).
• Additionally, as hominids evolved and adapted to their habitats, their brain sizes grew. Around 2.3 million years ago, Homo habilis, the earliest human-like hominid, had a brain size of 650–800 cc and started using stone tools.
• Fossils discovered in Java in 1891 revealed the existence of Homo erectus, the next stage of human evolution, some 1.5 million years ago. They have a 900cc larger brain due to evolution. Then they began to migrate from Africa to Eurasia, where they started to learn how to make fire and develop defenses.

Summary

The widely recognized Nebular Theory postulated that a massive cloud of dust, including hydrogen and other gases, created the solar system, including the planet Earth. The majority of scholars concluded that the earliest life form and subsequent other life forms on earth appeared as a result of chemical evolution, or the production of molecules. Dinosaurs were the most prevalent class of creatures on the planet for millions of years. The most well-known species, Homo sapiens, is a descendant of hominids, the first creatures that resembled humans.

Frequently Asked Questions  

1.What is Coal’s Formation Process? List the Types of Coal.
Ans. The layers of dead plants and animals underwent physical and chemical changes as a result of pressure and heat. Deposits rich in carbon were created as a result of this. Different forms of coal include lignite, bituminous coal, and anthracite.

2.Explain Index Fossils?

Ans. Index fossils are fossils that are used to identify geologic formations with broad regional distributions and short time scales. These fossils are numerous, dispersed, limited in geological time, and unique.

3.What Factors led to the Earth’s Changes?
Ans. Physical changes such as mountain development, tectonic movements, volcanic eruptions, climate changes, and biological changes on the planet resulted from the evolution of new life forms.

4.What are the Necessary conditions for Life to Sustain on Earth?
Ans. The necessary conditions for life to sustain on earth are as follows,

• Proper distance from the sun
• Presence of water and the atmosphere
• Existence of the lithosphere and biosphere
• Ideal temperature ranges (around 17 degrees Celsius).

Introduction

The topmost layer of the earth is called soil, and it is made up of several elements. Environmental elements like water, wind, temperature, and even living things usually have an impact on them. One type of soil may not have the same physical or chemical properties as another. The soil is now inhabited by microorganisms like bacteria, algae, fungi, and actinomycetes that fix nitrogen, decompose organic matter, transport vital nutrients, and improve the texture of the soil. High-yielding crops in agriculture depend on the texture, composition, and environmental tolerance of the soil. Consequently, the soil is first prepped before being used for improved harvesting.

What is Soil?

A complex material called soil develops on the earth’s surface. It emerged through the disintegration of rocks. By their porosity, aeration, and water-retention ability, they act as a medium for the growth of plants.

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Types of Soil

Based on its texture and composition, the soil is divided into different categories.

Clay soil:

• Compared to other soil types with a composition of very small particles, clay soil stands out for having particular qualities. 
• It is referred to as heavy soil because the soil particles are firmly packed and there are few or no air spaces between them. 
• It has trouble allowing air and humidity to enter the soil yet is effective at holding a lot of water. 
• Although clay is sticky when wet, it dries out when water vapour escapes from the ground.

Sandy soil:

• Sandy soil is hot and dry because it has a large proportion of sand and little clay. 
• It can be created through the fracturing of rocks. 
• When it rains heavily, the earth can quickly absorb water, which benefits the drainage system. 
• The lack of proper water retention and poor nutrient availability make the soil unsuitable for plant growth.

Loamy soil:

• Silt, clay, sand, and organic matter that has already decomposed make up loamy soil, which has a dark colour. 
• Because the soil’s particles are dispersed, air can easily penetrate it. 
• It works well for plant growth since clay and sand both have beneficial properties.

Silt:

• The particle size of such soil is medium. 
• Although the soil is fertile and smooth, it has few nutrients. 
• It is utilized for drainage since it effectively traps water.

Which Soil is Suitable for Agriculture?

Crops can only be grown in a particular soil if it meets certain criteria, including aeration, fertility, and crop type. Generally speaking, it differs amongst crops. To provide appropriate nutrients and maintain the water, the loam soil is made up of sand, silt, and clay. In this way, it is regarded as appropriate soil for farming.

Components of Soil

• From one place to another, the soil’s precise makeup varies. Minerals, water, and organic and inorganic substances make up the major volume of the soil. 
• Generally speaking, the abiotic (non-living) components are made up of about 45% air, 25% water, 25% minerals, and 5% organic stuff.

Preparation of Soil

Before planting, the soil is prepared to ensure that the region is suitable for farming. The proper growth of crops might benefit from soil preparation. The soil preparation process involves a variety of tools.

Tools Involved in Soil Preparation

Plough:

        Plough is dragged by two bullocks and is composed of wood or iron. The pieces are as follows: 

• Shovel shaft (a long batten of wood). 
• Ploughshare (heavy triangular metal item linked to one pole of shaft) (heavy triangular metal piece connected to one pole of shaft). 
• Beam (the other pole of the shaft is connected to the stand on the necks of bulls).

Hoe: 

• Hoe is used to break up the soil and remove overgrowth. 
• Bulls drag a long wooden pole with heavy metal attached to it to loosen the dirt.

Cultivator:

• Both labourers and cultivators plough the ground. 
• The main ways that tractors are beneficial are by eliminating physical labour and saving time.

Different Steps Involved in the Preparation of Soil

The process of preparing soil involves these three steps: 

Ploughing: 

• It is the process of agitating and moving the soil to bring nutrient-rich soil to the surface. 
• It is an essential phase in agriculture, and iron or wood has been used to apply it. 
• Bullocks or driven cultivators pull the plough. 

Leveling: 

• Due to the numerous huge lumps in the region that was ploughed, it is crucial to level the ground before beginning cultivation. 
• A leveler is a tool with a board made of metal or wood that is used to level the soil.

Manuring:

• Manure is decomposed organic matter that is used as fertilizer to improve the quality and growth of crops. 
• Manure is utilized to replenish the soil with nutrients necessary for the successful growth of crops.

Importance of Preparation of Soil

• By preparing the soil in a way that safeguards the crops from irritants and weeds, it is possible to meet the needs of crops, including those for sufficient water, minerals, oxygen, nutrients, and solar exposure. 
• Ploughing helps cultivators get nutrient-rich soil on the top, promote soil aeration, and get rid of unwelcome weed development. 
• Crops must be properly mowed to ensure a superior harvest.

For more help, you can Refer to Lesson 9 – Story of soil in Science Class 7. Checkout the video Lesson for a better understanding.

Summary

A complex material called soil develops on the earth’s surface. It emerged through the disintegration of rocks. Based on its texture and composition, the soil is divided into different categories, such as clay, sandy, silty, and loamy soil. Crops can only be grown in a particular soil if it meets certain criteria, including aeration, fertility, and crop type. Ploughing helps cultivators get nutrient-rich soil on top, promote soil aeration, and get rid of unwelcome weed development.

Frequently Asked Questions

1. What characteristics of Soil make it Appropriate for Farming?

Ans. A good supply of nutrients and oxygen, the ability to hold onto water, and weather tolerance are all characteristics of soil that make it suited for agricultural use.

2. What makes up Soil?

Ans. 45% of air, 25% of water, 25% of minerals, and 5% of organic matter make up soil. Organic matter is the byproduct of plants and animals that have decomposed.

3. What is Clay Soil?

Ans. Compared to other soil types with a composition of very small particles, clay soil stands out for having particular qualities. It is referred to as “heavy soil” because the soil particles are firmly packed and there are few or no air spaces between them.

4. Define Ploughing and what are the Components of the Plough.

Ans. Loosening and turning the soil is done through ploughing. A plough is a farming implement made up of a beam, ploughshare, and shaft.

5. What kind of Soil can hold a Significant Amount of Water, and Why?

Ans. Clay soil can store a huge quantity of water. It is referred to as “heavy soil” because the soil particles are firmly packed and there are few or no air spaces between them. It has trouble allowing air and humidity to enter the soil yet is effective at holding a lot of water.

Introduction

Agriculture is the practice of raising animals and cultivating crops. To meet the growing need of the population, the seed is crucial in the development of palatable foods. It is a fertilized ovule that germinates to give rise to new plants. The crucial phase in agriculture is choosing good quality seeds because they can reduce replanting, improve uniformity, and encourage the early growth of crops. Proper agricultural practices increase the yield and quality of crops produced.

Selection of Seeds

In general, seed quality affects plant development. Selecting effective seeds, and seed selection can boost agricultural yield. Getting seeds from healthy plants is crucial for agriculture since many different plant diseases can be spread through them. Spreading out chosen seeds over the initially prepared soil is the act of sowing. When choosing seeds for sowing, the following characteristics of the seeds are essential:

• Infections shouldn’t be present in the seeds. 
• They ought to have a strong ability to germinate. 
• A specific seed shouldn’t be combined with weeds or other seeds. 
• They ought to produce the desired amount of crops. 
• Avoid using seeds that have been damaged or crushed. 
• They ought to be immune to illness. 
• They ought to be able to endure challenging circumstances.

Steps to Ensure Proper Growth of Seeds

Agricultural practices are a set of rules used in the agricultural sector to make farming easier and produce better agricultural goods.

Preparation of Proper Soil

The agricultural area must be prepared for crop production through soil preparation. For seeds to germinate and help with efficient agricultural cultivation, it is necessary. The process of preparing soil involves these three steps:

• Tilling/Ploughing: ploughing is the process of liquifying and moving the soil to improve adequate aeration and bring the nutrient-rich soil to the surface of the land. It is done with a cultivator, hoe, or plough.
• Levelling: Because the earth is lumpy and irregularly dispersed, the levelling procedure distributes the soil evenly and levels it out. Additionally, it guards against soil erosion.
• Manuring: To grow and produce fruits and seeds, plants need the right nutrition. Applying manure to agricultural land is known as manuring. Manure is an organic material that has decomposed and is used to enrich the soil by delivering nutrients for crop growth.

Sowing of Seeds or Planting  

Sowing refers to the act of distributing or planting seeds. The right depth and quantity of water must be used while planting seeds. To achieve a desirable culture, the right seeding distance and interval are crucial. The following are some seeding techniques:

• Traditional method: For sowing, a funnel is employed that is filled with seeds that are travelling via pipes with sharp edges. The seeds are dispersed as the pipe’s edge penetrates the ground.
• Broadcasting: By distributing seeds throughout the ground, seeds are sown by the manual or mechanical method called broadcasting. However, owing to the uneven seed dissemination, this strategy is not advised for the growth of high-yielding crops.
• Dibbling: The act of “dibbling” involves evenly spacing the seeds in the seedbed before covering them with dirt. A long, pointed tool called a “dibbler” is used to make holes in the earth before sowing.
• Seed drill: Typically, tractors are utilized to assist in the sowing of seeds using a seed drill. The seeds can be sown at the proper depth and distance, and it is crucial to make sure the soil is covered after sowing.
• Transplantation: The seedlings are moved to the cultivable land after the seeds have initially been sown in a small garden. As a result, this procedure takes a long time.

Proper and Timely Irrigation

Agriculture requires proper irrigation since excessive watering can harm the soil by causing water logging, which hinders the soil’s ability to absorb nutrients and minerals. Because the farmer needs to supply enough water, successive irrigation necessitates breaks.

Supply of Proper Manure and Fertilizers

To provide the nutrients needed for plant growth, manure and fertilizers are added. Manure is made from decomposed animal and plant wastes, making it an environmentally benign substance that also improves soil fertility. Inorganic fertilizers like ammonium sulfate, ammonium phosphate, and NPK are produced commercially, and too much fertilizer can impair the soil’s ability to support plant growth.

Protection of Crops/Plants From Weeds

Unwanted plants, known as weeds, can harm farmed plants by growing near desirable ones. Crop yields are reduced, and pests and diseases use it as a host plant. These are eliminated by hand or using weed killers like naphthalene, acetic acid, etc.

Summary

The crucial phase in agriculture is choosing good quality seeds because they can reduce replanting, improve uniformity, and encourage the early growth of crops. Selecting effective seeds, and seed selection can boost agricultural yield. Agricultural practices are a set of rules used in the agricultural sector to make farming easier and produce better agricultural goods. The right depth and quantity of water must be used while planting seeds. 

Frequently Asked Questions

1. What makes Manure and Fertilizer different from one Another?
Ans. Fertilizers like ammonium sulfate are inorganic, whereas manure is an organic chemical made from the breakdown of plant and animal waste.

2. Write a note on Agricultural Practices.
Ans. Agriculture practices are a collection of rules that make farming easier. It entails the following: preparing the soil, choosing the right seeds, sowing, applying manure, fertilizers, and weedicides, as well as ensuring correct watering, harvesting, and storing.

3. Define Winnowing and Threshing.
Ans. Winnowing is the technique of separating grains utilizing the wind, whereas threshing is the act of freeing harvested grains by hand-battering or mechanical means.

4. What role does Seed Selection Play in Agriculture?
Ans. For the development of new individual plants, seeds are necessary. The development of desirable crops that decrease replanting and increase crop production can be achieved by choosing high-quality seeds.

Introduction

A system of ductless glands that secrete hormones is known as an endocrine gland system. In the blood, hormones are carried directly to their target organs as chemical messengers. As hormones are synthesized in certain tissues, they trigger a cascade of events that allow for certain cellular responses. Adrenal glands are located above the kidney. They are divided into regions cortex and medulla. Both regions produce hormones that regulate electrolyte balance.

What are Adrenal Glands?

The body contains two adrenal glands. These are located above each kidney. They are a part of our endocrine system. Despite their small size, the adrenal glands are quite important for your body’s hormone-related functions. As a result, elements that affect your adrenal glands may have a big impact on your general health. If you believe you might have an adrenal problem, see a doctor.

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Location of Gland

The adrenal glands are endocrine glands that are located over the lateral surface of each kidney’s upper poles. The adrenal glands are located at the back of the abdomen, between the kidney and the ribs. They are triangular, and the parietal peritoneum only covers the front of them. The right gland is pyramid-shaped, while the left gland is moderately-lunar.

                                    

Hormones Secreted by Adrenal Gland 

• The gland’s outer layer is called the cortex. It generates both cortisol and aldosterone. The medulla is the gland’s most interior area. It generates both adrenaline and noradrenaline.
• Epinephrine, also referred to as adrenaline, is a hormone that responds swiftly to anxiety by quickening the heartbeat and raising blood sugar levels in the body. 
• Corticosterone controls the immune system and reduces inflammation in conjunction with hydrocortisone. 
• Cortisol: With the help of cortisol, the body controls and utilizes fats, protein, and carbohydrates. In addition, it weakens the immune system and affects physiology, which the body uses to help it cope with worry. 
• Aldosterone: helps the kidneys keep the blood and tissues of the body’s healthy salt chloride level. 
• Norepinephrine, also referred to as noradrenaline, works in conjunction with epinephrine to respond to anxiety. Its primary function is to prepare the body and mind for combat.

Function

• The adrenal glands are responsible for producing several hormones that help control blood pressure, produce several reproductive hormones, and maintain the proper level of salt in our blood and cells. 
• The adrenal glands’ release of stress-inducing hormones causes one of the most well-known reactions, the “conflict of the panic response.” 
• When and how rapidly an adolescent develops their reproductive system, helping during birth 
• Our endocrine system’s pituitary gland, also known as the “master gland,” controls our adrenal glands. The main controller of your endocrine glands is the pituitary gland, which is located inside your skull. Abnormal signals may interfere with the number of hormones your pituitary gland advises your adrenal glands to generate.

Disease-related to the Adrenal Gland

Adrenal gland dysfunction might manifest when 

• When your master gland is unable to efficiently regulate your hormone production, the adrenal glands may form benign or non-malignant tumours or harmful or cancerous tumours. 
• Can suffer from disorders of the adrenal glands. 
• People are born with particular gene diseases.

Cushing’s Disease

People with Cushing’s syndrome have excessive cortisol production from their adrenal glands. The most common cause of this is prolonged use of high dosages of corticosteroids. Lupus, arthritis, and pneumonia are just a few of the disorders that are treated with corticosteroids. They have cortisol-like effects throughout the body. 

Symptoms:

• The round face, the fat accumulation at the base of the neck, and the fat bulge between the arms.
• Skinny arms and thighs
• Gaining weight unnecessarily
• Prone to scarring skin
• On the hips, chest, and stomach, there are wide, violet stretch marks.

Addison Disease

A rare autoimmune ailment called Addison’s disease may develop when your adrenal glands don’t produce enough cortisol or aldosterone. This self-harm sickness may cause your immune cells to attack the tissues of your adrenal glands. 

Symptoms: 

• Arterial pressure is high despite the weight 
• Loss or gain without cause. 
• Hyperglycemia or intolerance to glucose 
• low amounts of potassium 
• Discomfort, stress, or panic episodes

Congenital Adrenal Hyperplasia (CAH)

Extremely little cortisol is synthesized in congenital adrenal hyperplasia (CAH), a genetic disease. Furthermore, persons who have this condition may also have additional hormonal issues in which their bodies create too much testosterone but not enough aldosterone.

Symptoms: 

• Early acne, body hair, beards, or loud voices (women)
• Rapid growth in children
• Sterility due to underarm hair

Adrenocortical Carcinoma

Adrenocortical carcinoma is a malignant tumour that often develops on the exterior of the adrenal gland. Oftentimes, this type of tumour is only found after it has spread to the body’s other systems over generations.

Summary

The adrenal glands are located above the kidney. Despite their small size, the adrenal glands are quite important for your body’s hormone-related functions. The gland’s outer layer is called the cortex. It generates both cortisol and aldosterone. The adrenal glands’ release of stress-inducing hormones causes one of the most well-known reactions, the “conflict of the panic response.” When your master gland is unable to efficiently regulate your hormone production, the adrenal glands may form benign or non-malignant tumours or harmful or cancerous tumours.

Frequently Asked Questions

1. Is it necessary to have both Adrenal Glands to Survive?
Ans. Since the adrenal glands are necessary for human survival, removing both of them (which is quite unusual) forces the patient to take medications and hormone replacements.

2. Is it Possible to live with just one Adrenal Gland?
Ans. Your doctor will administer painkillers to you. Your body can function regularly if your adrenal gland is working properly. If both of your adrenal glands were lost or if your remaining adrenal gland isn’t functioning properly, you might take medication every day to restore the hormones they were making.

3. Do the Adrenal Glands play a role in Digestion?
Ans. The adrenal glands release the stress hormone cortisone to inhibit bodily processes like the immune response and digestion that are not necessary for immediate survival.

4. What are Hormones that make us Drained?
Ans. The adrenal glands also create the hormone aldosterone, which is problematic since it helps regulate your body’s normal fluid and electrolyte balances. As adrenal depletion increases, it makes your body generate less aldosterone, which results in dryness and electrolyte imbalances.

Introduction

Humans are sexually dimorphic i.e., they have two distinct sexes- male and female. This dimorphism is seen in humans in favour of sexual reproduction which is the main reason for the diversity among humans. Humans progress through a transitional stage known as adolescence as they develop from childhood to adulthood and reach reproductive maturity. Beginning at age 10, adolescence lasts until age 19, after which a person is regarded as an adult. Hormonal changes are the main cause that affects physical appearance and aid in the development of reproductive characteristics.

Secondary Sexual Characteristics

A group of physical traits that separate individuals of one sex from those of the other sex within the same species is known as secondary sexual characteristics. They are necessary for sexual presentation but not directly engaged in reproduction. Males typically attract females for sex, and most of the time, females bear children. Some secondary sexual traits in people include males with facial hair and voice alterations, as well as females with huge breasts and rounded hips. Through adolescence, these characteristics start to emerge.

For more help, you can Refer to our video in Class 8 Science in Lesson no 10. Check out the video Lesson for a better understanding.

Stages of Adolescence

There are 3 stages of adolescence they are-

• • • • Early puberty (ages 10 to 13): At this time, the majority of people experience weight gain and height growth. In females, the hips and breasts develop. Males develop a deeper voice as well as larger Penis and Testicles.
      • Middle puberty (ages 14 to 17): During this time girls stop growing physically in terms of weight and height while males continue to grow in height and weight. Females’ menstrual cycle becomes regular and facial acne affects both sexes equally.
      •  Late puberty (ages 18 to 21): During this stage, the majority of people suffer decreased physical growth. They were already tall, and they are emotionally more stable than middle adolescence teenagers

 

Human males and females show different sexual characteristics as given below-

Secondary Sexual Characteristics of Females

Estrogen‘s effects on females lead to secondary sexual traits. The following are secondary sexual characteristics seen in women:

• Breast enlargement
• rounded Hips
• A leaner upper torso
• A pitched high voice
• Hair in pubic and underarm regions

Secondary Sexual Characteristics of Males

Secondary sexual traits in men are caused by testosterone produced in the testes. The hypothalamus and the secretions of the pituitary gland regulate testosterone in turn. Males’ secondary sexual traits include

• the presence of body hair (arms, chest, and pubic hair)
• facial hair, such as a beard and moustache
• the deep voice brought on by laryngeal expansion,
• a body having enlarged upper body muscles (chest)
• The growth of Adam’s apple.

Summary

The physical attraction between the opposing sexes is the primary goal of sexual dimorphism. Some examples of sexually dimorphic traits in the animal kingdom are the colourful plumage of many bird species and the antlers of reindeer. Human life goes through various growth stages, and a variety of hormones work together to help us reach reproductive maturity. Even while male and female reproductive organs (testes and uterus) are present from birth in humans, reproduction is not feasible until the person reaches adulthood. The period between childhood and adulthood known as adolescence is marked by a range of physiological, physical, behavioural, and psychological changes in a person which gives them the capability to generate the next generation.

Frequently Asked Questions

1. Differentiate between Puberty and Adolescence
Ans: Puberty- Puberty is a condition where an individual reaches reproductive maturity. It is a result of hormones and is more focused on sexual characteristics.

Adolescence- The interval between childhood and adulthood is known as adolescence. Physical, behavioural, and cognitive thinking all undergo a transition. Adolescence deals with both secondary sexual traits as well as the emotional well-being of individuals.

2. What Hormones Regulate Secondary Sexual Traits?
Ans: Following are the hormones with regulating sexual traits in humans

• Male sex hormone testosterone, secreted by the testicular Leydig cells, gives men their secondary sexual traits.
• Secondary sexual traits in women are brought by the female sex hormone estrogen, released from the ovaries.
• Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the pituitary gland, which is regulated by gonadotrophin-releasing hormone (GnRH) of the hypothalamus, control the secretion of estrogen and testosterone.

3. What Causes Face Acne to Appear in Adolescence?
Ans: As a result of hormonal changes, adolescents’ have overactive oil glands. These oil glands release sebum which clogs the skin pores and hence creates face acne or pimples.

Introduction

The matter may be found on Earth in three different states: solid, liquid, or gaseous. Every matter is composed of incredibly tiny building components called atoms and molecules. These particles in a solid are strongly attracted to each other and vibrate in place without passing by each other. Despite not being as strong as it is in a solid, there is still an attraction between the particles in a liquid. The proximity and frequent movement of the particles in a liquid allow them to slip past one another. There is only a weak attraction between gaseous particles. They are continually moving and spread out compared to the particles in a solid or liquid. Here the particles do not interact when they collide; they just strike and bounce off of one another. This article provides a thorough understanding of the concept of matter of space between particles and attraction between the matter particles with specific instances.

Particles have Space between Them

Let’s observe a small activity to determine whether the particles are separated from one another; this is explained below.

Experiment

Take a beaker filled with 100 ml of water and then add 20 gm of sodium chloride (table salt) into it. Make sure to swirl the water with a glass stirring rod until all the salt has completely dissolved. The salt will dissolve, and then we will get a solution.

Observations

It has been observed that even after 20 gm of salt has been dissolved in 100 ml of water, the level of the water doesn’t actually rise. This displays how free and interparticle space-containing water atoms are. This area is known as the interparticle or intermolecular space. In this interparticle area, the salt granules that were scattered have settled.

Particles of Matter are Constantly Moving at Random

Diffusion and Brownian motion demonstrate that particles are moving.

Diffusion

A material will mix and disperse with another substance through a process called diffusion while its particles are in motion. To homogenize the mixture, this process is repeated. For instance, the ink diffuses in the water as a result of the random movement of water and ink particles. Ink migrates from areas of higher concentration to regions of lower concentration at a pace that is inversely associated with the liquid diffusion rate of the ink. Diffusion occurs in liquids, solids, and gases, however, it occurs more rapidly in gases and less efficiently in solids.

Brownian Motion

Brownian suspended several pollen grains in water and then examined them under a microscope. He saw that the pollen grains were moving in a zigzag pattern. The movement is significantly more evident when the water is warmed. Water is made up of randomly migrating atoms. As a result, the moving atoms frequently strike the pollen grains, causing them to migrate. As an example of Brownian motion, the pollen grains are travelling in this manner.

Particles of Matter Attract Each Other

A force acting on the particles of matter holds them together. Some substances crumble into powder, while others form tiny crystals, and still, others are challenging to separate. The strength of the force of attraction varies from one type of substance to another, depending on that substance. This is done so that the force of attraction between the particles can keep the particles inside them. This interparticle force of attraction exists in all substances that cause the attraction of particles. Therefore, to break objects, we must defeat the force of attraction. A varying amount of strength is necessary depending on the chemical.

Examples show that breaking a chalk is easier than breaking a nail. This illustrates how 

various material particles have varied levels of attraction. The attraction between particles of the same material is referred to as “cohesion.”

Summary

The particles are separated by a certain amount of space, in which the gaseous form of matter has the largest inter-particle space among the three states of matter. Interestingly, the interparticle gaps that exist in various types of matter are what give rise to the three states of matter, and therefore the density of different states of matter increases from a gas to a solid state (for example water vapor to water and then ice). 

Frequently Asked Questions

1. Define Matter.

Ans: A component that is made up of several types of particles, takes up space, and has motion is referred to as “matter.”

2. What Constitutes Matter?

Ans: Matter is made up of atoms, which are made up of electrons, protons, and neutrons.

3. How to Develop the Model of Particles of Gas and Liquid?

Ans: By compressing a flexible plastic container with a balloon on top, we can imitate the gas particles. We can also try to squeeze a water-filled container as part of their modelling of liquid particles.

Introduction

One type of energy that is essential to our existence is light. We are unable to envision a world without light. Light improves the beauty of everything around us and allows us to see. In both science and art, light is a crucial element. One of the crucial scientific instruments that enable scientists to examine things all across the world is light.

Some scientific theories claim that it is made up of particles, while others assert that it is made up of waves. What is the medium of propagation if the light is a wave? How does light move? We shall find answers to some of these questions in this article.

How does Light Travel?

Light can pass through a medium and in a vacuum. However, there won’t be any particles in a vacuum that light can’t reflect off of. Therefore, light is invisible in a vacuum. Light can reflect in the air when it strikes dust or other particles, making light visible in the atmosphere. Light may be thought of as having waves. Different light waves have varied wavelengths, and different light has different colours based on the wavelength. For instance, the shortest wavelength of light has a violet colour, whereas the highest wavelength of visible light has a red colour. Light, being a wave, may exhibit wave characteristics like diffraction and interference.

The answer to the question of how light typically moves is that it moves straightforwardly. However, the truth is that light’s smaller diffraction effect is the reason it appears to move in a straight line. The spreading out and the illumination of an area where a shadow is anticipated is known as diffraction, which is the bending of waves around an object. The wavelength of light is on the order of nanometers. We cannot see impediments of this size with our unaided eyes because the wavelength is too narrow. As a result, we see that light moves in a straight path. Rectilinear propagation of light is another name for the way that light moves in a straight line.

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Experiment with the Straight Line Motion of Light

Normal light travels in a straight line because there isn’t enough diffraction to cause any noticeable effects. We demonstrate that light moves in a straight line using a basic experimental setup. In front of a candle on the tabletop, arrange three cardboard sheets back to back. Ensure that the candles and cardboard sheets are arranged in a straight line. On each cardboard sheet, poke a pinhole after lighting the candle. To allow for the visibility of the candle’s flame, the holes must be made at equal heights. Now, observe which line light travels in by looking through the holes. Along the slender line of holes, the thin flame will be visible. Now move one of the cardboard sheets to either side and observe the flame. Can you see the flame? The flame won’t be seen when you move the cardboard sheet. Reposition the cardboard sheet in its original location. The flame may now be seen. The experiment diagram is shown below. From this experiment, we may infer that light moves in a straight line.

Examples of Straight-Line Motion of Light

• When a lamp, torch, or another source of light emits light, it travels in a straight line.
• When sunlight enters a dusty environment through tiny holes, a straight-line trail of light is apparent.
• The object will become invisible when an opaque object is placed in front of it. The reason for this is that an opaque object prevents light from bending through its corners.

Summary

The light rays move in a straight line. The minimized diffraction effects of light facilitate the propagation of the light in a straight path. Examples, where the light rays travel in a straight line, are the light ray that comes from a train, a torch, and/or a lamp.

Frequently Asked Questions

1. What is Rectilinear Propagation of Light?

Ans: The motion of the light rays in a straight line is termed the rectilinear propagation of the light.

2. Explain why Light Travels in a Straight Line?

Ans: Diffraction is a wave characteristic of light. Only when the wavelength of the light wave is of the order of the dimension of the size of the particle it collides with, and the phenomena of diffraction take place. The wavelengths of light are on the order of nanometers. Typically, a nanometer-sized item is invisible to the human eye. Light’s diffraction impact is therefore too modest to be taken into account and travels in a straight-line path.

3. Why is Light Invisible in a Vacuum?

Ans: Light can travel through the vacuum, however, since there are no particles available in the vacuum, light cannot reflect in a vacuum and therefore light is invisible in a vacuum.

Introduction

Pressure can be defined as the force exerted perpendicularly per square unit of area of any object. It is represented by the formula,                                                                                                                        

                                                             P = F ⁄ A

where P is the pressure, F is the force exerted on the object, and A is the area of the object. Pressure is measured in pascal, and is classified into absolute, atmospheric, differential, and gauge pressure. A change in pressure has different effects on different states of matter.

Change in Pressure

Since the pressure exerted on an object is the amount of force applied per unit area of that object, a change in area or a change in the amount of exerted force can result in a change in pressure. For example, if the surface area decreases, the pressure increases simultaneously when the surface area decreases, the pressure decreases provided that the force applied remains constant. 

Effect of Pressure on the States of Matter

Pressure change can have different effects on different states of matter. By exerting pressure on the matter particles, we can draw them closer. Therefore, applying pressure can cause liquids to turn into solids, and when pressure is applied to a gas that is contained in a cylinder, the gas begins to compress and turn into a liquid. As pressure rises, the volume of the gas reduces, which causes the gas to change into a liquid and then finally a solid. The volume of a gas is inversely related to its pressure and directly relates to the number of molecules it contains.

Pressure has less of an impact on solids because they are non-compressible forms of matter. By applying pressure and lowering the temperature, liquids can be transformed into solids.

Effect of Pressure on Equilibrium

The equilibrium will adjust to minimize a change in the pressure of a gaseous reaction mixture. If the pressure is raised, the equilibrium will change to favour a fall in the pressure. The equilibrium will change if the pressure is reduced to favour an increase.

When a system’s volume is reduced, the pressure will rise (and the temperature is constant). A greater number of collisions occur with the container’s walls. There will be fewer collisions and hence less pressure if there are fewer gas molecules. The equilibrium will change in a way that reduces the number of gas molecules, which will likewise reduce the pressure. To forecast which way equilibrium will shift in response to a change in pressure, we must consider how many gas molecules are involved in the balanced reactions.

For example, the chemical reaction between nitrogen and hydrogen is shown below:

                                                           N2 (g) + 3H2 (g)→ 2NH3↑

The proportion in the equation that balances is 1:3:2. In other words, the 1N2 molecule combines with the 3H2 molecule to produce NH3 gas (from the balanced equation). Four molecules of reactant gas must therefore be present to produce two molecules of product gas.

• Pressure buildup will favour the reaction which results in fewer gas molecules. Because there are fewer product gas’ molecules, the forward reaction is more advantageous. Due to the rightward shift in equilibrium, the yield of NH3 will rise.
• The reaction that produces more gas molecules will be more favourable as pressure drops. If there are more reactant gas molecules present, the reverse reaction is more favourable. As a result of the equilibrium shifting to the left, the yield of NH3 will decline.

Some Facts

• Pressure is directly proportional to the temperature.
• In contrast to solids and liquids, gases are more easily subjected to pressure.
• Compared to gases, solids and liquids are less sensitive to pressure.
• When air pressure is raised, the boiling point of water rises.
• The equilibrium will adjust to minimize the change in pressure of the gaseous mixture.

Frequently Asked Questions

1. Does Changing the Size of the Container Affect the Pressure?

Ans: No change in concentration could change the pressure if the equilibrium reaction does not involve a change in the number of molecules in the gas phase. Therefore, altering the container’s size without also altering the pressure would have no impact on the reaction. The number of molecules stays constant and applies the same pressure whether the container size decreases or grows.

2. How can the Physical Condition of the Matter be Altered?

Ans: It is also possible to change the physical state of matter by adjusting the pressure that is applied. For example, by applying pressure and lowering the temperature, gases can liquefy. 

3. How does Pressure Affect the Boiling Point of a Liquid?

Ans: All liquids evaporate with an expansion. The expansion and delay of vaporization are the results of pressure on the surface. As a result, when pressure is applied, the boiling point rises.