Standard Seven General Science Review

The Constitution of India and National Identity

Under Chapter IV A, Article $51A$, the Fundamental Duties are established for every citizen of India. These duties mandate that citizens must abide by the Constitution and respect its ideals and institutions, including the National Flag and the National Anthem. It is a duty to cherish and follow the noble ideals that inspired the national struggle for freedom, as well as to uphold and protect the sovereignty, unity, and integrity of India. Citizens are expected to defend the country and render national service when called upon, to promote harmony and a spirit of common brotherhood among all people regardless of religious, linguistic, and regional or sectional diversities, and to renounce practices derogatory to the dignity of women. Furthermore, citizens are tasked with valuing and preserving the rich heritage of India’s composite culture and protecting the natural environment, encompassing forests, lakes, rivers, and wildlife, while showing compassion for all living creatures. The development of a scientific temper, humanism, and the spirit of inquiry and reform is required, along with the safeguarding of public property and the abjuration of violence. Parents or guardians are obligated to provide opportunities for education to their children or wards between the ages of six and fourteen years.

The Preamble of the Constitution declares India to be a Sovereign, Socialist, Secular, Democratic Republic. It aims to secure Justice (social, economic, and political), Liberty (of thought, expression, belief, faith, and worship), and Equality (of status and opportunity), while promoting Fraternity to assure the dignity of the individual and the unity and integrity of the Nation. This Constitution was adopted, enacted, and given to the people in the Constituent Assembly on the twenty-sixth day of November, 1949.

National identity is further expressed through the National Anthem, Jana-gana-mana, and the National Pledge. The pledge affirms that all Indians are brothers and sisters, expresses pride in the country's rich and varied heritage, and commits to the devotion of its people, stating that happiness lies in their well-being and prosperity.

Adaptation and Diversity in the Living World

The earth hosts a vast diversity of living things. In plants, this is seen in varying flower colors, habitats ranging from water to water-scarce deserts, and sizes from microscopic to huge. Animals also show diversity through unicellular or multicellular structures, being vertebrates or invertebrates, and inhabiting aquatic, terrestrial, amphibian, reptilian, or aerial environments. Adaptation is defined as the gradual changes that occur in the body parts and behavior of organisms, helping them to adjust to their specific surroundings over a long period of time.

Geographical conditions dictate specific plant adaptations. In snowy regions like Kashmir, coniferous trees like deodar and pine flourish; their conical shape with sloping branches prevents snow accumulation, and thick bark helps withstand extreme cold. In the deserts of Rajasthan, plants like cactus and acacia (babhul) are found. Since deserts have a severe scarcity of water, these plants are either leafless or have leaves modified into thorns or needles to minimize water loss by evaporation. Their stems are green and fleshy, performing photosynthesis and storing water. Roots penetrate deep into the soil in search of water, and stems are often covered with a thick waxy layer.

Aquatic plants possess submerged stems with floating leaves and flowers. Surfaces of leaves and stems are often covered with a waxy layer. Leaves may be thin and ribbon-like to withstand fast water currents. Stems and petioles contain air spaces to facilitate floating. Conversely, forest regions see trees growing tall to compete for sunlight, with climbers and vines using spring-like tendrils for support to reach great heights. Grassland plants feature fibrous roots to prevent soil erosion. Equatorial regions have dense forests where animals like tigers and elephants hide, while cold regions have short grasses inhabited by animals like rabbits.

Adaptation for Nutrition and Ingestion in Plants

Most plants are autotrophic and anchored in the ground, but some exhibit parasitic behavior. The dodder (cuscuta) is a parasitic plant consisting of yellow wire-like stems. Being leafless, it cannot perform photosynthesis and instead relies on haustorial (sucking) roots that penetrate the host plant's conducting vessels to absorb nutrients and water. Fungi, lacking chlorophyll, obtain food from starchy materials like bread or bhakri using root-like fibers.

Insectivorous plants, such as the Drosera burmanii (identified by Johannes Burman in 1737), Venus flytrap, and pitcher plant, grow in nitrogen-deficient soil. They fulfill their nitrogen needs by consuming insects through specialized adaptations like attractive colors and sticky droplets that trap prey. Pitcher plants produce food via photosynthesis but still consume insects to supplement nitrogen.

Adaptations in Animals

Aquatic animals like fish have undergone changes such as developing scales on the skin and fins on the body. Their bodies are spindle-shaped, tapering at both ends to minimize water resistance. Fish breathe through gills and have air bladders to assist with floating; their eyes feature transparent eyelids. Higher amphibians like frogs and water birds like ducks have webbed toes that act like oars for swimming. Frogs have slippery, smooth skin and a triangular head for easy movement in water, and they can breathe through their skin in water and using lungs and nose on land.

Carnivorous animals like lions and tigers have strong legs for speed, sharp claws, and pointed canine teeth to tear flesh. Tigers have padded paws to stalk prey silently, and their eyes are positioned in front of the head to spot prey from long distances. Herbivores, such as deer and blackbucks, have eyes on the sides of the head for a wide-angle vision to detect predators. Their tapered legs and strong hooves allow for long leaps and fast running, while long, movable ears receive sounds from far away.

Desert animals have thick skin to prevent water loss, long legs with flat cushioned soles, and nostrils protected by skin folds. Their eyelashes are long and thick. Many desert creatures like snakes and lizards are active at night and live in deep burrows during the day. In snowy regions, animals like the polar bear and white fox have white or silver body colors and long, thick hair to survive the cold. Aerial animals like birds have light, hollow bones and feathers, with forelegs modified into wings and a spindle-shaped body to reduce air resistance. Insects similarly have light bodies and two pairs of wings for flight, alongside six stick-like legs. Reptiles like snakes have scaly skin, while house lizards use clawed toes and thin soles for creeping.

Theories of Evolution and Classification Hierarchy

Charles Darwin proposed two major principles regarding evolution. The first, the theory of survival of the fittest, suggests that organisms best adapted to a changing environment are most likely to survive. The second, natural selection, implies that if an organism is born with a new beneficial characteristic that helps it survive, that change is preserved in the next generation.

To manage the diversity of the living world, scientists use a hierarchy of classification starting with Kingdom (Animalia or Plantae) and descending through Phylum, Class, Order, Family, Genus, and finally Species. Binomial nomenclature, introduced by Carl Linnaeus, uses two names for each organism: the Genus (first part) and the Species (second part). For example, the scientific name for a human is Homo sapiens, and for a mango, it is Mangifera indica. Other examples include the dog (Canis lupus familiaris), cow (Bos taurus), hibiscus (Hibiscus rosa-sinensis), and jowar (Sorghum bicolor).

Plant Structure and Function

The root is the part of the plant growing below the soil for support. It originates from the radicle of the seed, while the part growing above is the plumule. Roots can be tap roots (thick near the ground, with secondary roots spreading wide) or fibrous roots (thread-like). Dicotyledonous plants usually have tap roots, whereas monocotyledonous plants have fibrous roots. Root tips are protected by a root cap and have root hairs for absorption. Some roots are modified for additional functions, such as prop roots in banyan trees, stilt-roots, or breathing roots (pneumatophores).

The stem grows from the plumule and features nodes, from which leaves emerge. The space between nodes is the internode, and the tip of the stem is the bud. Leaves are thin, flat, and green. The broad part is the lamina (leaf-blade) with edges called margins (entire, dentate, or lobed). Leaves can be simple (undivided blade) or compound (divided into leaflets). Arrangement on the stem can be alternate, opposite, whorled, or spiral. Venation patterns include reticulate (forming a network, like the peepal leaf) or parallel (running from base to apex, like the maize leaf).

Flowers possess a stalk called a pedicel and a base called the receptacle. The four main parts are: (1) Calyx (green sepals), (2) Corolla (colorful petals), (3) Androecium (male part with stamens consisting of anther and filament), (4) Gynoecium (female part with carpels consisting of stigma, style, and ovary). Pollination occurs when pollen grains from the anther fall on the stigma, leading to fertilization where ovules become seeds and the ovary develops into a fruit. Seeds can be dicotyledonous (divide into two equal parts) or monocotyledonous (cannot divide).

Properties of Natural Resources: Air and Water

Air is a mixture of gases that has mass and weight. It exerts atmospheric pressure, which at sea level is approximately $1,01,400\,N/m^2$. Bernoulli’s principle states that air pressure decreases as air velocity increases. Air has the capacity to hold water vapor; when this capacity is exceeded at low temperatures, vapor condenses into dew. Humidity refers to the proportion of moisture in the air. Air also exhibits the scattering of light as rays hit tiny particles of gas and smoke. It acts as a medium for sound transmission; air density increases in winter, making sounds like train whistles clearer.

Water is a fluid substance with volume but no fixed shape. It expands and increases in volume upon freezing, meaning ice is lighter than liquid water and floats. The anomalous behavior of water occurs when its temperature falls below $4^∘C$; while most liquids increase in density as they cool, water's density is maximum at $4^∘C$. Below this, it expands, allowing aquatic life to survive under frozen surfaces in cold countries. Water is a universal solvent due to the high number of substances that can dissolve in it. Its density is calculated as $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$, expressed in $g/cc$.

Properties and Structure of Soil

Soil is classified by its color, which depends on texture, organic ingredients, and chemical components like iron and lime. Soil texture is defined by particle size: (1) Sandy soil has large particles, drains rapidly, is easy to plough, but is less fertile as its minerals (silicon dioxide/quartz) do not dissolve to provide nutrients. (2) Silt soil has medium particles, is more fertile, and contains higher organic matter. (3) Clay soil has the smallest particles, feels smooth, and has high water-holding capacity, though it is difficult to plough.

Soil structure (columnar, laminar, granular, or block-shaped) is vital for fertility because it provides oxygen to roots and ensures good drainage. Plasticity is a property that allows soil to be shaped and baked into durable items like bricks or pots. Useful soil types include China clay (Kaolinite), which used for crockery; Shadu soil for statues; Terracotta soil for decorative pots; and Multani soil for cosmetics. Soil testing helps determine pH levels and deficiencies. Ideal soil $pH$ is between $6.5$ and $7.5$; values below $6$ or above $8$ indicate diminished fertility. Crop rotation, such as planting leguminous crops after wheat, helps restore soil nutrients.

Nutrition and Photosynthesis

Nutrition is the process of taking in and using food for energy, growth, and tissue repair. Macro-nutrients (carbohydrates, proteins, fats) are needed in large quantities, while micro-nutrients (minerals, vitamins) are needed in small amounts. Plants produce food via photosynthesis using sunlight, chlorophyll, water, and nutrients from soil, and carbon dioxide from air: $6 CO_2 + 6H_2O \xrightarrow{\text{Sunlight / Chlorophyll}} C_6 H_{12} O_6 + 6O_2$

The transport system in plants involves the xylem (transports water and minerals upward) and phloem (transports food from leaves to the rest of the plant). Although air contains gaseous nitrogen, plants cannot use it directly. Nitrogen fixation occurs biologically via micro-organisms like Rhizobium (in root nodules of leguminous plants) and Azotobacter (in soil), or atmospherically via lightning, which converts nitrogen into nitric acid that enters the soil as nitrates.

In animals, nutrition involves ingestion, digestion, absorption, assimilation, and egestion. Animals are classified as herbivores (eat plants), carnivores (eat other animals), omnivores (eat both), scavengers (crows, hyenas), or decomposers (microbes). Parasitic nutrition includes ectoparasites (lice, ticks living on the body surface) and endoparasites (tapeworms, roundworms living inside the body). Unicellular organisms like Amoeba use the whole cell surface for nutrition, surrounding food particles with pseudopodia.

Food Safety and Spoilage

Food spoilage involves changes in color, odor, texture, or taste, often caused by improper handling, storage, or chemical reactions with metals. Qualitative wastage occurs through over-cooking or washing vegetables after cutting. Methods of food protection and preservation include:

• Freezing: Slows biological/chemical reactions.

• Smoking: Uses aluminum phosphide.

• Irradiation: Exposes food to ionizing radiation (X-rays, gamma-rays) to destroy microbes and increase shelf-life.

• Pasteurization: Developed by Louis Pasteur, involves heating milk to $80^∘C$ for $15$ minutes and cooling it quickly.

• Chemical preservatives: Acetic acid (vinegar), citric acid, sodium benzoate.

• Inert gas: Filling packets with nitrogen to prevent fungus growth.

Food adulteration involves removing essential components (like milk fat) or adding lower-quality substances (like brick dust in chili powder, metanyl yellow in turmeric, or papaya seeds in black pepper). Testing for adulterants is critical; for example, iron filings in rava can be detected with a magnet, and water in milk can be spotted by a spread-mark on a glass slide.

Measurement, Motion, and Work

Physical quantities are divided into scalar (expressed by magnitude alone, e.g., mass, time, temperature) and vector (magnitude and direction, e.g., velocity, force). Mass is the amount of matter and is a scalar quantity, while weight is the gravitational force acting on that mass and is a vector quantity. Systems of measurement include MKS (metres, kilograms, seconds) and CGS (centimetres, grams, seconds). The SI system is the standard International System of Units.

Distance is the actual length of the route traversed, while displacement is the minimum distance in a specific direction. Velocity is displacement per unit time ($\text{Velocity} = \frac{\text{Displacement}}{\text{Time}}$). Acceleration is the change in velocity over time ($\text{Acceleration} = \frac{\text{Change in velocity}}{\text{Time}}$). Newton’s First Law of Motion states that if no force acts on a body, its velocity does not change. Work done is calculated as: $W = F \times s$ where $W$ is work (Joules), $F$ is force (Newtons), and $s$ is displacement (metres).

Electricity and Heat

Electric charge is an intrinsic property of particles; an object is neutral if positive and negative charges are balanced. Frictional electricity is generated by rubbing materials, and induction creates charges without contact. Repulsion between like charges is the definitive test for a charged object. A gold leaf electroscope detects these charges. Benjamin Franklin showed that lightning is a form of electric charge. A lightning conductor, made of a copper strip, protects buildings by conducting atmospheric charge surely into the ground.

Heat is transferred from hot to cold bodies via three modes: (1) Conduction (through solids via contact), (2) Convection (through liquids and gases via currents), (3) Radiation (through space without a medium). Metals generally expand on heating and contract on cooling. Sir James Dewar invented the thermos flask in 1892; its double-walled glass tubes with a silver coating and a vacuum prevent heat loss via conduction, convection, and radiation, keeping liquids hot or cold for long durations.

Disaster Management and Biology of the Cell

Disasters like famines, cloudbursts, floods, and tsunamis require preparedness. Famines result from long-term food and water scarcity, caused by droughts, war, or population growth. Cloudbursts involve sudden heavy rain exceeding $100\,mm$ per hour. Tsunamis are gigantic harbour waves generated by undersea earthquakes or volcanoes. Volcanoes erupt when hot molten magma and gases are pushed through the earth's crust.

Cells are the fundamental units of life. Robert Hooke first identified "cells" in cork in 1665. The cell theory by Schleiden and Schwann (1838) states that all living things are made of cells, and Virchow (1885) added that all cells come from pre-existing cells. Microscopes (compound and electron) are used for observation. Cells contain organelles like the nucleus (controls functions), mitochondria (powerhouse), and vacuoles (waste disposal). Plant cells are characterized by a cell wall and chloroplasts for photosynthesis. Prokaryotic cells, like bacteria, lack membrane-bound organelles.

The Human Body and Light Effects

Muscles are bundles of fibers that contract and relax to move bones via tendons. The human body has over $600$ muscles. They include voluntary (skeletal), involuntary (smooth), and cardiac muscles. The digestive system converts food into soluble forms; it includes the alimentary canal ($9\,m$ long) and glands like the liver (largest gland, stores glucose) and pancreas. Enzymes like ptyalin (in saliva) and pepsin (in the stomach) act as catalysts.

Light effects include the scattering of sunlight by atmospheric gas molecules, causing the sky to appear blue. Shadows have two parts: the umbra (darkest part) and penumbra (faint part). Eclipses occur when the sun, moon, and earth align in a straight line. A solar eclipse occurs on a new moon day when the moon is between the sun and earth, while a lunar eclipse occurs on a full moon night when the earth is between the sun and moon.

Sound, Magnetism, and Stars

Sound is produced by vibrations. Oscillation is a back-and-forth motion, and its frequency ($n$) is the number of oscillations per second, measured in Hertz ($Hz$). $n = \frac{1}{T}$, where $T$ is the time period. Sound level is measured in decibels ($dB$). Human hearing ranges from $20\,Hz$ to $20,000\,Hz$. Infrasonic sound is below $20\,Hz$, and ultrasonic sound is above $20,000\,Hz$. Magnetism involves magnetic fields shown by lines of force that run from north to south. The earth itself acts as a gigantic magnet.

Stars are spherical clouds of hydrogen gas born in nebulae. Their lifecycle depends on mass, progressing from ordinary stars to red giants and finally to white dwarfs, neutron stars, or black holes. All stars in the sky appear on a virtual celestial sphere. Points on this sphere include the zenith (directly overhead) and nadir (directly below). The ecliptic is the sun's apparent path. Constellations like Saptarshi (Great Bear), Mrug (Orion), and Vrushchik (Scorpio) are used for sky watching. The zodiac consists of 12 signs, while Indian astronomy uses 27 nakshatras based on the moon's revolution.