The Invisible Living World: Beyond Our Naked Eye - Class 8 Science
Which ancient Indian text refers to 'Krimi'?
The Atharvaveda, one of the four Vedas, refers to 'Krimi'. This shows that ancient Indians had some awareness of tiny organisms and their effects.
Ancient Indian texts mention both beneficial and harmful effects of tiny organisms.
Various Vedic texts mention the beneficial and harmful effects of tiny entities referred to as 'Krimi'. This shows ancient awareness of microorganisms.
Why does a round-bottom flask filled with water make letters appear larger?
The flask filled with water acts like a magnifying glass because of its curved shape. This is the same principle used in lenses and microscopes to magnify small objects.
What is the thin, transparent layer from the inner surface of onion called?
The thin, transparent layer from the inner surface of an onion is called the onion peel. This is used to observe plant cells under a microscope.
What is the liquid that looks dirty and contains fine particles of soil called?
The liquid which contains very fine particles of soil mixed with water is called soil suspension. When observed under a microscope, it shows various microorganisms.
Why should you place a coverslip at 45 degrees angle when making a slide?
The coverslip should be placed slowly at an angle (about 45 degrees) using a needle so that no air bubbles get trapped. Air bubbles can interfere with observation.
What kind of microorganisms can be found in pond water?
Pond water contains various microorganisms including Amoeba (protozoa), Paramecium (protozoa), algae, and bacteria. These can be observed under a microscope.
Which characteristics help identify Amoeba when observed under microscope?
Amoeba is identified as a single cell with an irregular shape that keeps changing. It moves by extending finger-like projections called pseudopodia.
Why do algae look green under the microscope?
Algae look green because of the presence of chlorophyll - a green pigment. This pigment helps them make food through photosynthesis.
Why does powdery or cotton-like growth appear on rotting food?
The powdery or cotton-like growth on rotting food appears because microbes have infected it. Microorganisms are present everywhere in air, water, and soil, and can grow on food.
Microorganisms can be found on surfaces of leaves, stems, and roots of plants.
You can use a foldscope or microscope to explore surfaces of leaves, stems, roots, or any other part to see microorganisms. They are present on many plant surfaces.
Microorganisms live only at moderate temperatures.
Microorganisms show great diversity and some can be found in extreme climatic conditions such as hot water springs and snow cold zones, as well as at moderate temperatures.
What are all living beings, whether plants or animals, called?
All living beings, whether plants or animals, are called organisms. They come in all shapes, sizes, and colours, and differ in structure and features.
All living beings are made up of:
All living beings are made up of cells. You might wonder what cells actually look like - they have basic parts like cell membrane, cytoplasm, and nucleus.
Though small in size, microorganisms play an important role in our lives.
Though microorganisms are small in size, they play an important role in our lives - from helping in digestion to making food like curd and bread to cleaning the environment.
All living beings, including microorganisms, are made up of one or more cells.
All living beings, including microorganisms, are made up of one or more cells. Their cells differ in size, shape, and structure, but the cell is the basic unit of all life.
Microorganisms can be beneficial or harmful to us.
Microorganisms can be beneficial (like those that help in digestion, food preparation, and environmental cleaning) or harmful (like those that cause diseases). Both types exist.
Our intestine contains many bacteria that help in digestion.
Our intestine has many bacteria that help in digestion. These beneficial bacteria in our gut form an important part of our digestive system and overall health.
Who first used the word "cell" to describe the basic unit of life?
Robert Hooke first used the word "cell" in 1665 when he observed thin slices of cork under his microscope. The small compartments reminded him of a honeycomb, and he called each small space a cell.
In which year did Robert Hooke publish his book Micrographia?
Robert Hooke published his famous book Micrographia in 1665. In this book, he showed detailed drawings of tiny things that people had never seen before, observed using a microscope.
Who is known as the Father of Microbiology?
Antonie van Leeuwenhoek, a Dutch scientist, is known as the Father of Microbiology. He made better lenses that allowed him to build more useful microscopes and was the first person to clearly see and describe tiny living things like bacteria and blood cells.
What did Robert Hooke observe when he looked at a thin slice of cork under his microscope?
When Robert Hooke looked at a thin slice of cork, he saw it was made of many small, empty spaces. These compartments reminded him of a honeycomb, and he called each small space a cell.
How many times could Robert Hooke's microscope magnify objects?
Robert Hooke's microscope made things look 200 to 300 times bigger than what one could see with the unaided eye. This allowed him to see the cellular structure of cork for the first time.
Why is the piece of curved glass called a "lens"?
The piece of curved glass was shaped like a lentil seed - thick in the middle and thin at the edge. Hence, they called it a lens. The word "lens" comes from the Latin word for lentil.
What was Antonie van Leeuwenhoek the first person to see and describe?
Antonie van Leeuwenhoek was the first person to clearly see and describe tiny living things like bacteria and blood cells. He made better lenses that allowed him to build more useful microscopes.
The invention of the microscope helped humans discover:
The invention of the microscope opened a fascinating hidden world filled with tiny living creatures that were invisible to the naked eye. This revolutionized our understanding of life.
Robert Hooke was a careful observer and a skilled artist.
Robert Hooke was indeed a careful observer and a skilled artist. In his book Micrographia, he showed detailed drawings of tiny things that people had never seen before.
Antonie van Leeuwenhoek was a scientist from Germany.
Antonie van Leeuwenhoek was a Dutch scientist, not German. He worked in the 1660s and made better lenses that allowed him to build more useful microscopes.
What are the three basic parts of a cell?
The three basic parts of a cell are cell membrane, cytoplasm, and nucleus. The cell membrane is the outer layer, the nucleus is in the middle, and cytoplasm fills the space between them.
What is the function of the cell membrane?
The cell membrane encloses the cytoplasm and nucleus, separates one cell from another. It is porous and allows the entry of materials essential for life processes and the exit of waste material.
What is the function of the nucleus in a cell?
The nucleus regulates all activities that occur within the cell. It also regulates growth. The nucleus is covered by a thin membrane and contains genetic material.
What does the cytoplasm contain?
Cytoplasm contains other components of the cell and compounds such as carbohydrates, proteins, fats, and mineral salts. Most of the life processes take place within the cytoplasm.
Where do most of the life processes take place in a cell?
Most of the life processes take place within the cytoplasm. The cytoplasm contains various cell components and compounds necessary for carrying out these processes.
What is the function of the cell wall in plant cells?
The cell wall in plant cells provides rigidity and strength to plants. This is why all cells are arranged compactly with each other and look firm in structure.
Which stain is used to observe onion peel cells clearly?
Safranin, a red-coloured stain, is used to observe onion peel cells. It gives a pinkish colour to the cells and helps us see them clearly under the microscope.
Which stain is used to observe human cheek cells?
Methylene blue, a blue-coloured stain, is used to observe human cheek cells. Adding stain improves the visibility of the material under the microscope by increasing contrast.
What is the purpose of adding glycerin while preparing a slide?
Glycerin is added to prevent drying of the cells and improve clarity for better visualisation of cells under the microscope.
What shape are onion peel cells?
When observed under a microscope, onion peel cells appear nearly rectangular in shape. These cells are closely arranged without any space between them.
What shape are human cheek cells?
Human cheek cells are polygon-shaped. These cells form the inner lining of the mouth and are thin and flat, forming a protective lining.
The cell membrane is porous.
The cell membrane is porous and allows the entry of materials essential for life processes and the exit of waste material. This selective permeability is crucial for cell function.
The nucleus is also covered by a thin membrane.
The nucleus, which is the round structure in the middle of the cell, is also covered by a thin membrane called the nuclear membrane.
All cells have a cell wall.
Not all cells have a cell wall. Only some cells like plant cells, fungal cells, and bacterial cells have a cell wall. Animal cells do not have a cell wall.
Which of the following is present in plant cells but NOT in animal cells?
Plant cells have a cell wall and chloroplasts which are not present in animal cells. The cell wall provides rigidity, and chloroplasts contain chlorophyll for photosynthesis.
What are chloroplasts?
Chloroplasts are plastids that contain chlorophyll, which makes them green and helps in photosynthesis. They are found in plant cells and are responsible for making food using sunlight.
What is the function of vacuole in plant cells?
The vacuole helps the plant cell store important substances, get rid of waste, and maintain the shape of the cell. This gives strength and support to the plant.
How is the vacuole in plant cells different from that in animal cells?
Plant cells have a large, empty-looking space called a vacuole. In animal cells, vacuoles are usually not present, and if present, they are usually small.
What are plastids?
Plastids are tiny rod-shaped structures found in all parts of a plant. Some plastids like chloroplasts contain chlorophyll, while others in non-green parts help in storage of substances.
A cell is just a simple bag of liquid.
A cell is not just a simple bag of liquid - it is a complex structure made up of many different parts, each with its own special function to allow the cell and the entire organism to work.
Animal cells have chloroplasts for photosynthesis.
Animal cells do not have chloroplasts. Chloroplasts are found only in plant cells and some algae. They contain chlorophyll and are responsible for photosynthesis.
Plant cells have a large vacuole that helps maintain the shape of the cell.
Plant cells have a large vacuole that helps store important substances, get rid of waste, and maintain the shape of the cell. This gives strength and support to the plant.
What is the shape of a muscle cell?
A muscle cell is shaped like a spindle - thin, flexible, and elongated at both ends. This shape allows muscle cells to contract and relax, making movement possible.
What is the shape of a nerve cell?
A nerve cell (neuron) is very long and has branches. The elongated shape and branched structure help them reach different parts of the body and pass on messages quickly.
Why are nerve cells long and branched?
Nerve cells are long and branched because this structure helps them reach different parts of the body and pass on messages quickly. Their shape is related to their function.
Why are inner cheek cells thin and flat?
Inner cheek cells are thin and flat because they form a protective lining on the inner surface of the cheek. Their shape is suited to their protective function.
What is the function of muscle cells in the food pipe?
Muscle cells in the food pipe contract and relax in a wave-like manner, pushing the food down to the stomach. This movement is called peristalsis.
What do some plant cells form to help carry water throughout the plant?
Some plant cells form long tubes that help carry water throughout the plant. Plant cells can be rectangular, elongated, oval, or even tube-like depending on their function.
The shape of a cell is related to its function.
The unique shape, size, and structure of cells help them carry out their specific functions. For example, nerve cells are long to transmit messages, and muscle cells are spindle-shaped to contract.
All cells in the human body have the same shape.
Cells in the human body have different shapes depending on their function. Muscle cells are spindle-shaped, nerve cells are long and branched, cheek cells are flat, and blood cells are round.
What is the correct order of levels of organization in living organisms?
The correct order of levels of organization is: Cell → Tissue → Organ → Organ system → Organism. Cells are the basic building blocks that come together to form complex living beings.
What is the basic unit of life?
Cell is the basic unit of life, just like a brick is the basic unit of a wall. All living organisms are made up of one or more cells.
What is formed when a group of similar cells come together?
A group of similar cells forms a type of tissue. Different tissues are then organized to form an organ.
What is formed when different tissues are organized together?
Different tissues are organized to form an organ. For example, the heart is an organ made up of different types of tissues working together.
What is an organ system?
Several organs work together to form an organ system that performs a major function of the body. For example, the digestive system includes the stomach, intestines, and other organs.
The life of complex living organisms begins with:
The life of complex living organisms begins with a single cell - the egg. This egg has an amazing ability to divide repeatedly to form a complete living being made up of many cells.
What are multicellular organisms?
Multicellular organisms are living beings made up of many cells. The egg divides repeatedly to form a complete organism. Animals, including humans, and plants are all examples of multicellular organisms.
A brick is to a wall as a cell is to:
Just as a brick is the basic building unit of a wall, a cell is the basic building unit of a living organism. Cells come together to form the complex structures of life.
All organ systems together make up a complete organism.
All the organ systems together make up a complete organism - like a plant or an animal. Each organ system performs specific functions that contribute to the survival of the organism.
What are microorganisms?
Microorganisms (micro means very small; organisms means living beings) are tiny creatures that cannot be seen with the naked eye. They are also called microbes.
Which of the following are examples of unicellular microorganisms?
Bacteria and Amoeba are made of just one cell (unicellular). These single-celled organisms carry out all the functions necessary for survival within that one cell.
Where can microorganisms be found?
Microorganisms are found all around us - in water, soil, air, and even inside our body! They can be found everywhere, including extreme conditions like hot water springs and snow cold zones.
What are the main categories of microorganisms?
Microorganisms can be categorized into different categories such as protozoa, fungi, bacteria, some algae, and more. Each category has distinct characteristics.
Amoeba is an example of which type of microorganism?
Amoeba is a protozoa - a single-celled organism with an irregular shape that can move. Protozoa are unicellular organisms often found in pond water and other moist environments.
Paramecium is an example of which type of microorganism?
Paramecium is a protozoa - a single-celled organism that moves from one place to another using specialized structures. It can be found in pond water.
What are the different shapes of bacteria?
Bacteria can be spherical, comma-shaped, spiral, or rod-shaped. They also have one long hair-like structure and many small hair-like projections around the cell.
What is special about fungi like bread mould?
Bread mould and other fungi are branched filaments without chlorophyll. Since they lack chlorophyll, they cannot make their own food through photosynthesis.
How many times does a microscope magnify microorganisms to make them visible?
Microorganisms are everywhere, and we can only see them with a microscope - a device that magnifies them 100 to 400 times. This magnification makes the tiny organisms visible.
What is a foldscope?
A foldscope is a low-cost and foldable paper microscope created by scientists. It makes the microscopic world accessible to many people, though it may not provide the same detail as high-powered laboratory microscopes.
Microorganisms can only be found in dirty places.
Microorganisms are found everywhere - in water, soil, air, inside our body, on clean surfaces, and even in extreme conditions like hot springs and cold zones. They are not limited to dirty places.
Bacteria are unicellular organisms.
Bacteria are unicellular (single-celled) organisms. They carry out all the functions necessary for their survival in a single cell.
Fungi can be both unicellular and multicellular.
Fungi can be unicellular or multicellular. For example, yeast is a unicellular fungus while mould is a multicellular fungus.
What are unicellular organisms?
Unicellular organisms are made up of just one cell. They carry out all the functions necessary for their survival in a single cell. Examples include bacteria and Amoeba.
Which of the following is a unicellular fungus?
Yeast is a unicellular fungus, meaning it is made of just one cell. In contrast, mould is a multicellular fungus made of many cells.
Which of the following is a multicellular fungus?
Mould is a multicellular fungus made of many cells. It appears as branched filaments that grow on decaying food and other organic matter.
What is the largest known cell in the living world?
The yolk (the yellow part of an egg) of an ostrich egg is a single cell - the largest known cell in the living world - measuring about 130 mm to 170 mm in diameter.
In multicellular organisms, cells:
In multicellular organisms, cells carry out specialized functions individually but also cooperate with each other to increase the chance of survival.
Plants and animals are examples of:
Plants and animals are multicellular organisms - they are made up of many cells. These cells work together to perform various functions.
The yolk of an ostrich egg measures about:
The yolk of an ostrich egg, which is a single cell, measures about 130 mm to 170 mm in diameter, making it the largest known cell in the living world.
Unicellular organisms can carry out all life functions in a single cell.
Unicellular organisms carry out all the functions necessary for their survival in a single cell, including nutrition, respiration, excretion, and reproduction.
What are viruses?
Viruses are microscopic and acellular (without cells). They are different from other microorganisms and can only multiply when they enter a living cell.
When do viruses multiply?
Viruses multiply only when they enter a living cell. They cannot reproduce on their own outside a host cell.
Viruses can infect:
Viruses may infect plants, animals, or bacterial cells and may cause disease. They are not selective about their hosts.
Viruses are cellular organisms like bacteria.
Viruses are acellular (without cells), which makes them different from bacteria and other microorganisms. They can only reproduce inside a host cell.
Viruses reproduce only inside the host organism.
Viruses are different from other microorganisms since they reproduce only inside the host organism. They cannot multiply on their own.
What do bacteria have instead of a well-defined nucleus?
Bacteria do not have a well-defined nucleus and a nuclear membrane. Instead, they have a nucleoid - a region containing genetic material. This distinguishes them from plant and animal cells.
Which feature distinguishes bacteria from cells of yeast, plants, and animals?
Bacteria lack a well-defined nucleus and nuclear membrane. They have a nucleoid instead. This feature distinguishes them from cells of yeast, protozoa, algae, fungi, plants, and animals.
Do fungi cells have chloroplasts?
Cells of fungi have a cell wall but do not have chloroplasts, so they cannot make their own food through photosynthesis. They obtain nutrition from other sources.
How much can an electron microscope magnify a cell?
An electron microscope magnifies the cell about 10,00,000 times (1 million times), allowing us to see subcellular components and more structures present in a cell.
Bacteria have a well-defined nucleus with a nuclear membrane.
Bacteria do not have a well-defined nucleus and a nuclear membrane. Instead, they have a nucleoid region that contains their genetic material.
What role do microorganisms play in cleaning the environment?
Microorganisms like fungi and bacteria break down plant and animal waste into simpler, nutrient-rich substances. They help recycle waste and return important nutrients to nature.
What is manure?
Manure is the dark-coloured material formed when microorganisms break down plant and vegetable waste. It is rich in nutrients and helps increase the fertility of the soil.
Why do gardeners collect dry leaves and plant waste in pits?
Gardeners collect dry leaves and plant waste and put them into pits to make natural manure. Microorganisms in the soil break down this waste into nutrient-rich manure.
Which microorganisms help in making manure from plant waste?
Fungi and bacteria act on the plant waste and slowly break it down into simpler, nutrient-rich manure. These decomposers play a key role in recycling nutrients.
What conditions are required for optimal manure formation?
Manure formation occurs at optimal temperature and appropriate moisture level. These conditions help microorganisms break down organic waste efficiently.
Who developed a special bacterium that could break down oil spills?
Dr. Ananda Mohan Chakrabarty (1938-2020) developed a special bacterium in 1971 that could break down oil spills, helping to clean the environment. His discovery received a patent in 1980.
Microorganisms decompose bodies of dead animals.
Microorganisms also decompose bodies of dead animals, not just plant waste. They help recycle waste and return important nutrients to nature.
Bacteria can decompose animal wastes like dung.
Helpful bacteria can decompose animal wastes like dung. This is one way microorganisms help clean the environment and recycle nutrients.
What is biogas?
Biogas is a mixture of gases containing carbon dioxide and a high proportion of methane, released when microorganisms decompose plant and animal waste in an oxygen-free environment.
Which gas is present in high proportion in biogas?
Biogas contains carbon dioxide and a high proportion of methane. Methane is the main combustible gas that makes biogas useful as a fuel.
What can biogas be used for?
Biogas has been used as a fuel source for cooking, heating, generating electricity, and even to run vehicles. It is a renewable source of energy.
In what kind of environment do biogas-producing microorganisms live?
Many microorganisms like bacteria and fungi that produce biogas live in an oxygen-free environment. They decompose waste and release gases during the process.
Biogas can be used to run vehicles.
Biogas has been used as a fuel source for cooking, heating, generating electricity, and even to run vehicles. The methane in biogas is a useful fuel.
Which microorganism is used in making bread and cakes?
Yeast is used in making bread and cakes. When yeast respires, it releases carbon dioxide which forms bubbles that make the dough soft and fluffy.
Which type of microorganism is yeast?
Yeast is a type of microorganism that belongs to a group called fungi. It is a unicellular fungus used in baking and fermentation.
What gas does yeast release that makes dough soft and fluffy?
During respiration, yeast releases carbon dioxide which forms bubbles that make the dough soft and fluffy. This is why bread rises when baked.
What gives dough with yeast a slightly different smell?
Yeast produces a small amount of alcohol during fermentation, which gives the dough a slightly different smell. This is part of the fermentation process.
In what conditions does yeast grow well?
Yeast grows well in warm conditions. This is why warm water and a warm place are used when making dough with yeast for bread and cakes.
Which bacterium is used in curd formation?
Lactobacillus is the bacterium used in curd formation. It feeds on the sugar in milk (lactose), multiplies, and ferments the milk to form curd.
What does Lactobacillus produce that makes curd sour?
Instead of producing alcohol (like yeast), Lactobacillus bacteria produce lactic acid, which makes curd sour. This acid also helps preserve the curd.
Why does milk kept in a warm place turn into curd faster than milk kept in refrigerator?
Lactobacillus bacteria grow well in warm conditions. That is why milk kept in a warm place turns into curd faster, while milk in a refrigerator takes much longer or does not curdle.
What sugar present in milk is used by Lactobacillus?
Lactobacillus feeds on the sugar in milk called lactose. It multiplies and ferments the milk, converting lactose to lactic acid and forming curd.
Which bacteria help in fermentation of batter for idli and dosa?
Some bacteria such as Lactobacillus help in fermentation of batter for making idli and dosa, and dough for making bhatura. The fermentation makes the batter fluffy.
Why do microorganisms not infect pickles and murabbas?
Pickles and murabbas contain spices with salt or sugar which act as preservatives. High concentration of salt or sugar does not allow microorganisms to grow on them.
Why does curd become more sour when left out for a day?
When curd is left out, Lactobacillus bacteria continue to multiply and produce more lactic acid, making the curd increasingly sour.
Yeast is used in making breads, cakes, and pastries.
Yeast is indeed used in making breads, cakes, and pastries. The carbon dioxide it produces makes the dough rise and become soft and fluffy.
Lactobacillus produces alcohol during curd formation.
Lactobacillus does not produce alcohol. Instead, it produces lactic acid during fermentation, which is why curd tastes sour. Yeast produces alcohol, not Lactobacillus.
Which bacteria live in the root nodules of leguminous plants?
Rhizobium bacteria form swollen regions called nodules and live in them. They are found in the roots of legumes such as beans, peas, and lentils.
What do Rhizobium bacteria do for plants?
Rhizobium bacteria trap nitrogen from the air and make it useful for the plants. This process is called nitrogen fixation and helps plants grow better without chemical fertilizers.
Which of the following plants have root nodules containing Rhizobium?
Roots of certain legumes such as beans, peas, and lentils have root nodules that contain Rhizobium bacteria. These are called leguminous plants.
Why do farmers grow legumes in rotation with other crops?
Farmers grow legumes in rotation with other crops because Rhizobium bacteria in legume roots trap nitrogen from the air and increase it in the soil. This keeps the soil healthy for the next crop.
What are root nodules?
Root nodules are swollen regions formed on the roots of leguminous plants where Rhizobium bacteria live. These bacteria fix atmospheric nitrogen for the plant.
Rhizobium bacteria help plants grow without chemical fertilizers.
Rhizobium bacteria trap nitrogen from air and make it useful for plants, helping them grow better without the need for chemical fertilizers.
What are microalgae?
Microalgae are microscopic plant-like organisms that live in water, soil, air, and even on trees. They make their own food using sunlight through photosynthesis.
How much of Earth's oxygen supply do microalgae produce?
Microalgae produce more than half of the Earth's oxygen supply. While making their food through photosynthesis, they release oxygen as a byproduct.
Which microalga is called a superfood?
Spirulina, a microalga, is called a superfood because of its health benefits. It has more than 60% protein content, is a good source of vitamin B12, and has only small amounts of fat and sugar.
What percentage of Spirulina's body weight is protein?
Spirulina has a lot of protein - more than 60 per cent of its body weight - and only a small amount of fat and sugar. This makes it a valuable nutritional supplement.
Which vitamin is Spirulina a good source of?
Spirulina is a good source of vitamin B12, which is essential for our body. It is especially valuable for vegetarians who may have limited sources of this vitamin.
What are some uses of microalgae?
Microalgae like Spirulina, Chlorella, and Diatoms are used as health supplements and medicines. They also help in cleaning water and are used to make biofuel.
What threatens microalgal diversity?
Pollution, climate change, and habitat destruction are threatening microalgal diversity and abundance. Conservation of microalgae is important for protecting the environment.
Microalgae help in cleaning water.
Microalgae help in cleaning water by absorbing pollutants and excess nutrients. They are also used in wastewater treatment processes.
Conservation of microalgae is important for maintaining oxygen balance on Earth.
Since microalgae produce more than half of Earth's oxygen supply, their conservation is important to protect the environment and maintain the oxygen balance on Earth.
What does the Sanskrit word 'Krimi' mentioned in ancient Indian texts refer to?
Ancient Indian texts, particularly the Vedas, have references to the word 'Krimi' which means different tiny entities including 'Drishya' (visible) and 'Adrishya' (invisible). Various Vedic texts mention their beneficial and harmful effects.
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