Notes-NCERT-Class-8-Science-Curiosity-Chapter-2-The Invisible Living World: Beyond Our Naked Eye-CBSE

Differences between Plant and Animal Cells :

Cell wall – Present in plant cells (rigidity & strength), absent in animal cells. forms the outermost layer.

Plastids – Present in plant cells; chloroplasts contain chlorophyll for photosynthesis; absent in animal cells.

Vacuole – Large in plant cells for storage & shape maintenance; small or absent in animal cells.

Organisms present in pond water :

Organisms present in soil suspension :

Glossary of Key Terms :

• Acellular: Not consisting of cells, or being without cells. Viruses are described as acellular.
• Algae: A diverse group of plant-like organisms, some of which are microscopic and can be unicellular or multicellular. They produce their own food through photosynthesis and release oxygen.
• Amoeba: A single-celled protozoan characterized by its ability to alter its shape, primarily by extending and retracting pseudopods.
• Antonie van Leeuwenhoek: A Dutch scientist from the 1660s known for making improved lenses and microscopes, allowing him to be the first to clearly see and describe tiny living things like bacteria and blood cells. He is known as the Father of Microbiology.
• Bacteria: A diverse group of single-celled microorganisms that lack a well-defined nucleus (prokaryotes). They can be spherical, rod-shaped, spiral, or comma-shaped.
• Cell: The basic structural and functional unit of all known organisms. It is the smallest unit of life that can replicate independently.
• Cell membrane: The thin outer lining of a cell that encloses the cytoplasm and nucleus, separating one cell from another. It is porous and regulates the passage of materials.
• Cell wall: An extra outer layer found in plant, fungal, and bacterial cells, providing rigidity and strength. It is located outside the cell membrane.
• Chlorophyll: The green pigment found in chloroplasts of plant cells and some algae, essential for photosynthesis.
• Chloroplasts: Tiny rod-shaped structures found in plant cells (and some plastids) that contain chlorophyll and are responsible for photosynthesis.
• Coverslip: A thin, flat piece of transparent material, usually glass, that is placed over a specimen on a microscope slide.
• Curd: A dairy product formed when milk coagulates and sours, primarily due to the action of Lactobacillus bacteria which ferment lactose into lactic acid.
• Cytoplasm: The jelly-like substance that fills the cell, located between the cell membrane and the nucleus. Most life processes occur within the cytoplasm.
• Electron microscope: A type of microscope that uses a beam of electrons to create an image of the specimen, allowing for much higher magnifications (up to 1,000,000 times) than traditional light microscopes.
• Fermentation: A metabolic process that converts sugar to acids, gases, or alcohol. It occurs in yeast and some bacteria, often used in food production.
• Foldscope: A low-cost, foldable paper microscope designed to make microscopic observation accessible to many people.
• Fungi: A kingdom of organisms that includes yeasts, moulds, and mushrooms. Some fungi are unicellular (e.g., yeast) while others are multicellular (e.g., mould). They lack chlorophyll and cannot make their own food.
• Glycerin: A substance used in microscopy to prevent cells from drying and to improve clarity for better visualization.
• Lactobacillus: A type of bacterium commonly found in dairy products, essential for the fermentation of milk into curd by producing lactic acid.
• Lenses: Curved pieces of glass, originally shaped like lentil seeds, used to make small things appear bigger. They are fundamental components of magnifying glasses and microscopes.
• Levels of Organization: The hierarchical structure of life, starting from the simplest components and building up to more complex systems. The levels mentioned are Cell → Tissue → Organ → Organ System →
• Magnifying glass: A simple tool that uses a single convex lens to produce a magnified image of an object.
• Manure: Nutrient-rich organic material, typically made from decomposed plant and animal waste, used to fertilize soil.
• Methane: A gas produced by some microorganisms (like bacteria and fungi) in oxygen-free environments, often used as a fuel source (biogas).
• Methylene blue: A blue-coloured stain used in microscopy to improve the visibility of cell structures by increasing contrast.
• Microalgae: Microscopic, plant-like organisms that live in water, soil, air, and on trees, producing their own food through photosynthesis and releasing oxygen. Examples include Spirulina, Chlorella, and Diatoms.
• Microbes: A shortened term for microorganisms.
• Micrographia: A book published by Robert Hooke in 1665, containing detailed drawings of tiny things observed through his microscope, including cork cells.
• Microorganism: A microscopic organism, either unicellular or multicellular, that is too small to be seen with the naked eye. Also called a microbe.
• Microscope: A scientific instrument that uses lenses to magnify small objects, making them visible for observation.
• Mitochondria: Organelles found in the cytoplasm of most eukaryotic cells, responsible for generating most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy (not explicitly defined in text but labeled in diagram).
• Multicellular organisms: Living beings composed of many cells, where cells carry out specialized functions and cooperate for survival. Examples include plants, animals, and some fungi and algae.
• Naked eye: Observation without the aid of magnifying tools like lenses or microscopes.
• Nerve cell (Neuron): A specialized animal cell, typically long and branched, responsible for carrying messages throughout the body.
• Nucleoid: The region in bacterial cells that contains the genetic material, which is not enclosed within a well-defined nucleus or nuclear membrane.
• Nucleus: A small, round structure typically found in the central region of eukaryotic cells, covered by a thin membrane. It regulates all activities within the cell and controls growth.
• Organ: A structure formed by a group of different tissues working together to perform a specific function (e.g., stomach, heart).
• Organism: A complete living being, made up of various organ systems working together.
• Organ system: Several organs working together to perform a major function of the body (e.g., digestive system).
• Ostrich egg: The largest known single cell in the living world, measuring about 130 mm to 170 mm in diameter.
• Paramecium: A single-celled protozoan that moves with the help of specialized structures (cilia).
• Plastids: Tiny rod-shaped structures in plant cells, some of which are chloroplasts. In non-green parts, they help in the storage of substances.
• Protozoa: A group of single-celled microorganisms (unicellular) that often move independently and can be found in water and soil.
• Rhizobium: A type of bacteria that forms swollen regions called nodules in the roots of certain legumes (e.g., beans, peas, lentils). These bacteria trap nitrogen from the air, making it useful for the plants and increasing soil fertility.
• Robert Hooke: An English scientist who, in 1665, published "Micrographia" and was the first to use the word "cell" to describe the basic unit of life, based on his observations of cork.
• Safranin: A red-coloured stain used in microscopy (e.g., for onion peel cells) to give a pinkish colour to cells and help in clearer visualization.
• Spirulina: A type of microalga considered a "superfood" due to its high protein content and health benefits.
• Tissue: A group of similar cells that work together to perform a specific function.
• Unicellular organisms: Living beings made up of just one cell. Examples include some bacteria, protozoa, and yeast.
• Vacuole: A large, empty-looking space in plant cells that helps store important substances, get rid of waste, and maintain cell shape and strength. In animal cells, vacuoles are usually small or absent.
• Viruses: Microscopic and acellular entities that can only multiply when they enter a living cell (host organism). They can infect plants, animals, or bacterial cells and cause disease.
• Yeast: A type of unicellular fungus that grows well in warm conditions and is used in baking to make dough rise by releasing carbon dioxide during respiration. It also produces a small amount of alcohol.