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Exploring the Invisible Living World: Cells, Microorganisms, and Their Roles

An 8th-grade chapter covering cell structure, differences between plant and animal cells, microorganisms, their environmental roles, and their importance in food and health.

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THE INVISIBLE LIVING WORLD: BEYOND OUR NAKED EYE 8 CLASS CHAPTER - 1
Topics to be covered in this chapter -  Introduction  What is a cell?  Basic structure of a cell  Comparison between a plant cell and an animal cell  Variation in shape of cells  Levels of organization in the body of a living organism  What are microorganisms?  How are we connected to microbes?  Key players in cleaning the environment  Microorganisms and food  Microalgae – Tiny helpers in water  Why is cell considered to be a basic unit of life?
introduction Q. Have you ever wondered what you might see if the invisible world around you became visible? Q. How do you think your observation of this hidden world might change the way you think about size, complexity or even what counts as ‘living’? Q. Have you thought how these tiny living beings interact with each other?
• In 1665, Robert Hooke published his book ‘Micrographia’. • In this book, he showed detailed drawings of tiny things that people had never seen before. • His self made microscope made things look 200-300 times bigger. • One day he looked at a thin slice of cork and saw it was made up of many small empty spaces. These compartments reminded him of a honeycomb. He drew what he saw and called each small space a cell. This was the first time the word cell was used in science. • Antonie van Leeuwenhoek, a Dutch scientist, made better lenses that allowed him to build more useful microscope. • He was the first person to clearly see and describe tiny living things like bacteria and blood cells. Because of this he is known as the ‘Father of Microbiology’. Discovery of cells
What is a cell?  Cells are the basic structural and functional units of life.  All living organisms are made up of one or more cells.  Cells can be observed under a microscope.
Activities to study cells Onion peel cell (plant cells)  Rectangular shaped cells.  Parts seen under the microscope –  Cell wall  Cell membrane  Cytoplasm  Nucleus Cheek cell (animal cell)  Polygon shaped cells.  Parts seen under the microscope –  Cell membrane  Cytoplasm  Nucleus
Onion cell Cheek cell
conclusion  A cell typically consists of three parts – cell membrane, cytoplasm and nucleus.  In plant cell, an extra outer layer called cell wall is present.
Difference between plant cell and animal cell Animal cell Plant cell Feature Irregular / round Rectangular/fixed Shape Absent Present Cell wall Absent Present Chloroplast Small or absent Large central vacuole Vacuole
Cell wall: • It is the outermost layer in the plant cell. • It is porous, rigid and permeable in nature. • It provides protection to the plant cell. • It also provides rigidity and strength to the plants. Cell membrane: • It is the outermost layer in the animal cell and present below the cell wall in the plant cell. • It is porous, elastic and semi permeable in nature. • It provides protection to the inner content of the cell and separate one cell from the other. Cytoplasm: • It is the jelly-like substance present between the cell membrane and nucleus. • It contains carbohydrates, proteins, fats and mineral salts. • Most of the processes takes place within the cytoplasm. Parts of a cell
Nucleus: • It is the round structure present in the middle of the cell. • It regulates all the activities of the cell. • It also regulates growth. Plastids: • These are the tiny rod-shaped structures found only in plant cells. • Chloroplasts are green coloured plastids containing chlorophyll which help in photosynthesis. Vacuole: • It is the empty looking spaces which helps in storing important substances, get rid of waste and maintain the shape of the cell. • It also gives strength and support to the plant. • In animal cells, vacuoles are generally absent. If present, they are usually small.
Variation in shape of cells Function Shape Type of Cell Helps in contraction and movement Long, spindle-shaped Muscle Cell Carries messages between body parts Long, branched Nerve Cell Carries oxygen throughout the body Round, disc-shaped (biconcave) Red Blood Cell Destroys germs and fights infections Irregular, amoeba-like White Blood Cell Stores fat and energy Round, large with storage space Fat Cell Provides structure and support to the body Star-shaped Bone Cell Covers and protects body surface Flat, thin, tightly packed Skin Cell Opens and closes stomata in leaves Kidney-shaped Guard Cell (Plant) Conducts water and minerals in plants Long, tube-like Xylem Cell (Plant) Conducts food in plants Elongated, tube-like Phloem Cell (Plant)
Level of organisation in the body of a living organism Description Level Basic unit of life (e.g., stomach cell). Cell Group of similar cells working together (e.g., muscle tissue). Tissue Group of tissues forming a specific body part (e.g., stomach). Organ Group of organs performing a major body function (e.g., digestive system). Organ System A complete living being (e.g., human, plant). Organism Flow: Cell → Tissue → Organ → Organ System → Organism
Types of organisms Unicellular organisms  The organisms made up of only one cell are called unicellular organisms.  Examples include amoeba, paramecium, bacteria. Multicellular organisms  The organisms made up of more than one cell are called multicellular organisms.  Examples include plants, animals including human beings. Note: 1. The life of all the multicellular organisms start from a single cell i.e. egg. 2. The largest cell is the ostrich egg (yolk of egg).
What are microorganisms?  These are tiny living organisms made of one or few cells.  They can not be seen with naked eyes.  They can found everywhere: air, water, soil, inside living beings.  Examples:  Unicellular: Bacteria, Amoeba  Multicellular: Algae, fungi
Activity – 2.4 (Observing pond water/stagnant water under the microscope) Remarks Diagram Name of the organsism Single cell, moving, irregular shape Amoeba (Protozoa) Single cell, moving from one place to another with the help of special structures called cilia. Paramecium (protozoa) Single cell, green, moving takes place with the help of special structures called flagella. Chlamydomonas (Algae)
Activity – 2.5 (Observing soil suspension under the microscope) Remarks Diagram Name of the organsism Branched filament without chlorophyll having sac like structures. Rhizopus(Bread mould) Fungi Branched filament without chlorophyll having brush like structures. Mould (Fungi) Single cell, green, moving takes place with the help of special structures called flagella. Algae Spherical, comma, spiral or rod shaped, one long hair-like structure and many small hair- like structure around the cell Bacteria
virus • Viruses are microscopic and acellular. • These multiply only when they enter a living cell. • They may infect plants, animals or bacterial cells and may cause disease.
How are we connected to microbes Microorganisms in our daily life:  Microorganisms are present everywhere: air, water, soil, plants, animals, and even inside our bodies.  They can grow on old or left over food, like tomatoes, lemons, or oranges forming white cotton-like layers due to fungal infection. Why do pickles and murabbas not spoil easily?  They contain high salt or sugar, which prevents the microbial growth by creating an unsuitable environment.
Role of microorganisms in the environment 1. Key players in cleaning the environment:  Microorganisms like bacteria and fungi (called decomposers) break down peels of fruits and vegetables into a dark coloured material called manure which is rich in nutrients.  This process improves soil fertility.  Microorganisms also decompose bodies of dead animals and thus help in recycle of waste and return of important nutrients in nature.
Microbes as a source of biogas  Many microorganisms like bacteria and fungi can live in an oxygen free environment.  Some of these bacteria have the ability to decompose plant and animal waste present in the environment or household wastewater.  During the process, they release a mixture of gases containing carbon dioxide and a high proportion of another gas called methane. This gas is used as a fuel source for cooking, heating, generating electricity and also to even run vehicles.
Microorganisms in our kitchen: making food Role of yeast(fungi):  It grows in warm and moist conditions.  It ferments sugar to produce carbon dioxide and alcohol.  It makes dough rise and become soft and fluffy.  Used in making bread, cakes, idli, dosa, bhatura.
Activity 2.8: observe dough rising (effect of yeast)  Take two bowls(A & B) with flour and sugar.  Bowl A: Add yeast and warm water, knead dough.  Bowl B: No yeast.  Keep both in warm places for 4-5 hours.  Observation: Bowl A dough rises, become fluffy due to carbon dioxide gas released by yeast.
Activity 2.9: curd formation (effect of warmth)  Take two bowls(A & B) with milk.  Bowl A: Lukewarm milk + curd  Bowl B: Cold milk + curd  Observe after few hours.  Observation: Curd forms in warm milk faster than due to bacteria like Lactobacillus. Testing for curd formation using milk in different conditions Possible reason Change in colour Change in appearance Condition Bacteria acted faster Slight change Milk thickness (curd) Bowl A Cold prevented bacterial activity No change Little or no change Bowl B
Contribution of dr. ananda mohan chakrabarty  In 1971, he developed a special bacterium that could break down oil spills, helping to clean the environment.  His discovery showed how microorganisms can be used to solve environmental problems like pollution.  His discovery received a patent in 1980.  Patent is a copyright given to a person so that no one else can copy, use or sell his/her invention without permission.
Nitrogen fixing bacteria (rhizobium)  Live in root nodules of legumes (beans, peas, lentils).  Convert atmospheric nitrogen gas into a usable form for plants.  Reduce the need for fertilizers for farmers.  Improves the soil fertility naturally.
Microalgae (tiny helpers in water)  They live in water, soil, air and even trees.  Examples: Spirulina, Chlorella, Diatoms.  Benefits:  Produce oxygen (more than half of the earth’s oxygen supply)  Clean water  Provide food for aquatic animals  Serve as superfoods (Spirulina) rich in vitamin B12 and protein.  Used in medicine, supplements, biofuel.
How to cultivate spirulina  Set up a glass tank, add pond water.  Collect and add living Spirulina.  Stir regularly.  Ready for harvest in 3-6 weeks.  Used for nutrition and livelihood improvement.
Why is cell considered the basic unit of life?  All living organisms are made of cells.  Unicellular organisms: One cell performs all life processes. Examples: Bacteria, protozoa, fungi like yeast.  Multicellular organisms: Many cells work together, with specialized functions. Examples: Algae, fungi like mould.  Like plants and animals, microorganisms’ cells are surrounded by cell membrane.  Fungi cells: Have cell walls but no chloroplasts.  Bacterial cell: Have no true nucleus (nucleoid region only)