A cell is the basic structural and functional unit of life.

A microscope is used to see microorganisms.

Robert Hooke first used the word “cell” after observing cork under a microscope.

Antonie van Leeuwenhoek is known as the Father of Microbiology.

The three basic parts are cell membrane, cytoplasm and nucleus.

Safranin is used to stain onion peel cells.

Methylene blue is used to stain human cheek cells.

The cell membrane encloses the cell and allows entry of useful materials and exit of wastes.

Cytoplasm is the material between the cell membrane and nucleus where most life processes take place.

The nucleus regulates the activities and growth of the cell.

Plant cells have an extra outer layer called the cell wall.

Microorganisms are very small living organisms that cannot be seen with the naked eye.

Amoeba and Paramecium are examples of protozoa.

Yeast belongs to fungi.

Carbon dioxide released by yeast makes dough soft and fluffy.

Lactobacillus helps in curd formation.

Rhizobium bacteria are present in root nodules of legumes.

Microalgae are microscopic plant-like organisms that live in water, soil, air and on trees.

Spirulina is a microalga called a superfood.

Viruses are acellular and multiply only inside living cells.

Microscopes are important because many cells and microorganisms are too small to be seen with the naked eye. A microscope magnifies them and helps us observe their shape, structure and movement.

A water-filled round-bottom flask has a curved surface. This curved surface bends light and makes letters or small objects appear larger, just like a magnifying glass.

Robert Hooke observed many small empty compartments in a thin slice of cork. These compartments looked like a honeycomb, so he called them cells.

Antonie van Leeuwenhoek made better lenses and observed tiny living things such as bacteria and blood cells. His work opened the study of microorganisms, so he is called the Father of Microbiology.

Safranin stains the onion peel cells and gives them a pinkish colour. This increases contrast and makes the cells easier to observe under a microscope.

Glycerin prevents the cells from drying and improves clarity, making the slide easier to observe under a microscope.

• Onion peel cells are nearly rectangular and closely arranged.
• Human cheek cells are polygon-shaped and do not have a cell wall.

Plant cells look firm because they have a cell wall. The cell wall provides rigidity, strength and support to the plant cell.

Nerve cells carry messages to different parts of the body. Their long and branched structure helps them transmit messages quickly over long distances.

Muscle cells are thin, flexible and spindle-shaped. This helps them contract and relax, allowing movement such as pushing food through the food pipe.

The levels of organisation are: Cell → Tissue → Organ → Organ System → Organism.

Unicellular organisms are made up of only one cell. Examples include bacteria and Amoeba.

Multicellular organisms are made up of many cells. Examples include humans and plants.

Pickles and murabbas contain high amounts of salt, sugar and spices. These act as preservatives and do not allow microorganisms to grow easily.

Bacteria and fungi decompose fruit peels, vegetable waste, dry leaves and plant waste into simpler nutrient-rich substances. This forms manure and improves soil fertility.

Yeast respires and breaks down food in warm conditions. It releases carbon dioxide, which forms bubbles in the dough and makes it soft and fluffy.

Lactobacillus grows and multiplies faster in warm conditions. It ferments lactose in milk and produces lactic acid, which changes milk into curd.

Rhizobium lives in root nodules of legumes. It traps nitrogen from the air and makes it useful for plants, improving soil fertility naturally.

Microalgae produce a large amount of oxygen, make their own food, support aquatic animals, help clean water and can be used for biofuel, supplements and medicines.

Bacteria do not have a nuclear membrane around their genetic material. Instead, their genetic material lies in a region called the nucleoid.

The human eye can see only objects above a certain size. Many tiny living organisms remained unknown for a long time because they were too small to be seen with the naked eye.

• Curved glass lenses were first used to make small things look bigger.
• Improved lenses led to magnifying glasses and microscopes.
• Robert Hooke used a microscope to observe cork and described small compartments as cells.
• Antonie van Leeuwenhoek observed tiny living things such as bacteria.
• Thus, microscopes opened a hidden world of cells and microorganisms.

A typical cell has three basic parts:

• Cell membrane: It encloses the cytoplasm and nucleus. It is porous and controls the entry of useful materials and exit of wastes.
• Cytoplasm: It is the material present between the cell membrane and nucleus. It contains many cell components and substances such as carbohydrates, proteins, fats and mineral salts.
• Nucleus: It controls and regulates all activities of the cell. It also regulates growth.

In plant cells, a cell wall is also present. It provides rigidity, strength and support.

• Both plant and animal cells have a cell membrane, cytoplasm and nucleus.
• Plant cells have a cell wall, but animal cells do not.
• Plant cells have chloroplasts in green parts, which help in photosynthesis.
• Plant cells usually have a large vacuole, while animal cells may have small vacuoles or no vacuoles.
• Plant cells are usually more regular and firm due to the cell wall, while animal cells may have different shapes.

The shape, size and structure of a cell help it perform its specific function.

• Cheek cells are thin and flat. They form a protective lining inside the mouth.
• Nerve cells are long and branched. They carry messages quickly to different parts of the body.
• Muscle cells are thin, flexible and spindle-shaped. They contract and relax to produce movement.
• Plant tube-like cells help transport water through the plant.

Thus, cell structure is closely related to cell function.

The body of a living organism is organised in levels:

1. Cell: The basic unit of life.
2. Tissue: A group of similar cells performing a function.
3. Organ: Different tissues working together.
4. Organ system: Several organs working together to perform a major function.
5. Organism: All organ systems together form a complete living being.

Microorganisms are tiny living organisms that cannot be seen with the naked eye. They are visible only under a microscope.

• Bacteria: Unicellular organisms with no well-defined nucleus. They may be spherical, comma-shaped, spiral or rod-shaped.
• Protozoa: Usually unicellular organisms such as Amoeba and Paramecium.
• Fungi: May be unicellular or multicellular. Yeast is unicellular, while mould is multicellular.
• Algae and microalgae: Some are microscopic and contain green pigment for making food.

Microorganisms such as bacteria and fungi act as natural cleaners.

• They break down fruit peels, vegetable waste, dry leaves and animal waste.
• This process is called decomposition.
• Complex substances are changed into simpler nutrient-rich substances.
• These nutrients return to the soil and help plants grow better.
• Decomposition helps recycle waste and keeps the environment clean.

• Yeast is used to make bread, cakes and similar food items soft and fluffy.
• Yeast releases carbon dioxide during respiration, which forms bubbles in dough.
• Lactobacillus converts milk into curd by producing lactic acid.
• Some bacteria help in fermentation of idli, dosa and bhatura batter.
• Fermented foods are important in many traditional diets and can improve taste and texture.

Rhizobium bacteria live in swollen regions called root nodules of legumes such as peas, beans and lentils.

• They trap nitrogen from the air.
• They make nitrogen useful for plants.
• This improves soil fertility naturally.
• Farmers grow legumes in rotation with other crops to maintain soil health.
• This reduces the need for chemical nitrogen fertilisers.

The cell is considered the basic unit of life because:

• All living organisms are made up of one or more cells.
• A single cell contains components that help in life processes.
• Unicellular organisms perform all life functions in one cell.
• In multicellular organisms, cells become specialised and work together.
• Cells help organisms grow, survive and function.

Microalgae are microscopic plant-like organisms found in water, soil, air and even on trees.

• They make their own food using sunlight.
• They release oxygen and contribute greatly to Earth’s oxygen supply.
• They are food for many aquatic animals.
• Some, such as Spirulina and Chlorella, are used as health supplements.
• They help clean water and can be used to make biofuel.
• Their conservation is important for oxygen balance and environmental health.

Bacterial cells are different because they do not have a well-defined nucleus. Their genetic material is present in a nucleoid region without a nuclear membrane.

• Like plant and animal cells, bacteria have a cell membrane.
• Like plant cells, bacteria also have a cell wall.
• Unlike plant cells, bacteria do not have chloroplasts.
• Unlike animal and plant cells, bacteria do not have a well-defined nucleus.

Answer: A. Microorganisms are tiny living beings, so a microscope is needed to observe them.

Answer: A. The cell wall provides rigidity and strength to plant cells.

Answer: C. Yeast makes dough fluffy by releasing carbon dioxide, not oxygen.

Answer: D. Bacteria do not have a well-defined nucleus or nuclear membrane.

Answer: A. Lactic acid makes milk curdle and gives curd a sour taste.

Answer: A. Rhizobium in legume root nodules increases nitrogen availability.

Answer: A. Viruses are acellular and reproduce only inside host cells.

Answer: A. Microalgae support aquatic food chains.

Answer: A. Glycerin keeps the material moist and improves clarity.

Answer: A. Cells form the basic structure of all living beings.

Yeast grows and respires better in warm conditions. In a refrigerator, low temperature slows down yeast activity, so less carbon dioxide is produced and the dough rises slowly.

Dry leaves and vegetable peels provide organic matter for microorganisms. Microbes decompose this waste into manure. Proper mixture also supports better moisture and air conditions for decomposition.

A unicellular organism performs all life processes within one cell. The single cell carries out nutrition, respiration, growth, movement and reproduction.

Many cells are transparent and difficult to see clearly. Stains increase contrast and make structures such as nucleus, cytoplasm and cell boundary more visible.

No. Some microbes cause disease, but many are useful. They help in curd formation, bread making, decomposition, manure formation, nitrogen fixation, biogas production and water cleaning.

Legumes have root nodules containing Rhizobium. These bacteria trap atmospheric nitrogen and enrich the soil, reducing dependence on chemical fertilisers.

Dead plants, dead animals and organic waste would not decompose properly. Nutrients would not return to the soil, soil fertility would reduce and the environment would become polluted with waste.

Nerve cells transmit messages across the body. Their long and branched shape helps them connect distant body parts and coordinate quick responses.

Microalgae release oxygen, support aquatic food chains, help clean water and can be used for biofuel and supplements. Their loss can disturb oxygen balance and aquatic ecosystems.

A bacterial cell lacks a well-defined nucleus and nuclear membrane. Its genetic material is present in a nucleoid region, unlike plant and animal cells.

Lactobacillus continues to multiply and produce more lactic acid. More lactic acid makes curd taste more sour.

Subcellular components are extremely small. An electron microscope provides very high magnification, allowing scientists to observe more detailed cell structures.

The cell wall gives rigidity and strength to the onion peel cell.

Human cheek cells are animal cells. Animal cells do not have a cell wall.

Chloroplast contains chlorophyll and helps the plant cell make food by photosynthesis.

The nucleoid represents the region where genetic material is present without a nuclear membrane.

Yeast releases carbon dioxide. Carbon dioxide turns lime water milky.

Root nodules contain Rhizobium bacteria, which trap nitrogen and make it useful for plants.

The main theme is the study of cells and microorganisms that are invisible to the naked eye but are important for life and the environment.

A microscope is required because cells and microorganisms are too small to be seen clearly with the unaided eye.

The most important cell parts are cell membrane, cytoplasm, nucleus, cell wall, chloroplast, vacuole and nucleoid.

Yeast helps in making bread and cakes. Lactobacillus helps in curd formation. Some bacteria help in fermentation of idli, dosa and bhatura batter.

No. Many microorganisms are useful. They help in digestion, decomposition, curd formation, bread making, nitrogen fixation and biogas production.

Microbes decompose dead plants, animals and organic waste into simpler substances, recycle nutrients and help keep the environment clean.

Legumes have root nodules containing Rhizobium bacteria, which trap nitrogen from air and make it useful for plants.

Spirulina is rich in protein, contains vitamin B12 and has health benefits, so it is called a superfood.

Unicellular organisms are made of one cell, while multicellular organisms are made of many cells.

Viruses are acellular and can multiply only inside living cells, so they are different from other microorganisms.