The Fundamental Unit Of Life: Cell

True, viruses are non-cellular living organisms as they exist without any cell.

False, Amoeba is a unicellular organism.

True, Plant cell wall is mainly composed of cellulose.

False, Cellulose is a structural carbohydrate.

True, Plasma membrane is present in both plant and animal cell.

True, blue green algae is an example of prokaryotic cell.

False, Plastid containing the pigment called chlorophyll are known as chloroplasts.

False, Nucleolus is not bounded by any membrane.

False, Grana are stakes of membrane-bounded discoid sacs containing chlorophyll.

False, Ribosomes are made up of ribonucleic acid and proteins.

True, Mitochondria is a site of cellular respiration or oxidation of food.

False, Chloroplast is known as kitchen of the cell as photosynthesis takes place in them.

False, Cell wall is not a living structure.

True, Cork is a substance which comes from the bark of a tree

False, Robert brown discovered nucleus in 1831.

True, some cells like Amoeba have changing shape.

False, the movement of a substance from the area of low concentration to an area of high concentration is called osmosis.

False, Dilute solution is known as hypotonic solution.

True, Lysosomes help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles.

True, SER plays a crucial role in detoxifying many poisons and drugs.

False, the central vacuole of some plant cells may occupy 50-90% of the cell volume.

Microscope is an optical instrument which renders minute objects distinctly visible. It consists of lenses or combination of lens.

The tiny objects which cannot be visible without the aid of a microscope, are called microscopic. E.g., Amoeba, bacteria, etc.

Microscope is used for obtaining magnified images of small objects.

Eye piece and objectives are parts of a compound microscope in which two different types of lenses are used.

Magnification of a microscope is calculated by multiplication of the power of objective lens and power of eyepiece lens.

{Magnification of object= Magnifying power of objective lens X Magnifying power of eyepiece lens.}

For example: If the magnifying power of the eyepiece lens is 10X and the magnifying power of objective lens is 4X, the magnification is 40X.

Light microscope has two or more sets of lens. That’s why, it is called a “compound microscope”.

In light microscope, visible light (sunlight, lamp light) is used as source of illumination whereas in electron microscope, electrons are used as source of illumination.

The stained material remains in its normal condition for a long period when mounted in glycerine. It does not get dried easily.

It is because dust particles of fingers may make the coverslip dirty if it is handled from its upper and lower surfaces.

Plasma membrane is the outer most layer in animal cells. It is a selective permeable membrane which permits the entry and exit of some materials in the cells.

In plant cell, cell wall is the outer most layer which is non-living and freely permeable.

Cell wall and chloroplasts are present only in plant cells.

In the given diagram, cell wall is present, hence we can say that it is a plant cell. This is because cell wall is present only in plant cell.

Lysosomes and centrioles are found only in animal cells and not in plant cells.

When a drop of ink is placed gently at the base of a beaker, it slowly moves in all direction due to diffusion. It makes the water uniformly coloured.

Plasma membrane is permeable to water; therefore, water can move inward as well as outward depending on the concentration of solution in which the cell is placed. The movement of water occurs from the region of high water concentration to a region of low water concentration. When a cell is placed in hypotonic solution (dilute solution), water enters into the cell, hence cell will show endosmosis. While a cell is placed in hypertonic solution, cell will show exosmosis because the medium has lower concentration of water than the cell sap.

Hypertonic solution is present between the shrunken protoplast and cell wall.

When animal cell (e.g., human erythrocytes) is placed in hypertonic solution, it gets shrink and gives wrinkled appearance called crenation.

The shell of an egg is mainly made up of calcium bicarbonate. It is impermeable to water. So, when the shelled egg is placed in water, there will not be any change in the size of the egg. While when the deshelled boiled egg is placed in water, it also does not show any change in size because its membranous covering has become dead due to boiling.

The movement of water occurs from the region of high water concentration to a region of low water concentration through osmosis. When dry apricot is placed in salt solution, it will not swell up because the concentration of external solution is high (hypertonic solution) while when it is placed in water (hypotonic solution), it will swell up because water enter into the cell through endosmosis.

Every cell is bounded by a thin, elastic, delicate, living membrane called plasma membrane or cell membrane. Plasma membrane is continuous lipid bilayer with protein molecules occurring both on inside and outside of the bilayer.

Lysosomes are tiny sac-like structures found in the cytoplasm. Each lysosome is surrounded by a single membrane and contains powerful enzymes.

Exosmosis.

True

1-B; 2-C; 3-A;

given figures are the parts of Endoplasmic Recticulum (ER).

Label A, B and C can see from the given figure.

Differences between plasma membrane and cell wall:

Structure of Nucleus: Nucleus is a dense, spherical or oval, dot like structure located centrally in the cell. It is bounded by two nuclear membranes, both forming nuclear envelope. Nuclear envelope separates the nucleus from the cytoplasm. It contains large number of pores which control the passage of substances outside or inside the nucleus.

Inside the nuclear envelope is the nucleoplasm or nuclear sap. It is transparent, semi-fluid and contains a large number of enzymes which are required for the synthesis and functioning of RNA and DNA. Within the nucleoplasm, two structures are embedded-chromatin material and nucleolus.

Chromatin material is a tangled fibrous mass. The chromatin material condenses to form chromosomes during cell division. Chromosomes contain information for inheritance of features from parents to next generation in the form of DNA (Deoxyribo Nucleic Acid) molecules. Chromosomes are composed of DNA and protein. DNA molecules contain the information necessary for constructing and organising cells. Functional segments of DNA are called genes.

Nucleolus may be one or more in number and is not bounded by any membrane. It is rich in protein and RNA molecules. Nucleolus acts as the site for ribosome formation, hence it is known as factory of ribosomes.

Functions of nucleus:

(i) Nucleus plays a central role in cellular reproduction, the process by which a single cell divides to form two new cells.

(ii) Nucleus controls cell metabolism and other activities of cell, hence it is also called Master or Director of the cell.

(iii) Along with the environment, nucleus directs the chemical activities of the cell. It determines the development and future form of the cell.

(iv) It is concerned with the transmission of hereditary traits from the parent to offsprings.

(a) Structure of mitochondria: Mitochondria are tiny bodies of varying shapes and size, found in the cytoplasm. Each mitochondrion is covered by a double-membrane envelope. Outer membrane is smooth and porous while inner membrane is projected with finger-like structures, the cristae. These cristae create a large surface area for ATP-generating chemical reactions. The cristae as well as inner membrane possess small tent like particles called F1 particles or oxysomes.

The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP (Adenosine triphosphate) molecules. Hence, Mitochondria are also known as the powerhouses of the cell. ATP is known as the energy currency of the cell. The body uses energy stored in ATP for making new chemical compounds and for mechanical work.

The cavity of mitochondria is filled with matrix. The mitochondrial matrix contains lipids, proteins, circular DNA and RNA.

Functions of mitochondria:

(i) Mitochondria is the site of cellular respiration or oxidation of food in a cell.

(ii) The energy, released in the form of ATP, is used by body cells to synthesise new chemical compounds and to carry out other metabolic activities.

(b) Differences in function of mitochondria and chloroplasts:

Main difference between animal cell and plant cell is nutrition.
Plant cells have chloroplasts which take part in the photosynthesis process whereas animal cells do not have chloroplasts.

Chromosomes are thread like structures usually present in the nucleus. They are composed of DNA (deoxyribose nucleic acid) and proteins.

When a cell is placed in hypertonic solution, it loses water through exosmosis and shrinks the cell content away from the cell wall. This phenomenon is known as plasmolysis.

A solution having higher concentration of solute with respect to another solution, is called hypertonic solution

When a cell is placed in hypotonic solution, the water molecule will enter into the cell and the cell will swell up.

Protoplasm is known as “physical basis of life”.

Lysosomes are sac-like structures which help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles. That’s why they are called suicide bags, digestive bags or demolition squads.

Grana are stacks of membrane-bounded, flattened sacs containing photosynthetic pigments called chlorophyll.

Lysosomes are sac-like structures which help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles. Thus, they act as garbage disposal system of the cell.

The major constituents of ribosomes are the ribonucleic acid (RNA) and proteins.

The leucoplasts are the colourless plastids of varied shapes and sizes with stored nutrients: Amyloplasts store carbohydrates (starch); elaioplasts store oils and fats whereas the aleuroplasts store proteins.

Grana are stacks of membrane-bounded, flattened sacs (thylakoid) containing photosynthetic pigments called chlorophyll.

The cell wall is mainly composed of cellulose. Cellulose is a complex substance which provides mechanical and structural strength to cell.

Plasmodesmata is a thin protoplasmic projection connecting two adjacent plant cells.

The inner membrane of mitochondria is projected with finger-like structures, called cristae. These cristae create a large surface area for ATP-generating chemical reactions.

Amyloplasts store carbohydrates (starch); elaioplasts store oils and fats whereas the aleuroplasts store proteins.

A Prokaryotic cell is primitive in organisation. It has a nucleoid (nuclear membrane is absent).

Mitochondria are the seat of kerbs cycle (aerobic respiration).

First living cells were observed by A.V. leeuwenhoek.

Semipermeable membrane allows or permits the entry and exit of only solvent molecules.

In unicellular organisms like Amoeba, gaseous exchange takes place through the process of diffusion.

Root hair absorb water from the surrounding soil using the process of osmosis.

A Prokaryotic cell is primitive in organisation. It has a nucleoid (nuclear membrane is absent).

Ribosomes are present both in prokaryotic and eukaryotic cells except in Matura sperms and RBCs. They are made up of ribonucleic acid (RNA) and proteins.

Two biologists, Schleiden (1839) and Schwann (1839) presented the cell theory. This stated that all the plants and animals are composed of cells and the cell is the basic unit of life.

Rudolf Virchow (1858) stated that the new cells originate from the pre-existing cells only (omnis cellula e cellula).

Chloroplast is known as kitchen of the cell as photosynthesis takes place in them.

Ribosomes are small and dense particles which occur freely in the cytosol or remain attached to the endoplasmic reticulum. They take part in the synthesis of proteins. Ribosomes are not bounded by a membrane.

Vacuoles are fluid-filled membrane-bound spaces. They are bounded by a single unit membrane known as tonoplast.

Smooth endoplasmic reticulum (SER) does not bear ribosomes. They are found in liver cells, interstitial cells, adipose cells and muscles cells, etc. They help in the manufacture of fat molecules and lipids.

Smooth endoplasmic reticulum does not bear ribosome. It helps in the synthesis of lipids While, rough endoplasmic reticulum is associated with ribosomes. Ribosomes are site of protein synthesis.

The main function of Golgi apparatus is secretory. It is also involved in the synthesis of new membrane and lysosomes.

Endocytosis is the ingestion of material by the cells through the plasma membrane. Amoeba acquires its food through endocytosis process.

Smooth endoplasmic reticulum (SER) does not bear ribosomes. It plays a crucial role in detoxifying many poisons and drugs.

Chromosomes are thread like structures usually present in the nucleus. They are composed of DNA (deoxyribose nucleic acid) and proteins.

Nucleus, mitochondria and plastid have their own DNA, hence they are able to make their own structural proteins.

The part of the cell which occur between the cell membrane and nucleus envelope is called cytoplasm. Cytoplasm contains many specialised cell organelles. While protoplasm consists of cytoplasm and nucleus.

Bacterial cell wall is made up of peptidoglycan.

If a cell placed in the hypotonic solution, then it will be swell up. This is because the higher concentration of water molecules is present outside the cell. So, the water molecules move from external solution into cell sap.

Plasmolysis is defined as the process of shrinkage of the cytoplasm of a plant cell occurred due to loss of water in the plant cell.

Endoplasmic reticulum serves as channels and helps in transporting the different materials like proteins between various regions in the cytoplasm as well as between the nucleus and the cytoplasm. It also provides a large surface area inside the cells for various chemical activities.

Plasma membrane is selective permeable membrane made up of lipids and proteins. The movement of water across a semipermeable membrane is affected by the amount of substances dissolved in it.

Osmosis is a movement of water molecules from a region of higher concentration to a region of lower concentration through a semipermeable membrane.

Lysosomes are membrane-bound organelles that contain powerful digestive enzymes. They digest excess or worn out organelles, food particles and engulfed viruses or bacteria. The membrane surrounding a lysosome prevents the digestive enzymes inside from destroying the cell. Sometimes, lysosomes can cause self-destruction of a cell by releasing these digestive enzymes within the cells, hence they are also known as suicide bags.

Yes, All living organisms are made up of cells. Cell are building block of life. In unicellular organisms, a single cell performs all basic functions of life. While in multicellular organisms, Cells become specialised to perform different functions. Similar cells group together to form tissue for e.g. muscular tissue. Tissues organised to form organs such as heart, kidney and then organ organise into organ system (Circulatory system, excretory system, digestive system, etc.) to perform major functions. A living organism has a number of organ systems. Thus, in all such organisational complexity, cell remains the basic building unit of the organism.

Soap and detergent solutions are used to wash clothes which are hypertonic compared to the skin cells. This results in exosmosis in the skin cells and thus the skin over the fingers shrinks when we wash clothes for a long time.

The process by which cells engulf food is called endocytosis. The flexiblility of plasma membrane helps the cell to engulf in food and other substances from its external environment. This is possible only when plasma membrane is in direct contact with external medium which happens only in the case of animals. In the case of plants, plasma membrane is covered with a wall.

Concentrated salt solution is a hypertonic solution which causes dehydration in the alimentary canal due to exosmosis. This causes stretching and hence vomiting.

Ribosomes are not bounded by a membrane.

Digested food is absorbed in the intestinal cells by the following process.

(i) Glucose and amino acids -Active transport.

(ii) Fatty acids and glycerol – Diffusion (Passive transport)

(iii) Water – Osmosis.

On adding salt, the external medium becomes hypertonic because of which exosmosis occurs and vegetables release water.

(b) RBC will burst easily while cells of onion peel will resist the bursting to some extent because RBC doesn’t have mechanism to resist endosmosis while onion cell wall puts a mechanical barrier to promote entry of water.

Bacteria which are photoautotrophic contain photosynthetic pigments inside small vesicles.

(a) iv; (b) v; (c) iii; (d) i; (e) ii.

1. Chromoplast : Flower (petals) and fruits.

2. Chloroplast : Green leaves and green stem.

3. Leucoplast : Root and underground stem.

(a) Endoplasmic reticulum; (b) Mitochondria; (c) Golgi apparatus; (d) Lysosome; (e) Vacuole; (f) Chloroplasts; (g) Nucleus.

Substances such as carbon dioxide and water move in and out of the cell by Diffusion and osmosis respectively.

Amoeba obtain its food through the process of endocytosis. The plasma membrane of Amoeba is flexible which help to engulf its food particles and other material from its external environment.

Mitochondria and plastids are two organelles in plant cell that contain their own genetic material and ribosomes.

Lysosomes are called scavengers of the cell because they remove cell debris consisting of dead and worn out cell organelle by digesting the same.

Nucleus controls cell metabolism and other activities of cell, hence it is also called Master or Director of the cell.

(a) Leucoplasts in roots; (b) Chloroplasts in leaves; (c) Chromoplasts in flowers and fruits.

Plant cells posses large sized vacuole because it performs following functions in plant cells:

(i) Vacuole helps in osmoregulation in a cell.

(ii) It stores toxic metabolic by-products or end products of the plant cell.

(iii) It helps in maintaining turgidity of the cell.

Chromatin is a tangled fibrous mass made up of DNA and protein. The chromatin material condenses to form chromosomes during cell division. Chromosomes are composed of DNA and protein. DNA molecules contain the information necessary for constructing and organising cells. Functional segments of DNA are called genes. A chromosome consists of two identical and spirally coiled threads called sister chromatids. They are joined at a constriction called centromere.

(a) A cell having higher water content than the surrounding medium, meaning that the surrounding solution is very concentrated solution (hypertonic solution), the cell will lose water by exosmosis. Such a solution is known as hypertonic solution.

(b) A cell having low water concentration than the surrounding medium, meaning that the surrounding solution is very dilute (hypotonic solution), the cell will gain water by endosmosis. Such a solution is known as hypotonic solution.

(c) A cell having equal water concentration to its surrounding medium, the cell will neither gain nor lose water to the external medium. Such a solution is known as isotonic solution.

(a) Nucleus

(b) Cell wall

(c) Golgi apparatus

(d) Nucleoplasm

(e) Cytoplasm

(b) Differences between plant and animal cells:

(b) Differences between nucleus and nucleoid:

Plasma membrane is made up of lipid and proteins. Endoplasmic reticulum is of two types-

(i) Rough endoplasmic reticulum with ribosomes attached on its surface for synthesizing proteins.

(ii) Smooth endoplasmic reticulum which is without ribosomes and is engaged in the synthesis of lipids.

Thus, endoplasmic reticulum acts as main site for synthesis of proteins and lipids which are needed for biosynthesis of plasma membrane. Hence, it is important for membrane biosynthesis.

(a) When dry apricot is placed in pure water, it gains water and swells due to endosmosis. After that if the swollen apricot is placed in the concentrated sugar solution, it loses water and consequently shrinks again due to exosmosis.

(b) When red blood cells are placed in concentrated salt solution, the water molecule will come out and it will shrink and give a shrivelled appearance (crenation).

(c) Breakdown of plasma membrane will result in death of the cell as protoplasmic structures will get dispersed.

(d) When Rheo leaves are boiled, all the cells of leaves become dead. When sugar solution is added on to the boiled rheo leaves, nothing will happen because liquid cannot pass through dead cell membrane.

(e) If Golgi apparatus is removed from the cell, the most cell activities performed by the Golgi apparatus will not take place.

Since external solution is hypotonic, when an animal cell is placed in it, the cell will swell up due to endosmosis for some extent and ultimately burst up.

Cell organelles: Endoplasmic reticulum; Golgi apparatus; mitochondria; vacuole; plastids; ribosomes; peroxisome.

itochondrion is a cell organelle that makes some of its own proteins with the help of its own DNA and ribosomes. Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP, hence they are called ‘power houses’ of the cell.

Prokaryotic cell (e.g. bacterium, blue green algae)

Differences between prokaryotic cell and human cell:

Cell is the functional unit of life because it is capable to performing all functions of life.

1. Plasma membrane is a selective permeable membrane which allows or permits the entry and exit of some materials in and out of the cell.

2. Cell wall provides rigidity and protection to cell. It is permeable.

The main cellular site of ATP generation is mitochondrion.

Peroxisome uses molecular oxygen like mitochondria to protects the cell from toxic metabolic by products.

Chromatin material is a tangled fibrous mass. The chromatin material condenses to form chromosomes during cell division.

Chromosomes are thread-like structures usually present in the nucleus that become visible only during cell divisions.

DNA and histone proteins are present in chromatin.

Prokaryotes have 70S ribosomes and eukaryotes have 80S ribosomes.

Nucleolus is called little nucleus.

Nucleus controls cell metabolism and other activities of cell, hence it is also called Master or Director of the cell.

(a) If excess amount of fertilizer is added to a green lawn, it will kill the grass plants because the process of exosmosis and plasmolysis take place.

(b) If salt is added to cut pieces of mango, exosmosis will take place and water will be released. This prevents mango from bacterial and fungal attack.

Cell Inclusions are non-living materials present in the cytoplasm of a cell such as fat droplets, pigment granules, etc.

Elaioplasts – Starch

Amyloplasts store carbohydrates (starch); elaioplasts store oils and fats whereas the aleuroplasts store proteins.

Chloroplast is the site of photosynthesis. If chloroplast is taken out of the cell, though illuminated, the plant cell will not able to synthesize the food and it will die.

(a) It is figure of nucleus of a eukaryotic cell.

(b) X-nucleolus; Y-chromatin.

(c) Function of nucleolus (X): Nucleolus helps in protein synthesis by forming and storing RNA.

(a) A cells- Turgid cells; B- cells – Plasmolysed cells.

(b) If B cells are kept in hypotonic solution just after plasmolysis, they will become deplasmolysed.

(c) If A cells are kept in hypertonic solution, they will become plasmolysed due to exosmosis.

(a) X is Cristae and Y is matrix.

(b) Cristae create a large surface area for ATP-generating chemical reactions.

(c) The mitochondrial matrix contains lipids, proteins, circular DNA and RNA.

(d) Mitochondrion. Its common name is power house of the cell.

W- Golgi apparatus; X- Vacuole; Y- Ribosome; Z-Lysosome.

(b) Covering membrane of X is called tonoplast.

(c) Lysosome (Z) contains the hydrolytic enzymes.

(d) Golgi apparatus takes part in storage, modification and packaging.

1. Osmosis helps fresh water unicellular organisms (Amoeba) to gain water in their bodies. 2. Contractile vacuole helps in osmoregulation. It throws out excess of water from their bodies.

(b) (i) Absorption of water by the plant root hairs occurs due to osmosis.

(ii) In plants, cells, tissues and soft organs such as leaves, buds, young shoots, flowers, fruits maintain turgidity due to osmotic absorption of water.

Viruses;

Nucleoid;

J.E. Purkinje;

Electron microscope;

Largest;

Shape;

Structural, functional;

Lysosomes;

Proteins;

Energy;

Proteins;

Schleiden, Schwann;

Cell wall;

Plant;

ATP;

Cellulose;

Similar;

Virchow;

1665;

A cell is the structural and functional unit of living beings.

A Prokaryotic cell is primitive in organisation. These cells do not have well organised nuclear region due to absence of nuclear membrane. These cells lake various membrane bound organelles like mitochondria, lysosome, endoplasmic reticulum, etc. E.g., bacteria and blue green algae.

Eukaryotic cells are those that have well organised nucleus. These cells have well developed membrane bound cell organelles such as mitochondria, lysosomes, endoplasmic reticulum, chloroplasts, nucleolus, etc. Eukaryotic cells occur in plants, animals, fungi and protists.

Robert Hooke coined the term cell.

Robert Hooke published his discovery of the cell in Micrographia (1665).

First living cells were observed by A.V. leeuwenhoek in 1674.

Shape of the cell depends upon functional adaptations and viscosity of the protoplasm.

The smallest cell is mycoplasma or PPLO. Its size is 0.1 to 0.5 mm (micrometre). Ostrich egg is the largest cell measuring about 170x135 mm in diameter.

Neuron or nerve cell is the longest cell in the human body.

100 trillion (10¹⁴) cells are present in human body.

All multicellular organisms develop from a single cell called zygote (fertilized egg) through cell division.

Bacteria and blue green algae (cyanobacteria) are examples of prokaryotic cell.

Unicellular organism- Amoeba

Multicellular organism- Human being.

Two biologists, M.J. Schleiden (1839) and T. Schwann (1839) proposed the cell theory.

The most common device used in the school laboratory is a light microscope. It is a simple microscope which uses light to illuminate the object and a combination of lenses to magnify the image.

In electron microscope, a beam of electrons is used to visualise cellular structures. The resolution of electron microscope is much greater than that of light microscope. It can be used to study molecules like DNA, RNA and proteins.

Plasma membrane is living, thin, delicate, selective permeable membrane.

Plasma membrane is living, thin, delicate, elastic, selective permeable membrane that separates the cell contents from the external environment.

A cell is the structural and functional unit of living beings. It is capable of independent existence and performs essential functions of life.

It is the living matter of the cell. It is made up of cytoplasm and nucleus.

The biomolecules present in plasma membrane are carbohydrates, proteins and lipids (phospholipids, cholesterol).

Membrane which allows or permits the entry and exit of some selected substances, is called selectively permeable membrane. Plasma membrane is an example of selective permeable membrane.

Fluid mosaic organization is found in the plasma membrane.

Diffusion is the process in which particles move from a region where they are in higher concentration to a region where they are in low concentration, until uniform concentration is finally achieved.

Osmosis is the diffusion of water molecules from the region of higher concentration to the region of lower concentration through a semipermeable membrane.

Plasma membrane regulates the movement of substances in and out of the cell by diffusion or osmosis. Thus, if the plasma membrane is ruptured, the cell contents might leak out and cell will die.

Plasma membrane bounds semi-fluid content of the cell and regulates the flow of substances into and out of the cell.

The process by which water molecules enter a cell is called endosmosis. This process takes place in hypotonic solution.

The process in which the water molecules move out of the cell is called exosmosis. It takes place in hypertonic solution.

(i) Hypertonic Solution: A solution having higher concentration of solute with respect to another solution, is called hypertonic solution.

(ii) Hypotonic Solution: A solution having higher concentration of solvent with respect to another solution, is called hypotonic solution.

(iii) Isotonic Solution: A solution that have exactly the same water concentration with respect to another solution, is called isotonic solution.

Endocytosis is the ingestion of material by the cells through the plasma membrane.

Exocytosis is the process to move materials to the outside of the cell with the help of special vesical which get fused with the plasma membrane and discharge its contents outside.

Endocytosis is the ingestion of material by the cells through the plasma membrane. The types of endocytosis are:

1. Phagocytosis, 2. Pinocytosis and 3. Receptor mediated endocytosis.

Active transport is a process to transport molecules across the membrane against a concentration gradient. Energy is used in the form of ATP.

Cell wall is non-living (dead) and freely permeable which lies outside the plasma membrane.

Mitochondria and plastids have their own genetic material (DNA), hence they are able to make their own structural proteins.

(a) Chloroplast is known as kitchen of the cell; (b) Mitochondrion is known as power house of the cell.

In plants, cell wall is made up of cellulose, whereas, in fungi, it is made up of chitin.

(a) Ribosome: It plays important role in the protein synthesis.

(b) Cell wall: It provides shape, rigidity and protection to the cell.

(a) Mitochondrion; (b) Chloroplast; (c) Centrosome; (d) Nucleus.

(a) Golgi bodies help in the formation of cell plate during cell division in plant cells.

(b) Vacuoles help the plant cells to remain turgid.

The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP (Adenosine triphosphate) molecules.

The full form of ATP is Adenosine triphosphate. ATP is also known as energy currency of the cell.

DNA (deoxyribose nucleic acid) and RNA (Ribonucleic acid) are present in an animal cell.

Lysosomes and centrioles are found only in animal cells and not in plant cells.

Differences between prokaryotic and eukaryotic cells:

Differences between organ and organelle:

Differences between nucleus and nucleoid:

In 1665, Robert Hooke, a British scientist took a thin slice of cork from an oak tree and observed it under the microscope. He observed honeycomb like compartments bounded by thick walls; hence, named them “cells”. These were dead cells.

There are two types of proteins molecules are found in plasma membrane:

(i) Intrinsic proteins -They completely cover the lipid bilayer.’

(ii) Extrinsic proteins – These occur either on the outer surface or on the inner surface of lipid layer.

Functions: (i) Plasma membrane is a selective permeable membrane. Therefore, it allows or permits the entry and exit of some materials in and out of the cell.

(ii) It protects the cell from injury.

(iii) The flexibility of plasma membrane helps the cell to engulf in food and other substances from its external environment. This process is known as endocytosis.

(iv) It bounds the semi-fluid content of the cell.

In unicellular organisms like Amoeba, gaseous exchange takes place through the process of diffusion.

(i) Put dried raisins or apricots in plain water and leave them for some time.

(ii) Then place them into a concentrated solution of salt or sugar.

(iii) We will observe, each gains water and swells due to endosmosis, when placed in pure water.

(iv) However, when placed in the concentrated solution, it loses water and consequently shrinks due to exosmosis.

Differences between diffusion and osmosis:

Endocytosis is the process of capturing a substances or particle from outside the cell by engulfing it with the plasma membrane, and bringing it into the cell. There are three types of endocytosis: 1. Phagocytosis, 2. Pinocytosis and 3. Receptor mediated endocytosis.

Endocytosis helps to bring molecules inside the cells. Endocytosis is an active transport process as it requires energy.

(i) When eukaryotic cells are placed in hypotonic solution (dilute solution), water molecules will enter into the cell and the cell will swell up due to endosmosis.

(ii) When eukaryotic cells are placed in hypertonic solution (concentrated solution), water molecules will move out of the cell and the cell will shrink due to exosmosis.

(iii) When eukaryotic cells are placed in isotonic solution, the water molecule will neither move out or will not go inside, hence the amount of water molecule remain the same. The cell will remain same.

(a) Ribosome is the smallest cell organelle.

(b) Largest cell organelle = Plastid in plants; Mitochondria in animal

(c) Rough endoplasmic reticulum contains ribosome attached to its surface.

(d) Genes are functional segments of the DNA molecule.

(a)

(b)

Differences between plant and animal cells:

If the nucleus is removed from a cell, the cell will die instantly because nucleus controls all the metabolic activities of the cell.

Spinach looks green due to the presence of green coloured plastid called chloroplast. Papaya is yellow and edible part of water melon is red due to the presence of chromoplast.

(a) Functions of endoplasmic reticulum:

(i) It forms supporting skeletal framework of the cell.

(ii) It serves as channels and helps in transporting the different materials like proteins between various regions in the cytoplasm as well as between the nucleus and the cytoplasm.

(b) Functions of lysosomes:

(i) Lysosomes help in intracellular digestion.

(ii) Lysosomes help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles.

(a) Ribosome (b) Leucoplasts

Lysosomes contain powerful digestive enzymes. They digest excess or worn out organelles, food particles and engulfed viruses or bacteria. The membrane surrounding a lysosome prevents the digestive enzymes inside from destroying the cell. Sometimes, lysosomes can cause self-destruction of a cell by releasing these digestive enzymes within the cells, hence they are also known as suicide bags.

(a) Cell inclusions: Cell Inclusions are non-living materials present in the cytoplasm of a cell such as fat droplets, pigment granules, etc.

(b) Cytosol: Cytosol is a liquid part of cytoplasm which is found inside a cell.

(c) Protoplasm: Nucleus and cytoplasm together are called protoplasm.

(d) Nucleoplasm: It is a fibrous transparent, semi-solid granular material that fills the nucleus.

Nucleolus is a condensed region of chromatin where ribosome synthesis occurs.

(a) Mitochondria

Mitochondria are tiny bodies of varying shapes and size, found in the cytoplasm. Each mitochondrion is covered by a double-membrane envelope. Outer membrane is smooth and porous while inner membrane is projected with finger-like structures, the cristae. These cristae create a large surface area for ATP-generating chemical reactions. The cristae as well as inner membrane possess small tent like particles called F1 particles or oxysomes.

The cavity of mitochondria is filled with matrix. The mitochondrial matrix contains lipids, proteins, circular DNA and RNA. Mitochondria is the site of cellular respiration or oxidation of food in a cell.

(b) Plastids: Plastids occur in plant cells and are absent in animal cells. They have their own genetic material and ribosomes. There are three types of plastids:

(i) Chloroplasts: These are green coloured plastids because of the presence of chlorophyll. Chloroplasts occur abundantly in green leaves and also to some extent in green parts of the plant. These are known as the kitchen of the cell.

(ii) Chromoplasts: These contain pigment other than chlorophyll. They impart colour to flowers and fruits to attract insects and other animals for pollination and fruit dispersal.

(iii) Leucoplasts: The leucoplasts are the colourless plastids of varied shapes and sizes. They store starch, proteins or lipids in the cell.

The cell organelles are- Endoplasmic reticulum (ER), Ribosomes, Lysosomes, Golgi apparatus, Mitochondria, Plastids, Vacuoles, Peroxisome and Centrosome.

The three main functional regions of the cell are plasma membrane, nucleus and cytoplasm.

(a) Chromatin- It is found inside the nucleus.

(b) Chromosome- It is found inside the nucleus.

(c) Tonoplast- It is outer covering of vacuole.

(d) Nucleolus- It is found inside the nucleus.

The functional segments of DNA are called genes. Genes carry heredity information from parents to offsprings. Genes are located on chromosomes.

Lysosomes can digest any foreign particles which enter the cell such as bacteria and virus, hence they are called digestive bags.

Mitochondrion is also known as power plant of the cell.

Centrioles are hollow, cylindrical structures which are made up of microtubules arranged in a specific manner.

Functions: (i) It helps in the formation of cilia and flagella by forming their basal bodies.

(ii) It helps in the spindle formation during cell division.

Smooth endoplasmic reticulum does not bear ribosome. It helps in the synthesis of lipids While, rough endoplasmic reticulum is associated with ribosomes. Ribosomes are site of protein synthesis.

When a living cell is placed in hypertonic solution, it loses water by osmosis and shrinks away from the cell wall. This process is known as plasmolysis and the plant cell is said to be plasmolysed.

Fluid mosaic organisation: It was proposed in the early 1970s by S.J. Singer and G. Nicolson. According this model, plasma membrane is composed of a bilayer of phospholipids. There are two types of proteins-intrinsic and extrinsic are embedded in the lipid bilayer. These proteins are:

(i) Intrinsic proteins -They completely cover the lipid bilayer.’

(ii) Extrinsic proteins – These occur either on the outer surface or on the inner surface of lipid layer.

The “fluid” part of the term comes from the belief that the proteins are able to flow and move around in the membrane.

(a) Endoplasmic reticulum: It forms supporting skeletal framework of the cell.

(b) Mitochondria: It is the site of cellular respiration or oxidation of food in a cell.

(c) Golgi apparatus: It is involved in the synthesis of cell wall, plasma membrane and lysosomes.

(d) Lysosome: It helps in intracellular digestion.

(e) Ribosome: It helps in protein synthesis inside the cell.

Structure of Nucleus: Nucleus is a dense, spherical or oval, dot like structure located centrally in the cell. It is bounded by two nuclear membranes, both forming nuclear envelope. Nuclear envelope separates the nucleus from the cytoplasm. It contains large number of pores which control the passage of substances outside or inside the nucleus.

Inside the nuclear envelope is the nucleoplasm or nuclear sap. It is transparent, semi-fluid and contains a large number of enzymes which are required for the synthesis and functioning of RNA and DNA. Within the nucleoplasm, two structures are embedded-chromatin material and nucleolus.

Chromatin material is a tangled fibrous mass. The chromatin material condenses to form chromosomes during cell division. Chromosomes contain information for inheritance of features from parents to next generation in the form of DNA (Deoxyribo Nucleic Acid) molecules. Chromosomes are composed of DNA and protein. DNA molecules contain the information necessary for constructing and organising cells. Functional segments of DNA are called genes.

Nucleolus may be one or more in number and is not bounded by any membrane. It is rich in protein and RNA molecules. Nucleolus acts as the site for ribosome formation, hence it is known as factory of ribosomes.

Functions of nucleus:

(i) Nucleus plays a central role in cellular reproduction, the process by which a single cell divides to form two new cells.

(ii) Nucleus controls cell metabolism and other activities of cell, hence it is also called Master or Director of the cell.

(iii) Along with the environment, nucleus directs the chemical activities of the cell. It determines the development and future form of the cell.

(iv) It is concerned with the transmission of hereditary traits from the parent to offsprings.

(a) Golgi Apparatus: Golgi apparatus first described by Camillo Golgi. There are three distinct components are visible in the Golgi complex. They are

• Flattened sacs or cisternae

• Clusters of tubules and vesicles, and

• Large vesicles or vacuoles

Golgi apparatus has a convex forming face and a concave maturing face. The forming face receives vesicles from ER and maturing face produces secretory vesicles and lysosomes.

Golgi apparatus absent in bacteria, blue green algae, mature sperms and RBC of mammals and other animals.

Function: (i) The main function of Golgi apparatus is secretory. It helps in the secretion of mucus, enzymes and hormones.

(ii) It helps in the storage of secretory products.

(iii) Golgi apparatus is also involved in the synthesis of cell wall, plasma membrane and lysosomes.

(b) Mitochondria: Mitochondria are tiny bodies of varying shapes and size, found in the cytoplasm. Each mitochondrion is covered by a double-membrane envelope. Outer membrane is smooth and porous while inner membrane is projected with finger-like structures, the cristae. These cristae create a large surface area for ATP-generating chemical reactions. The cristae as well as inner membrane possess small tent like particles called F1 particles or oxysomes.

The cavity of mitochondria is filled with matrix. The mitochondrial matrix contains lipids, proteins, circular DNA and RNA.

Functions of mitochondria:

(i) Mitochondria is the site of cellular respiration or oxidation of food in a cell.

(ii) The energy, released in the form of ATP, is used by body cells to synthesise new chemical compounds and to carry out other metabolic activities.

A cell consists of several organelles like plasma membrane, mitochondria, endoplasmic reticulum, ribosomes, Golgi apparatus lysosomes, vacuoles etc. Every cell organelle performs specific functions. For example – plasma membrane controls the entry and exit of vital molecules, chloroplasts synthesize food, ribosomes help in protein synthesis, mitochondria convert glucose into energy etc. This shows that there is division of labour in a cell. Likewise, human society also has specific set of people to perform specific tasks. For example- police and security personnel’s control entry and exit of people in the city, city planners design and develop the infrastructure of a city. In this way masons, electricians, carpenters, plumbers, transporters scavengers, traffic controllers, teachers, doctors, farmer, shopkeepers, managers, security persons, all have some specialised job/ task to do for the human society.

(i) Kidney beans have a porous cell wall and a semipermeable plasms membrane. When it was

soaked in water overnight, the water diffused inside the beans through the semipermeable membrane

and beans got swollen and soft after cooking.

(ii) Endosmosis.

(iii) White grams

(i) Muskan’s mother cut the vegetables into small pieces and put them in the sun for hours to dry them by losing water through diffusion and evaporation.

(ii) Mixing common salt in the vegetables triggered the process of exosmosis so that they lose more

water which then evaporated during heating. The prevents the growth of microorganisms like bacteria

and fungi on the vegetables.

(iii) She mixed acetic acid as it acts as a preservative and kills microorganisms which can destroy the

vegetables.

• Pickles and jams have high concentration of salt and sugar respectively which are osmotically active substances and do not allow microbial spores to germinate. Even if pickles or jams get contaminated, the microorganisms cannot survive as they undergo exosmosis and ultimately die.
• Moreover, turmeric or acetic acid used act as preservatives and kill the microbes. Thus, pickles and jams get a longer life and do not get easily spoiled. Their life is further enhanced by keeping them in dry and cool place and using neat and moisture-free spoons.

• This gives us a lesson that human beings can also have a long life if they live in a hygienic environment.

(i) Two reasons why plants have variously coloured flowers are –

(a) To attract insects and other animals which help in pollination

(b) Flowers are meant for sexual reproduction in plants.

(ii) Flowers emit fragrance to attract insects and other animals which help in pollination. Fragrance of

flowers spreads in the environment through the process of diffusion. Scent/fragrance spreads from flowers into surrounding environment through diffusion.

(iii) (a) The scientific phenomenon involved in this scenario is diffusion.

(b) The scientific phenomenon involved in this scenario is diffusion.

(i) A fruit is green in colour when unripe as its skin contains chloroplasts. When the fruit ripens, the chloroplasts are changed to chromoplasts which render an attractive colour to the fruit such as orange, yellow etc.

(ii) The colour of the fruits attracts animals and they come to feed over them.

(iii) While eating the fruits, the animals pick up the seeds and take them to different places which helps in the dispersal of seeds. Thus, both the animals and the plants are benefitted because of this. This is called mutualism.

(iv) Even in human society, nobody can live all by himself/herself. Everybody is dependent on somebody else for most of their activities. For example – a cook cooks food for you to eat and in return you pay the cook so that he/she is able to run his/her family.

Plasma membrane has diverse functions which includes providing shape to cell, acting as mechanical barrier between cell contents and environment, selective permeability, flow of information, passage of water, flow of external fluids by cilia or absorption of nutrients by its microvilli etc. Plasma membrane is able to performance varied functions due to adaptation of proteins to form channels, enzymes, carriers, receptors and their attachment to small carbohydrates (oligosaccharides). In human society, every human being has to perform various functions. For example - Mahak is daughter of her parents, student of her school, a table tennis player, sister of her brother, a companion of her pet, a gardner in home garden, a caretaker of her grandparents etc.

1-(c); 2- (e); 3- (b); 4- (a); 5- (i); 6- (j); 7 – (g); 8 – (f); 9 – (h); 10- (m); 11- (k); 12 – (n); 13. (i)

a.- (ii) IV; (b) (iv)-II; (c) (i)- III; (d)- (III)-I; (e) – (vi) – VI; (f) – (v) – V. (iv).

Check List

1. Mitochondria-Catabolism

2. Lysosomes-Catabolism

3. Chloroplast-Anabolism

4. ER-Anabolism

5. Golgi apparatus-Anabolism

Basic characteristics of a cell are as follows:

(i) Cell is structural and functional unit of all living beings.

(ii) Cells can replicate independently.

(iii) Cells perform all the life sustaining activities by themselves.

Unicellular organism is made up of only one cell whereas multicellular organism made up of many cells that work together.

In multicellular organisms, Cells become specialised to perform different functions. Similar cells group together to form tissue for eg. muscular tissue. Tissues organised to form organs such as heart, kidney and then organ organise into organ system (Circulatory system, excretory system, digestive system, etc.) to perform major functions. Thus, a living organism has a number of organ systems. This is known as division of labour in multicellular organisms.

Virus do not have nucleus and protoplasm hence they do not show characteristics of life until and unless they enter into a living organism and use their cell machinery to multiply. That’s why they are exception to cell theory.

The largest cell is ostrich egg (170 x 135 mm).

(I) Cell: Cell is the basic building units of an organism.

(ii) Prokaryotic cell: A Prokaryotic cell is primitive in organisation. It has a nucleoid (nuclear membrane is absent).

(iii) Eukaryotic cell: A cell having membrane bound cell organelles are called eukaryotic cell.

(iv) Organelle: Small membrane bound structures within a cell are called organelles. Example: Nucleus, mitochondria, lysosomes.

Cell wall: It is a characteristics of plant cell only and absent in animal cell. It is an outer, rigid, protective, supportive and freely permeable covering of plant cells. The cell wall lies outside of the plasma membrane. It determines the shape of a plant cell and prevents desiccation of cells. It is mainly composed up of mainly cellulose. Cellulose is a complex substance and provides mechanical and structural strength to plants.

Function of cell wall: (i) Cell wall provides shape and rigidity to the cell.

(ii) It protects plasma membrane and internal structures from the attach of pathogens and mechanical injury.

(iii) It provides mechanical strength to the cell.

(iv) It is freely permeable to water and substances in solution.

Structure of Nucleus: Nucleus is a dense, spherical or oval, dot like structure located centrally in the cell. It is bounded by two nuclear membranes, both forming nuclear envelope. Nuclear envelope separates the nucleus from the cytoplasm. It contains large number of pores which control the passage of substances outside or inside the nucleus.

Inside the nuclear envelope is the nucleoplasm or nuclear sap. It is transparent, semi-fluid and contains a large number of enzymes which are required for the synthesis and functioning of RNA and DNA. Within the nucleoplasm, two structures are embedded-chromatin material and nucleolus.

Chromatin material is a tangled fibrous mass. The chromatin material condenses to form chromosomes during cell division. Chromosomes contain information for inheritance of features from parents to next generation in the form of DNA (Deoxyribo Nucleic Acid) molecules. Chromosomes are composed of DNA and protein. DNA molecules contain the information necessary for constructing and organising cells. Functional segments of DNA are called genes.

Nucleolus may be one or more in number and is not bounded by any membrane. It is rich in protein and RNA molecules. Nucleolus acts as the site for ribosome formation, hence it is known as factory of ribosomes.

Functions of nucleus:

(i) Nucleus plays a central role in cellular reproduction, the process by which a single cell divides to form two new cells.

(ii) Nucleus controls cell metabolism and other activities of cell, hence it is also called Master or Director of the cell.

(iii) Along with the environment, nucleus directs the chemical activities of the cell. It determines the development and future form of the cell.

(iv) It is concerned with the transmission of hereditary traits from the parent to offsprings.

Diploid number means a set of paired chromosomes of each kind whereas haploid means a set of unpaired chromosomes of each kind.

Chromosomes are thread-like structures usually present in the nucleus that become visible only during cell divisions. Chromosomes contain information for inheritance of features from parents to next generation in the form of DNA (Deoxyribo Nucleic Acid) molecules. Chromosomes are composed of DNA and protein. DNA molecules contain the information necessary for constructing and organising cells. Functional segments of DNA are called genes.

A chromosome consists of two identical and spirally coiled threads called sister chromatids. They are joined at a constriction called centromere.

Plasma membrane: Every cell is bounded by a thin, elastic, delicate, living membrane called plasma membrane or cell membrane. It is the outermost covering of the cell which separates the cell content from its external environment.

Plasma membrane is continuous lipid bilayer with protein molecules occurring both on inside and outside of the bilayer. We can see plasma membrane with the help of electron microscope. Structurally, plasma membrane is very flexible. The flexibility of plasma membrane helps the cell to engulf in food and other substances from its external environment.

Functions: (i) Plasma membrane is a selective permeable membrane. Therefore, it allows or permits the entry and exit of some materials in and out of the cell.

(ii) It protects the cell from injury.

(iii) The flexibility of plasma membrane helps the cell to engulf in food and other substances from its external environment. This process is known as endocytosis.

(iv) It bounds the semi-fluid content of the cell.

Passive transport: It is the net movement of materials across membranes that does not require any special source of energy.

Active transport: It is a process to transport molecules across the membrane against a concentration gradient. Energy is used in the form of ATP.

Diffusion: Diffusion is the process in which particles move from a region where they are in higher concentration to a region where they are in low concentration, until uniform concentration is finally achieved. Diffusion is faster in the gaseous phase than in liquids and solids.

In unicellular organisms like Amoeba, gaseous exchange takes place through the process of diffusion.

Osmosis is a special type of diffusion. Osmosis is diffusion of water from the region of its higher concentration (pure water or dilute solution) to the region of its lower concentration (strong solution) though a semipermeable membrane.

There are two types of osmosis:

(i) Endosmosis: It is the process by which water molecules enter into the cell.

(ii) Exosmosis: It the process by which water molecules move out of the cell.

Importance of osmosis:

(i) Root hair absorb water from the surrounding soil using the process of osmosis.

(ii) Absorption of water by alimentary canal.

(iii) Absorption of water by unicellular freshwater animals.

When a living plant cell is placed in hypertonic solution, it loses water by osmosis and shrinks away from the cell wall. This process is known as plasmolysis and the plant cell is said to be plasmolysed.

Endoplasmic reticulum is an interconnected system of membrane lined channels distributed extensively throughout the cytoplasm. At one end ER is connected to the outer membrane of the nucleus and at the other end to the plasma membrane. It occurs in three forms:

• Cisternae: These are parallel interconnected flattened sac-like structures.

• Tubules: Often branched, network-like structures

• Vesicles: These are round or oval shaped structures.

Endoplasmic reticulum is of two types:

(a) Rough endoplasmic reticulum: Ribosomes are attached on its surface for protein synthesis.

(b) Smooth endoplasmic reticulum: It is not associated with ribosomes.

Functions: (i) It forms supporting skeletal framework of the cell.

(ii) Endoplasmic reticulum serves as channels and helps in transporting the different materials like proteins between various regions in the cytoplasm as well as between the nucleus and the cytoplasm.

(iii) It also provides a large surface area inside the cells for various chemical activities.

(iv) SER plays a crucial role in detoxifying many poisons and drugs.

Structure of Golgi apparatus: Golgi apparatus first described by Camillo Golgi. There are three distinct components are visible in the Golgi complex. They are

• Flattened sacs or cisternae

• Clusters of tubules and vesicles, and

• Large vesicles or vacuoles

Golgi apparatus has a convex forming face and a concave maturing face. The forming face receives vesicles from ER and maturing face produces secretory vesicles and lysosomes.

Golgi apparatus absent in bacteria, blue green algae, mature sperms and RBC of mammals and other animals.

Function: (i) The main function of Golgi apparatus is secretory. It helps in the secretion of mucus, enzymes and hormones.

(ii) It helps in the storage of secretory products.

(iii) Golgi apparatus is also involved in the synthesis of cell wall, plasma membrane and lysosomes.

Lysosomes are tiny sac-like structures found in the cytoplasm. Each lysosome is surrounded by a single membrane and contains powerful enzymes. These enzymes are made by rough endoplasmic reticulum. Lysosomes are budded off from Golgi bodies.

Functions of lysosomes: (i) Lysosomes help in intracellular digestion.

(ii) They help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles. That’s why they are called suicide bags, digestive bags or demolition squads.

Structure of mitochondria: Mitochondria are tiny bodies of varying shapes and size, found in the cytoplasm. Each mitochondrion is covered by a double-membrane envelope. Outer membrane is smooth and porous while inner membrane is projected with finger-like structures, the cristae. These cristae create a large surface area for ATP-generating chemical reactions. The cristae as well as inner membrane possess small tent like particles called F1 particles or oxysomes.

The cavity of mitochondria is filled with matrix. The mitochondrial matrix contains lipids, proteins, circular DNA and RNA.

Functions of mitochondria:

(i) Mitochondria is the site of cellular respiration or oxidation of food in a cell.

(ii) The energy, released in the form of ATP, is used by body cells to synthesise new chemical compounds and to carry out other metabolic activities.

Chloroplasts are present in green algae and higher plants. They are greenish plastids which possess photosynthetic pigment called chlorophyll. Chloroplasts take part in the synthesis of food, hence, they are known as kitchen of the cell.

Each chloroplast is bounded by two unit membranes. The inside of the chloroplast is filled with dense homogenous matrix called stroma. Stroma contains a variety of photosynthetic enzymes, starch grains, DNA and ribosomes. In the stroma, flattened thread-like structures called thylakoid are present. The thylakoids are stacked over one another to form granum (plural-grana). Granum is the site of light reaction during photosynthesis while stroma is the site of dark reaction during photosynthesis.

The term ‘cell’ was given by Robert Hooke.

Two biologists, Schleiden (1839) and Schwann (1839) presented the cell theory. This stated that all the plants and animals are composed of cells and the cell is the basic unit of life.

Neuron or nerve cell is the longest cell in an animal body.

Robert Hooke developed a compound light microscope by using two lenses for achieving greater magnification.

In 1665, Robert Hooke, a British scientist took a thin slice of cork from an oak tree and observed it under the microscope. He observed honeycomb like compartments bounded by thick walls; hence, named them “cells”. These were dead cells.

The idea ‘omins cellula e cellula’ which means that all living cells arise from preexisting cells was given by Rudolf Virchow.

Amoeba is a unicellular organism which has an irregular or variable shape.

Nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material.

Nucleolus is a condensed region of chromatin where ribosome synthesis occurs.

The cell wall of two cells are join together by the middle lamella. Middle lamella is a jelly like substance which is made up of calcium and magnesium pectate.

Plasma membrane is a selective permeable membrane. Therefore, it allows or permits the entry and exit of some materials in and out of the cell.

If a cell placed in the hypotonic solution, then it will be swell up. This is because the higher concentration of water molecules is present outside the cell. So, the water molecules move from external solution into cell sap.

The cells of plant, fungi and bacteria can withstand in hypotonic solution without bursting. This is because of cell wall. While animal cell bursts up in hypotonic solution because cell wall is not found.

Bulk transport occurs through endocytosis and exocytosis. The process by which cell engulfs food is called endocytosis and ejects solid is called exocytosis.

The part of the cell which occur between the cell membrane and nucleus envelope is called cytoplasm. Cytoplasm contains many specialised cell organelles. Each of these organelles performs a specific function for the cell.

Rough endoplasmic reticulum contains ribosomes attached to its surface for synthesizing proteins.

The leucoplasts are the colourless plastids of varied shapes and sizes with stored nutrients: Amyloplasts store carbohydrates (starch); elaioplasts store oils and fats whereas the aleuroplasts store proteins.

Chloroplast contain a green pigment called chlorophyll which is essential for the process of photosynthesis.

Mitochondria are the sites of aerobic respiration. They produce cellular energy in the form of ATP, hence they are called ‘power houses’ of the cell.

The main function of Golgi apparatus is secretory. It is also involved in the synthesis of new membrane and lysosomes.

Lysosomes are sac-like structures which help to keep the cell clean by digesting any foreign material as well as worn-out cell organelles. That’s why they are called suicide bags, digestive bags or demolition squads.

Contractile vacuoles take part in osmoregulation.

Centrosome is found in the animal cells and some lower plant cells. They help spindle formation during cell division.

Cell was discovered by Robert Hooke in 1665

Robert Hooke published his discovery of the cell in Micrographia.

J.E. Purkinje (1839) coined the term protoplasm for living matter.

The cell theory, that all the plants and animals are composed of cells and that the cell is the basic unit of life, was presented by two biologists, Schleiden (1838) and Schwann (1839).

The largest cell is ostrich egg.

Neuron or nerve cell is the longest cell in an animal body.

Bacteria and blue green algae are examples of prokaryotic cells.

Animal, plant and fungi cells are examples of eukaryotic cells.

When raisins are placed in hypotonic solution, the raisins swell up due to the inward movement of water. This process through which water moves inside the raisins from high concentration of water to low is known as endosmosis.

Osmosis is purely a mechanical diffusion process by which cells absorb water without spending any amount of energy.

Lignin deposition streathen the cell wall and provides support to it.

The nuclear envelope has many pores which allow the transfer of materials between the nucleoplasm and the cytoplasm.

Chromatin is interwined mass of fine thread-like structures made up of protein and DNA.

Nucleus is present almost at the centre of a cell.

The term for subcellular structures having characteristic forms and functions is organelles.

Cytosol is a liquid part of cytoplasm which is found inside a cell.

Food vacuole is formed by engulfing food particles.

Vacuole is surrounded by a membrane called tonoplast.

In plant cell, they are filled with a fluid called cell sap which consists of free water and a variety of compounds in solution.

Plant cells contain many freely distributed subunits of Golgi apparatus called dictysosome.

The maturing face of Golgi apparatus produces secretory vesicles.

The ATP synthesis occurs on F1 particles in mitochondria.

Cell was discovered by Robert Hooke in 1665.

Schwann- A British zoologist

Schleiden-A German botanist

Ernst ruska and Max knoll developed electron microscope.

These are circular and biconcave, disk like in shape.

Neve cell is the longest cell in human body.

When a plant cell is placed in hypertonic solution, the water molecules will come out of the cell and the cell will shrink.

When an animal cell is placed in hypertonic solution then it would lose water and shrink.

Plasmodesmata is a thin protoplasmic projection connecting two adjacent plant cells.

46 chromosomes are present in human cells.

The vacuole is bounded by a membrane, called tonoplast.

Inner mitochondrial membrane has a number of in foldings called cristae.

Ribosomes are the protein factories of the cells.

The photosynthetic pigment chlorophyll is present within the thylakoid membrane.

Contractile vacuole occurs in freshwater protists such as Amoeba and helps in osmoregulation.

(i) Differences between the endocytosis and exocytosis:

(ii) Differences between the Cis and trans faces of Golgi apparatus:

(iii) Differences between the chromosome and chromatid:

(iv) Function of nucleolus: Nucleolus helps in protein synthesis by forming and storing RNA.

Cell is the structural and functional unit of life. Many cells secrete proteins in their surrounding extracellular fluid which regulates various functions of our body. Some cells, for example secrete regulatory molecules such as hormones. Whereas other secrete digestive enzymes, mucus, antibodies.

Human cheek cells are commonly stained with methylene blue.

Safranin is commonly used to study plant cells.

Temporary mount of a tissue is made in glycerine because glycerine does not dry easily.

Safranin is a reagent that is used to stain cell wall of a plant cell.

We generally mount the material in the slide in the centre.

Coverslip is put on the mounted material on a slide very gently to avoid the entry of air bubbles into the slide.

The definite shape of cell is seen in plant cells as plant cells have cell wall.

The outermost layer of human cheek cells is plasma membrane. Cell wall is absent in animal cells.

Cell wall is the outer most covering of a plant cell. It is a non-living and rigid.

Cell wall in plant cells is mainly made up of cellulose.

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

Robert brown in 1831 discovered the nucleus in the cell.

In plant cells, vacuole occupies almost entire space of the cell. This is because the nucleus is generally placed on one side of the cell.

Since large vacuole is absent in animal cell, the nucleus is generally located in the centre.

In plant cells, cell wall is rigid and non-living.

In plant cells, cell to cell contact is maintained through plasmodesmata.

In plant cells, nucleus is generally rounded.

Vacuoles are fluid-filled and membrane-bound spaces. Plant cells generally have big but less number of vacuoles.

The cells are first focussed in microscope under 10 X.

Human cheek cells is an animal cell which does not have chloroplast. Chloroplast is found only in plant cells which take part in the photosynthesis.

The cell wall of plants is made up of cellulose which is a structural polysaccharide.