Fundamental unit of life

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THE FUNDAMENTAL UNIT OF LIFE CLASS:IX SUBJECT: SCIENCE PREPARED BY : Tushar Joshi

introduction:

introduction Any structure of a plant or animal is when seen under microscope it is found that it is made up of many, small units called cells. Cells are very small and cannot be seen by naked eyes. Cell: Cell is a Latin word for ‘a little room’. Cell is the smallest, structural and functional unit of life. There are two types of cell: prokaryotic cell (bacterial cell) and eukaryotic cell (plant cell and animal cell).

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Cork cell

Discovery:

Discovery Cell: Robert Hooke (1665). Free living cells in pond water (Bacteria): Anton Van Leeuwenhoek (1671). Nucleus: Robert Brown (1831). Protoplasm: Purkinje (1839). Cell theory: Schleiden (1838) and Schwann (1839) in plants and animals respectively. All cell arises from pre existing cell: Virchow (1855)

What are living organism made up of:

What are living organism made up of All living organisms are made up of cells. Cells can be easily seen in and onion peel. Shape and size of the cell varies according to the function. It may be cuboidal, polygonal, elliptical, small or very large. Smallest cell: PPLO ( Pleuro Pneumonia Like organism ). It is called mycoplasma Largest cell: Ostrich egg. Smallest cell in our body: Red blood cell. Largest cell in our body: Nerve cell (neuron).

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SMALLEST CELL LARGEST CELL SMALLEST CELL IN OUR BODY LARGEST CELL IN OUR BODY

Unicellular and multicellular:

Unicellular and multicellular There are some organisms which are made up of only single cell as in Amoeba, Euglena, Bacteria etc.These organisms are called unicellular organism. When many cells are grouped together in a single organism then they are called multicellular organism. E.g. Fungi, Plants, animals. Different cells perform different functions in these organisms. Every multicellular organism has come from a single cell. All the cells thus come from pre-existing cell ( Omnis Cellulae cellula ). Cells which are produced from single cell may differentiate to have different structures and function. In multicellular organism there is division of labour. This means that different part of an organism perform different function.

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UNICELLULAR ORGANISMS

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MULTICELLULAR ORGANISM

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ANIMALS

Structural organization of a cell:

Structural organization of a cell All the cells are made up of : Plasma membrane Nucleus Cytoplasm Plant cells have cell wall in addition to the above components. Plasma membrane/cell membrane: Discover by C.Nageli and C. Cramer in 1855. It is the outermost covering of cell except plant cell that separates the contents of the cell from its external environment. It allows the entry and exist of some materials ( ions and molecules ) in and out of the cell.

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PLASMA MEMBRANE

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It also prevents the movement of some other materials. It is a very thin, elastic, living and selective permeable membrane. It is made up of lipid and proteins. It encloses nucleus and cytoplasm. It helps in protection of cellular component. How does the movement of substance takes place into the cell? How do substances move out of the cell? Some substances like carbon dioxide and oxygen can move across the cell membrane by a process called diffusion. In this case there is spontaneous movement of a substance from a region of high concentration to a region of low concentration. Thus, diffusion plays an important role in gaseous exchange between the cells as well as the cell and its external environment.

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Osmosis: The movement of water molecules through a selectively permeable membrane is called osmosis. Osmosis takes place from a region of high water concentration to region of low water concentration through a semi permeable membrane. Thus, osmosis is a special case of diffusion. Significance of diffusion: Gaseous exchange between the leaves and air takes place. Transport of food through phloem takes place. Loss of water from the plants is based on the principle of diffusion. Movement of ions and solutes from one cell to another cell takes place through diffusion.

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Significance of osmosis: Absorption of water by roots and root hairs. Water moves from one cell to another cell. It controls the amount of water within the cell. It controls various physiological activities : Opening and closing of stomata. Splitting of fruits due to over irrigation. Dehiscence of fruits and seeds for dispersal.

Hypotonic, isotonic and hypertonic solution:

Hypotonic, isotonic and hypertonic solution Hypotonic solution: If the medium surrounding the cell has a higher water concentration than the cell, meaning that the outside solution is very dilute, the cell will gain water by osmosis ( endosmosis ) .Such a solution is called hypotonic solution. In this case the cell is likely to swell up. Isotonic solution: If the medium surrounding the cell has exactly the same water concentration as the cell, there will be no net movement of water across the cell membrane. Such a solution is called isotonic solution. In this case there is no overall movement of water. The cell will stay the same size.

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Hypertonic solution: If the medium surrounding the cell has a lower concentration of water than the cell, meaning that it is a very concentrated solution, the cell will lose water by osmosis ( exo-osmosis ) . Such a solution is called a hypertonic solution. In this case the cell will shrink. Endocytosis: The flexibility of the cell membrane also enables the cell to engulf in food and other materials from its external environment. Such a process is known as endocytosis. Amoeba acquires its food through this process. Types of endocytosis: Phagocytosis: Cell takes in solid food material through plasma membrane. Pinocytosis: Cell takes in fluid matter through plasma membrane.

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ENDOCYTOSIS

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Exocytosis: It is the process of exudation of secretions or the waste materials out of the cell through plasma membrane. It is opposite of endocytosis. When the metabolic wastes are thrown out of the cell, the process is called ephagy. Cell wall: In plant cells, in addition to the plasma membrane, there is another rigid outer covering called cell wall. It lies out side the plasma membrane. In plant cell , cell wall is mainly composed of cellulose. Cell wall is non-living. Function of cell wall: It gives a shape to the cell. It helps in giving rigidity to the cell. It gives mechanical strength. It also support the internal structure of the cell. It protects the cell from osmotic bursting. It helps in the expansion of cells.

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Plasmolysis: When a living plant cell looses water through osmosis then there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is called plasmolysis. Protoplasm: All living components of a cell is protoplasm. It is clear colourless or slightly translucent, jelly like, viscous semi fluid substance. It can be distinguished into a centrally located nucleus and cytoplasm.

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PLASMOLYSIS

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PLASMOLYSIS

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Nucleus: It is the largest and most prominent structure of the cell. Generally one nucleus is present in each cell. Generally present in the centre of younger cell but it is pushed towards the periphery in the mature cell. It governs the cell that is why it is called controlling centre of the cell ( governor of the cell ). It is bounded by double layer membrane. The membrane have pore called nuclear pore. Important parts of nucleus: Nuclear membrane. Nucleoplasm. Chromatin network. Nucleolus.

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Nuclear membrane: It is double layer membrane that separates nucleoplasm from cytoplasm. It has number of pores which helps in exchange of materials between nucleus and cytoplasm. It disappears during cell division. Nucleoplasm: The fluid which is present inside the nucleus is called nucleoplasm/ karyolymph. It is a gel like dense substance present within the nucleus. In this chromatin material and nucleolus are present.

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Chromatin net work or chromatin material: It is the entangled mass of thread like structures. During cell division, it is organized to form chromosomes. Chromosomes are made up of DNA (deoxyribonucleic acid) and proteins. DNA is the master molecule and it controls all the activities of the cell. Functional segment of DNA are called genes. Genes control the characters. On one chromosome many genes are present. Chromosome are considered as ‘heredity vehicle’ as it transfers the characters from parent to offspring.

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Nucleolus: Spherical or oval body present within the nucleus. It is generally bigger in size in those cells which are actively concerned with protein synthesis. It is more prominent in non-dividing cells. It contains large amount of RNA and protein, also a small amount of DNA. Function of nucleus: It helps in maintenance of cell. It helps in cell division. It is needed for inheritance of character from parent to offspring. It controls various cytoplasmic activities.

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Cytoplasm: The fluid which is present inside the cell but outside the nucleus is called cytoplasm. It is a larger region of each cell enclosed by a cell membrane. It is transparent, semi solid ground substances in which various cell organelles are present. Water is the main component of cytoplasm which contains fats, proteins, carbohydrates and various organic substances. It helps in exchange of materials between cell organelles. It acts as a site of chemicals reactions like glycolysis. Cytoplasm takes very little stain.

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CHARACTER PROKARYOTIC CELL EUKARYOTIC CELL Size Generally small (1-10 micro meter). Generally large ( 5-100 micro meter). Nuclear region Not well defined and not surrounded by a nuclear membrane & known as nucleoid. Well defined and surrounded by a nuclear membrane. Chromosomes Single and circular. More than one and linear. Membrane bound organelles Absent. Present. Cell division By simple fission (amitosis). By mitosis and meiosis. Nucleus Lack true nucleus. True nucleus present. Ribosome Smaller in size and randomly scattered in cytoplasm. Bigger in size and attached to the endoplasmic reticulum or freely present in cytoplasm. Example Bacteria and Blue green algae Plants, animals and fungi.

Cell organelles:

Cell organelles The membrane bound structures present in the cytoplasm are called cell organelles ( mitochondria, chloroplast, nucleus, endoplasmic reticulum etc.). The structures which are not bounded by membranes are called cell inclusions (ribosome, centriole ).

Endoplasmic reticulum:

Endoplasmic reticulum It consists of an irregular network of channels which are bounded by membrane and are interconnected with each other. They are seen with the help of electron microscope only. If ribosomes are seen attached to their surface, then they are called rough endoplasmic reticulum (R.E.R). If ribosomes are not present on endoplasmic reticulum, they are called smooth endoplasmic reticulum (S.E.R).

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FUNCTION OF ENDOPLASMIC RETICULUM: Ribosomes present are the sites of protein synthesis. The S.E.R helps in the manufacture of fat molecules or lipids. It helps in the intracellular transport of substances (proteins). It helps in the synthesis of steroid hormones (which detoxifying many poisons and drugs). It acts as skeleton system of the cell.

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Membrane biogenesis: The S.E.R helps in the manufacture of fat molecules or lipids, important of cell function. Some of these proteins and lipids help in building the cell membrane. This process is known as membrane biogenesis.

Golgi apparatus / golgi bodies:

Golgi apparatus / golgi bodies Discovered by Camillo Golgi. They are the membrane bound (single layer) structures that occur in the form of tubules, vesicles or cisternae. They are usually seen aggregated towards the nucleus. In plants they occur as unorganized and unconnected channels like structures called dictyosomes.

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FUNCTION OF GOLGI BODIES: Helps in the synthesis of some polysaccharides from simple sugar. Helps in formation of glycoprotein. It is involved in the transformation. Primary lysosomes are formed from golgibodies by budding. They are responsible for secretion and transport in the cell.

lysosomes:

lysosomes They are small sized enzyme containing vesicles which are bounded by single membrane. During the disturbance in cellular metabolism, for example when the cell gets damaged, lysosome may burst and the enzymes digest their own cell. Therefore lysosomes are also called suicide bags of the cell. Enzymes present in lysosomes are made by R.E.R. They also destroy the foreign materials which enter the cell.

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FUNCTION OF LYSOSOMES: They helps in the digestion of food within the cell ( intracellular digestion ). They protect the body from bacteria and other harmful organisms. They help in the removal of old worn out cell organelles.

mitochondria:

mitochondria They are small bodies that occur in large numbers. A mitochondrion consists of: An outer membrane. An inner membrane . Inner membrane folded inwards to form the cristae. The cristae lie in a ground structure called matrix. They have their own DNA and ribosomes.

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MITOCHONDRIA

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FUNCTION OF MITOCHONDRIA: Mitochondria have enzymes necessary for the oxidation of glucose thus releasing energy in the form of ATP. They are therefore called power house of the cell.

plastids:

plastids Only present in plant cell. It is of two types: chromoplast (coloured plastid) and leucoplast (white or colourless). It is a lamellated structure which is bounded by double membrane. Plastids containing the pigment chlorophyll (green pigment) are called chloroplast. Chloroplast is important for photosynthesis. Leucoplast stores starch, oil, protein granules. Plastids show two distinct regions: grana and stroma. Plastids have their own DNA and ribosomes.

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FUNCTION OF PLASTIDS: Chloroplast is called kitchen of the cell as food is synthesized by the process of photosynthesis. Chromoplast gives various colours to different parts of the plant (petals of flower). Leucoplast stores food.

vacuole:

vacuole Vacuoles are sac like structure meant for storage of solid and liquid material. Vacuoles are small sized in animal cells while large sized in plant cell. In plant cells vacuoles are full of cell sap that contains amino acids, water, protein, organic acid, sugar etc. This cell sap provide turgidity and rigidity to the cell. In unicellular organism like amoeba the vacuole having food is called food vacuole. The outer membrane of vacuole is called tonoplast. It is osmoregulatory in function.

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THANKS

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