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Class 9th Biology

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Published in: Biology
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“The Fundamental Unit of Life”

Kamal A / Delhi

5 years of teaching experience

Qualification: P.HD(PURSUING)

Teaches: Bio Technology, Biology, Botany, Zoology, Chemistry, Mathematics, Physics

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  1. "The Fundamental Unit of Life" 1. All the living organisms are made up of fundamental unit of life called" cell" The cell is a Latin word for "a little room" 2. 3. The scientist Robert Hooke saw a little room in the cork (the bark of a tree) resembled the structure of a honeycomb. The use of the word "Cell" to describe these units is used till this day in Biology as" Cell Biology' The Compound Microscope consist eye piece,objective lens and condenser to observe a 4. cell after putting a drop of Safranin (for plant cell) and methylene blue (for animal cell). Eyepiece Coarse adjustment 5. 6. 7. 8. 9. Body tube Clip Microscope sliue Condenser Fine adjustment Objective lens Stage Swivel Mirror Base Fig.l. Compound microscope The scientist Leeuwenhoek (1674) saw free living cells in the pond water for the first time. (father of microbiology) The scientist Robert Brown in 1831 discovered the nucleus in the cell. The cell theory states that all the plants and animals are composed of cells, it was proposed by Schleiden (1838) and Schwann (1839). The cell theory was further expanded by Virchow (1855) by suggesting that "all cells arise from the pre-existing cells". The cells differ in size, shape, structure (Please refer to Fig. 2/3: Onion peel/Various cells in Human body): Types of cells: Onion cells, Smooth muscle cell, Blood cells, Bone
  2. cell, Fat cell, Nerve cell, Ovum, Sperm etc. Each kind of cell performs specific function. Nucleus Blood Srnooth nauscle Bone cell Sperm Nave Cell Fat cell Fig. 2: Cells of an onion peel Fig.3: Various cells from the human body 10. Cells are the basic unit of life, all living things, are made up of one or more cells. single cells are called unicellular (Amoeba, 11. Organisms that exist as Chlamydomonas,Paramecium and Bacteria)and organisms that are made up of groups of cells working together are called multicellular (Human beings). 12. There are two kingdoms of unicellular organisms (Archaea and Bacteria), and three kingdoms of multicellular organisms (Animals, Fungi and Plants), and one kingdom which contains a mixture of both unicellular and multicellular organisms (the Protista). 13. There are three features in almost every cell; plasma membrane, nucleus and cytoplasm. Mitochondria Goli Apparatus Smooth Endoplasrnic Reticulum (SER) O Lysosornes O Mi crovilli Cell Membrane Centros o mes Ri bos o mes Nucle us Nuclear Membran e Nuclear Pores Nucleolus Rough Endoplasmic Reticutum (RER) Cytoplasm Fig. 4: Structural Organization of a Cell
  3. 14. PLASMA MEMBRANE OR CELL MEMBRANE - It is the outermost covering of the cell. - It is called as selective permeable membrane (because it prevents movement of some materials). - It helps in diffusion and osmosis -Diffusion: movement of substance from high concentration to low concentration. Eg; exchange of carbon dioxide or oxygen with external environment. Diffusion High Concentration Low Concentration -osmosis: it is the passage of water from the region of high water concentration to a region of low water concentration through a selective permeable membrane. O solute héh water concentration water 1.0 o bw water concentration a) The cell gains water, if the medium surrounding the cell has a higher water concentration (Hypotonic solution) than the cell.
  4. b) The cell maintains the same water concentration as the cell (Isotonic solution), water crosses the cell membrane in both directions. c) The cell loses water, if the medium has lower water concentration (Hypertonic solution) than the cell. Note - The cell drinking is endosmosis; - Omission of water is called ex-osmosis. 15. The cell engulfs food is called endocytosis and ejects solid is called exocytosis. Amoeba acquires food through endocytosis and excretion of solid is called exocytosis. Plasma membrane V icle• • Extracellular fluid ENDOCYTOS IS 16. The cell wall EXOCYTOSIS is a tough, flexible and sometimes fairly rigid layer that surrounds some types of cells. is a rigid outer covering composed of cellulose It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to act as a pressure vessel, preventing over- expansion when water enters the cell. They are found in plants, bacteria, fungi, algae, and some archaea. Animals and protozoa do not have cell walls. When a living plant cell loses water through osmosis there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is known as plasmolysis. 17. The Nucleus It is a dark colored, spherical or oval, dot-like structure near the center of a cell called Nucleus. The nucleus plays a central role in cellular activities/ reproduction. The chromatin material gets organized into chromosomes.
  5. The chromosomes contain information for inheritance of features from parents to next generations in the form of DNA (Deoxyribo Nucleic Acid) and protein molecules. The functional segments of DNA are called genes. 18. In some organisms like Bacteria nucleus is not covered by nuclear membrane. Hence it is called as prokaryote. (Pro= primitive; karyote = karyon = nucleus.) The organisms with cells having a nuclear membrane are called eukaryotes. 19. Differences between prokaryotes and eukaryotes Prokaryotes Size: generally small (1-10 um) Nuclear region: Not well defined and not surrounded by a nuclear membrane & known as nucleoids. Chromosome: Single Membrane-bound cell or anelles absent Eg- bacteria, blue green algae PilUS Plasmalemma Cell wall Capsule Cytoplasm Flagellum 20. Cytoplasm Eukaryotes Size: generally large. (5-500 um) Nuclear region: Well defined and surrounded by a nuclear membrane Chromosome: More than one chromosome Membrane-bound cell or anelles resent Eg- fungi, plant cell and animal cell. Ribosomes Nucleoid Mesosome Prokaryotic cell • The cytoplasm is the part of a cell that is enclosed within the plasma membrane.
  6. Cytoplasm is basically the substance that fills the cell. It is a jelly-like material that is eighty percent water. It is more like a viscous (thick) gel than a watery substance, but it liquefies when shaken or stirred. The cytoplasm is the site where most cellular activities occur, such as many metabolic pathways, and processes such as cell division. 21. Cell organelles Every cell has fluid matrix (other than nucleus) is called cytoplasm. The nucleus and cytoplasm is together called as protoplasm. The protoplasm term was coined by Purkinje. It has important cell organelles: Endoplasmic Reticulum (ER), Golgi apparatus, Lysosomes, Mitochondria, Plastids, and vacuoles. 22. Endoplasmic Reticulum (ER): It is a large network of membrane bound tubules and vesicles. - There are two types of Endoplasmic Reticulum - Rough Endoplasmic Reticulum (RER) (It looks rough because Ribosomes are attached to its surface. They are the sites of protein synthesis). - Smooth Endoplasmic Reticulum (SER) (It looks smooth because Ribosomes are not attached to its surface. They are the sites of fat molecules synthesis). 1. SER; help in the functioning of enzymes and hormones to carryout biochemical activities. 2. SER detoxifies many poisons and drugs from the cell. - ER serves as channel for the transport of material between various regions of the cytoplasm and the nucleus. -Proteins and fat molecules produced by ER help in membrane biogenesis. 23. Golgi apparatus It was first described by a scientist Camillo Golgi. It is a system of membrane bound vesicles called cisterns. It functions include the storage, modification and package of cell products. The complex sugars are made from simple sugars in the Golgi apparatus. It is also involved in the formation of lysosomes. 24. Lysosomes They contain membrane-bound sacs with powerful digestive enzymes (enzymes are made by RER) to digest the worn-out cell organelles. When the cell gets damaged, lysosomes may burst and the enzymes digest their own cell, hence called as "Suicidal bags of a cell"
  7. • It is a waste disposal system of the cell. 25. Mitochondria It is covered by a double membrane. Outer membrane is very porous and the inner membrane is deeply folded. These folds create a large surface area for ATP (Adenosine Triphosphate) molecule synthesis. ATP is the energy currency of a cell; hence the Mitochondria are called as Power House of a cell. Mitochondria have their own DNA and Ribosomes; therefore they can make their own proteins. 26. Plastids They are present only in plant cells. They are two types. 1. Chromoplasts (Colored Plastids: Chloroplasts Green pigmented and useful in Photosynthesis and also contains various other pigments like yellow or orange) 2. Leucoplasts (White or colorless plastids; stores materials such as oils, proteins, fats etc.) Plastids are also covered by a double membrane. The matrix is called Stroma, seat for enzymatic actions. Plastids have their own DNA and Ribosomes; therefore they can make their own proteins. 27. Vacuoles 28. Cell Storage sacs for solid or liquid contents. They are small in size in animals while plants have large, may occupy 50-90 % of the cell volume. Helps to provide turgidity and rigidity to the cell. Many substances like amino acids, sugars, organic acids and proteins are stored in vacuoles. In Amoeba food vacuole is specialized to play an important role. It is the fundamental structural unit of living organisms, helps in respiration, obtaining nutrition and clearing waste material or forming a new protein. Differences between Plant cell and Animal Cell ANIMAL CELL Cell wall absent Plasma membrane is the outer layer which provides tur idit to the cell Vacuoles are small in size Plastids are absent Nucleus lies in the centre. PLANT CELL Cell wall resent Cell wall is the outer layer which gives rigidity and tur idit to the cell Vacuoles are bi in size Plastids are resent Nucleus lies on one side
  8. Rough endoplasmic reticulum Lysosome Smooth endoplasmi reticulum Chloroplast Nucleus Golgi apparatus uclear envelope Plasma membrane jacent cell wall Golgi apparatu Smooth endoplasmi reticulum Nucle enve ope Nucleus o 0 O Cytop asm Chloroplast Cell wall Mitochondrion Ribosomes Plasma membrane Centriole ysosome Ribosomes Mitochondrion reticulum Cytoplasm

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