The Fundamental Unit of Life

Transcription

1 The Fundamental Unit of Life 1. Cork is a substance which comes from the bark of a tree (Quercus). 2. Robert Hooke observed a thin section of cork with the help of a self-designed microscope in year Hooke observed that the cork resembled the structure of a honeycomb consisting of many little compartments. Hooke called these boxes cells. Cell is a Latin word meaning 'a little room'. 4. All the living organisms that we see around us are made up of cells. 5. Some organisms like Amoeba,Chlamydomonas,Paramoeciumand bacteria have a single cell. Such organisms are known as unicellular or single celled. 6. Body of most of the animals and plants are made up of many cells these are called multicellular organisms. 7. The shape and size of cells are related to the specific function they performed by the cell. 8. In unicellular organism, all the functions vital for life are performed by the single cell. 9. In multicellular organisms, different groups of cells are present which perform specific functions. This is termed as division of labour i.e.,presence of different cells to perform different functions. 10. Cells have specific components within it. These are known as cell organelles. Each kind of cell organelle performs a specific function. 11. Leeuwenhoek 1674 with the help of an improved microscope, discovered the free living cells in pond water for the first time. 12. In 1831, Robert Brown discovered nucleus in the cell. 13. In 1839, J.E. Purkinje coined the term 'protoplasm' for the fluid substance of the cell. 14. Cell theory which states that all plants and animals are composed of cells and the cell is basic unit of structure and function was proposed by two German biologists, Schleiden (1838) and Schwann 0839). 15. Virchow (1855) further modified the cell theory by stating that all cells arise from pre-existing cells. (1)

2 16. In 1940, electron microscope was discovered. With the help of electron microscope, it was possible to observe and understand the complex structure of the cell and its various organelles. 17. Three features are common to all cells : (0 Plasma membrane (ii)nucleus (Hi)Cytoplasm 18. Plasma membrane or cell membrane is the outermost covering of the cell. Cell membrane separates the components of the cell from its external environment. 19. The cell membrane is called selectively permeable because it allows entry and exit of some materials in and out of the cell. It also prevents movement of some other materials. 20. Substances like CO, or O, can move across the cell membrane by a process called diffusion. Indiffusion, substances move from their higher concentration to lower concentration. 21. The movement of water molecules through semipermeable membrane from its higher concentration to lower concentration is termed osmosis. 22. When a cell is placed in a medium having higher concentration of water as compared to cell. Water will enter into the cell through osmosis (endosmosis). Such a solution is known as a hypotonic solution. 23. When a cell is placed in a medium having the same concentration as that of cell there will be no net movement of water through the cell membrane. Such a solution is known as an isotonic solution. When a cell is placed in a medium having lower concentration of water as compared to the cell. The cell will lose water by osmosis (exosmosis) and the cell will shrink. Such a solution is known as hypertonic solution. 24. Plasma membrane is flexible and is made up of organic molecules called lipids and proteins. Structure of plasma membrane can only be seen under an electron microscope. 25. Due to flexibility of the cell membrane unicellular organisms like Amoeba engulf their food from external environment. This process is known as endocytosis. 26. Endocytosis is categorised as phagocytosis, (engulfing of solid particles and pinocytosis (engulfing of liquid particles). 27. Reverse of endocytosis is known as exocytosis. 28. In plant cell, outside plasma membrane, a rigid cell is present. It is made up of cellulose. When a living plant cell is kept in a hypertonic solution, the cell loses water through exosmosis and the contents of cell contract or shrink and move away from the cell wall. This phenomenon is termed plasmolysis.all activity are controlled by the nucleus it has double membrane. the nuclear membrane h.s pore that allow the transfer of material. 29. All the contents of the cell inside cell membrane are collectively termed as protoplasm. 30. Cytoplasm refers to fluid content of cell minus nucleus. In other words, we can say that 31. Cytoplasm + Nucleus = Protoplasm or 32. Protoplasm - Nucleus = Cytoplasm 33. Cells having well defined nucleus and having membrane bound cell organelle is termed eukaryotic cell. Such cells have more than one chromosome. (2)

3 34. Some important cell organelle are : A. Mitochondria B. Golgi Apparatus (body) C. Ribosomes D. Lysosomes E. Vacuoles F. Plastids (found only in plant cells) G. Endoplasmic Reticulum (ER). 35. Mitochondria are known as powerhouses of the cell. The reason for calling them powerhouse cell is that respiration takes place in these organelle and energy is released in the form of ATP (Adenosine triphosphate). ATP is also known as the energy currency of the cell. This energy is used by cell to perform various functions such a mechanical work and making of new chemical compounds. 36. Mitochondria has a double membrane. The outer membrane is porous and the inner membrane is deeply folded. These folds are known as cristae, and they provide a large surface area for ATP-generating chemical reactions. Mitochondria have their own DNA, hence they are also known as semiautonomous bodies. 37. Endoplasmic reticulum consists of a large network of membrane-bound tubes and sheets. ER appears as long tubules or round or oblong bags called vesicles. In structure, the ER membrane is similar to that of plasma membrane. 38. There are two types of ER : i)rough endoplasmic reticulum (RER), i i)smooth endoplasmic reticulum (SER). 39. RER appears rough because ribosomes are attached to it. Ribosomes are membrane less cell organelle and are the site of protein synthesis 40. SER appears smooth because ribosomes are not attached to it. 41. Proteins and lipids synthesised by ER help in building the cell membrane. This process is known as membrane biogenesis. 42. Functions of endoplasmic reticulum :Serves as channel for transport of material. I. Provide mechanical support to cytoplasmic matrix. II. Release and uptake of calcium ions during muscle contraction and relaxation. III. Synthesis of lipids (SER). IV. Secretion of proteins (RER). V. In the liver cells in vertebrates (animals with backbone), SER plays an important role in detoxifying many poisons and drugs. (3)

4 43. Camillo Golgi discovered and described Golgi apparatus for the first time. 44. Golgi apparatus consists of a system of membrane-bound vesicles. These vesicles are arranged almost parallel to each other in stacks called cisterns. Membranes of Golgi apparatus have connections with the membranes of ER. Fig. 5.9 Golgi apparatus 45. The main function of Golgi apparatus is store, pack and despatch the material synthesised by ER through vesicles. It is also involved in formation of lysosomes. 46. Lysosomes are also known as 'suicide bags' of the cell. These are single membrane bound cell organelles. They contain powerful digestive enzymes. When the cell gets damaged lysosomes may burst and the enzymes digest the cell.plastids are present in plant cells only. 47. These are of two types:(i) Chromoplasts (coloured plastids). (ii) Leucoplasts (white or colourless plastids). 48. Plastids containing green pigment chlorophyll are known as chloroplasts. These are the site in which photosynthesis takes place. 49. Chloroplast is a double membrane organalle. Having tacks of chlorophyll containing structures thylakoid. Group of thylakoid is termed grana. 50. Thylakoids of one granum are connected to thylakoids of other granum through stroma lamellae. The space inside the membrane is termed stroma or matrix. Chloroplasts too have its own DNA and ribosome. 51. Leucoplasts are colourless and they store starch, protein and lipids. 52. Vacuoles are storage sacs. They store sugars, amino acids, some proteins and various organic acids. The vacuoles in plant cells are larger in size as compared to animal cells. In plant cells vacuoles are full of cell sap and provide turgidity and rigidity to the cell. 53. In unicellular organisms like Amoeba, the food vacuole contains the food items consumed by it and contractile vacuole expels excess water and some wastes from it. (4)

5 TEXTBOOK QUESTIONS Questions given on page number 59 of the Textbook. Q.l. Who discovered cells, and how? Ans. Robert Hooke, by observing a thin section of cork under self-designed microscope. Q.2. Why is the cell called the structural and functional unit of life? Ans. Cell is called structural and functional unit of life because i) all the living organisms are made up of cells. ii)all the functions taking place in body of organisms are also performed by cell. Questions given on page number 61 of the Textbook. Q.l. How do substances like CO, and water move in and out of the cell? Discuss. Ans. Gases like o2 and co2 move in and out of the cell by diffusion from their higher concentration to lower concentration. Water enters the cell by endosmosis through semi-permeable plasma membrane from its higher concentration to lower concentration. Similarly, water moves out of the cell by exosmosis when a cell is placed in a hypertonic solutions. Q.2. Why is the plasma membrane called a selectively permeable membrane? Ans. Plasma membrane allows or permits the entry and exit of some materials in and out of the cell. It also prevents movement of some other substances th rough it. Hence, it is called a selectively permeable membrane. Question given on page number 63 of the Textbook. Q.l. Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryoticcell. Ans. Prokaryotic Cell 1. Size : generally small (1-10 p.m) 2. Nuclear region : not well defined, is not surrounded by nuclear membrane and known as nucleoid. 3. Chromosome : single. 4. Membrane-bound cell organelles absent. Eukaryotic Cell 1. Size : generally large (5-100 (J.m). 2. Nuclear region : well defined and surrounded by a nuclear membrane. 3. More than one chromosome. 4. Membrane-bound cell organelles present. Questions given on page number 65 of the Textbook. Q.l. Can you name the two organelles we have studied that contain their own genetic material? Ans. Mitochondria and Chloroplast. Q.2. If the organisation of a cell is destroyed due to some physical or chemical influence, what will happen? Ans.The damaged cell will not be able to perform functions like respiration, obtaining nutrition and cleaning of waste materials or forming new proteins. Q.3. Why are lysosomes known as suicide bags? Ans.Because lysosomes contain powerful digestive enzymes which are capable of digesting the cell in case they burst. Q.4. Where are proteins synthesised inside the cell? Ans. Ribosomes are the site of protein synthesis. They are either free or attached to RER (5)

6 TEXTBOOK EXERCISES Q.l. Make a comparison and write down ways in which plant cells are different from animal cells. Ans. Difference between animal cell and plant cell. Animal cell Plant cell 1. Smaller in size. 1. Larger in size. 2. Contains centrosome with 2. These structures are not found one or instead polar caps are present. two centriole. 3. Contains subunits of Golgi 3. Golgi bodies are prominent. bodies 4. Plastids absent. known as dictyosomes. 5. Cell wall absent. 4. Plastid present. 6. Vacuole small in size if present. 5. Cell wall present. 6. Vacuole large in size. Q.2. How is a prokaryotic cell different from a eukaryotic cell? Ans. Difference between prokaryotic cell and eukaryotic cell. Prokaryotic cell 1. Small in size (1-10 p.m) 2. Nuclear region not well defined and bounded by nuclear membrane. It is known as nucleoid. 3. Chromosome single. 4. Membrane-bound cell organelles absent. Eukaryotic cell 1. Size generally large (5-10 u_m). 2. Nuclear region well defined bounded by nuclear membrane. 3. More than one chromosome. 4. Membrane-bound cell organelles present. Q.3. What would happen if the plasma membrane ruptures or breaks down? Ans.The cell will not be able to exchange material from its surrounding by diffusion and osmosis. The cell will also lose its shape. Q.4. What would happen to the life of a cell if there was no Golgi apparatus? Ans.The material synthesised in ER will not be packaged, stored and transported to various targets. Lysosome formation will also not take place. Q.5. Which organelle is known as the powerhouse of the cell?why? Ans. Mitochondria are known as the powerhouses of the cell. The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP molecules. Q.6. Where do lipids and proteins constituting the cell membrane get synthesised? Ans. Proteins in RER and lipids in SER. Q.7. How does an Amoeba obtain its food? Ans, Amoeba engulf its food by forming pseudopodia around the food particle. These pseudopodia are projections of cell membrane. Once surrounded by pseudopodia the food becomes part of cell and it forms a food vacuole. This method of engulfing food is termed endocytosis (phagocytosis). Q.8. What is osmosis? Ans. Osmosis is the process of movement of water molecules from its higher concentration to lower concentration through a semi-permeable membrane. (6)

7 OTHER IMPORTANT QUESTIONS Very Short Answer Type Questions (One Mark Each Q.l. Who discovered cell? Ans.Robert Hooke. Q.2. Who discovered nucleus? Ans. Robert Brown. Q.3. Who coined the term protoplasm? Ans. J.E. Purkinje. Q.4. Name the scientists, who presented cell theory. Ans. M. Schleiden and T. Schwann. Q.5. Who suggested that all cells arise from pre-existing cells? Ans. Virchow. Q.6. Who discovered Golgi apparatus? Ans. Camillo Golgi. Q.7. Why cell is known as structural and functional unit of life? Ans. Because all organisms are composed of cells and all functions in body are also done by cells. Q.8. Name some one celled (unicellular) organisms. Ans. Chlamydomonas,Amoeba. Q.9. On what factors shape and size of cell depends? Ans. The shape and size of cell depends on the functions they perform. Q.10. Why shape and size of cell is different? Ans. Because cells perform different functions. Q.ll. What is protoplasm? Ans. It is the life giving substance. Technically, all the contents of cell inside cell membrane are referred to as protoplasm. Q.12. Which cell organelle controls the various activities of cell? Ans. Nucleus. Q. 13.What function pores present on nuclear membrane perform? Ans. These pores allow the transfer of material between the nucleoplasm and the cytoplasm. Q. 14.Name the two chief components of nucleus. Ans. ( 1 ) Chromatin network. (2) Nucleolus. Q.15.Which nuclear component change into chromosome? Ans. Chromatin. Q.16.Name the two nucleic acid present in the cell. Ans. DNA (De-oxyribose nucleic acid) RNA (Ribose nucleic acid). Q.17.Where genes are located? Ans. On the chromosome. Q.18. Name the substance of which genes are made up of. Ans. DNA. Q.l9. Name the two types of Endoplasmic Reticulum (ER). Ans. Rough and Smooth ER. Q.20. Cells contain smooth flattened cisternae (sac like) structures. Name them. Ans. Golgi bodies. Q.21. Which cell organelle give rise to lysosome? Ans. Golgi body. Q.22. Which cell organelle is known as digestive or suicide bag of cell? Ans. Lysosome. Q.23. Which cell organelle contains powerful enzyme which can digest cell contents? Ans. Lysosome. (7)

8 Q.24. Which cell organelle carry oxidative reactions including removal of toxic substances? Ans. Peroxisome. Q.25. Which cell organelle is known as 'Power plant' or 'Powerhouse' of cell? Ans. Mitochondria. Q.26. In which cell organelle cristae are present? Ans. Mitochondria. Q.27. Name the cell organelle which are exclusively found in plant cell. Ans. Plastids and cell wall. Q.28. Name the cell organelle exclusively found in animal cell. Ans. Centriole. Q.29.In which chemical form energy is stored in our body? Ans. ATP (Adenosine Triphosphate). Q.30.In which cell organelle chlorophyll pigment is found? Ans. Chloroplast. Q.3I.What imparts colour to flower, fruits and vegetables in plants? Ans. Chromoplasts. Q.32. What is nucleoid? Ans. Nuclear material of prokaryotes is known as nucleoid. Q.33.Give example of prokaryotes. Ans. Bacteria and cyanobacteria. Q.34.What is Tonoplast? Ans. Outer membrane of vacuole. Q.35 What will happen to a plant cell if it is kept in a hypotonic solution? Ans.It will swell due to entry of water by the process of osmosis. Q.36. What will happen to a plant cell if it is kept in hypertonic solution? Ans. It will get plasmolysed due to exit of water from the cell into the hypertonic solution by the process of osmosis. Q.37. Which cell organelle detoxify poisons and drugs in liver of vertebrates? Ans. SER (Smooth Endoplasmic Reticulum). Q.38. Fill in the blanks : (a) Eukaryotic cell contains... nucleus. (b) Nuclear material of prokaryotic cell is known as... Ans. (a) Membrane bound or well-defined.(b)nucleoid. Q.39. In which way location of chlorophyll is different in eukaryotes as compared to prokaryotic photosynthetic bacteria? Ans.In prokaryotic bacteria, chlorophyll is in membranous vesicle associated with cell membrane. While in eukaryotes chlorophyll is present in plastids. Q.40. Name two cell organelle which have DNA apart from nucleus. Ans. (i) Chloroplast (ii) Mitochondria. Short Answer Type Questions (Two Marks Each) Q.l. Name the substance of which cell membrane and cell wall are made up of. Ans. Cell membrane is made up of proteins and lipids. Cell wall is made up of cellulose. Q.2. What is plasmolysis under which condition it takes place? Ans.When a plant cell is placed in a hypertonic solution, it loses water through osmosis. This results in shrinkage or contraction of contents of cell away from the cell wall. This phenomenon is known as plasmolysis. Q.3. What was the contribution of Robert Hooke and Virchow to our knowledge of cell. Ans. Robert Hooke discovered cell by observing a section of cork under a selfdesigned microscope in In 1885, Rudolf Virchow stated that each cell arises from a pre-existing cell. (8)

9 Q.4. Name a cell organelle found only in plant cell. Name its types and functions. Ans. Plastids are found only in plant. They are of three types : (i ) Leucoplasts (ii )Chromoplasts(iii)Chloroplasts. Leucoplasts store starch, protein and fat. Chromoplasts provide colour to fruits and flowers. Green coloured chloroplast is the site of photosynthesis and it contains chlorophyll. Q.5. Which cell organelle is known as kitchen of the cell and why? Ans. Chloroplast is known as kitchen of the cell as photosynthesis takes place in them resulting in synthesis of food. Q.6. Match the following : 1. Master of the cell - Mitochondria 2. Powerhouse of the cell - Nucleus 3. Protein factories of cell - Chloroplast 4. Kitchen of the cell - Ribosomes. Ans. 1. Master of the cell - Nucleus 2. Powerhouse of the cell - Mitochondria 3. Protein factories of cell - Ribosomes 4. Kitchen of the cell - Chloroplast. Q.7. What are genes? Where they are located 7 Ans. Genes are functional segments of DNA located on the chromosomes. Genes are bearers of heredity traits. They transmit traits (characters) from parents to their children (progeny). Q.8. Differentiate between RER and SER. Ans. Difference between RER and SER. RER SER 1. Ribosomes attached to its 1. Ribosomes absent. membrane. 2. Mainly concerned with synthesis 2. Mainly concerned with synthesis of lipids. of protein. Q.9. What is the role of vacuoles in unicellular organism? Ans.In single - celled organism like Amoeba, the food vacuoles contain the engulfed food item and the contractile vacuole expels waste and water from the cell. Q.10. What is known as energy currency of the cell? Where it is produced? Ans. Adenosine triphosphate (ATP) is known as energy currency of the cell. ATP is produced in the folded inner membrane of mitochondria. These folds create a large surface area for ATP-generating chemical reactions. Short Answer Type Questions (Three Marks Each) Q.l. What is cell theory and who proposed this theory? What modification Virchow made in this theory? Ans. Cell theory was presented by two biologists, Schleiden and Schwann. According to it :(0 Cell is the basic unit of structure. (i f )Cell is the basic unit of function.rudolf Virchow further modified the cell theory by stating that all cells arise from pre-existing cells Q.2. Name the three major functional regions of cells. Briefly mention the component of each and explain the function of each. Ans.Three major functional regions of cells are : (/) Nucleus (i i )Mitochondria (///) Golgi body. Nucleus : It is located near the centre of the cell. Its chief components are chromatin material and nucleous. Chromatin when condenses form rod like structures called chromosome. Chromosomes contain hereditary units genes which in turn are made up of DNA.Nucleus controls the various activities of the cell. Mitochondria : It is a divisible membranous structure. Its outer membrane is smooth and inner membrane have folds known as cristae. Mitochondria is known as powerhouse of the cell as respiration occurs in this organelle. (9)

10 Golgi body : It consists of a set of smooth flat sac like structures called cisternae. Main functions of golgi body is secretion storage and packaging. It also forms lysosome and peroxisome. Q.3. What is the main function of each of the following cell components? (1)plasma membrane (2) mitochondria (3) chromosomes (4)lysosomes (5) ribosomes (6)Golgi apparatus. Ans. (/) It regulates entry and exit of molecules from within the cell to exterior and vice-versa. (i i )Also known as powerhouse of the cell. Cellular respiration takes place in this organelle resulting in release of energy. (iii)chromosome contain genes. Genes are segments of DNA and are bearers of heredity characters. These are responsible for one or more cellular functions. (iv) These are also known as suicide bag of the cell. They contain digestive enzymes. They kill bacteria and remove worn out cell organelles. (v) Ribosomes are site of protein synthesis in a cell. (vi)golgi apparatus or Golgi body are the secretory organelle of the cell. They are also involved in formation of lysosomes. Cell or plasma membrane regulates entry and exit of molecule in and out of the cell. Cell wall provide structural strength to the plants. Long Answer Type Questions (Five Marks Each) Q.l. Describe the microscopic structure of plant cell with the held of the diagram. Q.2. Draw a labelled diagram of animal cells. Q.3. Write a note each on the main cell organelles. Ans.The main cell organelles of a cell are : (1) Cell membrane. It is the outer covering of a cell it controls the entry and exit of material from the cell to outside and from outside to inside. It also protects the cell. (2) Nucleus. It is the main cell organelle it controls all the activities of cell. It is surrounded by a membrane having pores. Inside it chromatin material (chromosomes) are present which contain genes. Genes are made up of DNA and are carriers of heredity characters from one generation to another. (3) Endoplasmic Reticulum (ER). It is a network and is of two types rough and smooth. Rough ER has ribosome on its surface which synthesise protein. Smooth ER is without ribosome it synthesises lipids. (4) Golgi Apparatus. It consists of set of smooth sac like structures which are placed one above other. It is secretory organelle of the cell. It packs material secreted by ER and sends it to cytoplasm. It is also responsible for formation of lysosomes and peroxisomes. (5) Lysosomes. These are membrane bound structures. They contain powerful enzymes which can digest the contents of cell. If they burst accidentally they destroy all the cell organelles. That is why, they are also known as suicide bag of the cell. (6) Peroxisomes. These are small membrane bound sacs and contain oxidative enzyme. (7) Mitochondria. These are rod shaped. In these structure, cellular respiration takes place resulting in release of energy. Hence, they are also known as powerhouse of the cell. (8) Plastids. These are found only in plant cells. They are of two type colourless leucoplast and colouredchromoplast. The green colouring material of plant chlorophyll is found inside a type of chromoplast termed chloroplast. Chlorophyll is responsible for photosynthesis in plants. (9) Centrosome. It is found only in animal cell. It consists of two granules centrioles. (10)

11 (10) Vacuoles. These structures are found in both plant and animal cells. In plant cell, vacuoles are large but in animal cells they are small. They are filled with a liquid cell sap and provide turgidity and rigidity to plant cells. The membrane of the vacuole is known as tonoplast. (11)