THE FUNDAMENTAL UNIT OF LIFE IMPORTANT TERMS: 1) Cisternae: A flattened sac like membranous structures, usually found in Golgi complex. 2) Nucleoid: The nucleoid region of a prokaryotic cell containing genetic material without nuclear membrane is called nucleoid. 3) Genes: A ganes is segments of DNA. It is the function unit of chromosome (formed of DNA). Genes are arranged in a single linear order along the chromosome. 4) DNA: DNA stands for Deoxyribonucleic acid. It forms the important component of a chromosome. It is responsible for storing and transmitting the hereditary information from one generation to another. 5) Chromatin material: It is found in the nucleus in the form of an intertwined mass of threadlike structures. It is mainly consists of DNA molecules. 6) Nucleolus: it is found in the nucleus and mainly contains RNA (ribonucleic acid); which is helpful in protein synthesis in the cytoplasm. 7) Suicide Bag: Lysosomes when burst can eat up their own cell, so they are called suicide bags. 8) ATP (Adenosine Triphosphate): ATP molecules store energy as chemical energy which can be used for doing mechanical work also. They are also called as the energy currency of the cell. 9) Chloroplasts: The plastids which contain the green pigment called chlorophyll are known as chloroplasts. 10) Power House of Cell: The energy required for various life activities is released by mitochondria in each cell in the form of ATP molecules. So, they are called power house cell. 11) Selective permeable membrane: It is the membrane which allows entry and exit of some materials in the cell prevents movement of some other materials. QUESTIONS: 1) Define diffusion. The spontaneous movement of a substance from a region of its high concentration to the region where its concentration is low, is called diffusion. 2) Why does plasma membrane called selectively permeable membrane? Plasma membrane permits the entry and exit of some materials in the cell while it also prevents movement of some other materials. So, it is called selectively permeable membrane. 3) Define osmosis. The passage of water from its region of higher concentration through a semiermeable membrane to a region of low water concentration is called osmosis. 4) Distinguish between plasma membrane and cell wall. Plasma Membrane Cell wall 1 It is consisted of plasma proteins and it is living. 2 It is found in both plant and animal cells. It is made up complex carbohydrate called cellulose and it is dead or non-living. It is found in plant cells only 3 It is semi-permeable. It is permeable. 4 It is soft and elastic. It is hard and rigid. 5) What is significance of cell wall in plant cell? It performs the following functions in the plant cell: (i) It gives a definite shape to the cell. (ii) It provides rigidity and strength to the cell. 2327 E SUDAMA NAGAR RING ROAD NEAR PHOOTI KOTHI SQUARE 9893821227, 8109438041 Page 1
(iii)it protects the inner cell organelles bounding the cell from outside. (iv) It also with stand the osmotic pressure which is developed by cell contents. (v) It helps in transport of the material across it. 6) Explain the structure of nucleus. Nucleus: It is the control centre of the cell. It is covered by an envelope and inside it has a nucleolus and chromatin which forms the chromosomes during cell division. On the chromosomes are lodged, the genes which are responsible for the hereditary characters of an organism. The chromatin material mainly formed of DNA. Genes are segments of DNA is responsible for storing and transmitting the hereditary information from one generation to the next generation. Nucleolus contains RNA (ribonucleic acid). RNA is required for protein synthesis in the cytoplasm. Fig: (a) generalised prokaryotic cell of Cyanobacteria (b) Generalised prokaryotic cell of Bacteria Fig: Ultra structure of nucleus 7) What are genes? Where are they found? Genes are segments of very long DNA molecules. Genes are arranged in a single linear order along the chromosome. They are formed due to condensation of chromatin material at the time of cell division. A gene is a functional unit of DNA/chromosome which controls one or many functions of organisms. Sometimes a set of many genes may control a single function. 8) Draw labelled diagram of a prokaryotic cell. (c) Generalized diagram of typical cell structure of bacteria 9) Differentiate between prokaryotic cell and eukaryotic cell. Prokaryotic cell Eukaryotic cell 1 Cell is generally small (1-10 μm) Cell is generally large (5-100 μm) 2 Nuclear region called Nuclear material is 2327 E SUDAMA NAGAR RING ROAD NEAR PHOOTI KOTHI SQUARE 9893821227, 8109438041 Page 2
nucleoid and not surrounded by a nuclear membrane. 3 Only a single chromosome is surrounded by a nuclear membrane. More than one chromosome are 4 Nucleolus is absent. Nucleolus is 5 Membrane bound cell organelles are absent. 6 Cell division by fission or budding (no mitosis) Cell organelles bounded by membrane are Cell division mitotic or meiotic. 10) What is endoplasmic reticulum? Write its main functions. Endoplasmic Reticulum: It is a membranous network, enclosing a fluid-filled lumen. Its main functions are: (i) Synthesis of protein (Rough ER) (ii) Synthesis of lipids and their secretion (SER). (iii)secretion of enzymes and hormones inside the cell or when secreted out of the cell. (iv) ER also produces substance for new cellular parts (especially cell membrane). (v) ER also provides internal support (Mechanical support) to the colloidal cytoplasmic matrix of the cell. 11) Briefly explain the structure of Golgi apparatus. Golgi apparatus is also known as Golgi complex. It consists of a set of smooth, flattened membranous sac like structures called cisternae. These are placed one above the other (staked) in parallel rows. Golgi apparatus may consists of cisternae (stack of membrane), tubules, vesicles (small sacs) and Golgian vacuoles (large sacs filled with granular substance). In plant cells, the Golgi apparatus consists of many unconnected units called dictyosomes. 12) What are the functions of Golgi apparatus? Functions of Golgi apparatus: (i) Golgi apparatus is the secretary organelle of the cell. It package and despatches the material synthesized in the cell to intracellular (plasma membrane and lysosomes) and extracellular targets. (ii) Golgi complex is also involved in the formation of lysosomes and peroxisomes. (iii)golgi apparatus is also involved in the synthesis of many substances such as polysaccharides, glycoprotein s etc. 13) What are lysosomes? These are membrane bound vesicles which contain powerful enzymes capable of digesting or breaking down all organic material. The membrane that bound protects the cell from Autolysis (self-dissolution or break down). 2327 E SUDAMA NAGAR RING ROAD NEAR PHOOTI KOTHI SQUARE 9893821227, 8109438041 Page 3
They are absent in RBCs and a few plant cells, for example, yeast, fungi and green algae. 14) What are the functions of lysosomes? Functions of lysosomes: (i) Extracellular digestion. Sometimes lysosome enzymes are released outside the cell to break down extracellular material. So, they are known as digestive bags. (ii) Digestion of foreign material inside the cell such as bacteria. (iii)cellular digestion. Lysosomes get ruptured, and enzymes are released free in damaged cells, ageing cells, dead cells or poorly working cell organelles to digest them. So, they are also known as suicide bags. In this process, they remove the cell debris. 15) What is the structure of mitochondria? Mitochondria are rod-shaped cell organelle found in the cytoplasm. Each mitochondrion (singular; plural mitochondria) is a double membrane bounded structure. The outermost membrane of mitochondrion is smooth. But the inner membrane of the mitochondrion is folded inwardly, into the matrix of mitochondrion, like finger projections. The inward finger-like projections of inner membrane are called Cristae. Cristae greatly increase the surface area of the inner membrane. Mitochondria contain extra-nuclear DNA. 16) What are functions of mitochondria? Functions of mitochondria: (i) They contain enzymes for cellular respiration. Due to cellular respiration of flood, mainly glucose, energy is released step-wised. Hence they are known as power house or power plants of the cell. (ii) The stepwise released energy by the oxidation of food (usually glucose) is converted into usable chemical energy in the form of ATP (adenosine triphosphate) molecules. (iii)the ATP molecules are released into the cytoplasm for providing energy for various vital functions. 17) Explain the term ATP. What is use of ATP? ATP stands for Adenosine triphosphate. Use: ATP molecules are rich in chemical energy. The body cells use the energy stored in ATP for synthesis of new chemical compounds, their transport, and for mechanical work done by cells/tissues. 18) What are plastids? Plastids are found in plant cells only. Plastids are double membrane bounded structures. They do not have cristae, like mitochondria. The major plastids also have extra nuclear DNA. Two types of plastids-leucoplastids (leucoplasts) and Chromo plastids (chloroplasts). 19) What are Chromoplasts? Which one is the most important and why? Chromoplasts are coloured plastids i.e. they may contain pigment of different colours. For example, blue green chromoplasts found in blue green algae. The most important chromoplasts are chloroplasts which contain green pigment, known as chlorophyll, chloroplasts are very important because they trap solar energy and prepare food for all non-green organism, directly or indirectly. The process of preparing 2327 E SUDAMA NAGAR RING ROAD NEAR PHOOTI KOTHI SQUARE 9893821227, 8109438041 Page 4
food by green plants is known as photosynthesis. Other non-green chromoplasts are responsible for characteristic colour of flowers and fruits. Fig: Ultra structure of a chloroplast 20) What is Plasmolysis? When a living plant cell looses water through osmosis, there is shrinkage or contraction of the protoplasm away from the cell wall. This phenomenon is called Plasmolysis. 21) What are vacuoles? Vacuoles are fluid-field structures surrounded by a membrane known as tonoplast. The fluid in the vacuoles is called cell sap. In animal cells either they are absent or are small and many. In most plant cells, vacuole is big and centrally placed. The liquid cell sap of vacuole provide turgidity and rigidity to plant cells. 22) What is the difference between a unicellular and multi cellular organism? How is multi cellularity advantageous over unicellularity? In an unicellular organism all functions are performed by the same cell. In a colony, some cells may be specialised for movement and others for storage and so on. The colony can thus be better adapted to survival than any of its individual cells. In a complex organism like a tree, while all cells perform a few basic function like respiration etc, there are other cells which are organised into tissues, tissues into organs and so on. As a consequence this is adequately adapted to perpetuating both itself and the race. In any well-organised unit-the whole function better than the parts thereof. Multi cellularity provides division of labour. This helps the organisms to perform various life processes in a better way. 23) What is the difference between a plant cell and an animal cell? Plant cell Animal cell 1 The outermost covering of the plant cell is the cell wall which is formed of cellulose. 2 Plastids (e.g. chloroplast) 3 Large vacuole 4 Centrioles are absent but polar caps are 5 Golgi apparatus is in the form of subunits, called dictyosomes. The outermost covering is the plasma membrane. Plastids absent. No or small vacuoles are Centrioles are present within centrosome. Prominent and highly complex Golgi apparatus is present near nucleus. Fig: comparison between a plant cell and an animal cell 2327 E SUDAMA NAGAR RING ROAD NEAR PHOOTI KOTHI SQUARE 9893821227, 8109438041 Page 5
24) Draw labelled diagrams of animal and plant cells to show their internal structure. Fig: Internal structure of a typical animal cell cell to function and to reproduce further cells of the next generation. Surrounding the nucleus is the Endoplasmic reticulum (ER) which may have the ribosome s which are the site of protein synthesis. Ribosome, a granular structures, also found in cytoplasm. The power house of the cell is the mitochondria which help in releasing energy by the oxidation of food in cell. There are flat membranous secretary structure in the cell the Golgi bodies. In plant cells there is an additional structure the chloroplast which is the site for photosynthesis. Cells also contain lysosomes which are also called suicide bags. They digest and remove the unwanted debris of the cell. Centriole helps in cell division. Cytoplasm also contains vacuoles filled with cell sap. In plant cells vacuole is large and centrally placed. 25) Write a note on the structure of cell? Cell is the fundamental unit of a living organism. The cell enclosed by an outer plasma membrane (PM) which is selectively permeable. Plant cells have an additional cell wall outer to the PM. Inside the cell is the translucent viscous substance the cytoplasm in which are embedded the organelles. The control centre of the cell is the nucleus, it contains all the information necessary for the 2327 E SUDAMA NAGAR RING ROAD NEAR PHOOTI KOTHI SQUARE 9893821227, 8109438041 Page 6