Cell Structure and Function PDF

MDCAT Biology Quick Practice Book www.nearpeer.org Oldest, Largest and Most Credible Platform  Unit 1: The Cell Learning Outcomes Compare the structure of typical animal and plant cell Compare and contrast the structure of prokaryotic cells with eukaryotic cells Outline the...

MDCAT Biology Quick Practice Book www.nearpeer.org Oldest, Largest and Most Credible Platform  Unit 1: The Cell Learning Outcomes Compare the structure of typical animal and plant cell Compare and contrast the structure of prokaryotic cells with eukaryotic cells Outline the structure and function of the following organelles: o Nucleus, Endoplasmic Reticulum, Golgi Apparatus and Mitochondria Discuss fluid mosaic model of cell membrane 1 Prokaryotic and Eukaryotic Cell Figure 1.1 Prokaryotic and eukaryotic cell PROPERTY PROKARYOTIC CELLS EUKARYOTIC CELLS Nuclear Since there is no nuclear membrane Present membrane therefore no distinct nucleus A nucleus is present in which The genetic material (DNA) is Chromatin nuclear material (chromosomes) is without any nuclear membrane and material enclosed in double nuclear freely present in the cytoplasm. membrane. Chromosome It is formed of DNA only It is formed of DNA and protein. Many organelles envelop-bound Few organelles organelles present e.g. nucleus, None are surrounded by an envelope mitochondria, and chloroplasts. (two membranes) internal Organelles Great diversity of organelles membrane scarce if present usually bounded by single membrane e.g. associated with respiration or lysosomes, vacuoles, micro bodies, photosynthesis. endoplasmic, reticulum etc. Ribosomes are 70S smaller subunit is Ribosomes are 80S smaller subunit Ribosomes 30S while larger subunit is 50S. is 40S while larger subunit is 60S. Cell wall is composed of peptidoglycan or murein. When The cell wall if present is formed of polysaccharide chains are bound Cell wall cellulose is most of the plant cells covalently to shorter chains of amino and is formed of chitin in fungi. acids. Peptidoglycan is formed. The entire cell wall is considered as a 2  single complex molecule called sacculus. In prokaryotes mitosis is missing and Cell division Cell division by mitosis. the cell divided by binary fission. Organisms possessing prokaryotic Organism possessing eukaryotic Organelles cells are called prokaryotes. cells is called eukaryotes. Origin/ Prokaryotes present primitive stage Eukaryotes probably evolved from Evaluation of evaluation. prokaryotes. Complex, with 9 + 2 arrangement Simple, lacking microtubules of microtubules intracellular Flagella extracellular (not enclosed by cell (surrounded by cell surface surface membrane) 20 nm diameter. membrane) 200 nm diameter Mesosomes in bacteria except Mitochondria for aerobic Respiration cytoplasmic membrane un blue respiration. green algae. Chloroplasts containing No chloroplasts no membrane Photosynthesis membranes which are usually stacking stacked into lamellae or grana. Nitrogen Mainly unicellular Mainly have the ability fixation Mainly multi-cellular (except Form Mainly unicellular Protoctista, many of which are unicellular) 10-100 µm diameter common Cell size Average diameter 0.5 – 20 µm commonly 1000-10000 times volume of prokaryotic cells. Eukaryotes include all other Prokaryotes include bacteria and unicellular or multi-cellular Examples blue green algae (cyanobacteria) organisms such as animals, plants fungi and Protista. 3 Comparison of Animal and Plant Cell Figure 1.2 Differences between plant and animal cell The figure above shows the features and differences between plant and animal cells Animal Cell Plant Cell 1. Usually smaller in size. 1. Comparatively larger in size. 2. Enclosed by plasma membrane 2. In addition to plasma membrane only. mostly surrounded by a thick cell 3. Plastids absent. wall. 4. Cytoplasm consists largely of 3. Plastids (chloroplast and smaller vacuole. chromoplast) are very common. 5. Prominent and highly complex 4. Cytoplasm peripheral, central Golgi bodies. space occupied by a large vacuole. 6. Possess centrosome with one 5. Contain several subunits of Golgi of two centrioles. bodies called dictyosomes. 6. No centrioles present, instead two small clear area called polar caps are present. 4  Large Small Nucleus. Vacuole Vacuoles Plasma membrane. Mitochondria. Plastids e.g. Rough ER. chloroplasts Centrioles Golgi bodies. Lysosomes. Cell wall Figure 1.3 The comparison between plant and animal cells. The union shows the features present in both the type of cells while the intersection depicts the characteristics specific to each of the organelle. § A large proportion of the inside of the cell is taken up with a fluid-filled compartment known as the vacuole. Together the wall and vacuole maintain the shape of the whole cell. § Plant cells have specialized organelles, the chloroplasts, which enable them to make their own food by photosynthesis. Cell Membrane Plasma membrane or cell membrane is the outer most boundary of the cell. However, in most plant cells, it is covered by a cell wall. Structure Under electron microscope it is a bi- layered structure, this structure is delicate and elastic it has some ability to repair itself. Models of Cell Membrane Structure There are two models of cell membrane structure: Unit Membrane Model According to this model the cell membrane is composed of lipid bilayer and sandwiched between two protein layers. This structure is present in all cell organelles (for example, mitochondria, chloroplast etc.) 5 Figure 1.4 Unit Membrane Fluid Mosaic Model According to the fluid mosaic model the cell membrane consists of a double layer of phospholipid molecules, known as a lipid bi-layers. It has proteins and other molecules. The name fluid mosaic is used because the bi-layer is a very fluid structure and it contains a mosaic of protein molecules. Figure 1.5 Fluid Mosaic Model Chemical Composition Cell membrane contains phospholipids 20-40% proteins, 60-80% cholesterol and polysaccharides. It is about 7 nm thick The basic structure is a phospholipid bilayer. The hydrophilic phosphate heads of the phospholipids face outwards. The result is the aqueous environment inside and outside the cell. The hydrocarbon tails face inwards and create a hydrophobic interior. Most protein molecules float about in the phospholipid bilayer forming a fluid mosaic pattern. The proteins stay in the membrane because they have regions of hydrophobic amino acids which interact with the fatty acid tails to exclude water. Some proteins and lipids have short branching carbohydrate chains like antennae forming glycoproteins and glycolipids respectively. Membrane also contains cholesterol. Like unsaturated fatty acids cholesterol disturbs the close packing of phospholipids and keeps them more fluid. This can be important for organisms living at low temperatures when membranes can solidify. Cholesterol also increases flexibility and stability of membranes, without it membrane break up. The two sides of a membrane differ in composition and function. Functions of Membrane The phospholipid bilayer provides the basic structure of membrane. It also restricts entry and exit of polar molecules and ions. Channel protein and carrier proteins are involved in the selective transport of polar molecules and ions across the membrane. 6  Point to Ponder Remem ber, dif Some proteins act as receptor molecules for chemical signaling between and pas fusion transpo sive cells. rt two nam are the es Some proteins act as an antigen these act as cell identity markers. same p of the rocess Glycolipids and glycoproteins help cells to recognize each other – allowing the immune system to tell the difference between body cells and invading bacteria. Energy transfer ion photosynthesis and respiration proteins take part in the energy transfer system. Transport Across The Cell Membrane Diffusion Facilitated Diffusion Diffusion is the movement of molecules Some substances enter and leave cells or ions from a region of their high much faster than you would expect it concentration to a region of their low only diffusion occurred. We now know concentration. The process is passive that some membrane proteins facilitate (does not require energy and happens the diffusion of some substances across spontaneously). the cell membrane. Two factors affect the rate of diffusion Two types of proteins are responsible for facilitated diffusion. a) Difference in concentration between Specific carrier protein takes point A and point B. The steeper the particular substance from the gradient, the faster the rate of diffusion. membrane to the other. b) The greater the surface area of a Ion channels are proteins that membrane through which diffusion is open and close to control the taking place the greater the rate of passage of selected charged diffusion. articles. Channel proteins have a fixed shape 7 Osmosis Osmosis is a passage of water molecules from a region of their high concentration to a region of their low concentration through a partially permeable membrane. We can say that it is a form of diffusion in which only water molecules move. Active Transport Active transport is the energy-consuming transport of molecules or ions across a membrane against a concentration gradient. Movement are usually in one direction only. Unlike diffusion which is reversible. The energy is supplied in the form of ATP made in respiration. Without respiration, active transport is therefore impossible. Q. What is the difference between active and passive transport? Endocytosis and Endocytosis Endocytosis and exocytosis are active processes involving the bulk transport of materials through membrane, either into cells (endocytosis) or out of cells (exocytosis). Endocytosis occurs by an enfolding or extension of the cell membrane to form a vesicle it is of two types. o Phagocytosis (cell eating) material taken up is in solid form. Cells specializing in the process are called phagocytes and are said to be phagocytic. For example, some white blood cells take up bacteria by phagocytosis. The sea formed during uptake is called a phagocytosis vacuole. o Pinocytosis (cell drinking) material taken up is in liquid form. The vesicles formed are often extremely small, in which case the process is known as micropinocytosis and the vesicles as micro pinocytosis vesicles. Exocytosis is the reverse process of endocytosis. Waste materials may be removed from cells, such as solid, undigested remain from the pancreas is achieved in this way. Plant cells use exocytosis to export the material needed to form cell walls. 8 The Nucleus § The nucleus is the largest and most prominent organelles in the animal cell. § Almost all eukaryote cells have a nucleus – red blood cells in mammals and phloem cells in plants are exception. § Every nucleus is surrounded by a nuclear envelope. This consists of two membranes that are separated by gap of 20 to 40 nm. § Nucleus may be irregular in shape and about 10 µm in diameter. It contains the cell’s DNA, which carries information that allows the cell to divide and carry out all its cellular processes. § Nucleus controls the life and activities of the cell. § In animal cells nucleus is generally present in the central part. In plant cells nucleus is pushed towards periphery due to a large central vacuole. § DNA/RNA and proteins (including enzymes) forms the chemical composition of coleus. § Nucleus consists of nuclear membrane, nucleoli, nucleoplasm and chromosomes. § The number of nuclear pores is highly variable. For example, the undifferentiated cells (e.g. eggs) have many pores (about 30000 per nucleus) while the differentiated cells (e.g. erythrocytes) have only 3 or 4 pores/nucleus. Each pore has a definite structure. Nucleolus Nucleolus is a darkly stained structure within the nucleus. It has no membrane. There are two regions of a nucleolus. The Peripheral Granular Area It contains the materials from which ribosomal subunits are formed. The Central Fibrillar Area It has large molecular weight RNA and rDNA. The heredity material is in the form of chromosomes, which controls all the activities of the cell. Chromosome is formed of DNA and proteins. Nucleus is visible when the cell is in non-dividing stage. It contains chromatin network and soluble sap called nucleoplasm. Dark staining chromatin, consisting of tightly packed DNA, is known as Heterochromatin. The lighter, more loosely packed material is called Euchromatin contains the DNA that is being actively read to produce proteins. In heterochromatin, the DNA is packed together and is not being read. Nucleus is stained 9  with the basic dyes because of the chromatin material. During cell division chromatin material is converted into darkly stained thread like structures called chromosome. Chromosome is made of arms and centromeres. Centromere is the place on the chromosome where spindle fibers are attached during cell division. o Each chromosome consists of two identical chromatids at the beginning of cell division which are held together at centromere. A chromatid is exact replica of the chromosome. The information to control cell activities is present on the chromosomes in the form of genes. The chromosome number varies which may be 2n = 2 to 2n = 1200 (Pteridophytes). The number of chromosomes in all individuals of the same species remains constant generation after generation. Some examples of chromosome No. are: Frog = 26, Chimpanzee = 48. Fruit fly (Drosophila melanogaster) = 8, Wheat = 42, Onion = 16, Potato. = 48. Garden pea = 14. Penicillium (a fungus) has two chromosomes (one pair), corn 20, wheat 42, sugarcane 80, some ferns have more than 500 pairs, mosquito 6, fruit fly 8, frog 26, honey bee 32, mouse 40 and human cells have 46 chromosomes (23 pairs). The number of chromosomes in normal body cells is diploid (2n) while the gem cells (sperms and eggs) have haploid chromosome number (11). Do you know? Germ cells have n number of chromosomes while somatic cells have Examples 2n number of chromosomes Human germ cells (eggs and sperms) = 23 chromosomes. Drosophila germ cells = 4 chromosomes. Endoplasmic reticulum (ER) The nuclear envelope joins with the membrane of the endoplasmic reticulum (ER). It is a system of complex network spread throughout the cell. These are present in Eukaryotic cells & are of two types: 1) RER 2) SER On the outside surface of the RER are ribosomes. The main function of RER is to keep together and transport the proteins made on the ribosomes. Instead of simply diffusing away into the cytoplasm, newly made proteins enter into RER. Here they fold into three-dimensional shape. A mature cell that makes and secretes large amounts of protein – such as one that makes digestive enzymes – has RER that occupies as much as 90 per cent of the total volume of the cytoplasm. RER is also a storage unit for enzymes and other proteins. 10  Small vesicles containing newly synthesized proteins pinch off from (the ends of the RER and either fuse with the golgi complex or pass directly to the cell surface membrane. The channels having material present in them which is separated from the cytoplasmic materials by the spherical or tubular membranes is called cisternae. E.R provides mechanical support to the cell. In some cells SER transmit impulses. For example, nerve and muscle cells. Both RER and SER are involved in the transportation of materials from one part of the cell to the other. ER with no ribosomes attached is known as SER. Smooth ER is not involved in protein synthesis but is the site of steroid (lipid hormone) production. It also contains enzymes that detoxify, or make harmless, a wide variety of organic molecules, and it acts as a storage site for calcium in skeletal muscle Figure 1. Endoplasmic reticulum. The diagram shows both cells. SER and RER Smooth Endoplasmic Reticulum (SER) Rough Endoplasmic Reticulum (RER) It does not bear ribosomes over the surface of It possesses ribosomes attached to its its membranes. membranes. It is mainly formed of, vesicles and tubules. It is mainly formed of cisternae and a few tubules. It is engaged in 'the synthesis of glycogen, It takes part in the synthesis of proteins and lipids and steroids. enzymes Ribosomes Ribosomes were discovered by Palade in 1955. § Ribosomes are small dense organelles, about 20 nm in diameter present in great numbers in the cell. Most are attached to the surface of RER but they can occur free in the cytoplasm. § Ribosomes are made from a combination of rRNA and protein. Eukaryotic ribosomes are compose-I of an equal quantity of RNA and protein. Therefore, they are also called as ribonucleoproteins. § Ribosomes are involved in protein synthesis. They assemble amino acids in the right order to produce new proteins. The ribosome uses the code on' messenger RNA (mRNA) to put amino acid together in chains to form specific proteins. 11 § Generally, proteins that are to be used inside the cell are made on free ribosome while those that are to be secreted out of the cell are made on ribosomes that are bound to ER membranes. § New ribosomes are formed in the nucleolus. § Eukaryotic ribosome is 80 S (60 S + 40 S). Mg++ controls this attachment. § A group of ribosomes attached to the same mRNA are called polysomes. The Golgi Complex The Golgi apparatus/Golgi complex was discovered by Camillo Golgi in 1898. It is found in eukaryotic cells. Golgi apparatus consists of stacks of flattened membrane bound sacs or flattened cavities or vesicles called Cisternae (5 – 8). The whole organelle is a shifting, flexible structure; vesicles are constantly being added at one side and lost from the other. Generally, vesicles fuse with the forming face (the one nearest to the nucleus) and leave from the maturing face (the one nearest to the cell surface membrane). Golgi complex has proteins, carbohydrates, glycoproteins and some enzymes. The Golgi complex appears to be involved with the synthesis and modification of proteins. lipids and carbohydrates. Major functions of Golgi complex are formation of conjugated molecules and Secretions. Proteins made on the ribosomes attached to ER are packaged into the vesicles by the ER. Some of the vesicles join with the Golgi complex and the proteins they contain are modified before they are secreted out of the cell. Golgi apparatus + Golgi vesicles = Golgi complex Secretions are products formed in the cells on ribosomes and then pass to the outside through endoplasmic reticulum and Golgi apparatus. In plants Golgi apparatus is involved in the synthesis of cell wall. Figure 1. Golgi Apparatus Figure 1. Ribosomes (Large and small subunits) 12 Mitochondria Mitochondria are important organelles of eukaryotic cells. They manufacture and supply energy to the cell. Therefore, they are also called powerhouse of the cell. Mitochondria are particularly abundant in metabolically active cells, tissues such (is muscle and tissues involved in active transport. The size (0.5 – 1.5 µn wide) and number of mitochondria varies and depend upon the physiological activity of the cell. Under compound microscope mitochondria may be rod shaped, vesicles or filaments. In Electron Microscope, Mitochondria have two membranes, outer smooth and inner with aristae. The inner surface of aristae in the mitochondrial matrix has small knob like structures called F1 particles. These are involved in ATP formation. Mitochondrial matrix contains enzymes, coenzymes and organic and inorganic salts. Mitochondria also contain DNA and ribosomes. Mitochondrial matrix helps in metabolic processes like Kreb's cycle, aerobic respiration and fatty acid metabolism etc. Their main function is to make ATP via the process of aerobic respiration. ATP diffuses into the cell and provides instant chemical energy. Mitochondria have a double membrane; the outer membrane is smooth while the inner one is folded. This arrangement gives as large internal surface area on which the complex reactions of aerobic respiration can take place. Mitochondrion is a self-replicating organelle. Centrioles Mitochondria Centrioles Centrioles are present in animal cells, some microorganisms and lower plants. They are absent in higher plants. § Centrioles are short bundles of filaments, set at right angles to each other. They are found in a clear area of cytoplasm known as the centrosome. § In a cross section, each centriole consists of a cylindrical array of 9 microtubules, each microtubule has 3 tubules. The tubules are composed of special protein caned tubulin. The chemical composition and structure is similar to that of cilia and flagella. 13  Additional Notes (a German Discovery of cell is linked with the Lorenz Oken in 1805 living beings invention of microscope because most scientist) said "all of vesicles or of the cells are microscopic originate from or consist Robert Brow cells". n said that present in th nucleus is A cell is the structural and e cell and th an empty sp e cell is not functional unit of life ace. He disc nucleus in th overed the e cells of orc Jean Baptist de-Lamarck (1809) said hids. Louis Pasteur (1862) "nobody can have life if it is not formed by cellular tissue." said that bacteria are formed from Cell theory is: "All living organisms existing bacteria. are composed of cells and cell products". A German physician Rudo lph Virchow (1855) said "omniscellula e cellula" (new cells formed by the division of existing living cells). It wa s opposite to the idea of Abiogenesis The main features of Cell Theory in its present form are: Robert Hooke discovered the cell in 1665 under his self-made compound microscope. All organisms are composed of one According to Hooke, cell is an empty space or more cells. surrounded by thick walls. He published his - All cells arise from pre-existing cells. work in Micrographia in 1665. Cell is the basic structural and n functional unit for all organisms. lo g is t T he odor Schwan oo leiden A German z rm a n botanist Sch The human naked eye can 9 ) a nd a G e n the ce ll (183 dently o differentiate between two points, 83 8 ) w o rk ed indepen (1 which are 1.0 mm apart. This is u nd th a t a ce ll has 3 parts: known as resolution of the eye. This They fo Nucleus cleus) and resolution can be increased by (flu id su rr o unding the nu ) Cytoplasm embrane lenses. a m e m b ra n e (outer thin m Plasm that In a compou st W ei sm an n (1880) said reso nd microscop e th Aug u ll s h av e a comm o n o ri gin lu ti o n is 2.0 µm. It is 500 X e all livin g ce of naked eye. that h av e b as ic similarity in because they mposition. structure and co Their function is the formation of spindle (that guides the chromosomes during cell division). In addition to spindle formation, the centrioles act as the center of formation for the whole cytoskeleton and they are known as microtubule organizing centers. 14  Additional Notes The process of separation of different parts of the cell into different layers (on the basis of their size and weight and density of the medium) in the centrifuge tube using a centrifuge machine at medium speed is called density gradient centrifugation. The function of an organism is due to The process of grinding to get a uniform activities and interactions of different composition/structure is called cells and cell components. homogenization. The source of illumination in compound ed. microscopes is visible light. In electron pa rt s, m odern techniques are us To study cell e is cell fractionat ion. microscope the source of illumination is er n te ch ni qu Most mod a beam of electrons. Cell size is measured in The magnification power of microscope is determined by micrometer (µm). One µm is multiplying X values of ocular lens and X value of objective lens. 0.000,001 meter or 1 x 10 – For example: A microscope with 10 X ocular lens and 40 X 6 of a metre. objective lens will have 10 X 40 = 400 X magnifying power. In most plant cells, cell membrane is surrounded by A compound microscope has cell wall. different magnification powers. The est egg ocular lenses may he 5 X and 10 X Ostrich's egg is the bigg while objective lenses may be 20 X, The electron Th40 X, 100 X etc. e re solution of ele ctron microsc microscope has shown – 4 Angstrom ope is 2. It is 500 X g that the cell wall is of the compo reater than th und microsco at formed by three main X greater tha pe and 250,0 n that of the 0 0 layers: naked eye. Middle lamella In multi-cellular organisms there is a Primary cell wall division of labour. Examples from animals Due to Secondary cell wall are: differe have d nt func ifferen ti Muscle cells contract and relax t shap ons the cells Nerve cells transmit impulses e s and siz Examples fro es. m animals are Gland cells secrete Xylem cells c : onduct wate Red blood cells carry oxygen soil to the ae r and minera rial parts of th l salts from Some stomach cells secrete gastric juice Phloem cells e plant translocate fo White blood cells (WBC) produce Sclerenchym od atous cells giv antibodies. Chlorenchym e support to atous cells ca the plants Eye cells detect and respond to light. Parenchyma rr y out photosy tous. cells sto nthesis Meristernati re surplus fo d are e cells produ o d and The tissues are taken an and developm ent of the pla ce new cells for g rowth instruments homogenized by special nt (like homogenizers). 15  Additional Notes The autophagosomes working on digestive vacuoles are also known as secondary Lysosomes. TAY-SACH'S disease is due to the absence of an enzyme that is involved in the catabolism of The protoplasm of a eukaryotic cell is lipids. Accumulation of lipids in brain cells divided into nucleus and cytoplasm. leads to mental retardation and even death. The living lated peroxisomes in content of De-Duve and coworkers iso protoplasm the cell is er tissues. These are. called 1965 from liver cells and oth (0.5 µm in diameter). single membrane organelles Primary wall is a true wall and develops Lysosomes are involved in: newly growin in g cells. It is m ainly made u Autophagy/self-eating (Autophagosomes) of cellulose w p ith some dep Phagocytosis and hemicell osition of pect ulose. in Extra-cellular digestion and autolysis First of all Middle Lamella is formed between the primary wall s of the neighboring cells. It is The polysaccharides in bacterial cell wall and not the true wall and is composed of pectin or cellulose in plant cell wall are carbohydrates. calcium pectate. If an enzyme that breaks glycogen into to glucose is absent from n o f dif fe re n t parts of the cell separatio ht and Lysosomes, the result is a disease The process of e b as is o f th e ir size and weig (on th sing a Glycogenosis type II. different layers ) in th e ce ntrifuge tube u e diu m adient density of the m h ig h sp e e d is called densityIngrthe primary cell wall the cellulose fibers hine at centrifuge mac are arranged in a criss-cross manner which trifugation. ultracenary give strength to the cell wall. Second cell wall is formed on Inner surface of primary wall. It is thick and rigid Cytosol has true solutions and colloidal than primary wall. Chemically it is solutions. The colloidal solution may be sol or composed of inorganic salts, silica, wax, gel. Sol is non-viscous and gel is viscous. cutin and lignin etc. Cell wall protects the cell from osmotiolysis. The peripheral part of the cell is like a gel. Cytoplasm is formed by an aqueous ground substance The free floating cell organelles (e.g. which contains: Mitochondria) move in the cytoplasm Many cell organelles due to cytoplasmic streaming Insoluble wastes and storage products (called inclusions) movements and is called active mass Cytosol (the soluble part of cytoplasm is called cytosol) movement of cytoplasm. Cytosol is 90 % water and 10 inorganic and organic molecules. De Duve in 1949 isolated lysosomes. They are found in most eukaryotic cells The material present in between Lysosomes are rich in acid phosphatases and the plasma membrane and the several other hydrolytic enzymes. nuclear membrane is called cytoplasm. Cytosol is 90 % water and 10 inorganic and organic molecules 16  Additional Notes Peroxisomes have oxidative enzymes such as Amoeboid movements are because of peroxidase, catalase and glycolic acid oxidase etc. micro filaments. Peroxisomes contain H2O2 In seeds rich in lipids (such are castor and producing oxidases and catalase. beans) glyoxysomes break fatty acids to succinate. Two important enzymes in glyoxysom es are The cytosol contains cytoskeletal fabric glycolic acid oxidase and catalase. formed of microtubules, microfilaments In lipid-rich seeds (e.g. castor, bean and soybeans and intermediate filaments. This is etc.), glyoxysomes are abundant during Cytoskeleton. germination period. In lipid poor seeds (e.g. pea), Central vacuole is formed by combining the they are absent. smaller vacuoles during the growth and In plant seedlings, Glyoxysomes convert development of plant. stored fatty acids to carbohydrates and Vacuoles are bounded by a single provide energy to grow a new plant. This membrane (tonoplast) process occurs through glyoxylate cycle. Enzymes of this cycle are present in the Microtubules are long, unbranched and glyoxisomes. slender structures, they are composed of The main protein in cytoskeleton are tubulin proteins. tubulin (in microtubules) actin, myosin, u le s are joined in a specific way The microtu b ples tropomyosin and other which are also so m e ce ll org anelles. For exam to form ioles etc. found in the muscles. , fl ag ella , b as al bodies and centr Microfilaments are cilia involved In internal motion also called cell Microfilaments are much more slender. cyclosis. They are made up of contractile actin Intermediate filaments play a role in maintaining protein linked to the inner face of the the cell shape and are also involved in the linkage plasma membrane. of the cell parts. Microtubules Microfilament Cilia Flagella They are non- They are contractile. The number of cilia per cell The number of flagella contractile. is usually very large per cell is usually (300 – 1400) 1–4 A micro tubule contains They do not possess They are smaller in size. They are larger (100- 13 proto filaments. longitudinal subunits. 200 nm in length) They are hollow tubules. They are solid Cilia are present all over the Flagella are present structures. surface of the cell. only at end of the cell. They are formed of α They are mainly made They beat in a coordinated The Flagella beat and β tubulin proteins. up of protein actin. rhythm either simultaneously independently. or one after the other. The diameter is 25 nm. The diameter is 6 nm. They help in locomotion, They help in aeration, feeding and locomotion. circulation, etc. They occur in centrioles, They occur below cell basal bodies, cilia. membrane and at the flagella, astral rays, interphase of spindle fibres etc. plasmagel-plasmasol. 17  Practice Questions 1) Which of the following are colorless? a) Chloroplasts c) Leucoplasts b) Chromoplasts d) None of these 2) Which of the following is most slender in structure? a) Microtubules c) Intermediate filaments b) Microfilaments d) Both A and B 3) Soluble part of the cytoplasm is termed as: a) Cisterna c) Endocytosis b) Cytosol d) Both A and B 4) Which of the following modifies proteins and lipids by adding carbohydrates? a) Golgi Apparatus c) Plasma membrane b) Polysome d) None of these 5) The nucleus contains: a) Mitochondria b) Cytosol c) Enzyme d) DNA 6) Another name for Golgi complex is: a) Dictyosome b) Endoplasmic Reticulum c) Cyto-membrane system d) None of the above 7) Leucoplasts are a kind of: a) Lysosomes b) Chloroplasts c) Plastids d) Grannum 8) Vacuole in plants is responsible for: a) Photosynthesis b) Cellular excretion c) Turgor pressure d) Starch storage 9) By which of the following can movements of materials across animal cell membranes be accomplished? a) Active transport b) Diffusion c) Pinocytosis only d) All of the above 10) Cell membranes are composed of: a) Lipids and proteins b) Phospholipids c) Proteins and carbohydrates d) Lipids and terpenoids 11) Hydrogen peroxide degradation in a cell is a function of: a) Peroxisomes b) Ribosomes c) Mitochondria d) Microbodies 18 12) Movement of substances from lower concentration to higher concentration across semi-permeable membrane is termed as: a) Facilitated diffusion b) Diffusion c) Passive transport d) Active transport 13) Robert Hook was the first person to see cells in: a) Various plants b) Fungi c) Animals d) Cork 14) The concept “OMNIS cellula-e-cellula” means that, new cells are formed from: a) Non-living material b) Pre-existing living cells c) Dead organic matter d) As a result of chemical reactions 15) In generalized plant cell the nucleus is: a) Present in the middle of the cell b) Displaced to the peripheral site of the cell c) Absent d) Modified into endoplasmic reticulum 16) Plasma membrane is found in the cells of: a) Animals only b) Plants only c) Both in plants and animals d) Bacteria only 17) The semi-circular channels and system of tubes found in the cytoplasm are known as: a) Ribosomes b) Endoplasmic reticulum c) Glyoxysomes d) Vacuoles 18) The structures that are involved in the manufacture and supply of energy to the cell are: a) Centrioles b) Nucleolus c) Plastids d) Mitochondria 19) In a plant cell chlorophyll is present in: a) Chromoplasts b) Stroma c) Leucoplasts d) Chloroplasts 20) Ribosomes have equal amount of: a) DNA and Protein b) mRNA and Protein c) RNA and Protein d) None 21) Plastids are only found in the: a) Animals and plants b) Plants c) Animals d) Viruses 22) The command center of an eukaryotic cell is: a) Nucleoid b) Small vacuoles c) Endoplasmic reticulum d) Nucleus 23) Lipids synthesis / metabolism takes place in which of the following organelle? a) Mitochondria b) Vacuoles c) Rough endoplasmic reticulum d) Smooth endoplasmic reticulum 19 24) Pick the odd one out in fungi: a) Polysome b) Golgi Complex c) Nucleolus d) Mesosomes 25) Ribosomes exist in two forms, either attached with the RER or freely dispersed in the: a) Tonoplasts b) Cytoplasm c) Golgi bodies d) SER 26) The ribosomal RNA is synthesized and stored in: a) Endoplasmic reticulum b) Golgi complex c) Nucleolus d) Chromosomes 27) The ______ model of plasma membrane suggests that proteins are embedded in lipid bilayer: a) Unit membrane b) Permeable c) Fluid mosaic d) Ultracentrifuge 28) Assemblage of _____ occurs in nucleolus: a) rDNA b) RNA c) Ribosomes d) Chromosomes 29) The enzymes of lysosomes are synthesized on: a) RER b) Chloroplast c) SER d) Golgi Apparatus 30) Centrioles are made up of _____ microtubules triplet. a) 9 b) 3 c) 27 d) 12 31) Which of the following structure is absent in higher plants and found in animal cells: a) Centriole b) Mitochondria c) Cytoskeleton d) Cytoplasm 32) The soluble part of cytoplasm or fluid that remains when all organelles are removed is known: a) Solution b) Cytoskeleton c) Gelatin material d) Cytosol 33) The outer membrane of the nuclear envelope is at places continuous with the: a) Golgi apparatus b) Lysozymes c) Endoplasmic reticulum d) Peroxisomes 34) The process by which unwanted structures within the cell are engulfed and digested within the lysosome is known as: a) Endocytosis b) Hydrolysis c) Exocytosis d) Autophagy 20 35) Detoxification of harmful drugs within the cell is done by: a) Nucleolus b) Smooth endoplasmic reticulum c) Ribosomes d) Food vacuoles 36) Peptidoglycan or murein is a special or distinctive feature of cell wall in: a) Algae b) Bacteria c) Fungi d) Plants 37) The intake of liquid materials across the cell membrane is: a) Phagocytosis b) Pinocytosis b) Endocytosis d) Exocytosis 38) Organelle involved in the synthesis of ATP is: a) Ribosome b) Nucleus c) Mitochondria d) Centriole 39) Which component of the cell is concerned with cell secretions? a) Plasma membrane b) Cytoskeleton c) Golgi complex d) Mitochondria 40) During animal cell division, the spindle fibers are formed from: a) Mitochondria b) Ribosomes c) Centriole d) Lysosomes 21  Key 1. c 2. b 3. b 4. a 5. d 6. a 7. c 8. c 9. d 10. a 11. a 12. d 13. d 14. b 15. b 16. c 17. b 18. d 19. d 20. c 21. b 22. d 23. d 24. d 25. b 26. c 27. c 28. c 29. a 30. a 31. a 32. d 33. c 34. d 35. b 36. b 37. b 38. c 39. c 40. c 22