PIONEER JUNIOR COLLEGE JC1 H2 BIOLOGY 2010 CELL STRUCTURE AND MEMBRANE TEST. Name:. Class:. Date: Marks: /30

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1 PIONEER JUNIOR OLLEGE J1 H2 IOLOGY 2010 ELL STRUTURE ND MEMRNE TEST Name:. lass:. Date: Marks: /30 Section : Multiple hoice Questions (15 mks 1 Which pair of organelles has internal membranes? nucleoli and golgi apparatus chloroplasts and mitochondria mitochondria and ribosomes D chloroplasts and nucleoli ( 2 The table gives description of four membranous structures in a cell. Which structure is correctly matched with its functions? Structure Function n extensive network of tubes and sacs, each tube and sac bounded by a single membrane Lipid synthesis spherical sac bound by a single membrane Protein synthesis D sac bound by two membranes, the inner membrane being highly folded stack of elongated, curved sacs, each sac bound by a single membrane Packaging of proteins Photosynthesis ( 3 What technique provided the primary evidence for the fluid mosaic model of the cell surface membrane? ell fractionation Freeze-fracture hemical analysis of proteins D Microscopic staining ( 4 Which of the following statement is true?

2 Prokaryotes have chromosomes that are found in the nucleus. nimals, plants, fungi and bacteria are examples of eukaryotes. Prokaryotes have nucleoid, ribosomes, cell wall, cell membrane, flagella, and fimbriae. D Prokaryotes are generally bigger in size as compared to eukaryotes. ( 5 The following contains images of a number of structures that can be seen in a cell Identify structures 1-4 and the process that occurs in structure Process chloroplast nucleus ribosome mitochondrion respiration mitochondrion Golgi rough ER chloroplast photosynthesis apparatus mitochondrion Golgi apparatus smooth ER rough ER protein synthesis D chloroplast nucleolus Golgi apparatus microfilaments cytoskeleton ( 6 The diagram shows the ultrastructure of a cell.

3 I II III IV Which of the following structure(s contain(s nucleic acids? I only I and II only I and IV only D I, II, III and IV ( 7 The absence of centrioles from higher plant cells means that during somatic cell division there is no apparent organiser of mitotic spindles. no equatorial arrangement of chromosomes at metaphase. no new cell wall laid down at telophase. D no spindle formed. ( 8 The diagram represents a model of the structure of a biological membrane. outside D inside Which of the following represents a glycoprotein? (D 9 tadpole s tail is gradually broken down during metamorphosis into an adult frog. Which organelle increases in number in the cells of the tail at this time?

4 centrioles Golgi apparatus lysosome D Pinocytic vesicles ( 10 higher concentration of sodium ions in extracellular fluid versus cytosol is most likely maintained by locking any passage of sodium ions through the plasma membrane ctively transporting sodium ions out of the cell Overcrowding the cell with potassium ions D None of the above ( 11 The figure below is a drawing of an animal cell nucleus as seen using an electron microscope. The actual diameter of the nucleus, measured along the line XY is 7.2µm. What is the magnification of the nucleus? 65X 650X 6500X D 65000X ( 12 certain cell surface membrane is made entirely of phospholipid and is 7nm thick. volume of 1mm 3 of this phospholipid membrane was homogenised and dropped onto the surface of water in a large tray. The phospholipid spread out to form a continuous thin film.

5 What is the expected surface area of this film? mm 2 because the phospholipids form a single layer mm 2 because the phospholipids form a double layer mm 2 because the phospholipids form a single layer. D mm 2 because the phospholipids form a double layer. ( 13 The diagram represents a cell membrane. Which structure allows the diffusion of l ions between the outside and the inside of the cell? ( 14 The diagram shows the pathway of diffusion of a particle through a cell surface membrane. What are the most likely properties of the particle? Lipid solubility Relative molecular mass Electrically charged High High Yes High Low No Low High No

6 D Low Low Yes (D 15 Which of the following are types of endocytosis? facilitated diffusion and bulk filtration pinocytosis and phagocytosis osmosis and active transport D none of the above (

7 Section : Structured Questions (15 mks Question 1 The micrograph below shows part of a cell. Identify the structures indicated by the labels. [4] H D G E F Golgi pparatus Rough endoplasmic reticulum Smooth endoplasmic reticulum D ribosomes E nuclear pore F Nucleus/nucleoplasm G- Nuclear envelope /Nuclear outer membrane H - Mitochondrion omments: Please search the internet for more exposure to electron micrographs of organelles. No other way to familiarize yourselves. Please ensure that you use the plural and singular terms accurately when naming the organelles. (b n experiment was carried out to determine what happens to amino acids after they are absorbed by animal cells. The cells were incubated for 5 minutes in a medium containing

8 radioactively labeled amino acids. The radioactive amino acids were then washed off and the cells were incubated in a medium containing only non-radioactive amino acids. Samples of the cells were taken at 5, 10 and 45 minutes after the start of the experiment and the sites of radioactivity in the cells were determined. The results are given in the table below. The figures show radioactivity in certain cell organelles expressed as a percentage of the total radioactivity within the cells. Percentage of total radioactivity Organelles t 5 min t 10 min t 45 min Rough endoplasmic reticulum Golgi apparatus Secretory vesicles (i Explain why the radioactivity is associated mainly with the rough endoplasmic reticulum after the first 5 minutes of the experiment. [1] RER has ribosomes which are the sites of protein synthesis; (ii Explain the changes in the pattern of radioactivity in the cell during the remaining 40 minutes of the experiment. [3] omments: The question did not describe the changes. So please describe the trend/changes as seen in the table first before explaining. s you are describing the trend/changes, always remember to quote values to support your observation. Many students did not fully describe the function of the G, thus losing precious marks too. 1. fter about 5-10 mins. there is a decrease radioactivity at RER increase in Golgi apparatus (quote decrease from 80% to 10% at RER while increases from 10% to 80% at G 2. polypeptides move to Golgi apparatus, 3. where they undergo final chemical modification for next 35 minutes; 4. t 45 mins, there was a decrease from 80% to 30%, while there was an increase from 5% to 60% at the secretory vesicles (quote - OWTTSE 5. most proteins have been sorted and packaged into secretory vesicles and 6. budded off from trans face of Golgi for transport to the plasma membrane (iii Suggest why the figures in the tables for each time interval total less than 100%. [2] mino acids moving between 3 listed organelles eg. in transport vesicles between RER and G; Proteins also synthesized on other organelles such as free lying ribosomes, mitochondria so the radioactive amino acids may be found there instead;

9 Question 2 The diagram below shows a plan diagram of a typical membrane which appears in electron micrograph. carrier protein (d hannel protein Y X Z (a What is the likely composition of layer Y? [1/2] omments: Students must mention that the phosphate head or fatty acid tails belong to phospholipid molecules. hydrophilic/charged/polar phosphate head of phospholipids (reject: polar/hydrophilic heads (b What is the likely composition of layer Z? [1/2] Hydrophobic hydrocarbon/fatty acid tails of phospholipids (reject: hydrophobic tails (d Draw on the diagram, a labeled structure which allows Na + ions to pass through. [1] (e Explain how this labeled structure is able to stay in the membrane and how it is able to carry out its function. [2] the surface next to phospholipids contains amino acids which are hydrophobic, forming hydrophobic interactions with the hydrocarbon tails of phospholipid molecules (hold protein within membrane hannel Protein: In order for it to be able to function as a channel proteins for polar and charged particles (eg. ions, amino acids, the channel surface of the protein is made up of stretches of amino acids which are hydrophilic, allowing charged n polar particles to pass through, Or arrier Protein: Undergo rapid changes in shape. They exist in 2 forms, known as the Ping & Pong states. The diffusing molecule or ion binds to the binding site of the carrier protein (made up of hydrophilic amino acids, which then undergoes a change in shape, depositing the molecule or ion on the other side of the membrane. (d Explain two ways in which the membrane fluidity is maintained. [2] omments: Explain. Do not simply identify factor only. 1. weak hydrophobic interactions that exist between the hydro chains in the hydrophobic core; breaks easily allowing phospholipid molecules to diffuse laterally in the plane of the membrane

10 2. unsaturated fatty acid chains which have kinks at the double bonds; disrupt/prevent the close packing of phospholipid molecules in the membrane 3. cholesterol found wedged between phospholipids; disturbs the close packing of phospholipids at low temperature & restrain movement of phospholipids at high temperature. (in the case of plants, only first 2 answers are accepted [Total: 6 marks]