SAJC 1 Tut 1 Cell theory Cell structures functions (Annotated MS)

St Andrew’s Junior College The Cell and Biomolecules of Life / Cell Theory, Structure & functions of oganelles 2022 H2 Biology 1 Full Name: Civics group: 22S Index no.: Date: Core Idea 1: The Cell and Biomolecules of Life Tutorial 1 Section A (Annotated MS) The Cell Theory Structures & functions of organelles MCQ SECTION A: CELL THEORY, TYPE OF CELLS, NUCLEUS, NUCLEOLUS, CENTRIOLES ANSWERS FOR SECTION A: 1 2 3 4 5 6 7 8 9 10 A D C B B A A C B D 1 Which of the following is not one of the main components of the cell theory? A Cells must contain DNA B All living things are made of cells C Cells can only come from other cells D Cells are the basic unit of life 2 Which size ranges can be viewed using a light microscope? A 4 only B 1 and 2 only C 2 and 3 only D 3 and 4 only 3 tenets of cell theory Refer to diagram on lecture notes pg 6

St Andrew’s Junior College The Cell and Biomolecules of Life / Cell Theory, Structure & functions of oganelles 2022 H2 Biology 2 3 The diagram shows a chloroplast drawn from an electronmicrograph. The length of the chloroplast from X to Y is 5000 nm. What is the magnification of the drawing of the chloroplast? A x100 B X1000 C X10 000 D X100 000 Working: Magnification = image / actual = 5.7 cm / 5000 nm = 5.7 x 10-2 m / 5000 x 10-9 m = 1.14 x 104 ~ x 10 000 SI unit is nm, hence indicate actual size of chloroplast. Indicated use of electron microscopy. Hence ultrastructure inside organelle can be seen.

St Andrew’s Junior College The Cell and Biomolecules of Life / Cell Theory, Structure & functions of oganelles 2022 H2 Biology 3 4 The electronmicrograph is of a chloroplast. The length of the chloroplast along the line shown is 80 mm. The actual length of the chloroplast is 10 µm. What is the magnification of the chloroplast? A x8 x 102 B x8 x 103 C x8 x 104 D x8 x 106 5 You are told that the cells on a microscope slide are plant, animal, or bacterial. You look at them through a microscope and see cell walls and membrane-bound organelles. You conclude that the cells are A Bacteria cells B Plant cells C Bacteria and plant cells D Bacteria, plant, and animal cells Working: Magnification = image / actual = 80 mm / 10 µm = 80 x 10-3 m / 10 x 10-6 m = 8 x 103 indicate either Plant cells (cellulose cell wall) or bacterial cell (peptidoglycan cell wall) - from Q cannot tell what type of material is cell wall made up of, without the use of specific dye staining - Presence of cell wall eliminate animal cell (which has no cell wall) from answer. confirmed Plant cells [eukaryotic cells] (prokaryotes eg bacteria cell lack membrane-bound organelles)

St Andrew’s Junior College The Cell and Biomolecules of Life / Cell Theory, Structure & functions of oganelles 2022 H2 Biology 4 6 Which features enable an organism to be identified as a prokaryote? 1 cell wall →both eukaryote (plant cells) & prokaryote (bacteria) have cell wall [plant cell has cellulose cell wall while bacteria has peptidoglycan cell wall. 2 circular DNA → only prokaryote (bacteria) has circular DNA; eukaryote has linear DNA 3 nucleus → double membrane-bound nucleus only present in eukaryotic cell; prokaryote does not have nucleus but has nucleoid – region where the DNA / genetic material is located. 4 ribosomes → both prokaryote and eukaryote have ribosomes but it is 70S ribosomes in prokaryote, 80S ribosomes in eukaryote A 2 only B 3 only C 1 and 4 only D 2 and 4 only 1 What do 70S and 80S mean? S = sedimentation coefficient of a particle (its behaviour during a sedimentation process – centrifugation) What is centrifugation? Application of the centripetal force for the sedimentation of mixtures with a centrifuge Bigger particles sediment faster and have higher sedimentation coefficient (eg 80S). 2 And why does 30S+50S not add up to 70S, and 40S+60S not add up to 80S? Sedimentation coefficients are not additive (they do not add up together) Thinking questions: 1. What do 70S and 80S mean? 2. And why does 30S+50S not add up to 70S, and 40S+60S not add up to 80S?

St Andrew’s Junior College The Cell and Biomolecules of Life / Cell Theory, Structure & functions of oganelles 2022 H2 Biology 5 Centrifugation vs Cell fractionation (pg 21) - Centrifugation is the use of an instrument called centrifuge where centripetal force is applied to each test tube containing a mixture (that contain different chemically inert materials* mixed together) to obtain sediments (pellets of each type of materials). * chemically inert materials (materials that do not chemically react with one another to form new materials) - Cell fractionation separate the different cell organelles eg nucleus , mitochondria, ribosomes etc via their relative mass with the use of centrifugation. How cell fractionation is carried out: Cells from a tissue sample are homogenised and mixed with a buffer in a glass tube. The mixture is then spun in a centrifuge at different speeds, starting with the lowest speed. After each spin the sediment at the bottom of the tube contains one type of organelle. The liquid portion is transferred to a new tube and spun at a higher speed, causing another type of organelle to settle in the second sediment. This process can be repeated several times to obtain different sediments containing different organelles. The faster/higher the speed, the smaller the relative mass of the organelles that will settle at the bottom of the glass tube

St Andrew’s Junior College The Cell and Biomolecules of Life / Cell Theory, Structure & functions of oganelles 2022 H2 Biology 6 7 The electronmicrograph shows part of two cells. Which of the labelled features enable these cells to be identified as eukaryotic? A W only B X only C W and X only D W, X and Y 8 What is the function of nucleoli? A formation and breakdown of the nuclear envelope B formation of centromeres → centromere is found on chromosome and it is a region where sister chromatids join (you will learn in nuclear division later) C formation of ribosomes (this is an A level equivalent question and question is given as-is. You should note that it is more accurate to state function of nucleoli is the formation of ribosomal subunits which assembled to form ribosomes). D formation of the spindle during nuclear division → centrioles Drawings of centrioles Electronmicrograph of centrioles Chloroplast (W) (inferred: plant cell → eukaryote) Cell wall (X) (both eukaryotic & prokaryotic cells have cell wall) Cell surface membrane (Y) (found in both prokaryote & eukaryote) Starch granule in chloroplast – may be shiny in appearance

St Andrew’s Junior College The Cell and Biomolecules of Life / Cell Theory, Structure & functions of oganelles 2022 H2 Biology 7 Please examine this diagram carefully: Note that rRNA is synthesised in nucleolus (in nucleus). rRNA combines with ribosomal proteins which pass through the nuclear pore of nuclear envelope to form ribosomal subunits. Ribosomal subunits then move out from the nucleus to the cytoplasm via the nuclear pores . The big and small ribosomal subunits attached together in the cytoplasm to form fully functional 80S ribosomes. proteins enter the nucleus via nuclear pore and associate with rRNA to form ribosomal subunits.

St Andrew’s Junior College The Cell and Biomolecules of Life / Cell Theory, Structure & functions of oganelles 2022 H2 Biology 8 9 The figure below shows an ultrastructure of a cell. 1