Tut 1 - Cell Ultrastructure (Teacher)

St Andrew’s Junior College Cell Ultrastructure 2021 H1 Biology 1 Full Name: Civics group: 21S Index no.: Date: Core Idea 1: The Cell and Biomolecules of Life Tutorial 1 Cell Ultrastructure MCQ ANSWERS 1 2 3 4 5 6 7 8 9 10 D C B B A B A C C C 11 12 13 14 15 16 B D A A B A 1 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 2 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 Refer to diagram on lecture notes pg 6 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 Unit is in nm, hence indicate actual size of chloroplast.

St Andrew’s Junior College Cell Ultrastructure 2021 H1 Biology 2 3 The electronmicrograph is of a chloroplast. The length of the chloroplast image along the line shown is 90 mm. The magnification of the organelle is x300,000. What is the actual length of the chloroplast? A 0.3 µm B 3.0 µm C 30 µm D 300 µm 4 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: Actual size = image / magnification = 90 mm / 300,000 = 90,000 µm / 300,000 = 0.3 µm mm is x10-3 m, µm is x10-6 m indicate either Plant cells (cellulose cell wall) or bacterial cell (peptidoglycan cell wall) - from Qn cannot tell what type of material the cell wall is 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 (prokaryotes e.g. bacteria lack membrane-bound organelles)

St Andrew’s Junior College Cell Ultrastructure 2021 H1 Biology 3 5 Which features enable an organism to be identified as a prokaryote? 1 cell wall →both eukaryote (plant cells) & prokaryote (bacteria) have cell wall 2 circular DNA → only prokaryote (bacteria) has circular DNA; eukaryote has linear DNA 3 nucleus → only in eukaryotic cell; prokaryote does not have membrane-bound nucleus but has nucleoid – region where the DNA / genetic material is located. 4 ribosomes → both prokaryote and eukaryote have ribosome 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 6 A scientist carried out an experiment to separate the organelles in an animal cell by mass. The scientist mixed the cells with a buffer solution which had the same water potential as the cells. He then broke the cells open with a blender to release the organelles. The extracted mixture was filtered and then spun in a centrifuge at a high speed to separate the heaviest organelle. This sank to the bottom, forming a solid pellet, 1. The liquid above pellet 1 was poured into a clean centrifuge tube and spun in the centrifuge at a higher speed to separate the next heaviest organelle. This organelle sank to the bottom, forming a solid pellet, 2. He repeated this procedure twice more to obta in pellet 3 and pellet 4, each containing a single organelle. What is the function of the organelle extracted in pellet 2? A digestion of old organelles B production of ATP C production of mRNA D synthesis of protein

St Andrew’s Junior College Cell Ultrastructure 2021 H1 Biology 4 In-class activity Arrange the following organelles in the order that they will be separated via cell fractionation: Endoplasmic reticulum, chloroplasts, nucleus, ribosomes, lysosomes, mitochondria Answer: nucleus → chloroplast → mitochondria → lysosomes → endoplasmic reticulum → ribosomes & other cell debris 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. Thinking questions: 1. What do 70S and 80S mean? 2. And why does 30S+50S not add up to 80S, and 40S+60S not add up to 100S?

St Andrew’s Junior College Cell Ultrastructure 2021 H1 Biology 5 2 And why does 30S+50S not add up to 80S, and 40S+60S not add up to 100S? Sedimentation coefficients are not additive (they do not add up together). This is because they represent a rate of sedimentation, and the rate of sedimentation of a molecule depends upon its size and shape, rather than simply its molecular weight. 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 Chloroplast (plant cell → eukaryote) Cellulose cell wall (both eukaryotic & prokaryotic cells have cell walls) Cell surface membrane (found in both prokaryote & eukaryote) Starch granule in chloroplast – may be shiny in appearance

St Andrew’s Junior College Cell Ultrastructure 2021 H1 Biology 6 8 The electronmicrograph shows part of a cell. Which organelles shown in the electronmicrograph have more than one membrane? A 1, 2 and 5 B 1, 3 and 5 C 2, 3 and 4 D 3, 4 and 5 9 What is the function of nucleoli? A formation and breakdown of the nuclear envelope → by cyclin-dependent kinases (not in syllabus) 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 that the function of nucleoli is the production of rRNA and partial assembly of ribosomal subunits). D formation of the spindle during nuclear division → centrioles Central vacuole Chloroplast Mitochondrion Nucleus Nucleolus

St Andrew’s Junior College Cell Ultrastructure 2021 H1 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 s ubunits 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. Electronmicrograph of centrioles Drawings of centrioles proteins associate with rRNA

St Andrew’s Junior College Cell Ultrastructure 2021 H1 Biology 8 Nucleolus contains rRNA genes (see lecture note pg 22) A diagrammatic structure of nucleolus [The ribosomal RNA genes in human cells are located near the tips of 5 different chromosomes (total: 10 chromosomes / 5 pairs of homologous chromosomes)] 10 Which cell organelles contain DNA? 1 centriole [non-membrane bound organelle – exist as a pair of rod -like structure, positioned with their longitudinal axis at right angles to each other. Each cylinder is made up of 9 triplets of microtubules (polymers of tubulin subunits which are proteins in nature) arranged in a ring. 2 mitochondrion [double-membrane bound organelle, evolved from prokaryotic cells based on endosymbiotic theory. Contain circular DNA, 70S ribosomes] 3 nucleolus [non-membrane bound organelle containing the rRNA gene (DNA)] 4 ribosome [non-me