A2.2 Cell Structure SL/HL PDF

SL / HL A2.2 Cell structure A2.2.1—Cells as the basic structural unit of all living organisms NOS: Students should be aware that deductive reason can be used to generate predictions from theories. Based on cell theory, a newly discovered organism can be predicted to consist of one or more cells....

SL / HL A2.2 Cell structure A2.2.1—Cells as the basic structural unit of all living organisms NOS: Students should be aware that deductive reason can be used to generate predictions from theories. Based on cell theory, a newly discovered organism can be predicted to consist of one or more cells. Robert Hooke theory Individual cells are fundamental units of life. Unicellular and multicellular organism (40 trillion cells) e.g. Human organism 3.8 x 1013 17th century used microscope to observe plant cells 19th century animal tissues are examined Both types of tissued consists of cells, Scientists concludes that all organisms are made of cells (Inductive reasoning- from specific to general) A2.2.2—Microscopy skills Light microscopes and drawing skills Using light microscope Lab practice Microscope Onion cell https://www.youtube.com/watch?v=quygiQgJ7b8 Cheek cell https://www.youtube.com/watch?v=TxB_Hj1BufM Magnification of an image Magnification is the number of times larger an Magnification = size of image image is than the specimen. size of specimen S.I. size unit Plant cell diameter: 150 um 1mm = 1,000 um size of the printed image: 15 cm (150 mm) 1 millimetre (mm) = 1,000 micrometers 150 000 um = x1000 1 um = 1,000 nanometers 150 um https://www.youtube.com/watch?v=FdaLMkoHF2o Eye-piece graticule A2.2.3—Developments in microscopy Leeuwenhoek (1670) Electron microscopes (1930) Microscope were invented Magnification 1.000 000x Electron microscope have higher resolution and higher magnification than light microscope. Light microscope Scientist are allowed to investigate ultrastructure 19th century microscopes were improve of cells. Magnification 400x Disadvantages: black and white images Image are in colour methods always need to kill the cells Used to examine living material beams of electrons are destructive Resolution: making the separated parts of an object distinguishable by eye Resolution Resolution Resolution milimeters micromete nanometer /mm rs/um s/ nm unaided 0.1 100 100.000 eyes Light 0.0002 0.2 200 microscope s Electron 0.000.001 0.001 1 microscope s Fluorescent stains and immunofluorescence Stains are coloured substances that bind to some chemicals in cells. e.g. methylene blue binds to DNA or RNA Fluorescence is when a substance absorb light and then re-emits it at a longer wavelength. e.g. some cell absorb ultraviolet light and re- emit it as blue light Immunofluorescence is a development of fluorescence staining. The fluorescence markers are link to antibodies. Freeze- fracture electron microscopy This technique is used to produce images of surface within the cell. - sample - liquefied propane -190 °C - freezes - fracture the frozen sample - vaporization of some structures - etching - create a replica of fracture surface with carbon This sample goes to electron microscope (2 nanometers thick). Gives impression of a 3D image through shadowing. CW cell wall PM plasma membrane LD lipid droplet Cryogenic electron microscopy - Cryo EM Use for researching the structure of protein. - solution of proteins applied to a grid - flash frozen (liquid ethane - 182.6 °C - sample move to electron microscope - detectors record the pattern of protein molecules - using algorithms - 3D image This technique allows scientist to research proteins that change from one form to another. Resolution 0.12 nanometers A2.2.4—Structures common to cells in all living organisms Typical cells have DNA as genetic material and a cytoplasm composed mainly of water, which is enclosed by a plasma membrane composed of lipids. Students should understand the reasons for these structures. Plasma membrane Outer boundary of the cell and enclosed all its content. Control entry and exit of substances. Prevent entry of toxic substances. Lysis- plasma membrane of a cell burst. It is a Allows cells to maintain their own vital structure so it cause death of the cell. concentrations of materials. Permeability is related to the structure based in lipids. Cytoplasm Water main component Substances dissolved or suspended in this water. Enzymes catalyse chemical reactions in the cytoplasm (metabolism) Metabolism provides energy and proteins make up structure or a cell. Cytoplasm breakdown proteins and replace them. DNA Genes made of DNA Contains information to carry out functions. Hold instructions for making proteins for growth and repair structures and other are enzymes. DNA is copied to pass information (inheritance) Plant and animals cells have a nucleus with DNA Bacteria have DNA in cytoplasm (no nucleus) A2.2.5—Prokaryote cell structure Include these cell components: cell wall, plasma membrane, cytoplasm, naked DNA in a loop and 70S ribosomes. The type of prokaryotic cell structure required is that of Gram-positive eubacteria such as Bacillus and Staphylococcus. Students should appreciate that prokaryote cell structure varies. However, students are not required to know details of the variations such as the lack of cell walls in phytoplasmas and mycoplasmas. PROKARYOTE CELLS Cell type – Prokaryotic cells structure in bacteria – in English Prokaryote cell structure Small size Simple Cell wall (peptidoglycan) No nucleus Nucleoid- region with DNA “naked DNA” circular No organelles Ribosomes 70 s - protein synthesis Flagella - movement Pilus (pili) Cytoplasm- enzymes Binary fission: Research skills Clostridium botulinum and cosmetic facial injections. What cellular processes are affected? A2.2.6—Eukaryote cell structure Students should be familiar with features common to eukaryote cells: a plasma membrane enclosing a compartmentalized cytoplasm with 80S ribosomes; a nucleus with chromosomes made of DNA bound to histones, contained in a double membrane with pores; membrane-bound cytoplasmic organelles including mitochondria, endoplasmic reticulum, Golgi apparatus and a variety of vesicles or vacuoles including lysosomes; and a cytoskeleton of microtubules and microfilaments. EUKARYOTIC CELLS Biology: Cell Structure I Nucleus Medical Media Class Activity https://www.thinkib.net/biology/page/17090/euk aryotic-cell-ultrastructure Eukaryote cell structure Contains organelles Nucleus DNA associated with proteins (histones) Ribosomes 80 s Cytoplasm - compartmentalized Areas with double membrane Nucleus Rough and Smooth endoplasmic reticulum Lysosomes (only in animal cells) Golgi Apparatus Lysosomes (only in animal cells) PLANT CELL ANIMAL CELL https://www.youtube.com/watch?v=zZtcMBTQaS4 Classwork A2.2.7—Processes of life in unicellular organisms Include these functions: homeostasis, metabolism, nutrition, movement, excretion, growth, response to stimuli and reproduction. Processes of life in unicellular organisms Paramecium Homework: Draw a paramecium and complete the chart in your notebook  FUNCTION OF LIFE Definition Nutrition supplying the nutrients required for energy, growth and repair in an organism Growths an increase in size or number of cells Response perception of stimuli and carrying out appropriate actions in response Excretion removal of waste products of metabolism from an organism Metabolism the sum of all the biochemical reactions that occur in a living organism Homeostasis maintenance of a constant internal environment in an organism Reproduction production of offspring, either sexually or asexually  FUNCTION OF LIFE PARAMECIUM CHLAMYDOMONAS p 65 Nutrition food vacuoles, gradually food vacuoles digested smaller organism Growths nutrients are absorbed and carbon dioxide is converted into provide energy and materials compounds needed for growth. needed for growth. Response Beating of whip-like cilia moves light sensitive eyespot containing Paramecium through the water carotenoid pigments is visible,swims toward the light Excretion Excretion happens by waste Oxygen (a waste product of products diffusing out through photosynthesis) is excreted by the membrane. outward diffusion through the plasma membrane. Metabolism Metabolic reactions, enzymes Photosynthesis Homeostasis contractile vacuoles contractile vacuoles Reproduction asexual asexual, sexual A2.2.8—Differences in eukaryotic cell structure between animals, fungi and plants Include presence and composition of cell walls, differences in size and function of vacuoles, presence of chloroplasts and other plastids, and presence of centrioles, cilia and flagella Generate movement Plastids for photosynthesis Flexible fluid- filled compartment Flagella Centrioles: microtubules  Feature Animals Fungi Plants Plastids none none chloroplast amyloplast (starch) Cell wall none chithin cellulose Vacuole temporary, digest permanent vacuoles for storage of food, pathogens, substances endocytosis Centrioles used to construct Absent spindles (mitosis) Undulipodia Cilia and flagella Absents, except in gametes that swim (tails) A2.2.9—Atypical cell structure in eukaryotes Use numbers of nuclei to illustrate one type of atypical cell structure in aseptate fungal hyphae, skeletal muscle, red blood cells and phloem sieve tube elements. Cell theory: living organism are made of cells  Cell theory Cells are the smallest possible Activities are chemical reactions units of live and that living catalyzed by enzymes organisms are made of cells. Cells have their own energy Cells consist of release system cytoplasm,enclosed in a plasma membrane. Nucleus with genes (only in plant and animal cells). Genetic material stores instructions for cell's activities. Exceptions to the cell theory 1. Red blood cells 2. Phloem sieve tube elements 3. Skeletal muscle 4. Aseptate fungi hyphae (Science: trends and discrepancies) Red blood cells Cells that do not have a nucleus. During development process the nucleus is destroy by phagocyte. They become more flexible. They cannot repair, 100 to 120 days of life. Phloem sieve tube element Plants move sap through tubular vessels (columns of cylindrical cells) Xylem: moves water from roots to leaves Phloem: sugar from leaves to the other parts through sieve tubes Sieve are atypical cells. division walls between adjacent cells are sieve- like with large pores, nucleus and other parts are breakdown. Plasma membrane remains for phloem transport. Companion cells are connected to sieve tube end they help sieve tube elements to survive and carry out their function. Muscle cells Muscle fibres: are surrounded by a membrane and are formed by division of pre-existing cells. Hyphae: uninterrupted tube-like structure with many nuclei spread along it. A2.2.10—Cell types and cell structures viewed in light and electron micrographs Application of skills: Students should be able to identify cells in light and electron micrographs as prokaryote, plant or animal. In electron micrographs, students should be able to identify these structures: nucleoid region, prokaryotic cell wall, nucleus, mitochondrion, chloroplast, sap vacuole, Golgi apparatus, rough and smooth endoplasmic reticulum, chromosomes, ribosomes, cell wall, plasma membrane and microvilli. A B A2.2.11—Drawing and annotation based on electron micrographs Application of skills: Students should be able to draw and annotate diagrams of organelles (nucleus, mitochondria, chloroplasts, sap vacuole, Golgi apparatus, rough and smooth endoplasmic reticulum and Syllabus content 40 Biology guide chromosomes) as well as other cell structures (cell wall, plasma membrane, secretory vesicles and microvilli) shown in electron micrographs. Students are required to include the functions in their annotations. ADDITIONAL Higher Level A2.2.12—Origin of eukaryotic cells by endosymbiosis Evidence suggests that all eukaryotes evolved from a common unicellular ancestor that had a nucleus and reproduced sexually. Mitochondria then evolved by endosymbiosis. In some eukaryotes, chloroplasts subsequently also had an endosymbiotic origin. Evidence should include the presence in mitochondria and chloroplasts of 70S ribosomes, naked circular DNA and the ability to replicate. NOS: Students should recognize that the strength of a theory comes from the observations the theory explains and the predictions it supports. A wide range of observations are accounted for by the theory of endosymbiosis. Endosymbiosis theory Endosymbiosis theory (video) | Khan Academy Evolution of mitochondria and chloroplast (evidence) Double membrane Circular DNA with genes They transcribe their own DNA 70 s ribosomes they can not be produced by division of pre- existing mitochondria and chloroplasts A2.2.13—Cell differentiation as the process for developing specialized tissues in multicellular organisms Students should be aware that the basis for differentiation is different patterns of gene expression often triggered by changes in the environment. Cell differentiation Cells can develop differently to perform different functions. Specialized cells develop only the features they need (efficient) e.g. Red blood cells produce haemoglobin to transport oxygen Humans: about 4000 genes are active in all types of cells (housekeeping genes) Other genes are active and expressed in a single type of cell. Specialization happens in very early stage of life in a embryo. Different genes are “switched on” (gene expression) A2.2.14—Evolution of multicellularity Students should be aware that multicellularity has evolved repeatedly. Many fungi and eukaryotic algae and all plants and animals are multicellular. Multicellularity has the advantages of allowing larger body size and cell specialization.  MULTICELLULAR ORGANISM Plants and animals are multicellular. They consist of many cells. Many fungi and eukaryotic cell are Cells are unit of live that has multicellular. distinctive properties. Multicellular organism have longer lifespans Large organisms are multicellular. Division of labour: different types Most of the individual living of cells - different tissues - organism on Earth are singled- different functions. celled organism. Linking questions What explains the use of certain molecular building blocks in all living cells? What are the features of a compelling theory?