OCR AS Biology Unit 1: Cells, Exchange and Transport Cell Structure Cell theory • The cell is the fundamental unit of life. All organisms, whatever their type or size, are composed of cells. The modern theory of cellular organisation states:– All living things are composed of cells and cell products. – New cells are formed only by the division of pre-existing cells – The cell contains inherited information (genes), which is used as instructions for growth, functioning and development. – The cell is the functioning unit of life; the metabolic reactions of life take place within the cells. Plan Diagrams – dicotyledonous leaf Cell Biology and Microscopy • When Scientists began to observe cells, they started with simple microscopes • There are two different types of microscope both use a form of radiation to create an image of the specimen: – Light microscope – uses light – Electron microscope – uses electrons Using a light microscope • Magnification – Number of times larger an image is compared with the real size of the object • Resolution – The ability to distinguish between two separate points Structure of a generalised animal cell (diameter ~ 20ųm) Structure of a generalised plant cell Examination cells -staining • What is the value of staining cells before you look at them under the microscope? OCR AS Biology Microscopy and magnification Microscopes • Light microscope • Long wavelength • Can only distinguish between two objects if they are 0.2µm apart. • Electron microscope • Shorter wavelengths • Can distinguish between objects 0.1nm apart Magnification • How many times bigger the image is compared to original subject. size of im age m agnification size of object • If asked to calculate the size of an object size of im age size of object m agnification Magnification • When calculating magnification make sure the units of length are the same for both object and image unit Kilometre Metre Millimetre symbol km m mm Equiv. in m 103 1 10-3 micrometre nanometre µm nm 10-6 10-9 Magnification - example • Object 100nm in length • How much is it magnified in a photo? • Measure object in photo (10mm long) size of im age 10m m size of object 100nm Magnification - example • The measurements need converting to the same unit (usually the smallest) • There are 10 000 000nm in 10mm • Magnification is: size of im age 10 000000nm 100000 size of object 100nm 1 100 000 tim es • 100 000 times The effect of progressive magnification of a portion of human skin OCR AS Biology Structure of plant and animal cells under an electron microscope The Electron Microscope • Two main advantages – High resolving power (short wavelength of electrons) – As electrons negatively are charged the beam can be focused using electromagnets • As electrons are absorbed by molecules of air, a near-vacuum has to be created within the chamber of an electron microscope. The Electron Microscope • Two types – Transmission Electron Microscope (TEM) – Scanning Electron Microscope (SEM) Comparison of advantages and disadvantages of the light and electron microscopes Light Microscope Advantages Electron Microscope Disadvantages Small and portable very large Operated in special rooms Unaffected by magnetic fields Affected by magnetic fields Preparation of material is quick and simple Preparation of material is lengthy Requires expertise Material rarely distorted by preparation Preparation may distort material Natural colour of object observed Images are in black and white Cheap to purchase and operate Expensive to purchase and operate Comparison of advantages and disadvantages of the light and electron microscopes Light Microscope Disadvantages Electron Microscope Advantages Magnifies objects up to Magnifies objects more 1500x only than 500 000X Depth of field is restricted Possible to investigate a greater field of depth Comparison of pathways of the light and electron microscopes Learn to label! Ultrastructure of an animal cell as seen through an electron microscope Ultrastructure of an Animal Cell Ultrastructure of a plant cell as seen through an electron microscope Ultrastructure of a Plant Cell Revision Activity – Cell Structure Animal Cell • On the NEXT few slides: – How many structures can you identify? – Look at the cells alive animation – how many have you correctly identified? • Label the paper copy of the diagram of an animal cell Animal Cell Animal cell - answers Activity – Cell Structure Plant Cell • In pairs label the diagram of the plant cell given. – How many structures can you identify? – Look at the cells alive animation – how many have you correctly identified? • Label the paper copy of a diagram of a plant cell Plant cell Plant cell - answers Activity: Introduction to organelle function • Using the cards, match up organelle, position and function. Organelle Position Function Nucleus Within cytoplasm Contains genetic code which controls the activities of the cell Cytoplasm Around nucleus Location of chemical reactions – does the work of the cell Cell surface membrane Around cytoplasm Controls exchange of substances between cytoplasm and surroundings Cell wall around cell membrane Gives cells rigidity, stops it bursting if put in water Cell vacuole Within cytoplasm Affects concentration of cytoplasm. Is a store of inorganic ions. Tonoplast Around cell vacuole Controls exchange of substances in plant cells between vacuole and cytoplasm Large granules Within cytoplasm Usually stores food e.g. starch OCR AS Biology FOUNDATION Organelle Structure and function Nucleus Structure of nucleus • • • • • Nuclear envelope Nuclear pores Nucleoplasm Chromatin nuceolus Function of the nucleus • Acts as the control centre of the cell through the production of mRNA and protein synthesis • Retain genetic material of the cell (DNA / chromosomes) • Start the process of cell division Structure of Nucleus • Chromatin – DNA and associated proteins, chromatin condenses into chromosomes when the cell divides. • nucleolus – Manufactures ribosomal RNA and assembles the ribosomes Structure of Nucleus • Nuclear envelope – Controls entry and exit of materials – Outer membrane continuous with endoplasmic reticulum • Nuclear pores – Passage of large molecules (mRNA) out of nucleus Chloroplasts Structure and Function of Chloroplasts • Chloroplast envelope – Entry and exit of substances • Stroma – Enzymes for the light independent stages of photosynthesis • Grana (thylakoids/lamellae) – Light dependent stage of photosynthesis • Starch grains – Temporary stores of carbohydrates Mitochondria Structure of Mitochondria • Double membrane – Inner membrane folded into cristae which provide a large surface area • Matrix – DNA, enzymes and ribosomes Function of Mitochondria • Site of Krebs cycle and oxidative phosphorylation in aerobic respiration • Production of energy rich ATP molecules from carbohydrates Endoplasmic reticulum Endoplasmic reticulum • Membranes spreading through the cytoplasm of cells, continuous with the nuclear membrane • Enclose flattened sacs called cisternae • Rough endoplasmic reticulum – Ribosomes present on outer surface of membrane • Smooth endoplasmic reticulum – No ribosomes, tubular in appearance. Function of endoplasmic reticulum • RER – Provide LSA for synthesis of proteins – Provides a pathway for the transport of materials (esp. proteins) throughout the cell. • SER – Synthesis, stores and transports lipids and carbohydrates – Contains lytic enzymes (liver cells) Ribosomes Structure and function of ribosomes • Two types – 80S – eukaryotic cells – 70S – prokaryotic cells • Make up 25% of dry mass of cell • Important in protein synthesis Golgi Apparatus Structure of golgi apparatus • Stack of membrane bound, flattened sacks Functions of Golgi Apparatus • Modifies and packages proteins – Adds carbohydrates to proteins to form glycoproteins – Produces secretory enzymes • Secretes carbohydrates • Transports, modifies and stores lipids • Forms lysosomes Lysosomes (animal cells only) Structure of lysosome • Spherical sac surrounded by a single membrane • Contains powerful digestive enzymes Functions of Lysosomes • Destroy foreign material inside or outside the cell. – Breakdown material ingested by phagocytic cells – Release enzymes outside the cell – Digest worn out organelles (autophagy) – Autolysis break down cells after they have died. Cilia Structure and function of cilia • Structure – Threads that extend from cell surface – Made of nine sets of 3 microtubules • Function – Move an entire organism – Move material within an organism • E.g. cilia lining respiratory tract move mucus towards the throat. Flagella / undulipodia • Structure – 9 sets of microtubules in a circle – 2 central microtubules • Function – Movement • Tail of a sperm • Whole of unicellular organism Centrioles (animal cells only) Structure and function of centrioles • Hollow cylinders of microtubules • Microtubules form spindle fibres for nuclear division • Maybe involved in formation of microtubules that make up cells cytoskeleton Plant cell wall • Structure – Made of cellulose • Function – Supports the cell • Cell turgor pressure Revision • Similarities between plant and animal cells – Make a list of the structures plant and animal cells have in common – Make a table of the differences between plant and animal cells • Include all structures in plant and animal cells not just the ones observed through a Light microscope Movement and Stability in cells Learning Outcomes • explain the importance of the cytoskeleton in providing mechanical strength to cells, aiding transport within cells and enabling cell movement; Cytoskeleton • Cells contain a network of fibres made of protein, providing an internal framework. • Fibres can move organelles round within a cell. • Microtubules – Move chromosomes around in cell division – Move vesicles from endoplasmic reticulum to Golgi apparatus • ATP is used to drive some of these movements Division of Labour Protein synthesis Learning Outcomes • outline the interrelationship between the organelles involved in the production and secretion of proteins Protein Production • Instructions in DNA is nucleus • Instructions copied onto mRNA • mRNA moves to ribosome, where protein is assembled • Protein transported to Golgi apparatus • Protein modified and packaged • Protein moves in a vesicle to the cell surface membrane • Protein secreted. Protein Production OCR AS Biology FOUNDATION Prokaryotic Cells Prokaryotic Cells “pro” – before “karyo“– nucleus • Prokaryotes were probably the first forms of life on earth. Their heredity material (DNA) is not enclosed within a nuclear membrane. There are no membrane bound organelles within a prokaryotic cell. Prokaryotic Cells • The absence of a true nucleus only occurs in 2 groups. – Bacteria – Blue green algae (cyanobacteria) • Five structures, which are always present in a prokaryotic cell, are: – cell wall, plasma membrane, cytoplasm, ribosome, circular DNA Structure of a bacterial cell Activity • Copy and complete the following table prokaryotic Eukaryotic organisms Cell size metabolism • Include organelles, DNA, RNA and protein synthesis, ribosome, cell division, cell wall, cellular organisation. Comparison of prokaryotic and eukaryotic cells prokaryotic Eukaryotic organisms Bacteria cyanobacteria Protista, fungi, plants, animals Cell size 1 – 10 µm 10 –100 µm metabolism Anaerobic and aerobic Aerobic organelles No membrane bound organelles Nucleus, mitochondria, chloroplasts, RER, SER Comparison of prokaryotic and eukaryotic cells prokaryotic Eukaryotic DNA Circular DNA in cytoplasm DNA organised into chromosomes bounded by nuclear envelope RNA and Protein Synthesis Synthesised in same compartment RNA synthesised and processed in nucleus Protein synthesis in cytoplasm Ribosomes 70S Type 80S Type Cell Division Binary fission Mitosis or meiosis