OCR AS Biology Unit 1: Cells, Exchange and Transport Cell Structure

Learning objectives To understand and discuss the basis of cell theory based upon milestones in cell biology To carry out practical work on cell size and magnifications using a light microscope To be able to draw a plant cell and an animal cell using a light microscope To prepare slides using stains to identify cell structure.

Milestones in Cell Biology Read through handout Group discussion Discuss the impact of the microscope on cell biology List things you think are the most important

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.

Cell Theory - Question Before the development of cell theory, it was commonly believe that living organisms could arise by spontaneous generation. Explain what this term means and why it has been discredited as a theory.

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 as seen with a very high power quality light microscope (diameter ~ 20ųm)

Structure of a generalised plant cell as seen with a very high power quality light microscope (diameter ~ 40ųm)

Light Microscope For the microscope in front of you, work out The magnification of each lens The field of view for each lens Using a graticule / stage micrometer Collect a prepared slide of Squamous epithelium, draw what you can see. Your diagram should include title, labels, magnification and a scale bar.

Examination of plant cells Strip a pieces of epidermis from the inner lining of one of the fleshy scales of an onion. Mount it in dilute iodine solution Observe and draw a cell under low power and high power Repeat the above procedure using water instead of iodine. what difference does this make to how much you can see?

Examination plant cells - conclusion What does this tell you about the value of staining cells before you look at them under the microscope? Make sure all diagrams have a title, label, magnification and scale bar.

Microscopy and magnification OCR AS Biology Microscopy and magnification

Microscopes Light microscope Electron 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. If asked to calculate the size of an object

Magnification When calculating magnification make sure the units of length are the same for both object and image unit symbol Equiv. in m Kilometre km 103 Metre m 1 Millimetre mm 10-3 micrometre µm 10-6 nanometre nm 10-9

Magnification - example Object 100nm in length How much is it magnified in a photo? Measure object in photo (10mm long)

Magnification - example The measurements need converting to the same unit (usually the smallest) There are 10 000 000nm in 10mm Magnification is: 100 000 times

The effect of progressive magnification of a portion of human skin

Structure of plant and animal cells under an electron microscope 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) Activity Read through the handout on the electron microscope Answer discussion questions 1 - 4

Electron Microscope Disadvantages 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 1500x only Magnifies objects more 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

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

Pupil Activity Cell structure Read through the information on each of the organelles as you colour them in Follow the guidance on colouring them in given at the bottom of the page This works on the theory that whilst you are colouring in, you have time to consider and think about the structure and function of the organelles

Cell Structure Activities OCR AS Biology FOUNDATION Cell Structure Activities

Pupil Activity – Cell Structure Animal Cell In pairs label the diagram of the animal 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 the diagram of an animal cell

Animal Cell

Animal cell - answers

Pupil 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 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 Usually stores food e.g. starch

Organelle Structure and function 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 nucleolus 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 Nuclear pores 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 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 Function Made of cellulose Supports the cell Cell turgor pressure

Homework – in for next lesson 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 Include organelles, DNA, RNA and protein synthesis, ribosome, cell division, cell wall, cellular organisation. prokaryotic Eukaryotic organisms Cell size metabolism

Comparison of prokaryotic and eukaryotic cells 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 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