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

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?

Microscopy and magnification OCR AS Biology

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. 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 unitsymbolEquiv. in m Kilometre km10 3 Metre m1 Millimetre mm10 -3 micrometre µm10 -6 nanometre nm10 -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 nm in 10mm Magnification is: 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

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 fieldsAffected 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

Light Microscope Disadvantages Electron Microscope Advantages Magnifies objects up to 1500x only Magnifies objects more than X Depth of field is restricted Possible to investigate a greater field of depth Comparison of advantages and disadvantages of the light and electron microscopes

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.

OrganellePositionFunction NucleusWithin cytoplasm Contains genetic code which controls the activities of the cell CytoplasmAround 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 wallaround cell membrane Gives cells rigidity, stops it bursting if put in water Cell vacuoleWithin cytoplasm Affects concentration of cytoplasm. Is a store of inorganic ions. TonoplastAround cell vacuole Controls exchange of substances in plant cells between vacuole and cytoplasm Large granulesWithin cytoplasm Usually stores food e.g. starch

Organelle Structure and function OCR AS Biology FOUNDATION

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

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

Prokaryotic Cells OCR AS Biology FOUNDATION

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. prokaryoticEukaryotic organisms Cell size metabolism

Comparison of prokaryotic and eukaryotic cells prokaryoticEukaryotic organismsBacteria cyanobacteria Protista, fungi, plants, animals Cell size1 – 10 µm10 –100 µm metabolismAnaerobic and aerobic Aerobic organellesNo membrane bound organelles Nucleus, mitochondria, chloroplasts, RER, SER

prokaryoticEukaryotic DNACircular 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 Ribosomes70S Type80S Type Cell DivisionBinary fissionMitosis or meiosis Comparison of prokaryotic and eukaryotic cells