Transcript Cell - msos
Cell Structure Chpt. 7 Microscopes Simple Microscope • uses single lens • max magnification x400 • uses light Compound Microscope • microscope used in our labs. • max magnification x1000 Compound Microscope • Has two magnifying lens: - the Eyepiece Lens is the lens that you look through. - the Objective lens is the lens that is immediately above the specimen. Compound Microscope The Objective Lens: • There are three objective lenses: - the scanning lens with the 4X label - the low power lens with the 10X label - the high power lens with the 40X label Compound Microscope Parts of the Microscope Compound Microscope Parts of the Microscope Part Function Lenses Magnification Stage To place the slide on Clips Hold the slide in place Diaphragm To control the amount of light Coarse Focus Knob To focus the image Fine Focus Knob To precisely focus the image Light To supply light to the object Compound Microscope Magnification Total Magnification: magnifying power of the eyepiece lens x the magnifying power of the objective lens Example: Eyepiece lens = 10X Objective lens = 4X Total magnification = 10 x 4= 40X Cell Structure seen using the Light Microscope Robert Hooke Robert Hooke looked at thin slices of cork under a microscope. He thought the spaces he saw reminded him of Monks Cells – Hence the name cells Cell Structure seen using the Light Microscope Animal Cell Cytoplasm: • living material outside the nucleus. • most reactions take place in cytoplasm. Protoplasm: • comprises all the living parts of the cell e.g. Nucleus and surrounding cytoplasm. Cell Structure seen using the Light Microscope Plant Cell Cell Wall: - made of cellulose - function: support Cell Membrane: - pressed close to cell wall Vacuoles: - contain cell sap - function: strength shape store materials Chloroplasts: - photosynthesis Electron Microscope Allow cell structure to be seen in greater detail - ultrastructure Electron Microscope •Uses Electrons instead of light •Electrons have much lower wavelength than light – image is shown on a screen or as a photograph •Resolution is much better •Magnification is much greater Images from Electron Microscope Bacteria Platelet Cytoplasm Electron Microscope 2 Types Transmission Electron Microscope (TEM) • beam of electrons sent through thin section of the sample and shows the INTERNAL structure Scanning Electron Microscope (SEM) • beam of electrons provides a surface view. Cells - All living things are composed of one or more cells. - Cells are the basic units of structure and function in an organism. - Cells come only from reproduction of existing cells. Organelles • Cells contain a variety of internal structures called ORGANELLES. • An organelle is a cell component that PERFORMS SPECIFIC FUNCTIONS FOR THE CELL Organelles we need to know •Cell membrane •Nucleus •Mitochondria •Chloroplast •Ribosomes •DNA •Cell Wall •Vacuole •Nucleolus Animal Cells Animal Cells contain the following structures Cell Membranes Mitochondria Nucleus Cytoplasm Only the cell membrane, the cytoplasm and the nucleus can be seen under the light microscope. Cell (Plasma) Membrane Cell Membrane: composed of phospholipids and proteins. Cell (Plasma) Membrane Phospholipids: • contain a water-loving phosphate group and a water-hating lipid group. Phosphate (Water loving) Lipid (Water Hating) • arranged into double layers - bilayers Cell (Plasma) Membrane Proteins: • completely or partially embedded in phospholipid bilayer. The phospholipids and proteins are in constant motion. Therefore membranes are thought of as fluids Functions of Cell Membrane • Separate the cell organelles and cytoplasm from the outside. • Semi permeable – controls what enters and leaves the cell. • Membranes give some support to the cell. • Membranes recognise molecules that touch them. Nucleus • A large organelle near the center of the cell is the NUCLEUS. • It contains the cell's genetic information. • It is the control centre of the cell. Ultra Structure of the Nucleus What’s in the Nucleus??? Double Membrane: nucleus is surrounded by a double membrane with nuclear pores. Nuclear Pores: allows the controlled entry and exit of molecules in and out of the nucleus e.g. - allow a type of RNA called mRNA to pass in and out of the nucleus. Nucleolus: • contains RNA, DNA and protein. • is responsible for making ribosomes which are made up of RNA (Ribonucleic acid). What’s in the Nucleus??? Chromosomes: • nucleus contains strands of DNA which are arranged into structures called Chromosomes. • genes are located randomly along chromosomes: genes = units of inheritance • when cell is not dividing the chromosomes form a mass of threads called chromatin. Functions of Nucleus • directs growth, development and activities of the cell. • makes replicas of DNA for new cells • carries out cell division • instructs the formation of enzymes and hormones Cytoplasm • liquid in a cell that surrounds the nucleus • small bodies called organelles are suspended in the cytoplasm: 1. Mitochondria 2. Chloroplasts 3. Ribosomes 4. Vacuoles Cytoplasm Organelles Mitochondria Cytoplasm Organelles Mitochondria • Found in all cells except bacteria. • Supply energy to the cell – sites of respiration: Lots of mitochondria Few mitochondria Lots of energy Less energy • Consist of a smooth outer membrane and a folded inner membrane. • It is on the inner membrane, especially the infoldings, that energy is released. Therefore the more infoldings the more energy produced. Cytoplasm Organelles Mitochondria Inactive mitochondria: - have a decrease in infoldings and as a result a decrease in the energy released. Active mitochondria: - have a increase in infoldings and as a result an increase in the energy released. Cytoplasm Organelles Chloroplasts (Plants Only) • Found in plant cells only. • Green structures in which photosynthesis takes place. • Contain the green pigment chlorophyll. Cytoplasm Organelles Ultrastructure of the Chloroplast The thylakoids contain the chlorophyll which traps the sun’s energy Cytoplasm Organelles Ribosomes • Found in all cells • Tiny, bead – like structures • Made up of ribonucleic acid (RNA) and proteins. • Function: - to make proteins by combining a sequence of amino acids. Cytoplasm Organelles Vacuoles • Vacuoles are membrane-bound sacs within the cytoplasm of a cell. • Vacuoles provide structural support, as well as serving functions such as storage, waste disposal, protection, and growth. • Plant cells have large vacuoles Cell Wall • Found in plant cells only • Made of cellulose • Very strong and contributes the following to the cell: - strength - protection - shape Ultra Structure of an Animal Cell Ultra Structure of a Plant Cell Differences between Plant and Animal Cells Plant Cells Animal Cells Have cell walls No cell walls Contain chloroplasts Do not contain chloroplasts Do not contain chlorophyll Have small (if any) vacuoles Contain chlorophyll Have large vacuoles Prokaryotic and Eukaryotic Cells Living things can be placed into special categories depending on the complexity and structure of their cells. Prokaryotic Cells Do not have a nucleus or membrane enclosed organelles. • They are single celled organisms e.g. Bacteria • Their DNA is found as circular loops found in the cytoplasm. • Do not have mitochondria or chloroplasts. • Respiration and photosynthesis is carried out on infolding of the plasma membrane. Eukaryotic Cells Have a nucleus and cell organelles, all of which are enclosed by membranes • More advanced than prokaryotic cells. • Larger than prokaryotic cells. • Plant and animal cells are examples of eukaryotic cells.