Unit : cells – the basic units of life Created BY: Ms Mwelase
HOW to study cells.The study of cells and micro organisms has changed overtime with the change in technology.These were studied in the beginning with hand lenses,single lens microscope, light microscopeToday we have electron microscopes.Two types of electron microscopes are used today: SEM –Scanning electron microscope and TEM – Transmissionelectron microscope.
1632-1723 ANTON VAN LEEUWENHOEK Developed a microscope with one lens. Discovered - bacteria - blood cells - spermatozoa - protozoa
1662 – ROBERT HOOK Uses the concept cell for the first time. He used it when he looked at the microscopic structure of cork cells.
1831 – ROBERT BROWN (Botanist)Describes the nucleus of a cell
1838-1839 MATTHIAS SCHLEIDEN (Botanist) THEODOR SCHWANN (ZoologistDeveloped the cell theory: - Plants and animals are made of groups of cells. - The cell is the basic unit of living organisms
1855 – RUDOLPH VIRCHOW Expanded the cell theory: He said that new cells formed by the division of existing cells
1880 – AUGUST WEISMANN Expanded the cell theory more: He said that all cells can be traced to their origin
Schleiden, Schwann and Virchow compiled the cell theoryAll living organisms are made out of cellsNew cells are formed by the division of existing cellsThe cell houses genes, which are the blueprint forgrowth, functioning and development of cellsThe cell is the functional unit of life because allchemical reactions of life take place inside the cell
A cell is the basic unit of structure and function in organisms. Cells differ in size, shape and in function. A cell consist of smaller structures called organelles.
Two types of cellsProkaryotic or Eukaryotic cells.Only organisms of the domains Bacteriaand Archaea consist of prokaryotic cells –cells without a membrane bound nucleus. Protists, fungi, animals and plants allconsist of eukaryotic cells – cell with amembrane bound nucleus.
General structure of an animal cell asseen under a light microscope (called a micrograph)
DIFFERENCES BETWEEN PLANT- AND ANIMAL CELL PLANT CELL ANIMAL CELL
STRUCTURE AND FUNCTIONS OF THE DIFFERENT ORGANELLS OF CELLS Chapter 6 p. 98 – 131
CELL WALL (ONLY IN PLANT CELLS)PorousVaries in thicknessConsist of pectin (elasticity), cellulose fibrils held togetherwith non-cellulose substances (hardens the cell whenmature) and lignin (adds strength to cell especially in woodyplants)Cell wall is permeable and protects the inside of the cell.Middle lamella (layer of adhesive substances) – holds thecells togetherPlasmodesmata (pores) that connects the cytoplasm of theconnecting cells – selectively permeable
CELL WALL WITH PLASMODESMATA AND INTERCELLULAR SPACES
CELL MEMBRANE/PLASMA- (ANIMAL- AND PLANT CELLS)Consist of 2phospholipid layers andproteins in between.The phospholipid layersare part hydrophillicand part hydrophobic
NUCLEUS+/- 5µm, largest organelle in cell.Enclosed by a nucleomembrane withnuclear pores. Function: Protection andadd to selective permeability.Filled with nucleoplasma, a nucleolusand chromatin. Function of chromatin:carries genetic material in the form ofchromosomes.Function of nucleolus: Produce r-RNA
MITOCHONDRIONConsist of 2 membranes: Outer – anda highly convoluted inner membrane-These folds are called cristae – theyincrease the surface area.Filled with matrix called stroma thatcontains DNA and ribosomes.Function: Produce energy in the formof ATP by means of cellularrespiration
CHLOROPLAST (PLANT CELL ONLY)Enclosed by a double membraneFilled with stroma and thylakoidsfilled with chlorophyll arrangedin groups called grana.Ribosomes and starch grains instroma.Function: Photosynthesis
VACUOLE (Large in plant-, small in animal-)Membranous sacFilled with cell sap.Causes turgor pressure in thevacuole.Function: Stores varioussubstances, including waste.Helps with osmotic potential ofcell.
OTHER SMALLER ORGANELLES Endoplasmic Reticulum – Transport system in cell Ribosomes – Protein synthesis Golgi-apparatus – Make lysosomes and acts as transport system. Lysosomes – Intracellular digestion. Plastids e.g.– Leucoplasts – Stores starch - Chromoplast – gives colour to flowers and fruit.* Centrioli – Mitosis in animal cells
PERMEABILITY OF THE CELL MEMBRANEThe cell membrane has the ability toregulate transport molecules across itsstructure.This function is essential to the cell’sexistence.The fluid mosaic model helps toexplain how membranes regulate thecell’s molecular traffic.
Permeability of the lipid bilayerHydrocarbons, carbon dioxide and oxygen– non-polarSo they can dissolve in the lipid bilayer ofthe membrane.They can cross the membrane without theaid of membrane proteins.Polar molecules like, water and glucosemove slowly across the membrane andneed the aid of proteins to get across themembrane.
TRANSPORT PROTEINSHydrophyllic substances can avoidcontact with the hydrophobic lipid bilayerby passing through transport proteins thatspan the membrane. Channel proteins – tunnel for polarmolecules to pass through membraneAquaporins – channel proteins for thetransport of water
Carrier protein: Hold onto solutes that wantto move across the membrane and changes shape as it moves through the membrane. Each carrier protein is specific to what it transports.
1. If the Golgi-apparatus of a cell is destroyed, that cell would_____________ stop releasing cellular products. become a dictyosome. release digestive enzymes in the cytoplasm for self-digestion. behave normally.2. Which of the following characteristics does not apply tomitochondria? Double unit membrane. Connected to the ER. Inner membrane is folded. Larger than ribosomes.
1. Which is not a key point in the cell theory? All living cells consist of one or more cells. The cell is the basic unit of life. No cell can exist unless at least one other cell is present. New cells arise only from cells that already exist.2. The main constituent of most cell walls in plants is_____. glucose. glycogen. proteins and phospholipids. Cellulose.3. Which of the following is found in both plant and animal cells? Chromosomes Chromoplasts Chondrocytes Leucoplast
Part of the nucleus that mainly consist of RNA.The inner plasma membrane in the cell surrounding thevacuole.Organelles in living cells that contain enzymes,Give 2 functions of the plasma membrane.What is Archaea?