1 The Cell The basic unit of life

2 Contents The Light Microscope Electron Microscope The Cell Cell Ultrastructure Cell membrane The Cell Wall Mitochondria Plastids Ribosomes Vacuoles Slides of cell types Prokaryotic or Eukaryotic?

3 The Light Microscope

4 Microscope Light microscope Light microscope: it focuses light with a combination of objective lens and an eyepiece to a maximum magnification of 1500 The parts of a light microscope include: The stage, to hold the slide The light source

5 Microscope cont’d The diaphragm, to adjust the brightness of the light The eyepiece The objective lens The total magnification is found by multiplying the magnification of the eyepiece with that of the objective lens.

6 Transmitting Electron Microscope (TEM) Electron microscope: a microscope that magnifies up to 500,000 times by passing beams of electrons through the specimen A TEM is much more powerful than a light microscope. It reveals the ultrastructure of cells because its resolving power is about 1 nm.

7 Scanning Electron Microscope (SEM) Photographs reflected electros from surfaces and reveals 3D structures. It has less detail than a TEM but can be used on slightly larger specimens

8 The Cell Cell: the basic unit of life. Cells consist of plasma membrane, cytoplasm, and nucleus (if present). Outside the plasma membrane there may be a cell wall e.g. plant, fungal and bacterial cells.

9 There are two kinds of cell prokaryotic cells, e.g. bacteria, do not have a true nucleus eukaryotic cells do have a nucleus. Eukaryotic cells may also have mitochondria and chloroplasts. Plant cells differ from animal cells in having A cell wall A large vacuole Chloroplasts.

10 Prokaryotic Cells Possess nuclear material Do not have a membrane surrounding this genetic material

11 Prokaryotic cells – mixed bacteria

12 Eukaryotic Cells Possess a true nucleus

13 Eukaryotic cells - amoeba

14 More eukaryotic cells Chlamydamonas Euglena Paramaecium Spirogyra

15 Cell Ultrastructure Cell ultrastructure: the cell organisation that is visible under the electron microscope.

16 Cell ultrastructure

17 Cell Components Cell wall Cytoplasm Nucleus Vacuole Chloroplast Cell membrane Mitochondria Nuclear pores Ribosome DNA

18 Cell Membrane Structure 2D

19 Cell membrane structure 3D

20 Phospholipid

21 Phospholipid

22 Cell Membrane Is not solid and is self-sealing if broken open, i.e. it is a fluid, moving barrier. Forms a bilayer around the perimeter of the cell The heads of the lipid molecules are hydrophilic – attracted to water The tails of the molecules are hydrophobic – repel water

23 Cell Membrane cont’d Large protein molecules float freely within the bilayer Carbohydrate molecules are often fixed to proteins and lipids on the outer side of the membrane These glycoproteins and glycolipids are involved in making contact with other cells and in cell protection

24 Functions of cell membrane Allow diffusion of gases Allow the passage of water by osmosis Allow the transmission of light Actively move specific chemicals from one side to the other Defend the cell against attack Generate nerve impulses (as in nerve cells)

25 The Cell Wall Lies outside the cell membrane Composed of tiny microfibrils of cellulose and other polysaccharides Very strong – contributes to strength, protection and shape of the cell Fully permeable Adjacent plant cells glued together by calcium pectate – the middle lamella

26 Mitochondrion structure Power house of cell Produces ATP Used during respiration 2 or 3 per skin cell 800 per muscle cell

27 Plastids Three types Chloroplasts (green - chlorophyll) – photosynthesis Chromoplasts (coloured) – petal colour Leucoplasts (colourless) – starch storage e.g. potato

28 Ribosomes Thousands found in the cytoplasm of every cell Made from protein and RNA Enzymes and proteins made here – DNA in the nucleus sends mRNA to the ribosomes with instructions for protein synthesis A single strand of mRNA often passes over several ribosomes

29 Vacuoles Plant cells have permanent vacuoles Fluid filled spaces surrounded by a membrane (the tonoplast) Contain cell sap – a mixture of food, minerals, pigments and water Animal cells have smaller, temporary vacuoles sometimes called vesicles

30 Examples of Animal Cells

31 Examples of Plant cells

32 Drawing of a Root cell - TEM

33 Prokaryotic? or Eukaryotic?

34 Prokaryotic cells Bacteria differ from plants, animal and fungi in the type of cell they possess Bacteria have prokaryotic cells – perhaps the type of cell that first appeared millions of years ago Do not have a definite nucleus and have fewer organelles

35 Eukaryotic cells Plants, animals and fungi possess eukaryotic cells A more advanced cell type Have a definite nucleus, bounded by a nuclear membrane, and many organelles

36 Prokaryotic Cells V Eukaryotic Cells No distinct nucleus No nuclear membrane Single, circular chromosome of DNA Have ribosomes No mitochondria No plastids Cell wall contains protein Small cell size 1 – 10 µm Distinct nucleus Nucleus bounded by a nuclear membrane Many chromosomes of DNA Have ribosomes Have mitochondria Have plastids Cell wall contains cellulose or chitin Larger cell size 10 – 100 µm

37 Generalised Animal Cell

38 Generalised Plant Cell

39 END