1. The wonderful world of cells!
A fascinating insight into the world of
cells, who discovered them, the
different types and what they are
made up of.

2. Microscopes
Light microscope Electron microscope
Uses light rays Uses electron ‘beams’
Magnification – x2000 Magnification – x500,000
Resolving power – 200nm Resolving power – 1nm
Focused by glass lenses Focused by electromagnets
Specimens can be living or Specimens must be dead
dead
Small, portable and Large, static and very
relatively inexpensive expensive

3. Microscopes
 Magnification – to make an image appear bigger
 To calculate the magnifying power of a
microscope:
eye piece lens magnification X objective lens
 Resolution – the minimum distance between 2
points at which they are still visible as 2 separate
points

4. Robert Hooke
He looked at cork
cells under a
microscope and
used the term
‘cell’. The holes
that he observed
where once filled
with living material
(cytoplasm)

5. Robert Hooke’s cells

6. Theodor Schwann

7. Matthias Schleiden

8. Cell theory with the cell
Schwann and Schleiden came up
theory.
They proposed that all plants and animals
were made up of cells and that cells were
the basic units of life
Another scientist, Rudolf Virchow discovered
that new cells can only arise from the
division of pre-existing ones.

9. Prokaryotic and Eukaryotic cells
 No true nucleus  Distinct nucleus
 Few organelles except for surrounded by a nuclear
envelope
small ribosomes
 Many membrane bound
 Single strand of genetic organelles
material free in the cell  Genetic material is stored
 Simple structure in the nucleus
 Small in size  Highly organized to carry
 Include bacteria and out complex functions
blue/green algae  Large in size
 Include plants, animals
and fungi

12. Eukaryotic cell

13. Animal cells: these are cheek cells as
seen with a compound microscope,
compare these cells to the next ones
seen through an electron microscope.

15. Plant and animal cells
 Cellulose cell wall  No cell wall
 Chloroplasts  No chloroplasts
 Large permanent  Small, temporary
vacuole with cell sap vacuoles
 No centrioles  Centrioles present
 Starch grains for  Glycogen granules
storage for storage

16. Plant cell

17. Animal cell

18. Cytoplasm
 Watery, jelly-like material
 Contains many substances for metabolism
 The other organelles are suspended in it

19. Cellulose cell wall
 Many cellulose fibers glued together
 Strong to resist expansion of the cell as
water enters – this supports the cell
 Provides mechanical strength to the cell
 Freely permeable

20. Vacuole
 Large permanent vacuole in plant cells is
called a central vacuole. It contains cell
sap, a solution of sugar and minerals.
 They are food stores
 They accumulate waste products
 Some contain pigments to give color
 Vacuoles in animal cells are small and
temporary

21. Nucleus
 Largest cell organelle
 Surrounded by a double membrane that
allows materials to pass in and out
 Contains genetic material (DNA) which is
used to make proteins
 Controls the metabolic activity of the cell

22. Nucleolus
 Found in the nucleus
 Dense, spherical structure
 Contains RNA for the production of
ribosomes

23. Ribosomes
 Small, dense organelles
 Can be free in the cytoplasm or attached to
rough endoplasmic reticulum
 They are made in the nucleolus
 They are the site of protein synthesis

24. Endoplasmic reticulum
 Complex system of double membranes with
fluid-filled sacs in between called cisternae
 Connected with the nuclear membrane and the
cell membrane
 It collects, stores and distributes materials
 Rough endoplasmic reticulum has ribosomes on
it. It packages and transports proteins made by
ribosomes
 Smooth endoplasmic reticulum is the site of lipid
(fat) synthesis.

26. Golgi complex
 Also known as golgi body or apparatus
 Made from small pieces of rough ER
pinched off at the end to form vesicles
which fuse together
 Site of protein modification
 Vesicles pinch off at the ends to carry the
new chemicals away (some vesicles
become lysosomes)

27. Lysosomes
 Small vesicles formed when pieces of the golgi
body pinch off
 Contain hydrolytic enzymes that can digest cell
material
 They destroy worn out organelles
 They can destroy material brought into the cell
(e.g. bacteria)
 They can release enzymes out of the cell to digest
other cells
 They can cause the cell to self destruct

28. Mitochondria
 Has a double membrane. The outer one
controls entry of materials and the inner
one has many folds called cristae
 Has a matrix containing DNA, ribosomes
and enzymes
 Site of aerobic respiration
 The more active the cell, the more
mitochondria it has

29. Chloroplasts
 Found in plants cells that carry out
photosynthesis
 They are the site of photosynthesis
 They have a double membrane filled with fluid
(stroma) where the photosynthesis reactions take
place
 The stroma contains piles of flattened scas
(grana) where chlorophyll is found and light is
absorbed

30. Cytoskeleton
 This is a network of fibrous proteins
 It allows movement and gives the cell
shape and support
 It is made up of microtubules and
microfilaments

31. Centrioles
 These are 2 short bundles of microtubules
positioned at right angles to each other.
 They are found just outside the nucleus in
animal cells
 During cell division, they move to opposite
ends of the cell and produce the spindle

32. Flagella
 Also made up of microtubules
 Often used to help cells move (e.g. sperm)

33. Cell membrane
 Made up of a bilayer of phospholipids that
allows some materials through but not
others (semi-permeable)
 Contains proteins that can act as pores,
carriers or be involved in cell recognition
 The main function is to regulate the
movement of molecules and ions

35. Cell membrane structure
 Made up of a bilayer of phospholipids.
They have a polar end (water liking) and a
non-polar end (water hating)
 Protein carrier molecules are found
embedded in the cell membrane; these
molecules form specific bridges allowing
specific molecules to pass through

36. Transport across membranes
 The cell membrane is thin and provides a large
surface area for diffusion to occur
 Diffusion is the movement of molecules or ions
from a region of high concentration to a region of
low concentration until they are spread out evenly
(down a concentration gradient)
 A big difference in concentration, an increase in
temperature, small molecules and a short
diffusion distance makes the rate of diffusion
faster

38. Facilitated diffusion
 This allows faster movement
 It involves the use of proteins to assist (facilitate)
diffusion
 Specific channel proteins form pores for specific
molecules
 Carrier molecules bind to specific molecules,
change shape and deliver the molecule to the
other side of the membrane

40. Osmosis
 This is the diffusion of water molecules
 They move from where they are in a high
concentration (a dilute solution) to where
they are in a low concentration (a
concentrated solution)

41. Osmosis in plant cells
 As water enters a plant cell, the cell starts to
swell. The cell wall starts to resist the stretching
which creates pressure
 When no more water can enter the cell, it is said
to be TURGID. This provides strength and
support to the cell
 If water leaves a cell, the membrane can pull
away from the cell wall. This causes a plant to
wilt

43. Different solutions
 Solution – a mixture of 2 or more substances
 Solvent – the liquid that a substance dissolves in
 Solute – the substance that dissolves in a solvent
 Hypotonic – a weak solution: weaker in solute
concentration than cell
 Hypertonic – a strong solution: stronger in solute
concentration than cell
 Isotonic – a solution with the same concentration
as cell.

45. Active transport
 Moving molecules
against a
concentration gradient
(from low to high
concentration)
 It requires special
carrier proteins called
membrane pumps
 It uses energy in the
form of ATP

46. Endocytosis and exocytosis
 For molecules too large to pass through the
membrane
 Endocytosis – taking materials into the cell by
closing the cell membrane around it to form a
vesicle (There are 2 types, pincytosis and
phagocytosis)
 Exocytosis – material in vesicles in the cell fuse
with the cell membrane and are released