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

2. Learning objectives
To understand and discuss the basis of cell theory based upon milestones in cell biology
To carry out practical work on cell size and magnifications using a light microscope
To be able to draw a plant cell and an animal cell using a light microscope
To prepare slides using stains to identify cell structure.

3. Milestones in Cell Biology
Read through handout
Group discussion
Discuss the impact of the microscope on cell biology
List things you think are the most important

4. 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.

5. Cell Theory - Question
Before the development of cell theory, it was commonly believe that living organisms could arise by spontaneous generation.
Explain what this term means and why it has been discredited as a theory.

6. Plan Diagrams – dicotyledonous leaf

7. 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

8. 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

9. Structure of a generalised animal cell as seen with a very high power quality light microscope (diameter ~ 20ųm)

10. Structure of a generalised plant cell as seen with a very high power quality light microscope (diameter ~ 40ųm)

11. Light Microscope For the microscope in front of you, work out
The magnification of each lens
The field of view for each lens
Using a graticule / stage micrometer
Collect a prepared slide of Squamous epithelium, draw what you can see.
Your diagram should include title, labels, magnification and a scale bar.

12. Examination of plant cells
Strip a pieces of epidermis from the inner lining of one of the fleshy scales of an onion.
Mount it in dilute iodine solution
Observe and draw a cell under low power and high power
Repeat the above procedure using water instead of iodine.
what difference does this make to how much you can see?

13. Examination plant cells - conclusion
What does this tell you about the value of staining cells before you look at them under the microscope?
Make sure all diagrams have a title, label, magnification and scale bar.

14. Microscopy and magnification
OCR AS Biology
Microscopy and magnification

15. Microscopes Light microscope Electron 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

16. Magnification
How many times bigger the image is compared to original subject.
If asked to calculate the size of an object

17. Magnification
When calculating magnification make sure the units of length are the same for both object and image
unit
symbol
Equiv. in m
Kilometre km
103
Metre m 1
Millimetre mm
10-3
micrometre µm
10-6
nanometre nm
10-9

18. Magnification - example
Object 100nm in length
How much is it magnified in a photo?
Measure object in photo (10mm long)

19. Magnification - example
The measurements need converting to the same unit (usually the smallest)
There are nm in 10mm
Magnification is:
times

20. The effect of progressive magnification of a portion of human skin

21. Structure of plant and animal cells under an electron microscope
OCR AS Biology
Structure of plant and animal cells under an electron microscope

22. 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.

23. The Electron Microscope
Two types
Transmission Electron Microscope (TEM)
Scanning Electron Microscope (SEM)
Activity
Read through the handout on the electron microscope
Answer discussion questions 1 - 4

24. Electron Microscope Disadvantages
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 fields
Affected 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

25. Comparison of advantages and disadvantages of the light and electron microscopes
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

26. Comparison of pathways of the light and electron microscopes

27. Ultrastructure of an animal cell as seen through an electron microscope

28. Ultrastructure of an Animal Cell

29. Ultrastructure of a plant cell as seen through an electron microscope

30. Ultrastructure of a Plant Cell

31. Pupil Activity Cell structure
Read through the information on each of the organelles as you colour them in
Follow the guidance on colouring them in given at the bottom of the page
This works on the theory that whilst you are colouring in, you have time to consider and think about the structure and function of the organelles

32. Cell Structure Activities
OCR AS Biology
FOUNDATION
Cell Structure Activities

33. Pupil Activity – Cell Structure Animal Cell
In pairs label the diagram of the animal 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 the diagram of an animal cell

35. Animal Cell

36. Animal cell - answers

37. Pupil 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

39. Plant cell

40. Plant cell - answers

41. Activity: Introduction to organelle function
Using the cards, match up organelle, position and function.

42. Organelle Position Function
Nucleus
Within cytoplasm
Contains genetic code which controls the activities of the cell
Cytoplasm
Around 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 wall
around cell membrane
Gives cells rigidity, stops it bursting if put in water
Cell vacuole
Affects concentration of cytoplasm. Is a store of inorganic ions.
Tonoplast
Around cell vacuole
Controls exchange of substances in plant cells between vacuole and cytoplasm
Large granules
Usually stores food e.g. starch

43. Organelle Structure and function
OCR AS Biology
FOUNDATION
Organelle Structure and function

44. Nucleus

45. Structure of nucleus Nuclear envelope Nuclear pores Nucleoplasm
Chromatin
nuceolus

46. 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

47. Structure of Nucleus Chromatin nucleolus
DNA and associated proteins, chromatin condenses into chromosomes when the cell divides.
nucleolus
Manufactures ribosomal RNA and assembles the ribosomes

48. Structure of Nucleus Nuclear envelope Nuclear pores
Controls entry and exit of materials
Outer membrane continuous with endoplasmic reticulum
Nuclear pores
Passage of large molecules (mRNA) out of nucleus

49. Chloroplasts

50. 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

51. Mitochondria

52. Structure of Mitochondria
Double membrane
Inner membrane folded into cristae which provide a large surface area
Matrix
DNA, enzymes and ribosomes

53. Function of Mitochondria
Site of Krebs cycle and oxidative phosphorylation in aerobic respiration
Production of energy rich ATP molecules from carbohydrates

54. Endoplasmic reticulum

55. 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.

56. 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)

57. Ribosomes

58. 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

59. Golgi Apparatus

60. Structure of golgi apparatus
Stack of membrane bound, flattened sacks

61. 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

62. Lysosomes (animal cells only)

63. Structure of lysosome Spherical sac surrounded by a single membrane
Contains powerful digestive enzymes

64. 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.

65. Cilia

66. Structure and function of cilia
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.

67. Flagella / undulipodia
Structure
9 sets of microtubules in a circle
2 central microtubules
Function
Movement
Tail of a sperm
Whole of unicellular organism

68. Centrioles (animal cells only)

69. 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

70. Plant cell wall Structure Function Made of cellulose Supports the cell
Cell turgor pressure

71. Homework – in for next lesson
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

72. Movement and Stability in cells

73. Learning Outcomes
explain the importance of the cytoskeleton in providing mechanical strength to cells, aiding transport within cells and enabling cell movement;

74. 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

75. Division of Labour Protein synthesis

76. Learning Outcomes
outline the interrelationship between the organelles involved in the production and secretion of proteins

77. 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.

78. Protein Production

79. OCR AS Biology FOUNDATION
Prokaryotic Cells

80. 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.

81. 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

82. Structure of a bacterial cell

83. Activity Copy and complete the following table
Include organelles, DNA, RNA and protein synthesis, ribosome, cell division, cell wall, cellular organisation.
prokaryotic
Eukaryotic
organisms
Cell size
metabolism

84. Comparison of prokaryotic and eukaryotic cells
organisms
Bacteria
cyanobacteria
Protista, fungi, plants, animals
Cell size
1 – 10 µm
10 –100 µm
metabolism
Anaerobic and aerobic
Aerobic
organelles
No membrane bound organelles
Nucleus, mitochondria, chloroplasts, RER, SER

85. Comparison of prokaryotic and eukaryotic cells
DNA
Circular 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
Ribosomes
70S Type
80S Type
Cell Division
Binary fission
Mitosis or meiosis