Slides covering material from Topic 1.1 of the updated IB Biology syllabus for 2016 exams

1. Introduction to Cells (1.1)
IB Diploma Biology

5. come
only
from
existing
cells.
4-cell stage of a sea biscuit by Bruno Vellutini on Flickr (CC) http://flic.kr/p/daWnnS
C
E
L
L
S

6. Hooke’s Micrographia in full! http://lhldigital.lindahall.org/cdm/ref/collection/nat_hist/id/0
1665
Hooke names “cells” in his book
“Micrographia” after observing
cork under a lense.
Alllivingthings
aremadeofcells.

7. 1676 van Leeuwenhoek, a master microscope maker identifies
“animalcules” and becomes the father of microbiology.
Alllivingthingsare
madeofcells.
http://en.wikipedia.org/wiki/Antonie_van_Leeuwenhoek

8. Robert Brown: http://en.wikipedia.org/wiki/Robert_Brown_(botanist)
1833 Robert Brown names the cell nucleus.
Cells are the smallest units of life.
He also discovered Brownian motion:
http://en.wikipedia.org/wiki/Brownian_motion

9. 1837 German Botanist
Mathias Schleiden posits
that all plants are made of
cells
http://en.wikipedia.org/wiki/File:Matthias_Jacob_Schleiden.jpg

10. 1839 German physiologist
Theodor Schwann, after a
lovely dinner with his mate
Schleiden and a chat about
nuclei, realised that animals
were comprised of cells too
and stated: “All living things
are composed of cells and
cell products”
He was also responsible for the discovery of Schwann cells in the PNS, pepsin in
the gut, the fact that yeast is organic… and he made up the word ‘metabolism’.
What a legend! Or, as they say in German, legende!
http://en.wikipedia.org/wiki/File:Schwann_Theodore.jpg

11. Robert Remak: http://en.wikipedia.org/wiki/Robert_Remak
1855 Robert Remak discovers cell division and confirms the existence
of the plasma membrane. Cells come only from pre-existing cells.
German doctor, pathologist and biologist Rudolf Virchow
plagiarized Remak’s work and got most of the credit…
(A.K.A. the father of modern pathology)

12. Image from Amoeba Mike’s Blog (go read the original post): http://amoebamike.wordpress.com/2009/10/06/spontaneous-
generation-a-brief-history-of-disproving-it
1864
Pasteur disproves the prevailing theory of “spontaneous
generation” with his swan-neck flask experiments.
Populations need to be seeded by existing populations: cells come
only from pre-existing cells.

15. 1.1.1 According to the cell theory, living organisms are composed of cells
Cells vary in many ways within and
between organisms, but some things
are common to all cells…
• Surrounded by a membrane
• Contain genetic material (DNA)
• Contain enzymes to catalyze
chemical reactions within the cell
• Have an energy-release system (or
metabolism)

16. 1.1.2 Organisms consisting of only one cell carry out all functions of life in that cell
All cellular organisms carry out the following
functions of life:
• Metabolism (chemical reactions that release energy for cellular use)
• Reproduction (either asexual or sexual)
• Homeostasis (maintain stable internal conditions)
• Growth
• Response to the environment
• Excretion (removal of waste)
• Nutrition (Obtaining food needed for energy & growth)

17. 1.1.2 Organisms consisting of only one cell carry out all functions of life in that cell

18. Sugar Cubes by Uwe Hermann on Flickr (CC) http://flic.kr/p/cFMMc
Which dissolves faster: sugar
cubes or sugar crystals? Why?

19. What will go cold faster: French
fries or a baked potato? Why?
French Fries by Ian Britton on Flickr (CC) http://flic.kr/p/6RLQ8j

20. 1.1.3 Surface are to volume ratio is important in the limitation of cell size

31. As the cell gets larger, it requires
more resources to be imported and
produces more products (and waste)
to be exported.
Therefore, a larger volume requires
more exchange across the membrane.
http://commons.wikimedia.org/wiki/Sphere

32. http://commons.wikimedia.org/wiki/Sphere
As the cell gets larger…

33. http://commons.wikimedia.org/wiki/Sphere
As the cell gets larger…
…the surface area to
volume ratio
actually gets
smaller…

34. http://commons.wikimedia.org/wiki/Sphere
As the cell gets larger…
…the surface area to
volume ratio
actually gets
smaller…
…so the
exchange
processes
become less
efficient with
increasing size.

35. http://commons.wikimedia.org/wiki/Sphere
Diffusion Pathways
are shorter (and
more efficient)
in
with a larger
surface are to
volume ratio.

36. Cells can get around this problem by
growing projections, having a flattened
form, or being long and thin.
Multicellular organisms have developed
circulatory systems to deliver nutrients
and oxygen and remove wastes.
Exchange structures with large surface
areas, such as the lungs and the gut,
have evolved.

38. http://en.wikipedia.org/wiki/Caulerpa
Big Cell Exceptions
Caulerpa species of algae are
one giant cell with many
nuclei distributed throughout.

40. Emergent Properties
Photo by Stephen Taylor: http://www.flickr.com/photos/gurustip/9668701965/in/photostream
the whole is
more than the sum
of its parts

41. 1.1.4 Multicellular organisms have properties that emerge from the interaction of their cellular
components

44. 1.1.5 Specialized tissues can develop by cell differentiation in multicellular organisms
• 220 recognized, different
highly-specialized cells
types in humans
• EX: Rod cells in retina of
the eye are light-sensitive
• EX: Red blood cells carrying
oxygen and nutrients
• Groups of similar cells form
tissues (epithelial, muscle,
connective, and nervous)

45. Screenshot from this excellent tutorial: http://www.ns.umich.edu/stemcells/022706_Intro.html
Differentiation (specialization) of cells:
All diploid (body) cells have the same chromosomes.
So they carry all the same genes and alleles.
BUT
Not all genes are expressed (activated) in all cells.
The cell receives a signal.
This signal activates or deactivates genes.
Genes are expressed accordingly and the cell is committed.
Eventually the cell has become specialized to a function.
Key Concept: Structure v. Function
How do the structures of specialized cells reflect their
functions? How does differentiation lead to this?
1.1.6 Differentiation involves the expression of some genes and not others in the cell’s genome

46. 1.1.8 Question the cell theory using atypical examples, including striated muscle,
giant algae and aseptate fungal hyphae

47. • Exception #1: Muscle Fiber
• Muscle fibers are much larger
than normal animal cells and
may have as many as several
hundred nuclei per “cell”

48. • Exception #2: Fungal Hyphae
• In some fungi, each hypha is a single, long tube structure with
many nuclei

49. • Exception #3: Giant Algae
• Can grow as large as 100mm (!)
yet only has one nucleus
• An organism this size would be
expected to be made up of
many cells…

50. 1.1.9 Investigate functions of life in Paramecium and one named photosynthetic
unicellular organism
• Nucleus replicates for asexual reproduction once cell
grows large enough
• Membrane maintain homeostasis, takes in nutrients,
and excretes wastes
• Metabolic reactions occur in the cytoplasm where
enzymes are
• Contractile vacuoles maintain stable water levels in cell
• Flagella and cilia allow for movement in response to
environment

51. Source: http://umanitoba.ca/Biology/BIOL1030/Lab1/biolab1_3.html#Ciliophora
Homeostasis – contractile vacuole fill up
with water and expel I through the plasma
membrane to manage the water content
Reproduction – The
nucleus can divide to
support cell division by
mitosis, reproduction is
often asexual
Metabolism –
most
metabolic
pathways
happen in the
cytoplasm
Growth – after consuming
and assimilating biomass
from food the paramecium
will get larger until it divides.
Response – the
wave action of
the cilia moves
the
paramecium in
response to
changes in the
environment,
e.g. towards
food.
Excretion – the plasma
membrane control the entry
and exit of substances
including expulsion of
metabolic waste
Nutrition – food vacuoles
contain organisms the
parameium has
consumed
1.1.9 Investigate functions of life in Paramecium and one named photosynthetic
unicellular organism

52. Source: http://www.algae.info/Algaecomplete.aspx
Homeostasis –
contractile
vacuole fill up
with water and
expel I through
the plasma
membrane to
manage the
water content
Reproduction – The nucleus can divide
to support cell division, by mitosis (these
cells are undergoing cytokinesis)
Metabolism –
most
metabolic
pathways
happen in the
cytoplasm
Growth – after consuming and assimilating
biomass from food the algae will get larger until
it divides.
Response – the
wave action of
the cilia moves
the algae in
response to
changes in the
environment,
e.g. towards
light.
Excretion – the plasma
membrane control the
entry and exit of
substances including the
difussion out of waste
oxygen
Nutrition –
photosynthes
is happens
inside the
chloroplasts
to provide
the algae
with food
1.1.9 Investigate functions of life in Paramecium and one named photosynthetic
unicellular organism

53. 1.1.12 Use a light microscope to investigate the structure of cells and tissues.

54. Modern Microscopy
Image: d2540-6 by USDA on Flickr (CC): http://flic.kr/p/dPqvvY
As we develop more and
more sophisticated and
precise imaging tools, we can
see more detail of the cells
and molecules that make us.
Scanning electron
microscopes deliver high-
resolution, 3D surface
images of structures,
whereas transmission
electron microscopes give us
a view inside cells and
organelles.

55. Transmission electron micrograph of HIV particles.
HIV-1. Transmission electron micrograph, via wikimedia commons: http://commons.wikimedia.org/wiki/File%3AHIV-
1_Transmission_electron_micrograph_AIDS02bbb_lores.jpg
120nm

56. False-coloured scanning electron micrograph of HIV (green) budding on a lymphicoyte (blue)
http://en.wikipedia.org/wiki/File:HIV-budding-Color.jpg OR http://phil.cdc.gov/phil/details.asp?pid=10000
1μm
Scanning electron micrograph of HIV particles
budding on a human lymphocyte.

57. 1.1.13 Draw cell structures as seen with the light microscope.
• Draw in pencil
• Make the drawing at least 1/3 page large
• Label with straight lines with a ruler
• Lines must exactly touch the structure which is named
• Include a title
• Size of parts must be correct in relation to the larger drawing
• Print all labels horizontally on the drawing

58. 1.1.14 Calculate the magnification of drawings and the actual size of structures
shown in drawings or micrographs.

59. 5μm
Scanning electron micrograph of
human sperm and egg cells.
Image from wikimedia commons http://en.wikipedia.org/wiki/Spermatozoon

60. 2.1.4 Compare the relative size of molecules, cell membrane thickness, viruses,
bacteria, organelles and cells, using appropriate SI units
Use the
10x
rule
of
thumb
http://www.flickr.com/photos/sanna_nixi/799023133/

61. Molecules ≈ 1nm
Cell Membrane ≈ 10nm thick
Virus ≈ 100nm
Bacteria ≈ 1μm (1000nm)
Eukaryotic animal cell ≈ 10μm
Eukaryotic plant cell ≈ 100μm
http://www.flickr.com/photos/rogerss1/3520043134/
http://click4biology.info/c4b/2/cell2.1.htm#size
Of course, there are
numerous egg-ceptions.
For example,
the yolk of an
egg is a single
animal cell

63. Bibliography / Acknowledgments
Jason de Nys
Chris Paine