This is all you need to know for topic 2 if you're an IB student testing out of SL Biology!

1. Topic 2
Cells

2. Introducing Cells
• Consist of cytoplasm
• Enclosed in a plasma membrane
• Usually controlled by a single nucleas

3. Unicellular Organisms
• Single cell that carries out all the functions
of life:
– Metabolism (chemical reactions inside the
cell)
– Response (reacting to stimuli)
– Homeostasis (controlling internal conditions)
– Growth (increasing in size)
– Reproduction (producing offspring)
– Nutrition (obtaining food)

4. Multicellular Organisms
• Consist of many cells that are specialized
for one specific function
• Differentiation: cells become specialized to
carry out one process efficiently
• Emergent properties: the whole organism
is more than the sum of its parts due to the
complex interactions between cells

5. The Cell Theory
• Living organisms are composed of cells
• Cells are the smallest units of life
• Cells can only be made from pre-existing
cells

6. Differentiation
• Differentiation: cells develop in different
ways to carry out different functions
• The cells need different genes to develop
in different ways
– each cell has all of the genes available
• Once a pathway of development has
begun in a cell, it is usually fixed

7. Stem Cells
• Stem cells: cells that have the capacity to
self-renew by cell division and to
differentiate
• Human embryos consist entirely of stem
cells early on
• Interest in stem cells are due to their
potential for tissue repair and for treating a
variety of degenerative conditions
– i.e. Parkinson’s disease

8. Therapeutic Use of Stem Cells
• Stems Cells can be used therapeuticly
– Blood from an umbilical cord contains stem
cells
– Red blood cells are taken from the cord blood
and the remaining fluid is then tested
– Cord blood is matched to the patient’s tissue
type
– Cord blood is introduced into the patient’s
blood system
• Used for leukemia patients

9. Limitations to Cell Size
• Cells have a maximum size
– If a cell was too large its surface area to
volume ratio would be too small
• The rate at which materials enter/leave
cell depends on the surface area
• The rate at which materials are
used/produced depends on the volume

10. Units for Size Measurements
• 1 meter (m) = 1,000 millimeters (mm)
• 1 millimeter (mm) = 1,000 micrometer (µm)
• 1 micrometers (µm) = 1,000 nanometers (nm)

11. Calculating Magnification
• To calculate magnification:
1. Choose an obvious length and measure it on the
drawing
2. Measure the same length on the actual
specimen
3. Convert the units
4. Divide the drawing length by actual specimen’s
length
• Magnification = size of image ÷ size of object

12. Scale Bars
• Scale bar: Line added to a micrograph or
drawing to help show the actual size of the
structures

13. Ultrastructure of Cells
• Two types of cells: prokaryotic and
eukaryotic
• Prokaryotic cells have existed longer
• Prokaryotic cells reproduce by binary
fission: dividing in two

14. Functions of Parts of a Prokaryotic
Cell
Structure Function
Cell Wall Protective outer layer from external danger and bursting from
internal pressures.
Plasma
Membrane
Controls entry and exit of substances. Uses pumps for active
transport.
Cytoplasm Contains enzymes to catalyze metabolism reactions. Contains
DNA in the nucleoid.
Pili Hair-like structures protecting the cell walls that allow bacteria to
adhere and share information
Flagella Protein structures that project from the cell wall that rotate and
cause locomotion
Ribosomes Synthesize proteins by translating messenger RNA.
Nucleoid Contains naked DNA (the genetic information of the cell)

15. Comparing Prokaryotic and
Eukaryotic Cells
Feature Prokaryotic Cells Eukaryotic Cells
Type of genetic
material
Naked loop of DNA Chromosomes consisting of
strands of DNA associated with a
protein.
Location of
genetic
material
In the cytoplasm within the
nucleoid region
In the nucleus inside the nuclear
envelope
Mitochondria Not present Always present
Ribosomes 70s (smaller size) 80s (larger size)
Internal
Membranes
Few or none present Many present: endoplasmic
reticulum, Golgi apparatus,
lysosomes

16. Comparing Plant and Animal
Eukaryotic Cells
Feature Animal Plant
Cell wall No cell wall, only plasma
membrane
Both cell wall and
plasma membrane
Chloroplasts Not present Present in cells that
photosynthesize
Polysaccharides Glycogen is used as a
storage compound
Starch is used as a
storage compound
Vacuole Not usually present; few
and temporary
Large vacuole often
present
Shape Able to change shape;
usually rounded
Fixed shape; usually
rectangular

17. Fluid Mosaic Model of a Biological
Membrane

18. Phospholipids
• Phosphate heads are hydrophilic
– They are attracted to water
• Lipid tails are hydrophobic
– They are not attracted to water, but are
attracted to each other
• Phospholipids form double layers with
hydrophilic heads facing outward and lipid
tails facing inward
• Very stable, yet fluid

19. Fluidity of Membranes
• Phospholipids in membranes are in a fluid
state
• Allows membranes to change shape
• Allows vesicles to be pinched off from or
fuse with the membrane

20. Functions of Membrane Proteins
• Hormone bonding sites
• Protein pumps for Active Transport
• Channels for Passive Transport
• Cell-to-cell communication and cell
adhesion
• Enzymes

21. Diffusion
• Diffusion: the passive movement of
particles from a region of higher
concentration to a region of lower
concentration, as a result of the random
motion of particles
• Can occur across semi-permeable
membranes if there is a concentration
graident

22. Simple and Facilitated Diffusion
• Partially permeable membranes: allow some
substances to diffuse through, but not others
• Simple diffusion: when substances move
between the phospholipid molecules in the
membrane
• Facilitated diffusion: substances that are
unable to pass between phospholipids are
moved through using specific channel
proteins
• Both processes do not need to use energy

23. Osmosis
• Solvent: liquid in which particles dissolve
• Solutes: dissolved particles in solvent
• Osmosis: passive movement of water
molecules from a region of lower solute
concentration to a region of higher solute
concentration, across a partially
permeable membrane

24. Pump Proteins and Active
Transport
1. Particle enters pump from the side of lower
concentration
2. Particle binds to a specific site on the protein
pump
3. Energy from ATP changes the shape of the
pump
4. The change in shape allows the particle to
be released on the side of higher
concentration
5. Pump returns to its original shape

25. Endocytosis and Exocytosis
• Endocytosis: enters the cell
1. Part of membrane is pulled inwards
2. Fluid becomes enclosed when a vesicle is
pinched off
3. Vesicles can then move inside the cell
• Exocytosis: exits the cell
1. Vesicles fuse with the plasma membrane
2. Contents of vesicle are expelled
3. Membrane flattens out again

26. Extracellular Components
• Extracellular components: components
produced by cells that are placed outside
the plasma membrane using exocytosis
• Examples:
– Plant cell wall
– Glycoproteins
• Carbohydrate attached to a protein in plasma
membrane

27. Interphase
• Interphase is the longest phase of cell
cycle of Eukaryotes
• Interphase has 3 stages:
1. G1: period of growth, DNA transcription,
protein synthesis
2. S phase: period during which all DNA in the
nucleas is replicated
3. G2: period in which the cell prepares for
division

28. Mitosis
• Mitosis: process that divides nucleus into two
genetically identical nuclei
• Mitosis is used during growth, embryonic
development, repairing tissues, produce
asexually
• Mitosis has four phases:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
• Ends with cytokinesis

29. Prophase
• Spindle microtubules grow
• Move to extend from each pole to the
equator
• Chromsomes supercoil to become shorter
and fatter
• Each chromosome are made up of
identical chromatids held together by a
centromere

30. Metaphase
• The nuclear membrane brakes down
containing the chromosomes
• Chromosomes move to the equator
• Spindle microtubules attach to each
centromere (on opposite sides of the
centromeres)

31. Anaphase
• The centromeres divide and the two
cromatids have become chromosomes
• Spindle microtubules pull the genetically
identical chromosomes to opposite poles

32. Telophase
• Chromsomes reach the poles and nuclear
membranes form around them
• Spindle microtubules break down within
the membranes
• Chromosomes uncoil and are no longer
individually visible
• Two cells are formed with genetically
identical nuclei

33. Cytokinesis
• The process of dividing the cytoplasm to
form two cells at the end of mitosis

34. Tumors
• The genes in a cell change and so the
normal control of mitosis fails
• Repeated uncontrolled divisions produce a
mass of cells
• These cells are called a tumor
– Can happen in any organ or tissue
– Can spread to other parts of body
– Cancer: diseases caused by tumors