SL Chemistry of Life
-1-
Cells Unit Plan
Lesson
Page
Homework (in addition to competing
unfinished work from the lesson)
CELL THEORY
Pre- What is Life?
topic
1
Cell theory
6
Read textbook pages 12-13
7
Complete readings on stem cells (p.10) and
be ready for class discussion next lesson.
CELL STRUCTURE
3
4
5
6
7
8-9
10
Stem Cells
Prokaryotic cells
Eukaryotic cells
10
11
13
Sizes of cells and cellular structures
Practical: Microscopy
Practical: Microscopy
Limits to cell size
19
Practical: Surface Area to
Volume Ratio
Structure of cell membranes
Practical: Bubbles as membrane
models
Work through pages 13-15 of your booklet
Homework questions in booklet (p17) – due
next lesson
22
Textbook pages 68-69 Questions 3,6-9,
11,13,14,22,23
Complete pages 24-26 in this booklet.
24
Complete the questions on page 27 in the
booklet
TRANSPORT IN CELLS
11
12
13 15
16
Diffusion and Osmosis
Practical: Diffusion
Practical: Observing Osmosis
Practical: Osmosis
28
Active transport & Vesicles
29
Complete homework task at end of lesson
32
Complete “Revision” questions on page 32.
Write up lab report – due in 1 week
CELLULAR PROCESSES
17
18
19
Cell division
Practical: Studying Mitosis
Revision
UNIT TEST
SL Chemistry of Life
-2-
Topic 2 Syllabus Statements
2.1 Cell theory
2.1.1
Outline the cell theory.
2.1.2
Discuss the evidence for the cell theory.
2.1.3
State that unicellular organisms carry out all the functions of life.
2.1.4
Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells,
using the appropriate SI unit.
Include the following.
• Living organisms are composed of cells.
• Cells are the smallest unit of life.
• Cells come from pre-existing cells.
Include metabolism, response, homeostasis, growth, reproduction and nutrition.
Appreciation of relative size is required, such as molecules (1 nm), thickness of membranes
(10nm), viruses (100 nm), bacteria (1 µm), organelles (up to 10 µm), and most cells (up to 100
µm). The three-dimensional nature/shape of cells should be emphasized.
2.1.5
Calculate the linear magnification of drawings and the actual size of specimens in images of known
magnification.
Magnification could be stated (for example, ×250) or indicated by means of a scale bar, for
example: 1 µm
2.1.6
Explain the importance of the surface area to volume ratio as a factor limiting cell size.
2.1.7
State that multicellular organisms show emergent properties.
2.1.8
Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing
some of their genes but not others.
2.1.9
State that stem cells retain the capacity to divide and have the ability to differentiate along different
pathways.
Mention the concept that the rate of heat production/waste production/resource consumption of a
cell is a function of its volume, whereas the rate of exchange of materials and energy (heat) is a
function of its surface area. Simple mathematical models involving cubes and the changes in the
ratio that occur as the sides increase by one unit could be compared.
Emergent properties arise from the interaction of component parts: the whole is greater than the
sum of its parts.
2.1.10 Outline one therapeutic use of stem cells.
This is an area of rapid development. In 2005, stem cells were used to restore the insulation tissue
of neurons in laboratory rats, resulting in subsequent improvements in their mobility. Any example
of the therapeutic use of stem cells in humans or other animals can be chosen.
2.2 Prokaryotic cells
2.2.1
Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as an example of a prokaryote.
2.2.2
Annotate the diagram from 2.2.1 with the functions of each named structure.
2.2.3
Identify structures from 2.2.1 in electron micrographs of E. coli.
2.2.4
State that prokaryotic cells divide by binary fission.
The diagram should show the cell wall, plasma membrane, cytoplasm, pili, flagella, ribosomes and
nucleoid (region containing naked DNA).
SL Chemistry of Life
-3-
2.3 Eukaryotic cells
2.3.1
Draw and label a diagram of the ultrastructure of a liver cell as an example of an animal cell.
2.3.2
Annotate the diagram from 2.3.1 with the functions of each named structure.
2.3.3
Identify structures from 2.3.1 in electron micrographs of liver cells.
2.3.4
Compare prokaryotic and eukaryotic cells.
2.3.5
State three differences between plant and animal cells.
2.3.6
Outline two roles of extracellular components.
The diagram should show free ribosomes, rough endoplasmic reticulum (rER), lysosome, Golgi
apparatus, mitochondrion and nucleus. The term Golgi apparatus will be used in place of Golgi
body, Golgi complex or dictyosome.
3 Differences should include:
• naked DNA versus DNA associated with proteins
• DNA in cytoplasm versus DNA enclosed in a nuclear envelope
• no mitochondria versus mitochondria
• 70S versus 80S ribosomes
• eukaryotic cells have internal membranes that compartmentalize their functions.
The plant cell wall maintains cell shape, prevents excessive water uptake, and holds the whole
plant up against the force of gravity.
Animal cells secrete glycoproteins that form the extracellular matrix. This functions in support,
adhesion and movement.
2.4 Membranes
2.4.1 Draw and label a diagram to show the structure of membranes.
The diagram should show the phospholipids bilayer, cholesterol, glycoproteins, and integral
and peripheral proteins. Use the term plasma membrane, not cell surface membrane, for the
membrane surrounding the cytoplasm. Integral proteins are embedded in the phospholipid
of the membrane, whereas peripheral proteins are attached to its surface. Variations in
composition related to the type of membrane are not required.
2.4.2
Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of
cell membranes.
2.4.3
List the functions of membrane proteins.
2.4.4
Define diffusion and osmosis. 1 Diffusion is the passive movement of particles from a region of high
concentration to a region of low concentration.
Osmosis is the passive movement of water molecules, across a partially permeable membrane,
from a region of lower solute concentration to a region of higher solute concentration.
2.4.5
Explain passive transport across membranes by simple diffusion and facilitated diffusion.
2.4.6
Explain the role of protein pumps and ATP in active transport across membranes.
2.4.7
Explain how vesicles are used to transport materials within a cell between the rough endoplasmic
reticulum, Golgi apparatus and plasma membrane.
2.4.8
Describe how the fluidity of the membrane allows it to change shape, break and re-form during
endocytosis and exocytosis.
Include the following: hormone binding sites, immobilized enzymes, cell adhesion, cell-to-cell
communication, channels for passive transport, and pumps for active transport.
SL Chemistry of Life
-4-
2.5 Cell division
2.5.1 Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis.
2.5.2
State that tumours (cancers) are the result of uncontrolled cell division and that these can occur in any
organ or tissue.
2.5.3
State that interphase is an active period in the life of a cell when many metabolic reactions occur, including
protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts.
2.5.4
Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and
telophase).
Include supercoiling of chromosomes, attachment of spindle microtubules to centromeres, splitting
of centromeres, movement of sister chromosomes to opposite poles, and breakage and reformation of nuclear membranes. Textbooks vary in the use of the terms chromosome and
chromatid. In this course, the two DNA molecules formed by DNA replication are considered to be
sister chromatids until the splitting of the centromere at the start of anaphase; after this, they are
individual chromosomes. The term kinetochore is not expected.
2.5.5
Explain how mitosis produces two genetically identical nuclei.
2.5.6
State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis.
SL Chemistry of Life
-5-
What is Life?
1.
2.
3.
4.
What makes something alive, or not?
Is a Bunsen flame alive? Give reasons for and against.
Can we classify cells as living? Why?
Are all cells alive? Explain
Read the article provided: “Life is …”
5. What is something new that you have learnt from the article?
6. What did you find interesting?
7. How do you think this article relates to our next topic on "Cells"?
SL Chemistry of Life
-6-
Cell Theory
IB Statements: 2.1.1-2.1.3, 2.1.7-2.1.10
Reading: Textbook pages 12-16
Cell Theory
There are three key generalizations that make up the cell theory:
 Living organisms are composed of cells
 Cells are the smallest unit of life
 Cells come from pre-existing cells
Development of the Cell Theory
A number of scientists contributed to the development of the cell theory.
ROBERT HOOKE (1665) examined pieces of cork through a microscope
and found it to be made up of many tiny boxes. He called these “cellulae”
which, in Latin, means small rooms. From this came the term “cells” that
we know today.
ANTON VAN LEEWENHOEK (1674) was a Dutch shopkeeper and a very
skillful lens maker. He observed very small “animalcules” in water from
ponds and rivers and in scrapings from his teeth. Within these
“animalcules” he observed what we know as nuclei.
ROBERT BROWN was a Scottish botanist. He noticed that plant cells, like animal cells, contain nuclei.
MATTHIAS SCHLEIDEN hypothesized that plants are made up of independent cells that work
together to allow the functioning of the whole organism.
MATTHIAS SCHLEIDEN later worked with THEODORE SCHWANN (1838). Together they proposed
the idea that both plants and animals are made up of cells that contain nuclei and cell fluid.
RUDOLF VIRCHOW was a physiologist who made studies of the growth and reproduction of cells. He
determined that “ominis cellula e cellula” (that is: All cells come from cells)

What piece of technology needed to be developed before any of the observations described above
could be made?
SL Chemistry of Life
-7-
Hypotheses and Theories
The cell theory (and our understanding of life) is based on observations. In fact all of our understanding
of the world is based on evidence gathered from observations and experiments. These observations
allow us to generate hypotheses – specific predictions that can be tested by experimentation. Theories
are based on an accumulation of evidence and are a more general group of ideas used as an explanation
for something. If evidence is obtained that cannot be fully explained by the theory, then the theory
needs to be modified or replaced.
Consider the following questions (adapted from Biology Course Companion by Allott and Mindorf) and discuss
your ideas with a partner.
1. Can we prove that all living things are composed of cells? How can we obtain evidence for this
part of the cell theory?
2. The statement that all cells come from pre-existing cells implies that life has always existed. Is
this possible? If it isn’t possible, do we need to discard this part of the theory?
3. Discuss the cell theory as it relates to the following observations.
a. Some fungi consist of narrow, tubular hyphae, containing
cytoplasm and many nuclei. They are surrounded by walls of
chitin but there are no membranes or wall dividing up the long
tubes.
b. Muscle cells, called fibres, are large structures, surrounded by a single membrane and
containing many nuclei.
c. Bone tissue contains a few scattered cells separated by large
amounts of acellular or extracellular matrix, made of proteins and
semi-crystalline minerals.
Characteristics of Life
The cell theory states that cells are the smallest units of life. Cells contain organelles (discreet units that
carry out a specific function) that carry out the processes that classify the cell as being “alive”. All
unicellular organisms are able to carry out these life processes.
 What are these processes?
SL Chemistry of Life
-8-
Cell Function and Differentiation
Unicellular (one cell) organisms are able to carry out all the functions of
life. Some unicellular organisms live together in colonies. The cells may
work cooperatively but they are not dependent on each other and so do
not function as a single, multicellular organism.
Volvox aureus is a colony of
green algae. Each dot is a
cell. Within the colony
‘daughter’ colonies are
forming.
A colony of 32 Pandorina (a green
algae) cells held together by a
jellylike substance. Each cell can
survive independently of the others.
To reproduce, each cell divides,
producing a new cell inside, and
then the parent colony breaks apart.
In multicellular (many cells) organisms, cells tend to differentiate early in development and become
specialized to carry out certain functions. They do this by switching off some genes and only expressing
those relevant to the function that they will perform. This process of differentiation occurs very early on
in development.
Use the Bioviewer to look at a number of different types of cells.
 In what ways do these cells differ?

In what ways are they the same?

Choose one of these cells and describe how its structure might relate to its function.
Emergent properties of multicellular organisms
Emergent properties arise from the interactions of component parts: the
whole is greater than the sum of its parts. (Syllabus)
Traditionally, in science, phenomena have been reduced to their basic components and studied; the idea
being, that in understanding each individual part, we will understand the whole. Systems biology
contends that emergent properties cannot be fully understood in isolation. We need to understand the
biological system as a whole. This can be likened to fully understanding a movie: we cannot do so if we
only watch a few scenes, rather, we need to watch the whole movie.
 Can we consider life itself an emergent property? Why?
“Life is not inherent in any single element constituting the living cell. DNA is not alive, neither
are proteins, carbohydrates or lipids. Indeed, for a single short moment, a living cell and a dead
cell may, upon analysis, be found to contain precisely the same catalogue of ‘dead’ chemicals in
identical concentrations…What distinguishes the living from the dead? Nothing more than actions
and interactions. Life emerges from inert matter as a consequence of metabolism, the continuous
transfer of energy and information systematically packaged in cells in a way that leads to selfperpetuation. The complexity of dynamic behaviour that generates metabolism, growth and
genetic inheritance is what we call life.”
SL Chemistry of Life
-9-
Excerpt from “Tending Adam’s Garden: Evolving the Cognitive Immune Self” by Irun Cohen
Stem Cells
Stem cells retain the capacity to divide and have the ability to differentiate along different pathways. At
an early stage of development a human embryo consists of stem cells but these then differentiate and
become specialized. These cells can still divide but the have become committed to the differentiated
path they took and resulting cells are no longer considered stem cells. Some stem cells may still be
found in the adult body (e.g. in bone marrow, skin and liver)
but they don’t have the same unlimited growth potential as
embryonic stem cells.
The therapeutic potential of stem cells is one of the major
research focuses in the scientific community. Stem cells
have the potential to be used for tissue repair and for
treating a variety of degenerative conditions such as
Parkinson’s disease and Multiple Sclerosis. In 2005, stem
cells were introduced into the injured spinal cords of rats, in
order to repair the myelin sheath around the nerve cells
necessary for nerve function. Some mobility was restored to
the rats, although there were side effects such as increased
pain sensitivity.
Stem cells from bone marrow can be used to treat acute
leukemia, SCID (severe combined immune deficiency) and
lymphoma. This is possible because stem cells found in
bone marrow are responsible for producing the many types
of blood cells found in the body. The diagram below shows how treatment is carried out.
Homework
 Read the information about stem cells on the website:
http://click4biology.info/c4b/2/cell2.1.htm#stem

Then download Powerpoint ‘Stem Cells’ from Moodle. Read through this as well and be prepared
to discuss the therapeutic uses and ethical issues concerning stem cells.
SL Chemistry of Life
- 10 -

Another interesting article is ‘Instant Expert: Stem Cells’ from New Scientist. It can also be
downloaded from Moodle.
SL Chemistry of Life
- 11 -
Prokaryotic Cells
IB Statements: 2.2.1-2.2.4
Reading: Textbook pages 16 - 19
Cells can be categorized into two groups – prokaryotes and eukaryotes. Prokaryotic cells include
bacteria. Plant and animal cells are eukaryotes. Eukaryotic cells that have membrane bound organelles
whereas the organelles of prokaryotic cells are not surrounded by membranes.
 Organelles are structures within the cell that carry out a specific function.
Most organelles cannot be seen using a light microscope; the magnification is not great enough. They
can only be viewed using an electron microscope. Below are diagrams of the main structures that can be
seen in prokaryotic cells using an electron microscope.
Prokaryotic Cells
This introduction to prokaryotic cells will be based on one of the best known bacteria, Escherichia coli.
These particular bacteria are rod shaped, but prokaryotes come in a variety of shapes, including spheres,
branched rods, spirals, club shaped rods and spheres (coccus). They may also exist as individuals or as
colonies.
Pili
Plasma
membrane
Cytoplasm
Cell wall
Ribosome
Flagella
Nucleoid
SL Chemistry of Life
- 12 -
Replication of Prokaryotes
Bacteria replicate (reproduce) by
binary fission. The cell replicates its
ribosomes, enzymes, and other cell
components in the cytoplasm, and
duplicate their DNA. Then, new plasma
membrane and cell wall material is laid
down along middle of the cell between
the two sets of DNA. The cell then
splits down the midline into two cells.
Use the internet and book resources in the room to complete the table below.
Structure
Nucleoid
Features
Region of cytoplasm that contains
DNA that is circular and naked (not
associated with proteins)
Cell wall
Plasma membrane
Cytoplasm
Ribosome
Pili
Flagella
SL Chemistry of Life
- 13 -
Function
DNA is the genetic/hereditary material
of the cell
Eukaryotic Cells
IB Statements: 2.3.1-2.3.6
Reading: Textbook pages 19 - 29
Cells can be categorized into two groups – prokaryotes and eukaryotes. Prokaryotic cells include
bacteria. Plant and animal cells are eukaryotes. Eukaryotic cells that have membrane bound organelles
whereas the organelles of prokaryotic cells are not surrounded by membranes.
 Organelles are structures within the cell that carry out a specific function.
Most organelles cannot be seen using a light microscope; the magnification is not great enough. They
can only be viewed using an electron microscope. Below are diagrams of the main structures that can be
seen in eukaryotic cells using an electron microscope.
Eukaryotic cells will be introduced using the liver cell of animals as an example. However, it is important
that plant cells are also eukaryotic cells, and have a somewhat different structure which we will look at
later. The electron micrograph below shows a section of two liver cells (the junction between them is
marked).
Nucleus
Ribosome
Golgi apparatus
Lysosome
Nucleus
SL Chemistry of Life
- 14 -
Use the internet and book resources in the room to complete the table below.
Structure
Features
Nucleus
Mitochondrion
Free ribosomes
Rough endoplasmic reticulum
Golgi apparatus
Lysosome
SL Chemistry of Life
- 15 -
Function
Plant and Animal Cells
Identify each of the cells below as either plant or animal.
Comparing Plant and Animal Cells
Show similarities by colouring
them in red on both cell
diagrams.
Show differences by colouring the
relevant structure green.
http://biodidac.bio.uottawa.ca
If you are unable to show a
similarity or difference on the
diagram, then write about it in a
space on this page.
http://biodidac.bio.uottawa.ca
SL Chemistry of Life
- 16 -
Extracellular Components
e.g. Plant Cell Wall
After watching the demonstration, suggest purposes for cell walls in
plants.



Cell walls are complex structures consisting of cellulose microfibrils
surrounded by a meshwork of hemicellulose, pectin and proteins. Some plant cells will impregnate their
cells with lignin – this is what makes them woody.
e.g. Extra Cellular Matrix
Below is an article about the extracellular matrix of animal cells by Carolyn Strange.
Consider a slab of meat – or an intact animal, for that matter. Why don’t their cells and tissues slip past
each other, flowing into a puddle a few cells deep? Cells in a tissue don’t only stick together – they work
together, and therefore must communicate. In multicellular animals, cells are intricately connected to
each other directly, and also via the extracellular matrix surrounding all cells – the ECM.
The ECM is not merely a passive scaffolding. Biologists are discovering that ECM molecules have striking
effects on cell behaviour. They influence shape, orientation and polarity, movement, metabolism and
differentiation. “Half the secret of life is outside the cell”, according to Zena Werb, an anatomy professor
at the University of California San Fancisco.
1. Major changes in the way that
“What really tells the cells to remember who they are?
scientists understand the natural
Why is your nose your nose, and your elbow your elbow,
world are sometimes called paradigm
and why don’t they turn into each other?” asks Mina
shifts. Explain the paradigm shift that
Bissell, director of the Life Sciences Division at Berkeley.
has occurred in our understanding of
She hypothesized more than 15 years ago that ECM
the ECM.
possesses information crucial to the cell’s ability to
2.
Why do paradigm shifts take decades
function properly. Although not widely embraced at the
to be accepted by all of the scientific
time, the idea is finally catching on as evidence mounts to
community?
support it. Frustrated with reductionist approaches, some
3.
Explain what is meant by
researches say that it is time to wade in and explore the
“reductionist approaches”.
complexity. “In the traditional view, the cell was his unit
4.
What other possible approach is
by itself and the matrix was something else”, says Fredrick
there?
Grinnell, of the University of Texas Southwestern Medical
5.
What is the best approach to
Center. “Its actually quite difficult to say where the edge
investigation for a biologist?
of the cell is.” The nature, composition, and amount of
ECM is tailored to the specific tissue. Tissue like bone and
cartilage contain more matrix than cells. One common ECM protein is collagen, which accounts for
approximately a third of a vertebrate’s dry weight.
ECM is made and oriented by the cells within it and takes two general forms. Interstitial matrix is a threedimensional gel that surrounds cells and fills space. The other form, basement membrane, is a mesh-like
sheet formed at the base of epithelial tissues, the thin layer of cells that cover internal and external
surfaces of the body and that perform protective, secretory, or other functions. Basement membrane is a
remarkable cellular organizer. In culture on plastic, the cells just sit in a layer, but when you put them on
basement membrane they differentiate. The cells that line blood vessels form capillary-like tubes all over
the culture dish. Neuronal cells send out long, thin extensions. Salivary gland cells join into little balls and
begin producing secretory proteins. Such behaviour is characteristic of normal cells. They do not grow
unless properly anchored to the matrix.
SL Chemistry of Life
- 17 -
Homework Questions
1. On the electron micrograph below of E. coli cells label a cell wall, plasma membrane, nucleoid,
cytoplasm, and ribosome.
2. In the electron micrograph above, what process has led to the two cells shown diagonally across the
picture?
3. On the electron micrograph below of liver cells, and on the diagram of a single liver cell, label a free
ribosome, rough endoplasmic reticulum (rER), lysomsome, Golgi apparatus, mitochondrion, nucleus and
plasma membrane.
4. Which type of cell, prokaryotes or eukaryotes, do you think evolved first? Why?
SL Chemistry of Life
- 18 -
5. Draw and label a diagram of the ultrastructure of E. coli.
6. Complete the table below based on what you now know about prokaryotic and eukaryotic cells.
Feature
Prokaryotic cells
DNA - form
DNA - location
Membranes
Ribosomes
Mitochondria
SL Chemistry of Life
- 19 -
Eukaryotic cells
Size of Cells
IB Statements: 2.1.4-2.1.5
Reading: Textbook pages 13 - 15
Size and Scale
The sizes of a variety of structures can be compared on the scale below. The scale is logarithmic where
each unit on the scale is 10 times bigger than the preceding unit. This allows us to compare a wide
variety of sizes on the same scale.
1m
10m
= 100cm
= 1000mm
= (1106m)
= 1109nm
1m
100mm
10mm
1mm
100m
10m
1m
100nm
10nm
1nm
0.1 nm
 Answer the following questions:
1. Approximately how many molecules wide is a cell membrane?
2. What fraction of the diameter of a bacterial cell is composed of cell membrane?
3. A student views a certain plant cell under the microscope and determines that it has a length of
100m. The chloroplasts it contains are each 3m long. If the cell is drawn with a length of
10cm, what will be the length of each chloroplast in the diagram?
4. An electron micrograph (14,000 magnification) shows a liver cell containing many mitochondria.
You measure a mitochondrion and find it to be to be 2.8cm long. What is its actual size?
SL Chemistry of Life
- 20 -
Investigating a knowledge claim …
“In the human body, for every one of our own cells there are ten prokaryote cells
resident in us.” (Black, J. Microbiology)
Does this seem like a reasonable claim?
Eukaryote cells are, on average, ten times larger, in a given dimension, than prokaryotic cells.
1. Obtain some plasticine (modeling clay).
2. Construct a model of a prokaryotic cell that is 5mm x 2mm x 2mm.
3. Use the plasticine to construct a model eukaryotic cell that is ten times larger in every dimension,
i.e. 50mm x 20mm x 20mm.
4. Compare the two models. Does the claim seem reasonable?
Viewing Cells
Cells are too small to see with the naked eye. Microscopes
are used to view cells and their contents. There are two
main types of microscopes – light microscopes and
electron microscopes. Light and electron microscopes
each have their own advantages and disadvantages,
however, the major difference is the magnifying power.
Electron microscopes allow for much greater magnification
of structures than light microscopes.
Magnification: refers to how much larger the image is
compared to the original object e.g. 40
Resolution: the ability to distinguish fine detail. It is
measured as the smallest distance between two points that
allows the points to be seen as separate from one another,
rather than blurred together as one image.
Light microscope
Field of View: The area of the specimen that is illuminated and can be viewed through the microscope.
Contrast: is necessary to distinguish objects from their backgrounds. It results from cells absorbing and
scattering light to various degrees.
Calculating Magnification
Often biologists need to carry out calculations to determine the size of specimens or the magnification of
their image or a drawing.
The size of a specimen is how large it actually is.
The image size is how large the specimen looks through the microscope, or in a drawing or photograph.
Magnification is how much bigger the image is compared to the specimen itself.
Magnification =
size of image
actual size of specimen
** make sure that all values have the same units/ metric prefixes
Magnification can be stated (e.g. x250) or indicated by means of a scale bar e.g.
Stage micrometer
SL Chemistry of Life
1m
To determine magnification, it will be necessary to know the actual size of the
specimen… but most rulers will not do the job! Stage micrometers are tiny scales
set on a microscope slide. They can be used to measure the diameter of the field
of view. Then, the size of structures seen in the field of view can be estimated.
- 21 -
 Consider the following:
A stage micrometer was used to determine that the diameter of a field of view was 2mm.
Estimate the length of one of the cells (they are all exactly the
same size).
Use the following information to determine the answers to each of the following questions.
Eyepiece
Objective
Total
Diameter of Field (approx. –
magnification should be measured for
of image
each microscope)
5000m
Low Power
10
4
Medium Power
10
10
2000m
High Power
10
40
500m
1. A cell is observed to stretch halfway across the high power field. How long is the cell?
2. A cell is observed under high power to be about half the field diameter. A student draws the cell
25 cm in length.
a. What is the magnification of the image?
b. What is the magnification of the drawing?
3. A student draws a cell diagram 24 mm long. She writes 400X below the diagram. How large is
the actual cell?
4. A cell is 80 m in length. If drawn 600X actual size, how long with the drawing be in cm?
5. Five onion cells are counted across the center of the high power field. One cell is drawn 18 mm
long. Calculate the drawing magnification.
6. 40 potato cells are counted across the center of the medium field of view. One cell is drawn 2
cm long. What is the drawing magnification?
SL Chemistry of Life
- 22 -
Limits to Cell Size
IB Statements: 2.1.6
Reading: Textbook pages 13 - 14
Activity: Heat Loss
Complete the activity on heat loss from different sized conical flasks (see separate instruction sheet)
Why Aren’t Cells Larger?
1. Rate of metabolism
a. Production of heat from respiration, waste products & resource consumption
b. Function of volume of the cell
c. Larger cells (e.g. eggs) tend to be inert  low or zero rate of metabolism
2. Transport of substances within the cell
a. The larger the cell, the greater its volume
b. Therefore, the further substances must move
3. Exchange of materials and energy
a. Getting things in and out of the cell
b. Occurs across cell membrane
c. Surface area of membrane determines rate of exchange
Surface area-to-volume ratio
As a cell’s size increases, its volume increases much more rapidly than its surface area.
Cell radius
Surface area (4r2)
Volume (4/3r3)
1 cm
12.57 cm2
4.189 cm3
10 cm
1257 cm2
4189 cm3
Note: as the cell radius increases 10X, the S.A. increases _______ and the volume increases ________.
Small cells have more surface area per unit volume and so can function more effectively.
The surface area to volume ratio of a cell is very important. If it is too small then substances won’t be
able to enter the cell as quickly as they are required and waste products will accumulate inside the cell
as they cannot be removed quickly enough. This also applies to heat loss from cells. Respiring cells
produce heat as a waste product that must be able to escape from the cell.
 What would be the consequences of cells not being able to lose heat quickly enough?
SL Chemistry of Life
- 23 -
Questions
1. Calculate the surface area and volume for each cell (block). Record your results in a table.
2. Calculate the surface area-to-volume ratio for each cell. Record your results in your table.
3. Anything that the cell takes in, like oxygen and food, or lets out, such as carbon dioxide, must go
through the cell membrane. Which measurement of the cells best represents how much cell membrane
the models have?
4. The cell contents, nucleus and cytoplasm, use the oxygen and food while producing the waste. Which
measurement best represents the cell content?
5. As the cell grows larger and gets more cell content, will it need more or less cell membrane to
survive?
6. As the cell grows larger, does the Total Surface Area -to- Volume Ratio get larger, smaller, or remain
the same?
7. Which size cell has the greatest Total Surface Area -to- Volume Ratio?
8. Why can't cells survive when the Total Surface Area -to- Volume ratio becomes too small?
9. Which size cell has the greatest chance of survival? Explain.
SL Chemistry of Life
- 24 -
Membranes
IB Statements: 2.4.1-2.4.3
Reading: Textbook pages 29 - 38
Membranes consist of a phospholipids bilayer, with molecules embedded in and attached to it.
Phospholipid bilayer
Phospholipids
Head
Fatty Acid
tails
NON-POLAR
- hydrophobic
POLAR
- hydrophilic
- forms H-bonds
with water
Phospholipid Bilayer
 Non-polar tails pack together to avoid contact with
water
 Polar heads orient towards water to form H-bonds
with non-polar tails forming the lipid bilayer
o form spontaneously in water
o prevents passage of water-soluble
substances through the membrane (sugars,
amino acids and proteins can’t pass
through)
o Proteins extend through the membrane to enable
these molecules to pass
 H-bonds make the lipid bilayer stable
Structures formed by lipids when immersed in water
SL Chemistry of Life
- 25 -
A micelle
Membrane Structure
In the early 1970’s S.J. Singer and Garth Nicolson proposed the fluid mosaic model to describe the
structure of cell membranes. The lipid bilayer is fluid in nature with the lipid molecules being able to
move around. Proteins are embedded in the lipid bilayer, much like a mosaic, and are able to diffuse
laterally (sideways).
The fluid mosaic model of a cell membrane
 Some questions to discuss …
1. In the case of the fluid mosaic model, the word model is used to mean a type of hypothesis.
What is the advantage to scientists of developing a model or hypothesis?
2. Suggest what happens in the period after a model or hypothesis has been developed.
3. The fluid mosaic model does not explain all phenomena occurring in membranes. For example:
a. Some lipids group together (in domains) in the membrane and cannot move around
independently.
b. Some proteins associated with these domains are restricted to that area and cannot move
outside of the domain.
c. Some membrane proteins are not free to move as they are anchored to proteins inside
the cell or other membrane proteins.
d. Some membrane proteins are arranged in non-random patterns.
What are the implications of the model not addressing all such conditions in the membrane?
SL Chemistry of Life
- 26 -
6
3
OUTSIDE
CELL
7
4
2
Use the information in this booklet and on the Click4Biology website
(http://www.patana.ac.th/secondary/science/c4b/2/cell2.4.htm#structure ) to complete the table below.
Cell Membrane Structures and their Functions
1
CYTOPLASM
5
3
Use this website (http://www.patana.ac.th/Secondary/science/c4b/2/cell2.4.htm#structure) and what
you have learnt this lesson to complete the table below.
Structures found in membranes and their functions
Structure
Purpose
1
2
3
4
5
6
7
SL Chemistry of Life
- 27 -
Functions of Membrane Proteins
Membrane proteins have a variety of functions. These include
 Hormone binding sites
 Immobilized enzymes (i.e. enzymes that are unable to move around freely)
 Channels for passive transport
 Pumps for active transport
 Cell adhesion
 Cell-to-cell communication
Transport
Hormone binding site
Enzyme
X
Evidence for the fluid mosaic model
Y
% of cells with markers fully mixed
after 40 minutes
In 1970 L.D. Frye and M. Edidin carried out an experiment that supplied evidence
for the fluid nature of membranes. The surface proteins of mouse and human cells
were tagged with fluorescent markers, red for human cells, and green for mouse
cells. The human and mouse cells were then forced to fuse together to produce
hybrid cells. At first the proteins were detected in different halves of the cells (one
green hemisphere and one red hemisphere). However, after 40minutes of
incubation, the proteins were completely mixed over the surface of the
membrane. It
100
was also found
90
that inhibition of
80
protein synthesis
70
and blocking of
60
ATP (supplies
50
energy for active
40
processes)
30
production did
20
not prevent the
© 2000 by Geoffrey M. Cooper
10
mixing.
0
1. Describe the trends shown in the graph for
0
5
10
15
20
25
30
35
40
the temperatures:
incubation temperature ( C)
a. between 15 and 30C.
b. below 15C.
2. Predict, with reasons, the results of the experiment if it was repeated using cells from Artic fish rather than
from mice or humans.
3. What can you conclude from each of these experimental pieces of evidence?
a. when the cells were kept at normal body temperatures for mouse and human cells, the red and
green markers became mixed.
b. Blocking ATP synthesis in the cells did not prevent the mixing of the red and green markers.
c. Inhibition of protein synthesis
SL Chemistry of Life
- 28 -
Transport Across Membranes
IB Statements: 2.4.4-2.4.8
Reading: Textbook pages 33 - 38
Membrane Permeability
Membranes are partially permeable – they let some substances through but not others.
Passive Transport
In passive transport molecules are moved down their concentration gradients – therefore no energy is
required.
Diffusion is the passive movement of particles from a region of high concentration to a region of low
concentration.
Diffusion across a membrane is a form of passive transport. Many of the molecules that are used by
cells in their metabolism are polar and therefore cannot cross the non-polar interior of the phospholipid
bilayer. There are special channels in the membrane that allow these molecules to pass through.
Channel Protein
Simple Diffusion
 e.g. transport of O2 and CO2
Carrier Protein
Facilitated Diffusion
 protein channels assist in moving molecules across the
membrane
 these transporters are molecule specific (hence,
membranes are “selectively permeable”)
 channel proteins are simply a gateway (e.g. for water,
ions)
 carrier proteins bond with the molecule to be
transported – this causes a shape change in the carrier
protein so that it opens towards the inside – the molecule
is released inside the cell (e.g. for glucose)
Osmosis is the passive movement of water across a partially permeable membrane from a region of low
solute concentration to a region of high solute concentration.

Use arrows to show the movement of water in each situation below.
What name is given to each solution in the beakers?
SL Chemistry of Life
- 29 -
Look at the diagram showing how red blood cells
respond to being placed in solutions of different
concentrations.
 What implications does it suggest for cells in our
body?

What does our body need to do to avoid the
problems shown in the diagram?
Osmosis in red blood cells
Elodea (also known as Canadian pond weed) is a
freshwater plant. The photo shows what happens to
its cells when it is placed in salt water.
You can see the cell walls and how the plasma
membrane has shrunk away from the walls.
 Explain why this has happened.
These cells are described as ‘flaccid’. The opposite of
this, when they are full of water is referred to as
‘turgid’.
 What could be done to the Elodea plant to make
its cells turgid?
Plasmolysis in Elodea cells
http://www.wisc-online.com/objects/index_tj.asp?objID=AP11003
Active Transport
Active transport is used to move molecules up their concentration gradient – therefore energy is
required. The process is similar to that for carrier proteins but ATP is required for the shape change of
the protein to occur.
e.g. The Sodium-Potassium Pump – moves Na+ out of the cell and K+ into the cell. On the next page is a
diagram outlining how the Sodium-potassium pump works. Write a description for each step shown in
the diagram.
SL Chemistry of Life
- 30 -
SL Chemistry of Life
- 31 -
Transport Using Vesicles
The plasma membrane is essentially the same as the membranes of the nuclear envelope, Golgi
apparatus and the rough endoplasmic reticulum. This means that sections of membrane can be
exchanged, which allow substances to be transported around the cell, as well as into and out of the cell.
The Golgi apparatus is responsible for packaging substances for export. It does this by exocytosis wrapping a small piece of membrane around the substance, which can then join with the plasma
membrane. Similarly, substances can be moved from the rough ER to the Golgi apparatus. The process
of endocytosis brings substances into the cell.
Activity
How do cells egest large particles? Some particles are so large that they cannot be transported across a
membrane. The large particles are often fuel molecules required for the normal metabolism of all cells.
This activity is intended to simulate exocytosis as observed in eukaryotic cells.
Materials:
1 plastic shopping bag
1 pair of scissors
15 cm of string
2 pieces of wrapped candy
Your Challenge:
Use the above materials to get your 2 pieces of candy out of the bag according to the following rules:
1.
2.
3.
4.
The
The
The
The
candy must exit through a solid part of the bag.
inside of the bag may not be directly open to the external environment.
candies leaving the bag must remain clustered together.
candy may be eaten only if it leaves the “cell” under the specified conditions
Homework
Draw an annotated diagram below to show the processes of endocytosis and exocytosis. You should also
explain how the fluidity of the membrane allows it to break and reform during these processes.
**Note: Your textbook (pages 37-40) and the website below may be helpful with this task.
http://highered.mcgraw-hill.com/olc/dl/120068/bio02.swf
http://www.wisc-online.com/objects/index_tj.asp?objID=AP11203
SL Chemistry of Life
- 32 -
Cell Division
IB Syllabus Statements: 2.5.1 – 2.5.6
Reading: Textbook pages 38 - 42
Earlier in this unit we determined that for something to be considered alive, it had to be able to
reproduce itself and have some sort of heritable material. This lesson focuses on the life cycles of cells
and how they replicate themselves. Cells can replicate (make identical copies of) themselves through the
process of mitosis. The heritable material in cells is DNA. In eukaryotic cells, the DNA is associated with
a number of proteins to form chromosomes. In prokaryotic cells the DNA does not have any associated
proteins (hence, it is referred to as ‘naked DNA’).
You have been given some focus questions to guide you through research on this topic. Some websites
with the relevant information have been suggested, and your textbook will also be helpful.
You should read through all of the information from the websites with the focus questions in mind (not
all of the information will be relevant – the questions will help you to decide what is). You should then
write your own set of notes, ensuring that answers to all of the focus questions are included. You can
organize your notes however you like but they should be in your own words (no cut and paste!).
Diagrams will be useful in summarizing information.
Cell Cycle
1) What is the cell cycle?
2) What happens during each phase (interphase (G1, S, G2), mitosis and cytokinesis) of the cell cycle?
http://www.cellsalive.com/cell_cycle.htm
http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/cells2.html
http://www.biologymad.com/ - AS Biology  Module 2  Cell Division  Topic Notes  Cell Cycle
http://highered.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::525::530::/sites/dl/free/0072464631/291136/cellCycle.swf:
:cellCycle.swf
Mitosis
1) For what reasons does mitosis occur in living organisms?
2) What are the four phases of mitosis and what happens in each phase?
*Include supercoiling of chromosomes, attachment of spindle microtubules to centromeres, splitting of
centromeres, movement of sister chromosomes to opposite poles, and breakage and re-formation of nuclear
membranes.
3) How do daughter cells compare to the parent cell? If the cell below were to divide by mitosis, draw
in how the two new nuclei would look.
http://www.cellsalive.com/mitosis.htm
http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/main.html
http://www.biologymad.com/ - AS Biology  Module 2  Cell Division  Topic Notes  Mitosis
http://www.accessexcellence.org/AB/GG/mitosis.html
http://biologyinmotion.com/cell_division/index.html
Mitosis out of control
Tumors form when cells divide uncontrollably. This type of cancer can occur in any organ of the body.
SL Chemistry of Life
- 33 -
Check your understanding
Go to the syllabus statements for this topic and check that you have all the information you need and
that you could respond to each of the statements.
SL Chemistry of Life
- 34 -
Revision
1. If a red blood cell has a diameter of 8 m and a student shows it with a diameter of 40 mm in
a drawing, what is the magnification of the drawing?
A.
× 0.0002
B.
× 0.2
C.
×5
D.
× 5000
2. Discuss possible exceptions to the cell theory. (4 marks)
3. What is the function of a plasmid?
A. The site of respiration in prokaryotes
B. The site of photosynthesis in eukaryotes
C. The site of protein synthesis in prokaryotes and eukaryotes
D. The site of hereditary material in prokaryotes
4. The diagram below shows the structure of a cell.
III
I
II
× 90 000
(a)
State the names of I. (1)
(b)
Calculate the actual length of the cell, showing your working. (2)
(c)
State the function of the structure labelled III. (1)
(d)
Deduce which type of cell is shown in the diagram, giving reasons for your answer. (2)
5. What is essential for diffusion?
A. A concentration gradient
B. A selectively permeable membrane
C. A source of energy
D. A protein
SL Chemistry of Life
- 35 -
6. In the diagram below macromolecules are being transported to the exterior of a cell.
What is the name of this process?
A. Exocytosis
B. Pinocytosis
C. Endocytosis
D. Phagocytosis
7.
8.
(a)
Distinguish between diffusion and osmosis. (1)
(b)
Explain how the properties of phospholipids help to maintain the structure of the cell
surface membrane. (2)
(c)
State the composition and the function of the plant cell wall. (2)
Draw diagrams to show the four stages of mitosis in an animal cell with four chromosomes. (5)
ANSWERS
1.
D
2.
skeletal muscle fibres are larger / have many nuclei / are not typical cells;
fungal hyphae are (sometimes) not divided up into individual cells;
unicellular organisms can be considered acellular;
because they are larger than a typical cell / carry out all life functions;
some tissues / organs contain large amounts of extracellular material;
e.g. vitreous humour of eye / mineral deposits in bone / xylem in trees / other example;
statement of cell theory / all living things/most tissues are composed entirely of
true cells;
3.
D
4.
(a)
I: is the plasma membrane/cell (surface) membrane/phospholipid bilayer
(b)
size of drawing divided by magnification /figures using this equation;
(units not required)
Award [1] for working even if length measurement is incorrect.
1.41 (0.02) m; (units required)
Accept answers given in m, cm, mm and nm.
SL Chemistry of Life
- 36 -
[2]
[1]
(c)
protection / support / maintains shape / prevents bursting
(d)
bacterium/bacteria/prokaryote;
[1]
reason: [1 max]
as no nuclear membrane / no nucleus;
as no mitochondria / membrane bound organelles;
as mesosomes / small size / circular DNA;
(Do not accept naked DNA or no histone.)
Reject reasons if cell type is incorrectly identified.
5.
A
6.
A
7.
(a)
Must have both for [1].
diffusion is the movement of molecules from an area of high
concentration to an area of low concentration;
osmosis is the diffusion of water across a partially
permeable membrane;
(b) hydrophillic head groups point outward;
hydrophobic tails form a lipid bilayer;
forms a (phospholipid) bilayer;
ions and polar molecules cannot pass through
hydrophobic barrier;
helps the cell maintain internal concentration
and exclude other molecules;
(c)
8.
cellulose;
structural support / protection / maintain turgor pressure;
prophase showing spindle fibres;
prophase showing condensed chromatin;
prophase showing replicated chromosomes;
metaphase showing replicated chromosomes lining up at the equator;
anaphase showing chromatids moving to opposite poles;
telophase showing nucleus reforming;
telophase showing cytokinesis occurring;
[2 max]
[1]
[2 max]
[2]
5 max
The four diagrams must have the name of the phase, otherwise award [3 max].
The four stages must be included to receive [5]. If correct number of
chromosomes is not shown award [4 max].
SL Chemistry of Life
- 37 -