3.1
Week 3
Chemical Nature of Cells
Area of Study 1
Molecules of Life
Key knowledge
 Structure and properties of membranes
 The role of the organelles and plasma membranes in the packaging and
transport of bio-molecules.
Key skills
 Investigate and inquire scientifically
 Apply biological understandings
 Communicate biological information and understandings
Tasks this week relate to Outcome 1.
 Analyse and evaluate evidence from practical investigation related to
biochemical processes.
Relevant websites – see online biology course environment. Go to the Links
section.
Glossary terms for Week 3 can be found here:
http://quizlet.com/_d8tu
3.2
Chemical Nature of Cells
Please note:
Read carefully through this week’s work before completing the tasks. Check
for any practical exercises that may require you to obtain materials and
equipment.
This is Week 3 – your third week of work. You do not need a text book to
complete it. Make sure that you have ordered the required text book for
future weeks of work.
The Objectives
By the end of this week you should be able to:
 Describe the molecular structure of cell membranes.
 Outline the particular role of phospholipids in membranes.
 Describe the different ways that molecules cross membranes.
 Describe the role of the nucleus, ribosomes, endoplasmic reticulum,
Golgi apparatus and lysosomes in protein production, handling and
export.
 Describe the roles of the endoplasmic reticulum and Golgi apparatus
in the synthesis of other biomolecules.
 Make a model of the cell membrane.
Introduction
Read through the following text and complete the tasks or questions that
follow. Use your own A4 paper or send work as MSWord documents
attached to an email.
The following text is courtesy of Nelson Biology VCE Units 3 and 4, second edition .
Prokaryote – cells that
lack a membrane-bound
nucleus and other
membrane-bound
organelles: all bacteria
are prokaryotic cells.
Eukaryote – a cell with
a membrane-bound
nucleus and other
membrane-bound
organelles.
In this chapter we investigate the dynamic nature of cells at the molecular
level: how the major biomolecules of life are packaged and transported in
cells, and how they interact with others in a controlled and efficient way.
Cells produce substances that need to be modified and stored in special
compartments. Prokaryotic organisms – bacteria – have a simple
structure and lack these special compartments. In eukaryotic cells,
however, the internal structure is made up of various organelles, which
can be viewed as ‘membrane-bound’ compartments – they have
membranes that separate them from the rest of the cell and some have
membranes that fold within which are sites of chemical activity. These
organelles concentrate reactants and maximize the surface area by the
3.3
folding and stacking of internal membranes. The membranes or organelles
also control the entry and exit of substances.
Every living cell of every part of an organism needs matter and a source
of energy to keep it alive. Each kind of organism has its own way of
making this happen but there are processes that are common to all. Cells
have a variety of strategies for importing and exporting substances that
are necessary for cell functioning. The strategies used depend upon the
chemical nature of the substances.
Unicellular (single celled) organisms take in materials (inputs) from their
external environment and process these materials inside their single cell.
The outputs or products of these activities are biomolecules, which form
the structures of the organism or do its work. Biomolecules provide
energy that drives the biochemical process, and the waste products of
these reactions have to be removed. The plasma membrane is the
boundary of the unicellular organisms and controls what goes in and what
goes out.
Read through the following text and complete the tasks or questions that
follow. Use your own A4 paper or send work as MS Word documents
attached to an e-mail.
The Molecular Structure of Cell Membranes.
The following text is courtesy of Heinemann Biology Two 4 th Edition.
Perhaps the most important part of a cell is the plasma membrane. It
encloses the contents of cells and allows the cystosol (the liquid part of
the cytoplasm) to have a different composition from the surrounding
external environment by selectively regulating the movement of
substances into and out of the cell. Most organelles of eukaryotes,
including the nucleus, endoplasmic reticulum, mitochondria, chloroplasts,
lysosomes and vacuoles, are also formed from membranes. These
membranes form discrete compartments within the cell and control the
movement of substances between these compartments. As a result the
chemical contents of various organelles are different.
Figure 3.1
Biological membranes are
composed of a phospholipids
bilayer with large protein
molecules embedded in the
bilayer. These proteins
provide channels for the
passive and active movement
of certain molecules across the
cell membrane. Short
carbohydrate molecules
attached to the outside of the
membrane are involved in cell
recognition and cell adhesion.
3.4
Membranes:
 permit selective control of molecules entering and leaving cells;
 are active environments in which many essential chemical reactions of
life occur;
 establish compartments within the cell, thereby separating hereditary
material (DNA), cytosol, lysosomal enzymes, secretory products of
cells, and energy-processing materials in mitochondria and
chloroplasts;
 restrict movements of substances between one part of a cell and
another, thereby permitting regulation of the many enzymatic
processes that take place within the cell;
 have protein receptors involved in intercellular communication
(directly between adjacent cells, and by hormones and nerves);
 are involved in cell to cell recognition; and
 produce electrical activity in excitable cells.
Membrane composition
The plasma membrane is 7-9 nm thick. (A nanometer, nm, is 10-9 of a
metre). It is somewhat thicker than the membranes of intracellular
organelles; for example, nuclear and endoplasmic reticulum membranes
are 5-7 nm thick. Otherwise the basic structure of all biological
membranes is the same. They are composed of two layers of
phospholipid molecules, associated with other molecules including
proteins, carbohydrates and cholesterol, as shown in the fluid-mosaic
model (Figure 3.1). Phospholipid molecules have one end that is
hydrophobic (water-hating) and the other end hydrophilic (water-loving).
This means that, when in contact with an aqueous solution, phospholipids
molecules line up with their hydrophobic tails pointing away from the
solution (Figure 3.2). The impermeability of membranes to water-soluble
(polar) molecules is due to the phospholipids bilayer. Most other
membrane functions are carried out by the proteins, which are located
throughout the membrane, hence the term ‘mosaic’.
Membranes are fluid structures: individual lipid molecules (and some of
the proteins) are free to move about within the layers. Membranes also
contain large numbers of cholesterol molecules located between the
phospholipids molecules, which makes the membrane less fluid and more
stable. Without these cholesterol molecules, the membrane breaks down
rapidly and releases its contents. Cholesterol also decreases the
permeability of the membrane to small water-soluble molecules.
Figure 3.2
When in contact with an aqueous solution, phospholipids molecules line up with their
hydrophobic ‘tails’ pointing away from the aqueous solution. At an oil/water interface,
this results in a monolayer. In water, if the tails are short, the phospholipids
spontaneously form a spherical ‘micelle’; if the tails are longer, the phospholipids
aggregate to form a bilayer membrane. Soaps and detergents cause fats to form micelles.
Protein molecules in the membrane may cross both phospholipid layers,
or be confined to only one layer (Figure 3.2). Like some phospholipid
molecules, they are able to move about to some extent, but this movement
may be limited to particular regions of the cell membrane. Proteins
3.5
provide the channels through which water-soluble molecules and ions
pass. Facilitated diffusion (passive movement) and active transport
(requiring energy) occur through selective channels formed by membrane
proteins. Membrane proteins may also be pumps that move ions across
membranes, and enzymes that catalyse membrane-associated reactions.
For example, the final digestion of some food molecules occurs as they
pass through the membrane of cells lining the gut (gut epithelium).
Carbohydrates associated with plasma membranes are usually found on
the outer surface of the membrane, linked to protruding proteins
(glycoprotein). They play a role in recognition and adhesion between
cells, and in the recognition processes that occur between cells and
antibodies, hormones, and viruses.
Molecules crossing membranes
The plasma membrane regulates the movement of molecules into and out
of the cell (Figure 3.3a). This movement depends on the composition of
the membrane and the surface area available for exchange (Figure 3.3b).
One of the most important properties of membranes is their lipid nature,
which makes them impermeable to most water-soluble molecules, ions
(molecules with an overall positive or negative charge) and polar
molecules (molecules with charged regions but no overall charge). These
substances require specific channels (made from protein molecules) to
pass through the plasma membrane.
Figure 3.3
(a) Cells exchange many substances
within their environment across the cell
membrane.
(b) Pathways for movement of substances
across the cell membrane
3.6
SEND…
Question 1
(a) What are the functions of cell membranes?
(b)
Explain why the structure of the membrane can be described as a
‘fluid mosaic’?
Question 2
Explain how the following affect the ability of a molecule to pass across a
cell membrane:
(a) size
(b) charge (e.g. ions, polar or non-polar)
(c) solubility (e.g. in lipids)
Question 3
Where are the signals for cell to cell recognition located?
Practical Activity 3A – Modelling the Plasma Membrane
The following practical exercise does not have to be presented as a
standard practical report. Simply complete the task and answer the
questions.
Aim
To create a memory aid that will help you understand and remember the
structure of the plasma membrane.
Equipment
You will need:

At least 4 full matchboxes of Redheads type (approx. 200 matches)

A tray / old shoebox lid approx 30cm x 20cm in size

Butter or margarine

Spaghetti – the thin type (will need to be soaked in water for a
couple of hours to be soft enough to bend for the hook).
Procedure
Make a model of the plasma membrane by using the diagram below as a
guide.
It is important that you actually make it as it will strengthen your
understanding and memory of the different parts. And it’s fun!
Remember… this is a cross section of a 3D thing.
3.7
As you make the model use the following associations to aid your
memory of the different parts
The matchbox with drawer represents a protein channel which will allow
certain things to cross the membrane.
The matchsticks represent the phospholipids. The head of the match has
phosphorus which is flammable, this ties in with the ‘phospho’ part of
‘phospholipids’ and the yellowish stick part ties in with the colour of fat
which is a lipid and relates to the lipid part of ‘phospholipids’.
‘Glyco’ – this term
relates to
carbohydrates. A
way to remember
this is that
carbohydrates are
broken down into
glucose through
digestion. The
glucose is stored in
the body as
glycogen. So…
glycol =
carbohydrates.
The spaghetti has two shapes; one has a hook and the other could be
thought of as a net or antenna. This reminds us of the role of
carbohydrates in the membrane as spaghetti is a carbohydrate. It is
attached to a protein making it a glycoprotein.
The hook shaped spaghetti reminds us of the use of some carbohydrates to
connect ‘hook’ cells together.
The ‘net/antenna’ shaped spaghetti reminds us of carbohydrates that are
used to ‘detect signals such as hormones released from your own cells in
another part of your body.
As a net it also catches foreign things such as antigens from bacteria.
Carbohydrates can also be connected to the lipids in the membrane
creating glycolipids.
The butter represents the cholesterol needed to make the membrane less
fluid and more stable. You’ll notice that the butter helps to hold the
matchsticks in place. Butter is also a food that is high in saturated fat
which causes a build up of cholesterol in the blood. Some cholesterol is
needed. Too much is bad for you. So butter is associated with
cholesterol… and is found in the lipid part of phospholipids.
3.8
Two layers – finally you’ll remember that there are two layers of
phospholipids. The match heads (‘phospho’ parts) arrange themselves to
face ‘out’ because they are water loving (matchhead = fire which goes
with water).
The yellowish stick part of the match – the ‘lipid’ part arranges itself on
the inside of the plasma membrane as fat “hates” water – so it hides away
from the water that surrounds it.
SEND…
Results
Draw a diagram of your plasma membrane model.
Label the parts that represent: phospholipids bilayer, glycolipid,
glycoprotein, protein channel, cholesterol, inside and outside the cell.
Discussion
Now that you’ve made your model, answer the following questions:
Question 1
Glycoproteins are parts of the plasma membrane. State two functions of
these molecules.
Question 2
Draw a single phospholipid molecule and label the ‘hydrophobic’ and
‘hydrophilic’ parts. What do these two terms mean?
Question 3
How does your model differ from the real plasma membrane? Give at
least three differences.
Question 4
How could you improve your model so that it relates more closely to the
real thing?
Read through the following text and complete the tasks or questions that
follow. Use your own A4 paper or send work as MSWord documents
attached to an email.
The following text is courtesy of Jacaranda Nature of Biology Book 2, Second edition.
Crossing the membrane
All cells must be able to take in and expel various substances in order to
survive, grow and reproduce. Generally, these substances are in solution,
but in some cases, may be tiny solid particles.
Because a plasma membrane allows only some dissolved materials to
cross it, the membrane is said to be a partially permeable boundary (see
Figure 3.5). (‘Partially permeable’ is also known as selectively or
differentially or semi permeable). Dissolved substance that are able to
3.9
cross a plasma membrane – from outside a cell to the inside or from
inside to the outside – do so by various processes, including diffusion and
active transport.
Free Passage: diffusion
Diffusion is the net movement of a substance, typically in solution, from
a region of high concentration of the substance to a region of low
concentration. The process of diffusion does not require energy.
Figure 3.5 shows a representation of this process for dissolved substance
X. At all times, molecules of X are in random movement. At first, some
molecules collide with and cross the cell membrane into the cell (see
figure 3.5a). As long as substance X is more concentrated outside the cell
than inside, more collisions causing molecules of X to move from outside
to inside occur than collisions from the opposite direction. As a result, a
net movement of molecules of substance X occurs from outside to inside
and the concentration of X inside the cell rises (figure 3.5b). Eventually,
the number of collisions occurring on both sides of the membrane become
equal. At that time (figure 3.5c), the number of molecules of X passing
into the cell is equal to the number passing out. Diffusion stops at the
stage when the concentration of substance X is equal on the two sides of
the membrane.
Figure 3.5 Diffusion in action. (a) At the start, substance X starts to move into the cell because of random movement that
results in some collisions with the membrane. (b) Midway, molecules of substance X are moving both into and out of the
cell, but the net movement is from outside to inside. (c) When the concentration of X is equal on each side of the
membrane, the number of collisions on either side of the membrane is equal and the net movement of molecules of
substance X stops. Does this mean that collisions of molecules of substance X with the membrane stop?
One special case of diffusion is known as osmosis. Osmosis is the net
movement of water molecules across a partially permeable membrane and
down a concentration gradient. In living cells, the process of osmosis
occurs when water molecules diffuse/move across a cell membrane either
into or out of a cell.
Substances that can dissolve readily in water are termed hydrophilic, or
‘water loving’. Some substances that have a low water solubility or do not
dissolve in water are able to dissolve in or mix uniformly with lipid.
These substances are termed lipophilic (sometimes called hydrophobic).
Examples of lipophilic substances include alcohol and ether. Lipophilic
substances can cross plasma membranes readily. This observation
3.10
provides indirect evidence for the presence of lipid in the structure of the
plasma membrane. The rapid absorption of substances, such as alcohol
across plasma membranes, appears to be related to the ability of alcohol to
mix with lipid.
The movement of some substances across the plasma membrane is
assisted or facilitated by carrier protein molecules. The form of diffusion,
involving a specific carrier molecule, is known as facilitated diffusion
(see figure 3.6a). The net direction of movement is from a region of
higher concentration of a substance to a region of lower concentration,
and so the process does not require energy. Movement of substances by
facilitated diffusion mainly involves substances that cannot diffuse across
the plasma membrane by dissolving in the lipid layer of the membrane.
For example, the movement of glucose molecules across the plasma
membrane of red blood cells involves a specific carrier molecule.
Figure 3.6 (a)
Facilitated diffusion.
Facilitated diffusion
occurs with substances
that cannot dissolve in
the lipid layers of the
cell membrane.
(b) Active transport.
Does this process
require an input of
energy?
Paid passage: active transport
Active transport is the net movement of dissolved substances into or out
of cells against a concentration gradient (see figure 3.6b). Because the net
movement is against a concentration gradient, active transport is an
energy-requiring (endergonic) process. Active transport enables cells to
maintain stable internal conditions in spite of extreme variation in the
external surroundings.
This process involves a carrier protein for each substance that is actively
transported. If the carrier protein for a particular substance is defective,
the organism may show a disorder. In human beings, a defect in the
carrier protein involved in the active transport of chloride ions (CI-) has
been found to be the cause of the inherited disorder, cystic fibrosis.
Bulk transport
Solid particles can be taken into a cell. For example, one kind of white
blood cell is able to engulf a disease-causing bacterial cell and enclose it
within a lysosome sac where it is destroyed. Unicellular protists, such as
Amoeba and Paramecium, obtain their energy for living in the form of
relatively large ‘food’ particles that they engulf and enclose within a sac
where the food is digested. This process of bulk transport of material into
a cell is known as endocytosis (see figure 3.7)
3.11
Figure 3.7 (a)
Endocytosis (bulk
transport into cells)
occurs when part of the
plasma membrane
forms around a particle
to form a vesicle, which
moves into the cytosol.
(b) Exocytosis (bulk
transport out of cells)
occurs when vesicles
within the cytosol fuse
with the plasma
membrane and the
vesicle contents are
released from the cell.
Bulk transport out of cells for example, the export of material from the
Golgi complex is called exocytosis. In exocytosis, vesicles formed within
a cell fuse with the plasma membrane before the contents of the vesicles
are released from the cell (see figure 3.7b). If the released material is a
product of the cell (for example, the contents of a Golgi vesicle), then
‘secreted from the cell’ is the phrase generally used. If the released
material is a waste product after digestion of some matter taken into the
cell, ‘voided from the cell’ is generally more appropriate.
Cell walls
The plasma membrane forms the exterior of animal cells. However, in
plants, fungi and bacteria, a rigid cell wall lies outside the plasma
membrane. The absence of a cell wall is characteristic of organisms in the
Kingdom Animalia.
The cell wall varies in composition between plants, fungi and bacteria
(see table 3.1).
Table 3.1
Composition of
cell wall in
various types of
organisms. Why
are animals
excluded?
TYPE OF ORGANISM
COMPOUNDS PRESENT IN CELL WALL
plants
include cellulose
fungi
include chitin
bacteria
include complex polysaccharides
In some flowering plants, the original or primary cell wall in certain
tissues becomes thickened and strengthened by the addition of lignin to
form secondary cell walls. This process provides great elastic strength
and support, allowing certain plants to develop as woody shrubs or trees.
3.12
SEND…
Question 4
a) What is meant by the label ‘partially permeable’ in reference to the
plasma membrane?
b) What is the definition of osmosis?
Question 5
Which of the following is an energy-requiring process?
a)
b)
c)
d)
osmosis
diffusion
active transport
facilitated diffusion
Organelles inside eukaryote cells
The nucleus: control centre
Cells have a complex internal organization and are able to carry out many
functions. The control centre of the cells of animals, plants, algae and
fungi is the nucleus. The nucleus in these cells forms a distinct spherical
structure that is enclosed within a double membrane, known as the
nuclear envelope. Cells that have a membrane-bound nucleus are called
eukaryote cells. The regular presence of a nucleus in living cells was first
identified in 1831 by a Scottish botanist, Robert Brown (1773-1858), who
collected and named many Australian native plants.
Cells of organisms from the Kingdom Monera, such as bacteria, contain
the genetic material (DNA), but it is not enclosed within a distinct
nucleus. Cells that lack a nuclear envelope are called prokaryote cells.
A light microscope view reveals that the nucleus contains many granules
that are made of the genetic material deoxyribonucleic acid (DNA). The
DNA is usually dispersed within the nucleus. During the process of cell
reproduction, however, the DNA granules become organized into a
number of rod-shaped chromosomes. The nucleus also contains one or
more large inclusions known as nucleoli which are composed of
ribonucleic (RNA).
Textbook diagrams often show a cell as having a single nucleus. This is
the usual situation, but it is not always the case. Your bloodstream
contains very large numbers of mature red blood cells, and each of these
has no nucleus. However, at an earlier stage, when they were immature
cells located in your bone marrow, each of these cells did have a nucleus.
Some of your liver cells have two nuclei.
3.13
SEND…
Question 6
True or false? Briefly explain your choice:
a)
b)
c)
A nucleus from a plant cell would be expected to have a nuclear
membrane.
Bacterial cells do not have any DNA.
A mature red blood cell is an example of a prokaryote cell.
Question 7
Suggest why the nucleus is sometimes called ‘the control centre’ of a cell.
Mitochondrion: energy-supplying organelle
Living cells use energy all the time. The useable energy supply for cells is
chemical energy present in a compound known as ATP (adenosine
triphosphate). The ATP supplies in living cells are continually being
used up and must be replaced.
Figure 3.8 (a) 3-D
representation of a
mitochondrion.
3.14
ATP is produced during cellular respiration (or just simply respiration).
In eukaryote cells, most of this process occurs in organelles known as
mitochondria (singular = mitochondrion) which form part of the
cytoplasm. Mitochondria cannot be resolved using an LM, but can be seen
with an electron microscope. Each mitochondrion has an outer membrane
and a highly folded inner membrane. Mitochondria are not present in
prokaryote cells.
SEND…
Question 8
Is the major site of ATP production the same in a plant cell as in an
animal cell?
Ribosomes: protein factories
Living cells make proteins by linking acid building blocks into long
chains. Human red blood cells manufacture haemoglobin, an oxygentransporting protein; pancreas cells manufacture insulin, a small protein
which is an important hormone; liver cells manufacture many protein
enzymes, such as catalase; stomach cells produce digestive enzymes, such
as pepsin; muscle cells manufacture the contractile proteins, actin and
myosin.
Ribosomes are the organelles where protein production occurs. These
organelles, which are part of the cytoplasm, can only be seen through a
TEM (see figure 3.9). Ribosomes are not enclosed by a membrane. In
most cells, the ribosomes are attached to membranes internal channels
within the cell. Chemical testing shows that ribosomes are composed of
protein and ribonucleic acid (RNA).
SEND…
Question 9
A scientist wishes to examine ribosomes in pancreatic cells. Where should
the scientist look – in the membrane or in the cytoplasm?
Endoplasmic reticulum and Golgi complex: transport, storage and
export
The proteins made by some cells are kept inside those cells. Examples are
contractile proteins made by muscle cells and the haemoglobins made by
red blood cells. Other cells, however, produce proteins that are released
for use outside the cells. The digestive enzyme, pepsin, is produced by
cells lining the stomach and released into the stomach cavity; the protein
hormone, insulin, is made by pancreatic cells and released into the blood
stream.
Transport of substances within cells occurs through a system of channels
known as the endoplasmic reticulum (ER). Figure 3.9 shows part of this
system of channels in a cell. The channel walls are formed by membranes.
3.15
Figure 3.9
(b) 3-D representation of
endoplasmic reticulum.
A structure known as the Golgi complex is prominent in cells that excrete
materials out of cells. This structure consists of several layers of
membranes (see figure 3.10). The Golgi complex packages material into
membrane-bound bags or vesicles for export. These vesicles carry the
material out of the cell.
Figure 3.10
(b) 3-D representation of a Golgi
complex.
SEND…
Lysosomes produce
enzymes that digest
substances that are no
longer needed within
cells. Defects may occur
in the enzymes found
within lysosomes. When
this happens, the
substance may
accumulate in the
lysosomes and the cells
can no longer function
normally. Diseases
resulting from these
errors in lysosome
enzymes include Tay
Sachs disease in which
abnormal accumulation
of lipids occurs and
Hurler syndrome in
which abnormal
accumulation of complex
carbohydrates occurs.
Question 10
A substance such as a protein, made in a cell is moved outside the cell.
Outline a possible pathway for this substance starting from where it is
made to how it leaves the cell.
Lysosomes: controlled destruction
The human hand is a marvellous living tool that allows a person to grasp
objects, manipulate and investigate them. Typically a human hand has
five digits that are separated from each other along their length. This is
not always the case – a rare condition, known as syndactyly (pronounced
sin-dack-till-ee), in which the fingers are fused, can occur. How does this
happen?
During human embryonic development, the hands appear first as tiny
buds with no separate digits. The separation of the fingers involves the
‘programmed death’ of groups of cells between the fingers. If this
programmed cell death does not occur, the fingers form but they remain
fused. A similar event occurs in a developing chick embryo (see figure
3.11).
3.16
Animal cells have sac-like structures surrounded by a membrane and
filled with fluid containing dissolved digestive enzymes. These fluidfilled sacs are known as lysosomes and they are part of the cytoplasm.
Lysosomes can release their enzymes within the cell causing death of the
cell. This process of controlled ‘self-destruction’ of cells is important in
development (it is called apoptosis); lysosomes appear to play a role in
the controlled death of zones of cells in the embryonic human hand so that
the fingers become separated.
Lysosomes are probably the means by which cells remove organelles that
are no longer functional.
Figure 3.11 In a chicken embryo,
cell death brought about by
lysosomes produces separate
digits. Blue areas are regions
where cell death occurs. In
contrast, in a duck embryo, cells
between the digits do not die but
are retained as webbing.
SEND…
Question 11
Lysosomes are sometimes called ‘suicide bags’. Suggest why this name is
given.
Question 12
Next week, in Week 4, you will have to complete a practical exercise for
your SAC (School Assessed Coursework). Have you worked out where
and how you will complete it and do you have some one to act as your
supervisor?
3.17
Question 13
In question 10 earlier you answered the following question:
A substance such as a protein, made in a cell is moved outside the cell.
Outline a possible pathway for this substance starting from where it
is made to how it leaves the cell.
Following are three different responses from three different students to
the same question:
i.
Protein is made inside the cell, sometimes it is moved outside a cell.
These cells have a structure known as the ‘Golgi complex’. It
consists of several layers of membranes. The Golgi complex
packages the proteins into membrane-bound bags, or vesicles for
export outside the cell.
ii.
A protein would be made in a ribosome, often found in the rough
endoplasmic reticulum. From here the protein will be transported to
the Golgi apparatus to be ‘packaged’ in a vesicle. This vesicle will
probably merge with the cell membrane (as it is made of the same
material) and the protein would be excreted from the cell - the
process is called exocytosis.
iii.
The ribosome’s create a protein, that protein is then moved to the
golgi complex through the endoplasmic reticulum, the protein is then
packed into a vesicle and is then transported out of the cell.
Read carefully through each of the above responses and then answer
the following questions:
a) Which student shows the best understanding of protein production?
Why do you think so?
b) Have another look at your answer to question 10. State what changes,
if any, you would make to your earlier answer.
c) What else could you do to ensure that you fully understand the protein
production pathway?
d) Do you think that this question (question 13) has added to your
understanding of protein production?
3.18
Key Summary Points
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Lipid-soluble substances of various sizes, such as chloroform and
alcohol, are able to simply dissolve into the phospholipid bilayer and
pass easily through membranes.
Tiny molecules, such as water and urea, can pass between the
phospholipids molecules.
Small uncharged molecules, such as oxygen and carbon dioxide, can
also go through the phospholipids bilayer.
Large water-soluble substances, including amino acids and simple
sugars, pass through channels made from protein molecules. Protein
channels may be selective for particular substances, and they may
require the expenditure of energy for transport to occur.
The plasma membrane forms the boundary of each living cell.
Several different processes exist whereby substances may cross
plasma membranes
Glycoproteins on plasma membranes are part of a system of ‘self’ and
‘non-self’ recognition.
Cell walls lie outside the plasma membrane of plant, fungal and
bacterial cells.
The nucleus contains the nucleic acid DNA, which is the genetic
material within a cell.
The nucleus of eukaryote cells is enclosed within a nuclear envelope.
Living cells use energy all the time, principally as chemical energy
present in ATP.
Mitochondria are the major sites of ATP production in eukaryotic
cells.
Prokaryote cells do not have mitochondria.
Ribosomes are tiny organelles where proteins are produced
The endoplasmic reticulum (ER) is a series of membrane-bound
channels.
The ER functions in the transport of substances within a cell.
The Golgi complex packages substances into vesicles for export.
Lysosomes are membrane-bound sacs containing dissolved digestive
enzymes.
Lysosomes can digest material brought into their sacs.
Lysosomes play a role in organised cell death.
3.19
Key Terms
You encountered the following terms in this week of work. Below is a list
of some of them.
Prokaryotic, eukaryotic, cytosol, organelle, nucleus, endoplasmic
reticulum, mitochondria, chloroplasts, lysosome, vacuoles, cytoplasm,
phospholipids, cholesterol, diffusion, Osmosis, glycoprotein, glycolipids,
hydrophobic, hydrophilic, lipophilic, facilitated diffusion, Active
transport, endocytosis, exocytosis, deoxyribonucleic acid, ATP
(adenosine triphosphate).
SEND…
Challenging Activity: Mnemonic Activity
Choose one or more of the terms encountered during this week from the
Key terms above and create a memory aid to help you remember the
definition of that term.
You may use drawings, poetry, song, sound, whatever works for you.
Log on to the www.decvonline.vic.edu.au check out the back of your DECV
book for your login details if you have forgotten.
Click on the link to the Unit 3 Biology course.
Click on the button “Discussion Room”
Place your Mnemonic as a comment to the Discussion post titled
Mnemonics Week 3.
Make sure you check out the other Mnemonics left by your classmates and
leave them a comment.
Challenging Activity: Personal Reflection
Log on to the VCE Biology Course. Place your Personal Reflection in the Biology
Blog as outlined on 0.7 in the introduction of this book.
Checklist
This week you should have submitted the following work to me.
Please tick the items you have sent, and keep this as your record.




Responses to Questions 1-13
Practical Activity 3A Modelling the Plasma Membrane
At least one mnemonic of a biological term placed online
Your personal reflection for week 3 placed online
Don’t forget to drink plenty of water!
END OF WEEK 3
3.20
Exam Practice Exercise
Past Exam Questions
Each week you will get at least one question that relates to the weeks
work, that comes from a past VCE exam paper. Answers provided at end
of this Week’s notes.
The purpose of this task is to familiarize yourself with the type of
questions you will encounter during the exam and the timing you should
devote to each.
Timing
You should allow 1 minute and 10 seconds per mark assigned to the
question.
Here are your practice exam questions:
Question 3 is taken from the 2005 VCE Biology Unit 3 exam paper.
It is a multiple choice question worth one mark. You should allow
yourself 1 minute and 10 seconds to complete it.
Choose the correct response for the question.
Question 3
The plasma membrane of a cell
A. is inflexible due to the presence of protein molecules.
B. allows substances to pass through only by active transport.
C. contains cholesterol molecules which can act as cell receptors.
D. is relatively impermeable to large water soluble molecules due to the
presence of the bilipid layer.
1 mark
Questions 3, 4 and 17 below, are taken from the 2006 VCE Biology
Unit 3 exam paper.
Choose the correct response for each question.
Question 3
The protein chymotrypsin is derived from a parent molecule,
chymotrypsinogen. Cell organelles that are essential for the production of
chymotrypsinogen include:
A. ribosomes.
B. microtubules.
C. cell membrane.
D. Golgi apparatus.
1 mark
3.21
Question 4
Molecules found in an animal cell membrane include
A. chitin.
B. cellulose.
C. cholesterol.
D. nucleotides.
1 mark
Question 17
The packaging and transport of biomolecules within a cell involves their
A. distribution through a series of microfilaments.
B. transport by Golgi apparatus to the endoplasmic reticulum.
C. movement from the ribosomes into the endoplasmic reticulum.
D. transport from the plasma membrane into the cytosol by secretory
vesicles.
1 mark
Questions 1 and 2 below, are taken from the 2008 VCE Biology Unit 3
exam paper.
Choose the correct response for each question.
The following information is relevant for Questions 1 and 2.
Consider the following plant cell
Question 1
A process occurring at structure W in this plant cell would be
A. packaging of molecules.
B. aerobic respiration.
3.22
C. protein synthesis.
D. DNA replication.
1 mark
Question 2
In this plant cell, the light-dependent reactions of photosynthesis occur in
structure
A. N.
B. M.
C. Q.
D. P.
1 mark
Online Discussion
Get to know your fellow students! Go to our online service at
http://www.decvonline.vic.edu.au to access our online community.
From the DECVONLINE page, click on the course link and join in the
discussion forum. Use your DECV number as the username and your
date of birth in reverse order as your password (YYYYMMDD).
Feedback
What, if anything needs to be improved, corrected, cleared up or
presented better from the material presented in this week? Your honesty is
appreciated. Write your comments on the back of the cover sheet.
Answers to Past Exam Questions
Question 3 (2005 paper): D is relatively impermeable to large water
soluble molecules due to the presence of the bilipid layer.
Question 3 (2006 paper) A - A ribosome is a cell organelle and the site
of protein production.
Question 4 (2006 paper) C
Question 17 (2006 paper) C
Question 1 (2008) C
Question 2 (2008) A
3.23
315 Clarendon Street, Thornbury 3071
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FAX (03) 9416 8371 (Despatch)
Toll free (1800) 133 511
Fix your student barcode
label over this space.
SCHOOL NO.
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[64803]
STUDENT NUMBER ___________________
SCHOOL NAME _______________________
STUDENT NAME ______________________
SUBJECT
Biology Unit 3
YEAR/LEVEL
TEACHER
12
WEEK
3
________________________
[ZX]
PLEASE ATTACH WORK TO BE SENT.
NOTE: Please write your number on each page of your work which is attached to this page.
SEND
Please check that you have attached:

Responses to Questions 1-13

Practical Activity 3A Modelling the Plasma Membrane

At least one mnemonic of a biological term placed online

Your personal reflection for week 3 placed online
If you have not included any of these items, please explain why not.
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
Use the space on the back of this sheet if you have any questions you would
like to ask, or problems with your work that you would like to share with
your teacher.
3.24
YOUR QUESTIONS AND COMMENTS
Please provide the following information:
Were you able to complete the tasks in the time frame allocated? ___________________
Roughly how long did it take for you to complete this week of work? _____________
Use this space for any queries or comments you have, (or maybe errors you’ve found).
DISTANCE EDUCATION CENTRE TEACHER’S COMMENTS
DISTANCE EDUCATION CENTRE TEACHER