VCE BIOLOGY UNIT 3
EXAM REVISION
Gary Simpson
Contents
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Area of Study 1 – Molecules of Life
Past Exam Questions
Area of Study 2 – Detecting and Responding
Past Exam Questions
• Don’t forget the Exam is on Tuesday 8
June from 9.00am to 10.45am.
Area of Study 1 – Molecules of Life
The chemical nature of the cell
• Biomacromolecules are the big molecules
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involved in the biomechanical processes of
organisms.
Autotrophs – organisms able to synthesise their
own organic macromolecules from inorganic
molecules, either by photosynthesis or
chemosynthesis.
Heterotrophs – organisms that must consume
other organisms to synthesise macromolecules
Structure and Function of
Carbohydrates
• Organisms use carbohydrates as an
energy source and for structural
components of cells.
The structure and function of lipids
• Lipids are a diverse
group of molecules
which include fats, oils
and steroids. Used for
energy storage, cell
membranes and
transmission of
chemical signals.
Structure and function of DNA and
RNA
• DNA is a large protein found
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in the nucleus of eukaryotic
cells and the cytoplasm of
prokaryotic cells. DNA
contains the codes for all
the proteins made by a cell.
RNA is used to transmit the
information contained in the
DNA and construct the
proteins coded for by the
DNA
Protein Synthesis
• Transcription – occurs in the nucleus. Section of DNA unzipped and
copied onto mRNA
• Translation – mRNA moves to the ribosome. tRNA bring amino acids
to the ribosome based on sequence of nucleotides (read as a triplet)
• Proteins are formed by the amino acids joining together into a
chain.
Genetic Code
• Pieces of information in the code based on triplets of nucleotides
• Code is non-overlapping
• Code is universal
• Code is said to be redundant or degenerate as more than one triplet
can code for the same amino acid
• Code contains instructions to assemble amino acids sub-units
• Information is unambiguous
• Always includes a START and a STOP instruction
The proteome
• The proteome is a term used to describe
the complete set of proteins produced by
a particular cell.
• Almost everything that occurs in the cell
relies on proteins.
• All the proteins are made from
combinations of just 20 amino acids.
Cell Organelles
• Plasma Membrane
• The plasma membrane
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or cellular membrane
is made up of two
layers of
phospholipids.
They control what
leaves and enters the
cell.
Movement of Molecules
• Diffusion/Osmosis
• Diffusion is the movement of molecules of a
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substance from an area of high concentration of
that substance to an area of low concentration.
Osmosis is the movement of water from an area
of low concentration of a dissolved substance to
an area of high concentration of that dissolved
substance.
Movement of Molecules
• Isotonic
• Hypotonic
• Hypertonic
Movement of Molecules
• Facilitated Diffusion
• Some molecules required by the cell are either
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too large to move by diffusion or the cell already
has a high concentration of the molecule, so
diffusion won’t take place.
Energy is required to move these molecules
across the membrane using either carrier
proteins or channel proteins – this is known as
active transport.
Cell Organelles
• Nucleus
• The nucleus
contains the DNA
which contains the
information that
controls the
production of
proteins by the cell.
Cell Organelles
• Ribosomes
• Ribosomes are extremely small molecules
that play an important role in translating
the code from the DNA into proteins.
Cell Organelles
• Golgi Apparatus
• The Golgi Apparatus
is responsible for
packaging these
molecules and
transporting them
around the cell or to
the membrane.
Cell Organelles
• Endoplasmic Reticulum
• Rough ER (with ribosomes attached) is
responsible for production of membrane
proteins and proteins secreted from the
cell.
• Smooth ER are responsible for the
production of phosopholipids and
cholesterol.
Cell Organelles
• Vesicles
• These are membrane bound organelles
that are associated with the transport of
biomolecules within the cell.
Enzymes
• Enzymes are protein based molecules that act as
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catalysts in chemical processes within cells.
They operate best within given ranges of
temperature and pH.
Outside those preferred ranges the enzyme
either stops working or becomes denatured –
the active site is changed and no longer matches
the substrate that the enzyme works upon.
Metabolism
Catabolic Reactions
• These reactions break down complex molecules
into simpler molecules.
• Cellular Respiration is the most important of
these, breaking down glucose to release energy.
• This occurs first in the cytosol and then is
finished within the mitochondria.
Metabolism
Anabolic Reactions
• These reactions build up complex molecules
from more simple molecules.
• Photosynthesis is the most important of these
making glucose to store energy from carbon
dioxide and water.
• This occurs in the chloroplasts of green plants.
Applications of Molecular Biology
• There are many applications of molecular
biology.
• Difficult to study for – rather you need to
be prepared to analyse situations to
explain how the molecular biology is being
used in a particular application.
• No useful questions for this in past papers.
Area of Study 2 – Detecting and Responding
Signal Transduction
• Organisms need to be able to detect and respond to
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changes in the external and internal environment.
There are five principles to communication:
– a signal is produced (by production of a signalling molecule in a
cell)
– the signal is detected (by a receptor protein on the target cell)
– the signal is transferred until it reaches its target – transduction
(through the cell)
– a response is made to the signal (the cell responds to the signal)
– the signal is switched off after the response is made (the
signalling cell switches off production of the signalling molecule).
• These principles can be applied to external signals and
to internal signals of the organism and the cells.
Coordination and Regulation
• Organisms need to be able to detect and
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respond to changes in their external and internal
environment.
Receive external information with
chemoreceptors, mechanoreceptors,
photoreceptors, thermoreceptors and pain
receptors (collectively known as
exteroreceptors).
Receive internal information from interoceptors
which measure changes in temperature, water
content, blood sugar etc throughout the body.
Homeostasis
The ability of an organism to maintain a relatively
stable internal environment.
• Stimulus-response model. A stimulus is received
by a receptor which passes the information to a
central processing unit which analyses the
information and send a message to an effector
which causes a response.
• Negative feedback. The response to the stimulus
is the opposite to the stimulus.
• Positive feedback. The response to the stimulus
is in the same direction as the stimulus,
reinforcing the stimulus.
Nervous System
This comprises two parts – the central nervous
system and the peripheral nervous system. This is
a system of nerves found throughout the body.
The response to a stimulus is quick, but the effect
is generally short lived.
Endocrine Systems
Both plants and animals use
chemical messengers, called
hormones, to respond to
changes within the internal
environment. The response
time is slow as the hormone
needs to move through the
blood system or along
phloem, but the response is
felt for a long period of
time.
Cellular Communication
• Cells need to communicate within the
cytosol to control cellular processes eg.
The reading of DNA sequences to create
proteins
• Cells communicate with each other to
regulate growth and development and
responses to external stimuli eg. The
presence of pathogens
Plant Hormones
• Plant hormones regulate growth, development
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and reproduction and respond to changes in the
external and internal environment of the
organism.
Auxins
Cytokinins
Gibberellins
Abscisic Acid
Ethylene
Detecting Self and Non-self
Molecules
Disease is defined as any change that
impairs the function of an individual.
Infectious disease is caused by organisms
known as pathogens.
• Bacteria
• Virus
• Viroid
• Prion
• Eukaryotic organisms
Lymphatic system
• The lymphatic system
consists of the bone
marrow, thymus gland,
lymph nodes, mucous
tissues, spleen and many
vessels which transports
lymphocytes and removes
foreign material from the
body.
Non-specific immunity
• The immune system recognises foreign material
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from body tissues by recognising proteins
embedded in the cell membrane.
The first line of defence is the bodies surfaces –
skin, digestive system, respiratory, urinary and
reproductive system.
The second line of defence is the phagocytes –
these white blood cells simply engulf all objects
that do not have self markers.
Specific immunity
• If a pathogen gets past the first two
lines of defence then two things may
occur.
Humoral response
• B lymphocytes recognise the pathogen
as non-self and releases antibodies to
bind with the active sites on the
pathogens.
Cell-mediated response
• T lymphocytes do not produce
antibodies, rather they either recognise
antigens and stimulate B cells or kill
body cells infected with viruses.
Disorders of the immune system
• Allergies tend to be exaggerated responses of
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the immune system to relatively harmless
substances. An allergic response sees the Mast
cells and Basophil cells releasing histamines
causing swelling and inflammation.
Auto-immune diseases such as multiple sclerosis
occur when the immune system does not
recognise self cells and starts to attack and
destroy them.
Acquired Immunity
• Organisms gain immunity to disease by learning
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to recognise the antigens of pathogens. Humans
have learnt to mimic this response by using
dead or attenuated organisms.
It is also possible to gain immunity by giving a
person another’s antibodies. This occurs when
nursing mothers feed their babies.
Barriers to infection in plants
• Physical – the thick bark of stems and
trunks, and hairs and thick waxy cuticle on
the leaves prevents infection.
• Chemical – wounds are filled with resin,
infected leaves and branches are shed and
enzymes and antibiotics are secreted to
destroy or deter pathogens.