Hyndland Secondary School
Biology Department
National 5 - Unit 1 Cell Biology
Summary Notes1
Unit Structure ............................................................................. 2
Cell structure .............................................................................. 4
Animal Cells ..................................................................................................................................... 4
Plant Cells......................................................................................................................................... 5
Fungi ................................................................................................................................................. 6
Bacteria ............................................................................................................................................. 8
Uses of Single Celled Organisms ................................................................................................... 10
Transport across cell membranes ....................................................... 12
Cell Membrane ............................................................................................................................... 12
Diffusion......................................................................................................................................... 13
Osmosis .......................................................................................................................................... 14
Active transport .............................................................................................................................. 18
Producing new cells ...................................................................... 19
Cell division ................................................................................................................................... 19
Chromosome structure ................................................................................................................... 19
Mitosis ............................................................................................................................................ 20
Cancer ............................................................................................................................................. 21
Tissue Regeneration ....................................................................................................................... 21
DNA, production of proteins and genetic engineering ................................ 22
Protein Production .......................................................................................................................... 23
Proteins. .......................................................................................................................................... 25
Enzymes ......................................................................................................................................... 26
Genetic Engineering ....................................................................................................................... 33
Chemical energy in cells ................................................................. 36
Photosynthesis ................................................................................................................................ 36
Carbon Fixation .............................................................................................................................. 42
1
This booklet is available for download from the Hyndland Secondary School website in the Biology/ National 5/ Downloads
section of the subject support
http://www.hyndland-sec.glasgow.sch.uk
Hyndland Secondary School
National 5 Unit 1 - Cell Biology
Unit Structure
Outline
The general aim of this Unit is to develop skills of scientific inquiry, investigation and analytical
thinking, along with knowledge and understanding of cell biology. You will apply these skills when
considering the applications of cell biology on our lives, as well as the implications on society/the
environment.
The Unit covers the key areas of: cell structure; transport across cell membranes; producing new
cells; DNA and the production of proteins; proteins and enzymes; genetic engineering;
photosynthesis and respiration. You will research issues, apply scientific skills and communicate
information related to your findings, which will develop skills of scientific literacy.
As a result you will be able to:
1 Apply skills of scientific inquiry and draw on knowledge and understanding of the key areas of this
Unit to carry out an experiment/practical investigation
2 Draw on knowledge and understanding of the key areas of this Unit and apply scientific skills.
Homework
The homework is spilt into two types, written and online. The written homework is designed to help
you learn problem solving skills and deals with graph drawing, calculations, data handling and
experimental design and conclusion. Online homework contains some problem solving questions, but
is more focussed on consolidating your knowledge of the course. Both types of homework are
designed to help your preparation for the exam that forms a part of the Unit and also the external
national 5 exam.
Tests
The unit includes 3 interim tests and a National 5 assessment at the end of the Unit.
QR codes
At points throughout this booklet you will encounter funny looking squares
(like the one opposite). These are called QR codes and are like the bar codes
on tins of beans. A mobile phone with a camera can be used to scan them and
they then take you to a web page. In your summary notes, they typically take
you to a Youtube video to help you better understand a particular part of
Biology, or remind you of an experiment you have carried out in class, or even
a 10 mark multi-choice quiz to help test your learning (the questions are selected at random, so you
can use them again and again. If you start a quiz, you need to finish it and review your score,
otherwise it can be difficult to start a new quiz).
To make use of them you need a little app, a phone, tablet or the like with a camera and access to
the internet. The system has been tested using an Android phone with the app Quick Barcode
scanner – which is free to download; Blackberry offers the free, QR Code Scanner Pro-Free,
which hasn’t been tested; the Appstore also offers free QR code scanners, QR reader or Bakodo –
again not tested.
Please ask your parents’ permission to use this feature and as always ensure your security when
downloading any app from the internet. In particular ensure you have disabled in app purchases
before downloading any of the apps.
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Hyndland Secondary School
National 5 Unit 1 - Cell Biology
The links have been carefully selected by your teachers, however if you find any link that you think
explains it better, please let us know and we will modify future editions for next session. Even
better if you create your own version, give us the link and we can add it in. Enjoy your learning.
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Hyndland Secondary School
National 5 Unit 1 - Cell Biology
Cell structure
cell ultrastructure and functions to include cell walls, mitochondria, chloroplasts, cell membrane, vacuole, nucleus,
ribosomes and plasmids in typical plant, animal, fungi and bacteria cells
Word Bank
aerobic respiration, cell sap, cellulose, controls, chemical reactions, function, information,
photosynthesis, ribosomes, support, unicellular
Every living thing is made of at least one cell.
The cell is the basic unit of life.
Multicelluar
organisms are made up of many cells that work together. ____________
organisms, such as
Amoeba,
one
are
made
of
only
cell.
Animal Cells
All animal cells have:
A nucleus that contains ____________
and _________ the activities of the
cell.
The information is contained in
chromosomes which are made of DNA.
The DNA carries the genetic code for
all the proteins a cell requires.
Cytoplasm,
where
most
of
the
_______ __________ take place. The
reactions are controlled by enzymes
A cell membrane that controls what enters and leaves the cell.
Mitochondria in the cytoplasm where ___________
_______________ takes place to
release energy.
The ________________ are where proteins are made.
Growing cells and cells producing
digestive enzymes would have many of these in the cytoplasm.
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National 5 Unit 1 - Cell Biology
Plant Cells
In addition to a nucleus, cytoplasm, cell
membrane,
ribosomes
and
mitochondria,
plant cells also always have:
A cell wall made of ______________, which strengthens the cell and provides ___________.
They often have:
Chloroplasts* which contain the green pigment chlorophyll. This absorbs light energy for
_____________.
A permanent vacuole filled with _____ _____ (a dilute solution of minerals, sugars and amino
acids), which also provides support.
* Chloroplasts are only found in green parts of plants e.g. root cells don’t have chloroplasts,
being underground, they can’t capture light and so can’t photosynthesise. They therefore don’t
need chloroplasts.
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National 5 Unit 1 - Cell Biology
Fungi
Word Bank
anaerobic, carbohydrate, carbon dioxide, cell wall, contamination, cytoplasm, decomposition,
energy, fermentation, malting, maltose, optimum, photosynthesise, plant, respiration, starch,
sterilising
The cells of fungi are similar to _________ cells. They have a nucleus, ______________,
ribosomes and mitochondria. Whilst fungi do have a________ ________, it is made of chitin,
a different type of ___________from cellulose. They are however not green – they don’t ________________and
Ribosome
so
don’t contain chloroplasts. Fungi
Nucleus
Mitochondria
need
to
get
nutrients
and
energy from other organisms.
Cell Membrane
Cytoplasm
Cell Wall
Fungi
are
involved
in
__________________recycling nutrients from dead
organisms back into the ecosystem. Humans have made great use of fungi, e.g. yeast are fungi
and are used to make wine, beer and bread.
Industrial Uses of Fungi
Yeast can use sugar as food to produce energy. It is used in BREWING and BAKING. In baking
__________ ____________ produced by the yeast causes bread to rise. This is produced as
a result of yeast respiring anaerobically.
In brewing (the manufacture of beer) and wine making the alcohol (ethanol) is produced by
yeast performing _____________ RESPIRATION:
GLUCOSE → ETHANOL + CARBON DIOXIDE + ENERGY*.
* As brewing occurs, the _________ released by yeast is detected as an
increase in temperature – the brew heats up! The carbon dioxide is released as a gas.
Anaerobic respiration by micro-organisms, such as yeast is called _______________.
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National 5 Unit 1 - Cell Biology
In commercial breweries, the yeast are given the best possible conditions for growth by
maintaining the following at _____________ levels:
Temperature
Oxygen supply
pH
glucose supply
They also ensure the brew is kept free from unwanted microbes, which would spoil the brew, by
_____________
all
the
equipment
using
high
temperatures
and/or
chemicals.
______________ would be expensive as the brew would need to be thrown away.
Beer is made from barley which is a seed. However, seeds, including barley only contain
_________, which yeast cannot use as a food source. Consequently, the brewer has first to
germinate the barley. This is called ___________ and as the seeds germinate, they produce
an enzyme (amylase) which breaks the starch down into___________. The yeast then use
anaerobic ___________ to change the maltose into alcohol.
Starch
malting of barley
maltose
anaerobic respiration
alcohol
(amylase enzyme in barley)
enzymes in yeast
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National 5 Unit 1 - Cell Biology
Bacteria
Word Bank
chemical reactions, cytoplasm, DNA, mitochondria, plasmid, proteins
Bacteria have a much simpler structure than either plant or animal cells. They do not have
______________ , but do have _____________.
its____________
The bacterial cell carries out all
_____________, including aerobic respiration (which occurs in the
mitochondria of the other cells types
above) in the cytoplasm.
cytoplasm,
bacteria
ribosomes,
upon
In the
also
which
have
bacterial
____________ are made.
Bacteria are the simplest of all cells.
They don’t have a nucleus, but keep
their
genetic
information
in
a
structure called a nucleoid, which is a
large ring of________. In addition,
they also have extra genetic information in a small ring of DNA called a ___________. These
plasmids can be swapped between bacteria and usually help the bacteria survive e.g. by giving
antibiotic resistance. Scientists have learnt to use plasmids to insert new genes, even human
genes into bacteria (see .
Test your knowledge of Cell Structure & Function
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National 5 Unit 1 - Cell Biology
Handling Micro-organisms
Industrial processes which handle or produce food must prevent contamination with microorganisms. Some micro-organisms produce spores which can survive very dry conditions and can
even withstand boiling water.
To avoid contamination, foods should be kept covered and containers and surfaces which food
contacts should be regularly cleaned and sterilised.
Culturing Micro-organisms
Micro-organisms are grown or cultured in petri dishes
designed to prevent escape or contamination from outside.
A suitable culture medium is needed for them to grow. This is agar, a jelly
to which certain nutrients have been added to suit the requirements of the organisms to be
grown.
In addition, the micro-organisms need to be protected from contamination. Aseptic technique is
used when handling micro-organisms in a lab to prevent contamination by unwnated microorganisms.
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Uses of Single Celled Organisms
Sewage Treatment
Sewage presents us with two main dangers:
1. Sewage is a source of energy and nutrients for bacteria. They use oxygen to break it down
and may lower the oxygen concentration so much that other organisms die.
2. Sewage contains many species of micro-organism. Some of these cause diseases including
typhoid, dysentery and cholera.
Treatment
The aim of sewage treatment is to break it down into products which are harmless to the
environment. As there is a large range of chemicals in sewage, a large variety of microorganisms is required to break them down.
The first stage in treatment is to separate the liquid waste from solid waste. This is done in
large settling tanks.
semi-solid sewage
Solid sewage is poured into digesters where anaerobic action by
micro-organisms produces methane gas which can be used as fuel.
The solids which remain are dried and used as fertiliser
Liquid sewage is treated by mixing it with air. This maintains
conditions in which a variety of micro-organisms break it down.
Without aerobic conditions, complete breakdown is not possible.
methane
aerobic
There are two main ways of adding air.
1. The liquid is sprinkled over a pile of stones
which contains many air spaces.
As it trickles down, micro-organisms on the
stones break down the sewage.
2. Liquid is poured into large tanks
propellers turn to mix it with the air.
where
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sprinkler
stones
treated
sewage
Hyndland Secondary School
National 5 Unit 1 - Cell Biology
Upgrading Waste
Recently, techniques have been developed in which micro-organisms are used to make useful
products from waste.
1. Anaerobic breakdown of solid sewage produces:
a) methane which is a useful fuel.
b) fertiliser.
2. Molasses left over from sugar refining are fed to yeast which produce alcohol and organic
acids such as vinegar.
In the yeast factory in Menstrie (near Stirling), molasses are used to grow yeast which is
then sold around the world for baking, brewing and flavouring.
3. Whey left over from cheese making can be converted by yeast to protein which can then be
used for animal feed.
Vitamins can also be extracted from the yeast.
4. Methanol produced in the gas and oil industry can be converted by bacteria to protein which
is suitable for animal feed.
5. Spoil heaps from metal mines often contain insoluble metal salts. Bacteria can be used to
convert them to soluble salts which can be extracted in water and the metal recovered.
Advantages of Upgrading Waste
1. The waste has greater value and so can lower the cost of disposing of it.
2. The waste can be used instead of dumping it.
3. The waste can produce materials more cheaply than from other sources, and it reduces the
need to access natural resources.
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National 5 Unit 1 - Cell Biology
Transport across cell membranes
cell membrane structure concentrations gradients, passive transport, including diffusion and osmosis
the energy requirement for active transport
Cell Membrane
Word Bank
channels, entry, phospholipids, proteins, selectively
All cells are surrounded by a cell membrane.
It is the cell membrane which controls the
_______ and exit of materials into or out of the cell. The cell membrane has tiny holes in it
that only small molecules can pass through; because of this, the cell membrane is described as
______________ permeable. A cell membrane is made of proteins and ________________.
The phospholipids form a double layer (bilipid layer) and the _____________ are found
stretching through, or on the surface of this bilipid layer. Some of the proteins can form
____________ which can allow the movement of molecules into or out of the cell.
Channel protein
Phospholipid
bilayer
protein
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Diffusion
Word Bank
concentration gradient, energy, equal, high, passive
Diffusion
is
the
substance
movement
from
concentration
to
a
of
a
________
a
LOWER
concentration.
Diffusion
continues
until
the
concentrations are__________.
A _____________ ____________ is a difference in the concentration of a substance
between two areas. Diffusion is said to occur down a concentration gradient.
For diffusion to occur, a cell does not need to add any extra __________, for this reason
diffusion is described as ___________ transport.
Importance of Diffusion
Substance needed by the cell pass INTO the cell by diffusion e.g. oxygen & dissolved food
(glucose).
Waste substances pass OUT of the cell e.g. carbon dioxide (from respiration) or urea (from the
breakdown of amino acids)
In the body, diffusion occurs in the lungs (to absorb oxygen into the blood and remove carbon
dioxide from the blood – the opposite occurs in the body’s tissues where respiration uses up the
oxygen and produces carbon dioxide) and small intestine, to allow the absorption of digested
food molecules.
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Osmosis
Osmosis is a special case of diffusion and the term only applies when describing, the diffusion
of water across selectively permeable membranes.
Osmosis = the movement of water from a higher water concentration (HWC) to a lower water
concentration (LWC) across a selectively permeable membrane*.
*The cell membrane is a selectively permeable membrane (only small molecules can pass through
them)
Visking tubing
(a man made
material containing
tiny pores).
In the diagram opposite:
Water moves by osmosis from a HWC outside the bag to a LWC
inside the bag.
Starch and glucose
solution
Glucose is at a high concentration inside the bag, so diffuses out.
water
so stays in the bag.
Starch is too large to move through the pores in the membrane
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Osmosis in Plant Cells
cytoplasm
LIQUID OUTSIDE CELL
WATER GAIN or LOSS
CHANGE to CELL
Water
Cell gains water
Cell swells
Solution
equal
to
cell No net gain or loss of water
Cell does not change
solution
Solution stronger than cell Cell loses water
Cell shrinks
sap
When plant cells take in water by osmosis they
swell and become TURGID.
When plant cells lose water by osmosis they
become FLACCID.
PLASMOLYSIS occurs when a cell becomes very
flaccid. So much water has been lost that the
cell membrane shrinks away from the cell wall.
This usually starts at the corners.
The membrane surrounding the vacuole is also
selectively permeable and so the vacuole shrinks
and expands with osmosis.
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Osmosis in Animal Cells
Animal cells contain weak solutions of salt and sugar and only have a cell membrane.
Consequently they BURST if too much pressure is placed on it. (Animal cells cannot become
turgid, because they don’t have a cell wall.) Similarly, the term plasmolysed does not apply to
animal cells because they don’t have a cell wall. Animal cells simply shrink if they lose water.
Animal cells can gain or lose water by osmosis:
Changes in red blood cells due to osmosis
Solution outside cell
Water gain or loss
Change to cell
Water
Cell gains water
Cell swells & bursts
than cell Cell gains water
Cell swells & bursts
Solution weaker
Solution
solution equal to cell solution
No loss/ gain
Solution stronger than cell Cells loses water
sap
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Cell does not change
Cell shrinks
Hyndland Secondary School
National 5 Unit 1 - Cell Biology
Industrial Applications of Osmosis
Using Osmosis for Power Generation
If a tank of seawater and fresh water are separated by a selectively permeable membrane
osmosis will cause water to move from the freshwater (higher water
concentration) to the seawater (lower water concentration. This increases
the height of the water in the seawater tank, storing potential energy.
The water can then be allowed to flow down through a turbine and
generate electricity as it does. Examples of working prototypes can be founds in continental
Europe.
Reverse Osmosis in desalination plants.
This process is called reverse osmosis because the water moves up its concentration gradient.
This requires energy, and the water has to be pressurised to allow this to
happen. A selectively permeable membrane only allows smaller molecules,
such as water to pass through. If pressure is applied to seawater, the
pressure will force the water across the selectively permeable membrane,
but the salt, which cannot pass through the membrane will be left behind. In this way freshwater
can be produced using reverse osmosis.
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Active transport
Active transport is the movement of molecules and ions against their concentration gradient
•
It requires energy supplied by respiration
•
It is controlled by carrier proteins (pumps) in the membrane
•
Ions may be actively pumped into the cell from the environment or out of the cell, to the
environment e.g. sodium ions are pumped out of cells and potassium ions are pumped into cells.
Around 1/3rd of the cell’s energy is used doing just this!
•
Ion uptake is selective i.e. each ion is concentrated to a specific level
•
Because active transport needs energy it is affected by the availability of glucose
(source of energy) and oxygen (required for aerobic respiration.
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Producing new cells
maintenance of chromosome complement (diploid) by mitosis sequence of events of mitosis, including equator
and spindle fibres cell production by cell culture using aseptic techniques
New cells are formed when existing cells divide (split in two) producing two new (daughter) cells.
In some complex organisms (e.g. plants), cell division may occur only in special places (e.g. root/
shoot tip) called meristems. After a cell divides, the two new cells increase in size and once
large enough may themselves divide to produce a further two new cells.
Cell division
When a cell divides the resulting two new cells are identical to the parent cell – cell division is a
form of asexual reproduction. In order that the cells are identical, it follows that each new cell
must receive exactly the same information as each other.
The structure of the genetic
material, which is DNA in the form of chromosomes, held in the nucleus
ensures this occurs.
Chromosome structure
Chromosomes are thread like structures found in the nucleus of all
plant and animal cells. Every cell in the body (except gametes) contains
the same number of chromosomes.
A chromosome consists of lots of genes joined together. Each gene
is responsible for producing a particular characteristic (e.g. hair
colour, eye colour, height etc.).
Before cell division occurs, each chromosome is
duplicated (replicated) and the chromosome then
appears as an X-shape, consisting of two chromatids,
joined at the centromere (see diagram).
The chromatids are
identical, carrying a full set of instructions for making a new cell.
Consequently, each new cell needs only to receive one chromatid
from each X-shaped chromosome in order to receive a full set of instructions. The process by
which this occurs is called mitosis.
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Mitosis
sequence of events of mitosis, including equator and spindle fibres.
The process of mitosis is shown in the diagram below.
Terms to know:
Equator: - this is the centre of the cell where the chromosomes assemble before being spilt
apart.
Spindle fibres: - these are protein “ropes” which attach to the centromere on the
chromosomes. Spindle fibres originate in the centrioles of the cell which move to opposite ends
of the cell as mitosis starts.
The spindle fibres shorten and pull the chromatids apart to
opposite ends of the cell. The cell subsequently splits down the equator, therefore each new
cell receives a chromatid from each of the original chromosomes, i.e. a complete copy of the
genetic information present in the original, parent cell.
If any genes become changed or lost during cell division, the information required to produce a
correctly functioning new cell will not be available. Consequently, cell processes will be changed
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or stop working altogether. New cells must contain exact copies of the genetic information.
The daughter nuclei need to contain the same number and kind of chromosomes as the parent
nucleus.
Cancer
If control of cell division is lost, then tumours can develop, which can lead to cancer. Cancer
develops when some damage occurs to the DNA of a single cell in the body. Sometimes the
damage is inherited from a parent, but more usually the damage occurs during the lifetime of
the patient. The damage can often be caused by exposure to chemicals called carcinogens (e.g.
in cigarette smoke, mustard gas, asbestos) or radiation (e.g UV radiation, X-rays or gamma
rays). If untreated the cell repeatedly divides forming a lump of cells, known as a tumour. Not
all tumours become cancerous, but if they do they can be fatal because they grow big enough to
damage surrounding parts of the body.
Nowadays, depending on the type of cancer and how early it is detected, many people are able to
be successfully treated for cancer. In the past, treatments have involved using poisons which
stop cell division (often breaking the spindle fibres). As a result, sometimes a patient’s hair can
fall out. In the future, cancer treatments will be less toxic and increase survival rates even
further.
Tissue Regeneration
Mitosis is important in the growth of an organism, producing the new cells to allow the growth to
happen. In addition, when tissue damage occurs, mitosis allows the production of new cells to
repair that damage. In humans, the ability to repair damage is limited, a cut in the skin can be
repaired although often the repair is not perfect, a full liver can be regenerated from a smaller
piece (this technique can be used to repair liver damage). However, lose a limb and no re-growth
is possible, despite the fact that all cells in the body (except gametes and red blood cells)
contain all the instructions needed to build a whole body (as demonstrated by Dolly the sheep).
Other animals are capable of much more extensive repair, amphibians like newts are able to regrow whole limbs, and lizards can re-grow tails. As scientists have begun to better understand
stem cells, in the future it is likely that humans will be able to be treated to allow them to regrow new body parts that have become damaged.
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DNA, production of proteins and genetic engineering
structure of DNA — double-stranded helix held by complementary base pairs
function of DNA — base sequence determines amino acid sequence in protein
messenger RNA in protein production; protein structure — amino acid sequence determines protein shape and
function; proteins to include structural, enzymes, hormones, antibodies, and their functions; the effects of
temperature and pH on proteins transfer of genetic information and genetic engineering
The chromosomes contained in every nucleus of every cell in the body (with a few exceptions) is
made from a complex substance called DNA (deoxyribonucleic acid). DNA is an extremely long
and thin molecule and is made of two strands which coil around each other forming a double
helix shape.
A double strand of DNA
DNA double helix
Hydrogen bonds
between bases
Each DNA molecule is made of only 4 different types of bases (A, G, C, T). The two strands of
DNA are held together because the bases pair up with each other; A pairs with T only and G
pairs with C only. The two strands are held together by weak forces (hydrogen bonds) which
means they can be easily separated. This ability to separate the strands easily is very
important when the cell wants to copy its DNA before mitosis starts.
DNA is the most important molecule in all living things. This is because it contains the code for
all the proteins needed to ‘run’ the cell’s reactions and all the proteins needed to make the cell
structure itself.
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Proteins are made by joining amino acids together into long chains, which then fold up to make
things like enzymes, hair, nails and every other protein in your body. There are around twenty
different types of amino acids which the cell can use to make the protein.
amino
acid
20
proteins.
nitrogen
If a cell places the wrong amino acid in the wrong place in the chain, the protein will not work
properly and the cell will likely die. The DNA tells the cell in which order to place the amino
acids to build the protein molecules correctly. It is the order in which the bases, in the DNA,
are arranged in each strand that tells the cell the correct order to place the amino acids. Any
change in the order of the bases on the DNA molecule (called a mutation) will lead to a change in
the protein, and the protein will not work correctly.
Protein Production
Protein synthesis takes place on the ribosomes found in the cytoplasm of a cell. However, the
instruction code for the protein is contained in the nucleus, on the DNA. Clearly the cell needs
to get that information from the nucleus into the cytoplasm. To do this it creates a special
copy (or transcript) of the code using RNA (ribonucleic acid). RNA is a very similar molecule to
DNA, but contains only one strand. There are different types of RNA, but the one used to
carry the code (or message) from the nucleus is called messenger RNA (or mRNA). mRNA is
made by enzymes in the nucleus and moves to the cytoplasm where the information it contains is
“translated” by the cell, using ribosomes, into the protein sequence. The ribosomes join
together amino acids in the order that the mRNA instructs them to. This process requires
energy.
Once made the protein is transported to the part of the cell in which it is needed.
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http://learn.genetics.utah.edu/content/begin/dna/
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Proteins.
protein structure — amino acid sequence determines protein shape and function
proteins to include structural, enzymes, hormones, antibodies, and their functions
Proteins are large organic molecules made up of the elements C, H, O, N
The sub-units of proteins are known as amino acids which are linked together into long chains by
peptide bonds
There are twenty different amino acids give rise to a huge variety of proteins all different in :
The number of amino acids in the chain

The order of amino acids in the chain

The variety of amino acids in the chain
Two main types of proteins are found:Fibrous Proteins - Long parallel chains often wound around each form very strong structures.
e.g.:
Collagen in bone and tendons

Elastin in ligaments

Keratin in hair
Globular Proteins - Long chains are folded into spherical structures similar to a tangled ball of
string. These proteins have a variety of functions. e.g. :
Structural proteins of the cell membrane

Enzymes which speed up reactions e.g. amylase

Hormones – these are chemical messengers in the body e.g. insulin

Antibodies – defend the body against bacteria and viruses.

Transport –e.g. haemoglobin in the blood. Proteins in the membrane involved in active
transport of materials across the cell membrane.
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Enzymes
the effects of temperature and pH on proteins
Catalysts
Word Bank
catalase, catalyst, changed, enzymes, manganese dioxide, oxygen, temperature, used, water,
There are two ways in which chemical reactions can be speeded up. You can either raise the
________________ or add a ______________. A catalyst speeds up the rate of a
chemical reaction without itself being _________ up in it, therefore the catalyst can be
used again.
Hydrogen peroxide breaks down very slowly without a catalyst to speed
up the reaction. A chemical, such as ________________
_______________ can be used to speed up this reaction.
The equation below shows the products of the breakdown of hydrogen
peroxide:
_____________ are biological catalysts and are found in all living cells. The enzyme that
speeds up the breakdown of hydrogen peroxide into water and oxygen is ______________.
Enzymes are needed in cells to:

Synthesise useful products

Release energy during cell respiration

Change poisonous wastes into safer materials

Change substances into a form that can be stored or used

Perform the chemical reactions of photosynthesis and respiration on which all life
depends.
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Examples of Enzymes:
Name of Enzyme
Where found
What it Does
Test for Activity
Degradation reaction (Breaking down reactions)
CATALASE
In plant and animal Breaks down hydrogen
Glowing splint relights
tissues
in the gas given off
peroxide into
OXYGEN and WATER
AMYLASE
In
digestive
(saliva,
juices STARCH is broken
pancreatic down into MALTOSE
Benedict’s
reagent
turns orange
juice)
Synthesis reactions (Building up Reactions)
PHOSPHORYLASE
In potato tubers
Builds special reactive
Iodine
turns
blue
glucose (GLUCOSE – 1
black as starch is built
– PHOSPHATE) into
up
STARCH
The Nature of Enzymes
Word Bank
active site, Biuret’s, complementary, lock, one, protein, specific, substrate, violet, unique
Enzymes are made of ____________. This is shown by using _________________ reagent,
which turns from blue to _____________ when gently heated in the presence of a protein.
The substrate is the substance on which an enzyme works.
Enzymes only work on a particular substance. This is because enzymes have a ____________
shape which is matched with the _____________ it works on. The shape of the substrate is
said to be _______________ to the substrate.
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The ________ ______ of an enzyme is where the substrate binds. When the substrate
binds to the active site, a chemical reaction occurs. From the diagram it is clear that the
relationship between the shape of the active site and the substrate is the reason enzymes can
act on only one enzyme. The two are said to match like a _____ and key because only one
specific key (substrate) will fit into a specific lock (enzyme). This means that a
_________________ enzyme is needed for every reaction in the body’s cells.
Breakdown Reactions
Word bank
amylase, Benedict’s solution, degradation, control, enzyme, iodine solution, maltose, product,
saliva, smaller, substrate,
Breakdown or _______________ reactions convert large molecules into ______________
molecules. ______________ is an example of an enzyme which will do this, breaking large
starch molecules into smaller ______________ molecules. Amylase is found in __________,
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Synthesis Reactions
Word bank
Calcium phosphate, chemical, diffuse, glucose-1-phosphate, glycogen, larger, light, phosphate,
phosphorylase, photosynthesis, structural, synthesis, respiration, water
Plants with green leaves, such as potatoes, can convert _____________ energy into
____________ energy in the process of _____________________. The plant’s leaf cells
will use some of the glucose produced as a source of energy and the rest will transported to the
growing potatoes, where it is stored.
In plants, energy is stored as starch for later use because the molecules are _____________
than glucose molecules and so will not _______________ out of the cells. Just like plants,
humans can also use synthesis reactions to build up storage molecules such as
_________________ which can be broken down when energy is required by the body.
Effect of Temperature on Enzymes
At low temperatures enzymes work slowly –
(Their reaction rate is at a MINIMUM)
As the temperature increases, they work faster, up to a MAXIMUM RATE.
The temperature at which an enzyme works at its maximum rate (not at which it works best!) is
called the OPTIMUM TEMPERATURE.
Any further increase in temperature causes the enzyme protein to be damaged. The enzyme’s
shape changes above the optimum temperature, it is said to be denatured and the activity
rapidly decreases to zero because the enzyme no longer works. It can no longer work because
the shape of the active site has changed and the substrate can no longer fit in.
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Denaturation of enzymes
.
The effect of pH on enzymes
The pH of a solution measures how acid or alkali it is. Use the words acid, alkalis or neutral to
label the pH scale below.
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An enzyme will work only in a narrow range of pH. The OPTIMUM pH is the pH at which the
enzyme has most activity. The optimum
pH is different for different enzymes.
Pepsin is found in the stomach (acidic) and
so has an optimum pH which is acidic.
Trypsin works in the small intestine which
is slightly alkali, and so it has an optimum
pH of around 9.
If the pH becomes more acidic or more alkali than the optimum pH, the enzyme becomes
denatured.
Rennet
Rennet is an enzyme which is used in the manufacture of cheese. There are several steps in the
manufacture of cheese:
 special bacteria are added to convert the milk sugar into lactic acid
 enzymes are added to clot the proteins in milk.
Rennet is a enzyme that clots milk, and originally, it came from animals such as calves. Nowadays
the enzymes used in cheese making can come from a variety of different sources including
bacteria or a genetically engineered fungus.
Washing Powders
Washing powders contain detergents (chemicals), which dissolve dirt and stains. The ability of a
washing powder to clean clothes improves as the temperature of the water increases. Boil
washes (90°C) gives the best clean.
Biological washing powders also contain detergents, but in addition have enzymes added. The
enzymes are typically proteases and lipases which digest the proteins and fats which make
clothes dirty. These enzymes have been produced by bacteria and are selected so that they
work well at low temperatures (40˚C). Biological washing powders wash better than non-
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biological washing powders at these low temperatures. At higher temperatures, the enzymes
are denatured.
The advantages of biological washing powders are:
Conserve heat energy, saving money
Allow cleaning of delicate fibres (e.g. silk), that would be damaged by high temperatures.
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Genetic Engineering
Genetic Engineering
chromosome
gene
plasmid
Like other cells, bacteria are controlled by genes.
Each bacterium has one chromosome which is
circular. It also has one or more smaller plasmids
which consist of genes.
In genetic engineering, new genes are transferred from one organism (such as a human), into
another organism, (such as a bacteria). In this way the bacteria can engineered to produce
human proteins e.g. the production of human insulin by bacteria. Insulin is used to treat
diabetes.
The bacteria produced in this way are “factories” producing useful products. The process of
genetic engineering involves locating and removing the human gene, then joining it into the
plasmid. Each step in the process below requires enzymes.
an enzyme is used to remove
the desired gene
from the chromosome
an enzyme is used
to open a plasmid
of a bacterium
The desired gene
is inserted into the
plasmid
using another enzyme
The plasmid is inserted into a fresh bacterium which is then cultured.
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Products of Genetic Engineering
1. Insulin is a hormone normally produced by humans. It is needed to maintain the correct sugar
concentration in the blood. People who cannot make insulin suffer from diabetes and
need
regular injections of insulin.
Until recently, the insulin came from pigs. As pig insulin is not identical to human insulin,
allergic responses sometimes occurred.
As a result of genetic engineering, diabetics now use human insulin made by bacteria.
2. Human growth hormone is given to babies who cannot produce enough of their own.
3. Enzymes. Biological soap powders depend on enzymes produced by bacteria.
4. Pyrethrum. This is a biodegradable insecticide extracted from the pyrethrum daisy.
Recently, the Kenyans found that it grew well in
their country and farms were set up to
produce it. However, scientists in the US transferred the gene to yeast so that the
insecticide can now be produced anywhere. The Kenyans saw this as genetic piracy.
5. Antibiotics such as penicillin are often produced by bacteria.
6. Vaccines such as that used against the rabies virus are produced by bacteria.
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Chemical energy in cells
chemistry of photosynthesis, as a series of enzyme-controlled reactions, in a two-stage process —
light reaction and carbon fixation
the end product of photosynthesis (sugar) and its use in cells
the impact of limiting factors on the rate of photosynthesis
chemistry of respiration as a series of enzyme-controlled reactions
ATP production and its use
in the absence of oxygen, energy is produced by alternative pathways, which produce different endproducts
Photosynthesis
Word bank
Carbohydrates, carbon, environment, increase, photosynthesis, producers, starch, stored
Plants are said to be ___________________ because they do not consume other living things
to obtain energy. Plants make their own food using simple chemicals from the _____________.
Foods made by plants contain the elements ____________, hydrogen and oxygen.
Consequently, they are known as ____________________. The process in which plants make
food from raw materials and energy from the sun’s light is called ____________________ .
Without plants and the process of photosynthesis, the planet’s animals would have virtually no
source of energy to sustain life.
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The need for light
When plants are not using glucose, it is converted into __________ and stored in their cells.
Testing leaves for starch indicates whether glucose was first made by photosynthesis or not.
If green plants leaves are kept in constant darkness they will not produce glucose because
photosynthesis requires light energy.
Starch Production during 24hours.
The dry mass of something is the mass of all the material in a plant apart from the water. If
there is an _________________ in the dry mass of a green plant, this shows that glucose is
being made and ______________ as starch by photosynthesis.
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Evidence for the importance of chlorophyll
Word bank
by-product, carbon dioxide, composition, glucose, light, oxygen, water
Need for Carbon dioxide
Plants are able to make their own food using light energy from the sun and raw materials from
the environment, including ____________ ___________ and _____________. Carbon
dioxide is a gas that is absorbed from the air, and water is absorbed from the soil.
If a green plant does not have both raw materials (carbon dioxide and water) as well as sunlight,
photosynthesis would not occur.
To carry out photosynthesis, plants combine the raw materials, carbon dioxide and water to
produce the useful material, glucose and the waste product oxygen, which the plant releases
into the atmosphere.
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As with all chemical reactions in living cells, photosynthesis occurs in a series of enzyme
controlled steps. These can be separated into two major sets of reactions: The light reaction
and carbon fixation.
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The Light Reaction
As the name suggests, the light reaction is the part of photosynthesis involving the capture of
light energy and its conversion into chemical energy.
Capture of Light Energy by Chlorophyll
Some of the _________ energy captured by chlorophyll is transformed into chemical energy.
The ___________ energy is then used to produce glucose from the raw materials carbon
dioxide and water.
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Light energy from the sun is captured by _______________ and converted into chemical
energy.
Water is split by some of the ___________ energy into oxygen and hydrogen.
Hydrogen captured here by a hydrogen acceptor is passed to the carbon fixation stage of
photosynthesis
Oxygen is released as a by-product: the majority of it is released from plant leaves into the
atmosphere.
Some light energy captured by chlorophyll is used to make ________, built up from ADP and Pi.
The process by which ATP is generated using the sun’s light energy is known as
photophosphorylation.
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Carbon Fixation
Carbon fixation is the set of enzyme controlled reactions in which the energy captured by the
light reaction is used to stick carbon dioxide molecules together, to form glucose. The
hydrogen, produced by the splitting of water in the light reaction is also used at this stage.
Energy is used up in this reaction. The energy is provided by the ATP, produced in the light
reaction above.
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Structure, Properties & Functions
200, glucose, linear, functions, coiled, grain, insoluble, building, energy, parallel, sheets.
permeable
Starch and cellulose molecules are both large molecules made up of smaller ____________
molecules.
The ways in which the glucose molecules link up to each other results in the different types of
molecule being formed.
The structural arrangements of starch and cellulose are different, consequently they have
different ___________________ .
Starch Molecules
A single starch molecule is made up of many glucose molecules. Glucose
units are joined together to form a ________________ shape so that
the molecule becomes entangled up with itself. With the addition of
more starch molecules a dense starch ________________ is formed.
Starch molecules are ________________ in water. They act as a
concentrated source of energy as they contain up to 800 glucose molecules.
Cellulose Molecules
A single cellulose molecule is made up of 1000 -1500 glucose molecules.
The cellulose molecules line up in _____________ chains to form
tough fibres. Cellulose is
also insoluble in water and
not easily broken down. The
fibres are arranged in _________________ at right
angles to each other. This arrangement adds strength
to the structure, while the gaps make cellulose freely
_____________________ to small molecules like
carbon dioxide, water and sugars.
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Limiting factors in Photosynthesis
Light intensity as a Limiting Factor
Darkness, limiting factor, slowly, increase, enzymes, denatured
A _______________ _____________ in photosynthesis is something, which, when in short
supply, stops the reaction of photosynthesis working at its
maximum possible rate. Light intensity can limt the rate of
photosynthesis. In dim light, the rate of photosynthesis is
slow, but increases if the light intensity is increased – all
other factors being kept the same. In _____________ no
photosynthesis will occur at all. The light intensity is
therefore a limiting factor.
An Elodea bubbler is used to investigate the effect of light intensity on photosynthesis. The
rate of photosynthesis is measured by counting the number of bubbles released for the cut
stem of the Elodea (pondweed).
The graph above shows the effect of light intensity on the rate of photosynthesis in pondweed.
The rate of photosynthesis increases as the light intensity increases up to a light intensity of
10 units. Above 10 units, the rate is not increased, this must be because another factor,
temperature or carbon dioxide concentration is limiting the rate of photosynthesis.
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A _____________ is a copy of an experiment in which all factors are kept exactly the same
except for the one being investigated in the original experiment. The control experiment shows
that the factor we think is causing any change does. If in the control experiment we get a
different result and as the only difference between the two experiments is a single factor, that
factor must be responsible for the difference we see in the results.
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