Greenfaulds High School
Biology Department
National 5
Summary notes
National 5 Biology summary notes
1
Cell Biology Unit
Cell structure
All living things are made from cells. Cells can not usually be viewed with the
naked eye, you must use a microscope to view cells and to see the detail in
the structures which make up cells.
There are lots of different types of cell, the structure of animal, plant,
bacteria and fungal cells are considered in this unit. Each of these cell types
has a different structure.
Animal cells have a nucleus, cytoplasm, cell membrane, ribosomes and
mitochondria.
Plant cells have all of these structures (nucleus, cytoplasm, cell membrane,
ribosomes and mitochondria) and they also have a vacuole, cell wall and
chloroplasts.
Both bacteria and fungi are types of micro-organism. Their structures are
also different; Fungi cells are similar to plant cells but they do not have
chloroplasts. Bacterial cells are different because they have no organelles.
The chemicals in the walls of bacterial cells, fungal cells and plant cells are
all different.
Plant cells walls are made of a structural carbohydrate called Cellulose.
Cellulose is freely permeable to all molecules. The cell wall helps to maintain
the cells rigid structure.
Structure
Function
Found in which cells?
Nucleus
Controls cell activities. Contains
Plant, animal and fungus
DNA
Cytoplasm
Site of many chemical reactions
All cell types (P,A,F,B)
Cell Wall
Give the cell a rigid structure
Plant, fungus and
bacteria
Cell Membrane Controls movement of substances All cell types (P,A,F,B)
in and out of the cell
National 5 Biology summary notes
2
Chloroplasts
Vacuole
Mitochondria
Plasmid
Ribosome
Site of photosynthesis
Stores cell sap, helps control
water balance
Site of aerobic stages of
respiration
Ring of DNA that can be removed
in genetic engineering
Site of protein synthesis
Only plant cells
Plant and fungus
Plant, animal and fungus
Bacterial cells only
All cell types (P,A,F,B)
Transport across cell membranes
All cells have a cell membrane. The purpose of
the cell membrane is to control which
substances enter and exit the cell. The cell
membrane is composed of lipids and proteins
and is described as being selectively permeable.
(i.e. it allows some substances to pass across it
but not all substances)
Molecules move across the cell membrane by
diffusion, osmosis and active transport.
Diffusion
Diffusion is the movement of molecules from an area of high concentration
to an area of low concentration (down a concentration gradient)
Diffusion is a passive process, this means that no energy is needed for it to
take place
Diffusion is important to cells as it is an important strategy to move
materials in and out of cells. To get raw materials in and to get rid of waste
materials.
The following substances move into cells by diffusion – glucose, oxygen and
amino acids.
National 5 Biology summary notes
3
Carbon dioxide moves out of cells by diffusion.
Osmosis
Osmosis is the movement of water molecules from an area of high water
concentration to an area of low water concentration through a semipermeable membrane.
Osmosis is a passive process, it does not require energy.
A solution is often made up by dissolving a substance in water. e.g. a 5%
glucose solution will contain 5% Glucose and 95% water.
It is important to remember that a 5% sucrose solution will contain more
WATER than a 10% sucrose solution which will contain only 90% water.
Cells respond differently to treatment in solutions. Pure water (100%) has a
higher water concentration than most cells. Animal cells will burst when
placed in a solution with higher water concentration than their cell contents.
Plant cells become turgid if left in a solution with higher water
concentration.
If placed in a solution with a lower water concentration that the cell
contents; animal cells shrink and plant cells become plasmolysed.
Stronger water
solution outside cell
Cell Bursts
Water concentration
is the same inside and
outside cell
Stronger water
solution inside cell
Cell is normal
Cell shrinks
4
National 5 Biology summary notes
Cell is turgid
Cell is normal
Cell plasmolysed
Active transport
Active transport it the movement of molecules from an area of low
concentration to an area of high concentration (against the concentration
gradient)
This is an active process, it requires energy from ATP.
Molecules are often pumped across the membrane during active transport by
the proteins in the membrane.
Because active transport is dependent on ATP, the factors which affect the
rate of respiration will also affect the rate of active transport e.g.
temperature and oxygen availability.
Producing new cells
In order for growth and repair to take place in multi-cellular organisms cell
division is essential.
Cell division is also called Mitosis. Cells produced by mitosis must have
exactly the same chromosome structure as the parent cell which divides to
produce them. This ensures that no genetic information is lost so that the
cell can function correctly.
1 chromosome
made up of 2
chromatids
Each of these structures is a
chromatid (when they are
joined together)
Most cells are diploid, this means that they have 2 copies of each
chromosome. Human diploid cells have 46 chromosomes (23 pairs).
During cell division the following stages take place;
National 5 Biology summary notes
5
Each chromosome makes an
identical copy of itself
Chromosomes line up at the
equator of the cell
This cell has 2
chromosomes –
diploid number
(2n) is 2.
Spindle fibres pull chromatids
apart to opposite ends (poles)
of cell
Nuclear membrane forms
around each set of
chromosomes
Cytoplasm divides and 2
separate diploid cells are
formed
Cell culture
Cells are often used by scientists for experiments and by industry to make
products that make money. In both cases cells have to be ‘grown’ by
providing them with the correct conditions for continuous cell division. This
is sometimes called cell culture.
In order to stimulate cell division, conditions need to be created where the
target cell is grown in conditions which suit is best. The environment needs
to be free from competition from other cells. This is facilitated by the use
of aseptic technique.
Examples of good working practices in aseptic technique.
o Wash hands thoroughly before you begin.
o Wear a lab coat.
National 5 Biology summary notes
6
Wipe down your work area with disinfectant.
Use sterile equipment which has been heated to 120˚C.
Have a Bunsen burner alight beside your work area.
Wash hand thoroughly after you’re finished.
Sterilise your equipment as you work by flaming in bunsen
burner flame.
o Label all your cultures clearly with name of cell and date.
o
o
o
o
o
In addition to aseptic technique, cells will also require;
 an appropriate growth medium, this is often provided by
broth or agar. Agar contains food and nutrients that the
cells need to grow.
 The factors in the environment surrounding the cell will
also need to be controlled these include the temperature,
oxygen availability and pH.
Proteins and enzymes
Proteins
Proteins are very important biological molecules. They control a lot of the
things which keep cells functioning. Proteins are built up from chains of
amino acids. There are about 20 naturally occurring amino acids, when they
are arranged in different combinations they make a very large variety of
molecules which are different shapes.
Enzymes, hormones and antibodies are all globular proteins. Proteins can also
be structural for example keratin in our skin. Hormones are chemical
messengers which allow different parts of our bodies to communicate with
each other, they travel around the body through the blood. Antibodies are
part of the body’s defence against disease, they are produced by white
blood cells to stop infection.
More detail about enzymes given below.
Enzymes
Enzymes are biological catalysts, they speed up chemical reactions without
being used up in the reaction. They are made by all living cells and have a role
to play in most cellular processes. Each enzyme has a different shape which
National 5 Biology summary notes
7
is very important to its function. Enzymes work by binding to the molecule
needing changed (this is called the substrate). Each enzyme only binds to
one substrate, because of the shape only 1 type molecule will fit into the
enzymes active site (like a lock and key). Enzymes are described as being
specific because of this property.
The activity of an enzyme is affected by the conditions in the environment
e.g. pH and temperature are very important. The conditions an enzyme
works best at are described as the optimum conditions for that enzyme; the
best temperature is the optimum temperature and the best pH is the
optimum pH. Other proteins are also affected by changing the pH and the
temperature, the reasons that temperature and pH affect proteins
(including enzymes) is they cause the shape of the protein to change so it
can not carry out its job as efficiently. If the shape is changed so that the
protein does not function anymore the protein is described as being
denatured.
DNA and production of proteins
Deoxyribonucleic acid (DNA) is stored in the nucleus of every cell. It is a
code made up of 4 letters (A, T, C and G) which contains instructions for
the cell to produce all proteins needed by cells.
DNA is a double-stranded helix (looks like a twisted ladder). The 2 strands
are held together by complementary base pairing between the bases (A=T
and C=G). The order of the bases on the DNA determines the order of
amino acids in a protein.
National 5 Biology summary notes
8
Protein Synthesis.
DNA is the master copy of the code for making proteins which the cells
need on a day to day basis. DNA must stay in the nucleus where it is unlikely
to be damaged. Proteins are made (synthesised) at ribosomes which are
outside the nucleus, in the cytoplasm. In order for the instructions to make
the protein to reach the ribosomes a copy of the DNA has to be made in the
nucleus and move to the ribosome. This copy is called mRNA, m standing for
messenger. mRNA copies the sequence of bases from the DNA and travels
to the ribosome where the amino acids are arranged into the correct order
for the protein. This is how protein synthesis (the production of protein)
occurs.
Genetic engineering
In nature some simple organisms (e.g. some bacteria) are able to transfer
sections of their DNA from on cell to another without input from humans or
other organisms. This allows them to share DNA for example antibiotic
resistance, and become stronger as a species.
National 5 Biology summary notes
9
The structure of DNA is identical in all living things, as is the process for
synthesising proteins at the ribosome. This means that it is possible from
humans to transfer DNA from one organism to another, this is called
genetic engineering.
Humans can use
genetic engineering to
get organisms to
produce proteins
which would they
would not normally
produce. For example
hormones like human
insulin and human
growth hormone are
both proteins which
can be used to treat
human conditions.
Scientists can put the
gene for either of
these products into
bacteria which grow
and multiply quickly so
that bacteria produce
the proteins and they
can be isolated from
the bacteria and used
to treat humans.
National 5 Biology summary notes
10
Respiration
Respiration is carried out by all cells to make energy. Respiration relies on
diffusion to get the raw materials into cells and to release dome of the
products. During respiration chemical energy trapped inside substrates such
as glucose is released by the cell in a series of enzyme-controlled reactions.
Energy is used and moved in cells by a molecule called adenosine triphosphate
(ATP). During respiration the chemical energy trapped in glucose is moved
into ATP molecules so that it can be used for other processes in the cell. In
cells energy is needed for many cellular activities including muscle cell
contraction, cell division, protein synthesis and transmission of nerve
impulses.
ATP can be broken down to release the energy trapped inside it. When ATP
is broken down the 3rd phosphate attached at the end of the molecule is
broken away to leave behind ADP (adenosine diphosphate and a free
phosphate) when this happens energy it released. This reaction is reversible.
It is summarised in the diagram below.
National 5 Biology summary notes
11
In the presence of oxygen (Aerobic)
During respiration in the presence of oxygen, glucose is broken down by
enzymes to pyruvate. Pyruvate is subsequently broken down to carbon
dioxide and water. This is complete breakdown of glucose as the products
are relatively harmless. Because the glucose is completely broken down 38
molecules of ATP produced for every molecule of glucose.
In the absence of oxygen – Fermentation (Anaerobic)
Cells still carry out respiration to make ATP if there is no oxygen available,
but the process is less efficient. The breakdown process is different in
animal cells and plant cells.
In animal cells glucose is broken down to pyruvate by enzymes. Pyruvate is
then turned into lactic acid. This process only produces 2 ATP from every
molecule of glucose.
In plant cells glucose is broken down to pyruvate by enzymes. Pyruvate is
then turned into alcohol and carbon dioxide. This process also only produces
2 ATP for every molecule of glucose.
Cell Type
All cells
Animal cells
Plant cells
Oxygen needed
Yes
No
No
Substrate
(source of
chemical energy)
glucose
glucose
glucose
carbon dioxide
and water
lactic acid
carbon dioxide
and alcohol
Number of ATP
produced (per
glucose)
38
2
2
Process
controlled by
enzymes
enzymes
enzymes
first stage in
cytoplasm;
aerobic stages
occur in
mitochondria
cytoplasm
cytoplasm
Final products
Location in cell
National 5 Biology summary notes
12
Photosynthesis
Photosynthesis is a process carried out by all green plants. It is a process
which results in the production of food (in the form of the carbohydrate
sugar) in plants. Photosynthesis provides all of the food that all organisms
rely on for survival so is an extremely important process. The word equation
for photosynthesis is
light energy
carbon
oxygen
dioxide
+
water
sugar +
There are 2 reactions which take place during photosynthesis, the light
reactions and carbon fixation, both reactions are controlled by enzymes.
Details about each process are given below;
Light reactions
Light energy is trapped by chlorophyll in
the chloroplasts of cells.
Light energy is used to split water (H2O)
molecules into hydrogen (H2) and oxygen (O2).
Energy is released in this process and is used to
produce ATP from ADP and Phosphate.
Oxygen is released as a by-product, Hydrogen
and ATP are needed for the next stage.
Water (H2O)
Hydrogen –
Oxygen –
H2
Needed for
carbon fixation
ADP + ATP
Phosphate
Carbon Fixation
Carbon dioxide is reduced using hydrogen and ATP from the light reactions
to produce sugar (chemical energy)
The energy change which occurs during photosynthesis is light energy ->
chemical energy.
The sugar which is produced has 3 uses inside the plant. Some of the sugar
will be used straight away for respiration (to make energy), if there is
excess sugar some of it will be stored as starch and some of it will be used
National 5 Biology summary notes
13
O2
(released as a
by-product)
to make the structural carbohydrate cellulose which is found in plant cell
walls.
The rate
o
o
o
of photosynthesis in plants is restricted by 3 limiting factors;
carbon dioxide concentration
light intensity
temperature.
If any of these factors is in short supply then the rate of photosynthesis
will not be at its optimum and cell may not have enough food to make energy
for growth.
Limiting factor graphs
It is common for questions about limiting factors to be made based on
graphs.
You usually have to give information about what the limiting factor is at a
given point on the graph.
National 5 Biology summary notes
14