Higher Biology
Unit 1
Cell Biology:
Cell structure in relation to function
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
•
In a multicellular (many-celled) organism
the cells are organised into tissues.
•
A tissue is a group of similar cells which
work together to carry out a specific
function.
Higher
Biology
Course
Unit 1
•
Some tissues have only one type of cell
(e.g. muscle). Other tissues have several
types of cells (e.g. phloem contains sieve
tubes and companion cells).
Higher
Biology
Course
Unit 1
•
The structure of a cell is related to its
function (what the cell does).
•
In a unicellular (one-celled) organism
(e.g. amoeba, paramecium, euglena or
yeast) all the processes necessary for
life are carried out in a single cell.
Paramecium
Higher
Biology
Course
Unit 1
Euglena
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Root hair
Leaf
epidermis
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Phloem
Higher
Biology
Course
Unit 1
Xylem
Higher
Biology
Course
Unit 1
Leaf mesophyll
Higher
Biology
Course
Unit 1
Parenchyma
Higher
Biology
Course
Unit 1
Lining of
kidney tubule
Higher
Biology
Course
Unit 1
Return
Lining of
trachea
Higher
Biology
Course
Unit 1
Lining of
trachea
Higher
Biology
Course
Unit 1
Lining of
mouth
Higher
Biology
Course
Unit 1
Bone cell
Higher
Biology
Course
Unit 1
Fat cell
Higher
Biology
Course
Unit 1
Red blood cell
Higher
Biology
Course
Unit 1
Muscle Cell
Higher
Biology
Course
Unit 1
Nerve cell
Higher
Biology
Course
Unit 1
Cell Ultrastructure
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Cell Boundries
Higher
Biology
Course
Unit 1
•
Cell wall
•
•
•
•
Outer boundary of plant cells
Made of cellulose fibres in layers
Strong, slightly elastic
Absorbs water, providing a pathway for
water movement through plant tissues.
• Plasma membrane
•
Higher
Biology
Course
Unit 1
Forms the cell membrane and forms or
surrounds all cell organelles.
•
Made of a double layer of
phospholipid molecules with protein
molecules embedded.
•
Called “fluid-mosaic” model because
•
1. Molecules move around like fluid
2. Proteins form a pattern on surface
(mosaic)
Some protein molecules enclose a
pore through which small molecules
can pass in/out of the cell.
Higher
Biology
Course
Unit 1
Functions of the plasma
membrane
Higher
Biology
Course
Unit 1
Molecules can enter or leave a cell, across
the membrane, in 5 ways:
1. Diffusion
2. Osmosis
3. Endocytosis
4. Exocytosis
5. Active Transport
Diffusion
•
Higher
Biology
Course
Unit 1
Movement of molecules of (gas or) liquid
from an area of high concentration to an
area of low concentration down a
concentration gradient.
Higher
Biology
Course
Unit 1
•
The concentration gradient is the
difference in concentration between two
areas.
Higher
Biology
Course
Unit 1
Molecules cross the plasma membrane in
two ways:
• Through the phospholipid layer
• Through pores in the protein molecules
Osmosis
•
Diffusion of water molecules
•
Through a selectively permeable
membrane (e.g. plasma membrane)
•
(S.P. Membrane is a membrane with
pores which allows small molecules to
pass but not large ones)
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
•
Water moves from a high water
concentration to low water concentration
HWC
LWC
Effects of osmosis on
cells
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Hypotonic – higher water concentration
Hypertonic – lower water concentration
Isotonic – same water concentration
Higher
Biology
Course
Unit 1
Turgid – cell swollen with water
Flaccid – cell limp through loss of water
Plasmolysed – in Plant cells, water loss
causes cytoplasm to shrink away from
the cell wall.
Endo- and Exo-cytosis
Cells sometimes take in, or expel, large
quantities of material by forming a
“pocket” in the membrane.
Higher
Biology
Course
Unit 1
This is called endocytosis (taking material
into the cell) or exocytosis (materials
leave the cell).
Higher
Biology
Course
Unit 1
An example of endocytosis is:
Phagocytosis
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
In this form of endocytosis the cell engulfs
solid particles (e.g. amoeba) – like
“eating” a bacterium.
Active Transport
Higher
Biology
Course
Unit 1
Movement of ions across the plasma
membrane against the concentration
gradient
i.e. Low concentration → High concentration
Higher
Biology
Course
Unit 1
Energy is needed.
Protein molecules transport ions across the
membrane.
IN
Higher
Biology
Course
HighUnit
conc.
1
Low conc. outside
the cell
inside the
cell
Energy
Low conc.
inside the
cell
High conc.
outside the
cell
OUT
Essay question
Higher
Biology
Course
Unit 1
Discuss the role of the plasma membrane
under the following headings:
1. The structure of the plasma membrane
(4 marks)
2. The role of the plasma membrane in
transport (6 marks)
Discuss the role of the plasma membrane under the following headings:
1.
The structure of the plasma membrane (4 marks)
2.
The role of the plasma membrane in transport (6 marks)
Higher
Biology
Course
Unit 1
Plasma membrane:
•
Composed of phospholipid bilayer (two layers)
•
Contains proteins.
•
Some proteins form pores through the membrane.
•
Described as a “fluid mosaic”
Role of plasma membrane:
•
Diffusion + movement of liquid/gas from area of high conc. to area of low
conc.
•
Osmosis + movement of water from area of HWC to area of LWC.
•
Endocytosis + description of engulfing a large molecule.
•
Phagocytosis is an example of endocytosis (eating bacteria).
•
Active transport + movement from area of low conc. to area of high conc.
•
Active transport requires energy and a carrier protein.
1 mark for each bullet point.
TOTAL 10 Marks
Lives in the sea
Lives in fresh
Higher
Biology
Course
Unit 1
water
Ion
Fresh
water
Sea
Water
Lobster
Mussel
Crayfish
Frog
Fresh
Water
Mussel
Na
0.24
478.3
530.9
79
212
109
15.6
K
0.005
10.1
8.7
152
4.1
2.6
0.5
Ca
0.67
10.5
15.8
7.3
15.8
2.1
6.0
Mg
0.04
54.5
7.6
34
1.5
1.3
0.2
Cl
0.23
558.4
558.4
94
199
78
11.7
SO4
0.05
28.8
8.9
8.8
-
-
-
Concentrations in mM per kg
Higher
Biology
Course
Unit 1
In the example above, the lobster actively
transports sodium inwards (higher
concentration in the body than the sea
water), actively transports magnesium
out (lower concentration in body than
sea water), but does not regulate
chloride (concentration equal).
Higher Biology
Unit 1
Cell Biology:
Photosynthesis
Absorption, reflection and
transmission of light by a leaf
Light
shining on
leaf (100 %)
12 % of
light
reflected
83 % of light absorbed but only 4 %
of this is used for photosynthesis
5 % of light
transmitted
Higher
Biology
Course
Unit 1
Light absorption by leaf
pigments
Higher
Biology
Course
Unit 1
Leaves contain several coloured pigments of
which chlorophyll is the most important.
These pigments absorb light energy.
Which wavelengths of light
are used
Higher
Biology
Course
Unit 1
White light is made up of several different
wavelengths of light from 400 nm to
700 nm.
Normal spectrum of white light:
violet
blue
green
yellow
orange red
Higher
Biology
Course
Unit 1
•
•
•
•
•
Collect a leaf and cut into small pieces.
Add some propanone and sand into a
mortar and pestle.
Grind this up, until the propanone turns
green.
Filter the mixture into a test tube.
Hold the spectroscope up towards the
test tube and look towards the light.
violet
blue
green
yellow
orange red
Higher
Biology
Course
Unit 1
Spectrum viewed through Chlorophyll
violet
blue
green
yellow
orange red
The blue and violet are no longer visible and
only some of the red is still seen. These
have been absorbed by the chlorophyll.
Higher
Biology
Course
Unit 1
The main wavelengths absorbed are violet
and blue, and some red.
These are most important wavelengths for a
plant in photosynthesis.
Absorbtion and Action
Spectra
Higher
Biology
Course
Unit 1
A leaf contains several pigments which can
be separated by chromatography.
The main pigments are:
1. Chlorophyll a (blue-green)
2. Chlorophyll b (yellow-green)
3. Carotene (yellow)
4. Xanthophyll (yellow)
Higher
An absorption spectrum shows the
Biology
Course
absorption of light of each wavelengthUnit 1
by each pigment.
An action spectrum shows the rate of
photosynthesis at each light wavelength.
Comparison of absorption and action
spectra reveals a close match – this is
good evidence for the importance of leaf
pigments in photosynthesis.
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
The presence of several pigments increases
the range of wavelengths the plant can
make use of.
Separation of photosynthetic
pigments by thin layer
chromatography
Higher
Biology
Course
Unit 1
Name
Carotene
Chlorophyll a
Chlorophyll b
Xanthophyll
Rf
value
Higher
Biology
Course
Unit 1
Chloroplasts
The main pigments (chlorophyll a+b,
carotene and xanthophyll) are contained
in the chloroplasts.
Lamella
Chloroplasts have:
•
•
•
•
Higher
Biology
Course
Unit 1
A double plasma membrane
A liquid stroma
Stacks of flattened membrane bags
called grana (singular – granum) which
contain chlorophyll
Connecting tubes between grana called
lamellae.
Chemistry of
photosynthesis
Higher
Biology
Course
Unit 1
Remember Standard Grade:
Carbon dioxide + water + light energy → glucose + oxygen
This takes place in 2 main stages:
1. Photolysis (needs light)
2. Carbon fixation (Calvin cycle)
Photolysis
Higher
Biology
Course
Unit 1
Happens in the GRANA of the chloroplasts.
Light energy is absorbed by chlorophyll and
used to split water molecules into
hydrogen and oxygen.
Energy is released.
Higher
Biology
Course
Unit 1
WATER
Oxygen
ENERGY
Hydrogen
Higher
Biology
Course
Unit 1
These products are treated like this:
OXYGEN – released as a by-product.
HYDROGEN – attached to a hydrogen
acceptor molecule (NADP) to form
NADPH2
ENERGY – stored as ATP
Higher
Biology
Course
Unit 1
The hydrogen and the ATP play an
important part in the second stage of
photosynthesis, called CARBON
FIXATION.
Quick Quiz
Higher
Biology
Course
Unit 1
3
5
Lamella
4
2
6
Answers
1.
Carbon dioxide + water + light energy → glucose +
oxygen
2. Grana/Granum
3. Outer membrane
4. Lamellae
5. Inner membrane
6. Stroma
7. Grana
8. Water split to hydrogen & oxygen, energy released
9. Picked up by NADP to form NADPH2/Picked up by
hydrogen acceptor
10. In ATP
Higher
Biology
Course
Unit 1
Carbon Fixation
Takes place in the STROMA of the
chloroplast.
Molecules of carbon dioxide diffuse into
the chloroplasts where they attach to
molecules of 5-carbon Ribulose
biphosphate (RuBP)
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
The resulting 6-carbon compound is
unstable and breaks down into two
molecules of 3-carbon glycerate-3phosphate (GP).
In the next step, GP is reduced to triose
phosphate (3-carbon) by the addition of
hydrogen (from the NADPH2) and energy
(from ATP).
CO2
(1C)
2 x GP (3C)
6C unstable
RuBP (5C)
NADPH2
ATP
NADP
ADP + Pi
Triose
phosphate (3C)
CALVIN
CYCLE
Glucose
Complex carbohydrates +
other organic molecules
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Triose phosphate has two possible fates:
1. Synthesis of glucose (6 carbon) which is
then built up into other carbohydrates
(e.g. starch and cellulose)
Plants also use carbohydrates to make
other organic molecules (e.g. proteins,
fats and nucleic acids)
Higher
Biology
Course
Unit 1
2. Conversion to RuBP so that more carbon
dioxide can be taken up.
The cycle of reactions involved in carbon
fixation is know as the calvin cycle.
Limiting factors
Higher
Biology
Course
Unit 1
A limiting factor is a factor which slows
down the process of photosynthesis if is
in short supply.
Limiting factors are light intensity , carbon
dioxide concentration and temperature.
Higher
Biology
Course
Unit 1
Rate of photosynthesis
B
30°C
B
20°C
A
B
10°C
Carbon dioxide concentration
Higher
Biology
Course
Unit 1
At point A: Rate of photosynthesis depends
on carbon dioxide concentration,
regardless of temperature.
Carbon dioxide is the limiting factor.
At point B: Further increase in CO2 has no
effect. The rate of photosynthesis is
increased by raising the temperature.
Temperature is the limiting factor
Limiting
factor either
Light or Temp
Carbon
dioxide
concentration
Rate of
photosynthesis
Rate of
photosynthesis
Limiting factor =
CO2 conc.
Limiting
factor either
CO2 or Temp
Higher
Biology
Course
Unit 1
Limiting factor =
Light intensity
Light
intensity
Aerobic Respiration
Unit 1: Higher Biology
Energy storage in the cell
Chemical energy is stored in cells in
molecules of ATP (Adenosine TriPhosphate).
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
(Pi = Inorganic phosphate)
In order to release the chemical energy,
the bond attaching the third phosphate is
broken (shown in red).
ATP formation
Higher
Biology
Course
Unit 1
A molecule of ATP forms when a molecule of
ADP (Adenosine Di-Phosphate) joins with
an inorganic phosphate.
The energy required to join the Pi to the
ADP comes from the chemical energy
released from the breakdown of glucose
during respiration.
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
The conversion of ADP to ATP is called
Phosphorylation.
Summary
Higher
Biology
Course
Unit 1
Aerobic respiration – SGrade
Higher
Biology
Course
Unit 1
Chemistry of Aerobic
respiration
Higher
Biology
Course
Unit 1
Aerobic respiration is the complete
oxidation of molecules of glucose to
release energy.
Oxidation is the removal of hydrogen with
the release of energy.
Higher
Biology
Course
Unit 1
Aerobic respiration takes place in 3
stages:
1. Glycolysis
2. Kreb’s Cycle
3. Cytochrome system.
Stage 1: Glycolysis
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Glucose molecules (6 carbons) are broken
down into 2 molecules of 3-carbon
molecule called Pyruvic acid.
Happen in the cytoplasm.
No oxygen is required.
Higher
Biology
Course
Unit 1
There is a net gain of 2 ATP molecules.
Hydrogen is released and temporarily
attached to a co-enzyme carrier
molecule called NAD.
NAD + 2H
NADH2 (reduced co-enzyme)
Stage 2: The Kreb’s Cycle
a.k.a. The Citric Acid cycle OR Tricarboxylic acid (TCA) cycle.
This takes place in the mitochondria.
Higher
Biology
Course
Unit 1
Mitochondria
Higher
Biology
Course
Unit 1
Mitochondria (singular = mitochondrion) are
sausage shaped organelles surrounded by
a double plasma membrane.
The centre of the called the Matrix and is
filled with fluid.
Higher
Biology
Course
Unit 1
The inner membrane is folded into cristae
which provide a large surface area for the
stalked particles on which the cytochrome
system takes place.
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
• The pyruvic acid diffuses from the
cytoplasm into the mitochondrion.
• In the matrix, the pyruvic acid is
converted to a 2-carbon compound
called acetyl Co-A, releases CO2 and
hydrogen. The hydrogen is bound to
NAD.
Higher
Biology
Course
Unit 1
• Acetyl Co-A now enters the Kreb’s cycle
by combining with a 4-carbon compound
to form 6-carbon citric acid.
• Citric acid is then broken down in a
series of oxidation reactions to the
original 4-carbon compound and the
cycle begins again.
• The Hydrogen which is released binds
with NAD.
Stage 3: Cytochrome
system
Higher
Biology
Course
Unit 1
• This takes place on the stalked particles
on the cristae.
• Hydrogen is released from the NADH2
and passed along a “chain” of hydrogen
carriers called the cytochrome system.
Higher
Biology
Course
Unit 1
• As each pair of hydrogen atoms are
passed along the chain enough energy is
released to make 3 molecules of ATP. This
is called oxidative phosphorylation.
• At the end of the chain the hydrogen
combines with oxygen to form water.
Higher
Biology
Course
Unit 1
Production of ATP
Higher
Biology
Course
Unit 1
• Complete oxidation of one molecule of
glucose produces 38 molecules of ATP (36
from oxidative phoshorylation in the
cytochrome system and 2 from glycolysis).
Higher
Biology
Course
Unit 1
As the organism respires it uses oxygen
(and produces carbon dioxide which is
absorbed by the sodium hydroxide). This
causes the liquid level to rise and the
syringe is used to find the volume of
oxygen consumed.
Anaerobic respiration
Higher
Biology
Course
Unit 1
Aerobic respiration only occurs if oxygen is
available to accept the hydrogen at the
end of the cytochrome system.
If no oxygen is available anaerobic
respiration occurs.
Higher
Biology
Course
Unit 1
During anaerobic respiration Glycolysis
occurs as normal, but there is no Kreb’s
cycle.
Oxygen available
Glucose
Pyruvic Acid
Kreb’s cycle
Oxygen not available
ANIMALS
Lactic Acid
Higher
Biology
Course
Unit 1
PLANTS
Ethanol + CO2
Higher
Biology
Course
Unit 1
Aerobic
respiration
Oxygen required?
Total ATP
production (per
glucose molecule)
Other products
(plants)
Other products
(animals)
Anaerobic
respiration
Higher
Biology
Course
Unit 1
Anaerobic respiration is animals occurs
during heavy exercise. After exercise
stops the lactic acid can be converted
back to pyruvic acid by repaying the
“oxygen debt” by breathing heavily. It is
therefore REVERSIBLE.
Anaerobic respiration is plants is
IRREVERSIBLE as the CO2 diffuses out
of the plants.
Measuring the rate of
aerobic respiration
The rate of aerobic respiration can be
measured using a respirometer.
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Parts of this apparatus have the following
purposes:
Glass beads: They are a control to show how
it would be with something that does not
respire.
Water bath: keeps the test tubes at a
constant temperature, as the volume of
gas would increase if the temperature
increased.
Higher
Biology
Course
Unit 1
Syringe: It measures the volume of oxygen
used, by pushing down and returning the
dye to the same level as before.
Sodium hydroxide: Absorbs carbon dioxide.
Higher
Biology
Course
Unit 1
Synthesis and release of
proteins
Higher Biology
Unit 1
Codons
Higher
Biology
Course
Unit 1
Amino
acids
Translation
Peptide
bonds
Ribosomes
tRNA
C,H,O,N
Proteins
Transcription
Fibrous
Rough
ER
Genetic
code
Secretion
DNA
Polymerase
Replication
Chromosomes
Uracil
mRNA
Globular
synthesis
Golgi body
Single
stranded
DNA
Double
helix
A,T,C,G
Base
Nucleotide
Genes
Sugar
Phosphate
A-T
C-G
Structure and variety of proteins
Higher
Biology
Course
Unit 1
• Proteins are composed of the following
elements:
• Carbon, Hydrogen, Oxygen, Nitrogen,
(often Sulphur) = HONCS
• Atoms of these elements form amino acids
(20 different ones).
• Amino acids link by peptide bonds to form
polypeptides.
• Polypeptides link up to form Proteins.
Higher
Biology
Course
Unit 1
Role of proteins
TYPE
ROLE
Globular
Enzymes
Structural
Hormones
Antibodies
Fibrous
Make hair and nails
EXAMPLES
Role of genes
• Chromosomes consist of many genes. These
carry out their instructions by producing
enzymes. Enzymes are made of protein.
• So, genes produce protein; Like this:
Higher
Biology
Course
Unit 1
Protein Synthesis
• Genes contain a chemical code.
• This code is part of a molecule of DNA
(Deoxyribonucleic acid).
• The structure of DNA enables the correct
amino acids to be assembled in the correct
sequence to make a particular protein.
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Structure of DNA
• A DNA molecule is made of 2 chains of
nucleotides.
• Each nucleotide contains:
1. A deoxyribose sugar molecule
2. A phosphate molecule
3. A base molecule
Phosphate
Base
Deoxyribose sugar
Higher
Biology
Course
Unit 1
Phosphate
Base
Deoxyribose sugar
• There are four different bases, and
therefore four different nucleotides:
Adenine nucleotide
(A)
Guanine nucleotide
(G)
Thymine nucleotide
(T)
Cytosine nucleotide
(C)
Higher
Biology
Course
Unit 1
• Nucleotides are linked together by
means of chemical bonds between
phosphate and sugar molecules –
called “sugar-phosphate bonds”:
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
• Two of these nucleotide chains are joined by
means of hydrogen bonds between bases.
ADENINE always bonds with THYMINE
CYTOSINE always bonds with GUANINE
Higher
Biology
Course
Unit 1
• The two, linked, nucleotide chains are twisted
into a coil called a double helix.
Higher
Biology
Course
Unit 1
• Each chromosome consists of one double-helix
shaped molecule of DNA containing many
thousands of base pairs.
• A gene is a section of DNA molecule whose
base order forms the code to make one
protein.
Higher
Biology
Course
Unit 1
Replication of DNA
Higher
Biology
Course
Unit 1
• Chromosomes must be able to copy
themselves so that cells retain the same
genetic information after cell divisions.
• This copying of the DNA in the chromosomes
is called replication.
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
• Replication requires:
(a) A DNA molecule
(b) unattached nucleotides of 4 types
(c) enzymes (DNA polymerase)
(d) energy (in the form of ATP)
Higher
Biology
Course
Unit 1
• Replication takes place in these stages:
1. DNA uncoils
2. The hydrogen bonds between bases break
(starting at the end like a zip)
3. Free nucleotides attach to exposed bases
4. Sugar-phosphate back bone reforms
The Genetic Code
Higher
Biology
Course
Unit 1
• Proteins are made of a long chain of amino
acid molecules.
• A gene contains a code (order of DNA bases)
to ensure that the amino acids are joined in
the correct order to make a specific protein.
• The order of the bases is called the genetic
code.
Higher
Biology
Course
Unit 1
• This is a triplet code because the sequence of
three bases is needed to code for each amino
acid.
•
•
•
•
e.g.
AAG codes for amino acid Phenylalanine
GAC codes for amino acid Aspartic Acid
GGA codes for amino acid Glycine.
So a DNA strand with base sequence:
A
A
G
G
A
C
G
G
A
Would code for (part of) protein:
A
A
G
Phenylalanine
G
A
C
Aspartic acid
G
G
A
Glycine
(one protein molecule may be hundreds or
thousands of amino acids long)
Higher
Biology
Course
Unit 1
RNA (ribonucleic acid)
Higher
Biology
Course
Unit 1
• Protein synthesis takes place on the
ribosomes in the cytoplasm.
• The instructions in the genetic code are
carried from the DNA (in the nucleus) to the
ribosomes by a molecule of messenger RNA
(mRNA)
Higher
Biology
Course
Unit 1
• RNA differs from DNA in 3 ways:
1. RNA is single stranded
2. RNA contains ribose sugar
3. In RNA the base thymine is replaced by
Uracil
Higher
Biology
Course
Unit 1
There are two types of RNA:
• Messenger RNA (mRNA) which carries
the genetic code from the DNA in the
nucleus to a ribosome in the cytoplasm.
• Transfer RNA (tRNA) which carries
amino acids to the ribosomes for
assembling into polypeptide chains.
Transcription
Higher
Biology
Course
Unit 1
• The piece of DNA containing the relevant
gene uncoils and the base pairs separate.
• Complementary RNA nucleotides then attach
to the exposed DNA bases.
• They link together (ribose-phosphate
chemical bonds) to form a messenger RNA
(mRNA) molecule.
G
A
G G T C A C T A T A G G C T
Higher
Biology
Course
Unit 1
A
C
C
DNA
strand
G
A T T
C G
G A
T A A
G C C T
G
C
T
C
C A G T G A T A T C C G
One gene
A
T
G
C
Ribosomes and rough endoplasmic
reticulum
• Ribosomes are:
• Found in all cells
• Free in cytoplasm or attached to rough
endoplasmic reticulum
• Spherical, with two halves
• Site of translation of mRNA into protein
Higher
Biology
Course
Unit 1
Ribosomes
Fluid filled cavity
between sheets
Higher
Biology
Course
Unit 1
Sheets of
endoplasmic
reticulum
Assembling the protein =
translation
• In the cytoplasm are molecules of transfer
RNA (tRNA).
• These are composed to one triplet of bases
and an amino acid molecule.
• e.g.
Alanine
Leucine
G C A
C U G
• Codon: triplet of bases on mRNA
• Anti-codon: Complementary triplet of bases
on tRNA
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Stage 1
Stage 2
Stage 3
Higher
Biology
Course
Unit 1
• The mRNA attaches to a ribosome.
• The ribosome moves along the mRNA with
successive codons entering the “active site”.
• Here, a tRNA with the appropriate anti-codon
is attached.
• Adjacent amino acids then link up by a peptide
bond to form a polypeptide and eventually a
protein.
Secretion of proteins
Nucleus
Nuclear
membrane
Higher
Biology
Course
Unit 1
Rough
endoplasmic
reticulum
Pore
Ribosome
Golgi
Apparatus
Vesicle
Cell
membrane
Higher
Biology
Course
Unit 1
• The golgi apparatus is made up of many
flattened fluid filled sacs.
• Vesicles containing newly made protein are
pinched off the rough endoplasmic reticulum.
• These move towards the Golgi and use with
the outermost sac.
Higher
Biology
Course
Unit 1
•
•
The contents then move down through the
golgi from sac to sac, becoming modified in the
process.
The finished product (e.g. glycoprotein), in a
vesicle, leaves the golgi and moves to the cell
membrane and discharges its contents out of
the cell.
Higher
Biology
Course
Unit 1
Cellular Defence Mechanisms
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Virus Structure
Higher
Biology
Course
Unit 1
Reproduction of viruses
Higher
Biology
Course
Unit 1
Viruses can only reproduce inside the cells
of a host organism.
They use the host’s nucleotides for
replication and the host’s amino acids to
construct protein coats.
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Defence against viruses
Higher
Biology
Course
Unit 1
First line of defence
Higher
Biology
Course
Unit 1
Mechanisms by which our bodies attempt to
prevent entry of harmful microbes.
Second line of defence
Higher
Biology
Course
Unit 1
Mechanisms by which our bodies attempt to
kill harmful microbes which have
succeeded in entering.
Immunity
Immunity is the ability of an organism to
resist disease. The blood is usually
involved.
There are two types:
1. Non-specific immunity (phagocytosis)
2. Specific immunity (antibodies)
Higher
Biology
Course
Unit 1
1. Non-specific Immunity
Higher
Biology
Course
Unit 1
Provides protection against a wide range of
invading microbes e.g. by phagocytosis
carried out by white blood cells.
Higher
Biology
Course
Unit 1
Read page 70 of Torrance and make your
own notes on “Phagocytosis”.
Then:
Higher
Biology
Course
Unit 1
• Prepare a 2-3 min illustrated presentation to
give to the class on the topic, explaining:
• How invading bacteria are detected
• How invading bacteria are engulfed
• What a lysosome is, what it contains and what
it does
• What pus is
Phagocytosis
Phagocytosis is the process by which
foreign bodies such as bacteria are
engulfed and destroyed.
Cells capable of phagocytosis are called
phagocytes.
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
A phagocyte detects chemicals released
by the bacterium and moves up a
concentration gradient towards it.
The phagocyte adheres to the bacterium
and engulfs it into a vacuole formed by
an infolding of the plasma membrane.
Lysosomes fuse with the vacuole and
release their enzymes into it.
Higher
Biology
Course
Unit 1
The bacterium becomes digested and the
breakdown products are absorbed by
the phagocyte.
Higher
Biology
Course
Unit 1
During infection hundreds of phagocytes
migrate to the infected area and engulf
many bacteria by phagocytosis.
Dead bacteria and phagocytes often
gather at a site of infection forming
pus.
2. Specific immunity
Higher
Biology
Course
Unit 1
A specific invading particle (e.g. A virus) is
attacked by a specific defending chemical.
Higher
Biology
Course
Unit 1
Antigen: a complex molecule recognised
by our body as alien (e.g. A virus coat
particle).
Antibody: a chemical produced a
lymphocyte white blood cell to destroy
antigens.
How antibodies work
An antibody is a Y-shaped molecule:
Higher
Biology
Course
Unit 1
The binding sites on the arms attach to
antigen molecules making them
harmless:
Higher
Biology
Course
Unit 1
Higher
Biology
Course
Unit 1
There are many types of lymphocyte, each
type targeting one antigen with specific
antibodies.
Types of specific
immunity
Higher
Biology
Course
Unit 1
(a)Active immunity:
We produce our own antibodies by:
(i) Suffering from the disease and
retaining the antibodies in the blood –
(natural)
(ii) Receiving a vaccine of treated antigen
(e.g. Empty virus coats) which triggers
antibody formation – (artificial).
Higher
Biology
Course
Unit 1
(b) Passive immunity
We receive ready-made antibodies from:
(i) Mother, across the placenta – (natural)
(ii) Another mammal (e.g. A horse) which
has made the antibodies in response to
treatment – (artificial).
Rejection of transplanted
tissues
Make your own notes from Page 73 of
Torrance.
Higher
Biology
Course
Unit 1
Cellular Defence
Mechanisms in Plants
Higher
Biology
Course
Unit 1
Plants defend themselves from attack by:
(a) Producing toxic compounds
(b) Isolating the infected area or infectious
organism
(a) Production of toxic
compounds
Higher
Biology
Course
Unit 1
(i) Cyanide
• Made by clover plants by a process called
cyanogenesis.
• Cyanide works by blocking the
cytochrome system of e.g. Slugs
• It is produced when non-toxic glycoside
and an enzyme are mixed as a result of
leaf damage.
Higher
Biology
Course
Unit 1
(ii) Tannins
• Tannins are toxic to micro-organisms
• They defend by preventing pathogens
e.g. Fungi from gaining access to the
plant organ under attack.
• The tannins act as enzyme inhibitors.
• Therefore, they interfere with the
invading pathogen’s metabolism and
render it harmless.
Higher
Biology
Course
Unit 1
(iii) Nicotine
• This is toxic chemical produced in the
root cells of tobacco plants and
transported to its leaves.
• Since it is poisonous it protects leaves
against attack by herbivorous insects.
• Nicotine can be extracted from tobacco
plants and used as an insecticide.
(b) Isolation of the
problem
Higher
Biology
Course
Unit 1
(i) Insect galls
• When a parasite penetrates the cuticle
of a leaf, the leaf produces a gall in
response to a chemical stimulus.
• A gall is an abnormal swelling of plant
tissue resulting from active division of
cells at the site of the injury.
Higher
Biology
Course
Unit 1
• The combination of the extra layers of
cells and rich deposits of tannin in a gall
provides the plant with a protective
barrier where the parasite can be
isolated.
Higher
Biology
Course
Unit 1
(ii) Resin
• Resin is a sticky substance produced by
many trees.
• When a plant becomes wounded by a
pathogen the resin-secreting cells
increase in activity, trapping pathogens.