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Higher Biology

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Speyside High School Biology Department S3 Biology Course – PowerPoint PPT presentation

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Title: Higher Biology


1
Higher Biology
  • Unit 1
  • Cell Biology
  • Cell structure in relation to function

2
  • 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.

3
  • 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).

4
  • 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.

5
Paramecium
6
Euglena
7
Root hair
8
Leaf epidermis
9
Phloem
10
Xylem
11
Leaf mesophyll
12
Parenchyma
13
Lining of kidney tubule
14
Return
Lining of trachea
15
Lining of trachea
16
Lining of mouth
17
Bone cell
18
Fat cell
19
Red blood cell
20
Muscle Cell
21
Nerve cell
22
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23
Cell Ultrastructure
24
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25
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26
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27
Cell Boundries
  • 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.

28
  • Plasma membrane
  • Forms the cell membrane and forms or surrounds
    all cell organelles.

29
  • Made of a double layer of phospholipid molecules
    with protein molecules embedded.
  • Called fluid-mosaic model because
  • Molecules move around like fluid
  • Proteins form a pattern on surface (mosaic)
  • Some protein molecules enclose a pore through
    which small molecules can pass in/out of the cell.

30
Functions of the plasma membrane
  • Molecules can enter or leave a cell, across the
    membrane, in 5 ways
  • Diffusion
  • Osmosis
  • Endocytosis
  • Exocytosis
  • Active Transport

31
Diffusion
  • Movement of molecules of (gas or) liquid from an
    area of high concentration to an area of low
    concentration down a concentration gradient.

32
  • The concentration gradient is the difference in
    concentration between two areas.

33
  • Molecules cross the plasma membrane in two ways
  • Through the phospholipid layer
  • Through pores in the protein molecules

34
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)

35
  • Water moves from a high water concentration to
    low water concentration
  • HWC LWC

36
Effects of osmosis on cells
37
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38
  • Hypotonic higher water concentration
  • Hypertonic lower water concentration
  • Isotonic same water concentration

39
  • 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.

40
Endo- and Exo-cytosis
  • Cells sometimes take in, or expel, large
    quantities of material by forming a pocket in
    the membrane.
  • This is called endocytosis (taking material into
    the cell) or exocytosis (materials leave the
    cell).

41
  • An example of endocytosis is

42
Phagocytosis
43
  • In this form of endocytosis the cell engulfs
    solid particles (e.g. amoeba) like eating a
    bacterium.

44
Active Transport
  • Movement of ions across the plasma membrane
    against the concentration gradient
  • i.e. Low concentration ? High concentration

45
  • Energy is needed.
  • Protein molecules transport ions across the
    membrane.

46
IN
High conc. inside the cell
Low conc. outside the cell
Energy
Low conc. inside the cell
High conc. outside the cell
OUT
47
Essay question
  • Discuss the role of the plasma membrane under the
    following headings
  • The structure of the plasma membrane (4 marks)
  • The role of the plasma membrane in transport (6
    marks)

48
  • Discuss the role of the plasma membrane under the
    following headings
  • The structure of the plasma membrane (4 marks)
  • The role of the plasma membrane in transport (6
    marks)
  • 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

49
Lives in the sea Lives in the sea Lives in fresh water Lives in fresh water Lives in fresh water
Ion Fresh water Sea Water Lobster Mussel Cray-fish Frog Fresh WaterMussel
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
50
  • 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).

51
Higher Biology
  • Unit 1
  • Cell Biology
  • Photosynthesis

52
Absorption, reflection and transmission of light
by a leaf
12 of light reflected
Light shining on leaf (100 )
83 of light absorbed but only 4 of this is
used for photosynthesis
5 of light transmitted
53
Light absorption by leaf pigments
  • Leaves contain several coloured pigments of which
    chlorophyll is the most important.
  • These pigments absorb light energy.

54
Which wavelengths of light are used
  • 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
55
  • 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.

56
violet blue green yellow orange red
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.
57
  • The main wavelengths absorbed are violet and
    blue, and some red.
  • These are most important wavelengths for a plant
    in photosynthesis.

58
Absorbtion and Action Spectra
  • A leaf contains several pigments which can be
    separated by chromatography.
  • The main pigments are
  • Chlorophyll a (blue-green)
  • Chlorophyll b (yellow-green)
  • Carotene (yellow)
  • Xanthophyll (yellow)

59
  • An absorption spectrum shows the absorption of
    light of each wavelength 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.

60
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61
  • The presence of several pigments increases the
    range of wavelengths the plant can make use of.

62
Separation of photosynthetic pigments by thin
layer chromatography
63
Name Rf value
Carotene
Chlorophyll a
Chlorophyll b
Xanthophyll
64
Chloroplasts
  • The main pigments (chlorophyll ab, carotene and
    xanthophyll) are contained in the chloroplasts.

65
  • Chloroplasts have
  • 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.

66
Chemistry of photosynthesis
  • Remember Standard Grade
  • Carbon dioxide water light energy ? glucose
    oxygen
  • This takes place in 2 main stages
  • Photolysis (needs light)
  • Carbon fixation (Calvin cycle)

67
Photolysis
  • 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.

68
WATER
Oxygen
Hydrogen
ENERGY
69
  • 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

70
  • The hydrogen and the ATP play an important part
    in the second stage of photosynthesis, called
    CARBON FIXATION.

71
Quick Quiz
3
5
4
2
6
72
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

73
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)

74
  • The resulting 6-carbon compound is unstable and
    breaks down into two molecules of 3-carbon
    glycerate-3-phosphate (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).

75
CO2 (1C)
6C unstable
2 x GP (3C)
NADPH2
ATP
RuBP (5C)
NADP
ADP Pi
Triose phosphate (3C)
CALVIN CYCLE
Glucose
Complex carbohydrates other organic molecules
76
  • Triose phosphate has two possible fates
  • 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)

77
  • 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.

78
Limiting factors
  • 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.

79
B
Rate of photosynthesis
30C
B
20C
B
A
10C
Carbon dioxide concentration
80
  • 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

81
Limiting factor either Light or Temp
Limiting factor either CO2 or Temp
Rate of photosynthesis
Rate of photosynthesis
Limiting factor Light intensity
Limiting factor CO2 conc.
Light intensity
Carbon dioxide concentration
82
Aerobic Respiration
  • Unit 1 Higher Biology

83
Energy storage in the cell
  • Chemical energy is stored in cells in molecules
    of ATP (Adenosine Tri-Phosphate).

84
  • (Pi Inorganic phosphate)
  • In order to release the chemical energy, the bond
    attaching the third phosphate is broken (shown in
    red).

85
ATP formation
  • 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.

86
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  • The conversion of ADP to ATP is called
    Phosphorylation.

88
Summary
89
Aerobic respiration S-Grade
90
Chemistry of Aerobic respiration
  • Aerobic respiration is the complete oxidation of
    molecules of glucose to release energy.
  • Oxidation is the removal of hydrogen with the
    release of energy.

91
  • Aerobic respiration takes place in 3 stages
  • Glycolysis
  • Krebs Cycle
  • Cytochrome system.

92
Stage 1 Glycolysis
93
  • 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.

94
  • 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)

95
Stage 2 The Krebs Cycle
  • a.k.a. The Citric Acid cycle OR Tri-carboxylic
    acid (TCA) cycle.
  • This takes place in the mitochondria.

96
Mitochondria
  • 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.

97
  • The inner membrane is folded into cristae which
    provide a large surface area for the stalked
    particles on which the cytochrome system takes
    place.

98
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100
  • 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.

101
  • Acetyl Co-A now enters the Krebs 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.

102
Stage 3 Cytochrome system
  • 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.

103
  • 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.

104
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105
Production of ATP
  • Complete oxidation of one molecule of glucose
    produces 38 molecules of ATP (36 from oxidative
    phoshorylation in the cytochrome system and 2
    from glycolysis).

106
  • 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.

107
Anaerobic respiration
  • 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.

108
  • During anaerobic respiration Glycolysis occurs as
    normal, but there is no Krebs cycle.

109
Oxygen available
Krebs cycle
Glucose
Pyruvic Acid
Oxygen not available
ANIMALS
PLANTS
Lactic Acid
Ethanol CO2
110
Aerobic respiration Anaerobic respiration
Oxygen required?
Total ATP production (per glucose molecule)
Other products (plants)
Other products (animals)
111
  • 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.

112
Measuring the rate of aerobic respiration
  • The rate of aerobic respiration can be measured
    using a respirometer.

113
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114
  • 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.

115
  • 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.

116
Synthesis and release of proteins
  • Higher Biology
  • Unit 1

117
Codons
Amino acids
Translation
Single stranded
Ribosomes
Uracil
Peptide bonds
tRNA
C,H,O,N
mRNA
Globular
Transcription
Proteins
Fibrous
Rough ER
synthesis
Genetic code
DNA Polymerase
Replication
Secretion
Golgi body
Double helix
Chromosomes
A,T,C,G
DNA
Base
Nucleotide
A-T C-G
Genes
Sugar
Phosphate
118
Structure and variety of proteins
  • 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.

119
Role of proteins
TYPE ROLE EXAMPLES
Globular Enzymes
Globular Structural
Globular Hormones
Globular Antibodies
Fibrous Make hair and nails
120
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

121
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.

122
Structure of DNA
  • A DNA molecule is made of 2 chains of
    nucleotides.
  • Each nucleotide contains
  • A deoxyribose sugar molecule
  • A phosphate molecule
  • A base molecule

123
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124
  • There are four different bases, and therefore
    four different nucleotides

Adenine nucleotide (A)
Guanine nucleotide (G)
Thymine nucleotide (T)
Cytosine nucleotide (C)
125
  • Nucleotides are linked together by means of
    chemical bonds between phosphate and sugar
    molecules called sugar-phosphate bonds

126
  • Two of these nucleotide chains are joined by
    means of hydrogen bonds between bases.
  • ADENINE always bonds with THYMINE
  • CYTOSINE always bonds with GUANINE

127
  • The two, linked, nucleotide chains are twisted
    into a coil called a double helix.

128
  • 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.

129
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130
Replication of DNA
  • 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.

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132
  • Replication requires
  • A DNA molecule
  • unattached nucleotides of 4 types
  • enzymes (DNA polymerase)
  • energy (in the form of ATP)

133
  • Replication takes place in these stages
  • DNA uncoils
  • The hydrogen bonds between bases break (starting
    at the end like a zip)
  • Free nucleotides attach to exposed bases
  • Sugar-phosphate back bone reforms

134
The Genetic Code
  • 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.

135
  • 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.

136
  • So a DNA strand with base sequence
  • Would code for (part of) protein
  • (one protein molecule may be hundreds or
    thousands of amino acids long)

137
RNA (ribonucleic acid)
  • 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)

138
  • RNA differs from DNA in 3 ways
  • RNA is single stranded
  • RNA contains ribose sugar
  • In RNA the base thymine is replaced by Uracil

139
  • 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.

140
Transcription
  • 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.

141
G
T
C
A
C
T
A
T
A
G
G
C
G
T
DNA strand
A
A
G
C
C
G
A
T
T
C
G
G
A
T
A
A
C
G
C
T
G
C
C
G
T
T
C
A
C
A
G
T
G
A
T
A
T
C
C
G
One gene
142
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

143
Fluid filled cavity between sheets
Ribosomes
Sheets of endoplasmic reticulum
144
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
  • Codon triplet of bases on mRNA
  • Anti-codon Complementary triplet of bases on tRNA

145
Stage 1
Stage 2
Stage 3
146
  • 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.

147
Secretion of proteins
Nucleus
Rough endoplasmic reticulum
Nuclear membrane
Pore
Ribosome
Golgi Apparatus
Vesicle
Cell membrane
148
  • 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.

149
  • 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.

150
Cellular Defence Mechanisms
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153
Virus Structure
154
Reproduction of viruses
  • Viruses can only reproduce inside the cells of a
    host organism.
  • They use the hosts nucleotides for replication
    and the hosts amino acids to construct protein
    coats.

155
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157
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158
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159
Defence against viruses
160
First line of defence
  • Mechanisms by which our bodies attempt to prevent
    entry of harmful microbes.

161
Second line of defence
  • Mechanisms by which our bodies attempt to kill
    harmful microbes which have succeeded in entering.

162
Immunity
  • Immunity is the ability of an organism to resist
    disease. The blood is usually involved.
  • There are two types
  • Non-specific immunity (phagocytosis)
  • Specific immunity (antibodies)

163
1. Non-specific Immunity
  • Provides protection against a wide range of
    invading microbes e.g. by phagocytosis carried
    out by white blood cells.

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165
  • Read page 70 of Torrance and make your own notes
    on Phagocytosis.
  • Then
  • 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

166
Phagocytosis
  • Phagocytosis is the process by which foreign
    bodies such as bacteria are engulfed and
    destroyed.
  • Cells capable of phagocytosis are called
    phagocytes.

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168
  • 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.

169
  • Lysosomes fuse with the vacuole and release their
    enzymes into it.
  • The bacterium becomes digested and the breakdown
    products are absorbed by the phagocyte.

170
  • 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.

171
2. Specific immunity
  • A specific invading particle (e.g. A virus) is
    attacked by a specific defending chemical.

172
  • 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.

173
How antibodies work
  • An antibody is a Y-shaped molecule

174
  • The binding sites on the arms attach to antigen
    molecules making them harmless

175
  • There are many types of lymphocyte, each type
    targeting one antigen with specific antibodies.

176
Types of specific immunity
  • Active immunity
  • We produce our own antibodies by
  • Suffering from the disease and retaining the
    antibodies in the blood (natural)
  • Receiving a vaccine of treated antigen (e.g.
    Empty virus coats) which triggers antibody
    formation (artificial).

177
  • (b) Passive immunity
  • We receive ready-made antibodies from
  • Mother, across the placenta (natural)
  • Another mammal (e.g. A horse) which has made the
    antibodies in response to treatment
    (artificial).

178
Rejection of transplanted tissues
  • Make your own notes from Page 73 of Torrance.

179
Cellular Defence Mechanisms in Plants
  • Plants defend themselves from attack by
  • Producing toxic compounds
  • Isolating the infected area or infectious
    organism

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(a) Production of toxic compounds
  • 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.

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  • (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
    pathogens metabolism and render it harmless.

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  • (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.

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(b) Isolation of the problem
  • 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.

184
  • 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.

185
  • (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.
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