Biology Revision notes

Section 1
What are they? Molecules made and used by living organisms such as carbohydrates,
proteins, lipids, DNA, ATP, Water and inorganic ions.
Carbohydrates
Functions :
 Energy storage (Starch and glycogen)
 Energy source in respiration (glucose)
 Structural support (Cellulose in plants)
Monomer- Monosaccharides
Types of monosaccharides
 Alpha and Beta glucose
 Galactose
 Fructose
Formula: - C6H12O6 (isomers = same formula but different arrangement)
Alpha and beta glucose: Alpha glucose has an OH group on the bottom of the first carbon
whereas beta glucose has the OH group on the top

Monosaccharides are joined by a condensation reaction (Removal of H2O from 2 OH groups). This is
known as a glycosidic bond
Disaccharides general formula is C12H22O11
 A Glucose + A Glucose = Maltose
 A Glucose + Galactose = Lactose
 A Glucose + Fructose = Sucrose
Polymers can be seperated by hydrolysis (Addition of H2O). Polysaccharides are many monosaccharides joined by
glycosidic bonds. Examples:
 A Glucose = Amylose which makes starch or glycogen
 B Glucose = Cellulose which makes up the cell wall in plants
Starch acts as an energy store in plants whereas glycogen acts as an energy store in animals. Cellulose makes cell
walls in plants.
Starch and glycogen are good energy stores because:
 They are insoluble so do not affect water potential of the cell which results in them
not diffusing out of the cell.
 They are coiled/branched which means they are compact and more fit in a cell
 They have many C-H bonds which are high in energy and release it when they break
Cellulose structure:
 B glucose is in a straight chain
 Many chains are cross linked by hydrogen bonds to form microfibrils
 Many microfibrils crossover to form macrofibrils
 This forms the structure of the cell wall
 This is very strong so it helps resist bursting or shrinking
Tests:
 Starch- Adding iodine turns blue/black
 Reducing Sugar- Heat with benedict's reagent. Blue means no sugar, green means
traces, yellow means low amounts, orange means moderate and red means high
amounts.
  Non-Reducing- If benedict's came out as blue, add HCl to hydrolyse the glycosidic
bond and add sodium hydrogencarbonate to neutralise it. Heat the solution with
benedict and it should give a positive result if sugars are present.
Proteins
There are 2 types of proteins- Globular and Fibrous. Globular proteins are soluble proteins
with a specific 3D shape e.g. enzymes, hormones, antibodies, haemoglobin. Fibrous proteins
are strong/insoluble/inflexible material e.g. collagen and keratin .
Monomer- Amino Acids

Structure: Central carbon, carboxyl group to the right (COOH), amine group to the left
(NH2), hydrogen above and R group below

Different amino acidcs have different R groups e.g. glycine has a hydrogen in its R group

Amino acids join by condensation reaction between the carboxyl group of one and
amino group of another, leaves a bond between carbon & nitrogen (called a peptide bond)
forming a dipeptide
Structure of proteins
 Primary = sequence of AA, polypeptide chain (held by peptide bonds)
 Secondary = the primary structure (polypeptide chain) coils to form a helix,
held by hydrogen bonds
 Tertiary = secondary structure folds again to form final 3d shape, held
together by hydrogen/ionic/disulfide bonds
 Quaternary = made of more then one polypeptide chain

Examples of quaternary structure proteins are collagen (3 chains), antibodies (3

chains), haemoglobin (4 chains)

Structure of collagen?

 strong material, used to build tendons/ligaments/connective tissues

 primary structure mainly made up of glycine (simplest amino acid)
 secondary structure forms a tight coil (not much branching due to glycine)
 tertiary structure coils again
 quaternary structure made from 3 tertiary structures wrapped around each
other like rope
 = a collagen molecule
 many of these collagen molecules make the tendons/ligaments/connective
tissues

Test: Add biuret's reagent and the solution should turn purple
What is an enzyme? A biological catalyst (substance that speeds up the rate of reaction
without being used up – lowers activation energy)
Enzymes
What makes an enzyme specific? has a specific active site shape, only complementary
substrates can bind to the active site to form enzyme-substrate complexes
Lock and Key Model vs Induced Fit Model?

 LK = active site shape is rigid, only exactly complementary substrates can bind
to form ES complexes
 IF = active site changes shape, the substrate binds to the active site – the
active site changes shape so the substrate fits exactly forming an ES complex

Affect of substrate concentration on enzyme activity?

 increase substrate concentration, increases chance of successful collisions,

increase chance of forming an ES complex, increase rate of reaction
 this continues until all the enzyme's active sites are full/saturated = maximum
rate of reaction

Affect of enzyme concentration on enzyme activity?

 increase enzyme concentration, increases chance of successful collisions,

increase chance of forming an ES complex, increase rate of reaction
 this continues until all the substrates are used up = maximum rate of
reaction

Affect of temperature on enzyme activity?

 as temperature increases
 the kinetic energy increases
 the molecules move faster
 increase chance of successful collisions
 increase chance of forming ES complex
 increase rate of reaction
 carries on till optimum
 after optimum
 bonds in tertiary structure break (hydrogen and ionic bonds)
 lose active site shape
 substrate no longer complementary
 cant form ES complexes
 enzyme denatured

Affect of pH on enzyme activity? if change pH away from optimum, bonds in tertiary

structure break, lose active site shape, no longer form ES complex, enzyme
denatured

Competitive vs Non-Competitive Inhibitors?

 Competitive = a substance with a similar shape to the substrate and a

complementary shape to the enzyme's active site, binds to the active site, blocking
it, preventing ES complexes from forming
  Non-Competitive = a substance that binds to another site on the enzyme
other then the active site, causes the active site to change shape, so less ES
complexes can form

What are the 3 types of Lipids?

 Triglycerides (fat for energy store, insulation, protection of organs)

 Phopholipids (to make membranes)
 Cholesterol (for membrane stability and make hormones)

Structure of triglyceride?

 made of 1 glycerol and 3 fatty acids

 joined by condensation reaction, ester bonds
 bond is COOC
 there are 2 types of triglycerides: saturated fat and unsaturated fat

Saturated vs Unsaturated Fat?

 Saturated = has no carbon double bonds in the R group of the fatty acid
 Unsaturated = has carbon double bonds in the R group of the fatty acid

Structure of phospholipid?

 made of 1 glycerol, 2 fatty acids and 1 phosphate

 phosphate forms a hydrophillic head, fatty acids form hydrophobic tails
 forms a phospholipid bilayer, basic structure of membranes

What are Nucleic Acids? Polymers made from Nucleotides (2 types = DNA and RNA)

What is DNA?

 DeoxyriboNucleic Acid
 found in all organisms (animals, plants, microorganisms)
 carries genes
 genes = section of DNA that codes for a protein
 all organisms are built of proteins

Building block of DNA?

 DNA nucleotide (made of phosphate, deoxyribose sugar, nitrogenous base)

 4 types of nucleotides (each has a different base,
either
Adenine/Thymine/Cytosine/Guanine)

DNA structure?
  DNA Double Helix
 join nucleotides by condensation reaction between sugar and phosphate to
form a polynucleotide
 join 2 polynucleotides by hydrogen bond between the bases
 A joins with T, C joins with G (complementary base pairing)
 produces double strand
 then coil double strand into Double Helix

Properties of DNA Structure?

 Double Stranded = makes DNA more stable & 2 strands act as templates in
semi-conservative replication
 Coil into Helix = more compact
 Sugar-phosphate backbone = protects bases (bases code for protein)
 Hydrogen bonds between bases = weak, so double strand separates more
easily for semi-conservative replication
 Complementary Base Pairing = ensures identical copies of DNA made by
semi-conservative replication

DNA Replication?

occurs in interphase before mitosis & meiosis

occurs by semi-conservative replication

Describe Semi-Conservative Replication?

DNA double strand separate and act as templates, producing 2 identical copies of the
DNA, each has half the original strand and half the new strand
process:

 DNA Helicase breaks hydrogen bonds between the complementary bases

 double strand separates, leaves 2 template stands
 free complementary nucleotides bind to exposed bases on template strands (A to T,
C to G)
 DNA Polymerase joins the sugar-phosphate backbone of the new strand

Evidence for SCR?

 Replicating Bacterial DNA in 2 types of Nitrogen Isotopes, 15N and 14N

 15N = heavy isotope
 14N = light isotope
 Nitrogen found in nitrogenous bases of DNA
 Bacterial DNA made from 15N will have a Heavy Density
 Bacterial DNA made from 14N will have a Light Density
 Experiment = Bacterial DNA made of 15N is replicated in an environment of
14N – produces DNA molecules with half 15/half 14 (semi-conservative replication,
 original strand = 15N & new strand = 14N), therefore, DNA molecule has medium
density

What is RNA?

 RiboNucleic Acid
 2 types (mRNA and tRNA)
 mRNA = messenger RNA
 tRNA = transfer RNA
 both single stranded
 both made of RNA Nucleotides (phosphate, ribose sugar, nitrogenous bases -
AUCG)

What is ATP? Adenosine Triphosphate (Energy Carrier Molecule – delivers energy for
life processes)

Structure of ATP?

 Adenosine Triphosphate
 made from 1 adenosine and 3 phosphates
 formation: ADP + Pi (+ energy used) = ATP
 condensation reaction using ATP Synthase
 carries energy in its bonds
 breakdown: ATP = ADP + Pi (+ energy released)
 hydrolysis reaction using ATP Hydrolase
 releases energy from its bonds

What makes ATP a good deliverer of energy?

 immediate source = need to only break one bond (plus bond is weak)
 manageable source = releases small amount of energy

Uses of ATP (releases energy) in organisms?

 protein synthesis
 organelle synthesis
 DNA replication
 cell division (mitosis)
 active transport
 metabolic reactions
 movement
 maintaining body temperature

Role of Water in Biology?

  found in living organisms = cytoplasm (all organisms), xylem/phloem (in
plants), tissue fluid and blood (in animals)
 also acts as habitats for living organisms

Properties of Water?

 Water Molecules (H20) are dipolar

 Hydrogen has slightly +ve charge and Oxygen has slightly -ve charge
 therefore H20 molecules can form hydrogen bonds with each other

Role of Water in Living Organisms?

I. Habitat (e.g. sea): Water has high specific heat capacity meaning that
a lot of heat needs to be applied before it evaporates due to the presence
of the hydrogen bonds between the water molecules. Also when water
freezes it becomes Ice, which is less dense then liquid water – so it floats
on the surface insulating the water beneath it, preventing it from freezing.
In both cases the water remains liquid to provide an habitat for
organisms.
II. Solvent: Because H20 molecules are dipolar they can separate out
solutes based on their charge, +ve Hydrogen side mixes with -ve solute and
-ve Oxygen side mixes with +ve solute, so solute mixes with water and
becomes dissolved. This is useful in cytoplasm of all cells and supports the
reaction of these solutes, it is also useful in the processes of
diffusion/active transport, and is also useful in transport such as blood and
phloem.
III. Hydrostatic Pressure: Water when pressurised can provide a strong
physical pushing force. Used particularly in Mass Flow (where mass of
water carries large amounts of substances e.g. tissue fluid in capillaries and
phloem in plants). Also helps to support turgidity in plants.
IV. Homeostasis: Mammals and Humans control body temperature by
sweating. Sweat on the skin uses heat from the blood to evaporate, hence,
cooling the individual. Because sweat/water is made up of hydrogen bonds,
it has a stable structure, so requires a large amount of heat for it to
evaporate. This is called Latent Heat of Vaporisation.

What are Inorganic Ions?

 Salts/Minerals
 Inorganic = do not contain carbon, Ion = charged (+ve/-ve)
 e.g. Sodium Ions (Na+), Chloride Ions (Cl-)

Section 2:
Kingdoms in Biology?

 Living Organisms can be placed into 5 groups (Animal, Plant, Bacteria,

Fungi, Protoctista)
 Animal and Plant are Multicellular Organisms (made up of billions of cells
working together)
 Bacteria, Fungi, Protoctista are Microorgansism (made up of one or a few
cells)
 [note: Viruses are not defined as living organisms because they do not have
the standard components of a cell – acellular, and cannot perform MRS GREN
without a host]
 all living organisms are made from cells (multicellular = millions,
microorganism = one/few), all cells have 4 properties = DNA, ribosomes,
cytoplasm, cell membrane

Eukaryotic vs Prokaryotic Cells?

 Eukaryotic = animal/plant cell, has membrane bound organelles (nucleus,

endoplasmic reticulum, golgi body, lysosome, mitochondra)
 Prokaryotic = bacteria, has no membrane bound organelles

What are the 2 forms of Reproduction?

 Sexual & Asexual

 Sexual Reproduction in Animals & Some Plants
 Asexual Reproduction in Microorganisms & Some Plants
 Sexual Reproduction uses 2 parents (each provides a gamete which fuse to
form a zygote, zygote develops into organism)
 Asexual Reproduction uses 1 parent to produce genetically identical
offspring

How does a Zygote develop into an Organism?

 Zygote is a stem cell

 stem cell = undifferentiated/unspecialised cell, can form any type of cell
 zygote divides by mitosis to make many stem cells
 each stem cell differentiates into specialised cell
 each specialised cell divides by mitosis to make many copies and form a
tissue
 different tissues join to form an organ
 different organs join to form an organ system
 this is surrounded by the Body

Define a tissue, organ and organ system?

tissue = a group of specialised cells

organ = made of different tissues
 organ system = different organs working together

What is an Animal Cell made of?

 Organelles (nucleus, endoplasmicreticulum, golgi body,lysosomes,

mitochondria, ribosomes) – all have membrane except the ribosomes
 Cytoplasm (site of chemical reaction)
 Cell Membrane (holds cell contents together, controls what enters/leaves
cell, cell signalling)

Structure of Nucleus?

 contains DNA (made of genes, genes code for making proteins)

 DNA wrapped around histones to form Chromatin
 nucleus has a double membrane, called Nuclear Envelope, which contains
pores
 at centre of nucleus is Nucleolus – produces mRNA (copy of a gene)
 rest of nucleus made of Nucleoplasm (contains the DNA/chromatin)

Endoplasmic Reticulum?

 2 types = Rough and Smooth

 Rough Endoplasmic Reticulum has ribosomes on it, makes proteins
 Smooth Endoplasmic Reticulum has no ribosomes on it, makes
lipids/carbohydrates

Golgi body?

 modifies and packages proteins

 packages them into vesicles for transport
 digestive enzymes are placed into lysosomes (vesicles with membranes
around them)

Mitochondria?

 site of respiration, releases energy, produces ATP (energy carrier molecule)

 has a double membrane, inner membrane folded into Cristae (increases
surface area for enzymes of respiration)
 middle portion called Matrix

Ribosomes?

 attached to RER
 site of protein synthesis

What is a Plant Cell made of?

  Organelles (nucleus, endoplasmic reticulum, golgi body, lysosomes,
mitochondria, chloroplast, vacuole, ribosomes) – all have membrane except the
ribosomes
 Cytoplasm (site of chemical reaction)
 Cell Membrane (holds cell contents together, controls what enters/leaves
cell, cell signalling)
 Cell Wall (made of cellulose, prevents cell from bursting or shrinking)

Structure of chloroplast?

 organelle for photosynthesis

 has double membrane
 contains discs called thylakoids
 thylakoids contain chlorophyll
 stack of thylakoids called granum
 thylakoids surrounded by a fluid called stroma

Vacuole?

Surrounded by a membrane called a tonoplast, contains Cell Sap (water, sugar,

minerals)

What is Bacteria made of?

 No nucleus – loose DNA in the form of a single loop and plasmid

 No membrane bound organelles: smaller ribosomes, mesosomes – infolding
of cell membrane for respiration
 Cytoplasm
 Cell Membrane & Cell Wall (made of peptidoglycan/murein)
 some have a Capsule (reduce water loss, protect from phagocytosis) and
Flagella (movement)

What is Virus made of?

 DNA or RNA (if RNA, also has a enzyme called reverse transcriptase to turn
RNA into DNA)
 Protein Coat called Capsid and Lipid Coat
 Attachment proteins on outside
 (infects host cells by attaching using their attachment protein, send in their
DNA which uses the cell to make the viruses components and uses the cell
membrane to make the viruses lipid coat, hence, producing copies of the virus and
destroying the host cell)

What is a Chromosome?

 DNA in coiled form

 formed during interphase of cell division (mitosis/meiosis) in Animals/Plants
  made of 2 identical/sister chromatids joined by a centromere
 carries 2 copies of the same DNA molecule

What is a homologous pair of chromosomes?

a pair of chromosomes: 1 maternal (from mother)/1 paternal (from father)

carries same genes but different alleles – there are 23 pairs in humans

What is Cell Division?

 formation of new cells in multicellular organisms (animals & plants)

 2 methods = mitosis & meiosis
 mitosis = produces genetically identical cells for growth & repair of tissues
 meiosis = produces genetically different haploid cells as gametes for sexual
reproduction

What does Mitosis (cell cycle) produce?

2 genetically identical cells, diploid (have full set of chromosomes/DNA)

Benefit of Mitosis? growth and repair of tissues

Stages of Mitosis? Interphase/Mitosis/Cytokinesis

Interphase? G1: protein synthesis

S: DNA replication (doubles set of DNA)
G2: organelle synthesis

Mitosis?

Prophase: DNA coils to form chromosomes, nucleus breaksdown, spindle fibres form
Metaphase: chromosomes line up in middle of cell and attach to spindle fibre via
centromere
Anaphase: spindle fibres pull, centromere splits, sister chromatids move to opposite
sides
Telophase: chromatids uncoil, nucleus reforms (left with 2 genetically identical
nuclei)

Cytokinesis? separating cell into 2 (each receives a nucleus and organelles/cytoplasm)

What happens to DNA mass in mitosis? halves

What happens to Chromosome number in mitosis? stays the same (diploid)

What is Cancer? formation of a tumour due to uncontrolled cell division (uncontrolled

mitosis)
How does uncontrolled cell division occur?

 due to mutation of DNA/cells forming cancer cells

 mutation can occur randomly or due to mutagens (chemicals/radiation)
 cancer cells are rapidly dividing cells (like hair cells, skin cells, red blood cells),
they spend less time in interphase and more time in the other stages (mitosis)

Treatment for Cancer?

Surgery = aim is to remove tumour

Chemotherapy = - using drugs that inhibit mitosis in rapidly dividing cancer cells
- problem, also affect normal healthy cells (hair cell, skin cells, rbcs) causing side
effects (hair loss, dry skin, tiredness)
- treatment given as regular doses to allow time for normal healthy cells to recover
in number

Radiotherapy = radiation used to destroy cancer cells

How do Bacteria do Cell Division?

 Binary Fission
 Copy their DNA (Single Loop and Plasmids) and then separate into 2 new
genetically identical bacteria [Asexual Reproduction]

2 types of microscopes? Light and Electron (transmission and scanning)

How to judge a microscope? by Magnification and Resolution

Magnification? how much larger the image size is compared to the actual size

Which has higher magnification? TEM > SEM > LM

Formula for magnification? magnification = image size/actual size

Conversion? 1 mm = 1000 micrometre. 1 mm = 1,000,000 nanometre

Why can organelles appear different in images? viewed from different angles and at
different levels/depth

Resolution? minimum distance at which 2 very close objects can be distinguished

Which has higher resolution? TEM > SEM > LM

Why does electron microscopes have a higher resolution? Electron microscope uses
electrons which have a shorter wavelength (light microscope uses light which has a large
wavelength)
Difference between TEM and SEM? in Transmission the electrons pass through the
specimen, in Scanning the electrons bounce off the specimen's surface

Advantage and Disadvantage of TEM?

 Advantage = highest magnification and highest resolution

 Disadvantage = works in a vacuum so can only observe dead specimens,
specimen needs to be thin, black and white image, 2D image, artefacts

Advantage and Disadvantage of SEM?

 Advantage = produces 3D image

 Disadvantage = works in a vacuum so can only observe dead specimens, black
and white image, artefacts

Cell Fractionation?

 Breakdown tissue into cells (cut, pestle & mortar)

 add cold/isotonic/buffer solution (cold = reduce enzyme activity, isotonic =
same water potential so organelle does not shrink or burst, buffer = maintains
constant pH)
 homogenate – breaks open cells releasing organelles
 filter = removes large debris and intact cells
 centrifuge – spin at low speed, largest organelle builds at bottom (nucleus),
leaves supernatant, spin at higher speed, next heaviest organelle forms at bottom
(chloroplast or mitochondria)
 (organelle by size: nucleus, chloroplast, mitochondria, endoplasmic
reticulum/golgi body/lysosomes, ribosomes)

Simple vs Facilitated Diffusion?

 Simple = molecules move directly through the phospholipid bilayer

 Facilitated = molecules pass through transport proteins (large use carrier,
charged use channel)

Factors that affect rate of diffusion?

 surface area (increase = increase rate of diffusion)

 concentration gradient (increase = increase rate of diffusion)
 thickness (decrease = decrease diffusion distance = increase rate of
diffusion)
 temperature (increase = increase kinetic energy = molecules move faster =
increase rate of diffusion)
 size of molecules (smaller molecules = increase rate of diffusion)
What is Ficks Law? (Surface Area x Concentration Gradient)/Thickness

Define Osmosis? movement of water molecules from an area of high water potential to an
area of low water potential through a partially permeable membrane

Which liquid has the highest water potential?

 distilled/pure water
 has a value of 0kPa
 lower water potential by adding solutes (makes water potential negative)
 water moves from less negative water potential (e.g. -35 kPa) to more
negative water potential (e.g. -75 kPa)

Surround animal cell with pure water? swells and burst (water enters by osmosis)

Surround plant cell with pure water?

 swells but does not burst

 cell wall prevents it from bursting
 made of cellulose – strong material
 the cell is Turgid

Surround animal cell with concentrated sugar/salt solution? shrinks (water leaves by
osmosis)

Surround plant cell with concentrated sugar/salt solution?

 water leaves by osmosis

 cell wall prevents cell from shrinking, keeps it rigid
 the protoplast (cell membrane plus contents) shrink
 the cell is Plasmolysed

Define Active Transport? movement of molecules from an area of low concentration to an

area of high concentration using ATP and carrier proteins (against
concentration gradient)
Describe the process of active transport?

 molecules (in area of low concentration) bind to carrier protein

 ATP breaksdown to ADP, Pi and Energy
 the Pi and Energy cause the carrier protein to change shape
 carrier protein releases molecules on opposite side (in area of high
concentration)
 the carrier protein releases the attached Pi to return to its original shape

Adaptations of SI?
  folded to form Villus (large surface area)
 cells lining SI have Microvilli (large surface area)
 wall of SI is thin (short diffusion distance)
 rich blood supply (maintains concentration gradient)
 cells lining SI have transport proteins and mitochondria

Active Transport of Glucose in SI?

 sodium ions are actively transported from the cells lining the SI into the
blood
 lowers the sodium ion concentration in the cell
 therefore sodium ions move from the lumen of the SI into the cell
 this pulls in glucose via a cotransport protein
 therefore glucose builds up in the cell and moves into the blood by diffusion

What is a pathogen?

 a disease causing micro-organism

 e.g. bacteria, virus, fungi
 bacteria cause disease by producing toxins
 virus cause disease by dividing in cells causing them to burst

Body's defence against pathogens?

 I, Barriers (prevents pathogens entering the body)

 II, Phagocytes (perform phagocytosis and stimulate specific response)
 III, Specific Response (uses lymphocytes to produce memory cells and
antibodies)

What are the Barriers (I)?

 Skin, an impermeable barrier made of keratin

 Cilia & Mucus in Lungs
 Stomach Acid (denatures/breaksdown pathogens)

Describe the process of Phagocytosis (II)?

 pathogen releases chemicals

 this attracts the phagocyte
 the phagocyte binds to the pathogen
 the phagocyte engulfs the pathogen
 forms a phagosome around the pathogen
 lysosomes inside the phagocyte release digestive enzymes into the
phagosome
 breaking down the pathogen by hydrolysis

Describe the Specific Response (III)?

  phagocytes perform phagocytosis (engulf and destroy pathogen) without
destroying the antigen, they place antigens on their surface, they present
antigens
 t lymphocytes (t cells) bind to the antigen and become stimulated
 they divide by mitosis to form 3 types of cells: t helper, t killer, t memory
 t helper cells stimulate b lymphocytes (b cells)
 t killer cells kill infected cells (infected by virus)
 t memory cells provide long term immunity
 b lymphocytes (b cells) engulf and present antigens on their surface, the t
helper cells bind to this
 the b cells become stimulated and divide by mitosis to make 2 types of
cells: Plasma Cells & B Memory Cells
 Plasma cells make antibodies
 B memory cells provide long term immunity

What is a antigen? a protein on the surface of a pathogen that stimulates an immune

response

How does the immune response lead to production of antibodies? the phagocytes stimulate
the t cells, the t cells form t helper cells, the t helper cells stimulate the b cells, the b cells
form plasma cells, the plasma cells make antibodies

What is an antibody?

 a globular protein
 made by plasma cells
 has 3 regions: variable region, hinge region, constant region
 variable region has a different shape in each antibody, contains the antigen
binding sites, these bind to complementary antigens (on a pathogen) to form an
antigen-antibody complex, destroying the pathogen
 hinge region gives the antibody flexibility
 constant region the same shape in all antibodies, binds to phagocytes to help
with phagocytosis

How do Memory cells (B/T) work?

 made during the specific immune response after a new infection by a

pathogen (called a primary infection)
 B and T memory cells remain in the blood
 if person is reinfected by the same pathogen (called a secondary infection)
the memory cells will recognise the pathogen and produce antibodies RAPIDLY and
to a LARGE amount
 therefore the pathogen is killed before it can cause harm = immunity
How does a vaccine produce immunity? involves giving an injection that contains
dead/weakened pathogens that carry antigens which stimulates the immune response
leading to production of antibodies & memory cells

Active vs Passive immunity?

 Active = individual has memory cells – can make their own antibodies &
provides long term immunity
 Passive = person given antibodies, these work then die, no long term
immunity, no memory cells.

How does activity immunity occur? naturally = by primary infection, artificially = by

vaccination

How does passive immunity occur? naturally = from mother to baby (placenta or breast
milk), artificially = by injection

Successful Vaccination Programme?

 produce suitable vaccine (effective – make memory cells, does not cause
disease, no major side effects, low cost, easily
produced/transported/stored/administered)
 herd immunity

What is herd immunity? when a large proportion of the population is vaccinated, therefore
most people will be immune, only a few will not be a immune, increases chance of non-
immune person coming into contact with immune person, so the pathogen has no where to
go, so it dies out

Problems with Vaccination Programmes?

 vaccine does not work (dead form ineffective, pathogen hides from immune
system)
 vaccine not safe (no weak/inactive form, causes major side effects)
 many strains of pathogen
 cannot achieve herd immunity (logistic of vaccinating large proportion)
 antigenic variability

What is antigenic variability? the pathogen mutates, the antigen changes shape, so the
memory cells no longer complementary – do not recognise the pathogen, therefore the
pathogen can reharm

What is a monoclonal antibody? one type of antibody, complementary to one type of

antigen, made by one type of plasma cell
What are monoclonal antibodies used for? identify specific antigens or antibodies in
person's blood, or pregnancy tests

How do monoclonal antibodies identify specific antigens in the blood?

 e.g. identify PSA antigen made by prostate cancer

 place monoclonal antibodies complementary to PSA antigen on test plate
 add person's blood to test plate
 if PSA antigen is present in the blood, it will bind to the monoclonal
antibodies
 then a 2nd set of monoclonal antibodies with an enzyme attached is added
 if the PSA antigen is present, this 2nd set will bind to it
 if the PSA antigen is not present, this 2nd set will not bind
 the test plate is then washed
 if PSA antigen is present, 2nd set of monoclonal antibodies will attach, this will
not be washed away, so the enzyme will be present
 if PSA antigen not present, 2nd set of monoclonal antibodies will not attach,
this will be washed away, so enzyme also washed away
 a colourless substrate is then added, if the enzyme is present it will
breakdown the substrate causing a colour change, if the enzyme is not present
there will be no colour change
 therefore: colour change occurs = enzyme present/PSA antigen is present, no
colour change = no enzyme present/no PSA antigen is present

How do monoclonal antibodies identify specific antibodies in the blood?

 e.g. identify TB antibodies in the blood

 place antigen complementary to TB antibodies on test plate
 add person's blood to test plate
 if TB antibodies are present in blood, they will bind to the antigen
 then a set of monoclonal antibodies (with an enzyme attached)
complementary to the TB antibodies are added
 if the TB antibodies are present, the monoclonal antibodies will attach
 if the TB antibodies are not present, the monoclonal antibodies will not
attach
 the test plate is then washed
 if the TB antibodies are present, the monoclonal antibodies will attach, this
will not be washed away, so the enzyme will be present
 if the TB antibodies are not present, the monoclonal antibodies will not
attach, this will be washed away, so the enzyme will be washed away
 a colourless substrate is then added, if the enzyme is present it will
breakdown the substrate causing a colour change, if the enzyme is not present
there will be no colour change
 therefore: colour change occurs = enzyme present/TB antibody is present, no
colour change = no enzyme present/no TB antibody is present

How are monoclonal antibodies used in pregnancy testing?

  Pregnant Women produce HCG Hormone in their Urine
 Test Strip has 3 parts to it (1st: start contains antibodies complementary to
HCG, 2nd: middle contains antibodies complementary to HCG-Antibody complex, 3 rd:
end contains antibodies complementary to HCG Antibodies)
 if woman is pregnant, HCG in the urine binds to antibodies on 1st part forming
a HCG-Antibody complex, the HCG-Antibody complex then binds to antibodies on
the 2nd part forming a blue line (positive result), HCG Antibodies also bind to 3rd part
as a control
 if woman is not pregnant, no HCG in urine so nothing binds to HCG
Antibodies in 1st part, so nothing binds to antibodies in 2nd part leaving no blue line
(negative result), the HCG Antibodies still bind to 3rd part for the control

What is HIV/AIDs?

 HIV = Human Immunodeficiency Virus

 AIDs = Acquired Immunodeficiency Syndrome
 HIV is the Pathogen, AIDs is the Infectious Disease
 HIV is spread by fluid to fluid contact (unprotected sexual intercourse,
sharing needles, mother to child via placenta or breast feeding)
 HIV damages and destroys T Helper Cells, therefore person no longer
produces Immune Response and has no defence to against pathogens/infections =
AIDs
 With AIDs, individual at risk from all sorts of pathogens/infections called
Opportunistic Infections

Section 3:
How do Microorganisms Obtain Nutrients & Remove Waste?

 by exchange via their surface

 nutrients (e.g. glucose, oxygen) move in by diffusion via their surface
 waste (e.g. carbon dioxide) move out by diffusion via their surface

Why are Microorganisms able to perform exchange via their surface?

 have a large surface area to volume ratio

 have a short diffusion distance
 have low demand

Why can't Animals/Plants perform exchange via their surface?

 have a small surface area to volume ratio

  multicellular (large diffusion distance and high demand)
 impermeable surface (prevent pathogens entering and reduce water loss)
 therefore, require specialised Exchange & Transport systems
 exchange system = increases rate of diffusion of nutrients in and wastes out
 transport system = deliver nutrients and remove waste from all cells

Why do Fish have Specialised Gas Exchange Systems?

o multicellular organism so has a small surface area to volume ratio, large

diffusion distance, high demand & body surface impermeable
o therefore, cannot perform gas exchange (O2 in/CO2 out) via their surface, they
require a specialised gas exchange system called Gills

Structure of Gills in Fish?

 many gill filaments and gill lamellae = large surface area

 gill lamellae have a thin wall (short diffusion distance) and are permeable
 ventilation brings in pure water (high oxygen, low carbon dioxide) and circulation
brings in deoxygenated blood (low oxygen, high carbon dioxide), the water and blood
pass over in opposite directions (countercurrent flow), which maintains concentration
gradient all the way along the gill lamellae

Why do Insects have Specialised Gas Exchange Systems?

o multicellular organism so has a small surface area to volume ratio, large

diffusion distance, high demand & body surface made of exoskeleton
(impermeable barrier to reduce water loss)
o therefore, cannot perform gas exchange (O2 in/CO2 out) via their surface, they
require a specialised gas exchange system called Tracheal System

Structure of Tracheal System in Insects?

 starts with openings on body surface called Spiracles

 spiracles contain valves, open = gas exchange, closed = prevent water loss
 spiracles connect to Trachea
 trachea connect to Tracheoles
 tracheoles connect directly to Respiring Cells (delivering oxygen, removing
carbon dioxide)

How does Gas Exchange occur in Tracheal System of Insects?

 at rest = down a concentration gradient, oxygen moves in & carbon dioxide

moves out by simple diffusion
 when active = by ventilation, air inhaled for mass flow of O2 in & air exhaled
for mass flow of CO2 out
Function of Lungs? site of gas exchange in
mammals (oxygen into blood – used in cells for
respiration,
carbon dioxide out of the blood – toxic waste product of respiration)

What is Lungs made up of? Trachea, Bronchi, Bronchioles, Alveoli (+ capillaries)

Function of trachea, bronchi, bronchioles? transport of air and filter air, (bronchioles also
controls amount of air reaching alveoli)

Structure of trachea/bronchi?

 wall made of c-shaped cartilage

 cartilage is strong so trachea/bronchi do not collapse
 cartilage is c-shaped to give flexibility
 lining made of goblet cells and ciliated epithelial cells
 goblet cells make mucus, which traps pathogens/particles
 ciliated epithelial cells have cilia, which pushes mucus up and out of lungs

Structure of bronchioles?

 wall made of smooth muscle

 smooth muscle contracts, lumen narrows, bronchiole constricts
 (occurs when surrounded by noxious gases – reduces amount reaching
alveoli)
 lining made of goblet cells and ciliated epithelial cells

Adaptation of alveoli?

 millions of tiny alveoli that are folded (large surface area)

 thin wall/one cell thick/squamous epithelial cells (short diffusion distance)
 elastic tissue in wall (stretches when breathing in to increase surface area,
recoils when breathing out to push the air out)
 ventilation maintains concentration gradient (high oxygen, low carbon
dioxide)

Adaptation of capillaries?

 millions of tiny capillaries (large surface area)

 thin wall/one cell thick/squamous epithelial cells (short diffusion distance)
 narrow lumen (increases diffusion time, decreases diffusion distance)
 circulation maintains concentration gradient (low oxygen, high carbon
dioxide)

How O2 moves from the alveoli to the capillaries? by simple diffusion passing thru the
alveolar epithelium and capillary epithelium
How CO2 moves from capillaries to the alveoli? by simple diffusion passing thru
the capillary epithelium and alveoli epithelium

Describe the process of Breathing/Ventilation?

 Breathing In/Inhalation = external intercostal muscles contract (rib cage

moves up and out) & diaphragm contracts (flattens), therefore increase in volume
in chest and decrease in pressure, so air moves in
 Breathing Out/Exhalation = external intercostal muscle relax (rib cage moves
down and in) & diaphragm relaxes (back to dome shape), therefore decrease in
volume in chest and increase in pressure, so air pushed out (aided by elastic recoil
in the alveoli)

Formula for Pulmonary Ventilation?

 PV = tidal volume x ventilation rate

 tidal volume = volume of air breathed in/out in one breath
 ventilation rate = number of breaths per minute
 Pulmonary Ventilation = volume of air breathed in/out per minute

Function of Intestines? site of exchange of digested nutrients in mammals

What is Digestion?

 Breakdown of Large Insoluble Molecules into Small Soluble Molecules (so

they can move into the blood and then into the body cells)
 Starch/Glycogen (Carbohydrates) into Glucose by Amylase (Salivary in mouth,
Pancreatic in small intestine) and Maltase/Lactase/Sucrase (on lining of small
intestine)
 Proteins into Amino Acids by
Endopeptidase/Exopeptidase/Dipeptidase (Endopeptidase in stomach,
Exopeptidase in small intestine, Dipeptidase on lining of small intestine)
 Lipids into Monoglyceride and 2 Fatty Acids by Lipase (in small intestine)

What do Intestine Absorb?

 Small Intestine absorbs small soluble nutrients (glucose, amino acids,

monoglyceride and fatty acid, vitamins and minerals)
 Large Intestine absorbs water

Why do Humans/Mammals require a Specialised Transport System?

 multicellular organisms therefore have large diffusion distances and high

demand
 need a transport system to deliver nutrients and remove waste from all
cells
  transport system in humans/mammals called Circulatory System
 Circulatory System made of heart, blood vessels, blood
(heart pumps blood, blood vessels carry blood, blood carries nutrients/waste)

Why is the transport system in mammals called a double circulatory system?

the heart pumps twice, the blood goes through the heart twice – generates enough
pressure to supply all body cells

Why is the transport system in mammals called a closed circulatory system?

blood is transported in blood vessels – helps to maintain pressure and redirect blood
flow

Layout of Circulatory System?

 heart pumps blood which is carried in arteries which flow into arterioles
which flow into capillaries which then are carried in venules then veins back to the
heart
 Artery to Arterioles to Capillaries to Venules to Veins
 Artery/Arterioles carry blood away from the heart
(arterioles are small arteries)
 Capillaries are the site of exchange (nutrients out, waste in)
 Veins/Venules return blood back to the heart
(venules are small veins)

Heart?

 job is to pump blood around the body (delivers nutrients to cells and remove
waste)
 made of 4 muscular chambers (2 atria, 2 ventricles)
 atria pumps blood to ventricles, ventricles pump blood out of heart (R to
lungs, L to body)
 ventricles thicker then atria (has to pump blood further)
 left ventricle has a thicker muscular wall then right ventricle, therefore has
stronger contractions, so can generate higher pressure and pump the blood further
around the body

Blood vessels of the heart?

 artery takes blood away from the heart, vein returns blood to the heart
 Vena Cava supplies R atrium (with deoxygenated blood from body)
 Pulmonary Vein supplies L atrium (with oxygenated blood from lungs)
 R ventricle supplies Pulmonary Artery (deoxygenated blood to lungs)
 L ventricle supplies Aorta (oxygenated blood to body)
Job of valves in heart?

 Ensure one way flow of blood, no backflow

 (blood flows from atria to ventricles to arteries)
 2 sets of valves: Atrio-ventricular Valve & Semi-lunar Valve
 AV valve = between atria and ventricles
 SL valve = between ventricles and arteries

When are AV valves open or closed? Open = pressure in atria greater then pressure in
ventricles, Closed = pressure in ventricles greater then pressure in atria

When are SL valves open or closed? Open = pressure in ventricles greater then pressure in
arteries, Closed = pressure in arteries greater then pressure in ventricles

Describe the processes of the cardiac cycle?

 Filling Stage = atria relaxed, ventricles relaxed, AV valve open, SL valve

closed
 Atria Contracts = the SAN located in the R atrium initiates the heart beat and
sends the impulse across both atria making them contract, this pushes all the
remaining blood into the ventricles so it becomes full
 Ventricles Contract = the AVN picks up the impulse, delays it (stops the atria
and ventricles contracting at the same time, so the atria empties and the ventricles
fill), sends the impulse down the septum in the Bundle of His, then at the apex the
impulse goes up both walls of the ventricles in the purkine fibres, so the ventricles
contract from the base upwards, pushing the blood up thru the arteries, when the
ventricles start to contract the AV valve closes then the SL valve opens and blood
leaves the heart
 Ventricles Relax = the SL valve closes then the AV valve opens and filling
starts again

What causes the Heart Sounds?

 when the valves close

 1st = AV closes
 2nd = SL closes

Formula for Cardiac Output?

 CO = Stroke Volume x Heart Rate

 stroke volume = volume of blood pumped out of the heart in one beat
 heart rate = number of beats per minuted
 Cardiac Output = volume of blood pumped out of the heart in one minute

Coronary Heart Disease and Myocardial Infarction?

  high blood pressure damages lining of coronary artery
 fatty deposits/cholesterol builds up beneath the lining, in the wall = Atheroma
 the atheroma breaks thru the lining forming a Atheromatous Plaque on the lining, in
the lumen
 this causes turbulent blood flow
 a blood clot (thrombus) forms
 this block the coronary artery
 therefore less blood flow to the heart muscle
 less glucose and oxygen delivered
 the heart muscle cannot respire
 so it dies (myocardial infarction)

Risk Factors of CHD?

 Age, gender, ethnicity

 Saturated fats (increases LDL, LDL deposits cholesterol in the arteries to form
atheroma)
 Salts (increases blood pressure – lowers water potential of the blood so it holds the
water)
 Smoking (nicotine = increase HR and makes platelets more sticky – blood clot, carbon
monoxide = permanently blocks haemoglobin)
 Obesity and Lack of Exercise

Atheroma & Aneurysm? atheroma weakens wall of artery, blood builds up in the wall, the
wall swells then bursts = aneurysm

Role of Arteries/Arterioles?

 generally carry oxygenated blood away from the heart

 for example, Coronary Artery to heart muscle
Hepatic Artery to liver
Renal Artery to kidneys
 exception = Pulmonary Artery carries deoxygenated blood to lungs

Role of Veins/Venules?

 generally carry deoxygenated blood back to the heart

 for example, Coronary Vein from heart muscle
Hepatic Vein from liver
Renal Vein from kidneys
 exception 1 = Pulmonary Vein carries oxygenated blood back to the heart
 exception 2 = Hepatic Portal Vein carries deoxygenated blood from digestive
system to liver (for filtering)

Function of Arteries/Arterioles?
 carry blood away from the heart so should be able to withstand high blood pressures
& maintain high blood pressures

Structure of Arteries/Arterioles?

 narrow lumen = maintains pressure

 lining made of squamous epithelial cells = smooth lining to reduce friction
 thick wall = withstand pressure
 elastic tissue in wall,
ventricles contract – elastic tissue stretches to withstand
pressure ventricles relax – elastic tissue recoils to maintain pressure and smooth out
flow
 smooth muscle in wall (particularly in arterioles),
smooth muscle contracts – lumen narrows and arteriole constricts
smooth muscle relaxes – lumen widens and arteriole dilates
 collagen in wall
prevents artery from tearing

Function of Veins/Venules? return blood back to the heart, the blood is under low pressure

Structure of Veins/Venules?

 wide lumen = ease of blood flow

 lining made of squamous epithelial cells = smooth lining to reduce friction
 thin wall = vein can be squashed by skeletal muscle pushing blood back to the heart
 valves in lumen = prevents backflow of blood

Function of Capillaries?

 site of exchange
 3 locations,
With Alveoli, takes in O2 and removes CO2
With Microvilli, takes in glucose/amino acids/monoglyceride and fatty
acids/vitamins/minerals
With All Cells, deliver nutrients and remove waste

Adaptation of Capillaries?

 many small capillaries = large surface area

 thin wall, one cell thick, squamous epithelial cells = short diffusion distance
 pores between cells = allows fluid to move in and out
 narrow lumen = increase diffusion time and decrease diffusion distance

Content of Blood?

 main component = Plasma (fluid)

 plasma carries,
  Cells = red blood cells, white blood cells, platelets
 Solutes = nutrients, waste, protein

How does exchange occur between Capillaries & All Cells?

 by mass flow
 fluid moves out of the blood in the capillaries carrying the nutrients
 fluid moves back into blood in the capillaries carrying the waste
 (fluid in the blood called plasma, fluid surrounding cells called tissue fluid,
fluid in lymph system called lymph)

How is tissue fluid formed and returned to circulatory system?

 at the start of the capillary (arterial end) there is a build up hydrostatic pressure
 this pushes fluid out of the capillary via the pores
 the fluid carries the nutrients with it
 the fluid surrounds the cells, this is called tissue fluid
 at the finish of the capillary (venous end) the fluid moves back in by osmosis
 the capillary has low water potential due to the presence of proteins (too large to
move out of capillaries)
 any excess tissue fluid is picked up by the lymph system and deposited in the vena
cava

Why does high blood pressure cause accumulation of tissue fluid?

increases hydrostatic pressure, so more tissue fluid is formed – not as much can be
returned to the circulatory system

Why does diet low in protein cause accumulation of tissue fluid?

the water potential in the capillary is not as low as normal, so not as much fluid can
move back into the capillary by osmosis

Blood Pressure changes along the Circulatory System?

Arteries =- highest pressure (connects directly with heart/ventricles)

- pressure fluctuates (increases when ventricles contract which
causes the elastic tissue to stretch, decreases when ventricles relax which causes the
elastic tissue to recoil)
- overall decrease in pressure due to friction

Arterioles = large decrease in pressure due to increase in total cross-sectional

area (ensures pressure is not to high to damage capillaries)

Capillaries = pressure here is called hydrostatic pressure (decreases due to a loss

in fluid)
 Venules/Veins = blood under low pressure

Job of Red Blood Cells?

 found in humans/mammals (animals)

 carries haemoglobin
 haemoglobin carries oxygen

Structure of Haemoglobin?

 globular protein (soluble & specific 3d shape)

 quaternary structure made of 4 polypeptide chains (2α, 2β)
 each chain carries a haem group
 each haem group carries Fe2+
 each Fe2+ carries an O2
 therefore, each haemoglobin carries 4 lots of O2

Job of Haemoglobin? load oxygen in the lungs and deliver it to the respiring tissues

What is Affinity?

the level of attraction haemoglobin has to oxygen

(high affinity = strong attraction, low affinity = weak attraction)

Role of haemoglobin in oxygen transport?

 haemoglobin has High Affinity in the lungs – due to high partial pressure of
oxygen and low partial pressure of carbon dioxide, so haemoglobin
loads/associates oxygen in the lungs and becomes saturated (full)
 the haemoglobin is transported in the blood in the red blood cell
 at the respiring tissues, haemoglobin has Low Affinity – due to low partial
pressure of oxygen and high partial pressure of carbon dioxide, so oxygen is
unloaded/dissociated/delivered and haemoglobin becomes unsaturated

Relationship between O2 Partial Pressure & Affinity/Saturation of Haemoglobin?

 positive correlation
 as O2 partial pressure increases, affinity/saturation of haemoglobin increases
 the correlation is not linear but is curved (produces a s-shaped, sigmoid curve
called Oxygen Dissociation Curve)
 middle portion of ODC has a steep gradient so when respiring tissues change
from resting to active and partial pressure of O2 falls, there is a large drop in
affinity, so more O2 would be delivered to the respiring tissues
Relationship between CO2 Partial Pressure & Affinity/Saturation of Haemoglobin?

 negative correlation
 as CO2 partial pressure increases, affinity/saturation of haemoglobin
decreases
 this occurs at the site of respiring tissues = the carbon dioxide lowers the pH
of the blood, makes the haemoglobin change shape, so oxygen is released,
lowering affinity. this shifts the ODC to the right, called the bohr shift. benefit =
more oxygen delivered to respiring cells

How does a Fetus receive oxygen? from mother's blood, oxygen dissociates from mother's
haemoglobin and associates with fetal haemoglobin in the placenta – fetal haemoglobin has
a higher affinity compared to mother's haemoglobin

Benefit of fetal haemoglobin having high affinity? fetal haemoglobin's ODC will be to the
left, it has high affinity – so the oxygen will dissociate from the mother's haemoglobin and
associate with the fetal haemoglobin at the low partial pressures of oxygen in the placenta,
so it has enough oxygen for its needs

Why do adults not keep with fetal haemoglobin? the high affinity will mean less oxygen will
be unloaded at the respiring tissues

Affinity of Organisms in a Low Oxygen Environment?

has a high affinity, curve to the left, therefore it can readily associate oxygen at the
low oxygen partial pressures

Affinity of Active Organisms?

has a low affinity, curve to the right, therefore more oxygen can be unloaded to meet
the cell's demand for more respiration

Affinity of Small Organisms?

have a large surface area to volume ratio, lose a lot of heat, needs to respire to
generate heat, therefore has a low affinity, curve to the right, so unloads enough oxygen for
the cells demand of more respiration

What are the Exchange & Transport Systems in Plants?

 exchange systems = leaf and root

 leaf to absorb light and CO2 for photosynthesis
 roots to absorb water and minerals
 transport systems = xylem and phloem
 xylem transports water and minerals
 phloem transports glucose/sugars
  xylem transports in one direction from roots to leaves, phloem transports in
both directions

Job of the Roots?

 absorb water and minerals

 absorbs water by osmosis
 absorbs minerals by active transport
 plants need water for photosynthesis, cytoplasm hydration, turgidity of cells
 plants need magnesium, nitrate, phosphate (magnesium to make chlorophyll,
nitrate to make amino acids, phosphate to make phospholipids/ATP/DNA)

Function of the Xylem? transport water and minerals from roots, up the plant, to the
leaves

Structure of the xylem?

 long continuous hollow tube (no resistance to water flow)

 narrow lumen
 wall made out of lignin
 lignin: strong, waterproof, adhesive
 wall contains pits/pores (water and minerals can leave)

How does water move up the xylem?

 loss of water at the leaves (transpiration)

 water moves from the top of the xylem into the leaf by osmosis
(transpirational pull)
 this applies TENSION to the column of water in the xylem
 the column of water moves up as one as the water particles stick together,
COHESION
 this is is the cohesion-tension theory
 it is supported by capillary action, adhesion and root pressure
 (capillary action = water automatically moves up narrow lumen of xylem)
 (adhesion = water particles stick to lignin in wall of xylem)
 (root pressure = water absorbed at the roots pushes the column of water up slightly
by hydrostatic pressure)

Why does the diameter of a tree decrease during the day?

 more light and higher temperature

 increase rate of transpiration
 increase transpirational pull
 water pulled up xylem by cohesion-tension
 because the water particles stick to the wall of the xylem (adhesion)
 the walls of the xylem are pulled inwards
Structure of Leaves?

 upper layer called Upper Epidermis

 waxy cuticle on upper epidermis (barrier to reduce water loss)
 beneath the upper epidermis are Palisade Cells
 palisade cells are were photosynthesis takes places
 beneath palisade cells are Spongy Mesophyll Cells
 are loosely packed leaving air spaces to allow ease of gas exchange
 lower layer called Lower Epidermis

Adaptation of palisade cells for photosynthesis?

 located near top of leaf, closer to light

 large size, large surface area for light
 thin cell wall, short diffusion distance for carbon dioxide
 contains many chloroplasts, site of photosynthesis
 large vacuole, pushes chloroplast to the edge of the cell closer to light

Structure of chloroplast?

 organelle for photosynthesis

 has double membrane
 contains discs called thylakoids
 thylakoids contain chlorophyll
 stack of thylakoids called granum
 thylakoids surrounded by a fluid called stroma

How does Exchange occur in Leaves?

 lower epidermis of leaf contains pairs of cells called Guard Cells

 when turgid, guard cells form an opening called Stomata
 gas exchange occurs via the stomata
 In Day, plant photosynthesises and respires, CO2 moves in
for photosysnthesis and O2 moves out (some is used in respiration)
 At Night, plant only respires, O2 moves in for respiration and CO2 moves out

What is Transpiration? loss of water vapour from the leaf via the stomata

How does Transpiration occur?

o moist lining of spongy mesophyll cells evaporate forming water vapour

o water vapour builds up in air spaces
o if water vapour concentration is high enough & stomata is open, water
vapour diffuses out
Factors that increase rate of transpiration?

 light = more light, more stomata open, increase surface area for transpiration
 temperature = more temperature, more evaporation (increase water vapour
concentration) & more kinetic energy
 wind = more wind, maintains concentration gradient
 humidity = less humidity, less water vapour in the surrounding air, increase in water
vapour concentration gradient

What is a Potometer? apparatus used to measure rate of transpiration

Principle of potometer?

 as transpiration occurs from the leaves, the plant will pull up more water
from the potometer by cohesion-tension causing the bubble to move towards the
plant
 the more water lost by transpiration, the more water taken up, the further
the bubble moves

Measuring Rate of Transpiration?

 rate of transpiration = volume of transpiration divided by time

 for volume of transpiration, distance bubble moved x cross-sectional area of
tube (πr2)

How to set up a potometer?

 choose healthy leaf and shoot

 cut shoot underwater and connect to potometer underwater (prevents air bubbles
entering/blocking xylem)
 ensure potometer is air tight and water tight

What does a potometer actually measure?

measures rate of water uptake as a result of water loss from plant

(water loss can be due to: transpiration, photosynthesis, making cells turgid, loss
from potometer)

What is a Xerophyte? a plant adapted to reduce water loss (reduce transpiration)

Adaptations of Xerophyte?

 spiky, needle like leaves = reduced surface area

 thick waxy cuticle = waterproof, impermeable barrier
 densely packed spongy mesophyll = less air spaces, less water vapour build up
 sunken stomata/hairy leaves/rolled up leaves = traps moist layer of air,
 reduces concentration gradient

Function of Phloem? transport organic material (e.g. Sucrose) up and down a plant

Structure of phloem? made of 2 parts (Sieve Tube with Companion Cells alongside)

How does phloem transport organic material like sucrose?

 by principle of Mass Flow (mass flow of water carries the sucrose)

 Sucrose loaded into Phloem at Source
 Hydrogen Ions (H+) actively transported from companion cells into source
 therefore, H+ diffuses back into companion cells from source
 as they do, they pull in sucrose with them by co-transport
 sucrose then diffuses into sieve tube
 this lowers the water potential of sieve tube so water follows by osmosis
 this water will carry the sucrose by hydrostatic pressure (mass flow)
 Sucrose unloaded from Phloem at Sink
 sucrose moves out of phloem/sieve tube into sink by diffusion
 water follows by osmosis
Section 4:

What is Biodiversity?

 variety in an ecosystem
 variety of habitats and variety of species

What is Species Diversity?

 number of different species

 number of individuals for each species

What is Genetic Diversity?

 variety of alleles in a species population

 the larger number of individuals in a species, the larger the genetic diversity

Benefit of high species diversity?

 Stable ecosystem
 each species is less likely to become extinct (due to high genetic diversity)
 & if a species does become extinct it will not affect the food chain as there
are other species available

How to measure Species Diversity for an area?

o Species Diversity Index

 o takes into account the number of different species and how many individuals
there are for each species
o the larger the species diversity index, the larger the species diversity

How does deforestation lower species diversity?

 (deforestation is the removal of trees for wood & space)

 decreases plant species diversity
 less variety of habitats
 less variety of food sources
 decreases animal species diversity

How does agriculture/farming lower species diversity?

 deforestation to make space for farm

 only grow a few plants & keep a few animal species
 selectively breed plants & animals
 use pesticides to kill other species

What is Classification? placing organisms into groups

What is Hierarchical Classification?

 large groups divided into smaller groups with no overlap

 domain, kingdom, phylum, class, order, family, genus, species

What is Binomial Naming System?

 using Genus name and Species name to name organism

 Genus name first in capital, Species name second in lower case
 e.g. tiger = Felix tigris

What is a Species?

A group of individuals with similar characteristics that can interbreed to produce fertile
offspring

Why are the offspring from 2 different species mating infertile?

 offspring will have a odd number of chromosomes

 therefore, cannot perform meiosis, cannot produce gametes
 example: horse + donkey = mule, mule is infertile,
Horse has 64 chromosomes/donkey has 62 chromosomes, horse gamete has 32
chromosomes/donkey gamete has 31 chromosomes,
therefore, mule has 63 chromosomes

What is Phylogenetic Classification?

based on evolutionary relationships – how closely related different species are and
how recent a common ancestor they have

3 ways of comparing relationship between different species?

DNA Hybridisation: comparing DNA base sequence

- take DNA from 2 species to be compared

- radioactively label one of the DNA
- heat both sets so double strand separates
- cool so single strands join together
- look for Hybrid DNA (one strand from species A, one strand from species B)
- identify Hybrid DNA by 50% radioactivity
- heat Hybrid DNA to measure similarity

results =higher temperature required

more hydrogen bonds present
more complementary base pairing
more similar the base sequence
more similar the species
more closely related
more recent a common ancestor

AA Sequence: comparing AA sequence for the same protein (e.g. haemoglobin in

mammals)

results = more similar the AA sequence

more similar the DNA base sequence
more similar the species
more closely related
more recent a common ancestor

(comparing DNA sequence better then comparing AA sequence:

DNA sequence provides information on INTRONS and triplet code is DEGENERATE)

Protein Shape: comparing shape of the same protein (e.g. albumin) using immunological
technique

- comparing species A and species B

- take albumin from species A
- place in a blood of rabbit
 - rabbit will make antibodies against albumin of species A
- takes these antibodies and place in blood from species B
- if the albumin in species B has a similar shape to species A,
the antibodies will bind to form antigen-antibody complexes,
this will then form a precipitate

results = more precipitate

more complexes
more similar shape
more similar the species
more closely related
more common recent ancestor

What is Variation? difference in characteristics between organisms

Types of Variation?

intraspecific = differences between organisms of the same species

interspecific = differences between organisms of different species

Causes of Intraspecific Variation?

Genetic Factors = same genes but different alleles (allele are different type/forms of
genes)

Environmental Factors

Causes of Interspecific Variation?

Genetic Factors = different genes and different alleles

Environmental Factors

Types of Characteristics? Discontinuous and Continuous

Properties of Discontinuous Characteristics?

characteristics fall into certain groups with no overlap (e.g. blood group) – determined
by genetics only (a single gene)

Properties of Continuous Characteristics?

characteristics show a range (e.g. height) – determined by genetics (a few genes,

polygenes) and environment
What is Genetic Diversity? genetic variation, the variety of alleles within a population of a
species

Benefit of high genetic diversity? species able to adapt with changes in the environment
e.g. if a new disease arises, some individuals will have characteristics to survive, and will
reproduce passing on their alleles, so the species does not become extinct

What can lower genetic diversity? small population size (e.g. founder effect – where the
numbers start low, or genetic bottleneck – where the numbers decrease)

What is natural selection and adaptation?

 variation in population of species

(genetic diversity/genetic variation/variety in gene pool)
 new alleles arise by random mutation
 environment applies a selection pressure on the population
 those with favourable characteristics/favourable alleles/selection
advantage/better adapted survive, the others die [natural selection]
 the ones that survive will reproduce, passing on their favourable alleles
 if this happens for many generations, then that characteristic will become
most common – the allele will become more frequent [adaptation]

What are the 2 types of selection? stabilising and directional

What is stabilising selection?

 when the environment favours those with the most common characteristic –
those on the extreme dies out
 the common characteristic increases in proportion
 the range (standard deviation) will reduce

What is directional selection?

 when the environment favours those individuals with characteristics on one

of the extremes
 over time this will become the most common characteristic
 normal distribution will shift to that extreme

What is a Gene?

 a section of DNA that codes for a protein

 made out of intron and exon
  intron = non-coding DNA (function e.g. turns gene on or off)
 exon = coding DNA (codes for protein)

How does a Gene/Exon code for a Protein?

 made out of a sequence of bases

 each 3 bases code for 1 amino acid (called triplet code)
 therefore,
 sequence of bases
 determines sequence of triplet codes
 which determine the sequence of AAs
 = polypeptide chain/primary structure (folds to secondary, then to
tertiary/quaternary)

Properties of triplet code?

 degenerate = each AA has more than one triplet code

 non-overlapping = each base is read only once
 stop codes = occur at end of sequence – do not code for an AA

How does a mutation lead to a non-functional enzyme?

 change in base sequence

 change in sequence of triplet codes
 change in sequence of AAs
 change in primary structure
 change in hydrogen/ionic/disulfide bonds
 change in tertiary structure (3D shape)
 change in active site shape
 substrate no longer complementary
 can no longer form enzyme-substrate complex

How is a protein assembled?

 by transcription and translation

 transcription = production of a single stranded complementary copy of a
gene (called mRNA)
 translation = use sequence of codons on mRNA to assemble protein
(tRNA brings in AAs)
DNA vs RNA?

 deoxyribose sugar vs ribose sugar

 thymine vs uracil
 double stranded vs single stranded
 one type vs two types (mRNA and tRNA)
What is mRNA?

 messenger RNA
 single stranded complementary copy of a gene
 carries the code for assembling protein (on DNA called triplet code, on mRNA
called codon)

What is tRNA?

 transfer RNA
 single stranded RNA folded over into a 'clover leaf' shape (held by hydrogen
bonds between the bases)
 has an AA attachment site on the top
 has 3 specific bases on the bottom (anticodon)
 anticodon binds to complementary codons on mRNA

What is Transciption?

 occurs in nucleolus of nucleus

 producing a single stranded complementary copy of a gene (called mRNA)
 DNA is double stranded, 1 strand called coding strand & 1 strand called
template strand, the template strand will be used to build mRNA
 process,
 DNA Helicase breaks the hydrogen bonds between complementary bases in
the gene
 the double strand of the gene unwinds
 leaves 2 separate strands (1 coding strand and 1 template strand)
 complementary RNA nucleotides bind to exposed bases on the template
strand
 RNA Polymerase joins the sugar-phosphate backbone of the RNA strand
 leaves pre-mRNA (contains introns and exons)
 the copies of the introns are removed by splicing
 leaves mRNA

What is Translation?

 takes place on ribosomes of Rough Endoplasmic Reticulum

 uses the sequence of codons on the mRNA to assemble the protein
(tRNA brings in AAs)
 process,
 mRNA leaves nucleus via nuclear pore
 mRNA attaches to a ribosome
 complementary tRNA carrying specific AAs bind to the codons on mRNA via
their anticodon
 the AAs on the tRNA are joined by peptide bonds
What does Meiosis produce?

4 genetically different cells, haploid (half the amount of chromosome/DNA)

Benefits of Meiosis?

produces gametes which will be used in sexual reproduction in animals & plants
(2 gametes fuse to form a zygote, zygote develops into organisms)

Stages of Meiosis? Interphase/Meiosis I/Meiosis II/Cytokinesis

Interphase? G1: protein synthesis

S: DNA replication (doubles set of DNA)
G2: organelle synthesis

Meiosis I?

Prophase I: DNA coils to form chromosomes, nucleus breaksdown, spindle fibres

form, crossing over occurs
Metaphase I: homologous pair of chromosomes line up in middle of cell and attach
to spindle fibre via centromere
Anaphase I: spindle fibres pull, homologous pair of chromosomes separate to
opposite sides by independent assortment
Telophase I: chromosomes uncoil, nucleus reforms (left with 2 nuclei)

Meiosis II?

Prophase II: DNA coils to form chromosomes, nucleus breaksdown, spindle fibres form
Metaphase II: chromosomes line up in middle of cell and attach to spindle fibre
via centromere
Anaphase II: spindle fibres pull, centromere splits, sister chromatids move to opposite
sides by independent assortment
Telophase II: chromatids uncoil, nucleus reforms (left with 4 genetically different nuclei)

Cytokinesis: separating cell into 4 (each receives a nucleus and organelles/cytoplasm)

How does Meiosis produce Variation? Crossing Over and Independent Assortment
What is crossing over? Occurs in Prophase I of Meiosis I. Homologous pairs of
chromosomes wrap around each other and swap equivalent sections of chromatids –
produces new combination of alleles

What is independent assortment?

- in Anaphase I of Meiosis I – the homologous pairs of chromosomes separate

- in Anaphase II of Meiosis II – the chromatids separate
- independent assortment produces a mix of alleles from paternal and maternal
chromosomes in gamete

What happens to DNA mass in meiosis? quarters

What happens to Chromosome number in meiosis? halves (haploid)

What is Mutation?

 Change in DNA
 2 types: Chromosome Mutation and Gene Mutation

What causes mutation? random or due to mutagens (e.g. chemicals, radiation)

What is a Chromosome Mutation?

 In plants, inherit more than one diploid set of chromosomes – called

polyploidy
 In animals, homologous pair of chromosome do not separate in meiosis, so
either inherit one extra or one less chromosome – called non-disjunction

What is a Gene Mutation?

 a change in the base sequence of DNA

 2 types = substitution and insertion/deletion
 substitution = replace one base for another, changes one triplet code
can be silent (new triplet code codes for same AA), miscodes for a different AA,
so protein shape changes slightly), non-sense (codes for a stop codon, so polypeptide chain
not produced)
 insertion = adding a base, deletion = removing a base
both insertion/deletion causes frameshift, all the triplet codes after the
mutation changes, so normal polypeptide chain/protein not produced