as biology unit 2 notes

Unit 2 Bullet Point Handouts
Tests for closely-related species
(Compare) DNA;
Sequence of bases/nucleotides;
DNA hybridisation;
Separate DNA strands / break hydrogen bonds;
Mix DNA/strands (of different species);
Temperature/heat required to separate (hybrid) strands indicates relationship;
Compare same/named protein;
Sequence of amino acids /primary structure;
Immunological evidence – not a mark
Inject (seahorse) protein/serum into animal;
(Obtain) antibodies/serum;
Add protein/serum/plasma from other (seahorse) species;
Amount of precipitate indicates relationship;
Treatment of Control group
Given the placebo/dummy drug; (in context)
Otherwise treated the (exact) same
Usage of logarithmic scale
Large range of results so logarithmic scale needed to plot them.
Cellulose structure: function relationship
Long straight chains of glucose molecules (with a 1-4 linkage)
Held together by hydrogen bonds
Can form microfibrils
Importance of courtship behaviour
Recognition of same species;
Stimulates release of gametes;
Recognition of mate/opposite gender;
Indication of sexual maturity/fertility;

Prediction of something using a graph
Use line of best bit
Extrapolate line and read off

Hierarchy
Groups within (larger) groups; with no overlap
OR
Smaller taxa are grouped into one larger taxon where there’s no overlap between taxa

Classification rankings
Kingdom
Phylum
Class
Order
Family
Genus
Species

Comparison of species
Fossil records
Homologous features
Evolutionary history
DNA Base sequence
Ecological Niches

Oxygen dissociation curve of haemoglobin with increase of respiration

Increase in/more carbon dioxide;
Curve moves to the right/depressed;

Reduction of genetic diversity
Reduced variety/number of different alleles/DNA / reduced gene pool (in new population);
Founder effect;
A few individuals from a population become isolated/form colonies
(Genetic) bottlenecks;
(Significant) fall in size of population
Selective breeding / artificial selection;
Using organisms with particular alleles/traits/phenotypes/characteristics;

Pathways by which water moves in plants

Symplastic pathway — water moves through the membrane and cytoplasm of cells
Apoplastic pathway — water moves only through cell walls and intercellular spaces

Features of gas exchange system
Protocist
Fish
Insect
Plant leaf
Respiratory Medium

Water
Water
Air
Air
Exchange Surface

Plasma Membrane
Gill lamellae
Tracheoles
Plasma membranes of spongy mesophyll cells
Ventilation

None
Movements of mouth and gill create one-way flow
Abdomen dilates/contracts, pressure decreases/
Increases
None
Large surface area to volume ratio due to:

Small volume of cells
Large area of lamellae
Large area of tracheoles
Large surface area of cell surfaces and loose packing of cells

Oxygen concentration maintained by:

Use of oxygen in cell
Ventilation/counter-current system in lamellae
Ventilation/use of oxygen in body cells
Use of oxygen by mesophyll cells
Exchange surface thin due to:

Thin plasma membrane
Thin layer of cells in walls of lamellae
Thin walls of tracheoles
Only cell wall and plasma membrane at exchange surface

Roles of three main types of blood vessel
Arteries — carry blood under high pressure away from heart to the organs – where they branch into the arterioles
Veins — carry blood under low pressure away from the organs towards the heart
Capillaries — carry blood close to every cell within an organ.

Formation of tissue fluid
At (arteriole) end of capillary;
Hydrostatic / blood pressure;
Forces out soluble / small molecules;
And water;
Protein remains in blood / plasma;
Molecules too large;
More negative / lower water potential at (venule) end;
Water drawn in by osmosis / diffuses in;
Some fluid returned (to blood) by lymphatic system;

Difference between viral DNA and other organisms
Viral DNA is single-stranded/not double-stranded

How a protein is synthesised from information in the DNA
DNA splits / separates / hydrogen bonds break; (accept DNA unzips) to make mRNA; using RNA nucleotides; via RNA polymerase; complementary pairing / eq.; introns/non-coding DNA spliced out; (accept junk DNA spliced out)

Effect of mutation of a gene on the encoded protein and cell function

Change in base of DNA;
Change in codon;
Different amino acid (sequence) in protein;
Different primary structure;
(so) different secondary and tertiary structure (because primary structure determines the rest of the structure);
If relating to enzymes: Tertiary structure is the active site of the enzyme;
Mutation can cause protein/enzyme misfolding;
Produces an incorrectly shaped active site becomes non-functional (both enzymes and proteins in general)

Spread of antibiotic-resistant populations

Vertical gene transmission;
Bacteria divides via binary fission;
Daughter cells receive plasmids;
Plasmids carry antibiotic-resistant genes;
Increase in frequency of (resistant) allele/gene (in future generations);
Horizontal gene transmission
Bacteria pass plasmids to nearby bacteria through the conjugation / cytoplasmic tube / bridge / pilus can occur between different species

How inhibitors can disrupt protein synthesis

for the principle that inhibitor could be a competitive / non-competitive inhibitor; details about the mode of inhibition (competition with a substrate for the active site / changed shape of active site so substrate does not fit); translation (is affected); effect on the role of tRNA (allow tRNA does not bind / not attracted to ribosome); effect on the role of mRNA (allow mRNA does not bind to ribosome / tRNA); peptide bonds do not form; amino acids do not join;

What is transcription and translation?
Transcription: The copying of a gene which takes place in the nucleus
Translation: Using the gene copy made during transcription to assemble a protein; this takes place on the ribosome.

Factors to take into consideration in trials
Age
Gender
Ethnicity
If they were previously infected (health)
Body mass
Genetic factors / family history;

Structure of a chloroplast

Adaptations in (different) Xerophytes relating to water shallow roots enable rapid uptake of rainfall; widespread/shallow roots allow collection of larger volume water/over a larger area/rapid uptake of water; swollen stem for water storage; deep roots for accessing deep groundwater; small/ no leaves so little transpiration;

How AT of mineral ions into xylem vessels in the roots results in water entering vessels and then being moved up the xylem tissue

Water potential in xylem reduced (by entry of ions);
Water potential gradient established between xylem and surrounding cells;
Plasma membranes of surrounding cells are partially permeable;
Water enters xylem by osmosis;
Volume of water in xylem increases;
Cannot move back due to gradient;
Pressure in xylem increases (and forces water upwards);

Cohesion-tension theory – why an air bubble in the xylem vessel in a stem stops transport of water

Evaporation from leaves / transpiration;
Water in xylem under tension*/negative pressure/pulled up;
Water molecules cohere*/stick together/form hydrogen bonds; [Ignore: references to adhesion]
So water a single column;
Air bubble breaks column / prevents cohesion;

Structure of leaves of Xerophytes to keep water in
Reduce number of stomata; reduce surface area
Thick waxy cuticle; increases diffusion distance
Leaves reduced to spines; reduces surface area
Epidermal hairs; reduced diffusion gradient
Sunken stomata; reduced concentration difference
Curled leaves; reduced concentration gradient
Evaporation relating to upward movement of water
WP in leaf cells decreases / becomes more negative; therefore water moves out of xylem (to surrounding tissues) by osmosis; creates a pull/tension on the water in xylem;

How water moves through plant root from the soil, to the endodermis water enters root hair cells; by osmosis; because active uptake of mineral ions has created a WP gradient; water moves through the cortex;
(by osmosis) down a WP gradient; through cell vacuoles and cytoplasms / symplastic pathway; through cell walls / apoplastic pathway;

Xylem tissue long cells / tubes with no end walls; continuous water columns; no cytoplasm / no organelles/named organelle; to impede/obstruct flow / allows easier water flow; thickening/lignin; support / withstand tension / waterproof / keeps water in cells; pits in walls; allow lateral movement / get round blocked vessels;

Decrease in diameter of tree trunks adhesion/attraction of water molecules to walls of xylem; results in tension as water pulled up stem; pulling in walls;

Structure of DNA related to function of storage

Double helix; stable so doesn’t get damaged easy;
4 different bases; can appear in any order so can encode information; very long molecules; store a large amount/a lot of (genetic) information; (idea of “lots”) two complementary strands; useful for repair, copying & error checking;

Structure of a nucleotide
Phosphate group/backbone
Pentose sugar
Nitrogenous base

Replication of DNA

Begins at specific sequence on the DNA molecule/original molecule/replication origin;
(enzyme) DNA Helicase unwinds to separate the two strands of DNA; by breaking the hydrogen bonds;
New DNA built up from the 4 nucleotides (that are present in the nucleoplasm); nucleotides attach to bases of old strands by complementary base pairing;
DNA Polymerase joins nucleotides together; by covalent bonds; forms the sugar phosphate backbone; another enzyme winds the new strands up to form double helices
2 new DNA molecules identical to old molecule (contains 1 new strand and 1 old)
Semi-conservative replication

Starch & Glycogen
Cellulose
α-glycosidic bonds β-glycosidic bonds
Flexible chains
Straight chains
H bonds within each chain, forming helix
H bonds between chains, forming microfibrils
Reacts with Iodine to form purple complex
Doesn’t react with Iodine
Forms H-Bonds with water, so soluble
Can’t form bonds with water, so insoluble
Easy to digest
Difficult to digest
Storage role
Structural role

Gills of fish – adaptation to gas exchange Large surface area provided by lamellae/filaments;
Q Candidates are required to refer to lamellae or filaments. Do not penalise for confusion between two Increases diffusion/makes diffusion efficient; Thin epithelium/distance between water and blood;
4 Water and blood flow in opposite directions/countercurrent;
Point above maintains concentration gradient (along gill)/equilibrium not reached;
* Not enough to say gives steep concentration gradient
As water always next to blood with lower concentration of oxygen;
Circulation replaces blood saturated with oxygen;
Ventilation replaces water (as oxygen removed); 6 max
6-8 Accept answers relating to carbon dioxide
Why water is always lost from the gas exchange surfaces of terrestrial organisms
Gas exchange surfaces are permeable (to small molecules); higher concentration of water molecules inside animal than out /  gradient; water will diffuse outwards / evaporation;

Rate of water loss in insects low during gas exchange
Reference to spiracles; limits exposure of respiratory surface / can close spiracles; OR sunken spiracles / hair round spiracles; trapping moist air;
OR
trachea cuticle lined; only lose water through tracheoles;
OR
trachea / tracheoles inside; limiting exposure of respiratory surface;

Gas exchange in insects
Waterproof exoskeleton;
Rigid to prevent insects drying out;
Network of tubes carry air directly to cells;
Spiracles;
Lead to network called trachea;
Branch into tracheoles (held together by chitin);
Tracheoles go deep into insect tissue, carrying air quickly to every cell;
Oxygen diffuses directly to cells;
Carbon dioxide diffuses out, down their concentration gradients;
Production of lactic acid when insects fly;
Which lowers water potential;
Water diffuse via osmosis from the tracheoles;
So diffusion of oxygen quicker

DNA Hybridisation
Extract DNA from 2 species and remove non-coding regions;
Heat to break hydrogen bonds;
Mix DNA from both species and put DNA in tube, and DNA from just one species in the other;
Cool so that base pairs can form;
DNA with complementary base sequences will form ;
The more similar the base sequence, the more hydrogen bonds;
Heat again – amount of heat required to separate (hybrid) strands indicates relationship;

Feature
Artery
Arteriole
Capillary
Vein
Structural Features

Thick wall and small lumen
Thinner wall than artery with relatively more muscle
Microscopic vessels, wall only once cell thick
Thin wall; little muscle; larger lumen; valves
Blood flow

Away from the heart
Within an organ, to capillaries in different parts of the organ
Around cells of an organ
Away from an organ towards the heart
Type of Blood

Oxygenated*
Oxygenated*
Oxygenated* then becomes deoxygenated
Deoxygenated*
Blood pressure

High and in pulses (pulsatile)
Lower than arteries and less pulsatile
Pressure falls through capillary network
Low and non-pulsatile
Main functions of vessels

Transport of blood to organs
Transport of blood within an organ; redistribution of blood flow
Formation of tissue fluid to allow exchange between blood and cells
Transport of blood back to the heart
Adaptations to main features
Large amount of elastic tissue allows stretching due to surges in pressure and recoil afterwards; endothelium provides smooth inner surface to reduce resistance
Large amount of smooth muscle under nervous control allows redistribution of blood; constriction limits blood flow; dilation increases blood flow
Small size allows close contact with all cells In the body; thin, permeable walls allow formation of tissue fluid for exchange
Large lumen of and thin wall offer least resistance to blood flow as blood is under low pressure; valves prevent backflow of blood
Summary of different blood vessels | * reversed in pulmonary arteries and veins

How penicillin destroys bacteria
Disrupts/weakens cell wall;
Water enters weakened wall via osmosis;
Osmotic lysis / cell bursts;

Effects of deforestation on species diversity
Reduces number of trees;
Destroys habitats;
Loss of food source/shelter causes organisms to die;
(so) diversity reduced;
Migration of organisms may cause diversity increase in those areas

High activity in relation to haemoglobin & oxygen dissociation curves
Increase in CO2/Carbon Dioxide decreases pH; decreases affinity of haemoglobin for oxygen more oxygen is released from oxyhaemoglobin; dissociation curve shifts to right;
Bohr effect

Key features in meiotic cell division
Involves 2 nuclear divisions; 4 daughter cells; daughter cells are haploid; daughter cells show genetic variation (same genes but different combination of alleles)

Stages of Mitosis
Prophase
Chromosome coils and becomes visible, as two chromatids held by a centromere.
Nuclear envelope & Nucleolus break down.
Metaphase
Spindle fibres form, and centrometres attach chromatids to spindle fibres so they lie across the equator/centre
Anaphase
Centromeres divide.
Spindle fibres shorten and pull the sister chromatids to opposite poles of the cell.
Once the chromatids are separated, they are called chromosomes.
Telophase
Spindle fibres break down.
The two sets of chromosomes group together at each pole
Nuclear envelope reforms.
Chromosomes uncoil and can’t be seen as individual structures.

(After mitosis, cell then divides into two during cytokinesis)