AS BIOLOGY UNIT 2
biol 2 aqa, aqa, biology
- Created by: Alice
- Created on: 06-05-11 15:31
VARIATION
Sampling; random sampling
sampling bias
Chance
using a large sample size
Causes of variation:
- Mutations; random changes to genes
- Meiosis; nuclear division forms gametes
- Fusion of gametes; in sexual reproduction offspring inherit from parents
Environmental Influences- plants in poor light
Types of Variation
Variation due to genetic factors:
- A character displaying variation usually controlled by a gene.
Variation due to environmental influences:
- normal distribution curve
- Diet
Mean and Standard Deviation
DNA
AT CG
CT- single rings
AG- double rings
3 hydrogen bonds link CG
2 hydrogen bonds link AT
Function of DNA- hereditary material responsible for passsing genetic info form cell to cell
Adaptations: Stable, pass without change, can carry large amount of genetic information.
The Triplet Code
What is a gene?
Genes are sections of DNA that code for specific polypeptides.
The Triplet Code
Each amino acid has own code of bases on DNA
As code has 3 bases its called triplet code
ATC|GTA|AAC|TAG|GAT|AGA|TCG|AGA
Chromosomes
Allele- form of a gene
DNA combines
w/ proteins, which is coiled,
then into loops, which pack
together to form chromosome
Homologous chromosomes
- Occur in pairs
- homologous pairs= diploid number, in humans=46
- 2 chromosomes that determines same genetic characteristics but not identical
MEIOSIS
Process of Meiosis
1) homologous chromosomes pair up and chromatids wrap round each other, these may be exchanged by crossing over, by the end of this homologous pairs have been separated into different cells.
2) Chromatids move appart, 4 cells have been formed
Locus- the position of a gene on a chromosome of DNA molecule
Independant segregation of Homologous Chromosomes
- chromosomes line up alongside homologous partner
- lying side by side organised randomly
- one of each will go to daughter cell
Genetic combinations
Genetic recombination by crossing over
- Chromatids twist round each other
- portions of chromatids break off
- these portions rejoin with homologous chromatids
New combinations are produced
Genetic Diversity
•Genetic diversity- variation in a species due to difference in alleles
•Genetic Bottleneck- when a population suffers a dramatic loss in numbers. The new population will show much less variation to the fall in the number of alleles
•Founder effect- When a few individuals from a population colonize a new area. The new population will not have all of the alleles of the original population and shoe much less variation.
Artificial selection, choosing those with desired characteristics- selective breeding
Taxonomic Definitions
•Hierarchy- groups arranged on different levels
•Analogous structures- structures with same function, but not based on phylogenetic relationships
•Phylogenetic- related through evolution.
•Artificial classification-grouping based on analogous structures
•Natural classification- grouping things together based on homologous structure, and phylogenetic relationships.
- Species- Similar to one another but different to members of other species, capable of breeding to produce living, fertile offspring.
- •Binomial system- Two names, Genus, Species
•Homologous structures- based on phylogenetic relationships
•Taxonomy- the classification w/ groups in a hierarchical order.
Haemoglobin
4 polypeptide chains-Q' structure
Role of haemoglobin:
- Readily associate w/ O2 at gas-exchange surface
- Readily dissociate from O2 at tissues requiring it
Why have different haemoglobin?
Haemoglobin with a high affinity for O2; take up O2 more easily but release it less readily
Haemoglobin with low affinity for O2; take up O2 less easily but release more readily
Different haemoglobin have different affinities for O2 due to differing amino acid sequence and tertiary structure
loading/associating- haemoglobin +O2
unloading dissociating- haemoglobin -O2
Oxygen dissociation curves
further to the right in pressure= lungs
Effects of Carbon Dioxide concentration
The Bohr effect- haemoglobin has a reduced affinity for oxygen, higher concentration of CO2, the more readily haemoglobin releases its O2.
higher partial pressure- at the lungs
Loading, transport and unloading of oxygen
The higher the rate of respiration -> the more CO2 the tissues produce -> the lower the pH -> the greater the haemoglobin shape change -> the more readily O2 is unloaded -> the more oxygen available for respiration
Surface are to volume ratio
small animals= large surface area to volume ratio, lose heat rapidly, so have a high metabolic rate
Starch
joined by condensation reactions linked by glycosidic bonds
Role of Starch
- Energy storage
- as its insoluble in water, doesn't diffuse out of cells easily
- compact, stored in small space
Glycogen
- shorter chains than starch
- more highly branched than starch
- animal starch, as mainly stored in small granules in the liver of animals
- as made of smaller chains; more readily hydrolysed to a-glucose
Cellulose
- made of B-glucose!
- Different structure- OH group reversed
- forms straight unbranched chains, running parallel
- Weak H bonds, but as so many of them overall is fairly strong
Plant Cell Structure
Leaf palisade cell
- long thin cells-> continuous layer to absorb sunlight
- numerous chloroplasts
- large vacuole pushing chloroplasts to the edge
Chloroplasts
Xylem
- Transport Water
- Thick cell walls
- As they mature they walls incorporate a substance called lignin and the cells die
- the end walls break down, allows cells to form a continuous tube to form
- like a straw as its hollow
- the lignin often forms rings or spirals arounf the vessel
Replication of DNA
Semi-conservative replication
- DNA helicase separates strands
- free nucleotides match up to complimentary bases
- DNA polymerase continues to attract complimentary nucleotides
- Two identical strands of DNA are formed
- Each strand retains half the original DNA, so is semi-conservative
Evidence of semi-conservative
Mitosis
Interphase- proteins synthesised, DNA replication, organelles grow and divide
Metaphase- chromosomes arrange themselves at the centre (equator) of the cells
Anaphase-- spindle pulls appart, chromatids move to pole of spindle
Telophase- chromatids become indistinct, nuclear envelope reforms
Cytokinesis - the cell division
CANCER
Treatment- preventing DNA from replicating; interphase
or inhibiting the metaphase stage, interfering with spindle formation
Cancer cells have fast rate of division
Treatment of chemo in doses , to not kill of healthy body cells
Cell differentiation and organisation
cell-differentiation=process in which a cell becomes more specialised
Tissue- group of same type of cell working together to perform specific function
Organ- Tissues coordinated to perform variety of functions
Organ systems-digestive, respiratory, circulatory
Exchange between organisms
Features of specialised exchange surfaces:
large SA:V
very thin- short diffusion pathway
partially permeable, to allow selected materials across
movement of internal/environmental medium, to maintain a diffusion gradient
Gas-Exchange Insects
Waterproof coverings- over body surfaces
Small SA:V
Spiracle- air pore
Trachea- strengthened by rings
Tracheoles- smaller tubes into body tissues, atmospheric air brought straight to respiring tissues
Along a diffusion gradient
Ventilation- movement of muscles to create mass movements of air in and out of tracheae
Gas-Exchange Fish
Gas Exchange leaf
Leaf Tissues
Circulatory system of a mammal
Blood Vessels
ARTERY-carry blood away from heart- O2, to arterioles
Vein= carry blood to heart, de- O2, to capillaries
Artery structure related to function-
thick muscle layer- to constrict/dialate
thick elastic layer- high blood pressure
thick wall- resists vessel bursting under pressure
Vein structure related to function-
thin muscle-carry blood away from tissues
thin elastic layer- low pressure
Valves- to prevent backflow
Capillary
one cell thick, short diffusion path,highly branched, large surface area for diffusion, spaces between lining, white blood cells can escape
Arteriole
Arterioles carry blood under lower pressure than arteries
Thicker muscle layer than arteries- controls blood flow, movement into capillaries
thinner elastic layer than arteries- blood is under lower pressure
Return of Tissue fluid to the circulatory system
- loss of tissue fluid from capillaries reduces hydrostatic pressure inside them
- at venous end , has lower hydrostatic pressure than outside it in tissue fluid
- tissue fluid is forced back into capillaries by the higher hydrostatic pressure inside them
- osmotic forces from proteins in blood plasma pull water back into capillaries
Movement of water through roots
symplastic pathway- as result of osmosis, through cytoplasm
apoplastic pathway- through cell wall
uptake of water by root hairs
long, thin maximum surface area
thin surface layer- shorter diffusion path
water moves in by osmosis as root has lower water potential than soil as has solutes eg amino acids etc
Movement of water up stems
out through stomata when humid, stomata are open, H2o moves out
across a leaf:
mesophyll cells lose water to the air spaces
(replaced by xylem by apoplastic/symplastic pathway)
these cells now have a lower water potential, they in turn take up water by osmosis
Xylem
Water molecules-cohesive (stick together) by H bonds as H2o evaporates out of leaf by transpiration
water forms continuous pathway across mesophyll cells and down the xylem
water drawn up when evaporated
this is process is called the TRANSPIRATION PULL
Transpiration
Factors that affect transpiration:
- Light-stomata open in daylight, water moves out of stomata (evaporate)
- Temperature-how much air can hold- hotter more, water potential of air, speed at which molecules move
- Air movement-water vapour builds on underside of leaf, if breezy it carries the water vapour, changes water potential gradient by altering rate of water vapour removed
- Humidity-affects water potential between air spaces in the leaf and the atmosphere
Potometer
capillary tube w/bubble in
- shoot cut under water to prevent air being drawn into stem up through xylem which would stop transport of water
- Potomer filled with water trying to avoid bubbles
- joints sealed with agar jelly
- millimetre scale used
- potometer set up under water
- air bubble introduced into capillary tube
to measure water lost, calculate volume of capillary tube, then treat it as a prism to measure volume of water lost in millimetres cubed per however long
Xerophytes
Adaptations:
- thick cuticle- forms waterproof barrier, less water can escape
- hairy leaves- trap moist air near to leaf surface
- stomata in pits/grooves- to trap moist air next to leaf and reduce water potential gradient
- spines for leaves, reduce surface area, slower rate of diffusion
Classification
Artificial classification- dividing organisms up by eg, if they had wings
natural classification- based on evolutionary relationships, based on shared features,groups in a hierarchy in which groups are contained within larger groups on different levels, with no overlaps
Evidence for relationships between organisms
Comparison of DNA base sequences- due to mutations the sequences of bases of DNA of new species will change, similarity in bases-close related species
DNA hybridisation:
- DNA from 2 species extracted & cut
- DNA from one is labelled
- mix both sets, DNA heated to break hydrogen bonds
- mixture cooled to allow combination
- non-complimentary bases don't join
- more heat required to break strands, more closely related
Courtship behaviour
recognise members of same species- to produce fertile offspring
identify fit mate- fertile
form a pair bond-lead to successful mating and raising of offspring
Synchronise mating- so it takes place when maximum chance of the sperm and egg meeting
can see how closely related animals are by comparing similarities/differences in courtship behaviour
Genetic Variation in bacteria
Mutations- random
Conjugation, bacterial cell transfers plasmid linear strand forms new plasmid
Gene transmission
Horizontal gene transmission- Conjugation, passing DNA to another bacterial cell, can go between other species, resistance spreading to other pathogens if present at the same time
Vertical gene transmission- a mutation, bacteria becomes resistant to antibiotic, high proportion of resistant bacteria, they then grow and divide
Antibiotics
How antibiotics work:
- by preventing bacteria from making normal cell walls
- By inhibiting the synthesis and assembly of important peptide cross-linkages in bacterial cell walls
- Weakened walls, so when water moves in by osmosis, cell bursts by osmotic lysis
Biodiversity- Species diversity
Ecosystem diversity- refers to range of different habitats within a particular area
Measure of species diversity, 2 components;
- the no. different species in a given area
- the proportion of the community that is made up of an individual species
Species diversity equation:
d = N (N-1) d= species diversity index N=total no organisms all species
En (n-1) n=total no organisms each species E= the sum of
Species diversity and human activities
Impact of agriculture:
- reduced genetic diversity, reduced alleles
Impact of deforestation:
- deforestation- loss of biodiversity
- loss of species
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