Biology AQAModule 2

Causes of VariationInterspecific – variation that exists between different species

Intraspecific – variation that occurs within a species

Intraspecific Variation:Genetic:

All members of species have same genes

Individuals within a species have different alleles

Environmental:e.g. food, health, temperature

Variation is often a combination of both

Mitosis

Asexual

No Gametes

Cloning

Single Parent

Chromosomal Number Unchanged – Diploid

No Variation In Genes

Spindle Fibre

Meiosis

Sexual

Gametes – Egg & Sperm

No Cloning

Two Parents

Chromosomal Number Halved – Haploid

Variation in Gene Pool

Mutations in the DNA of Chromosomes are mistakes

Homologous Pairs

Chiasmata (Cross-Over) – Bivalent cross up to 8x

Cytokinesis (New Membrane Formed)

¼ of Original Cell ½ of Original Cell

The assortment of genes changes the outcome, depending on which side they stay on

MeiosisProduces four daughter cells each with half the units of DNA

Needed for reproduction

Meiosis 1:Homologous chromosomes pair up and chromatids wrap around each other.

When chromatids twist around other chromatids, tension is created. Parts of the chromatids break off. These broken parts rejoin with the other chromatid called recombination

Independent segregation lines up homologous pairs randomly down the centre of the cell

Meiosis 2:Chromatids move apart by the end 4 cells have been produced

Gene – A section of DNA that codes for a polypeptide

Locus – Position of a gene on a chromosome or DNA molecule

Allele – Different form of a gene

Genetic BottleneckAn event causes a large reduction in number of individuals within a species

Reduces the number of different alleles in the gene pool

This reduces genetic diversity

The few survivors reproduce and a larger population is created from few individuals

When a few members of a species move away creating a new colony

So only a few individuals contribute to gene pool, so more inbreeding occurs, therefore there is a higher incidence of genetic disease

Founder Effect

Life Cycle of a Cell

PM

A

T

Cytokinesis

G1

S

G2

Chart Title

Organelles Copied

DNA Replication Proteins made, Ribosomes copied etc…

G1 G2 is Interphase

How DNA is made & it’s Function

It’s a large polymer of repeating Nucleotides.

G & A Large Bases (Purines) C & T Small Bases (Pyrimidines)

A - T, C - G are the complementary pairs

20 amino acids so we need to use a triplet code e.g. AAA, ATA The triplet code makes 64 codes so 1 amino acids can have different codes. (Degenerate Code)

If AAA made badly/mutates and ATA produced won’t affect the outcome as both are Glycine.

Small % of DNA are genes, the rest is junk (VNTRS) used to create a DNA fingerprint

A – AdenineG – GuanineC – CytosineT (U) – Thymine(Uracil in RNA)

P – Phosphate GroupS – SugarN – Nitrogen Base (Varies)

Gene Loci

Exon

Intron

A & T have 2 H bondsG & C have 3 H bonds

Allele: A variant of a gene

DNA ReplicationDuring Interphase

DNA helicase breaks H-bonds between strands creating 2 single strands

Each original strand acts as a template for a new strand

Free floating nucleotides join to nucleotides on the original strands

In the complementary pairing A & T, G & C

The nucleotides on the strand are bonded together by DNA polymerase creating H-bonds

Each new DNA molecule contains 1 original & 1 new strand

This is called Conservative Replication

S-Phase of the Cell Cycle

DNA Replication – Semi - Conservative Replication

Helicase – breaks ‘H’ bond between Nitrogen bases DNA Polymerase – aligns complementary nucleotides

New Strand

Old StrandMeselson & Stahl:

Creation of Tissue FluidIt supplies cells with O2, Glucose, H2O, AAs, Fatty Acids, Salts. It takes away waste products e.g. CO2.

Large molecules stay in blood RBCs & Proteins

Hydrostatic pressure, at the arterial end, is created due to narrowing of blood vessels.

Blood H2O potential more –ve, due to fluid loss, so some water re-enters the capillaries at the venule end by osmosis, known as the osmotic pressure.

Hydrostatic > Osmotic (Pressure)

Reabsorption of Tissue Fluid

Loss of fluid from capillaries reduces hydrostatic pressure

Osmotic pressure increases due to larger H2O potential gradient, so more H2O enters the capillaries by osmosis.

Excess tissue fluid drains into the lymphatic system (which puts it back into the circulatory system).

Osmotic > Hydrostatic (Pressure)

Plant Gas ExchangePlants need: CO2 for photosynthesis to produce own food (Autotrophs) O2 for respiration to produce ATP (energy compound)

Disproportionate cell wall thickness when guard cell is turgid opens the stoma.

At night no photosynthesis so guard cells become flaccid closing the stoma

Gas Breathed In

Breathed Out

CO2 0.04% 4%

N2 79% 79%

O2 20% 16%

Others

<1% <1%

Waxy Cuticle

Upper Epidermis

Palisade LayerNumber of Chloroplasts

Airy Cells, lots of space Spongy Mesophyll

Lower Epidermis

Substomatal Cavity

Guard Cell

Contains chloroplasts – photosynthesis – glucose produced – more –ve H20 potential – more water into cell by osmosis

Blood VesselsArteries:

Carry O2 blood away from heart

Pulmonary Arteries carry deO2 blood to lungs

Thick & muscular walls

Folded lining to be able to expand

Capillaries:Link arterioles to veins

Found near exchange tissues

One cell thick

Lots of them so a high SA

created

Veins:Carry deO2 blood to the heart

Little muscle or elastic

Wide lumen , low pressure

Contain valves to stop counter flow

Pulmonary veins carry O2 blood to heart from lungs

Arterioles:Smaller arteries

Gas Exchange in Humans

RBC – Large SA:V ratio, no nucleus, more room for Hb

Hb made from 2 polypeptides with Fe ion in centre (prosthetic group)

Hb has 4 binding sites for O2 to bind onto

Hb high affinity for O2 – oxyhaemoglobin (HbO8 when saturated)

Hb higher affinity for CO2 than O2 – when binded to CO2 won’t release

O2 binds to Hb in high PO2 and unloads when there is a low PO2

Bohr EffectWhen cells respire they produce CO2, increasing the PCO2

This increases the rate of O2 unloading

2+

Hb – Quaternary Protein

Hb Saturation Graphs

Bohr Effect

Gas Exchange in Animals

Frog: moist skin & basic lungs – moist skin to avoid gas bubbling in blood (the bends)

Arthropods: Spiracles allow large SA & limited H2O loss. Tracheoles carry gas to every cell. Tracheole walls made of Keratin, very strong. When insect moves it squeezes tubes pushing gases to the cells. Moist tracheole tip to allow quick gas diffusion. Contain air sacs in Haemocoel (blood storage).

Fish: Gill flap (Operculum) Water forced over gills in opposite direction to blood (counter current multiplier) Gill filaments stacked closely on the gill bar (high SA). Blood vessels flow through gill bar.

Large Surface Area : Volume Ratio in smaller animals

Classification

Prokaryotes – No organelles Eukaryotes – With a nucleus

Kingdoms: Animalia, Plantae, Fungii, Monera (Bacteria), Proctoctista (if not sure), Viruses

Kingdom, Phylum, Class, Order, Family, Genus, Species

Taxonomy – shared characteristics – reducing group size – each more similar

A species is a group of similar organisms able to reproduce to give fertile offspring

PhylogeneticsOn DNA & Protein Sequences Protein Sequences: Look at common protein e.g. Haemoglobin of both Compare primary structure and count number of differences e.g. 1 difference between us & gorilla

25 differences between us & cow

DNA Sequencing: Order of nucleotides, to real any mutations hidden by degenerate code

DNA-DNA Hybridisation:Heat mixture to break strands apart. Then allowed to re-bond with other strands. Heated 1 degree at a time until bonds break. Higher temp = more related

Α Β

Anneal – Where there is complementary pairing

Behaviour of OrganismsAlarm Signal – higher chances of survival

Territorial Behaviour – males establish territories for breeding rights and control of food

Courtship – reduces interbreeding and DNA wastage, show they are ready to mate

Social Behaviour – usually developed from parents

Antibiotic Resistance & Bacterial Interactions

Antibiotic – a chemical that only affects bacteria

Either – Bacteriocidal – kill bacteria or – Bacteriostatic – holds bacteria, stops them multiplying

This can lead to osmotic lysis when the cell wall is weakened so the pressure is too great and the cell bursts

Antibiotics tend to be produced by fungi e.g. Penicillin from Penicillium – weaken cell wall (affects glycoproteins) aka Lysis

Bacteria can swap DNA so they can pass on resistant DNA

Bacteria have a higher rate of mutation because they multiply more often.

Efflux Pump – Sucks antibiotics out of the bacterium

Gene Transfer in BacteriaVertical:

Bacteria reproduce asexually, creating an exact copy of the parent

So the parent passes on the resistant DNA

Conjugation – Horizontal:Plasmid copies itself, it passes into another bacterium

Requires cell contact, creating a Pilus (tube)

Usually occurs between related species

Transposon, is a large piece of DNA other than a plasmid

Transduction:Using a Phage, which takes up DNA from host

If phage doesn’t kill the host cell then the host receives the phage’s DNA

Quite Large

BacteriumPhage

Passage of Water through a Plant

Water and mineral ions absorbed by root hairs. They have a large SA and thin surface layer.

Soil has less –ve water potential, water moves by osmosis into root.

Water moves through root cells by the apoplastic and symplastic pathway

Symplastic Pathway:

Water travels through cytoplasm. Through small gaps, Plasmodesmata. Continuous column of

cytoplasm. Each cell will have a less –ve H2O potential when water enters it. So water will

move into the next cell along.

Apoplastic Pathway:

Water travels through the cell walls. Due to cohesive properties of water. Cellulose cell walls

have water-filled spaces, reducing resistance. When water reaches the endodermis cells a

Casparian strip pushes water in cytoplasm. (waterproof barrier)

Apoplast

SymplastEndodermis

Phloem

Xylem

Root Hair

Cortex

Epidermis

Casparian Strip

Plasmodesma

Passage of Water through the Xylem

Endodermal cells actively transport alts into xylem (using energy and proteins).

Water potential of xylem more –ve, so water moves into xylem by osmosis

This creates root pressure

Evidence for Root Pressure:

Pressure increases with temp rise

Pressure decreases with metabolic inhibitors (e.g. cyanide, stops cells respiring)

Pressure decreases with lack of O2 & respiratory substrates

Movement of water up stem:

Water evaporates from stomata pulling more water up xylem (transpiration)

Supported by root pressure & cohesion-tension theory

Cohesion-Tension Theory:

Water evaporates from stomata by transpiration. H-bonds stick H2O molecules

together. Forming a continuous column. So as some water evaporates more water is

pulled up the xylem. Transpiration puts xylem under –ve tension.

Evidence for CT Theory:

Diameter of tree trunks smaller during day (due to –ve tension).

Xylem broken, air enters xylem so continuous column broken.

Xylem broken, water doesn’t leak out as its under tension

Factors Affecting TranspirationLight:

Stomata allows CO2 into leaf needed for photosynthesis, so stoma need to be open, when open water is lost from leaf. Increased light = increased transpiration.

Temperature:Increased temp = increased kinetic energy = increased movement = increased evaporation = increased transpiration

Humidity:Number of water molecules in air. Increased humidity = decreased concentration gradient = decreases transpiration

Air Movement:Water accumulates around stomata once evaporated. Wind blows the water away = increasing water potential gradient = increased transpiration

TranspirationEnsures all material are moved around the plant dissolved in water (e.g. sugars, mineral ions etc…)

Xerophytic PlantsThick Cuticle:

Less water evaporates

Rolled LeavesTraps moist air, air saturated with water. No water potential gradient

Hairy LeavesTraps moist air next to leaves

Stomata in Pits:Traps moist air next to leaf

Reduced SA:VolSlower diffusion rate, so water loss reduced, needs to balanced against plant’s need to PS

Reduction in Air Flow:Small hairs reducing water loss, by breaking up air flow

Size & Surface AreaExchanged between organisms & environment: Respiratory Gases, Nutrients, Excretory Products, Heat by Osmosis, Diffusion & Active Transport

Small organisms = Large SA:VolAllows efficient exchange across their body

As organisms size increases = SA:Vol decreasesTakes too long to diffuse gases into middle of organism

These organisms have adapted:A flattened shape so all cells are nearer the surface

Specialised exchange surfaces with large SA:Vol e.g. Lungs

Features of Specialised Exchange Surface:Large SA:Vol, very thin, partially permeable, movement of internal & environmental medium – maintaining a concentration gradient

Fick’s Law: Diffusion Rate = (SA x Conc Grad) Thickness of Exchange Surface

BiodiversityBiodiversity:

The number & variety of living organisms in a particular area

Species Diversity:Describes a community in terms of the number of different species present & the number of organisms in each species

Measuring Species Diversity:Allows us to assess the diversity in a community, using species diversity index

N = Total number of individuals of all species present in the community

n = Total number of individuals of each individual species

D = N(N – 1) Total n(n – 1)

More BiodiversityLower Value:

Unfavourable (e.g. desert), fewer species present and in smaller populations. Abiotic factors affect which species are present e.g. rainfall, temperature

Ecosystems are usually unstable in these conditions

Higher Value:Favourable (e.g. rainforest), many species present and in larger populations. Biotic factors affect which species are present e.g. competition

Ecosystems are usually stable

Why don’t we just count the number of species present:Species diversity measures both number of species & number of individuals

Doesn’t take into account that some species will have very small populations and be very rare

Species Diversity & Human Activities

Impact of Agriculture:Chosen by humans and only certain species are chosen to grow. To be economical large areas of land are need to grow the species. This means less land is available for other species. Therefore there is more competition. So fewer species survive. Pesticides also increase competition as the crops grown by farmers will be of better health etc..

Deforestation:Deforestation is the permanent removal of forests for land to be used for farming etc…

This reduces the number of habitats present to organisms. Lowering the species diversity.

Glucose:Forms a Glycosidic link between 2 glucose units (condensation reaction)

Starch:Energy storage in plants, polysaccharide of alpha-glucose. Two type of alpha-glucose:

Amylose: contains 1,4 – glycosidic bonds, unbranched chain

Amylopectin: contains 1,4 &1,6 – glycosidic bonds, branched chain

How is is structure related to its function?Compact shape – lots can be stored in a small space

Easily Hydrolysed – Glucose rapidly available for respiration

Insoluble – no osmotic effect on cells & stays in cells (for respiration)

Test = add Iodine Brown – Black +ve

Glycogen:Energy storage in animals, polysaccharide of alpha-glucose, similar to amylopectin but more branched. More easily hydrolysed than starch due to more branches

Glucose, Starch & Glycogen

CelluloseFound in plant cell walls, providing strength

Polysaccharide of beta-glucose

To bond 2 beta units, alternate units are upside down

Cellulose contains 1,4 – Glycosidic bonds, unbranched chain

H-bonds form between chains, forming Microfibrils

Microfibrils then come together to form Cellulose fibres, overlapping to give strength

Cellulose is permeable due to gaps between fibres

Plant CellPalisade Cell:

Absorb light for photosynthesis

Adaptations for it’s function:Lots of chloroplasts – more light absorbed = more PS

Long & thin – large SA = more PS

Vacuole pushes chloroplasts to edge of cell – less distance for light to travel = more PS

Chloroplasts:Contain chlorophyll – absorbs light – for PS

Converts light energy into chemical (in the form of glucose)

Inner & Outer Membrane – controls what enters & leaves the cell

Thylakoid – 1st stage of PS takes place here

Stroma – 2nd stage of PS takes place here

Granum – Large SA for 1st stage of PS

Starch Grain – Energy storage of alpha–glucose

StromaStarch GrainThylakoid

Granum

Inner & Outer membrane

More Plant Cell StuffCellulose cell wall:

Middle lamellae cements plant cells together, increasing stability

Vacuole:Stores cell sap (water, glucose, salts, amino acids)

Vacuole membrane called the Tonoplast

Xylem:Thick cell walls, when matured they contain lignin

End of cells break down creating a vessel

Xylem made up of dead cells

Plant Cells Animal Cells

Cellulose Cell Wall & Cell – Surface Membrane

Cell – Surface Membrane

Chloroplasts (in most cells) No Chloroplasts

Large, Central Vacuole filled with Cell Sap

Small Vacuole Scattered through Cell

Starch Grains store energy Glycogen Granules store energy

Lignin

Variation & SamplingVariation:

Exists between members of the same speciesSimilarities & differences are a result of genetics, environmental factors or both

Genetic Variation:Due to Mutations – changes to DNADue to Meiosis – cross-over & independent assortmentFusion of Gametes – Offspring inherit mixed characteristics from parents

– Which gamete fuses at fertilisation is random

Environmental Variation:Climatic Changes e.g. temp, rain, sunlightSoil Conditions e.g. type of soil, nutrient availabilityFood AvailabilitypH

Genetic & Environmental Combined:Most cases involve both factorsHard to distinguish between the effects of the factorsAny conclusions drawn are usually tentative (not clear) and should be treated with caution

Discontinuous Variation:Only due to genetic factors (there are few distinct groups e.g. blood group A, B, AB, O)Usually controlled by a single gene (little or no environmental influence)

Continuous Variation:Due to genetic & environmental factors (characteristics merge together, forming a continuum)Controlled by many genes (polygenic), environmental factors have a large influence

Selective Breeding

It involves humans selecting certain plants or animals that have the desired characteristics (e.g. high-yield)

This reduced the genetic diversity in some populations

Once an organism has the desired characteristics, only that type of organism will be produced

So nearly all the population have similar alleles

So they are more susceptible to diseases

Interpreting Normal Distribution

Mean:Measurement of the maximum height of the curve

The mean of a sample provides an average useful when comparing

No information about the range though

Standard Deviation:Measure of the width of the curve

Gives an indication of the range of values either side of the mean

Distance from mean to point of inflexion (where curve changes from convex to concave)

SD better than Range:Spread around the mean instead of the highest lowest values

Not influences by single outlier

Allows statistical tests to be carried out