Biology Unit 2

• SD- Spread of data around the mean, better than range because range affected by outliers
• SD of 2 different means overlap = the difference between the 2 means is not signigicant but is due to chance and vice versa
• What do twin studies test? Influence of genetics + environment on charecteristics
• Idential twins share? Same alleles and same environment
• Non identical twins similar? Due to environment. Different? Due to different alleles
• Discontinuous= characteristics fall into certain groups w no overlap e.g. blood group- determined by genetics ONLY
• Continuous= characteristics show range e.g. height- determined by genetic and environmental factors

• made out of a sequence of bases
• each 3 bases code for 1 amino acid (triplet code)
• therefore
• sequence of bases
• determines sequence of triplet codes
• which determine the sequence of AAs
• = primary structure (folds to secondary, then to tertiary/quaternary) 

• 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

• change in base sequence
• change in sequence of triplet codes
• change in sequence of AAs
• change in primary structure
• change in tertiary structure
• change in active site shape
• substrate no longer complementary
• can no longer form enzyme-substrate complex

• Interphase/Mitosis/Cytokinesis

Interphase?

• G1: protein synthesis
• S: dna replication
• 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 identical nuclei) 

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

Difference between Metaphase I and Metaphase II?

• Metaphase I = homologous pairs line up in centre of cell (23 pairs), Metaphase II = single chromosomes line up in middle of cell (23 chromosomes at this stage)

Produces 2 identical copies of the DNA – each has half the old 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 (A to T, C to G)
• DNA Polymerase joins the sugar-phosphate backbone of the new strand

Evidence for SCR? 

• DNA made of 15N (heavy nitrogen) is replicated in an environment of 14N (light nitrogen) – produces DNA molecules with half 15, half 14 – medium density

What is founder effect

• Small group from the main population becomes isolated
• Small number of individuals = low variety of alleles = low genetic diversity, if this group interbreeds and repopulates
• all the individuals will have alleles from this limited range. if a mutated allele is present, individuals would be more likely to inherit the allele.

What is Genetic bottleneck

• large reduction in population size due to a natural disaster (or hunting)
• low number of individuals = low variety of alleles = low genetic diversity

• haemoglobin loads oxygen in the lungs
• due to high partial pressure of oxygen and low partial pressure of carbon dioxide
• haemoglobin has a high affinity and becomes saturated (full)
• the haemoglobin is transported in the blood in the red blood cell
• at the respiring tissues
• oxygen is unloaded
• due to low partial pressure of oxygen and high partial pressure of carbon dioxide
• haemoglobin has low affinity and becomes unsaturated. 

• high partial pressure of carbon dioxide lowers affinity
• 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
• this shifts the ODC to the right
• called the bohr shift
• Benefit = more oxygen delivered to respiring cells. 

• fetal haemoglobin's ODC will be to the left
• it has high affinity
• in the placenta
• there is low partial pressure of oxygen
• so the oxygen will dissociate from the mother's haemoglobin
• however the fetal haemoglobin will readily associate with the oxygen at the low partial pressures
• so it has enough oxygen for its demands. 

• 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 respiration 

Properties of Starch and Glycogen as energy stores?

• Insoluble = do not affect water potential of the cell, do not diffuse out of the cell
• Coiled/Branched = compact, more can fit into a cell
• Branched/Chained = glucose removed from the end 

Structure of Cellulose?

• Beta glucose arranged in a straight chain (each alternative beta glucose is rotated 180 degrees) = cellulose straight chain
• many cellulose chains are cross linked by hydrogen bonds to form microfibrils
• many microfibrils are cross linked to form marcrofibirils (fibres)
• forms structure of cell wall
• strong material (prevents plant cell from bursting or shrinking)

• have a small surface area to volume ratio
• multicellular (high demand and large diffusion distance)
• impermeable surface (prevent pathogens entering and reduce water loss) 

• 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), maintains concentration gradient 

• 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 

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

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

• The heart pumps twice, the blood goes thru 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 

Role of Hepatic Artery, Hepatic Vein, Hepatic Portal Vein?

• hepatic artery = takes oxygenated blood to the liver
• hepatic vein = takes deoxygenated blood from the liver back to the heart
• hepatic portal vein = takes deoxygenated blood from the digestive system to the liver to be filtered

• narrow lumen = maintains pressure
• lining made of squamous epithelial cells = smooth lining
• thick wall = withstand pressure
• elastic tissue in wall = ventricle contract
• elastic tissue stretches to withstand pressure, ventricle relax
• elastic tissue recoils to maintain pressure and smooth out flow
• smooth muscle in wall = smooth muscle contracts- lumen narrows and arteriole constricts,
• smooth muscle relaxes – lumen widens and arteriole dilates
• collagen in wall – prevents artery from tearing

Veins

• wide lumen = ease of blood flow
• lining made of squamous epithelial cells = smooth lining
• thin wall = vein can be squashed by skeletal muscle pushing blood back to the heart
• valve in lumen = prevents backflow of blood 

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 

• at the arterial end of the capillary there is a build up hydrostatic pressure  
• this pushes fluid out of the capillary thru the pores
• the fluid surrounds the cells, this is called tissue fluid
• at the venous end of the capillary 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

Why is there a large decrease in pressure in the arterioles? increase in total cross-sectional area 

• mineral ions are actively transported from the soil into the roots
• from the soil into root hair cells into cortex cells into endodermis cells into the xylem
• this lowers water potential
• so water follows by osmosis
• water can move by symplast or apoplast
• symplast is when the water moves directly thru the cells, passing thru the cell membrane
• apoplast is when the water moves between the cells or in the cell wall
• apoplast continues until the endodermis cells
• these cells have a casparin ***** around them (a waterproof, impermeable barrier)
• so water enters the cell by symplast and then the xylem

What is root pressure?

• when the water is absorbed by the root and enters the xylem – this applies hydrostatic pressure to the column of water in the xylem, pushing the water up slightly 

• 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 adhesion and root pressure − (adhesion = water particles stick to lignin in wall of xylem)

• 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

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

Factors that increase rate of transpiration?

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

How to set up a potometer?

• choose healthy leaf and shoot
• cut shoot underwater and connect to potometer underwater (maintains continuous column and prevents air entering/blocking xylem)
• ensure potometer is air tight and water tight

How to measure rate of transpiration?

• measure distance bubble moves in a certain time, measure cross-sectional area of tube for answer in volume

What does a potometer actually measure?

• measures rate of water uptake (due to: transpiration, photosynthesis, making cells turgid)

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 

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 double strands can reform look for hybrid dna (half one species, half other species)
• 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

Compare for the same protein (e.g. haemoglobin)

• results = more similar the AA sequence
• more similar the species
• more closely related
• more recent a common ancestor
• (comparing dna sequence better then comparing aa sequence: dna contains INTRONS and triplet code is DEGENERATE)

Compare 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 rabbit
• rabbit will make antibodies against albumin of species A
• takes these antibodies and place in 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

• identify same species
• identify opposite gender
• identify when individual is ready for mating
• form a pair bond 

• prevent cell wall from forming, water enters bacteria by osmosis
• it swells and bursts (osmotic lysis)
•  increase membrane permeability
•  inhibit dna replication
• inhibit protein synthesis
• inhibit respiration

• variation in the population
• some of the bacteria are resistant to the antibiotic
• have an antibiotic resistant gene (carried on plasmid, appeared by random mutation)
• if antibiotic is used
• the ones with the resistant gene will survive and the others will dies out (selection)
• the resistant ones that survive will pass on their resistant gene by vertical gene transmission (asexual reproduction) and horizontal gene transmission (conjugation)
• if this occurs for many generations, then most of the bacteria will be resistant to the antibiotic (adaptation) 

What is species diversity?

• number of different species and the number of individuals for each species

Benefit of high species diversity?

• Stable ecosystem – each species is less likely to become extinct and if a species does it will not affect the food chain as there are other species availab

• reduces variety of plants
• less habitat 
• less variety of food sources
• lowers animal species diversity