Biology Unit 2
- Created by: Afsara123
- Created on: 04-06-17 15:49
Standard deviation and Discontinuous vs Continuous
- 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
How does a gene/exon code for a protein?
- 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)
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 enzym
- 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
Stages of Cell Cycle?
- 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)
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
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)
Describe Semi-Conservative Replication?
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? What is genetic bottleneck
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
Role of haemoglobin in oxygen transport?
- 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.
Affects of high levels of carbon dioxide on affini
- 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.
Benefit of fetal haemoglobin having high affinity?
- 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.
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 respiration
Starch, Glycogen and Cellulose
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)
Why do large organisms need specialised exchange a
- have a small surface area to volume ratio
- multicellular (high demand and large diffusion distance)
- impermeable surface (prevent pathogens entering and reduce water loss)
Adaptation of the 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), maintains concentration gradient
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?
- double membrane
- contains discs called thylakoids
- thylakoids contain chlorophyll
- stack of thylakoids called granum
- thylakoids surrounded by a fluid called stroma
Blood flow in humans
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
Structure of arteries?
- 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 And Capillaries
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
How is tissue fluid formed and returned to circula
- 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
How is water absorbed at the roots? What is root p
- 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
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 adhesion and root pressure − (adhesion = water particles stick to lignin in wall of xylem)
Why does the diameter of a tree decrease during th
- 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
Transpiration
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
Potometer
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)
Xerophytes
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
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 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
AA Sequence
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)
Protein Shape
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
Benefits of courtship behaviour?
- identify same species
- identify opposite gender
- identify when individual is ready for mating
- form a pair bond
5 ways an antibiotic can destroy a bacteria?
- 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
How a population of bacteria may become resistant
- 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)
Species Diversity
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
How does deforestation lower species diversity?
- reduces variety of plants
- less habitat
- less variety of food sources
- lowers animal species diversity
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