Bio Mistakes

AQA A Level Biology

what are fungi cell walls made of?

chitin

what are bacterial cell walls made of?

murein

what does the nucleolus contain?

chromatin

aseptic techniques to place a sample on an agar plate

1. wash hands with soap and disinfect surfaces

2. use a sterile pipette

3. open culture bottle and flame the neck

4. lift lid of agar plate at an angle

5. work close to upward air movement

6. use a sterile spreader

7. place pipette and spreader into disinfectant immediately after use

transport in the phloem

1. sucrose is co-transported into the phloem with H+ by companion cells

2. this lowers water potential in phloem and so water enters from the xylem by osmosis

3. this produces a higher hydrostatic pressure

4. mass flow of sucrose to respiring cells occurs

5. sucrose is removed from the phloem by active transport into the respiring cells

shape of starch molecule

helical, coiled, branched

do red blood cells contain DNA?

no

Calvin cycle

1. carbon dioxide combines with RuBP to produce 2 GP molecules and this is catalysed by Rubisco

2. GP is reduced to triose phosphate using reduced NADP and energy from ATP

3. triose phosphate is converted to RuBP and one carbon is used to from glucose

reasons why phenotypic frequency differs from the Hardy-Weinberg prediction

selection, mutation, immigration/emigration, no random mating

temporal summation

multiple impulses arrive within quick succession and so the effect of the impulses can be added together to reach the threshold potential to generate an action potential

spatial summation

multiple impulses arrive simultaneously at different synaptic knobs that are all connected to the same neurone causing one large action potential to be generated that reaches the threshold potential

where is ADH produced?

posterior pituitary gland

genetic screening process

1. use PCR to amplify DNA

2. cut DNA into fragments using restriction endonuclease enzymes

3. separate DNA fragments using electrophoresis

4. add DNA probes which will bind to their complementary DNA fragment by DNA hybridisation

5. identify fluorescent DNA probes using UV light

structural adaptations of gills

many lamellae provide large surface area, thin so provides a short diffusion pathway

adaptations of the insect tracheal system

tracheoles have thin walls so short diffusion distance, highly branched so large surface area/ short diffusion distance, tracheae provide tubes full of air so fast diffusion, fluid in ends of tracheoles that moves out during exercise so faster diffusion, body can be moved to move air which maintains concentration gradient

where is water reabsorbed in the nephron?

collecting duct and distal convoluted tubule

where are blood pressure receptors?

carotid artery

how to remove a specific section of DNA from a sample

restriction endonucleases cut DNA at specific base sequences

why is it important to know base sequences either side of the required gene in PCR?

for primers to produce a complementary base sequence

importance of fatty acids during exercise

involved in the Krebs cycle

process of increasing the heart rate during exercise

1. increase in CO2 is detected by chemoreceptors

2. more impulses are sent to the medulla

3. more impulses are sent along the sympathetic pathway to the SAN

role of creatine in muscle cells

used to form phosphocreatine which combines with ADP to form ATP

role of carbohydrates in muscle cells

stored as glycogen, then undergoes glycogenolysis to form glucose for respiration

why add HCl to a sample of cells to observe mitosis

to break down cell walls to stop mitosis and allow the stain to pass into cells

why apply pressure to sample on a slide

to ensure a thin sample of cells so that light could pass through the sample

why recombinant DNA can be produced with bacteria

the genetic code is universal, mechanism for transcription and translation is universal

what does the Hardy-Weinberg principle predict?

the frequency of alleles will stay constant from one generation to the next providing no mutation/selection/migration, population is large, mating at random, population is genetically isolated

microvilli

highly folded cell surface membrane

facilitated diffusion

the movement of charged molecules down a concentration gradient via a carrier or channel protein

active transport

the movement of charged molecules against a concentration gradient via a carrier protein using ATP

process of fat absorption in ileum cells

1. micelles form by combining fats with bile salts which makes them more soluble in water

2. micelles break down close to ileum cells

3. contents diffuse into cells

behaviour of chromosomes in anaphase

centromeres divide and chromosomes are pulled to opposite poles of the cell

structural differences between mRNA and tRNA

mRNA contains codons and tRNA contains anticodons, mRNA has no hydrogen bonding and tRNA does, mRNA has no amino acid binding site and tRNA does, mRNA is straight and tRNA is a clover shape, mRNA has many nucleotides and tRNA has few nucleotides

structural adaptations of artery walls

smooth muscle withstands high blood pressure, elastic layer stretches and recoils to maintain blood pressure, smooth endothelium reduces friction, protein coat prevents artery wall splitting

differences between fast and slow twitch muscle fibres

fast contract quickly whereas slow contract slowly, fast mainly use anaerobic respiration and slow use aerobic respiration

soil nutrients that plants need

nitrates to produce amino acids, phosphate to produce DNA/ATP

process of contraction of atria and ventricles in the heart

1. sinoatrial node releases wave of electrical activity

2. atria contract at the same time

3. atrioventricular node relays electrical activity after a short delay via Purkyne tissue in Bundle of His

4. ventricles contract at the same time from the bottom upwards

formula to estimate the size of a population using mark-release-recapture

number in first sample x number in second sample divided by number recaptured

relationship between surface area to volume ratio and metabolic rate

as ratio increases, metabolic rate increases because more heat is lost, higher metabolic rate replaces heat so maintains body temperature

population

a group of organisms of the same species in a particular space at a particular time that can successfully interbreed

process of cell fractionation and ultracentrifugation

1. homogenise to break open cells

2. filter to remove cell debris

3. cold solution to prevent enzyme activity

4. isotonic solution to prevent organelles bursting/shrinking

5. buffered solution to stop enzymes denaturing

6. centrifuge at lower speed initially and remove pellet

components of ATP

adenine, ribose sugar, 3 phosphate groups

what happens to pyruvate when oxygen is available?

it’s transported to the mitochondrial matrix via active transport and it’s oxidised, forming NADH and H+, carbon dioxide is removed

how do higher temperatures increase transpiration?

water molecules have more kinetic energy so more evaporation occurs and there is a faster rate of diffusion out of stomata

water transport in the xylem to leaves

1. water evaporates and diffuses out of leaves via stomata

2. this creates a water potential gradient between spongy mesophyll and xylem, causing water to move up the xylem

3. hydrogen bonds between water molecules cause cohesion and they adhere to xylem walls, causing it to move up in a continuous column

4. water moves by osmosis from the xylem to the spongy mesophyll

structure of a mammalian heart

4 chambers with a septum dividing the left and right chambers, walls of the left ventricles are more muscular than the right, atrioventricular valves between atria and ventricles, semilunar valves between ventricles and arteries

quaternary protein structure

multiple polypeptide chains held by hydrogen bonds in a specific shape

why do chloroplasts and mitochondria have their own DNA?

it contains genes for photosynthesis/respiration so there is no need to import specific proteins or enzymes from the cytoplasm

how the structure of ATP synthase allows its function in mitochondria

it’s a transmembrane protein which connects the matrix and inter membrane space and is a channel specific for H+ ions, has an active site for ADP and Pi and is able to rotate to catalyse ATP production

why is mitochondrial DNA not inherited from fathers?

no mitochondria from sperm cells enter the egg during fertilisation

differences in transcription in prokaryotes and eukaryotes

no pre-mRNA is formed in prokaryotes and it occurs in cytoplasm in prokaryotes v nucleus in eukaryotes

differences between prokaryotic and eukaryotic DNA

prokaryotic is circular, not associated with histones, shorter, no introns and in the cytoplasm

eukaryotic is linear, associated with histones, longer, has introns and in the nucleus

non-overlapping DNA

the same DNA base is not used in different triplets

roles of non-coding DNA

promoter sequences which regulate transcription, pseudogenes which are non-functional due to mutations

why is only a small proportion of all genes transcribed?

most gene products are not needed, only transcribed when needed, genes are switched off when cells become specialised

why is organic produce more expensive?

increased farm labour input, higher non-labour production costs, supply limited compared to demand

species richness

the number of different species in a community

order of classification

domain, kingdom, phylum, class, order, family, genus, species

genetic diversity

the number of different alleles of each gene in a population

how genetic diversity can be measured between species

compare base sequence of DNA, base sequence of mRNA, amino acid sequence of proteins, observable characteristics

how a gene is inserted into a plasmid vector

plasmid and isolated gene are cut using restriction endonucleases and are joined together by ligase

adaptations of gills

lamellae provide a large surface area, lots of capillaries maintain a steep concentration gradient, thin epithelium provides a short diffusion pathway

effects of smoking on gas exchange and ventilation

alveoli are damaged so less oxygen diffuses into blood from alveoli and less carbon dioxide diffuses into alveoli from blood, causing breathlessness and irritation of the trachea

effect of smoking on immune system

T helper cells are unable to stimulate cytotoxic T cells or stimulate B cells so no plasma cells are produced

how do fish maintain water flow over gills?

1. mouth opens and operculum shuts

2. floor of mouth is lowered

3. water enters due to decreased pressure inside mouth

4. mouth closes and operculum opens

5. mouth floor is raised which increases the pressure

6. increased pressure forces water over gills

impact of damaged diaphragm on gas exchange system

difficulty inhaling and reduced oxygen capacity when inhaling

why larger animals have lower metabolic rates

they have lower surface area to volume ratios so have less heat loss

how impulses from the nervous system are transmitted in the heart

sinoatrial node diffuses impulse across atria which causes atrial systole, there is a delay at the atrioventricular node as the impulse travels down the bundle of His which releases the impulse at the apex causing ventricles to contract from apex upwards

factors that affect metabolic rate of an organism

surface area to volume ratio, age of organism, activity level of organism, temperaturer

role of micelles

to facilitate the absorption of lipids in the ileum by emulsifying triglycerides from larger to smaller globules and allowing monoglycerides and fatty acids to enter ileum cells because micelles are amphipathic

which cells produce insulin?

beta cells

bonding in tertiary protein structure

ionic bonds between side chains, strong covalent bonds

uses of genetic fingerprinting

classification, medical diagnosis, forensics, animal/plant breeding

advantage of variable number tandem repeats over amino acid sequences in analysis

more variation in VNTRs and more likely to be unique

process of PCR

1. DNA sample is heated to 95 degrees to break hydrogen bonds to separate strands

2. cooled to 55 degrees to enable primers to bond to strands

3. temperature raised to 72 degrees to enable Taq polymerase to join nucleotides to each strand

reasons why not all strands are formed in PCR

not enough primers/ nucleotides, primers don’t join, temperature damages fragment, strands fail to separate

enzyme used to insert genes

DNA ligase

genetic screening process

1. produce DNA probe using PCR complementary to a known allele sequence for a disease

2. probe is labelled with a fluorescent marker and will anneal if sequence is present

reasons why a DNA mutation may not change the function of a protein

mutation is in non-coding DNA, different primary structure has little effect on tertiary structure, mutation causes same amino acid to be produced

translocation mutation

a section of DNA reattaches to a different chromosome

effect of a transcription factor

it binds to DNA to either increase or decrease transcription

how substitution of an amino acid affects the protein’s properties

different amino acids have different R groups which can form different hydrogen/ionic bonds with other polypeptide chains

how is genetic recombination achieved by crossing over?

1. chromatids of each pair cross over and form a chiasma

2. sections of chromatids are broken off

3. broken sections of chromatids re-join with chromatids of homologous pair

4. alleles swap to form chiasmata

how hyper-methylation of tumour suppressor genes leads to cancer

tumour suppressor gene is switched off so cell division is uncontrollable so apoptosis doesn’t occur

genetic drift

random changes in allele frequencies within a population due to chance events rather than natural selection, typically in small population

compounds made from triose phosphate

glucose, amino acids (using nitrates from soil), lipids (using fatty acids and glycerol)

site of light-independent stage of photosynthesis

chloroplast stroma

site of chemiosmosis

stroma and thylakoid

where RuBP is found in the chloroplast

inner chloroplast membrane

how sunlight causes redox reactions in chloroplasts

photoionisation causes excited electrons to leave chlorophyll, making it oxidised, electron carriers in thylakoid membrane take up electrons which reduces them and NADP receives protons and electrons which reduces it

why are carbohydrates and lipids preferred to proteins in aerobic respiration

many proteins have essential biochemical functions in the body, breakdown of essential proteins can cause health problems

stage of anaerobic respiration in yeast where decarboxylation occurs

ethanol fermentation

how does lactate decrease rate of respiration in cells?

lowers pH which denatures enzymes

process which converts lactate to useful carbohydrates

glycogenesis in the liver

gross primary production

total quantity of chemical energy stored in plant biomass in a given area

role of bacteria in nitrogen-fixation

nitrogen-fixing bacteria convert gaseous nitrogen to ammonium, mutualistic nitrogen-fixing bacteria obtain carbohydrates from plants, ammonium can be readily absorbed by plants and converted to nitrate ions and then amino acids

differences between nitrogen cycle and phosphorus cycle

no gaseous phase in phosphorus cycle but there is in nitrogen cycle, main reservoir in phosphorus cycle is in mineral form but atmospheric in nitrogen cycle

how ATP hydrolysis is involved in muscle contraction

ATP breaks myosin-actin cross bridge, ATP is hydrolysed to ADP and Pi, myosin head returns to its original position

which twitch muscle fibre has a higher density of myoglobin

slow twitch