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