Biology Corrections

Explain why oxygen uptake is a measure of metabolic rate in organisms

organism requires oxygen for aerobic respiration which produces ATP and is a metabolic process

Explain what a student should have done when counting cells to make sure the mitotic index he obtained was accurate

• count cells in multiple fields of view

• to ensure a representative sample

• only count whole cells

• to standardise counting

• repeat count

• to ensure figures are accurate

[picture of non evenly distributed chromatids in anaphase, in a root tip cell, chemical has been applied] Use all of this information to suggest how the chemical stops the growth of roots

• stops anaphase

• stops spindle fibres forming

• stops chromatids being evenly pulled apart to opposite poles of the cell

• no new cells added to root tip

explain why a control is used

• to provide comparison with other tubes/set ups

• to show the effect of substance X

common points for evidence for/against mass transport questions

• name the source and name the sink

• no bulge

• no role for water

• could be due to gravity

• no photosynthesising bits to act as source

Why would you not use a 1 in 10 dilution to look at some cells

• dilution too concentrated so cells overlap

• so count unlikely to be accurate

Why are tetracyline resistant bacteria more common than streptomycin resistant bacteria?

• Animals more commonly given tetracyline over streptomycin

• so resistant bacteria more likely to survive, reproduce, pass on allele for resistance

Why do farm animals still have tetracyline resistant bacteria even though they aren’t being given it anymore?

no selection against resistant bacteria

differences between eukaryotic and prokaryotic DNA

• mitochondrial in eukaryotes similar to prokaryotes

• phosphodiester bonds

describe one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange (not surface area or moisture)

• wall is single layer of cells

• resulting in short diffusion distance

How does reduced tidal volume affect the exchange of carbon dioxide between the blood and the alveoli

• reduces volume of oxygen exhaled in a single breath

• so less steep concentration gradient

• so less rate of diffusion of CO2 out of blood so slower movement

Apart from mutation/meiosis, explain one way genetic variation within a species is increased

• random fertilisation of gametes

• forms zygotes with different combinations of alleles

Why is there a faster rate of plasmid replication in cells growing in a culture with high amino acid concnetration

• more polypeptides can be produced so more enzymes

• via protien synthesis

A student used a ruler to measure the diameter in mm of an area. Why should this value be given to the nearest whole number?

• ruler isn’t accurate enough to measure to less than this

• 1mm is resolution of ruler

Why does an enzyme encoded for by the ADf allele catalyse the breakdown of alcohol faster than the enzyme encoded by the ADs allele?

• two enzymes have different primary structures

• so different tertiary structures

• so active site of ADf is more complementary to alcohol

• so ES complexes are more likely to form

Why would you transfer the same volume of liquid culture onto each agar plate in an experiment?

to ensure same number of bacteria are transferred

How would you obtain a more accurate value of a concentration of alcohol needed to stop bacterial growth (100x at 10, 0 at 15)?

• repeat at smaller intervals between 10 and 15

• repeat 3x for each value

Describe how the golgi body is involved in the absorption of lipids

• modifies triglycerides

• combines triglycerides with proteins to form chylomicrons

• produces vesicles that transport triglycerides to cell membrane

Explain the role of the heart in formation of tissue fluid [2]

• contraction of left ventricle forces blood out at high pressure

• causes water to be forced out of the capillary creating tissue fluid

Describe the process of crossing over and how it increases genetic diversity [4].

• homologous pairs of chromosomes associate in the cell

• chiasmata form

• equal lengths of alleles are swapped between chromosomes

• increases genetic diversity as gametes are formed with a different combination of alleles

important thing to write about in centrifugation questions

• differential centrifugation

• i.e. increasing speed of centrifugation

Give two types of cell, other than pathogens, that stimulate an immune response [2]

• abnormal body cells

• cells from other organisms f

why might a nucleus not be visible in an electron micrograph of a cell? [1]

image is of a slice so nucleus must be in another part of the cell

Describe and explain the mechanism that causes lungs to fill with air [3]

• diaphragm contracts and flattens

• external intercostal muscles contract, causing the ribcage to move up and out

• increases volume and decreases pressure of thorax so air moves down a pressure gradient into lungs

Haemotoxylin solution stains DNA. Iodine solutin stains starch. Why would a scientist use Haemotoxylin solution to stain lung tissue?

• lung tissue does not contain starch

• staining DNA makes nucleus visible as DNA is in nucleus

define exon

base sequence coding for polypeptide

Give and explain environmental variables you could change to increase growth rate of bacterial cells [2 per pair]

• increase glucose concentration SO more respiration

• increase oxygen concentration SO more respiration

• increase phosphate concentration SO more DNA/RNA/ATP

• increase nucleotide concentration SO more DNA synthesis

define the term proteome

how would you ensure beetroot cylinders are kept at the same temperature throughout the experiment? [1]

continually monitor temperature AND correct it if it changes

explain how a competitive inhibitor decreases rate of reaction

• inhibitor has a similar shape to the substrate

• so binds to the active site of the enzyme, preventing the substrate from binding

• means enzyme-substrate complex cannot form

why are offspring produced from farmed trout (mother has 2x normal chromosomes) sterile? [2]

• cells will have too many chromosomes

• homologous chromosomes will not pair

• so no meiosis/mitosis

Suggest why combined action of endo and exo peptidases is more efficicent than just exopeptidases?

• endopeptidases hydrolyse internal peptide bonds

• so increased number of ends for exopeptidases

why would you count the number of stomata in several parts of leaf tissue?

• to obtain representative sample

• to obtain mean

Worms live in water with less than 0.2kPa pO2. Tubifex worms have 50% saturation of Hb at 0.08kPa. How does this enable them to survive?

• high saturation of Hb below 0.2kPa

• so lots of O2 available for respiration

Seeds have a requirement to be chilled, which in some species is an adaption to survive in countries with seasonal changes in environmental conditions. How? [3]

• seeds remain dormant in winter

• seeds germinate in summer when temp + light increases

• plants photosynthesise in summer

• produce more seeds in summer

explain the importance of determining a mean FEV1 value of 25-year-olds in this investigation (on the effect of smoking). [2]

• allows comparison to be made

• so effect of smoking can be seen

How could a low FEV1 value cause difficulty when walking upstairs? [3]

• less CO2 removed in one breath

• less O2 diffuses into blood from alveoli

• less aerobic respiratoin

The frequency of a mutation which helps prevent AIDS is highest in Europe. Explain how scientists have concluded that the high frequency is not due to natural selection in response to HIV. [2]

• mutation around for many years

• mutation advantageous for something else

• low HIV exposure in europe

• HIV only present for a short time

Why do people with a high ventricular blood pressure than normal have tissue fluid build up? [2]

• higher hydrostatic pressure of blood entering capillary means more fluid forced out

• less return of fluid due to high pressure or lymph cannot drain all the fluid

How does widening of blood vessels reduce ventricular blood pressure? [2]

• increases volume/widens lumen of blood vessel

• reduces pressure in vessel

• increases resistance to blood flow

what should always be included on biological drawings?

magnification/scale

draw and label a DNA nucleotide

give two features of DNA and explain how they are important in semi-conservative DNA replication

• double stranded so two strands to act as template strand

• has complementary base pairing allowing accurate replication

Describe translation [5]

1. mRNA associates with a ribosome / ribosome attaches to mRNA

2. Ribosome moves to / finds the start codon / AUG;

3. tRNA brings / carries (appropriate / specific) amino acid;

4. Anticodon (on tRNA complementary) to codon (on mRNA);

5. Ribosome moves along to next codon; OR Ribosome ‘fits’ around two codons / can fit two tRNAs;

6. (Process repeated and) amino acids join by peptide bonds / condensation reaction (to form polypeptide); OR (Process repeated and) amino acids joined using (energy from) ATP (to form polypeptide);

describe the pathway taken by an O2 molecule from alveolus to blood

• diffuses across alveolar epithelium

• to endothelium of capillary

Explain why a drug may only be effective in treating some people with the disease [2]

• some people are allergic so can’t take the drug

• some produce serious symptoms which the drug can’t control

explain why it is important to control the volume of water put into each test tube in the beetroot experiment [2]

• as if too much water, concentration of pigment will be lower (and vice versa)

• so to make results comparable

at birth 98% of Hb is HbF. By 6 months, this is completely replaced by HbA. Explain why this is an advantage for the baby. [2]

• HbA has lower affinity for O2 at lower pO2

• which makes it easier to unload O2 for aerobic respiration

ABA reduces stomatal diameter. Why might this help a species survive in dry conditions? [2]

• reduces surface area for transpiration

• so more water available for photosynthesis

NMO is a disease that leads to damage to nerve cells in the spinal cord. A person with NMO produces anti-AQP4 antibody that attacks only these nerve cells. Why does it only attack these nerve cells? [4]

• anti AQP4 antibody has a specific tertiary structure

• has binding site complementary to only one antigen

• antigen to this antibody only found on those nerve cells

• antigen-antibody complexes only form with these nerve cells

Why will all the cells of the body have a mutation that occurs in the zygote? [2]

• mutation occured in one of the gametes that formed the egg

• all cells are derived from a single zygote by mitosis

• mitosis produces genetically identical cells

describe how mRNA is produced in a plant cell [5]

1. The DNA strands separate by breaking the H bonds; OR H bonds broken between (complementary) (DNA) bases;

2. (Only) one of the strands/template strand is used (to make mRNA/is transcribed);

3. (Complementary) base pairing so A→U, T→A, C→G, G→C;

4. (RNA) nucleotides joined by RNA polymerase;

5. pre-mRNA formed;

6. Splicing / introns removed to form mRNA;

what is the role of single stranded DNA fragments in semi conservative DNA replication? [2]

• act as template strands

• so determines order of nucleotides and ensures is correct

Describe and explain the role of antibodies in stimulating phagocytosis [2]

• Antibodies bind to antigens that they are complementary to form an antigen-antibody complex

• this causes agglutination

• this attracts phagocytes

Scientists hypothesised that memory B cells formed in mice 180 days after the 3rd injection of a vaccine. Suggest and explain a practical method that could be used to test this hypothesis. [2]

• expose to meningitis antigen

• memory cells present if faster antibody production than first injection

Describe and explain 3 aseptic techniques. [3]

• wash hands to kill microbes

• burn bunsen burner close by to create upward current of air

• disinfect bench to prevent contamination and kill microbes

• flame instruments to kill microbes

• lift lid slightly to prevent microbes entering

Notes on evaluate conclusion/what can you conclude etc.

• always use numbers (like can see only 10 spores had crossing over)

• always link scenario to experiment done (i.e. if larger fish removed in tank, say sea fishing will do x because the large fish were removed as like tank C)