Red-Pen mistakes (AS-level)

What is meant by the term cancer (2)

Cells that divide out of control, caused by a mutation

Suggest why a Pulmonary embolism can result in these symptoms: Difficulty breathing and rapid heart rate

• blood clot (in pulmonary artery) {prevents / reduces} (deoxygenated) blood reaching lungs (1)

• so blood will {not become oxygenated / contain less oxygen} (1)

• therefore there will {not be enough / less} oxygen supplied to the {cells / tissues} (1)

• difficulty in breathing due to body trying to increase gas exchange (1)

• rapid heart rate to pump more {(oxygenated) blood / oxygen} {around the body / to the cells} (1)

Explain why high Blood pressure is a risk for CVD

• (high blood pressure could) damage the {endothelial lining / endothelial cells / lining of the blood vessels} (1)

• which would cause {an inflammatory response / inflammation} (1)

• therefore {cholesterol may accumulate (in the blood vessel) / formation of blood clots} (1)

Describe the role of DNA polymerase in the process of DNA replication

• adds nucleotides to each (new) DNA strand / {assembles / lines up} nucleotides (against the old strand / in new strand) (1)

• forms phosphodiester bonds between (DNA) nucleotides (1)

• repairs {damage / mistakes} in DNA (1)

State the meaning of semi-conservative replication

• (semi-conservative) one {original / parent} strand retained (in each molecule) (1)

• (replication) more DNA (molecules) is produced / two new molecules made (1)

Explain how a substitution reaction results in collagen that lacks strength

• substitution mutation results in nucleotide being replaced with another (1)

• (substitution mutation) could affect one amino acid (1)

• change in one amino acid could affect {triple helix / collagen secondary structure / collagen tertiary structure} (1)

• fewer H bonds would form (1)

• H bonds involved in strength (1)

• a larger R group would loosen the triple helix (1)

Describe the role of a Golgi body in formation and transport of extracurricular enzymes

• vesicles fuse with / protein enters} Golgi (1)

• {protein / enzyme} modified (1)

• {protein / enzyme} is packaged into vesicles (by Golgi) (1)

What is meant by resolution?

Being able to distinguish between two points that are close together

Explain how 3 active mRNA strands are produced

• post-transcriptional {modification/change} (to pre-mRNA) (1)

• (all) introns are removed by {enzymes / spliceosomes} (1)

• (some) exons removed (to form each strand) (1)

Suggest why society has approved of using stem cells

• can specialise into different cells (1)

• great potential of the research in developing medical therapies (1)

Describe the acrosome reaction

• acrosome fuses with sperm cell membrane (1)

• digestive enzymes released (1)

• which breakdown the zona pellucida (1)

• sperm cell membrane fuses with egg cell membrane

Describe how sucrose is formed from monosaccharides.

• Glucose and fructose.

• Joined by a condensation reaction/water produced.

• forming a glycosidic bond/link.

define correlation

relationship between 2 variables thats reflected by a change in the other variable

Compare and contrast the structures of globular and fibrous proteins.

• Both are chains of amino acids joined by peptide bonds.

• both contain named bonds (holding molecule in its three dimensional shape).

• Globular proteins have hydrophilic groups on the outside, whereas fibrous proteins have hydrophobic groups on the outside.

• Globular have tertiary or quaternary structures, whereas fibrous have little or no tertiary structure.

• globular are folded into compact shapes, whereas fibrous have long chains.

Explain the meaning of the term recessive allele.

• idea that both of these alleles need to be present in order for the recessive phenotype to be expressed.

• when two copies are present (homozygous recessive)

Roles of mRNA.

• reference to transcription

• copy of the genetic code.

• copy of the protein being synthesised.

• moves to ribosome.

• template for translation.

Explain the term phenotype

Is the observable feature.

define allele

different/variant form of a gene.

describe the structure of starch

• (many) glucose molecules joined by glycosidic bonds /links.

• amylose and amylopectin.

• amylose is linear / is unbranched / is helical / has 1,4 bonds.

• amylopectin is branched/has 1,4 and 1,6 bonds.

Roles of tRNA in protein synthesis.

1) correct reference to translation.

2) binds to an amino acid/takes the amino acid to the ribosome/mRNA.

3) reference to tRNA being specific to amino acid.

4) holds the amino acid in place/eq.

Explain the structure of Haemoglobin is related to its function in transporting oxygen and carbon dioxide

• (four) haem groups to bind to oxygen (molecules) (1)

• globular to dissolve (in cytoplasm) (1)

• four subunits have different affinities for oxygen at different partial pressures of oxygen (1)

• carbon dioxide is able to bind to the amino groups of polypeptide (1)

• a structure that has higher affinity for carbon dioxide to cause the oxygen to dissociate (1)

Describe the roles of messanger RNA (mRNA) and transfer RNA (tRNA) in protein synthesis

• to produce a polypeptide chain in order of amino acids (1)

• mRNA involved in transcription and tRNA involved in translation (1)

• mRNA carries a copy of the gene out of the nucleus (1)

• tRNA holds the specific amino acid until the peptide bonds have formed (1)

Explain what determines the properties of an active site

• the {primary structure / amino acids / R groups} properties of the active site (1)

• credit an example of how the R groups might vary (1)

OR

• pH (1)

• as this affects the ionisation of the R groups (1)

Explain why damage to endothelial cells might be an indication that a person is at risk of CVD

• because damage to endothelial cells, triggers {an inflammatory response / build up of white blood cells / blood clotting} (1)

• and a build up of {cholesterol / atheroma / plaque} (1)

• (atheroma / blood clot) {blocks / narrows / reduces blood flow in} a {(blood) vessel / named blood vessel / lumen} (1)

Explain how viral diseases could result in change of allele frequencies of genes in a animals species(example rabbit)

• viral disease acts as selection pressure (1)

• some animals species had advantageous allele(s) that enabled them to survive (the viral disease) (1)

• (these) animal species reproduced and passed the advantageous allele(s) on to their offspring (1)

• increasing the frequency of the {advantageous / beneficial} allele(s) (1)

• one gene may have greater effect so there will be a greater change in allele frequencies for this gene (1)

Describe how the structure and arrangement of cellulose microfibrils contribute to their function in cell walls of xylem vessels

• many hydrogen bonds form between {cellulose molecules / microfibrils} (1)

• microfibrils arranged in {layers / sheets} at different angles (1)

• (microfibril arrangement / it) gives added {tensile strength / rigidity / structural support / stability} (to maintain the structure of the xylem) (1)

• gaps between cellulose microfibrils allow movement of {water / mineral ions / dissolved solutes} (1)

Explain the advantages for this Millipede of being able to make holes in xylem and phloem

• millipede gains {water / mineral ions} from xylem (1)

• millipede gains {sucrose / organic solutes / organic substances / amino acids} from phloem (1)

• appropriate description of use of gained material (1)

Describe how post-transcriptional changes of pre-mRNA can produce active mRNA

• all introns {cut out / removed} (1)

• some exons {cut out / removed} (1)

• by {spliceosomes / enzymes} (1)

• exons are joined together to form active mRNA (1)

Suggest the role of the enzyme DNA methyltransferase (DNMT) in the process of DNA methylation

• binds methyl group to DNA (1)

• to cytosine (in promoter region) (1)

Describe how a seed bank would successfully select, prepare and store seeds from these trees to aid the conservation of this endangered species

• seeds would be selected from {different trees / different areas / genetically different trees} (1)

• seeds would be x-rayed (1)

• seeds would be prepared by being {dried / dehydrated} (1)

• seeds would be treated with an antimicrobial (1)

• seeds would be stored in suitable conditions (1)

Describe the role of the pollen tube in plant reproduction

• (digests a) pathway (through the style) / releases (digestive) enzymes (1)

• for {male gametes / male nucleus generative nucleus(ii) / sperm} to get to the ovule (1)

Give two reasons why the grains were germinated before being transferred to a Petri dishes(with trifluralin)

• trifluralin may prevent / slow down / speed up / inhibit / stimulate} germination (1)

• to ensure that the {seeds / seedlings} (used) were {viable / healthy} (1)

• all started treatment at the same stage (1)

Describe how a root sample could have been prepared and examined to obtain results

• obtain root tip (1)

• (root tips) {placed in (warm) acid / macerated / teased / described} (1)

• (root tips) then placed in appropriate named stain (1)

→ (acetic) orcein, Schiff’s reagent, methylene blue, toluidine blue, acetocarmine, Feulgen’s

• (root tip) squashed (1)

• view through microscope on high power (1)

• mitotic stages counted (1)

Explain the effect of trifluralin could have on processes in mitosis

• there are no cells in {stage 3 / anaphase} or {stage 4 / telophase} / the division stops at {stage 2 / metaphase / before anaphase} (1)

• because the chromosomes are not moving apart (1)

• the spindle apparatus is not formed (1)

Describe how to determine the total mass of starch present in a root tip

• cut out a piece of root tip (1)

• determine mass (of B) / determine the mass of the layers (1)

• determine the starch content of each layer by experiment described (1)

→ e.g. a simple description of use of iodine and colorimeter or colour standard

• convert colorimeter readings {into starch concentrations} (1)

Describe how an investigation could be extended to determine the variability in the concentrations of starch if different root tips

• repeat measurements in same conditions / using same equipment (1)

• calculate the mean (1)

• {calculate / determine} named measure of variability (1)

Give one difference between an organ and a tissue.

• an organ has many functions, tissue has one.

• an organ has many cell types, tissue only has one.

Name the adaptation that allows sheep to learn to ignore sounds that have no importance to them.

behavioural

Describe and explain 2 adaptations of the human egg cell.

1) haploid/ 23 chromosomes.

→ so that diploid number can be restored at fertilisation.

2) lipid droplets/ food store.

→ supplies energy/ nutrients for division.

3) large cell surface area.

→ increased change of fertilisation.

4) cortical granules/ lysosomes/ zona pellucida.

→ to prevent polyspermy.

Define double blind trial and suggest why its important.

• a clinical drug trial

• Neither the patient nor the doctor knows who is receiving the drug and who is receiving the placebo

• One group receives the drug / treatment and another group receives a placebo / control

• To avoid bias / psychological effect / placebo effect (in evaluating results or behavior)

• to see if new drug works better than placebo/ old drug/ eq.

Explain what happens in: Pre-clinical trials

•testing on animlas such as rats

• to monitor success of the drug uptake of target cells, if it is changed chemically and if its excreted safely.

• believed to be unethical to perform on humans first.

• rats carry genes that are similar to those of humans - both suffer from similar diseases.

Explain what happens in: Phase 1 clinical trails

• tested on small number of humans without diseases/ are healthy

• drug is trialled on a small number of healthy volunteers.

• Safety is monitored.

Explain what happens in: Phase 2 clinical trails

• tested on small group of sick patients volunteers

• effectiveness monitored

Explain what happens in: Phase 3 clinical trails

Double-blind trial begins on sick patients

. safety + effectiveness is monitored.

. normally carried with actual trug and Placebo (eg Sugar pill, Saline solution)

Explain how differential gene expression could result in the specialisation of cells.

1) ref. to correct stimulus e.g. chemical.

2) some genes switched off/ on/ eq.

3) mRNA from switched on/ eq. genes.

4) mRNA translated/ eq.

5) idea of protein synthesised/ different proteins produced.

6) which permanently modifies cell (to become specialised)/ description of modification/ eq.

State what is meant by Endemic

A species found only in one area

Describe how substitution, insertion and deletion mutation effect the DNA base sequence of a gene.

• Substitution: swaps bases

• Insertion and deletion: changes number of bases

Explain why this difference ensures the Fetus obtains enough oxygen during development

• Fetal Haemoglobin has higher affinity then adult Haemoglobin

• So oxygen will leave aduld haemoglobin and bin to fetal haemoglobin

Name two structures present in animal cell but not present in plant cells

• cilia

• flagella

• glycogen granules

• centrioles

• lysosomes

Describe how the protein insulin is transported from the ribosome and then secreted by a beta cell

Explain why beta cells can produce insulin but other cells in pancreas do not

Draw and labelled diagram of the Golgi apparatus

Describe the role of rough endoplasmic reticulum in the synthesis of haemoglobin

Describe the evidence that carl Woese used to support his system of classification

Give two reasons why initial rate of reaction was measured

• (the initial rate) would not be influenced by a {change / reduction} in substrate concentration (1)

• (the initial rate) would not be influenced by a {change / build-up} of products (1)

State what is meant by magnification

how many times bigger an object appears in an image then in real life

Describe how the nucleus of a sperm cell enters an egg cell

• {sperm cell / acrosome} releases {enzymes / acrosin / protease} (1)

• (therefore) the {enzymes / acrosin} digest the zona pellucida (1)

• (resulting in) the sperm cell membrane fusing with {egg cell / oocyte} membrane (allowing the nucleus to enter the egg cell) (1)

Describe the role of rER and Golgi apparatus in the production of these enzymes

• translation occurs on the {rough endoplasmic reticulum / rER / ribosomes} (1)

• formation of {2° / 3° / 3D / correct named bonds} structure in rER (1)

• {polypeptide / protein} is packaged into vesicles by rER / {vesicles fuse with / protein transported to} Golgi (1)

• modification occurs in Golgi (apparatus) (1)

Suggest how these enzymes will prevent more then one sperm nucleus enteribg the egg cell

• the cortical granules fuse with cell membrane and release {enzymes / proteases} (1)

• (which result in) {hardening / thickening} of the zona pellucida (1)

• {acrosome enzymes / acrosin} can no longer {digest / penetrate} the zona pellucida (1)

Explain one role names molecule that uses calcium ions

• Calcium pectate

• it holds cell wall together

Describe what happens in DNA during interphase

• (at start of interphase) DNA unwrap from histones / {DNA / chromosomes} {uncoil / uncondensed} (1)

• DNA {is replicated / synthesis / is checked for errors} (1)

• DNA undergoes transcription (1)

Describe how a chain of amino acids can form an enzyme molecule

• (chain) becomes {secondary structure / alpha-helix / (beta) pleated sheet (1)

• (secondary structure) becomes {tertiary / quaternary / 3D / globular} structure (1)

• with an active site (1)

• with hydrophilic R groups arranged on the outside

Describe the role of RNA polymerase in protein synthesis

• transcription / transcribe the DNA / synthesis of RNA (1)

• credit detail of role of RNA polymerase in transcription (1)

→ e.g. RNA polymerase: binds to the (DNA) promotor (region), unwinds the DNA (helix), separates the DNA strands, lines up the (RNA) nucleotides on the {DNA / template strand}, forms phosphodiester bonds between (RNA) nucleotides

• repairs mistakes in the (newly-synthesised) RNA (1)

Compare and contrast the structure of the start and stop codons and how they work

Similarities:

• both {consist of three bases / are three bases / are triplets} (1)

Differences:

• start codon start translation and the stop codon ends translation (1)

• {three / more than one} possible codons for the stop codon but start codon {does not / has only one codon} (1)

• (first) transfer RNA binds to the start codon but there is not a tRNA for the stop codon (1)

• start codon codes for {an amino acid / methionine} but a stop codon does not code for an amino acid (1)

Name two factors that effect the rate of diffusion

surface area (of diffusion surface)

concentration {gradient/difference}

---

membrane permeability

temperature

pressure

type of molecule

Name the law of diffusion that can be used to calculate the rate of diffusion

Fick’s Law

Explain how reduced thrombin will effect blood clotting

• as thrombin is an {enzyme / catalyst / catalyses} (1)

• without thrombin, fibrinogen will not be converted to fibrin (by thrombin) (1)

• without fibrin there will be nothing to trap {platelets / blood cells} (1)

What is meant by the term organ

A group of tissues that work together to perform the same function

Explain 3 ways in which mammalian egg cell is specialised for its functions

• (egg cells are) {haploid / contain one copy of each chromosome} (1)

• to ensure the zygote {is diploid / has two copies of each chromosome} (1)

• (egg cell) has {cortical granules / zona pellucida} which {prevent polyspermy / additional sperm cells entering egg cell} (1)

• (egg cell) has {lipid / oil / fat} (droplets) as a source of energy / mitochondria which {release energy / provide ATP} (1)

Some alleles are found at the same locus

State what is meant by the term locus

• {location / position} of a {gene / allele} on a chromosome

Explain how alleles can produce fruit flies with different coloured eyes

• different alleles have a different DNA base sequence (1)

• which may result in a different {polypeptide / protein} being produced (1)

• flies may inherit two different alleles / (different allele combinations) may result in {further / intermediate} {phenotypes / eye colours} (1)

Explain how histone modification can affect gene expression

• post-transcriptional modification (during development of the embryo) (1)

• introns removed by {enzymes / spliceosomes} (1)

• removal of some exons (1)

• translation occurs (of active mRNA) (1)

• (resulting in) a different {primary sequence / sequence of amino acids / polypeptide} (1)

Explain why it is important to cut a fruit in equal sizes for experiment

• because the surface area needs to be the same (1)

• so they have the same {number / amount / substrate} of protein (molecules) (1)

• to produce valid {(set of) data / results / experiment / test / comparisons} / for validity (1)

State the importance of using a control group in this study

• allows comparisons (1)

What is one hazards for dissection and one for preservation of a heart and explain how to reduce the risk.

Hazard:

1. (using / cutting oneself with) {knife / scissors / scalpel} OR (contact with / allergy to) fish (1)

2. (use of / inhalation of / spilling of) formalin (1)

How to reduce risk:

1. cut {away from fingers / hands / oneself / on a board or tile / wearing gloves} wear {gloves / mask}(1)

2. use in a well-ventilated room / use in a fume cupboard / wear gloves / wash hands / wear protective eye wear / wear mask (1)

Describe how Data could have been collected in a investigation and present to show its repeatability

• repeat {for all 3 groups / experiment} (1)

• (calculate) mean and standard deviation (1)

• plot (mean and) {standard deviation / error bars} (on a graph) (1)

What to use to test for proteins + colour change

Biuret test, Blue → purple

What to use to test for carbohydrates (reducing sugars/ glucose) + colour change

Benedict’s solution, blue to green, yellow, orange or brick-red.

What to use to test for starch + colour change

iodine solution, orange-brown to blue-black

What to use to test for lipids + colour change

4cm³ of ethanol, positive test will show a cloudy emulsion forming

Explain why each codon for DNA genetic code must contain at least 3 bases

• enough codons needed for 20 different amino acids

• four bases used in genetic code

• triplet code provides enough possible codons

Describe how two strands of DNA forming the double Helix in a gene are held together

• complimentary bases

• It enables the formation of two hydrogen bonds between adenine and thymine

state what is meant by a gene

sequence of DNA that codes for polypeptides

Explain why people with cystic fibrosis may develop lung infections

• produces lots of thick and sticky mucus

• Because of reduced water transport from cells

• cilia lining airways are unable to move mucus

• therefore microorganisms are trapped in mucus

• mucus provides suitable growth conditions for other microorganisms.

State what is meant by a allele

a version of a gene

compare and contrast the structure of mRNA and tRNA

• Both contain RNA nucleotides

• Both are single-stranded

---

• mRNA is a straight chain and tRNA is folded

• mRNA has codons and tRNA has anticodons

State what is meant by osmosis

Diffusion of water molecules down a water potential gradient through a partially permeable membrane

Compare and contrast exocytosis and endocytosis

• Exocytosis exports, endocytosis imports.

• Both use vesicles and require ATP for energy.

What is a triplet code?

• 3 bases code for one amino acid

Non-overlapping code

each base is only used once

Degenerate code

when amino acid have more then one code

(eg AAA and AGG code for lysine)

Which pair of membrane transport mechanism, only involves a solute moving down a concentration gradient?

Diffusion and facilitated diffusion

Which transport mechanism involves carrier proteins in the membrane?

1. active transport

2. diffusion

3. exocytosis

Active transport

Which cell transport mechanism is used to take large particles or bacteria into a cell?

Endocytosis

Which cell transport mechanism moves small lipid-soluble molecules through the membrane

Diffusion

Name the current model for the structure of the cell membrane

Fluid moisac model

Explain why number of Cystic fibrosis cases could fall over the years

• Improved genetic screening

• More carriers identified → more couples doing IVF

• more couples choosing not to have (biological) children

Describe the role of enzymes in the synthesis of mRNA using DNA molecule

• RNA polymerase unwinds the DNA helix (1)

• RNA polymerase lines up the (RNA) nucleotides against the DNA strand (1)

• RNA polymerase involved in detecting mistakes in mRNA synthesis (1)

Draw a diagram for the structure of a amino acid Phenylalanine
The R group for Phenylalanine us:

Totipotent stem cells

These can differentiate into any cell type and go on to form whole organisms.