Extended Response Questions

describe how starch and cellulose related to their function:

STARCH

1. helical shape so compact

2. insoluble so doesn’t affect water potential of cells

3. branched so glucose easily released for respiration

4. large molecule so cant leave cell surface membrane

CELLULOSE

1. long straight chains of beta glucose

2. joined by hydrogen bonding

3. to form fibrils

4. provides strength

describe the processes in the transport of sugar in the plant stems

1. at source sucrose is actively transported into phloem

2. by companion cells

3. lowers water potential and water enters by osmosis from xylem

4. produces high hydrostatic pressure

5. mass flow towards sink

6. at sink sucrose is unloaded

describe the cohesion-tension theory in xylem

1. water lost from leaf by evaporation

2. lowers water potential of mesophyll

3. water pulled from xylem - creating tension

4. water molecules cohere by hydrogen bonds

5. forms continuous water column

6. adhesion of water to walls of xylem

describe the production of mRNA

1. DNA strands separate by breaking H-bonds

2. one template strand is used

3. complementary base pairing occurs

4. nucleotides joined by RNA polymerase

5. pre-mRNA spliced to remove introns forming mRNA

1 Contrast how an optical microscope and a transmission electron microscope work and contrast the limitations of their use when studying cells.

1. TEM use electrons and optical use light; 2. TEM allows a greater resolution;

3. (So with TEM) smaller organelles/named cell structure can be observed

4. TEM view only dead/dehydrated specimens and optical (can) view live specimens;

5. TEM does not show colour and optical (can);

6. TEM requires thinner specimens;

7. TEM requires a more complex/time consuming preparation;

8. TEM focuses using magnets and optical uses (glass) lenses;

measure the difference in size using an investigation between two seeds

1. Use random sample of seeds (from each population);

2. Use (large enough) sample to be representative of whole population;

3. Indication of what size was measured eg mass;

4. Calculate a mean and standard deviation (for each population);

5. Use the (Student’s) t-test;

6. Analyse whether there is a significant difference between (the means of) the two populations;

Describe the gross structure of the human gas exchange system and how we breathe in and out.

1. Named structures – trachea, bronchi, bronchioles, alveoli;

3. Breathing in – diaphragm contracts and external intercostal muscles contract;

4. (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);

5. Breathing out - Diaphragm relaxes and internal intercostal muscles contract;

6. (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);

Mucus produced by epithelial cells in the human gas exchange system contains triglycerides and phospholipids. Compare and contrast the structure and properties of triglycerides and phospholipids.

1. Both contain ester bonds (between glycerol and fatty acid);

2. Both contain glycerol;

3. Fatty acids on both may be saturated or unsaturated;

4. Both are insoluble in water;

5. Both contain C, H and O but phospholipids also contain P;

6. Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group;

7. Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region;

8. Phospholipids form monolayer (on surface)/micelle/bilayer (in water) but triglycerides don’t;

Explain five properties that make water important for organisms

1. A metabolite in condensation/hydrolysis/ photosynthesis/respiration;

2. A solvent so (metabolic) reactions can occur ;

3. High heat capacity so buffers changes in temperature;

4. Large latent heat of vaporisation so provides a cooling effect (through evaporation);

5. Cohesion (between water molecules) so supports columns of water (in plants);

6. Cohesion (between water molecules) so produces surface tension supporting (small) organisms;

Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample.

.1. Add ethanol/alcohol then add water and shake/mix

2. White/milky emulsion

Non-reducing sugar

3. Do Benedict’s test and stays blue/negative;

4. Boil with acid then neutralise with alkali; 5. Heat with Benedict’s and becomes red/orange (precipitate);

Amylase

6. Add biuret (reagent) and becomes purple/violet/mauve/lilac;

7. Add starch, (leave for a time), test for reducing sugar/absence of starch;

Describe how mRNA is formed by transcription in eukaryotes.

1. Hydrogen bonds (between DNA bases) break;

2. (Only) one DNA strand acts as a template;

3. (Free) RNA nucleotides align by complementary base pairing;

4. (In RNA) Uracil base pairs with adenine (on DNA) OR (In RNA) Uracil is used in place of thymine;

5. RNA polymerase joins (adjacent RNA) nucleotides;

6. (By) phosphodiester bonds (between adjacent nucleotides);

7. Pre-mRNA is spliced (to form mRNA) OR Introns are removed (to form mRNA);

Describe how a polypeptide is formed by translation of mRNA.

1. (mRNA attaches) to ribosomes

2. (tRNA) anticodons (bind to) complementary (mRNA) codons;

3. tRNA brings a specific amino acid;

4. Amino acids join by peptide bonds;

5. (Amino acids join together) with the use of ATP;

6. tRNA released (after amino acid joined to polypeptide);

7. The ribosome moves along the mRNA to form the polypeptide;

Define ‘gene mutation’ and explain how a gene mutation can have: • no effect on an individual • a positive effect on an individual.

(Definition of gene mutation)

1. Change in the base/nucleotide (sequence of chromosomes/DNA);

2. Results in the formation of new allele; (Has no effect because)

3. Genetic code is degenerate (so amino acid sequence may not change);

4. Does change amino acid but no effect on tertiary structure;

5. (New allele) is recessive so does not influence phenotype;

(Has positive effect because)

6. Results in change in polypeptide that positively changes the properties (of the protein)

7. May result in increased reproductive success OR May result in increased survival (chances);

Describe the structure of DNA.

1. Polymer of nucleotides;

2. Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;

3. Phosphodiester bonds (between nucleotides);

4. Double helix/2 strands held by hydrogen bonds;

5. (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine

Name and describe five ways substances can move across the cell-surface membrane into a cell.

1. (Simple) diffusion of small/non-polar molecules down a concentration gradient;

2. Facilitated diffusion down a concentration gradient via protein carrier/channel;

3. Osmosis of water down a water potential gradient;

4. Active transport against a concentration gradient via protein carrier using ATP;

5. Co-transport of 2 different substances using a carrier protein;

contrast prokaryotic and eukaryotic cells

1. Magnification (figures) show A is bigger than B;

2. A has a nucleus whereas B has free DNA; 3. A has mitochondria whereas B does not; 4. A has Golgi body/endoplasmic reticulum whereas B does not;

5. A has no cell wall whereas B has a murein/glycoprotein cell wall;

6. A has no capsule whereas B has a capsule;

7. A has DNA is bound to histones/proteins whereas B has DNA not associated with histones/proteins OR A has linear DNA whereas B has circular DNA;

8. A has larger ribosomes;

Compare and contrast the structure of starch and the structure of cellulose

1. Both polysaccharides

2. Both contain glycosidic bonds (between monomers);

3. Both contain carbon, hydrogen and oxygen/C, H and O;

4. Starch has α-glucose and cellulose has βglucose;

5. Starch (molecule) is helical/coiled and cellulose (molecule) is straight;

6. Starch (molecule) is branched and cellulose is not/unbranched;

7.Cellulose has (micro/macro) fibrils and starch does not;

describe the full digestion of starch in mammas

1. Hydrolysis; 2. (Of) glycosidic bonds;

3. (Starch) to maltose by amylase;

4. (Maltose) to glucose by disaccharidase/maltase;

5. Membrane-bound (disaccharidase/maltase);

Describe how a quaternary protein is formed from its monomers.

1. Amino acids joined by peptide bond(s);

2. (By) condensation reaction(s);

3. Secondary structure is formed by hydrogen bonding;

4. Tertiary structure formed by interactions (between R groups);

5. Quaternary structure contains >1 polypeptide OR Quaternary structure formed by interactions/bonds between polypeptides;

Describe the structure of DNA and the structure of a chromosome.

1. Polymer of nucleotides;

2. (Nucleotide) consists of deoxyribose, phosphate and an organic/nitrogenous base;

3. Phosphodiester bonds (between nucleotides);

4. DNA double helix held by H bonds OR 2 strands held by H bonds;

5. (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine;

6. DNA is associated with histones/proteins; 7. (During mitosis/when visible) chromosome consists of two chromatids joined at a centromere;

3 Mutation can result in an increase in genetic variation within a species. Describe and explain the other processes that result in increases in genetic variation within a species.

independent segregation of homologous Chromosomes/pairs;

2. Crossing over between homologous chromosomes/pairs;

3. Random fertilisation of gametes;

4. (Produces) new combinations of alleles;

Describe how proteins are digested in the human gut.

1. Hydrolysis of peptide bonds;

2. Endopeptidases break polypeptides into smaller peptide chains;

3. Exopeptidases remove terminal amino acids;

4. Dipeptidases hydrolyse/break down dipeptides into amino acids;

Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells

1. Nucleotide structure is identical;

2. Nucleotides joined by phosphodiester bond; OR Deoxyribose joined to phosphate (in sugar, phosphate backbone);

3. DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes; Contrasts

4. Eukaryotic DNA is longer;

5. Eukaryotic DNA contain introns, prokaryotic DNA does not;

6. Eukaryotic DNA is linear, prokaryotic DNA is circular;

7. Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not;

Haemoglobins are chemically similar molecules found box in many different species. Differences in the primary structure of haemoglobin molecules can provide evidence of phylogenetic (evolutionary) relationships between species. Explain how.

1. Mutations change base / nucleotide (sequence);

2. (Causing) change in amino acid sequence;

3. Mutations build up over time;

4. More mutations between distantly related species

5. Distantly related species have earlier common ancestor

Describe the roles of iron ions, sodium ions, and phosphate ions in cells.

Iron ions

1. Haemoglobin binds/associates with oxygen

Sodium ions

2. Co-transport of glucose/amino acids (into cells);

3. sodium moved out by active transport/Na – K pump;

4. Creates a sodium concentration/diffusion gradient;

5. Affects osmosis/water potential; Phosphate ions

6. Affects osmosis/water potential;

7. Joins nucleotides/in phosphodiester bond/in backbone of DNA/RNA/in nucleotides

; 8. Used in/to produce ATP;

9. Phosphorylates other compounds (usually) making them more reactive;

10. Hydrophilic/water soluble part of phospholipid bilayer/membrane;

The movement of substances across cell membranes is affected by membrane structure. Describe how.

1. Phospholipid (bilayer) allows diffusion of nonpolar/lipid-soluble substances;

2. Phospholipid (bilayer) prevents movement/diffusion of polar/ charged/lipid-insoluble substances

3. Carrier proteins allow active transport

; 4. Channel/carrier proteins allow facilitated diffusion/co-transport;

5. Shape/charge of channel / carrier determines which substances move;

6. Number of channels/carriers determines how much movement;

7. Membrane surface area determines how much diffusion/movement;

8. Cholesterol affects fluidity/rigidity/permeability;

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels.

1. Micelles contain bile salts and fatty acids/monoglycerides;

2. Make fatty acids/monoglycerides (more) soluble (in water

3. Fatty acids/monoglycerides absorbed by diffusion;

4. Triglycerides (re)formed (in cells);

5. Vesicles move to cell membrane;

1 Describe how the structure of the insect gas exchange system: • provides cells with sufficient oxygen • limits water loss. Explain your answers.

1. Spiracles, tracheae, tracheoles;

2. Spiracles allow diffusion (of oxygen)

; 3. Tracheoles are highly branched so large surface area (for exchange);

4. Tracheole (walls) thin so short diffusion distance (to cells)

5. Tracheole permeable to oxygen/air;

6. exoskeleton (impermeable) so reduce water loss;

7. Spiracles (can) close so no/less water loss

8. Hairs around spiracles reduce water loss;

Outline the similarities in, and the differences between, the structures of DNA and RNA molecules.

1. Polymers of nucleotides;

2. (Nucleotide has) pentose, (nitrogen-containing organic) base and a phosphate (group);

3. Cytosine, guanine and adenine (as bases);

4. Have phosphodiester bonds; Differences 5. Deoxyribose v ribose; 6. Thymine v uracil; 7. Long v short;

8. Double helix/stranded v single stranded;

Outline the similarities in, and the differences between, the structures of chloroplasts and mitochondria.

Similarities

1. Double membrane;

2. Both contain (circular) DNA;

3. Both contain ribosomes;

Differences

4. Thylakoids/lamellae/grana v cristae;

5. Stroma v matrix;

6. Pigments v no pigments;

7. Starch grains v no starch grains;

When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how.

1. Vaccine contains antigen from pathogen; 2. Macrophage presents antigen on its surface;

3. T cell with complementary receptor protein binds to antigen;

4. T cell stimulates B cell; 5. (With) complementary antibody on its surface;

6. B cell secretes large amounts of antibody; 7. B cell divides to form clone all secreting/producing same antibody;

Describe the difference between active and passive immunity

1. Active involves memory cells, passive does not;

2. Active involves production of antibody by plasma cells/memory cells;

3. Passive involves antibody introduced into body from outside/named source;

4. Active long term, because antibody produced in response to antigen;

5. Passive short term, because antibody (given) is broken down;

6. Active (can) take time to develop/work, passive fast acting;