Extended Response PPQs

Describe how the structure of glycogen is related to its function

1. coiled so compact

2. Polymer of glucose so easily hydrolysed

3. branched so more ends for hydrolysis

4. glucose polymer so provides energy for respiratory substrate energy release

5. insoluble so does not affect water potential of the cell

Describe how the structures of starch and cellulose molecules are related to their functions

Starch:

1. Helical/coiled so compact

2. Large/ insoluble so does not affect water potential of the cell

3. Branched so glucose is easily released for respiration

4. Large so cannot leave cell

Cellulose:

5. Long, straight chain of beta glucose

6. joined by hydrogen bonding

7. forms microfibrils

8. provides strength

Describe how the structure of a protein depends on the amino acids it contains

1. determined by the position R group/interactions (bonding)

2. Primary structure is the order and sequences of amino acids

3. Secondary structure is the folding into alpha helix or beta pleated sheet with hydrogen bonding

4. Tertiary structure formed by further folding into 3D shapes with hydrogen bonds, disulphide bridges, ionic bonds and hydrophobic interactions

5. Quaternary structure is folding of one or more polypeptide chain

6. Creates active site in enzymes

Compare and contrast the structure AND properties of triglycerides and phospholipids

1. Both contain ester bonds

2. Both contain glycerol

3. Fatty acids on both may be saturated or unsaturated

4. Both insoluble in water

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

6. Triglycerides has 3 fatty acids and phospholipid has 2 with a phosphate group

7. Triglycerides are fully hydrophobic and phospholipids have hydrophilic and hydrophobic region

8. Phospholipids form monolayer in water but triglycerides don’t

Explain why maltase:

• only breaks down maltose

• allows this reaction to take place at normal body temperature

1. Tertiary structure/ 3D shape of an enzyme

2. Active site is specific to maltose

3. Induced fit model (substrate mostly complimentary to active site but active site changes shape to fit substrate)

4. Enzyme is a catalyst

5. Forming enzyme-substrate complexes

Describe competitive and non-competitive inhibition of an enzyme

1. Inhibitors prevent formation of enzyme-substrate complexes

   Competitive:

2. Inhibitor similar shape to substrate

3. Binds in active site

4. Can be overcome by more substrate

   Non-competitive:

5. Inhibitor binds to allosteric site of enzyme

6. Changes the shape of the active site

7. Cannot be overcome by adding more substrate

Describe the role of the enzymes of the digestive system in the complete breakdown of starch

• Amylase

• Starch to maltose

• Maltase

• Maltose to glucose

• Hydrolysis

• Glycosidic bond

Describe the structure of DNA

1. Polymer of nucleotides

2. Each nucleotide formed from deoxyribose, phosphate and nitrogenous base

3. Phosphodiester bonds between nucleotides

4. Double helix held by hydrogen bonds

5. Between adenine, thymine, cytosine and guanine

Contrast how optical and transmission microscopes work AND contrast limitations of each

1. TEM use electrons and optical use light

2. TEM allows greater resolution

3. Smaller organelles can be observed

4. TEM view only dead 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 staining process

8. TEM focuses on using magnets and optical uses lenses

Contrast the structure of a bacteria cell and the structure of a human cell

1. Bacteria cell much smaller than human cell

2. Bacteria cell has a cell wall but a human does not

3. Bacteria cells does not have a nucleus but a human cell does

4. Bacteria lack membrane-bound organelles but human ell has membrane-bound organelles

5. Bacterial ribosomes 70s whilst human cells have 80s

6. Bacterial DNA is circular but human DNA is linear

7. Bacterial DNA not bound to histone proteins whilst human DNA is

Name and describe 5 ways substances can move across cell surface membrane into cell

1. Simple diffusion of small non-polar molecules down a concentration gradient

2. Facilitated diffusion down a concentrate gradient via proteins (channel/carrier)

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

Explain how the transport of Na⁺ is involved in the absorption of glucose by epithelial cells

1. Na⁺ leave epithelial cells and enter blood

2. By active transport via Na⁺ / K⁺ pump

3. Na⁺ conc. in cell lower than lumen

4. Na⁺ enter via facilitated diffusion

5. Glucose absorbed with Na⁺ against concentration gradient, glucose absorbed down an electrochemical gradient

Describe the behaviour of chromosomes during mitosis and explain how this results in two genetically identical cells

1. Chromosomes shorten and thicken

2. Two identical chromatids due to replication

3. Chromosomes more to equator

4. Attach to individual spindle fibres

5. Spindle fibres contract/ centromere divides

6. Sister chromatids more to opposite poles of the cell

7. Each pole receives identical copies of each chromosome

8. Nuclear envelopes forms around each group of chromosomes

Describe how phagocytic white blood cells destroy bacteria

1. Phagocyte attracted to bacteria by chemicals/ recognise bacteria as foreign

2. Engulf bacteria

3. Bacteria in vesicle

4. Lysosome fuses with vesicle producing phagolysosome

5. Bacteria digested by lysozymes

Describe how vaccination can lead to protection against bacterial meningitis

1. Antigen binds to surface protein on specific B cell

2. B cell divides by mitosis during clonal expansion

3. This is stimulated by cytokines/ T cells

4. Plasma B cells produce antibodies

5. Some B cells become memory B cells

6. Memory B cells produce antibodies faster

Describe the difference between active and passive immunity

1. Active involves memory cells, passive does not

2. Active involves production of antibodies by plasma cells

3. Passive involves antibody introduced into body from outside

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

5. Passive, short term, because antibody is broken down

6. Active can take time to develop, passive fast acting

Describe how the structure of the insect gas exchange system:

• Provides cells with sufficient oxygen

• limits water loss

1. Spiracles, tracheae, tracheoles

2. Spiracles allow diffusion of oxygen through tracheae and tracheoles

3. Tracheoles highly branches so large surface area for gas exchange

4. Tracheole walls thing so short diffusion distance

5. Tracheole walls are permeable to oxygen

6. Chitin exoskeleton so reduce water loss

7. Spiracles close so less water loss

8. Hairs around spiracles reduce water loss

Describe how humans breathe in and out

Breathing in:

1. Diaphragm muscle contracts and flattens

2. External intercostal muscles contract and ribs pulled up

3. Volume increases and pressure decreases in thoracic cavity below atmospheric pressure

   Breathing out:

4. Diaphragm muscle relaxes and raises

5. External intercostal muscles relax and ribcage moves in

   Volume decrease and pressure increases in thoracic cavity above atmospheric pressure

Explain how ventilation mechanism of a fish and structure of its gill result in the efficient uptake of oxygen from water

• Gill filaments/ lamellae, large surface area

• Large no. of capillaries, to maintain concentration gradient

• thin epithelium, short diffusion pathway

• pressure changes, to maintain concentration gradient

• counter current flow, concentration gradient maintained across the whole length of the lamella

Describe the processes involved in absorption and transport of digested lipid molecules from ileum to lymph

1. micelles contain bile salts and fatty acids/ monoglycerides

2. bring monoglycerides to the cell lining

3. Monoglycerides absorbed by diffusion

4. Triglycerides reformed in cells

5. Vesicles move to the cell membrane

Explain how the heart muscle and valves maintain a one-way flow of blood from left atrium to aorta

1. Atrium has higher pressure than ventricle due to contraction causing atrioventricular valves to open

2. Ventricle has higher pressure than atrium due to contraction causing atrioventricular valves to close

3. Ventricle has higher pressure than aorta causing semi-lunar valve to open

4. Higher pressure in aorta than ventricle as heart relaxes causing semi-lunar valve to close

5. Atrial/ventricular contraction causes increase in pressure

Explain how tissue fluid is formed and how it may be returned to circulatory system

1. High hydrostatic pressure of blood at arterial end

2. Water/ soluble molecules pass out

3. Proteins/ large molecules remain

4. Lowers the water potential in the blood

5. Water moves back into venous end of capillary by osmosis

6. Lymph system collects any excess tissue fluid which returns to blood

Describe the cohesion-tension theory of water transport in the xylem

1. Water lost from leaf because of transpiration/ evaporation of water

2. Lowers water potential of mesophyll

3. Water pulled up from xylem creating tension

4. Cohesion of water molecules by hydrogen bonds

5. Forming continuous column of water

6. Adhesion of water to walls of xylem

Describe the process involved in the transport of sugars in plant stems

1. At source, sucrose is actively transported into phloem/sieve tube element

2. By companion cells

3. Lowers water potential in phloem and water enters by osmosis

4. Leads to high hydrostatic pressure

5. Mass flow to wards sink

6. At sink, sugars are removed/ unloaded

Describe how mRNA is formed by transcription in eukaryotes

1. Hydrogen bonds break

2. One DNA strand acts as a template

3. RNA nucleotides align by complimentary base pairing

4. Uracil base pairs with Adenine

5. RNA polymerase joins adjacent nucleotides together

6. By phosphodiester bonds

7. Pre-mRNA is spliced/ introns are removed

Describe how a polypeptide is formed by translation of mRNA

1. mRNA attaches to ribosomes

2. Anticodons bind to complimentary mRNA codons

3. tRNA brings a specific amino acid

4. Amino acids join by peptide bonds

5. With the use of ATP

6. tRNA released

7. Ribosom moves along mRNA to form the polypeptide

Describe how meiosis causes variation and explain advantage of variation to the species

1. Crossing over of non-sister chromatids

2. Independent segregation of homologous chromosomes in meiosis I

3. Independent segregation of homologous chromatids in meiosis II

4. Different adaptations

5. Some survive

6. To reproduce

7. Can pass on gene/allele

8. Allows for changing environment

Explain how a high density of species can occur in one area

1. No interbreeding/ gene pools are separate/ geographical isolation

2. Mutation

3. Different selection pressures (food/ niches/ habitats etc)

4. Adapted organisms survive and breed

5. Increases in allele frequencies

Describe how you could estimate the size of a population of sundews in a small marsh

1. Use tape measures to form a grid

2. Use a random number generator to generate co-ordinates

3. Place quadrate at co-ords and count number of sundews in quadrat

4. Repeat many times for a large sample and calculate mean

5. mean no. of sundews per quadrat x area of the marsh

Describe how you could use the mark-release-capture method to estimate number of lizards on an island

1. Capture sample, mark and release

2. Methods of marking does not harm lizard or make it more visible to predators

3. Leave sufficient time for lizards before collecting a second sample

Population = (no. in first sample x no. in second sample) / no. marked in second sample

Describe how a scientist should collect and process data from seeds to investigate whether there is a difference in seed size between these two populations of trees.

1. Use random samples of seeds

2. Use large sample so representative of the whole population

3. Measuring mass of seed

4. Calculate a mean and standard deviation for each population

5. Use student t-test

6. Analyse whether differences are significant between the means of the two populations

Describe the light-dependent reaction

1. Chlorophyll absorbs light energy

2. Electrons become excited and are removed from chlorophyll

3. Electrons move along electron transport chain releasing energy

4. Energy used to join ADP and Pi to form ATP

5. Photolysis of water produces protons, electrons and oxygen

6. NADP reduced to NADPH by gaining electrons

How is CO₂ converted into organic substances during the light-independent reaction

1. CO₂ combines with ribulose bisphosphate (RuBP)

2. Produces 2 x glycerate 3-phosphate (GP)

3. GP reduced to triose phosphate TP

4. Using NADPH

5. Using energy from ATP

6. 5/6 TP regenerated into RuBP, 1/6 TP converter into glucose

Describe how ATP is made in the mitochondria

1. ATP produced in the Krebs cycle

2. Krebs/ Link reaction produce NADH and FADH

3. Electrons release from NADH and FADH

4. Electrons pass along electron transport chain through series of redox reactions

5. Energy is released

6. ADP + Pi

7. H⁺ move into intermembrane space

8. ATP synthase

Describe and explain how succession occurs

1. Colonisation by a pioneer species

2. Change in environment

3. Enable other species to colonise and survive

4. Change in biodiversity

5. Conditions become less hostile

6. Climax community

Explain how nitrate may cause death of fish in fresh water

1. Algal bloom blocks light

2. No photosynthesis so aquatic plants die

3. Saprobionts

4. Aerobically respire and use oxygen in respiration

5. SO less oxygen available for fish to respire

Explain how farming practices increase the productivity of agricultural crops

1. Fertilisers and ions are added to the soil

2. Nitrates and Phosphates used by the plant to make ATP and DNA for growth

3. Selective breeding/ GMO crops

4. Ploughing decreases denitrification

5. Crop rotation as left over nitrates from last harvest can be used by new crops

Describe how the action of microorganisms in the soil produce a source of nitrates for crop plants

1. DNA/ amino acids into ammonia

2. BY saprobionts

3. Ammonia into nitrite

4. Nitrite into Nitrate

5. By nitrifying bacteria

6. Nitrogen to ammonia

7. By nitrogen-fixing bacteria

Describe the sequence of events involved in transmission across a cholinergic synapse

1. Action potential arrives at presynaptic membrane

2. Ca²⁺ channels open and Ca²⁺ enter

3. Vesicles fuse with the presynaptic membrane and release acetylcholine

4. Acetylcholine diffuses across synaptic cleft

5. Acetylcholine binds to receptors on the post synaptic membrane

6. Na⁺ enter and cause a new action potential in the post synaptic membrane

Describe how the cardiac cycle is controlled by the SAN and the AVN

1. SAN initiates a heartbeat

2. SAN sends impulses across atria causing atria contraction

3. AVN delays

4. Allowing atria to empty before ventricles contract

5. Sends impulses down bundle of His and Purkyne tissue

6. Causing the ventricles to contract from base up

Explain how a rise in blood pressure results in a decrease in the rate of a heartbeat

1. Baroreceptors

2. Send impulses to medulla

3. via parasympathetic neurone

4. to SAN

5. release of acetylcholine decreases impulse form SAN

6. Leads to decrease of impulses to AVN

Describe the roles of Ca²⁺ and ATP in the contraction of a myofibril

1. Ca²⁺ diffuse into the myofibrils from the sarcoplasmic reticulum

2. Causes movement of tropomyosin on actin

3. Exposes the binding site on the actin

4. Myosin heads attach to binding sites on the actin

5. Hydrolysis of ATP on mysosin heads causes heads to bend

6. Pulling actin molecules

7. Attachments of new ATP molecule to each myosin head causes the heads to detach from actin sites

Describe how ultrafiltration produces glomerular filtrate

1. High hydrostatic pressure

2. Small molecules e.g water

3. Pass through basement membrane and the basement membrane acts as a filter

4. Proteins that are too large remain and are not filtered out

5. Through pores in capillaries

How does having a long loop of Henle and large amounts of ADH benefit organisms in desert conditions

In general:

1. More water reabsorbed from filtrate

2. By osmosis

3. from collecting duct

4. Due to longer loop of Henle

   For loop of Henle:

5. Sodium and chloride ions absorbed from filtrate in ascending limp

6. Gradient established in medulla

   For ADH:

7. Acts on collecting duct and distal convoluted tubule

8. Makes cells more permeable by adding more aquaporins in plasma membranes

Explain the role of the loop of Henle in the absorption of water from the filtrate

1. In ascending limp, Na⁺ actively removed

2. Ascending limo impermeable to water

3. In descending limp, Na⁺ diffuse in

4. Descending limb permeable to water
   Low water potential in medulla

5. The longer the loop, the lower the water potential in medulla

6. Water leaves collecting duct/ DCT

7. By osmosis down a water potential gradient

How can two species of palm tree arise by sympatric speciation

1. Occurs in the same habitat

2. Mutations can cause different flowering times

3. Reproductive isolation so gene pools remain separate

4. Change in frequency of alleles as different alleles are passed on

5. Disruptive natural selection

6. Eventually species cannot interbreed to produce fertile offspring

Gene 1: Aa Gene 2: Bb

Explain how the two genes are incvolved in producing white, red or purple flowers

1. Alleles A makes enzyme converting colourless to red

2. Allele a produces a non-functional enzyme

3. Allele B makes enzyme converting red to purple

4. Allele b produces a non-functional protein

5. White flowers result from a genotype aa

6. colourless produces white

7. Red flowers when A_bb only

8. Purple flowers when A_B_ enzymes 1 & 2

Describe how bacteria may be produces which have the resistance gene in their plasmids from oat plants

1. Cut desired gene from DNA of oat plant/ use mRNA from oat which code for resistance/ make artificial DNA with correct sequence of bases

2. Using restriction endonucleases/ and use reverse transcriptase to form desired DNA/ using DNA polymerase

3. Cut plasmids open

4. With the same restriction endonuclease

5. Leaves sticky ends

6. Use DNA ligase to join

7. Return plasmid to bacteria cell

Describe how PCR is carried out

1. DNA heated to 95°C

2. Strands separate

3. Cooled to 55°C

4. Primers bind

5. Nucleotides attach

6. By complimentary base pairing

7. Increase temperate to 72°C

8. DNA polymerase joins nucleotides together

9. Cycle repeated

Describe how a gene could be removed from cells of an amaranth plant and inserted into cells of a potato plant

1. Cute gene using restriction endonucleases

2. At recognition site

3. Leaves sticky ends

4. Use the same enzyme to cut

5. Plasmid/ potato DNA

6. Fixed by ligase

7. Vector e.g. virus to inject DNA

8. remove plant cell wall