A level paper 1

Na+/K+ pump, a type of carrier protein, is linked to a membrane-bound ATP hydrolase enzyme

Explain the function of this ATP hydrolase

• Releases energy

• Allows ions to be moved against a concentration gradient

The movement of Na+ out of the epithelial cells lining the ileum allows the absorption of glucose into the cell lining the ileum. Explain how

• Maintains a concentration/diffusion gradient for Na+ from ileum into epithelial cell

• Na+ moves in by facilitated diffusion, via a co-transport protein, bringing glucose with it

Describe and explain 4 features you would expect to find in a cell specialised for absorption

• Folded membrane/microvilli so large surface area

• Large number of co-transport/carrier proteins to increase rate of facilitated diffusion/active transport

• Larger number of mitochondria so make ATP to release energy

• Membrane-bound digestive enzymes so maintains concentration gradient for fast absorption

Describe the role of micelles in the absorption of fats into the cells lining the ileum

• Micelles include bile salts and fatty acids

• Make the fatty acids more soluble in water

• Bring/release/carry fatty acids to cell/lining of the ileum

• Maintain high concentration of fatty acids to cell/lining of the ileum

• Fatty acids absorbed by diffusion

Describe how an enzyme can be phosphorylated

• Attachment/association of inorganic phosphate to the enzyme

• Released from hydrolysis of ATP

Explain why death of alveolar epithelium cells reduces gas exchange in human lungs (3)

• Reduced surface area

• Increased distance for diffusion

• Reduced rate of gas exchange

Define non-coding base sequences and describe where the non-coding multiple repeats are positioned in the genome

• DNA that does not code for protein/sequences of amino acids

• Positioned between genes

What 2 things must you consider when choosing the right statistical test?

• The type of data (categoric data or continuous data)

• What you’re testing (difference or correlation)

When would you use the students t-test?

• When comparing means of two groups to determine if there is a significant difference

• Data must be continuous

When would you use the Spearman’s rank correlation coefficient test?

• When testing for a correlation between 2 variables to determine if there is a significant correlation

• Data must be collected from the same sample and ranked

When would you use the chi-squared test?

• When testing if observed frequencies are significantly different from an expected ratio

• Data must be categoric (counts, not measurements)

Describe how a polypeptide is formed by translation of mRNA

• mRNA attaches to ribosomes

• tRNA anticodons bind to complementary mRNA codons

• tRNA brings a specific amino acid

• Amino acids join by peptide bonds with the use of ATP

• tRNA released after amino acid joined to polypeptide

• Ribosome moves along the mRNA to form the polypeptide

Define gene mutation

• Change in the base/nucleotide sequence of chromosomes/DNA

• Results in the formation of new allele

Explain 4 ways a gene mutation can have no effect on an individual

• Genetic code is degenerate so amino acid sequence may not change

• Mutation is in an intron so amino acid sequence may not change

• Changes amino acid but has no effect on tertiary structure

• New allele is recessive so does not influence phenotype

Explain 2 ways a gene mutation may have a positive effect on an individual

• Results in change in polypeptide that positively changes the properties

• Results in increased survival/reproductive success

Suggest and explain ways in which cell-surface membranes may be adapted to allow rapid transport of nutrients

• Membrane folded so increased/large surface area for transport

• Large number of protein channels/carriers for facilitated diffusion

• Large number of protein carriers for active transport

• Large number of protein for co-transport

NHE3 is a carrier protein that actively transports one sodium ion into the cell in exchange for one proton out of the cell

How does NHE3 do this?

• Co-transport

• Uses hydrolysis of ATP

• Sodium ion and proton bind to the protein

• Protein changes shape

Describe how bacteria divide

• Binary fission

• Replication of circular DNA

• Division of cytoplasm to produce 2 daughter cells

• Each with single copy of circular DNA

Some proteases are secreted as extracellular enzymes by bacteria

Suggest advantages to a bacterium of secreting an extracellular protease in its natural environment

• To digest protein

• So they can absorb amino acids for growth/reproduction/protein synthesis

• Or so they can destroy a toxic substance/protein

Mammals have some cells that produce extracellular proteases. They also have cells with membrane-bound dipeptidases

Describe the action of these membrane-bound dipeptidases and explain their importance

• Hydrolyse peptide bonds to release amino acids

• Amino acids can cross cell membrane, dipeptides cant

• They maintain concentration of amino acids for absorption

• They ensure maximum yield from protein breakdown

Scientists investigated the effect of 2,4-D (a herbicide) on wheat plants (a crop) and on wild oat plants (a weed)

Give 8 environmental variables that should be controlled when growing the plants before treatments with the spray

• Concentration of mineral ion in soil

• Soil pH

• Temperature

• Light intensity

• Distance between seeds/plants

• Volume of water given

• CO2 concentration

• Humidity

Explain 6 ways in which an insects tracheal system is adapted for efficient gas exchange

• Tracheoles have thin walls so short diffusion distance to cells

• Highly branched/large number of tracheoles so short diffusion distance to cells

• Highly branched/large number of tracheoles so large surface area for gas exchange

• Tracheae provide tubes full of air so fast diffusion (into insect tissues)

• Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas exchange surface

• Body can be moved by muscles to move air so maintains diffusion gradient for oxygen/co2

The damselfly larva is a carnivore that actively hunts prey. It has gills to obtain oxygen from water

Explain how the presence of gills adapts the damselfly to its way of life

• Damselfly larvae has higher metabolic/respiratory rate

• So uses more oxygen

Suggest 5 ways to improve the quality of a scientific drawing

• Don’t use shading

• Only use single lines/dont use sketching/ensure lines are continuous/connected

• Add labels/annotations

• Don’t cross label lines

• Add magnification/scale bar

Describe how a sample of chloroplasts could be isolated from leaves

• Break open cells/tissue and filter

• In cold, isotonic, buffered solution

• Centrifuge/spin and remove nuclei/cell debris

• Centrifuge/spin at higher speed, chloroplasts settle out

Scientists investigated whether one type of monoclonal antibody combined with a drug to inhibit mitosis could be used to treat human breast cancer using mice

Suggest and explain 3 further investigations that should be done before this monoclonal antibody is tested on human breast cancer patients

• Test on other mammal to check for safety/side effects

• Test on healthy humans to check for safety/side effects

• Investigate different concentrations of the antibody to find suitable/safe dosage

Suggest 3 reasons why scientists used biomass instead of the number of individuals of each plant species when collecting data to measure diversity

• Individual organisms could not be identified/separated

• Too small/numerous to count individuals

• Too time consuming

Antibiotic-resistant strains of a bacteria species have become a common cause of infection acquired when in hospital

Explain how the use of antibiotics has led to antibiotic-resistant strains of bacteria becoming a common cause of infection when in hospital

• Some bacteria have alleles for resistance

• Exposure to antibiotics us the selection pressure

• Non-resistant bacteria die and resistant bacteria survive/reproduce

• More antibiotics used in hospital compared with elsewhere/patients have weakened immune system

• So high frequency of resistance allele in population

Describe how you can use aseptic techniques to transfer a bacterial species in liquid culture from a bottle onto an agar plate

• Wash hands with soap

• Disinfect surfaces

• Use sterile pipette/syringe to transfer bacteria

• Remove bottle lid and flame neck of bottle

• Lift lid of agar plate at an angle

• Work close to upwards air movement

• Use sterile spreader

• Place pipette/spreader into disinfectant immediately after use

Give 7 features of all prokaryotic cells that are not features of eukaryotic cells

• No membrane-bound organelles

• Single circular/loop DNA

• DNA free in cytoplasm

• DNA not associated with proteins/histones

• Murein/peptidoglycan cell wall

• Only have smaller ribosomes (60S/70S)

• No introns

Describe viral replication

• Attachment proteins attach to receptors

• Viral nucleic acid enters cell

• Reverse transcriptase makes DNA from RNA

• Cell produces viral protein

• Virus assembled and released

Define the quaternary structure of a protein

More than 1 polypeptide

Give 7 differences between DNA molecules and tRNA molecules

• Deoxyribose vs ribose

• Double-stranded vs single-stranded

• Many nucleotides vs few

• Thymine vs uracil

• Linear vs clover-leaf

• Doesn’t bind to amino acid vs does bind to amino acid

• No exposed bases vs anticodon

Describe the transport of carbohydrate in plants

• Sucrose actively transported into phloem

• By companion/transfer cells

• Lowers water potential in phloem and water enters from xylem by osmosis

• Produces high hydrostatic pressure

• Mass flow to respiring cells or storage tissue/organ

• Unloaded/removed from phloem by active transport

Describe the complete digestion of starch by a mammal

• Hydrolysis

• Of glycosidic bonds

• Starch to maltose by amylase

• Maltose to glucose by (membrane-bound) disaccharidases/maltase

Suggest one way in which the structure of a chromosome could differ along its length to result in a stain binding more in some areas

Differences in base sequences

Or

Differences in histones/interaction with histones

Scientists investigated how biodiversity of bees varies in three different habitats during a year. They collected bees from eight different sites of each habitat four times per year for three years

Suggest and explain 3 ways in which the scientists could have improved the method used for data collection in this investigation

• Collect at more times of the year so more points on graph

• Counted number of individuals in each species so that they could calculate index of diversity

• Collected from more sites/more years to increase accuracy of data

When a person is bitten by a venomous snake, the snake injects a toxin into the person. Antivenom is injected as treatment. Antivenom contains antibodies against the snake toxin. This treatment is an example of passive immunity.

Explain how the treatment with antivenom works and why it is essential to use passive immunity, rather than active immunity

• Antibodies bind to toxin/antigen and causes its destruction

• Active immunity would be too slow/slower

Where in the cell would lactose be attached to a polypeptide to form a glycoprotein?

Golgi apparatus