The keyword library.

Describes non-living physical or chemical components of an environment.

Examples include temperature and pH.

How close a measurement is to the true value.

Do not confuse accuracy with repeatability or resolution.

The minimum amount of energy that must be supplied for a chemical reaction to start.

Enzymes lower the activation energy by providing a different reaction pathway. They do not supply energy and do not change the energy of the substrate or products.

Example: Catalase lowers the activation energy for breaking down hydrogen peroxide.

The small region of an enzyme, formed by its tertiary structure, that has a specific shape into which the substrate binds.

Say the active site has a specific shape and is complementary to the substrate. Never say the substrate is the same shape.

A jelly-like substance from seaweed that can be formed into beads to trap enzymes for immobilisation.

Substrate must diffuse into alginate beads, which can make immobilised enzymes slower at moderate temperatures.

An alternative version of a gene at a particular locus.

Alleles are not separate characteristics.

A site on an enzyme, away from the active site, where a molecule such as a non-competitive inhibitor can bind and change the enzyme's shape.

You can simply say 'a site other than the active site' in WJEC answers.

An enzyme that hydrolyses starch into maltose. Salivary amylase has an optimum pH of about 7.

In practicals, iodine shows whether starch remains.

Adenosine triphosphate, a molecule that couples energy-releasing processes to processes requiring energy in cells.

It is an immediate energy carrier.

A device that uses an immobilised biological molecule, such as an enzyme, to detect a specific substance and convert the result into an electrical signal.

A glucose biosensor is specific because the active site of glucose oxidase is complementary only to glucose.

Describes living components of an environment or influences arising from organisms.

Competition and predation are biotic influences.

A solution that resists changes in pH when small amounts of acid or alkali are added, so it keeps pH constant.

In enzyme practicals, say a buffer maintains a constant pH because changes in pH would change the rate.

Example: Adding pH 7 buffer to every tube in a temperature investigation.

An intracellular enzyme that breaks down toxic hydrogen peroxide into water and oxygen.

Without catalase, hydrogen peroxide builds up to toxic levels and damages tissues.

Example: Potato extract contains catalase.

A substance that speeds up a chemical reaction without being used up or permanently changed by it, so it can be used again.

Catalysis is the process of speeding up a reaction with a catalyst. Enzymes are biological catalysts.

An organelle where photosynthesis occurs in plants and algae.

It contains thylakoid membranes and stroma.

DNA and associated proteins that form chromosomes in a eukaryotic cell.

It can be more or less condensed.

An instrument that measures how much light a coloured solution absorbs, giving an objective reading of colour intensity.

Suggest a colorimeter as an improvement when a method relies on judging a colour change by eye.

Inhibition involving competition with substrate for an enzyme’s active site.

Increasing substrate concentration can reduce its effect.

An inhibitor with a similar shape to the substrate that binds to the active site, competing with the substrate. Its effect is reduced by increasing substrate concentration.

Both the inhibitor and the substrate are complementary to the active site, not to each other.

Example: Ethanol competes with ethylene glycol for the active site of alcohol dehydrogenase.

Having shapes that fit together, like neighbouring jigsaw pieces. A substrate is complementary to the active site of its enzyme.

The enzyme is specific; the active site is complementary. A competitive inhibitor is complementary to the active site, not to the substrate.

A difference in the concentration of a substance between two regions.

State which substance you mean.

A separate test set up in the same way but without the factor thought to cause the effect, to show that this factor is responsible.

For enzyme practicals, use boiled and cooled enzyme. State the expected result and the purpose.

Example: Discs soaked in boiled potato extract sink but do not rise.

A factor that is kept the same throughout an investigation so that it cannot affect the results.

A controlled variable is not the same as a control experiment. Name each factor and how it is kept constant.

Example: pH is kept constant with a buffer when investigating temperature.

The fluid component of cytoplasm in which cellular structures are suspended.

Cytoplasm also includes structures outside the nucleus.

A permanent change to the tertiary structure of an enzyme, caused by bonds such as hydrogen and ionic bonds breaking, so that the active site changes shape and is no longer complementary to the substrate.

High temperature and extreme pH denature enzymes. Low temperature does not.

The factor that is measured in an investigation to see the effect of changing the independent variable.

Say exactly how it is measured, for example the time until iodine no longer turns blue-black.

Example: The time for a catalase disc to sink and rise is the dependent variable.

Net movement of particles down their concentration gradient due to random motion.

Particles still move at equilibrium.

Making a less concentrated solution by adding solvent, such as water or buffer, to a more concentrated stock solution.

Volume of stock = (concentration needed ÷ stock concentration) × total volume.

Example: 8 cm³ of 20 vol hydrogen peroxide plus 12 cm³ of water makes 20 cm³ of 8 vol.

Having two complete sets of chromosomes, usually one set from each parent.

Represented as 2n.

Describes an allele expressed in the phenotype of a heterozygote under a simple dominance model.

Dominant does not mean common or beneficial.

A community of organisms and its non-living environment, interacting as a system.

Include both living and non-living components.

The moment in a reaction when a clear change shows that it is complete, such as iodine no longer turning blue-black because all the starch has gone.

Judging an end point by eye is subjective. A colorimeter is more objective.

A biological catalyst made of protein. It speeds up a specific chemical reaction by lowering the activation energy and is not used up by the reaction.

Enzymes are not alive, so they are denatured, not killed.

Example: Amylase speeds up the hydrolysis of starch into maltose.

The temporary structure formed after the reaction has happened in the active site, just before the products are released.

It comes between the enzyme-substrate complex and the release of products.

The temporary structure formed when a substrate binds to the active site of an enzyme.

Many WJEC mark schemes award a mark for stating that an enzyme-substrate complex forms. Fewer complexes means a slower rate.

To leave solutions long enough to reach the same temperature, usually in a water bath, before starting a reaction.

Equilibration ensures the reaction happens at the test temperature from the start. It does not mean reaching the optimum.

Describes cells with a membrane-bound nucleus and other membrane-bound organelles.

Animals, plants and fungi are eukaryotes.

An enzyme that is made inside a cell but is secreted by exocytosis and acts outside that cell.

All enzymes are made inside cells. Extracellular enzymes act outside them.

Example: Trypsin is made in the pancreas and acts in the small intestine.

Passive movement down a concentration or electrochemical gradient through a membrane protein.

No direct ATP input is required.

The allele combination of an organism, often stated for a particular gene.

For example, two specified alleles.

A protein folded into a compact, roughly spherical shape with hydrophilic R groups mostly on the outside, which makes it soluble in water.

Enzymes are globular proteins, which is why they can dissolve in cytoplasm and body fluids.

The covalent bond that joins two sugar units together in a carbohydrate.

Lysozyme and amylase both hydrolyse glycosidic bonds.

The steepness of a line, calculated as the change in the y value divided by the change in the x value.

Rate from a graph is the gradient of the curve or of a tangent to it.

Having two different alleles at a particular locus in a diploid cell.

This does not necessarily imply intermediate expression.

Having two identical alleles at a particular locus in a diploid cell.

Specify the gene when useful.

A reaction that breaks a chemical bond by adding a molecule of water.

Mark schemes describe hydrolysis as the addition of water to break a bond. Do not confuse it with condensation, which removes water to form a bond.

Example: Amylase hydrolyses glycosidic bonds in starch.

Describes a solution that causes a cell to lose water compared with the solution inside it.

It is a comparison, not an absolute property.

An enzyme that is fixed in place, for example trapped in alginate beads, so that it does not mix with the product and can be reused.

The specification highlights reuse and improved stability. Also mention that the product is not contaminated.

Example: Lactase immobilised in alginate beads is used to make lactose-free milk.

A temporary loss of enzyme activity, for example at low temperature, when the enzyme's shape is unchanged and activity returns once conditions improve.

At low temperatures enzymes are inactive, not denatured.

The factor that is deliberately changed in an investigation to find out its effect.

Name the actual factor and say how it is changed, for example temperature set with thermostatically controlled water baths.

Example: In the temperature investigation, temperature is the independent variable.

A theory of enzyme action in which the active site changes shape slightly as the substrate binds, moulding closely around it and putting strain on bonds in the substrate.

One-mark definition: the active site changes shape as the substrate binds to give a closer fit. The specification uses lysozyme as the example.

Example: Lysozyme's groove shaped active site closes around a polysaccharide chain from a bacterial cell wall.

A substance that reduces the rate of an enzyme controlled reaction by reducing the number of enzyme-substrate complexes that can form.

Commit to one type of inhibition when explaining data. Mixing both types can cancel marks.

The rate of reaction at the very start of a reaction, found from the gradient of a tangent drawn at time zero.

The initial rate is the fastest rate because substrate concentration is highest at the start.

An enzyme that acts inside the cell that made it.

The term describes where the enzyme acts, not where it is made.

Example: Catalase breaks down hydrogen peroxide inside cells.

Describes conditions in which a cell has no sustained net gain or loss of water by osmosis.

Water molecules continue moving both ways.

The energy a molecule has because it is moving. Molecules move faster and collide more often at higher temperatures.

Use kinetic energy and successful collisions to explain why rate increases with temperature below the optimum.

A molecule or ion that binds to a particular site on another molecule.

In signalling, it can bind a receptor.

The factor that is in shortest supply and so holds back the rate of a process. Increasing it increases the rate.

Name the limiting factor for each part of a concentration graph: substrate on the rising part, enzyme on the flat part.

A model of enzyme action in which the active site is a rigid shape that exactly fits a complementary substrate, like a key fitting a lock.

It explains specificity well, but induced fit is better supported by evidence. Vague references to lock and key alone lose marks.

The position of a gene or other DNA sequence on a chromosome.

The plural is loci.

An enzyme found in tears, saliva and mucus that hydrolyses glycosidic bonds in the polysaccharides of bacterial cell walls, causing bacteria to burst.

Do not confuse lysozyme, an enzyme, with a lysosome, which is an organelle.

The highest rate an enzyme reaction can reach at a given enzyme concentration, when all active sites are occupied.

Non-competitive inhibitors lower the maximum rate. Competitive inhibitors do not.

The average of a set of values, found by adding them together and dividing by the number of values.

Round a mean to the same number of decimal places as the data, or as instructed.

Example: The mean of 300, 330 and 300 is 310.

A sequence of linked chemical reactions in which the product of one reaction becomes the substrate for the next, with each step catalysed by a different enzyme.

If one enzyme in a pathway is missing, its substrate builds up and later products are not made.

Example: A → B → C → D, with a different enzyme for each arrow.

All of the chemical reactions that take place in a cell or an organism, including reactions that break molecules down and reactions that build molecules up.

WJEC describes metabolism as a series of enzyme controlled reactions. Link each step to a specific enzyme.

Example: Respiration and protein synthesis are both part of metabolism.

An organelle containing sites of aerobic respiration and oxidative phosphorylation.

Glycolysis occurs outside it, in the cytosol.

Inhibition where binding away from the active site reduces catalytic activity.

Extra substrate does not overcome the simple model.

An inhibitor that binds to a site other than the active site, changing the tertiary structure and the shape of the active site. Increasing substrate concentration does not reduce its effect.

It lowers the maximum rate. The alternative binding site is sometimes called an allosteric site.

Example: Copper ions from copper sulfate inhibit catalase.

A membrane-bound cell compartment containing the main chromosomes of a eukaryotic cell.

Mitochondria and chloroplasts also contain DNA.

The value of a condition, such as temperature or pH, at which an enzyme has its highest rate of reaction.

Quote the optimum from the graph as a value. Do not say a water bath or buffer keeps an enzyme at its optimum.

Example: Pepsin has an optimum pH of about 2.

A specialised structure within a cell that carries out a particular function.

Not every organelle has a membrane.

Net movement of water through a partially permeable membrane from higher to lower water potential.

Water moves, not the dissolved solute.

A membrane that allows some substances to cross more readily than others.

Permeability depends on both membrane and substance.

The uncertainty of a measurement expressed as a percentage of the measured value.

Percentage error = (uncertainty ÷ measured value) × 100.

Example: A 5 cm³ volume measured to ± 0.1 cm³ has a percentage error of 2%.

A measure of how acidic or alkaline a solution is, based on its hydrogen ion concentration. Lower pH means more hydrogen ions and a more acidic solution.

A higher pH is less acidic. pH changes alter the charges on R groups in enzymes.

The observable or measurable characteristics arising from genotype and environmental influences.

It includes biochemical characteristics.

The sequence of amino acids in a polypeptide chain.

A change in primary structure can change the tertiary structure and so the active site.

An organism that makes organic substances from inorganic carbon using light or chemical energy.

Producers are not always plants.

A molecule made by a chemical reaction. In an enzyme reaction, products are released from the active site so the enzyme can be used again.

Rate can be measured as the amount of product made per unit time.

Example: Water and oxygen are the products of catalase.

The variable part of an amino acid. Different amino acids have different R groups, which may be charged, polar or non-polar.

Changes in pH alter the charges on R groups, which affects bonding in the active site and tertiary structure.

Vertical lines on a graph that show the lowest and highest repeat readings at each value of the independent variable.

Shorter range bars show more repeatable readings. Draw them from the lowest to the highest reading.

How quickly a reaction happens, measured as the amount of product made or substrate used per unit time.

Give units such as cm³ s⁻¹. When only a time is measured, rate = 1 ÷ time, with the unit s⁻¹.

A molecule that binds a particular signal and helps initiate a cellular response.

Some receptors are inside cells.

Describes an allele whose effect is masked in a heterozygote under complete dominance.

Recessive does not mean rare or harmful.

How close the results are when a measurement is repeated by the same person using the same method and equipment.

Judge repeatability from the spread of repeat readings, shown by the length of range bars.

The smallest change in a quantity that a measuring instrument or method can show.

Sampling every 30 seconds gives a timing resolution of 30 seconds.

A structure made of ribosomal RNA and proteins where polypeptides are assembled during translation.

It is not membrane-bound.

The steps that convert detection of a signal into changes within a cell.

The signal molecule need not enter the cell.

The property of an enzyme that means it catalyses only one reaction or acts on only one type of substrate, because only a complementary substrate fits its active site.

Explain specificity using the shape of the active site and its tertiary structure.

Example: Tyrosinase acts on tyrosine but not on valine.

The molecule that an enzyme acts on. It binds to the active site of the enzyme and is converted into products.

An enzyme is specific to its substrate. The active site is complementary to the substrate.

Example: Hydrogen peroxide is the substrate of catalase.

A collision between a substrate and an active site with the right orientation, so that an enzyme-substrate complex forms.

More successful collisions per second means more enzyme-substrate complexes and a faster rate.

A straight line that touches a curve at one point and has the same gradient as the curve at that point.

To find a rate at a given time, draw a tangent there and divide the change in y by the change in x using two points far apart on the tangent.

Example: A tangent at 30 s through (10, 18.3) and (50, 37.6) has a gradient of 0.48 cm³ s⁻¹.

A cell able to respond to a signal because it has the appropriate receptor and response machinery.

Receptor specificity helps determine the response.

The precise three dimensional folding of a whole polypeptide chain, held in place by hydrogen bonds, ionic bonds, disulfide bonds and hydrophobic interactions between R groups.

The tertiary structure determines the shape of the active site. Denaturation changes the tertiary structure.

A container of water with a heater and thermostat that keeps the water at a set, constant temperature.

Say it keeps temperature constant, so all molecules have the same kinetic energy.

A feeding position within a food chain or food web.

An organism can occupy different levels.