Biology AQA Year One A-Level

the similar biochemical basis for life for all living things evidences ____

small units from which larger molecules are made

made from many monomers joined together

two molecules react to form a chemical bond and eliminate a water molecule

a chemical bond between two molecules is broken by addition of a water molecule

commonly used by cells as respiratory substrates, form structural components in plasma membranes and cell walls

the monomers from which larger carbohydrates are made

formed by the condensation of two monosaccharides

glucose + glucose

glucose + fructose

glucose + galactose

glucose has two ____ called alpha and beta glucose

alpha glucose has a ____ group above the ring on carbon 5 whereas beta glucose has a ____ group below the ring

test for ____: two drops of iodine + two drops of food sample, blue black coloration

test for ____: heat in a water bath at 75C for 5 minutes, brick red precipitate

test for ____: heat in a water bath with dilute HCl, neutralise with sodiumhydrogencarbonate, test for reducing sugars

polysaccharide of alpha glucose used for storage in plants

(1) found in seeds and ____ organs like tubers

(2) chains may be ____ or un____

(3) the unbranched chain is ____ and wound into a tight coil to compact the molecule

(4) large and ____ so does not affect cell water potential or diffuse out of cells

(5) the branched form has many ends for ____ enzymes to act on

polysaccharide of alpha glucose used for storage in animals

more highly branched due to the higher ____ needs of animals

made up of monomers of beta glucose to form straight, unbranched chains

(1) ____ bonds form cross links between individual chains

(2) molecules are groups into ____ which are further grouped into fibres

(3) major component of the ____ that provides rigidity to the plant cell

(4) exerts an inward pressure that prevents osmotic lysis so allows cells to be ____

turgidity is important to maximise ____ for photosynthesis

the primary constituents of the plasma membrane bilayer, used in hormones and as respiratory substrates

formed by condensation of one molecule of glycerol with 3 fatty acids

glycerol and fatty acids are bonded by an ____ bond

the R group of a fatty acid may be ____ or un____

(1) high ratio of energy storing C-H ____ so are a good source of energy

(2) low ____ to energy ratio

(3) large and ____ so don't affect water potential

(4) release ____ when oxidised

in ____ one fatty acid of a triglyceride is substituted by a phosphate group

comprise of a ____philic phosphate head and a ____phobic fatty acid tail

(1) form a ____ in an aqueous environment

(2) form ____ by combining with carbohydrates within the cell surface membrane

test for ____: shake with ethanol then add water and gently shake, milky white emulsion

form many cell structures and are important as enzymes, chemical messengers, components of the blood

____ are the monomers of protein

chiral ____ around which R, COOH, H and NH2 are found

condensation between 2 amino acids forms a ____ bond

formed by condensation of two amino acids

formed by condensation of many amino acids (a functional protein may contain one or more)

the sequence of amino acids joined by peptide bonds

initial folding by formation of hydrogen bonds into alpha helices or beta pleated sheets

further folding into the complex specific 3D structure maintained by disulfide, ionic, hydrogen bonds and van der Waal's forces

the combination of a number of polypeptide chains and sometimes a non-protein

a non-protein group associated with a protein

test for ____: Biuret test. add equal volumes of sample and sodium hydroxide, add very dilute copper sulfate, purple coloration

biological catalysts

the active site forms as the enzyme and substrate interact and conformational change in the active site weakens bonds in the substrate

prior model of enzyme action

enzymes are specific because they have different shaped ____

increasing temperature increases rate of reaction up until the optimum is passed, where the enzyme ____

changing pH alters the ____ on the enzyme's amino acids so changing it from the optimum decreases rate

increasing enzyme or substrate concentration increase rate until the other factor becomes ____

occupy the enzyme's active site in competition with the substrate

occupy the enzyme's allosteric site and deform the active site

DNA holds genetic information and RNA transfers that from DNA to the ____

pentose sugar + nitrogeneous base + phosphate group

a condensation between two nucleotides forms a ____ bond

nitrogenous bases: adenine, guanine, cytosine and then thymine/____ for DNA/RNA

DNA is a ____ helix with hydrogen bonds between complementary base pairs

____ is a short polynucleotide chain

____ replication of DNA ensures genetic continuity between generations of cells

(1) the ____ bonds between bases in the double helix are broken

(2) ____ catalyses this

(3) free DNA nucleotides pair to the strands by ____ base pairing

(4) ____ catalyses formation of phosphodiester bonds between adjacent nucleotides

this model was proved by ____ and Stahn

(1) grew bacteria in a broth containing a heavy ____ of nitrogen

(2) bacteria with DNA containing only heavy ____ replicated in a broth containing light ____

(3) DNA was extracted and ____

____ replication would predict two distinct bands

the actual result was one band somewhere in the middle indicating ____ replication

ribose + adenine + 3 phosphate groups

hydrolysis of ATP to ADP and an inorganic phosphate is catalysed by ____

the inorganic phosphate released can ____ other compounds and make them more reactive

ATP is resynthesised by ____ during photosynthesis or respiration

water is a ____ in many reactions such as hydrolysis

water is a ____ in which metabolic reactions occur

water has a high specific ____ buffering changes in temperature

water has a high ____ heat of vaporisation, providing a cooling effect through evaporation

water is ____ which supports columns of water in plants and produces surface tension on the surface of water supporting small organisms

____ ions determine pH (more hydrogen ions means lower pH)

____ ions are used in haemoglobin to bind to oxygen

____ ions are used in cotransport of glucose and amino acids

____ ions are components of DNA and ATP

all life on Earth exists as ____ which have basic features in common

all cells arise from other ____

all cells have a ____

phospholipid bilayer, controls movement of substances into and out of cells, selectively permeable, cell signalling

contains genetic information in the form of chromosomes

transcribes ribosomal RNA

site of aerobic respiration

site of photosynthesis

series of cisternae and vesicles - process, package and transport lipids and proteins, synthesises lysosomes

contains hydrolytic enzymes used to break down waste material

site of protein synthesis

network of cisternae covered in ribosomes involved in the synthesis and transport of proteins

network of cisternae that synthesises, stores and transports lipids and carbohydrates

supports the cell, prevents it from bursting, made up of polysaccharides

large and central, contains cell sap, surrounded by the tonoplast (membrane), maintains pressure within the cell

____ are specialised by having no nucleus and a large amount of haemoglobin

____ have a lobed nucleus to fit through small gaps in capillary walls and have large quantities of RER to produce lytic enzymes

____ cells have many mitochondria to give energy for swimming

____ cells have many chloroplasts to absorb light for photosynthesis

prokaryotic cells do not have ____

instead of a nucleus they have a ____ DNA molecule

their cell wall contains ____

many also have plasmids, flagella, pilli, and/or a ____ capsule

viruses are ____ and non-living. they comprise of genetic material, capside and attachment proteins

image size / actual size

minimum distance apart two objects can be and still appear as separate items

resolution of a light microscope is about ____ micrometres

light microscopes have poor resolution due to the long ____ of visible light

____ microscopes have a higher resolution because ____s have a short wavelength

in light microscopes the beam is focussed by glass ____

in electron microscopes the beam is focussed by ____

resolution of electron microscopes is about ____ nanometres

an electron microscope requires a ____ to prevent electrons being absorbed or deflected by molecules in the air

____ electron microscope: the beam passes though a thin section of the specimen

parts of the specimen ____ electrons and appear dark, others transmit them and appear bright

the image can be photographed to give a 2D ____

cannot observe ____ specimens because the system is in a vacuum

requires a complex preparation and even then the image is not in ____

the specimen must be very ____

the image may contain ____

things that result from the way the specimen is prepared

____ electron microscope: passes the beam back and forth across a portion of the specimen

the electrons are ____ according to the specimen's surface contours so we can build up a 3D image based on the scattering pattern

its resolving power is ____ than a TEM but specimens need not be so thin

we measure the size of objects on a light microscope using an ____

we calibrate this using the ____

process where cells are broken up and the different organelles they contain are separated out

(1) the tissue is placed in a ____ solution to reduce enzyme activity

the solution is ____ to prevent organelles bursting or shrinking

the solution is ____ to prevent the structure of organelles or enzymes changing

(2) cells are broken up by a ____

(3) the ____ is filtered to remove debris

(4) ____ separates the fragments by density

spin on a low speed, and the densest organelles will form the ____

spin the ____ on a slightly higher speed and the next densest organelles will be separated out

eukaryotic cells that retain the ability to divide have a ____

the part of the cell cycle where DNA replication occurs

a eukaryotic cell divides to produce 2 daughter cells, genetically identical to each other and the parent

the chromosomes condense and become visible, spindle apparatus starts to form at the centrioles, nucleolus disappears, nuclear envelope breaks down

chromosomes arrange themselves at the equator and the spindle fibres attach at the centromere, mitochondria gather around spindle fibres

centromere divides and the spindle fibres contract to pull the individual chromatids to opposite poles

chromosomes uncondense into chromatin, spindle fibres disintegrate, nuclear envelope and nucleolus reform

the cytoplasm divides

prokaryotic cells divide by ____

the circular DNA and plasmids replicate and the cytoplasm divides to produce two daughter cells with a single copy of the circular DNA and a ____ number of plasmids

phospholipids in the cell surface membrane: (1) allow ____ substances to enter/leave the cell

(2) prevent ____ soluble substances entering and leaving the cell

(3) make the membrane flexible and self ____

proteins that occur in in the surface of the bilayer, give mechanical support or act with glycolipids as cell receptors e.g. for hormoes

span the bilayer, carrier or channel proteins

restricts the movement of molecules making up the membrane

carbohydrate covalently bonded to a lipid, extend outside of the cell, act as recognition sites and help cells attach and form tissues

carbohydrate attached to extrinsic protein, help cells attach, help cells recognise one another

the cell membrane is ____ to control what enters and leaves

the cell membrane is modelled as the ____ model

____ because the individual phospholipids move relative to each other

____ because the proteins embedded vary in size and shape

net movement of molecules or ions from a region of higher concentration to a region of lower concentration directly across the bilayer

diffusion using channel or carrier protein

the net movement of water from a region of higher water potential to a region of lower water potential

the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins

(1) substance binds to receptor sites on the inside of the ____

(2) ATP ____ the protein and changes its shape

(3) the carrier opens to the opposite side of the ____ and releases the substance

(4) the ____ is released and the protein reverts to its original shape

the movement of one molecule down its concentration gradient drives the transport of a second molecule against its gradient

occurs notably in the ____

(1) ____ ions are actively transported out of epithelial cells into the blood

(2) sodium ions diffuse into the epithelial cells from the ____ down a concentration gradient

(3) they diffuse in through a ____ protein and carry glucose or amino acids with them

cells specialised for membrane transport may have: (1) folded membranes to increase ____

(2) large numbers of ____ proteins

(3) many mitochondria to produce ATP for ____

a molecule present on the surface of a cell which triggers an immune response

____ limits effectiveness of vaccines because antibodies are no longer complementary

process of phagocytosis: part of the ____ immune response

(1) chemical products of pathogens act as attractants and the ____ move towards the pathogen

(2) they engulf the pathogen to form a ____

(3) lysosomes fuse with the vesicle to form a ____

(4) hydrolytic enzymes destroy ingested bacteria by ____ their cell walls

(5) the soluble products are absorbed into the cytoplasm and the ____ are presented on the cell surface membrane

cells that display foreign antigens on their surface

T-lymphocytes are responsible for ____ immunity

the receptors on each T-cell respond to a specific ____ and a specific T-cell binds to the ____s on an APC

this activates ____ of the specific T-lymphocyte

these cloned T-cells can do one of four things: (1) develop into ____ cells that enable a rapid response to future infections by the same pathogen

(2) stimulate phagocytes to engulf pathogens by ____

(3) stimulate B-lymphocytes to divide and secrete their ____

(4) activate ____ T-cells which produce perforin and kill abnormal cells by making their membranes freely permeable

B-lymphocyte are responsible for ____ immunity

(1) the surface ____ of an invading pathogen are taken up, processed and presented by a B-cell

(2) the T-____ cells attach to the antigens and activate clonal expansion of the B-cell

(3) the B-cell clones to give ____ cells that produce and secrete the specific antibody

some B-cells will differentiate into ____ cells to respond to future infections

where a lymphocyte is chosen and activated to respond to a specific antigen

a protein produced by the immune system in response to foreign substances with specific binding sites

antibodies are made up of ____ polypeptide chains: 2 heavy and 2 light

the two binding sites that fit the antigen precisely to form an antigen-antibody complex

the part of the antibody that is not specific to an antigen

antibodies cause ____ of bacterial cells to group them together and make it easier for the phagocytes to locate them

production of antibodies and memory cells

memory cells differentiate into plasma cells to produce antibodies, faster and to an increased quantity

produced by the introduction of antibodies into individuals from an outside source

produced by stimulating the production of antibodies by the individual’s own immune system

the introduction of antigens into the body in order to stimulate an immune response

when a large proportion has been vaccinated so it's difficult for a pathogen to spread

HIV structure: capsid, RNA, enzymes including ____, lipid envelope, attachment proteins, capsid

HIV is a retrovirus because its RNA is converted to DNA by ____

process of HIV replication: (1) a protein on the HIV attaches to a CD4 ____ cell

(2) the ____ fuses with the cell surface membrane and the RNA and enzymes enter the cell

(3) the RNA is transcribed to DNA by ____

(4) the viral DNA is moved into the nucleus and inserted into the ____

(5) the viral ____ and polypeptides are produced by the cell and assembled into new virus particles

(6) the particles break away from the T-cell, taking with them a piece of the cell surface membrane to form the ____

HIV causes the symptoms of ____ by interfering with helper T-cell function

without enough T-helper cells the immune system can't stimulate B cells or ____ T cells so the immune response is weakened

viruses are not susceptible to ____ because they do not have their own cell wall/metabolic pathway for them to target

a ____ is formed by fusion of a B-plasma cell and a tumour cell from mice

these are then cloned and can produce ____

you can produce monoclonal antibodies specific to ____ cells, attach a therapeutic drug, allowing for a localised approach to killing a tumour

monoclonal antibodies ethics: (1) involves deliberately inducing ____ in mice

(2) saved lives but also deaths associated with their use in treating ____ sclerosis

(3) human ____ for safety of new drugs are dangerous

vaccines ethics: (1) ____ often used for production and testing, harming them

(2) can have ____ effects that cause long term harm

(3) hard to make fully effective without making them ____ which can be seen as unethical

ELISA test

(1) apply the sample to a surface to which all the ____ in the sample will attach

(2) ____ to remove unattached antigens

(3) add ____ specific to the antigen we are trying to detect and leave to bind

(4) ____ to remove excess antibody

(5) add a second antibody that binds to the first one with an attached ____

(6) ____ to remove any unattached antibody

(7) add the colourless ____ of the enzyme - colour change will occur if enzyme is present

(8) amount of ____ present is relative to the intensity of the colour

used in tests for HIV, tuberculosis, hepatitis, drug tests (because the ____ nature of the test is important)

as organisms become larger, their surface area decreases compared to their ____

large organisms thus need specialised ____ associated with mass transport systems to increase their SA:V ratio

features of these: (1) large ____ to increase rate of exchange

(2) very thin for a short ____

(3) movement of the ____ to maintain a diffusion gradient

(4) a transport system to ensure the movement of the ____ also to maintain a diffusion gradient

in single-celled organisms, gases are transported across the ____

insects have an internal network of ____ supported by strengthened rings

the tracheae divide into smaller dead-end ____

these extend through all the insect's body tissues, allowing atmospheric air to be brought directly to all the ____ tissues

respiratory gases move in and out of the ____ system in 3 ways:

(1) when cells respire, oxygen is used up, so its concentration falls in the tracheoles, so oxygen diffuses in (opposite direction for ____)

(2) the contraction of muscles in insects can squeeze the trachea allowing ____ movement of air in and out

(3) the ends of the tracheoles are filled with ____

during ____, lactate is produced which lowers water potential of muscle cells

therefore water moves into the cells by osmosis and the ____ of water in the ends of the tracheoles decreases so air is drawn in

gases enter and leave the trachea through ____

in fish, the gills are made up of stacks of ____

gill ____ are perpendicular to the filaments and increase surface area

water is taken in through the ____ and forced over the gills

____ flow of water and blood maintains a diffusion gradient across the whole length of the gill

leaves have many small pores called ____

there are numerous air spaces in the ____ so gases readily come in contact with ____ cells (which have a large surface area)

stomata are surrounded by a pair of ____ cells which open and close dependening on water potential

water loss is limited in insects by: (1) waterproof ____ on body surface

(2) ____ can be closed to reduce water loss (largely done when organism is at rest)

(3) small SA:V ratio to minimise ____ over which water is lost

plants limit water loss by: (1) stomata close when ____ is low to conserve water when necessary

(2) waterproof waxy ____ on parts of the leaf

plants that live in areas with low supplies of water

xerophyte adaptations: (1) thicker ____

(2) leaves roll up to trap ____ and reduce the water potential gradient between the internal and external environment

(3) the leaves have ____ to trap moist air next to the leaf surface

(4) ____ in pits or grooves trap air and reduce the water potential gradient

(5) reduced surface area of the leaves (but must be balanced with sufficient area for ____)

in humans: (1) flexible airway supported by cartilage

(2) two divisions of the trachea are the ____ which branch into the ____oles

(3) air sacs at the end of the bronchioles

inspiration: (1) ____ intercostal muscles contract

(2) ribs are pulled up and out to increase volume of the ____

(3) reduces ____ to below atmospheric and forces air into the lungs

expiration: (1) ____ intercostal muscles contract

(2) ribs move downwards and inwards, ____ volume, increasing pressure, forcing air out

gas exchange is very rapid between the alveoli and blood because: (1) red blood cells are slowed as they pass through ____ capillaries allowing more time for diffusion

(2) the distance between alveolar air and red blood cells is reduced as the red blood cells are flattened against the ____ walls

(3) capillary and alveoli walls are both very thin to reduce ____

(4) alveoli and pulmonary capillaries have a very large ____

(5) breathing movement ventilates the lungs and the action of the heart circulates blood to ensure a steep ____

large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes

carbohydrates are initially digested by ____ which denatures in the low pH of the stomach

the pancreas releases enzymes into the ____ including carbohydrases

muscles in the intestinal wall push food along the ____

membrane-bound ____ hydrolyse maltose to glucose for example

lipids are hydrolysed by pancreatic ____ into fatty acids and monoglycerides

a glycerol molecule with a single fatty acid attached

lipids being split up into smaller droplets by bile salts to increase surface area

in absorption, monoglycerides and fatty acids remain associated with bile salts to form ____

bile salts make lipids water soluble because they are ____

(1) the micelles come into contact with the ____ cells lining the villi of the ileum

(2) they break down and release the non-polar monoglycerides and fatty acids which enter the epithelial cells by ____

(3) once inside the epithelial cells, the monoglycerides and fatty acids are transported to the ____ and recombined

(4) they are packaged into ____ in the ER and Golgi by associating with cholesterol and lipoproteins

(5) these move out of the epithelial cells by ____

they enter capillaries by ____ that are found at the centre of each villus

proteins are digested by: (1) ____ which hydrolyse peptide bonds in the centre of polypeptides

(2) ____ which hydrolyse peptide bonds at the end of polypeptides

(3) ____ which hydrolyse the peptide bonds between two amino acids of a dipeptide

amino acids and monosaccharides are both absorbed from the ileum by ____

haemoglobin structure: four polypeptide chains each with an associated ____ group

the process by which haemoglobin binds with oxygen. takes place in the lungs

the process by which oxygen is released. takes place in the tissues

haemoglobin has a greater affinity for oxygen where ____ of oxygen is higher

oxygen binds ____ because the first oxygen binding changes the shape of the haemoglobin and makes it easier for the next to bind

the ____ effect: a greater carbon dioxide concentration decreases pH of the blood and changes the shape of the haemoglobin to one that more readily unloads oxygen

____ circulatory system: blood is confined to vessels

____ circulatory system: blood passes twice through the heart for each complete circuit of the body

the double system is useful because blood ____ is reduced in the lungs and it needs to be high enough to reach all the tissues

thin walled, elastic chamber, stretches as it collects blood

thicker, muscular wall, contracts strongly to pump blood

connected to left ventricle and carries oxygenated blood to all parts of the body except the lungs

connected to the right atrium and brings deoxygenated blood back from the tissues of the body (except the lungs)

connected to the right ventricle and carries deoxygenated blood to the lungs, where oxygen is replenished and carbon dioxide is removed

connected to the left atrium and brings oxygenated blood back from the lungs

____ artery ____ renal vein: carry blood to and from the kidneys

semilunar valves closed, atrioventricular valves open, blood moves into atria and ventricles

atria contact and force blood into ventricles. semilunar valves closed, atrioventricular valves open

atria relax, ventricles contract, push blood away from heart. atrioventricular valves closed, semilunar valves open

use of ____ valve: prevent backflow of blood when contraction of ventricles makes ventricular pressure exceed atrial pressure

use of ____ valve: prevent backflow of blood into the ventricles when pressure in the vessels increases when elastic walls recoil

use of ____ valve: ensure that when veins are squeezed when skeletal muscles contract, blood does not flow backwards

carry blood away from the heart and into arterioles

smaller arteries that control blood flow from arteries to capillaries

tiny vessels that link arterioles to veins

carry blood from capillaries back to the heart

arteries, arterioles and veins have the same layers. from the ____ layer:

(1) tough, fibrous layer that resists ____ changes

(2) ____ layer that can contract to control the flow of blood

(3) ____ layer that helps maintain blood pressure by stretching and recoiling

(4) ____ to reduce friction that is thin to allow diffusion

(5) the central cavity through which blood flows

____ have a thicker muscle layer than veins so they can constrict and dilate to control volume within them

they also have a thick elastic layer to keep pressure ____

____ have a thinner elastic layer and thicker muscle layer due to lower blood pressure and a need to restrict flow into capillaries respectively

____ are numerous and highly branched to increase surface area for exchange

they have a narrow diameter to permeate tissues and ensure no cell is far from a capillary (short ____)

their ____ is narrow so red blood cells are flat against the side to reduce diffusion distance

there are spaces between the endothelial cells that make them up to allow ____ blood cells to deal with infections in tissues

networks of capillaries that connect veins and arterioles

watery fluid containing glucose, amino acids, ions, bathes all the cells of the body

relatively constant environment for the cells it surrounds because it is formed from ____ whose composition is controlled by homeostasis

formed when ____ pressure at the arterial end of the capillary is great and fluid moves into the tissues

____ occurs because cells and proteins remain in the blood

tissue fluid exchanges ____ materials with the cells it bathes and then returns to the circulatory system

it can do this because hydrostatic pressure is lower at the venuous end (and ____ also occurs)

some tissue fluid is carried back via the ____ system which drains its contents into the bloodstream via two ducts that join veins close to the heart

the contents of this system are moved by hydrostatic pressure of tissue fluid and by ____ of body muscles that squeeze the lymph vessels

____ inside the vessels ensure unidirectional flow

mass transport of water in plants: ____ theory

water ____ out of the mesophyll cells and stomata

more molecules are drawn up behind due to ____

a column of water is pulled up the xylem due to transpiration: ____

this puts the xylem under ____ - there is negative pressure within the xylem

mass flow theory of ____ in the phloem:

(1) sucrose moves into ____ down a concentration gradient from photosynthesising cells

via facilitated ____

(2) sucrose is contransported with ____ ions into the sieve tube elements

(3) this reduces water potential so water moves in from the xylem by ____

(4) this creates a ____ pressure gradient from source to sink so sucrose moves in that direction

(5) sucrose moves into companion cells at the sink by facilitated diffusion and is ____ into storage and respiring cells

ringing experiment: remove a section of the outer layers around the circumference of a woody stem and the region above will ____

non-____ tissues below the ring will die but those above will grow

this suggests the ____ accumulate above the ring and disrupt flow to regions below

tracer experiment: make radioactively labeled ____ using carbon-14 and grow a plant in an environment with that

this isotope will be incorporated into sugars which can be traced as they move within the plant using ____

this means removing a thin cross section and placing it on ____ film

the blackened regions only occur where the phloem tissue is suggesting only the phloem is responsible for ____

a base sequence of DNA that codes for a particular protein at a locus

the DNA code is ____ (same for all living things)

the DNA code is ____ (some amino acids are coded for by more than one codon)

the DNA code is ____ (each base is read exactly one)

a DNA molecule plus its associated histone proteins in a eukaryotic cell

sequences of DNA that code for a polypeptide

sequences of DNA that do not code for a polypeptide

complete set of genes in a cell

full range of proteins a cell is able to produce

transcription: (1) the ____ bonds between the strands are broken

(2) free RNA nucleotides pair with the exposed bases on the ____ strand

(3) ____ joins nucleotides to form a pre mRNA molecule

(4) the DNA strands rejoin behind the enzyme which detaches when it reaches a ____ sequence

(5) in eukaryotic cells the introns are removed by ____ (prokaryotic cells do not have introns)

(6) the mRNA leaves the nucleus through a ____

translation: (1) a ribosome attaches to the ____ codon on the mRNA

(2) the tRNA molecule with the complementary ____ moves to the ribosome and pairs to the complementary mRNA codon

(3) the ____ moves along the mRNA, bringing together two tRNA molecules at any one time

(4) the amino acids are joined by a ____ bond using ATP and when this happens the tRNA is released

(5) this continues until the ribosome reaches a ____ codon at which point the polypeptide is released

spontaneous changes to the base sequence of DNA

____ agents increase rate of gene mutation

mutations in the number of chromosomes arise spontaneously by chromosome ____ in meiosis

meiosis: two nuclear divisions result in the formation of four ____ daughter cells from one diploid parent cell

genetically different daughter cells arise due to ____ of homologous chromosomes when they line up at random during metaphase 1

where homologous chromosomes exchange genes at their loci

number of different alleles in a population

natural selection (1) mutation gives rise to a new ____

(2) the allele may benefit its possessor and increase chance of survival and ____

(3) the advantageous allele is more likely to be inherited and increases in ____ over many generations

the population moves towards an extreme

the population moves towards the median

____ results in species better adapted to their environment in a way that is anatomical, physiological or behavioural

organisms that can breed to produce living fertile offspring

____ behaviour allows individuals to identify a species-specific partner to mate with

a ____ classification system arranges species into groups based on their evolutionary relationships

Linnaeus taxa

the number of different species in a community

the relationship between the number of species in a community and the number of individuals of each species

farming techniques reduce ____ because it reduces variation in habitat and food sources

you need to balance ____ with farming

e.g. maintain and plant hedgerows at field boundaries, reduce pesticide use, crop rotation that includes a nitrogen fixing crop to increase soil fertility, ____ to control weeds and pests, maintain existing ponds instead of draining for farmland

you can find information about genetic diversity by comparing: (1) ____ of measurable or observable characteristics

(2) ____ sequence of DNA or mRNA

(3) ____ sequence of the proteins encoded by DNA and mRNA

gene ____ has changed methods of investigating genetic diversity by favouring direct investigation of DNA sequences over investigating observable and measurable characteristics