Genetic engineering using bacteria
Genetic engineering invovles transferring genes from one type of organism to another.
Usefull protein such as human insulin can be inserted into bacterial cells.
They grow in a solution(culture) in huge containers called ferments --> they produce large amounths very quickly.
genes are transferred from each cell using bacterial enzymes.
- large yield
- human insulin so now allergic reactions or intolerances
- not animal products used, so vegetarians or religious groups can use it.
There is a concern that it has unknow and unforeeen effects on other organisms, including humans.
Feeding the world
Developments in GM Crops; Worries of GM Crops
- Grow in places with low rainfall - Not natural
- Produce there own pesticides - May affect our healt
- resist diseases - Harm Wildlife
- resist effects of herbicides - Cross Contamination
- produce own fertiliser
Golden Rice - GM to produce beta-carotene - this converts to vitamin A in our cells.
- Human cells convert beta-carotene efficiently, - improving the diet of poor people.
- Golden rice is not meant to be the only solution to the vitamin A problem
- Golden rice has never undergone trails to check it is safe for people to eat. - fixing this problem with a single GM solution is too limited
when parent cells divide, new cells called daughter cells are formed.
the nuclues of the parent cells can divide in one of two ways - mitosis or meiosis.
Mitosis results in two daughter cells with identical chromonsomes to the parent cells. If the parents have two sets of chromosomes (diploid) then the daugther cells will also be diploid. Asexual reproduction only happens this way, the offspring created are genetically identical to each other and the parent, they are clones.
- Mitosis is used in order for organisms to:
- Repair damage; damaged or old skin cells are replaced by mitosos with identical new skin cells
- Grow: the mass of a plant root incease beacause the existing root cells produce more by mitosis.
Meisois - process that is used to form gametes.(egg and sperm)
the four daughter cells each have half the number of chromosomes of the parent cell, resulting in genetically different haploid gametes.
when a parent cell is about to divie, its chromosomes replicate themselves
this results in chromosome with two identical strands called chromaids
during meiosos each chromosome pairs up with its corresponding partner along the centre of the cell.
the pair of chromonsome copies exchange pieces of dna with one another before the cell divides into two.
another division takes place -> the chromatids are spilt in half. each daughter cell gets a different chromosm. this means the gametes that are haploid and are genetically different from one another
during ferilistation, a haploid male gamete(sperm) fuses with a haploid female gamete(egg) the chromosomes of each cell combine
the result is a diploid zygote (fertilised egg), this has inherited a new combination of chromosomes - and therefore genes are 50;50 from each parent gamete.
in flowering plants, plants of the root, leaf or stem can grow ino new plants, this type of asexual reproduction is sometimes called vegetative reproducion.
It produces news plants which are clones to the parent plants, this is useful to gardeners and farmers who want stocks of plants with preferred characteristics such as disease resistance, fruit colour, flower shape etc.
a simple type of vegetative reproduction is to take cuttings.
1. take a healthy plant and cut off a small length of stem(the stem should have leaves on in it)
2. dip the end of the cut stem into hormone rooting powder.
3. put the steam into a flowerpot full of damp compost.
4. cover the pot with a plastic bag to keep it moist.
5. this will grow into a new plant.
Tissue culture is a process that involves cutting small pieces of tissue from the parent that is to be cloned.
the piecesz are grown in a sterile liquid or gel, which provides all the substances needed for their development.
Embryo transplants begin in the laboratory and end in normal births;
- donor eggs are taken from female animals and fertilised in the lab.
- each embryo that forms is spilt up into its separate cells
- some of the seperated cells are transplanted into the womb of a host mother, where they develop into identical embryos
- the host mother later gives birth to several genetically identical youngesters, they are clones.
- cloning allows scientists to produce animals with desirbale characteristics quickly and reliably.
- helps build up rare animals which might otherwise be threatened with extinction.
- host mothers can carry transplanted embryos of different species even after the original parents have died. Fertilised eggs can be kept frozen for many years
Disadvantges; - cloned animals have medical issues - short and painful lives.
1. nucleus removed from sheep one, (enucleated)
2. diploid nucleus removed from cell body from sheep two.
3. the diploid nucleus inserted into enucleated egg shell.
4. diploid cell divides by mitosis and forms an embryo, an electrical stimulaion of the diploid nucleus to divide by mitosos.
5. embyro implanted into surrogate sheep
6. the new lamb created is a clone of sheep two.
Dolly the sheep was the first cloned mammal she suffered medical issues that eventually caused her to be put down.
Such points raise issues about the safety and ethics of cloning.
after fertilisation, cell division takes place and a hollow ball of cells called an embyro is formed.
the cells on the inside of the embyro are called embryonic stem cells.
they are unspecialised, as the embyro develops the cells begin to differentiate and change into different types of cells.
As the cells mature they can no longer differentiate but some of our stems cells remain into adulthood,
if stem cells can be made to multiply and differentiate we would have unlimited supply of different types of cells, which could be transplanted into people whose tissues are damaged, this is called stem cell therapy.
once stem cells mature they lose their ability to differentiate and their role stays with them for life.
Stem cell therapy
as embryonic stem cells can differentiate into many more types of cell than adult stem cells, they are ideal for therapies that repair damaged tissues, treating parkinson's disease and diabetes are examples.
risks of stem cell therapy include;
- rejection of the embryonic stem cells
- possibiliy that adult stem cells may carry geneic mutations for disease of may become defective
- side effects or complications in the recipient; stem cell therapy may trigger adverse immune responses or the development of cancers.
scientists are researching new ways of producing stem cells that offer the benefits of embryonic stem cells but do not destory embryos.
The Human Genome
genome refers to all of the DNA in each cell of an organism
the human genome project (HJP) began in 1989, a group of scientists from all over the world contributed to work out the human genome, the result was announced in april 2003
Scientists broke up chromosomes of cells to get their DNA, thousands of copies of the pieces of DNA into machines called sequencers which display the most likely order of the bases.
powerful computers were used to help math the base sequences of genes with the proteins for which they are the code
understanding the human genome enables scientists to look at how genes control our vulnerability to particular diseases and to personalies drug treatments to work with an individual genome.
the human genome revealed that some races are more or less vulnerable to certain diseases than others, some people are concerned that if genetic data identifying ethnicity were available it might encourage discrimination against certain groups of people.
Cells make, or syythesise proteins by joining together amino acid units in the correct order.
Proteins have a complicated shape that helps them carry out their jobs, Protein molecules that are the wrong shape cannot perform their functions correctly
DNA makes sure that the correct numbers of amino acid units join together in the right order
The more amino acids units joined together, the larger the molecule; peptides are chains of 2-20 amino acids; polypeptides contain 21-50; proteins contain more than 50 amino acids.
Ribonucleic acid (RNA) is a chemical like DNA, however RNA is a single strand and has U base instead of T.
RNA has two roles in protein synthesis;
- messenger RNA (mRNA) carrues the protein-making information from the DNA inside the nucleus of the cell to the Ribosomes in the cytoplasm, where the protein is made.
Transfer RNA (tRNA) carries the amino acids needed to from the protein to the ribosomes.
There are two stages in protein syntheisis; transcription and translation.
- 1) the strands of DNA separate
- 2) strands of mRNA form as the bases of RNA nucleotides combine with their complementary bases of the single stranged DNA
- 3) the strands of mRNA separate from their respective complementary strands of DNA, they pass from the nucleus through gaps.
- 4) each strand of mRNA binds to the ribosome, forming an mRNA-ribosome complex
- 5) each type of tRNA molecule binds to its particular type of amino acid dissolved into the cytoplasm depending on the triplet of bases(codon) it carries.
- 6)tRNA/amino acid cominations pass to the mRNA -ribosome complex, the exposed bases of each tRNA binds to their complementary baes on the mRNA. (chemical bonds)
- 7) once the bonds form, each tRNA separates from its amino acid and the mRNA strand
- 8) the linked amino acids form a polypeptide.
Variation and mutation
If a sperm or an egg carries a mutated gene, the mutation will be inherited by off spring after fertilisation has taken place.
they can by harmful - altering the proteins producedd can ruin the activity of the cells. therefore affected ogranisms are less likely to survive.
some genes that are now 'normal' were once mutants, the mutations added gentic variation that happened to be good and bring benefits.
this meant some organisms carrying the mutated genes survived, their descendants inherited the genes and now they are normal versions.
some mutations are neutral - the do not affect an organism's chances of survival one way or another.
How mutations change DNA
mutations occur because of copying errors in the sequence of bases during DNA replication
a base may be deleteed or inserted. this changes the sequence of bases along the gene from where the mutation occurs.
the order of amino acid units from where the mutation occurs changes in each mutate#d gene, thhis affects the structure of the protein.
the structure and therefore the shape of a protein affects its function. changes in structure can therefore affect how well the protein works or may even prevent it from working at all.
a codon is a section of DNA or RNA that codes for an amino acid, almost all amino accis are specified by more than on codon,
if a mutation changes a codon to an alternative that still specifies the same amino acid, and the sequence of codons is unchanged, then the amino aid sequence and the structure of the protein remains unchanged.
this is known as silent mutation.
Rates of reaction
Enzymes are biological catalysts, they increase the rate of chemicals reactions inside and outside the cells.
Enzymes are specific in their action - each enzyme only cataylses a particular chemical reaction or type of chemical reaction.
during digestion, enzymes break down large insoluble food molecules into smaller, soluble ones that can dissolve into blood.
How enzymes work
The substrate binds to a part of the enzyme called the active site.
they fit together like a lock and key, an enzyme will only catalyse a particular reaction when the shape of itts active site matches the shape of the substrate molecule.
the enzymes catalyses the breakdown of the substrate into the products, which then leave the enzyme. the enzyme is then free to join to another substrate molecule.
two examplesb of enzymes at work in the body include;
- DNA polymerase which breaks up the double helix before DNA replication. it is also invovled in checking the copying of the DNA strand
- speeding up the rate of joining together the individual amino acids during protein synthesis.
Factors affecting enzymes
most enzymes are proteins, they are sensitive to changes in temperature and pH
the activity of enzymes increaseds as the temperature goes up, when the activity of the enzyme is at a max, we say this is the optimum temperature. this is around 37'c for enzymes in the human body, after this point as the temp increases the activity will decrease.
different enzymes have different optimum pHs, eg. the enzyme amylase has an optimum pH of around 8.
enzyme activity is also affected by substrate concentration.
1- when there is more than enough enzymes the rate of reaction is proportional to the concentration of substrate.
2- when all the enzymes active sites are filled with substrate molecules the rate of reaction levels off.
3. adding more enzyme increase the rate of reaction because more active sites are available to substrate molecules which fill them.
At extremes of temperature of pH an emzye will become denatured
denaturing is a permanent change in shape of protein molecule. it is caused by the breaking up of the hydrogen bonds that hold the structure together.
a change in a proteins shape will affect is activity because the active site will change, so the substrate will no longer fit
glucose + oxygen -> carbon dioxide + water + energy
energy released is used to keep us warm and drive life processes.
glucose -> lactic acid + energy
energy released is much less than the aerobic respiration as the glucose is not fully broken down.
after exercise rapid breathing drawms more air into the lungs and the fast beating heart sends the oxygen to muscle cells, where it helps break down the lactic acid into carbon dioxide and water.
this is called excess post-exercise oxygen consumption (epoc)
the time taken for the lactic acid to be removed and breathing and heart rates to return to normal is the recovery period.
molecules in liquids and gases are in constant random motion, some molecules will spread from areas where they are highly concentrated to areas of lower concentration. As a result there is a net movement of molecules in this direction. This is called diffusion.
the greater than difference between the regions of high and low concentration, the faster the substances rate of diffusion.
substances move into and out of cells of living things by diffusion.
capillary vessels supply body tissue with blood via the circulatory system.
substances such as glucosee, oxygen and hormones pass between the blood and tissues via diffusion.
gaseous exchange is the process by which oxygen enters the blood and carbon dioxide leaves, it takes place across the walls of the alveoli (air sacs) in the lungs.
high concentration --> low concentration
the concentration gradient is the difference in concentration of a substance between high and low concentration regions.
the greater the difference between the regions, the greater the concentration gradient. as a result the rate of diffsuin is maximised.
the diffusion of glucose and oxygen to respiring cells relies on a high concentration gradient between the cells and the blood capillaries.
the is maintained because the cells are constantly respiring, breaking down the glucose and oxygen and lowering their concentration inside the cells.
exercise and rates
exercise increases the heart rate and breathing rate.
during exercise aerobic respiration in the muscle cells releases energy, enabling muscles to contract quickly and strongly
respiration produces carbon dioxide, which passes from the muscles cells to the blood, raising its acidity and lowering its pH below 7.0
the lowered pH stimulates an increase in the heart rate and breathing rate.
heart and breathing rates remain high from some minutes after exercisin, as a result, more blood - with its load of carbon dioxide - passes to the lungs where it is exhaled.
the concentration of carbon dioxide in the blood decreases, restoring the pH of the blood to its normals value of 7.4, heart rate and breathing rate return to normal.
Investigating the effects of exercise
breathing rate can be investigated by using limewater to test for carbon dioxide.
an easy way to measure your carbon dioxide output is to place a straw in limewater and note the time taken for the limewater to turn cloudy as tou breathe out through the straw.
counting to number of times your back rises and falls in a minute gives the breathing rate.
taking your pulse is an easy way of measuring heart rate (the number of pulses per minute)
breathing and heart rate
The more air we breathe in, the more oxygen reaches the muscles and the more energy is released through aerobic respiration.
the muscles contract more vigorously enabling us to exercise more.
the increased rate of aerobic respiration in the muscle cells produces more carbon dioxide. the increased breathing rate rapidly removes the carbon dioxide from the lungs.
the larger the volume of air moving in and out of our lungs with each breath, the higher the volume of oxygen that can reach the muslces.
this is calculated by; breating rate x volume of air per breath = volume of exchanged per minute
one complete contraction and relaxation of the heart produces one heartbeart.
the volume of blood pumped from the heart each minute(cardiac output) depends on the heart rate and volume of blood out with each beat ( the stroke volume)
cardiac output = stroke volume x heart rate
Light and photosynthesis
Plants use sunlgith, carbon dioxide and water to produce glucose throughout the process of photosynthesis.
carbon dioxide + water ---light engery----> glucose + oxygen
plants are green because of the green pigment chlorophyll inside the chloroplasts in their cells.
chlorophyll absorbs the light engery required to drive photosynthesis.
leaves and photosynthesis
leaves are thin and flat, exposing a large surface area, this maxmimises the absorption of light.
the palisade cells, just under the upper surface of the leaf where the light is brightest, are packed with chloroplasts containing chlorophyll for a maximum rate of photosynthesis.
air spaces enable gases inclduing water vapour to circulate within the leafe, so the reactants for photosyntheisis can reach the cells that need them.
oxygen, carbon dioxide and water capour diffuse between the leaf's air spaces and the atmosphere through the gaps called stomata that perforate the underside of the leaf.
The rate of photosynthesis
the rate at which plants make glucose is affected by conditions of;
- light intensity
- carbon dioxide
if levels of any of these factors drop too low, photosynthesis slows even if the others are in abundant sypply. this is called a limiting factor.
most plants grow best in warm, light conditions and when there is a high concentration of carbon dioxed and plenty of water, growing plants in greenhouses can help maximise these conditions.
the higher the temperature, the faster the rate of photosynthesis and the faster the production of materials that enable plants to grow.
if the temperature continues to increase beyond an optimum, photosynthesis slows because the enzymes controlling the different reactions of photosythesis are denatured.
plants grow more vigorously in bright sunlight because high light intensity maximises the rate 0f photosyntheisis. the rate of increase is up to a maximun value. even though light intensity increases further, the rate of photosynthesis does not.
xylem tissue consists of columns of hollow, dead cells, it carries water and dissolved mineral salts from the roots, through the stem and out into every leaf and flower.
phloem tissue runs by the side of the xylem, its tube-like cells carry dissolved glucose and other substances to all parts of the plant.
water evaporates from stomata in a process called transpiration.
as water is lost from the leave, ore is drawn up through the xylem tissye from the roots, which absorb more water from the soil, this continous movemnt of water is called the transpiration stream.
Osmosis is the movement of water from a high water concentration to a lower one across a partially permeable memebrane(one that will only let water molecules across)
you can investigate osmosis by studing cells under a microscope, cells left in a concentrated salt or sugar solution will lose water by osmosis, they will become flaccid(limp)
visking tuving is a partially permeable membrane that cna be used to investigate the movemnet of substances into and out of the cells.
A solution that is highly concentrated, e.g has a high sugar concentration will have a low water concentration.
Root hairs cells are fine, hair like extensions of a root.
water flows into root hair cells by osmosis. their large surface area is an adaptionation that enables plants to maximise their absorption of water from the soil.
root hairs also take up mineral salts in solution, the solotions are much more concentrated in the cells of root tissue than in the soil. therefore mineral salts cannot pass into the roots by diffusion. Active transport is used, which requires energy from aerobic respiration.
organisms and their environment.
fieldwork investigations are designed to find out more about where organisms live, and why they live where they do.
techinques used include;
- pooters, nets and traps to collect animals in order to estimate their distribution.
- quadrats to count the number of animals or plants in a known area.
- probes to measure temperature, pH and light intenisty.
ecosystems and their populations are usaully too large for us to study everything about the, instead we study small parts called samples.
errors in sampling techniques can be reduced by taking a number of random samples and standardising the samples taken e.g the same time of day or in the same season/weather conditions.
The fossil record
Fossils are the remains or impressions made by dead organiss, they are usally found in sedimentary rock. they are preserved over millions of years as rock particles from ancient seas fell on dead organisms on the seabed.
each layer of fossils records life on earth at the time the layer formed, this helps us trace the hisotry and evolution of life. fossils provide evidence for darwins theory of natural selection.
some fossils have gaps in the ancestors and descendants this is because;
- most organisms decompose quickly when they die; so only a small number of fossils from.
- many fossils have not be found yet
- even it a fossile survies, it may not surive geological cycles.
most vertebrates today have pentadactyl limb, - a forelimb with five fingers or toes.
the discovery of pentadactyl limbs in fossibles has led scientists to believe that all vertebrates directily descend from a common ancestor. the use this as evidence as evolution.
growth is measured as an increase in an organisms size, length and mass, the increase is the result of ;
- cell division; the number of cells increases
- cell elongation; the length of cells increase
- synthesis of organic materials, (carbs, proteins, fats and oils); the mass of cells increase.
plants grow throughtout their life from cell divison in tissues called meristems.
behind the meristems is where cells elongate and increase in size by water and other organic materials flowing into them.
these cells are undifferenetiated, as growth continues differentiation of cells being producing the types of cell that make up the tissue and orgaints of the plant.
cell division in animals occurs in all tissues of the body. in young animals cell division produces more cells than die through age or damage, Animals continue to grow untill the gain of cells balances the loss of cells. growth than stops making the start of becoming an adult.
Cells join together
Cells are the building blocks from which humans and all other living things are made.
tissues are a group of similar cells with a particular function.
an organ is a group of different tissues that work together, an organ has a particular function.
an organ system is a group of different organs that work together, organ systems also have specifif functions.
cells; cardiac cells --> tissues; cardiac muscle --> organ; the heart.
all the diffrerent types of human cells are the result of cell division(miitosis) and differentiation during the development of the egg to the embryo to the foetus.
each type of human cell is specialised to enable it to carry out a particular function, for example; neurones(nerve cells) transmirt nerve impulses and muslces cells contract (shorten)
genetically the cells may be the same, but the pattern of genes switching on and off (gene activity) is different.
this process occurs in the development of all living things.
Blood contains the following components;
- red blood cells- have a red pgiment called haemoglobin - dont have a nucleus.
- white blood cells have a nucles - contain cytoplasm -> allows them to access tissues so they can protect the body by attacking and destroying bacteria and virusues.
- platelets - fragments of cells with no nuclus - contain proteins
- Plasma- straw coloured liquid that transports - CO2, soluble food products, and urea. Plasma circulates the heart relased by the chemical reaction in body cells and this helps maintain body temp.
the function of red blood cells is to transport oxygen from the lungs to repsiring tissues.
lungs --> high oxygen concentration --> haemoglobin becomes oxyhaemoglobin. (this breaks down to release oxygen where the concentration is low.
when platelets are damaged by a cut or torn tissue- they relasease a substances that start a chain reaction of chemicals in the blood, - end with plasma protein called fibrinogen changing into insoulube fibrin-this forms a mesh of fibres to cover the wound - traps RBC's, forms a clot.
the heart pumps blood.
the heart lies inside the chest cavity, protected by the rib cage. much of the wall of the heart is made of cardic musle, this muscle contracts and realxes to pump blood through the circulatory system.
the heart has four chambers; two atria and two ventricles.
the wall of the left ventricle is thicker than that of the right ventricle becuase it has to pump blood to all the parts of the body. the reight ventricle only pumbs blood to the lungs, so less effort is required.
the heart also has four major blood vessels; pulmonary artery(to the lungs), pulmonary vein(from the lungs), vena cava(from the body) and aorta(to the body).
the heart is a douvle pump, each side pumps blood along a different route.
artiers carry oxygenated blood away from the heart, veins carry deoxygenated blood to the heart.
the left artium and ventricle pump oxygenated blood from the lungs around the rest of the body.
the right artium and ventricle pump deoxygenated blood to the lungs, where it can be oxygenated.
when the muscular walls of the heart relax, blood fills the chambers, when the mucles contract, blood is forced from the chambers.
the valves control the flow of blood throuhg the heart and into the arteries leading from the heart, preventing backflow.
The Circulatory System
- the circulatory system is a network of tube-like vessels called arteris and veins.
- the heart pumps blood through arteries to body tissues.
- blood drains from the tissue through the veins back to the heart.
- smaller vessels branch from the arteries and veins, the smallest are called capillaries, they link arteries and veins.
- blood in veins flow more slowly than blood in arteries because it is at lower pressure, the large diameter of a vein enables the blood to flow easily.
- blood flow through the veins is helped by the contractions of the muscles in the arms and legs which the veins pass.
- the heart pumps blood into arteris at high pressure, as the bloods needs to reach the extremities of the body.
- elastic fibres in the artery wall help maintain the flow of blood away from the heart and prevent backflow, so no valves are needed.
- capillares form dense networks called capillary beds, in the tissues of the body.
- they provide a large surface area for the efficent exchnage of materials between the blood and tissue
- the higher pressues forces plasma through the thin capillary walls, the liquid called tissue fluid carries nutrients and oxygen to the surronding cells
Make up of the digestive system
the digestive system is made up of a alimentary canal, liver and pancreas.
- mouth - food is taken in and chewed into smaller piecs and mixed with saliva, begins breakdown of food.
- oesophagus; musclaer tube pushes food into the stomach.
- stomach; muscles here contract and relax to mix food with digestive juices.
- pancreas; produce pancreatic juice containing digestive enzumes that pass to the small intestine.
- small intestine; where digestion and absorption takes place.
- liver; proccess the nutrients from the small intestine and produces bile, which helps digest fat.
- large intestine; absorbs water from the remaining indigestible food matter.
- ****; undigested food is removed as faeces.
peristalsis - contraction and relaxation of the muscle layers in the wall of the alimentary canal --> moves food through the digestive system.
the gall bladder is a small sac like structure connected to the small intestine by the bile duct, it stores the greenish alkaline liquied called bile produced by the liver.
Digestion and absorption
Enzymes break down large, insoluble molecules of carbs, fats and protein into smaller molecules which the body can absorb; eg;
carbohydrases digest carboydrates -> amylase -> mouth and small intestine -> starch -> glucose
proteases digest proteins -> pepsin -> stomach -> proteins -> amino acids
lipases digest fats and oils -> lipase -> small intestine -> fats and oils -> fatty acids and glycerol
Bile and Villi
bile breaks down fats into small droplets (emulsification) which increases the surface area, speeding up the action of lipase
bile also neutralies the stomach acid present in the food, which enters the small intestine to allow enzymes to work at their optimum pH of around 8.
Tiny projections called villi line the small intestine, they increase its surface area, allowing more efficient absorption of the soluble products of digestion
Functional foods are foods that have health-promoting benefits over and about their basic nutritional value;
- probiotic - contain bacteria such as bifidobacteria and lacit acid bacteria (lactobacillus) that are believed to maintain a healthy digestive system,
- Prebiotic -contain added sugars called oligosaccharies, these cannot be digested, but act as a food supply to the good bacteria in the alimentary canal.
- Plant stanol esters - they have been clinically proven to reduce the absorption of harmful cholesterol. (by 10%)
the bacteria we carry in our digestive system can be divided into;
- bad bacteria - lead to diseases of the alimentary canal
- good bacteria - suppres the activites of the bad bacteria
probiotic and prebiotic --> aim to boost the number of good bacteria
Evaluating functional foods
there are concerns about the effectiveness of functional foods. the use of lactobacillus and bifidobacterium bacteria in some diary products is in an example, there are concerns involving;
- how well the bacteria survive the manufacture and storage of probiotics before sale
- their passage through the digestive system
- competition with the trillions of other microorganisms already in the gut.
the health claims made for most functional foods remains in doubt, much more research is still needed.