B3

animal cell structure- nucleus: contains DNA in the form of chromosomes. cytoplasm: most of cells chemical reactions happen. cell membrane: holds the cell together and controls what goes in/out. ribosome: where proteins are synthesised. mitochondria: most reactions ivolved in respiration take place. provides energy for cell processes. cells that need lots of energy contain many e.g. liver cells (carry out lots of energy) and muscle cells (need energy to contract).

plant cell structures- nucleus, cytoplasm, cell wall: made of cellulose, supports cell. vacuole: large structure that contains cell sap, weak solution of sugar and salts. cell membrane, chloroplasts: photosythesis happens.

bacterial cells- cell membrane, cytoplasm, cell wall, single circular strand of DNA.

chromosomes- long molecules of coiled up DNA, DNA divided up in short sections (genes). DNA is a double helix. each 2 strands is made up of lots of small groups called "nucleotides" each contains small molecule called a "base" DNA has 4 different ones: A, C, G and T. each forms cross links to base on other strand, keeps DNA strands tightly wound. pairs: A/T, C/G (complementary base-pairing).

watson and crick- first to build a model of DNA (1953). used data from other scientists to help understand structure of molecule. included: x-ray data showing DNA is a double helix formed from 2 chains wound. data showing bases occurred in pairs. putting this together they built a model showing what it looks like.

DNA can replicate itself- copies itself when a cell divides, so new cell has full amount of DNA. to copy itself, DNA double helix 'unzips'-form 2 single strands. new nucleotides join on using complementary base-pairing, makes an exact copy of DNA on other strand. result in 2 double-stranded molecules of DNA that are identical to original.

proteins made by reading code in DNA- DNA controls production of proteins in a cell. section of DNA that codes for a particular protein (gene). proteins made up of chains of molecules called amino acids. gives each protein a different shape, so each protein has a different function. order of the bases in gene that decides order of amino acids in protein. each is coded for by a sequence of 3 bases in gene. they are joined together to make proteins, following the order of bases in gene. each gene contains a different sequence of bases- allows it to code for unique protein.

mRNA carries code to ribosomes- proteins made in cell cytoplasm by ribosomes. to make proteins, they use the code in DNA, found in cell nucleus, cant move out of it; it's too big. so cell needs to get code from DNA to ribosome, done through mRNA- made by copying code from DNA, acts as a messenger between DNA and ribosome- carries code between them.

DNA controls a cell by controlling protein production- proteins produced in cell affect how it functions. some determine cell structure, others control cell reactions. different types of cell have different functions; make different proteins. some genes are "switched off" proteins they code for aren't produced. genes that are switched on determine function of cell. genes that code for proteins specific to bone, nerve or skin cells, switched off. allows muscle cell to function.

proteins- the four: enzymes, carrier molecules: used to transport smaller molecules (e.g. haemoglobin). hormones: carries messages around body (e.g. insulin). structural proteins: physically strong (e.g. collagen- strengthens connective tissue).

enzymes control cell reactions- cells have chemical reactions: respiration, photosynthesis, protein synthesis. need to be controlled- to get right amount of substances/keep organisms working properly. make a reaction happen quicker by raising temperature, speed up useful reactions, there's a limit to how high the temperature can go inside a living creature before cells are damaged. living things produce enzymes, act as biological catalysts. enzymes reduce need for high temperatures and we only have enzymes to speed up useful chemical reactions in body. every biological reaction has it's own enzyme designed for it. each coded for by different gene, has unique shape, which it needs to do it's job.

enzymes are specific- every one has an active site- part where it joins on to it's substrateto catalyse reaction. enzymes are picky-only work with one substrate, have high specificity for their substrate. for them to work, substrate has to fit into active site, if shape doesn't match the active site's shape, reaction won't be catalysed, called 'lock and key' mechanism; substrate fits into enzyme like a key fits in lock.

enzymes like it warm- changing temperature chnges rate of enzyme-catalysed reaction, higher tempertaure increases rate; more heat means the enzymes/substrate particles have more energy. makes enzymes/substrate particles move about more, they're more likely to meet up and react- higher collision rate. low temperatures- lower collision rate, slower reaction. if gets too hot, some bonds holding enzymes together will break. makes the enzyme lose it's shape- active site doesn't fit shape of substrate any more. means can't catalyse reaction and reaction stops-enzyme can't function. enzyme now denatured. shape is irreversible. each enzyme has it's own optimum temperature when reaction goes fastest. just before it gets too hot and starts to denature. optimum temperature for important enzymes in humans is about 37 degrees.

enzymes like right pH- if too high or low, interferes with bonds holding enzymes together. changes shape of the active site and denatures enzyme. all have an optimum pH that work best at. often neautral pH 7, not always.

Q10 values show how rate of reaction changes with temp- Q10=rate at higher temp/rate at lower temp.

gene mutations- if mutation occurs within a gene, could stop production of the protein the gene normally codes for/might mean a different protein is produced instead.

most mutations are harmful- if occurs in reproductive cells, then offspring might develop abnormally or die at early stage of development. if occurs in body cells, mutant cells sometimes start to multiply in an uncontrolled way and invade other parts of body (cancer).

some mutations are beneficial, some no effect- different protein may be produced after mutation that beenfits organism- new protein improvement, gives organism survival advantage over rest of population. passes on mutated DNA to offspring, soon mutation becomes common in population. mutation in bacterium that makes it resistant to antibiotics, so mutant gene lives on, creating resistant "strain" of bacteria. some mutations aren't harmful/helpful- don't change protein coded for, no effect on organism.

radiation and certain chemicals cause mutations- can happen spontaneously- when chromosome doesn't quite copy itself properly. chance on mutation increased if exposed to: ionising radiation, including x-rays/ultraviolet light. greater dose of radiation, greater chance of mutation. certain chemicals, chemicals called mutagens. cigarette smoke contains carcinogens (cancer)

multicellular- advantages: you can be bigger- so you can travel further, get your nutrients in a variety of ways, and fewer things can eat you/squash you. allows cell differentiation. instead of being just one cell that has to do everything, you can have different cells that do different jobs. cells adapted for particular jobs. can be more complex-have specialised organs, different shapes and behaviour, adapted to their particular enviroment. however it means an orgnism has to have specialised organ systems: system to communicate between different cells, system to supply cells with nutrients they need, a system that controls the exchange of substances with the enviroment.

mitosis- before it starts, DNA in cell is replicated, then at beginning, DNA coils into double-armed chromosomes. these arms are exact copies of each other- contain same DNA. chromomsomes line up at centre of cell and divides as cell fibres pull them apart. two arms of each chromosome go to opposite poles of one cell. membranes form around each of these. cytoplasm divides, you get 2 new cells containing the same genetic material. ended up with 2 new cells that are genetically identical to each other. before you divide these again DNA has to replicate itself to give each chromosome 2 arms again.

meiosis is another type of cell division, creates gametes (formed in ovaries and testes)- are sex cells- egg and sperm. body cells of mammals are diploid. but gametes are haploid- only have one copy of each chromosome, when the egg and sperm combine, they'll form a cell with diploid number of chromosomes.

meiosis involves two divisions- DNA replicates and curls up to form double-armed chromosomes. the chromosomes arrange themselves into pairs. humans have 23 pairs, that's 46 altogether. both chromosomes in a pair contain information about same faetures. one chromosome from mum and one from dad. in first division pairs split up- chromosomes in each pair move to opposite poles of the cell. in each of the two new cells, there are no pairs- one of each of the 23 different types. each new cell ends up with a mixture of mums and dads chromosomes, but only half the usual number. second division each chromosomesplits in half and one arm up in each new cell. you end up with 4 new cells- 2 after cell division and then each of those split again, cells are genetically different.

fertilisation creates genetic variation- male and female gametes combine to form diploid cell (called zygote). characteristics are controlled by combination of genes on it's chromosomes. since zygote inherited chromosomes from parents, will show features of both, won't be exactly like either of them.

sperm cells adapted to their function- function is to transport males DNA to females egg. are small and have long tails, have lots of mitochondria to provide energy needed to swim distance, also have acrosome at front of 'head' release enzymes needed to digest their way through membrane of egg cell.

animals stop growing, plants grow continuously- in animals growth happens by cell division. in plants, growth in height, due to cell enlargment (elongation) growth by cell division happens in areas of plant (meristems- at tips of roots/shoots).

stem cells can turn into different types of cells- in animal cells, the ability to differentiate is lost, but not in plants. most cells in body are specialised for a particular job. some cells are undifferentiated, can develop into different types of cells, tissues and organs, these are called stem cells. found in early human embryos, potential to turn into any kind of cell. adults have stem cells, found in certain places like bone marrow, not as versatile, can't turn into any cell type.

stem cells may cure many disorders- medicene already uses it to cure disease e.g. people with blood disorders can be cured by bone marrow transplants. contains adult stem cells, turn into new blood cells. early human embryos contain alot, can be extracted and growth, may eventually be able to grow tissues, treat medical conditions.

against stem cell research- each one is a potential life. others think curing patients who are suffering is more important. embryos used in research are unwanted from fertility clinics, which would be destroyed. there are now 'stocks' of stem cells that scientists can use. some countries won't fund research to make new stem cell stocks.

measuring growth- length: measure length of a plant/animal, adv-easy to measure. dis- doesn't tell you about changes in width, diameter, number of branches ext. wet mass: weigh plant/animal, adv- easy to measure, dis- changeable, plant heavier if rained, animal heavier if just eaten or full bladder. dry mass: dry out organism before weighing, adv: not affected by amount of water in plant/animal or how much it's eaten, dis: kill the organism to work out.

human growth phases- five main phases of growth: infancy- first 2 years of life, rapid growth. childhood- between infancy and puberty, steady growth. adolescence- begins with puberty and continues until body development and growth complete, rapid growth. maturity/adulthood- between adolescence and old age, growth stops. old age- considered to be between 65 and death.

body parts grow faster/slower than others- organisms don't grow evenly, different times, different parts of the body will grow at different rates. when baby is in womb, brain grows at greater rate than rest of the body.

respiration- process of releasing energy from glucose, the energy cant be used directly by cells- used to make substance ATP. acts as a energy source fo cell processes and transport energy to where it's needed in cell. respiration, controlled by enzymes- means rate of reaction is affected by temp and pH. there are 2 types, aerobic and anaerobic.

aerobic needs oxygen- most efficient way to release energy from glucose, respiration using most of the time. word equation= glucose + oxygen - carbon dioxide + water (+ENERGY). chemical equation= C(6)H(12)O(6) + 6O(2) - 6CO(2) + 6H(2)O (+ENERGY). when respiration rate increases oxygen consumption and carbon dioxide production increase. means rate of oxygen consumption can be used to estimate metabolic rate.

anaerobic respiration, no oxygen- not the best way to convert glucose to energy; releases much less energy per glucose molecule. the glucose is partly broken down, and lactic acid is produced. it builds up in muscles, gets painful and makes muscles fatigued. word equation= glucose - lactic acid (+ENERGY). after exercising you'll have oxygen debt. you need extra oxygen to break down lactic acid that's built up in muscles and allow aerobic respiration. you have to keep breathing hard after you stop exercising to repay debt. lactic acid has to be carried to liver to be broken down, so heart rate has to stay up. respiratory quotient tells you whether someone is respiring aerobically or anaerobically. RQ=amount of CO(2) produced/amount of O(2) used. RQ is between 0.7 and 1 means person respiring aerobically. if RQ greater than 1 person respiring anaerobically.

plasma, liquid bit of blood- is pale yellow liquid which carries everything that needs transporting around body: red blood cells, white blood cells, platelets (used in blood clotting), water, glucose, amino acids (from gut to body cells), carbon dioxide (from body cells to lungs), urea (from liver to kidneys) hormones (act as chemical messengers), antibodies (proteins involved in body's immune response)

red blood cells- transport oxygen from lungs to all cells in the body. structure is adapted to it's function: are small and have biconcave shape to give large surface area to volume ratio for absorbing and releasing oxygen. contain haemoglobi, gives blood it's colour, contains alot of iron. in lungs it combine with oxygen to become oxyhaemoglobin. in body tissues the reverse happens to release oxygen to the cells. dont have a nucleus- frees up spacefor more haemoglobin, so can carry more oxygen. are very flexable- can easily pass through tiny capillaries.

blood vessels designed for their function- three types: arteries, capillaries and veins

arteries carry blood under pressure- heart pumps blood out at high pressure, artery walls are strong and elastic, thick compared to size of hole down middle (lumen), contain thick layers of muscle to make them strong.

capillaries are small- arteries branch into capillaries, are really tiny, carry blood close to every cell in body to exchange substances. supply food and oxygen, take away wastes like CO(2). walls only one cell thick. increases rate of diffusion by decreasing distance over which it occurs.

veins take bllod back to heart- capillaries join up to veins. blood is at lower pressure so walls don't need to be thick as artery walls. have bigger lumen than arteries to help blood flow. have valves to help keep blood flowing in right direction.

mammal have a double circulatory system- first system connects the heart to lungs. deoxygenated blood pumped to lungs to take in oxygen. blood then returns to heart. second system connects heart to rest of body. oxygenated blood in heart is pumped out to body. gives up oxygen, and deoxygenated blood returns to heart to be pumped out lungs again. not all animals have double circulatory system. adv: returning blood to heart after it's picked up oxygen at lungs means it can be pumped around body at higher pressure, increaes rate of blood flow to tissues, so more oxygen can be delivered to cells. important to mammals; use up alot of oxygen maintaining body temp.

heart- right atrium receives deoxygenated blood from body(through vena cava). deoxygenated blood moves through to right ventricle, which pumps it to the lungs (via the pulmonary artery). the left atrium receives oxygenated blood from lungs (through pulmonary vein). oxygenated blood moves through to left ventricle, which pumps it round the body (via aorta). left ventricle has a thicker wall than the right. needs more muscle; has to pump more blood around body, whereas the right has to pump it to the lungs. the semilunar, tricuspid and bicuspid valves prevent backflow of blood.

selective breeding- humans artificially select plants/animals that are going to breed and have their genes remain in population, what we want from them. selective bred to develop best features: maximum yeild of meat, milk, grain etc. good health and disease resistance. other qualities like temperament, speed, attractiveness, ect. basic process: from existing stock select ones with best characteristics, breed them with each other, select best offspring, then breed them. continue process over several generations, desirable trait gets stronger.

drawback, reduction in gene pool- the number of different alleles in a population; farmer breds from the best animals/plants- which are related, known as inbreeding. can cause health problems; more chance of organisms developing harmful genetic disorders when gene pool is limited. because lots of genetic conditions are recessive- need 2 alleles to be same for effect. breeding from closely related organisms means recessive alleles more likely to build up in population. could be serious problems if new disease appears; not much variation. all stock related, if one killed by new disease, so may the others.

genetic engineering- move genes from one organism to another, so it produces useful biological products. adv: produce organisms with new/useful features quickly. dis: inserted gene may have unexpected harmful effects.

genetic engineering stages- gene responsible for producing desirable characteristic is selected. then 'cut' from DNA using enzymes, and isolated. useful gene is inserted into DNA of another organism. organism replicates, soon there are loads of similar organisms all producing the same thing.

3 examples- some parts of world, population relies on rice, in these areas vitamin A deficiency can be a problem; rice doesn't contain much. genetic engineering allowed scientists to take gene that controls beta-carotene production from carrot plants and put it in rice plants. gene for human insulin production has been put into bacteria. cultured in a fermenter, and human insulin is extracted from medium as they produce it. some plants have a resistance to things. its not always plants we won't to grow that have these features. we can cut out gene responsible and stick it into useful plants such as crops.

moral and ethical issues- think its wrong to genetically engineer organisms for human benefit. people worry we won't stop at engineering plants/animals. in future people might be able to decide the characteristics they won't their children to have. the evolutionary consequences are unknown, some people think it's irrisponsible to carry on when we are not sure what the impact on future generations may be.

gene therapy- involves altering a person's genes in an attempt to cure genetic disorders. the 2 types: first would involve changing genes in body cells, the cells that are most affected by disorder. it doesn't affect the individual's gametes, any offspring will still inherit the disease, second type involves changing genes in gametes. means every cell of any offspring produced from gametes will be affected by gene therapy. its currently illegal. genetherapy involving gametes is controversial- might have unexpected consequences, cause a new set of problems, would be inherited by future generations. fears could lead to creation of 'designer babies'.

cloning an adult animal  done by transferring a cell nucleus- first was a sheep called 'dolly' produced using a method called nuclear transfer. involves placing nucleus of body cell into egg cell: nucleus of sheeps egg cell removed- left the egg cell without genetic information. another nucleus inserted in it's place. this was a diploid nucleus from an udder cell of different sheep, had all it's genetic information. cell given electric shock so it started dividing by mitosis. dividing cell was inplanted into uterus of a surrogate mother sheep, to develop. result was Dolly.

benefits- allows you to mass produce animals with desirable characteristics. e.g. animals that produce medicenes in their milk and then cloned. researchers managed to transfer human genes that produce useful proteins into sheep and cows, means animals can produce things like blood clotting agent. human embryos could be produced by cloning adult body cells. embryos could then be used to supply stem cells for stem cell therapy. these would have exactly the same genetic information as patient, reducing risk of rejection.

risks- cloned animals might not be as healthy as normal ones. cloning is new and it might have consequences that we're not yet aware of.

cloning humans is a possibility- ethical issues to consider: lots of surrogate pregnancies, probably with high rates of miscarriage and stillbirth. clones of other animals have been unhealthy and often die prematurely. it might be psychologically damaged by the knowledge that it's a cloneof another human being.

commerical cloning- first choose plant you want to clone based on characteristics. remove several small pieces of tissue from parent plant. best results if you take tissue from fast-growing root and root tips. grow the tissue in a growth medium containing nutrients and growth hormones. done under aseptic conditions to prevent growth of microbes that could harm plants. as tissues produce shoots and roots they can be moved to potting compost to carry on growing.

commercial use of cloned plants has pros and cons- fairly sure of characteristics of the plant; it'll be genetically identical to the parent. possible to mass produce plants that are hard to grow from seeds. if plants suffer from a disease or do badly due to change in enviroment, they'll all have the same problems; have the same genes. lack of genetic variation.