B2.

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What is the function of the nucleus, cytoplasm and cell membrane in plant and animal cells?
The nucleus controls cells activities, chemical reactions take place in cytoplasm & the cell membrane controls movement of materials in and out of the cell.
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What are the functions of mitochondria and ribosomes in cells?
Mitochondria: Where energy is released during aerobic respiration. Ribosomes: where protein synthesis occurs.
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What do plant and algal cells have in addition to a nucleus, cytoplasm, membrane etc?
Rigid cell wall made of cellulose for support, chloroplasts that absorb light energy and contain chlorophyll for photosynthesis and a permanent vacuole containing cell sap.
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What are the properties of Bacterial cells and bacteria?
Cell membrane + cell wall surrounding the cytoplasm. No nucleus so genetic material is in the cytoplasm. When bacteria multiply they form a Bacterial colony.
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What is yeast?
A single celled organism. Yeast cells have a nucleus, cytoplasm + cell membrane + wall.
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How can a root hair cells and plant cells be specialised?
Root hair cells increase the S.A of the root so that it can absorb water + mineral ions efficiently. Plant cells with many chloroplasts will be photosynthesising.
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How are neurons and receptor cells specialised?
Receptor cells have structures enabling them to detect stimuli (cone cells in eye are light sensitive), Neurons are specialised to carry impulses from receptors to the CNS.
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How are cells with tails, many mitochondria or many ribosomes specialised?
A cell with many mitochondria must need a lot of energy (sperm/muscle cells). A cell with many ribosomes is making a lot of protein (gland cells). Cells have tails for movement (sperm cells).
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What is diffusion?
The spreading out of particles of a gas or of any substance in a solution. The larger the difference in concentration between the two areas (concentration gradient), the faster the rate of diffusion.
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What does the net movement into or out of cells dependant on?
The concentration of the particles on each side of the cell membrane. As the particles move randomly there will be a net movement from an area of high concentration to an area of low concentration.
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Give examples of diffusion.
Diff of O2 into the cells of the body from the bloodstream. Diff of CO2 into photosynthesising plant cells. Diff of simple sugars + amino acids from the gut through cells membranes.
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What happens during the development of multicellular organisms (i.e animals)?
The cells differentiate as different cells have different functions. A tissue is a group of cells with similar function + structure.
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What are the three types of animal tissue?
Muscle tissue (can contract to bring about movement), glandular tissue (produces substances – enzymes/hormones) & epithelial tissue (covers some parts of the body)
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What do the organs in plants (leaf, stem + root) consist of?
Epidermal tissue (covers the plant), mesophyll (can photosynthesise) & xylem + phloem (transports substances around the plant.
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What are organs made of? Give an example and what tissues it may be made of?
Organs are made of tissues. The stomach consists of; muscular tissue (to churn contents of stomach), glandular tissue (to produce digestive juices) & epithelial tissue (to cover outside + inside of stomach)
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What is an organ system?
A group of organs that perform a particular function. I.e. the digestive system is responsible for changing insoluble molecules into soluble molecules so that they can be absorbed into the blood.
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What is the process for photosynthesis (occurs only in green plants and algae)?
CO2 is taken in by the leaves through the stomata + water is taken up by the roots. Chlorophyll traps the light energy needed to convert the CO2 + H2O into glucose + sugar. Carbon Dioxide + Water ---> glucose + Oxygen.
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How can we test that photosynthesis has occurred in leaves?
By testing leaves with iodine solution as some of the glucose produced in photosynthesis is converted into insoluble starch for storage. If testing a variegated leaf, the green part of the leaf will turn the iodine solution blue-black.
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What are limiting factors in photosynthesis?
Anything that puts a cap on/slows down the rate of photosynthesis – A lack of light as light provides the energy for photosynthesis, if it is cold as enzymes will not work efficiently or if there is too little CO2 (i.e. in an enclosed space).
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What do you have to note when doing a photosynthesis experiment?
The independent variable ( the one being tested i.e. concentration of CO2) and the dependent variable (the one you measure usually the volume of O2 produced in this case). Control variables – light, temperature and the type of plant being used.
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How may he glucose produced in photosynthesis be used?
It may be: converted into insoluble starch or fats & oils for storage, used for respiration, used to produce cellulose which strengthens cell walls or used to produce proteins.
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What do plant and algal cells need in addition to CO2, H2O and light energy?
A supply of mineral ions such as nitrate ions to produce protein. Plants absorb nitrate ions from soil + Algae absorb nitrate ions from the water they live in.
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What do plant growers have to consider when controlling the environment in which their plants grow in?
Plant growers have to evaluate the benefits of increasing the growth with the cost of heating, lighting + providing CO2. They have to compare the biomass of plants grown indoors and outside without these extra factors.
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How can plant growers give their plants the best conditions by controlling their environment?
They can construct Greenhouses/polytunnels with heaters and lamps (if too high, it will stop photosynthesis), by adding CO2 to the air + by adding nitrate ions to the soil to ensure that plants can make protein (needed for growth).
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Name 6 physical/external factors that can affect the distribution or organisms.
Temperature + Availability of nutrients, water, oxygen, CO2 and light.
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How can you obtain quantative data on the distribution of organisms using a quadrat?
Random quantative sampling (consider sample size so that the sample size is representative of whole habitat/field) or along a transect (A line marked between two points i.e.every 5m).
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How can you make sure the investigation about the distribution of organisms is valid?
Only the independent variable should affect the results, all other variables must be controlled.
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What are proteins and what can they be used for?
Protein molecules are made of long chains of amino acids, folded to produce specific shapes depending on its function. Proteins can be: structural components (tissues), hormones, antibodies and catalysts.
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What are enzymes and what do they do?
Chemical reactions in cells are controlled by enzymes which are biological catalysts (speed up reactions). Enzymes are large proteins that have an active site where the substrate can be held to be broken down or connected to another molecule.
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What are the three things enzymes can do?
Enzymes can build large molecules from smaller molecules (i.e. starch from glucose molecules), Change one molecule into another (convert one sugar into another) & break down large molecules into smaller one (digestive enzymes).
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What happens when the temperature is increased in an enzyme reaction?
The molecules move more quickly + so collide with each other more often + with more energy so that the reaction takes place faster but if it gets too hot then the enzyme denatures (stops working as it changes shape).
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How does the pH of the conditions that the enzyme is working in affect the rate of reaction?
Each enzyme works best at a particular pH value. If the pH is too acidic or alkaline for the enzyme then the active site could change shape and the enzyme could become denatured.
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Where are digestive enzymes produced and what does digestion involve?
By specialised cells in glands ad in the lining of the gut. The enzymes pass out of the cells and come into contact with the food. Digestion involves the breakdown of large, insoluble molecules into smaller soluble molecules.
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What is the function of amylase (a carbohydrase), where is it produced and where is it used?
Amylase is produced by the salivary glands, pancreas + small intestine. Amylase catalyses the digestion of starch into sugars in the mouth and small intestine (slightly alkaline).
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What is the function of protease, where is it produced and where is it used?
Protease is produced by the stomach, pancreas + small intestine & catalyses the breakdown of proteins into amino acids in the stomach (best in acidic conditions, HCl produced by glands in walls) + small intestine.
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What is the function of Lipase, where is it produced and where is it used?
Lipase is produced by the pancreas + small intestine. Lipase catalyses the breakdown of lipids (fats/oils) to fatty acids and glycerol. Lipase work best in slightly alkaline conditions.
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Which organ produces bile and how can it be used to speed up digestion?
The liver produces bile (stored in the gall bladder) and is squirted into the small intestine to neutralise the stomach acid and make the conditions in the small intestine slightly alkaline.
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How can proteases and lipases be used in industry?
Biological detergents use proteases and lipases to digest food stains – work at lower temp saving energy + money spent on electricity. Proteases are also used to pre-digest proteins in some baby foods.
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How are enzymes used to convert starch and sugars?
Isomerase is used convert glucose syrup into fructose syrup which is twice as sweet and so less is needed (less fattening). Carbohydrases are used to convert starch into sugar syrup for use in foods.
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How can enzymes save money in a factory?
Enzymes can be used to bring about reactions that require expensive equipment, high temp + pressures at normal temperature and pressures.
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What are the advantages of using enzymes?
Enzymes in biological detergents are more effective in removing stains, can be used at lower temp (saving money + energy). Some used in medicine to diagnose/control/cure diseases. Industry- cost of equipment/energy can be reduced.
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What are the possible disadvantages of using enzymes?
If misused washing powder can trigger an allergic reaction, may enter waterways via the sewage system, industrial enzymes can be costly to produce, Enzymes denature at the high temp needed to kill pathogens. Wool etc. digested by proteases.
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Where does aerobic respiration take place and what is chemical equation?
In the mitochondria. Glucose + oxygen  CO2 + water + energy
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What can the energy released from respiration be used for?
Build larger molecules from smaller ones (i.e. amino acids  proteins), thermoregulation, muscle contraction in animals
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What happens to your heart rate blood vessels and breathing during exercise?
Heart rate increases + blood vessels dilate to allow more blood containing O2 + glucose to reach the muscles. Breathing rate + depth of each breath increases to allow a greater uptake of O2 + release of CO2 at the lungs.
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How do muscles store glucose?
As glycogen-converted back to glucose for use during exercise.
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What does your body need for exercise?
Muscles need more energy to contract – Need to increase the rate at which O2 + glucose reach muscle cells for aerobic respiration + need to remove the extra waste CO2 produced more quick
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What happens if you use your muscles over a long period of time?
Fatigued due to build-up of lactic acid + less energy is released from aerobic respiration.
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What happens when your muscles cannot get enough oxygen to respire aerobically?
Respire anaerobically, producing lactic acid (as glucose is not completely broken down). Lactic acid removed by blood flowing through muscles.
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Why is anaerobic respiration inefficient?
As breakdown of glucose is not complete + lactic acid is produced as waste product instead of CO2 + water.
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Why do runners in a marathon pant so heavily even after they have stopped running?
As you need a lot of oxygen to completely break down lactic acid after exercise - the “oxygen debt” must be repaid. O2 oxidises lactic acid into CO2 + H2O.
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Why is cell division necessary?
For the growth of an organism or for the repair of damaged tissues (repair and replace)
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When do cells differentiate?
Most animal cells differentiate early in development whilst plant cells differentiate throughout the plants life.
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How does cell division take place?
A copy of each chromosome containing genes (alleles) is made before the cell divides and one of each chromosome goes to each new cell. In early development
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What is mitosis?
Cells of offspring produced by asexual reproduction are produced by mitosis from the parent cells resulting in two identical cells (containing the same alleles) being produced by the original cell.
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How do cells in reproductive organs (i.e.testes +ovaries) divide?
By meiosis to form gametes (sex cells). Human gametes = sperm + ova. Each gamete only has 1 chromosome from each original pair. All of the cells are different from each other + the parent
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How is a new individual formed as a result of sexual reproduction?
Sexual reproduction results in variation as gametes from each parent fuse (½ genetic info from each. At fertilisation a single body cell with new pairs of chromosomes is formed. This cell repeatedly divides by mitosis to form a new individual.
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How does meiosis occur?
Before division a copy of each chromosome is made. The cell then divides twice to form 4 gametes and each gamete has a single set of chromosomes each with a different combination of genes.
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What are stem cells?
Unspecialised cells found in the human embryo (differentiate in layers, changing into all the diff types of body cells i.e. nerve/muscle cells) + in adult bone marrow where it can change into other types of cell (i.e. blood cells).
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How do scientists hope to use stem cells?
It is hoped that human stem cells can be made to differentiate into many types of cell that could, for example, be used to treat paralysis by forming (differentiating into) new nerve cells.
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Who was Gregor Mendel and why were his ideas not accepted until long after his death?
He was a monk who worked out how characteristics were inherited + was the first person who suggested the idea of separately inherited ‘factors’ but his ideas were not initially accepted as scientists didn’t know about chromosomes + genes until after
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How did Mendel’s experiments impact the knowledge that we have of genetics today?
Mendel’s ‘factors’ are now called genes, found on chromosomes made of DNA – long molecule with a double helix structure. Genes are short sections of DNA + everybody (except from identical twins) has a unique DNA pattern that can be used to identify p
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What is a genetic code?
Each gene codes a particular combination (order) of amino acids which make a specific protein
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What are sex chromosomes?
Human beings have 23 pairs of chromosomes, one pair are the sex chromosomes. Human females have 2 X chromosomes (**) + males have an X + a Y chromosome (XY).
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What are alleles?
Genes controlling the same characteristics. An allele that ‘masks’ the effect of another it is said to be dominant. The allele where the effect is masked is said to be recessive.
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What is the difference between genotypes and phenotypes?
Genotype describes the genetic make-up of an organisms (the combination of alleles) + the alleles that the individual inherits whilst phenotype describes the physical characteristics that an organism has, often related to a particular gene.
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How can people inherit genetic disorders such as Polydactyl (where a baby is born with extra finger/toes)?
An affected individual only has to inherit one dominant allele to have the genetic disorder (can be passed on by one parent who has the allele) but if the allele is recessive then the individual must inherit two recessive alleles to have the disorder
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What is cystic fibrosis?
Genetic disorder caused by recessive allele affecting cell membranes to cause the production of thick, sticky mucus affecting organs i.e. lungs + pancreas. The parents don’t need to have cystic fibrosis but have to be carriers of the allele.
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How can we use genetic diagrams?
To see how a disorder (or allele) has been inherited and to predict whether future offspring will inherit it/ Genetic diagrams i.e. family trees can be constructed to predict/explain how alleles + characteristics are inherited.
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What is meant by the terms homozygous and heterozygous?
A pair or alleles is described as homozygous if both alleles are same: DD (homozygous dominant) + dd (homozygous recessive) and if described as heterozygous the two alleles are different (Dd).
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What are embryonic stem cells?
Taken from spare embryos from IVF or the umbilical cord of a new-born baby or created from adult cells. Doctors have investigated embryonic stem cells which have the potential to differentiate into a wide variety of cells as they could be used to gro
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What is embryonic screening?
Embryonic screening involves tests to diagnose disorders before the baby is born and the results of the test may give the parents the option to terminate the pregnancy or decide that it is unethical and prepare for the delivery of an affected baby.
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Why do some people believe that embryonic screening is unethical in IVF?
As after the embryos are screened only the healthy embryos are implanted into the mother whilst embryos carrying faulty genes are destroyed.
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Give an example of how adult stem cells can be used?
Bone marrow cells are useful in treating some disorders such as leukaemia.
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How old is the earth believed to be?
4500 million years old and life is believed to have begun 3500 mill years ago, but there is some debate as to whether the first life developed because of the conditions on earth or if they arrived from another planet.
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How can we date when different organisms existed?
We can date when different organisms existed by dating the rocks that fossils are found in.
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Why didn’t most organisms leave a fossil?
Most organisms didn’t leave a fossil because the exact conditions for fossil formation were not present. Many early life forms had soft bodies and traces which were left are likely to have been destroyed by geological activity i.e. earthquakes
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What is Extinction?
Extinction means that a species that once existed has completely died out.
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Extinction always involves a change in circumstance. What can cause extinction?
A new disease. The environment may change over geological time. New predator may evolve/be introduced. New competitor may evolve/be introduced -> little to eat. Natural disaster destroys habitat. Over time natural changes occur in the species.
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What is the biggest influence on species survival?
Changes in the environment. Climate change is an important influence in determining which species survive as it may make it too cold/hot, wet/dry for a species. One well adapted to a hot climate may become extinct in the ice age – too cold to breed?
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How have many species died out over several million years (short time in geological terms)?
The habitat the species lives in may be destroyed by catastrophic events i.e major volcano eruption. The environment may change dramatically following a collision between a giant asteroid and earth.
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What is the most famous of the various ideas suggested to explain the extinction of dinosaurs?
The collision of a giant asteroid caused huge fires, earthquakes, landslides + tsunamis. The dust which rose masked the sun causing darkness so that plant could not grow + temps fell.
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What is the less known idea suggested to explain the extinction of dinosaurs?
The idea that the extinction was a slower process as a result of sea ice melting + cooling the sea temperature by about 9 degrees Celsius resulting in less plankton and therefore less food available.
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How can new species arise from existing species and how can geographical isolation occur?
New species can arise from existing species if a group becomes isolated from the rest. Geographical isolation could occur if an island separates from the mainland or if a new river separates two areas. Mountain ranges + old craters can isolate organi
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How does isolation occur in the case of an island separating from mainland?
The organisms left on the island may be exposed to different environmental conditions, food availability or predators. Natural selection will occur on the mainland + the island but diff characteristics would be beneficial in the 2 populations.
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The organisms left on the island may be exposed to different environmental conditions, food availability or predators. Natural selection will occur on the mainland + the island but diff characteristics would be beneficial in the 2 populations.
If the two populations are brought together and cannot interbreed, we say that they belong to two different species.
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What is speciation?
Isolation-->genetic variation-->alleles selected-->interbreeding no longer possible-->new species (speciation)
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