1059075
Descrição
FlashCards por Chima Power, atualizado more than 1 year ago
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Criado por Chima Power
aproximadamente 10 anos atrás
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| Questão | Responda |
| Animal cells and plant cells: Nucleas | Controls all the activities in the cell and contains the genes on the chromosomes carry instructions on making new cell and organisms |
| Animal and plant cells: Cytoplasm | Liquid gel in which most of the chemical reactions needed for life take place |
| Animal cells and plant cells: Cell membrane | Controls the passage of substances into and out of the cells |
| Animal and plant cells: Mitochondria | Structure in cytoplasm where oxygen is used and most of the energy is released during respiration |
| Animal and plant cells: Ribosomes | Where protein synthesis takes place, all the protein needed in the cell are made from information from the nucleus from genes |
| Plant cells: Cell wall | made of cellulose that strengthens cell and gives it support |
| Plant cells (not all): Chloroplasts | Found in green part of plant this colour as contain chlorophyll which absorbs light energy to make food for photosynthesis root hair cells do not have as underground so no sunlight |
| Plant cells (not all): Permanent vacoule | Space in cytoplasm containing cell sap important for keeping the cells rigid to support the cells |
| Bacteria | Single celled organism that are much smaller than animal and plant cells most bacteria less that 1 nanometre in length when you grow bacteria you can see a bacteria colony with eye |
| Bacterial cells | Made of cytoplasm surronded by membrane and cell wall inside is genetic material genes are not contained in nucleus there are long strands of DNA usually circular and found free in the cytoplasm. Many also contain plasmids small circular bits of DNA carrying extra info may also have slime capsule over the cell wall. Some have flagellum long protein strands used for movement. |
| Bacteria cell uses | Some do cause disease most are harmless some have uses as they used to make yogurt, cheese, sewage treatment and medicine. |
| Yeast | Single cell organisms have nucleus with genetic material, cytoplasm and membrane surrounded by a cell wall, cells vary in size from 3 to 4 nanometres so bigger than bacteria. |
| Yeast structure | Specalised to be able to survive for a long time with little oxygen. When enough oxygen aerobically respire when there isn't much oxygen they anaerobically respire breaking down sugar for energy and producing ethanol and carbon dioxide. This process is also called fermentation as ethanol is alcohol. Can also be used to make bread |
| Fat cells | These cells help animals to survive when in short supply of food this are able to do this because of these adaptations: small amount of cytoplasm large amount of fat Have few mitochondria as the cell needs little energy They can expand can become 1000 times original size as fill with fat |
| Cone cells (human eye) | Light sensitive layer of our eye (retina) make it possible to see colour there adaptations: Outer segment contains a special chemical that changes chemically in coloured light it requires energy to change back to its original form The middle layer is packed with mitochondria which gives the energy needed to change back its original form Final part is a special synapse that connects to the optic nerve, when coloured light makes your visual pigment change an impulse is triggered, the impulse carries the synapse and travels along the optic nerve to your brain |
| Root hair cells | Close to tip of growing roots plants need water and dissolved mineral ions the root hair cells help to do so more efficiently they are close to xylem tissue that carry these products to the rest of the body. There adaptations are: their increased surface area to allow more water in Large permanent vacuole that speeds up the movement of water by osmosis from the soil through the root hair cell |
| Sperm cells | Contain genetic information for male parent, they must travel through female reproductive system to reach female egg and must break into the egg. There adaptations: Long time, flagella, flaps used for movement Middle section full of mitochondria provides energy for flagella Acrosome, at the tip, stores digestive enzymes for breaking outer layer of egg large nucleus contains the genetic info to be passed on |
| Diffusion | This is the spreading out of particles in a gas, or of any substance in a solution resulting in net movement of particles to an area of high concentration to one of low concentration due to random movement of particles. |
| Rates of diffusion | The larger the distance between concentration of two areas the faster the rate of diffusion. Difference between the difference of the two concentrations is called the concentration gradient bigger difference higher concentration. Diffusion occurs down a concentration gradient. Higher temperature the faster the rate of diffusion particles move with more energy and speed. |
| diffusion in living organisms | Many important substances move across cell membrane by diffusion such as water and glucose and amino acids. Oxygen diffusion in lungs and into red blood cells. Individual cells can be adapted to make this process faster mainly by increasing surface area, more space for diffusion to occur so rate of diffusion increased |
| Tissues | A group of cells with similar structure and serve the same function working together. For example muscular tissue can contract to bring about movement, glandular tissue contains secretory cells that can produce enzymes and hormones, epithelial tissue covers the outside of your body as well as organs. Example of plant tissues: Epidermal tissues cover the surface and protect them, mesophyll tissues contain a lot of chloroplasts and can carry out photosynthesis, xylem and phloem tissues are transport tissues in plants. |
| Organs | These are made up of tissues one organ can contain several tissues. So it is a collection of different tissues working together to carry out important functions in your body |
| Organ systems | Different organs combined to carry out major functions in the body such as transporting food or digesting food |
| Adaptations for exchange | exchange of gases in lungs Digested food moves from small intestine to blood Many different dissolved substances from blood to kidney tubes faster due to increased surface area |
| Photosynthesis | Provides plant and algae energy for respiration, growth and reproduction takes part in green part of plant mainly leaves |
| Process of photosynthesis | carbon dioxide + water -> (light energy) glucose + oxygen. green parts contain chloroplast full of chlorophyll . During process chlorophyll absorbs light energy through chloroplast energy used to convert co2 and water to a simple sugar glucose and oxygen, released into air we breath it in. |
| Uses of glucose | Some glucose used immediately for energy in the plant by the cells however a lot is converted into insoluble starch and stored iodine solution can be used identify starch in plant turning from yellowy brown to dark blue |
| Leaf adaptations | Most leaves are broad giving a large surface area for light to fall on Contain chlorophyll in chloroplast to absorb sunlight Have air spaces to all Co2 in and oxygen out by diffusion Have veins which bring plenty of water to cells of the leaves |
| Limiting factors: Light | If lots of light large amount of photosynthesis can take place of little or none photosynthesis will stop |
| Limiting factors: Temperature | As the temperature increases so does the rate of photosynthesis as rate of reaction speeds up. Although photosynthesis controlled by enzymes which denature at 40 to 50'c, so rate of photosynthesis will fall |
| Limiting factors: Carbon dioxide | Greater amount of Co2 the faster the rate of photosynthesis as Co2 is a reactant in the reaction. On a sunny day this is lacking as plants use up Co2 and is most abundant in the evening as plants respire not photosynthesise. In greenhouses this can be controlled hence not be a limiting factor |
| Uses of glucose explained | Energy in respiration is used to build smaller molecules into larger ones. Also glucose is built up into more complex carbohydrates like cellulose, to strengthen cell walls. Glucose is also used to make amino acids by combining sugars with nitrate ions and other mineral ions. Amino acids built up to make protein for cells uses respiration for energy. |
| Fats and oils | Built up by energy for respiration and photosynthesis. They may be used in cells as energy store, in cells as to make cell wall stronger, plants also use as energy store in seeds, provides energy for new plant as germinates. These are being seen as possible biofuels in future. |
| Starch for storage | Glucose is soluble in water so can affect the water balance in the plant while starch is insoluble so does not affect water balance so large amounts can be stored in plant. The starch provides an energy source when dark and little light. Kept in and found all over plant a lot in tubers and bulbs where plants store for over winter for example potatoes |
| Greenhouse gardens | Farmers use same idea as greenhouses in polytunnels where they grow a variety of crops. It affects the rate of photosynthesis as limiting factors can be better controlled. Most importantly it is warmer speeding the growth and allowing the growth of plants that would not usually be able to be used. |
| Controlling a crops environment | There is a contiinous interaction between the differenct factors so when for instance there is a lot of light there is low amount of carbon dioxide |
| Control environment through electricity | Big companies take advantage of knowledge on limiting factors light, carbon dioxide and temperature, levels varied to get greatest outcome. Plants can also be grown in water with perfect mix of minerals ions speeding growth known as hydroponics. |
| Consequences of greenhouses | Positive: Turnover is fast so large profit, huge conditions controlled by computer, crops clean and unspoiled, no preparing the land and can be used on poor so cheap land, requires few staff. Negative: consumes large amount of electricity, costs a lot of money |
| Factors affecting living organisms: Temperature | In cold climates this is always a limiting factor as plants are small which means only a low amount of herbivore can survive in the area |
| Factors affecting living organisms: Nutrients | Level of mineral ions has a big impact on the distribution of plants except for venus flytrap which limits the number of herbivores that can survive in the area. |
| Factors affecting living organisms: Amount of light | Light limits the rate of photosynthesis so affects the distribution of plants and consequently animals. Some plants are adapted to live in low light levels. Breeding cycles for many plants and animals depend on day length and light intensity being right for them |
| Factors affecting living organisms: Availability of water | This is particularly important in a desert where there is a low availability of water until it rains then plant distribution is affected as seeds grow where plants are available. Animals then eat these plants consequently if there are no water there is no life. |
| Factors affecting living organisms: Availability of oxygen and carbon dioxide | Availability of water has a big affect on water living organisms, some invertebrates can survive in low oxygen levels though most fish need a high level of dissolved oxygen. Carbon dioxide limiting factor for photosynthesis affects distribution of plants so animals . While mosquitoes feed on blood with high carbon dioxide levels and so plants with high carbon dioxide levels are susceptible to their attack. |
| Quadrats | This is the simplest way to sample an area which is square frame made of wood or metal sides 0.5m long. They are used to investigate plant population and slow moving animals such as snails. Same quadrat must be used every time and in as many areas as possible to make results as reliable as possible so reflective of true distribution by incorporating sample size and using random placement of the quadrat. Could do so by using random number generator. Must find a number of random readings and find a mean number of organisms per m^2 technique known as quantitative sampling. You can compare the distribution of organisms for different habitats. Can be used to measure changes in distrubtion as can be done over intervals and find the range, median and mode. |
| Counting along a transect | Another useful way of measuring distribution of organisms line transect is most commonly used. These are not random you strech a tape at regular intervals using a quadrat, you sample the organisms at regular intervals along the line. Showss how the distrubtion of animals change along that line. Can also measure physical factors such as pH level in soil and light levels |
| Reproducible, valid data | Data must be reproducible and valid when trying to prove environmental change. In reproducible investigations other people can repeat the experiment and they get very similar results. For the investigation to be valid it must answer the question. Sample size is important larger normally more reproducible and valid. Method must justifiable so is valid. Must use a method that anyone can use. |
| Controlling variables | In a lab many variables can be controlled so can be repeated so reproducible. In fieldwork this is not possible but some can be controlled such as taking results at the same time each day. Must be clear of problems on collecting data if you want to use as evidence for environmental change. Many variables are responsible for change |
| Protein molecules | These are very important to our body they are made of long chain of small units of amino acids different arrangements of amino acids givens different proteins. Have many functions: structural components such as muscles hormones such as insulin antibodies catalysts in form of enzymes |
| Controlling the rate of a reaction | Done in everyday life decreasing temperature like in fridge reducing the rate of a reaction sometimes special chemicals known as catalysts can be used to speed up reactions for us but does not get used up in the reaction so can be used again and again. |
| Enzymes - biological catalysts | These are large protein molecules the long chain of amino acids are folded to produce a molecule with a specific shape this special shape allows other molecules substrates to fit into the enzyme protein call this the active site shape vital for how it works |
| Enzyme functions | Building large molecules from small molecules - For instance making glycogen from glucose Changing one molecule into another - One sugar to another glucose to fructose Breaking down large molecules into smaller ones - breaking down insoluble molecules into soluble molecules such as sugars starch to glucose. Do not change a reaction just make it faster different enzyme catalyze specific types of reactions. |
| Effect of temperature on enzyme action | Reaction that take place in a cell react relatively low temperatures. The rate of enzyme controlled reactions increases as the temperature does, but only up to temperature of about 40c afterwards protein shape is affected by temperature long amino acid chains begin to unravel shape of active site changes say it becomes denatured. Can longer act as a catalyst so the rate of the reaction drops dramatically most human enzymes work best at 37c optimum temperature. |
| Effect of pH on enzyme activity | Shape of the active site comes from forces between the different parts of the protein molecule, forces hold the folded chains in place, a change in pH affects these forces, why changes the shape of the molecule. As a result active site is lost so no longer acts as catalyst. Different enzymes have different optimum pH levels. |
| Importance of enzymes | Without these none of the reactions in the body would happen fast enough to keep alive, thats why so dangerous if temperature is too high in case of an illness. Once body temperature is about 41c enzymes begin to denature and you will soon die. |
| Digesting carbohydrates | Enzymes that breakdown carbohydrates are called carbohydrases. For example starch is broken down into sugars in the mouth and small intestines reaction is catalyzed by a reaction called amylase. Amylase is produced in the salivary glands so the digestion of starch begins in your mouth. Also made in pancreas and small intestines but no digestion occurs in the pancreas all the enzymes in pancreas flow into the small intestines where most starch is digested. |
| Digesting proteins | Breakdown of proteins into amino acids is catalysed (sped up) by protease enzymes, produced by stomach, small intestines and pancreas. Breakdown of amino acids takes place in stomach and small intestines |
| Digesting fats | The lipieds (fats and oils) are broken down into fatty acids and glycerol in the small intestines, reaction catalysed by lipase enzymes. Made in pancreas and small intestines. Pass into bloodstream to be carried around body to cells in great need for their reputable services. |
| Speeding up digestion: Changing pH in the gut | Different enzymes work best at different pH for instance protease enzyme works best in acidic condition so found in stomach but protease made in pancreas work best in alkali conditions. The 35 million glands in the lining of the stomach that secrete protease enzymes that work best in acidic pH also secrete a concentrated solution of HCL about 3 litres of acid from these glands is secreted each day. This allows protease to work highly effectively and kills most of the bacteria in the food. Stomach also produces thick layer of mucus protects from being digested by acid and enzymes. |
| Speeding up digestion: Changing pH in small intestine | Some of the enzymes that catalyse digestion in small intestine are made in pancreas some in small intestine all work best in alkaline conditions. Liver makes a greenish-yellow liquid called bile stored in gile bladder until needed when food enters small intestine bile is squirted onto it neutralising the acid and making it alkaline provides prime condition for enzmye. |
| Speeding up digestion: Altering the surface area | Larger the surface area the reaction no problem with carbohydrates and proteins however fats do not mix with watery liquids in gut but bile emulsifies the fats in the food so the bile physically breaks down up large drops of fat into smaller droplets provides a much larger surface area for it to react on helps lipase quicker break down fats. |
| Enzymes in the home | In washing biological detergents are mostly used which include enzymes protease and lipase these break down fat and protein stains, help to give cleaner wash. These such detergents work better than non biological detergents at low temperatures as denatured if too hot so require less electricity. |
| Enzymes in industry | Proteases used to make baby foods they predigest some of the protein in the food making baby digestive system easier to cope with the food. Easier for them to get the amino acids they need from the food. Carbohydrates are used to convert starch into sugar syrup high quantities used in food production. As starch is made of plants like corn and cheap using enzymes provides a cheap source of sweetness for food manufacturers. Also important in process of making fuel in plants (ethanol). The isomerase enzyme can also convert the sugar syrup into fructose syrup which is sweeter than glucose syrup so less must be used in food so contains fewer calories and regarded as slimming food. |
| Advantages and disadvantages of using enzymes | Require low temperature, low energy so cheaper than conventional means. Problem is denature at high temperatures and pH levels must be kept within certain limits, costs money to control these limits. Many enzymes are expensive to produce. |
| Pros and cons of biological detergents | Biological stains from parents and children can be treated, very effective at cleaning at low temperatures use a lot less energy than non biological detergents good for environment cheaper for consumer. Can develop allergies but put in tiny capsules most allergy's stopped although caused bad publicity. May contaminate water supply and low temperature ineffective at killing pathogens on the clothes |
| Enzymes in medicine: To diagnose disease | If liver damaged or diseased some of liver enzymes may leak into bloodstream, doctors can test blood for liver enzymes tells them if liver is really damaged. |
| Enzymes in medicine: To diagnose and control disease | Enzymes can be used to detect diabetes as will have too much glucose in their urine. Commonly used test relies on color change on a test strip. Test strip contains a chemical indicator and enzyme, enzyme catalyses breakdwon of glucose in products present chemical indicator tuns certain color. |
| Enzymes in medicine: To cure diseases | If pancreas damaged or diseased supplementary enzymes must be taken in special capsules so not digested by stomach. In case of heart attack enzyme called streptokinase injected into blood as soon as possible dissolves clots in arteries of heart wall and reduces the amount of damage done to your heart muscle. Enzyme used to treat a type of blood cancer in children. Enzyme speeds up the breakdown of amino acids cancer cells require without it they die as they cannot make a particular type of amino acids normal cells can make this so unaffected. |
| Aerobic Respiration | Process uses glucose and oxygen to release energy, carbon dioxide and water are produced as waste products. Most take place in the mitochondria and are controlled by enzymes. Energy used to build larger molecules from smaller ones, enable muscle contraction in animals, maintain a constant body tmperature in colder surroundings in mammals and birds, build sugars, nitrates and other nutrients into amino acids and then proteins in plants. Limewater used to detect carbon dioxide shows is aerobic respiration taking place, quicker limewater turns cloudy faster CO2 produced. Can also test rise in temperature when respiration occuring. Germinating peas are left in a thermos flask, rise in temperatue can be monitored. |
| Effect of exercise on the body | Your muscles need more energy to contract Need to increase the rate at whic oxygen and glucose reach the muscle cells for aerobic respiration. Need to remove extra waste carbon dioxide produced more quickly. Heart rate increases and blood vessels suppling the muscles dilate. allows more blood containg oxygen and glucose to reach the body. Breathing rate and the depth of each breath increase. Greater uptake of oxygen and release of carbon dioxide into the lungs. Muscles store glucose as glycogen, can be converted to glucose during exercise. |
| Anaerobic Respiration | Muscles used over long time fatigue and stop contracting effeciently, when cannot get enough oxygen aaerobically start to respire anaerobically. Glucose not completely broken down and lactic acid produced. Less energy released from the glucose, cause of muscle fatigue is th ebuild up of lactic acid, blood flowing through the muscles removes the lactic acid. When aerobic respiration finished lactic acid must be completely broken down take in a lot of oxygen to do so known as oxygen debt oxidieses lactic acid inot carbon dioxide and water. |
| Cell Division and Growth | Necessary for growth of an organism, or for the reapir of damaged tissures. Mitosis results in two identical cells being produced from the original cell. Chromosomes contain the genes(alleles) which must be passed on to a new cell. Copy of each chromosome is made before the cell divides and one of each chromsome goes to each cell. In early development of animal and plant embryos cells unspecialised called stem cells. Animal cells differentiate early in development and cell division is mainly for repair and replacement. Plant cells differentiate throughout the life of the plant as it continues to grow. Cells of offspirng produced by asexual reproduction are produced by mitosis from the parent cell, contain same alleles as the parents |
| Cell division in sexual reproduction | Cells in reproductive overies like testes and ovaries divide by meiosis to form sex cells (gametes). In humans the gametes are the sperm and ova. Each gamete has only on chromosome from original pair. All the cells are different from each other and the parent cell. When gametes join at fertilisation, a single body cell with new pairs of chromosomes is formed. New individual then develops by this cell repeatedly dividing by mitosis. |
| Meiosis | before division a copy of each chromosome is made. Cell now divides twice to form four gametes. Each gamete has a single set of chromosomes, each with a different combination of genes. |
| Stem Cells | Unspecialised, found in the human embryo and in adult bone marrow, change into different types of body cells like nerve cells, muscle cells. Layers of cells in the embryo differentiate into all the cells the body needs. Stem cells in the adult bone marrow can change into other types of cell like blood cells. Hoped that can be made to differentiate into many types of cells could then be used to treat conditions like paralysis by differentiating into new nerve cells. |
| Mendal to DNA | Gregor Mendel was a monk who worked out how characteristics were inherited first person to suggest the idea of separately inherited factors. took a long time for his ideas to be accepted because many scientists didn't know about chromosomes and genes until after Mendal died. Mendels factors now called genes found on chromosomes. Chromosomes made of DNA a very long molecule with a double helix structure. Genes are short sections of DNA. Each individual except identical twins have different DNA can be seen in fingerprint. |
| Inheritance in Action | Humans have 23 pairs of chromosomes, one pair are the sex chromosomes. Females have two X chromosmes (XX) and males have X and Y chromosome (XY). If an allele masks affect of another it is said to be dominant, allele where affect is masked is said to be reactive. Genetic diagrams including family trees illustrate how alleles and characteristics are inheritd. |
| Genetic terms and models | Genetic diagrams are biological models which can be constructd to predict and explain the inheritance of particular characteristics. Punnet squares are grids used to insert the alleles symbols. Phenotype-physical apperance of the characeristic Genotype-genetic make up-whic alleles does the individual inherit Homozygous-both alleles are the same DD(dominant) or dd (recessive) |
| Inherited conditions in humans | Many different genetic disorders some caused by a dominant allel some by recessive allele. If allele is dominant the person only has to inherit one dominant allele to have the genetic disorder. Polydactyly where baby born with extra finger or toe can be passed on by one parent who has the allele. If reccessive must inherit two. Cystic fibrosis caused by recessive allele affects cell membranes and causes the production of mucus can affect several organs lungs and pancreas. Can be given by two parents who don't have the disorder, parents are described as carriers of the allele. |
| Genetic disorders | If a parent is heterozygous for polydactyly each child has a 50% chance of inheriting the disorder. both parents are heterozygous for cystic fibrosis each child has a 25% chance of inheriting the disorder. Outcome of genetic crosses can be shown on a Punnet square |
| Stem cells and embryos- science and ethics | Adult stem cells bone marrow cells useful in treating some disorder like leukaemia. doctors have investigated the use of embryonic stem cells which have the potential to differentiate into a wide variety of cells. Can be taken from spare embryos from IVF, created from adult cells, or taken from the unmbilical cord. embryonic stem cells could be used to grow nw tissues and organs for transplants. Embryos have potential to be babies and are destroyed, the embryo cannot give permission and research is expensive so some people have concerns about the use use of embroys because research is experimental. Embryo screening involves test to diagnose disorders before the baby is born. Results of test may give parents choices, sometimes parents decide to terminate the pregnancy other parents may so unethical but can prepare for the delivery of an affected baby. In IVF embryos are screened and only healthy embryos are implanted into the mother, embryos carrying faulty genes are destroyed and some people thinki this is unethical. |
| Origins of life on Earth | Believed that the Earthis about 4500 million years old and that life began about 3500 million years ago. Debated whether first life developed due to conditions on Earth or arrived from another planet. Can date rocks fossils found in rocks so can date when different organisms existed. Fossils formed: hard parts of animals that don't decay likes bone, parts of organisms that have not decayed becausesome of the condition for decay are absent, animals preserved in ice. Parts of organisms are replaced by other materials like minerals as they decay. Preserved traces of organisms like footprints, burrows. Most organisms that died do not leave a fossil because conditions not present. many early life forms had soft bodies so few traces left behind. Traces which were left are likely to have been destroyed by geological activity like earthquakes. |
| Exploring the fossil evidence | Fossil record in incomplete but we can learn a lot about fossils which exist. Some organisms have changed a lot over time. Some changed little while others become extinct-A species which once existed has completelyy died out. Causes of extinction: a new disease, environment changes for geological reasons, new predator evolve or introduced, new competetitor evolve or introduced, single catastrophic event destroying habitat massive volcanic erupton, natural changes in species occuring overtime. |
| More about extinction | Biggest influences on species survival are changes in the envionment, climate change important influence in determining which species survive, for example if too cold could be insufficient food or too cold to breed. Fossil evidence shows that there have been mass extinctionn on a global scale. Many species died out died out in a period of several million years short geological time. Caused by catastrophic evnt or environment change following collision with giant asteroid and Earth. |
| Ideas on why dinosaurs became extinct | Nobody knows for sure: Collision of a great asteroid causing huge fires, earthquakes, landslides and tsunamis. Dust which rose masked the Sun causing darkness and lower temperature, plants could not survive and temp fell. Extenction was a slower process due to sea ice melting and cooling the sea temp by about 9'c therefore less plankton less food available |
| Isolation and evolution of species | New species can arise from existing species if a group becomes isolated from the rest. Geographical isolation could occur if an island seperates from the mainland or if a new river sepertes two areas. Mountain ranges and old craters can isolate organisms. Organsims in isolated condition may be exposed to different environmental conditions, food availabilty or predators. Natural selection will occur in both areas, but different charactreistics will be beneficial in the two population. If populations brought together and cannot interbreed say belong to two differnt species. |
| Speciation | New species can occur following separation of two populations. Each population has a wide range of alleles that control their characteristics genetic variation. Natural selection wil occur in each population, alles that control the charcteristics which help the organism to survive will do so and breed. if environment, competitors, food supply and predators are different for each population they will evolve differently. Speciation has occured whent the two population can no longer successfully interbreed. |
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