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Organisms and Experiments Name Illustration Comments and common experiments This is a tiny beetle, easily reared in flour and with a short life cycle of only 7-12 weeks. Experiments: population growth; competition; genetics. Tribolium flour beetle Easily found in damp leaf litter. Experiments: taxis (behavioural response)/food choice typically using choice chambers. Woodlice various species Daphnia water fleas Easily purchased from pet shops where they are used as fish food. Experiments: examining factors affecting feeding rate or heart rate e.g. nicotine. Lemna duck weed Common plants on slow moving water and ponds. Easily reared in the laboratory in small containers e.g. Petri dishes or old 35mm film containers. Capable of rapid growth. Experiments: examining factors affecting population growth such as competition, space, availability of a range of different nutrients and toxicity testing. Seeds various species Experiments: examining factors that affect the distribution of seeds by air or animals or factors affecting the germination of seeds such as salinity, inhibitors etc. Artemia brine shrimp Brine shrimp are easily reared in laboratory conditions. Eggs can be obtained from most aquarium shops where they are used as fish food. Experiments: see the British Ecological Society guide. Hydra Hydra is a little bit harder to keep in a lab. Experiments: examination of factors that affect their feeding behaviour and growth. Hydra will feed on Daphnia and brine shrimp. Hydra eating brine shrimp Arabidopsis thaliana thale cress This tiny plant, a rapid-cycling Brassica (cabbage) can complete its entire life cycle in just six weeks. It is used extensively as a model organism by biologists and the entire base sequence of its genome has been established. Experiments: a very large number of experiments is possible. A good starting point would be to look at the Science & Plants for Schools (SAPS) website for further guidance. 1 Organisms and Experiments Name Saccharomyces cerevisiae yeast Illustration Comments and common experiments Yeast has been used since ancient times in baking and brewing. It is one of the most intensively studied eukaryotic model organisms. It can be grown in a sugar solution where it grows rapidly producing ethanol and CO2. Experiments: examining the effect of pH, temperature, different types/concentrations of sugar on growth. Lumbricus terrestris earthworm Locust Fly larvae Earthworms can be easily obtained by digging in damp fertile soil. Experiments: the dorsal blood vessel can easily be seen under a binocular microscope and the contraction rate measured in various conditions. Locusts can be obtained from most pet shops. Experiments: often used to examine the ventilation rate in different gas environments. Easily purchased from most fishing shops in large numbers. Experiments: the larvaeās sensitivity/response to light, temperature, food, etc. This would fit in well with the A2 topic that deals with forensics. Fruit various species Experiments: fruit produce a hormone called ethylene that is a gas. This hormone has several effects including that of ripening fruit. Pectinase enzyme breaks down fruit cell walls in ripening. Damage to fruit causes browning as phenolic compounds are released. See the Science & Plants for Schools (SAPS) website for more details. Drosophila fruit fly Drosophila has been the standard experimental organism for geneticists for a long time. They can be obtained from suppliers although they can be expensive. However, they can also be found around any over-ripe fruit in the wild. Experiments: genetic experiments would be the most obvious although there are others. However, care would have to be taken to make sure the experiment fits the A-level specification. Homo sapiens Humans In theory, readily available; however, it is not always easy to obtain enough of them for a suitable sample size. There are usually ethical issues to be considered here: generally people are not enthusiastic about giving up limbs or fingers for the sake of improving your A-level practical, unlike plants which rarely protest. Experiments: common experiments include looking at the effect of exercise on breathing rate, factors affecting reaction time, eyes and perception. 2