School Science Lessons
Biology experiments
Updated: 2010-01-26
Biology names
Table of contents
9.205 Levels of organization 1
9.1.0 Study animals
9.2.0 Study populations
9.3.0 Study communities and ecosystems
9.4.0 Levels of organization 2
9.205 Levels of organization 1
1.0 Kingdom Protista (Protoctista), heterotrophic protists
9.0.2 Division Chromista, heterokonts, haptophytes, cryptomonads
9.0.3 Phylum Heterokontophyta
9.0.4 Phylum Haptophyta
9.0.5 Phylum Cryptophyta
9.0.6 Phylum Dinoflagellata
9.0.7 Phylum Apicomplexa
9.0.8 Phylum Ciliophora, ciliates
9.0.10 Phylum Percolozoa
9.0.11 Phylum Actinopoda, radiolarians
9.0.12 Phylum Foraminifera,
9.0.13 Phylum Cercozoa
9.0.14 Phylum Rhodophyta, red algae
9.0.15 Phylum Glaucophyta,
9.0.16 Phylum Amoebozoa, (Phylum Rhizopoda)
9.0.17 Phylum Myxomycota, Class Mycetozoa  Myxomycetes
9.0.18 Phylum Choanozoa
9.0.19 Phylum Metamonada
9.0.20 Phylum Acrasiomycota, Kingdom Discicristates, Family Acrasiomycetes
9.1.0 Study animals
9.1.1 Birds
9.1.2 Chickens and chicken hatching
9.1.3 Sea animals and fish
9.1.4 Insects
9.1.5 Earthworms and flatworms
9.1.6 Amphibians and reptiles
9.1.7 Mammals
9.1.1 Birds
2.1 Bird feathers (Primary)
2.2 Bird sounds (Primary)
2.3 Bird beaks and feet (Primary)
2.4 Different birds (Primary)
2.5 Protect our birds (Primary)
2.6 Care of birds (Primary)
Duck Project
9.1.2 Chickens and chicken hatching
9.11 Study an unfertilized chicken egg
9.12 Make a cardboard box incubator
9.13 Make a Styrofoam cool box incubator
9.14 Study the development of the chicken embryo
9.15 Measure the eggs
9.16 Make a warm brooder
9.17 Study the development of the hatched chickens
9.18 Find the sex of the chickens
6.3 Chicken life cycle (Primary)
Chicken Project
9.1.3 Sea animals and fish
5.1 Sea animals and plants (Primary)
5.2 Protect sea animals (Primary)
5.3 Corals and jellyfish, coelenterates (Primary)
5.4 Shellfish, molluscs (Primary)
5.5 Starfish, echinoderms (Primary)
5.6 Fish life cycle (Primary)
4.3 Parts of a fish (Primary)
5.7 Food chains in the sea (Primary)
9.1.4 Insects
9.19 Insect collecting net, air net
9.20 Insect collecting net, sweep net
9.21 Insect-killing container
9.22 Insect stretching board
9.23 Mounting boxes for insect collections
9.24 Make a mounting block guide
9.25 Make a simple insect cage
9.26 Make an insectarium
9.27 Keep a diary of insect behaviour
9.28 Collect night insects
9.29 Insect collector
9.7 Butterfly life cycle
9.8 Mosquito life cycle, Culex
9.9 Body of cockroach or grasshopper
9.34 Ant study
9.34.1 Flying ants and termites
9.35 Cultures of fruit flies
9.1.7 Honeybee body structure, Apis mellifera
9.1.5 Earthworms and flatworms
9.33 Earthworm behaviour, Lumbricus
9.36 Flatworm behaviour, Dugesia, Planaria
9.1.6 Amphibians and reptiles
4.4 Frog life cycle (Primary)
4.5 Lizards and snakes (Primary)
6.2 Protect our turtles (Primary)
9.1.7 Mammals
9.30 Simple animal traps
9.31 Cages
9.32 Food and water
4.6 Care of dogs (Primary)
3.6 Care of cats (Primary)
6.4 Pig life cycle (Primary)
Cattle Project
Goat Project
Pig Project
9.2.0 Populations
9.204 Yeast population, bakers' yeast Saccharomyces cerevisiae, Phylum Ascomycota
9.205 Sampling yeast populations
9.206 Find wild yeasts in flowers
9.29 Human population growth
9.3.0 Communities and ecosystems
9.34 Establish an artificial community of aquatic organisms
9.35 Succession in a pond community, hay infusion cultures
9.36 Rotting log community
9.37 Desert community
9.38 Meadow community
9.39 Forest floor community
9.40 Pond ecosystem
6.1 Food chains in the forest (Primary)
3.32 Soil animals (Primary)
5.32 Protect our mangroves (Primary)
6.29 Protect our coral reefs (Primary)
9.5.0 Sense-organs
1.15 Our five senses (Primary)
9.5.1 Ears and hearing, balance
1.16 Hearing sounds game (Primary)
4.101 The ear and hearing
9.247 Direction of sound heard
26.6.0 Ear, voice, hearing, voice, audible limits
9.5.2 Eyes and sight
2.17 Move our eyes (Primary)
5.19 Test our eyesight (Primary)
6.15 How far you can see? (Primary)
9.248 Distance of object seen
9.250 Test our eyes
28.12.0 The eye, structure and physiology (physics)
9.5.3 Nose and smelling, taste
2.18 Smelling game (Primary)
9.245 Sense of smell, the olfactory system
9.246 Sense of taste, the gustatory system
9.5.4 Touch and feeling
1.17 Touch and feel game (Primary)
1.18 Feelie bag game (Primary)
9.243 Sense of touch
9.244 Sense of feeling temperature
9.5.5 Voice and speaking
4.102 The voice and speaking
26.6.0 Ear, voice, hearing, voice, audible limits
9.6.0 Nervous system
4.22 Memory game (Primary)
4.23 Test our reflexes (Primary)
4.24 Speed of reaction (Primary)
9.249 Test the reaction distance
9.251 Test the reflexes
9.252 Memory game
9.4.0 Levels of organization 2
Life can be understood as a natural order of living things, groups of living things, and parts of living things. Organisms are individual life forms, e.g. a dog, tree, fish, earthworm, mushroom, or yeast cell. At both the upper level of organization, the biosphere, and the lower level, the possibility of another level of organization is uncertain. Students will study life most frequently at the central levels of organization, near the level occupied by organisms.
Conceptual scheme:
Group of organisms:
1. Biosphere
2. Biome
9. Community
4. Population
5. Organism
6. Organelle
Parts of organisms
7. Macromolecule, e.g. chlorophyll
8. Molecule
9. Atom
10. Atomic particle
Higher levels of organization
1. Population: A group of organisms comprising all of a particular kind is called a population. A sub population refers to the space that it occupies. For example, one may refer to the snail population in a classroom aquarium, or the population of that kind of snail in a pond. If no space is mentioned, it is assumed that the population consists of all snails of that type in the world.
2. Community: Populations do not exist in isolation. They are commonly found in an environment that they share with other populations. All the populations within a defined space form a community. A lake community consists of all the plant and animal populations found in the lake. The populations found in school grounds would be a community.
9. Biome: Certain large areas of the earth contain communities that are similar. This collection of similar communities is called a biome. A biome may occupy a large portion of a continent. For example, a grassland biome is found in the central portion of North America or inland Australia. Climate and topography are uniform across a biome.
4. Biosphere: Life on the earth is normally found within a few metres of the surface. This hollow spherical space is the biosphere. It contains all life on the planet.
Lower levels of organization
5. Organ systems: Animal organisms contain systems of organs that do vital functions, e.g. the circulatory system.
6. Organ: Most plants and animals contain basic structures called organs that in turn are composed of tissues, e.g. heart, leaf, lung, root. Simple plants and animals may not have distinct organ systems.
7. Tissue: A tissue is a group of similar cells that do a single function, e.g. muscle tissues are composed of cells that can contract and produce the "pull" of the muscle. Some organisms are composed of tissues, but do not have organs.
8. Cell: Tissues consist of individual units called cells. The cell is the fundamental unit in most organisms. Cells vary considerably in size from the largest, an ostrich egg, to one of the smallest micro-organisms. Cells vary in their function and degree of specialization. Organisms composed of a single cell are called unicellular organisms.
9. Organelle: Cells contain parts called organelles that you can easily see with a light microscope, e.g. the nucleus. The electron microscope allows study of the structure of organelles.
10. Macromolecule: Organelles are composed of large molecules, macromolecules, e.g. proteins, lipids (fats and oils) and nucleic acids (DNA and RNA).
11. Molecule: Macromolecules are long chains of linked individual molecules. A molecule is the smallest possible piece of a substance that retains the properties of the substance. Molecules are composed of atoms joined or bonded together. An atom is the smallest part of an element.
12. Atomic particle: Atoms are composed of fundamental particles, e.g. protons, neutrons, and electrons. This is the present limit of understanding of organization at the lower level.
9.0.2 Division Chromista, heterokonts, haptophytes, cryptomonad
9.0.3 Phylum Heterokontophyta
Class Bacillariophyceae, Diatomophyceae, diatoms, Arachnoidiscus ehrenbergi
Diatoms are unicellular microscopic with a silica wall and occurs as plankton and fossil forms, e.g. diatomaceous earth. The word diatom means cut in two.
 Class Chrysophyceae, Chrysophyta golden algae golden-brown algae Ochromonas, Dinobryon, Chrysamoeba
Class Chytridiomycetes (Phylum Chytridiomycota) chytrids, Algae: Heterokontophyta zoosporic fungi, aquatic fungi
Class Dictyochophyceae, Actinochrysophyceae, Silicoflagellates, Dictyocha
Class Eustigmatophyceae, Nannochloropsis
Class Hyphochytridiomycetes (Phylum Hypochytridiomycota)
Class Phaeophyceae, phaeophyta, brown algae, rock weed, kelps Macrocystis, Sargassum
Class Raphidophyceae, red tides
Class Xanthophyceae yellow-green algae
Class Opalinea Opalina in frogs, Protoopalina
Class Oomycetes (Phylum Oomycota) water moulds, rusts, Phytophthora infestans causes potato blight, Phytophthora ramorum causes oak blight, downy mildews damage grapes, Pythium, Aaprolegnia, Achyla
9.0.4 Phylum Haptophyta, algal blooms
9.0.5 Phylum Cryptophyta, Class Cryptophyceae, Cryptomonas
9.0.6 Phylum Dinoflagellata, dinoflagellates, red tides
9.0.7 Phylum Apicomplexa, sporozoans, Babesia causes Babesiosis, Plasmodium causes Malaria, Cryptosporidium causes Cryptosporidiosis, Toxoplasma gondii causes Toxoplasmosis
9.0.8 Phylum Ciliophora, ciliates, Paramecium, Tetrahymena, Balantidium, Vorticella
9.0.9 Phylum Euglenozoa, (Phylum Sarcomastigophora) Euglenophyta, Euglenoidea, euglenoids, Euglena, Peranema, Phacus, Trachelomonas, Trypanosoma brucei causes African sleeping sickness, Trypanosoma cruzi causes Chagas disease in South America, Leishmania causes leishmaniasis, Giardia lamblia causes diarrhoea, dehydration
9.0.10 Phylum Percolozoa Naegleria fowleri
9.0.11 Phylum Actinopoda, radiolarians, plankton, shells form geologic beds
9.0.12 Phylum Foraminifera, shell form limestone rocks, White cliffs of Dover, England
9.0.13 Phylum Cercozoa, amoeboids and flagellates, Euglypha, Trinema, cabbage club root fungus Plasmodiophora
9.0.14 Phylum Rhodophyta, red algae, used to make agar, dulse, nori, carrageenan, Gracilaria, Palmaria
9.0.15 Phylum Glaucophyta, Cyanophora, Glaucocystis
9.0.16 Phylum Amoebozoa Phylum Rhizopoda, Amoeba, Entamoeba histolytica causes amoebic dysentery (amoebiasis) blood in stools, peritonitis (Entamoeba has no mitochondria.)
9.0.17 (Phylum Myxomycota), Class Mycetozoa  Myxomycetes (acellular or plasmodial or coenocytic slime moulds) unit is a plasmodium, Stemonitis, Physarum polycephalum
9.0.18 Phylum Choanozoa Proterospongia
9.0.19 Phylum Metamonada, have no mitochondria, Giardia lamblia causes "beaver fever", Trichomonas vaginalis causes trichomoniasis, Trimastix
9.0.20 Phylum Acrasiomycota, Kingdom Discicristates, , Family Acrasiomycetes, (cellular slime moulds) cause powdery scab on potatoes
9.29 Human population growth
Compare the results obtained with yeast populations with a curve of human population growth. If a microscope is not available for yeast cell counting, compare daily counts of fruit flies or another available population that grows rapidly.
Let b = birth rate, d = death rate, and r = rate of natural increase. So if birth rate is 14 per 1000 per year and death rate is 8 per 1000 per year, the rate of natural increase is 6 per thousand, 0.6%. In February 2008, the total human population was estimated at almost 7 billion, 7 000 000 000. However, the rate of increase has declined since the 1963 peak of 2.2% per year.
In 1798, the Rev. T. R. Malthus (1766-1843) published a famous "Essay on population" which included the idea that population tends to outrun the means of subsistence. He advocated late marriage and sexual continence to control the increase of population. However, he may not have realized that the apparent increase in population was influenced by the decrease in death rate. Nowadays, an important factor in population growth is that people in developing countries are living longer.
9.34 Establish an artificial community of aquatic organisms
See diagram 9.37: Daphnia | See diagram 9.39.1d: Algae
1. Study communities. A grouping of populations in a particular location is called a community. Typically, communities consist of plants and animal populations that perform certain roles. Some populations are the producers. They are so called because they can trap energy from sunlight and producing food. Populations that feed on other living populations are called consumers. Those populations that feed on dead material are called reducers, since they disorganize organic matter to yield simpler chemical substances.
2. Establish natural communities. Use a closed plastic container or a fish tank with a glass lid so that only light can enter. Seal the lid with melted wax. Submerge the container in water to show that the system is not open to air. Try to create a balanced community so that the different kinds of organisms survive for a long time. Select a community to enclose, e.g. a square spade width of your garden or lawn, a forest floor community, ferns and liverworts, a dead animal, a rotting log, water from a pond.
3. Study living things both in the classroom or laboratory, especially aquatic plants and animals by making an aquarium for aquatic organisms. Make it ready in advance, so that you may put samples taken from a visit to a pond or stream in it upon our return.
4. Jam container aquarium: Use a large glass tank for a simple aquarium if it is well stocked with submerged water plants to aerate the water, e.g. Elodea or Myriophyllum. Use a jam container for keeping caddis larvae, pond snails, small crustaceans and plants. The pond life will remain balanced if carefully stocked. Feed Dytiscus beetles or other predacious larva on tadpoles and keep in a separate tank. Use 3 cm clean sand to provide hibernating quarters for the caddis flies at the bottom of the container, and attach a muslin cover to ensure that the caddis flies do not escape. Record egg laying, other changes, and habits. Use a strainer or net to collect aquatic specimens. Do not put an aquarium in direct sunlight because excessive light produces a heavy growth of algae on the glass walls that obscures the contents of the aquarium. Wipe off algae growths with an abrasive dish cloth.
5. Large aquarium: Find fine silt from the bottom of a clear stream or pond and wash it carefully in running water. Use it to cover the floor of the aquarium to a depth of 3 cm. Plant water plants and weigh down the roots with stones. Add coarse sand, gravel and stones for hiding places. To reduce cloudiness, fill with a slow stream of water falling on a sheet of cardboard and leave to stand for a day or two until clear. Then plant washed water plants. If many waterweeds are present aerating by pumps is not needed. Add live food, e.g. Daphnia, and snails to keep the glass clean. Very little feeding will be necessary. Fish will eat the snails' eggs and small water organisms introduced with the water plants. If worms are used as food, add them only once a week. Cut them in pieces small enough to eat. Remove food not consumed immediately or fungi will grow and infect the fish. Cover the aquarium with a glass plate to keep out dust. If frogs or newts are kept, put in a floating piece of cork to sit on.
9.35 Succession in a pond community, hay infusion cultures,  closed community
See diagram 9.38: Amoeba, Paramecium, Euglena
1. Put dry grass in boiled water in two sealed containers. Keep one container in the light and the other in the dark. Examine the container daily with the eye, with a magnifying glass and examine a water sample with a microscope. At first see bacteria, later ciliated protozoa and later rotifers, nematodes and crustaceans. Note the disappearance of populations and the appearance of new populations. Compare gross changes seen with the eye to the changes seen with the microscope.
2. Use the hanging drop technique. Dip the open end of a test-tube in petroleum jelly to make a ring on the centre of a microscope slide, slightly smaller than the size of a coverslip. Put the sample drop of water on the centre of the coverslip. Pick up the coverslip and invert it so that the drop hangs down. Lower the coverslip over the microscope slide so that the petroleum jelly supports the coverslip. Examine the contents of the hanging drop with low power.
3. To culture pond organisms, dissolve 1/2 teaspoon of bakers' yeast in 1 litre of boiling water and add some vegetable, e.g. peas. Inoculate the solution at room temperature and keep in indirect sunlight.
4. Combine or average the data derived from a ten day population growth study and graph the results for the entire class. (Remember that the two-day-old culture was started on the eighth day!). Compare the results obtained with yeast populations with a curve of human population growth. If a microscope is not available for yeast cell counting, compare daily counts of fruit flies or some other available population that grows rapidly.
9.36 Rotting log community
See diagram 9.36.2: Rotting log community
Break open a rotting log with a trowel, put two or three chunks into a plastic bag, and take them back to put in the terrarium. Construct a terrarium from an aquarium with a cloth cover. No soil is needed. If the log was in a damp place, add water to the terrarium from time to time. Many creatures may live in the log including ants, termites, spiders and horned beetles. If the log contains ants, provide a few crumbs and sugar water on a piece of sponge for them. To keep the ants from crawling out of the terrarium, spread a layer of Vaseline along the upper edge. Water to see what kinds of insects and other animals come from the log. Some may be eggs when you collect the log and may develop into adults while in the terrarium.
9.37 Desert community
See diagram 9.36.3: Desert community
Get sand from a beach or garden supply store. Some kinds of desert animals, including horned lizards, can be found in pet shops. The lizards will eat small insects, e.g. ants and meal worms, available from pet shops. Get small cacti and other succulents, which are plants that hold water in their fleshy leaves. Put rocks in the terrarium, making cliffs or overhangs near the edges. Put a small dish of water in one corner. Leave an open area of sand in the centre, especially if you have a horned lizard. Keep the temperature of the desert terrarium between 20oC and 27oC.
9.38 Meadow community
See diagram 9.36.4: Meadow community
Use only few of the grasses, weeds, seedling trees, and other plants that grow in meadows. Choose from the many animals. Orb spiders need lots of room to make their webs, e.g. a 50 litre aquarium tank. Find plants with insect eggs or cocoons on them and watch them to see what hatches. A small snake will eat earthworms and large insects but keep the terrarium dry because snakes often get skin diseases if kept in damp surroundings
9.39 Forest floor community
See diagram 9.36.5: Forest floor community
This is the kind of habitat most often modelled in a terrarium. For plants, obtain small ferns, tree seedlings, wildflowers, and especially evergreen plants, e.g. partridge berry or wintergreen. Put a few of these plants into the soil and cover the rest of the surface with mosses, attractive stones, and perhaps a small limb. For animals, look for small toads, frogs, e.g. cricket frogs or tree frogs, and red newts, small salamanders. These animals and the plants of the forest floor all need moisture, so keep the terrarium watered and make a small woodland pool in one corner.
9.40 Pond ecosystem
See diagram 9.36: Pond ecosystem
An ecosystem is the living community plus the non-living surroundings. An ecosystem is studied by observing and measuring relationships between its various subsystems. For example a pond community contains a great variety of plants (producers) animals (consumers) and decomposing micro-organisms (reducers). Observe the feeding habits and dissect organisms' stomach contents to understand the food chain in the ecosystem without destroying the ecosystem being studied. Beware of using inference instead of direct observations. The presence of a frog and a bee in the pond ecosystem may to the conclusion that a link on the food chain is bee to frog. However, the bee may not be eaten by frogs and would never appear in the frog stomach contents.

9.243 Sense of touch
See diagram 9.243: Touch with dividers
1. Meissner corpuscles are just below the epidermis of the skin and are sensitive to light touch. They occur mainly in the face, fingertips, genitals, lips, palms of hands, soles of feet, and tongue. Merkel nerve endings are in superficial skin layers and fingertip ridges and are sensitive to pressure. Pacinian corpuscles are deep in the skin, in mesenteries (membranes connecting the small intestine to the posterior wall of the abdomen) and around joints and detect vibration and big pressure changes. These mechanoreceptors are not uniformly distributed in the skin, so some parts of the body are more sensitive to touch than others. When the skin is touched in two separate points within a single receptive field, the student will be unable to feel the two separate points. If the two points touched span more than a single receptive field then both will be felt. The closer the receptive fields, the greater the resolution of touch. So mechanoreceptors are more dense in the fingertips and less dense in the palms of the hands.
2. Investigate the sensitivity to touch of different parts of the body. Tie a blindfold over the eyes and touch objects with the fingers, e.g. table top, coins, cup, pins, clothing. Describe the feelings. Repeat the experiment by touching the same objects with the back of the hand. Describe the feelings and whether they are the same as before.
3. Tie a blindfold over the eyes and ask another student to touch gently different parts of the back of the hand with a touching bristle. Note when and where you feel the touching bristle. Repeat the experiment on the end of a finger and on the bare forearm. Do not test on other parts of the body.
4. Use a pair of dividers with the points 40 mm apart or the points of two pins or two hairs. Tie a blindfold over the eyes and ask another student to touch gently different parts of the back of the hand with only one point or with both points. Point to where the body was touched and say whether it was one point or two points. Repeat the experiment by reducing the distance between the points of the dividers. Note the distance between the points when a touch with both points feels like a touch with only one point. When the points touch close together, they feel like one point. Repeat the experiment on the end of a finger and on the bare forearm. Do not test on other parts of the body.
9.244 Sense of feeling temperature
See diagram 9.244: Feeling temperature
Fill three containers with water at 10oC, 20oC and 30oC. Put the containers in one line on the table. Dip the left hand in the water at 10oC. Dip the right hand in the water at 30oC. After two minutes, take both hands out of water and dip them simultaneously in the middle container 20oC. Compare the temperature sensations of the right hand and by the left hand. You do not have an absolute sense of temperature.
9.245 Sense of smell, the olfactory system
See diagram 1.13: Smelling technique
Do not inhale gases directly from a test-tube. Fan the gas towards the nose with the hand and sniff cautiously. If you detect no odour, move closer and try again.
1. The olfactory neuroepithelium is located at the upper area of each nasal chamber. As humans age, the number of olfactory neurones steadily decreases. The sense of smell is caused by stimulation of the olfactory receptor cells by volatile chemicals carried as airborne molecules. An odour's stimulating effectiveness depends on the duration, volume, and velocity of a sniff. Each olfactory receptor cell is a sensory neurone. The average nasal cavity contains more than 100 million sensory neurones generated throughout life by the underlying basal cells. So new receptor cells are generated every 30-60 days. Humans have many hundreds of different olfactory receptors, but each neurone expresses only one receptor type, part of an olfactory "map". An odour activates a set of odour receptors depending on its chemical composition. The vomeronasal organ (VNO) (Jacobson organ) is a membranous structure within pits of the anterior nasal septum. Its opening 2 cm from the nostril is visible in nearly all adult humans. It detects the external chemical signals called pheromones but these signals are not detected as perceptible smells by the olfactory system. Pheromones send messages to all individuals in the species to mediate behaviour, e.g. alarm, food trail for ants, sex responses and possibly synchronization of menstrual cycles among women living together.
2. Pour 1 cm of methylated spirit into a small beaker. Hold the beaker under the nose and note the smell while breathing:
2.1 without inhaling,
2.2. inhaling steadily,
2.3. inhaling with jerky sniffs.
Repeat the experiments with different foodstuffs.
3. Repeat the experiment with one nostril closed. Note whether both nostrils give the same smell sensation.
4. Test the ability to detect the smell of baby powder, chocolate, cinnamon, coffee, mothballs, peanut butter, soap, banana, petrol (gasoline) lemon, onion, paint thinner, pineapple, rose, and turpentine
5. Collect different substances that have different kinds of smell. Be careful! Do not let students smell volatile liquids, e.g. petrol, methylated spirit, alcohol, pesticides, correcting fluid and dry-cleaning fluid. A description of smells may include the following: "fruity" from ripe fruit, "fragrant" from flowers and perfume, "onion" from onion or garlic, sulfur from sulfur or volcanic gases, "burning" from burning meat or coffee or tobacco, "burning feathers' from feathers or silk or wool or rubber or hair, "sweaty", from sweat, old cheese, and goats, "foul" from rotten meat, rotten vegetables and faeces. Repeat the experiment with the students blindfolded.
9.246 Sense of taste, the gustatory system
See 12.3.1: Taste of acids | See 19.3.1: Taste, smell, flavour
1. Taste perception occurs in individual taste buds with multiple receptor cells in each bud. Taste buds are modified epithelial cells, with a life span of about 10 days and arise continuously from the underlying basal cell layer. So if you burn your tongue new taste buds can later replace any damaged taste buds. Taste buds occupy projections embedded in the tongue epithelium called lingual papillae. A single nerve fibre innervates multiple taste papillae. A single nerve fibre can respond to different types of tastes, called "broad tuning". Lingual papillae have 4 forms, each in different areas of the tongue. Taste buds also occur in the soft palate, epiglottis and larynx, and the pharynx.
2. The five different taste qualities are salty, sweet, sour, bitter, and umami (monosodium glutamate). There are no "taste areas" on the tongue. The five taste qualities can be detected in all regions of the tongue, but certain areas of the tongue have lower thresholds for each quality. Sweetness is most readily detected at the tip of the tongue. Salty taste receptors focus on the front and side borders of the tongue. Sour tastes are best perceived along the lateral border, and bitter sensations are tasted most in the posterior one third. Another proposed taste quality is chalky (calcium salts). Salt taste is caused by sodium ions and sour taste is cause by hydrogen ions in solution. Sweet taste, bitter taste and umami taste is caused by reactions with proteins on the surface of the taste buds.
3. Never taste a chemical or any substance in the laboratory! Crush different fruits and vegetables into a pulp using a food chopping mill. Tie a blindfold over the eyes, taste the different foods and record the tastes in order of tasting. Repeat the experiment while holding your nose and breathing only through the mouth. Taste the different foods and record the tastes in the same order of tasting. If the nose is held tight, no air can move through the nasal space and you cannot smell anything. You may notice that different foods taste the same when you have a cold. Flavour is a mixture of taste, smell and feel of the food in the mouth.
4. Report on the taste sensations of your tongue. Dry the surface of the tongue with a clean handkerchief, stretch it out as far as possible and look at the tongue with a mirror to note the many taste buds. Describe the taste sensation after you place on different parts of the tongue a drop of the following:
4.1 dilute solution of sucrose, saccharin or aspartame for sweet taste,
4.2 dilute vinegar solution for sour taste,
4.3 dilute table salt solution for salt taste,
4.4 dilute quinine solution (tonic water) or raw almond for bitter taste
4.5 dilute solution of the amino acid monosodium glutamate, MSG, for "umami" taste.
You can experience all the qualities of taste in all regions of the tongue where taste buds occur. Some people experience differences in sensitivity and people may vary in the number of taste buds in different regions of the tongue.
5. Put a drop of boiled starch solution on your tongue and let it mix with the saliva. Leave it there until you can notice a slight change in taste. The saliva contains an enzyme ptyalin that changes starch to maltose sugar. It causes the sweet taste. Repeat the experiment with a piece of raw meat and a piece of pure fat. You do not notice any change of taste because ptyalin does not act on protein or fat.
9.247 Direction of sound heard
All students form a large circle. One student stands in the middle of the circle with a blindfold tied over the eyes. Each student in the circle claps once, one at a time, in any order. After each clap, the blindfolded student turns in that direction with one arm extended. Record the number of successful turns and their direction relative to the direction at the time of the clap. Repeat the experiment with the right ear of the blindfolded student blocked with cotton wool and with the right index finger pressed into that ear. Repeat the experiment with the student's left ear blocked with cotton wool and the left index finger pressed into that ear. Record the number of successful turns and their direction relative to the direction at the time of the clap. Examine the records and describe the necessary conditions to tell the direction of sound correctly.
9.248 Distance of object seen
1. Hold a pencil in each hand horizontally in front of the face with the points of the pencils 50 cm apart. Move the pencils towards each other so that the points touch. Repeat the experiment with the right eye closed. Repeat the experiment with the left eye closed. Describe the necessary conditions to tell correctly the distance of objects.
2. Look outside the classroom at something far away. Hold up one finger 20 cm in front of the eyes but keep looking at the distant object. Note whether you can see the distant object clearly. Note whether you can, at the same time, see the finger clearly. Note whether you feel any movement in your eyes. Keep looking at the finger and note whether the distant object is clear.
3. Hold a printed page at arms length. Bring the book closer and closer until it is too close to read the letters. Measure the distance from the book to the eyes. Move the book away from the eyes until it is too far to read the letters. Again, measure the distance from the book to the eyes.
4. Work in pairs. One student in a pair puts a hand over one eye. The other student holds up one finger about 40 cm in front of the partner's eyes. The student with one eye covered has to place the tip of one finger on top of the finger that the partner is holding up. Repeat the experiment with both eyes open.
9.249 Test the reaction distance
See diagram 9.249: Dropping the ruler
1. Hold the end of a ruler so that it hangs down vertically with the zero in line with the thumb of an outstretched hand. Drop the ruler through the space between the thumb and fingers held wide apart. Record the distance that the ruler fell before it was caught. The distance the ruler fell is called the reaction distance, i.e. the length of the ruler that fell between the fingers before it was caught.
2. Use the thumb and index finger to hold the bottom end of a vertical ruler. The zero on the ruler must be in line with the thumb. Open then close the thumb and index finger as quickly as possible. Record the distance the ruler travelled as an indication of the reaction distance.
9.250 Test our eyes
See diagram 28.1.1.6
If sheep eyes are used for dissection, soak them lens down in 1.0% sodium chloride solution before freezing, to avoid lens clouding.
1. Work in pairs. Look at the partner's eyes and identify each part seen.
2. Clap your hands in front of the partner's face. The partner blinks.
3. Tell your partner to watch your finger as you move it towards the nose. The partner blinks. Repeat the experiment by staring into your partner's eyes and trying not to blink. The first student to blink loses the game.
4. Tell your partner to walk slowly around you in a big circle. Follow the partner with your eyes but do not move your head or body. See how long you can keep your partner in sight. Put your hand up when you can no longer see your partner.
4. By moving your eyes only and not your head, note how far you can move your hand up and down in front of your face and keep it in sight.
5. Face your partner with both kneeling on the floor. Put a stone between you on the floor. Cover your right eye with one hand. Test who can pick up the stone first.
9.251 Test the reflexes
1. Work in pairs. Stare into each other's eyes. The eyes blink.
2. Wave your hand in front of the other student's eyes. The eyes blink.
3. Tickle the arch of the foot. The big toe wiggles.
4. Sit on the desk with the knee just over the edge. Let the leg below the knee swing slightly. See the place just below the knee cap. Hit this place sharply with the side of the hand. Leg swings up. This is called the "knee jerk reflex".
5. Kick your toe. The reflex is to shift weight on to the other foot.
6. Stand on one leg. The reflex is to wave your arms to help balance.
7. Hold your breath for a long time. The reflex is to breathe. You cannot stop yourself breathing in.
9.252 Memory game
If the school does not allow playing cards, make memory cards with symbols, e.g. black and white triangles or other symbols.
Spread playing cards face down. The first player turns up two cards, e.g. a 7 and a 10, lets the other players see them, then turns the cards face down in the same places. The second player turns up two more cards, e.g. a king and a 10, then turn the cards face down in exactly the same places. The third players remember where the two tens are and turns them face up. That player wins one point, removes the two tens, and has another go by turning up two more cards. That player first turns up a king but cannot remember where the previous king was, and turns up a jack. Then the fourth player turns up two cards. The game finishes when all the cards have been turned up in pairs. The player who has turned up the most pairs wins. This game is called "Pelmanism".
9.45.7 Diurnal variation on body temperature
See diagram 9.242
Body temperature is an example of a circadian rhythm, regular cyclic activity about 24 hours long and the regulator of the sleep wake cycle. In a healthy person average temperature for healthy adults is 36.3°C to 37.1°C for males, 36.5°C to 37.3°C for females, with the highest temperatures between 6.00 a.m. and 6.00 p.m. and lowest temperatures between 2.00 a.m. and 6.00 a.m. An oral temperature between 35.9°C and 37.5°C is usually considered normal. Body temperature is sensitive to hormone level in the female. Blood vessels in the skin expand to carry the excess heat to the skin surface. Also, evaporating sweat cools the body as sweat absorbs the heat of vaporization. Blood vessels in the skin contract to reduce loss of heat. Also, involuntary shivering, contraction of the muscles, generates more heat. A rectal or ear temperature is 0.3°C to 0.6°C higher than an oral temperature reading. An armpit temperature is 0.3°C to 0.6°C lower than an oral temperature reading. The forehead temperature is the same temperature as the arterial blood supply under the skin. It is said to be more accurate that ear temperature because the position of the probe in the ear canal in sequential readings is usually inconsistent. The forehead thermometer scans the forehead area for the temporal artery by positioning the probe flush on the centre of the forehead, midway between the eyebrow and the hairline. Fever is present if rectum temperature or ear temperature > 38.0°C, mouth temperature > 37.5°C, under the arm > 37.2°C.
A lady on a diet finds that after eating her body temperature drops and she feels very cold. She probably experiences what doctors call a post-prandial effect to a rush of blood to the stomach leaving the skin feeling cool as blood carrying body heat is shunted away from below the skin. So she should eat her meals slowly. Similarly, she should not go swimming straight after consuming a heavy meal because the skeletal muscles may be starved of enough oxygen for rapid contraction to cause cramps and death by drowning.
1. Measure the temperature under your tongue every hour and draw a graph of the results.
2. Note the changes in your body at high ambient temperature
2.1 Capillaries in the skin swell (vasodilation) to release more heat.
2.2 The arrector pili muscles in the skin pull the hairs to make them lay flat down on the surface of the skin and allow air to circulate freely over the skin.
2.3 Sweat glands secret sweat onto the skin surface where the latent heat of vaporization of water is lost.
Animals, e.g. dogs, can lose heat by panting. Can you lose heat by panting?
3. Note the change in your body at low ambient temperature
3.1 Capillaries in the skin constrict (vasoconstriction) to release less heat.
3.2 The arrector pili muscles in the skin pull the hairs up to not allow air to circulate freely over the skin. This action of the arrector pili muscles causes "goose pimples". Animals can increase the thickness of their coats and birds can ruffle their feathers.
3.3 The sweat glands stop secreting and the hypothalamus of the brain sends messages to internal muscles to contract violently and cause shivering. The oxygen consumption increases 2 to 5 times and the internal organs are warmed.
Hypothermia begins when body temperature drops to 35°C when normal metabolism slows until the internal organs no longer function and the person dies.