Studying the environment Key words and terms Population: A group of organisms of the same kind (species) found in a particular area. Community: Several populations living together in a particular place, for example, all the organisms living under a fallen tree. Niche: The position occupied by a particular type of organism within the community. Habitat: The place where the organism lives. Habitats can be either terrestrial on land, or aquatic - fresh water, sea water (marine), brackish water estuaries. Ecosystem: The interaction of living organisms with their environment. Species density: The average number of organisms belonging to a particular species captured in 10 throws of a 1m2 quadrat. Example Quadrat throws: 1 2 3 4 5 6 7 8 9 10 Organisms: 10 5 6 7 10 11 10 13 8 10 Total # of organisms = 90 Density = 90/10 = 9 per m2 Percentage cover: This is used to describe the distribution of organisms whose individual units cannot be easily counted. These include organisms such as grass, lichens and small molluscs on the seashore, such as periwinkles. It is the proportion of a measured ground area covered by that portion of the organism that is above the ground. Estimating populations Not only is it almost impossible to count the total number of individuals in a population, it could also cause unacceptable levels of damage both to the organisms and their habitats. Hence, estimates of population numbers have to be made. which is done by using sampling methods. Example: Quadrat sampling A quadrat is a square of a known area usually 1m, made out of wood or metal. It is most commonly used for estimating the size of plant populations but it can also be used for estimating the size of slow-moving or sessile animals, those on the rocks of the seashore. This square of 1m can be further subdivided into smaller squares (see diagram below). In order for the use of the quadrat to be accurate, certain conditions must be met. These include: The size of quadrat to be used The number of quadrats to be used The placing or positioning of the quadrats At this level of your studies, the third point is the most important of the three. In order to reduce bias, the placing of the quadrats should be done randomly. This can be done by dividing the area to be studied into squares and using random numbers as coordinates, for example, if random numbers three, four are generated, then walking three squares from one corner in a straight line along the edge and then four squares down into the field would indicate the position to place the quadrat. The first of the above two points are usually arrived at by doing computations. Transects Transects are useful for estimating populations where one type of habitat is changing to another, for example, along a shoreline moving from the water unto land. It can also be used to show zonation of species. A transect is a straight line crossing an area recording all the species that actually touch the line as it crosses the habitat. Alternatively, the line can be marked at regular intervals, for example, every 5/10 m and the organisms present at these points recorded. The transect can be formed using a rope or a piece of string or a wire; a rope is more commonly used since it is not only flexible but is also strong. The transect can be converted to a belt transect by placing a second line at a measured distance, usually 0.5m2 from the first. All of the species within the two lines are then recorded. The transect can also be used for the placing of quadrats; these are placed at regular intervals along the line and the species within the quadrats are recorded. For the belt transect, two parallel lines with a predetermined distance between them are set up. Sampling now takes place between the lines. Belt transects provide more information than line transects because they cover a wider area. Their use can be time-consuming, however. Collecting animals Animals are everywhere. They include the more obvious vertebrates and the not-so-obvious invertebrates. Some invertebrates are showy and are seen quite frequently, for example the butterflies. There are some that are also seen frequently, but which we wish we didn't have to see at all, like flies and worms. Others are seen infrequently since they prefer to live their lives hidden from the rest of the world, such as the wood louse, the millipede and the centipede. Wherever these animals are, we would like to know more about them, and in order to do so we will need to get close to them so that we can catch them! How can we do this? Most of these organisms are quite elusive. However, we can catch them if we use the proper pieces of equipment. These pieces of equipment can be homemade and, hence, quite inexpensive, so there is virtually no excuse for you not to do your own study. Using jam jars A jam jar with a cover can be used to capture a sedentary animal or even one that is creeping or crawling. It can also be converted to a trap to capture crawling animals. For the pitfall trap, a hole is dug into the ground and the jar is placed into the hole. The mouth of the jar is covered with a stone in such a way that there are tiny gaps underneath. Animals that walk under the stone will fall into the jar and can then be collected. Depending on how often the bottle is going to be checked, food can be provided for the captured animals. The food can also be used as a lure for the animals. Nets There are two main types of nets. These are the sweep net and the butterfly net. You can easily construct your own net, using a coat hanger and an old stocking or a piece of mosquito netting. Nets are used to catch flying insects or to catch insects that are found in grass or on trees. They are also used to collect aquatic animals. Animals caught in the net are then transferred to jars or pill bottles to secure them. Bags Something as simple as a plastic bag can be used as a collecting tool. Use your imagination to determine how you can get the animal into the bag! Rules for collecting both plants and animals If the plant is in flower, collect one or two of its flowers as well as a small piece of stem with leaves. Use a large spoon to collect soil samples. Scrape off mosses and snails with a knife. Look under fresh and rotting leaves for animals. Look under large stones and rotting wood for animals. Remember to replace these. Put food inside the jars to attract the animals. Keep animals with a piece of the plant on which they were found. This will provide them with food. Keep aquatic animals in a sample of the water in which they were found. Label your containers to indicate where the organisms were found. Handle all animals with care, returning them to their habitat as soon as you have finished studying them. Try to make your study non-destructive. Last week, we began looking at the feeding relationships of organisms in the environment and we stopped our lesson at the definition of the food web. Now we need to look at how the food web is structured. One important point that must always be remembered when constructing a food web is the direction in which the arrows point. The arrows must always point from the producer, that is the plant, to the consumer, that is the animal. Having them point in any other direction will not gain you any marks for your efforts. Look carefully at the drawing of the food web and Notice the following: All the arrows point to the organism that is feeding, that is, away from the organism that is being eaten. The organism at the base of the web on the first line is the plant, that is, the cherry tree. This line represents trophic level #1 and the cherry tree is the producer. All the organisms that feed on the producer are placed on the lines above the producer. The first line represents trophic level #2 and the organisms placed there are the herbivores or primary consumers. From our food web, these are: the caterpillar, the aphid, the stink bug and the moth. The organisms that feed on the primary consumers are placed in a line above the primary consumers. This line represents trophic level #3. These organisms are the secondary consumers. Again, from our food, these are the ladybird beetles. The organisms feeding on the secondary consumers are placed in a line above the secondary consumers. This line represents trophic level #4 and these organisms are the tertiary consumers. These are the bird and the spider. Some organisms can be classified as both secondary and tertiary consumers, for example, the bird is a secondary consumer when it is feeding on the moth and a tertiary consumer when it is feeding on the ladybird beetle. You should also be able to extract several food chains from this food web. Let us do this now. Cherry tree ---> aphidlady ---> bird beetle ---> spider Cherry tree ---> stink bug ---> ladybird beetle ---> bird Cherry tree ---> moth ---> bird We are now going to put our newly gained knowledge to use. In question one (c) June 2009 biology exam, candidates were given the following table and asked to construct a food web with ten organisms. Here is the table: Organism Food Eaten Crab Decaying plant matter Guppy (fish) Mosquito larvae, tadpoles Water bird Guppy, frog, crab Water snail Algae, water weed Mosquito larvae Moss, decaying plant matter Water weed Makes own food Frog Dragonfly, mosquito larvae Tadpoles Water weed What is the first thing that we need to do? Did you answer "Identify the producer/producers?" I hope you did because that is what we must do! The producer has to be first identified since it forms the base of the food web. Let us take a look at the organisms that are included in the table. Notice that the only organism that could meet the requirements of the producer is the water weed since it makes its own food. Notice also that there is mention of other plant material in the table. Some of the organisms feed on decaying plant material and the mosquito larvae also feed on moss; these are also classified as producers. The next level belongs to the primary consumers or the herbivores. Remember these are the organisms that feed on the plant material. From the table we can identify that tadpoles, water snail, crab and mosquito larvae are the herbivores. All of the other organisms in the table are carnivores. These are the frog, the guppy, water bird. Although they are all carnivores, this does not mean that they are all secondary consumers. Notice that the water bird feeds on the guppy which feeds on the tadpole. This makes the guppy a secondary consumer and the water bird a tertiary consumer. Was that confusing? Let us put it in the form of a food chain to make it simpler. Water weed ---> tadpole ---> guppy ---> water bird. There you go, "Do you see it now?" Below is an example of the type of food web that could be constructed. Try to create your own! Good luck! See you next week. Environment and human activities Factors affecting population growth A population is a group of organisms of the same species living in a particular habitat. The following are some of the reasons why individuals live in populations: The habitat provides food, shelter, light or any other factors that might be needed for survival. The organisms can find mates. The organism is afforded some degree of protection from being in a group. How does a population grow? The growth of a population can be measured and the data obtained and be used to plot a graph. The graph obtained is called a population curve. At stage 1, the rate of growth is slow because there are very few organisms of reproductive age present, therefore, very few babies are born. At stage 2, the rate of growth is rapid - the growth at this point is exponential because the birth rate exceeds the death rate. This is facilitated by abundant resources in the habitat. At stage 3, the growth rate slows as the death rate approaches the birth rate. This is accompanied by a corresponding decrease in resources. At stage 4, the growth rate is constant, birth rates are equal to death rates. Many natural populations do not go beyond a certain size due to the impact of biotic and abiotic factors. The following are some of the factors that affect the size of a natural population: Predators If there are many predators present, this leads to the organism being unable to avoid the predators so they are easily captured and killed. This reduces the size of the population. Unsuitable ABIOTIC conditions What are these abiotic conditions? These are the physical conditions that exist in the environment and include: Water - Water is needed for all life to survive. All the metabolic reactions that take place in the animals' cells need water. Organisms that live in areas where water is limited have adaptations that prevent them from losing too much water, thus becoming dehydrated. Temperature - Mammals and birds need to maintain a constant body temperature. The enzymes needed for metabolic reactions can only work at a particular temperature. Extremes of temperature can limit the spread of populations unless they have developed special adaptations. Few animals live outside of the 0ºC - 40ºC range. Poor soil - The soil provides the water, minerals, air for the plants as well as the animals that live in it. Any soil which cannot provide these in the correct proportion is described as poor soil. Unsuitable BIOTIC conditions. Biotic factors are factors caused by other living organisms in the environment. Susceptibility to disease - In a large, closely knit population, introduction of disease-causing organisms can wipe out the entire population as the microbes pass from one individual to another. Competition - Within a population there will always be competition for space, food and mates. Competition lessens the individual's ability to survive and pass on its genes to the next generation. This will cause a reduction in the number of organisms in the population. Individuals within populations have to rely on the resources that are provided by the environment to survive. Let us look at these resources now. Resources and their limits Resources are defined as features of the environment which can be used by humans. These can be classified into two main groups. These are: Renewable and Non-renewable Renewable resources are those that can be reused or replaced in a short period of time. Renewable resources include: Soil - this can be unlimited if it is properly care for and erosion is prevented. Biotic resources - food, trees can also be unlimited if properly managed and cared for. Water - this is renewable as long as pollution is prevented. Non-renewable resources are those which, when used, take many, many years to be replaced. The supply of these is limited. These include: Minerals - once these are removed from the earth they cannot be replaced. Fuels - fossil-based fuels are non-renewable. Reducing resource consumption Non-renewable resources will eventually run out. In order to preserve some for future generations, we need to: Reuse Reduce Recycle all of these resources that are to be found in discarded manufactured materials. These include paper, glass, metals, plastics and textiles. These materials are used in all aspects of life - work, home school and entertainment. The environment and human activities As human consumers, we generate a tremendous amount of waste. A few Sundays ago, one newspaper reported that in Jamaica, five million plastic bottles were disposed of every week and of this quantity only a meager five per cent is recycled; the rest is dumped. This is having a considerably negative impact on our environment, clogging up streams and gullies and landfills. When one considers that it takes 450 years for the decomposition of this type of plastic, the impact becomes even more negative. Let us look at some of the manufactured materials that we use to fuel our consumption. Manufactured material Source Uses paper pulp from wood writing glass molten mixture of soda ash, sand silica and lime bottles, windows, doors, furniture metals iron, gold, tin, aluminum containers, packaging material, cars plastics petroleum bottles, bags, containers, utensils, fibres Some of these materials, when discarded, break down with the help of micro-organisms into harmless forms. These are said to be biodegradable. Organic materials are included in this group. Others, such as plastic bottles are non-biodegradable. They, like the plastic bottles, either take a very long time to break down or cannot be broken down by micro organisms. Non-biodegradable materials cause the accumulation of wastes in the environment, leading to the pollution of both the aquatic and terrestrial environments. Items made from styrofoam and disposable diapers take hundreds of years to decompose. The waste generated by an average household can be divided into the categories shown in the following table. Notice that non-biodegradable waste accounts for over 40 per cent of the waste generated. Waste Percentage (%) organics 26.7 paper 19.7 glass 10.5 metals 10.4 plastics 19.9 textiles 7.3 others 5.5 Faced with this, how can we put the three 'Rs' into action in order to preserve our resources? Do you remember the three 'Rs'? Of course you do. They are reduce, reuse and recycle! Reduce In order to reduce we simply need to change our buying patterns and our lifestyle habits and consume less. Old clothes can be sold or given away, or the material from them can be used to make something else. Give used books and magazines to friends, schools and other institutions. Donate used furniture to children's homes and to people who need it. Cut down on the amount of food that is purchased but not eaten. Refuse to purchase goods with elaborate packaging. In many developed countries, consumers are not allowed to use disposable plastic bags to transport goods that are purchased. This serves to reduce the amount of plastic that would go to landfills. Reuse Some materials can be reused, for example tins, bottles, jars. Others, such as organic waste from kitchens and gardens, can be used to generate compost, a natural organic fertiliser. Recycle This entails collecting waste by separating them into types and using these to make new products. Paper and cardboard can be converted into pulp and used to make recycled paper. Old clothes can be shredded and used to make new cloth. Glass, metals and certain types of plastic can be used to make new goods. Advantages of recycling Reduces the depletion of resources, for example, forests are preserved as fewer trees are cut for lumber and pulp to make paper. Less land will be required for landfills. This will also help to reduce the risk of pollution from the landfills as well as conserve the habitats of many plants and animals. Less pollution of soil and water from the indiscriminate disposal of waste. Reduces the risk of harm to animals as a result of pollution. Reduces the risk of generating toxic wastes Saves energy. It takes less energy to recycle than it takes to make items from scratch. Difficulties of recycling It is tedious and time consuming. It requires initial capital outlay for special containers to separate the different types of waste. It requires the placing of recycle bins at strategic places so that consumers can get to them easily. It requires the provision of transport to take the materials to the different centres. In many instances, it requires a fair quantity of storage space. Last, but by no means least, it requires that education be provided for the consumer. Sample questions Monacia Williams, Contributor How are you this week? Did you do the revision that I asked you to do? I hope you did, because if you have not done so yet, you will need to do so before the end of the course. So, why not get it over and done with now? Let us look at a typical question for this section of the course. It is taken from a CXC biology specimen Paper 02. Question A sample of soil was collected from under a tree in a backyard where chickens used to be seen pecking at the dirt. The soil sample was sifted through a very fine sieve. Figure 1 below shows a sample of what remained in the sieve afterwards. (a)(i) Identify three organisms that belong to the same group. (1 mark) How can we arrive at an answer? In order to answer this question you will need to draw on your knowledge of classification. What are the features that can be used to group these organisms? First, do you recognise any of them? Of course you do! 'T' is a grasshopper. What else do you know? Grasshoppers are insects and insects have three pairs of legs. Do any of the other organisms have three pairs of legs? Look carefully at the diagram. 'V' and 'Y' also have three pairs of legs! The more knowledgeable student will also recognise 'P' as a beetle larva; larval forms of organisms belong to the same group as the adult. This places the larva among the insects. Answer Three organisms belonging to the same group are V, Y and T or P. (ii) State one characteristic that the three organisms have in common. (1 mark) Arriving at an answer We have already mentioned one feature in the previous question, so we can write that now. We also know that they are insects so we can add any other feature that is used to classify insects. Answer All three animals have three pairs of legs Their bodies are divided into three parts - head, thorax and abdomen They all have antennae Any one of the above responses will get you the mark. (iii) Although organisms P and R look somewhat similar, they have several differences. Identify two differences shown in the diagrams. (2 marks) Arriving at an answer Well, if you are one of the more knowledgeable students, then you would already know that P is a beetle larva and, hence, an insect. Do you recognise R? Of course you do, it is an earthworm. Here you can do one of two things or a combination of both to help you to answer the question. You can look at the diagrams and arrive at your answer or you can look and also use your theoretical knowledge to assist you. Answer R does not have a definite head while P has one R has a smooth area, the clitellum, where there are no segments The segments of P are much wider than those of R and increase in size towards the rear of the organism Any two of the three answers given above would earn you the full two marks. (b)(i) What type of organisms found in the soil would have passed through the holes of the sieve even if the holes were extremely small? (1 mark) Arriving at an answer Since the holes of the sieve were very fine, it means that only extremely small or microscopic organisms would have been able to pass through them. What organisms do you know about that could be put in this group? Answer Microorganisms/Bacteria (ii) What role do the organisms identified in (b)(i) play in the life of the tree? Arriving at an answer This requires you to draw on your theory. What processes involve microorganisms? That's right, breakdown of organic matter, recycling of nutrients. You have drawn on your resources; now you can answer the question! Answer Bacteria/microorganisms help to breakdown the leaf litter produced by the tree. They help in the recycling of the nutrients between the animals and the tree. I hope that the time we spent in going through the questions has given you an understanding of the information that you will need going into the examination. Good luck and best wishes as you study. Remember to also enjoy yourselves.
