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Ecology
Energy flow, nutrient cycling, ecological systems, biodiversity and conservation
| Question | Answer |
|---|---|
| Define ecosystem | A self-contained community and all the physical features that influence it and the interactions between them. |
| Define habitat | The place where an organism lives. |
| Define ecological niche | The role of a species in a community including its position in the food chain and interactions with other species and the physical environment. |
| What is a food chain? | Diagram that shows flow of energy in an ecosystem between named organisms at two or more trophic levels; arrows point in the direction of energy flow. |
| What is a food web? | Diagram that shows interrelated food chains in an ecosystem. |
| State the advantages of food webs. | 1) They are show that there are more than one consumer feeding on the consumer and at any trophic level. 2) They show that there is a mesh of interlinking food chains that characterize the real world. |
| State disadvantages of both food chains and food webs. | 1) They cannot show ALL the feeding relationships in an ecosystem as these are too complex. 2) They are purely qualitative and cannot show how much energy flows at each level. |
| What is a biological pyramid? | These are quantitative diagrams arranged in horizontal blocks representing a tropic level and they are centered on to of one another. They can display the numbers of organisms, their biomass or energy at different trophic levels in an ecosystem. |
| What is shown on a pyramid of numbers? | The number of organisms at each trophic level per unit area. The area of each block is proportional to the number of organisms. |
| This type of pyramid shows the dry mass of organisms at each trophic level. | Pyramid of biomass |
| What is shown on a pyramid of energy? | The productivity of each trophic level or the energy flow between trophic levels. |
| List 3 limitations of pyramids of numbers. | 1) Size of organisms is not considered; pyramids can be inverted if there are many small consumers to one large producer 2) They only account for visible organisms and not microorganisms. 3) No. of organisms changes due to reproduction and migration. |
| One advantage of pyramids of biomass is that the potential food available at each trophic level is indicated. List 3 LIMITATIONS of pyramids of biomass. | 1) All the mass indicated is not edible. Pyramid can be inverted. 2) They do not indicate how much energy is available to be transferred and all the material eaten may not be digestible. 3) They do not show changes with time. |
| List 3 advantages of the pyramid of energy. | 1) They can never be inverted. The size and edibility of organisms have no effect on the blocks. 2) They show the energy transferred from one trophic level to the next. 3) They show that energy decreases from one trophic level to the next. |
| State 3 limitations of the pyramid of energy. | 1) Time consuming 2) Estimation is involved since not all samples can be burnt 3) They suggest that consumers only feed on the trophic level below them and this is not the case for many top predators which feed at multiple levels. |
| Give the formula for ecological efficiency. | (energy available to a trophic level/energy consumed by previous trophic level) x 100 |
| What is ecological efficiency? | The energy consumed by the organisms in one trophic level as a percentage of the energy entering the previous trophic level. |
| T or F. Only the energy in new growth and new individuals (reproduction) is available to the next trophic level. | T |
| How is energy lost in a food chain? | It is transferred to the surroundings as heat when organisms respire and move. It is transferred to detritus food chains. |
| The rate at which plants convert light energy into chemical potential energy is called | primary productivity |
| Differentiate between gross primary productivity (GPP) and net primary productivity (NPP). | GPP is the total quantity of energy transferred by plants from sunlight into plant tissues. NPP is the energy that is left as chemical energy after the plants have supplied their own needs by respiration. |
| List 4 examples of nitrogen containing compounds in biological systems. | 1) Amino acids 2) Proteins 3) Nucleotides (E.g NAD, NADP and ATP) 4) Nucleic acids |
| T or F. Nitrogen gas (dinitrogen) has a triple covalent bond, is unreactive and not available to most organisms in that form. | T |
| What is the difference between nitrogen gas and fixed nitrogen? | Fixed nitrogen is nitrogen attached to other atoms such as oxygen, hydrogen and carbon whereas nitrogen gas is simply N2. |
| T or F. Plants reduce nitrate ions to nitrite ions and then to ammonium ions which are made into amino acids then proteins. | T |
| What happens in AMMONIFICATION in the nitrogen cycle? Mention microorganisms involved. | Ammonia is produced from the deamination of amino acids (in protein) by microorganisms (decomposers/saprophytes such as fungi) which break down excreted and egested materials + dead bodies of plants and animals. |
| What happens in NITRIFICATION? | Ammonia (is converted to) --> nitrate ions via nitrifying bacteria - Nitrosomonas Nitrates --> Nitrites via nitrifying bacteria - Nitrobacter |
| What happens in NITROGEN FIXATION? | Nitrogen gas --> nitrates (also ammonia) in soil via nitrogen fixing bacteria e.g. Rhizobium, Azotobacter. Certain prokaryotes have the enzyme nitrogenase which converts nitrogen gas to ammonia. |
| The industrial Haber process involves the combination of hydrogen with nitrogen gas. To which natural process in the nitrogen cycle is this similar? | Nitrogen fixation. |
| T or F. Lightning discharges can cause nitrogen fixation to occur. | T |
| T or F. Nitrate ions are an important limiting factor for growth of plants. This is why farmers add fixed nitrogen in the form of compounds such as ammonium nitrate. | T |
| What happens in DENITRIFICATION? | Nitrate ions are converted to nitrogen gas via denitrifying bacteria - Pseudomonas |
| Why are energy flow and nutrient cycling important ? | They enable ecosystems to be self-sustaining units through interaction of biotic and abiotic components... E.g. The cycling of nitrogen is important in plant growth as well as maintaining the composition of the atmosphere. Microorganisms play key roles. |
| What is energy flow? | The transfer of energy from one trophic level to another in a linear, non-cyclic manner. |
| What is nutrient cycling? | The cyclic movement of chemical elements between organisms and their physical environment in the ecosystem. Nutrient pool (air and soil) -> producers -> consumers -> decomposers -> nutrient pool |
| State 3 major differences between energy flow and nutrient cycling. | Energy flow 1) Linear 2) Energy is lost as heat and not recycled 3) Energy comes from the Sun Nutrient cycling 1) Cyclic 2) No loss of nutrients as they are recycled 3) Nutrients come from Earth's reservoir (air and soil) |
| Distinguish between biotic and abiotic factor. | Biotic factor - any factor that results from the activities of another organism of the same or different species. Abiotic factor - any aspect of the physical or chemical environment of a species eg. temp, light, salinity etc |
| Give 4 examples of biotic factors in an ecosystem. | 1) Competition 2) Cooperation with organisms of the same and other species 3) Predation 4) Disease |
| What is interspecific competition? | Competition between different species. |
| What is intraspecific competition? | Competition between members of the same species. |
| Describe the principle of competitive exclusion. | Only one species occupies a particular niche within an ecosystem while other competing species are excluded. |
| Discuss the principle of resource partitioning. | Different organisms feed on the same prey but avoid direct competition with each other e.g grazing at different heights and locations, different plants, different plant parts, |
| Define cooperation. | Organisms working together for a mutual or common benefit. |
| What is altruism? | A cooperative behaviour in which all individuals work together for the benefit of all even when some individuals do not get a chance to breed e.g. soldier ants and worker bees. |
| What is mutualism? | Any association between two or more different species for mutual benefit e.g. algae (zooxanthellae) which gain protection, carbon dioxide and other excreta from corals and provide the corals with carbohydrates from their photosynthesis. |
| What is predation? | The killing and consumption of one organism by another. |
| What is commensalism? | An association between two organisms in which one benefits and the other derives neither benefit nor harm. |
| What is parasitism? | Relationship between two species of plants or animals in which one benefits at the expense of the other, sometimes without killing the host organism. |
| Define biodiversity. | The measure of the 1) different ecosystems 2) number of species 3) number of individuals of each species and 4) genetic variation within each species present in an area |
| Give 2 examples of species rich ecosystems on Earth. | 1) Tropical rainforests 2) Coral reefs |
| Define species richness. | The measure of the species diversity. The greater the number of species, the greater the richness. |
| Define genome. | The sum of all the genes in an organisms or in a species. |
| What is species diversity? | The number and abundance of different species in an ecosystem. |
| Why is species diversity important? | Great species diversity is considered important as it makes an ecosystem more stable than one with limited diversity and more able to resist changes. |
| What is genetic diversity? | The sum of all the different alleles of the genes in a single species. All the individuals of a species have the same genes but they do not all have the same alleles of those genes. |
| How can disease affect corals? | They can become infected by viral, fungal and protoctist parasites which cause bleaching as the polyps respond by expelling their zooxanthellae. |
| Corals are considered sessile predators. What does this mean? | They cannot move from place to place (locomote) but they move their tentacles (containing tiny polyps with stinging cells) to catch their prey (small animals). |
| What is ecosystem diversity? | The number of different ecosystems in a certain area. |
| T or F. Species diversity is related to the stability of an ecosystem. | T |
| List three major events which can devastate species diversity. | 1) Hurricanes (natural disasters) 2) Coastal development 3) Deforestation |
| How do hurricanes affect ecosystems? | Hurricanes destroy mangroves resulting in a loss of a rich and diverse ecosystem under water. |
| How has coastal development affect ecosystems? | They have destroyed many seagrass communities around the Caribbean. |
| How does deforestation affect ecosystems? | It removes trees that provide many habitats for a wide range of other organisms. Forest floor becomes exposed to the elements. Thin topsoil is washed away. Re-establishing the original ecosystem is difficult. |
| Describe the effect of the Crown-of-thorns starfish in the Great Barrier Reef. | Flooding increases nutrients in coastal waters. Phytoplankton population (food of starfish larvae) increases which increases the population of adult starfish. These starfish feed on corals; if this is too frequent, corals do not have the time to recover. |
| Describe the effect of sea otters in the Pacific. | Sea otters fed on sea urchins. Sea otters were hunted for their fur and this led to an explosion of sea urchins which fed heavily on kelp leading to losses in several other species - algae, abalones, crabs, smaller fish, larger fish etc |
| What is a keystone species? | Organisms which play a pivotal role in ecosystems. Their loss leads to many other losses in the ecosystem. E.g. sea otters are a keystone species. |
| Describe the effect of loss of apex predators from an ecosystem. | Loss of top predators (e.g Nassau grouper) leads to population explosions in smaller predatory fish and herbivorous fish, intensifying feeding pressure on lower trophic levels. This contributes to loss of biodiversity in coral reef ecosystem. |
| Describe the effect of sea urchins in Caribbean coral reefs. | The sea urchin was considered a keystone species for controlling excessive algal growth on coral reefs. A disease killed 99% of them. This as well as overfishing of herbivorous fish has reduced grazing on coral reefs thus increasing algal growth. |
| Give two factors which can contribute to increased algal growth on corals. | 1) Excess nutrients (nitrates and phosphates) in water leading to eutrophication 2) Removal of grazers which feed on algae. |
| Why is excess algal growth bad for coral reefs? | Excess algae attract large numbers of microorganisms which feed on them. These reduce the oxygen supply available to the corals as well as introduce diseases. |
| What are alien species in an ecosystem? | Plants, animals, pathogens and other organisms that are non-native to an ecosystem. They may be harmful (invasive). |
| What is conservation in ecology? | The protection of species, habitats and ecosystems from damage and encouraging their survival through maintaining the interactions that sustain them. |
| Give three viewpoints/reasons for maintaining biodiversity. | 1) Humans are custodians of the Earth 2) Other living organisms have the right to exist 3) Humans have tenants of Earth and should take care of it for future generations |
| What is meant by intrinsic value of an ecosystem? | An objective value of the ecosystem in and for itself. The value is independent of potential usefulness of biodiversity for human beings. |
| What is meant by extrinsic value of an ecosystem? | The importance of the ecosystem to human beings through goods, services, information and enjoyment. |
| Distinguish between direct and indirect values of biodiversity. | Direct (extrinsic) - usually obtained through a removable product(goods) in nature - an economic benefit can be gained by humans Indirect (intrinsic) - usually a non-removable product (services) in nature - no direct economic benefit |
| State whether the example given in a direct or indirect value of biodiversity: Medicine and natural products obtained from nature. | Direct |
| State whether the example given in a direct or indirect value of biodiversity: Artists and photographers receiving inspiration from the environment. | Direct |
| State whether the example given in a direct or indirect value of biodiversity: Nutrient cycling maintains soil fertility. | Indirect |
| State whether the example given in a direct or indirect value of biodiversity: Reefs and mangroves protect coasts from erosion | Indirect |
| State whether the example given in a direct or indirect value of biodiversity: Tourists entering the country to view the ecosystem. | Direct |
| State whether the example given in a direct or indirect value of biodiversity: Water is filtered through soils and rock before it enters the supply. | Indirect |
| Differentiate between in situ and ex situ conservation methods. | In situ - conserving a species in its natural habitat e.g. protected areas (by law) and reserves Ex situ - conserving a species outside of its natural habitat due to threats e.g. zoos, sperm and embryo banks, botanic gardens, seedbanks |
| List 5 ways in which natural habitats of organisms can be protected in their habitats. | 1) Reclaiming damaged ecosystems 2) Creating new habitats 3) Providing exclusion zones on fishing certain times of year 4) Preventing/limiting pollution 5) Clear permits and guidelines to timber companies to remove products without long-term damage |
| What is a gene bank? | Any method of conservation that keeps whole organisms, gametes, embryos, seeds, tissues or any other part of an organism. |
| Apart from enjoyment of viewers, list 3 functions of zoos. | 1) Protection of endangered species 2) Cooperate with other zoos breeding programmes to prevent inbreeding 3) Reintroduction of captives into the wild when habitat has been restored * Points 2 and 3 are expensive, time-consuming and multifactoral. |
| What is the difference between artificial insemination (AI) and in vitro fertilization (IVF)? | In artificial insemination, sperm are placed in the female's reproductive tract so fertilization is internal. In vitro fertilization occurs outside the body in a lab. The zygote divides to form a small embryo and is inserted into the uterus or frozen. |
| How do sperm banks work? | They store motile sperm in small at temperatures of -96C in liquid nitrogen. When needed, they are thawed and used for artificial insemination. Rhinoceros, Cheetah and Chinese pheasant have been successfully bred from this method. |
| How do embryo banks work? | Eggs are fertilized in vitro (outside body). The embryo is then frozen until a surrogate mother becomes available. Wild ox and African antelope have been successfully bred from this technique. |
| How do botanic gardens work? | They protect endangered plant species by removing them from their original habitat, reproduce them and reintroduce them to habitats where they have become rare or extinct. |
| How do seed banks work? | Seeds are collected from plants in the wild, dehydrated to contain only 5% water and stored at -20C. Reducing water content slows their metabolism so they remain viable longer. Periodically they are tested and more seeds collected to top up the bank. |
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