CHPT 18 : ORGANISMS AND THEIR ENVIRONMENT

[Audio] CHPT 18 : ORGANISMS AND THEIR ENVIRONMENT.

[Audio] Sub-chapter Energy flow Food chains and food webs Nutrient cycles Population.

[Audio] Energy flow Ecology: The study of organisms in their environment Habitat: The place where an organism lives Community: All of the population of all the different species in an ecosystem Ecosystem: A unit containing all of the organisms in a community and their environment, interacting together.

[Audio] Niche: The role of an organism in its natural environment, the way in which it interacts with other organisms and with the nonliving parts of the environment The Sun is the principal source of energy input to biological systems Light energy from the Sun and chemical energy in organisms, and its eventual transfer to the environment.

[Audio] Food chain and food web Food chain: A diagram showing the flow of energy from one organism to the next, beginning with a producer.

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[Audio] Food chain and food web Food web: a network of interconnected food chains.

[Audio] Producer : an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis Consumer : an organism that gets its energy by feeding on other organisms Classed in consumers : a. Primary d. quaternary b. Secondary c. Tertiary.

[Audio] Herbivore : an animal that gets its energy by eating plants ( Primary consumers) Carnivore : an animal that gets its energy by eating other animals (secondary, tertiary, quaternary) Decomposer : an organism that gets its energy from dead or waste organic material.

[Audio] Tropic levels Tropic level : The position of an organism in a food chain, food web or pyramid of biomass or numbers Type of pyramid number : Pyramid of numbers A diagram in which the area of the bar at each trophic level shows the relative number of organisms at that level in the food chain.

[Audio] 2. Pyramids of biomass A graph showing the relative quantity of biomass at each tropic level The advantages of using a pyramid biomass Take the size of each organism into account Give a better idea of the quantity of energy at each level than a pyramid of numbers does.

[Audio] Example A scientist counted the number of grass, rabbit, snake, and eagle. She found that for every 1000 grass, there were 100 rabbits, 20 snakes, and 5 eagles. The mean masses of the organisms in this food chain are : Grass = 0,5 kg rabbits = 3 kg snakes = 6 kg eagles = 10 kg Use this information, to construct a pyramid of numbers and biomass.

[Audio] Exercise A scientist counted the number of cabbage, caterpillar, sparrow, and kestrel. She found that for every 200 cabbage, there were 100 caterpillars, 10 sparrows, and 2 kestrels. The mean masses of the organisms in this food chain are : Cabbage = 4 kg Caterpillar = 0,5 kg Sparrows = 3 kg Kestrels = 10 kg Use this information, to construct a pyramid of numbers and biomass.

[Audio] Tropic levels 3. Pyramids of energy A graph showing the relative quantity of energy at each tropic level Energy at each level is given in kJ per square meter per year. Advantages of using a pyramid of energy : 1. A pyramid of energy is considered to be more accurate than a pyramid of biomass or a pyramid of numbers in representing the flow of energy through an ecosystem.

[Audio] Energy losses As energy is passed along a food chain, some of it is lost to the environment. Reason : a. When an organism uses glucose and other organic compounds for respiration b. When one organism eats another, it rarely eats absolutely all of it c. When an animal body/human does the metabolism.

[Audio] This means, the further you go along a food chain, the less energy is available for each successive group of organism For this reason, there are usually not more than five trophic levels More energy efficient for humans to eat crop plants than to eat livestock that have been fed on crop plants.

[Audio] Human impact on food chains 1. Overharvesting of food species This will damage food chains, because the organisms will not have enough food to survive, meaning that many of them will die 2. Introducing foreign species to a habitat , which could damage existing competition for resources increase species by interfering with the food chain..

[Audio] 18.2 Nutrient cycles 1. Carbon cycle The carbon cycle is used to show how carbon atoms move between the atmosphere and living organisms 0,04% of the air is carbon dioxide Photosynthesis Carbon dioxide is taken in by plants during photosynthesis. The carbon atom from CO2 become part of glucose and starch molecule in the plant.

[Audio] b. Respiration These carbon molecules from glucose are passed to the air by respiration c. Feeding These carbon molecules are passed through the food chain when feeding occurs, hence carbon is also passed between the trophic levels.

[Audio] d. Decomposers The carbon becomes part of decomposers’ bodies, and when the decomposers respire they release carbon dioxide into the air e. Formation of fossil fuels Carbon can be trapped in dead organisms when decomposition does not occur. These organisms become fossilised over thousands of years to form fossil fuel.

[Audio] f. Combustion Carbon combines with oxygen The carbon and oxygen combine to form carbon dioxide and is released into the air.

[Audio] 2. Nitrogen cycle Nitrogen is used to make amino acids, DNA, and ATP. Nitrogen must first be changed into a more reactive form Nitrogen fixation : Converting inert nitrogen gas into a more reactive form, such as nitrate ions or ammonia.

[Audio] Process nitrogen fixation : 1. Lightning : Nitrogen + oxygen = Nitrogen oxides Nitrogen oxides dissolve in the rain and are washed into the soil, forming nitrates 2. Artificial fertilisers Nitrogen + hydrogen = ammonia Ammonia is used to make ammonium compounds and nitrates.

[Audio] 18.2 Nutrient cycles Process nitrogen fixation : 3. Nitrogen fixing bacteria 1. Absorption of nitrate ions by plants Bacteria in soil/root nodules (peas, beans, and clover). Use nitrogen gas from the air spaces in the soil to make ammonium ions 2. Production of amino acids and protein After the nitrogen has been fixed, plants use it to make amino acids and change to make protein..

[Audio] 18.2 Nutrient cycles Process nitrogen fixation : 3. Feeding and digestion of protein Animals eat the plants, so animal get their nitrogen in the form of protein 4. Decomposition of plant and animal protein Bacteria and fungi decompose the body, so the protein containing nitrogen is broken down to ammonium ions and released.

[Audio] 18.2 Nutrient cycles 5. Nitrification Converting ammonium ions to nitrate ions. A group of bacteria called nitrifying bacteria . Turn ammonium into the nitrate. 6. Deamination Nitrogen is also returned to the soil when animals excrete nitrogenous waste material by deamination of excess amino acids into the ammonia or urea.

[Audio] 18.2 Nutrient cycles 7. Denitrification Converting nitrate ions to nitrogen gas A group of bacteria complete the nitrogen cycle, called denitrifying bacteria. Bacteria turn nitrates and ammonia in the soil into nitrogen gas which goes into the atmosphere.

[Audio] 18.3 Population Births and deaths are more important in determining population sizes than immigration and emigration If the birth rate is less than the death rate, the population will decrease. If the birth rate and death rate are equal, the population will stay the same size..

[Audio] 18.3 Population Factor affecting population growth : 1. Food supply As the population gets larger, there is not enough food left for them all 2. Competition Because there is not enough food left competition will happen for food.

[Audio] 18.3 Population 3. Predation In predator-prey relationships, when one population of an organism (producer/consumer) increases, the consumer population also rises shortly. A drop in the producer/consumer is rapidly followed by a drop in the consumer. 4. Disease The amount of infection by a virus which causes a fatal disease and drops the population.

[Audio] Process changes in population size : a. Lag phase: The stage at the start of a population growth curve where the population remains small and grows only very slowly b. Log phase/exponential phase : The stage in a population growth curve where the population grows at its maximum rate, birth rate exceeds death rate.

[Audio] Process changes in population size : c. Stationary phase: The stage in a population growth curve where the population remains roughly constant. Birth rate equals death rate d. Death phase: The final stage in a population growth curve where the population falls. Death rate exceeds birth rate Sigmoid growth curve: An S-shaped curve showing the change in the size of a population through all the phases in population growth.

[Audio] Project 1. Make a 3D model about (Food web, Pyramid of number, Pyramid of biomass, Carbon cycle, nitrogen cycle).