🏥 Chapter 13 - Organisms and their Environment

• nutrient and energy flow

  • living organisms in an ecosystem can be classified as producers, consumers and decomposers
• producers

  • organisms that make their own food via photosynthesis (process whereby $CO_2\ +$$\ H_2O\ \rightarrow\ C_6H_{12}O_6\ +$$\ O_2$)
• consumers

  • organisms that cannot make their own food and obtain energy and nutrients by feeding on other organisms

  can be classified as:

  • primary consumers ; that feed on plants only
  • secondary consumers ; feed on primary consumers
  • tertiary consumers ; feed on secondary consumers
• decomposers

  • organisms that obtain energy via breaking down dead organisms, and their activities return nutrients like mineral salts to the environment
• population

  • group of organisms of the same species that live together in a habitat
• community

  • group of all populations of different species living and interacting with one another in the same habitat
• ecosystem

  • a community of organisms interacting with one another and the non-living environment
• food chain

  • a series of organisms, starting with a producer, through which energy and nutrients are transferred
  • a position that an organism occupies in the food chain is its trophic level. a food chain typically does not have more than 4 trophic levels
• food webs

  • consists of a network of interconnected food chains`
• energy flow in an ecosystem (I)

  • in an ecosystem, energy flow is non-cyclic (linear)

  1. in an ecosystem, the principle source of energy is the sun
  2. during photosynthesis, energy is absorbed from sun by chlorophyll and transferred to chemical stores of energy in glucose
  3. energy in the producers is passed from one trophic level to another via feeding. amount of energy at each trophic level decreases as only some energy gets transferred to the next trophic level
• energy flow in an ecosystem (II)

  1. rest of the energy is largely transferred to the environment as heat, through respiration. energy does not return to the same system as the organisms that produce it, hence energy cannot be recycled
  2. excreted materials and dead organisms contain trapped chemical energy, that is released through the activity of decomposers. decomposers use some of these energy for their needs and the rest are released into the environment
• why shorter food chains are more efficient

  • as you go up the trophic levels of a food chain, energy transferred decreases. Hence, the shorter the food chain, the greater the amount of energy available to the final consumer
• predator-prey relationship

  • an increase in the population of prey results in more food available for the predators, leading to an increase in the population of predators, in turn a decrease in the population of prey.
  • the decrease in the population of prey leads to decrease in the population of predators as less food is available
  • this leads to an increase in the population of prey and this cycle repeats over time
  • the average population of prey is usually higher than the population of predator

  
• pyramid of numbers

  • compare the number of organisms present in each trophic level at a particular time
  • however, pyramid of numbers do not show size and mass of organisms, and whether the organism is adult or juvenile (young)
• pyramid of biomass(g/m2)

  • allows us to compare the dry mass (no water) of organisms present at a trophic level at a particular time
  • however, its disadvantages are that the organisms have to be killed to calculate their biomass, and the pyramid has to be constructed at a particular point in time
• carbon cycle (I)

  • the constant release and absorption of carbon dioxide that keeps amount of carbon dioxide in atmosphere relatively constant
• carbon cycle (II)

  1. carbon dioxide absorbed by plants for photosynthesis to synthesis carbohydrates that can convert to proteins and fats
  2. animals obtain carbon compounds by feeding on other plants and animals
  3. plants and animals respire, releasing carbon dioxide to the environment
  4. decomposers break down dead organic matter to release carbon dioxide
  5. dead bodies buried deep into the earth are subjected to high pressure and temperature, where they are converted to fossil fuels. combustion of such fossil fuels release carbon dioxide to the environment
• carbon sink

  • area that stores carbon from the atmosphere for a long period of time.
  • stores more carbon than it releases
• oceans

  • biggest carbon sinks on earth
  • carbon dioxide dissolves in the oceans' water and is absorbed and used by aquatic plants during photosynthesis
• forests

  • carbon sink as tree absorb carbon dioxide from the environment for photosynthesis
  • large amount of carbon compounds are found in tries, and when they die and get buried deep in the ground, they form coal after a long time and carbon dioxide is released during combustion of fossil fuels
• how do humans affect the ecosystem

  • air , water , soil , forests and wildlife are renewable natural sources, and can be replaced by natural cycles as long as humans dont overuse them
  • however, fossil fuels take millions of years to form, they cannot be replaced quickly enough and hence are considered non-renewable natural resources
• deforestation(I)

  • the clearing of forest for various needs such as land for urban development , farming livestock and agriculture , as well as for firewood and construction materials
  • can cause extinction of certain species of organisms as land may not be enough to support breeding populations of these organisms
• deforestation (II)

  • furthermore, when trees grow, rate of photosynthesis is higher than rate of respiration, so excess carbon is stored in trees trunks roots and soil. when trees get cut down, these carbon get released into the atmosphere, and there is also a decrease in the number of trees absorbing CO2 due to deforestation. this leads to global warming due to high CO2 concentration in atmosphere
• greenhouse effect

  • greenhouse gases form a layer over the earths atmosphere, and traps heat within this layer around the earth
  • leads to global warming and in turn, climate change whereby ice caps melt and sea levels rise, which may cause flooding in some countries
• greenhouse effect on aquatic ecosystems

  • high atmospheric carbon dioxide concentrations means that more carbon dioxide dissolves in the sea water, causing the sea to be more acidic, resulting in shellfish having weakened shells, making them more vulnerable to predators
• how can we reduce the effects of enhanced global warming

  • use less fossil fuel and more renewable energy sources
  • reduce energy consumption by using energy efficient devices
  • use electric vehicles instead of petrol-powered vehicles
  • reduce electricity, water, paper, and plastic consumption
  • reforestation
  • control of forest fires
  • educating public on the importance of forests in our lives
• pollution

  • process whereby harmful substances are added to the environment, making life more undesirable
• sewage

  • waste water from households and industries
  • should be treated before it can enter water bodies, because untreated sewage contains excess nitrates, phosphates and harmful bacteria
  • entry of such excess nutrients into water bodies is called eutrophication
• eutrophication

  1. untreated sewage enters water bodies
  2. nitrates and phosphates enhance the growth of algae and water plants, leading to increased multiplication of algae and floating water plants in rivers and lakes
  3. overcrowding of such plants prevent light from reach submerged plants
  4. submerged plants die due to lack of sunlight
  5. dead water plants are decomposed by aerobic bacteria and fungi
  6. as bacteria feed on dead matter their population grows and multiplies rapidly , using up oxygen
  7. other organism die due to lack of oxygen
• insecticides

  • disadvantages include it being ineffective after awhile, and that if it is carried into water bodies, it could accumulate in high concentrations in the bodies of aquatic organisms
  • DDT (dichlorodiphenyltrichloroethane) is a non-biodegradable insecticide that is insoluble in water. This means that it can stay in soil and water for many years. it cannot be excreted and will instead accumulate in the body. this is called bioaccumulation
  • biomagnification is when such pesticides are passed from one trophic level to the next with increasing concentration along the food chain
• non-biodegradable plastic

  • plastic waste such as straws can be harmful to marine animals
  • burning of plastic affects global warming
  • can be broken down to microplastics and ingested by marine animals, leading to biomagnification down the food chain
• biodiversity

  • the range of species present in an ecosystem
• conservation

  • protection and preservation of natural resources in the environment
• why is conservation needed

  • maintenance of a large gene pool from plants and animals so that by cross-breeding, we can improve agricultural produce
  • many tropical plants are sources of medicinal drugs
  • wildlife useful information for scientific research
  • marine life and tropical rainforests are major sources of human food
  • tropical plants raw materials for industries
  • prevent disruption of natural cycles such as carbon cycle that reduce global warming
  • nature enables outdoor recreational activities
• how can we conserve resources

  • forests ; (already mentioned previously)
  • mangroves ; start projects that plant mangrove seedlings or raise awareness on conservation and reservation of mangrove areas and its impact on global warming and climate change
  • coral reefs ; avoid sunscreen as it contains chemicals that can be harmful to corals, avoid purchasing live corals which will encourage people to extract more corals, and avoid polluting coastline with non-biodegradable trash