Ecology and impact by humans Flashcards
Explain the term ‘producer’. [4]
Producer produces their own food through photosynthesis [1] by absorbing light energy and converting it to chemical energy [1] and synthesizing organic food substances from inorganic molecules [1]. Producers are the first organisms in the food chain or food web such as the microscopic green plants and water plants. [1]
Explain why a typical food chain in nature rarely exceeds 4 levels [4]
About 90% of the energy is lost as it passed down the food chain / up the trophic level. [1] stored chemical energy is lost in organic waste matters during egestion and excretion [1] and not passed on to the next trophic level. A large amount of energy is lost as heat due to respiration and during egestion. [1] Insufficient energy left to sustain the next trophic level [1]
Describe natural selection and evolution [6]
Organisms having desirable traits adaptable to the environment will survive [1] and reproduce to produce the next generation with the same desirable traits [1], whereas organism not having the desirable traits will not be able to survive [1] and produce the next generation, thus they will perish overtime[1].
After many generations[1], the survival of the fittest will result in the gradual shift in the phenotype and genotype of the population [1] leading to evolution of the species.
Define carbon sink and explain how oceans / forest can act as carbon sinks [6]
A carbon sink stores more carbon than it releases [1] for infinite periods of time [1] such as forests/oceans.
Forest
More carbon dioxide is taken up by plants for photosynthesis than given out during respiration [1] Carbon dioxide taken in is converted to / trapped in organic substances, which will form part of plant tissue [1] and overtime dead trees and vegetation get buried underground and become coal after millions of years.[1]
Oceans
Much carbon dioxide is dissolved in the water[1]. The dissolved CO2 is taken up by aquatic plants and planktons as raw materials for photosynthesis and converted to organic substances[1], which enters into food chain when animals eat aquatic plants and planktons [1]; Dead organisms sink to sea bed and get buried. After many years under great pressure the organic matter will become fossil fuels [1]
Describe how the carbon in a glucose molecule in the body of an animal is cycled in an ecosystem. [6]
Glucose molecule is oxidised during respiration in mitochondria to release carbon dioxide, water and energy. [1]
The carbon dioxide molecule is transported to the lungs by the blood and released into the atmosphere through exhalation. [1]
Plants will absorb the atmosphere carbon dioxide through the stomata in the leaves. [1]
Carbon dioxide and water, in the presence of sunlight and chlorophyll in the chloroplasts of the leaves are used to produce glucose molecules during photosynthesis. [1] Excess glucose is converted to starch to be stored.
Plants are eaten by consumers and the carbon in the starch enters the animal. The starch is digested into glucose and absorbed by the animal in the alimentary canal.[1]
The absorbed glucose with the carbon can be transported to various tissues to be assimilated to synthesize new protoplasm in the animals. [1]
Describe the process of eutrophication [5]
Excess nitrates and phosphates promote rapid growth of algae on the surface of the water body (river, lake or sea).
This prevents sunlight from reaching the submerged plants.
Submerged plants cannot photosynthesize and dies.
Dead plants are decomposed by bacteria.
Excessive decomposition depleting the oxygen in the water. Other organisms
die due to lack of oxygen.
Explain how mercury dumped into the river can eventually lead to fish farmers suffering from heavy metal poisoning [6] *apply to all bio-accumulative toxins
Plankton takes in mercury which is non-biodegradable and cannot be excreted and is accumulated in the fatty tissues [1]; this is bioaccumulation [1]. The fishes consume a lot of planktons, mercury is passed from the planktons to the fish higher in the trophic level [1], causing the mercury level to increase exponentially in the small fish, leading to bio-amplification. [1] Humans being highest in the food chain eat the fishes with increasing level of mercury, thus accumulating highest level of mercury in our body[1], resulting in severe harmful effects.
Describe briefly the processes involved in sewage treatment [5]
The sewage treatment process takes place in water reclamation plants through several stages:
i. Settling tanks: Heavier and bigger particles settle at the bottom and are removed as sludge.
ii. Aeration tanks: Bacteria and fungi (decomposers) is mixed with sewage. Aerobic bacteria digest organic waste into harmless soluble inorganic substances and carbon dioxide.
iii. Final settling tank: Microogranisms are removed as sludge from the treated sewage before being discharged into the sea.
iv. Anaerobic digesters: Sludge from settling tanks are treated. Anaerobic bacteria digest the sludge to produce methane gas to be used as biogas.
v. Treated sludge is dewatered and disposed of as a soil conditioner.
Describe how the organisms in the food chain form the pyramid of biomass. [3]
The total dry standing mass of all the organisms [1] in each trophic level at any one time [1] the total dry standing mass of each trophic level decreases as it goes up because less energy is transferred to higher trophic level to support growth. [1]
Describe the part played by decomposers in a food web. [3]
Decomposition of dead / excreted organic matter into inorganic substances to recycle the nutrients and mineral salts back to soil. [1] Plants as producers will absorb the nutrients from soil to synthesize new protoplasm. [1] The CO2 released from decomposition of organic matter will return to atm for plants to take in again during photo to synthesize glucose and pass down the food chain. [1]
Describe two impacts to food chains in the ecosystem due to human activities and suggest possible measures to counteract its effect. [4]
Deforestation
Impact: reduction of producers / habitat causing decline in population in the food
chain
Measures: reforestation / set up conservation areas
Over-hunting / over-fishing
Impact: rapid decline in certain species numbers causing unbalance in food chain / food web.
Measure: quota on fishery / set hunting seasons / impose ban on hunting animals that are too small / ban on hunting female animals
Use of insecticides in farmlands
Impact: kill pests and useful insects indiscriminatingly, result in disruption of food chain on organisms feeding on those insects / affecting pollination by insects (eg. Butterflies and honey bees)
Some insects evolve to become resistant to the insecticide.
Measures: reduce use of insecticides and introduce natural predators to control pests
