biology ecology

• An individual is part of a species, but lives in its habitat within a population.
• Many different populations interact in the same habitat, creating a community.
• The populations are often dependent on each other.
• An ecosystem is the interaction of a community with non-living (abiotic) parts of the environment.
• Organisms are adapted to live in the conditions of their environment.
• Deforestation is the clearing of an area of trees on a mass scale.
• Imbalance in oxygen and carbon dioxide is a result of the removal and burning of trees, leading to higher atmospheric carbon dioxide levels and lower oxygen levels.
• Soil erosion is a process where soil is washed away by the rain due to the absence of tree roots.
• Leaching is a process where nutrients and minerals are washed into rivers and lakes due to the absence of trees.
• Transpiration from trees releases water vapour which contributes to the water cycle and the carbon cycles.
• Disturbance to cycles is a term that refers to the changes in the water cycle and the carbon cycle due to the removal and burning of trees.
• Quadrats are used to study ecology, as they make it easier to estimate distribution and abundance of organisms within a large area by looking at a few smaller representative samples.
• A transect is a defined area where the samples will be taken and is used to estimate the number of the organism across the whole area, such as across a whole field.
• The quadrats are placed along the transect and the amount of the chosen organism is counted.
• The quadrats can also be randomly placed across the whole area, rather than using a transect.
• Alternatively, percentage cover can also be estimated but this is subjective and less accurate than counting which gives a quantitative value.
• The accuracy of the quadrat estimations can be improved by doing more samples, repeat testing or completing the sampling over larger transects.
• Biodiversity is a measure of the range of species living within an ecosystem.
• Using the same method as above we can measure biodiversity, but instead of counting how many of a single organism is found in each quadrat, we count the populations of different species.
• The reliability is improved by placing the quadrat randomly (e.g using a random generator), using the same size quadrats each time, increasing the number of samples taken in each area.
• Light intensity is required for photosynthesis and the rate of photosynthesis affects the rate at which the plant grows.
• Plants can be food sources or shelter for many organisms.
• More food means organisms can breed more successfully and therefore the population can increase in numbers.
• Temperature affects the rate of photosynthesis.
• New predators can pose a threat to the population.
• Moisture levels are necessary for both plants and animals to survive.
• New pathogens can wipe out a population quickly when they arise.
• Pyramids of numbers show the population of each organism at each trophic level of food chain.
• Decomposers are bacteria and fungi that break down dead animal’s body and waste for energy, using enzymes.
• Only approximately 10% of the biomass of each trophic level is transferred to the next, as: not all biomass can be eaten, carnivores cannot generally eat bone, hooves, claws and teeth, and lots of glucose is used in respiration, which produces the waste product carbon dioxide.
• Producers (e.g plants and algae) transfer about 1% of the incident energy from light for photosynthesis, as not all the light lands on the green (photosynthesising) parts of the plant.
• Plants and algae are primary consumers, also known as herbivores that only eat plants (producers).
• Tertiary consumers are carnivores that eat secondary consumers.
• Food chains show the feeding relationships between organisms and are organised by trophic levels.
• Food webs are a collection of different food chains to show how all the organisms in the habitat interact, showing interdependence and therefore how population number changes can affect the entire ecosystem.
• Carbon cycle: plants and animals aerobically respire, which releases CO2 into the air, dead plants and animals are broken down by decomposers, and the carbon is then returned into the atmosphere.
• Nitrogen cycle: nitrogen gas in the atmosphere is too unreactive so cannot be used directly by plants, nitrogen-fixing bacteria present in the root nodules of legume plants (e.g.) remove nitrogen from the atmosphere and convert it into a form that can be used by plants.
• Secondary consumers are carnivores that eat primary consumers.
• Efficiency of biomass transfers: (Biomass transferred to the next level / Biomass available at the previous level) x 100.
• Apex predators are primary consumers with no predators.