IB Biology Topic 4

• Species: A group of organisms that can breed to produce viable, fertile offspring.
• Limitations of the biological species concept:

  1. Boundaries of a species gene pool can be unclear, and in some cases different members of a species can interbreed to create (likely infertile) hybrid offspring
  2. Variation within the species might limit mating within the species
  3. Members of the same species might be capable of interbreeding but do not because of geographical isolation
  4. Asexual species do not interbreed
• Population: a group of organisms of the same species, in the same place, at the same time
• Reproductive isolation is when two or more populations of the same species are prevented from interbreeding. If they do not interbreed, there is no gene mixing. Over time, the populations may change to the point of not being able to interbreed and produce viable offspring, in which case they are no longer considered the same species.
• Speciation: The process by which a population of organisms becomes reproductively isolated from other populations
• Autotroph: synthesizes its own organic molecules via photosynthesis or chemosynthesis
• Heterotrophs: organisms that obtain organic molecules from other organisms
• Herbivore: An organism that eats plant matter
• Carnivore: organisms that eat animal matter
• Scavenger: organisms that eat dead/decaying matter
• Detrivores: Organisms that feed on dead organisms and feces by internal digestion.
• Ecosystem: The biological community of an area, including the abiotic factors and the interactions between the biotic and abiotic factors
• Community: A group of populations of different species living in the same area.
• Quadrat sampling: A method of sampling in which a square is drawn on the ground and each square is assigned a number.
• The supply of inorganic nutrients on Earth is finite, and the supply is maintained by nutrient cycling
• Mesocosm: a small experimental area set up for ecological research. It proves that ecosystems have the potential to be sustained over long periods of time as long as nutrients are recycled and the ecosystem has an energy supply.
• autotrophs are essential to mesocosms because they produce carbon compounds and regenerate oxygen used in cell respiration by organisms in the mesocosm
• Saprotrophs are essential to mesocosms to decompose dead organic matter and recycle nutrients
• Sustainability: the ability to be maintained at a certain rate or level
• An unsustainable mesocosm is one that is not able to support the population of organisms through nutrients or energy
• Sampling must be random because it removes bias from research
• Statistically significant: A result that is statistically significant is one that is unlikely to have occurred by chance. In a chi-square test, a p-value of less than 0.05 is considered statistically significant.
• Examples of mesocosms: plastic bottles, glass jars, plastic bags (anything that can be sealed)
• Plants, algae, and some bacteria absorb light energy and convert it by photosynthesis into chemical energy in carbon compounds. Because these organisms make their own food, they are called producers
• Light is the initial source of energy for almost all communities
• Autotrophs use energy to make organic compounds like sugar from inorganic sources like CO2. Heterotrophs ingest these organic compounds to derive chemical energy in the form of ATP, which fuels metabolic processes
• Trophic levels:

  1. Producers
  2. Primary consumers
  3. Secondary consumers
  4. Tertiary consumers
• Food chains show linear feeding relationships between trophic levels, using arrows to represent transfer of energy
• Grassland food chain example:

  1. Carrot – producer
  2. Rabbit – primary consumer
  3. Feral cat – secondary consumer
  4. Red fox – tertiary consumer
• Not all of the energy stored in organic molecules is transferred by heterotrophic feeding – it is lost by excretion (10%), respiration(25%), and heat (40%).
• Chemical energy can be converted to kinetic energy (muscle contraction), electrical energy (nerve impulses), or light energy (bioluminescence)
• All energy transformation reactions are exothermic, meaning they release heat as a by-product, which is why some energy is lost through heat
• Energy transformations can be between 5 and 20% effective because of energy losses
• As energy is lost between trophic levels, higher trophic levels store less energy as carbon compounds and so have less biomass (total mass of a group of organisms)
• Higher trophic levels receive less energy from feeding, so they need to eat more. If the energy required to hunt is greater than the energy from the food eaten, the trophic level is non-viable
• Energy pyramid: a graphical representation of the amount of energy present at each trophic level, expressed in energy per area per time. Each level is about 1/10 the size of the previous, with tertiary consumers at the top of the pyramid.
• The carbon cycle: a biogeochemical cycle where carbon is exchanged between the 4 spheres of the earth:

  1. Atmosphere (air)
  2. Lithosphere (ground)
  3. Hydrosphere (water)
  4. Biosphere (living things)
• Carbon is exchanged between:

  • Atmospheric gases (CO2 and CH4)
  • Oceanic carbonates (bicarbonates, calcium carbonate)
  • Organic materials (carbohydrates, lipids, proteins)
  • Non-living remains (detritus, fossil fuels)
• Autotrophs convert inorganic CO2 into organic compounds via photosynthesis. Since autotrophs use CO2 for photosynthesis, it should always be at a higher concentration in the air/water than other molecules. This concentration gradient ensures passive diffusion of CO2 into the organism.
• If net photosynthesis is greater than cellular respiration, atmospheric CO2 levels will drop, and vice versa