biology 9.1 to 9.8b (ecosystems topic)

9.1 - describe the different levels of organisation in the whole ecosystem

• all the organisms and the environment they live in form an ecosystem

• all the organisms that live in an ecosystem form a community

• the community is made of different populations of diff species

• each population lives in a different habitat in the ecosystem

9.2 explain how communities can be affected by abiotic factors

• Water – if there is a drought or flood then it will cause a species to die out

• Temperature – if the species are not at the optimum temperature to survive, they won’t be adapted well and they will die

• Light – plants need enough light to photosynthesise

9.2 how can communities be affected by biotic factors

• Competition – when organisms need the same resources at the same time, they will struggle against other organisms. An increase or decrease in population results in a change of competition

• Predation – if there is lots of predators, number of prey will decrease. And if there are not many predators, number of prey will increase

9.3 describe the importance of interdependence in a community

• Interdependence is important because certain species depend on others for food, shelter, pollination etc.

• This means that a change in the population of one species will have a great knock-on effect on other species in the same community

9.4 describe how the survival of some organisms is dependent on other species

• Parasitim – where one species benefits and the other is harmed. E.g fleas and humans → the fleas feed off the humans, but the human skin gets irritated

• Mutualism – when both species benefit from the relationship. E.g. ants and acacia trees → ants kill caterpillars (which eat acacia leaves), and in return the acacia tree grows thorns to provide homes for ants

9.5 core practical - the relationship between organisms and their environment - method, variables

• Method: use a random number generator to select the position of each quadrat. Place each quadrat in the random position and record the number of species in each quadrat.

• Variables:

control = number of quadrats, time of day. Independent variable = location of quadrat in area. Dependant = number of species counted

9.7B explain how some energy is transferred to less useful forms at each trophic level

• Some energy is transferred to less useful forms at each trophic level through respiration

• This affects the number of organisms at each trophic level and limits the length of a food chain.

• It also determines the shape of a pyramid of biomass

9.8b Calculate efficiency of energy transfers between trophic levels

(Energy transferred to next level / energy available at previous level) / 100