iGCSE Biology Notes Organisms and their environment

[q] Energy flow

[a] Sun is the principal source of energy input to biological systems

[q] Producers

[a] 

○ Organisms that produce their own organic nutrients usually energy from sunlight.
○ Plants are producers as they carry out photosynthesis to make glucose

[q] Herbivore

[a] An animal that get its energy by eating plants

[q] Carnivore

[a] An animal that get its energy by eating other animals

[q] Primary consumers

[a] Organisms that feed on producers

[q] Secondary consumers

[a] Predators that consume on primary consumers

[q] Tertiary consumers

[a] Predators that consume on secondary consumers

[q] Decomposers

[a] Bacteria and fungi that get their energy from feeding off dead and decaying organisms and undigested waste by secreting enzymes to break them down

[q] Food chain

[a] Food chain is showing the transfer of energy from an organism to the next, beginning with a producer

[q] Energy is transferred between organisms in a food chain by

[a] ingestion

[q] Food web

[a] Food web is a network of interconnected food chains

[q] Trophic level

[a] Trophic level is the position of an organism in the food chain, food web, pyramid of numbers or pyramid of biomass
○ Producers convert light energy into chemical energy and it flows in this form from one consumer to the next
○ Eventually all energy is transferred to the environment
■ Some being used by each and lost at each stage

[q] Food webs are more realistic way of showing connections between organisms within an ecosystem as

[a] animals rarely exist on just one type of food source

[q] Transfer of energy

[a] 

○ Very inefficient
○ It has to be consumed
○ Not all of the energy grass plants receive goes into making new cells that can be eaten
○ Organisms lose energy through
■ Making waste products
■ As movement
■ As heat
■ As undigested waste
○ Food chains are rarely more than 5 organisms long

[q] A pyramid of numbers

[a] A pyramid of numbers shows how many organisms we are talking about at each level of a food chain
○ Width of the box indicates the number of organisms

[q] A pyramid of biomass

[a] A pyramid of biomass shows how much mass the creatures at each level would have without including all the water that is in the organisms

[q] Carbon cycles

[a] ○ Carbon is taken out of the atmosphere in the form of carbon dioxide by plants to be used for photosynthesis
○ It is passed on to animals by feeding
○ It is returned to the atmosphere in the form of carbon dioxide by plants, animals and microorganisms as a result of respiration
○ If animals and plants die in conditions where decomposing microorganisms are not present the carbon in their bodies can be converted into fossil fuels
○ Increased use of fossil fuels is contributing to an increase in the carbon dioxide content of the atmosphere
○ Mass deforestation is reducing the amount of producers available to take carbon dioxide out of the atmosphere by photosynthesis

[q] Water cycles

[a] 

○ Water enters the atmosphere as water vapour by
■ Energy from the sun heats the Earth’s surface and water evaporates from oceans, rivers and lakes
■ Transpiration from plants release water vapour into the air
○ The moist air cools down as it rises
○ Water vapour condenses back into liquid water, forming clouds
○ As the water droplets in the cloud get bigger and heavier, they begin to fall as rain, snow and sleet
○ This is called precipitation

[q] Nitrogen cycle

[a] 

○ Plants nor animals absorb nitrogen from the air
○ There are two ways it can be taken out of the air and converted into something easier to absorb:
■ Nitrogen fixing bacteria
■ Lighting can ‘fix’ N2 gas
○ Plants absorb nitrates they find in the soil and use the nitrogen to make proteins
○ Animals eat the plants and get the nitrogen they need from the proteins in the plant or animal
○ Waste from animals sends nitrogen back into the soil as ammonium compounds
○ When the animals and plants die, they decay and all the proteins inside them are broken down into ammonium compounds and put back into the soil by decomposers
○ The plants can’t absorb ammonium compounds though, so then nitrifying bacteria
○ Convert the ammonium compounds to nitrites and then to nitrates, which can then be absorbed by plants
○ The third bacteria called denitrifying bacteria found in poorly aerated soil
■ Take nitrates out of the soil and convert them into N2 gas

[q] Population

[a] Population is the group of organisms of one species, living in the same area, at the same time

[q] Community

[a] Community is all of the populations of different species in an ecosystem

[q] Ecosystem

[a] Ecosystem is a unit containing the community of an organisms and their environment interacting together

[q] Human population

[a]

Human population has exponentially increased in the last 150 years
○ There are many reasons for this exponential growth
○ Improved technology leading to an abundance of food = rapid increase in birth rate
○ Improved medicine, hygiene and health care = decrease in death rate

[q] Growth and death graph

[a]