ecology igcse edexcel combined science

what is a sample?

when you take a smaller representative part of a population

define environment

the total non-biological components of the ecosystem like water soil and air

define habitat

the place where a specific organism lives

define population

all the organisms of a particular species found in an ecosystem

define community

the population of all species found in a particular ecosystem

describe how a quadrat can be used to investigate the population size of an organism in two different areas

-Divide the sample areas into a grid
- Place quadrat randomly using a random number generator
- Count how many of the species is present
- Repeat
- Multiply to total area
- Repeat procedure for second area

what are biotic factors?

biological or living factors
like predation, parasitism, food availability, nesting sites and disease

what are abiotic factors?

non-biological/non-living factors
like temperature, pH of soil, light intensity, number of daylight hours

define producer

plants which photosynthesise to produce food

define consumer

animals which eat plants or other animals

what is a decomposer

organisms which decay dead material and help to recycle nutrients

define parasite

an animal which lives inside another animal, gaining food and causing harm to host animals

define predator

an animal which kills and eats another animal

define the trophic level

the position in a food chain / web
- eg: producer, primary consumer, secondary consumer, tertiary consumer

what is meant by a food chain or food web?

shows feeding relationships
by showing which organisms eat which organisms
shows the flow of energy from producer to top consumer through trophic levels

how does chemical energy flow through food chains or webs?

by feeding

what do the arrows in a food chain or web represent?

direction of energy transfer

what is a pyramid of numbers?

they represent the number of organisms at each trophic level, irrespective of their biomass

what is biomass?

the total amount of living material in an organism

how is biomass measured?

organism killed
heated to remove water
constant dry mass measured

what is a pyramid of biomass

they represent the total mass of organisms in each trophic level, irrespective of their number

give the advantage and disadvantage of using a pyramid of biomass?

advantage: more accurate as organism's size taken into account
disadvantage: data difficult to obtain as dry mass required

Describe how a quadrat can be used to estimate plant biomass in a region

divide the sample area into a grid
record the dry mass of a plant using scales
repeat
multiply to total area

explain why only 10% of energy is transferred from one trophic level to the next

- not all of the plant is eaten (in the case of producer -> primary consumer)
- some parts are indigestible (in the case of producer -> primary consumer)
- some energy lost in excretory products like sweat and urine
- respiration leads to loss of carbon dioxide and water
- maintenance of steady body temperature like homeostatis in cows

what is the carbon cycle?

- Carbon dioxide is absorbed by green plants in photosynthesis
- Carbon used to make glucose and proteins
- Plants respire releasing carbon dioxide
- Plants eaten by animals and carbon becomes part of their bodies
- Animals respire releasing carbon dioxide
- Plants and animals die and are decomposed by microorganisms
- Microorganisms respire, releasing carbon dioxide
- Complete combustion of fossil fuels releases carbon dioxide

how is acid rain made?

- impurities in crude oil (a fossil fuel) → sulfur dioxide → sulfuric acid
- nitrogen and oxygen react in car engines → nitrogen oxides → nitric acid

react with condensing water vapour

what effect does acid rain have

- Destroys limestone buildings - Kills trees
- Makes ponds too acidic leading to death of fish

what produces carbon monoxide?

incomplete combustion

what effect does carbon monoxide have on the body?

combines irreversibly with haemoglobin so less oxygen is transported

what is a greenhouse gas?

gas that traps heat by reflecting infrared radiation

give examples of greenhouse gases

methane (cows, rice paddy fields)
water vapour
carbon dioxide (burning fossil fuels)
nitrous oxide (burning fossil fuels, car engines)
CFCs

where do CFC's come from?

aerosols, fridges

what effect do CFCs have on the environment

damages the ozone layer
contributes to the greenhouse effect

explain how the greenhouse effect causes global warming

sun emits energy that enters Earth's atmosphere
energy absorbed and reemitted by Earth's surface as IR radiation
some IR radiation reflected back out into space
some IR radiation absorbed by greenhouse gases
heat is trapped within Earth's atmosphere
as greenhouse gases levels increase, Earth's average temperature increases
causing global warming

how have humans contributed to the increase in atmospheric greenhouse gases?

- Carbon dioxide produced by combustion of fossil fuels
- Methane produced by grazing cattle
- Methane released by rice paddy fields
- Deforestation results in more CO2 in atmosphere
- Less photosynthesis occurring
- CFCs from fridges and aerosols released into atmosphere

what possible effects does an enhanced greenhouse effect have?

Global warming- Ice caps melt- Sea levels rise - Low lying land floods- Destruction of habitats- Loss of biodiversity- Extreme weather - Change in bird migration patterns

how can humans reduce the build up of greenhouse gases in the atmosphere?

burn less fossil fuels
plant more trees/reduce deforestation
use renewable energy
reduce cattle farming and use fewer paddy fields

describe the effects of leached sewage and excess fertilisers on the environment

eutrophication
fertilisers and sewage are washed into rivers
water plants grow quickly - algal bloom
competition for sunlight
plants die
bacteria feed on the dead plats
bacteria use up all the oxygen in respiration
fish die as not enough oxygen