Biology topic 5

Ecology

The study of living things in their environment

Ecosystem

A self-sustaining life-supporting environment (with biotic and abiotic factors)

Habitat

The place where an organism lives

Population

Group of organisms of the same species

Community

All the populations of different species

Niche

Role of an organism in the community

Abiotic factors

Non-living elements of the habitat that affect survival

Biotic factors

Living elements of the habitat that affect survival

Anthropogenic

Factors arising from human activity that affect survival

Biosphere

Global ecosystem, all organisms on earth

Biomes

Major ecosystems on earth

Succession

The process by which communities of organisms colonise an area and then over time are replaced by other usually more varied communities

Primary succession

Succession on inorganic surface devoid of any vegetation

Stage 1 of succession

• pioneer species eg. Lichens and mosses

• Help break down rock surface

• Rock grains and dead organic matter form soil

Stage 2 succession

• intermediate species

• Establish root systems in soil

• Soil system develops (more water and nutrients retained) allowing other plants to survive

Stage 3 succession

• climax community

• Remains unchanged unless conditions change

• Dominant species influence rest of community

Secondary succession

Development of an ecosystem from existing soil that has been cleared of vegetation

Deflected succession

A community that is kept stable by human activity which prevents succession from running its course

heterotrophic nutrition

get food from somewhere else e.g. fungi, animals

autotrophic nutrition

make their own food e.g. plants, algae, some bacteria

phototrophs

make food using solar energy e.g. plants

chemotrophs

make food using chemical reactions e.g. sulphur bacteria use chemosynthesis

photosynthesis equation

6CO2 + 6H2O —> C6H12O6 + 6O2

chlorophyll

one of several photosynthetic pigments

chlorophyll a and b

• hydrophilic head - Mg2+ at centre of porphyrin ring

• hydrophobic tail - hydrocarbon chain anchors molecules into chloroplast membrane

carotenoids

• red, orange, yellow pigments

• hydrophobic

• membrane attached

• assist chlorophyll by passing light on to them = accessory pigment

outer membrane of chloroplast

allows free passage of CO2, O2 and H2O

inner membrane of chloroplast

contains many transporter proteins

thylakoid membrane

• interconnected flat fluid-filled sacs of membrane

• membrane contains photosynthetic pigments

• light-dependent reaction occurs across thylakoid membrane

granum

stack(s) of thylakoids

stroma

• fluid surrounding thylakoids

• light independent reaction occurs here

starch granule in chloroplasts

storage of photosynthetic products

DNA loop in chloroplasts

chloroplast DNA coding for some proteins

functions of the light dependent reaction

• production of ATP to supply energy for synthesis of carbohydrates

• production of NADPH to supply H+ ions for synthesis of carbohydrates

ATP

adenosine triphosphate - transport of chemical energy

how does ATP release energy?

when it is hydrolysed to form ADP and Pi

NADPH

• nicotinamide adenine dinucleotide phosphate

• coenzyme

• functions as reducing agent by carrying hydrogen

photosystem 1

P700 - reaction centre is chlorophyll a

photosystem 2

P680 - reaction centre is chlorophyll a

diagram of light dependent reaction

light dependent reaction steps 1-4 in detail

1. PS 2’s P680 reaction centre emits 2 excited electrons when light hits it which pass to an electron acceptor which is reduced

2. the electrons lost from PS 2 are replaced by the photolysis of H2O which produces 2H+ ions, 2 free electrons and 1/2O2

3. electrons then pass to a series of electron carriers along an electron transport chain. each carrier becomes reduced, then oxidised as it passes the electrons on

4. each electron carrier has a lower energy level than the last so as the electrons pass on energy is released which is used to synthesise ATP in a reaction called photophosphorylation

light dependent reaction steps 5-7 in detail

5. PS 1’s P700 reaction centre also emits 2 excited electrons. these are replaced by the two electrons from the PS 2 electron transport chain

6. electrons emitted from PS 1 are captured by an electron acceptor and pass down another chain of electron carriers

7. the 2 electrons combine with H+ from H2O to reduce NADP+ to NADPH

chemiosmosis

• Movement of ions across a semi permeable membrane, down their electrochemical gradient

• occurs as H+ ions move across the thylakoid membrane

function of the light independent reaction

to use NADPH and ATP to reduce CO2 to produce glucose in a series of reactions called the Cavlin cycle

Calvin cycle diagram

step 1 of the Calvin cycle : CO2 fixation

• CO2 combine with RuBP to form 2x GP

• catalysed by enzyme RuBisCO

step 2 of Calvin Cycle: reduction

• GP is reduced to form GALP

• hydrogen for reduction is from NADPH

• energy for reduction is from ATP

step 3 of Calvin Cycle: regeneration of RuBP

• GALP uses ATP to resynthesise RuBP

• glucose is produced (cycle completed 6 times per glucose molecule)

primary consumer

herbivores - eat photosynthetic material

secondary consumer

carnivores - feed on herbivores

tertiary consumer

top carnivores - feed on herbivores and other carnivores - aren’t eaten by anything

autotrophs

photosynthetic or chemosynthetic organisms

heterotrophs

consumers of other organisms

omnivores

feed on photosynthetic organisms and animals

trophic level

feeding level

food chain

diagram showing a simple linear feeding relationship

food web

diagram showing complex feeding relationships (often representing all organisms in an ecosystem)

detritivores

primary consumers that feed on dead organic matter

decomposers / saprotrophs

bacteria and fungi that feed on dead organic matter and faeces; recyclers of nutrients; use external digestion

on average, how much energy is lost between trophic levels?

about 90%

primary productivity

rate at which energy is incorporated into organic molecules

limiting factors to photosynthesis

• light intensity

• H2O from soil

• temperature

• CO2 from air

gross primary productivity (GPP)

the rate at which energy is incorporated into organic molecules

net primary productivity (NPP)

the rate at which energy is incorporated into organic molecules that make up new biomass

NPP equation

NPP = GPP - respiration

secondary productivity

the rate at which energy is used to make new consumer biomass

secondary productivity equation

energy consumed = energy lost in respiration + energy lost in waste + energy in biomass

factors that affect how much energy is lost in respiration

• SA/vol ratio

• time spent foraging for food

• temperature of environment

• digestibility of food

temperature records as evidence for climate change

• data from more than 1000 weather stations around the globe

• precise records begin in 1880

• overall trend is increasing temperature

paleoclimatology

the study of changes in climate taken on the scale of the entire history of Earth

use of ice cores for evidence of climate change

• drilled from ice sheets and glaciers

• encloses small bubbles of air that contain a sample of the atmosphere at that time

• older ice is further down

• concentration of gases can be measured and can be interpreted for temperature

• in warmer climates more 18O in polar ice than usual

peat bogs

• substrate made of dead organic matter

• acidic, cool and anaerobic/anoxic

• forms in layers - age can be determined by carbon dating

how do anaerobic conditions reduce decomposition?

• low (or no) oxygen, decomposing bacteria and fungi cant respire so die

• digestive enzymes not present

• acidic pH reduces enzyme activity

pollen in peat bogs as evidence for climate change

• pollen is resistant to decomposition

• different plant species grow best in different conditions

• plants can be identified and climate at the time can be interpreted

insect records in peat bogs as evidence for climate change

• exoskeleton preserved in peat bogs

• populations respond faster than plants to climate change

• thrive in particular climate conditions

dendrochronology

the dating of tree wrings to the year they were formed in order to analyse climatic conditions during different periods in history

atmosphere

a layer of gases surrounding a planet

how does the atmosphere sustain life?

• oxygen for respiration

• carbon dioxide for photosynthesis

• ozone layer absorbs UV light reducing genetic damage

• maintains stable temperature

greenhouse effect

1. short wavelength solar radiation passes through the atmosphere

2. some radiation is absorbed, warming the Earth

3. some longer wavelength infrared radiation is reflected off the Earth

4. most longer wavelength IR radiation escapes to outer space allowing the Earth to cool

5. some longer wavelength IR radiation is absorbed by greenhouse gases in the atmosphere, warming the earth and lower atmosphere

global warming

enhanced effect due to an increased level of greenhouse gases

source of carbon dioxide

• combustion of fossil fuels

• respiration

source of methane

• anaerobic bacteria in marshes and rice paddies

• anaerobic bacteria in guts of ruminants e.g. cows

• decomposition of organic material

• leakage from gas pipes and coal mines

source of nitrous oxide

• combustion of fossil fuels

• denitrifying bacteria acting on nitrates and nitrites

sources of CFCs

• coolants

• propellants

source of ozone

reaction product of car exhaust pollutants and sunlight

scientific theory

comprehensive explanation of some aspect of nature that is supported by a vast body of evidence and upon which predictions can be made

extrapolation

an estimate outside the recorded or observed range

factors to take into account to predict future CO2 concentration

• price of fossil fuel

• Kyoto protocol

• development of clean technology

• amount of photosynthesis

• increase in word population

climate models

quantitative methods to simulate the interactions of the different factors to project future climate

limitations of climate models

• limited data

• limited knowledge on how climate works

• limited computing resources

• not all factors considered

• changing factors or new factors

how flora and fauna are adapting to climate change

• changes in distribution

• changes in development

• changes in life cycle

alien species

non-native species that can reduce biodiversity through disease, competition or predation

coral bleaching

loss of the photosynthetic symbiont

increase in temperature below optimum

• as temperature increases, rate of reaction increases

• more collision of substrate and enzyme due to higher kinetic energy

enzyme optimum temperature

highest rate of reaction

effect of temperature increase on enzymes above optimum

• as temperature increases, rate of reaction decreases

• secondary and tertiary bonds break due to high vibration of molecules

• enzyme denature

• active site change shape

• no binding of substrate

phenology

study of periodic plant and animal life cycles and how these are influenced by seasonal climate

how natural selection works

• features encoded by genes

• natural variation due to alleles increasing the gene pool of the population

• selection pressure gives some individuals an advantage

• these are more likely to survive, reproduce and pass on their alleles

chromosome mutation

a change in the structure of a chromosome

e.g. duplication, inversion, deletion, insertion, translocation

gene mutation

change in the DNA base sequence in genes