Unit 4

HideShow resource information
  • Created by: emma
  • Created on: 30-12-14 17:07


Overview- 6H2O + 6CO2 = 6O2 + C6H1206. Thylakoids have large surface area for attachment of enzymes, stroma fluid has enzymes for light independent reaction, chloroplasts have DNA and ribosomes to make proteins. ATP provides energy, NADPH provides reducing power

Light dependent reaction- occurs in the thylakoids

  • light hits chlorophyll
  • electrons excited and raised to higher energy levels
  • electrons pass down electron transport chain via redox reactions
  • lose energy which is then used to make ATP from ADP and Pi
  • Water is split into H+ ions, electrons and O
  • electrons replace those lost in chlorophyll
  • electrons from a second electrons transport chain combine with NADP and H+ from photolysis to make NADPH
  • O is a useful waste product

Light independent reaction (Calvin cycle) - in the stroma

  • RuBP combines with CO2 to make 2x GP
  • GP reduced to TP requires reducing power of NADPH and energy from ATP
  • Some TP used to make organic molecules, some to regenerate RuBp (requires ATP)
1 of 13

Nitrogen cycle

  • Primary consumer eats producer and digests nitrogen containing compounds
  • Secondary consumer eats primary consumer and digests N containing compounds
  • Decomposers break down waste and dead organic matter by secreting digestive enzymes
  • The decomposers are saprobiotic bacteria and convert N compounds in organic molecules into ammonia (ammonification)
  • Ammonia converted to nitrites which are then converted to nitrate by nitrifying bacteria (nitrification)
  • Nitrates are taken up by plants through root hair cells via active transport
  • Some nitrates are converted to N gases by denitrifying bacteria (denitrification)
  • Nitrogen converted back to ammonia by nitrogen fixing bacteria, free living and mutualistic (nitrogen fixation)
  • In lightning storms N and O in the atmosphere combine to make nitrates
2 of 13

Carbon cycle

  • Plants take in CO2 in photosynthesis and the C is stored in organic molecules e.g. starch
  • Primary consumers eat producers and digest and assimilate C containing compounds
  • Secondary consumers eat primary consumers and C is passed along the food chain
  • Plants and animals respire and release CO2 to atmosphere
  • Decomposers break down dead organic matter and C containing molecules
  • Decomposers respire and release CO2 to the atmosphere
  • Burning fossil fuels release CO2

Short term CO2 increase due to- seasons (shorter days, less leaves and cold temperatures mean less photosynthesis.) Air movement (less air movement means CO2 around plants not mixed in air.) Time of day (day photosynthesis, night respiration.) Short term CO2 fluctuations depend on the balance between rate of photosynthesis and rate of respiration and the overall net CO2 uptake/output.

Long term CO2 increase due to- deforestation (clearing and burning) and burning fossil fuels

Greenhouse effect- when suns energy is reflected back into the earth’s atmosphere but prevented from escaping by greenhouse gases. To many greenhouse gases results in global warming. Greenhouse gases include CO2 and methane. Methane conc increased due to more cattle (bacteria in gut that break down cellulose produce CH4) and paddy fields are perfect conditions for anaerobic bacteria.

Global warming affects distribution of organisms- mobile species move to favourable climates, pests life cycles are shorter so more suvrive winter and there are more generations of pests.

3 of 13

Energy and food production, fertilisers

Agricultural ecosystems- Productivity high, energy input from the sun, fossil fuels for machinery and food for workers. Low diversity, less trophic levels in food chain, less predation and competition, abiotic factors reduced with fertilisers

Macronutrients- Nitrogen (for amino acids, DNA, RNA) Phosphorous (phospholipid bilayer, ATP, DNA, NADP) Potassium (protein synthesis and K+ pumps)

Micronutrients- Magnesium and Iron (chlorophyll production) Sulphur (protein production)

Organic (manure) - +Cheap, provide steady release of minerals over time, less leaching problems, improves soil structure. - Difficult to spread, takes time for minerals to be released, need large amounts

Inorganic- + Easy to spread, known composition, soluble so ions immediately available, no seed or pests, concentrated so small amount needed. - Expensive, leaching, doesn't improve soil


  1. Ions leach in water causing an algal bloom, preventing light reaching plants underneath algae
  2. Plants cannot photosynthesis and die, algae dies
  3. Increase in aerobically respiring decomposers breaking down dead matter, deplete oxygen levels in water
  4. Other animals in the water die as they cannot respire with no oxygen
4 of 13

Energy and food production, pests

Pests- Organisms that reduce the yield of a crop plant directly or indirectly

  • Weeds- interspecific competition with crop for space, light, nutrients
  • Insects- Eat part of crop used by humans (direct) eat leaves reducing surface area for photosynthesis (indirect)
  • Fungi- Spread disease

Monocultures- One crop grown over a large area. Disease is easy to spread, pests travel easier

Insecticides, herbicides and fungicides- Residual, sprayed on soil, fungal spores, seeds and larvae before pest grows. Contact, sprayed directly on pest, absorbed through stoma on leaves and spiracles on insects. Systematic, taken in through leaves and transported around plant (kills all of weed) insects eat plant containing pesticide.

Biological control- control agent is a natural predator of pest. Reduce pest levels to below harmful but doesn’t wipe them out completely. Pests don't become resistant to pesticides and no environmental damage from pesticide. Control agent may become pest or maybe subject to predators.

Intergrated systems use biological control and pesticides

Bioaccumulation- Build up in conc of a substance along the food chain to toxic levels.

5 of 13

Energy and food production, domestic livestock

Energy losses at each stage in the food chain are reduced so more energy is converted to biomass

  • Kept indoors so temperature is controlled resulting in less energy lost as heat loss
  • Small spaces less energy lost through respiration as less movement (muscle contraction)
  • Fed optimum nutrition so more nutrients are absorbed and used for growth and less energy lost as faeces
  • Predators excluded
  • Selectively bred, most efficient breeds at converting energy into new tissue are chosen
  • Hormones increase growth rate
  • Slaughtered when still growing so more energy transferred to biomass

There are ethical concerns to consider with domestic livestock

6 of 13

Human populations

Sigmoid growth curve- Lag phase, slow growth as organisms adapt to environment. Log phase, rapid exponential growth as no limiting factors. Stationary phase, birth and death rate reached equilibrium limiting factors. Decline phase, population decreases as build-up of toxic waste.

Calculations- Birth rate =no of births/total pop x 1000, Death rate=no of deaths/total pop x 1000, Growth rate= Birth rate – Death rate, %growth rate= pop increase/ pop at start x 100

Demographic transition- High stationary phase, high birth and death rate, slow pop growth. Early expansion stage, high birth, falling death rate, increased pop growth. Late expansion stage, falling birth, low death rate, increased pop. Low stationary phase, low birth and death rate, slow pop growth

Increased birth rate- Better care for mothers, religion, lack of contraception, less developed countries have high infant mortality rate, politics, poor economic conditions

Increased death rate- Poor health care, disease, lack of food, poor sanitation and water, war, natural disaster, low life expectancy.

Population pyramids- Wide base and narrow top, high birth and death rate, low life expectancy, less developed countries. Narrower base and wider top, low birth and death rate, long life expectancy, developed country with aging pop.

Life expectancy- age at which 50% of population still survive

7 of 13


Succession- A series of changes in a community over time.

Key points- Pioneer species are the first to colonise an area and have special adaptations to survive hostile conditions. Change environment to make it less hostile (build up humus when decay). Other species become established. Pioneers are outcompeted by other species. Other species establish and out compete others until climax community is reached. During succession abiotic become less harsh and biotic factors harsher. Plants get bigger/ faster growing. Climax community most stable as most diverse and more complex food web.

Primary succession- Begins with bare rock, pioneer species usually lichen then moss

Secondary succession- After a forest fire, flood, agricultural clearing. Seeds and spores remain viable. Big influx of animals into area due to migration and seeds due to seed dispersal. Begins with species from an intermediate seer.

Deflected succession- Climax community is prevented from establishing due to agriculture. Cattle grazing, use of herbicides, ploughing, weeding, burning, crop planting.

8 of 13


Glycolysis- In cell cytoplasm. Glucose is activated when phosphorylated (requires ATP). Phosphorylated glucose split into 2x TP. TP is oxidised to form Pyruvate, producing NADH2 and 2x ATP.

Link reaction- In matrix. Pyruvate combines with enzyme co A to make acetyl co A. NADH2 and CO2 is produced.

Krebs cycle- In matrix. Acetyl co A combines with 4c compound to make a 6c compound. This is oxidised to a 5c compound (NADH2 and CO2 produced). 5c compound oxidised to 4c compound (NADH2, FADH2, ATP and CO2 produced)

Electron transport chain- In cristae (inner membrane). NADH2 and FADH2 oxidised. Electrons pass down etc in redox reactions, losing energy. Energy used to pump H+ into intermembrane space. H+ pumped back through inner membrane via ATPase providing energy to make ATP. H+ combine with electron from etc and oxygen to form H2O. O is a terminal electron acceptor.

Substrate phosphorylation- ATP generated directly through respiration

Oxidative phosphorylation- ATP generated from chemical energy released when hydrogen carrier or co enzyme is reduced

9 of 13

Energy transfer

Food chain- Producers are autotrophic as they can convert energy into organic molecules. Consumers are heterotrophic as rely on an external source of organic molecules. Trophic levels show level of feeding stage of an organism. Usually 4 trophic levels as energy transfer is inefficient.

Food webs- More complex the more stable and diverse the ecosystem. One loss has little effect.

Pyramid of numbers- Number of organisms at each trophic level. Hard to draw to scale, doesn’t take into account biomass of organism (trees and parasites)

Pyramids of biomass- Biomass of organisms at each trophic level. Overcomes problems of differing sizes. Dry mass must be measured (organisms killed) so small sample size. Only considers one particular time, no account for seasonal changes.

Pyramids of energy- Energy utilised at each trophic level. kJMm-2year-1. Hard to measure.

Energy lost at each level- Sun and producer, some light reflected, some misses chlorophyll, some light the wrong wavelength. Producer and consumer, some of the plant is indigestible, not all the plant is eaten, some energy is lost to respiration some energy is lost as heat or faeces.

Net productivity = Gross productivity – Respiration. Net productivity is energy stored as biomass. Gross productivity is energy converted into organic molecules

%efficiency= energy after / energy before X 100

10 of 13

Investigating populations

Random quadrating- Place tape measures at right angles to each other to produce an axis. Generate random numbers on a calculator to create co-ordinates. Place quadrat at intersection of co-ordinates and measure abundance.

Systematic sampling- Place tape measure across area to create transect. Place quadrat at predetermined intervals along transect, generated randomly by a calculator. Helps to measure how diversity changes across an area.

Abundance- Percentage cover, percentage of the quadrat that a species covers. Population density, actual number of species in the quadrat. Population frequency, the number of different quadrats a species is present in.

Mark release recapture- Capture a number of individuals from a certain species. Mark individuals captured and count them. Release individuals and allow time to redistribute. Capture more individuals of the species. Count the number captured and the number of individuals that are marked. Must be no births and deaths, no immigration or emigration, allowed time to redistribute and mark must not make them more vulnerable to predation or be toxic.

11 of 13


Gene- section of DNA that codes for a protein. Allele- different form of the same gene

Genotype- genetic constitution of an organism including alleles

Phenotype- observable characteristics of an organism. A result of the interaction of the genotype and the environment.

Pedigrees- Genetic inheritance in the form of a family tree. Males are squares, females are circles. Particular phenotype shown if shaded in. If phenotype misses a generation the allele is recessive. If all males/females display phenotype the genotype is sex linked.

Co dominance- Both alleles are dominant so are expressed in a heterozygous individuals phenotype as an intermediate.

Sex linkage- Males genotype XY, females **. 50% chance male, 50% female. The X chromosome carry normal body genes and these are linked to the genes that determine sex. In male’s alleles on the X chromosome has no corresponding alleles on the Y chromosome. So a male only need one recessive allele whereas a female need two. This is why sex linked diseases are more common in males.

Hardy Weinberg- P + Q = 1,    Psquared + 2PQ + Qsquared = 1, Psquared is homozygous dominant, Qsquared is homozygous recessive, 2PQ is heterozygous.

12 of 13

Selection and speciation

Selection- process by which organism better adapted to the environment are more likely to survive and reproduce resulting in the increase of the frequency of the advantageous allele in the population.

Selection pressure- Organisms are subject to a selection pressure due to the environment they live in. It determines the spread of alleles within a gene pool

Stabilising selection- stable environment, selective pressure at both ends of distribution, eliminates extremes, favours average, reduces variability, and reduces opportunity for evolution.

Directional selection- environmental change produces new selection pressure that favours the extreme characteristic, optimum necessary for survival changes, some organisms possess new optimum, and these will predominate.

Speciation- evolution of a new species from existing species

Geographical isolation- physical barrier prevents 2 populations meeting. Population subject to different selection pressure and adapts due to natural selection. Changes in genotype and phenotype. Two populations are reunited and unable to interbreed and are reproductively isolated.

13 of 13


:) PurpleJaguar (: - Team GR


Really useful for last minute reading, thanks! :)

Similar Biology resources:

See all Biology resources »See all everything in unit 4 resources »