Ecology

• Photosynthesis equation:

  Carbon dioxide + water --> glucose + oxygen
• abiotic factors that affect the growth of a plant:

  • light intensity
  • water level / humidity
  • temperature
  • pH of soil
  • mineral level in soil
  • concentration of CO2
• Biotic factors that affect growth of plants:

  insects and pests
• Why do farmers want to increase their yield?

  they want to maximise their profit by balance managing factors
• factors that have a major influence on farmer yield?

  • exposure to the weather
  • exposure to low temperature
  • pests
• how to protect plant from extremes of temperature?


  grow vulnerable crops in polythene tunnels and glass houses

  this also controls the factors that have a major influence on yield
• How does increasing temperature affect a plant's rate of photosynthesis?

  1. low rate : low kinetic energy therefore low collision with enzymes
  2. increasing temperature --> increasing KE therefore increases rate
  3. Max temperature = max rate --> enzymes are working at optimum temp
  4. increasing temperature even further causes PS to stop as enzymes denature
• How will temperature affect the yield of a crop plant?

  increased photosynthesis --> increased glucose --> increased respiration --> increased release of energy in form of ATP for growth
• Change in CO2 in a glass house effect on rate of PS?

  more CO2 --> more photosynthesis --> greater yield

  BUT rate would plateau due to limiting factors (e.g. light/water/temp)
• nitrates use?

  form amino acids + DNA (bases) --> for growth
• nitrates deficiency?

  stunted growth

  older leaves turn yellow
• magnesium ions use ?

  formation of chlorophyll
• magnesium ions deficiency?

  yellow leaves
• What is the problem with pests?

  a factor that will affect crop yield if it is attacked by pests
• how to control pests?

  • use of pesticides
  • introduce a natural predator (biological control)
• Pesticides:

  • can kill non target species
  • works better in glasshouses
  • could contaminate human food
  • pests can become resistant
  • can be affected by rainfall
  • can enter food chain and accumulate in animals
• biological control:

  • works better in glasshouses
  • could become a pest
  • might migrate away from the fields
  • only targets pest species
  • does not need to be reapplied
• Bioaccumulation:

  • build up
  • when toxins accumulate in the body of an organism
• two ways bioaccumulation can occur?

  1. an organism consumes small levels of the toxin; it is not broken down or excreted and instead stored in fatty tissue. over time the chemical accumulates in the animal until it reaches harmful levels
  2. toxin can become more concentrated as it goes up trophic levels of a food chain. e.g. after spraying, field insects picked up a low level of pesticide. sparrows eat lots of these insects and end up getting a higher dose. this then repeats and a hawk will get an even bigger dose of pesticide
• Problems with overfishing:

  • increasing demand for fish as a source of protein
  • causes many fish species to decrease significantly or disappear
  • modern fishing techniques are very destructive to the ecosystem
  • trawling for fish involves dragging a net along the seabed
  • kills invertebrates animals by crushing them or burying them beneath a layer of sediment
  • any unwanted species of fish or animals are also killed
• fish farming:

  • has been helping meet the shortfall in fish
  • most commonly farmed fish are the more economic species (e.g. salmon)
  • not all used for human food: about 1/4 farmed fish is used to make animal food
• advantages of fish farming:

  • fish are kept in large seawater enclosures or tanks where water quality can be carefully controlled
  • temperature and pH levels are also controlled
  • diet of fish is carefully controlled in both quality and quantity of feeding
  • fish are protected against predators
  • pesticides are used to kill parasites
  • selective breeding programs increase quality of the fish e.g. bred to produce faster growth and be more placid than wild fish
• Disadvantages of fish farming

  • Animals are close together so spread of disease is more common
  • Risk that pesticides have not fully degraded and may enter human food chain
  • Pollution from organic materials in excess food and faeces causing eutrophication of lakes
  • Pesticides used to kill parasites can kill non-harmful species of invertebrates
  • Antibiotics used to treat bacterial diseases can lead to the development of antibiotic resistance bacteria
  • Farmed fish may be fed on fish pellets made from wild fish, decreasing wild fish stocks further
  • Competition between same species of fish (intraspecific competition) can reduce the yield
  • Competition between different species (interspecific competition) can also reduce yield
• reducing intraspecific competition?

  1. Preventing overcrowding

  2. Keeping different sized fish in separate cages
• Reducing interspecific competition

  Keeping only one species in each closure
• sustainable farming:

  • farming methods that minimise harm to the environment but still give good yields
• abiotic: something non-living that can affect an organism e.g. the mineral content of the soil or air temperature
• biodiversity: a measure of the variety of organisms in the area
• biotic: something living that can affect an organism e.g. what other plants and animals are around
• community: all of the organisms living in a set area
• consumers: an animal that eats other living things for food
• ecosystem: all of the biotic and abiotic factors found in a safe contained area
• habitat: the part of the ecosystem where an organism lives
• population: all the individuals of a species living in a set area
• producers: organisms that can produce their own food
• trophic level: the level in a food chain that an organism is found
• feeding relationship:

  • plants make their own food by photosynthesis --> they are the basis of all food chains/webs
  • all organic compounds in an animal can be traced back to plants
  • arrows in a food chains point towards the consumer as they show the movement of compounds
  • most important compounds that move along food chains are those involving carbon and nitrogen
  • decomposers (e.g. bacteria and fungi) are linked to all levels of a food chain --> they break down waste products and dead bodies
• food web is made up from many interlinked food chains
• pyramid of numbers show the numbers at each level of food chain

  not all pyramids of numbers are regular

  
• pyramid of biomass:

  • measure mass of each trophic level in a food change (biomass)