ecosystems, nutrient cycles + human impact on environment

• plants are producers
• plants change the energy from sunlight into stored chemical energy
• plants only capture about 5% of the energy in sunlight
• • Organisms rarely eat every bit of another organism (e.g. a herbivore will often not eat the roots of a plant) and so do not take in all the energy available. Even what is eaten is often not completely digested, so some energy never gets into the feed organism
• • Each stage in a food chain uses some of the energy it takes in for its own purposes (e.g. movement, cell repair, reproduction). That energy is dispersed and cannot be passed on
• • A lot of light energy misses plants completely. Some of the light which does hit a plant is reflected or goes through the leaves and so is not absorbed
• As energy is lost at each stage of a food chain, the numbers of organisms that can exist at each level of a food chain goes down as the food chain progresses
• 1. Producer
  2. First Stage Consumer
  3. Second Stage Consumer
  4. Third Stage Consumer
  5. Fourth Stage Consumer
  6. Fifth Stage Consumer
• A pyramid of numbers shows the number of organisms per unit area or volume at each feeding level
• A pyramid of biomass shows the dry mass of organic material per unit area or volume at each feeding level
• Pyramids of biomass give a more accurate picture than pyramids of numbers. And they are always a pyramid shape
• Microorganisms get rid of animal wastes and dead bodies (animals and plants) and in doing so, return vital nutrients to the soil, which can then be used for new growth.
• the two main processes in the carbon cycle are photosynthesis, which removes carbon dioxide from the atmosphere and builds the carbon into living tissue, and respiration, which returns carbon dioxide to the atmosphere as a waste product
• Respiration of bacteria is important in returning the carbon locked in the dead bodies of plants and animals to the atmosphere
• In some cases, dead bodies do not decay but become fossilised to form fossil fuels (col and oil, plus the gas released in the process)
• When fossil fuels are burnt, the carbon in them is released as carbon dioxide, adding to the levels in the atmosphere
• humans have only started extracting fossil fuels in large quantities in the last 200 years, this has disrupted the balance and led to an increase in the levels of carbon dioxide in the atmosphere
• Nitrogen in the air is changed by nitrogen-fixing bacteria in the soil into nitrates, which plants absorb and use. Nitrogen-fixing bacteria are found in the root nodules of legumes. The nitrates absorbed by the plants are passed on to animals that eat plants, the nitrogen is eventually returned to the soil in urine and faeces from animals and when dead organisms decay, nitrogen the form of ammonia, which cannot be used directly by plants, bacteria in the soil convert the ammonia into nitrates, which are then absorbed by plants. Nitrogen is returned to the air by denitrifying bacteria
• In agricultural land the level of nitrogen in the soil can drop for 2 reasons -

  1. The density of plants can be very high, so that a lot nitrogen is removed from the soil
  2. The plants that grow in the fields are harvested and removed. As they do not die in the fields, the nitrogen in them never gets returned to the soil.
• The imbalance of nitrogen in agricultural land can be restored by the addition of nitrogen-containing fertilisers, either natural or artificial to the soil
• Animal urine contains nitrogen in the form of urea. To re-cycle this, it is broken down into ammonia by bacteria. The ammonia by bacteria. The ammonia can be converted in the soil to nitrates. The enzyme that converts urea to ammonia is urease.
• Intensive farming is an agricultural system that aims to produce a maximum yield from the land available
• Intensive farming involves the use of chemicals such as pesticides and fertilisers to increase yield and control disease
• Farm animals may be kept indoors in restricted conditions so that as many as possible can be kept in a given space this is called battery farming
• Advantages of Intensive Farming -

  1. The yield is high - food is cheaper, more profit for the farmer, UK is more self sufficient
  2. Increased yield means the UK has more food for the increasing population
  3. Food being cheaper allows people to make healthier diet and lifestyle choices
• Disadvantages of Intensive Farming -

  1. The chemicals used could enter the human food chain and get into our bodies
  2. The chemicals can cause pollution and harm wildlife and other pests
  3. Natural environments are destroyed. e.g. hedgerows are uprooted to make large fields suitable for intensive farming
  4. Likely that it causes animals stress and discomfort due to the animals quality of life being poor