Energy transfer and nutrient cycle

• Define an ecosystem.

  All the organisms living in a particular area and all the

  abiotic conditions.
• What are producers?

  organisms that make their own food
• What are the sugars made in photosynthesis used for? (2)

  - used in respiration to release energy for growth- to make biological molecules, such as cellulose, that make up plant’s biomass
• Define biomass (2)

  ​The total mass of organic material, measured in a specific area over a set time period. This can be calculated in terms of dry mass or mass of carbon per given area.
• How is energy transferred through an ecosystem?

  Energy transferred through living organisms when organisms eat other organisms
• How can biomass be measured? (3)

  - mass of carbon that an organism contains-dry mass of its tissue per unit area- using a calorimeter
• Define dry mass.

  mass of an organism with water removed
• How can you measure dry mass?

  dry sample of an organism in an oven at low temperatures weigh every day until mass becomes constant
• How can you measure mass of carbon?

  50%of the dry mass
• How can you measure biomass using calorimetry?

  Sample of dry biomass burnt and energy released to heat a known volume of water - Change in temperature used to calculate chemical energy
• What does GPP stand for?

  gross primary production
• What is GPP?

  total amount of chemical energy converted from light energy by plants, in a given area
• What does R stand for?

  Respiratory losses
• What is R?

  chemical energy lost to the environment as heat when plants respire
• What does NPP stand for?

  net primary production
• What is NPP?

  energy available to organisms at next stage in the food chain
• What is primary production called when expressed as a rate?

  primary productivity
• What is the formula for NPP?

  NPP = GPP - R
• How do consumers get energy?

  Ingesting plant material, or animals that have eaten plant material
• How is energy lost between trophic levels? (3)

  • Not all of the food is eaten e.g. bones
  • Some parts of food are indigestible so are excreted.
  • Lost to environment as heat from respiration
• What is the consumer's net production?

  Energy stored in consumer’s biomass that is available to next trophic level.
• What is the formula for consumer's net production?

  N = I - (F + R)
• What does I stand for?

  chemical energy ingested in food
• What does F stand for?

  chemical energy lost in faeces and urine
• What does R stand for?

  energy lost through respiration
• What do food chains show?

  simple lines of energy transfer. Each stage called a trophic level
• What do food webs show?

  show lots of food chains in an ecosystem and how they overlap
• What is the role of decomposers?

  break down dead or undigested material, allowing nutrients to be recycled
• How can farmers increases efficiency of energy transfer? (2)

  1. reduce energy lost to other organisms by simplifying food webs
  2. reduce energy lost through respiration
• How do pest in food webs reduce efficiency of energy transfer?

  Pests reduce the amount of energy available for crop growth and therefore the NPP, which reduces the energy available for humans.
• How do chemical pesticides reduce pest numbers? (2)

  Insecticides kill insects that eat and damage crops, so less biomass is lost from crops so they grow larger and NPP is greater. Herbicides kill weeds which removes direct competition with the crop for energy from the sun, as well as habitats/food sources of insect pests, helping to further reduce their numbers and simplify the food web
• How do biological agents reduce pest numbers? (2)

  Parasites live in or lay their eggs on a pest insect, which either kills them or reduces their ability to function. Pathogenic bacteria and viruses are used to kill pests
• How does reducing respiratory losses increase efficiency of energy transfer?

  More of their energy is used for growth and less is lost through respiration
• How can farmers reduce respiratory losses? (2)

  restrict movement and keep temperatures warm
• What do saprobionts do?

  feed on the remains of dead organisms and their waste products, breaking them down so that chemical elements are recycled
• How do saprobionts digest their food and what is the process called?

  extracellular digestion- secrete enzymes and digest food externally and absorb the nutrients they need. During this process organic molecules are broken down into inorganic ions. Obtaining nutrients from dead organic matter using extracellular digestion is known as saprobiotic nutrition
• What are mycorrhizae?

  Symbiotic relationships between fungi and roots of plants. The fungi are made up of long thin strands called hyphae which connect to the plants roots. Hyphae greatly increase surface area of plants root system, helping plant to absorb ions from the soil that are usually scarce e.g phosphorus. Hyphae also increase uptake of water by the plant. In turn the fungi obtain organic compounds such as glucose from the plant
• How are mycorrhizae beneficial? (3)

  - fungi made up of long thin strands called hyphae which connect to roots

  - hyphae greatly increase surface area of roots system, and help with uptake of scarce ions and water

  - fungi obtain organic compounds like glucose from the plant
• Why do plants and animals need nitrogen?

  to make proteins and nucleic acids
• Why is the nitrogen cycle important?


  Plants and animals can’t use nitrogen gas in the atmosphere so need bacteria to convert it into nitrogen containing compounds.