Microorganisms and decomposition

what is nitrogen cycle

• Many microorganism break down organic material to produce simple inorganic molecules eg CO2, water and inorganic nitrogen which returns to the soil in the nitrogen cycle.

• Nitrogen cycle: the recycling of nitrogen between living things and the environment by the actions of microorganisms

why decomposers important

• Decomposers make sure that the chemical constituents of life are continually recycled within ecosystem as plants constantly take minerals such as nitrates from the soil and compounds eg CO2 from air to build macromoelcules in their cells.Release waste products and these provide nutrients in a form plants can use again

• decomposers prevent the bodies of plants and animals and all the excrement from all of the animals from covering the surface of the Earth. Feed and digest them and using the nutrients for respiration.

how decomposers break down large organic moelcules

• These decomposers secrete enzymes eg cellulase that break large organic molecules, such as cellulose, down into smaller ones

  • These small molecules, such as glucose, can be broken down further during respiration

  • During decomposition they also release waste products which provides nutrients to plants

what other gases do microorganisms produced

• The microorganisms involved in decomposition produce CO₂ and methane which are released into the atmosphere. CO2 is also released into the atmosphere by combustion when anything that has been living is burned.

• Carbon dioxide can then be absorbed by green plants which will fix the carbon back into carbohydrates during photosynthesis

conditions needed for recycling nutrients

• chemical reactions in microorganisms work faster in warm conditions but if temp gets too hot they stop as enzymes denature or if get too cold.

• Microorganisms grow better in moist conditions, which makes it easier to dissolve their food and also prevent them from drying completely. So decay occurs faster in warm, moist conditions.

• Decay occurs more rapidly when plenty of oxygen available

use of decomposers

• in treatment of sewage and production of compost

• cycling of resources by decomposers plays a vital role in maintaining the fertility of our soil and the health of our atmosphere

• Processes that remove materials from the soil are balanced by processes that return materials in a stable community of plants and animals. The time taken to break down waste product and dead bodies in ecosystem equivalent to time taken for most of the energy originally captured by green plants in photosynthesis to be transferred to other organisms or back into the environment

what is forensic science

the application of scientific techniques to the investigation of a crime

how can temperature of body give indication of how long person has been dead

• after death the metabolic reactions which have warmed the body begin to slow and eventually stop

• At same time, energy is transferred from the surface of the body into the surroundings by radiation, conduction and the evaporation of water, which cools the body

• the body reactions do not all stop immediately when a mammal dies, so although the body temperature starts to fall immediately after death, it stays almost stable fro a time before decreasing steadily to room temperature 

factors affect how quickly the body temperature drops

• Fat levels: outside of the body cools much more rapidly than the inside and the amount fo body fat affects the rate of cooling because it acts as insulation

• Mode of death: people who dies somewhere cold will cool more rapidly than someone who dies on land in a hot climate or a heated room

• Surrounding temperatures: bodies cool faster in cold countries or if they are placed in fridges or freezers than they do in hot countries or in heated rooms

• Surface area: volume ratio: smaller people will cool faster because they have a larger surface area: volume ratio than larger people

• Clothing and covering: a body which has clothes on to insulate it, or a body wrapped in bed covering, will be insulated and so will cool more slowly than a body without any coverings

what is rigor mortis

temporary muscle contraction causing the body to become rigid after death

how muscle contraction occurs?

• Muscles contract due to the action of two protein filaments; myosin and actin

• The binding of myosin heads to actin proteins followed by the bending of the myosin heads causes muscle contraction

• ATP is required to allow the myosin heads to detach from the binding sites on actin

why rigor mortis occurs?

• Rigor mortis comes about as a result of changes to the proteins in muscle cells after death

  • Since no more oxygen reaches the muscle cells after death they will start to respire anaerobically, producing lactic acid. Muscle cells have alrge stores of ATP and glycogen for anaerobic respiration. 

  • The accumulation of lactic acid decreases the pH in the muscle cells, denaturing the enzymes that produce ATP

  • Without ATP the myosin heads cannot be released from the actin filaments, locking the muscles in a contracted state as ATP is needed to maintain the muscles in a relaxed state

  • This leads to the stiffness that is the main characteristic of rigor mortis

timing of rigor mortis

• On average, rigor mortis starts about 2-4 hours after death and takes between 6 and 8 hours to take full effect.

• Rigor mortis would have taken place in every muscle between 12 and 18 hours after death, but will wear off again after about 24 to 36 hours from TOD

• It begins in the smaller muscles in the face and neck, progresses down the body, and spreads steadily to the larger muscles of the body

what is rigor mortis affected by?

• The process is affected by the level of muscle development and the temperature of the surroundings

• Main factor which determines how quickly rigor mortis begins is the amount of ATP stored in the muscles at the time of death. Eg rigor mortis usually starts very quickly in drowning victims because they have used up all their muscle ATP trying to stay on the surface

• The temperature of the person when the die and the temperature of their surroundigs also affect how quickly rigor mortis begins. Relaxation of the muscles as rigor mortis passes happens because muscles soften as enzymes released from the lysosones begin to break down the tissue

  • Higher temperatures will speed up the rate of rigor mortis