Unit 5 - Energy transfers in and between organisms
Class notes
Energy and Ecosystems
8 views 0 purchase
Course
Unit 5 - Energy transfers in and between organisms
Institution
AQA
Book
AQA Biology A Level Year 2 Student Book
Energy and Ecosystems notes for AQA A level Biology. These are hand written notes from a year 13 student and not simply copied from the textbook.
They're focused notes, meaning that over excessive detail isn't covered. Just enough info to smash the exams :)
Unit 5 - Energy transfers in and between organisms
All documents for this subject (153)
Seller
Follow
Alireza18
Content preview
Section 5 ( Energy Transfers in between Organisms ), Topics 13
Energy constantly enters ecosystems via sunlight and is lost as heat. Heat cannot be
recycled, and the flow of energy is therefore in one direction. Provided that the sun
continues to supply energy to the Earth, the ecosystems are always stable. However,
nutrients do not have an extraterrestrial source, and there is limited availability of nutrient
ions in a usable form. It is therefore crucial that elements such as carbon, nitrogen and
phosphorus are recycled, and this flow is cyclic.
All nutrient cycles have one simple general sequence at their heart:
Nutrients are taken up by producers ( plants ) as simple inorganic molecules.
Producers incorporate the nutrient into complex organic molecules.
When the producer is eaten, the nutrient passes into consumers ( animals )
Nutrients pass through the consumers.
When consumers and producers die, their complex molecules are broken down by
saprobiontic microorganisms ( decomposers ) that release enzymes ( extracellular
digestion ), releasing the nutrients in its original inorganic form.
o The role of these saprobionts in nutrient cycles is to ensure that nutrients are
released for reuse in their inorganic form. Without them, nutrients would
become locked up in organic form and cannot be taken up by plants again.
Nitrogen Cycle
Living organisms require a source of nitrogen from which to manufacture biological
molecules such as Proteins ( Amino Acids ), Nucleic Acids ( Nucleotides, DNA ) and other
nitrogen containing compounds. Although 78% of the Earth's atmosphere contains
Nitrogen, they are pretty much useless as it is a diatomic triple bonded molecule. Plants take
up most of the nitrogen in the form of Nitrates ( NO3-) from the soil. These ions are absorbed
using active transport by the root cells. This is where plants obtain Nitrates, and animals
obtain such compounds by absorbing and digesting plants. Nitrate ions are very soluble and
easily go beyond the reach of plant roots. In ecosystems, these nitrates are restored by the
recycling of nitrogen containing compounds. In agriculture, fertilisers containing nitrogen
are used to increase the amount of Nitrates. When plants and animals die, the process of
decomposition happens, by which microorganisms replenish the nitrates concentration in
the soil.
There are 4 main processes in the Nitrogen Cycle:
Atmosphere nitrogen is converted to Ammonia by nitrogen fixing bacteria in the soil. These
bacteria form a mutualistic relationship with plants and inhabit their roots, increasing its
surface area for a quicker uptake of ions. The bacteria provide a source of ammonium ions
for the plants and the plant provides sugars from photosynthesis.
Nitrogen fixation happens during lightning storms, but the vast majority of this reaction
occurs within two types of nitrogen fixing bacteria.
Free Living Nitrogen Fixation Bacteria
o These bacteria reduce nitrogen to ammonia, which is then used to
manufacture amino acids.
Mutualistic Nitrogen Fixing Bacteria
o These bacteria live in nodules on the roots of plants. They obtain
carbohydrates from the plant, and the plant obtains amino acids from the
bacteria.
Ammonification ( Saprobiontic Organisms )
Ammonification is the production of Ammonia from organic nitrogen containing
compounds. In nature, these compounds include urea ( from the breakdown of excess
amino acids ) and proteins, nucleic acids, vitamins ( found in faeces and dead organisms ).
Saprobiontic microorganisms mainly fungi and bacteria, feed on faces and dead organisms,
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller Alireza18. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $5.15. You're not tied to anything after your purchase.
