Organisms need carbon to make all sorts of biological molecules including lipids, carbohydrates, and proteins. Just like we saw with nitrogen and phosphorus, carbon is transferred around ecosystems in a cycle called the carbon cycle. The carbon cycle The Earth's atmosphere is about 0.04% carbon dioxide (CO2), which is where we will start the carbon... Continue Reading →
Phosphorus is another essential element for living organisms. Phosphate ions are needed to make phospholipids, ATP, and nucleotides (the monomers of DNA and RNA). Phosphates are transferred through an ecosystem in the phosphorus cycle. In this article we will look at the cycle itself, and the role of mycorrhizae and saprobionts. The phosphorus cycle Many... Continue Reading →
Nitrogen is an essential element for living organisms. It is needed to make proteins, nucleic acids and ATP. The nitrogen cycle shows how this element is transferred between different parts of an ecosystem. In this article we will look at the four major steps and the microorganisms involved in the processes. The nitrogen cycle The... Continue Reading →
To wrap up the muscle series we are looking at neuromuscular junctions - the synapses between motor neurones and muscle fibre cells. This article will relate closely to the synapse article, but there are some differences between cholinergic synapses and neuromuscular junctions. Neuromuscular junction structure There are three main differences between neuromuscular junctions and a... Continue Reading →
Not all muscles are the same. In this article we will look at the three types of muscle: skeletal muscle, cardiac muscle, and smooth muscle. Skeletal muscle Skeletal muscle is under conscious control, so is sometimes called voluntary muscle. There are two types of skeletal muscle fibres: fast twitch and slow twitch. Fast twitch fibres... Continue Reading →
Muscle contraction requires a large amount of energy, meaning that a constant source of ATP is needed. In this article we will look at the three sources of ATP which muscle fibre cells can use. Phosphocreatine ATP has to be made by adding a phosphate group (Pi) to ADP. In the ATP-phosphocreatine system, the phosphate... Continue Reading →
Muscle contraction is a tricky bit of A-Level biology. There are lots of new terms to learn and a complex process to get your head around. Make sure to review it regularly so that it sticks in your brain. Before beginning this article, make sure you are happy with the different parts of a muscle... Continue Reading →
Muscle fibre cells are a great example of how animal cells can be highly specialised for their function. In this article we will look at the structure of muscle fibre cells and how it relates to their function. Muscle fibres cells - structure and function The below diagram shows a cross-section of a muscle fibre... Continue Reading →
Producing a serial dilution is a really useful skill for all sort of biology experiments. In this article we will look at how to prepare a serial dilution, and how it could be used to produce a calibration curve for a colorimeter experiment. How to prepare a serial dilution In A-Level biology, you will probably... Continue Reading →
Cystic fibrosis is an inherited disorder affecting specific channel proteins in cell membranes. In this article we will look at how it is inherited, how chloride ion transport is affected, and the symptoms which develop as a consequence. Inheritance of cystic fibrosis Cystic fibrosis is an inherited recessive disorder, meaning it is caused by a... Continue Reading →
