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 →
The Nitrogen Cycle – Nutrient Cycles Ep 1
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 →
Muscle Contraction – Muscles Ep 2
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. Before beginning this article, make sure you are happy with the different parts of a muscle fibre cell. Sarcomeres Myofibrils are made up of two main protein filaments: actin... Continue Reading →
Muscle Fibre Cells – Muscles Ep 1
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 fibre cells - structure and function The below diagram shows a cross-section of a muscle fibre... Continue Reading →
Cystic Fibrosis – Diseases Ep 3
Cystic fibrosis is an inherited disorder affecting specific channel proteins in cell-surface 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 →
Control of Blood Water Potential – Homeostasis Ep 6
In the first article about the kidneys, we learnt how blood is filtered in the Bowman's capsule and how some substances are reabsorbed in the proximal convoluted tubule. Today we will focus on the loop of Henle, distal convoluted tubule, and collecting duct, and look at how blood water potential is controlled using negative feedback.... Continue Reading →
Synapses – Nervous Communication Ep 5
We know that nerve impulses are transmitted along neurones in a wave of depolarisation. But how does a nerve impulse get transmitted from one neurone to the next? Well, that is where synapses come in. Structure of synapses Synapses are the microscopic gaps between neurones. The neurone before the synapse is called the presynaptic neurone,... Continue Reading →
Action Potential – Nervous Communication Ep 3
In the last article we learnt that neurone cell-surface membranes are polarised at rest (when they are not being stimulated). However, when a stimulus is detected, a nerve impulse must be transmitted along the neurone. Today we will look at the sequence of events that happens during an action potential and how ion channels bring... Continue Reading →
Neurones and Resting Potential – Nervous Communication Ep 2
The nervous system communicates information by propagating nerve impulses. In the last article we saw how impulses are generated at receptors in response to a stimulus. Now the impulses must be transmitted by neurones. In this article we will look at some of the different types of neurones found in the nervous system, and see... Continue Reading →
Receptors – Nervous Communication Ep 1
Today we are beginning a new series about nervous communication (the type that happens in animals, not making a speech in front of the class). We will cover the nervous system in a lot of detail over the next few articles, but today we are going to start by looking at receptors. What are receptors?... Continue Reading →
