Welcome to the Zoë Huggett Tutorials website. Visit the online tuition page to find out more about me and how I might be able to help you with your A-Level biology or A-Level chemistry (or GCSEs). This site provides A-Level biology revision resources to help you on your journey to a better understanding and your

You know when you look at a word too much and it starts to look weird? That will definitely happen with the word 'enzyme' as we move through this topic. Today we're going to take a look at the basics of what enzymes are and how they act. What are enzymes? Perhaps the first phrase

An enzyme inhibitor is a molecule that binds to an enzyme and prevents it from catalysing a reaction. In this article we will look at two types of enzyme inhibition - competitive and non-competitive inhibition. Although enzyme inhibitors can sometimes have devastating consequences, some of them are actually quite important. We will look at some

Sometimes the body comes under attack from pathogens (microorganisms that can cause disease). If pathogens get into our body, it is down to our immune system to spring into action and destroy them. In this article we will be looking at how foreign antigens trigger our immune response, and how that results in the pathogens

A diploid organism (e.g. a human) has two alleles for each gene in their chromosomes. Alleles are alternative forms of a gene, so an organism could have two of the same allele (homozygous) or two different alleles (heterozygous). The alleles an organism has (the genotype) will determine what characteristics it has (the phenotype). There is

So far in this series we have looked at how enzymes work, what can affect the rate at which they work, and how their action can be inhibited. Today we are looking at coenzymes and cofactors: non-proteins that are needed in order for some enzymes to be able to catalyse their reaction. Coenzymes Coenzymes are

In the last article we left photosynthesis at a point where ATP, reduced NADP, and oxygen had been produced in the light-dependent reaction. Oxygen is a waste product of photosynthesis, however the ATP and reduced NADP are used for the light-independent reaction. So although light energy isn't specifically needed for any reaction in this next

Transcription is the first stage of protein synthesis. It transcribes a DNA sequence into a messenger RNA (mRNA) sequence. In eukaryotic cells, DNA is found in the nucleus so that is where transcription occurs. In prokaryotic cells it happens in the cytoplasm because the DNA is not contained in a nucleus. In this article will

Electrophoresis is a method used to separate fragments of DNA or RNA based on their size (length*) using an electric current. It has applications in processes such as genetic fingerprinting and disease diagnosis. DNA and RNA are negatively charged which means they will move towards a positive electrode. This technique can be used for proteins,

In the last article we looked at how enzymes work as biological catalysts. However, there are various factors affecting enzyme activity, and consequently the rate of the reactions they catalyse. Today we will look at the four main factors that influence the rate of enzyme activity. Substrate concentration This one makes quite good sense. If

Welcome to the Zoë Huggett Tutorials website. Visit the online tuition page to find out more about me and how I might be able to help you with your A-Level biology or A-Level chemistry (or GCSEs). This site provides A-Level biology revision resources to help you on your journey to a better understanding and your

In the last article we looked at how the body uses negative feedback mechanisms to control the concentration of glucose in the blood. Diabetes mellitus is a condition where these feedback systems fail and blood glucose is not controlled, with potentially fatal consequences if left untreated. In this article we will look at the two

So far in the exchange and transport series we have mainly been looking at exchange and transport of gases. However, organisms also need to absorb nutrients such as glucose and amino acids so they can carry out processes like respiration and protein synthesis. In this article we will cover how large food molecules are broken

Epistasis is when the expression of an allele of one gene masks the expression of the alleles of another. The genes must code for the same characteristic in order for this to work. Let's use flower colour as an example. Epistasis example: flower colour In the diagram below, the flower pigment molecule begins as white.

Once a DNA fragment has been isolated or produced (see the last article), the next step is often to produce many copies of it. One common way to do this is to use the polymerase chain reaction, which is a fairly simple process that can be automated. In this article we will look in detail

Photosynthesis is the process used by plants and other photosynthetic organisms to make their own glucose. The glucose can then go on to be used in respiration, stored as starch, or used in other reactions. Photosynthesis requires light energy, but it is actually only the first stage which is light-dependent. We will focus on the

Cardiovascular disease is a non-communicable disease; it is not caused by a pathogen and cannot be passed from person to person. Most cardiovascular disease begins with atherosclerosis developing in an artery due to factors such as high blood pressure. In this article we will look at how atheromas develop, cardiovascular disease risk factors, and treatments.

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?

Welcome to the Zoë Huggett Tutorials website. Visit the online tuition page to find out more about me and how I might be able to help you with your A-Level biology or A-Level chemistry (or GCSEs). This site provides A-Level biology revision resources to help you on your journey to a better understanding and your

Welcome to the Zoë Huggett Tutorials website. Visit the online tuition page to find out more about me and how I might be able to help you with your A-Level biology or A-Level chemistry (or GCSEs). This site provides A-Level biology revision resources to help you on your journey to a better understanding and your

Welcome to the Zoë Huggett Tutorials website. Visit the online tuition page to find out more about me and how I might be able to help you with your A-Level biology or A-Level chemistry (or GCSEs). This site provides A-Level biology revision resources to help you on your journey to a better understanding and your

In this series we are going to be looking at respiration. This is the process that releases energy from glucose to produce ATP. In the first few articles we'll be focusing on aerobic respiration (which uses oxygen) and then we will cover anaerobic respiration (which doesn't use oxygen) in the last article. Please bear in

Mitosis is a method of cell division used by multicellular organisms for growth and repair of tissues. Some plants and fungi (and rarely some animals) also use it for asexual reproduction - producing genetically identical offspring from one parent. Mitosis results in two daughter cells which are genetically identical to the parent cell. In this

We've reached the final stage of aerobic respiration - oxidative phosphorylation. This step takes place using proteins in the inner mitochondrial membrane. Now we will find out what all the reduced NAD and reduced FAD produced in glycolysis, the link reaction, and the Krebs cycle is used for. Oxidative phosphorylation The coenzymes NAD and FAD

So far in the genetic engineering journey we have learnt how to isolate or produce a DNA fragment, and amplify it in vitro using PCR. Bacterial transformation is a method to amplify a DNA fragment in vivo (in a living organism), and to engineer bacteria to produce a protein. In this article we will look

Anaerobic respiration happens when there isn't enough oxygen present for aerobic respiration to continue. Different types of organism use different pathways - lactate fermentation or alcoholic fermentation. For both pathways, the amount of ATP produced is much lower than in aerobic respiration because the only ATP produced comes from glycolysis (2ATP per glucose molecule). You

This article begins a new series about gene technologies. Many gene technologies, especially recombinant DNA technologies, begin with the need to isolate or make DNA fragments. We will look at three different ways that this can be achieved. Restriction enzymes This method allows DNA fragments to be "cut out" of existing DNA. Restriction enzymes, sometimes

Dihybrid inheritance looks at the possibilities of two characteristics being inherited together. Each characteristic is coded for by a separate gene. In this case it is much easier to use a Punnett square to work out the possible genotypes of the offspring as a genetic diagram would get very messy and difficult to read. In

We've been talking about movement of blood a lot over the last few articles, so it's time we looked at blood itself in a bit more detail. But don't worry if like me you're a little squeamish because there will be no pictures of actual blood today. We will take a brief look at all

Autosomal linkage and sex linkage are two cases where inheritance is very dependent on which chromosome the genes are found on. This is definitely the most difficult concept to get your head around for this topic for A-Level biology - make sure to have a good understanding of meiosis before you start. Autosomal Linkage Autosomes

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

HIV (human immunodeficiency virus) is a virus which can eventually lead to development of AIDS (acquired immunodeficiency syndrome). However, it is not the virus itself which causes AIDS symptoms; HIV weakens the immune system, meaning other infections can take hold more easily. In this article we will look at HIV structure, replication, and development of

Welcome to the Zoë Huggett Tutorials website. Visit the online tuition page to find out more about me and how I might be able to help you with your A-Level biology or A-Level chemistry (or GCSEs). This site provides A-Level biology revision resources to help you on your journey to a better understanding and your

The aim of this practical is to investigate the rate of enzyme-controlled reactions. The details of the practical itself vary depending on what the enzyme, substrate, and product are. Let's use catalase as an example. Catalase is an intracellular enzyme which catalyses the conversion of toxic hydrogen peroxide (the substrate) into oxygen and water (the

In the last post we looked at the structure of the xylem vessels, so now we're going to take a look at their function. Water transport in plants happens up the xylem vessels in a transpiration stream from roots to leaves due to the properties of water and transpiration at the leaves. Let's break the

Welcome to the Zoë Huggett Tutorials website. Visit the online tuition page to find out more about me and how I might be able to help you with your A-Level biology or A-Level chemistry (or GCSEs). This site provides A-Level biology revision resources to help you on your journey to a better understanding and your

Welcome to the Zoë Huggett Tutorials website. Visit the online tuition page to find out more about me and how I might be able to help you with your A-Level biology or A-Level chemistry (or GCSEs). This site provides A-Level biology revision resources to help you on your journey to a better understanding and your

In the last article I mentioned that red blood cells contain a protein called haemoglobin. In simple terms, the haemoglobin protein binds to oxygen and transports it around the body. As with most of biology there's a bit more to it than that, so here we will look at how this process works in more

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

The Krebs cycle has many names. Sometimes it is called the tricarboxylic acid (TCA) cycle or the citric acid cycle. But whatever name you give it, it's an important part of aerobic respiration. In the last article we covered the first two stages of aerobic respiration (glycolysis and the link reaction). We ended the link

Welcome to the Zoë Huggett Tutorials website. Visit the online tuition page to find out more about me and how I might be able to help you with your A-Level biology or A-Level chemistry (or GCSEs). This site provides A-Level biology revision resources to help you on your journey to a better understanding and your

The kidneys are important organs for maintaining blood water potential and excreting waste products from the blood. In this article, we will look at the structure of the kidneys and how substances are filtered out and reabsorbed into the blood using ultrafiltration and selective reabsorption. Kidney structure The kidneys have an outer layer called the

Welcome to the Zoë Huggett Tutorials website. Visit the online tuition page to find out more about me and how I might be able to help you with your A-Level biology or A-Level chemistry (or GCSEs). This site provides A-Level biology revision resources to help you on your journey to a better understanding and your

So far, all the organelles we have looked at (the nucleus, mitochondria, ribosomes and RER) are found in both animal and plant cells. Today's organelle, the chloroplasts, are only found in plant cells and some eukaryotic algae. The main function of chloroplasts is to carry out photosynthesis - the reaction that uses light energy to

Translocation is the movement of dissolved solutes (also called assimilates) through the phloem vessels. If you haven't already, make sure to read about the structure of the phloem vessels here first so you've got a good grounding to take this topic further. Source to sink Solutes move from a source to a sink. A source

Antibodies are very important proteins in the immune response. We've already mentioned them a lot in the last few articles but today we will take a detailed look at their structure and function, and how they can be used in medical applications. Antibody structure Antibodies are proteins with a quaternary structure. They have two longer

Control of body temperature is the first example of homeostasis we will look at in this series. For humans, normal body temperature is 37°C. It is important to maintain this temperature as it is the optimum temperature for enzymes involved in many metabolic processes such as respiration. Humans are endotherms, meaning that they control their

Welcome to this series looking at how the genetic code instructs cells to make proteins. We will be talking about DNA, RNA, and proteins a lot so head over to those articles if you are unsure about the basic structure or function of those molecules. Today, we're going to be taking a look inside the

Welcome to the Zoë Huggett Tutorials website. Visit the online tuition page to find out more about me and how I might be able to help you with your A-Level biology or A-Level chemistry (or GCSEs). This site provides A-Level biology revision resources to help you on your journey to a better understanding and your

Last time we looked at an action potential happening in a section of a neurone cell membrane. The membrane was depolarised and repolarised. However, that depolarisation must travel along the whole length of a neurone in the right direction. Today we will look at how an action potential travels in a wave of depolarisation. The