Summarised notes on Cells, Lungs, Heart and Digestion

Just a few explained points on the lungs, heart, cells and digestion

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Parts of the cell and the functions of the organelles:

Cell Wall: Cell wall's are found in plant cells and in prokaryotic cells. Cell Walls can be made of peptido gylcan (prokaryotes) or cellulose (plant cell). Cell walls main function is to maintain the structure and rigidity of the plant cell.

Mitochondria: Mitochondria are the site of cellular respiration. They produce energy by using ATP (adenosine triphosphate) and that is converted to ADP (adenosine diphosphate) and energy which is used for many things such as active transport or for cell contraction for example muscles.

Golgi Body: The golgi body is essentially the organelle which packages up proteins made by the RER and modifies the protein (can add a lipid to the protein). It also plays a vital role in transporting the packaged proteins to other cells and into the blood stream.

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Rough Endoplasmic Reticulum:The RER is attached to the nucluer membrane of the nuclues and is in charged of storing and transporting the ribosomes. On a TEM machine, you can decipher which is is RER or SER as RER is rough and 'spotted' because of the ribosomes on RER.

Smooth Endoplasmic recticulum: Plays a vital role in the synthesis of lipids and steroids. Does not contain any ribosomes on it like RER.

Chloroplasts: The site of photosyntesis in plant cells and produces food (glucose) for the plant by using sunlight, water and taking in carbon dioxide to produce glucose and energy.

Ribosomes: Present in both prokaryotes (like bacteria) and eukaryotes. Site of protein synthesis and can be situated freely in the cytoplasm or is usually found attached to the RER. Ribosomes are created by RER's and the sequence is created in the nucleus of the cell and copied using a type of RNA e.g tRNA and that is sent to the RER to be manufactured.

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Nucleus:The brain of the cell. Controls cellular processes.Only one per cell and contains genetic information of a person which codes for a their characteristics.     

  • Nucleolus: Found inside the nucleus, and has the main role for making RNA which is used for making specific proteins for example ribosomes.

Cell membrane: Controls what comes in and out of the cell. It also helps maintain the cells fluidic structure. It also contains carrier protein which work alongside the concentration gradient (high to low) however uses ATP to move the proteins. Also there are protein channels which open and close depending on the concnetration gradient and they allow other molecules like water in and glucose. There is also a carbohydrate chain attached to the cell membrane which tells the immune system that it is not a foreign body. Also cell membrane has a fluidic structure and that allows different moleucles to enter at different places not in one place.

The structure of a cell membrane is a phospholipid bilayer.

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A phospholipid bilayer is made with 2 layers of 2 hydrophobic tails ('afraid of water' never touches water) made of lipids and oils, and finally 1 hydrophillic head ('loves water' attracted to water) which is made of a phosphate. This layer allows non-polar molecules to pass through by osmosis and diffusion.

Centrioles: Are made of nine tubules and is a very important in cellular division (acts as the spindle to pull away copied DNA) and are paired together and found near the nucleus of a cell.

Cytoskeleton: Composed of microtubules and is found in the cytoplasm of a cell. This adds to the structure of the cell and supports the cells fluidic shape and also aids movement in and out of cell.

Lysosome:  A water filled sac containing many digestive enzymes to break down lipids, proteins etc. It also has a key role of transporting waste materials out of the cell and into the blood stream. Also plays a key role in phagocytosis (forms the white blood cell which engulfs pathogens and breaks it down.

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There are four types of transportation used in the body which you will have to know. These are:

  • Bulk Transport
  • Active Transport
  • Osmosis
  • Difussion

Bulk transport: Bulk transport is split into two sections "in" and "out" or endocytosis and exocytosis.

Endocytosis is the bulk movement of raw materials (amino acids, glucose, lipids etc) into the cell and they enter the cell via a vesicle.

Exocytosis on the other hand is the bulk movement of materials out of the cell. Bulk movement in cells is a quicker way of getting loads of materials at once and therefore saves time instead of getting it slowly.

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A good way to remember which one is in or which one is out is to look at the word exocytosis...... the first 3 letters are 'exo' and if you try an use your imagination, then you can see that there is a resemblance between the word exit and the word exocytosis. So just remember that exocytosis means exit which means bulk movement out of the cell.

Osmosis: "The passive movement (involuntary) of ONLY water molecules from an area of high concentration to an area of low concentration through a partially permeable membrane.

A bit like diffusion however it is only for water molecules.

Osmosis is very important in keeping our water concentration level in a way that the cells don't become turgid because of too much water in one area or cells don't become flaccid because there is too little water. Now below on the next slide I have used an example of a question  which has popped up on many test papers and is actually very simple to answer. Here it is:

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They might ask you to define osmosis using water potential and this is essentially the same principle ===> If you have a high water potential on one side and on the other side a low water potential then particles from the high water potential will leave and go to the low water potential to reach equalibrium (equal on both sides) soooo...... just replace concentration with water potential as i have done below:   

"Osmosis is the passive movement of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane." 

Diffusion: Diffusion like I said earlier is the same as osmosis, (follow the concentration gradient). The definition is below:

"Diffusion is the passive movement of particles in fluids (gases and liquids) from an area of high concentration to an area of low concentration"

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Active Transport: Active transport is very different to osmosis or diffusion. It is a key process usually found in the small intestine. Active transport uses specific proteins key to a single molecule to transport into the blood stream (a bit like carrier proteins in the cell membrane of cells). However it is different to carrier proteins found in the cell membranes because other carrier proteins e.g ones found in the small intestine in the lining of the villi, they use ATP energy to move the molecule into the blood stream because it is working against the concentration gradient. So a correct definition would be as stated:

"Active transport is the movement of molecules against the concentration gradient (from an area of low concentration to an area of high concentration ) using ATP via a specific carrier protein."

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Digestion is the process in which large molecules of food we eat are broken down physcially and chemically to their main monomers which can be used in many cellular processes.

I am going to explain in part of the digestive system and their role in digestion and how they are specialised to their function.

Mouth: The mouth is the beginning of digestion. The food enters the mouth and this is where the beginning of mastication or physical breakdown occurs. You have different types of teeth which are specialised in their part of breaking down the food such as inscisors, molars etc are examples of teeth.

Salivary Glands: Secrete salivary amylase which is an enzyme (a biological catalyst which reduces the activation energy of a reaction) begins chemically breaking the hydrogen bonds, disulfide bonds etc between the carbohydrates (also known as polysaccharide).

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Mouth is roughly pH 7 and is around 30-37 degrees celcius and therefore at optimum pH and temperature where the rate of reaction is at its fastest for that specific enzyme. Anyway, the salivary amylase coats the food and forms a bolus. This bolus is swallowed and travels down the oesophagus and not down the trachea because : 

Epiglottis: A small flap which separates the windpipe and the oesophagus. This flap closes which prevents food from entering the trachea and into the lungs.

The bolus then travels down the oesophagus.

Oesophagus: This is a long tube lined with muscle. The bolus enters the oesophagus where peristalsis occurs which is the contraction and relaxation of the muscles in the endothelium lining of the oesophagus. This contraction and relaxation forces the bolus down the tube and then it reaches the stomach where the cardia sphincter which separates the stomach and the oesaphagus opens and allows the bolus to enter. 

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Stomach: Chewed up food, scientifically known as bolus, enters the stomach through the oesophagus after being swallowed. The stomach walls release proteases, which are protein digesting enzymes like pepsin, and hydrochloric acid which kills or inhibits any bacteria that was swallowed along with the food. The hydrochloric acid, which is a very strong acid with a pH value of 1, provides the stomach with a acidic pH environment so the proteases can work efficiently

The food, enzymes and acid are churned around in the stomach through contractions of the stomach walls. This process converts the bolus into chyme (partially digested food). Also the cardia sphincter closes to prevent acid reflux and burn the squamous epithelial cells found along the small intestine. The chyme then passes slowly through the pyloric sphincter and into the duodenum.

Liver (gall bladder): Secretes bile which is a green alkaline solution which emulsifies fats and enters the duodenum.

Pancreas: Secretes digestive enzymes like proteases, carbohydrases, lipases

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Duodenum: Bile, enzymes mix with the chyme here and begin to again break down the chyme. The Brunner's Glands found in the duodenum secrete sodium hydrogen carbonate which changes the pH from an acid (because of stomach) to a alkaline surrounding. This allows the bile to effectively emulsify the fats by making the into smaller globules which increases the surface area and therefore increases the rate of reaction. Also the enzymes break the bonds between the macromolecules changing them into their monomers, these are known as  hydrolytic enzymes

The chyme enters the middle of the small intestine - the site of absorption.

Small intestine: The small intestine is lined with many villi and those villi are lined with microvilli and this increases the surface area of the small intestine to absorb more nutrients at once. Also the small intestine is folded in many twists and turns which increases the time in which the digested food is in the absorption process. Also in the microvilli cells, there are many mitochondria to produce ATP which is needed for active transport (explained in previous slides).

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 Also, each individual villi has a large network of cappilaries and they are very close to the villi endothelium so therefore it reduces the diffusion path which means diffusion happens at a faster rate. A picture on the next slide shows how efficient the villi are.

Large Intestine: The left over food passes into the large intestine by muscular peristalsis and this is the last part of the digestion process (other than getting rid of the waste). The large intestines primary role is reabsorption of water from stool. It also absorbs some nutrients not taken up efficiently by the small intestine, and houses most of the symbiotic bacteria in your gut. These bacteria break down any unwanted microbes or nutrients and the left over product also known as stool or faeces

Rectum & Anus: The faeces enters the rectum where it is stored until egested. Then the stool passes into the **** where it is egested!

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A picture showing muscluar peristalsis in the oesophagus

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The Lungs

The lungs is a vital organ in keeping us humans alive. The lungs primary job is inhale air and exhale air. I am going to go through what happens when you inhale and how you actually inhale air and finally what happens to that air when it enters the body. I will also include a few diseases which can affect the functioning of the lungs.

How the air gets into the lungs:

  • First the diapragm contracts and flattens
  • Then intercostal muscles between ribs contract and push out.
  • This causes the volume in the thorax to increase
  • The pressure inside the thorax to decrease.
  • Pressure in the thorax is lower than pressure outside the body
  • Air is drawn into the lungs for that reason.

Pulmonary Ventilation = Tidal Volume X Respiratory Rate

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Now the path the air takes:

As all the factors above happen, the air is drawn in through the nose / mouth (I'll talk about the nose instead).

Air is breathed in by the nose and the air is filtered because of the many nose hairs (cilia) which line the endothelium. Also there are goblet cells which secrete mucus and trap any dust and dirt before it enters the thorax.

The air passes into the oesophagus however this time the epiglottis opens and the air travels into the windpipe instead of following the digestive track.

The enters the trachea which is lined with mucus-secreting cells and is held in place with strong cartilage to support the difference in pressure at each breath.

The air continues down the path and the trachea splits into either side of the lung and the air passes into the bronchi.

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The bronchi is pretty much similar to the trachea accept smaller! The bronchi like the trachea is held in place with ringed shaped cartilage to keep its structure during pressure changes.After that the air enters the bronchioles;

  • First the terminal bronchiole
  • Then respiratory bronchiole

The terminal bronchiole are lined with simple cuboidal epithelium containing Clara cells. These cells secrete a  onsticky, proteinaceous (high in protein) compound to maintain the airway in the smallest bronchioles. The secretion, called surfactant, reduces surface tension, allowing for bronchioles to expand during inspiration and keeping the bronchioles from collapsing during expiration.

The respiratory bronchiole is the smallest subdivision of a bronchiole, connecting a terminal bronchiole to an alveolar duct. At this point air is directed to alveoli and gas exchange begins.

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The air finally reaches the alveoli. The alveoli are little cloud shaped sacs attached to the ending of the respiratory bronchiole. These sacs are the key to effcient gas exchange.

What makes alveoli good at it's job?

  • Thin membrane = This allows a shorter diffusion path
  • Copious blood supply (a lot) = This means that oyxgen diffuses into the blood quicker. Also it is close by = increased ventilation
  • Large surface area = Increased diffusion rate
  • Moist Lining = Gases are able to diffuse in/out of the blood quicker

The oxygen diffuses into the blood from the alveoli and at the same time the carbon dioxide produced by bodily processes like respiration diffuse out of the blood and into the alveoli for exhalation.Also one way in which the blood increase diffusion and makes sure that the concentration gradient stays different is by ventialtion.

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Pulmonary ventilation (ventilation in the lungs) means that there is always new blood entering the alveoli. What that means, is that as oxygenated blood leaves the alveoli there is always deoxygenated blood entering the alveoli at the same time and therefore this maintains the concentration gradient (high oxygen in alveoli, low carbon dioxide in alveoli= opposite in deoxygentated blood).Then when exhaling it is just opposite to inhaltion e.g:

  • Diaphragm relaxes and pushes up
  • Intercostal muscles between the ribs relaxe and push back inwards
  • This causes a higher pressure inside the body and a lower pressure outside
  • The volume in the lungs decrease and that causes the air to be forced out of the body.

That is the process of inhaltion and exhalation and the different parts of the lungs the air has to pass and how oxygen enters our bloodstream and how carbon dioxide leaves our blood by diffusing into the alveoli.

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The Heart

Finally my favourite topic in Biology is THE HEART!!!!!!!!!

Ok I'll start with the circulatory system, then talk about ECG's, and then I'll talk about the nodes and the Bundle of His + Purkinje fibers etc.

The Heart

The heart is a huge bundle of cardiac muscle. Now you might be thinking "oh right the same type of muscles on my arms and legs etc". Im afraid you would be wrong. These type of cells are called skeletal and are found on your arms etc.

Cardiac muscle cells are much different to skeletal muscles. Cardiac muscle cells are myogenic meaning the muscle doesn't rely on nerve impulses to work and it stimulates itself and is separate from the nervous system. Also cardiac cells are highly resistant to fatigue and therefore much more beneficial for the heart.

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The circulatory system

The small cells are "fused" to each other at the dark areas called intercalated disks
Electrical resistance across these disks is very low, thanks to the relatively free diffusion of ions through their gap junctions which contain many channels through which ions can travel from on cell to the next. As a result, if one cell fires an action potential, the signal will quickly spread to the whole tissue of connected cells.
Therefore, the heart muscle cells function all together as a syncytium. .

Also the cardiac muscle are striated. The striations are due to the same myofibrils (composed of actin and myosin) that are present in skeletal muscle cells. The sliding cross-bridge contraction mechanism of these myofibrils is also the same as in skeletal muscle.

The circulatory system

Now for the circulatory system! I am going to start at the right atrium!!!

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Right side of the heart

  • Deoxygenated blood enters the right atrium via the inferior and superior vena cava (biggest vein in the body)
  • The Sino atrial node (will be explained later) releases an electrical impulse generated by specialised cells called myocytes.
  • This impulse tells the atrium to contract and at the same time the semilunar valves close and the sino atrial node releases another impulse for later.
  • The atrioventricular valves open (in this scenario it is the tricuspid valve) and the blood enters the right ventricle.
  • The second impulse which was released by the SAN earlier went to the atrioventricular node to delay the impulse for 2 reasons:
  • To allow the blood in the atrium to empty and allow the blood in the ventricle to fill
  • To make sure that the ventricle contracts from the base - upwards (bottom of the apex to the top of ventricle) and this allows the blood to be forced through the right vessel.
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Right side of the heart

  • Anyway the second impulse is delayed as the impulse is sent down some insulated-conductive tissue in the septum which is called the Bundle of His
  • The impulse is then sent down the apex and around the ventricle on small microfibrils called Purkinje Fibers and this allows the ventricle to contract from base upwards as explained on the previous slide.
  • After that the ventricle is given the signal to contract, therefore the atrioventricular valves close (stop backflow of blood in the wrong chamber) and the semilunar valves open.
  • The venticle forces the blood into the pulmonary artery (which is the only artery which contains deoxygenated blood) where the blood is directed to the lungs to be oygenated.
  • The blood enters the left atrium in the heart via the pulmonary vein (the only vein containing deoxgenated blood).
  • The same thing happens on left as it happens on the right so I won't go into too much detail!
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Left side of the heart

  • Again SAN releases a impulse causing the atrium to contract and also tells the atrioventricular valves to open (this time it is called bicuspid valve as it is on the left hand side of the heart)
  • Another impulse is relayed by the SAN and is sent to the AV node  and that is sent to the Bundle of His  and then that is sent to the Purkinje Fibers causing contraction of ventricles from the base of the apex upwards.
  • The atrioventricular valves close and the aortic valve opens (semi lunar valve for the left hand side) and the blood is forced out onto the biggest artery in the body which is called the aorta and the blood is sent all around the body.  THAT IS THE CIRCULATORY SYSTEM DONE !!!!!



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The correct translation for ECG is Electrocardiogram (You would be surprised how many people get that wrong).

ECG's is a graphical method of portraying the electrical impulses during each systole and diastole.

ECG's are used by medical officers and heart specialist ot highlight different peaks of electrical activity in the heart. They are used to in many heart cases for example they help highlight irregular heart beats produced by the heart. This is called a cardiac arrhythmia (irregular heartbeat).

Below on the next slide is an example of a cardiac arrhythmia whille compared to a normal ECG of a regular heart beat just to help you visualise the difference between an irregular heart beat and a regular one and the effect on the heart rate. After that I will just go over a few key terms and equations you need to know !!!

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Systole: The phase of the heartbeat when the heart muscle contracts and pumps blood from the chambers into the arteries ===> Basically when there is contraction! 

Diastole: The phase of the heartbeat when the heart muscle relaxes and allows the chambers to fill with blood. =====> Basically when blood is drawn in!

Below there is a ECG graph. It has a few labelled points such as :

  • Atrial systole (atrium contraction)
  • Aortic pressure (pressure in the aorta at different intervals)
  • Diastole (atrium ad ventricles relax causing blood to enter in the atrium)
  • A-v valve opens (atrioventricular valves e.g bicuspid + tricuspid valve) = due to a pressure difference in the atrium and in the ventricle [atrium higher pressure than in the ventricle due to atrial systole] ======> then they close due to ventricular systole = the LUB sound!
  • Ventricular volume ===> in oher words the amount of blood in the ventricle at a given time.
  • Phono cardiogram (dont need to know) = records the sounds made by the heart.
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There are many diseases associated with the lungs and can be caused by many factors such as lifestyle, genetics (if it was hereditary), and other factors.But one of the main factors is smoking. Smoking causes so much damage to the lungs and to other parts of the body like it affects the brain also. This is because in a cigarette there are many components which are harmful to the body for example:

  • Carcinogens = Causes cancer and tumour formations in the body
  • Benzo-pyrene = A substance which is absorbed by epithelial cells in the lungs and it causes mutations in DNA which when replicated forms tumours.
  • Carbon monoxide = Very dangerous, colourless gas as it can't be smelt however causes big damage to red blood cells as it is absorbed by the red blood cells and bonds to the haemoglobin reducing the amount of oxygen that can be absorbed into the blood therefore creating problems like fatigue and minimal exertion before becoming breathless and can also cause angina's
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  • Nicotine = a main substance which causes the high addiction to smoking as it interfere's with the neurotransmitters released acrossed the synapse between two nerves and is replaced with a different signal which causes the body to become "attached" to nicotine. This can lead to psychological breakdown's and also very agressive behaviour.
  • Irritants =  They begin to attack cilia hairs in the top region of the bronchioles causing build up of mucus due to an irritation along the mucus membranes.
  • Tar = As the cilia hairs are blocked, the tar in the cigarette smoke are deposited and collect on the walls of the respiratory tract and the lungs, and cause them to turn black. It also plays a vital role in blocking goblet cells and damaging the epithelial cells in the windpipe meaning harmful microbes and gas can enter the lungs.
  • Acetone = this chemical is used in solvents. It irritates the eyes, nose and throat. Long-term exposure can damage the liver and kidneys.
  • Formaldehyde = It can cause nasal cancer, as well as damaging the digestive system, skin and lungs.
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  • Hydrogen Cyanide = It weakens the lungs and causes fatigue, headaches and nausea. Also cyanide is very dangerous because it acts as a inhibitor during respiration and therefore your body can't respire and produce energy.

It contains many other compounds which you won't need to know much about. In the specification the types of pulmonary (lung) diseases you will need to know are:

  • Pulmonary Fibrosis
  • Asthma
  • Emphysema
  • Tuberculosis (caused by a pathogen)

In the next few slides I will explain the different diseases to the best of my ability explaining the symptoms and there affect on the lungs function.

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Pulmonary fibrosis is a disease which arises when scarring can be seen on the epithelium of the lungs. This causes them to become irreversibly thickened. This affects the diffusion rate in the alveoli because a key feature of alveoli is that it has a thin membrane however in fibrosis this membrane is thickened and therefore affects diffusion as it increases the diffusion pathway which significantly reduces the rate of diffusion meaning less oxygen is able to diffuse in. There are many symptoms of fibrosis such as:

  • Shortness of breath which is due to a thick alveolar membrane and that reduces the rate of diffusion and the amount of oxygen which can be absorbed into the blood. Also a reduced elasticity of the lungs meaning less air can be drawn into the alveoli for diffusion.
  • Weakness & Fatigue results from the reduced intakke of oxygen into the blood. This means less energy can be released by respiration.
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  • Chronic and Dry cough occurs because the fibrous tissue an obstruction in the airways of the lungs. The body will try to get rid of what is in the lungs by coughing but to no avail as the tissue cannot be removed by coughing.
  • Pain and discomfort because of the presence of the fibrous tissue damaging the lungs and adding pressure to the lungs tissue and scarring which to pain and discomfort.


Asthma is an example of a allergic reaction. Asthma can be stimulated by many different types of allergens such as pollen, animal fur and the faeces of the house dust mite. It can also be triggered or made even worse by a range of factors including air pollutants like sulur dioxide, exercise, infection and stress.

When these allergens enter, white blood cells on the lining of the bronchi and bronchioles to release a chemical called histamine (an inflammatory agent)

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Histamine has the following effects on the body:

  • The lining of these airways becomed inflamed
  • The goblet cells begin to release excess mucus
  • Muscle surrounding the bronchioles contracts and so constricts the airways

The symptoms of asthma include:

  • Difficulty in breathing due to the constriction of the bronchi and the bronchioles, their inflammed linings and the additional mucus and fluid within them.
  • Wheezy sound made when breathing due to the narrowing of the bronchioles and therefore that restricts the air entering lungs.
  • Coughing due to a reflex response by the lungs to try an remove the obstruction in the bronchioles (but to no avail).
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Asthma can become very serious in patients as it can reduce the lumen of the bronchioles so much that it can completely clog up. If that happens you are injected with adrenaline and that helps to ease the contraction in the bronchioles.

Pulmonologists (consultants specialising in the lungs) do endograms and they pass a small camera through your nostril and they not only flush out the mucus that gets trapped inside but also they try and relieve some of the contraction in the bronchioles.

(P.S ==> The information about the pulmonologists you won't need to know! Just a bit of information! :-) )


Emphysema is a disease which can be caused by smoking. It permanently damages the lungs for a few reasons. One reason is that symptoms are not seen till about 20 years and once diagnosed it can't be reversed. The second reason is that it reduces the elasticity of the lungs and that affects the amount of oxygen that is taken in to body by inhalation.

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As well as in fibrosis, one of the symptoms would be:

  • A shortness of Breath due to a reduced elasticity in the lungs which therefore means less air can be inhaled in one breath.

However emphysema shows other symptoms such as:

  • A chronic cough  the consequence of lung damage due to emphysema and the lungs natural reflex reaction to try and remove any  damage substance/ blockage in the lungs.
  • Bluish skin due to low levels of alveoli and reduced levels of elasticity of the lungs, the amount of oxygen that eventually enters the bloodstream is significantly reduced and therefore causing a blue colouration of the skin (in other words low levels of oxygen in the blood!)
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Above is a table showing the different functions of the lungs and how each disease interferes with that function either by damaging its structure or affecting a process to get oxygen into the body (e.g. reduced surface area, longer diffusion path, reduced elasticity)

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shuld be finished... if you require further explanation or want me to add sumethin on... just ask ;)


Thanks :)


Nicely Done! =)


useful cuzi have exams in less than 2 months :O


Amazing, once again! ;)


Very good notes, and I hate to be picky, but a few facts are misleading:  It isn't hydrogen or disulfide bonds within the starch polysaccharide, they are 1,4-glycosidic bonds (though this name isn't required), and the reaction is a hydrolysis reaction in which a C-O bond between the sugars is broken (R-C-O-C-R'  --->  R-C-O-H + H-O-C-R').  Also, nuclei aren't 'one per cell'; some have none (red blood cells) and some have multitudes (in the sarcoplasm, for instance, where muscle cells have fused.) As I said, don't want to be picky, but don't want peeps to lose marks in the exam because they misinterpreted this stuff.  Otherwise, excellent notes! :)


Ah, also 'the pulmonary vein is the only vein containing deoxygenated blood'.  Other way round, it's oxygenated :)

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