Sunday, 29 January 2012

2.85 Reflex Arc

Describe the structure and function of a simple reflex arc illustrated by the withdrawal of a finger from a hot object

In this example of the reflex of withdrawing your hand from the hot object:
  • The stimulus is the hot object
  • The receptor is the heat sensor in our skin
  • The impulse travels to the spinal cord along the sensory neuron
  • In the spinal cord the impulse is passed on to the relay neuron
  • This then passes on to the motor neuron
  • The motor neuron carries the impulse to the muscle and the response is the muscle contracts to move away
(Notice how this impulse does not go through the brain first, this is because it makes the response faster and reduces further cell damage due to slow response)

Another Detailed Diagram:
Add caption

2.84 Electrical Impulses

Understand that stimulation of receptors in the sense organs send electrical impulses along nerves into and out of the central nervous system, resulting in rapid responses.

  • The messages that nerves carry are called the nerve impulses and they are electrical signals.
  • They pass along quickly along the axon of the neuron.
  • Some axons have a fatty sheath around them which insulates the axon and allows the impulse to travel faster along the axon.
Diagram showing how it works:

2.83 Central Nervous System

Recall that the central nervous system consists of the brain and spinal cord and is linked to sense organs by nerves.

  • The nervous system controls your action and coordinates different parts of the body.
  • The main parts of the nervous system are the brain and the spinal cord and together they are called the central nervous system. They are both made of delicate nervous tissue so both are protected by bones. The brain is protected inside the skull and the spinal cord is protected inside your backbone.
  • The central nervous system is connected to different parts of the body by nerves which is made up by nerve cells or neurons.
  • Sense organs are our receptors and they send messages to the central nervous system and are sent along the sensory neurons
  • When the central nervous system sends messages telling effectors what to do, the message is sent along the motor neuron

2.82 Communication

Describe how responses can be controlled by nervous or by hormonal communication and understand the differences between the two systems.

1. The part on the left of the diagram (the cell body), would be embedded in our spine and on the other end it would be connected to an effector, and in this case, the muscle fibres. The electrical impulse or the nerve impulse is carried inside the walls from the cell body to the synaptic knot where it connects to the muscles through the axon which can be as long as one meter and only one cell wide. In Mammals the axon would be surrounded by another type of cell known as the Schwann cell and these contain a great deal of fat and these form the myelin sheath. The effect of having a myelin sheet is that it increases the speed of nerveconduction and this is one way of connecting the coordinator to the effector.

Diagram of the Motor nerve:

2. The second way is known as the endocrine system. This involves the Endocrine gland which produces chemicals (hormones) which can be either protein or steroids. An example would be the adrenal gland, the adrenal gland would be secreting adrenaline to the blood which will travel through the blood stream and will arrive at the organ it affects (target tissue) and will have an effect upon it. It is possible for hormones to have multiple targets and bring about multiple effects.

Difference between Nerves and Hormones:

  • Nerve impulses are fast, Hormones normally take longer.
  • Nerve impulses re sent through neurons whereas hormones are sent through blood.
  • Nerve impulses enables body to response to external environment and the hormones enable body to respond to internal environment

Monday, 23 January 2012

2.77b Thermoregulation

Understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis.

Negative Feedback lop is the control of constant conditions.
The receptor of our body is called the hypothalamus which is in the brain. It responds to a stimulus which in this case, is the temperature of the blood. Our bodies tries to maintain the body temperature to around 37-38 C. So body temperature is fed back into the brain and if the body temperature needs to be increased and decreased the changes will be made by the effectors such as our skin. The response would be an increase or decrease of body temperature and this will be fed back to the loop.

In our skin we have sweat glands but also the capillary network which allows blood to be closer or further away from the skin.

If the body temperature increases, the hypothalamus will bring around cooling effect with responses such as:
  • Sweating 
  • Increase blood flow and dilate which increases the exchange of heat to the outside with the process such as radiation and evaporation of sweat 

In a cold environment, our body temperature will fall which brings about regulation to increase body temperature:
  • Shivering 
  • Vasoconstriction 
  • Hairs raised

Monday, 16 January 2012

2.9 Effect of temperature on the rate of reaction

Understand how the functioning of enzymes can be affected by changes in temperature

There are two main principles for this topic:

  1. If we increase the temperature, then we increase the 'average' kinetic energy with the particles.
  2. If we increase the kinetic energy, then we increase the number of collisions, so therefore we will have more reactions
The particles here, in particular, are the substrates (s) and the enzyme (e)
Enzyme + Substrate => Enzyme Substrate Complex + Enzyme 
Here we are looking at temperature affects it:

At low temperatures, we will except a slower rate of reaction, but as we increase the temperature, the effect is that the kinetic energy of both e and s increase so more complexes are formed more quickly.
However, we find that we reach a temperature at which the rate of reaction decreases quite dramatically

In section A, we a increasing the average kinetic energy of both reactants e and s, so we have more collisions and more reactions. After a given temperature (section C), the rate of reaction declines really quickly, this is because the kinetic energy is changing the shape of the active site of the enzyme - so it doesn't work to produce products. This is called denatured (not killed). The peak of the curve is at a given temperature so that the maximum rate is achieved at the temperature which is called the optimum temperature.

2.77a Thermoregulation

Understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis.

Where the conditions are kept the same or constant.

The temperature are kept the same or constant.

Some animals, mammals as an example, when the environmental temperature either increases or decreases the body temperature remains constant. These are homeothermic organisms and this is a process called thermoregulation. This is an example of homeostatis.

From the rate of reaction to temperature graph, we can tell that there is an optimum temperature of that enzyme in the animal. Which is why the mammals keeps the body temperature at that optimum temperature if possible.

2.76 Sensitivity

Understand the organisms are able to respond to changes in their environment.

Stimuli (changes in the environment) can be either light, temperature, pressure or chemicals, in order to detect the changes in the environment, organisms are required to have receptors and in order to respond, organisms have effectors such as muscle/glands. It is the response that ensures the organism is able to survive the changes in the environment.

Monday, 9 January 2012

2.8b Enzyme Reactions

Understand the role of enzymes as biological catalysts in metabolic reactions.

We will take C6H12Oand the presence of Oand convert this to a release of energy+CO2+H2O

In the beginning of the reaction the glucose and oxygen will place in around the middle of our graph in which the y axis indicates the energy of the substrate. The bottom line represents the energy released and the energy release is indicated by the energy drop in the graph.
However, without an enzyme to break down glucose to carbon dioxide and water we will have to input energy in order to break the bonds in glucose just like the process of combustion. So initially we will need to add energy [Energy of Activation] which could be in the form of heat or extreme ph, however, they are both damaging to human cells; our biological system has found a way to overcome the energy of activation - through enzymes.
The enzymes would combine with the glucose and oxygen to form an activated complex weakening the structure without the need of heat or extreme ph and overcome the energy of activation (shown in red line). The role of the enzyme here is to reduce the energy of activation, so we can say that it makes the reaction occur more easily or faster.

2.8a Enzymes

Understand the role of enzymes as biological catalysts in metabolic reaction.

As a catalyst, the enzyme is making a reaction faster but also under moderate conditions. Metabolic reactions refer to biological reactions taking place in the cell - building cells up and breaking molecules down.

To explain how enzymes work, here is the lock and key hypothesis:

The red structure represents in the enzyme and you will notice that it has a particular shape. It is a protein and within the molecule and there is a part of molecule (b) called the active site and this is the part of the enzyme molecule where the substrate (c) fits in and they are complimentary.When they fit together they form the structure (d) which is called a activated complex. The enzyme is able to weaken the structure of the substrate in this process.

The products (f) emerge from the enzymes but the enzymes remains unchanged by the reaction. The substrate is turned into product by the action of the enzyme. Since the enzyme is unchanged by the reaction it can react again with another substrate.

2.7 Test for Starch and Glucose

Describe the tests for glucose and starch


  1. Begin by taking glucose power and dissolve it into a test tube and add to the same test tube benedict's reagent which is blue. 
  2. Take the test tube and place it in a water bath (around about 60 - 70 degree centigrade)
  3. After just 2/3 minutes we can remove the test tube and what we would be would be a colour change from blue to orange  *In weak solutions of glucose we will see a green colour developed*
  1. Put some starch powder into a spotting tile
  2. We will then add iodine solution (brown)
  3. If we add this to the spotting tile, we would see a change from the brown colour to a dark blue/black powder

Friday, 6 January 2012

2.6 Biological Molecules

Describe the structure of carbohydrates, proteins and lipids as large molecules made up from smaller basic units: starch and glycogen from simple sugar; protein from amino acids; lipid from fatty acids and glycerol.

are made up of C(arbon)H(ydrogen)O(xygen)
The simplest carbohydrate are sugars which are monomers. The large molecules are formed through combining sugars are those such as starch and glycogen.  Starch is a straight long chain of glucose whereas glycogen is a long chain of glucose with branches. The stored form of sugar in animals is glycogen and the stored form of sugar in plants is starch.
are made up of C(arbon) H(ydrogen) O(xygen) N(itrogen)
The simple smallest molecules in protein is amino acids. The amino acids are also joined together in long chains and it is these chains we describe as proteins.
are made up of C(arbon) H(ydrogen) O(xygen)
But the story here is slighty different.
The lipids contain a small molecule glycerol and another called fatty acids. Lipids have two different types of molecules joining together to form the structure of the molecule lipid.

Wednesday, 4 January 2012

2.32 Energy Content of Food

Recall how to carry out a simple experiment to determine the energy content in a food sample.


  • Thermometer
  • Boiling Tube filled with 20 cm3 Water
  • 10 cm3 of food sample in Crucible


  1. Measure the initial temperature of the water (degree centigrade)
  2. Ignited the food source
  3. Heat the water with the ignited food
  4. Measure the final temperature of the water (degree centigrade)
Let's say our initial temperature was 20 degrees Celsius and the final temperature was 30 degrees Celsius
1 cm3 of water has a weight of 1g and in order to increase one degrees it would take 4 joules

Energy released from food per gram (J) = (mass of water (g)*temperature rise (degree centigrade)*4.2)/Mass of food sample (g)

In our case:
Energy released from food per gram (J)= (20g*(30-20)*4.2)/10
=84 J/g
So in our food there were 84 joules per gram

2.31 Villi Structure and function

Explain how the structure of a villus helps absorption of the products of digestion in the small intestine.

The inside wall of the small intestine is folded which increases the surface area. When we look at the surface of the small intestine, we see finger-like projection called villi, and each villi has its own blood supply.

We can see that in a villi there are blood vessels that bring blood supply in and blood supply out. The villi is surrounded by glucose, amino acids, glycerol, fatty acids and in the space around the villi these molecules are in high concentration. The villi increases the surface area for absorption. Villi also has a small diffusion distance meaning that the diffusion happens fast. The blood vessel's distant is also quite close to the space outside meaning the molecules can diffuse in the bloodstream fast. Because the blood is flowing in and out, the blood supply out removes the molecules which are diffused into the blood and this maintains the concentration gradient by keeping the concentration in the blood low which is maintained by the blood flow.

The small intestine helps with the absorption of the lipid, and the lacteal collect the lipids before it is returned to the circulatory system.

2.30 Bile

Recall that bile is produced by the liver and stored in the gall bladder, and understand the role of bile in neutralising stomach acid and emulsifying lipids.

In the stomach is approximately 3, due to the presence of HCL [Hydrochloric Acid], the structure below the stomach, the pancreas, produces digestive enzymes, the liver is responsible for the production of a substanc named bile and is stored in the structure called Gall Bladder. When food is released from the stomach into the small intestine, the ph is approximately 3, this stimulates the release of bile from the gall bladder through the bile duct and to pancreatic duct. So the bile mixes with the digestive enzymes. The point where the pancreatic duct reaches the food the bile has two effects: the first effect is to neutralise the stomach acid and to create a ph whih is approximately 7. This ph is the optimal ph for the digestive enzymes. The second effect of bile is that the fat molecules are broken down into smaller droplets this is a process known as emulsification. A common misunderstanding is that this is an enzyme action. The purpose of the bile breaking fat down into smaller droplets is to increase surface area of the lipid, and that means lipase enzymes can digest the lipid more quickly.

2.29 Digestive Enzymes

Understand the role of digestive enzymes to include the digestion of starch to glucose by amylase and maltase, the digestion of proteins to amino acids by proteases and the digestion of lipids to fatty acids and glycerol by lipases.

Digestive enzymes turns the insoluble food into soluble molecules which can then be absorbed in the bloodstream and then assimilated into our cells. This is promoted by digestive enzymes.

There are three types of this process:

Starch- This molecule is a long chain of glucose molecules, this is insoluble and this forms the main components of food such as rice and potatoes. Amylase is used to break down starch into two molecule structures known as disaccheride  (two molecule sugars)
Maltose- The maltose is digested by maltase into glucose, this is the soluble molecule that can be absorbed by the bloodstream.

Protein- Protein is a chain of amino acids which is broken down by proteases into their monomers - amino acids. The amino acids are then absorbed in the bloodstream and then assimilated into our cells for use.

Lipid - Lipid structure is different than that of carbohydrates and proteins. The lipase breaks the bond between Glycerol and Fatty Acids and forms the two soluble molecules.

2.28 Peristalsis

Explain how and why food is moved through the gut by peristalsis.

The important thing to remember about the gut wall is that they have muscle tissues which allows them to contract. The muscle is organised around the oesophagus, and when the muscle contracts the muscle gets shorter - this means the diameter of the oesophagus will decrease. Enters the gut and stretches the wall, this causes a reflex of the muscle behind the bolus, this contraction pushes the bolus downwards through out guts.


Tuesday, 3 January 2012

2.27 Stages of Digestion

Understand the processes of ingestion, digestion, absorption, assimilation and egestion.

Location- Mouth, Teeth, Salivary Glands
Brief Summary- The teeth carries out the chewing process which technically is known as mastication, this creates a ball of food [bolus] so we can swallow. The salivary glands add mucus for lubrication and also add the salivary enzymes amylase  which begins to digest the starch.

Location- Small Intestine and to lesser extent Stomach
Brief Summary- This is the stage in which the insoluble food particles are digested to become soluble which is done with the addition of enzymes.

Location- Small Intestine
Brief Summary - In the small intestine there are structures such as the villi/microvilli which absorbs soluble food into our bloodstream. So the nutrients gets absorbed from the gut to the blood.

Location- Tissues/ Organs
Bried Summary- The food now in the blood diffuses into the cells for use.

Location- Rectum/Anus
Brief Summary-  Removal of undigested material. Passing of solid waste.

Monday, 2 January 2012

2.26 The human alimentary canal

Recognise the structures of the human alimentary canal (digestive system) and describe in outline the functions of the mouth, oesphagus, stomach, small intestine and pancreas.

Food is introduced into the digestive system through the tongue and mouth, this is a process known as ingestion. Teeth helps to break food down so we can swallow, and we call this process chewing. We also have the addition of mucus which lubricates the food and helps the food to slide down through the digestive system. We begin with the addition of salivary amylase which is an enzyme which breaks down starches.

The oesphagus is a tube which carries food from the mouth to the stomach in which there is no digestion. The food moves down the tube with a process called peristalsis.

The food is then stored in the stomach, and also in the stomach there will be acid which kills off the bacteria in the food. Another feature of the stomach is the presence of a group of enzymes known as proteases. These enzyme begin the digestion of protein.

As the food then moves from the stomach to the small intestine, there is an addition of enzymes from the pancreas. These enzymes will bring about the complete breakdown of the food so that it can be absorbed in the small intestine.

The liver has a structure which manufactures bile and is stored in the gall bladder. The bile neutralises the stomach acid so that the ph in the small intestine is roughly 7 and emulsifies (breaks down into small droplets) the fat in out diet.

The function of the small intestine is the absorption of nutrients into our bloodstream, after that the food travels from the small intestine into the large intestine [colon]. This is where we absorb water into out bloodstream. Finally, the food in which we cannot digest is stored in the rectum and then released from the anus.

Sunday, 1 January 2012

2.25 Energy and Diet

Understand that energy requirements vary with activity levels, age and pregnancy.

If we had a graph plotting energy on the y axis and the age on the x axis, we would see an upwards trend of demand for energy from baby to adult and then decline when it reaches the elderly stage. This will be modified to the activity of the person, such as whether they require lots of energy doing work or whether they exercise regularly.

2.23 Balanced Diet

Understand that a balanced diet should include appropriate proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fibre.

In our diets there are protein, carbohydrate, lipid, vitamin ADC, Calcium, Iron, water, and fibre in which we have to balance with our life style (your age, gender, activity and pregnancy). The demands for diet has to be set to demand the balancing act (your life style).

2.24b Vitamins and Minerals

Recall sources and describe functions of carbohydrate, protein, lipid (fats and oils), vitamins A, C and D, and the mineral ions calcium and iron, water and dietary fibre as components of the diet.

A- The function of Vitamin A is to produce light sensitive pigments in our eye and this allows us to see in poor light conditions. The source for Vitamin A are fish liver oils and liver oil. Deficiency of Vitamin A can lead to poor sight in poor light conditions which is a condition known as night blindness.
C- The function of Vitamin C is allowing the body to form connective tissue which helps cells stick to each other so that cells can stay together as a tissue. The source of Vitamin C comes from citrus fruits such as oranges, limes etc and the deficiency disease is called scurvy and the symptoms of scurvy are bleeding gums.
D- Vitamin D allows us to absorb calcium from our diet. Vitamin D can be produced by our body itself while under sunshine or you can obtain it from fats, eggs or fishes. The disease that occurs if you don't obtain enought Vitamin D is called richets and which can be determined by the bending of bones.

Calcium-You can obtain calcium through dairy products such as milk, cheese etc. The function of calcium is increasing bone strength and a lack in calcium can also cause richets.
Iron- We can find iron in food in liver and the famous vegetable spinach. The function of Iron is the synthesis to make the haemaglobin which we find in red blood cells and that carries oxygen. If you lack Iron in your diet and results in a condition called Anaemia. People with Anaemia looks pale and gets tired quickly.

Fibre is a plant's cell wall, this means it's the cellulose. We get these from plants from our diet. A lack in fibre can cause what we know as constipation. The main role of fibre is peristalsis in our gut.

The function of water is to produce solutions and in those solutions there is the chemistry of life. Substances dissolve and substances react in these solutions. We can obtain water through drinking directly or it may be inside the food inside. If we lack water we will be dehydrated.