B2

Cells are the basic building blocks of all living organisms

A tissue is a group of cells with a similar structure and function

Organs are a group of tissues performing specific functions

Organs are organised into organ systems which work together to form organisms

The digestive system is an example of an organ system in which several organs work together to digest and absorb food

Enzymes are all large proteins and all proteins are made up of chains of amino acids. These chains are folded into unique shapes which enzymes need to do their job

Changing the temperature changes the rate of an enzyme catalysed reaction. A higher temperature increases the rate at first but if it gets too hot some of the bonds holding the enzyme together break. This changes the shape of the enzyme’s active site so the substrate won’t fit anymore. The enzyme is denatured. All enzymes have an optimum temperature they work best at

If the pH is too high or low the pH interferes with the bonds holding the enzyme together which changes the shape of the active site and denatures the enzyme. All enzymes have an optimum pH.

Rate = 1000/time

Enzymes catalyse specific reactions in living organisms due to the shape of their active site

The lock and key model - Every enzyme has an active site with a unique shape that fits onto the substance involved in a reaction.

Enzymes usually only catalyse one specific reaction. This is because for the enzyme to work the substrate has to fit onto its active site. If the substrate doesn’t match the enzyme’s active site then the reaction won’t be catalysed. The model is simpler than how enzymes actually work.

Amylase breaks down starch

Amylase is made in the salivary glands, the pancreas and the small intestine

Protease breaks down proteins and is made in the stomach (pepsin), the pancreas and the small intestine

Lipases breaks down lipids and is made in the pancreas and the small instestine

Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream

Carbohydrases break down carbohydrates to simple sugars. Amylase is a carbohydrase which breaks down starch

Proteases break down proteins to amino acids

Lipases break down lipids to glycerol and fatty acids

The products of digestion are used to build new carbohydrates, lipids and proteins. Some glucose is used in respiration

Bile is made in the liver and stored in the gall bladder. It is alkaline to neutralise hydrochloric acid from the stomach. It also emulsifies fat to form small droplets which increases the surface area. The alkaline conditions and large surface area increase the rate of breakdown by lipase

Food tests

Preparing a food sample:

Get a piece of food and break it up using a pestle and mortar

Transfer the ground up food to a beaker and add some distilled water

Give the mixture a good stir with a glass rod to dissolve some of the food

Filter the solution using a funnel lined with filter paper to get rid of the solid bits of food

Benedict’s test for reducing sugars

Prepare a food sample and transfer 5cm^3 to a test tube

Prepare a water bath so that it’s set to 75 degrees C

Add some Benedict’s solution to the test tube (about 10 drops) using a pipette

Place the test tube in water bath using a test tube holder and leave it there for 5 minutes. Make sure the tube is pointing away from you

If the food sample contains a reducing sugar, the solution in the test tube will change from the normal blue colour to green, yellow or brick red depending on the amount of sugar in the food

Iodine test for starch

Make a food sample and transfer about 5cm^3 of your sample to a test tube

Then add a few drops of iodine solution and gently shake the tube to mix the contents. If the sample contains starch, the colour of the solution will change from browny orange to black or blue black

Biuret reagent for protein

Prepare a sample of your food and transfer 2cm^3 of your sample to a test tube

Add 2cm^3 of biuret solution to the sample and mix the contents of the tube by gently shaking it

If the food sample contains protein, the solution will change from blue to purple. If no protein is present the solution will stay blue

Sudan III test for lipids

Prepare a sample of the food you’re testing but you don’t need to filter it. Transfer about 5cm^3 into a test tube

Use a pipette to add 3 drops of Sudan III stain solution to the test tube and gently shake the tube

Sudan III stain solution stains lipids. If the sample contains lipids, the mixture will separate out into two layers. The top layer will be bright red. If no lipids are present, no separate layer will form at the top of the liquid

Investigate the effect of pH on the rate of reaction of amylase enzyme

Put a drop of iodine solution into every well of a spotting tile

Place a Bunsen burner on a heat proof mat and a tripod and a gauze over the Bunsen burner. Put a beaker of water on top of the tripod and heat the water until it is 35 degrees C (use a thermometer to measure the temperature). Try to keep the temperature of the water constant throughout the experiment.

Use a syringe to add 1cm^3 of amylase solution and 1cm^3 of a buffer solution with a pH of 5 to a boiling tube. Using test tube holders, put the tube into the beaker of water and wait for five minutes

Use a different syringe to add 5cm^3 of a starch solution to the boiling tube

Immediately mix the contents of the boiling tube and start a stop clock

Use continuous sampling to record how long it takes for the amylase to break down all of the starch. To do this use a dropping pipette to take a fresh sample from the boiling tube every 30 seconds and put a drop into a well. When the iodine solution remains browny orange starch is no longer present

Repeat the whole experiment with buffer solutions at different pH values to see how pH affects the time taken for the starch to be broken down

Remember to control any variables each time (… concentration and volume of amylase solution) to make it a fair test

The lungs

The thorax is the top part of the body

It’s separated from the lower part of the body by the diaphragm

The lungs are like sponges and are protected by the ribcage. They’re surrounded by the pleural membranes

The air that you breathe in goes through the trachea. This splits into two tubes called bronchi (each one is a bronchus) one going to each lung

The bronchi split into progressively smaller tubes called bronchioles

The bronchioles finally end at small bags called alveoli where the gas exchange takes place

The lungs contain millions of alveoli surrounded by a network of blood capillaries. This is where gas exchange happens

The blood passing next to the alveoli has just returned to the lungs from the rest of the body so it contains lots of carbon dioxide and very little oxygen. Oxygen diffuses out of the alveolus (high concentration) into the blood (low concentration). Carbon dioxide diffuses out of the blood (high concentration) into the alveolus (low concentration) to be breathed out

When the blood reaches body cells oxygen is released from the red blood cells where there is a high concentration into the body cells where there is a low concentration

At the same time carbon dioxide diffuses out of the body cells where there is a high concentration into the blood where there is a low concentration and it is then carried back to the lungs

The heart is an organ that pumps blood around the body in a double circulatory system. The right ventricle pumps blood to the lungs where gas exchange takes place. The left ventricle pumps blood around the rest of the body

The heart is a pumping organ that keeps the blood flowing around the body. The walls of the heart are mostly made of muscle tissue

The heart has valves to prevent the backflow of blood

Blood flows into the two atria from the vena cava and the pulmonary vein

The atria contract pushing the blood into the ventricles

The ventricles contract forcing the blood into the pulmonary artery and the aorta and out of the heart

The blood then flows to the organs through arteries and returns through the veins

The atria fill again and the whole cycle repeats

The heart also needs its own supply of oxygenated blood. Coronary arteries branch off the aorta and surround the heart making sure it gets all the oxygenated blood it needs

The natural resting heart rate is controlled by a group of cells located in the right atrium that act as a pacemaker. Artificial pacemakers are electrical devices used to correct irregularities in the heart rate

The body contains three different types of blood vessel

Arteries - Carry blood away from the heart

The heart pumps blood out at high pressure so the artery walls are strong and elastic

The walls are thick compared to the size of the lumen in the middle

They contain thick layers of muscle to make them strong and elastic fibres to allow them to stretch and spring back

Veins - Carry blood to the heart

Capillaries join up to form veins

The blood is at lower pressure in the veins so the walls don’t need to be as thick as artery walls

They have a bigger lumen than arteries to help the blood flow despite the lower pressure

They have valves to help keep the blood flowing in the right direction

Capillaries - Involved in the exchange of materials at the tissues

Arteries branch into capillaries

Capillaries are really small

The carry the blood really close to every cell in the body to exchange substances with them

The have permeable walls so substances can diffuse in and out

They supply food and oxygen and take away waste like CO2

Their walls are usually only one cell thick. This increases the rate of diffusion by decreasing the distance over which it occurs

Rate of blood flow = volume of blood flow/number of minutes

Blood is a tissue consisting of plasma, in which the red blood cells, white blood cells and platelets are suspended

Red blood cells carry oxygen

Red blood cells carry oxygen from the lungs to all the cells in the body

Their shape is a biconcave disc which gives a large surface area for absorbing oxygen

They don’t have a nucleus which allows more room to carry oxygen

They contain a red pigment called haemoglobin

In the lungs, haemoglobin binds to oxygen to become oxyhaemoglobin. In body tissues the reverse happens - oxyhaemoglobin splits up into haemoglobin and oxygen to release oxygen to the cells

White blood cells defend against infection

Some can change shape to engulf invading pathogens in phagocytosis

Others produce antibodies to fight microorganisms as well as antitoxins to neutralise any toxins produced by the microorganisms

Unlike red blood cells they do have a nucleus

Platelets help blood clot

These are small fragments of cells. They have no nucleus

They help the blood to clot at a wound - to stop all your blood pouring out and to stop microorganisms getting in

Lack of platelets can cause excessive bleeding and bruising

Stents

Tubes that are inserted inside arteries. They keep them open making sure blood can pass through to the heart muscles. This keeps the person’s heart beating

Advantages:

Lower the risk of a heart attack in people with coronary heart disease

Effective for a long time

Relatively quick recovery time

Disadvantages

Risk of complications during the operation (heart attack)

Risk of infection from surgery

Risk of patients developing a blood clot near the stent which is called thrombosis

Statins

Drugs that can reduce the amount of bad cholesterol present in the bloodstream which slows down the rate of fatty deposits forming

Advantages:

By reducing the amount of bad cholesterol in the blood, statins can reduce the risk of strokes, coronary heart disease and heart attacks

As well as reducing the amount of bad cholesterol, statins can increase the amount of beneficial type of cholesterol in your bloodstream. This type can remove bad cholesterol from the blood

Some studies suggest that statins may also help prevent some other diseases

Disadvantages:

Statins are a long term drug that must be taken regularly. There’s the risk that someone could forget to take them

Statins can sometimes cause negative side effects like headaches. Some of these side effects can be serious like kidney failure, liver damage and memory loss

The effect of statins isn’t instant. It takes time for their effect to kick in

Valve replacement

The valves in the heart can be damaged or weakened by heart attacks, infection or old age. The damage could cause valve tissue to stiffen so it won’t open properly or a valve could become leaky allowing blood to flow in both directions rather than just forward. This means that blood doesn’t circulate as effectively as normal

Advantages:

Less drastic procedure than a whole heart transplant

Disadvantages:

Still a major surgery

There can still be problems with blood clots

Artificial heart

Advantages:

Less likely to be rejected by the body’s immune system than a donor heart. This is because they are made from metals or plastics so the body doesn’t recognise them as foreign and attack them in the same way as it does with living tissue

Disadvantages:

Surgery to fit an artificial heart can lead to bleeding and infection

Artificial hearts don’t work as well as healthy natural ones as parts of the heart could wear out or the electrical motor could fail

Blood doesn’t flow through artificial hearts as smoothly which can cause blood clots and lead to strokes

The patient has to take drugs to thin their blood and make sure this doesn’t happen, which can cause problems with bleeding if they are hurt in an accident

In coronary heart disease layers of fatty material build up inside the coronary arteries, narrowing them. This reduces the flow of blood through the coronary arteries, resulting in a lack of oxygen for the heart muscle. Stents are used to keep the coronary arteries open. Statins are widely used to reduce blood cholesterol levels which slows down the rate of fatty material deposit

In some people heart valves may become faulty, preventing the valves from opening fully, or the heart valve might develop a leak. Faulty heart valves can be replaced by using biological or mechanical valves

In the case of heart failure a donor heart, or heart and lungs can be transplanted. Artificial hearts are occasionally used to keep patients alive whilst waiting for a heart transplant or to allow the heart to rest as an aid to recovery

People who have problems with their immune system have an increased chance of suffering from communicable disease such as flu because their body is less likely to be able to defend itself against the pathogen that causes the disease

Some types of cancer can be triggered by infection by certain viruses. For example infection with some types of hepatitis virus can cause long term infections in the liver where the virus lives in the cells. This can lead to an increased chance of developing liver cancer. Another example is infection with HPV which can cause cervical cancer in women

Immune system reactions in the body caused by infection by a pathogen can sometimes trigger allergic reactions such as skin rashes or worsen the symptoms of asthma for asthma sufferers

Mental health issues such as depression can be triggered when someone is suffering from severe physical health problems, particularly if they have an impact on the person’s ability to carry out everyday activities or if they affect the persons’ life expectancy

Health is the state of physical and mental well being. Diseases are often responsible for causing ill health

Diseases, both communicable diseases and non communicable diseases are major causes of ill health. Other factors including diet, stress and life situations may have a profound effect on both physical and mental health

Different types of disease may interact

Defects in the immune system mean that an individual is more likely to suffer from infectious diseases

Viruses living in cells can be the trigger for cancers

Immune reactions initially caused by a pathogen can trigger allergies such as skin rashes and asthma

Severe physical ill health can lead to depression and other mental illness

Risk factors are linked to an increased rate of a disease

They can be: aspects of a person’s lifestyle, substances in the person’s body or environment

A casual mechanism has been proven for some risk factors but not in others

The effects of diet, smoking and exercise on cardiovascular disease:

Obesity as a risk factor for Type 2 diabetes - makes the body less sensitive or resistant to insulin meaning that it struggles to control the concentration of glucose in the blood

The effect of alcohol on the liver and brain function - Too much alcohol can affect brain function. It can damage the nerve cells in the brain causing the brain to lose volume

The effect of smoking on lung disease and lung cancer - It damages the walls of arteries and the cells in the lining of the lungs

The effects of smoking and alcohol on unborn babies - Can cause lots of health problems for the unborn baby

Carcinogens including ionising radiation, as risk factors in cancer

The human cost of non communicable disease: tens of millions of people around the world die from non communicable diseases per year. People with these diseases may have a lower quality of life or a shorter lifespan. This not only affects the sufferers themselves but their loved ones too

The financial cost of non communicable disease: the cost to the NHS of researching and treating these diseases is huge and it is the same for other health services and organisations around the world. Families may have to move or adapt their home to help a family member with a disease which can be costly. Also if the family member with the disease has to give up work or dies, the family’s income will be reduced. A reduction in the number of people able to work can also affect a country’s economy

In developed countries, non communicable diseases are more common as people generally have a higher income and can buy high fat food. Nationally, people from deprived areas are more likely to smoke, have a poor diet and not exercise. This means the incidence of cardiovascular disease, obesity and Type 2 diabetes is higher in those areas. Your individual choices affect the local incidence of disease

Cancer is caused by uncontrolled cell growth and division. This uncontrolled growth and division is a result of changes that occur to the cells and results in the formation of a tumour (a mass of cells). Not all tumours are cancerous. They can be benign or malignant

Benign tumours are growths of abnormal cells which are contained in one area usually within a membrane. They do not invade other parts of the body

Malignant tumour cells are cancers. They invade neighbouring tissues and spread to different parts of the body in the blood where they form secondary tumours

Scientists have identified lifestyle risk factors for various types of cancer. There are also genetic risk factors for some cancers

Smoking - Linked to lung cancer but research has also linked it to other types of cancer including mouth, bowel, stomach and cervical cancer

Obesity - Linked to many different cancers including bowel, liver and kidney cancer. It’s the second biggest preventable cause of cancer after smoking

UV exposure - People who are often exposed to UV radiation from the sun have an increased chance of developing skin cancer. People who live in sunny climates and people who spend a lot of time outside are at a higher risk of developing skin cancer

Viral infection - Infection with some viruses has been shown to increase the chances of developing certain types of cancer. For example infection with hepatitis B and C viruses can increase the risk of developing liver cancer

Sometimes you can inherit faulty genes that make you more susceptible to cancer

Mutations in the BRCA genes have been linked to an increased likelihood of developing breast and ovarian cancer

Epidermal tissues - covers the whole plant

• The epidermal tissues are covered with a waxy cuticle which helps to reduce water loss by evaporation

• The upper epidermis is transparent so that light can pass through it to the palisade layer

Palisade mesophyll - Where most photosynthesis happens

• The palisade layer has lots of chloroplasts which means that they are near the top of the leaf where they can get the most light

Spongy mesophyll - Contains big air spaces to allow gases to diffuse in and out of cells

• The air spaces in the spongy mesophyll tissue increase the rate of diffusion of gases

Xylem and phloem - Transport things like water, mineral ions and food around the plant

• The xylem and phloem form a network of vascular bundles which deliver water and other nutrients to the entire leaf and take away the glucose produced by photosynthesis. They also support the structure

Meristem tissue - found at the growing tips of shoots and roots and is able to differentiate into lots of different types of plant cell allowing the plant to grow

The tissues of leaves are also adapted for efficient gas exchange

The lower epidermis is full of stomata which let carbon dioxide diffuse directly into the leaf. The opening and closing of stomata is controlled by guard cells in response to environmental conditions

The roots, stem and leaves form a plant organ system for transport of substances around the plant

Root hair cells are adapted for the efficient uptake of water by osmosis, and mineral ions by active transport

Xylem tissue transport water and mineral ions from the roots to the stems and leaves. It is composed of hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream

The role of stomata and guard cells are to control gas exchange and water loss

Phloem tissue transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage. The movement of food molecules through phloem tissue is called translocation

Phloem is composed of tubes of elongated cells. Cell sap can move from one phloem cell to the next through pores in the end walls

Phloem tubes transport food

Made of columns of elongated living cells with small pores in the end walls to allow cell sap to flow through

They transport food substances made in the leaves to the rest of the plant for immediate use or for storage

The transport goes in both directions

This is translocation

Xylem tubes take water up

Made of dead cells joined end to end with no end walls between them and a hole down the middle. They’re strengthened with a material called lignin

They carry water and mineral ions from the roots to the stem and leaves

The movement of water from the roots through the xylem and out of the leaves is called the transpiration stream

Light intensity

The brighter the light, the greater the transpiration rate

Stomata begin to close as it gets darker. Photosynthesis can’t happen in the dark so they don’t need to be open to let carbon dioxide in. When the stomata are closed very little water can escape

Temperature

The warmer it is the faster transpiration happens

When it’s warm the water particles have more energy to evaporate and diffuse out of the stomata

Air flow

The better the air flow around a leaf, the greater the transpiration rate

If air flow around a leaf is poor, the water vapour just surrounds the leaf and doesn’t move away. This means there is a high concentration of water particles outside the leaf as well as inside it so diffusion doesn’t happen as quickly

If there is good air flow the water vapour is swept away maintaining a low concentration of water in the air outside the leaf. Diffusion then happens quickly

Humidity

If the air is humid there is a lot of water in it already so there is not much of a difference between the inside and the outside of the leaf

Transpiration is the loss of water from the plant

Transpiration is caused by the evaporation and diffusion of water from a plant’s surface. Most transpiration happens at the leaves

This evaporation creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of the plant through the xylem vessels to replace it

This in turn means more water is drawn up from the roots and so there’s a constant transpiration stream of water through the plant

Transpiration is just a side effect of the way leaves are adapted for photosynthesis. They have to have stomata in them so that gases can be exchanged easily. As there is more water inside the plant than in the air outside the water escapes from the leaves through the stomata by diffusion