Organisation

Specialised cells form tissues, which form organs, which form organ systems. Large multi-cellular organisms have different systems inside them for exchanging and transporting materials.

A tissue is a group of similar cells that work together to carry out a particular function. For example, muscular tissue contracts to move, glandular tissue makes and secretes chemicals and epidermal tissue covers some parts of the body.

An organ is a group of different tissues that work together to perform a certain function. For example the stomach contains muscular tissue (to move the stomach walls and churn food), glandular tissues (to make digestive juices to digest the food), and epitherial tissue (to cover the outside and inside of the stomach).

Organ systems are a group of organs working together to perform a particular function, for example the digestive system contains glands, the stomach, the small intestine, the liver and the large intestine.

Enzymes act a a biological catalyst, making it possible to speed up specific reactions and without having to raise the temperature. A catalyst is a substance which increases the speed of a reaction without being changed or used up in it. Enzymes are all large proteins, made up of chains of amino acids.

Chemical reaction often involve things being split apart or joined together. Every enzyme has an active site with a unique shape that fits onto the substate involved in a reaction. Each one is specific, and if the substate does not match the active site, the reaction wont be catalysed. The model to show this is called the 'lock and key' method, however the 'induced fit' model is more accurate - where the active site changes shape slightly to become a tighter fit.

A higher temperature will increase the rate of reaction at first, however if it gets too hot the bonds will start to break and the enzme's active site will no longer fit the substate, the enzyme has been denatured.

If the pH is too high or low, it can also interfere the bonds holding the enzymes together. Therfore, all enzymes have an optimum temperature and pH.

Amylase breaks down starch to maltose. Iodine will turn from brown to blue-black when starch is present. You can investigate how pH affects amylase activity using this practical:

• Put a drop of iodine solution into every well of a spotting tile.
• Set up a bunsen burner, heat-proof mat, tripod and gauze, placing a beaker of water on top until it reaches 35*c. Try to keep the temperature constant (could use a water bath).
• Use a syringe to add 1cm of amylase solution to a buffer slution with a pH of 5 to a boiling tube and usng test sube holders, place into the beaker and wait 5 minutes.
• Use a different syringe to add 5cm of startch to the boiling tube, mix and start the stop watch.
• use contineous sampling with 30 second intervals to record how long it takes for the amylase to break down all the starch (when the iodine remains brown).
• Repeat the experiment with different buffer solutions with different pH values.

Rate of reaction = 1000 / time

Rate of change = change / time

Big molecules must be broken down so they can easily pass through the walls of the digestive system, allowing them to be absorbed into the bloodstream.

• Carboydases, for example amylase, converts carbohydrates into simple sugars. Amylase turns starch into maltose and other sugars. Amylase is made in the salivary glands, the pancreas and the small intestine.
• Proteases convert proteins into amino acids, They are fund in the stomach (pepsin), the pancreas, and the small intestine.
• Lipases convert lipids into glcerol and fatty acids. They are found in the pancreas and the small intestine.

These products of digestion are used for energy and can be coverted back to the nutrient.

Bile is produced in the liver and stored in the gall bladder, before being released into the small intestine. Bile is an alkaline and neutralises the acid coming from the stomach, making it alkaline and better for enzymes to work. It also emulsifies fats, breaking them down into droplets so they have a bigger surface area for the enzyme lipase it work on, speeding up the reaction.

• Salivary glands - Produce amylase enzyme in the saliva.
• Gullet (oesophagus) - Food travels down into the stomach.
• Stomach - Pummels the food with its muscular walls, produces the protease enzyme pepsin, produces hydrochloric acid to kill bacteria and provide the right pH for protease.
• Liver - Where the bile is produced to neutralise stomach acid and emulsify fat.
• Gall Bladder -  Where bile is stored before its released into the small intestine.
• Pancreas - Produces protease, amylase and lipase enzymes and releases them into the small intestine.
• Small intestine - Produces protease, amylase and lipase to compleate digestion and allows food to be absorbed out the the digestive system and into the bloodstream.
• Large Intestine - Where excess water is absorbed from the food.
• Rectum - Where faeces are stored before being excreted by the anus.

Get a piece of food and break it up using a pestle and mortar. Transfer to a beaker of distilled water and stir until dissolved. Filter using a funnel and filter paper so you are left with no solid.

Benedict's Test (for reducing sugars) -

• Prepare a water bath set to 75*c
• Transfer 5cm^3 of a test sample into a beaker and add some Benedict's solution.
• Place the test tube in the water bath and leave for 5 minutes. Face it aay from you.
• If the food sample contains a reducing sugar the blue solution will turn to green, yellow or red.

Iodine Solution (for starch) -

• Make a food sample and transfer 5cm^3 into a test tube.
• Add a few drops of iodine and gently shake, if t contains starch it will change from brown to black or blue-black

Biuret Test (for proteins) -

• Transfer 3cm^3 of your sample to a test tube.
• Add 2cm^3 of biuret solution to the sample and mix by gently shaking them.
• If the solution changes from blue to pink or purple, protein is present.

Sudan III Test (for lipids) -

• Transfer 5cm^3 of the food sample into a test tube.
• Use a pipette to add 3 drops of Sudan III stain solution and gently shake.
• If the sample contains lipids, the mixture will seperate out and the top will be bright red.

Diseases are often responsible for causing ill health, -physical and mental.

Communicable diseases can be spread from among organisms (the are contagious or infectious) and can be caused by things like bacteria, viruses, parasites and fungi. For example, measles or malaria.

Non-communicable diseases cannot be spread and generally last longer, getting worse slowly. For example, asthma, cancer and coronary heart disease.

Some diseases can lead to other physical or mental health issues, for example:

• People with bad immune systems are sometimes unnable to defend themselves against pathogens and so are more likely to pick up influenza.
• Viruses can casue long-term infections, meaning you are more likely to get cancer.
• Immune system reactions caused by pathogens can trigger allergic reactions.
• Severe health problems can lead to mental health problems like depression.

A good, balanced diet, enough exercise, little stress and a good quality of life can positively help your health. Also, acess to medications and things like condoms to prevent diseases.

Risk factors increase the risk factor of someone getting a disease. They can be casued by lifestyle, substances in the enviroment or substances in the body. Many diseases are caused by more than one risk factor. Individual choice and where you live effects your risk factors. People in developed countries in deprived areas are likely to smoke, have a poor diet, and not exercise enough.

Some risk factors cause specific diseases:

• Smoking has been proved to to cause cardiovascular disease, lung disease and lung cancer. This is because it damages the walls of arteries and the cells in the lining of the lungs.
• Obesity makes the body less sensitive or resistance to insulin, meaning that it stuggles to concentration of glucose in the blood, causing type 2 diabetes.
• Drinking alcohol can cause liver disease. It can also damage nerve cells in the brain causing the brain to lose volume, affecting brain function.
• Smoking or drinking alcohol can cause health poblems to unborn babies.
• Cancer can be directly caused by exposure to certain substances or radiation - carcinogens, for example ionising radiation.

Other things, like a lack of exercise and a high fat diet do not directly cause cardiovascular disease but increase the chance of having it (correlation does not always mean caussation). High blood pressure and high levels of LDH in the blood actually cause it.

A tumour forms when cells grow and divide uncontrollably as the result of changes within the cell. There are two types of tumours:

• Benign - Where the tumour grows until there is no more room, yet staying in one place (usually within a membrane). This is usually not very dangerous.
• Malignant - Where the tumour grows and spreads to neighbouring healthy tissues through cells breaking off and travelling through the bloodstream. These malignant cells infect other parts of the body to form secondary tumours. These are very dangerous and sometimes fatal. They are cancers.

Cancer survival rates have increased due to improved treatment, earlier diagnosis and increased screening.

Some risk factors include:

• Smoking - can increase the chance of lung, mouth, bowel, stomach and cervical cancer.
• Obesity - can increase the chance of bowel, liver and kidney cancer.
• UV exposure - can increase the chance of skin cancer.
• Viral infection - for example infections from hepatitis B and C increase the chance of getting liver cancer.

Inheriting faulty genes can make you more susceptible to cancer, for example mutations in the BRCA genes have been linked to an increased liklihood of developing breast and ovrian cancer.

Plants are made of organ systems made from organs like strems, roots and leaves. The organs are made of tissues, for example:

• Epidermal tissue - covers the whole plant, covered with a waxy cuticle to prevent water loss by evaporation. The lower epidermis is full of stomata controlled by guard cells to allow gas exchange.
• Palisade mesophyll tissue - where most of the photosynthesis happens. Contains lots of chloroplasts to absorb light for photosynthesis.
• Spongy mesophyll tissue - contains big air sacks to allow gasses to diffuse in and out and increasing the rate of diffusion.
• Xylem and phloem - transports water, mineral ions and food around the plant. They form a network of vascular bundles to deliver the substances to the entire leaf and take away glucose produced by photosynthesis. They can also help 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 cells, allowing the plant to grow.

Phloem (translocation) - Made of coloumns of elonged living cells with small pores in the end walls to allow cell sap to flow through. They transport food substances, like dissolved sugars, made in the leaves for immediate use in the rest of the leaf or for storage. They transport in both directions.

Xylem (transpiration) - Made of dead cells joined end to end with no end walls, just a hole down the middle. They are strenthened with a material called lignin. They carry water and mineral ions from the roots to the stem and leaves.

Transpiration is caused by the evaporation and diffusion of water from a plants surface. This evaportaion creates a slight storage of water in the leaf and so more water is drawn up through the xylem tubes through the transpiration stream.

Affected by four main things:

• Light intensity - the brighter the light the greater the transpiration rate. This is because stomata begin to close when its dark as photosynthesis cannot happen.
• Temperature - the warmer it is, the faster the transpiration rate. This isbecause aticles hav more energy to evaporate and diffuse out of the stomata.
• Air flow - the better the air flow around a leaf, the greater the traspiration rate. This is becasue the water vapour is swept away easily, maintaining  low concentration of water particles outside the leaf, increasing the rate of diffusion.
• Humidity - the drier the air around a leaf, the faster the transpiration rate. This is for the same reason as air flow.

You can measure the rate of transpiration by measuring the uptake of water yb a plant and assuming it is direcly related to how much os lost through transpiration. Set up a potometer with a beaker of water, capillary tube with a scale, tap, and tube with a plant at the top. start a stopwatch and record the distance moved by each bubble per unit time, keeping the conditions constant.

Guard cells - Kidney shaped cells which open and close the stomata depending on whether the plant has lots of water and they cells go turgid or whether the plant is short of water and the cell dgoes flacid. Thin outer walls and thickened inner walls make the opening and closing work. They are also sensitive to light and close at night to save water. Most stomata are usually  on the bottom of the leaf as it is shaded and cooler so less water is lost.

• The thorax is the top half of your body, seperated from the lower part by the diaphragm.
• The lungs are protected by the ribcage and are surrounded by pleural membranes.
• When you breathe, air goes throught the trachea and splits into the two lungs via bronchi. The bronchi split into progressively smaller tubes called brochioles which end at the alveoli.
• Gas exchange happens at the alveoli which are tiny air sacs surrounded by a network of capilaries. Carbon dioxide from the muscles are exchanged with oxygen.
• Breathing rate can be calculated using number of breaths / number of minutes.

Humans have a double circulatory system:

• 1 -  the right ventricle pumps deoxygenated blood to the lungs, where it picks up oxygen and is returned to the heart.
• 2 -  the left ventricle pumps dexoygenated blood to the organs of the body, where the oxygen diffuses into cells and returns to the heart deoxygenated.

The heart is a pumping organ with walls mostly made of muscle tissue. The heart has valves to make sure blood flows in the right direction and prevent backflow. The heart pumps blood in this way:

• 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 pumonary arterty and the aorta, and out of the heart. Coronary arteries branch of the aorta and surround the heart, goving it a good supply of oxygen.
• The blood flows to organs via arteries and returns through the veins.
• The atria with blood and the cycle begins again.

The resting heart is ocntrolled by a group of cells in the right atrium wall which act as a pacemaker, poducing a small electric impulse which spreads to the surrounding muscles, causing them to contract. An artificial pacemaker can be usedd if a patient has an irregular hearbeat. This is a device implanted under the skin with a wire to the heart which poduces electric currents to keep the heart beating regularly.

Arteries - carry blood at high pressure away from the heart. Must have strong, elastic walls which are thick compared to the size of the lumen. They contain thick layers of muscle to make them strong ad elastic fibres to allow them to stretch and spring back.

Veins - carry blood to the heart at lower pressure, therfore the walls are quite thin but the have a larger lumen to aid blood flow. They also have valves to prevent backflow.

Capillaries - these are involved in the exchange of materials at the tissues. They join arteries and capillaries together though branches. They are extremely small and carry blood close to every cells in the body to exchange blood with them. They have a permeable wall only one cell thick so substances can easily exchange in and out - larger ration to area volume means the rate of diffusion is increased. They supply food and oxygen, and take away waste like CO2.

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

Red blood cells - carries oxygen from the lungs to the cells in the body, using a red pigmant called hamoglobin which binds to oxygen to become oxyhaemoglobin and in body tissues splits up into haemoglobin and oxygen to relase the oxygen into the cells. Their shape is a biconcava disc, giving it a large surface area for absorbing oxygen. They dont have a nucleus so theas to be able to carry more oxygen.

White blood cells - some can change to absorb unwelcome microorganisms, in a process called phagocytosis. Others produce antibodies to fight microorganisms, as well as antitoxins to neutralise any toxins mad by the microorganisms. They do have a nucleus.

Platlets - small fragments of cell with no nucleus. They help to clot blood at a wound to stop excessive bleeding, to stop microrganisms getting in and to prevent excessive bruising.

Plasma - a pale liquid carrying things like hormones, proteins, antibodies and antitoxins produced by the white blood cells, urea from the kidneys to the liver, carbon dioxide from the organs to the lungs, red and white blood cells, platlets, and nutrients like glucose and amino acids which are soluble products of digestion absorbed from the gut and taken to the body cells.

Cornonary heart disease is where the coronary arteries that supply blood to the heart get blocked by fatty material builing up. This causes the arteries to become narrow, so blood flow is restricted and theres a lack of oxygen, which can result in a heart attack.

Stents - tubes inserted inside arteries to keep them open making sure blood can flow through, keeping the person's heart beating. They lower the risk of someone getting a heart attack if they have coronary heart disease. They are effective for a long time and the recovery time from sugery is relatively quick, however there are risks of complications and a risk of infection. There is also a risk of a blood clot near the stent, thrombosis.

Statins - statin are drugs that reduce the amount of LDL cholestrol in the blood which can cause fatty deposits to form inside arteries, which can lead to cornonary heart disease. This reduces the risks of strokes, coronary heart disease and heart attacks, increases the amount og HDL cholestrol which can help remove the LDL cholestrol, and some studies show they can halp prevent other diseases. However, they are a long-term drug which must be taken regulaly (they coould be forgotten) and they sometimes have negative side effects like headaches or even kidney failure, liver damage and memory loss. Also, the effect is not instant and takes tme to work.

Artificial hearts - a heart transplant can be performed using donor organs from people who have recently died, however theres often not enough available, or it is not the best option. Artifical hearts are mechanical devices that pumps the blood if the heart deos not work, however they are often just temporary until a donor heart is found, or to help the heart to rest and heal. The main advantage is that theyre less likely to be rejected by the body's immune system as they are made of plastic and matal, not live body tissue. However, surgery can lead to bleeding and infection. Also, they do not work as well as natural ones, as parts of the heart could wear out or the electric motor could fail. Blood does not flow through artifical hearts as smoothly, which can cause blod clots and lead to strokes. Therfore, the patient must take drugs to thin the blood, which may cause excessive bleeding at a wound.

Mechanical valves - the valves in the heart can be damaged or weakened by heart attacks, infection or old age. The damage may cause the valve tissue to stiffen so that it doesnt open properly, or it may become leaky allowing blood to flow in both direction, meaning it does not circulate as effectively as normal. Replacement valves can be taken from humans or other mammals (biological valves) or they can be man-made (mechanical-valves). Replacing a valve is a less drastic procedure than a whole heart transplant, but still requires major surgery and there can be problems with blood clots.

Artificial blood - a blood substitute, e.g. a salt solution (saline) which is used to replace a lost volume of blood, for example after an accident. As long as no air bubbles get into the blood, its safe and can keep people alive even after they've lost 2/3 of their red blood cells, giving the body enough time to make more or helping them stay alive until a blood transfusion can occur.