Biology (B3)

1. Osmosis

   Nota:

   • -The movement of water. -Random and requires no energy from the cell. -The diffusion of water across a partially permeable membrane.
   1. Concentration gradeient

      Nota:

      • Water moves from a region of high water concentration (dilute) to a region of lower water concentration (a more concentration solution). This is a concentration gradient. 
2. Active transport

   Nota:

   • -Cells may need to absorb substances which are in short supply, against a concentration gradient.  -Lower concentration to a higher concentration.
   1. Cells

      Nota:

      • Cells use active transport to absorb substances across a partially permeable membrane against the concentration gradient.
   2. Energy

      Nota:

      • Active transport REQUIRES some of the energy released by respiration. 
   3. Examples

      Nota:

      • Ions, from dilute solutions, and other substances such as sugar can be absorbed by active transport. 
      1. The Kidneys

         Nota:

         • Glucose can be reabsorbed in the kidney tubules by active transport.
   4. Diagram
3. The sports drink dilemma

   Nota:

   • -When you do exercise, your cells respire to produce energy.  -Glucose is used in respiration. 
   1. Sweat

      Nota:

      • -Sweat contains water and mineral ions. -If you sweat A LOT, your body cells may become dehydrated. -If you exercise for a long time, it may be necessary to replace the sugar, mineral ions and water that have been used or lost.
   2. Sports drink

      Nota:

      • -Solutions of sugar and mineral ions. -Water in the drinks helps us to rehydrate body cells.
      1. Isotonic

         Nota:

         • -Designed to help balance the concentration of body fluids and the concentrations inside cells. -If the drink concentration matches the body fluids the solution is called ISOTONIC.
      2. Evidence

         Nota:

         • -Varied opinions among scientists -Some say it is just as good to have a drink of water for short periods of exercise. -Drinks may help athletes who need to replace mineral ions and sugar as well as water.
4. Exchanging materials - the lungs

   Nota:

   • -Large, complex organisms have special exchange surfaces to obtain all the substances they need.  -They have features to make them very efficient. 
   1. Absorption of substances

      Nota:

      • -Soluble food materials (solutes) are absorbed by the intestine. -Oxygen is absorbed by the lungs and carbon dioxide is removed from them.
   2. Features of the lungs
      1. Alveoli

         Nota:

         • -Gaseous exchange surface in the lungs. -Increases the surface area of the lungs.
         1. Features

            Nota:

            • -Thin walls. -A large surface area. -A good blood supply.
      2. Ventilation

         Nota:

         • The lungs are ventilated to maintain a steep diffusion gradient.
      3. Capillaries

         Nota:

         • Oxygen diffuses into many capillaries surrounding the alveoli and the carbon dioxide diffuses back out into the lung to be breathed out. 
5. Ventilating the lungs

   Nota:

   • -Lungs contain the exchange surface of the breathing system. -Lungs are situated: --In the thorax. --Inside the ribcage. --Above the diaphragm, which separates the lungs from the abdomen. 
   1. Breathing in

      Nota:

      • -The intercostal muscles, between the ribs and the diaphragm contract. -The ribcage moves up and out and the diaphragm flattens. -The volume of the thorax increases. -The pressure in the thorax decreases and the air is drawn in.
   2. Breathing out

      Nota:

      • -The intercostal muscles of the ribcage and the diaphragm relax. -The ribcage moves down and in and the diaphragm becomes domed. -The volume of the thorax decreases. -The pressure increases and the air is forced out. 
   3. Diagram
   4. Ventilation

      Nota:

      • The movement of air in and out of the lungs.
6. Artificial breathing aids
   1. Reasons for oxygen deprivatoin

      Nota:

      • -If the alveoli are damaged, the surface area for gas exchange is reduced. -If the tubes leading to the lungs are narrowed, less air can be moved through them. -If the person is paralysed, their muscles will not work to pull the ribcage up and out. 
   2. Iron lung

      Nota:

      • -Used for people with polio who were paralysed. -Person lay with their chest sealed in a large metal cylinder. -When air was drawn out of cylinder, the person's chest moved out and they breathed in. -The vacuum which was formed inside the cylinder created a negative pressure. -When air was pumped back in to the cylinder, it created pressure on the chest and forced air out of the person's lungs. 
   3. Positive pressure

      Nota:

      • -Breathing aids which force measured amounts of air into the lungs use positive pressure. -Bags of air linked to masks can force air down the trachea. -Smaller. -Easier to manage in the home. -Can be linked to computers for control. 
7. Exchange in the gut

   Nota:

   • -The food we eat is digested in the gut into small, soluble molecules. -In the small intestine, these solutes are absorbed into the blood.
   1. Villi

      Nota:

      • Line the inner surface of the small intestine and are the exchange surface for food molecules.
      1. Features
         1. Finger-like

            Nota:

            • -Shape of the villi. -Greatly increase the surface area for absorption to take place.
         2. Thin walls

            Nota:

            • -Only 1 cell thick. -There is only a short distance across which diffusion takes place.
         3. Capillaries

            Nota:

            • -Rich blood supply produces a steep concentration gradient for efficient diffusion. 
      2. Absorption

         Nota:

         • The soluble products of digestion can be absorbed into the villi by either diffusion or active transport.
8. Exchange in plants
   1. Stomata

      Nota:

      • -Gases diffuse in and out of these tiny holes (stomata). -Size of stomata is controlled by guard cells, which surround them. -Lose water vapour through stomata due to evaporation in the leaves.
      • -Gases diffuse in and out of these tiny holes (stomata). -Size of stomata is controlled by guard cells, which surround them. -Lose water vapour through stomata due to evaporation in the leaves.
      1. Gases

         Nota:

         • -Oxygen: needed for respiration and is a waste product of photosynthesis. -Carbon dixoide: --Needed for photosynthesis. --Waste product of respiration. -Movement of these gases depends upon which process is taking place the most quickly. 
   2. Leaves

      Nota:

      • -Very flat and thin. -Gases do not need to diffuse very far. -Also internal air spaces.
   3. Roots

      Nota:

      • -Water and mineral ions are taken up by roots. -Root hair cells INCREASE the surface area of roots. -Causes more absorption of water and mineral ions, 
   4. Wilting

      Nota:

      • If plants lose water faster than it is replaced. the stomata can close to prevent wilting. 
   5. Other features
      1. Waxy cuticle

         Nota:

         • Waterproof layer which stops water loss.
      2. Cells not tightly packed

         Nota:

         • -Larger surface area. -More area available for gas exchange.
      3. Guard cells

         Nota:

         • Open and close the stomata to control water loss.
9. Transpiration

   Nota:

   • -Water is taken up through the roots. -Water passes through the plant to the leaves. -In the leaves, the water evaporates from the leaf cells. -Water evaporates from leaf cells. -Water vapour diffuses out through the stomata.
   1. Transpiration stream

      Nota:

      • The movement of water through a plant. 
   2. Dehydration

      Nota:

      • Can happen if the rate of evaporation in the leaves is GREATER than the water uptake by the roots.
   3. Evaporation

      Nota:

      • MORE rapid if the conditions are: -Hot -Dry -Windy -Bright 
   4. Significance of wilting

      Nota:

      • -Reduces water loss. -Leaves collapse and hang down. -Reduces surface area. -THUS, reduces water loss.

1. The circulatory system and the heart

   Nota:

   • -Humans have a double circulatory system which consists of blood vessels, the heart and blood.
   1. The circulatory system
      1. Heart

         Nota:

         • A muscular organ that pumps blood around the body. It is actually two pumps held together.
         1. Chambers
            1. Atria

               Nota:

               • -The upper chambers. -Right atrium receives blood from the vena cava. -Left atrium receives blood from the pulmonary vein.
            2. Ventricles

               Nota:

               • -The lower chambers. -Atria contract to move blood into them. -Right ventricle contract to force blood into the pulmonary artery. -Left ventricle contracts to force blood into the aorta.
         2. Valves

            Nota:

            • Prevent the blood from flowing in the wrong direction.
      2. Left pump

         Nota:

         • When the blood returns to the heart, the oxygenated blood is pumped to the rest of the body (via the left pump).
      3. Right pump

         Nota:

         • Forces the deoxygenated blood to the lungs where it picks up oxygen and loses carbon dioxide.
      4. Coronary arteries

         Nota:

         • Supply the heart muscle with oxygenated blood.
      5. Sequence

         Nota:

         • Veins → Atria → Ventricles → Arteries
2. Keeping the blood flowing

   Nota:

   • Blood flows round the body in three main types of blood vessel: the arteries, veins and capillaries. 
   1. Arteries

      Nota:

      • -Carry blood away from the heart. -Have thick walls containing muscle and elastic tissue.
   2. Veins

      Nota:

      • -Have thinner walls than arteries. -Often have valves along their length to prevent backflow of blood.
   3. Capillaries

      Nota:

      • -Are narrow, thin walled vessels. -Carry the blood through the organs. -Allow the exchange of substances with all the living cells in the body.
   4. Blockages

      Nota:

      • -If blood vessels are blocked or too narrow the blood WILL NOT flow efficiently. -Organs will be deprived of nutrients and oxygen.
      1. Stents

         Nota:

         • -Can be inserted to keep blood vessels open. -Particularly useful when coronary arteries become narrowed due to fatty deposits, cutting off the blood supply to the heart muscle.
   5. Leaky valves

      Nota:

      • -Mean the blood could flow in the wrong direction. -Artificial or animal valves can be inserted in the heart to replace damaged valves.
3. Transport in blood

   Nota:

   • -Blood is a tissue. -The fluid plasma contains red blood cells, white blood cells and platelets.
   1. Blood plasma

      Nota:

      • Transports: -Carbon dioxide from the organs to the lungs. -Soluble products of digestion from the small intestine to other organs. -Urea from the liver to the kidneys where urine is made.
   2. Red blood cells

      Nota:

      • -They are biconcave discs which DO NOT have a nucleus. -Contain the red pigment haemoglobin. -Uses their haemoglobin which combines with oxygen to form oxyhaemoglobin in the lungs. -Carry the oxygen to all the organs where the oxyhaemoglobin splits into haemoglobin and oxygen.
      1. Haemoglobin

         Nota:

         • -A protein in red blood cells. -Contains iron. -Forms oxyhaemoglobin when combined with oxygen.
   3. White blood cells

      Nota:

      • -Have a nucleus. -Form part of the body's defence system against microorganisms.
   4. Blood platelets

      Nota:

      • -Are small fragments. -Do not have a nucleus. -Help blood to clot at the site of a wound.
4. Artificial or real?
   1. Donors

      Nota:

      • -People can give blood. -This can be separated into cells and plasma. -Donated blood must be refrigerated. -Some blood products can be frozen.
      1. Plasma

         Nota:

         • This can be given to patients in a transfusion to increase blood volume.
   2. Artificial blood

      Nota:

      • -Perfluorocarbons may be used which does not need to be refrigerated. -Does not contain cells. -Blood matching is not necessary.
      1. Issues

         Nota:

         • -Very expensive. -Does not carry as much oxygen as whole blood. -Some types are insoluble in water so do not mix well with blood. -Some artificial bloods cause unpleasant side-effects.
   3. Artificial hearts

      Nota:

      • -People who suffer heart failure may need a new heart. -A lack of heart donors so artificial hearts are being developed to keep the patients alive.
      1. Advantages

         Nota:

         • -Do not need to match the person's tissue. -No need for immunosuppressant drugs.
      2. Disadvantages

         Nota:

         • -Blood clotting. -Long stays in hospitals. -Expensive.
5. Transport systems in plants

   Nota:

   • Flowering plants have separate transport systems.
   1. Xylem

      Nota:

      • -Tissue. -Transports water and mineral ions from the roots to the stem, leaves and flowers.
   2. Phloem

      Nota:

      • -Tissue. -Carries dissolved sugars from the leaves to the rest of the plant, including the growing regions and the storage organs.
   3. Roots

      Nota:

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

Nota:

• B3.3.6 has been missed out. Find out if this is needed.

1. Controlling internal conditions

   Nota:

   • -These must be carefully controlled.
   1. Homeostasis

      Nota:

      • Keeping the internal body conditions within a narrow range.
   2. What must be controlled?

      Nota:

      • -Temperature. -Blood glucose. -Water. -Ion content. -Levels of waste products.
   3. Waste products
      1. Carbon dioxide

         Nota:

         • -Produced by respiration. -Removed via the lungs when we breathe out.
      2. Urea

         Nota:

         • -Produced in the liver from the breakdown of amino acids. -Removed by the kidneys in the urine and temporarily stored in the bladder.
   4. Water and ions

      Nota:

      • -Enter the body when we eat and drink. -If the water or ion content in the body is wrong, too much water may move into or out of the cells. -This could DAMAGE or DESTROY the cells.
2. The human kidney

   Nota:

   • -The body has two kidneys.
   1. Function

      Nota:

      • They filter the blood, excreting substances you do not want and keeping those that the body needs.
   2. Producing urine

      Nota:

      • -Filtering the blood. -Reabsorbing all the sugar. -Reabsorbing the dissolved ions needed by the body. -Reabsorbing as much water as the body needs. -Releasing urea, excess ions and water in the urine.
      1. The bladder

         Nota:

         • The urine is temporarily stored in the bladder before being removed from the body.
3. Dialysis

   Nota:

   • When kidneys fail, the patient can be treated by dialysis.
   1. Dialysis machine

      Nota:

      • This carries out the same job as the kidneys. The blood flows between partially premeable membranes.
   2. Dialysis fluid

      Nota:

      • -Contains the same concentration of useful substances that the patient's blood does. --E.G glucose and mineral ions. -These substances WILL NOT diffuse out of the blood so they do not need to be reabsorbed. -Urea diffuses out from the blood into dialysis fluid.
   3. Benefits and drawbacks

      Nota:

      • -Restores the concentration of substances in the blood back to normal. -Needs to be carried out at regular intervals.
   4. Kidney transplant

      Nota:

      • -A patient may have a kidney inserted if one becomes available.  -In a successful transplant, the person WILL NOT need any further dialysis. 
4. Kidney transplants

   Nota:

   • -A kidney transplant is a better option than dialysis. -It involves replacing a diseased kidney with a healthy one. 
   1. Rejection

      Nota:

      • The new kidney MUST BE a very good 'tissue match' to prevent rejection.
      1. Attack on kidney

         Nota:

         • -Proteins called antigens on surface of cells. -The recipient's antibodies may attack the antigens on the donor organ because they recognise them as being foreign. 
      2. Medication

         Nota:

         • -Following the transplant, the recipient MUST take drugs to suppress the immune response to prevent rejection. -These are called immunosuppressant drugs.
   2. Evaluation
      1. Advantages

         Nota:

         • -Cheaper for the NHS. -People don't have to watch what they eat as much. -You don't have to have dialysis therefore it has economical benefits on your own life.
      2. Disadvantages

         Nota:

         • -Rejection. -Immunosuppressant drugs leave the body vulnerable to common infections. -
5. Controlling body temperature

   Nota:

   • -The human body must be kept at about 37°C so that the enzymes will work efficiently.
   1. Core body temperature

      Nota:

      • This is the temperature deep inside the body and IT MUST be kept stable.
      1. Rises

         Nota:

         • -Blood vessels near the surface of the skin dilate allowing more blood to flow through the skin capillaries. -Energy is transferred by radiation and the skin cools.
         • -Sweat glands produce more sweat. -Its water evaporates from the skin's surface. -The energy required for the water to evaporate comes from the skin's surface. -So we cool down.
      2. Falls

         Nota:

         • -Blood vessels near the surface of the skin CONSTRICT and less blood flows through the skin capillaries. -Less energy is radiated.
         • -We 'shiver'. -Muscles contract quickly. -This requires respiration and some of the energy released warms the blood.
   2. Thermoregulatory centre

      Nota:

      • -This is where body temperature is monitored and controlled. -This centre has receptors which detect the temperature of the BLOOD flowing through the brain.
      1. Skin

         Nota:

         • Temperature receptors in the skin also send impulses to the brain to give information about skin temperature.
         1. Look

            Nota:

            • Skin looks red when we are hot due to increased blood flow.
   3. Sweating

      Nota:

      • -Helps to cool the body. -When it is hot, more water is lost from the skin so more water must be taken in with drinks and food to balance the loss.
6. Controlling blood glucose
   1. Pancreas

      Nota:

      • Monitors and controls the level of glucose in our blood.
      1. Insulin

         Nota:

         • -Produced if there is too much glucose in our blood. -Causes the glucose to move from the blood into the cells. -This means that it causes our blood glucose to fall. -If the level gets too low, receptors in the pancreas detect the low level.
      2. Glucagon

         Nota:

         • -Produced if there is too little glucose in our blood. -Causes the glycogen in our liver to change into glucose. -Glucose is released back into the blood
   2. Liver

      Nota:

      • In the liver, excess glucose is converted to glycogen for storage.
   3. Type 1 diabetes

      Nota:

      • If no, or too little, insulin is produced by the pancreas the blood glucose level may become very high. This is type 1 diabetes.
      1. Control

         Nota:

         • -Controlled by injections of insulin. -Careful attention to diet and levels of exercise.
7. Treating diabetes
   1. Traditional

      Nota:

      • -Traditionally treated with human insulin produced by genetically engineered bacteria. -Diabetic MUST inject before meals every day of their life.
      1. Very active diabetics

         Nota:

         • Have to match the amount of insulin injected with their diet and exercise.
   2. Pump

      Nota:

      • -Some diabetics opt for the pump attached to the body. -They can adjust the level of insulin injected by the pump.
   3. New ways

      Nota:

      • Doctors are constantly trying to come up with new ways to treat and even cure Type 1 diabetes: -Pancreas transplants. -Transplanting pancreas cells. -Using embryonic stem cells to produce insulin secreting cells. -Using adult stem cells from diabetic patients. -Genetically engineering pancreas cells to make them work properly.

1. Effects of population explosion

   Nota:

   • -Current population of Earth is about 7 billion. -Many people want and demand a better standard of living.
   • -We are using up raw materials and those that are non-renewable cannot be replaced. -When goods are produced there is a lot of industrial waste.
   • -The continuing increase in the human population is affecting the ecology of the Earth.
   1. Reduction of land

      Nota:

      • Humans reduce the amount of land available for animals and plants by building, quarrying, farming and dumping waste.
   2. Humans pollute..

      Nota:

      • -Waterways with sewage, fertiliser and toxic chemicals. -Air with smoke and gases such as: sulfur dioxide, which contributes to acid rain. -Land with toxic chemicals such as pesticides and herbicides and these can then be washed into the water.
2. Land and water pollution
   1. Land

      Nota:

      • -Sewage contains human body waste and waste water from homes. -Must be treated properly to remove gut parasites. -Also, toxic chemicals must be removed. -Otherwise, these can get onto the land.
      • -Large quantities of household and industrial waste in landfill. -Toxic chemicals can leak out. -Industrial waste (e.g. radioactive waste) can be VERY hazardous.
      • -Farming can pollute land. -Herbicides and pesticides are also poisons. -Poisons sprayed onto crops can get into the soil and into the food chain. -Eventually, they can get into rivers. -Farmers also used chemical fertilisers, to keep the soil fertile, which is washed into rivers.
   2. Water

      Nota:

      • -Herbicides, pesticides and chemical fertilisers all get washed into rivers and streams. -Fertilisers and untreated sewage can causes a high level of NITRATES in the water. -Toxic chemicals from landfill also leak into the waterways and pollute the water, killing organisms such as fish.
3. Air pollution

   Nota:

   • -Burning fuels can produce sulfur dioxide and other acidic gases. -Power stations and cars release acidic gases.
   1. Sulfur dioxide

      Nota:

      • Dissolves in water in the air, forming acidic solutions.
      1. Acid rain

         Nota:

         • -A solution of acid in water. -KILLS organisms.
         1. Soil

            Nota:

            • -Can change the pH of soil. -Damages roots and may release toxic minerals. -Aluminium ions are released which also damages organisms in the soil and in waterways.
         2. Enzymes

            Nota:

            • Enzymes are very sensitive to pH.
         3. Trees

            Nota:

            • -Trees can be damaged if the leaves are soaked in acid rain for long periods. -When trees are damaged, food and habitats for many other organisms are lost.
4. Deforestation and peat destruction
   1. Deforestation

      Nota:

      • -Many trees are cut down.
      1. Effect

         Nota:

         • -Increase in release of CO2 in the atmosphere due to burning of the trees or decay of the wood by microorganisms. -Reduced the rate at which CO2 is removed from the atmosphere, by photosynthesis. -Reduced biodiversity due to loss of food and habitats.
      2. Why?

         Nota:

         • -Crops can be grown to produce ethanol-based biofuels. -There can be an increase in cattle and rice fields for food. -The need for timber.
      3. Methane

         Nota:

         • An increase in cattle and rice growing fields means that more methane is released into the atmosphere.
   2. Peat destruction

      Nota:

      • Destruction of peat bogs results in the release of CO2 into the atmosphere.
      1. Why?

         Nota:

         • -Used in composts for gardens. -Compost is decay by microorganisms.
      2. Peat-free

         Nota:

         • By using peat-free composts, peat bogs will not be destroyed.
5. Global warming

   Nota:

   • -Warming of the Earth. -Levels of CO2 and Methane are increasing in the atmosphere. -They are called greenhouse gases and cause the greenhouse effect.
   1. Normal balance

      Nota:

      • In the normal balance of nature, carbon dioxide is released into the air by respiration and removed by plants and algae by photosynthesis.
   2. Sequestration

      Nota:

      • -Carbon dioxide also dissolves in oceans, rivers, lakes and ponds. -The CO2 is sequestered (locked up) by plants and water.
   3. Increase in Earth's temperature

      Nota:

      • An increase by only a few degrees Celsius may: -Cause big changes to the Earth's climate. -Cause a rise in sea level due to melting of ice caps and glaciers. -Reduce biodiversity. -Causes changes in migration patterns (like birds). -Result in changes in the distribution of species.
6. Biofuels

   Nota:

   • -Made from natural products. -Two types of biofuel: ethanol-based fuels and biogas.
   1. Fermentation

      Nota:

      • -Microorganisms respire anaerobically to produce ethanol, using sugar from crops as the energy source. -Glucose is produced from maize starch by the action of a carbohydrase. -Glucose and sugar cane juices can be fermented by yeast to produce ethanol.
   2. Distillation

      Nota:

      • Ethanol can be extracted by distillation and then used as a fuel in motor vehicles.
   3. Benefits

      Nota:

      • -Could be a fuel to replace fossil fuels in the future. -In terms of the 'greenhouse effect', ethanol is much more 'carbon friendly'.
   4. Carbon neutral

      Nota:

      • -Ethanol is carbon neutral. -The CO2 used for photosynthesis by the maize and sugar cane crops is returned to the atmosphere when ethanol is burned.
7. Biogas

   Nota:

   • Biogas, mainly methane, can be produced during anaerobic fermentation by bacteria.
   1. Fuel

      Nota:

      • Biogas generators use any waste material containing carbohydrate and plants, which can be broken down.
   2. Generators

      Nota:

      • -Provide the ideal conditions for bacteria to reproduce and ferment the carbohydrates. -Must be maintained at a suitable temperature in oxygen-free conditions. -Either buried in the ground for insulation or have insulating jackets.
      1. Scale

         Nota:

         • -Large scale, commercial generators use waste from sugar factories or sewage works. -Small scale, generators can be used by a home or farm.
   3. Uses

      Nota:

      • -Gas produced is a fuel and provides energy for heating etc.
   4. Quality

      Nota:

      • The more methane in the gas mixture, the better the quality of biogas.
   5. ANAEROBIC
8. Making food production efficient

   Nota:

   • -The SHORTER the food chain, the less energy will be wasted. -More efficient for us to eat plants than it is to eat animals.
   1. Producing meat more efficiently

      Nota:

      • -Preventing the animal from moving so it doesn't waste energy on movement; CRUELTY and is controversial. -Keeping the animal in warm sheds so it doesn't use as much energy from food to maintain its body temperature.
9. Sustainable food production

   Nota:

   • -Managing resources, and finding new types of food such as mycoprotein. -Ensures there is enough food for the current population in the future.
   1. Fish stocks

      Nota:

      • -Monitored. -Fisherman: --Can only remove a strict allocation of fish per year - a quota. --Must use certain sized nets to avoid catching small, young fish.
   2. Fusarium

      Nota:

      • -Grown to produce mycoprotein. -This is protein-rich and suitable for vegetarians. -Grown aerobically on cheap sugar syrup made from waste starch and the mycoprotein is harvested.
   3. Fermenters

      Nota:

      • -Used to grow microorganisms on a large scale. -Conditions in a fermenter must be controlled to ensure maximum growth of the Fusarium.
      1. Large vessels

         Nota:

         • These vessels have: -An air supply providing oxygen for respiration. -Stirrers or gas bubbles used to keep the microorganisms spread out and to provide an even temp. -A water-cooled jacket around the outside, as the respiring microorganisms release energy which heats the contents. -Sensors to monitor both pH and temperature.
   4. AEROBIC
10. Environmental issues

    Nota:

    • Scientists need to check the validity and the reproducibility of the data.
    1. Harmful human activities

       Nota:

       • -Deforestation which can cause increase levels of CO2 in the atmosphere. -Increases in rice growing and rearing cattle resulting in more methane being released. -Building dams, to store water in reservoirs, causing loss of habitats, drying out of rivers below the dams and reduction in fertile land to grow crops.