Gas and Solute Exchange
Substances can move by:
Diffusion, Osmosis, and Active Transport
- Life processes need gases or other dissolved substances.
- Waste substances also need to move out of the cells so that they can be disposed.
- In life processes, the gases and dissolved substances move through an exchange surface.
- The exchange surface structures allow enough of the necessary substances to pass through.
- Exchange surfaces in bigger organisms becomes more difficult. The places where the substances are needed end up being a long way away from exchange surfaces.
Exchange surfaces are adapted so that they are more effective:
Thin - substances don't have to diffuse far.
Large surface area - lots of substances can get through at once.
Lots of blood vessels (in animals) - to get stuff into and out of the blood quickly.
Gas ES are often ventilated (in animals) - air can move in and out.
The structure of a leaf lets gases diffuse in and out of cells:
- Carbon dioxide diffuses into the air spaces within the leaf, then into the cells.
- The underneath of a leaf is an exchange surface - its covered in biddy little holes called stomata which the carbon dioxide diffuses through.
- Oxygen and water vapour also diffuse through the stomata.
- The size of the stomata are controlled by guard cells. These close the stomata if a plant is losing water in total. Without the guard cells, the plant would soon wilt.
- The flat shape of a leaf increases the are for the stomata, so it is more effective.
- The walls of the cells inside the leaf form another exchange surface - The air spaces inside the leaf increase the area of this surface.
- The water evapourates from cells inside the leaf. It then escapes by diffusion.
- Evapouration is quickest in hot, dry, windy conditions.
The Breathing System
The Lungs are in the Thorax (The top part of your body)
- It is seperated from the lower part of your body (the abdomen) by the diaphragm.
- The air that you breath in goes through the trachea.
- This splits into two tubes caalled bronchi (each one is bronchus), one going to each lung.
- The bronchi splits into progressively smaller tubes called bronchioles.
- The bronchioles end up at small bags called alveoli where the gas exchange occours.
Ventilation: Breathing in
- Intercostal muscles and diaphragm contract (made smaller and tighter).
- Thorax volume increases.
- This decreases the pressure, drawing air in.
- Intercostal muscles and diaphragm relax.
- Thorax volume decreases.
- This increases the pressure, so air is forced out.
Artificial Ventilators help people to breathe
- Ventilators are machines that move air (often with extra oxygen) into or out of the lungs.
- They used to be a giant case (an 'iron lung').
- Nowadays, ventilators work by pumping air into the lungs. Thi s causes the ribcage to expand. When the pumping stops, the ribcahe realxes and pushes air back out of the lungs. It doesn't interfere with blood flow, but can cause damage (burst alveoli).
Diffusion Through Cell Membranes
Blue = blood with carbon dioxide.
Red = blood with oxygen.
The alveoli are specialised to maximise the diffusion of oxygen and CO2:
An enormous surface area.
A moist lining for dissolving gases.
Very thin walls.
A good blood supply.
The villi provide a huge surface area
- The inside of the small intestine is covered with millions of tiny projections called villi.
- They increase the surface area in a big way so the digested food is absorbed much more quickly into the blood.
- They have a single layer of surface cells.
- A very good blood supply to assist quick absorbtion.
Sometimes substances need to be absorbed against the concentration gradient.
Root hairs are specialised for absorbing water and minerals
- The cells on the surface of the plant roots grow into long 'hairs' that stick out into the soil.
- This gives the plant a big surface area for absorbing water and mineral ions from the soil.
Root hairs take in minerals using active transport
- The concentration of minerals is usually higher in the root hair cell than in the soil around.
- Active transport allows the plant to absorb minerals from a very dilute solution, against a concentration gradient. This is essential for its growth.
- Active transport needs energy from respiratiob to make it work.
We need active transport to stop us starving
- It is used in the gut when there is a low concentration of nutrients in it, but a high concentration in the blood.
- When there's a higher concentration of amino acids and glucose in the gut, they diffuse naturally into the blood.
- Active transport allows nutrients to be taken back into the the blood.
Water Flow Through Plants
Phloem tubes transport food:
- They are made of columns of living cells with small holes in the ends to allow stuff to move through.
- They transport food substances (mainly dissolved sugars) made in the leaves to growing regions (eg. new shoots) and storage organs of the plant.
- The transport goes in both directions.
Xylem tubes take water up:
- They are made of dead cells joined end to end with no end walls between then and a hole down the middle.
- They carry water and minerals from the root to the stem and leaves in the transpiration stream.
Transpiration is the loss of water from the plant:
- It is caused by the evapouration and diffusion of water inside the leaves.
- This creates a slight shortage of water in the leaf, and so more water is drawn up from the rest of plant through the xylem vessels to replace it.
- Tjis means more water is drawn up from the roots, and so there's a constant transpiration stream through the plant.
- Transpiration is just a side effect of the way that leaves are adapted for photosynthesis.
- They have to have stomata in them so gases can be exchanged easily.
- Beacuse there is more water inside the plant, it escapes through the stomata.
Circulatory System - The Heart
The circulatory system's main function is to get food and oxygen to every cell in the body. It's also a waste collection service - it carries waste productis like CO2 and urea to where they can be removed from the body.
Humans have a double circulatory system - two circuits joined together
- The first one pumps deoxygenated blood to the lungs to take in oxygen. The blood then returns to the heart.
- The second one pumps oxygenated blood around all the other organs of the body. The blood gives up its oxygen at the body cells and the deoxygenated blood returns to the heart to be pumped out to the lungs again.
The heart contracts to pump blood around the body
- The heart has valves to prevent blood going in the wrong direction.
- 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 thorugh veins.
Circulatory System - Blood Vessels
Three types of blood vessels:
Arteries - Carry blood away from the heart.
Capillaries - Involved in the exchange of materials at tissues.
Veins - Carry blood to the heart.
- Heart pumps out blood at a high pressure, so the walls need to be strong and elastic.
- The walls are thick compared to the hole (the lumen).
- They contain thick layers of muscle to make them strong.
- They contain elastic fibres to allow them to stretch and spring back.
- Arteries will branch into capillaries (which are really small).
- They carry blood really close to all cells so substance can be exchanged.
- They have permeable walls - substnaces can diffuse in and out.
- They supply food and oxygen, and take away waste like CO2.
- Walls often one cell thick - increases rate of diffusion by decreasing distance.
- Cappilaries join to form veins.
- The blood is now at a lower pressure - walls don't need to be as thick.
- They have a bigger lumen to help the blood flow in the lower pressure.
- Valves keep the blood flowing in the right direction.
Circulatory System - The Blood
Red blood cells carry oxygen
- They have a doughnut shape for a large surface area - to absorb oxygen.
- They contain a red pigment called haemoglobin.
- In the lungs, haemoglobin combines with oxygen to form oxyhaemoglobin.
- In the body tissues,the reverse happens, so the oxygen can be released into the cells.
White blood cells defend against disease
- They can change shape to consume microorganisms.
- They produce antibodies to fight microorganisms.
- They produce antitoxins to neutralise toxins produced by microorganisms.
Platelets help blood clot
- These are small fragments of cells with no nucleus.
- They help blood to clot a wound - blood doesn't pour out and to stop microorganisms getting in.
Plasma is the liquid that carries everything in the blood
- It carries red and and white blood cells and platelets.
- Nutrients like glucose and amino acids.
- Carbon dioxide from the organs to the lungs.
- Urea and hormones, antibodies and antitoxins.
Artificial blood can keep you alive in an emergency
It is a blood substitute. For example, a salt solution (saline) is used to replace lost volume of blood. Its safe if no air bubbles get into the blood. It gives patients a chance to make blood cells.
The heart can be repaired with artificial parts
- Artificial hearts are used as a temporary fix, to keep the person alive until a donor is found.
- Sometimes they can be a permenant replacement.
- An advantage is that they aren't rejected by the body's immune system. this is because they are made up of metals or plastics, and so the body doesn't recognise them as foreign.
- A disadvantage is that the surgery could be risky.
- Also, they don't work as well as natural ones. Parts could stop working.
- Blood may not flow through it smoothly, which increases clots and can lead to strokes.
- The patient therefore has to take drugs to thin their blood, which can lead to bleeding problems.
Stents keep arteries open
- Coronary heart disease - arteries that supply blood to the muscle of the heart get blocked by fatty deposits. This causes the arteries to become narrow and restrict blood flow. Can cause heart attack.
- Stents are tubes inserted into the arteries to keep them open.
- Over time, the artery can narrow again because stents can irritate the artery and make scar tissue grow.
- The patient must also take drugs to stop blood clotting on the stent.
Nephrons are the filtration untis in the kidneys
1 - Ultrafiltration:
- A high pressure is built up which squeezes water, urea, ions and sugar out of the blood and into the bowman's capsule.
- The membranes between the blood vessels and the bowman's capsule act as filters - big molecules like protein are not squeezed out.
2 - Reabsorbtion:
- As the liquid flows along the nephron, useful substances are absorbed back into the blood.
- All the sugar is reaborbed by active transport.
- Sufficient ions are reabsorbed (not excess ions). This requires active transport.
- Sufficient water is reaborbed.
3 - Release of wastes
- The remaining substances continue out of the nephron, into the ureter and down the bladder as urine.
Human Impact on the Environment
The more people, the more demands on the environment, like using energy and resources.
We're producing more waste
- As we amke more things, we have more waste.Unless it is properly handled, there will be harmful pollution. This affects water, land and air:
- Water: Sewage and toxic chemicals from industry can pollute lakes, rivers and oceans.
- This affects the plants and animals that rely on them for survival.
- Chemicals used on land like fertilisers can also be washed into water.
- Land: We use toxic chemicals for farming.
- We also bury nuclear waste underground.
- We dump a lot of household waste in landfill sites.
- Air: Smoke and gases released into the atmosphere can pollute air.
More people means less land for plants and other animals
- The four main human activites that do this are:
- Building - Farming - Dumping waste - Quarrying
Carbon Dioxide and the Greenhouse Effect
Carbon dioxide is removed from the air and stored
- CO2 can be sequestered (locked up) in natural stores:
- Oceans, lakes and ponds.
- Green plants during photosynthesis (stored as carbon compounds).
- Peat bogs.
Carbon dioxide and methane trap heat from the sun
- The temperature on the earth is a mixture of what it gets from the sun and what it radiates back into space.
- Gases in the atmosphere naturally act like an insulating layer. they can absorb a lot of the heat that would have been radiated back into space, and re-radiate it in all directions.
- If this didn't happen, at night no heat would be kept in. However this is getting a bit out of hand.
- Greenhouse gases help keep the heat in. We mainly worry about the levels of carbon dioxide and methane, because they are rising a lot.
- The earth is gradually heating up due to increasing levels of greenhouse gases - this is called global warming.
- It is a type of climate change, that causes other types of climate change like rainfall patterns.
Deforestation and Destruction of Peat Bogs
Deforestation leads to four main problems:
More methane in the atmosphere
- Rice is grown in warm, waterlogged conditions, ideal for decomposers. They produce methane.
- Cattle produce methane, and rearing them means more methane is released.
More carbon dioxide in the atmosphere
- It is released when trees are burnt to clear land. CO2 is only released in wood when burnt.
- Microorganisms feeding on dead wood release CO2 by respiration.
Less carbon dioxide taken in
- Trees are no longer able to remove carbon dioxide from the atmosphere by photosynthesis.
- This is when there is a variety of different species in a habitat.
- Rainforests for example can provide a huge range of different species. When they are destroyed, they can become extinct.
- This means there are lost oppourtunities - some of the species that have gone extinct could have been useful. Newly discovered plants and animals are a great source of foods, clothing and medicines.
Destroying peat bogs also adds more CO2 to the atmosphere
- Bogs are areas of land that are acidic and waterlogged. Plants that live in bogs don't fully decay because there isn't enough oxygen. The half rotted plants gradually build up and form peat.
- The carbon in these plants is stored in peat and not released into the atmosphere.
- Unfortunatly, peat bogs are often drained so the area can be used as farmland. Also, peat is used as a fuel. Finally, it can be sold to gardeners as compost.
Serious consequences of global warming
- The sea expands when it gets warmer. This causes the sea level to rise.
- Ice can be melted, therefore the water level rises even more.
- Dramatic weather changes such as more hurricanes, more extreme weather.
- Distribution of species can change as the animals seek their ideal conditions.
- Biodiversity can be reduced if species become extinct in the changed climate.
- Changes in migration patterns, birds may go further north, because northern areas are getting warmer.
Climate change evidence
- Evidence is only useful if it covers a large enough area in a long period of time.
- We use satelites to measure snow and ice cover, and the temperature of the sea surface.
- We are recording the temperature and the speed of ocean currents.
- Automatic weather stations constantly record atmospheric temperatures.
Fuels can be made by fermentation
- Natural products can be used, and waste products.
- It is when bacteria or yeast break sugars down by anaerobic respiration.
Ethanol is made by anaerobic fermentation of sugar (glucose)
Glucose (broken down by yeast) --> Ethanol + Carbon Dioxide + Energy
- Sugar cane juices can be used, or glucose can be derived from maize starch by the action of carbohydrase.
- The ethanol is distilled to seperated it from the yeast and remaining glucose before it is used.
- In some countries cars are adapted to run on ethanol and petrol - the mixture is called gasohol.
Biogas is made by anaerobic fermentation of waste material
- Biogas is often 70% methane and 30% CO2.
- Lots of different microorganisms ferment plant and animal waste, which contains carbohydrates.
- Sludge waste from sewage works or sugar factories (for example) is used to make biogas on a large scale.
- It's made in a simple fermenter called a digester or generator.
- They need to be kept at a constant temperature to keep the microorganisms respiring.
- Biogas cannot be stored as liquid (it needs too high a pressure), so it must be used straight away.
- It is used for heating, cooking, lighting, or to power a turbine to generate electricity.
Using Biogas Generators
Batch generators make biogas in small batches
- They're manually loaded up with waste, left to digest, then by-products are cleared away at the end of each session.
Continuous generators make biogas all the time
- Waste is continuously fed in, biogas is produced at a steady rate.
- Continuous generators are suited to large scale biogas projects.
Biogas generators need:
- An inlet for waste material to be put in
- An outlet for digested material to be removed through
- An outlet so that biogas can be piped to where it is needed.
Four factors considered when designing a generator
- Cost: Continuous are more expensive due to mechanical processes.
- Convienience: Batch generators aren't as convienient due to humans having to constantly load and empty.
- Efficiency: It should be kept at 35 degrees for fastest gas production. It may need to be insulated or heated, and should have no leaks so gas can't escape.
- Position: It will smell, so should be away from homes. It should also be near a waste source.
Using biofuels has economic and environmental effects
- Using biofuels doesn't produce large amounts of sulfur dioxide or nitrogen oxides, which causes acid rain.
- Methane is given off from untreated waste. Burning it as biogas means its not released into the atmosphere.
- The raw material is cheap and available.
- The digested material (by-products) are better fertilisers than undigested dung.
- In developing countries, the energy can be more easily available.
- It disposes waste, that may have caused diseases or pollute things.
It is protein from fungi.
The fungus fusarium is the main source of mycoprotein.
- It is grown in fermenters, using glucose syrup as food.
- The glucose syrup is made by digesting maize starch with enzymes.
- The fungus respires aerobically, so oxygen is suppplied, as well as nitrogen (as ammonia) and other minerals.
- It is importortant to stop other microorganisms growing in the fermenter. The fermenter is initially sterilized using steam. The incoming nutrients are heat sterilized and the air supply is filtered.
- The mycoprotein is then harvested and purified.
An advantage is that it is good for developiung countries when meat is hard to aquire.
It is very quick, and doesn't need much space. The fungus can even feed on waste material.