OCR Gateway B -Biology -B4, B5, B6.

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B4 -Ecology in the local environment

Artificial ecosystems have poor biodiversity, as they are created by humans.

Transect lines can be used to map the distribution of an organism. At regular intervals the number of organisms in a quadrat are counted and displayed on a kite diagram.

Sampling can be used to obtain an estimate for the total population size.

- Capture

- Mark

- Release

- Recapture

Population size = (1st sample size x 2nd sample size) / number of marked organisms in second sample.

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B4 -Photosynthesis

Glucose from photosynthesis can be used for releasing energy, converted into cellulose to make cell walls, converted into proteins for growth and repair, or converted into starchfats or oils for storage.

Photosynthesis: 1) water split by light energy into oxygen gas and hydrogen ions.

2) Carbon dioxide combines with the hydrogen ions forming glucose and water.

Modern experiments use the green alga chlorella to prove this process.

Rate of photosynthesis can be increased by having more light or carbon dioxide, or by a higher temperature -which increases enzyme action.

The limiting factors of photosynthesis are lightheat and carbon dioxide because it cannot take place without them.

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B4 -Leaves

A green leaf has many specialised cells, which are adapted for efficient photosynthesis:

- Transparent outer epidermis to allow light to enter the leaf

- Upper palisade cells containing most of the leaf's chloroplasts as they get the most light

- Spaced out spongy mesophyll cells so that diffusion between the cells and outer atmosphere can take place

- Particular arrangement of mesophyll cells to form a large surface area and allow large amounts of diffusion.

Leaves are also broad to get as much light as possible, containing different pigments to be able to use light from a broad range of the spectrum.

They have vascular bundles (xylem and phloem) to transport chemicals and specialised guard cells to control the opening of stomata.

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B4 -Diffusion and Osmosis

Diffusion: net movement of particles in a gas or liquid from an area of high concentration to an area of low concentration.

The rate of diffusion can be increased by having a shorter distance to travel, a greater difference in concentrations or a greater surface area.

Osmosis: the diffusion of water across a partially-permeable membrane.

When water enters a plant cell is increases the pressure put on the cell wall (turgor pressure), which supports the plant and prevents it from collapsing. A plant cell full of water is turgid.

If too much water leaves the cytoplasm the contents shrink and become plasmolysed and the cell is flaccid.

When too much water enters an animal cell the lack of a supporting cell wall allows the cell to swell and burst (lysis).

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B4 -Transport in plants

Xylem are vessels -dead cells without any contents, their walls thickened with lignin. They transport water and absorbed minerals from the root to the leaves,

Pholem are living cells aranged in columns which transport substances such as sugars around the plant.

Transpiration: evaporation and diffusion of water from inside leaves. It allows there to be a constant flow of water up from the roots.

The rate of transpiration is controlled by:

- light intesity which controls opening of stomata

- temperature which controls evaporation

- humidity and air movement which both alter the concentration gradient

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B4 -Minerals

Plants need: nitrates for cell growth, phosphates respiration and growth, potassium to help enzyme action in respiration and photosynthesis, and magesium to make chlorophyll for photosynthesis.

A lack of nitrates results in poor growth and yellow leaves.

A lack of phosphates causes poor root growth and discoloured leaves.

A lack of potassium results in poor root and flower growth as well as dicoloured leaves.

A lack of magnesium causes yellow leaves.

Minerals are taken in by the root hair cells using the process of active transport, which works against the concentration gradient and requires energy for respiraton.

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B4 -Decay

Detritivores (earthworms, maggots, woodlice) feed on dead and decaying material, speeding up the rate of decay by breaking down the dead matter for further microbial breakdown.

Increasing the temperature to an optimum (37 for bacteria, 25 for fungi) increases the rate of respiration.

Increasing the amount of oxygen, causes bacteria to respire aerobically, causing them to grow and reproduce faster. 

A higher water content will allow material to be digested more efficiently.

saprophyte feeds on dead and decaying material, an example being a fungus. Fungi produce enzymes which allow them to digest their food outside their cells (extracellular digestion) before reabsorbing the more simple substances.

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B4 -Farming

Using pesticides can be disadvantageous, as the can enter into food chains, accumulating and potentially proving fatal to a predator. They can also harm other non-pests living nearby. It is also possible that pests come resistent to some forms of pesticide.

Biological control uses living organisms such as ladybirds to kill pests. It is more advantageous as it avoids all problems associated with artificial methods and once the organisms are intorduced into the area, they don't need replacing. However, these new species could prove harmful by killing other useful oranisms.

Intensive farming uses methods which could raise moral concerns, but it increases the yield by improving the efficiency of energy transfer.

Hydrophonics is a type of intensive farming which allows plants to grow without soil. This means that plants can grow in areas of barren soil or low rainfall. There can be many more plants grown in a smaller space and artificial fertilisers are used. It also means that there is better control over mineral levels and disease.

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B5 -Skeletons

Cartilage and bone are living tissue, so can be infected by viruses and bacteria, but are able to repair themselves and grow.

Ossification is the process in which calcium and phosphorus are deposited into cartilage, turning it to bone.

The bones of the elderly are lacking in calcium and phosphorus, which can lead to osteoporosis, making them prone to fractures. 

Synovial joints such as ball and socket joints and hinge joints contain synovial fluid which acts as a lubricant for easier, friction-free movement.

This fluid is contained in a synovial membrane.

Synovial joints also have cartilage which protects the head of the bone, with ligaments holding the bone in place.

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B5 -Cardiac cycle

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B5 -Repairs

hole in the heart causes the mixing of oxygenated and deoxygenated blood, and can be corrected by open heart surgery.

Damaged or weak valves can be replaced with artificial ones.

blocked coronary artery can be by-passed by transplanting a blood vessel from another part of the body.

When blood platelets are exposed to air, it leads to the formation of fibrin fibres, causing blood clotting.

Agglutination happens when the an antigen on the surface of a red blood cell reacts with an antibody in the plasma, which could endanger someone's life.

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B5 -Respiratory systems

When humans breathe in, the intercostal muscles contract moving the ribs up and out, as the diaphragm is moved down. This increases the volume of the lungs, decreasing the internal pressure. Due to the higher outside pressure, air is forced to enter the lungs.

In order to breathe out, the intercostal and diaphragm musles relax, causing the ribs to move down and in, as the diaphragm curves upwards. The volume decreases, causing the pressure to increase which pushes air out of the lungs.

Tidal air: amount of air breathed in and out at rest. Vital capacity: maximum amount of air which can be exchanged. Residual air: air which cannot be forced out of the lungs.

Gaseous exchange takes place by diffusion between the alveoli and the air in the lungs. The surfaces are well adapted, with a large surface area as well as being moist, permeable and only one cell thick.

During an asthma attack, the lining of the airways become inflamed, causing mucus and fluid to build up in the airways. The muscles around the bronchioles contract, narrowing the airway causing breathing difficulties.

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B5 -Digestion

In the mouth, carbohydrase breaks down starch into maltose, which is then broken down into glucose.

In the stomach, protease breaks proteins down into amino acids. The strong stomach acids provide the optimum conditions for protease enzymes.

In the small intestine, lipase breaks down fats into fatty acids and glycerol. The gall bladder releases bile into the small intestine to emulsify fats, increasing the surface area for more efficient digestion.

The small intestine is adapted for food absorption. It's villi and microvilli create a large surface area, perfect for the diffusion of digested foods into the blood capillaries (glucose, amino acids) and into the lacteals of the lymphatic system (fatty acids).

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B5 -Waste disposal

The kidney contains nephrons where ultrafiltation takes place under high pressure. Small molecules such as glucose and urea are filtered out of the blood. Useful molecules such as glucose, amino acids and some salts and water are absorbed back into the blood by selective reabsorption. 

During strenuous exercise or hot conditions, water is lost by sweating which causes the concentration of the blood to increase. This is detected by the hypothalamus, which causes the pituitary gland to secrete an anti-dieretic hormone into the blood. This increases the permeability of the collecting duct, so that more water is reabsorbed into the blood. Therefore, concentrated urine is excreted and more water is reserved.

When a lot of water is drunk, the concentration of the blood decreases which stops the production of ADH, so the urine excreted is more dilute, as less water is reabsorbed.

An increase in carbon dioxide levels is detected by receptors in the carotid artery, which stimulates nerve impulses to inform the brain, causing a higher breathing rate to remove the carbon dioxide.

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B5 -Fertility

During the menstrual cycle, FSH and LH are released from the pituirary gland, stimulating egg growth (FSH) and controlling ovulation (LH).

If fertilisation does not occur, the oestrogen and progesterone levels decrease, when these levels are low, menstruation occurs.

If fertilisation does occur, progesterone levels remain high and no FSH is produced, so no more eggs develop.

Fertility treatments such as IVF and hormone treatment can be used to combat infertility, allowing those with fertility problems to concieve.

A foetus can be checked for genetic abnormalities by amniocentesis (extracting and testing cells in the amniotic fluid) or by chromosomal analysis (using a foetal blood test).

These methods cause a small risk of foetal expulsion.

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B5 -Organ donation

Any living person can donate blood and bone marrow as these are naturally replaced by the body, and a kidney, as we can live with only one.

The supply of donated organs is limited due to a shortage of donars and restrictions due to tissue matches as well as size and age. These problems can be avoided by using mechanical replacements, but these can also be problematic because of their dependance on a power supply and the body's reaction to the 'foreign matter'.

Any transplant runs the risk of being rejected, so the recipient must take immuno-suppressives, which can cause problems with the body not protecting itself against microorganisms.

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B6 -Understanding microbes

Bacterial cells have: a flagellum for movement, a cell wall to maintain shape and structure, DNA to control the cell's activities. They can be sphericalrod-shapedspiral, or curved rods. They reproduce by an asexual method called binary fission. Bacteria are very successful in terms of numbers because they can survive on such a wide range of energy sources, live in a wide range of habitats and usually make their own food.

Yeast is a single celled fungus. Its growth rate can be affected by changes in: food availability, temperature, pH, and the removal of waste products. The growth rate of yeast doubles for every 10 degree rise in temperature until the optimum is reached.

Viruses are not living cells. They are structures made up of a strand of genetic material and a surrounding protein coat. In order to reproduce, it will attach itself to a specific host cell and inject its genetic material. It uses the cell to make the components of the new viruses, causing the host cell to split open and die, releasing the new viruses.

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B6 -Harmful microorganisms

Disease-causing microorganisms can be spread by: food (Salmonella), water (Vibrio cholera), airbourne droplets (Influenza) and some by direct contact.

An infectious disease has four stages: 1) microbe enters the body 2) reproduces without causing symptoms (incubation period) 3) production of toxins 4) toxins cause symptoms

Pasteur realised that microbes from the air could make food go bad.

Lister invented the first antiseptic, using carbolic acid to prevent the infection of wounds.

Fleming discovered the first antibiotic (Penicillin).

Strains of bacteria are becoming resistant to antibiotics, through random mutations allowing them to survive and reproduce.

In order to prevent antibiotic restistance, antibiotics are only prescribed when really necessary and the course of antibiotics must be finished in order to kill off any partially resistant bacteria.

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B6 -Useful microorganisms

A type of bacterium called Lactobacillus is used to turn milk into yoghurt. First the milk is pasteurised by heating it to 78 degrees, then it is cooled and incubated with the bacteria culture. The bacteria causes the lactose in the milk to be broken down into lactic acid, making the yoghurt taste acidic.

Yeast can be used to make alcohol in the process of fermentation, where the yeast respires anaerobically. It is added to natural sugars from fruits such as grapes and kept warm.

Glucose -(yeast)-> ethanol + carbon dioxide

In fermentation, only a limited concentration can be made, as a high concentration of alcohol kills the yeast. It can only reach a maximum of around 15%, so in order to make spirits, the alcohol must then be distilled.

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B6 -Biofuels

Biofuels use the energy that is trapped in biomass. They are seen as a good alternative to using fossil fuels for fueling cars, but it could mean that the fuel isn't carbon neutral because space is taken up meaning that other plants cannot remove carbon dioxide from the atmosphere.

Biogas production increases with temperature increase until 45 degrees, where it begins to slow down. This is because the bacteria multiply faster and the enzymes work more efficiently, however, above 45 degrees the enzymes denature and the bacteria die.

Biogas can be burned to produce hot water and to generate electricity. However, biogas containing a percentage of methane lower than 10% can be extremely explosive.

Gasohol is petrol mixed with alcohol made by fermentation. It can be used to fuel cars in countries such as Brazil where there are ample amounts of sugar cane and it is cheaper than importing oil.

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B6 -Life in soil

Soil is made up of different sized minerals. Sandy soil contains larger particles than clay soil. This means that the air content and permeability of sandy soil is usually higher. Loam contains a mixture of clay and sandy soil, as well as large amounts of humus (partly decomposed plant and animal matter). The larger the humus content, the more water and air the soil will hold.

Humus content can be tested by burning off the humus using a bunsen burner.

Air content can be tested by seeing how much water is needed to fill the air spaces.

Water content can be tested by slowly heating the soil to evaporate it.

Humus is important because it releases minerals back into the soil and increases the air content, allowing organisms an oxygen supply to survive.

Earthworms aerate and drain the soil, allowing organisms to respire aerobically. They also neutralise acidic soil, meaning that plants are able to grow as the pH isn't too low.

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B6 -Life in Water

Advantages of living in water include: no risk of dehydration, less variation in temperature compared to air, easily disposal of waste products.

However, water is denser than air so resists movement more and living in water can cause the water content of the body to vary, so it needs to be controlled. In freshwater, organisms can take in too much water, and in salt water too much water can be lost by osmosis.

Amoeba have contractile vacuoles which store excess water.

Some chemicals such as PCBs and DDT don't break down, so accumulate in the food chain, increasing in concentration in higher trophic levels, becoming toxic with a lethal dose to top consumers.

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B6 -Enzymes

Enzymes such as lipase, protease ans carbohydrase are used in biological washing powder to digest food stains and make them easier to wash out.

The enzyme sucrase is used to break down sucrose molecules to produce the sweeter products glucose and fructose, used as sweeteners. They are sweeter, so less is added to food, lowering the cost and calorie content.

Enzymes can be mixed with alginate and dropped into calcium chloride solution, immobilising them. They are useful in reactions because they don't contaminate the mixture, and can be used in continuous flow processes.

Milk can be treated to convert lactose into glucose and galactose, which can be absorbed more easily for people with lactose intolerance.

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B6 -Gene Technology

Gene therapy is the transferral of a gene from one organism to another, making a transgenic organism. This is done by identifying and isolating the gene responsible for the desired characteristic, then cutting it out using restriction enzymes,which leave several unpaired bases to act as a sticky end. The gene is then inserted into the new DNA, using ligase enzymes to join the two together.

Bacteria can be used to create human insulin, through genetic engineering. The gene for insulin is removed from human DNA and placed into a bacterial plasmid and allowed to multiply. Scientists use an assaying technique to find out if the bacterium have taken on the human gene: they also add a gene for restistence to antibiotics and flood the bacteria with said antibiotic, choosing to continue with the surviving bacteria which took on the gene.

DNA fingerprints are produced in order to identify individuals.This is done by extracting DNA from a sample, fragmenting the DNA using restriction enzymes and separating the fragments by electrophoresis and making the fragmets visable using a radioactive probe.

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