AQA BIOL2~3rd June 2013~AS Biology (Now Closed) Watch
I was like that last year for AS but literally learn the mark scheme off by heart and you will be fine i got an A in this exam and i usually get c's but i learnt this mark scheme
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I never did GCSE science so this is my first science exam; it all seems to be applied and not directly relevant to the spec.
I'm doing A2 History and Psychology this year (took up biology this year), so I'm used to creative writing. How can I get the hang of the language style and structure in Biol.?
I did do Double BTEC science last year mind :P (D*s)
Glycogen is often known as 'animal starch' as it is the main carbohydrate storage product of animals and its structure is similar to that of starch, but has a shorter chain. Due to its shorter chain glycogen is more readily hydrolysed to form α-glucose than starch. Glycogen is very compact making it good for storage; Its coiled structure is folded up to form small granules and stored in the muscle fibers.
Haemoglobin and Oxygen
DNA controls the shapes of proteins, as its genes code for the primary structure of polypeptides which in turn determines the polypeptides tertiary structure. When multiple polypeptides are linked together (this can be in addition to non-protein group) they gain quaternary structure.
Haemoglobin have quaternary structure. The primary structure of haemoglobin consists of 4 polypeptide chains. Its secondary structure is where its polypeptide chains each coil into a helix. Their tertiary shape is given by the helixes folding in to a specific shape enabling them to carry oxygen. The linking of the 4 polypeptides give the haemoglobin its quaternary structure.
A human haemoglobin can carry up to 4 oxygen molecules (O2), due to the 4 ferrous ions (Fe2+) each contained within 1 of the 4 haem groups. Each polypeptide has a haem group associated with it.
At the gas exchange surface where the oxygen levels are high and the carbon dioxide levels are low the haemoglobin has a high affinity with the oxygen molecules and so oxygen is attached to its ferrous molecules. This occurs as the pH is higher (alkali, due to lessened acidic carbon dioxide) making the haemoglobins a shape which gives it a higher oxygen affinity.
The haemoglobin does not release the oxygen it carries in the blood due to its increased oxygen affinity
At respiring tissues the oxygen levels are low and due to presence of a greater carbon dioxide concentration, the haemoglobin changes its shape and its affinity with oxygen drops and so the oxygen molecules are released. This explains the haemoglobins change in oxygen affinity throughout the body.
Different organisms have different haemoglobins, the shape of the haemoglobin determines the strength of its oxygen affinity:
Haemoglobin with high oxygen affinity load oxygen easier than when they unload.
Haemoglobin with a low oxygen affinity load oxygen less easily but can unload far more efficiently.
Organisms living in an environment with little oxygen which also have a low metabolism have haemoglobin with a high oxygen affinity. Organisms living in an environment with lots of oxygen that have high metabolisms have haemoglobin with a low oxygen affinity.
The Bohr effect is where the greater the carbon dioxide concentration, the easier the haemoglobin unloads oxygen.
In the presence of low oxygen the haemoglobins polypeptides are closely united, making it difficult to load oxygen however after the haemoglobin loads 1 oxygen molecule the haemoglobin can load the other 3 far more easily. This is shown in the oxygen dissociation curve: pic.twitter.com/pAZ8d2oKYr
The oxygen curves for different haemoglobin keeps roughly the same shape however their positioning changes; haemoglobin with a higher oxygen affinity will be positioned more to the left, haemoglobin with a lower oxygen affinity will be positioned more to the right.
In a resting human, the haemoglobins leave the lung saturated with oxygen molecules and return to the lung normally having lost only 1 of the 4 oxygen molecules it carried. In an exercising human the haemoglobin they may return to the lung having lost 2-3 of their oxygen molecules. This is due to the tissues greater rate in respiration which produces more carbon dioxide, reducing the pH levels further, which changes the haemoglobins shape more resulting in more oxygen being unloaded.
Materials (e.g. respiratory gases, minerals, excretory products and heat) are exchanged from the environment to organisms and the waste materials from the organism to the environment using various transport systems. The larger the animal or the higher its metabolic rate, the more materials that will be exchanged between it and the environment. The type of gas exchange system and transport systems the organism has will have evolved to meet its requirements.
Exchange of materials can either be passive (e.g. diffusion/osmosis) or active (e.g. active transport).
The larger the surface area to volume ratio, the more effective the exchange of materials. Organisms either have a body with a flattened shape, with all the cells close to the surface or a specialised exchange surface, with a large surface area to volume ratio, short diffusion pathway, a partially permeable membrane allowing some molecules through. The movement of both the internal and external medium increases the rate of diffusion.
Arteries carry (normally oxygenated) blood away from the heart to the arterioles, smaller arteries controlling the blood flow to the capillaries. Veins carry (normally deoxygenated) blood away from the capillaries back to the heart.
Arteries, arterioles and veins all have a similar structure, they all have a tough outer layer resisting the internal and external pressure changes.
The muscle layer (beneath the outer layer) contracts and controls the blood flow. The arterioles have the thickest muscle layer as they control the flow of blood into the capillaries; arteries have the next thickest muscle layer simply controlling the volume of blood passing through them; veins have the thinnest muscle layer.
The elastic layer (beneath the muscle layer) helps maintain the vessels blood pressure by stretching and recoiling. The elastic layer in the arteries is the thickest, as the blood pressure must be kept high to push the blood to the body's extremities; the arterioles elastic layer is thinner as the blood pressure is lower than in the arteries; the veins elastic layer is thiner than the arteries too as there is such little blood pressure.
The thin lining (endothelium) (beneath the elastic layer) is smooth, preventing friction and thin, allowing efficient diffusion.
The lumen (at the center of the vessels) is the cavity where the blood flows.
Vessel Specific Structures
Veins have valves throughout them to ensure that the blood only flows towards the heart, without the valve the blood could flow the opposite way due to the low pressure. The contraction of body muscles causes the compression of veins, which results the in pressure, which pushes the blood through the veins.
Capillaries are tiny and are the only vessels to carry out exchange (exchanging the metabolic materials between the blood and the cells) due to this the blood within them moves slowly and they have a different structure to the other vessels; they have a narrow diameter, narrow lumen and only a single cell thick epithelium; these features ensure that the external cells are as close to the internal red blood cells as possible. They occur in numerous quantities as a branched network, hence increasing the rate of diffusion.
Tissue fluid is a watery liquid composed of blood plasma in which the bodies tissue is located; the blood plasmas composition is controlled by homeostasis.
After metabolic substances (such as oxygen, glucose, salts, amino acids and fatty acids) have passed out from the capillaries they must travel in the tissue fluid to reach the tissue cells. The tissue cells then produce waste products (such as carbon dioxide) which are then transported through the tissue fluids back into the capillaries.
Hydrostatic pressure (the pressure created by the heart pumping blood) at the arterial end of the capillaries forces tissue fluid out of the blood plasma, whilst the hydrostatic pressure in the tissue fluid and the bloods low water potential forces the tissue fluid back into the blood plasma. However the net pressure is one that pushes the tissue fluid out of the capillaries along with some small molecules (not cells and proteins).
At the venous end of the capillaries, having lost a lot of its hydrostatic pressure, the higher hydrostatic pressure in the tissue fluid (in addition to osmotic forces) causes the fluid to flood back into the capillaries (taking with it the waste materials).
The Lymphatic System
The lymphatic system is driven by the hydrostatic pressure of the tissue fluids (external to the capillaries) and the contraction of body muscles (like with veins, are compressed, and the tissue fluid is consequently moved up through a the vessel system, with valves at regular intervals preventing back-flow). The lymphatic system transports excess tissue fluid back to the bloodstream, via ducts that join the veins near the heart.
Mammals have specialised exchange surfaces to absorb nutrients and respiratory gases excrete waste products. They also have mass transport systems which transfer the nutrients and respiratory gases from their exchange surface to their cells and then the waste products from their cells to the exchange surfaces. They require these mass transport systems, as due to their small surface area to volume ratio (larger size), diffusion would be far too inefficient for the transfer of materials around their body.
The more active an organism and the smaller the surface area to volume ratio (the larger it is), the more likely it is to have developed a specialist transport system with a pump (to circulate the transport medium).
Transport systems often have a water based transport medium (e.g. blood), where the materials are dissolved in to the medium and then transported through the system. The systems also often have sections where mass transport occurs, transporting the materials over large distances quickly. Transport systems consist of branching networks containing the transport medium, which distributes the materials over the organisms entire body. They also have a mechanism (reliant on pressure changes) for the movement of the transport medium within the transport system; in mammals this is a result of various muscle contractions or a pumping organ (e.g. the heart). The transport system also have ways of controlling the rate of flow of the transport medium to suit the demands of the different parts of an organism and have mechanisms such as valves to prevent back-flow.
Mammals Circulatory System
Mammals have a closed blood system where their transport medium (blood) is carried around their transport systems (blood vessel network).
Mammals have a double circulatory system, where the blood passes through the heart twice per circuit of the body. Deoxygenated blood leaves the heart at a low pressure to the lungs where it becomes oxygenated , it then passes back to the heart where it is pumped out at high pressure to reach the organisms extremities very quickly. Mammals need the supply of oxygenated blood to their cells to be quick as they often have a high metabolism and need to maintain a high body temperature.
When the materials reach the areas where they are required, they diffuse from the capillaries, into the plasma and then into the cells. The diffusion here is quick as the diffusion pathways are very short (approximately 1mm), with a steep diffusion gradient and a large surface area (over all the capillaries).
Fish also have a small surface to volume ratio and therefore have developed gills, a specialised gas exchange surface, appropriate to their environment. In fish, gills are located internally behind their head. Water is taken in through their mouth, forced over their gills and then exits through slits on the side of their body.
The gills are made of long structures stacked in a pile, called gill filaments. On the gill filaments and positioned perpendicular to them, are smaller structures called the gill lamellae which increase the surface area.
In the gills, deoxygenated blood flows up the filaments on one side and oxygenated blood flows back down the other; the lamellae carry blood from the deoxygenated side over to the oxygenated side, whilst the flow of water passes in the opposite direction, this is known as counter current flow.
The countercurrent flow maintains a concentration gradient, so that the maximum amount of gas exchange between the water and the gills occurs. The blood that starts to flow through the lamellae (with a very low oxygen concentration) comes into contact with water that has lower oxygen concentration than normal however the lamellae has a lower concentration so diffusion still occurs. Traveling across the lamellae the blood becomes more saturated with oxygen but diffusion is maintained as it travels closer to the source of water where oxygen is at its normal concentration.
Single-celled organisms have a large surface area to volume ratio (they are very small) and so diffusion is sufficient enough to transport materials across its body surface. Oxygen must diffuse into its body and carbon dioxide from respiration must diffuse out.
Terrestrial insects are insect that live on land. Insects gas exchange systems required a thin, permeable surface however this conflicts with their need to conserve water as this aids its evaporation. To prevent the loss of water via evaporation, insects have a small surface area to volume ratio and an exoskeleton covered with a waterproof cuticle.
In insects air enters through spiracles (tiny pores on the bodies surface), into an internal network of tubes called tracheae (supported by strengthened rings) which branch into tracheoles (smaller tubes) and extend throughout the entire insects body tissues to supply its cells with oxygen and remove the carbon dioxide they produce in respiration.
Respiratory gases move in and out of the tracheal system by ventilation (the mass movement of air in and out of the trachea caused by the insects muscle movements) and generally down a diffusion gradient, caused by the cells respirating at the end of the tracheoles reducing the oxygen concentration.
Insects spiracles stay closed to prevent water loss and using valves, open periodically allowing gas exchange.
THE END OF PART 4/5
note: I will be writing up notes for BIOL1, If you would like me to send you a copy of these in an email just ask or PM me and I'll send them as I write each part or as a whole when all the notes are complete complete, add your your preference when you request the notes. I can also send you a copy of the BIOL2 notes when they are complete if you would like, feel free to ask ^.^
(I do not always check my TSR messages often so be prepared for a little wait, however I am beginning to check back more often at the moment)
Well Im doing the BIOL2 exam in June and my teacher says we need to research gas exchange in amphibians, birds and reptiles ourselves. You havent included that in your notes so im assuming its just extra information you dont really need to know?
Plus i really cant be bothered with the extra work, loll