• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month

# AS and A Level: Exchange, Transport & Reproduction

Browse by
Rating:
4 star+ (27)
3 star+ (58)
Word count:
fewer than 1000 (130)
1000-1999 (150)
2000-2999 (60)
3000+ (53)
Submitted within:
last month (1)
last 3 months (1)
last 6 months (1)
last 12 months (4)

Meet our team of inspirational teachers

find out about the team

Get help from 80+ teachers and hundreds of thousands of student written documents

## Five tips on presenting and analysing data from core practicals

1. 1 Raw data should be presented in a table with clear headings. All table column and row headings should contain units and readings should all be recorded to the same decimal place.
2. 2 Raw data should be processed to provide descriptive statistics such as the mean and standard deviation.
3. 3 Present data using the relevant graph type. Ensure that you add error bars showing either standard deviation or standard error.
4. 4 When describing trends and patterns, manipulate data to calculate the size of key changes. For example, absorbance increases by 0.09 absorbance units between 10◦C and 40 ◦C. Preferably express the change as a percentage increase or decrease. Do not simply quote points, eg at 10 ◦C absorbance was 0.01 and at 40 ◦C it had gone up to 0.1 absorbance units.
5. 5 Discuss each phase of the graph. For example if there is a slow increase, followed by a rapid increase, and then the graph levels off and shows a decrease, discuss these four key phases. Do not give detailed descriptions of each small fluctuation. The trends and patterns are the important things.

## Meiosis and Mitosis facts

1. 1 Meiosis generates gametes/sex cells, whereas mitosis is for growth/repair and generates daughter cells identical to the parent cell.
2. 2 During Meiosis chromosome number is halved producing haploid gametes with a single copy of each chromosome. During Mitosis chromosome number is maintained producing diploid daughter cells with maternal and paternal copies of each chromosome, i.e. homologous chromosome pairs.
3. 3 Before mitosis and meiosis all chromosomes are copied as part of interphase. At the end of interphase there are two identical copies of every maternal chromosome and every paternal chromosome, so chromosome number has doubled (i.e. at the end of interphase a human cell contains 46 x 2 = 92 chromosomes). The identical copies of chromosomes are referred to as sister chromatids and they are joined by a centromere.
4. 4 In meiosis, genetic variation is generated by crossing over during prophase 1, and independent chromosome assortment at metaphase 1 and metaphase 2. During crossing over maternal and paternal chromosomes cross each other, and break at points known as chiasma. Maternal and paternal alleles below the chiasma change places so that the paternal chromosome contains maternal alleles and vice-versa. During metaphase 1 and 2, maternal and paternal chromosomes align randomly on one side of the equator. As the maternal and paternal chromosomes can align on either side, different potential chromosome combinations can occur.
5. 5 The events in metaphase, anaphase and telophase are identical in both mitosis and meiosis 1 and 2. In mitosis a single division occurs, whereas in meiosis cells undergo 2 meiotic divisions.
a) During meiosis 1, maternal and paternal sister chromatids are separated so that 1 cell contains both maternal sister chromatids of a pair and the other contains both paternal sister chromatids.
b) During the second meiotic division, sister chromatids are separated. The gametes that result contain only 1 chromosome from each pair, i.e. they are haploid.

## How to evaluate experimental methods

1. 1 When evaluating the reliability of experimental methods, always consider whether all variables other than the independent variable have been adequately controlled. If a variable cannot be controlled has it been monitored to establish any effect it might have?
2. 2 All experiments must be repeated to establish reliability. Has the experiment been repeated at least three times? Preferably you should repeat it more than 3 times.
3. 3 What does the standard deviation suggest about the spread of the data? If the mean is 5, but the standard deviation is 3, readings vary from the mean considerably. This suggests that the mean does not represent the actual readings.
4. 4 How precise are the measurements? If a balance used to measure change in mass only measures to 0.1 g then the reading could be 0.12 g, 0.15g, or 0.18g etc.
5. 5 How accurate are the readings? If equipment is re-used for different repeats for example, cross contamination could affect the accuracy of subsequent readings. If tubes are shaken different amounts, different volumes of gas could be released. Consider all potential sources of error and discuss how the procedure could be improved to reduce these sources of inaccuracy.

1. ## Function of the Golgi Body.

* Columnar - these particular cells are tall and narrow, and the nucleus is near the basement membrane. (3) * Cliliated - these cells are in a columnar shape, with the free surface of each cell covered in many cilia, which is capable of beating rapidly and rhythmically. (4) * Pseudostatified - this is only one layer of cells as they all have contact with the basement membrane, these cells are just misshapen. (5) 2. Compound Epithelium - this is made up of many layers.

• Word count: 1561
2. ## Investigation into reducing sugar content of a variety of soft drinks (not diet).

Fruit is a major constituent of the drink. Panda Lemonade: Ingredients: Carbonated water, sugar, flavorings, preservative (sodium benzoate), sweetener (sodium saccharin), acidity regulator (trisodium citrate). Hypothesis: The reducing sugar content of a variety of soft drinks will be different. The reducing sugar content of each soft drink should be different due to the fact that they are all made with different ingredients and are products of different companies therefore each different flavour would have a different sugar content. The Ribena, Lilt and Orange Fanta all contain fruit juices, therefore I do expect reducing sugar content.

• Word count: 1605
3. ## Using Different Carbon Sources For Growth.

Include one flask containing 200cm3 of distilled water as a control. * Add 2g of dried yeast and 1g of culture nutrients to each flask. The culture nutrients are a mixture of equal masses of ammonium phosphate and ammonium sulphate. Swirl the flasks, or stir the contents thoroughly with a glass rod, to ensure that the nutrients dissolve and that the yeast is resuspended. * Plug each flask with cotton wool and incubate overnight at 25�C. * Set up a burette containing 0.1mol dm-3 sodium hydroxide solution.

• Word count: 842
4. ## The mechanism of Negative feedback.

The extent of the correction is monitored by a system called negative feedback. This makes sure that, as levels return to normal, the corrective mechanisms are scaled down. This type of system in which a change in level of a factor triggers a corrective mechanism, is called a self-adjusting system. (Diagram showing how negative feedback keeps a system in a stable condition.) All homeostatic control mechanisms that use negative feedback, whether they by physical or biological, share the same components.

• Word count: 1769
5. ## Homeostasis In Mammals.

This glucose is then converted by cells into glycogen for storage in the liver and muscles. Should the blood sugar level be too low, which could be due to strenuous exercise, then glucagon is secreted which results in the conversion of glycogen to glucose. Someone that suffers from diabetes mellitus is unable to control their blood sugar level, in one form of diabetes no insulin is secreted and regular insulin injections are needed to manually regulate blood sugar. Osmoregulation is the regulation of the amount of water in the blood, in mammals this involves the kidneys and more specify the nephrons.

• Word count: 861
6. ## How and Why do Organisms maintain, a Constant Internal Environment?

If a fall in surrounding temperature is detected, impulses are sent to skeletal muscles, which induce shivering, and to adrenal glands, which release adrenaline to increase metabolic rate. If thermoreceptors detect an increase in core body temperature, or in surrounding temperature, the hypothalamus sends impulses to muscles in arterioles, which causes vasodilatation, to sweat glands which then produce more sweat, and to thyroid glands, which release les thyroxin, and therefore reduce metabolic rate. Blood Glucose levels are also controlled. Glucose regulation depends upon a part of the pancreas called the islets of Langerhans.

• Word count: 1287
7. ## Osmosis is the phenomenon of water flow through a semi permeable membrane that blocks the transport of salts or other solutes through it.

In such a case the phenomenon is called reverse osmosis. If there are solute molecules only in one side of the system, then the pressure that stops the flow is called the osmotic pressure. The movement of a solute molecule within a solvent is over damped by the solvent molecules that surround it. In fact, the solute movement is wholly determined by fluctuations of thermal collisions with nearby solvent molecules. However, the average thermal velocity of the molecule is the same had it been free in a gas phase Whenever a solute movement is blocked by a wall it will transfer momentum to it and, therefore, generate pressure on it.

• Word count: 706
8. ## An Investigation to find the water potential of a plant cell.

* Distilled water (excess) * Potato ?1 * Borer (approx.1cm width) * Paper towel ?1 * Weighing scale ?1 * Weighing boat ?1 Method 1) Appropriate apparatus was collected. (Stated previously) 2) The percentage sucrose solutions, 0%, 10%, 20%, 40%, 60%, 80%, and 100% were created using 1M sucrose solution distilled water. It was important pure water was used as its water potential was zero kilopascals, this would then not have any affect on the final results. 3) Before the solutions were made, two pipettes were labelled.

• Word count: 1945
9. ## Investigate the effect different concentrations of glucose in a yeast & Glucose solution has on the rate of respiration in Yeast.

Another factor that plays a big part in the outcome of the experiment is the temperature. The temperature has to be right because if it is to high then the enzymes will start to denature. If the temperature is right though (40�c) then the reaction will go quicker, this is because of the collision theory. Collision theory states that as particles are heated they will gain more energy, thus making them collide quicker. If the glucose diffuses into the yeast faster, and then collides with the enzymes in the yeast cells more often. There are also many other factors that will affect this experiment these are things like: * Glucose concentration * Time * pH *

• Word count: 1505
10. ## Statistical Technique.

- Ra = Ub = 36 + 21 - 22.5 = 34.5 2 Na = 6 Nb = 6 CV = 5 U CV 1.5 < 5 As the smallest U value is less than the critical value the null hypothesis can be rejected. Therefore it has been statistically proven that there is a difference between the volume of gas produced by sucrose and the volume of gas produced by glucose. Interpretation of Results Results Table: This table shows the volume of gas collected in five minutes in cm from each carbohydrate .

• Word count: 1792
11. ## Osmosis in Potatoes.

If any of the non-variables aren't kept constant it would mean it would not be a fair test. Apparatus: Test Tube Rack - We used this to put the test tubes in so they wouldn't fall over. 5 Test Tubes - We used these in order to put our chips and the sucrose solution in. 1 Measuring Cylinder - We used this in order to measure accurately the amount of Sucrose Solution being put into the test tubes. Chipper - This was used in order to cut the chips to the same size so that all the chips would have the same surface area 5 Bungs - We used these to prevent evaporation.

• Word count: 1177
12. ## Explore and explain the main features involved in the anabolic metabolism of carbohydrate (glycogenisis), lipid metabolism (triglyceride storage, transport and ketosis) and protein metabolism (transamination and deamination).

Carbohydrates are made up of many single sugars (monosaccharides) such as glucose; two monosaccharides join together to form a double sugar (disaccharide) such as maltose (glucose + glucose). Many monosaccharides joined together are polysaccharides such as starch, glycogen and cellulose. Below is how glucose joins together with another glucose molecule to form maltose. Alpha Glucose as shown here above on both the left and the right join together with water being produced from the H group on the left hand glucose and the HO group from the right glucose. A glycosidic bond then forms between the two with the oxygen that is left; this final product is shown below.

• Word count: 1296
13. ## Osmosis In Potatoes.

This is due to the fact that the cell walls are made from cellulose, which is extremely strong. Eventually, the cell stops swelling, and when this point is reached, we say the cell is turgid. This is important, because it makes plant stems strong and upright. Osmosis diagram: Key: Semi permeable membrane Solvent molecule Water molecule Preliminary Work: In a sense, preliminary work is as important as the actual experiment. It allows you to make hypotheses before performing actual tests. For my preliminary work, I used 33mm of potato. It was easy to cut 33mm and get it to weigh around 1g.

• Word count: 2225
14. ## Find out what the cell strength of a potato is.

The chips will become flaccid. This is a diagram to help explain my prediction. In order to show the reason behind my predictions I have done some research on the internet and I chose this diagram from my biology book as it best interprets what I mean. Apparatus The equipment which I will use are 6 test tubes, one for each molar solution, a test tube rack in order to keep my test tubes safe, a knife which I will use to cut the potato, a potato which will be tested to see if it has lost or gain weight

• Word count: 1642
15. ## Investigating Water Potential Of Potatoes.

What happens? Quite quickly, the level of solution in the tube starts to rise. Analysis of this solution shows that it gradually becomes more dilute, indicating that water is passing into it from the surrounding beaker. In seeking for an explanation of this, it is necessary to appreciate that the membrane is permeable to the water molecules but impermeable to the much larger sugar molecules. With this in mind, consider the situation on either side of the membrane. In the beaker, there is nothing but water molecules and in the funnel, there are water molecules and sugar molecules.

• Word count: 5528
16. ## The structure and function of carbohydrates.

Starch and Glycogen are two common chain polymers. Just as the removal of water joins carbohydrates together via condensation synthesis, hydrolysis is the reaction using water to break apart Disaccharides and polysaccharides. A Disaccharide is bound by sharing an oxygen with one hydrogen on each opposing side. When H2O is re-introduced via hydrolysis the two monomers in the disaccharide no longer need to share one H2O, and as a result the opposing sides absorb the OH and H and break apart.

• Word count: 1596
17. ## "It makes no sense to believe that Christ is really present in the Eucharist"- Evaluate this statement.

This is a similar idea to that of Christmas where people know the story of the birth of Christ but they do not believe that he is present today preferring to believe in the commercial values of Christmas such as Father Christmas. Others might be like Thomas (one of the twelve disciples) and only believe what they hear when they see it before their very eyes; therefore not believing in Christ as they have not seen him in the flesh.

• Word count: 666
18. ## Diabetes mellitus.

This type of diabetes usually appears before the age of 40. It is treated by insulin injections and diet. Non insulin dependent diabetes (also known as Type 2 diabetes) develops where the body can still make some insulin, though not enough for its needs, or when the insulin that the body does make is not used properly. This type of diabetes usually appears in people over the age of 40. It is treated by diet and tablets or, sometimes, by diet and insulin injections.

• Word count: 665
19. ## Nerve Impulses - Action Potentials.

The axoplasm becomes progressively more positive with respect to the outside of the membrane. Then, almost instantly, the permeability of the membrane to sodium ceases (net flow stops). Potassium ion channels start to open and potassium ions flow from the axoplasm where they are in high concentration. The axoplasm now starts to become less positive again (process of re-establishing the resting potential). An Action Potential (impulse) The impulse, in the form of this reversal of charge, then runs the length of the neurone fibre: The transmission of an impulse The Refractory Period For a brief period following the passage of an action potential, the axon is no longer excitable.

• Word count: 800
20. ## Notes on Dialysis testing.

Suspend the dialysing tubing in a beaker and fill it with distilled water up to the level of knot. Immeadiately start your stop clock and, using a pipette, take three small samples from the distilled water in the beaker and put them into three test tubes. 5. Test your samples for the presence of starch, glucose and chlorides. 6. Leave the mixture for five minutes, take a second set of three samples and place them in clean test tubes. Repeat the test at five minute intervals for 25 minutes. After 25 minutes take sample from the dialysing tubing as well.

• Word count: 732
21. ## Forensic Science - Skills For The Laboratory - Experiment Title: The Absorption of Light (Calibration Curve).

= ?cl Where A is the absorbance (optical density) ? (=?/2.303) is the molar absorption coefficient (extinction coefficient) It isn't necessary to use a sophisticated spectrophotometer in order to determine the concentration of the absorbing species in solution. All that is required is a simple instrument which uses a diffraction grating to limit the range of wavelengths passed. Calibration data are obtained by measuring the absorbance's of solutions of known concentration at a particular path-length (or path-lengths). Any absorption by the solvent, and reflection and scattering by the cell, is compensated for by the use of an identical cell containing the pure solvent as a 'blank.'

• Word count: 1438
22. ## The Biological Significance Of Sugars.

and the non-sugars (polysaccharides). Monosaccharides are a single sugar, which is made up of small molecules with low masses. These are always sweet tasting, soluble in water and form crystals when in solid form. Examples of monosaccharide sugars include alpha & beta glucose, ribose, fructose, glyceraldehydes and deoxyribose etc. The general formula for them is: (CH�O)n where n is the number of carbon atoms present. The ratio is always 1:2:1. Most monosaccharides are the producers of energy, however some are used for structural purposes, for example ribose and deoxyribose, both pentose sugars, are used to make RNA and DNA.

• Word count: 683
23. ## Diabetes is a complex metabolic disorder.

* Type 2 diabetes, also known as non-insulin dependent diabetes. Type 1 diabetes develops if the body is unable to produce any insulin. This type diabetes usually appears before the age of 40. It is treated by insulin injections, diet and regular exercise is recommended. Type 2 diabetes develops when the body can still make some insulin but not enough. Also when the insulin that is produced does not work properly. This type of diabetes usually appears in people over the age of 40.

• Word count: 578
24. ## The Renal System.

If a person is unfortunate to suffer from complete kidney failure, the blood allows waste materials to build up within the body as a result the levels of toxicity in the body rises. The body will eventually become poisoned internally if the kidneys can't clean the blood. Urea is produced in the liver; it is white in colour and is a crystalline substance. As the body doesn't store protein instead it converts it into glucose and uses the process of respiration for energy.

• Word count: 1003
25. ## Homeostasis & Control of BGL.

Source - http://pespmc1.vub.ac.be/HOMEOSTA.html Homeostasis is one of the most remarkable and most typical properties of highly complex open systems. A homeostatic system (an industrial firm, a large organization, a cell) is an open system that maintains its structure and functions. Such a system reacts to every change in the environment, or to every random disturbance, through a series of modifications of equal size and opposite direction to those that created the disturbance. The goal of these modifications is to maintain the internal balances. Source - www.revision-notes.co.uk/revision/858.html Things maintained by homeostasis: -blood pH (controlled by both nervous and endocrine system)

• Word count: 1868