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# AS and A Level: Exchange, Transport & Reproduction

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## 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. ## Biology: Field Project

The reason why there is a higher light intensity is because there are much fewer trees which block the sunlight, unlike the older coupe. In figure 1 I have included a picture of old coupe and this shows that the trees are tall and blocking sunlight. The reason why there are different coupes is because of a woodland system called coppicing; this system is used for the management of woodland. A common example of coppicing is short-rotation coppicing, this is when cuttings are planted closely and then at the end of the first year they are cut off (near the ground).

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2. ## beetroot experiment

Biological membranes are bilipid layers. Phospholipids create a spherical three dimensional lipid bilayer shell around the cell. Each of the phospholipids molecules has two parts: ? The circle or head is the negatively charged phosphate group which is has a strong polarity because of sharing of electrons within this part of molecule is not quite even. One end becomes slightly positive and other end is negative. So this makes the phosphate head attract other polar molecule- the water. It is hydrophilic.

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3. ## The Endocrine System

The pituitary gland is found at the base of the brain. It resembles a pea hanging from a stalk connected to the hypothalamus of the brain. The anterior pituitary gland produces and secretes a number of hormones. The posterior lobe of the pituitary gland is composed of nerve tissues continuous with the hypothalamus. Testes The testes are paired oval bodies. The testes are located in the scrotum, outside of the male pelvic cavity, in the groin. Ovaries The ovaries are paired oval bodies.

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4. ## The Skeletal and Muscular System

For example, the pituitary gland secrets growth hormone, which stimulates division of cartilage cells during ossification. Some of the bone conditions caused due to hormonal imbalance in the body are as follows: a. Dwarfism. A condition caused by low levels of growth hormone during childhood causing the body to under-develop. This leads to an individual who is short height with limbs that are in proportion to the rest of the body. b. Gigantism. A condition caused by abnormally high levels of growth hormone during childhood before the bone growth plate has closed. This causes the child to grow abnormally tall.

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5. ## human sexuality

The American Psychiatric Association agreed that homosexuality was a mental condition which could be cured. But what really makes a person gay-is it genetics-maybe, maybe not. If one was born with a twin brother or sister-is it truly impossible for one twin to be homosexual and the other to be heterosexual? No, it is not impossible. There is no evidence linking homosexuality to DNA however, there maybe a link between homosexuality and hormones. The lack of testosterone release during fetal development may cause male newborns to grow up to having less male character traits and some female character traits.

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6. ## Optimal Conditions For Everyday Enzymes

The results will show how well the enzyme functions in the varying levels of pH. Purpose The purpose of this lab is to investigate the effect pH has on the efficiency of an enzyme, and to find the optimal pH range of a specific enzyme (meat tenderizer). Hypothesis The percent absorption of the light will gradually go up as the pH rises from very acidic, the enzyme function will peak at its optimal pH, and then begin to decline as the pH becomes higher. It is hypothesized that the optimal pH will be a neutral one, at 7.

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7. ## Effects of exercise on cardiovascular system

Before exercise the resting pulse will be taken three times for each subject and recorded. Subject will be resting for 5 minutes prior to exercise (Table 1) After exercise the heart rate of each subject will be taken immediately and recorded in one-minute intervals for 15 minutes or until both rates return back to the normal value for that particular subject, whichever is longer.

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8. ## Effect of Surface Area On The Rates Of Transpiration

This process is called transpiration. Apparatus... Potometer Short Rubber Tubing Calibrated Capillary Tube Gas Syringe Leafy shoots X2 (Specie living in wet environment, and a Specie living in dry environment) Petroleum Jelly Method... * A leafy shoot is cut under water to prevent air entering the xylem. Care taken not to get water on the leaves. * The potometer is filled completely with water, making sure there are no air bubbles. * Using a rubber tube the leafy shoot is fitted to the potometer under water.

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9. ## Blood System Assignemnt

Elastic lamellae and smooth muscle cells are imbedded in a ground substance rich in proteoglycans. Proteoglycans are formed of disaccharides bound to protein and serve as binding or "cement" material in the interstitial spaces. The outer layer of the media is penetrated by branches of the vasa vasorum. 4. Between the smooth muscle layer and the adventitia, there is again another layer of elastic fibres, the elastic external. Layers 2, 3 and 4 form the media. 5. The outer layer or adventitia is formed of irregularly arranged collagen bundles, scattered fibroblasts, a few elastic fibres and blood vessels which, because of their location, are called vasa vasorum or vessels of the vessels.

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10. ## Transmission of nerve impulses

Na+ are kept outside and their inward diffusion is prevented due to low permeability. Therefore outside the membrane has a positive charge. This is known as the resting potential or membrane potential. This ionic difference across the membrane produces an electric potential of -50 to -90 mV. The membrane is considered to be polarized. At excited stage If a stimulus is applied at one end it will give rise to an excitation. This leads to variation of a membrane potential accompanied by a change in the permeability of the membrane. This sudden reversal of the resting potential is called the action potential and is due to the sudden depolarization of the nerve membrane.

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11. ## Rate of Respiration

The first of the steps of respiration is known as glycolysis. In glycolysis the glucose/ sugar molecule is split into 2 molecules of pyruvate and thus a net gain of 2 ATP molecules takes place. The process occurs within the cytoplasm of the yeast, and occurs when 2 molecules of ATP are hydrolysed to form ADT + Pi. To get the sugar in a more reactive form 2 phosphate groups are added to it, it is then in the form known as Glyceraldehyde 3-phosphate, this has 6 carbons.

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12. ## The Vitamin C content of fruit juice.

It is also widely used as a food additive. In humans, vitamin C is a highly effective antioxidant. Vitamin C deficiency, which usually causes abnormalities in bones and teeth, many citric fruits and vegetables contain large quantities of vitamin C. DCPIP (dichlorophenol-indophenol) is a blue dye which is decolourized by ascorbic acid on account of its reducing properties. DCPIP is a redox dye usually used as a monitor of the light reactions in photosynthesis as it is an electron acceptor that is blue when oxidized and colourless when reduced.

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13. ## AS biology coursework on enzymes

This will make all my experiments a fair test due to the total volume for all of them being the same. As my range increases, my substrate volume will increase and distilled water volume will decrease. The enzyme volume will stay constant at 10cm3 for all my experiments because it is the factor that will not vary. DEPENDANT VARIABLE: My dependant variable will be the time it takes for the solution containing both enzyme and substrate concentration to go colourless.

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14. ## Plan an investigation to find out what effect changing the concentration of calcium ions has on the rate of coagulation of milk.

* Substrate concentration - As this increases the initial rate of creation increases up to a certain point, called Vmax, at which the enzyme is working at its fastest possible rate. * Temperature - The greater the temperature the more energy both the substrate and enzymes have, and so there is a higher probability of forming an enzyme-substrate complex, however, if the temperature is too high, the enzyme will be denatured and can no longer function. As Rennin is used in the body, it should have an optimum temperature around 37oC.

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15. ## Does Caffeine affect heart rate?

In order to make my experiment fair I will control the following variables: ?The temperature of the solutions I am using, as a change of temperature may increase or decrease the Daphnia's heart rate. ?The level of oxygen, as a decrease would cause the Daphnia's heart rate to drop. ?The amount of stress the Daphnia feels, as stress increases heart rate. ?Any contamination from one solution to another, as this would lead to inconsistent concentrations, therefore affecting my overall results.

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16. ## Investigation into the effects of different

S.cerevisiae contain enzymes such as yeast invertase, sucrase and maltase, which are involved in the hydrolyses of the large polymers into small easily transported monomers, (this process is known as extra-cellular digestion).However, they do not contain enzymes to hydrolyse Starch. Reproduction; Yeast reproduce asexually by "Budding". it is the most common mode of vegetative growth in yeasts, and is a typical reproductive characteristic of S.cerevisiae.

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17. ## Why did the colour leak out of cooked beetroot?

- 1 cm in length Variables that needs to be controlled (independent variable) The variables that needs top be controlled under experimental procedure are as follows: > The amount of distilled water - 5cm3 > The temperature of the water ---- 00C, 100C, 200C, 300C, 400C, 500C,600C, 700C Dependant variable: 1. Amount of die solution. 2. Surface area of the beetroot. Statement of fairness: We are going to investigate the effect temperature has on the permeability of the membrane and there by transporting substances across the membrane. And also we will look the method of transport of substances around the body.

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18. ## Investigating water relations in two different plant tissues

to summarise the food tests results on samples of potato and swede Analysis Graph I shows the average percentage change in potato and swede tissue samples in six different concentrations of sucrose solutions after being submerged for 24 hours. The average changes in mass are taken from table's III & IV and plotted as a graph where a line of best fit is drawn. On graph I, there is a clear trend to show that the average percentage mass of the tissue samples decreases as the sucrose solution concentration increases. This is because in a more concentrated sucrose solution (e.g.

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19. ## Effect of Caffeine on the Heart Rate of Daphnia

Also, Daphnia has been proven to be very sensitive to poor water conditions. As such, Daphnia may be used to test the effects of toxins on an ecosystem. Thus, a number of research and industrial groups use Daphnia to test water quality. In addition to that, Daphnia are also a popular live food for tropical and marine fish keeping. In this experiment, Daphnia is used because they are prone to caffeine intoxication. Small amounts of chemicals will have dramatic effects on them. Thus, they are chosen as subjects for studying the effects of the stimulant on the nervous system.

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20. ## Investigate how enzyme concentration can affect the initial rate of reaction.

5. Repeat steps 1-5 using the 0.5% trypsin solution and 0.25% trypsin solution, tabulating the data afterwards. Potential errors in readings - Systematic errors (values differing from the true value by the same amount) - any errors caused by the method is a systematic error as repeats will not improve the reliability of the results. 1. The colorimeter readings may have been above the actual value for each reading. 2. The 1% trypsin solution may not have been exactly 1%, creating an error in all of the readings. 3. There was a delay in starting the stopwatch and taking out the mixture from the boiling tube into the cuvette, causing a potential error in the reading.

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21. ## Affects of Alcohol on the Body & Fermentation

is converted into alcohol. The actual process occurs when sugars are converted into alcohol using yeast during anaerobic respiration, meaning it does not require oxygen. Firstly, the yeast metabolises the sugars from the original extracted grains. The sugar is then the substrate that breaks down the wort into ethanol, producing carbon dioxide. The word equation for this reaction is: Sugar (glucose or fructose) -> alcohol (ethanol) + carbon dioxide (+ energy) Ref 8 Yeast is a microorganism and is responsible for the different types of beer like ale or lager.

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22. ## OCR AS Biology Planning Exercise 2003

Pure water has a water potential of zero, so all water potentials are negative. When potatoes are grown, they are supplied with water. This means that the cells would probably get excess water, making them very full and stiff or turgid. The water potential in normal air is lower than the water potential in the potatoes, so over time water would move via osmosis to the air. This is shown in the diagram below. Therefore, potatoes that are left for a very long time would lose a lot of water, making the cells in the potato flaccid, which would cause them to look soggy or floppy.

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23. ## The Morning After Pill

In truth, there is only a slight distinction between the two. Moral opinions are made in more of a puritan fashion; it is either right or wrong. However, ethical opinions are voiced when moral attitudes are employed in context with the situation; the margin for 'wrong' is somewhat wider. The main advantages of the morning-after pill as to other forms of contraception are that they are highly effective (prevents pregnancies 95% of the time 10), user-friendly and need not be administered by a doctor. Figure 1 shows the disadvantages and advantages of the main methods of contraception.

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24. ## permeability of beetroot membranes

Factors affecting rate of Osmosis: * Temperature: Particles can gain energy by heat transfer. Therefore if the temperature of one or both of the concentrations increases then the particles will gain more energy and move a lot faster. They will thus collide more frequently will the partially permeable membrane and so the speed at which osmosis takes place. * Concentration: Concentration has a great effect on plant cells; if the concentration of the glucose solution is higher than the concentration inside the potato cells, then water will pass out of the potato cells and into solution by osmosis.

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25. ## Dangers of calcium low.

The number of fractures among children and young adults has increased, probably due to lower intakes of calcium. Pediatricians are also seeing the emergence of rickets, a bone disease that results from low levels of vitamin D. As these children get older, this calcium crisis will become more serious as the population starts to show its highest rate of osteoporosis and other bone health problems. Getting children to pay attention to their calcium needs is a challenge for scientists and educators. '"/> Salt in the body The benefits of salt in the body Sea salt contains about 80 mineral elements that the body needs.

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