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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.

• Marked by Teachers essays 46
• Peer Reviewed essays 14
1. ## Reproduction, Gamete formation and fertilisation

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A Muscle layer called the Dartos muscle relaxes in hot weather to drop the testes away from the body to keep them cool. In cold weather the muscle contracts to draw up the testes so they do not become too chilled. The spermatic cord suspends each testis within the s*****m, and contains the testicular artery and vein, lymph vessels, nerves, and the sperm-carrying vas deferens. Sperm Production Each testis is a mass of more than 800 tightly looped and folded vessels known as Seminifeous tubules.

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2. ## Investigation of the effect of different carbohydrate substrates on yeast growth

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Maltose will have a slight effect on yeast growth. Sucrose will have the least effect on the yeast growth. Null hypothesis (necessary for statistical model: Chi square) Glucose will have no effect on yeast growth. Maltose will have no effect on yeast growth. sucrose will have no effect on the yeast growth. Variables Independent; glucose, maltose and sucrose (the carbohydrates) Dependent; the growth of the yeast cells (numerical growth/ change in population) is what will be measured and the yeast cell will be counted by a method called: "The Haemocytometer technique" using a light microscope and a counter to count the yeast, use of a microscope will be required due to cell size being no bigger than �10�m.

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3. ## To investigate the effect of trampling on the frequency of creeping moss - Plan

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Plants growing on shallow soils also have less mechanical support than those growing in deep soils. Trees growing in shallow soils are more easily blown over by wind than are those growing in deep soils." (cals.arizona.edu/pubs) Independent Variable: Soil Depth (trampling) Variables: My measured factors are soil pH and soil temperature. My assumed factor is light intensity. My first variable is soil pH. I will be measuring this to find out if it will have any impact on the abundance of creeping moss.

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4. ## Investigating how sugars are metabolised by yeast

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* Repeat this exercise 3 times for each sugar for reliability. * Calculate the difference between start and end volume to find out the amount Carbon Dioxide produced. Background Information Respiration is the release of energy from [1]glucose or other organic substances. Energy is required for growth, repair, movement and other [2]metabolic activities. There are two main types of respiration, aerobic and anaerobic. Aerobic respiration takes place in the presence of oxygen. This is the normal type of respiration that takes place in all living cells. However, in some cases respiration takes places in the absence of oxygen and this is called anaerobic respiration.

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5. ## Homeostatic Control of Blood Glucose Levels

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Essentially, blood glucose levels are controlled by the pancreas. It is in this organ that areas of cells called the Islets of Langerhans exist, which consist of alpha cells and beta cells. These cells monitor blood glucose and secrete the hormones glucagon and insulin respectively. Glucagon and insulin regulate blood glucose levels through their antagonistic and opposite effects in a system of negative feedback. The most important effects of insulin work to lower blood glucose levels, which may be too high following a large, carbohydrate heavy meal for example and are as follows.

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6. ## The effect of caffeine on heart rate

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This made the results valid as caffeine was the only variable that was manipulated in the experiment. Ethics: Since this experiment involves living organisms, ethical issues were raised. Consideration has been taken into account and the following guidelines were used: * Make sure the Daphnia is kept in a natural environment comfortably * Don't leave them in the solution of caffeine for too long * As they are God's creatures, some religions believe that humans were given responsibility to look after the world.

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7. ## Compare and Contrast the Transport System of a Mammal and a Plant

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A slower blood flow is desired when going to the lungs to allow more time for gas exchange and prevent damage on lung tissues. Blood never leave the vessels during transport so that a quicker blood flow rate can be obtained and this also allows vasoconstriction or vasodilatation to occur. The Transport System of Plants: Plants also require a regular supply of oxygen and nutrients, yet their requirements differ from those of animals in several ways. Instead of oxygen, carbon dioxide is required for photosynthesis while oxygen is the waste product.

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8. ## Properties of Water

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Its properties as a solvent depend on the fact that it is a polar molecule. A polar molecule is one which has an unevenly distributed charge. Water is made up of 2 oxygen atoms and one hydrogen atom. Oxygen has a bigger nucleus and because of this, the oxygen attracts electrons more strongly ten oxygen. Therefore, oxygen is slightly negative and hydrogen is slightly positive. Water's polarity is also caused by its shape. Instead of being a straight line (180�), the angle between the two hydrogen atoms is 105�: It can also act as an ionic substance because of this property.

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9. ## Daphnia experiment - Does caffeine affect heart rate?

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They mature in just a few days, so it does not take long to grow a culture of test organisms. They possess fairly transparent bodies which make observation on heart rate in daphnia fairly observable. Foster, in the journal of Biological education (1997) provides a method using a stroboscope to freeze the motion. Use of the stroboscope may overcome the problems of counting faster heart rates. However, we would not recommend this method. Positioning the light sources of the strobe is tricky.

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10. ## Daphnia experiment - Does caffeine affect heart rate?

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The more caffeine present in the bloodstream, the faster the heart rate. Equipment * Culture of Daphnia (water fleas) * Cavity slides * Pipette * Distilled water * Caffeine tablets * Cotton wool * Standard glass wear (beakers, measuring cylinders) * Stop clock * Paper towels * Microscope Procedure 1. Using 6 beakers, label and set up the following solutions using the correct volumes: - % Weight per volume 50ml (Total volume) Caffeine solution (ml) Water pond (ml) 0.5 5 5 0.4 4 6 0.3 3 7 0.2 2 8 0.1 1 9 0.0 0 10 2.

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11. ## This is an experiment to find out what factors affect osmosis in potato chips.

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Measuring Cylinder- To measure out the amount of solution accurately 15. Calculator- To calculate the percentage mass change Diagram showing how some of the apparatus will be used. Measurements We are going to weigh the potato chips before they are put in the varied sucrose solution and then after and calculate the total percentage mass change. I feel that the accuracy of the investigation and the simplicity would be jeopardised if we chose just to try and get the weight of the potato chips the same before putting them in the solution and then getting a weight difference after.

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12. ## Investigation to Calculate the Water Potential of Potato Tissue.

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Table 1: Mass difference of potato tissue in varying concentration of Sucrose solution. Boiling tube Concentration of Sucrose (aq) Initial weight of potato (g) Final weight of potato (g) Mass gain (g) % Mass gain 1 0 3.08 3.30 0.20 6.5 2 0.25 3.10 3.14 0.04 1.3 3 0.5 3.07 2.94 -0.13 -4.2 4 0.75 3.09 2.91 -0.18 -5.8 5 1.0 3.04 2.75 -0.29 -9.5 With the above table using the concentration of sucrose concentration against the percentage mass gain, a graph was plotted. The second graph plotted with the use of a table showing solute potentials of given sucrose solutions at 20 �C.

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13. ## Investigating osmosis in plant tissue.

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We have done an experiment to try and investigate osmosis further; we performed an experiment with visking tubing and a glucose solution. We filled up a visking tubing with water, and weighed it, we then placed the visking tubing inside a glucose solution that had a very low water concentration. After approximately twenty minutes we took the visking tubing out of the glucose solution and weighed it again, it had lost weight. This proves our theory that osmosis can only move along the concentration gradient.

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14. ## Can heart disease be prevented?

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This deposit is also known as atheromatous plague or an atheroma. Rheumatic heart disease used to be one of the most serious heart diseases in both children and adolescence as it involves damage to the entire heart and its membranes.It is a complication of rheumatic fever and usually occurs after attacks of rheumatic fever. (1) This condition has been greatly reduced with the widespread use of an antibiotic effective against the streptococcal bacterium which causes rheumatic fever. There are three main types of congenital defects.

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15. ## Difference in number of Stomata in different leaves

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3- Add nail varnish to the bottom of the leaf 4- Wait for the nail varnish to dry, you can place it on a warm object to dry it quicker but it should no be placed on a hot object as it can affect the leaf. 5- Once the nail varnish is dry put tape on in and then remove the tape, making sure the nail varnish sticks to the tape. 6- Stick the tape on the microscopic slide 7- Count the number of stomata in your marked areas 8- Add the results to a table (see Table1)

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16. ## The Importance and Biological Functions of Carbohydrates.

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The carbohydrate in milk is lactose and it is formed from Glucose and galactose. Important polysaccharides include Starch, Glycogen and Cellulose. They are all made up from Glucose but have different functions. Starch is the main store of carbohydrates on plants, Glycogen is the main store in animals and Cellulose is important for plant cell walls. All have the formula C H O but they are structurally different. This gives them different properties. Glucose exists in two different forms, ? and ?. The carbons are numbered as shown. Carbon number one has a hydroxyl group that can be in the up position or the down position. ? is in the down position and ?

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17. ## Infertility and Assisted Reproduction Technology.

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grows outside the uterus. Other conditions that can occur are Ovulation problems are any condition (usually hormonal) that prevents the release of a mature egg from an ovary. Poor egg quality is when eggs that become damaged or develop chromosomal abnormalities cannot sustain a pregnancy. This problem is usually age-related. The egg quality declines significantly in the late 30s and early 40s. Polycystic ovary syndrome is when the patients whose ovaries contain many small cysts have hormone imbalances and do not ovulate regularly. Female tube blockages are blocked or damaged fallopian tubes prevent eggs from getting to the uterus and sperm from getting to the egg.

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18. ## the heart

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Main: The heart is a muscular organ that it part of the cardiovascular system. It is located between the lungs, behind the sternum and is approximately the size of a fist. The heart is protected by a membrane called the pericardium which surrounds the heart and secretes a fluid that reduces friction when the heart beats. The atria's job is to receive blood and the ventricles job is to be filled with blood and send it to everywhere in the body. There are three layers which make up the wall of the heart. The outer layer is epithelial tissue, the middle layer is cardiac muscle and the inner layer is connective tissue.

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19. ## Osmosis. Finding the water potential of potato tuber cells

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I know form prior work, investigation and study that the water potential will be around 0.4M. So I have decided to use 6 different solutions that are on either side of this figure. Table 1 below shows which molarity's I will be using. Table 13 Molarity (mol dm3) Water Potential (kPa) 0.00 �0 0.05 -130 0.10 -260 0.15 -410 0.20 -540 0.25 -680 0.30 -860 0.35 -970 0.40 -1120 0.45 -1280 0.50 -1450 0.55 -1620 0.60 -1800 0.65 -1980 0.70 -2180 0.75 -2370 0.80 -2580 0.85 -2790 0.90 -3000 0.95 -3250 1.00 -3500 Making the solution Of these 7 solutions I will have to make myself form the 1 mole stock sucrose solution.

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