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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. ## Sand Dune Succession Coursework

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This could be achieved by seaweed or driftwood lying on the beach. This dune is very unstable and could easily disappear as quickly as it was formed. The next sere is the fore dunes where sea couch grass and marram grass colonise. These plants are drought resistant xerophytes and are capable of withstanding burial by the shifting sand. As they grow up through the sand they trap more of it which results in the dunes increasing in height. The yellow dunes begin to show a greater diversity of plants as conditions become more idealistic.

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2. ## Biology coursework planning - the effect of lead chloride on the growth of cress seeds

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Lead is able to cross the cell membranes via voltage-gated calcium channels. These channels are for the transport of calcium. Lead blocks these channels and causes the inhibition of their activity, preventing calcium being transported. Plants require water for photosynthesis. Photosynthesis provides plants glucose, an energy source, which is needed for the plants to grow. When lead is present in high concentrations in the soil, it decreases the water potential of the soil. It therefore, has a lower water potential than the root cells, causing water to move from a region of higher water potential (root cells)

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3. ## Investigate the water potential of celeriac.

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The test tube will be used to provide a safe environment for the experiment to take place in. Test tube rack - this will be used to hold the test tubes in a steady position when the experiment is carried out. Prediction I predict that as the concentration of the sucrose solution increases, the mass of celeriac will decrease. I think this because, as the concentration of the sucrose solution increases, the water potential of the solution increases in negativity. So therefore as the molarity increases, the water molecules will travel by osmosis from the less negative celeriac to the more negative sucrose solution.

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4. ## Human Reproductive System

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It transports and store sperm cells that are produced in the testes. It also brings the sperm into maturity, since the sperm that emerge from the testes are immature and incapable of fretilisation. Glans penis The glans penis, commonly referred to as head of the penis, is a sensitive bulbous structure at the end of the penis. It is the conical expansion of the corpus spongiosum. It is anatomically homologous to the glans clitoris in females. Membranous Urethra The membranous urethra is a short portion of the urethra which is situated between the prostatic urethra and spongy urethra. It connects the parts of urethra passing through the prostate gland and the penis.

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5. ## Affect Of Varying Salt Concentration on Red Blood Cell Haemolysis

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Water molecules will diffuse from a solution with a high water potential to a solution with lower water potential down an osmotic gradient. "Osmosis is the diffusion of water molecules from a higher (less negative) water potential to a lower (more negative) potential through a partially permeable membrane" (Molecules and Cells Text book, P66) Water potential plays a key factor during the haemolysis of erythrocytes if the water potential within the cytosol is greater than that of the saline solution to which it has been introduced there will be a net movement of water molecules from the cytosol through the plasma membrane into the saline solution resulting in the shrinking of the red blood cell.

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6. ## Osmosis. Aim: To find the molarity of potato tubers cell sap. BIOLOGICAL KNOWLEDGE

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This reduces the concentration of free water molecules. Therefore, as the amount of solute increases, the number of free water molecules decrease. Osmosis takes place due to the difference in the concentration of free water molecules on either side of the semi-permeable membrane. It continues as long as the concentration in both sides of the membrane is equal. The sugar molecules on the right have 'captured' half the water molecules. There are more free water molecules on the left of the membrane than on the right, so water will diffuse rapidly from left to right across the partially permeable membrane by osmosis.

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7. ## Describe the molecular structure of starch (amylase), glycogen and cellulose, and relate these structures to their functions in living organisms.

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form. The chemical and physical properties of the two isomerism are the same. Many enzymes will however only act on one type. Glucose easily forms stable ring structures and most molecules exist as rings rather than a chain. Carbon atom no 1 however may combine with oxygen atoms on carbon no 5 to form a ring (two further isomers). ? D(+) Glucose � D(+) Glucose Alphadextroglucose Betadextroglucose Monosaccharides are sugars. They dissolve easily in water to form sweet solutions (saccharide refers to sweet or sugar). Monosaccharides have the general formula (CH2O)n and consist of a single sugar molecule (mono).

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8. ## Determining the Water Potential of Sweet Potato Tissue

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of a solution. This value is therefore always negative and the symbol for solute potential is ?s. WATER POTENTIAL is a measure of the tendency of water molecules to move from one place to another. The symbol for this is ?. PRESSURE POTENTIAL is the contribution made by pressure to increase the ? of a solution. It is therefore positive, and its symbol is ?p. The more solute the more negative the ? becomes: the ? of pure water is therefore zero. As the solute molecules prevent the water molecules leaving a solution, the ? of the solution will be a negative value.

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9. ## The Effect Of Temperature On The Permeability Of The Cell Membrane

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Temperature has an affect on membranes. In this experiment I will be looking at how temperature has the effect on membranes and what factors increase and decrease it. The cell membrane controls the substances moving into and out of the cell. The structure of the cell membranes is proteins floating in it. The proteins span the membrane and touch the inside and outside of the cell. The cell membrane is between 6-8nm thick and contains many distinct molecules. The fatty acid tails are non-polar which is difficult for polar molecules/ions to pass through them.

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10. ## Effect of temperature on membranes

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The phospholipid is made of two parts that is the polar hydrophilic (water-loving) heads and the non-polar hydrophobic (water-hating) fatty acids tails. In the cell membrane, the hydrophilic heads point into the water on both external surfaces of the bilayer while the hydrophobic tails are protected in the middle. Various types of protein which are embedded (integral proteins) or attached on the surface of the bilayer (peripheral proteins) are found within the bilayer. There are also cholesterol present in the bilayer to strengthen it and make it more flexible and less permeable to water-soluble substances.

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11. ## What is Type 1 diabetes

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The hospital healthcare team dietitian, general practitioner and diabetic nurse are all on hand to give advice and guidance. Ways to help yourself Keep an eye on any signs indicating either high or low glucose levels. Learn how to measure glucose levels and do it regularly. The most important piece of equipment is the home blood glucose meter, which enables you to measure your blood glucose levels and control your insulin dose. Try to follow the diabetic diet as rigorously as possible.

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12. ## The comparison of antibacterial properties of herbal products and standard antibiotics

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* Broad spectrum antibiotics- these are used to destroy a large range of bacteria. * Narrow spectrum bacteria- these are specific, and are only effective against minimal numbers of bacteria. This investigation will entail the use of penicillin and streptomycin, which are both narrow spectrum antibiotics. Penicillin, being the first discovered antibiotic, has a mode of action that involves interference with the formation of small peptide chains cross-linking in the peptidoglycan; the main wall polymer within bacteria during cell wall synthesis.

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13. ## "An investigation into the Respiration of Carbohydrate Substrates by Yeast."

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According to the Collision theory however, in order for a reaction to take place a certain level of energy, called the activation energy, must be reached. This energy needs to be reached by the particles colliding in the right way and fast enough, so a reaction can take place. By giving the particles more energy it encourages more to collide therefore the activation energy can be reached and a reaction can happen. The kinetic theory explains the effect of temperature, volume and pressure on the number of collisions.

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

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It is the most commonly used mind-altering drug in the world. When used in moderation, caffeine acts as a mild stimulant to the nervous system, blocking the neurotransmitter adenosine and resulting in a feeling of well-being and alertness. Also, it is found that caffeine binds to receptors on the surface of heart muscle cells which leads to an increase in the level of cAMP inside the cells (by blocking the enzyme that degrades cAMP), mimicking the effects of epinephrine (which binds to receptors on the cell that activate cAMP production). cAMP acts as a "second messenger," and activates a large number of protein kinase A (PKA; cAMP-dependent protein kinase).

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