BIOLOGY

BIO3X EMPA

REVISION GUIDESection 1: Graphs and Processing Data

Identifying variablesIndependent variable This is the variable that you decide to change.

Dependent variable The variable that changes as a due to the independent variable changing. This is the variable you measure.

Control variable This variable must be kept the same to make the experiment valid.Control variables also allow a valid comparison to be made, as it ensures only the independent variable is bringing a change in the dependent variable.

Drawing tablesThree marking criteria:1. Independent variable is in the first column.Dependent variable is in the second column.

2. Full headings so that an observer could look at the table and understand the experiment.e.g. Time taken for solution to turn from pink to completely colourless.

3. Units in brackets in the heading, e.g. (seconds), (cm3), (big booty hoes).

Example:You are investigating how the temperature of an enzyme solution affects the time it takes for the reaction to complete (the time it takes for the solution to go from milky to colourless).Temperature of the enzyme solution (C)Time taken for the reaction to complete, as shown by the solution turning from milky to colourless (seconds)INDEPENDENT LEFTDEPENDENT RIGHT.REMEMBER MOFO

123FULL TITLE,.LAZY MOFO

AverageUNITS,. STUPID MOFO

Data typesCategorical data Discrete/non-continuous data e.g. eye colour, blood group.Continuous data Quantitative data on a continuous scale, e.g. time, temperature.

If the independent variable is categorical, draw a bar chart. If continuous, draw a line graph.

GraphFive marking criteria:1. Scale Be sensible with your intervals, and remember 2/3 of the graph paper must be used. Start from zero on the y-axis whenever possible.

2. Title Make it obvious to an observer precisely what the graph is trying to demonstrate make it as detailed as possible and mention both your independent and dependent variable.

3. Units Easy to miss, dont be a moron and miss out on this mark it should just be copying off your table.

4. Label This is just copying off the table again write in full, the rules havent changed.

5. Line Clearly plotted points (sharpened pencil) joined by a ruler. Dont extrapolate.

S T U L L get it in your f***ing SKULL. Five easy marks.

pHTime taken for the solution to turn clear (s)Rate of enzyme reaction (s-1)

3101/10 = 0.1

7141/14 = 0.07

10211/21 = 0.05

Processing dataThere might be a sneaky little extra mark on the table or the graph this will be to process the data.For example: You are asked to investigate the rate of an enzyme reaction in different pHs, but you were asked to measure the time taken for there to be a colour change. Simple sh*t here all you have to do is divide 1 by the time taken to give the rate in s-1.Section 2: Evaluating Experimental Data

Limitations and errors No set of data can be perfect there must have been some limitations or sources of error in the experiment.Identifying them can be tricky, but consider the following:1. Consider the control variables how easy are they to control?e.g. Add three drops to each test tube how would you control the size of the droplets?

2. Was the experiment repeated? This would increase the reliability, along with the accuracy of the standard deviation.

3. Was it difficult to measure the dependent variable? Subjective things like colour change, meaning it is difficult to judge the end point. Situations like where it is difficult to judge the end temperature as the temperature will continue to rise after the time has finished. Was the reaction very quick, and over too quickly for accurate measurements to be taken?Do not mention limitations to do with your own ineptitude e.g. I find it hard to find my pulse you just look retarded and dont get the mark.Examples:You are trying to view a cell under a microscope under a microscope using a slide you prepared with a scalpel. Scalpel is not precise enough to isolate one cell; multiple layers of cells will be seen.You are judging potometer bubble movement in a certain time period during a transpiration experiment. Difficult to judge the distance moved as the bubble will continue to move after the time has finished.

ReliabilityQuestion comes up all the time. This is all you have to say for three easy marks:How can you improve the reliability of the mean?1) Take repeats.2) Identify anomalies so that they can be removed before calculating the mean.3) Reduces the effect of extreme values on mean.They might ask the question the other way around:Why do we take repeats in this experiment?1) To improve the reliability of the mean.2) Identify anomalies so that they can be removed.3) Reduces the effect of extreme values on mean.

Accuracy and precision Accuracy The choice of equipment so that the reading is closest to the true value.e.g. Gas syringe as opposed to measuring cylinder.Precision The use of measuring equipment with smaller intervals between units of measurement.e.g. mm as opposed to cm.BiasThis is removed by selecting a sample at random, ensuring that the selected sample is representative of the whole population.

Sample sizeThe larger the sample size, the more representative it is of the whole population.

Control experiment vs Control variableControl experimentControl variables

An experiment in which you remove the independent variable being investigated.This allows the effect of the independent variable on the dependent variable in other experiments to be seen as they can easily be compared to the control experiment.This shows whether the change in the dependent variable is due to the independent variable or another confounding variable.A variable which is kept constant.This is done to ensure results are valid and allows a valid comparison to be made.This is because only the independent variable causes the change in the dependent variable.NOTE: State the effect not controlling this variable would have on the dependent variable.

Standard deviation

Standard deviation is the spread of all the data around the mean.

Therefore a large standard deviation means a large spread of data about the mean. This means there is greater variation in the data set.

A small standard deviation means a small spread of data about the mean. This means there is less variation in the data set.

Why use standard deviation rather than range?Always say the following three points: SD shows the spread of all data values about the mean. Range shows just the highest and lowest values/extremes. Range is therefore more affected by outliers.Also, if there are more than five values add: Standard deviation allows for statistical use allowing you to tell if differences are statistically significant.

You should be familiar with the appearance of a normal distribution curve for a set of data.

Standard deviation error barsOn graphs standard deviation for each data set is marked by error bars. You will be expected to comment on these if asked to describe a graph showing them.Note these two things concerning standard deviation bars:1. The relative sizes of the SD bars. Larger bars mean greater SD, and smaller bars mean less SD. Comment on how this affects the variation of the data set.

2. Mention any overlaps or lack of overlap in the standard deviation bars. This is an indication of the significance of the differences in the data. No overlap means there is a statistically significant difference. Overlap means no statistically significant difference.

ExampleIn this example:Sugar maple has the greatest variation in the effect of full sunlight as it has the largest standard deviation.Red maple shows the least variation as it has the smallest standard deviation.There is no statistically significant difference in the effect of full sunlight on Sugar Maple and Black Maple as the SD error bars overlap.There is, however a statistically significant difference between the Sugar Maple and Red Maple as the SD error bars do not overlap.

Calculating standard deviation on a calculator1. Go into variation mode by entering: MODE followed by STAT followed by 1-VAR.

2. Enter the values, pressing = after each one. Press AC.

3. Find the value for the standard deviation by pressing: SHIFT followed by 1. Select Var and then select sx.Data analysis from a graph or tableWhen describing the results from a table or graph, make sure your answer takes the SE format: (not SEE we arent being asked to explain).Statement The pattern or trend you see.Evidence Give some data from the graph to back up your statement.Top TipChunk up the data split graphs into segments based on things such as changes in gradient/ plateaus. Give the values at which these patterns occur, and note any maximum/minimum values in the data.Make sure you look at overall trends as opposed to individual figures.

ExamplesDescribe the results from this graph. (2)

Statement As the temperature increased so did the enzyme activity, but then it decreases steeply.Evidence It increased from 0 - 40C, then decreased from 40- 65C.

Describe the relationship between light intensity and photosynthesis using data from the table. (2)Statement There is an increase in photosynthesis when the light intensity increases at first, but then it levels off (plateaus).Evidence When the light intensity was 1 unit the number of bubbles was 43, this increased until 3 units to 122 but then it levels off after that.

Correlation and causationA graph may suggest that there is a correlation between two variables. Does this prove that the change in the independent variable will cause the dependent variable seen?How to answer this: NO only shows a correlation - this does not necessarily prove causation May be other factors involved. Such as _____. (Give some suggestions of other factors known to affect the variable).Example:Does this prove that smoking causes cancer? (3)

NO only shows a correlation. No actual evidence to prove that it causes lung cancer.Might be another factor causing this, such as changing diet/exercise.

Predicting data valuesIf asked how you would go about predicting data values from data gathered in an experiment:1) Plot the independent variable on the x axis against the dependent variable on the y axis.(You must name them and say which axis).2) Draw a line/curve of best fit.3) Extrapolate to predict the value of the data.

Percentage change calculationsPercentage change = End value start value x 100 % Start valueThis holds true for all calculations of percentage change use it for percentage increases and decreases in the case of a decrease just convert the negative value into a positive percentage.Evaluating dataThe big evaluation question three, maybe four marks. Remember you have to argue equally for both sides, no matter how much you have to bullsh*t. Here are some ideas for pros and cons that you can use to argue: Sample size. Usually you state this is small so conclusions unreliable. The sample will also not be representative of the population. If this is mentioned in the information given, you must refer to it.

Is the organism the same species that the conclusion is being drawn for? e.g. tested on rabbits, but conclusion is applied to humans. If not, their response to the independent variable may be different.

Subjective measurements. e.g. a pain scale used by a patient is unreliable as they could easily over/underrate their feelings, or any arbitrarily divided scale (e.g. Healthy, Slightly injured, Severely injured).

Limitations to the experiment. e.g. each mouse was fed three drops this reduces the accuracy of the experiment.

Are they tested on cells/tissues (in vitro) rather than whole organisms?

Standard deviation Are there overlaps/lots of spread of data about the mean?

Is there a source of bias? e.g. only one population, age group etc.? And never miss out the fact that: Correlation does not prove causation. Always then state that another variable may be causing a change in the independent variable with a named example.

Top TipsStep 1 Identify the facts youve been givenThere will be some information concerning an experiment in the written paper. You have to be able to glean through the information to find the stuff thats relevant, e.g.A group of scientists tested a new drug Novartis on a group of 2,560 heart cells taken from mice of a variety of ages and both sexes. They found that there was a significant effect on decreasing the effect of heart disease. I found the following pros: 2,560 heart cells Thats a large sample size, increasing the reliability of the results. Variety of ages and both sexes The experiment has taken into account different confounding factors and reduces bias. There was a significant effect The results indicate that there is an effect.And the following cons: Mice Obviously a different species with very different physiology. Heart cells Experiment carried out in cells (in vitro) as opposed to in the whole organism.

Step 2 Respond to the statementThere will be a statement like: A newspaper claimed from this that Novartis was the new wonderdrug for curing high blood pressure. Evaluate this claim.Use the points you have found from the earlier stage, and then relate back to the statement. Add something like: Therefore, we cannot predict the effect on humans.

Section 3: Application of Syllabus Knowledge

You will investigate water movement through plants. In addition, you will need tounderstand the following topics: The effect of lifestyle on the heart The biological basis of heart disease Mitosis Mass transport

Water Movement through PlantsThis will probably be the practical element of the EMPA as found in papers 1 and 2 so whilst referring back to some theory you should bear in mind the practical elements of this topic.Roots and water transport

The roots of a plant extend underground in order to absorb vital water and nutrients. The structure of a typical root is as follows: A thin walled outer layer known as the epidermis, upon which there are many root hair cells. Water enters these cells from the surrounding soil by osmosis.

The inner part of the cortex is the endodermis, which is a single layer of cells around the vascular bundle containing the xylem and phloem. The walls of the endodermal cells are impermeable to water due to a waxy waterproof lining this is called the Casparian strip.

Water can take two possible routes from the root hair cells to the xylem: The apoplastic pathway:

Water moves only through the cellulose cell walls of the cortex by cohesion tension of water molecules. The cellulose is made of fibres with water filled spaces to give little resistance. However, once the water reaches the impermeable Casparian strip it cannot pass and is forced to pass through the protoplast to join the symplastic pathway.

The symplastic pathway:

Water passes through the cytoplasm from cell to cell along the water potential gradient maintained by root pressure by osmosis. The cytoplasms of neighbouring cells are joined by fine tubes known as plasmodesmata which form an unbroken water transport pathway.

Found within the cell membrane, are carrier proteins which allow ions, such as nitrate, to be moved from the cortex into the xylem by the process of active transport.

As the dissolved ions are now found within the xylem vessel, this can be termed a hypertonic solution with a higher water potential than the cortex cells. As a result, water moves from the cortex into the xylem by the process of osmosis.

Cohesion tension

When water molecules evaporate from the stomata, the hydrogen bonds between water molecules pull water up the xylem. This pull is transmitted all the way down through the roots, forming an unbroken stream of water molecules. It is unbroken through the xylem due to adhesion from the xylem walls.

Transpiration

The transpirational stream is the continuous passage of water from the roots of a plant up to the leaves. The speed of the transpiration stream is dictated by the rate of evaporation of water out of the plants exchange surfaces.

The rate of transpiration is affected by:

Temperature:

Increased temperature increases the kinetic energy of water molecules. This makes water molecules move faster. This increases the rate of evaporation and diffusion of water molecules out of the leaf.

Light intensity:

More stomata open to allow more carbon dioxide to diffuse the leaf for photosynthesis. This means more water is able to diffuse out of the leaf as there is an increased surface area for diffusion.

High wind speed:

Water vapour is removed quickly from outside the leaf by air movement. This increases the water potential gradient between the moist air in the air spaces and outside of the leaf. This increases the rate of diffusion of water out of the leaf.

High humidity:

Diffusion of water vapour out of the leaf slows down as the leaf is already surrounded by moist air. This is because the water potential gradient has been reduced (or removed). This decreases the rate of diffusion of water out of the leaf.

Transpiration during the day

During the day there is increased light intensity and temperature, increasing the rate of transpiration as detailed previously.

Increased evaporation and diffusion of water out of the leaves decreases the water potential of mesophyll cells in the leaves. This increases the rate of osmosis between the xylem and mesophyll cells.

This means there is more tension in the xylem as more water molecules are being drawn up to replace them; this tension is caused by the cohesion between water molecules (due to hydrogen bonds).

This reduces the diameter of the xylem vessels as there is more adhesion of water molecules to the walls of the xylem, pulling them together and making them narrower.Adaptations of the xylem vessel:

They are long cells/tubes with no end walls. This maintains continuous water columns. They have no cytoplasm and no organelles which allows easier water flow. They have lignin which provides support to withstand tension. The lignin is waterproof to keep water in cells; There are pits in walls to allow lateral movement.

AdaptationHow it reduces water loss by transpiration

Reduced number of stomataReduces the surface area through which water can diffuse.

Leaves curledReduces surface area for water vapour loss & reduces the water potential gradient by keeping moist air near the leaf

Thick waxy cuticle or stems and leavesReduces evaporation through cuticle

Stomata in sunken pits or groovesMoist air is trapped close to leaf - reduces water potential gradient

Fleshy or succulent leaves & stemsWater is stored in leaf and stem tissue so it is readily available it times of low water availability

Leaf surface covered with fine hairsMoist air is trapped close to leaf - reduces water potential gradient

Leaves reduced to spines or scalesReduces surface area to volume ratio for evaporation and diffusion of water vapour to occur over.

Deep root systemDeep roots to tap into lower water tables. Shallow roots to quickly absorb surface moisture from overnight condensation

Xerophytes Plants which live in hot/dry conditions and have adaptations to minimise water loss are known as xerophytes. These adaptations include:

Practical Elements of Water Transport

The rate of transpiration can be measured using a potometer:

A cut shoot is placed in one end of a capillary tube. A single air bubble in the capillary tube is formed. As water is drawn up through the shoot, the air bubble moves. The speed at which the air bubble moves can be used to determine the rate of transpiration.

Precautions such as cutting the shoot under water and making the joint water tight ensures that air bubbles do not enter which would block the xylem.

Factors affecting the rate of water loss from a plantAlong with the usual factors (temperature, light intensity, humidity, wind speed), surface area of the leaves should be controlled, as this means that there is the same number of stomata through which water can escape.To control this, leafs from the same species of plant, and the same number of leaves in total should be used.Limitations of the experiment

Transpiration is not just used to provide water for photosynthesis; only 1% is used for this purpose. The water can also be used for:

Keeping the cells turgid. Acts as a solvent for transport. Component of cell cytoplasm. Medium for chemical reactions. Keeping plant cells cool.

This means it should not be assumed that the same volume of water entering the plant is being lost.

The Biological Basis of Heart Disease

Coronary heart disease (CHD) is caused when the heart receives an inadequate amount of blood or oxygen via the coronary arteries.This oxygen is needed for the cardiac muscle to respire and generate sufficient energy for its contractions. A lack of oxygen can lead to myocardial infarction, i.e. a heart attack.The following problems can lead to CHD:AtheromaAn atheroma is a fatty deposit in arteries. It forms within the endothelium of the arteries as streaks. It is caused by damage to the endothelial lining of an artery. An inflammatory response causes the aggregation of white blood cells which take in LDLs/cholesterol and form the streaks.An enlarged streak is known as an atheromatous plaque, which also contains cholesterol, fibres and dead muscle cells. An atheroma is dangerous as it bulges into the lumen of an artery, narrowing it and reducing blood-flow.Someone suffering from these plaques is said to have atherosclerosis.ThrombosisIf an atheroma breaks through the epithelium of a cell it is known as a thrombus.Thrombosis is dangerous as it causes platelets to aggregate and form a blood clot. This could block the vessel and increase the likelihood of myocardial infarction. Atherosclerosis increases the likelihood of thrombosis as the plaques stiffen and make the epithelium prone to damage.Aneurysm An atheroma can weaken the artery wall, causing it to swell. It can then burst, leading to haemorrhage (bleeding). Aneurysms in the brain cause strokes.The Effect of Lifestyle on Heart Disease

InheritanceSome people are genetically predisposed to some diseases.

DietA diet high in saturated fat, salt and alcohol can increase the risk by causing hypertension.

Cholesterol levels LDLs can cause CHD as they can infiltrate the endothelial lining of the arteries and cause an atheroma. HDLs remove cholesterol from tissues and organs and transport it to the liver to be excreted; they thus protect the arteries from disease.

AgeThose most at risk are over the age of 40.

GenderWomen are more likely to suffer than men.

High Blood PressureHypertension can be caused by stress, smoking, diet, inactivity. It causes CHD as heart has to work harder pumping blood into arteries with high pressure. High blood pressure in arteries means that aneurysms are more likely to form, which can burst and cause haemorrhaging. Artery walls can become thickened and hardened to resist higher pressure, restricting the flow of blood.

SmokingChemicals in tobacco smoke can increase the risk. Nicotine acts as a stimulant; it causes production of adrenaline, which increases heart rate and causes hypertension, increasing the likelihood of stroke. It also makes platelets in the blood stickier, increasing the likelihood of thrombosis. Carbon monoxide from cigarette smoke binds more strongly to haemoglobin in red blood cells than oxygen to form carboxyhaemoglobin. This means less oxygen is taken around the body, and the heart has to work harder to supply tissues with oxygen, increasing blood pressure. It can also cause oxygen deprivation to cardiac muscle during exercise, causing angina.

Physical InactivityExercise can help decrease the risk, as the stroke volume of the heart is greater, meaning it does not have to work as hard.

MitosisThis is the process of nuclear division which forms two genetically identical daughter cells, carrying the same number of chromosomes as the parent cells (diploid).

It is a continuous process, but is often arbitrarily divided into four phases:

Prophase: The chromatin in the nucleus shortens and thickens (supercoils) into chromosomes. They are visible as two sister chromatids joined by centromeres. The nuclear membrane disintegrates and disappears. The centriole divides in two and moves to the opposite poles. The daughter centrioles form the spindle apparatus: this is a network of microtubules which help to carry out mitosis.

Metaphase: The centromeres of the sister chromatids line up along the equator of the cell. The spindle fibres attach to the sister chromatids at the centromeres.

Anaphase: The spindle fibres attached to the chromosomes contract and shorten. This pulls the centromeres apart, causing them to split. This causes the sister chromatids to separate and migrate as individual chromosomes to the opposite poles of the cell.

Telophase: Then the two sets of chromosomes reach opposite poles the nuclear envelopes reform around them; the spindle apparatus disappears. The chromosomes uncoil and are no longer visible.

Mitosis is normally followed by cytokinesis. The cell membrane pinches and separates into two separate diploid cells.

Identifying stages of mitosis:

Mitosis and cancer

Cancer is a group of diseases caused by uncontrolled growth of cells.

It is caused by damage to the genes regulating mitosis and the cell cycle.

Treating cancer

Block the cell cycle to disrupt the cell division of new cancer cells using chemotherapy:

Prevent DNA from replicating (interphase) e.g. cisplatin.

Inhibit metaphase stage of mitosis by interfering with spindle formation e.g. vinca alkaloids.

Drug that prevents spindle fibres shortening (anaphase).

Mass TransportRefer back to water transport in plants.Mammalian blood transport

The circulatory system is used to transport nutrients and gases to cells by mass transport: the bulk transport of substances from one area to another by pressure changes (initiated by the heart). It also maintains concentration gradients and removes waste products. Mammals have closed circulatory systems with a network of blood vessels: arteries carry blood away from the heart, and lead to arterioles small, narrow-walled vessels connecting arteries to capillaries. Capillaries are microscopic vessels forming networks in the bodys tissues. They are connected via venules (narrow, vein-like vessels) to veins, which carry blood back to the heart.

Mammals also have double circulatory systems: blood passes through the heart twice in a single circuit of the body. The pulmonary circulatory system transports between the heart and lungs; the systemic circulatory system between the heart and the rest of the body. Each organ has a major artery and vein connecting it to the heart:

Brain = jugular vein/carotid artery. Liver = hepatic vein/artery. Stomach and intestines = gastric and mesenteric arteries; deoxygenated blood from the stomach and intestines passes through the hepatic portal vein to the liver before returning to the heart. Kidneys = renal vein/artery.

Arteries, capillaries and veins

Arteries carry blood under high pressure away from the heart. They have the following features:

The lumen is relatively narrow to maintain a high pressure. Thick layer of muscle fibres so that smaller arteries can be constricted (vasoconstriction) or dilated (vasodilation) to control the blood-flow through them. Thick layer of elastic fibres to maintain blood pressure in order for blood to reach extremities. It stretches in time with each contraction of the heart (systole) and recoils when the heart relaxes (diastole). This helps keep a relatively constant pressure. No valves; the pressure of blood is too high for backflow. Folded endothelial lining, to accommodate for the constriction and dilation of the arteries.

Arterioles are similarly structured, except they transport blood under lower pressure than the arteries in order to control the blood-flow into capillaries. This means their muscle layer is relatively thicker than the arteries, as when it contracts, blood flow into capillaries is restricted and controlled. The elastic layer is relatively thinner due to the lower pressure.

Veins carry blood back to the heart. They have the following features:

Wide lumen to allow least resistance to blood-flow. Thin muscle layer and elastic layer, as blood-flow is under lower pressure, and controlling it is not usually necessary. Valves present to prevent backflow of blood. Skeletal muscles which contract to raise pressure and force blood along. Smooth endothelial lining to reduce friction against the blood-flow.

Capillaries allow metabolic materials to be exchanged between blood and tissues of the body. The flow of blood in the capillaries is much slower to allow this to happen. It has the following features:

Very small lumen, wide enough to allow one red blood cell through at a time. The blood cells are squeezed against the ride of the capillary, reducing diffusion pathway and greater friction allows more time for diffusion. Increases the surface area of the red blood cell with the capillary for faster diffusion of oxygen. Endothelial lining is one cell thick, reducing the diffusion pathway for faster diffusion. Lining made up of flattened endothelial cells which again reduces the diffusion pathway. Fenestrations, small gaps in the walls, increase permeability for molecules passing out of capillaries. Numerous there are large numbers of capillaries throughout the bodys tissues, giving a large combined surface area.

Tissue fluid and lymph

Tissue fluid forms the immediate environment of most mammalian cells. It has specific chemical makeup and temperature etc. to provide optimum conditions for the cells.

Tissue fluid forms because of the high hydrostatic pressure at the arterial end of capillaries. This squeezes water and small molecules out of the capillaries in a process known as ultrafiltration. Tissue fluid, because it comes from blood, has a similar composition to plasma, but without the globular proteins these are too large to be squeezed out of the capillaries. This establishes a water potential gradient between the capillaries and the tissue fluid, known as osmotic pressure.

At the venous end, the osmotic pressure is greater than the hydrostatic pressure, and fluid moves back into the capillaries. Any excess tissue fluid drains into the lymphatic system.

The lymphatic system is a second circulatory system made up of lymph vessels which are similar to veins. Lymph, the fluid in the lymph vessels, is similar to tissue fluid but contains more fatty substances and white blood cells. Lymph flows slowly through the lymphatic system by external pressures such as from breathing or contraction of skeletal muscles. The lymph system re-joins the circulatory system through ducts at the vena cava.