WELCOME TO LIFE SCIENCES

Transcription

1 WELCOME TO LIFE SCIENCES GRADE 10 (your new favourite subject)

2 Scientific method Life science is the scientific study of living things from molecular level to their environment. Certain methods are generally used in order for a study to be accepted as science. These methods include: Formulating a hypothesis Carrying out investigations and experiments as objectively as possible to test the hypothesis The results are analysed, evaluated and debated before the community of scientists accepts them as valid

3 Scientific observations All scientific investigations are a result of observations of aspects of the world we live in. Based on these observations scientists ask questions about how the world works. An investigative question is a question formulated from observations. Scientific investigation Investigations involve written work planning, recording data, experimenting and reporting and practical work in the lab or field.

4 Scientific method Scientist generally conduct investigations in a similar way. This method is referred to as the scientific method. 1. Stating a hypothesis It is a tentative explanation for an observation which can be tested by an investigation or experiment. A hypothesis leads to an prediction about the investigation and it can be accepted or rejected based on the result of the investigation. An example of a hypothesis: The ph has an effect of the growth rate of plant A.

5 2. Designing a method for your investigation Research, plan and draw up a step-by-step method for your investigation If appropriate, compare your chosen method with other methods and give reasons for your preference. Make sure you consider the following: List all apparatus and materials needed for the investigation Consider experimental procedures that would minimise experimental error. List all the safety precautions that should be taken Make sure you identify all the variables in the experiment. A variable is any characteristic or property able to take any one of the range values (a factor that can change). Investigate the effect of varying Aim On the following Independent variable Variables Dependent variable Temperature Enzyme activity Temperature Enzyme activity Light intensity Rate of photosynthesis Light intensity Rate of photosynthesis Soil ph Plant height at age 3 months ph Plant height

6 Investigations test the effect of changing one variable on another. The variable that the investigator WILL CHANGE = INDEPENDENT VARIALBE The variable that will change as a result of the changes made = DEPENDENT VARIABLE The variables that are kept CONSTANT throughout the experiment = CONTROLLED VARIABLE

7 3. Collecting and presenting data (Results) Perform the investigation, make observations and record the data obtained. Record this raw data in a table. Make use of the following guidelines when creating tables: A table heading must be present and it should include all the variables represented in the table. Each column should have an appropriate heading. The units of measurement should be included in each column heading and should not appear in the table itself. Simple calculations to check possible relationships should be included in the table. (Pencil and ruler)

8 4. Identifying patterns in data and drawing conclusions Identify and explain the relationships, patterns or trends in the results and match these to the hypothesis. The conclusion interprets the data and relates it back to the aim of the investigation. You will need to identify if your hypothesis was correct or not. If the hypothesis was correct then you need to verify the results. If the hypothesis was incorrect then a new hypothesis must be generated. Mention all factors that could possibly interfere with the results and influence the outcome of the experiment. Evaluating the investigation is part of the discussion. It justifies the findings in the conclusion by considering the validity of the method and the reliability of the results.

9 Important biological principles RELATIONSHIP BETWEEN SURFACE AREA AND VOLUME This relationship has important implications for organisms. REMEMBER: Volume: = length x breadth x height; measured in cm 3 Area = length x breadth; in cm 2 Surface area = the sum of the six surfaces of the cube; and measured in cm 2

10 Important biological principles RELATIONSHIP BETWEEN SURFACE AREA AND VOLUME This relationship has important implications for organisms. REMEMBER: Volume: = length x breadth x height; measured in cm 3 Area = length x breadth; in cm 2 Surface area = the sum of the six surfaces of the cube; and measured in cm 2 Surface area 6(1x1) = 6cm 2 6(2x2) = 24cm 2 6(3x3)= 54 cm 2 Volume 1x1x1 = 1cm 3 2x2x2 = 8cm 3 3x3x3 = 27cm 3 Surface area : volume 6:1 3:1 2:1

11 It can be seen from the previous slide that the volume of the biggest cube is 27 times larger than that of the smallest cube, but its surface area is only 9 times larger. Therefore: the surface area to volume ratio of the big cube is much smaller (2:1) than that of the smaller cube (6:1) So we can say that the smaller the volume, the larger the surface area to volume ratio. This principle is very important in living organisms, the surface area of an organism is the part that is in contact with the environment. Small organisms, such as unicellular organisms, have a large surface area to volume ratio. This means that all parts of the organism are close to the surface. This facilitates diffusion Larger organisms, like vertebrates, have a small surface area to volume ratio. This means that many internal tissues are not close to the surface of the animal.

12 Biological drawings In Life Sciences you will be expected to make drawings of your observations and interpretations, and also to illustrate the build of a structure. The following guidelines must be followed when making a drawing: Use a sharp HB pencil to draw Drawings must be an appropriate size so that all labelled parts are clearly visible Use continuous smooth lines (no sketching) Do not shade your drawings; this makes them unclear Labels and label lines must be done in pen Label lines must be drawn with a ruler and they must not cross each other The label lines must point to the exact labelled part and it must not end in an arrow head When making a drawing of an object that is being studied under a microscope; only draw what you see A drawing must have an appropriate heading that describes it If required, indicate the scale of the drawing alongside the heading.

13 Graphs Graphs and charts condense large amounts of information in a format that is easier to understand, showing important points clearly and effectively. Line graphs show the relationship between two types of information where the independent variable is continuous. Line graphs are useful in showing trends over time and are often used for biological data. Bar graphs show different categories of data and are used when the independent variable is not a set of continuous numbers or continuous groups (discontinuous data). They are best used to compare values across categories. Histograms have connected bars displaying continuous data. They are used when the values of the independent variables are continuous but fit into categories or groups that follow on after the other. Pie charts are circular charts used to compare parts of the whole. They are divided into sectors that are equal in size to the quantity represented. They are used for discontinuous data.

14 How to draw a line graph Step 1 Identify the dependent and the independent variables from the information you are given (usually in table format). Table 1 Air temperature recorded over a 24 hour period

15 Dependent: This is the variable or factor that is being measured, i.e. the temperature in degrees Celsius in this example. Independent: This is the variable that the investigator can change. The dependent variable changes as the independent variable changes, i.e. the time in hours in this example. Step 2 Draw a set of axes and label the X and Y axes. The dependent variable goes on the Y-axis and the independent variable on the X- axis. Include the unit in each label, e.g. temperature in C and time in hours. Do NOT forget to label the axes. Step 3 Choose a scale for the X and the Y axes. Make sure that the scale includes the highest numbers in the table for each of the variables. Do not use the values for the Y-axis directly from the table unless they have regular intervals

16 Step 4 Place a dot at the point where the two values for each result intersect (meet). In the example, the point where 5 hours and 24 C intersect on the graph is indicated by the second dot on the graph. Plot all the points using the information in the table. Step 5 Join the dots using a ruler until all the dots have been joined in sequence. Step 6 Give the graph a heading or caption. The heading or caption should include both variables. In this case both air temperature and the time period of 24 hours must be mentioned in the heading.

17

18 How to draw a bar graph Steps 1 to 3 To draw a bar graph, you follow the same first three steps that you followed to draw a line graph. Use the table to identify the dependent and independent variables. Draw the axes and choose a scale. Note that there will be no units when labelling the X- and the Y-axes in this particular graph. Table 2: Number of organisms found in the water at different points along a river

19 Step 4 Draw a bar to show that 10 organisms were found at point number 1 on the river. Then draw bars to represent the number of organisms found at each of the points along the river. Since this is a bar graph, the bars should not touch as the points along the river have no direct relationship with each other. Step 5 Give the graph a heading or caption. See step 6 under the line graph for instruction on how to give your graph a caption. Graph 6: The final bar graph

20 How to draw a histogram A histogram is drawn in exactly the same way as a bar graph. The only difference is that a histogram is used when the independent variable is groups of information along a continuous scale. Note that in a histogram, the bars (equal width) are drawn without any spaces between them. NOTE: When the independent variable is continuous data (an infinite number of values are evenly distributed), we use a line graph or histogram. When the independent variable is discontinuous data (a fixed number of values that do not form an ordered scale), we use a bar graph or pie chart.

21 How to draw a pie chart Step 1 Add all the data in the table together. In this case, you will add all the numbers in the 'Number of women' column to find out how many women took part in the investigation = 200 When you do the calculations for the pie chart, then 200 will be the denominator (the number that you divide by). Different type of contraceptive use by a sample group of women

22 Step 2 Convert your data to angles. Divide each number by 200. Then, since there are 360 in a circle, the angles are worked out by multiplying by /200 x 360 = 61.2 (round down to 61 ) 30/200 x 360 = 54 38/200 x 360 = 68.4 (round down to 68 ) 76/200 x 360 = (round up to 137 ) 22/200 x 360 = 39.6 (round up to 40 ) Check that your calculations are correct. All the degrees should add up to 360. In our example: = 360 If the degrees don t add up to 360, you have done something wrong. Go back and check your work.

23 Step 3 Use a mathematical compass to draw a circle. Step 4 Draw in one radius on the circle. Start at the exact middle of the circle and draw a line to the edge of the circle. Draw a circle and then draw a radius Step 5 Use a mathematical protractor to measure out the sectors of the pie chart according to the angles you calculated in step 2.

24 Step 6 Label each of the sections of the pie chart with the correct information. In this example, each section should be labelled with the correct contraceptive method used by women (OR provide a key for the different sections). Step 7 Give the pie chart a heading or caption. Remember that both variables should be included in the caption. In this example the two variables are the types of contraceptive and the number of women. Final pie chart with caption

25 Apparatus and lab safety Never eat and drink in the lab Report all accidents to your teacher Perform investigations in a clear and logical way to prevent risks Do not taste or inhale any chemicals found in the lab Read labels of chemicals substances before and note any specific precautions and warnings Handle scalpels, blades and other sharp instruments with care Ensure that the dissection tools are clean and rust free, blunt scissors, scalpels and blades are more hazardous than sharp, clean equipment.

26 How to write a life sciences essay TACKLING ESSAY QUESTIONS Look at what has been asked. How do you need to present it to the marker? Look at the terminology for this must you explain, comment critically, discuss etc. Read the questions carefully before answering. Make sure you understand exactly what is being asked. Jot down your ideas regarding the question that comes to you Jot down a brief, informal outline of your essay before you start writing. It will help you organise your train of thought. BEWARE! If you start to write an essay without organising your thoughts first, your essay will be haphazard, things will be left out and it will not give the reader a good impression of your abilities. Write neatly, leave margins and use complete sentences. Allow time at the end for a final check.

27 WRITING ESSAYS When writing essays, always use the following format: Introduction: this is a short brief paragraph that summarises what is to be discussed in the essay. Its main aim is to introduce the reader to the essay. A good introduction should guide the reader in what approach is being taken. Do not use the introduction to reword the topic. Keep the introduction to one paragraph. Body: this is where the content is written in a logical sequence as paragraphs. Include definitions or explanations of terms that will be used in the topic. Get to the point, keep answers simple and concise and make sure you present facts logically and keep to the theme. Deal with one topic or point in each paragraph and link consecutive paragraphs properly using connecting phrases. Start a new paragraph on a new line. Do not be bogged down by including waffle and irrelevant points. Conclusion: this paragraph rounds off the essay. Here you consolidate what the essay is about. Refer to the introduction or summarise the argument of the essay in the conclusion but do not restate the body of the essay in the conclusion.