biology4alevel600

Once you have collected, tabulated and displayed your results, you can use them to draw a conclusion. When you are thinking about a conclusion, look right back to the start of your experiment where you were told (or you decided) what you were to investigate. For example: • In investigation 1, investigating the effect of temperature on the rate of breakdown of hydrogen peroxide by catalase, your conclusion should provide an answer to this question. • in investigation 2, investigating the effect of immersion in solutions of different sucrose concentration on the change in length of potato strips, your conclusion should state the relationship between the concentration of sucrose solution and the change in length of the potato strips. • in investigation 4, testing the hypothesis: the density of stomata on the lower surface of a leaf is greater than the density on the upper surface, your conclusion should say whether your results support or disprove this hypothesis. Explaining your reasonin...

When you have collected your data and completed your results table, you will generally want to display the data so that anyone looking at them can see any patterns. 1. Line graphs  Line graphs are used when both the independent variable and the dependent variable are continuous. This is the case for the potato strip data on the table below. The graph can help you to decide if there is a relationship between the independent variable and the dependent variable. This is what a line graph of these data might look like. Notice: • The independent variable goes on the x-axis, and the dependent variable goes on the y-axis. • Each axis is fully labelled with units. You can just copy the headings from the appropriate columns of your results table. • The scales on each axis should start at or just below your lowest reading, and go up to or just above your highest reading. Think carefully about whether you need to begin at 0 on either of the axes, or if there is no real reason to do this. • Th...

You will often need to construct a table in which to record your measurements, readings and other observations. It is always best to design and construct your results table  before  you begin your experiment, so that you can write your readings directly into it as you take them. Let's think about  investigation 2  again (investigating the effect of immersion in solutions of different sucrose concentration on the change in mass of potato strips). You've made your decisions about the range and intervals of the independent variable (concentration of solution) - you've decided to use six concentrations ranging   from 0.0 moldm -3  to 1.0 moldm -3 . Your dependent variable is the change in length of the potato strips, and you are going to find this by measuring the initial length and final length of each strip. These are the things you need to think about when design ing your results table: • The independent variable should be in the first column. • The rea...

You will often be asked to take measurements or readings. In biology, these are most likely to be length, mass, time, temperature or volume. You could be taking readings from a linear scale (for example, reading temperature on a thermometer, reading volume on a pipette, or reading length on a potometer tube). You could be reading values on a digital display, for example reading mass on a top pan balance or time on a digital timer. There are some special terms that are used to describe measurements, and the amount of trust you can put into them. It's easiest if we think about them in terms of a particular experiment, so let's concentrate on investigation 1: Investigating the effect of temperature on the rate of breakdown of hydrogen peroxide by catalase.   Look back at the the post #69  to remind yourself what is being measured. Validity This is about whether what you are measuring is what you actually intend to measure. For example, in investigation 1, does measuring the...

Many of the experiments that you will do during your AS course, and usually Question 1 in the examination paper, will investigate the effect of one factor on another. These factors are called variables . Types of variables The factor that you change or select is called the independent variable. The factor that is affected (and that you measure when you collect your results) is the dependent variable. The table shows some examples. Table 1 If you are investigating the effect of one variable on another, then you need to be sure that there are no other variables that might be affecting the results. It is important to identify these and - if possible - keep them constant. These are sometimes called control variables . Making decisions about the independent variable You may have to make your own decisions about the range and interval of the independent variable. Let's think about investigation 1 in the table above - investigating the effect of temperature on the rate of breakdown of h...

Almost one quarter of the total marks for your AS examination are for experimental skills and investigations. These are assessed on Paper 3, which is a practical examination. There is a total of 40 marks available on this Paper. Although the questions are different on each paper 3, the number of marks assigned to each skill is always the same. This is shown in the table below. The syllabus explains each of these skills in detail, and it is important that you read the appropriate pages in the syllabus so that you know what each skill is, and what you will be tested on. The next few pages explain what you can do to make sure you get as many marks as possible for each of these skills. They give you guidance in how you can build up your skills as you do practical work during your course, and also how to do well in the examination itself. They are not arranged In the same order as in the syllabus, or in the table above. Instead, they have been arranged by the kind of task you will be asked ...

1 A habitat is a place where an organism lives. The niche of an organism is the role that it plays in the community. 2 A population is a group of organisms of the same species, living in the same place at the same time, that can interbreed with one another. A community is all the organisms, of all the diff erent species, living in the same place at the same time. 3 An ecosystem is an interacting system of organisms and their environment, more or less self-contained.  4 Energy flows from one organism to another in the form of chemical energy in organic molecules in food. The pathways of energy flow can be shown in a food chain or food web, in which the arrows show the direction of energy flow.  5 The first organism in a food chain or food web is a producer. In most food chains, plants are the producers. They transfer energy from sunlight into chemical energy in organic molecules in the process of photosynthesis. All other organisms in a food chain are consumers.  6 Each s...