4.2 The reduction of chromosome number: meiosis If you look at the chromosomes shown in Figure 8 you will see that they have been lined up in pairs. The members of each pair are of similar shape and size, and unlike the members of other pairs. At a molecular level these distinctions are maintained: the order of the bases in the DNA is very similar in both members of a pair, but is quite different from that found in other pairs. By ‘very similar’ we mean that the order of the particular genes on each chromosome of the pair is the same,
4.1 Why are cells different? Now let us go on with our story and assume that we have decided the time is right to have a baby. The primary requirement for conception is that healthy gametes should be produced. We shall therefore look first at how gametes are made, and then examine some of the factors affecting their quality. But we must start with an explanation of what gametes are, and what sets them apart from other kinds of cell. In other words, what makes gametes special? Gametes are the cells that fuse to form a new
3.3.3 Mechanical methods of contraception While hormone-containing pills represent a very sophisticated kind of contraceptive, mechanical contraceptives are a straightforward idea: they act by preventing sperm and egg from meeting. Mechanical contraceptives in their simplest form have been around since before Roman times; some are shown in Figure 4. The earliest ‘penis protectors’ were allegedly used less for contraception than as protection against disease, and as a badge of rank. 1.3.2 Chemical contraceptives These methods rely to a large extent on an understanding of the physiology of the reproductive process. They are targeted at preventing the production or release of gametes, i.e. the sex cells – sperm and eggs – which need to fuse to produce a new individual. To date, most effort in this area has been directed towards preventing a woman from ovulating, i.e. releasing an egg, although more recently trials have begun on ‘male pills’ which block sperm production. Ovulation i 2.5 Public engagement From the examples outlined in sections 2.2 to 2.4, which are just a fraction of what is available, you could conclude that the UK public are, in general, offered a wide range of science promotion events. These events provide valuable insights into many aspects of science for laypeople, perhaps especially the ‘high tech’ science that they might otherwise never experience. They also provide a useful opportunity for scientists to engage with the public – should that be wanted. And where th 2.4 ‘Go Use’ science promotion events Science shops, created in the Netherlands in the 1960s and now spread throughout Europe, first emerged in the UK in 1988 (at Queen's University, Belfast). They act as a demand-driven link between a university or independent research facility and the community (usually via citizen groups, such as pressure groups, social groups, consumers and residents associations), putting one in touch with the other upon request. They carry out scientific research on practical, scientific problems at the loc Introduction The plant predators, or herbivores, are a varied group, but they share certain characteristics. Many of them are large; among the smallest is the chevrotain (or mouse-deer) at about two kilograms weight, and the elephant is the largest, with a typical bull male weighing around six tonnes. In this unit we'll be looking in more detail at some of the problems and consequences of adopting a plant-eating way of life. Leaves are a much less nutritious food than most kinds of animal material, so lar Acknowledgements The content acknowledged below is Proprietary (see terms and conditions). This content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: The content acknowledged be 6 Reflection If you are working through all the units in this series, you'll be aware that this unit has taken a somewhat different tack from earlier ones. I've used rodents to explore some fundamental biological principles that have a relevance far beyond this particular order. It is especially appropriate to talk about issues such as biological success in connection with rodents, given their very wide geographical distribution and the very large number of rodent species and individuals. You'll recall (f 5.3 The effect of environment on reproductive behaviour Review your reading of Section 4.2 on the family life of marmots (or re 5.1.6 Pulling it all together The electric and magnetic fields given by Equations 7.21 and 7.23 can satisfy all four of Maxwell's equations in empty space. Gauss's law and the no-monopole law are immediately satisfied because the fields are transverse. Faraday's law and the Ampère–Maxwell law will also be satisfied if we can find electric and magnetic fields that obey Equations 7.24 and 7.26. We are looking for wave-like solutions, so it is sensible to try 3.2 The impact of climate change on global freshwater resources The availability of freshwater will be significantly altered in a future world affected by climate change (Houghton, 2004). In some regions, water availability will decrease; in others it will increase. Precise predictions about the extent and exact location of such changes cannot be made because they are based on climate models, the accuracy of which is uncertain. However, there is wide agreement that probable changes will include: More rain in north 3.6.1 Radioactivity and bugs! Many natural processes involve repeated doublings or halving at regular intervals. You may have come across this already in your work, in the context of bacterial growth or radioactivity. In this section, we are going to look in more detail at bacterial growth and radioactivity and we will be using graphs to examine how the numbers of bacteria or numbers of radioactive atoms change over time. 3.2.2 Choice of scale It's important to choose a scale that covers the range of values you have recorded for that particular axis. If the scale is too big, then all of your measurements will be bunched up at one end of the graph, making it difficult to read. It is also very important to keep the scale consistent all along the axis, i.e. don't suddenly change the spacing between the units of measurement on an axis. 3.2.1 Axes A graph is made using two different scales or axes, forming a right angle. The horizontal axis (x-axis) is used to represent the variable that changes in a consistent way, such as time, or in a way that you can control. The vertical axis (y-axis) is used to represent a variable that you measure but may not be able to control directly, such as a patient's temperature. Each axis should be carefully labelled to indicate what it represents. To plot a graph, you put a mark at the poin 5.2 Summary of Part D Part D explored several of the reasons which may result in a word or phrase in an Act of Parliament having an unclear meaning. This was illustrated by a number of examples. Interpretation of those words or phrases becomes a task for the courts. In this role, it can be argued that the courts are involved in the law-making process as they have been required to interpret and define a statute. 3.2 Converting to a percentage Fractions and decimals can also be converted to percentages, by multiplying by 100%. So, for example, 0.17, 0.3 and   0.17 × 100% = 17%;   0.3 × 100% = 30%;   Author(s): 2.3.1 Try some yourself 1 A piece of computer software is to be developed by a team of programmers. It is estimated that a team of four people would take a year. Which of the following times is the length of time taken by three programmers?   A 1 year 2.4 Complex conjugate Many manipulations involving complex numbers, such as division, can be simplified by using the idea of a complex conjugate, which we now introduce. The complex conjugate
1.2 Real numbers The rational and irrational numbers together make up the real numbers. The set of real numbers is denoted by
Activity 5
can be expressed as percentages as follows:
Definition
Author(s):
. Like rationals, irrational numbers can be represented by decimals, but unlike the decimals for rational numbers, those for irrationals are neither finite nor recurring. All such infinite non-recurr
