Learning outcomes

By the end of this unit you should be able to:

  • explain the principles that underlie the ability of hydropower to deliver useable energy;

  • outline the technologies that are used to harness hydropower;

  • discuss the positive and negative aspects of hydropower in relation to natural and human aspects of the environment.


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Introduction

Energy from sources other than fossil or nuclear fuels is to a large extent free of the concerns about environmental effects and renewability that characterise those two sources. Each alternative source supplies energy continually, whether or not we use it. Many alternative sources of energy have been used in simple ways for millennia, e.g. wind and water mills, sails, wood burning – but only in the last two centuries has their potential begun to be exploited on an industrial scale. Except
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4.3 Iron storage

In humans, iron is stored mainly in the bone marrow, spleen and liver. About 10 per cent of all the iron in the body is in storage. Two proteins are involved in iron storage; these are called ferritin and haemosiderin (they also occur in other organisms). We shall only study the better characterised (and simpler!) ferritin.

Each ferritin molecule can store iron up to about 20 per cent of its total mass. This is a very high percentage, considering that less than 0.2 per cen
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4.2 Iron transport

It is obvious that iron must be transported around the human body. Firstly, it must be transported from the food in the gut to the places where it is required. Mostly, iron is required in the bone marrow, where red blood cells are formed. Red blood cells have a finite lifetime of about only four months, and old cells are destroyed, usually in the spleen. Iron from the destruction of these cells is then transported from the spleen back to the bone marrow to be recycled.

Iron cannot be tr
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3.2 Removal of iron

Before leaving enterobactin to look at iron transport and storage in humans, it is worth asking the question: how does E. coli remove the iron from such a stable complex as the iron(III)–enterobactin once it has been absorbed?

The answer to this question can be found if we look back to reaction 38. The rigid, three-dimensional structure of the triserine ring of enterobactin is the main reason why enterobactin is such an effective ligand. If the structure of the ring is destroye
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2.1 The problems of iron uptake

Iron has a high natural abundance. It is the second most abundant metallic element by mass in the Earth's crust (7.1 per cent).

Activity 1

What are the main oxidation states of iron?


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Introduction

In this unit we will see that, despite having a high natural abundance, iron is in very short supply because of the insolubility of its oxides and hydroxides. A result of this is that organisms have developed methods for the uptake, transport and storage of iron. For example, iron storage in mammals, including humans, is achieved by ferritin, which stores iron as a hydrated iron(III) oxide – an example of biomineralisation.

This unit is from our archive and is an adapted extract from
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References

Green, S. (1971) The Curious History of Contraception, Ebury press, London.

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3.9 Questions for Unit

Question 1 (Objective 2)

Figure 19 is a graph showing how the viscosity (thickness and stickiness) of a woman's cervical mucus changes with time. Day 0 is the start of her menstrual period.


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3.7 Selecting the sex of a child

Once a pregnancy has been established, many couples are anxious to know the sex of their unborn baby. The reasons for this are many, ranging from the prosaic (will the baby be able to use its brother's or sister's old clothes) to the deeply religious (as described for Hindus in Section 2). In many communities there is so much social pressure on mothers to produce the ‘right’ sex (usually male) that infanticide of the ‘wrong’ sex is widely practised. Because this is illegal in most soc
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3.5 A new life

There is a common belief that life begins at the moment of conception, i.e. when a sperm fuses with an egg. This is a step forward from past years, when life was alleged to start at the time of ‘quickening’, i.e. when a woman could feel her fetus moving inside her. However, both these opinions suffer from an underlying falsehood: that life ‘begins’ at all. Life is a continuum; gametes are produced by living parents, and fuse to produce new living individuals, but unfused gametes are n
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3.4.3 Summary of Section 6

  1. For the first week after fertilization, the conceptus (early embryo) foats freely in the female reproductive tract, obtaining some of its nutrients from the fuid in which it is bathed.

  2. The fertilized egg begins a series of divisions to give 2, then 4, then 8 undifferentiated cells. There is no net cell growth, so each generation of cells is smaller than the last.

  3. The 8- to 16-cell division is different, and important. Each
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3.4.2 Compaction and adhesion

Around the time of the 8- to 16-cell division, the conceptus undergoes a morphological (shape) change, called compaction, in which the cells fatten on each other, and the outlines of individual cells become hard to distinguish. This stage, sometimes referred to as a morula, from the Greek word for mulberry, is shown in Figure 17i. At this stage it is hard to see individual cells; in fact, unless the cells are separated by various laboratory treatments, it is not possible to see the two
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3.4.1 Pre-implantation and assymetric division

Let us now return to the Fallopian tube, where a fertilized egg is assembling its chromosomes prior to commencing a series of mitotic divisions which will eventually give rise to the millions of cells that make up the human body. Obviously these millions of cells do not just exist as an amorphous mass: they are differentiated into many different types of cell, and they are organized into recognizable, discrete structures: tissues and organs. This is accomplished by a coordinated sequen
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3.3 Summary of Section 5

  1. After ejaculation some sperm penetrate the cervical mucus, and on arriving in the uterus become capacitated.

  2. A few sperm swim up the Fallopian tube containing the recently ovulated egg.

  3. In the tube the sperm become activated. This involves changes to the membranes and a change in the swimming pattern.

  4. Enzymes from the acrosome allow the sperm to get next to the egg, by removing follicle cells and digesting
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3.1 How fertilization happens

Now that we have dealt with the basic biology, we can resume and give more detail to our story, and return to where we left it: fully mature, strongly swimming sperm have been deposited in the vagina, and will begin their race to the newly ovulated egg.


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4.4 Hormonal control of sperm production

The most important hormone involved in controlling sperm production is a steroid called testosterone. This is produced in the testis itself, by the Leydig cells (see Figure 12a). The testosterone is released from the Leydig cells between the tubules, and taken up by the neighbouring Sertoli cells. The Leydig cells are stimulated to make testosterone by two other hormones, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which are both produced by the pituitary gland and
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4.3 Gamete production in men

A sexually mature man is producing sperm all the time at a rate of around 300–600 per gram of testis per second. This provides the 500 million or so which are released at each ejaculation. But the formation of an individual sperm takes about nine weeks (64 days). Sperm are produced in the testes, and production is most efficient at a temperature several degrees lower than the normal body temperature of 371°C. For this reason the testes (plural of testis) are suspended outside the body cavi
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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,
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