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4 Fossil fuels

Part of the incoming solar energy becomes stored in fossil fuels (oil, gas and coal:
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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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8 Summary

  1. The rate at which water infiltrates into the ground depends on the permeability of the rocks and the state of the ground surface. Below the ground surface there is an unsaturated zone which has air in the pore spaces, and a saturated zone which has all the pores filled with water. The water table is the boundary between the unsaturated zone and the saturated zone, and is the level at which water stands in wells. Water below the water table is called groundwa
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6 Permeability

It is important to distinguish clearly between porosity and permeability. Porosity is a measure of how much water can be stored in a rock, whereas permeability is a measure of the properties of a rock which determine how easily water and other fluids can flow through it (see Section 4). Permeability depends on the exte
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1 Wave energy

The energy carried by ocean waves derives from a proportion of the wind energy transferred to the ocean surface by frictional drag. So, ultimately it stems from the proportion of incoming solar energy that drives air movement. Just how much energy is carried by a single wave depends on the wind speed and the area of ocean surface that it crosses; wave height, wavelength, and therefore wave energy, are functions of the distance or fetch over which the wind blows. Not surprisingly the ma
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6 Summary

  1. Waterlogged organic matter accumulates in deltaic, coastal barrier or raised mires to form peat. Coal forms by the compaction and decomposition of peat. Chemical changes imposed by increasing temperature and pressure over time determine the coal rank.

  2. Coalfields can be classified as either exposed or concealed, depending on whether or not the coal-bearing rocks are hidden by younger strata. In most coalfields, mining commenced in the shallower
    Author(s): The Open University

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2.7 Summary

  1. Eukaryotic cells contain numerous distinct types of membrane-bound compartment. Transport vesicles move proteins and other molecules between the compartments.

  2. Proteins contain signalling sequences or patches that specify their destination compartment.

  3. Proteins destined for lysosomes, secretion or the plasma membrane are synthesised in the ER, transported to the cis Golgi, modified in the Golgi apparatus, and sorted and pa
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1.7 Localization of signalling proteins

Since signalling proteins cannot diffuse as rapidly as small second messengers, they need be close to their downstream target in order to be able to function. Where they are located with respect to both their subcellular position and their immediate neighbours is therefore vitally important. The plasma membrane is usually the initial location, and proteins can be attached to the plasma membrane in various ways (Author(s): The Open University

Learning outcomes

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

  • recognise the terminology which is used to describe the properties and behaviour of active galactic nuclei (AGN);

  • manipulate numbers, algebraic symbols and mathematical functions in equations.


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6 Inheritance of more than one pair of contrasting characters

We have considered the inheritance of one pair of contrasting characters that involves the segregation of the two copies of one gene in maize. A single chromosome carries many genes, of the order of 2 000 to 4 000 in each human chromosome, each carrying its own information, and each with its specific location, its own locus, on the chromosome. In a pair of homologous chromosomes, there will be many pairs of genes strung along their length.

These observations raise some intriguing questi
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1.3.1 Inheritance of colour in maize

We can trace the inheritance of characters in animals and plants by following the phenotype from generation to generation, in breeding experiments. We will describe work with maize (Zea mays), alternatively called corn (sweetcorn, or corn on the cob), which occurs throughout the world as an extremely important commercial crop plant, and which is used extensively in genetic research. We can also study the inheritance of characters at the level of the genotype. In this section we will ju
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1.2 Like begets like

It is possible to follow a character, such as eye colour or hair colour in humans, that is handed down from generation to generation. Such characters are said to be inherited characters (or heritable characters) and are determined by genes. A gene can be considered as a unit of inheritance, which determines a particular character and which is passed on from parent to offspring.

Genes maintain the differences between species, such as oak and human, but they also contribute
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Learning outcomes

After studying this unit you should know:

  • the number of chromosomes is characteristic of each species and can vary enormously between species

  • genetics is based on the concept of the gene as the unit of inheritance

  • that sexual reproduction always includes two distinctive processes: the production of gametes, which involves meiosis, and fertilisation. The two processes are accompanied by changes in the chromosome number, from diploid to haploid and fr
    Author(s): The Open University

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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
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5.2 Madagascan diversity

Activity 7

Watch the video sequence below, which focuses on just three lemur species – the ring-tailed (in a very brief sequence, leaping from one tree to another), the golden bamboo lemur, already mentioned, and the sifaka, plus the
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4.2 Other members of the bear family

Other omnivorous species of bear include the Asian black bear, the North American black bear and the Andean spectacled bear. Although polar bears spend their winters hunting seals out on the Arctic sea-ice, they have to come ashore when the ice melts in spring and find other sources of food.

Activity 2
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3.3 Variation

Fossil rodents are first found in rocks that date from around 65 million years ago (from the Eocene) and are thought to have evolved from insectivore/omnivore-type mammals that lived 100 million years ago (in the Cretaceous period). To say that they evolved from simply means that there probably is a direct line of descent but that the descendants have changed from their forebears. One of the most significant ways that evolutionary change can be brought about is by a process known as na
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1 Overview

As you walk down the street one day, you hear a voice from somewhere behind you that seems to be discussing this unit. It says:

‘My dad's tutor's no joker, and he told me the TMA's going to hit home with a bang.’

You turn to find the face behind the voice, which is a gravelly Glaswegian baritone, but the man has gone, leaving you to ponder what he has said. Let us call his sentence exam
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2.2.1 Do GM crops pose unique problems?

It is perhaps overly simplistic to take the line that only ‘natural foods’ should be commended and that GM plants are unnatural. Arguably, very few of our modern foodstuffs can be termed ‘natural’, in that they are not derived from naturally evolved crops. Tremendous changes in genetic make-up have been achieved by conventional (i.e. non-GM) breeding methods. Traditional plant breeding involves selection of individuals seen as superior, and then crossing, i.e. transferring the pollen
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