9u6.1 - Ecosystems

An ecosystem describes a natural biological unit that is made up of both living and non-living parts. It is made up of a number of:

• habitats - the place where an organism lives
• communities - all the living organisms that live within a habitat. A community can contain a number of different species.

Species

A species is a group of organisms that can interbreed to produce fertile offspring. For example, a horse and a donkey can interbreed with one another but their offspring (a mule) will be unable to reproduce as mules are infertile. The fact that offspring cannot reproduce shows that horses and donkeys belong to two different species.

Biodiversity

Biodiversity is the degree of variation that exists among all living organisms on Earth.

The infinite variety of life

When examining the biodiversity on Earth it is useful to consider the populations of organisms in a species. These can fluctuate in an ecosystem depending on factors such as:

• competition between organisms for resources
• predator numbers
• disease

All living things within an ecosystem are interdependent. A change in the size of one population affects all other organisms within the ecosystem. This is shown particularly clearly by the relationship between predator and prey populations.

A balance naturally arises between predators and prey in any given ecosystem. Too many predators and there is not enough food, so the predators die. Too few predators and the consumers can eat too much causing famine and the consumers die.

There are also cautionary tales of this delicate balance being disturbed by human intervention.

China's war on sparrows

Food chains and webs

A food chain shows the feeding relationship between organisms. A food chain starts with an organism that makes food, the producer. In the example below, it's grass.

The transfer of energy between organisms in each ecosystem is balanced. Some of the organisms are producers, some are consumers and others are predators.

A food chain shows how the energy is passed from producers, that obtain their energy from photosynthesis, to consumers and on to predators.

A food web shows the interconnnected food chains in an ecosystem.

Food Chains Worksheet

Habitats

Comparison of animal homes/nests (bees, ants, birds, wasps, bears, beavers). What is it’s function. Why do they build nests, what does it provide. Research different types of nests from other animals. Temporary or permanent?

• Questions:
• 1. How many individuals does it hold?
• 2. Is it temporary and permanent?
• 3. Location (floor, tree, water)
• 4. Sophisticated construction: Materials used to build
• 5. How long does it take to build?
• 6. How does this home suit this organisms needs?

What does the ideal home need? Divide your list into necessity and luxury/comfort

9u6.2 - Evolution and natural selection

All of the information needed to produce new copies of an organism is passed on by its parent(s) in the form of a genetic code built into a chemical called DNA. This code may get slightly changed by natural processes, so that each new offspring has slightly different characteristics. Most of these changes go unnoticed, some cause the organism to fail, while others produce organisms that are better suited to survive in the environment in which they live.

The survivors themselves go on to have offspring with the same adaptation that made them better survivors and so the species develops to be better suited to the environment.

This is called natural selection.

9u6.3 - Properties of materials

Building materials

• concrete
• wood
• steel
• brick
• glass
• ceramics
• plastic

The requirements are structural strength, insulation, aesthetics.

Think of the materials used to build your home.
Where can you find the materials in the list?
Why have they been used there?

Concrete

Concrete is a hardened mixture of cement, sand and water. It has been known about for thousands of years. Some cultures added powdered rock into the mix that provided special properties to the hardened concrete. The Pantheon (literally "all the gods") in Rome has been standing for nearly two thousand years. It has a large concrete dome that is unsupported apart from the walls.

The Pantheon in Rome

Nowadays, other materials are also included in the mixture to provide improved properties. For example, steel rods are included to give a composite material with much greater tensile strength for construction of large buildings, such as skyscrapers.

Cement

Cement is a powdered substance that hardens on exposure to water (hydraulic) or carbon dioxide (dry cement). The Romans were the first to develop cement by mixing volcanic ash with lime (calcium oxide, CaO). The lime was made by heating limestone (calcium carbonate in a large oven (a lime kiln).

CaCO₃ → CaO + CO₂

The lime, CaO, reacts with the water in the mix and forms calcium hydroxide, Ca(OH)₂.

CaO + H₂O → Ca(OH)₂

This calcium hydroxide then slowly reacts with the carbon dioxide in the air forming calcium carbonate, which is the same substance as limestone.

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

These reactions are exothermic, they produce heat, which helps to evaporate away the water formed.

9u6.4 - Adaptation of environment

Human beings have taken another step in that we are very good at adapting our environment to suit our needs. This has allowed people to inhabit even the most inhospitable of environments, such as snowy polar wastes, to baking deserts.

We adapt our environment to suit using foundations, walls, rooms, roof.

We need protection, energy and water supply, entertainment and aesthetics.

9u6.5 - Electrical circuits

Since the discovery and development of electricity, starting with the experiments of Benjamin Franklin, Volta et al, electricity energy has been the way that society transfers energy for personal and social use.

This is particularly true in the home, where lighting, heating, communication and entertainment all depend on electricity.

Voltage

This is the "push" or force applied to the electrical current. It is also called the electromotive force (E.M.F) or potential difference. The voltage is measured in Volts, V.

Current

The charge is carried by electrons. Each electron has a single negative charge, but when this is measured in units called Coulombs it is a very tiny value, about 1.6 x 10^-19 Coulombs per electron. However, there are so many electrons flowing that 1 Amp of current is equal to 1 Coulomb of charge passing around the circuit per second.

Resistance

The electrical current does not have things all its own way, however. There is always some resistance to the flow of currect in every circuit. This is measured in Ohms, Ω.

Electrical circuits

Electricity must always flow in a complete circuit. If there is any break in the connection then the current cannot flow.

Electrical component symbols

The components found in an electrical circuit have established symbols to make the circuits easier to represent. You should know the symbols for the power source/supply (battery), switch, bulb, resistance, ammeter, voltmeter, etc..

9u6.6 - Water supply

Access to clean, safe water is expected in a developed society. For this water needs to be gathered, stored, disinfected, cleaned and distributed to homes.

9u6.7 - Soaps and detergents

Soap

Soap was discovered thousands of years ago and its ability to dissolve non-polar substances was soon used to clean clothes and the accumulated grease of people.

The substance is formed by mixing animal fats with basic substances like sodium hydroxide. After boiling the two substances together, soap floats to the surface from where it can be gathered and pressed into cakes.

Nowadays both fats and oils are used to manufacture soaps. The soap is mixed with dye, scents and perfumes to make a product that it highly agreeable to consumers.

How soap works

Detergent

These are artificial products that behave in a very similar way to soaps

9u6.8 - Temporary and permanent hardness

Hardness in water

This is when the soap has difficulty forming a lather (a foam). It usually happens in areas where the water runs through limestone rocks before domestic or industrial use.

Hard water does not just affect soap, it also causes so-called "furring" in pipes (a dirty white deposit called lime scale) that leads to blockages and damage to appliances that use water, such as washing machines and central heating systems.

Lime scale in pipes

Cause of hardness in water

The root cause is the presence of calcium and magnesium ions (Ca²⁺ & Mg²⁺) in the water.

These may be introduced in the form of calcium hydrogen carbonate(aq) giving rise to temporary hardness, or calcium sulfate and chloride, giving rise to permanent hard water.

Mechanism of hardness in water

In order for soap to do its cleaning job it must be dissolved in the water. Soap mainly contains a chemical substance called sodium stearate, which dissolves giving dissociated (separated) sodium and stearate ions in solution.

C₁₇H₃₅COONa → C₁₇H₃₅COO^-(aq) + Na⁺(aq)

The dissolved calcium (or magnesium) ions react with the cations from the soap making an insoluble precipitate, removing the soap from solution. This precipitate is called 'scum', although its chemical name is calcium stearate.

C₁₇H₃₅COO^-(aq) + Ca²⁺(aq) → (C₁₇H₃₅COO)₂Ca(s)

In summary, there are two problems:

• 1. The soap gets removed from the solution
• 2. A solid precipitate is formed