B3 Life on Earth

b3 life on earth

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  • Created on: 03-01-11 15:08

The Variety of Life

Scientists use similarities and differences between things to put them into groups. This is called CLASSIFICATION. The names are in Latin

Humans are in many groups. (order from largest group to the smallest.

Animals -> Vertebrates -> Mammals -> Primates -> Homo sapiens.

What makes a species is if the can breed together, and if their offspring can breed with each other (they are fertile).

The animals in the species, can be very different from each other, tale dogs for example, dogs are not identical – you can have poodles, Labradors, Spaniel etc. This is due to VARIATION

There are different causes of variation.

You can have men and women, which is controlled by their genes. This is due to GENETIC  variation

Pierced Ears in humans are due to ENVIRONMENTAL variation.

People with different skin colours is partly due to genetic variation, but also due to environmental variation. 

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The Variety of Life

Most scientists believe that life on Earth started from a few simple beings, and this simple beings evolved into more complicated things. This is called EVOLUTION. This explains why there are similarities between some animals.

The evidence for evolution is Fossils, which are made from the dead bodies of living things. Almost all fossils found are  of extinct species. This is more than 99% of all living things that have ever lived on Earth.

Conditions for Fossils have to be right, and not every living thing has ended up as a fossil, so there are gaps in records. Sometimes a new species has been formed, without an in-between link of fossils.

There are gaps in fossil records because evolution happens in spurts, and there is a chance that it did not make quite the right conditions for fossilisation to happen, so there would be no evidence for the small changes that happened in the species that involved.

The more genes that one species share with another makes the species more related. For example, over 98% of Human genes are the same as a chimpanzees. 

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Evidence for change NOW

Selective breeding is when humans choose two breeds in a species, and breed them together to create a perfect breed with features such as biggest yield or high immunity

Some selective breeding is not wanted, such as the creation of superbugs and super-louse (head lice)

Changes that of animals mainly came round before humans existed. This is because of the environment, The process is called NATURAL SELECTION, this is how evolution happens.

The steps of natural selection
1. Living things in a species are not identical, they have variation
2. They compete for things like food, shelter, and a mate. But what if something in the environment happens?
3. Some will have features that help them survive. They are more likely to breed, and so they pass their genes on to their offspring
4. More of the next generation will have the useful feature. If the environment stays the same, even more of the generation will have the useful feature. 

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The story of Charles Darwin

First Darwin realized that animals or plants from the same species are all different – there is variation

Next he realized that there are always too many of any species to survive

All the plants or animals of one species are in competition with each other for food and space.

Lamarck was a French scientist, who explained evolution with giraffes, by saying: the giraffe stretched it’s neck to reach the food; the neck becomes longer; the longer neck is passed on to its offspring.

Darwin’s explanation was better because: it accounts for all the observation; it explains a link between things that people hadn’t thought of before (linking variation and competition)

Almost everyone in the Victorian society disagreed with natural selection and believed in the Bible, that  the world was created in 6 days, no natural selection, no evolution.

There are three big problems with Natural Selection they were: The record of fossils was not full; The age of the Earth had not been worked out accurately enough; He could not explain the reasoning between variation and how we pass on features to our offspring

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The Story of Charles Darwin

A plant scientist named Mendel, crossed red plants with white plants. The new plants weren’t pink, but red.

He then took the new red flowers and bred them together. He came out with mainly red flowers and a few white ones.

He described the red flowers as being DOMINANT and the white flowers being RECESSIVE.

He assumed that features were passed on from one generation to the next and without this, natural selection would not work. But Darwin did not realise this and ignored it.

Suppose that when DNA is copied, a mistake is made and that MUTATION could result in different colour spots or colour flower. Mutations can happen naturally, but they can also be caused by some chemicals or ionizing radiation.

Mutations form differences in species (variation). Without mutation and variation, natural selection could not take place.

DNA helped scientists to explain how a new species can evolve by: mutations produce variation in a population of the same species; a change happens in the environment; natural selection means that only some of the population survive; over many generations, these individuals form a new species.

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Where did Life Come From?

All living things can reproduce. The first living things were molecules that could copy themselves – like DNA.

There are two main ideas of where life on earth came from these are:
          1. Life started somewhere else in the Solar System. It was brought to Earth on a comet or a meteorite. Early Earth was too hostile for life to have started here. Life began in water-soaked rocks beneath the surface of another planet.
          2. Life started at the bottom of the oceans. Hot water springs on the ocean floor contain dissolved minerals. When the hot water from the springs meets cold sea water, minute bubbles of iron sulphide, filled with a solution of different chemicals, are formed. These bubbles could have acted like tiny cooking pots. The chemicals may have made a thin layer of fatty protein on the inside of the bubbles, making the first cell membranes.

The conditions on earth 3500 million years ago where very different to what they are now.

Living things on Earth are suited to survive where they live. It they’re not well suited, they die out. This is natural selection.

The first living things were only one cell big. MULTICELLULAR living things appeared hundreds of millions of years later. 

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Keep In Touch

Response changes happen outside of the organism’s body. But many changes happen inside of the body of which your body must respond to as well in order to survive. For example: When you have just eaten the meal, some of the food contained glucose (a sugar); the sugar is absorbed into your blood; your blood sugar level rises above normal levels; if your body does not respond to this change, you will become unwell. This is HOMEOSTASIS.

Parts of your body communicates with each in two ways.
1. NERVE CELLS (neurons) – are very long thing cells. They link up cells in different parts of the body. They carry electrical impulses around the body.
2. HORMONES – chemicals carried in the blood. They are made in one part of the body. They make something happen in a different part of the body.

Your body needs two different communication systems, because if you need a fast response, nerve cells carry electrical impulses very quickly, but their effects only last a very short time. Other times you need a response which lasts for a longer time, such as growing. Hormones travel much more slowly but their effects last much longer. 

 

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Keep in Touch

Explaining how the nervous system works: Take the example of touching a hot plate.  Temperature receptors in the skin detect the stimulus; this sends a nerve impulse to the central nervous system; the central nervous system coordinates all the information it receives; another nerve impulse is sent to the effectors; in this case it is the arm muscle which contracts; The hand moves away from the hot plate.

Hormone responses are the thyroid gland that makes a hormone that controls chemical reactions in a body; Pituitary gland which makes the hormones which controls the other glands; Pancreas which makes insulin for the control of blood sugar; adrenal glands which make adrenaline which speeds up the heartbeat and breathing rate; In males the testes make the hormone testosterone which causes the body changes at puberty; in females the ovaries make the hormones oestrogen and progesterone, These cause the body changes at puberty and menstrual cycle.

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Human Evolution

Human DNA is less than 2% different from chimp DNA. We did not evolve from apes, but we share an ancestor

Humans have two big differences from apes: we have bigger brains and walk upright.

Hominids are animals which are more like humans tan apes. The skull had a small brain which was not much different to apes and they walked upright

Another Hominid found in 1974 skeleton also showed that it walked upright, and then in 1978, a set of footprints were found preserved in mud, which showed that hominids really did walk upright.

There were several different species of hominids. They all shared a common ancestor. Over time, most hominids died out, but the species with the largest brains died out. This helped them to survive. They were known as early humans.

But a small group of them evolved into modern humans (Homo sapiens). They started to leave Africa and explored the rest of the world. 

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Extinction!

Where an animal or plant lives is called its HABITAT. Any quick changes in their habitat can put them at risk of EXTINCTION.

Around the world, over 12000 species of plants and animals are at risk of extinction. They are ENDANGERED.

Animals and plants compete with each other for the things they need. If a new species moves into the habitat, it could be a predator of the species already living there, it could carry a disease, which could wipe out the native population.

In food webs, if one of the species died out, then the next animal in the chain could be at risk of extinction and the next and the next.

Most animals eat more than one thing, many different food chains contain the same animals.

Humans can cause other species to become extinct by: directly for example, hunting; or by indirectly for example: by taking away their habitat or bringing other species into their habitat.

If many species become extinct, there will be less variety on Earth. Variety on Earth is called Biodiversity.

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Key Words

Species A group or organisms that can breed to produce fertile offspring
Fertile  An organism that can produce offspring
Infertile An organism that cannot produce offspring
Variation Differences between living organisms. This could be differences between species. There are also differences between members of a population from the same species.
Genetic Factors that are affected by an organisms genes
Environmental Things in your environment which affect the way you develop
Evolution the change in the inherited traits of a population of organisms through successive generations
Fossils The stony remains of an animal or plant that lived millions of years ago, or an imprint of it’s mark in a surface.
Selective Breeding Choosing parent organisms with certain characteristics and mating them to try to produce offspring that have these characteristics
Populations  A group of animals or plants of the same species living in the same area
Natural Selection When certain individuals are better suited to their environment they are more likely to survive and breed passing on their features to the next generation
Competition  the challenge to gain what you want
Dominant Describes and allele that will show up in an organism even if a different allele of that gene is present. You only need to have one copy of an dominant allele to have the feature it produces
Recessive An allele which will only show up in an organism when a dominant allele of the gene is not present. You must have two copies of the recessive allele to have the feature it produces.

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Key Words

Multicelluar An organism made up of many cells
Specialized A specialized cell is adapted for a particular job
Response Action or behaviour that is caused by a stimulus
Homeostasis Keeping a steady state inside your body
Nerve cells A cell in the nervous system that transmits electrical signals to allow communication with the body
Neurons Nerve Cells
Electrical impulses  The reaction sent from the nerve cell to the control centre
Hormones A chemical messenger secreted by specialized cells in animals and plants. Hormones bring about changes in cells or tissues in different parts of the animal or plant
Insulin A hormone produced by the pancreas. It is a chemical which helps to control the lever of sugar in the blood
Adrenaline A hormone which has many affects on the body. For example, increasing hate rate, increasing breathing rate
Hominid Animals more like humans than apes that lived in Africa millions of years ago
Common ancestor A species which two or more other species both evolved from
Extinct A species is extinct when all the members of the species have died out

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Key Words

Habitat The place where an organism lives
Endangered Species which are at risk of coming extinct
Predator An animal which kills other animals for its food
Disease an impairment of health or a condition of abnormal functioning
Food Web A series of  linked food chains showing the feeding of relationships in a habitat
Indirectly When something humans do affects another species, but this wasn't the reason for the action

Biodiversity the variation of life forms within a given ecosystem, biome, or for the entire Earth.
Sustainability the property of being sustainable
Mutation A change in the DNA of an organism. It alters a gene and may change the organisms characteristics 

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Checklist

 All life on Earth has evolved from the first very simple living things.
Evidence for evolution comes from fossils and by comparing the DNA of different organisms
The first living things appeared on Earth 3500 million years ago and were molecules that could copy themselves
These living things may have developed on Earth, or the may have come to Earth from somewhere else.
If conditions on Earth had been different at any time since life first began, the evolution may have happened differently.
Members of a species are not identical, there is variation between them
Variation is caused by the environment or genes, but most features are effected by both.
Evolution happens by natural selection
More of the next generation have these useful features.
The difference between natural selection and selective breeding
Genetic variation is caused by mutations in  an organism’s genes
The main parts of the human nervous system
How nervous and hormonal systems communicate information around the body.
That the evolution of a larger brain gave some early human a better chance of survival
.

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Checklist

That many hominid species evolved from a common ancestor, but only one survived and became modern humans.
Living organisms depend on their environment and each other for survival
Animals and plants in the same habitat compete for different resources
How a change in a food web can affect all the species there
Species may become extinct if: their environment changes; a new species arrives that is a competitor, a predator, or causes disease.
Another plant or animal in the food web becomes extinct
Two examples of modern extinctions cause: directly by humans, for example, by hunting; in directly by humans, for example, destroying their habitat
Why keeping biodiversity is important for us and future generations

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