The Variety Of Life
- Scientists use similarities and differences between living things to classify them
- A species is a group of organisms that can breed together and produce fertile children
- Variation is important in evolution. It can be cause by genes (genetic variation), your environment (environmental variation) or both
- Almost all variation is caused by both genes and environment
- Life on Earth started from simple living things. These changed (evolved) to produce all the things on the Earth today. These changes also made some species extinct
- Fossils are made from the bodies of living things. Almost all fossils are from extinct creatures, 99% of all species that have ever been on Earth are extinct
- Conditions have to be perfect to form fossils, so very few species end up as fossils
- Although there are gaps in the fossil records, scientists have collected 1,000,000's of fossils
- Evolution never happens at the same speed, it happens in spurts over 1000's of years
- Scientists can compare the genes of living things to see if they are related
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Evidence for change
- Species are evolving now and are mainly caused by humans
- Early farmers noticed variation between crops and animals and used the most successful ones for breeding (selective breeding)
- 1 shampoo was used to kill head lice, but soon 1 louse became resistant and survived to breed. It's children also became resistant and a new shampoo was used.
- Most changes to species happened before humans arrived, something in the environment caused them to change (natural selection). Natural selection is how evolution happens
- Individuals in a species have variation and they compete ( for food, shelter and a mate). Some individuals will have a feature that makes them more successful and they breed. Their genes are passed to their offspring and more of the next generation has the useful feature
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The Story of Charles Darwin
- Charles Darwin noticed that some animals in a population are better suited to survive than others. They would breed and pass on their features to the next.This natural selection would make a species change over time. Darwin explained evolution and proved it by using fossils
- A good explanation accounts for all observations and explains a new link
- There were 3 problems with Darwin's theory. The fossil record was incomplete, the age of the Earth was unknown, so there didn't seem to be enough time for natural selection. These 2 problems have now been solved
- Lastly, Darwin could not explain why species are varied and how features are inherited. These have been answered with genes
- Mendel discovered dominant and recessive alleles and how information is inherited
- When DNA is copied (to make new cells) mistakes can occur and cause mutations
- Mutations produce differences in a species, they are a cause of variation
- Most mutations have no effect on the individual. Rarely, they cause a change that improves survival and if the mutation is in a sex cell, it will be passed to the offspring
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Where Did Life Come From?
- Life on earth began about 3500 Million years ago.
- Living things can all reproduce, the first living thing were molecules that could copy themselves.
- Scientists have 2 ideas about where life came from: 1 - life started somewhere in the solar system and was brought to earth on a comet; 2 - life started at the bottom of the ocean in bubbles of iron sulfide.
- Conditions on earth 3500 mil. yrs ago were different to now but the living things were suited to the conditions.
- Iona marble contains the oldest living things in Britain formed from the remains of billions of single cell organisms.
- The 1st living things were only one cell, multi-cellular organisms appeared millions of years later.
- Multi cellular things could get bigger and cells could become specialised. The cells changed so that they could do one job better.
- Bigger multi cellular organisms needed ways for cells to communicate.
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Keep in Touch
- Many changes happen inside the body and the organisms communication systems must respond, in order to survive
- Homeostasis is keeping a steady state inside the body
- Your body communicates in 2 different ways. 1- Neurons (nerve cells) carry electrical impulses to parts of the body. 2- Hormones are chemicals that are carried in the blood.They are made in one body part and affect another
- Neurons carry electrical impulses fast but they only last a short time.
- Receptors detect a stimulus and send a nerve impulse to the brain and spinal cord (central nervous system). The CNS processes the info. and sends an impulse to an effector (muscle) which causes a response.
- Hormones are used when you need a response that is slow and long-lasting, like growing.
- Hormones are made by parts of the body called glands - thyroid, pituitary, pancreas, adrenal, ovaries and testis
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- Apes and humans share many features. They evolved from an ancestor and at some point developed differently.
- Humans have 2 differences from apes, 1 - bigger brains, 2 - walk upright. Scientists predicted that big brains came before walking upright.
- The skull of a hominid was found in Africa. Hominids are more like humans than apes and lived 1.4 Mil Yrs ago. They had small brains but walked upright.
- In Africa 7 Mil Yrs ago grass was tall and hominid had to stand up to see over it. This helped them survive.
- There were several species of hominid which shared a common ancestor. Most of these species died out apart from the ones that had bigger brains. This species evolved into modern humans.
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- Most species that have lived on e4arth in the last few million yrs have become extinct.
- There is fossil evidence of at least 5 mass extinctions on earth and we are beginning one.
- Changes in a habitat can put animals at risk of extinction. They are endangered.
- Changes in factors like food and temperature can make things endangered.
- New species can put animals at risk in 3 ways, 1 - species compete with each other for food, 2 - the new species could be a predator, 3 - new species could cause a disease.
- Animals in a food web are joined together and a new animal could effect the whole food web.
- Human beings can cause other species to become extinct in 2 ways, 1 - directly (by hunting), 2 - in-directly (taking away the habitat).
- Biodiversity is the variety of life on earth.
- Sustainability means meeting the means of people today without damaging for the people of the future.
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