Who Discovered DNA?

Who Discovered DNA? — page 5 — How are living things made It was all perforated and porous much like a honeycomb these pores or cells were indeed the ﬁrst microscopical pores I ever saw and perhaps that were ever seen Robert Hooke from Micrographia talking about his observations of cork bark Pictured below are the magniﬁed cells of cork bark drawn by the scientist Robert Hooke and ﬁrst published in 1665 Hooke was the ﬁrst person to coin the term cells for these tiny parts of living things Building blocks By the 17th century both farmers and scientists knew they could inﬂuence heredity but no one knew how it worked To know how organisms worked scientists needed to ﬁnd out what organisms are made from and how they are put together This important step was made just under 350 years ago by an English scientist named Robert Hooke Hooke was born in 1635 and as a young man studied many different scientiﬁc subjects He was a genius at making and using scientiﬁc instruments One of these instruments was a microscope Cells Hooke examined many different things through his microscope In 1665 he published Micrographia a book about the things he had seen It contained one of his most famous drawings an enlarged section of a piece of cork bark The bark was made up of tiny sections that he called cells after the tiny cells that monks slept in 10

Who Discovered DNA? — page 6 — What are cells We now know that cells are filled with a salty substance called cytoplasm but they also contain tiny working parts called organelles The most important of these organelles is the nucleus which controls what the cell does Most but not all of the DNA in a cell is in the nucleus In order for an organism to grow and repair any damage to itself new cells must grow New cells come from the division of old ones Cells divide making two new cells almost identical to each other This is called mitosis Cell membrane Cytoplasm Original cell Organelle Nucleus Cells reproduce by dividing over and over again Before a cell divides everything inside it including its central nucleus is duplicated The cell then gradually splits into two identical new cells Animal cells The wall of a plant cell is fairly thick so it is easy to see under a microscope Animal cells lack cell walls and are instead surrounded by a membrane which is not as obvious as a wall In the 1830s German scientist Theodor Schwann was one of the ﬁrst to see animal cells In 1839 he and fellow scientist Matthias Jacob Schleiden published their theory that all living things are made of cells They went on to ﬁnd out more about what happens inside a cell The original cell has divided into two new cells Breakthrough Robert Hooke made better microscopes than most of those made previously Through them he saw parts of organisms too tiny to see before He and others after him discovered that cells make up all living things They are among the basic building blocks of life 11

Who Discovered DNA? — page 7 — Life changes The story of evolution Studying living things closely through a microscope is one way of learning about them Looking at the way they live and behave is important too Charles Darwin was a naturalist who was interested in all aspects of the different varieties of animals and plants In 1831 he embarked on what was to be a momentous journey to South America A journey of discovery The ﬁve-year voyage on a British naval ship the Beagle eventually took Darwin around the world He studied an amazing variety of creatures He was particularly interested in those on the Paciﬁc islands of the Galapagos His experiences gave him the clues he needed for what was to be a groundbreaking theory Darwin began to understand how living things change or evolve over long periods of time and how new species come into being Back home Darwin continued his research by studying the way farmers and pigeon breeders used selective breeding to get the kinds of animals they wanted by choosing characteristics they most valued This led Darwin to conclude that selective breeding happened in nature too Variation The secret lay in what Darwin called variation Variation describes the natural differences that occur among individuals in a population group of the same species or type Charles Darwin Date of birth February 12 1809 Place of birth Shrewsbury England Greatest achievement Developing the theory of evolution through natural selection Interesting fact He almost didn’t make the voyage on the Beagle Darwin’s father was not eager to let him go but an uncle managed to change his father’s mind Date of death April 19 1882 12

Who Discovered DNA? — page 8 — While visiting the Galapagos Islands Darwin saw several types of ﬁnches including this large ground ﬁnch He noted that each had a different type of beak Later scientists realized that the shapes of the ﬁnches beaks had evolved to suit the food available on different islands Darwin suggested that variations can occur randomly A variation that helps an organism survive in its natural environment will give it a better chance of living longer A long life means it can produce plenty of offspring which will inherit the variation Other individuals of the same species may be born with other useful variations and these too will be passed on Gradually those organisms that are not so well adapted will die out and their place will be taken by the better-adapted ones We say the species has evolved by a process called natural selection Darwin did not know what caused the variations or exactly how they were passed on from one generation to the next But over the next 100 years or so the more that scientists discovered the more support their ﬁndings gave to Darwin’s theory any variation if it be proﬁtable to an individual of any species will tend to the preservation of that individual and will generally be inherited by its offspring which will thus have a better chance of surviving Charles Darwin in On the Origin of Species Breakthrough Darwin’s greatest achievement was working out that evolution happens through the process of natural selection This theory is accepted to this day by scientists 13

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