Biology by Bradford
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The subtopic in the middle and nine tasks round it: label three diagrams, complete a table, put a process in order and fill 44 gaps. The whole subtopic is higher level. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
After a week the water held : carbon compounds that life needs can form from simple molecules with no living thing involved. But early Earth's atmosphere was probably different from what they put in the flask, and no formed.
All living things use the same , and many are shared by every major group of organisms. This is evidence that all life descends from one . Other early forms of life may have arisen too, but became through with it and its descendants.
Life has been evolving for an immense time: at least 3.5 billion years. Rocks are dated from the decay of , which dates the inside them. LUCA is dated with a , from the number of base differences between the genes of living groups. Some of the oldest signs of life lie in rock that formed round on the ancient sea floor, and the genes conserved since LUCA suit life in hot water with no .
| Early Earth | Earth today | |
|---|---|---|
| Free oxygen in the air | about 21% | |
| Ozone layer | none | absorbs the most harmful |
| Greenhouse gases | more carbon dioxide and | less of both |
| Temperature | lower |
In these conditions, carbon compounds may have formed by chemical processes that no longer happen.
A cell is the smallest unit of self-sustaining life: on its own it carries out all the functions of life, from nutrition and growth to response and reproduction. Viruses are usually counted as : they have no , carry out no of their own, and can reproduce only inside a .
In water, molecules like these gather of their own accord into spheres walled by a : . A closed compartment lets the chemistry inside become from the chemistry outside.
Number the steps in order.
Today cells arise only from existing cells, so the first ones must have formed another way. These hypotheses are hard to : early Earth cannot be recreated exactly, and protocells did not .
RNA may have been the first genetic material. Its base sequence carries information that can be , and some RNA molecules reactions: these are . So RNA could have been both the genes and the enzymes of the earliest cells. One still works in every cell today: in the , RNA joins amino acids with .
1234| Early Earth | Earth today | |
|---|---|---|
| Free oxygen in the air | none | about 21% |
| Ozone layer | none | absorbs the most harmful ultraviolet |
| Greenhouse gases | more carbon dioxide and methane | less of both |
| Temperature | higher | lower |
In these conditions, carbon compounds may have formed spontaneously by chemical processes that no longer happen.
A cell is the smallest unit of self-sustaining life: on its own it carries out all the functions of life, from nutrition and growth to response and reproduction. Viruses are usually counted as non-living: they have no cytoplasm, carry out no metabolism of their own, and can reproduce only inside a host cell.
Today cells arise only from existing cells, so the first ones must have formed another way. These hypotheses are hard to test: early Earth cannot be recreated exactly, and protocells did not fossilise.
After a week the water held amino acids: carbon compounds that life needs can form from simple inorganic molecules with no living thing involved. But early Earth's atmosphere was probably different from what they put in the flask, and no polymers formed.
In water, molecules like these gather of their own accord into spheres walled by a bilayer: vesicles. A closed compartment lets the chemistry inside become different from the chemistry outside.
RNA may have been the first genetic material. Its base sequence carries information that can be replicated, and some RNA molecules catalyse reactions: these are ribozymes. So RNA could have been both the genes and the enzymes of the earliest cells. One still works in every cell today: in the ribosome, RNA joins amino acids with peptide bonds.
All living things use the same genetic code, and many genes are shared by every major group of organisms. This is evidence that all life descends from one last universal common ancestor. Other early forms of life may have arisen too, but became extinct through competition with it and its descendants.
Life has been evolving for an immense time: at least 3.5 billion years. Rocks are dated from the decay of radioactive isotopes, which dates the fossils inside them. LUCA is dated with a molecular clock, from the number of base differences between the genes of living groups. Some of the oldest signs of life lie in rock that formed round hydrothermal vents on the ancient sea floor, and the genes conserved since LUCA suit life in hot water with no oxygen.