O LEVEL BIOLOGY COMPLETE NOTES

Biology- A Way of Life

Life appeared on Earth approximately 4.3 billion years ago. The earliest practices of biology were done by the ancient Babylonians and Assyrians.

Biology is the study of living organisms.

Living things have some crucial characteristics which enables us to differentiate between a living and a non-living thing.

They are as follows:
1. Respiration-releases energy
2. Feeding
3. Sensitivity (Irritability)- ability to sense stimuli such as light intensity, gravity, to sense toxins etc
4. Movement- locomotion to search for food
5. Excretion- removal of metabolic waste
6. Growth
7. Reproduction- to produce offsprings and thus prevent extinction
8. Adaptability- to adjust to the surrounding environment accordingly

Living organisms are usually classified into prokaryotes & eukaryotes.

PROKARYOTES

By definition it means 'early nucleus'. Therefore, prokaryotes are organisms which do not have proper nuclei. Their genetic material is exposed and lies in the cytoplasm. Double membrane organelles such as mitochondria and chloroplasts are absent here. 70s ribosomes (site of protein synthesis) are present.
- Example of prokaryotes- Bacteria

EUKARYOTES

These organisms have a proper nucleus where genetic material is surrounded by the nuclear envelope. Here, double membrane organelles are present along with 70s and 80s ribosomes.

Protoctista are a group of mostly unicellular eukaryotes such as Protozoa, plasmodium (malarial parasite) etc. Whereas yeast is a unicellular fungus, algae are plants which range from unicellular forms to larger forms and amoeba, which is a unicellular animal.

All other organisms are mostly multicellular.

We will take a closer look at cells in the next chapter. Hope this book helps you all :)

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