Biology

The document covers various topics in biology, including the cell, tissues, life processes, and classification of living organisms.

The Cell:

• Definition and Discovery: The cell is the building block, fundamental, and structural or functional basis of life. Cell study is called cytology. Robert Hooke first discovered the cell in 1665 by observing cork, a dead cell with a honeycomb shape. Antonie van Leeuwenhoek discovered free-living cells in water (1674), and Robert Brown discovered the nucleus (1831).

• Cell Theory: The cell theory states that all plants and animals are composed of cells and that the cell is the basic unit of life. It was given by Schleiden and Schwann (1838), with Virchow later adding that new cells are formed from pre-existing cells.

• Cell Parts:

  • Cell Membrane: Thin, elastic, flexible, living, outermost covering, selectively permeable, and composed of proteins and lipids.

  • Cell Wall: Only present in plants, bacteria, and fungi. It is non-living, freely permeable, determines shape, is made of cellulose, and provides strength and turgidity.

  • Nucleus: Centrally located, large in size, the largest cell structure, and the "Brain of the cell". It was discovered by Robert Brown.

Life Processes:

• Life Process Components: The four components of the life process are Digestion, Respiration, Circulation, and Excretion.

• Human Digestion: Salivary amylase breaks complex carbohydrates to simple carbohydrates in the mouth. In the stomach, HCl kills bacteria and creates an acidic medium (pH 1.6), and Pepsin breaks protein into amino acids. Major digestion occurs in the small intestine, which is the longest part of the alimentary canal.

Classification of Life:

• 5 Kingdoms: Robert Whittaker proposed the 5 kingdoms classification in 1969. The kingdoms are Monera (prokaryotic, unicellular), Protista (eukaryotic, unicellular), Fungi (multicellular except yeast, cell wall made of chitin), Plantae (multicellular, eukaryotes, cell wall present), and Animalia (multicellular, eukaryotic, cell wall absent, heterotrophic).

• Animal Phyla: The document mentions 9 phyla: Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Mollusca, Arthropoda, Echinodermata, and Chordata. Arthropoda is the largest phylum in the animal kingdom.