Biology – Patterns in nature – 1. Organisms are made of cells that have similar structural characteristics

Historical development of the cell theory

The development of the cell theory began in the late 1400s and early 1500s when lenses were first being used. In 1965, Robert Hooke was the first to look at an object (cork) under a microscope. A few years later in 1676, Leuinhooke looked at water and observed "living things". In 1827, Robert Brown showed that all living things were made of cells and that all cells were made up of smaller organelles.

Evidence supporting the cell theory

Cell theory is the theory of Schleiden and Schwann in 1838 that states "all living things are made up of cells, and all cells are made from pre-existing cells". There is much evidence supporting the cell theory, including the observation of cells through microscopes, the use of stains and dies to observe chemical processes for example observing chemical processes such as cell division, and the use of electron microscopes to gain an understanding of cell and organelle structure.

Identify cell organelles, their structure and function

Organelle	How organelle can be observed	Structure and function of organelle
Cell membrane	Light microscope	Composed of a bi-layer of phospholipids with proteins embedded within. Acts as a wall to control the flow of substances in and out of a cell.
Cytoplasm	Light microscope	A watery fluid which contains water and dissolved salts. Supports and suspends organelles and provides the cell organelles with water.
Nucleus	Light microscope	Control centre of a cell, surrounded by a double layered cell membrane which serves to protect DNA and stop it from leaving the nucleus. The nucleus houses DNA and regulates cell functions via protein synthesis.
Nuclear membrane	Electron microscope	A double layered membrane surrounding the nucleus which allows RNA and proteins in and out of the nucleus.
Nucleolus	Electron microscope	A dark spherical area inside the nucleus, contains RNA
Mitochondria	Electron microscope	Double membrane, inner membrane is folded into a cristrae for increased SA. Mitochondria converts chemical energy into biological energy, performing cell respiration. (glucose + oxgen -> carbon dioxide + water + ATP (chemical energy – Adenosine triphosphate)
Endoplasmic Reticulum	Electron microscope	A system of membranes, which act to connect the nuclear membrane to the cell membrane. Used for transport and provides a surface for chemical reactions. There are two types of E.R. smooth: detoxifies harmful bacteria and makes lipids and steroids. No attached ribosomes Rough: aids the production of proteins thanks to attached ribosomes.
Ribosomes	Electron Microscope	The site of protein synthesis, where protein is built by the cell. They can be attached to rough E.R. or floating in cytoplasm.
Golgi body	Electron Microscope	Flattened sacs of cell membrane, stacked loosely on top of one another. Collects proteins produced by cells and packages them into vesicles.
Vacuoles and vesicles	Electron Microscope	Storage sacs containing food water and waste. Cacuoles are larger and formed in phagocycotis (cell eating) Vacuoles are smaller and formed by phagocytosis (cell eating)
Lysosomes	Electron Microscope	Double membraned vacuoles which contain lytic enzymes (digestive enzymes) Digest food vacuoles and allow an organism to destroy old/ malfunctioning cell parts.
Cilia and flagella	Optical Microscope	Hair like projectiles which use energy to move cells. Made of "microtubules" and function to move the cell or fluids. Cilia – short and many flagella – long and few
Centrioles (animal cell only)	Electron microscope	A pair of organelles which grow spindle fibres to attach and move chromosomes during mitosis
Cell wall (plant cell only)	Optical microscope	Made of long strands o cellulose, lignin and pectin and support the structure of an organism, protect the cell and form a bridge to adjacent cells
Chloroplasts (plant cell only)	Electron microscope	Have a double layered membrane and structures called stroma, which are bound to the membrane and organized into stacks called grana. Contain pigments and enzymes for photosynthesis as well as ribosomes and DNA.