Essay on HL Bio Notes

Submitted By Daniel-Cao
Words: 8674
Pages: 35

Unit 1: Cell Biology

Introduction to Cells

Outline: Cell Theory

1. All living things are made of cells which: are surround by a membrane contain genetic material perform enzyme-catalyzed reactions can harness and use energy to power activities This was proven by biologists who, through microscopes, were able to see that all living things contained cells, albeit various types.
2. Cells are the smallest unit of life. Viruses were thought to be living, and thus would make them the smallest unit of life, but evidence proved that viruses are non-living. Organelles show signs of life, but cannot be sustained. Thus, cells are the smallest known unit of life.
3. All cells come from other cells. Louis Pasteur noticed the development of microbes in his fermenting vessels; could see the development of new cells through mitosis. Some cells defy the standard characteristics of most cells. Examples are:
Giant Algae
Aseptate Fungal Hyphae
Striated Muscle Cell

Functions of a Cell

1. Homeostasis (maintaining internal temperature when the outside changes)
2. Response
3. Metabolism (chemical process in an organism to maintain life)
4. Nutrition
5. Reproduction
6. Growth

All cells (including unicellular organisms) were able to perform these six basic functions to sustain life.


The word “cell” was first used by Robert Hooke when looking at a cork using a homemade microscope in the 17th century.

The first living cell was first looked upon in 1674 by Anton van Leeuwenhoek.

Today’s microscopes:

Electron Microscope
Compound Microscope
Resolution for substances 0.001 μm (1 nm)
Allow us the see the ultrastructure of cells
Shines light through a living or dead specimen in 2D
Stains are used to separate each component
Cannot resolve images of structures smaller than 0.2 μm (200 nm)
Maximum magnification: 400x
Allow us to see the structure of cells

What is resolution? making separate parts of an object distinguishable to by eye light microscopes reveal the structure of a cell, electron microscopes reveal the ultrastructure

Ultrastructure of Cells

Ultrastructure: all the structures of a biological specimen that are at least 0.1nm in their smallest dimension.

Prokaryotes are smaller than eukaryotes and came first in terms of evolution.
The word prokaryote can be broken down into “pro” (before) “karyotes” (nucleus).

Example of a prokaryote: E. coli

Note: Parts of a Prokaryote are called parts/ultrastructure rather than the term “organelle” as very structures in prokaryotes are regarded as organelles.

Prokaryotes reproduce asexualy by the process of binary fission: the DNA is replicated semi-conservatively the two DNA loops attach to a membrane the membrane elongates and pinches off (cytokinesis) forming two separate cells the two daughter cells are genetically identical (clones)

Eukaryotes have compartmentalized cell structures

Advantages to being compartmentalized:

1. Efficiency of Metabolism - enzymes and substrates are can localized and much more concentrated
2. Localised conditions - pH and other such factors can be kept at optimal levels. The optimal pH level for one process in one part of the cell
3. Toxic / damaging substances can be isolated - e.g digestive enzymes (that could digest the cell itself!) are stored in lysosomes.
4. Numbers and locations of organelles can be changed - depending on the cell’s requirements


Nucleus: generally spherical with a double membrane pores (holes) are present in the membrane contains genetic information in the form of chromosomes (DNA and associated Histone proteins uncoiled chromosomes are referred to as chromatin - they stain a dark color and are concentrated at the edges of the Nucleus mRNA is transcribed in the nucleus (prior to use in protein synthesis in the cytoplasm) mRNA leaves the nucleus via the pores (DNA is too large to move through the pores)

Mitochondrion pl. (Mitochondria) has a double membrane (smooth outer membrane and a folded…