This includes the perfect and complete summary notes from Topics 1 to 3 for the Biology B AS/A level exam using the Person Edexcel exam board. These notes are written following the Person Edexcel Specification, including all the necessary requirements according to the specification. They also incl...
Topic 2: Cells, Viruses and Reproduction of Living Things
2.1 Eukaryotic and prokaryotic cell structure and function
Cell Theory; an unifying concept that states cells are a fundamental unit of structure, function and organisation in all living
organisms
1. Matthias Schleiden; plants are made of cells
2. Theodore Schwan; animals are made of cells
3. Rudolf Virchow; cells come from pre-existing cells
Organisation of eukaryotic cells;
1. A Cell is a basic functional and structural unit in organisms
2. A Tissue is a group of cells working together to carry out a particular function
3. An Organ is made from different tissues working together to perform specific functions
4. An Organ system is a group of organs working together to carry out body functions
Specialised Tissue Organ Organ Organism
cells System
Endosymbiotic Theory; eukaryotic organelles derive from prokaryotic cells that were engulfed by larger prokaryotic cells
- Organelles have a double membrane as though it has been engulfed by a larger cell
- Organelles and bacteria cell;
1. Circular DNA
2. 70S ribosomes (mitochondria + chloroplast)
3. Reproduce by binary fission
Prokaryotic Cells; Bacteria, cyanobacteria and Eukaryotic cells; Animals, plants, protoctists, algae and
archaebacteria fungi
Small (5 um) and older Big (10 um) and younger
Always unicellular Often multicellular
No membrane bound nucleus/organelles Double membrane bound nucleus/organelles
Circular DNA with no protein Linear DNA with protein
Small ribosomes (70S) Large ribosomes (80S)
No cytoskeleton Always has a cytoskeleton
Mobility by flagellum made of flagellin Mobility by undulipodium made of tubulin
Cell division by binary fissions Cell division by meiosis/mitosis
Asexual reproduction Asexual/sexual reproduction
- Svedberg (S); a unit to measure how quickly particles settle in a centrifuge depending on the size and shape of
the particle
Prokaryotes (*only found in prokaryotic cells)
, Plasmids* - Small, circular, single length of DNA
- Codes for bacterial phenotype- in addition to the genetic information of the nucleoid
- Reproduces independently of the nucleoid
- Transfers from one bacterium to another using the pili- sexual reproduction
Nucleoid - Long, circular strand of DNA with no proteins
- Folded and coiled to fit
- Does not have a membrane-bound nucleus
70S - Free in the cytoplasm- not attached to membranes
Ribosomes - Carry out protein synthesis
- Subunits; 30S and 50S
Cell Wall - Made of peptidoglycan (polymer of sugar and amino acids)
- Thick layer to maintain the shape
- Strength and support
- Prevents the cell from bursting
Cell Surface - Site of respiratory enzymes as they have no mitochondria
Membrane - Infolding in the membrane- mesosomes
Pili* - Pili; thread-like protein projections
- Used for attachment to a host and sexual reproduction
- Make bacteria more vulnerable as bacteriophage use them as an entry point to the cell
- Allow plasmids to move from cell to cell
Flagella - Used to move
- A rigid rotating tail
- Made of many stranded helix of protein flagellin
Capsule/slime - Protective layer
layer* - Retain moisture and stick to surfaces
Eukaryotes
Nucleus - Largest organelle (1-20 um)
- Surrounded by a nuclear envelope; double nuclear membrane containing nuclear pores (large
holes containing proteins that control the movement of substances so that the nucleus can
control events in the cytoplasm)
- Inside there are proteins and nucleic acids (DNA and RNA)
- When the cell is not dividing DNA is bonded to the protein chromatin
- During cell division the chromatin becomes condensed into chromosomes
- Nucleolus; region of dense linear DNA and protein which produces ribosomes
- Protoplasm; cytoplasm and the nucleus
- Nucleoplasm contains chromatin
80S Ribosomes - Smallest and most numerous organelle
- Made of ribosomal RNA and protein
- Site of protein synthesis
- No membrane
- Found free in the cytoplasm or attached to the rough endoplasmic reticulum
- Mitochondria and chloroplast contain 70S; reproduced independently in these when the cell
divides
Endoplasmic - 3D network of membrane bound cavities in the cytoplasm making up a large part of the cellular
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