Summary Complete AS/A level Biology B Pearson Edexcel noted
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Topics 1-3
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Edexcel A level Biology B Student Book 2 ActiveBook
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...
Complete notes on Topic 2 Biology- Pearson Edexcel
Complete notes on AS/A level Biology B Pearson Edexcel
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Topics 1-3
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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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