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AQA AS Biology notes Topic 2 – Cells
Topic 2 – Cells
Table of Content
2.1 Cell structure......................................................................3
2.1.1 Structure of eukaryotic cells....................................................................................................................................................3
Nucleus.......................................................................................................................................................3
Mitochondria..............................................................................................................................................4
Chloroplasts................................................................................................................................................4
Golgi apparatus..........................................................................................................................................5
Lysosomes..................................................................................................................................................5
Ribosomes..................................................................................................................................................5
Cell wall of plants......................................................................................................................................6
Vacuoles.....................................................................................................................................................6
Cell organization.........................................................................................................................................7
2.1.2 Structure of prokaryotic cells and of viruses...........................................................................................................................7
Prokaryotic cells.........................................................................................................................................7
Viruses........................................................................................................................................................8
2.1.3 Methods of studying cells.......................................................................................................................................................9
Microscopy.................................................................................................................................................9
Optical microscope (light microscope).......................................................................................................9
Transmission electron microscope (TEM)..................................................................................................9
Scanning electron microscope (SEM).......................................................................................................10
Cell fractionation......................................................................................................................................11
2.2 All cells arise from other cells...........................................12
Mitosis......................................................................................................................................................12
Cancer.......................................................................................................................................................15
2.3 Transport across cell membranes.....................................16
Cell-surface membrane............................................................................................................................16
Phospholipids bilayer...............................................................................................................................17
Proteins....................................................................................................................................................17
Glycocalyx.................................................................................................................................................17
Cholesterol...............................................................................................................................................18
Fluid-mosaic model..................................................................................................................................18
Diffusion across cell membrane...............................................................................................................19
Simple diffusion........................................................................................................................................19
1
, AQA AS Biology notes Topic 2 – Cells
Facilitated diffusion..................................................................................................................................19
Channel proteins (for charged ions).........................................................................................................19
Carrier proteins (for large molecules)......................................................................................................19
Factors that affect rate of diffusion.........................................................................................................19
Fick's Law..................................................................................................................................................20
Osmosis....................................................................................................................................................20
Active transport........................................................................................................................................22
Co-transport.............................................................................................................................................22
Sodium-potassium pump.........................................................................................................................23
2.4 Cell recognition and the immune system..........................23
Antigen & Phagocytosis............................................................................................................................23
3 lines of defence.....................................................................................................................................24
Phagocytosis (non-specific immune response)........................................................................................24
Lymphocytes............................................................................................................................................25
Antibodies................................................................................................................................................26
Immunity..................................................................................................................................................27
Vaccination...............................................................................................................................................27
Influenza: Antigenic Drift & Shift..............................................................................................................31
Monoclonal Antibodies............................................................................................................................32
ELISA (enzyme linked immunosorbent assay) test..................................................................................32
HIV & AIDS................................................................................................................................................33
2
, AQA AS Biology notes Topic 2 – Cells
2.1 Cell structure
2.1.1 Structure of eukaryotic cells
Nucleus
Contains DNA / chromosomes / holds genetic info of cell
May have 1+ nucleoli
Controls cell's activities through transcription on mRNA
Structure
Nucleolus Makes ribosomes with proteins & ribosomal RNA (ribosome synthesis)
Chromatin Made of histone, which package linear DNA into compact structure to fit
nucleus
Nucleoplasm Granular, jelly-like material makes up rest of nucleus
Nuclear envelope Double membrane surrounds nucleus
Enclose & protect DNA
Controls materials in & out of nucleus
Nuclear pores Allow substance eg mRNA to move between nucleus & cytoplasm
Endoplasmic 3D sheet-like membrane that spread through cytoplasm
reticulum Cisternae - membrane made of flattened sacs which enclose a network of
tubules
Rough endoplasmic reticulum (RER) Smooth endoplasmic reticulum (SER)
Has ribosomes on outer surfaces of No ribosome but more tubular in
membrane appearance
Function Function
Provide large SA for protein Synthesise, store & transport
synthesis carbohydrate & lipids
Describe how the RER is involved in the production of enzymes. (2)
RER has ribosomes that make proteins which an enzyme is
3
, AQA AS Biology notes Topic 2 – Cells
Mitochondria
Structure
Double membrane Outer membrane: permeable to small molecules; inner: selectively permeable
Cristae Extensions of inner membrane
Provide large SA for enzymes & other protein involved in aerobic respiration to
attach for ATP production
Mitochondria in muscle cells have more cristae than mitochondria in skill cells.
Explain the advantage of mitochondria in muscle cells having more cristae (2)
Large SA for more enzymes for ATP production
Muscle cells use more ATP than skin cells
Matrix
Functions
Site of aerobic respiration producing ATP for energy release
Cells that have high level of metabolic activity eg muscle & epithelial cells, require plentiful supply
of ATP, so no & size of mitochondria & no of cristae are high
Chloroplasts
Structure
Chloroplast envelope Double plasma membrane
Highly selective in material in & out of cell
Grana (stacks of 100 disc-like Thylakoids contain chlorophyll
structure called thylakoids) Some thylakoids have intergranal lamellae (tubular extensions) to
connect thylakoids in adjacent grana
Granal membranes provide large SA for attachment of
chlorophyll, electron carries & enzymes that carry out 1st stage of
photosynthesis (light absorption)
Stroma Fluid filled matrix, which
possess all enzymes
4
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