B1: Cell-level systems
Chapter 1.1: Cell structures
Seven life processes
● Movement
● Reproduction
● Sensitivity
● Growth
● Respiration
● Excretion
● Nutrition
Two main types of cells:
● Prokaryotes
○ Do not contain nucleus
○ Genetic material floats in cytoplasm
○ Smaller than eukaryotes (1-10μm)
○ Mostly bacteria cells
● Eukaryotes
○ Contain nucleus
○ Genetic material in nucleus
○ Larger than prokaryotes (10-100μm)
○ Mostly plant and animal cells
Subcellular parts in cells:
● Cell membrane
○ Controls which substances go in and out of cell
○ Eukaryotes and Prokaryotes
● Nucleus
○ Controls activities of cell
○ Contains genetic material - instructions to make new cells or organisms
○ Eukaryotes only
● Mitochondrion
○ Where respiration happens - enzymes allow oxygen and glucose to react with each
other and reaction transfers energy to organism
○ Eukaryotes only
● Cytoplasm
○ Jellylike substance where chemical reactions happen
○ Prokaryotes and Eukaryotes
● Vacuole
○ Full of cell sap (sugar and salts solution) - keeps cell rigid and supports plant and cell
○ Plant cells only
● Cell wall
, ○ Made of cellulose in plants, peptidoglycan in bacteria - makes wall rigid and supports
cell
○ Plant cells and Prokaryotes
● Chloroplast
○ Contains green chlorophyll - transfers energy from sun to plant as light
(photosynthesis)
○ Only in green parts of plant - needed by plants to make their own food
○ Plant cells only
● Genetic material
○ In nucleus for Eukaryotes - floats freely in cytoplasm
○ One long strand of DNA
○ Prokaryotes only
● Pili
○ Hairlike structures outside cell wall that allow cell to attach to structures
○ Can also be used to transfer genetic material between bacteria
○ Bacteria only
● Slime capsule
○ Outside cell wall
○ Protects bacteria from drying out and from poisonous substances
○ Helps bacteria to stick to smooth surfaces
○ Bacteria only
● Plasmid
○ Circular piece of DNA used to store extra genes
○ Only needed for situations of stress eg. antibiotic resistance genes
○ Bacteria only
● Flagella
○ Tail-like structures that allow cell to move through liquids
○ Bacteria only
Bacteria
● Smallest living organisms
● Unicellular
● Usually 1μm
Light microscopes:
● Properties
○ Cheap to buy and operate
○ Small and portable
○ Simple to prepare sample
○ Natural colour of specimen is seen unless stains are
used
○ Specimen can be alive or dead
○ Up to 0.2μm (2x10-7m)
○ Uses light to make image
● How to use
○ Select objective lens with lowest magnification
○ Place slide on stage
○ Move stage to highest position
○ Turn coarse focus knob slowly until you can see object
○ Turn fine focus slowly until object comes into clear focus
○ To see clearer, repeat steps with higher magnification objective lens
● Calculating magnification
, ○ Eyepiece x Objective
● Staining cells
○ Many cells are colourless
○ Stains make structures easy to see
○ Common stains:
■ Methylene blue: easier to see animal cell’s nucleus
■ Iodine: easier to see plant cell’s nucleus
■ Crystal violet: stains bacterial cell walls
○ How to apply
■ Place cells on glass slide
■ Add one drop of stain
■ Place coverslip on top
■ Press coverslip gently to remove air bubbles
Electron microscopes:
● Properties
○ Expensive to buy and operate
○ Large and difficult to move
○ Sample preparation is complex
○ Black and white images - false colour can be added to
image
○ Specimens are dead
○ Up to 0.1nm (1x10-10m)
○ Uses electrons to make image
○ Developed in 1930’s
● Transmission Electron Microscopes (TEM)
○ Most magnified
○ Beam of electrons pass through thin slice of sample
○ Beam is focused to produce image
● Scanning Electron Microscopes (SEM)
○ 3D image of surface
○ Send beam of electrons across surface of specimen
○ Reflected electrons are collected to produce image
Chapter 1.2: What happens in cells?
DNA
● Inside nucleus
● Long molecule of DNA is chromosome
● Most people have 23 pairs of chromosomes
● Half of chromosomes come from mother and half from father
● DNA is identical only in identical twins and clones
● Arranged into sections
● Genes: short sections of DNA that code for certain characteristics eg. eye colour
● Code inside genes causes certain proteins to be made
● Proteins determine cell’s function eg. protein haemoglobin
● Combination of genes in an organism controls how it functions and what it looks like
Structure of DNA
● 2 strands joined by bases
● Strands are twisted together to form a double helix
● Made of lots of small units called nucleotides joined together, meaning DNA is a polymer
Chapter 1.1: Cell structures
Seven life processes
● Movement
● Reproduction
● Sensitivity
● Growth
● Respiration
● Excretion
● Nutrition
Two main types of cells:
● Prokaryotes
○ Do not contain nucleus
○ Genetic material floats in cytoplasm
○ Smaller than eukaryotes (1-10μm)
○ Mostly bacteria cells
● Eukaryotes
○ Contain nucleus
○ Genetic material in nucleus
○ Larger than prokaryotes (10-100μm)
○ Mostly plant and animal cells
Subcellular parts in cells:
● Cell membrane
○ Controls which substances go in and out of cell
○ Eukaryotes and Prokaryotes
● Nucleus
○ Controls activities of cell
○ Contains genetic material - instructions to make new cells or organisms
○ Eukaryotes only
● Mitochondrion
○ Where respiration happens - enzymes allow oxygen and glucose to react with each
other and reaction transfers energy to organism
○ Eukaryotes only
● Cytoplasm
○ Jellylike substance where chemical reactions happen
○ Prokaryotes and Eukaryotes
● Vacuole
○ Full of cell sap (sugar and salts solution) - keeps cell rigid and supports plant and cell
○ Plant cells only
● Cell wall
, ○ Made of cellulose in plants, peptidoglycan in bacteria - makes wall rigid and supports
cell
○ Plant cells and Prokaryotes
● Chloroplast
○ Contains green chlorophyll - transfers energy from sun to plant as light
(photosynthesis)
○ Only in green parts of plant - needed by plants to make their own food
○ Plant cells only
● Genetic material
○ In nucleus for Eukaryotes - floats freely in cytoplasm
○ One long strand of DNA
○ Prokaryotes only
● Pili
○ Hairlike structures outside cell wall that allow cell to attach to structures
○ Can also be used to transfer genetic material between bacteria
○ Bacteria only
● Slime capsule
○ Outside cell wall
○ Protects bacteria from drying out and from poisonous substances
○ Helps bacteria to stick to smooth surfaces
○ Bacteria only
● Plasmid
○ Circular piece of DNA used to store extra genes
○ Only needed for situations of stress eg. antibiotic resistance genes
○ Bacteria only
● Flagella
○ Tail-like structures that allow cell to move through liquids
○ Bacteria only
Bacteria
● Smallest living organisms
● Unicellular
● Usually 1μm
Light microscopes:
● Properties
○ Cheap to buy and operate
○ Small and portable
○ Simple to prepare sample
○ Natural colour of specimen is seen unless stains are
used
○ Specimen can be alive or dead
○ Up to 0.2μm (2x10-7m)
○ Uses light to make image
● How to use
○ Select objective lens with lowest magnification
○ Place slide on stage
○ Move stage to highest position
○ Turn coarse focus knob slowly until you can see object
○ Turn fine focus slowly until object comes into clear focus
○ To see clearer, repeat steps with higher magnification objective lens
● Calculating magnification
, ○ Eyepiece x Objective
● Staining cells
○ Many cells are colourless
○ Stains make structures easy to see
○ Common stains:
■ Methylene blue: easier to see animal cell’s nucleus
■ Iodine: easier to see plant cell’s nucleus
■ Crystal violet: stains bacterial cell walls
○ How to apply
■ Place cells on glass slide
■ Add one drop of stain
■ Place coverslip on top
■ Press coverslip gently to remove air bubbles
Electron microscopes:
● Properties
○ Expensive to buy and operate
○ Large and difficult to move
○ Sample preparation is complex
○ Black and white images - false colour can be added to
image
○ Specimens are dead
○ Up to 0.1nm (1x10-10m)
○ Uses electrons to make image
○ Developed in 1930’s
● Transmission Electron Microscopes (TEM)
○ Most magnified
○ Beam of electrons pass through thin slice of sample
○ Beam is focused to produce image
● Scanning Electron Microscopes (SEM)
○ 3D image of surface
○ Send beam of electrons across surface of specimen
○ Reflected electrons are collected to produce image
Chapter 1.2: What happens in cells?
DNA
● Inside nucleus
● Long molecule of DNA is chromosome
● Most people have 23 pairs of chromosomes
● Half of chromosomes come from mother and half from father
● DNA is identical only in identical twins and clones
● Arranged into sections
● Genes: short sections of DNA that code for certain characteristics eg. eye colour
● Code inside genes causes certain proteins to be made
● Proteins determine cell’s function eg. protein haemoglobin
● Combination of genes in an organism controls how it functions and what it looks like
Structure of DNA
● 2 strands joined by bases
● Strands are twisted together to form a double helix
● Made of lots of small units called nucleotides joined together, meaning DNA is a polymer
