2.1 - Cell Structure and Microscopes Flashcards
What is the eyepiece graticule?
A measuring device
Placed in the eyepiece of a microscope
Acts as a ruler when viewing object under the microscope
What is the stage graticule?
Small scale placed placed on a microscope stage
Used to calibrate the value of eyepiece divisions at different magnifications
What is resolution?
The clarity of an image, the higher the resolution the clearer the image
What is magnification?
The number of times larger an image appears, compared with the size of the object
What is the maximum magnification of a light and electron microscope?
Light: X1500
Electron:
What is the maximum resolution of both a light microscope and an electron microscope?
Light:
Electron:
How big are typical eukaryotic cells?
20 micrometers
How big are typical prokaryotic cells?
0.1 - 5 micrometers
What is a photomicrogtaph?
Photograph of an image seen using and optical microscope
Advantages of optical microscopes
Relatively cheap
Easy to use
Portable, able to use in the field and laboratories
Able to study living specimens
Disadvantages of an optical microscope
Low Resolution
Low Magnification
So cannot see some organelles in a cell
Equation for total magnification of a microscope
Total magnification = objective lens x eyepiece lens
About laser scanning (confocal) microscopes
Use laser light to scan object and show it on a computer screen
High res and high contrast images
Used mainly in medical profession
Can study living specimens
How electron microscopes work
Beam of fast-travelling electrons hit object, focused by magnets
Have much greater magnification and resolution than optical microscopes
Details of Transmission Electron Microscopes(TEM)
Form 2D black-and-white images
Magnification: x 2 million
Can study living specimens
Electrons go through specimen
Features of Scanning Electron Microscopes
Electrons bounce off the specimen
Max magnification: x 200,000
Gives a 3D image
How are specimens for micro graphs prepared?
Specimens are dehydrated
Embedded in wax - reduced distortion when slicing
Cut into thin slices called sections
Preserved in special chemicals
Importance of staining specimens
Bind to certain molecules
Makes them easier to see
What organelle do animal cells not have that plants do, and what do animal cells have that plants do not?
Plant cells have:
Large Vacuole
Chloroplast
Cell Wall
Animal Cells have:
Centriole
Lysosome
Definition of organelles
Small structures within cells, each of which has a specific function
Describe the structure of the nucleus?
Surrounded by a double membrane, called the nuclear envelope
There are pores in the nuclear envelope
Contains genetic material of the cell
Genetic material is in form chromatin.
Describe the structure of the nucleolus
Does not have a membrane around it
Contains RNA
What is the function of the nucleus?
Controls the cell’s activity
Stores the genetic information(genome) of the cell
Transmits genetic information(during mitosis)
Provides instructions to ribosomes for protein synthesis
What is the function of the nucleolus?
Assembles ribosomes in the cell
Structure of the RER
System of membranes, containing fluid-filled cavities(cisternae) that are continuous with the nuclear membrane
It is coated with ribosomes
What is the function of the RER?
Processes proteins from ribosomes
Proteins actively pass through membrane
Sent to the Golgi apparatus
Structure of the SER
System of membranes, containing fluid-filled cavities(cisternae) that are continuous with the nuclear envelope
No ribosomes on its surface
Function of the SER
Involved with absorption, synthesis and transport of lipids(from the gut)
Structure of the Golgi apparatus
A stack of membrane-bound flattened stacks.
Secretory vesicles bring material to and from the Golgi apparatus
Function of the Golgi apparatus
Synthesis proteins from the RER
Packages them into vesicles
(Then stored in the cell or moved to plasma membrane)
- modifies and repackages proteins from the RER - repackaged back into secretory vesicles
- modified - add a protein/carb group
Structure of the mitochondria
Spherical, or rod-shaped
Surrounded by two membranes with a fluid-filled space between them
Inner membrane highly folded into cristae
Inner part of mitochondrion is a fluid-filled matrix
Function of the mitochondria
Site of ATP production during aerobic respiration
Abundant in cells where much metabolic activity takes place, e.g muscles
Structure of the chloroplasts
Surrounded by a double membrane or envelope
Inner membrane contains flattened membrane stacks called thylakoids
Each stack of thylakoids is called a granum
Fluid filled matrix called the stroma
Chloroplasts contain loops of DNA and starch grains
Function of the chloroplasts
Site of photosynthesis
Create ATP in the plant, occurs in grana
Hydrogen reduces carbon dioxide
Uses energy form ATP to make carbohydrates
Occurs the stroma
Structure of the vacuole
Surrounded by a membrane called the tonoplast, and contains fluid
Function of the vacuole
Only found in plants
Contains cell sap(water and solutes)
Maintains cell stability as pushes against cell wall makes cell turgid
Helps support the plant
Structure of lysosome
Small bags formed from Golgi Apparatus surrounded by a single membrane
Contain digestive enzymes
Abundant in phagocytic cells(white blood cell)
Function of lysosome
Separates digestive enzymes from rest of cell
Engulf old cell material to digest and reuse them
Structure of cilia
Hair like structures protruding from cells
Each contain microtubules
Formed from centrioles
Function of cilia
Line airways to move mucus
What does the undolipodia do?
Flagella
Allows the sperm cell in humans to move
Propels it forward
Structure of ribosomes
Made of ribosomal DNA Made in the nucleolus Pass through nuclear envelope into cytoplasm Some remain free in cytoplasm Some attach to RER
Function of Ribosomes
Site of Protein Synthesis
Structure of centrioles
Two bundles of microtubules
Made of tubulin protein subunits
Arranged to form a cylinder
Function of centrioles
Involved in formation of cilia and undulipodia(sperm flagella)
Structure of cytoskeleton
- consists of rod-like microfilaments made of subunits of actin
- polymers of actin
- straight, cylindrical microtubules- made of tubular subunits
Function of cytoskeleton
3 Marks
- Change shape of cell - E.g. exocytosis, requires ATP
- Provide support and structural integrity to cell
- Movement of organelles within cell - E.g. movement of vesicles towards plasma membrane
- Movement of undulipodia to move cell - requires ATP
- Formation of spindle - for movement of chromosomes in mitosis
Structure of cell wall(cellulose)
Made form bundles of cellulose fibres
Outside of plasma membrane
Function of cell wall
Provides strength and support
Maintains cells shape
Contribute to strength and support of plant
Permeable - allow solutions to pass through
(Fungi have cell wall of chitin)
Process of making and secreting a protein(simple)
- mRNA copy of the instructions (gene)
for insulin is made in the nucleus. - mRNA leaves the nucleus through a nuclear pore.
- mRNA attaches to a ribosome
- Ribosome reads the instructions to assemble the protein (insulin).
- Insulin molecules are ‘pinched off’ in vesicles and travel towards Golgi apparatus.
- Vesicle fuses with Golgi apparatus.
- Golgi apparatus processes and packages insulin molecules ready for release.
- Packaged insulin molecules are ‘pinched off’ in vesicles from Golgi apparatus and move towards plasma membrane.
- Vesicle fuses with plasma membrane.
Protein leaves plasma membrane by exocytosis - requires ATP
Prokaryotic and eukaryotic cells similarities
A plasma membrane
Cytoplasm
Ribosomes
DNA and RNA
Differences between eukaryotes and prokaryotes
Much smaller No nucleus No membrane-bound organelle(mitochondria) Cell wall made of peptidocglycan Smaller ribosomes DNA floats free in cytoplasm
What different organelles do prokaryotes have?
Protective waxy capsule
Plasmid DNA
Flagella - allows cell to move
Pili - small hair like projections that enable bacteria to adhere to host cell
Resolution def
The ability to distinguish between two objects as separate in an image
- it is the ability to see detail in an image
Suggest two processes inside cells that rely on the cytoskeleton for movement.
- Movement of chromosomes/chromatids in cell division
- movement of cytoplasm in cytokinesis
- vesicles are moved/shuttled across the cytoplasm by the cytoskeleton (to RER) in protein synthesis
- RNA/proteins are moved by microtubules in protein synthesis
Structures C and E are both examples of mitochondria. Suggest why E looks so different to C.
(2 Marks)
- cut in different planes / angles
- mitochondria may naturally vary in shape - longer than wide etc.
- artefact / deformed during preparation of section
Membranes are a fundamental part of the cell. They are found both at the surface of a cell and inside a cell.
(a) State three roles of membranes inside cells.
(3 Marks)
- make compartments within cell organelles - e.g. vesicles
- isolation of organelle contents from substances or metabolic pathways outside the cell, e.g. hydrolytic enzymes in lysosomes
- site of attachment for enzymes on organelle membranes, e.g. ribosomes and tRNA
- provide selective permeability
- creation of concentration gradients
Outline how the vesicles are moved from one organelle to another.
(3 Marks)
- cytoskeleton
- provides pathways for movement
- vesicles move along microtubules
- microtubules extend
- this requires ATP
Units of measurement in terms of metres
Km - 1x10^3 metres Metres - 1x10^1 metres Dm - 1x10^-1 metres Cm - 1x10^-2 metres Mm - 1x10^-3 metres Micrometre- 1x10^-6 metres Nanometer- 1x10^-9 metres
Describe the advantages of staining specimens to be viewed under a microscope.
(2 Marks)
- Easier to view different organelles
- (staining) provides / increases, contrast ;
- identify / recognise, cell types / organelles / parts of cell ;
- identify / recognise, different (named), compounds / molecules
