A2.2 Cell Structure Flashcards
what does the cell theory state?
(3 things)
that:
- All organisms are made up of one or more cells
- Cells are the smallest unit of life
- All cells come from pre-existing cells
Compare the use of the word theory in daily language and scientific language
daily:
- a theory = a guess (there is doubt)
scientific:
- a theory = has been shown to be true through repeated observations and experiments (no current doubt)
inductive VS deductive reasoning?
inductive: theories developed from specific observations
(specific –> general)
deductive: generating predictions from theories (general –> specific)
what type of reasoning (inductive / deductive) led to the development of the cell theory? why?
inductive!
because the cell theory is based on observations (specific observations –> general theory)
Outline the process of inductive reasoning that led to the development of the cell theory
- Biologists examined tissues from plants and animals (later from fungi, bacteria and protists)
- They saw that every specimen contained at least one or more cells (basically, they noticed a trend)
- From this, they developed a general theory: that all organisms consist of cells
What is a use of deductive reasoning? What can it be used for?
it can be used to predict characteristics of a newly discovered organism
How can deductive reasoning be used to predict characteristics of a newly discovered organism?
it can do this because it is capable of making predictions based on general background info to form a specific conclusion (about the new organism)
–> it’ll take existing general knowledge to make an inference about possible characteristics of the new organism
(ex. based on cell theory, we can predict that a newly discovered organism will consist of one or more cells!)
what are the 2 most commonly used microscopes?
- Light microscope
- Electron microscope
light microscope? (5 things)
- Widely used in schools
- Inexpensive
- Simple specimen prep
- Magnifies up to x2000
- Specimens can be dead or alive
electron microscope? (4 things)
- Expensive
- Preparation of specimens = very complex
- Magnifies up to x500,000
- Specimens have to be dead
Definition of Magnification?
The number of times larger an image is than the object
Definition of Resolution?
The minimum distance between two points at which they can still be distinguished
- NOTE! A resolution of 0.1 nm is higher than a resolution of 200 nm.
- The greater the value, the lower the resolution.
similarities between a light and electron microscope? (3 things)
they both:
- use radiation to create images
- rely on magnification and resolution to make specimens visible
- are used to examine objects that are too small to be seen with the naked eye
how do you calculate the total microscope magnification?
you calculate the total microscope magnification by:
- multiplying the magnifying power of the ocular by the magnifying power of the objective lens
(ex. if the magnifying power of the ocular is 10x and the magnifying power of an objective is 4x, the total magnifying power = 40x)
how to use a light microscope? (including how to focus the microscope on the image)
- Place a slide on the stage + center it under the objective lens
- Turn the revolving nosepiece so that the lowest power objective lens is “clicked” into position
- Turn the coarse focus knob so that the stage moves upward toward the objectives
- Move the stage as far as it will go without touching the slide
- Look through the eyepiece + adjust light source and diaphragm until you attain the maximum comfortable level of light
- Slowly turn the coarse adjustment so that the stage moves down (away from the slide)
- Continue step 6 until the image comes into broad focus
- Then turn the fine adjustment knob until you get perfect focus
Temporary mounts are also known as?
wet mounts!
what is a wet mount and why is it used?
- a wet mount is when a drop of water is used to suspend the specimen between the slide and cover slip
- it is done to observe motile samples that need to be stained prior to viewing
what are stains and why are they used?
- stains = chemicals that bind to structures within the sample
- they are used to help visualise certain structures (because cells and their structures are usually transparent)
- usually added when making a wet mount slide
how do you make a temporary wet mount?
*if bubbles do occur, you can gently press the cover slip with the eraser end of a pencil to push out the bubble
what is a cover slip?
a small, thin piece of glass used to flatten and hold a specimen in place
how do you stain a microscopic sample?
instead of using water, use a stain!
most common stains used in a wet mount?
- iodine: used for plant cells BC it binds to the starch present in the plant cells
- methylene blue: used for animal cells BC it binds to the nuclei of cells
- gram stains: used for bacteria
how do you draw cell structures seen with a microscope? (equipment, guidelines, for low + high power)
EQUIPMENT:
- pencil (NO PEN)
- ruler
- eraser
- UNlined paper
GUIDELINES:
- do not shade
- use clear continuous lines
- draw on the center of the paper
- add a title stating what has been drawn and what lens power it was drawn under
- use accurate proportions based on observations (not just off the textbook)
- make it large enough
- use straight edge lines for labels
- do not use arrowheads
- label lines should not cross over each other
- add a scale line at the bottom of the drawing if appropriate
FOR A LOW-POWER DRAWING:
- do not draw individual cells
- draw all tissues completely enclosed by lines
- draw a correct interpretation of the distribution of tissues
FOR A HIGH-POWER DRAWING:
- Draw only a few representative cells
- Draw the cell wall of all plant cells
- Don’t draw the nucleus as a solid blob
low vs high power drawings?
low-power:
- show the overall tissue distribution and outlines
high-power:
- focus on detailed cell structures and features
how would you measure the field of view diameter of a microscope under low power?
Often, the eyepiece lens of light microscopes will be fitted with an eyepiece graticule (a transparent ruler that measures the actual size of objects). You use this to measure the diameter!
BUT, the graticule itself doesn’t have a set scale on it (because the size of objects you’re viewing changes with magnification), so we need a way to calibrate it to actual measurements.
- SO, you use a stage micrometre to calibrate!
- The stage micrometre will show the actual size of the image using divisions that are each 100 µm (0.1 mm) apart
(Each 100 µm division of the stage micrometre = 20 eyepiece graticule divisions)
how would you measure the field of view diameter of a microscope under medium/high power?
you must use an equation:
LP = low power
HP = high power
formula to calculate the magnification of a micrograph or drawing?
magnification = image size / actual size
quantitative VS qualitative observations?
Quantitative:
- numerical values (measurable)
- examples: measurements of time, length and temperature
Qualitative:
- describe a quality (not measurable)
- examples: colour, behaviour or texture
BUT: they both aim to understand phenomena + collect data (just different kinds of data)
how do you convert between units?
- nanometres (nm)
- micrometres (μm)
- millimetres (mm)
- metres (m)
examples of what can be viewed with the naked eye, light, and electron microscope?
how does an electron microscope work?
instead of passing light through a specimen (like a light microscope does), electron microscopes pass a beam of electrons through a specimen
then:
- Electrons will be absorbed by the denser parts of the sample and scattered or able to pass through less dense areas
after:
- They are picked up by an electron detector and used to form an image
why do electron microscopes have a much higher resolution than light microscopes?
because electrons have a much shorter wavelength than light
4 techniques commonly used in microscopy?
- Freeze fracture microscopy
- Cryogenic electron microscopy
- Immunofluorescence
- Fluorescent dyes
what is freeze fracture microscopy?
it’s a process of preparing a sample for electron microscopy
How to do freeze fracture microscopy?
- Freeze a sample
- Use a specialised tool to break the sample into small pieces (fracture it)
- Observe the internal structure of the small pieces using an electron microscope
Why is freeze fracture microscopy useful?
Because it can visualise structures that are not normally visible, such as the internal plasma membrane
- it was important in understanding the structure of the cell membrane
what is cryogenic electron microscopy?
it’s a recent advancement in electron microscopy
- it’s been revolutionary in understanding the structure of viruses and other cellular proteins
how to do cryogenic electron microscopy?
- freeze specimens in ice using very low temperatures (AKA cryogenic temperatures)
–> this makes them more firm + stable - use computer enhancements to form an image (the enhancements show the 3D framework of proteins)
Freezing the sample improves the resolution and reduces damage that may occur from the electron beam
Electron microscopes produce ___ images.
Electron microscopes produce black and white images.
sometimes, scientists add color to help distinguish structures
what is immunofluorescence?
it’s a technique used in light microscopy to better visualise certain structures
how to carry out immunofluorescence?
- Attach a fluorescent tag (AKA a fluorophore) to antibodies on a structure or cell being viewed
- When the antibody binds to the antigen, the structure is then ‘tagged’ with immunofluorescence
- So, when a certain wavelength of UV light is shone onto the fluorescence tag, the tag will emit light of a different wavelength that can then appear as brightly coloured spots
- This allows the visualisation of the location of these target molecules
How to use fluorescent dyes?
- Stain cells with special dyes that bind to specific cellular components
- When UV light is shown on the specimen, the parts that the dye bind to will be visible as brightly coloured spots
these dyes are used in light microscopy
A benefit of using fluorescent stains to visualize cell structures?
it will give a clearer image with great specificity and contrast
–> this allows researchers to visualize specific cellular components and their interactions with high precision
which structures are common to all cells?
- DNA
- Cytoplasm
- Plasma membrane
DESCRIBE + state the FUNCTION of the structures common to all cells
DNA
- it contains genetic information
- it contains instructions needed for the cell to survive, mature and replicate
Cytoplasm
- a jelly-like fluid made mostly of water
- it contains many dissolved solutes, including nutrients and waste products
- it suspends other cell structures
- many chemical reactions occur here
Plasma membrane
- composed of a bilayer of phospholipids that surround the cell
- it separates the interior of the cell from the exterior environment
what are prokaryotes?
THEY ARE…
- a type of cell that is believed to have been among the first life forms on Earth
- unicellular organisms that do not contain membrane-bound organelles
- simpler than eukaryotes
- 10-100 microns in size
- Filamentous (strings of single cells)
examples of prokaryotes?
- Bacteria
- Archaea
Typical components of prokaryotic cells?
- Cell wall
- Plasma membrane
- Cytoplasm
- Naked DNA in a loop
- 70S ribosomes
- Plasmid
- Capsule (most have)
SOME HAVE:
- flagellum
- pili
outline the function of the cell wall in a prokaryotic cell
- protects the cell from toxins that may be in the external environment
- resists high osmotic pressures
- maintains the shape of the cell
outline the function of the plasma membrane
- separates the cell’s interior from its external environment
- controls what can enter and exit the cell
outline the function of the cytoplasm
- suspends ions, organic molecules, DNA, and ribosomes
- it is the site of metabolic reactions
outline the function of the 70s ribosome in a prokaryotic cell
- it is where translation (protein synthesis) occurs
outline the function of the nucleoid DNA in a prokaryotic cell
- DNA stores the information necessary for synthesising proteins
what does the term “naked” mean in relation to prokaryotic DNA?
if DNA is “naked”, it means that:
- it is not associated with histone proteins
- it is mostly found in a region called the nucleoid
what is a capsule? + what does it do?
- it is a hydrated polysaccharide complex that covers the outermost part of the cell wall
- (in most bacteria) it is composed of monosaccharides joined together by glycosidic linkages
- it keeps phagocytes from ingesting and destroying the bacterial cell (protects the cell)
what is a flagellum + what does it do in a prokaryote?
how does a flagella work?
- it is a hair-like appendage that protrudes from certain cells
- in a prokaryote, it is thinner than a eukaryotic flagella
- consists of a filament attached to the plasma membrane by a basal body
- it provides motility
- works by a molecular motor causing the hook to rotate, giving the filament a whip like motion which propels the cell
what are pili?
- they are protein filaments on the cell wall
- they help with cell adhesion and transferring DNA
describe the nucleoid region in prokaryotes
- consists of one supercoiled chromosome
- genes are grouped into operons
- contains plasmids that transfer DNA between different bacteria
operons = clusters of genes that are switched on or off together
describe 70S ribosomes
- Smaller than those in eukaryotes (which are 80S, not 70S)
- Consists of a large and small subunit –made of RNA and protein
- Has the same function as those in eukaryotes: protein synthesis
describe the cell wall
- made of peptidoglycan (murein)
- it’s a polymer formed from amino acids and sugars
- some prokaryotes have a capsule, which surrounds the cell wall
prokaryotic VS eukaryotic cell structure?
similarities?
SIMILARITIES:
- being alive
- having a cell membrane
- having DNA
- having ribosomes
- having the ability to reproduce
70S = smaller than 80S
Label this diagram of a eukaryotic animal cell
KNOW HOW TO DRAW THIS!
what is a eukaryotic cell?
they are:
- complex cells that contain a nucleus and other organelles that are bound by membranes
- more complex and usually much larger than prokaryotic cells
- (sometimes) multicellular
structures in a typical eukaryotic cell?
TYPICALLY ALWAYS:
- plasma membrane
- cytoplasm
- mitochondria
- 80S ribosomes
- nucleus
- smooth endoplasmic reticulum
- rough endoplasmic reticulum
- golgi apparatus
- vesicle
- vacuole
- cytoskeleton of microtubules and microfilaments
SOMETIMES:
- chloroplasts (plant)
- centrioles (animal)
- lysosomes (animal)
outline the function of the 80s ribosomes in a eukaryotic cell + describe it
- they are tiny organelles which can be found in the cytoplasm or bound to the rough endoplasmic reticulum
- each one consists of two sub-units
- it is where translation (protein synthesis) occurs
what is chromatin?
- a mixture of DNA and proteins
- seen as darkened patches when seen on a light micrograph
outline the function of the nucleus in a eukaryotic cell + describe it
- it’s the largest organelle in the cell
- it contains chromatin
- it has a nuclear envelope (w/ pores) + a nucleolus
- it houses nearly all the cell’s genetic material + makes ribosomes
describe the function of different parts of the nucleus
label this diagram of a nucleus
describe the nuclear envelope
- it’s a dense spherical structure
- it surrounds the nucleolus
- it’s made of two membranes (inner and outer) with fluid separating them
outline the function of the mitochondria in a eukaryotic cell + describe it
- it contains its own DNA
- it has a double membrane
- a site of cellular respiration where glucose is converted into ATP in the process of respiration (where ATP is generated)
describe the mitochondria’s double membrane
- the outer membrane = smooth
- the inner membrane = folded (cristae)
WHY? this provides a large surface area to create ATP (which is the mitochondria’s function)
outline the function of the chloroplast in a eukaryotic cell + describe it
- found inplant cells
- larger than the mitochondria
- surrounded by a double-membrane
- contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis
- act as the site of photosynthesis
outline the function of the nucleolus in the nucleus + describe it
- it’s the most obvious structure in the nucleus
- it produces ribosomes (which move out of the nucleus to latch onto the outside of the rough endoplasmic reticulum where they produce proteins)
outline the function of the rough endoplasmic reticulum in a eukaryotic cell + describe it
- consists of a series of flattened membrane-bounds sacs (AKA cisternae)
- studded with ribosomes
- transports proteins that were made on the ribosomes attached to its surface
–> (NOTE: some of the proteins will be secreted by the cell, others will be placed on the surface of the cell membrane)
outline the function of the smooth endoplasmic reticulum in a eukaryotic cell + describe it
- it has the same structure as a rough endoplasmic reticulum BUT without ribosomes
- makes phospholipids and cellular lipids
- produces sex hormones
- detoxifies drugs in the liver
- stores calcium ions in the muscle (which are needed for muscular contraction)
- helps the liver release glucose into the blood when needed
outline the function of the golgi apparatus in a eukaryotic cell + describe it
- consists of a stack of flattened cisternae and associated vesicles
- has two layers
- receives proteins from the endoplasmic reticulum and modifies them (may add sugar molecules to them)
- packages the modified proteins into vesicles that can be transported
outline the function of the vesicles in a eukaryotic cell + describe it
- it’s a small sac
- transports and releases substances produced within the cell by fusing with the cell membrane
function of the cell membrane?
Controlling the movement of substances in and out of the cell
outline the function of the vacuoles in a eukaryotic cell + describe it
- formed in the Golgi apparatus
- occupy a very large space in plant cells, but can be small and numerous in animal cells
- Stores nutrition in plant cells
- Metabolises toxins for removal
- Uptakes water to provide rigidity
- (Sometimes) has hydrolytic functions similar to lysosomes
When large, it is referred to as a central vacuole
outline the function of the lysosomes in a eukaryotic cell + describe it
- they are spherical sacs surrounded by a single membrane
- they are specialised vesicles
- contain powerful hydrolytic digestive enzymes
- ROLE: to break down materials (especially in the destruction of microbes engulfed by white blood cells)
outline the function of the centrioles in a eukaryotic cell + describe it
- self-replicating organelles
- made up of nine bundles of microtubules
- only in animal cells
- Provides mechanical strength to cells
- Aids transport within cells
- Enables cell movement
what does compartmentalisation do?
it allows for the interior of the organelles to have separate conditions to the cytoplasm of the cell
advantages of compartmentalisation?
- ability to create higher concentrations of certain substances within organelles
- ability to separate toxins and from the rest of the cell
- control over conditions inside organelles (such as pH) to maintain the optimal conditions for enzymes
A single cell can be classed as an organism if ________?
if it can carry out the life processes
list the common processes carried out by all life + define
REMEMBER MR SHENG!
what is paramecium? + what enables it to perform the functions of life?
a genus of unicellular protozoa
- usually less than 0.25 mm in size
- eukaryotic
- widespread in aquatic environments
- heterotrophs
- can move in all directions using their cilia (small hair-like structures that cover the whole body and beat rhythmically to propel the cell)
what is chlamydomonas? + what enables it to perform the functions of life?
a genus of unicellular green algae
- autotrophs (can manufacture their own food using photosynthesis)
- range from 10 to 30 μm in diameter
- have a cell wall, a chloroplast, + an ‘eye’ that detects light
- has two flagella, which they use to swim
summarize how paramecium and chlamydomonas carry out all the functions of life (growth, movement, sensitivity, homeostasis, nutrition, reproduction, excretion, metabolism)
Growth:
- Paramecium: as it consumes food, it enlarges + later divides into two daughter cells
- Chlamydomonas: same, expect it grows in size via photosynthesis and absorption of minerals
Movement:
- Paramecium: beating cilia helps it move (respond) to changes in environment
- Chlamydomonas: flagella rotates, letting it move
Sensitivity:
- Paramecium: able to detect changes in the water temperature around them
- Chlamydomonas: senses light changes using its eye spot
Homeostasis:
- BOTH: uses osmoregulation (collects excess water in the contractile vacuoles and then expels it through the plasma membrane)
Nutrition:
- Paramecium: (heterotroph) engulfs food particles in vacuoles
- Chlamydomonas: (autotroph) uses photosynthesis to produce its own food
Reproduction:
- Paramecium: can do both sexual and asexual (asexual = more common + uses binary fission to divide)
- Chlamydomonas: also can do both (uses either binary fission or sexual reproduction)
Excretion:
- Paramecium: waste collected in vacuoles + moved to the anal pore, where it ruptures to expel its contents (some waste = removed using the contractile vacuole)
- Chlamydomonas: uses the whole surface of its plasma membrane to excrete its waste products
Metabolism:
- Paramecium: rely on external organic sources for energy and carbon compounds
- Chlamydomonas: can grow heterotrophically or autotrophically
Eukaryotic cells are classified as?
they are classified as 3 different organisms
- Animal
- Plant
- Fungal
compare and contrast animal, plant, and fungal eukaryotic cells
- exterior of cell
- chloroplasts
- vacuoles
- carbohydrates
- cilia / flagella
- shape
- centrosomes / centrioles
what are centrioles?
- they are found in animal cells
- they are two cylindrical organelles that help to establish and organise the microtubules
- they help form basal bodies
- they are small, cylindrical components inside the centrosome
- they are important during cell division
what are centrosomes?
- it consists of two centrioles oriented at right angles to each other embedded in a mass of amorphous material
- they organize microtubules, regulate cell division, + do spindle formation
what does a cell being atypical mean? why are some eukaryotic cells labelled as atypical? give examples.
“atypical” is when a cell does not contain, or contains abnormal numbers of the cell structures and organelles that are found in most other eukaryotic cells
–> some cells are labelled this way because these unique structures allow them to carry out specific functions
- skeletal muscle fibers
- aseptate fungal hyphae
- red blood cells
- phloem sieve tube elements
what makes skeletal muscle fibers an atypical cell?
they’re atypical because….
- they are multinucleated (one single cell contains many nuclei)
- allows it to have more control over the production of proteins + enhanced muscle growth and repair
what makes aseptate fungal hyphae an atypical cell?
they’re atypical because….
- they do not have the cellular partitions that are normally present in the hyphae of fungi
–> so, so there are many nuclei in a single cellular unit - this lets it have increased efficiency in nutrient flow + faster growth and flexibility
what makes red blood cells an atypical cell?
they’re atypical because….
- they are anucleate (do not contain a nucleus)
- this means that the cell has a greater haemoglobin capacity and can transport more oxygen
what makes phloem sieve tube elements an atypical cell?
they’re atypical because….
- they are anucleate (do not contain a nucleus)
–> so, they contain very little cytoplasm and few organelles - this means that there is a very low resistance for substances moving through a sieve tube element (so, it’s easier for substances to move)
Compare the number of nuclei in
- aseptate fungal hyphae
- skeletal muscle
- red blood cells
- phloem sieve tube elements
- Aseptate Fungal Hyphae: MANY
- Skeletal Muscle Fibers: MANY
- Red Blood Cells: NONE
- Phloem Sieve Tube Elements: NONE
Label this diagram of a eukaryotic plant cell
KNOW HOW TO DRAW THIS!
Label this diagram of a prokaryotic cell
KNOW HOW TO DRAW THIS!
outline the function of the cytoskeleton in a eukaryotic cell + describe it
the cytoskeleton provides structural support and organization within a cell
there are 3 types of cytoskeleton:
- microtubules: shape + support the cell, function as movement paths though the cell for some organelles
- intermediate filaments: reinforce cell shape as well as anchoring some organelles (keeping them in place)
- actin filaments (microfilaments): involved in cell division + cell movement
prokaryotes don’t have a cytoskeleton
enzymes are not _____
NOT metabolites
