1.2 cell structure and organisation Flashcards
which microscope has a greater magnification and higher resolving power?
electron microscope because it uses electrons (rather than light), which have a much shorter wavelength
(so electron microscopes can see many more structures called organelles in eukaryotic cells)
organelle definition
a specialised structure with a specific function inside a (eukaryotic) cell
eukaryotic cells (eukaryotes) definition
they contain DNA in chromosomes in a nucleus, and possess membrane-bound organelles e.g plants and animals
resolving power definition
the minimum distance by which two points must be separated in order for them to be seen as two distinct points rather than a single focused image
what surrounds organelles?
and what are the advantages of this?
a membrane
potentially harmful chemicals, such as enzymes, are isolated, and molecules with particular functions, such as chlorophyll, can be concentrated in one area
what do membranes provide for organelles?
a large surface area for the transport of molecules and attachment of enzymes
what are the different units of measurements in biology? and what are they used to measure?
- metre (m) = used to measure larger organisms
- millimetre (mm) = used to measure tissues and organs
- micrometre = cells and organelles (10^-6m)
- nanometre (nm) = molecules (10^-9m)
what is the most convenient unit for measuring cells and organelles?
micrometres
what is the nucleus?
- the largest organelle of the cell, bounded by a double membrane
- present in the cytoplasm of a eukaryotic cell
- CONTAINS DNA WHICH CODES FOR PROTEIN SYNTHESIS
what are the different components in a nucleus?
- nucleolus
- chromatin
- nucleoplasm
- (nuclear) pore
- nuclear envelope
- endoplasmic reticulum
- ribosome
what is the nucleolus?
- a small spherical body found within the nucleus
- responsible for the production of rRNA and ribosomes
what is the nucleoplasm?
- like the cytoplams of a cell, but for a nucleus
- contains chromatin (which condenses to form chromosomes during cell division)
what is the nuclear envelope?
- the double membrane which encloses the genetic material
- has pores (to allow movement)
what are nuclear pores?
- gaps in the nuclear envelope that allow movement
- allows the passage of large molecules, such as mRNA and ribosomes
- allows transport of messenger/mRNA/nucleotides/ribosomes
where is the endoplasmic reticulum in the nucleus?
the outer membrane of the double membrane is continuous with the endoplasmic reticulum
what is chromatin?
- made of coils of DNA bound to protein (DNA-protein complex) but uncoils (is linear) when not during cell division
- condenses to form chromosomes during cell division
what are the main functions of the nucleus?
- enable protein synthesis (by creating ribosomes), cell division, growth and differentiation into specialised cells
- stores genetic material in the form of chromatin
- exchange of RNA with the rest of the cell
what is the endoplasmic reticulum?
- a network of membranes connected to the nucleus of the cell by the nuclear envelope
- has two types: rough and smooth
- main role is concerned with the transport of material through the cell
- a continuous membrane with many folds
- form interconnected flattened fluid-filled sacs called cisternae
what is the smooth endoplasmic reticulum?
- more tubular (tubular membrane)
- lacks ribosomes
- involved with the synthesis and transport of lipids
what is the rough endoplasmic reticulum?
- has ribosomes on the outer surface
- transports the proteins once they’ve been synthesised at the ribosomes (via the cisternae)
packages and transports proteins
what are cisternae?
interconnected flattened fluid-filled sacs in the endoplasmic reticulum
vesicle definition
a ‘bubble’ that can contain and transport molecules inside of it
what is the golgi body?
- stack of curves cisternae
- vesicles containing polypeptides (building blocks of protein) pinch off from the rough endoplasmic reticulum, and fuse with the golgi
- proteins are modified and packed into vesicles by the golgi body for export
- also involved in the transport and storage of lipids, and the production of glycoproteins and lysosome
what are the components of a mitochondria?
- circular DNA
- matrix
- outer membrane
- inter-membrane space
- inner membrane
- crista (cristae)
- 70s ribosomes
what is the usual size and shape of a nucleus?
usually spherical
and 10-20 micrometres in diameter
what is the usual size and shape of a mitochondria?
often cylindrical
1-10 micrometers in length
what type of cells have extensive endoplasmic reticulum?
cells that store large quantities of carbohydrates, proteins and fats, including liver and secretory cells
why type of cells contain lots of mitochondria?
they are present in all cells, but are found in much higher number in metabolically active cells e.g in muscle cells, that need a plentiful supply of ATP
what is the mitochondria?
- the site of aerobic respiration/ ATP production (energy)
- RELEASES energy
- has a double membrane
- being cylindrical, has a larger surface area than a sphere of the same volume (big surface area to volume ratio) + reduces the diffusion distance b/w the edge and the centre, making aerobic respiration more efficient
what is the cristae?
why is this useful?
- the inner membrane of the mitochondria is folded into structures called cristae
- it PROVIDES A LARGE SURFACE AREA for the attachment of enzymes involved in respiration
what is the inter-membrane space?
- the space in between the two membranes (outer membrane and the inner membrane) in a mitochondria
- fluid-filled
what is the matrix?
- the volume enclosed by the inner membrane in a mitochondria
- a solution containing many compounds, including lipids and proteins, 70s ribosomes and a small circle of DNA
- contains the enzymes we need for respiration
what are the 70s ribosomes and the small circle of DNA for in a mitochondria?
they enable mitochondria to make some of their own proteins and self-replicate
in a mitochondria, where do the reactions occur?
some occur in the matrix and others on the inner membrane
what are the components of a chloroplast?
- double membrane
- thylakoid
- thylakoid membrane
- inter-granal lamella
- granum
- 70s ribosomes
- starch grain
- stroma
- circular DNA
what are the chloroplasts?
- the site of photoynthesis
- absorbs sunlights and converts into sugar molecules
- found in photosynthetic plants
- surrounded by two membranes, comprising the chloroplast envelope
what is the thylakoid?
- a flattened membrane
- site of light absorption in the chloroplasts
- stacks of thylakoid contain the photosynthetic pigments, which include chlorophyll
what is the granum?
- stacks of thylakoids (between two and a hundred parallel stacks) in a chloroplast
- this arrangement produces a large surface area, efficient for trapping light energy
what is the lamella?
- they connect the stacks of thylakoids together and allow transport between the stacks in a chloroplast
what is the stroma?
- fluid-filled
- got enzymes used in photosynthesis
- filled with starch grains, 70s ribosomes and a circle of DNA
- like the cytoplasm/nucleoplasm but in a chloroplast
in chloroplasts, what do the 70s ribosomes and circular DNA enable them to do?
enable them to make some of their own proteins and self-replicate
(like mitochondria)
in chloroplasts, is the inner membrane folded?
no
(only in mitochondria)
why are thylakoids arranged how they are in chloroplasts?
it produces a large surface area so is efficient for trapping light energy
prokaryotes definition
a single-celled organism lacking membrane-bound organelles, such as a nucleus, with its DNA free in the cytoplasm
what are the components of a ribosome (when drawing a diagram)?
- 2 tRNA attachment sites
- mRNA attachment site
- large subunit
- small subunit
what are ribosomes made from? and where are they found?
- made from rRNA and protein
- found within the cytoplasm
are ribosomes surrounded by a membrane?
no
what is the role of ribosomes?
- the assembly of proteins during translation
- they are important in protein synthesis, as they are the site of translation, where mRNA is used to assemble the polypeptide chain
what is the size of ribosomes in prokaryotic cells? in eukaryotic cells?
- prokaryotic cells = 70s in size
- in the cytoplasm of eukaryotic cells = 80s, where they occur singly or attached to membranes on the RER (except 70s in mitochondria and chloroplasts)
what does the small subunit contain? the large subunit? in a ribosome
- the small subunit contains a mRNA attachment site
- the large subunit contains two tRNA attachment sites
how do ribosomes compare in size between nucleus and mitochondria?
ribosomes are much smaller than the nucleus and mitochondria
what is the endosymbiotic theory?
the theory that describes the origin of chloroplasts and mitochondria
- it has been suggested that these organelles arose from a symbiotic relationship between early cells that engulfed photosynthetic and respiratory bacteria over 1.5 billion years ago
- they both have 70s ribosomes and circular DNA (which are the type found in prokaryotes including bacteria)
what are lysosomes? what is their role?
- vesicles with (hydrolytic/digestive) enzymes inside to break down waste product
- their role is to digest worn out organelles within the cell, and foreign material that has been engulfed by phagocytosis e.g bacteria engulfed by a white blood cell
(also contain digestive enzymes that break down/recycle worn out organelles or cells)
how are lysosomes formed?
formed by being pinched off from the golgi body
what enzyme do lysosomes contain?
the digestive enzyme lysozyme
what are centrioles?
- present in all animal cells and most protoctistans (but not in the cells of higher plants)
- consist of two rings of microtubules (making cylinders) positioned at right angles to each other
- they organise the microtubules that make the spindle during cell division
- located just outside the nucleus
what is the function of a vacuole?
- supporting soft plant tissues
- but also store chemicals such as glucose and amino acids in the cell sap
what are vacuoles?
- fluid-filled sac bounded by a single membrane, the tonoplast
- most are large and permanent
in plants, what is the cell wall mostly made from?
cellulose
what are the functions of the cell wall?
- STRENGTH = providing strength to the cell wall, which resists the expansion of the vacuole due to osmosis, and so the cell becomes turgid, supporting the plant
- TRANSPORT = transports water and dissolved molecules and ions through gaps in the cellulose fibres (known as the apoplast pathway - the main way that water crosses the plant root)
- COMMUNICATION BETWEEN CELLS = communication between cells via pores in the cell wall which allow strands of cytoplasm called plasmodesmata to pass. this allows water to pass via the symplast pathway (important in the transport of water through a plant)
what is plasmodesmata?
- strands of cytoplasm
- they pass through the pores in the cell wall
- plasmodesma occurs where there is no cellulose thickening between two cells
- they run from one cell to the next
(this network of cytoplasm in connected cells is called the symplast)
do all plant cells contain chloroplasts?
no - root cells for example, being underground, would have no use for them
are cell walls found in animal cells? plant cells?
animals cells - absent
plant cells - present = it surrounds the cell membrane
are chloroplasts found in animal cells? plant cells?
animal cells - absent
plant cells - present = in cells above ground
are plasmodesmata found in animal cells? plant cells?
animal cells - absent
plant cells - present
are vaculoes found in animal cells? plant cells?
animal cells - present = but small, temporary; scattered throughout cell
plant cells - present = large, permanent, central; filled with cell sap
are centrioles found in animal cells? plant cells?
animals cells - present
plant cells - absent
what energy store is found in animal cells? plant cells?
animal cells - glycogen
plant cells - starch
what does the nucleus contain and what does it do?
- contains chromosomes
- in which the DNA encodes proteins
what do the nuclear pores in the nuclear envelope allow?
it allow mRNA molecules, transcribed off the DNA, to leave the nucleus and attach ribosomes in the cytoplasm or on the rough ER
what do ribosomes contain?
rRNA, transcribed from DNA located at the nucleolus
where does protein synthesis occur? what does it produce?
- occurs on ribosomes
- produces proteins in their primary structure
where are polypeptides made? where are they then moved to?
- polypeptides made on the ribosomes are moved through the RER and are packaged into vesicles
- the vesicles bud off the RER and carry polypeptides to the Golgi body, where they are chemically modified and folded
what does the Golgi body produce? what may they be?
- produces vesicles containing newly synthesised proteins
- these may be lysosomes, containing digestive enzymes, used within the cell
- they may be secretory vesicles, which carry the proteins to the cell membrane for exocytosis
what do secretory vesicles do?
carry the proteins to the cell membrane for exocytosis
what do phospholipids and triglycerides move through? where do they go?
- they move through the smooth endoplasmic reticulum
- to various destinations in the cell
what have eukaryotic cells?
- fungi
- protoctista
- plants
- animals
are viruses made of cells?
no - they are not made of cells and they are not classified with living organisms
- they seem to exist at the interface between living and non-living systems
prokaryote definition
a single-celled organism lacking membrane-bound organelles, such ad a nucleus, with its DNA free in the cytoplasm
eukaryote definition
an organism containing cells that have membrane-bound organelles, with DNA in chromosomes within the nucleus
what is an example of a prokaryotic cell?
a bacterium
what is the major distinguishing feature of prokaryotic cells?
- they have no nucleus
- or any internal membrane
so unlike eukaryotic cells, they have no membrane-bound organelles
- also they are unicellular and rarely form multicellular structures
in some prokaryotes, what increases the surface area of the cell’s membrane?
the infolding of the cell membrane in a mesosome or photosynthetic lamellae
for each one, state whether it’s in all prokaryotes or only some prokaryotes?
- DNA molecule loose in cytoplasm
- peptidoglycan (murein) cell wall
- slime coat
- 70S ribosomes
- flagella (one, some or many)
- photosynthetic lamellae holding photosynthetic pigments
- cytoplasm
- cell membrane
- mesosomes - possible site of aerobic respiration
- plasmids
- DNA molecules loose in cytoplasm - ALL
- peptidoglycan cell wall - ALL
- slime coat - SOME
- 70S ribosomes - ALL
- flagella - SOME
- photosynthetic lamellae - SOME
- cytoplasm - ALL
- cell membrane - ALL
- mesosome - SOME
- plasmids - SOME
what is the difference between prokaryotes and eukaryotes?
prokaryotes:
- smaller
- no organelles
- DNA free in cytoplasm
- no nuclear envelope
- plasmids may be present
- peptidoglycan (murein) cell wall
- no chloroplasts (but may use photosynthetic lamella for photosynthesis)
- no mitochondria (but may use mesosome for respiration)
- 70s ribosomes, free in cytoplasm
eukaryotes
- larger
- membrane-bound organelles
- DNA combined with protein in chromosomes
- double membrane nuclear envelope
- plasmids absent
- cellulose cell wall in plants, chitin in fungi
- chloroplasts in plants and some protoctista
- mitochondria present
- mesosome absent
- 80s ribosomes, free in cytoplasm or attached to ER
why can’t viruses be seen in the light microscope?
they are so small
what does being small allow viruses to do?
pass through filters that can trap bacteria
why are viruses described as ‘acellular’?
they are not made of cells
- there are no organelles, no chromosomes and no cytoplasm
what happens when a virus invades a cell?
they are able to take over the cell’s metabolism and multiply inside the host cell
what is each virus particle made up of?
- a core of nucleic acid, either DNA or RNA surrounded by a protein coat, the capsid
- in some viruses, a membrane derived from the host cell surrounds the capsid
what cells can be infected with viruses?
cells of all groups of organisms
what is the virus that attacks bacteria called?
bacteriophages
what is an example of a well-known bacteriophage?
T2, which attacks Escherichia coli (E.coli)
what is the only characteristic of life that viruses show?
their ability to reproduce
can viruses be crystallised?
yes - not a property associated with living organisms
what are examples of infective viruses in human hosts?
- flu
- chickenpox
- cold
- HIV
- mumps
- rubella
- Ebola
what are examples of infective viruses in plants hosts?
- tobacco mosaic virus
- cauliflower mosaic virus
what are examples of infective viruses in bird hosts?
- avian flu
what are examples of infective viruses in other mammal hosts?
- swine flu
- cow pox
- feline leukaemia virus
in an exam, read the question very carefully. notice if you are asked for the name of a virus or the name of the disease it causes
e.g tobacco mosaic virus causes tobacco mosaic disease
HIV causes HIV-AIDS
what is the function of single-celled organisms?
single-celled organisms carry out all life functions within a single cell
what is the function of multicellular organisms?
multicellular organisms have specialised cells, forming tissues and organs, which have various structures and roles
what do stem cells have the potential to do?
to become any cell type in the body
what is differentiation?
the development of a cell into a specific type
what happens when cells differentiate?
they become specialised in structure and in the chemical reactions that they perform
tissue definition
group of cells with the same structure and function working together
(a group of one type of cell/ similar/same cells working together to perform a function)
what do cells near each other in the embryo, that often differentiate in the same way, group together as?
a tissue
do mammals have several tissue types?
yes
what are 3 examples of mammalian tissues?
- epithelial tissue
- muscular tissue
- connective tissue
epithelial tissue properties:
- forms a continuous layer, covering/lining the internal and external surfaces of the body
- have no blood vessels (but may have nerve endings)
- the cells sit on a basement membrane (made of collagen and protein) and they vary in shape and complexity
- often have a protective or secretory function (also often the sites of absorption of substances)
do epithelial tissues have blood vessels?
no (but they may have nerve endings)
what do epithelial tissue cells sit on?
a basement membrane
what are basement membranes made of?
collagen and protein (and they vary in shape and complexity)
what function does epithelial tissue usually have?
protective or secretory function
what are the three types of epithelial tissue?
- cuboidal epithelium
- columnar epithelium
- squamous epithelium
cuboidal epithelium properties?
- cells have a cube shape
- tissue is just one cell thick
- occurs in the proximal convoluted tubule of the kidney nephron and the ducts of salivary glands
- they reabsorb useful substances that are filtered out of the blood
how thick are cuboidal epitheliums?
just one cell thick (simple)
where do cuboidal epithelium occur?
in the proximal convoluted tubule of the kidney nephron and the ducts of salivary glands
columnar epithelium properties:
- elongated cells
- those lining tubes that substances move through, such as the oviduct (fallopian tube) and trachea, have cilia
- the cilia move and sweep substances along
squamous epithelium properties:
- consist of flattened cells on a basement membrane
- they form the walls of the alveoli and line the renal (bowman’s) capsule of the nephron
- short diffusion distance
what do squamous epithelium form? what do they line?
- they form the walls of the alveoli
- they line the renal (bowman’s) capsule of the nephron
what are the three main muscle tissue types?
- skeletal muscle
- smooth muscle
- cardiac muscle
skeletal muscle properties:
- attached to bones
- generates locomotion in mammals
- has bands of long cells, or fibres, which give powerful contraction, but these muscles tire easily
- you can choose whether to contract these muscles of not, so they are called voluntary muscles
- because you can see stripes on them in the microscope, they are also called striped or striated muscle
what enables skeletal muscles to give powerful contractions?
- it has bands of long cells, or fibres, which give powerful contraction
do skeletal muscles tire easily?
yes
why are skeletal muscles called striped or striated muscle?
because you can see stripes on them in the microscope
what are skeletal muscles attached to?
- they are attached to bones
smooth muscle properties:
- have individual spindle-shaped cells that can contract rhythmically, but they contract less powerfully than skeletal muscle
- they occur in the skin, in the walls of blood vessels and in the digestive and respiratory tracts
- you cannot control these muscles, so they are called involuntary muscles
- they do not have stripes and so are called unstriped or unstriated muscle
are skeletal muscles called voluntary or involuntary muscles?
voluntary - because you can choose whether or not to contract these muscles
do smooth muscles contract powerfully?
- they contract less powerfully than skeletal muscles
what makes smooth muscles contract?
- they have individual spindle-shaped cells that can contract rhythmically
(but they contract less powerfully than skeletal muscles)
where do smooth muscles occur?
in the skin, in the walls of blood vessels and in the digestive and respiratory tracts
are smooth muscles called voluntary or involuntary muscles?
involuntary - you cannot control these muscles
do smooth muscles have stripes?
no - so they are called unstriped or unstriated muscle
cardiac muscle properties:
- only found in the heart
- its structure and properties are somewhat in between skeletal and smooth muscle
- have stripes
- but lack the long fibres of skeletal muscle
- they contract rhythmically, without any stimulation from nerves or hormones, although these can modify their contraction
- do not tire
where are cardiac muscles found?
only in the heart
are cardiac muscles similar to skeletal and smooth muscles in terms of structure and properties?
- they are somewhat in between skeletal and smooth muscles
- the cells have stripes, but lack the long fibres of skeletal muscle
do cardiac muscles contract rhythmically?
yes - without any stimulation from nerves and hormones, although these can modify their contraction
do cardiac muscles tire?
no
connective tissue properties:
- connects, supports or separates tissues and organs
- contains elastic and collagen fibres in an extracellular fluid or matrix
- between the fibres are fat-storing cells (adipocytes) and cells of the immune system
what does connective tissue do?
- connect, support or separates tissues and organs
what does connective tissue contain?
elastic and collagen fibres in an extracellular fluid or matrix
what are between the fibres of connective tissue?
fat-storing cells (adipocytes) and cells of the immune system
organ definition
a group of tissues in a structural unit, working together and performing a specific function
what does an organ do?
comprises of several tissues working together, performing a specific function
what is an example of on organ?
in humans e.g the eye contains nervous, connective, muscle and epithelial tissues and is the organ of sight
what is an organ system?
a group of organs working together with a particular role
what is an example of a mammalian organ system?
the circulatory system consists of the heart and aorta
what is an organism?
- is a discrete individual
- when all of the systems of the body are working together, making an organism
where are prokaryotic cells found?
in bacteria and cyanbacteria
in what kingdom are prokaryotic cells?
prokaryotae
where are eukaryotic cells found?
in all organisms apart from bacteria
in what kingdoms are eukaryotic cells?
- protoctista
- fungi
- plantae
- animalia
do prokaryotes have any membrane bound organelles?
no
how are ribosomes different in prokaryotic cells than eukaryotic cells?
in prokaryotic cells:
- the site of photosynthesis
- BUT not attached to any membranes
- also slightly smaller (70s not 80s)
what is the mesosome in prokaryotic cells?
- site of respiration
- in-foldings of the cell membrane
- for enzymes to attach
- large surface area
what are the plasmids in prokaryotic cells?
- tiny loops of DNA
- carrying only a few genes
- occur though out the cytoplasm
what is the flagellum in prokaryotic cells?
- the ‘tail’
- it rotates
- allowing the bacteria to move
- not all bacteria have one (and some have more than one)
what is the capsule (slime layer) in prokaryotic cells?
- type of protein
- stops cell drying out (helps it to retain moisture)
- protects the cell
- helps the cell adhere to surfaces
how is the cell wall different in prokaryotic cells than eukaryotic cells?
in prokaryotic cells:
- made of a protein called murein
how is the cell membrane different in prokaryotic cells than eukaryotic cells?
it’s not - they are the same
what is the nucleoid/DNA in prokaryotic cells?
- single circular piece of DNA
- forming the bacterial chromosomes
- but no nuclear membrane
what do all eukaryotic cells contain?
a nucleus and membrane bound organelles
what does the rough endoplasmic reticulum do?
folds and processes proteins made on the ribosomes
what does the nucleolus do?
it’s the site of ribosome production
what does the smooth endoplasmic reticulum do?
produces, packages and transports a lipids
what does the golgi apparatus do?
processes and packages proteins and lipids.
it also produces lysosomes
what are viruses?
non-living structures which consist of nucleic acid (DNA or RNA) enclosed in a protective protein coat called the capsid, sometimes covered with a lipid layer called the envelope
are centrioles found in pairs?
yes
they are found in pairs in centrosomes
what is the function of centrioles?
- they migrate to opposite poles of the cell during prophase
- they are involved in the organisation of spindle fibres
what is the function of pili in prokaryotic cells?
what is the structure of pili in prokaryotic cells?
they enable the attachment of bacteria to each other and to other surfaces
they are hair-like microfibres made of pilin that extend through the cell wall
what is cell theory?
- new cells can be formed from other existing cells
- the cell is a fundamental unit of structure, function and organisation in all living organisms
- cells contain genetic information which can be transferred to daughter cells
- organisms can be unicellular e.g amoeba or multicellular e.g animals
why do scientists not believe that viruses are cells or even alive?
because:
- they have no cell membrane
- they have no cytoplasm
- they cannot carry out respiration and synthesise ATP
- they do not grow
- they cannot replicate or reproduce on their own - they must invade a host cell and use the cell’s metabolic processes to produce more viruses particles
what components of prokaryotic cells are not present in ALL prokaryotic cells?
- pili
- capsule
- flagellum
are centrioles found in animal cells, plant cells or both?
only animal cells
what is found in only prokaryotic cells?
- mesosome
- plasmids and nucleoid
- peptidoglycan (murein) cell wall
what is found in only plant cells?
- chloroplasts
- plasmodesmata
- vacuoles
- cellulose cell wall
what does the process of protein synthesis involve at every component?
- in the nucleus = the transcription of the genetic code in DNA into messenger RNA (mRNA)
- in the nucleolus = production of ribosomes
- the nuclear pores = the mRNA leaves the nucleus and enters the cytoplasm through nuclear pores
- in the cytoplasm = ribosomes translate of the code in mRNA into polypeptides (amino acids are bonded together by peptide bonds t form a polypeptide)
- in RER = a vesicle pinches off the RER and transports the polypeptide to the golgi body
- in Golgi bodies = the processing of the polypeptide to produce functional proteins (folding to give secondary/tertiary structure, adding carbohydrate chains, combining polypeptides) and packaging of the proteins into secretory vesicles for secretion
what is an advantage of squamous epithelium being very thin?
because they line the alveoli in the lungs, being very thin reduces the diffusion distance for the exchange of gases
what are muscle tissues responsible for?
moving parts of the body through contractions
what are the main differences between a light microscope and an electron microscope?
light microscope:
- uses a beam of light (longer wavelength)
- can see colour images
- can observe live specimens
- resolution power is lower
- magnification is lower
electron microscope:
- uses a beam of electrons (shorter wavelength)
- can only see black and white images
- specimens must be dead
- resolution power is higher
- magnification is higher
because electron microscopes use beams of electrons rather than light, they can…?
- produce images at a higher magnification
- produce images which are clearer and with greater detail - they have greater resolution
what is used to give more contrast between cell structures and make them easier to see when using microscopes? what is a disadvantage with this?
staining
however, staining cells kills them so cannot be used when observing live cells
how do you work out the magnification?
magnification = image/actual
resolution definition
the smallest distance between two points that can be separately distinguished
why do electron microscopes have greater resolution than light microscopes?
because electrons have a much shorter wavelength than visible light so they distinguish objects that are smaller and closer together
what does the resolution of a microscope tell you?
how close two points can be and still be separately distinguished, rather than being seen as a single image
it tells you the detail which can be seen
what is the cell wall of prokaryotic cells made from?
peptidoglycan
do viruses possess a cytoplasm, organelles or any chromosomes?
no - just a core of nucleic acid surrounded by a protein coat, called the capsid
how do you work out the size of object, using magnification and size of image?
size of object = size of image/magnification
how can mitochondria differ in appearance when looking at a diagram?
- cut in different plane
(another reason that could account for the difference in their appearance : self-replication / stage (of division) / stage of development/ size / not fully formed / age)
what kingdom has eukaryotic characteristics, has a nucleus and in some species have chloroplasts and a cell wall?
protoctista
what is an example of a cell that contains lots of mitochindria?
muscles/secretory cell
what is the function of mitochondria? (exam question)
- site of respiration
- RELEASES energy in the form ATP
what is the function of the nucleus?
- contains DNA coiled around chromatin into chromosomes
- coordinates cellular activities
describe the sequence of events that lead to the production of digestive enzymes in a cell (using the nucleus, nuclear pores and ribosomes)
nucleus : contains DNA which codes for the production of proteins/polypeptides - production of mRNA (1)
nuclear pores : allow mRNA/rRNA to leave the nucleus
ribosomes : carry out protein synthesis
describe the sequence of events that lead to the secretion of digestive enzymes from a cell (by RER, golgi body and vesicles)
RER: transports proteins through the cell to golgi body where it packages proteins into vesicles
golgi body : packaging/modification of protein
vesicles : transports proyeins to the cell membrane
exocytosis (of enzymes from the cell)
what is the role of mitochondria in the production and secretion of digestive enzymes?
- provide ATP for protein synthesis/transcription/translation
- exocytosis
where are cuboidal tissues found in the body?
kidney tubule
where are cilliated tissues found in the body?
trachea/bronchi
what are two differences between the ribosomes found in animal cells and those found in prokaryotic cells?
- ribosomes are not attachrd to membranes/ER in prokaryoyes - (some) are in animal cells
- ribosomes larger (80s) in animal cells than prokaryotes (70s)
state which 2 structures found in prokaryotic cells are also found in mitochondria
- (loop of) DNA
- 70s ribosomes
explain why e.g liver cells have large numbers of mitochondria present
they are metabolically active so large amounts of ATP required
what is the edge of the vacuole in a plant cell called?
tonoplast
what is the gap in the cell wall and cell membrane in a plant cell called?
plasmodesmata
describe the structure and function of lysosomes
- fluid-filled vesicles surrounded by a single membrane, contain enzymes
- role in phagocytosis, digest unwanted materials in the cytoplasm
describe the functions of the permanent vacuole in plants
- control turgor pressure
- water storage
- isolates harmful waste products
- maintained pH
how is genetic information stored in prokaryotes?
- plasmids - small rings of DNA that carry non-essential genes, exchanged between bacterial cells via conjugation
- loop of DNA - circular DNA stored in the nucleoid region of the cell
describe the structure and function of mesosome
- infolds of the cell membrane
- increase the surface area of the cell, aiding cellular respiration
by what do prokaryotes reproduce?
binary fission
in viruses, what is the genetic material in the form of?
DNA or RNA
(while prokaryotes and eukaryotes’s genetic material is only in the form of DNA)
what is the function of the double nuclear membrane/nuclear envelope in nuclei?
separates the DNA from the rest of the cellular contents/hold DNA/chromosomes
following processing by the golgi body, describe how proteins are secreted from the cell [3]
- MEMBRANE of (secretory vesicles/vesicles containing product), fuses with cell membrane
- contents released from cell (secreted is neutral)
- exocytosis
