cells Flashcards
1
Q
what is magnification? (cells)
A
- how many times bigger an image is compared to the actual object
2
Q
what is resolution? (cells)
A
- the ability to distinguish between two points that are very close together
3
Q
what is the resolution of light microscopes like & why? (cells)
A
- poor resolving power
- they have a long wavelength of light
4
Q
what is the resolution of electron microscopes like? (cells)
A
- high resolving power
- they have a shorter wavelength of light
5
Q
what are the two main advantages of using electron microscopes over light microscopes? (cells)
A
- they have a high resolving power
- as electrons are negatively charged the beam can be focused using electromagnets
6
Q
what are the two types of electron microscopes? (cells)
A
- transmission electron microscopes (TEM)
- scanning electron microscope (SEM)
7
Q
how does a transmission electron microscopes (TEM) work? (cells)
A
- consists of an electron gun that produces a beam of electrons if focused onto a specimen by a condenser electromagnet
- beam passes through thin section of specimen
- if electrons absorbed then dark appearance
- if electrons pass through then bright appearance
- imaged produces is photographed & given to a photomicrograph
8
Q
what is a photomicrograph? (cells)
A
- a photograph of an image produced by a microscope
9
Q
what is the resolving power of a TEM & why is it difficult to achieve in practice? (cells)
A
- 0.1nm
- difficulties preparing specimens limit the resolution that can be achieved
- a higher energy electron beam is required & this may destroy the specimen
10
Q
what are the main limitations of both TEMs & SEMs? (cells)
A
- whole system must be in a vacuum so no live specimens
- complex ‘staining’ process is required & image is not in colour
- specimen must be extremely thin (TEM only)
- image may contain artefacts (things that may result from the way the specimen is prepared) so we can’t be sure it actually exists in the form seen
11
Q
can 3D images be obtained from a TEM? (cells)
A
- yes
- thin specimens result in a flat 2D image
- 3D images can be built up by looking at a series of sections through a specimen & the photomicrographs produced
- process is slow & complicated
12
Q
how does a scanning electron microscope (SEM) work? (cells)
A
- directs a beam of electrons onto the surface of the specimen from above
- beam is then passed back & forth across specimen in a regular pattern
- electrons are scattered by the specimen & pattern of scattering depends on the contours on the specimens surface
- specimens do not need to be thin to penetrate
13
Q
what is the resolving power of an SEM? (cells)
A
- 20nm
14
Q
can 3D images be produced by scanning electron microscopes? (cells)
A
- yes
- they can be built by computer analysis of the pattern of scattered electrons & secondary electrons produced
15
Q
what is cell fractionation? (cells)
A
- the process where cells are broken up & the different organelles are separated out
16
Q
what happens before cell fractionation takes place? (cells)
A
- tissue sample of cells must be put into a cold buffered solution that is of the same water potential as the tissue
17
Q
why does the pre-cell fractionation solution need to be cold, buffered & of the same water potential is the tissue? (cells)
A
- cold: to reduce enzyme activity that may break down organelles
- buffered: so the pH doesn’t fluctuate (any change in oh could alter the structure of organelles or affect enzyme function)
- same water potential: to prevent organelles from bursting/shrinking due to an osmotic loss or gain of water
18
Q
what is stage one of cell fractionation? (cells)
A
- homogenisation
19
Q
what is the process of homogenisation? (cell fractionation) (cells)
A
- cells are broken up by a homogeniser
- this releases organelles from the cell
- the resultant fluid (homogenate) is filtered to remove any complete cells or large pieces of debris
20
Q
what is the second stage of cell fractionation? (cells)
A
- ultracentrifugation
21
Q
what is the process of ultracentrifugation? (cell fractionation) (cells)
A
- tube of filtrate is placed in centrifuge & spun at slow speed
- heaviest organelles (nuclei) are forced to bottom of the tube & form a thin sediment
- fluid at top of tube (supernatant) is removed leaving only the sediment of nuclei
- supernatant is transferred to another tube & spun in centrifuge at a faster speed than before
- next heaviest organelles (mitochondria) forced to bottom of tube
- process continued to at each increase of speed the next heaviest organelles are sedimented & separated out
22
Q
what are the revolutions min-1 of nuclei, mitochondria & lysosomes? (cell fractionation) (cells)
A
- nuclei = 1 000 revolutions min-1
- mitochondria = 3 500 revolutions min-1
- lysosomes = 16 500 revolutions min-1
23
Q
what is the plasma cell membrane? (cells)
A
- found in all cells
- controls entrance & exit of molecules
- protein & lipid (phospholipid bilayer)
24
Q
what is the nucleus? (cells)
A
- contains nuclear envelope & nuclear pores
- DNA is either chromosomes or chromatin
- chromatin stains darkly
- lighter area of chromatin carry DNA for protein synthesis
25
what is the nucleolus? (cells)
- ribosome production
- built ribosome subunits from rRNA (ribosomal RNA) & proteins
- exit through nuclear pores to cytoplasm & combine to form functional ribosomes
26
what is the centriole? (cells)
- found only in animal cells
- found in pairs
- hollow cylinders made up of a ring of nine protein microtubules
- organise microtubules
- involved in cell division: spindle formation
27
what is the golgi apparatus? (cells)
- stacks of membrane-bound sacs formed by fusion of vesicles from rER
- continually changing
- received vesicles from ER
- packages & received proteins
28
what is the rough endoplasmic reticulum (rER)? (cells)
- interconnected membrane-bound flattened sacs
- has ribosomes attached to the outer surface
- provides a large surface area for the synthesis of proteins & trafficking
29
what is the smooth endoplasmic reticulum (sER)? (cells)
- lacks ribosomes on its surface & is more tubular
- synthesise, store & transport lipids
- synthesise, store & transport carbohydrates
30
what are the chloroplasts? (cells)
- surrounded by a double membrane (envelope)
- site of photosynthesis
- found only in plant cells
- thylakoid: site for the light dependent photosynthesis reaction
31
what is the thylakoid in chloroplasts? (cells)
- the site for the light dependent photosynthesis reaction
32
what is the mitochondria? (cells)
- double membranes
- inner membrane called the cristae
- site of aerobic respiration
- ATP production
33
what are lysosomes? (cells)
- bags of digestive enzymes
- breakdown of unwanted structures within the cell or whole cell (e.g. acrosome)
34
what is the vacuole? (cells)
- filled with water or ‘sap’
- surrounding membrane = tonoplast
- helps maintain pressure inside the cell to keep it rigid
- involved in isolation if unwanted chemicals in the cell
35
what are the ribosomes? (cells)
- found in all cells either free or bound to the rER
- used for protein synthesis
- work by reading triplet codons & stringing amino acids together
- messenger RNA (mRNA)
- ribosomal RNA (rRNA)
36
what is the cellulose cell wall? (cells)
- found in all plant cells
- contains microfibrils of cellulose to provide strength
37
what do we use to measure cells in a light microscope? (cells)
- eyepiece graticule
38
what is used to calibrate an eyepiece graticule? (cells)
- stage micrometer
39
what size ribosomes are in eukaryotic cells? (cells)
- 80S
40
what size ribosomes are in prokaryotic cells? (cells)
- 70S
41
what are the stages of protein synthesis? (9 steps) (cells)
- 1. transcription of DNA to mRNA
- 2. mRNA leaves nucleus
- 3. protein made on ribosomes enter rER
- 4. protein moves through the ER assuming a 3D shape en route
- 5. vesicles pinched off rER contain the protein
- 6. vesicles from rER fuse to form flattened sacs of golgi apparatus
- 7. proteins are modified within the golgi apparatus
- 8. vesicles pinched off rER off golgi apparatus contain the modified protein
- 9. vesicle fuses with cell surface membrane releasing protein (e.g. as extra cellular enzymes)
42
what is folded & modified in the rER?(protein synthesis)
- polypeptide chain
43
how are cells in organisms produced? (cells)
- mitotic divisions from a fertilised egg
44
how are specialised cells different from each other? (cells)
- they have different genes depending on the cell
45
give an example of how cells are adapted for their function (cells)
- muscle & sperm cells have lots of mitochondria (for respiration) because they undergo more movement
46
what is a tissue? (cells)
- a collection of similar cells that work together to perform a specific function
47
what is epithelial tissue? (cells)
- found in animals
- consists of sheets of cells (thin, flat cells) that line organs where diffusion takes place (e.g. alveoli in the lungs)
- line the surfaces of organs
- often have a protective secretory function
48
what is xylem tissue? (cells)
- found in plants
- made up of a number of similar cell types
- used to transport water & mineral ions throughout the plant
- also gives mechanical support
49
what are organs? (cells)
- a combination of tissues that are coordinated to perform a variety of functions
50
what tissues does the stomach contain & what do they do? (cells)
- muscle tissue to churn & mix stomach contents
- epithelial tissue to protect the stomach wall & produce secretions
- connective tissue to hold together other tissues
51
what tissues do leaves have & what do they do? (cells)
- palisade mesophyll made of leaf palisade cells that carry out photosynthesis
- spongy mesophyll adapted for gaseous diffusion
- epidermis to protect the leaf & allow gaseous diffusion
- phloem to transport organic materials away from the leaf
- xylem to transport water & ions into the leaf
52
why are capillaries not organs but arteries & veins are? (cells)
- capillaries are only made up of one type of tissue (epithelium)
- arteries & veins are made up of many tissues (epithelial, muscle & more)
53
what is an organ system? (cells)
- organs working together as a single unit to perform a specific function
54
what is the digestive system? (cells)
- digests & processed food
- includes organs like the salivary glands, oesophagus & stomach
55
what is the respiratory system? (cells)
- used for breathing & gas exchange
- included organs like the lungs, bronchi & trachea
56
what is the circulatory system? (cells)
- pumps & circulates blood
- included organs like the heart, arteries & veins
57
give some examples of differences between prokaryotic & eukaryotic cells (cells)
- prokaryotes don’t have a nucleus but eukaryotes do
- prokaryotes have smaller ribosomes (70S) than eukaryotes (80S)
- prokaryotes have no membrane bound organelles (e.g. mitochondria) but eukaryotes do
58
what is the structure of a bacterial cell? (8 features) (cells)
- capsule (only certain species)
- cell wall
- cell surface membrane
- plasmid (only certain species)
- ribosomes
- cytoplasm
- genetic material
- flagellum (only certain species)
59
what is the bacterial cell wall? (cells)
- complex
- mesh work of murein (tough protein)
- murein is also called peptidoglycan
60
what is the mucilaginous slime capsule? (bacteria) (cells)
- protects cell
- type if protein that stops cell from drying out
- on the outside of cells
- helps cells to stick to other cells
61
what is the plasma membrane? (bacteria) (cells)
- same structure in eukaryotes & prokaryotes
- main boundary between the outside of cells & the environment
62
what is circular DNA? (bacteria cells) (cells)
- possesses the genetic information for the replication of cells
63
what are plasmids? (bacteria) (cells)
- possesses genes that at aid the survival of bacteria in adverse conditions
- tiny circles of DNA carrying only a few genes which occur throughout the cytoplasm
64
what are flagellum? (bacteria) (cells)
- rotates & allows bacterium to move
- not all bacterium have one but some have more than one
65
what are viruses? (cells)
- acellular, non-living particles
- 200nm - 300nm in size
- contain nucleic acids as genetic material but can only multiply in host cells
- capsid = protein coat that covers a nucleic acid
- lipid envelope/capsid have attachment proteins (essential so virus can identify & attach to host cells)
66
what is mitosis? (cells)
- cell division that produces two identical daughter cells that have the same number of chromosomes as the parent cells & eachother
67
what is the order of the cell cycle? (cells)
- interphase (pre mitosis)
- prophase (mitosis)
- metaphase (mitosis)
- anaphase (mitosis)
- telophase (mitosis)
68
what is interphase? (cells)
- happens before mitosis
- period of cell growth & replication
- three separate growth stages (gap phase 1, synthesis, gap phase 2)
69
what is gap stage 1 (G1) of the cell cycle? (cells)
- part of interphase
- cell grows
- new organelles & proteins are made
70
what is synthesis (S) in the cell cycle (cells)
- part of interphase
- cell replicates its DNA so it is ready to divide by mitosis
71
what is gap phase 2 (G2) of the cell cycle? (cells)
- part of interphase
- cell keeps growing
- proteins needed for cell division are made
72
- what is the early prophase stage of mitosis? (cells)
- DNA has already replicated
- chromosomes become visible as long thin threads
- each replicated chromosome is held together at the centromere (spindle apparatus)
- these are called sister chromatids)
73
what is the mid prophase stage of mitosis? (cells)
- chromosomes shorten & thicken
- nucleolus disappears & nuclear envelope breaks down
- centrioles move to opposite ends on the cell
- chromosomes are left free in the cytoplasm
74
what is the late prophase stage of mitosis? (cells)
- centrioles produce spindle fibres
- chromosomes are drawn to the equator of the cell by spindle fibres attached to the centromere
75
what is the metaphase stage of mitosis? (cells)
- chromatids love to the equator of the cell & line up
- chromatids are joined by the centromere that some microtubules from the poles are attached to
76
what is the metaphase stage of mitosis? (cells)
- chromatids love to the equator of the cell & line up
- chromatids are joined by the centromere that some microtubules from the poles are attached to
77
what is the anaphase stage of mitosis? (cells)
- centromeres divide into two
- spindle fibres shorten & pull the sister chromatids apart
- chromatids move to opposite poles & are now known as chromosomes
- ATP is required & is provided by the mitochondria (which gather around the spindle fibres)
78
what happens to cells that are treated with chemicals that destroy spindle fibres? (cells)
- chromosomes remain at the equator & are unable to reach the poles
79
what is the telophase stage of mitosis? (cells)
- chromosomes reach their poles & become longer & thinner (leaves chromatin)
- spindle fibres disintegrate
- nuclear membrane & nucleolus reform
- cell divides by mitosis
80
what is cytokinesis? (cells)
- cytoplasm divides
- two new daughter cells with identical DNA are formed
81
why can’t some cells divide? (cells)
- because they don’t have centrioles
- e.g. nerve cells - evidence = paralysis & brain death
82
what is mitosis important for? (cells)
- growth
- repair
- reproduction
83
how do prokaryotic cells divide? (cells)
- binary fission
84
what is the process of binary fission? (cells)
- circular DNA molecule replicates & both copies attach to the cell membrane
- plasmids also replicate
- cell membrane begins to grow to two DNA molecules & begins to pinch inward (divides cytoplasm in two)
- new cell wall form between the 2 DNA molecules & original cell divides into two identical daughter cells
- DCs have one circular DNA molecule & lots of plasmids
85
how do viruses replicate? (cells)
- non living so can’t undergo cell division
- replicate by attaching to their host cell with their attachment proteins
- they then inject their nucleus acid into the host cell
- genetic information in the infected viral nucleus acid provides the ‘instructions’ for host cells metabolic processes to start producing viral components/nucleic acids/enzymes/structural proteins which are assembled into new viruses
86
how do viruses replicate? (cells)
- non living so can’t undergo cell division
- replicate by attaching to their host cell with their attachment proteins
- they then inject their nucleus acid into the host cell
- genetic information in the infected viral nucleus acid provides the ‘instructions’ for host cells metabolic processes to start producing viral components/nucleic acids/enzymes/structural proteins which are assembled into new viruses
87
name & summarise the three stages of the cell cycle (cells)
- interphase (occupies most of the cell cycle, no division occurs)
- nuclear division (when nucleus divides into two (mitosis) or four (meiosis)
- cytokinesis (cytoplasm divides to produce two (mitosis) or four (meiosis) cells
88
what causes cancer? (cells)
- uncontrolled cell division
- growth disorder of cells
89
what are tumours? (cells)
- a group of abnormal cells that develops as a result of uncontrolled cell division
- can develop in any organ of the body but are most commonly found in the lungs, prostate gland, breast & ovaries
90
name the two types of tumour (cells)
- malignant
- benign
91
what is a malignant tumour? (cells)
- grow rapidly
- less compact
- more likely to be life threatening
92
what is a benign tumor? (cells)
- grow slowly
- more compact
- less likely to be life threatening
93
what can the rate of mitosis be affected by? (cells)
- environment of the cell
- growth factors
- (2) types of gene (mutation of one of the genes leads to uncontrolled mitosis, which can lead to tumours)
94
what is involved in the treatment of cancer? (cells)
- killing dividing cells by blocking part of the cell cycle
- this means that the cell cycle is disrupted & cell division ceases (hence the cancer growth also ceases)
95
how do cancer drugs (chemotherapy) disrupt the cell cycle? (cells)
- prevent DNA from replicating
- inhibits the metaphase stage of mitosis by interfering with spindle formation
96
how can cancer drugs impact normal cells? (cells)
- disrupts cell cycle of normal cells
- the drugs are more effective against rapidly dividing cells
- cancer cells have a fast rate of division so are damaged to a greater degree
- normal cells (e.g. hair producing cells) that divide rapidly are also vulnerable to damage (explains hair loss in cancer patients)
97
what is a plasma membrane? (cells)
- the membrane around & within cells
- includes the membranes around & in organelles
98
what is the cell surface membrane? (cells)
- the plasma membrane that surrounds cells
- forms the boundary between the cell cytoplasm & the environment
- allows different conditions to be established inside & outside of cells
- controls movement of substances in & out of cells
99
what do phospholipids do in the cell membrane? (cells)
- hydrophilic heads point to the outside of the membrane & are attracted by water on both sides
- hydrophobic tails point into the centre of the membrane & are repelled by water on both sides
- lipid-soluble material moves through the membrane via the phospholipid portion
100
what are the functions of phospholipids in the can membrane? (cells)
- allow lipid-soluble substances to enter & leave the cell
- prevent water-soluble substances entering & leaving the cell
- make the membrane flexible & self-sealing
101
where do proteins occur in the cell membrane? (cells)
- in the surface of the membrane
- completely span the phospholipid bilayer
102
what do proteins that occur in the surface of the phospholipid bilayer do? (cells)
- never extend completely across it
- give mechanical support
- (along with glycolipids) act as cell receptors for molecules like hormones
103
what do proteins that span the length of the phospholipid bilayer do?
- protein channels form water filled tubes to allow water-soluble ions to diffuse across the membrane
- carrier proteins bind to ions/molecules (e.g. glucose or amino acids) then change shape in order to move those molecules across the membrane
104
what are the functions of proteins in the membrane? (cells)
- provide structural support
- act as channels transporting water-soluble substances across the membrane
- allow active transport across the membrane through carrier proteins
- form cell-surface receptors for identifying cells
- helps cells adhere together
- acts as receptors (e.g. for hormones)
105
what does cholesterol do in the cell membrane? (cells)
- add strength to membranes
- are very hydrophobic so prevent the loss of water & dissolved ions from the cell
- pull together fatty acid tails of phospholipid molecules which limits their movements & that of other molecules without making the membrane too rigid
106
what is the function of cholesterol in the cell membrane? (cells)
- reduces lateral movement of other molecules (including phospholipids)
- makes the membrane less fluid at high temperatures
- prevent leakage of water & dissolved ions from the cell
107
what are glycolipids? (cells)
- a carbohydrate covalently bonded with a lipid
- carbohydrate extends from the bilayer into the watery environment outside of the cell where it acts as a cell-surface receptor for specific chemicals
- e.g. the human ABO blood system operates as a result of glycolipids
108
what are the functions of glycolipids in the cell membrane? (cells)
- act as recognition sites
- help to maintain the stability of the membrane
- helps cells to attach to one another so form tissues
109
what are glycoproteins & what do they do? (cells)
- carbohydrate chains are attached to many proteins on the outer surface of the cell membrane
- act as cell-surface receptors (more specifically for hormones & neurotransmitters)
110
what are the functions of glycoproteins in the cell membrane? (cells)
- act as recognition sites
- helps cells to attach to one another & so form tissues
- allows cells to recognise one another (e.g. lymphocytes can recognise an organism’s cells
111
why do most molecules not freely diffuse across the cell surface-membrane? (cells) (4 things)
- many are not soluble in lipids & therefore can’t pass through the phospholipid layer
- many are too large to pass through the channels in the membrane
- may are of the same as the charge on the protein channels & so even if they are small enough you pass through, they are repelled
- many are electrically charged (polar) & therefore have difficulty passing through the non-polar hydrophobic in the phospholipid bilayer
112
why is the arrangement of the cell-surface membrane known as the fluid mosaic model? (cells)
- fluid because the individual phospholipid molecules can move relative to one another. This gives the membrane a flexible structure that is constantly changing shape
- mosaic because the proteins that are embedded in the phospholipid bilayer vary in shape, size & pattern
113
define diffusion (cells)
- the net movement of molecules or ions from a region where they are in high concentration to one where they are in low concentration until evenly distributed
114
is diffusion a passive process & why/why not? (cells)
- yes because it enquires no external energy
- the energy used comes from the natural motion of the particles
115
outline simple diffusion (3 points) (cells)
- all particles are constantly in motion due to the kinetic energy they possess
- this motion is random with no set pattern as to the way the particles move around
- particles are constantly bouncing off one one another as well as off other objects
116
what is facilitated diffusion? (cells)
- diffusion that is made easier (facilitated) by transmembrane channels & carriers that span the plasma membrane
117
outline facilitated diffusion (3 points) (cells)
- it is a type of passive transport
- occurs down a concentration gradient but occurs at specific points on the plasma membrane where there are special protein molecules
- there are two types of proteins involved (protein channels & carrier proteins)
118
outline the role of protein channels in the plasma membrane in terms of diffusion (6 points) (cells)
- from water-filled hydrophilic channels across the membrane
- allow specific water-soluble ions to pass through
- channels are selective & each opens in the presence of a specific ion
- if the particular ion is not present the channel remains closed
- this means that there is control over the entry & exit of ions
- the ions bind with the proteins causing it to change shape in a way that closes it to one side of the membrane & opens it to the other side
119
what happens when specific ions bind to the protein channels in terms of diffusion? (cells)
- it causes the protein to change shape in a way so that it closes to one side of the membrane & opens to the other side of it
120
why is there control over the entry & exit of ions the protein channels? (cells)
- the channels are selective & each opens in the presence of a specific ion
- if the specific ion is not present the channel remains closed
- this means that there is control over the entry & exit of ions
121
outline the role of carrier proteins in the plasma membrane in terms of diffusion (4 points) (cells)
- span the plasma membrane
- when a molecule that is specific to the protein is present it binds with the protein
- this causes it to change shape so that the molecule is released to the inside of the membrane (no external energy is needed for this)
- the molecules move from a region where they are highly concentrated to one of lower concentration using only the kinetic energy of the molecules themselves
122
how do carrier proteins change shape when they come into contact with their specific ions in terms of diffusion? (cells)
- they change shape so that the molecules is released to the inside of the membrane
123
what happens to molecules in carrier proteins in terms of diffusion? (cells)
- the molecules move from a region where they are in high concentration to one of lower concentration
- they only use the kinetic energy of the molecules themselves meaning the process is passive
124
name the 4 factors that affect the rate of diffusion (cells)
- distance
- surface area
- concentration difference
- temperature
125
how does distance affect the rate of diffusion? (cells)
- the shorter the distance the faster the rate of diffusion
- the further the particles have to travel the longer diffusion takes
126
how does surface area affect the rate of diffusion? (cells)
- the greater the surface area the faster the rate of diffusion
- the greater the surface area the more space for molecules to diffuse across the membrane
127
how does concentration difference affect the rate of reaction? (cells)
- the greater the difference in concentration the faster the rate of diffusion
- the greater the difference in concentration the greater the difference between a solute & solvent
128
how does temperature affect the rate of diffusion? (cells)
- the higher the temperature the faster the rate of diffusion
- the higher the temperature the more kinetic energy the particles have
129
what is the equation for Fick’s law? (cells)
- the rate of diffusion is proportional to:
- surface area X difference in conc./length of diffusion path
- length of diffusion path is also known as membrane thickness
130
define osmosis (cells)
- the net movement of water from an area of higher water potential to one of lower water potential across a selectively permeable membrane
131
define water potential (cells)
- the pressure created by a water molecule)
132
what symbol represents water potential & what is it measured in? (cells)
- symbol = ψ (psi)
- measured in kPa
133
what are the standard conditions for water potential? (cells)
- 25˚C
- 100kPa
134
what is the water potential of pure water under standard conditions? (cells)
- zero
135
what happens to the water potential of pure water when a solute is added? (cells)
- the water potential of pure water decreases/is lowered
136
what must the water potential of a solution always be? (cells)
- less than zero/have a negative value
137
what happens to water potential when more solute is added to a solution? (cells)
- the more concentrated the solution, the lower/more negative the water potential
138
outline an explanation of osmosis (5 things) (cells)
- one side of the membrane has a low solute concentration & the other side has a high concentration of solute molecules
- both the solute & water molecules have random motions due to their kinetic energy
- the selectively permeable membrane only allows water molecules across it & not solute molecules
- the water molecules diffuse from the side with a low concentration of solute molecules (with a higher water potential) to the other side (with a lower water potential) down a water potential gradient
- when there is an equal concentration of solute molecules on each side of the membrane, a dynamic equilibrium is reaches & there is no net movement of water
139
what is the highest value of water potential? (cells)
- zero
140
what is an isotonic solution? (cells)
- when a solution has the same water potential as the cell within the solution
141
what is a hypotonic solution? (cells)
- when the water potential of a solution is more positive (closer to zero) than the cell
142
what is a hypertonic solution? (cells)
- when the water potential of a solution is more negative than the cell
143
what happens when an animal cell is placed in an isotonic solution? (cells)
- the water potential of the solution & cell are the same
- this means that there is no net movement of water & therefore no change in the cell
144
what happens to plant cells if they are placed in an isotonic solution? (cells)
- the water potential is equal so no water enters or leaves
- this means that there is no charge & the cell goes through incipient plasmolysis (protoplast begins to pull away from the cell wall)
145
what happens to animal cells if they are paced in a hypotonic solution? (cells)
- a lot of water will move into the cell via osmosis
- because the cell membrane does not stretch & does not have a cell wall the pressure will eventually cause the cell to burst
146
what happens to plant cell if they are placed in a hypotonic solution? (cells)
- water enters the cell. Causes it to swell
- this causes the plant cell to become turgid, but it doesn’t burst as it has a strong cell wall
- the protoplast begins to push against the cell wall
147
what happens to animal cells if they are placed in a hypertonic solution? (cells)
- the cell shrinks & becomes shrivelled as large volumes of water leave the cell via osmosis
148
what happens to plant cells if they are placed in a hypertonic solution? (cells)
- the cell shrinks & becomes shrivelled as large volumes of water leave the cell via osmosis
- the protoplast completely pulls away from the cell wall
149
what is active transport? (cells)
- the net movement of molecules/ions from a region of higher concentration to one of lower concentration using ATP & carrier proteins
- moves substances against a concentration gradient
150
what is ATP used for in active transport? (cells)
- directly moves molecules
- individually move molecules using a concentration gradient which has already been set up by (direct) active transport (co-transport)
151
how does active transport differ from other passive transport processes? (4) (cells)
- metabolic energy (ATP) is required
- substances are moved against a concentration gradient (from a lower to higher concentration)
- carrier proteins molecules (which act as ‘pumps’ are involved
- the process is selective, with specific substances being transported
152
outline the process of direct active transport of a single molecule/ion (5) (cells)
- the carrier proteins span the plasma membrane & bind to the molecule/ion to be transported on one side of it
- the molecule/ion binds to the receptor sites on the carrier protein
- on the inside of the cell/organelle, ATP binds to the protein, causing it to split into ADP & a phosphate molecule. As a result, the protein molecule changes shape & opens to the opposite side of the membrane
- the molecule/ion is then released to the other side of the membrane
- the phosphate molecule is then released from the protein, which causes the protein to revert back to its original shape, ready for the process to be repeated. The phosphate molecule then recombines with the ADP to form ATP during respiration
153
what 2 things sometimes occur with the movement of molecules during active transport? (cells)
- more than one molecule/ion may be moved in the same direction at the same time by active transport
- the molecule/ion is moved into a cell/organelle at the same time as a different one is being removed from it
154
what do epithelial cells have that increases the rate of movement across the membrane? (cells)
- they have microvilli (are 0.6 micro metres in length)
- they provide more surface area or the insertion of carrier proteins through which diffusion, facilitated diffusion & active transport occur
- this increases the rate of movement across the membrane
155
name two ways that the rate of movement across membranes can be increased in epithelial cells (cells)
- microvilli increase the surface area & allow for the insertion of carrier proteins for diffusion, facilitated diffusion & active transport
- increase the protein channels & carrier proteins in any given area of membrane
156
what is the role of diffusion in absorption? (4) (cells)
- there is normally a greater concentration of glucose & amino acids in the ileum than in the blood as carbohydrates & proteins are constantly being broken down
- therefore there is a concentration gradient down which glucose moves by facilitated diffusion from the ileum to the blood
- because blood is constantly being circulated by the heat, the glucose absorbed into it is continuously being removed by cells as they use it during respiration
- this helps to maintain the concentration gradient between the inside of the ileum & the blood, meaning that the rate of movement by facilitated diffusion across epithelia cell-surface membranes is increased
157
what is the role of active transport in absorption? (3) (cells)
- diffusion only results in the concentrations on wither side of the intestinal epithelial being equal
- this means that not all the available glucose & amino acids can be absorbed & some may pass out of the body
- this does not happen as they are also absorbed by active transport (co-transport more specifically)
158
outline the process behind the sodium potassium pump (4) (cells)
- sodium ions are actively transported out of the epithelium cells creating a concentration gradient between the gut lumen & cell (this maintains a much higher concentration of Na ions in the lumen of the intestine than the epithelial cells)
- sodium ions diffuse from the lumen into the cell through a concentration gradient between-transport (carrier) protein
- as they do so they couple with a glucose molecule, which is carried into the cell with it
- glucose in the cell is at a high concentration so moves out of the cell by facilitated diffusion into the blood
159
state 3 factors that affect the rate of active transport (cells)
- the speed of the individual carrier proteins (the faster they work, the faster the rate of active transport)
- the number of carrier proteins present (the more proteins there are, thee faster the rate of active transport)
- the rate of respiration in the cell & the availability of ATP (is respiration is inhibited, active transport can’t take place)
160
state, define & give examples for the two types of defence mechanism in the body (cells)
- specific: slower, specific to certain pathogens
- e.g. T-lymphocytes (cell mediated response) & B-lymphocytes (humoral response)
161
what is a pathogen? state the 4 types (cells)
- a disease causing organism
- protist, virus, fungi, bacteria
162
what is an antigen? (cells)
- the specific part of a pathogen (usually a protein) that is recognised as non-self (foreign) by the immune system
163
what 4 things can the immune system identify? (cells)
- pathogens
- non-self material (e.g. cells from other organisms - organ transplant)
- toxins
- abnormal body cells (e.g. cancer cells)
164
how do lymphocytes recognise cells belonging to the body? (8) (cells)
- 10 million different lymphocytes present at any time & each can recognise a different chemical shape
- in fetuses the cells constantly collide with other cells (infection as rare as F is shielded from outside world)
- lymphocytes collide with body’s own material
- some have receptors that exactly fit body cells (either die or are suppressed)
- remaining may fit foreign material (so only respond to foreign material)
- in adults, lymphocytes produced in bone marrow only encounters self-antigens
- only Ls that show an immune response to them have programmed cell death before they differentiate into mature lymphocytes
- no clones of anti-self lymphocytes appear in blood, leaves only ones that may respond to non-self antigens
165
what is the first stage of non-specific immune response? (cells)
- phagocytosis
166
outline the process of phagocytosis (5) (cells)
- phagocyte is attracted to the pathogen via chemical products of pathogen or dead/damaged/abnormal cells
- phagocyte attaches to the pathogen via receptors in their CSM & engulfs it, forming a phagosome
- lysosomes migrate to the phagosome & fuse with the vesicle
- lysosomes release lysozymes that hydrolyse the bacteria (cell walls), forming phagolysosomes
- soluble breakdown products are absorbed into the cytoplasm of the phagocyte & the rest is expelled
167
what type of response are T-lymphocytes & B-lymphocytes associated with? (cells)
- T-lymphocytes = cell-mediated response
- B-lymphocytes = humoral response
168
what is cell-mediated immunity? (cells)
- immunity involving body cells
- T-lymphocytes
169
how can T-lymphocytes distinguish between invader (foreign) & normal cells? (4) (cells)
- phagocytes that have engulfed & hydrolysed a pathogen present some of a pathogens antigens on their own cell-surface membrane
- body cells invaded by a virus present some of the viral antigens on their own cell-surface membrane
- transplanted cells from individuals of the same species have different antigens on their cell-surface membrane
- cancer cells are different from normal body cells & present antigens on their cell-surface membrane
170
what are antigen-presenting cells? (cells)
- cells that display foreign antigens on their surface
171
outline & explain the four main stages to immune response (cells)
- phagocyte engulfs pathogens - carries out phagocytosis, found in blood & tissues, first to respond
- phagocyte actives T-lymphocytes - T-cells have receptor proteins on their surface that bind to complimentary antigens presented by the phagocyte, this activates the T-cell
- T-cells activate B-cells, which divide into plasma cells - B-cells have antibodies (each one has different shapes so bind to different antigens), this (with substances released from T-cells) activates the B-cell (process = clonal selection), activated B-cells divide into plasma cells
- plasma cells make mere antibodies to the specific antigen - plasma cells divide by mitosis to produce clones of B-cell, secrete lots of monoclonal antibodies that are specific to the one antigen (clonal expansion)
172
give some examples of T-cells (cells)
- helper T-cells release chemical signals that activate & stimulate phagocytes
- cystitis if T-cells kill abnormal & body cells)
173
how to cytotoxic T-cells kill abnormal/body cells infected by pathogens? (cells)
- produce a protein called perforin that makes holes in the cell-surface membrane
- these holes mean that the cell membrane becomes freely permeable for all substances & the cell dies as a result of
174
what is humoral immunity & which lymphocyte is responsible for it? (cells)
- involves antibodies, which are soluble in the blood & tissue fluid of the body
- B-lymphocytes are responsible for
175
outline the role of B-lymphocytes in immunity (7) (cells)
- the surface antigens of an invading pathogen are taken up by a B-cell
- the B-cell processes the antigens & presents them on its surface
- helper T cells attach to the processed antigens on the B-cell, activating it
- the B-cell becomes activated to divide by mitosis to give a clone of plasma cells
- the cloned plasma cells produce & secrete the specific antibody that exactly fits the antigen on the pathogen’s surface
- the antibody attaches to antigens on the pathogen & destroys them (primary immune response)
- some B-cells develop into memory cells. These can respond to future infections by the same pathogen by dividing rapidly & developing into plasma cells that produce antibodies (secondary immune response)
176
outline the process of clonal selection (cells)
- B-cells bind to their complementary antigens
- this (along with substances secreted by helper T cells) activates the B-cell to divide to produce plasma cells
- the plasma cells all produce the antibody that is specific to the foreign antigen
177
how are monoclonal antibodies secreted by B-cells? (cells)
- plasma cells divide my mitosis to produce clones of the B-cell
- these cells secrete lots of monoclonal antibodies that are specific to one antigen
178
outline the primary immune response & state the cell responsible for it (cells)
- plasma cells
- only survive for a few days
- creates antibodies that lead to the destruction of the antigen
- responsible for the immediate defence of the body against infection
179
outline the secondary immune response & state the cell responsible for it (cells)
- memory cells
- can live for decades
- do not produce antibodies directly but circulate in blood & tissue fluid
- when they encounter the same antigen at a later date, they divide rapidly & develop into cells plasma cells (produce the antibodies needed to destroy the pathogen) & more memory cells (circulate so they can fight future infections)
- memory cells provide long-term immunity & is faster than the primary immune response as an increased quantity of antibodies are secreted at a faster rate
180
what is an antibody? (cells)
- a protein produced by lymphocytes in response to the presence of the appropriate pathogen
- they have specific binding sites synthesises by B-cells
181
outline the structure of an antibody (3) (cells)
- made up of 4 polypeptide chains (2 light, 2 heavy - heavy on inside)
- the binding site is different for each antibody so is called the variable region
- the rest of the structure is called the constant region
182
what is an antigen-antibody complex? (cells)
- formed because each antibody has a specific binding sites synthesises that fits precisely onto a specific antigen
183
how are antibodies involved in the destruction of antigens? (cells)
- they don’t destroy antigens directly but instead prepare the antigen for destruction
- different antibodies lead to the destruction of antigens in a range of ways
184
what is agglutination? (cells)
- the clumping together of molecules (e.g. cells)
- e.g. bacteria cells - this helps them to be easily located by phagocytes as they are not spread-out within the body
185
what are monoclonal antibodies? (cells)
- antibodies that are produced by a single clone of a specific white blood cell
186
how are monoclonal antibodies used to treat cancer? (3) (cells)
- monoclonal antibodies are produced that are specific to antigens on cancer cells
- these antibodies are given to a patient & they attach themselves to the receptors on their cancer cells
- they attach to the surface of their cancer cells & block the chemical signals that stimulate their uncontrolled growth
187
outline 2 advantages of direct monoclonal antibody therapy (cells)
- that antibodies are not toxic & are highly specific so they lead to fewer side effects than other forms of therapy
- they only need to be used in smaller doses (because they target specific sites) & therefore it is cheaper than other forms of therapy
188
what is indirect monoclonal antibody therapy? (cells)
- involves attaching a radioactive/cytotoxic drug to the monoclonal antibody
- when the antibody attaches to the cancer cells, it kills them
189
why are monoclonal antibodies used to diagnose illness? (cells)
- they produce much more rapid results than conventional methods of diagnosis
190
how are monoclonal antibodies used in pregnancy tests? What are control windows? Name the hormone associated with this (cells)
- pregnant women have the hormone hCG in their urine
- MABs on the test strip are linked to coloured particles
- if hCG is present in the urine, it binds to the particles
- the particles move up the test strip & present the coloured line
- control windows prevent false negatives
- show that the antibody has moved up the test strip even if it hasn’t bound the to hCG
- hormone = human chorionic gonanotropin (hCG)
191
outline 3 ethical issues associated with monoclonal antibodies (cells)
- production of MABs involves use of mice
- production of tumour cells deliberately induces cancer in mice
- some people don’t agree with using animals in this way
- MABs have saved lives but there have been death in its use in the treatment of MS
- it is important for patients to be able to give informed consent
- testing the safety of new drugs has risks
- one group who tested them all suffered from organ failure but survived
- this raises issues about the conduct of drug trials
192
define immunity, active immunity & passive immunity (cells)
- immunity: the ability of an organism to respond quickly to a pathogen it has encountered before
- active immunity: a type of immunity that occurs when your immune system makes its own antibodies after being stimulated by an antigen
- passive immunity: a type of immunity that occurs when antibodies are introduced into the body from an outside source
193
what is the difference between natural active immunity & artificial active immunity? (cells)
- natural active immunity: people become infected with a disease under normal circumstances. The body produces its own antibodies & may continue to do so for many years
- artificial active immunity: forms the basis of vaccination. Involves inducing an immune response in an individual without them suffering the symptoms of the disease
194
what is the difference between natural & artificial passive immunity? (cells)
- natural passive immunity = maternal antibodies are introduced into an infant’s body via breastmilk
- artificial passive immunity = come from antibody transfusions (e.g. anti-venom given to victims of snake bites
195
outline some key features of a successful vaccination programme (cells)
- must be possible to vaccinate the vast majority of the vulnerable population to produce herd immunity
- must be few side effects (if any) of the vaccine
- must be economically available in sufficient quantities to immunise most of the vulnerable population
- must be means of administering the vaccine properly at appropriate times
196
what is meant by the concept of herd immunity? Outline where it came from & state why it is important (cells)
- arises when a sufficiently large proportion of a population has been vaccinated to make it difficult for a pathogen to spread within that population
- concept is based on the idea that pathogens are passed from person to person, so when the majority of a population is immunised, it is unlikely that a vulnerable person will come into contact with an infected person. This means the vulnerable person is protected
- it is important as not everyone in a large population can be vaccinated (e.g. babies/very young children & immunocompromised people are unable to recieve vaccinations as it could cause them harm)
197
outline the differences between active & passive immunity (4) (cells)
- active immunity requires exposure to antigens
- passive immunity doesn’t require exposure to antigens
- in active immunity, protection takes a while to develop as antibodies need to be made
- in passive immunity, the effect is immediate
- memory cells are produced in active immunity as B lymphocytes are activated so both memory & plasma cells are made
- memory cels are not produced in passive immunity as B lymphocytes are not activated, therefore no plasma/memory cells can be produced
- in active immunity, the protection is long term as antibodies are produced after the activation of memory cells to divide by mitosis
- in passive immunity, protection is short term as antibodies are broken down
198
give some reasons as to why vaccination may not eliminate a disease (cells)
- vaccination fails to induce immunity of certain individuals (e.g. immunocompromised people)
- people may develop the disease immediately after vaccination, but before their immunity levels are high enough to prevent it. They may harbour the pathogen & infect others
- the pathogen may mutate frequently so that vaccines become ineffective (as the new antigens on the pathogen aren’t recognised by the immune system, so antibodies aren’t made to destroy the pathogen)
- there may be so many varieties of a pathogen that it is impossible to make a vaccine that is effective against all of them
- certain pathogens can conceal themselves within cells, making it harder for the immune system to destroy them
- people may oppose vaccines for religious, medical or ethical reasons
199
state some of the ethical issues surrounding vaccination (cells)
- production of existing vaccines & development of new ones often uses animals
- vaccines have side effects that may sometimes cause long-term harm. How can the pros be balanced against the cons?
- who should vaccines be tested on? Should people be asked to take the rest in the interest of public health?
-should expensive vaccination programmes continue if it means less money for the treatment of other diseases?
- should vaccination be compulsory? Should people be able to opt out, & on what grounds? (medical/ethical/religious)
200
describe the structure of HIV (cells)
- has a lipid envelope on the outside, which has attachment proteins embedded in it
- inside the lipid envelope is a capsid (protein layer) than encloses 2 single RNA strands & some enzymes
- encloses the enzyme reverse transcriptase that catalyses the production of DNA from RNA (reverse transcription)
- presence of reverse transcriptase means HIV is a retrovirus
- also has a matrix
201
outline the replication process of HIV (cells)
- following infection, HIV enters the bloodstream & circulates around the body
- a protein on the HIV binds to a CD4 protein on another cell. HIV most frequently attaches to helper T cells
- the protein capsid fuses with the cell-surface membrane. The RNA & enzymes of the HIV enter the helper T cells
- the HIV reverse transcriptase converts the virus’s RNA to DNA
- the new DNA is over into the helper T cell’s nucleus, where it is inserted into the cell’s DNA
- the HIV DNA in the nucleus creates mRNA using the cell’s enzymes. This mRNA contains the instructions for making new viral proteins & for the RNA to go into the new HIV
- the mRNA passes out of the nucleus via a nuclear pore & uses the cell’s protein synthesis mechanisms to make HIV particles
- the HIV particles break away from the helper T cells with a piece of its cell-surface membrane surrounding them (this forms their lipid envelope)
202
how does HIV cause symptoms of AIDS? (3) (cells)
- HIV causes AIDS by killing/interfering with the normal functioning of helper T cells
- without a sufficient number of helper T cells, the immune system can’t stimulate B cells to produce antibodies or cytotoxic T cells to kill infected cells
- as a result, the body is unable to produce a good immune response & becomes susceptible to infections & cancers (these secondary conditions ultimately cause death)
203
what is the ELISA test? How does it work? (cells)
- enzymes linked immunoabsorbant assay
- uses antibodies to detect the presence of a protein in a sample
- apply the sample to a surface to which the antigens in a sample will attach to
- wash the surface several times to remove any unattached antigens
- add the antibody that is specific to the antigen & leave the two to bind
- wash the surface to remove excess antibody
- add a secondary antibody that bonds with the first antibody. The second antibody has an enzyme attached to it
- add the colourless substrate of the enzyme. The enzyme acts on the substrate to change into a coloured product
- the amount of the antigen present is relative to the intensity of the colour
- can be used to detect HIV
204
why are antibiotics ineffective against viral diseases like AIDS? (cells)
- viruses rely on host cells to carry out metabolic processes so lack their own metabolic pathways
- are ineffective as there are no metabolic mechanisms/cell structures for them to disrupt
- they have a protein coat instead of a murein cell wall so don’t have sites where antibiotics can work
- when viruses are in an organisms own cells, antibiotics can’t reach them
