3.2 Cells Flashcards
1
Q
3.2.1 Cell structure
What is a eukaryotic cell? (1 point)
A
A cell that has a true nucleus with a nuclear envelope surronding the chromosomes and membrane-bound organelles
2
Q
Describe the nucleus of a eukaryotic cell (4 points)
A
A large organelle surrounded by a nuclear envelope (double membrane), which contains many pores. Nucleus contains chromosomes and nucleolus
The nucleus controls the cell’s activities by controlling the transcription of DNA.
DNA contains instructions to make proteins.
The pores allow substances to move between the nucleus and cytoplasm.
The nucleolus makes ribosomes
3
Q
Describe the cell surface plasma membrane of a eukaryotic cell (4 points)
A
The membrane found on surface of animal cells and inside cell wall of other cells.
Mainly made of lipids and protein
Regulates the movement of substances into and out of the cell.
Also has receptor molecules on it which allow it to respond to chemicals like hormones
4
Q
Describe the mitochondrion of eukaryotic cells (6 points)
A
Usually oval-shaped.
Have double membrane.
Inner membrane folded to form structures called cristae.
Inside is matrix, which contains enzymes involved in respiration
The site of aerobic respiration, where ATP is produced.
Found in large numbers in cells that require a lot of energy as they are very active
5
Q
Describe the chloroplasts in eukaryotic cells (5 points)
A
A small, flattened structure found in plant and algal cells.
Its surrounded by a double membrane and also has membranes inside called thylakoid membranes.
These membranes are stacked up in some parts of the chloroplast to form grana.
Grana linked together by lamellae thin, flat pieces of thylakoid membrane
The site of photosynthesis
6
Q
Describe the Golgi Apparatus in eukaryotic cells (4 points)
A
A group of fluid-filled, membrane bound flattened sacs.
Vesicles are often seen at the edges of the sacs
It processes and packages new lipids and proteins.
Also makes lysosomes
7
Q
Describe the Golgi Vesicles in eukaryotic cells (2 points)
A
A small fluid-filled sac in the cytoplasm, surrounded by a membrane and produced by the golgi apparatus
Stores lipids and proteins made by the golgi apparatus and transports the out of the cell via the cell-surface membrane
8
Q
Describe the lysosome of a eukaryotic cell (4 points)
A
A round organelle surounded by a membrane, with no clear internal structure.
Its a type of golgi vesicle
Contains digestive enzymes called lysozymes. These are kept separate from the cytoplasm by the surrounding membrane, and can be used to digest invading cells or to break down worn out components of the cell.
9
Q
Describe the ribosomes in eukaryotic cells (4 points)
A
A very small organelle that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum.
Its made up of proteins and RNA.
Its not surrounded by a membrane
The site where proteins are made
10
Q
Describe the Rough Endoplasmic Reticulum in eukaryotic cells (3 points)
A
A system of membranes enclosing a fluid-filled space.
The surface is covered with ribosomes
Folds and processes proteins that have been made at the ribosomes
11
Q
Describe the Smooth Endoplasmic Reticulum in eukaryotic cells (2 points)
A
Similar to RER but has no ribosomes
Synthesises and processes lipids
12
Q
Describe the Cell Wall in eukaryotic cells (4 points)
A
A rigid structure that surrounds cells in plants, algae and fungi.
In plants and algae its made mainly of the carbohydrate cellulose.
In fungi its made of chitin
Supports cells and prevents them from changing shape
13
Q
Describe the Cell Vacuole in eukaryotic cells (6 points)
A
A membrane-bound organelle found in the cytoplasm of plant cells.
It contains cell sap which is a weak solution of sugar and salts.
The surrounding membrane is called the tonoplast
Helps to maintain pressure inside the cell and keep the cell rigid.
This stops plants wilting.
Also involved in the isolation of unwanted chemicals inside the cell
14
Q
What are specialised cells? (2 points and example in small intestine)
A
Eukaryotic cells can become specialised to carry out specific functions
E.g. Epithelial cells in small intestine adapted to absorb food efficiently because:
Walls of small intestine lined with villi which increase surface area for absorption
Epithelial cells have folds in cell-surface membranes called microvilli to increase surface area even more
Have lots of mitochondria to provide energy for transport of digested food molecules into cell
Specialised cells grouped together to form tissues which work together to form organs which make up an organ system
15
Q
What is a prokaryotic cell? (1 point and example)
A
A cell that lacks a membrane-bound nucleus or any other membrane bound organelle
E.g. Bacteria
16
Q
Describe the cytoplasm in prokaryotic cells (1 point)
A
Contains no membrane bound organelles whereas eukaryotes do (mitochondria)
17
Q
Describe the ribosomes in prokaryotic cells and how they differ to eukaryotic cells (1 point)
A
Same function and structure as in eukaryotic cells but are smaller (70s) whereas eukaryotes have 80s
18
Q
Describe DNA in prokaryotic cells (2 points)
A
Prokaryotic cell doesn’t have a membrane bound nucleus unlike eukaryotic cells instead has circular DNA present as one long coiled up strand and floats free in cytoplasm.
DNA is not attached to any histone proteins
19
Q
Describe prokaryotic cell Plasmids (4 points)
A
Small loops of DNA that aren’t part of main circular DNA molecule.
Plasmids contain genes for antibiotic resistance and can be passed between prokaryotes.
Not always present but some can have several.
Eukaryotes don’t have a plasmid
20
Q
Describe prokaryotic cell Capsule (2 points)
A
Some have capsule made up of slime
Helps to protect bacteria from attack by cells of the immune system
21
Q
Describe prokaryotic cell wall and how it differs from eukaryotic cell wall (3 points)
A
Supports the cell and prevents it from changing shape
Made of a polymer called murein which is a glycoprotein.
In eukaryotes however cell wall is made from cellulose
22
Q
Describe prokaryotic cell plasma membrane (2 points)
A
Mainly made of lipids and proteins
Controls the movement of substances into and out of cell
23
Q
How does prokaryotic cell size differ from eukaryotic cell? (1 point)
A
Prokaryotic cell is 1 - 10 micrometres whereas eukaryotic cell is 10 – 100 micrometres
24
Q
What is a virus? (1 point)
A
A virus is a microscopic, intracellular, parasitic organism that infects other organisms
25
Features of a virus (4 points)
Require a host in order to take over the nucleus and release their DNA
Viruses use host enzymes, energy and ribosomes
Have no ribosomes, RER, SER, Golgi apparatus or mitochondria unlike eukaryotic cells
Have no cytoplasm, no ribosomes or plasma membrane unlike bacteria
26
Structure of a virus (6 points)
```
Lipid envelope = Phospholipid
Genetic material = viral RNA
Enzyme = viral enzyme (Reverse transcription
Attachment protein = CD4 proteins
Matrix
Capsid
```
All viruses have nucleic acid (RNA or DNA)
All viruses have a capsid which protects the genetic material
All viruses have attachment proteins which attach to host
Some have an outer phospholipid membrane surrounding the capsid
27
Life cycle of a virus (5 points)
Attachment proteins bind to complimentary receptors on the cell surface membrane
Capsid fuses with membrane
Genetic material incorporates with cell genetic material
Viral structure is replicated
Virus particle leaves the cell
28
Explain HIV’s replication cycle (10 points)
Following infection HIV enters the bloodstream and circulates around the body
A protein on HIV binds to a protein called CD4 mostly on T- helper cells
The protein capsid fuses with the cell surface membrane.
The RNA and enzymes of HIV enter the T-helper cell
The HIV reverse transcriptase converts the virus’s RNA to DNA
The newly made DNA moves into the T-helper cell’s nucleus where it is inserted into the cell’s DNA
The HIV DNA in the nucleus creates mRNA using the cells enzymes. This mRNA contains instructions for making new viral proteins
The mRNA passes out of the nucleus through a nuclear pore and uses the cells protein synthesis mechanisms to make new HIV proteins
The HIV particles break away from the T-helper cell with a piece of its cell membrane surrounding it.
The new virus matures and moves on to infect other cells
29
Why are microscopes useful? (4 points)
Increased understanding at subcellular level
Can identify specialised cells to see how organisms’ function
Diagnostic tools e.g. magnify blood samples
Enlarge tiny viruses to develop vaccines and cures
Can see things you can’t with naked eye
30
What is magnification? (1 point)
The act/process of enlarging the physical appearance or image of something
31
What is resolution? (1 point)
The minimum distance apart 2 objects can be in order to appear as separate items
32
What is the calculation for magnification?
Magnification = size of image/ Size of actual object
I
A M
33
What are Optical Light Microscopes? (definition, 3 disadvantages, 1 advantage and preparation)
Use light radiation to form an image
- Have poor maximum resolution of 0.2 micrometres because electrons have short wavelength
- Have maximum magnification of x1500
- Less detailed images and cannot see small organelles
+Cheaper
Preparation: Sample washed and stained with iodine solution then covered with cover slip
34
What are Transmission Electron Microscopes? (definition, 7 disadvantages, 2 advantages and preparation)
Electrons pass through the specimen and only the electrons that pass through are seen and produce an image. Denser parts of specimen absorb more electrons, which makes them look darker on the image. Use electromagnets to focus the beam of electrons, which is then transmitted through the specimen
- Expensive
- Specimen must be dead
- Vacuum required
- Only produces a 2D image
- No colour
- Stained with heavy metal
- Can only pass through a thin slice of specimen
+ High Resolution of 0.1 nanometres so chloroplasts
can be seen
+ High magnification of x 1,500,000
Preparation: Slice and stain specimen with heavy metal and must be in a vacuum
35
What are Scanning Electron Microscopes? (definition, 5 disadvantages, 4 advantages and preparation)
Scan a beam of electrons across the surface of the specimen. This reflects electrons off the surface of the specimen, which are gathered in a cathode ray tube to form an image. Reflected beam is observed
- Expensive
- Specimen must be dead
- Vacuum required
- Lower resolution than TEMs
- Stained with gold
+ 3D images produced
+ Colour images produced
+ High resolution of 20 nanometres apart
+ High magnification of x 1,500,000
Preparation: Coat surface of specimen with thin layer of gold, must be in a vacuum
36
What are artefacts and how are they a problem? (Definition, 2 problems and an example)
They are something we see that is not visually present
Gives appearance of structures which are not really there
Create uncertainty about structures apparently seen in electron microscopes
May include wrinkles in cells
37
What are the common scales? (5 points)
```
1km = 1000m
1m = 100cm
1cm = 10mm
1mm = 1000µm micrometres
1µm = 1000nm nanometres
```
38
What is the stage micrometre and how do you use it? (definition and 7 steps)
Stage micrometre is a slide with a small etched scale on it
1. Select magnification
2. Remove specimen slide
3. Place stage micrometre onto microscope stage
4. Focus at selected magnification
5. Measure diameter of field of view
6. Remove the slide and place specimen back onto stage
7. Using the size you have calculated for field of view you can then estimate the size of whole cell, a particular organelle or an interesting section
LIMITATION = Could make an error as it is only an estimation
39
What is the eyepiece graticule? (2 points)
Gives more accurate way to measure
| An eyepiece graticule is fitted into the eyepiece lens and is visible all the time whilst looking down microscope
40
Calibrating the graticule (6 points)
1. Choose which magnification to use. You want one that takes up most of field of view
2. Replace the specimen with a stage micrometre
3. When focused, line up the stage micrometre with the eyepiece graticule so one main division of each is in line
4. Work out the length of one eyepiece graticule unit in micrometres
E.g. 3 eyepiece graticule units = 4 stage micrometre units. Since 1 division on stage micrometre is 1000µm, you do 4 x 1000 = 4000µm. So 1 eyepiece graticule unit = 4000/3 = 1333µm
5. Remove the stage micrometre and put the specimen back on the stage
6. Calculate how many eyepiece graticule units the cell measures
41
What is cell fractionation? (2 points)
The process where cells are broken up and different organelles they contain are separated out
Useful for studying individual specific organelles
42
Describe the process of cell lysis (3 points)
Breaking down of the membrane of a cell
A buffer solution is added
The buffer solution is:
1. Buffered to maintain same pH and prevent proteins being denatured
2. Ice cold to slow down enzyme activities that could damage the cell
3. Isotonic so the water potential in the cytoplasm is the same as outside the cell to prevent water entering or leaving the organelles by osmosis to prevent damage (osmotic lysis)
43
Describe the process of cell fractionation (5 stages)
1. Cell lysis
2. Homogenisation to disrupt the tissue and cells and break open the cell. This can be done by high frequency sound, mild detergent to make holes in plasma membrane, High pressure by forcing cells through small holes or shear cells between close-fitting rotating plunger and thick wall of glass vessel
3. Filter the homogenate through a gauze to remove debris, unopened cells and damaged cells
4. Place solution in centrifuge
5. Ultracentrifugation where you crush and filter cell using pestle. Then spin at a low speed where the heaviest organelles like nuclei form a thick sediment at the bottom (the pellet). The rest of organelles are suspended in a fluid above pellet (the supernatant). Drain off supernatant into another tube and spin supernatant at a higher speed to release mitochondria and then repeat at a higher speed. The order of sedimentation is heaviest density to lightest
44
3.2.2 All cells arise from other cells
What is the cell cycle? (1 point)
A regular cycle of cell division separated by periods of cell growth
45
Why does the cell cycle need to happen? (2 points and 1 however
The cell needs to grow and synthesise proteins such as enzymes to make sure the cell and nucleus are prepared to divide for replication
DNA has to be replicated because the resulting cells all need to contain 23 pairs of chromosomes
HOWEVER, not all cells go through the cell cycle as some go into cell arrest
46
What is cell arrest? (2 points and 2 examples)
The G₀ stage of the cell cycle
Some cells don’t divide at all and some cells stop dividing such as when we reach adulthood due to overcrowding and differentiation
E.g. 1. Liver cells are in G₀ but can be called back into cell cycle by external causes for example if the cell is damaged
2. Nerve and muscle cells are highly specialized so are arrested in G₀ and nerve cells can never divide but some muscle cells can
47
What are the stages of the cell cycle? (5 points)
G₁ Phase = Growth of the cell and synthesis of DNA polymerase which is needed to form long chains of repeated nucleotides to create DNA. It is important to ensure the cell has correct organelles to replicate and produce 2 functional cells
S Phase = DNA Replication to ensure each of 46 chromosomes are duplicated to produce 2 cells with 23 pairs
G₂ Phase = Replication of other organelles and prepare cell for division. This is important as it acts as a check point to ensure there are no errors
Stage 5 = Mitosis (nuclear division) to form new nuclei
Stage 6 = Cytokinesis where the cytoplasm divides and new membranes form
48
What happens during uncontrolled cell division? (3 points)
Uncontrolled cell division happens as a result of mutated genes if they are not picked up at the checkpoint
Most mutated cells die or are destroyed but some may continue to divide and form tumours either benign or malignant
Cancer is a result of damage to the genes that control mitosis
49
What is the mitotic index? (3 points)
The ratio between the number of cells in a population undergoing mitosis to the number of cells
Number of actively dividing cells in field of view / Total number of cells in field of view
X100 if expressed as percentage
50
How do chromosomes change before, during and after mitosis? (3 points)
Chromosome before mitosis: 1 chromatid per chromosome
Chromosome after S-phase (replication): 2 chromatids per chromosome (sister chromatids) 2 copies remain attached at centromere but still regarded as 1 chromosome
Chromosome after mitosis: Each cell receives 1 chromatid per chromosome
51
What is the centromere? (1 point)
The site where spindle fibres attach
52
What are the stages of mitosis? (5 stages)
Stage 1 Prophase:
Chromosomes condense and become visible
Nuclear membrane breaks down
Stage 2 Metaphase:
A microtubule spindle forms within the cell
All chromosomes line up along the equator (middle) of the cell attached to the spindle
Stage 3 Anaphase:
Microtubules shorten pulling apart the sister chromatids
Chromosomes are pulled to opposite poles of the cell
Stage 4 Telophase:
Nuclear membranes form
Chromosomes decondense become longer, thinner and less visible
After Mitosis – Cytokinesis:
Cell membrane divides
2 daughter cells each has own nucleus containing full set of chromosomes
Cell cycle continues into G₁
53
How do cancer treatments work? (1 point and 1 problem of treatment)
Disrupt cell cycle by preventing DNA from replicating and inhibit metaphase by inhibiting formation of spindle fibres
PROBLEM: Rapidly dividing cells e.g. hair cells are also killed in the process
54
What is binary fission? (3 points)
A-sexual form of reproduction
Cell division used by all prokaryotes
A-sexual reproduction has one parent, no mixture of genetic material, identical offspring, produces clones, quick process
55
What are the stages of binary fission? (6 stages)
1. DNA Replication:
DNA uncoils
Plasmids and DNA replicate
Copies of DNA stay attached to cell membrane
2. Segregation:
Replicated DNA and plasmids move to opposite ends of cell
3. Elongation:
DNA and plasmids moving to opposite ends causes cell to lengthen
4. Formation of the membrane:
The equatorial plate separates the plasma membrane
5. Formation of the cell wall:
New cell wall forms to separate the new cells
6. 2 cells are formed:
Two genetically identical cells are formed (clones)
56
Compare and contrast the process of nuclear division in prokaryote and eukaryote cells (4 similarities and 6 differences)
Similarities:
Both binary fission and mitosis are a-sexual
Both create two new identical daughter cells
Both processes involve replicated DNA moving to opposite poles
Both involve DNA replication
Differences:
Prokaryotes divide by binary fission whereas eukaryotes use mitosis
Mitosis requires spindle fibres to pull cell apart whereas binary fission does not
Mitosis requires formation of a nuclear envelope whereas binary fission does not
Only Binary fission requires replication of plasmids
Only mitosis has sister chromatids joined at centromere
Binary fission is quicker than mitosis
57
Why can bacteria multiply in less than 20 minutes? (1 main points and 4 sub-points)
Binary fission is much simpler and very quick because there is no nuclear envelope/nucleus, there are fewer/no membrane bound organelles to replicate, free floating DNA, simpler DNA
58
How does prokaryote DNA differ from eukaryote DNA? (5 points)
1. In prokaryote it is single, circular DNA whereas in eukaryote it is multiple, linear chromosomes
2. In prokaryote DNA condenses in nucleoid whereas in eukaryote DNA condenses in nucleus
3. Majority of prokaryotes contain only 1 copy of each gene (haploid) whereas eukaryote cells contain 2 copies of each gene (diploid)
4. In prokaryotes plasmids are present whereas in eukaryotes plasmids are not commonly present
5. In prokaryote cells there is no non-coding and repetitive DNA as the genomes are efficient and compact whereas in eukaryotes there is large amounts of non-coding and repetitive DNA
59
3.2.3 Transport across cell membranes
What is the Fluid Mosaic Model and why is it called Fluid Mosaic? (Definition and 2 points)
The structure of a cell membrane
Called fluid because the phospholipids are constantly moving
Called mosaic because proteins are scattered through the bilateral like a mosaic
60
What is the membrane? (4 points)
A bilayer (two)
Made of phospholipids (phospholipid bilayer)
Mosaic of different components
Selectively permeable
61
What molecules can pass through the phospholipid bilayer? (2 points)
1. Lipid-soluble substances such as Oxygen and Carbon Dioxide as they can dissolve in lipids so pass
2. Fatty acids as they have the same properties/are lipid based so can pass
62
What molecules cannot pass through? (3 points)
1. Large molecule such as glucose as are too large to pass between phospholipids
2. Water soluble ions as cannot pass through hydrophobic tails (repel water)
3. Polar (electrically charged) molecules as charged molecules prefer to interact with polar heads of the membrane (outside). The inside is non-polar/hydrophobic
63
What are the components of the membrane? (5 points)
1. Phospholipid bilayer
2. Glycolipids (extrinsic protein)
3. Glycoproteins (extrinsic protein)
4. Intrinsic proteins
5. Cholesterol
64
What do the glycolipids do in the membrane? (3 points)
Are lipids with a carbohydrate chain
On the surface of the membrane so help with cell recognition and cell adhesion
Also form hydrogen bonds with water which helps to increase stability of the membrane
65
What does the phospholipid bilayer do in the membrane? (2 points)
Makes up the overall structure of the membrane
| Is main barrier preventing passage of specific molecules such as large molecules, water soluble ions and polar molecules
66
What do intrinsic proteins do in the membrane? (3 points)
Pass through the membrane and enable molecules to pass from outside of cell to inside
Form water filled channels which they open and close to allow passage of specific ions or charged molecule
Also form a carrier protein which moves larger molecules
67
What do glycoproteins do in the membrane? (4 points)
On surface of membrane and similar to glycolipids
Have a lipid and a protein linked with a carbohydrate chain
Have similar role of helping cells adhere (join together to form tissues) and be recognised
Also involved in signalling by acing as receptor site for hormones
68
What does cholesterol do in the membrane? (3 points)
Found between phospholipid molecules because are very hydrophobic molecules
Packed in between phospholipid molecules so they are not able to move around as easily.
This increases strength of the membrane and reduces fluidity of it
69
How would you investigate the permeability of the cell membrane? (7 points)
1. Use a scalpel to carefully cut five equal sized pieces of beetroot
2. Rinse the pieces to remove any pigment released during cutting
3. Add five pieces to five different test tubes each containing 5cm3 of water using a measuring cylinder/pipette to measure volume
4. Place each test tube in water bath at different temperatures e.g. 10, 20, 30, 40, 50 for same length of time
5. Remove pieces of beetroot from tubes, leaving just liquid
6. Use a colorimeter to measure how much light is absorbed. The higher the absorbance, the more pigment released, so higher permeability of the membrane
7. Connect the colorimeter to a computer and use a software to collect the data and draw a graph of results
70
What is diffusion? (1 point)
The net movement of particles from an area of high concentration to low concentration, down a concentration gradient, until equilibrium is met
71
Why is diffusion a passive process? (1 point)
No energy is required for it to happen
72
What is simple diffusion? (1 point)
When molecules move directly through a cell membrane
73
What does simple diffusion depend on? (3 points)
1. Concentration gradient - higher it is, faster the rate of diffusion
2. Thickness of exchange surface - thinner it is, faster the rate of diffusion
3. Surface area - larger surface area, faster rate of diffusion
74
Where does diffusion happen? (3 points)
1. Intestine - Glucose diffusion from intestine to blood
2. Lungs - Oxygen in, carbon dioxide out
3. Plants - Carbon dioxide in, oxygen in/around leaf
75
What is Fick's Law? (1 point)
Rate of diffusion is directly proportional to surface area multiplied by concentration gradient divided by length of diffusion pathway
76
What is facilitated diffusion? (2 points)
The process of allowing larger molecules (e.g. glucose), polar molecules (e.g. water) or charged molecules (e.g. ions) to pass through via carrier and channel proteins
Also a passive process
77
How do carrier proteins work in facilitated diffusion?
| what they do, what each different carrier protein does and steps of carrier protein
Carrier proteins move large molecules across membranes, down their concentration gradient
Different carrier proteins facilitate the diffusion of different molecules
1. A large molecule attaches to a carrier protein in the membrane
2. Then the protein changes shape
3. This releases the molecule on opposite side of membrane
78
How do channel proteins work in facilitated diffusion? (2 points)
Channel proteins form pores in the membrane for charged particles to diffuse through
Different channel proteins facilitate the diffusion of different charged particles
79
What does facilitated diffusion depend on? (2 points)
1. Concentration gradient - higher concentration gradient, faster rate up to point until equilibrium is reached and rate levels off
2. Number of channel or carrier proteins - Once all proteins in use, facilitated diffusion can't happen any faster, even if increase concentration gradient. Greater number of proteins, faster the rate
80
What is osmosis? (1 point)
Osmosis is the net movement of water molecules through a partially permeable membrane from a region of higher water potential to a region of lower water potential
81
What is water potential? (5 points)
The pressure created by water molecules
Measured in units of pressure (kPa)
Pure distilled water has highest water potential of 0.0kPa
Any solution has negative water potential as more substances are dissolved in water
Further from zero = lower water potential
82
What water potential would a solution of lower concentration have? (1 point)
Higher water potential as fewer solute molecules
83
What water potential would a solution of higher concentration have? (1 point)
Lower water potential as more solute molecules
84
In what direction will water move? (1 point)
To the solution with a more negative water potential
85
Where and why does diffusion happen in animal cells? (1 point)
Across the cell membrane as the cytoplasm contains high concentration of sugar and salts whereas the surrounding conditions in blood may be different due to variety of chemical reactions taking place
86
What happens in hypertonic conditions in animal cells? (4 points)
Concentration of solutes in solution surrounding cell is higher than inside cell (less water)
The solution has more negative water potential
Movement out of the cell
The animal cell may shrivel as do not have cell wall to keep stable
87
What happens in isotonic conditions in animal cells? (3 points)
Concentration of solutes in the solution surrounding the cell is the same as the inside the cell
No net movement
The cell remains normal
88
What happens in hypotonic conditions in animal cells? (4 points)
Concentration of solutes surrounding the cell is lower than inside the cell (more water)
The solution surrounding cell has higher water potential
Movement into the cell
The cell may become lysed and burst
89
What happens in hypertonic conditions in plant cells? (4 points)
Net outward movement of water
Cell membrane pulled away from cell wall
Vacuole shrinks
Cell is plasmolyzed
90
What happens in isotonic conditions in plant cells? (3 points)
No net movement
Vacuole gives the cell its support
Cell is flaccid
91
What happens in hypotonic conditions in plant cells? (4 points)
Net inward movement of water
Cell membrane pushed against cell wall
Vacuole swells
Cell becomes turgid
92
What factors affect the rate of osmosis? (3 points)
Water potential gradient - higher the WP gradient, faster the rate of osmosis. As osmosis takes place, difference in WP on either side of membrane decreases, so rate levels off
Thickness of exchange surface - thinner exchange surface, faster rate
Surface area of exchange surface - larger SA, faster rate
93
Describe how to make a serial dilution (4 points)
Line up 5 test times in a rack
Add 10 cm3 of initial 2M sucrose solution to first test tube and 5 cm3 of distilled water to other 4
Using a pipette draw 5 cm3 of solution from first test tube, add to distilled water in second test tube and mix. Now have 10 cm3 of solution that's half as concentrated as first (1M)
Repeat 3 more times to create solutions of 0.5M, 0.25M and 0.125M
94
Describe method to find water potential of potato cells (8 points and 2 explanations)
Use cork borer to cut potatoes into identically sized chips
Measure mass of each potato using a mass balance
Place one into each of sucrose solutions
Leave chips in solutions for at least 20 mins
Remove and dry with paper towel
Weigh potatoes again
Calculate %change in mass
Plot results on graph
Potato chips will gain water and mass in solutions with higher water potential than in lower
Point at which curve crosses x-axis is point at which water potential of sucrose solutions is same as water potential of potato cells
95
What is active transport? (1 point)
The movement of substances from an area of low concentration to an area of high concentration, against a concentration gradient
96
Where does the energy for active transport come from? (1 point and explanation)
The break down of ATP into ADP:
Solute bonds to carrier protein
ATP attaches to carrier protein and phosphate group binds (phosphorylation)
Addition of phosphate group changes the proteins tertiary structure
Ion can now be released, moving against the concentration gradient
Phosphate group leaves and protein returns to original shape
97
Compare Active Transport and Facilitated Diffusion (1 similarity and 3 differences)
Both Active Transport and Facilitated Diffusion use carrier proteins
Facilitated diffusion also uses channel proteins whereas active transport doesn't
Active transport moves solutes from low to high concentration whereas in FD moves from high to low
Active transport requires energy whereas FD does not
98
What factors affect the rate of active transport? (3 points)
The speed of individual carrier proteins – the faster they work, faster rate
The number of carrier proteins present – more proteins, faster rate
Rate of respiration in cell and availability of ATP – if respiration inhibited active transport cannot take place
99
What cellular adaptations can take place to increase rate of transport? (4 points)
High concentration gradient
Lots of intrinsic proteins – prevents saturation
Increase surface area
Mitochondria – increased rate of respiration
100
How is the ileum in the small intestine adapted? (2 points)
Increased surface area – ileum wall has villi and epithelial cells that line cell wall have microvilli
Villi and microvilli mean more membrane surface for the insertion of channel and carrier proteins to decrease saturation
101
Describe the process of co-transport (5 points)
Sodium ions are actively transported out of the ileum epithelial cells, into the blood, by sodium-potassium pump
This creates a concentration gradient (higher concentration of sodium ions in lumen of ileum than inside
This causes sodium ions to diffuse from lumen of ileum into epithelial cell, down concentration gradient via the sodium-glucose co-transporter proteins
The co-transporter carries glucose into the cell with sodium. As a result, concentration of glucose inside cell increases
Glucose (or amino acids) diffuses out of cell, into blood, down its concentration gradient through a protein channel, by facilitated diffusion
102
How many sodium and potassium ions move? (2 points)
3 sodium into cell
| 2 potassium out
103
3.2.4 Cell recognition and the immune system
What is a pathogen? (1 point)
Pathogens are disease causing microorganisms/microbes
104
What are infections? (1 point)
An interaction between the body and a pathogen
105
What are the two options if an infection develops? (2 points)
Pathogen overwhelms body’s defences – death
| Body’s defences overwhelm pathogen – recovery
106
What is immunity? (2 points)
The ability to resist infection by protecting against pathogens/toxins that have invaded the body
Being able to combat a 2nd infection before symptoms arise
107
What are non-specific defences? (3 points)
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Respond to all pathogens in the same way
Act immediately
2 forms: A barrier to block
pathogens
Phagocytosis
```
108
What are the body’s barrier to block pathogens? (6 points)
Eyes:
Eyelashes acts as
dust barrier
Tears contain salt and lysozyme to kill microbes
Blink to keep eyes wet and wipe microbes to corners of eyes
Nose:
Hairs to filter out microbes
Mucus to trap microbes
Lungs:
Air passages lined with two types of cells – Goblet cells (make mucus) and Ciliated cells (have cilia)
Skin:
Outer layer acts as a tough barrier
Hair follicles make sebum to keep skin moist and stop cracking
Blood:
Blood clots to form a scab
White blood cells – phagocytes
Stomach:
Hydrochloric acid kills ingested microbes
109
How do lymphocytes distinguish between self and non-self-material? (1 point)
All cells have specific molecules on their surface that identify them
110
What would happen if the body could not distinguish between self and non-self? (1 point)
Auto-immune diseases – Lymphocytes would destroy your own tissue
e.g. rheumatoid arthritis, Multiple Sclerosis, Type 1 diabetes, Inflammatory Bowel Syndrome
111
Why are there a huge variety of cell marker proteins? (4 points)
Range of amino acids allows for huge variety of protein molecules
They have highly specific tertiary structure
This gives them a variety of specific 3D structures
This allows one cell to be distinguished from another
112
What are antigens? (1 point)
Molecules on the surface of pathogens that trigger the immune response
e.g. Glycoproteins, Polysaccharides, Lipids, Nucleic acids
113
What do antigens allow the immune system to identify? (4 points)
Pathogens
Non-self-material – transplanted cells
Toxins
Abnormal body cells – cancer cells
114
What implications could antigens have for transplant patients? (3 points)
Immune system recognises transplant organ/tissue as non-self
Immune system amounts an immune response against foreign cells
Attempts to destroy foreign tissue
115
What can be done to stop antigens destroying transplants? (3 points)
Donor tissues are closely matched with recipient
Family member if possible as most likely to have similar tissue
Immunosuppressant drugs given to reduce immune response but whole body susceptible to disease
116
What is clonal selection? (3 points)
When an infection occurs, the matching lymphocyte has to replicate and build up its own numbers to a level where it can destroy the pathogen
There is a time lag between infection and defences fighting back
Also explains why people become ill or die before body can mount a defence
117
How do lymphocytes recognise own cells in a foetus? (4 points)
In a foetus the lymphocytes are constantly colliding with other own body cells
Some of the lymphocytes will have protein receptors that match body's own cells
These lymphocytes either die or are supressed
The only remaining lymphocytes at birth are ones that will fit non-self material
118
How do lymphocytes recognise own cells in adults? (4 points)
In adults, lymphocytes produced in the bone marrow initially only encounter self-antigens
Any lymphocytes that produce an immune response to self-antigens undergo apoptosis (programmed cell death)
This must happen before they differentiate into mature lymphocytes
This prevents any appearing in the blood
119
What do white blood cells do and what are the two types? (2 points)
White blood cells combat pathogens that are inside the body
2 types are: phagocytes (non-specific)
lymphocytes (specific)
120
Describe the process of phagocytosis (10 points)
Pathogen or dead/damaged cells releases chemoattractants
Phagocyte is attracted to chemoattractants
Phagocyte moves towards pathogen
Phagocyte has several receptors on its cell surface membrane
These receptors attach to chemicals on the surface of the pathogen
The phagosome is formed by engulfing the bacterium
Lysosomes inside the phagocyte move towards the phagosome
Lysosomes release lysozymes (lytic enzymes) into phagosome
Lysozyme hydrolyse the bacterium
The hydrolysis products of the bacterium are absorbed by the phagocyte
121
What is a specific response? (4 points)
A specific response reacts to specific antigens
The response is slower than non-specific but leads to long-term immunity which non-specific does not
Requires lymphocytes
They are produced by stem cells in the bone marrow
122
What are the features of T lymphocytes/T cells? (5 points)
T lymphocytes mature in the thymus gland
Provide cell mediated immunity/ cellular response
Respond to antigens presented on body cells (not in fluids)
Responds to foreign material inside body cells
Responds to own cells altered by viruses/cancer or transplanted tissues (cell mediated immunity)
123
What are the four ways in which T lymphocytes are able to distinguish between altered cells and own cells? (4 points)
1. Phagocytes that have engulfed and hydrolysed a pathogen present some of the foreign pathogen's antigens on their surface (antigen presenting cells)
2. Body cells invaded by a virus present viral antigens on their surface (distress signal)
3. Cancer cells are different from healthy cells and present antigens on their surface
4. Transplanted cells from the same species have different antigens on their cell surface
124
What are the stages of T lymphocyte response? (4 points)
Pathogens invade body cells or are taken in by phagocytes
The phagocyte places antigens from the pathogen on its own cell-surface membrane
Receptors on certain helper T cells (TH cells) fit exactly onto these antigens
This activates other T cells to divide rapidly by mitosis and form a clone
125
What are the 4 things that cloned T cells can do? (4 points)
Develop into memory cells that allow a fast future response to the same pathogen
Stimulate phagocytes to engulf pathogens by phagocytosis
Stimulate B cells to divide and secrete their antibody
Activate cytotoxic T cells (TC cells)
126
What do cytotoxic T cells do? (3 points)
Cytotoxic T cells attack abnormal body cells
They produce a protein called perforin that makes holes in the cell surface membrane
This makes the abnormal cell freely permeable, killing it which is very effective against viruses as they replicate inside of cells
127
What are B cells? (3 points)
B lymphocytes mature in the bone marrow
Involved in humoral immunity (immunity involving antibodies present in bodily fluids) as antibodies are soluble in blood and tissue fluids
They respond to foreign material outside the body cells
128
Describe the stages of the B cell response (7 points)
1. The surface antigens are taken up by B cell (endocytosis)
2. B cells process and present these on their surface
3. T helper cells attach to the processed antigens on the B cells. This activates the B cells
4. The activated B cells now divide by mitosis
5. The cloned plasma cells produce antibodies that fit the antigens on the pathogen
6. The antibodies attach to the antigens on the pathogen destroying them = primary response
7. Some B cells remain and become memory cells which can respond in the future = secondary response
129
What can B cells develop into? (2 points)
Plasma cells
| Memory cells
130
What do plasma cells do? (6 points)
```
Secrete antibodies into blood plasma
Survive for only a few days
Make around 2000 antibodies/sec
Destroy pathogens and toxins
Immediate defence only
PRIMARY IMMUNE RESPONSE
```
131
What do memory cells do? (5 points)
| Diagram
Can live for decades so provide long term immunity
Circulate in blood and tissues
Do not produce antibodies directly
When they encounter same pathogen again they divide rapidly into more plasma and memory cells to immediately fight infection
SECONDARY IMMUNE RESPONSE - faster and more intense than primary and fights infection before symptoms occur
132
How does antigen variation impact the immune response? (2 points)
Some pathogens such as flu virus have over 100 different strains so their antigens are constantly changing - ANTIGENIC VARIATION
The body has to start from scratch with a primary immune response as their antibodies will no longer complement the antigens so symptoms will develop
133
What is the structure of an antibody? (6 points)
4 polypeptide chains
Long chains called heavy chains
Shorter chains called light chains
Variable region since binding site of antigen changes. Sequence of amino acids gives each variable region its specific 3D shape
Remainder of antibody called constant region which binds to receptors on cells such as B cells
Each binding site is complementary to specific antigen to form antigen- antibody complex
134
What is the role of antibodies? (2 points)
Antibodies do not directly destroy antigens
Different antibodies lead to antigen destruction in a number of ways: Agglutination
Markers
135
What is agglutination? (2 points)
Antibodies clumps bacterial cells together
| Makes it easier for phagocytes to locate and engulf as they are less spread out
136
What are markers? (2 points)
Antibodies act as markers that stimulate phagocytes
| Phagocytes can easier engulf pathogen as it is attached
137
What are polyclonal antibodies? (1 point)
Antibodies produced from a variety of B cells
138
What are monoclonal antibodies? (1 point)
Antibodies produced from only one type of B cell
139
What are the uses of monoclonal antibodies? (3 points)
Cancer treatment
Pregnancy testing
Medical diagnosis
140
How can monoclonal antibodies be used to treat cancer? (7 points)
Monoclonal antibodies can target cancerous cells due to their specificity
Cancer cells have antigens called tumour markers that are not found on normal body cells
Monoclonal antibodies can be made that will bind to the tumour markers
You can also attach anti-cancer drugs to antibodies
When antibodies come into contact with cancer cells, they will bind to the tumour markers
This means the drug will only accumulate in the body where there are cancer cells
So side effects of an antibody-based drug are lower than other drugs because they accumulate near specific cells
141
How does Herceptin work in cancer treatments? (2 points)
Can be used to treat breast and ovarian cancers
| Herceptin marks the cancer cells for destruction or blocks the chemical signal that stimulates their uncontrolled growth
142
How can monoclonal antibodies be used in pregnancy testing? (5 points)
Pregnancy tests detect the hormone human chorionic gonadotropin (hCG) that’s found in urine of pregnant women:
1. Application area contains antibodies for hCG bound to a blue coloured bead
2. When urine is applied to application area, any hCG will bind to antibody on beads, forming an antigen-antibody complex
3. The urine moves up the stick to the test strip, carrying any beads with it
4. The test strip contains antibodies to hCG that are immobilised
5. If there is hCG present the test strip turns blue because immobilised antibody binds to any hCG – concentrating the hCG - antibody complex with the blue beads attached. If no hCG present, the beads will pass through the test area without binding to anything, and so it won’t go blue
143
How can antibodies be used in medical diagnosis (ELISA Test)? (3 points)
It uses antibodies to detect the presence and amount of protein in a sample
Highly sensitive because antibodies are really specific
Used to detect HIV, TB and Hepatitis
144
What are the ethical implications of using monoclonal antibodies? (3 points)
Use of mice to generate antibodies and tumour cells
There have been many deaths associated with using monoclonal antibodies
Drugs testing can have high risks e.g. organ failure due to T cells over producing chemicals that stimulate an immune response or attack own tissues
145
What is immunity and what are the two forms? (2 points)
The ability of an organism to resist infection
| Two forms: Passive and Active
146
What is passive immunity? (definition, 2 examples, positive and negative)
Antibodies introduced from an outside source
e.g. Anti-venom or immunity acquired by a fetus from the mother
- Does not lead to long term immunity as antibodies are not produced by the individual so they are broken down and memory cells are not produced
+ It is a quick response
147
What is active immunity? (definition, positive, negative and 2 forms)
Production of antibodies is stimulated by the individual
+ Direct contact with the pathogen/antigen so long term immunity
- Immunity takes time to develop
Comes in two forms:
Natural Active Immunity (individual infected with so a normal immune response is stimulated)
Artificial Active Immunity
(Vaccination so induced immune response with few symptoms)
148
What are vaccinations? (4 points)
Involves putting vaccine into body that will generate immune response
Vaccines can be administered orally or subcutaneously (injection)
Vaccines contain antigens from pathogens and lead to the formation of memory cells
Large scale vaccination programmes can lead to protection for an entire population
149
How do you make vaccination programmes successful?
1. Vaccination must be cheap enough to immunise all vulnerable population
2. Few side effects as people are easily discouraged
3. Ability to produce, store and transport vaccine which requires hi-tech equipment, hygienic conditions and refrigeration
4. Vaccine must be administered correctly at the appropriate time so trained staff are required
5. Must vaccinate the majority of the population at one time so that for a period no individuals carry the disease so transmission is interrupted (herd Immunity)
150
What is herd immunity?
When a large enough proportion of the population is vaccinated which makes it difficult for the pathogen to spread
The vaccinated population provide a measure of protection for individuals who have not developed immunity
151
Why are vaccination programmes rarely 100% successful?
1. Vaccinations dont induce immunity in some individuals due to immune system defects
2. Disease develops immediately after vaccination before immunity is established so these individuals harbour the disease and can re-infect others
3. Pathogens can mutate frequently, rapidly changing their antigens so vaccine is ineffective as new antigens not recognised by immune system so antibodies are not produced so immunity is short lived and repeat infections are common
4. Each pathogen has many varieties so would be difficult to create vaccine for all
5. SOme pathogens hide from immune system in cells or gut where it is difficult to kill
6. Some individuals object to vaccinations for religious, ethical, medical or safety concerns
152
What are the ethical implications of vaccinations?
1. Animals used in development
2. Side-effects can cause long term harm
3. Who should the vaccinations be tested on?
4. Is it fair to test on a popualtion where target disease is common based on idea they will gain most benefit if its successful?
5. Is it right to make vaccinations compulsory?
6. SHould expensive vaccination programmes continue when disease is almost eradicated?
153
What does HIV stand for?
Human Immunodeficiency Virus
154
What does HIV cause?
AIDS - Acquired Immune Deficiency Syndrome
155
Where did HIV come from?
Virus jumped the species barrier and was transferred from primates to humans due to eating/slaughtering chimpanzees
156
How can HIV enter the body and infect us?
```
Sexual intercourse
Drug taking using infected needles
Blood infection of wounds
Blood transfusion and blood products
Mother to child across the placenta during pregnancy and via breast milk
```
157
What are the symptoms of HIV?
```
Fever
Sore throat
Body Rash
Tiredness
Joint pain
Muscle pain
Swollen glands
```
158
What are the symptoms of AIDS?
```
Weight loss
Chronic diarrhoea
Night sweats
Skin problems
Recurrent infections
Serious life threatening illnesses
```
159
What are the key features of structure of HIV?
```
Attachment protein
Matrix
Transmembrane protein
Lipid envelope
Genetic material (RNA)
Reverse transcriptase
Capsid
```
160
How does HIV belong to a group called retroviruses?
Reverse transcriptase is an enzyme that catalyses the production of DNA from RNA
This ability makes HIV a retrovirus
161
Describe the process of how HIV repicates
1. P120 molecyles on HIV bind to CD4 receptor proteins on T helper lymphocytes and macrophages
2. The protein capsid fuses with the cells membrane
3. HIV RNA and enzymes enter the T cell
4. HIV reverse transcriptase converts the virus' RNA to DNA
5. The new DNA is moved to where it is inserted into the cells DNA
6. The HIV DNA in the nucleus creates mRNA using the cells enzymes. This mRNA contains the instructions for making new viral proteins and the RNA from new HIV
7. The mRNA leaves the nucleus of the host cell through nuclear pore and uses the cells protein synthesis mechanisms to make HIV particles
8. The HIV particles bud away from helper T cell with piece of its cell surface membrane surrounding them which forms their lipid envelope
162
How does HIV turn to AIDS?
HIV specifically targets helper T cells
HIV leads to AIDS by destroying/interfering with T cells normal function
When helper T cells reach 200 or more per mm3 of blood you have aids
163
How does the HIV/AIDS disease lead to death?
Since there are no longer enough helper T cells, B cells cannot be stimulated to produce antibodies and cytotoxic T cells cannot be stimulated
Memory cells are also sometimes infected and destroyed which leads to an inadequate immune respinse leaving the body vulnerable to infections and cancer
AIDS sufferers are therefore prone to infections of the lungs, brain, eyes and intestine
It is the secondary illnesses, not HIV that cause death
164
WHy dont antibiotics work against viruses?
Antibiotics inhibit enzymes that synthesise bacteria cells walls and stop them from forming peptide cross-linkages
This means they cannot stand turgor pressure from osmosis so burst
However, viruses inhibit a host cells so there is nothing for the antibiotics to disrupt
