1
Q
Describe the structure and function of the nucleus
A
Structure
Nuclear envelope - double membrane containing pores which allows mRNA to leave and nucleotides to enter
Nuclear pores-(allow mRNA to come out nucleus)
Nucleoplasm - granular jelly like material. Contains chromatin which when condenses it forms the Chromosomes
Chromosomes - protein bound, linear DNA
Nucleolus- small sphere inside which is the site of RRNA production and makes ribosomes
Function
Site of DNA replication and transcription (making mRNA)
Stores genetic code for production of proteins
2
Q
Endoplasmic reticulum structure and function
A
Structure
Rough endoplasmic reticulum - covered in ribosomes. Proteins are synthesised here and transported/ folded in the cisternae
Smooth endoplasmic reticulum- no ribosomes. Lipids and steroids are synthesised here
Function - system of flattened membrane bound sacs called cisternae found throught the cell
3
Q
Golgi apparatus/body structure and function
A
Structure
(Stack of dynamic flattened cisternae formed from vesicles from the RER).
Modified lipids
In the cisternae the proteins are modified eg to form glycoproteins and packaged into vesicles which bud off to be transported either to another part of the cell or out of the cell. If the vesicles contain digestive enzymes they form lysosomes
Function - packages/ modifies proteins received from the Rough endoplasmic reticulum and produces lysosymes
4
Q
Lysosomes structure and function
A
Structure-
Release hydrolytic enzymes to hydrolyse pathogens and bacteria that would have been taken in by phagocytosis. Lysosomes fuse with the membrane of the vesicles containing the material to be digested and release the lysozymes
Function - spherical membrane bound sacs containing lysozomes
5
Q
Mitochondria structure and function
A
Structure-
Double membrane - Inner membrane folded to form cristae.
Intermembrane space - contains a high concentration of hydrogen ions
Matrix - containing circular dna and 70s ribosomes used to make proteins and self replication
Function- site of aerobic respiration using oxygen to make ATP. Many found in cells with a high atp requirement
6
Q
Ribosomes structure and function
A
Structure-
Composed of 2 sub units one large and one small which are each made up of only rRNA and protein (no mebranes) it’s the site of translation
In eukaryotic cells the ribosomes are bigger( 80s) than in prokaryotes (70s)
Function - Site of protein synthesis
7
Q
Vacuole structure and function
A
Animal cells do contain vacuoles but theyre small and temporary. They make act as contractile vacuoles or they may be formed in phagocytosis
Plant cells all contain a large permanent vacile surrounded by a membrane called tonoplast. This maintains cell turgor and contains cell sap (stores sugars amino acids eg)
8
Q
Chloroplasts structure and function
A
Structure-
double membrane- inner membrane folded into thylakoids. Thylakoids stacked onto grana, photosynthetic pigments eg chlorophyll located on these membranes. This is the site of lifht dependent reactions
stroma–contains circular dna and 70s ribesomes used to make proteins and self replication. It’s the site of light dependent reactions.
Often contains starch grains
Function- site of photosynthesis
9
Q
Cell wall structure and function
A
Structure -
plant/algal cells- made of cellulose
Fungi- made of chitin
Prokaryotic cells made of murein
Function - provide structural strength to the cell and prevents from bursting. Its fully permeable to water and solutes
Between the cell walls in plants there are often plasmodesma which provide cytoplasmic Continuity between plant cells allowing rapid transport of material
10
Q
Plasma membrane structure and function
A
Structure- found in all cells
Phospholipid bilayer - molecules embed within and attached on the outside (proteins, carbohydrates, cholesterol)
Function - controls the entrance and exit of molecules
11
Q
Types of eukaryotes
A
Plant, animal, fungi and protists(eg algae)
12
Q
What are specialised cells organised into
A
Tissue, organ, organ system
13
Q
What’s a tissue, organ and organ system
A
Tissue- aggregation of similar cells carrying out the same function
Organ- aggregation of several tissues to perform a particular funtion for the whole organism
Organ system - several organs working together
14
Q
What do all prokaryotes have
And some things that only some have
A
Murein cell wall
70s ribosomes
Circular naked dna which isn’t associated with histone proteins
Things only SOMe have
One or more plasmid
Capsule surrounding cell
Flagella
15
Q
Differences between eukaryotes and prokaryotes
A
1)Dna is enclosed within a nucleus in eukaryotes whilst in prokaryotes DNA is floating free in cytoplasm (no nucleus)
2)Eukaryotes dna is long and linear whilst in pro it’s circular
3)Eukaryotes dna is attached to proteins called histones prokaryotes dna isn’t attached to histones
4)eukaryotes has membrane bound organelles whilst prokayrotes has no membrane bound organelles
5)Eukaryotes- cell wall contains cellulose in plants and chitin in fungi
6) eukaryotes - Ribosomes 80s pro 70s
Eukar- no capsule pro yes
16
Q
Differences in dna between eukaryotes and prokaryotes
A
Dna is longer in eukaryotes whilst in prokaryotes its shorter
Dna is linear in eukaryotes whilst in pro its circular.
Dna is associated with histone proteins in eukayrotws but not in prokaryotes
Dna contains axons and introns in eukaryotes whilst in prokaryotes it only contains axons
In pro ribesomes are smaller than cytoplasmic ribesomes
17
Q
What are viruses
A
Viruses are acellular as they have no cell surface membrane, have no organelles, can’t respiration and no metabolic reactions. They’re extremely small and can’t be seen with light microscope. They enter living cells and multiply with the assistance of the host cells, causing diseases
18
Q
What are viruses composed of and function
A
Genetic information (DNA or RNA) - codes for viral protein
Capsid(made of proteins)- protects genetic information
Attachment proteins- are complementary to and bind to receptors on its specific host cell
Some viruses have additional structures
Reverse transcriptase, viral envelope as if contains rna not dna
19
Q
What are attachment proteins in the HIV virus structure
A
They’re specific for each virus. This means different viruses will attach to different receptors that are complementary to their attachment proteins. Therefore viruses are specific and can only infect one type of cell
20
Q
What’s magnification and resolution
A
Magnification - how much bigger image is compared to the r4al structure
Resolution- ability to see 2 points as 2 points, rather than merged into one.
21
Q
Light microscope principle and limitations
A
Uses lenses to focus a beam of light through the specimen
Lower resolution than electron microscopes
Can view live specimens
Simple staining and slide preparation
Can see colours
22
Q
Electron microscopes
A
Uses electromagnets to focus a beam of electrons through or onto the specimen
Denser parts absorb more electrons and appear darker
Higher resolution than light, due to smaller wavelength of electrons
Specimen must be placed in a vacuum, can’t look at living material
Longer preparation time, with more complex staining procedure, which can produce artefacts
Specimen must be extremely thin
23
Q
Transmission electron microscopes principles and limitations
A
- Small objects can be seen;
- TEM has high resolution as wavelength of electrons shorter
- Cannot look at living cells as cells must be in a vacuum;
- Must be thin specimen;
- Preparation may create artefact;
- Does not produce colour image;
24
Q
Scanning electron microscope principles and limitations
A
Resolution not as high as transmission electron microscope. (But more higher than light)
3D Image produced of the surface (not internal structre)
Black and white image only (computer often used to add colour)
25
Outline stages for cell fractionation
Cells broken down so that organelles are free to be separated. This is fond using homogeniser, a blender
Once this happens solution must be filtered to remove large pieces of debrils
26
Why must solution be isotonic, buffered and ice cold when doing cell fractionation
Isotonic- to prevent any movement of water by osmosis resulting in organelles shrivelling or bursting
Buffered- to maintain pH so enzymes don't denature
Ice cold to reduce enzyme activity to prevent the digestion of organelles
27
Describe role of lysosome
Fuse with vesicle containing material to be digested and then releases lysozymes/hydrolytic enzymes
28
In large cells mitochondria are dlose to cell membrane but in small cells they're distributed evenly. Why?
In larger cells the surface area to volume ratio is smaller so it takes longer for oxygen to diffuse to mitochondria
(So that's why they have to be close)
29
Explain why viruses are described as a cellular and non living
Can't respiration, no metabolic reactions and have no cell membrane
30
Wy are antibiotics not effective against viruses
No bacterial enzymes
31
Describe how you would use cell fractionation to obtain sample of chloroplasts
Break open cells AND FILTER
In ice cold, buffered isotonic solution,
Centrifuge and remove nuclei
Centrifuge at higher speed, chloroplast settle out
32
Describe how temporary mounts are made
Take thin slice, put slide in water and put a cover slip over it
33
Name 3 features of HIV that aren't found in bacteria
Capsid
Lipid envelope
Reverse transcriptase
34
Process of centrifugation
First low speed spin to give a pellet of the heaviest organelles eg nuclei.
Then respin supernatant at higher speed to get pellets of chloroplasts (if its a plant cell)
Repeat at progressively higher speeds to attain mitochondria, then lysosomes, then ribosomes
Nuclei-chloroplasts-mitochondria-lysosomes- ribesomes
35
What's mitosis
Part of cell cycle in which a eukaryotic cell divides to produce 2 daughter cells each with identical copies of dna produced by the parent cell during dna replication
36
Which type of cells can't divide
Highly specialised cells
37
Describe the cell cycle but not the mitosis in detaip
Interphase, G1 - organelles replicates. S- dna replicates
G2- protein/atp synthase
Mitosis - nucleus divides forming 2 daughter nuclei
Cytokinesis - cytoplasm divides into 2 identical daughter cells
38
Describe stages of mitosis on
Prophase- Chromosomes condense/shorten from chromatin and become visible as 2 chromatids joined at a centromere
Nuclear envelope and nucleoli disappear
Metophase - Chromosomes line up at the equator of the cell.The spindle fibres released from opposite poles. Chromosomes attached to spindle fibres by their centromere. Spindle fibres attach to chromatids and centrometre
Anophase- Chromosomes split as centromeres divide as spindle fibres contract. Sister chromatids seperate. Pulled to opposite poles of the cell by centromere first
Telephose- Chromosome elongates and uncoils. Nuclear envelope reforms and nucleoli reappear as 2 new nuclei are formed
39
What does the cytoplasm divide by? And also in plant cells
By membrane cleavage
In plant a cell plate and then forms and goes onto make a cell wall
40
What are bacteria composed of
70s ribesomes
Murein cell wall
Circular single dna which isn't associated with histone proteins
Cytoplasm
SOME
one od more plasmid
Capsule surrounding cell
One or more flagella
41
Describe how you'd make temporary mount of plant tissue to see starch grains
Add drop of water
Obtain thin section and place on slide
Stain with iodine
Add cover slip
42
Cell membrane was stained and it appeared as 2 dark lines why?
Membrane has a phospholipid bilayer
Starch binds to phosphate on outside and inside of membrane
43
Why do we increase speed that we Spon Centrifuge at as we move on?
Organelles less denser
44
Describe how a sample consisting only of chloroplasts could be obtained from homogenised plant tissue.
Use different centrifugation
Spin at low speed to remove cell debris
Supernatant re sun at higher speed until pellet with chloroplasts found
45
What is the basic structure of all cell membranes?
The basic structure of all cell membranes, including cell-surface membranes and the membranes around organelles of eukaryotes, is the same.
46
How do membranes appear under an electron microscope?
Membranes appear as a double line under the electron microscope.
47
What is the distance across a cell membrane?
The distance across the membrane is 7-8 nm.
48
What is the function of the cell surface membrane?
The cell surface membrane surrounds cells and forms a boundary between the cell cytoplasm and the environment, allowing different conditions to exist inside and outside the cell.
49
What is the main composition of the cell membrane?
The membrane is composed mainly of phospholipid molecules arranged as a bilayer.
50
What are the components of a phospholipid?
A phospholipid consists of a hydrophilic head (composed of glycerol and phosphate) and hydrophobic tails (composed of fatty acids).
51
How do phospholipids arrange themselves in a membrane?
Phospholipids arrange themselves in a bilayer with hydrophilic heads facing the aqueous extracellular fluid and the aqueous cytoplasm, while hydrophobic tails face inward.
52
What effect does the percentage of unsaturated fatty acid tails have on the membrane?
The higher the percentage of unsaturated fatty acid tails present, the more fluid the membrane.
53
What types of substances can pass through the phospholipid bilayer?
Phospholipids allow lipid-soluble substances to pass through but prevent water-soluble substances from passing through.
54
What additional components are found in cell membranes?
In addition to phospholipids, membranes also contain proteins, carbohydrates, and cholesterol.
55
What role does the phospholipid bilayer play in the membrane?
It forms a barrier to certain molecules and gives the membrane fluidity.
56
What substances can pass through the membrane?
Non-polar substances (lipid soluble) such as vitamins A, D, and K, as well as oxygen and carbon dioxide, can pass through, but polar molecules like glucose and vitamin B1 are blocked.
57
What are extrinsic proteins?
Extrinsic proteins are located on the surface or only in half the membrane, may have charged hydrophilic areas that attract to hydrophilic heads, and uncharged hydrophobic areas that associate with hydrophobic tails.
58
What functions do some proteins serve in the membrane?
Some proteins act as enzymes (e.g., disaccharidases on ileum epithelial cells) and receptors for hormones.
59
What are Protein channel/(Intrinsic proteins)
Intrinsic proteins that have hydrophilic linings that allow passage of polar substances that can't pass through the phospholipid hydrophobic layer. May be gated and allow facilitated diffusion
60
How do channel proteins function?
Channel proteins have hydrophilic linings that allow passage of polar (ionic) substances (water soluble) that cannot pass through the phospholipid hydrophobic layer. They may be gated, allowing facilitated diffusion.
61
What is glycosylation in the context of membrane proteins?
Glycosylated proteins have a carbohydrate chain attached on the extracellular side to form the glycocalyx, which helps cells recognize each other and act as recognition sites for hormones.
62
How does cholesterol affect the membrane?
Cholesterol restricts the movement of other molecules in the membrane, reducing fluidity and therefore leakage.
63
The structure of a plasma membrane is described as a fluid mosaic. Explain why (2 marks)
Mosaic = not just phospholipids, made of different sorts of molecules;
Fluid = molecules move around;
64
What are protein carriers
May act as transport carrier protein. Eg active transport or facilitated diffusion of polar and or large substances that can't pass through the phospholipids
65
Describe process of binary fission (Bacterial replication)
Circular dna replicates (once)
Plasmids replicate (can be many times)
The cytoplasm divides and 2 daughter cells are produced each containing one copy of the circular dna molecuke and some of the plasmid copies
66
Describe replication of viruses
Attachment proteins attach to host cell receptors
The viral nucleic acid (DNA or RNA) enters the cell
The nucleic acid is replicated inside the cell (if RNA enters, reverse transcriptase makes dna from rna)
The host cell then produces viral proteins.
The virus particles are assembled and the host cell bursts releasing viruses
67
How do drugs target the G1 S phase and more to prevent cancer
G1(cell growth and protein prodction) Some chemical drugs prevent the synthesis of enzymes needed for dna replication. If these aren't produced the cells unable to enter the S phase, disrupting the cell cycle and forcing cell to kill itself
S phase (dna replication) radiation. And drugs can damage dna. At several points in cell cycle,d its checked for damage. If damage detected cell kills itself preventing further tumour growth
Some drugs can prevent dna unwinding prior to replication. Others can stop making dna nucleotides
68
What are the role of enzymes and receptors in the cells membrane
Enzymes - digest disaccharides are found in cell surface members of the epithelial cells in the small intestine
Receptors for hormones - a hormone will only act on a cell that had the right protein receptors In its cell surface membrane or cytoplasm
69
What are the role of protein channels and carriers in cell surface membrane and cell recognition
Channels - proteins which span the whole membrane(integral or instrinsic) and act contain water filled channels which allow hydrophilic ions or molecules through
Carriers - integral proteins which act as carriers and play important role In transporting larger molecules in and out of cell
Cell recognition. - Act as antigens
70
What's osmosis and describe it
Movement of water from a solution of higher water potential to a solution of lower water potential across a partially permeable membrane
Water moves through a special channel protein called aquaporins or since its small directly across the phospholipids
71
What's water potential
The tendency of water to leave or enter a system or cell
The greater number of free water molecules the greater the water potential
72
What has the highest water potential
Pure water 0
Every other solution has a negative water potential
73
What's isotonic hypertonic and hypotonic
Isotonic - solution of equal water potential (same in solution and cell)
Hypertonic - very concentrated solution with a more negative water potential (than cell)
Hypotonic - dilute solution with a higher water potential
74
What do water soluble substances use to get through cell and large molecules
Water soluble substances use protein channels and carriers
Large molecules use carrier protein only
75
What's diffusion
Movement of molecules or ions from a region of higher concentration to one of lower concentration.
Passive process no atp needed
Occurs naturally in all liquids and gasses
76
What's simple diffusion
Simple diffusion across the phospholipids of a membrane
The gaps between the phospholipid are small, and the centre of the bilayer is hydrophobic
Particles must be small, uncharged, nonpolar, lipid soluble
Larger molecules and charged polar particles can't move by simple diffusion
77
What does the rate of diffusion depend on
Concentration gradient - the rate is proportional to the concentration gradient
Distance of travel - the shorter the distance, the faster the rate
Temp- increase=increase kinetic energy, so increase rate
Size of molecule- smaller molecules diffusemore quickly as can pass between phospholipids easier and more kinetic energy, if molecuke too big it can't
Membrane surface area- more SA! Faster rate
Lipid solubility- lipid soluble molecules diffuse across plasma membrane. There soluble in the phospholipid bilayer
78
What's facilitated diffusion
Diffusion of particles across a membrane using protein carriers or channels without needing atp energy, passive process
Uses carrier proteins or channel proteins to transport particles DOWN concentration gradient
79
Describe channel proteins
Proteins lined with polar groups to make them hydrophilic so that water soluble charged ions can pass through
Each channel proteins is specific to one type of ion
Can open and close
Protein changes shape
80
Describe carrier proteins
Large molecules attach to carrier proteins the proteins change shape and molecule is released onto the opposite side of the membrane
When used in facilitated diffusion, atp not required
81
What's active transport
Movement of molecules or ions against a concentration Gradient using atp and protein carriers, which act as pumps
Lipid soluble/non polar molecules can't be actively transported as they move freely through phospholipid
Selective process specific substances transported
Ion/molecule moved binds to complementary receptors sites on the carrier protein. Atp binds to the protein whe splits into adp and pi, causes protein to change shape, and opens opposite site of the membrane releasing ion/molecule. Phosphate then released
Active process needs atp
82
What's co transport
Coupled movement of 2 different substances across a cell membrane via carrier protein
2 types of molecules moved across membrane at same time, movement of one's dependent on the other
83
Describe process of co transport in absorption of amino acids and glucose from ileum
1) sodium ions actively transported out of cells into blood
2) this creates lower sodium concentration inside epithelial cells
3) sodium ions enter the cell from the intestinal lumen down a concentration gradient through co transport protein that only allows entry with glucose
4) glucose is now at high concentration in the cell and so exists to the capillary by facilitated diffusion down a concentration gradient
84
Explain 2 environmental variables which could increase growth of Bacterial cells
Increased temperature, increased enzyme activity
Increased concentration of oxygen, Increased respiration.
85
Named the fixed position occupied by a gene on a dna molecule
Locus
86
Why did student only use first 5mm from the tip of an onion root and press down firmly on the cover slip when preparing squash of cells
1) it's where dividing cells are found/ mitosis occurs
2)thin layer of cells so light passes through
87
What should be done when counting cells to ensure mitotic index is accurate
Examine many cells to ensure its a representative sample
88
Give 2 things you would see In cells undergoing mitosis (prophase)
Chromosomes visible because they have condensed
Each Chromosome consists of 2 chromatids as dna has replicated
89
Suggest one way the structure of the Chromosome could differ along its length to result in the stain binding more in some areas
(Dark stain used on Chromosome binds more to some areas)
Difference in base sequences
90
What's a homologous pair of Chromosomes
2 Chromosomes that carry the same genes
91
Describe 2 aseptic techniques to do when transferring a sample of broth culture onto an agar plate
(Bacteria onto that)
Keep lid on petri dish to prevent unwanted bacteria from contaminating the dish
Wear gloves to prevent contamination from bacteria on hands
92
Girl investigating mitosis In tissue, was told to push down hard on cover slip but not sideways, why?
Hard- to spread tissue
Not sideways- avoid rolling cells together or breaking Chromosomes
93
Name and describe 5 ways substances can move across the cell surface membrane into a cell
1)Diffusion of non polar molecules down a concentration gradient
2)Facilitated diffusion of large molecules down a concentration gradient via protein carrier/channel
3) active transport against a concentration gradient using atp and protein carriers
4) co transport of 2 different substances using a carrier protein
5) osmosis of water down a water potential gradient
94
Explain how the movement of Na* out of the cell allows absorption of glucose into the cell linings the ileum
Generates a concentration gradient for Na
Na moving in by co transport brings glucose with it
95
Explain how sodium ions actively transported in exchange for one proton (hydrogen ion) out of the cell
Co transport uses atp
Sodium ion and proton bind to the same protein . Protein changes shape
96
What would happen to an animal cell if it was placed in a 1) isotonic 2)hypotonic 3)hypertonic solution?
1) No net gain of water as its already at equilibrium (same water potential inside and outside)
2)water moves into the cells by osmosis(as outside of cell more positive than inside)has no cell wall so,bursts and becomes lysed
3) Water leaves cell by osmosis resulting in cell to shrivel as cell is more positive than outside of solution
97
What would happen to plant cell if it was placed in
1) isotonic
2hypotonic
3)hypertonic
1) No net gain of water as its already at equilibrium (same water potential inside and outside)
2)water moves into the cells by osmosis(as outside of cell more positive than inside) becomes turgid
3) Water leaves cell by osmosis resulting in cell to become plasmolyzed as cell is more positive than outside of solution
98
What's an antigen
Any part of a molecule that's recognised as a foreign Protein and stimulates an immune response and the production of antibodies. )
99
What 4 different structures does the immune system recognise
The different surface molecules of antigens enable them to identify
Pathogens, cells from other organisms of the same species, abnormal cells and toxins
Once they discover them the immune systerm will be triggered to destroy the cells
100
What type of cells does our immune system recognise
Our immune system is designed to only respond to non self antigens. Sometimes this process doesn't work properly and the immune system does react and attack self antigens. Can be short lived after an infection or it can result in an autoimmune disease developing
101
What is an example of self antigens
Blood grouping- need to be understood before blood transfusions.
ABO system is based on the antigens on the surface of the red blood cells and the antibodies that can be produced by that person.
Group O is a universal donor bc the blood doesn't contain any antigens that could trigger antibody production and so blood clots.
Group AB is a universal recipient. Because the immune system will recognise either marker as self
102
What's antigen variability
Some pathogens change their surface antigens as their dna mutates which changes the tertiary structure of the surface pathogens. This could affect the ability of the immune system to recognise and destroy them
103
What are the range of defences which help the human body to protect itself from pathogens
Non specific immune response(general and immediate)
1) barrier to entry eg skin, tears, ear wax, mucus
2) phagocytosis - involving phagocytes
Specific immune response (less rapid but long lasting)
1) cell mediated response involving T lymphocytes
2) humoral response involving B lymphocytes
104
What's phagocytosis
Involves a type of white blood cell called a phagocyte which originate and mature in the bone marrow. Its a non specific response (All phagocytes act in the same way on any pathogen)
105
Stages of phagocytosis
1) phagocytes recognise antigens on the pathogens as foreign and engulfs it into a vesicle called a phagosome. This is endocytosis
2) lysosome fuses with the phagosome and releases lysozymes into it
3) lysozymes hydrolyse the pathogen and the harmless products of digestion are absorbed by the phagocyte or released by exocytosis
4) antigens from the pathogen are displayed on the phagocytes cell membrane, turning it into an antigen presenting cell
106
Describe how a phagocyte destroys a pathogen present in the blood 3 marks
Engulfs Forming vesicle and fuses with lysosome
Enzymes digest
107
What are antigen presenting cells give eg
Any cell that presents a non self antigen on their surface
Infected body cells will present the virus antigens on their surface
A phagocyte which has engulfed and destroyed a pathogen will present the antigens on their surface
Cells of a transported organ will have different shaped antigens on their surface compared to your self cell antigens
Cancer cells will have abnormal shaped self cell antigens
108
What's endocytosis
Active process which allows large or large amounts of material to enter or exit the cell without crossing the membrane. It relies on the fluidity and flexibility of the plasma membrane
Active process, the cell membrane invaginates and pinches off to form a vesicle. This is called phagocytosis when a phagoctye takes in a pathogen in this way.
109
What's exocytosis
Active process which allows large or large amounts of material to enter or exit the cell without crossing the membrane. It relies on the fluidity and flexibility of the plasma membrane
Here the vesicle carrying the material fuses with the cell surface membrane to release the material
110
what happens if you increase the saturation/ reduce unsaturated fatty acid to the cell surface membrane?
decreases fluidity and permeability
111
describe the effect of temperature on the movement of pigment out of the beetroot cell through the membrane
increase as more kinetic energy causes gaps in phospholipid bilayer, proteihs denature, and increased fluidity. membrane permeable and pigment leaks out. Damage to cell membrane and darker colour as more pigments released
112
What are lymphocytes
Cells of the specific immune response white blood cells
113
What are t cells
Part of the cell mediated response, include helper t cells killer cells and t memory cells
114
whats cell mediated immunity
This type of response is brought about by the T lymphocytes. T lymphocytes will only respond to antigens that are presented on a body cell (an APC).Each T cell has receptors that recognises (is complementary to) a single antigen and there are millions of different T cells in the body. These T cells are known as T helper cells (or CD4 cells).
115
whats the cell mediated response process
1. Pathogens invade the body cells or are taken up by phagocytes.
2. These cells become antigen presenting cells as they place the pathogen antigens on to their cell surface membrane.
3. Receptors on a specific T helper cell fit exactly onto these antigens (clonal selection)
4. This attachment activates the T cell to divide rapidly by mitosis and form a clone of
genetically identical cells (clonal expansion)
5. These cloned T cells:
a. Develop into memory cells that enable a rapid response to future infections by the
same pathogen (secondary response)
b. Stimulate phagocytes to engulf more pathogens
C. Stimulate the correct cells to divide and secrete antibodies
d. Activate cytotoxic T cells (killer T cells)
116
what do T cells do in the cell mediated response
1)The specific helper T cell (with complementary receptor) will bind to the antigen on the APC
2)This T helper cell will divide (by mitosis) and will activate three types of WBC.
3) The cell releases chemical called cytonines that stimulate other cells
Stimulate specific B cells to produce antibodies (complementary to antigen)
Stimulate phagocytes
Stimulate cytotoxic cells to destroy infected cells
117
what do cytotoxic or killer t cells do
kill abnormal cells and cells that are infected by pathogens by producing a protein called perforin. This makes holes (perforates) the cell surface membrane which means they become too permeable and the cell dies as a result. T cells very effective against viral attack, as infected body cells will display viral antigens on their surface and so the T cells can recognise an infected cell and kill it, so preventing viral replication inside the cell
118
whats humoral immunity
The humoral response is brought about by B lymphocytes. Like T cells, there are millions of B cells in the body each having a specific shaped antibody receptor in its surface, that will recognise a specific antigen. Each B cell will produce and secrete those specific antibodies, when stimulated by a T helper cell.
119
whats the humoral response process
1. Pathogen invades the body
2.Antigen on surface of bacterium binds to surface receptor on a B cell. Cytokines/ T cell stimute the B-cell. This is clonal selection.
3. The activated B-cell divides by mitosis into plasma cells and memory cells (clonal expansion)
4)Plasma cells are clones of the B-cell which secrete the specific monoclonal antibody- release antibodies. Antibody transported via lymph/blood to the site of infection. Antibody combines with the antigen on the surface of pathogenic cells to produce an antibody-antigen complex. This stimulates phagocytosis of the pathogen.
5) b cells become Memory cells which produce antibodies faster. remain in the body for many years. Can reproduce rapidly to produce an instant supply of plasma cells if the same pathogen invades the body again (secondary response)
120
What do B cells do in humoral response
T helper cell activates a specific B cell
The B cell divides by mitosis to produce clones
Most B cells differentiate to become plasma cells. Some become memory cells
The plasma cells make antibodies that have a specific tertiary structure that can only bind this antigen. each type of B cell produces one type of antibody- monoclonal antibodies
each pathogen will have many different antigens on its surface soon infection, many different types of B cells will be stimulated to produce many different types of antibody. this is therefore polyclonal response, in addition some pathogens such pathogens such as the bacterium that causes cholera produce toxins that can also act as antigens
121
whatre antibodies
Proteins specific to an antigen. Produced by B-cells. Bind to specific antigens to clump them together to aid phagocytosis/bind to pathogen to on changes prevent entry to host cells/bind to toxins to neutralise them
122
whats the antibodies structure and formation of antigen antibody complex
Proteins, made up of 4 polypeptide chains
They have a quaternary structure
Released from B Plasma cells
They cause agglutination (clumping) of pathogens for phagocytosis
Heavy chains (longer) and light chains (shorter)
Polypeptide chains joined by disulfide bridges
Each antibody has 2 specific antigen binding sites that fits very precisely onto a specific antigen to form an antigen-antibody complex
Specificity of an antibody depends on its variable regions, which form the antigen binding sites
Each antibody has a variable region with a specific 3D tertiary structure due to different amino acid sequences that is complementary to one specific antigen
Hinge region gives flexibility when binding to antigen
All antibodies have the same constant regions (the rest of the antibody)
123
whats immunological memory and
Primary and secondary response
most B cells differentiate to become plasma cells. some become memory cells.
the primary immune response is the first time that an individual comes into contact with a particular antigen. Slower as there arent many specific B cells to produce specific antibodies. the patient will develop symptoms as the pathogen increases ij number and damages cells. B and T cells produce memory cells which remain in the body for a long time
Secondary immune response is the next time the individual comes into contact with the antigen. clonal selection is much faster, more antibodies are produced in a short space of time. a rapid response prevents full infection so person is immune
immunity is ability of an organism to resist infection and takes 2 forms
124
What are the 2 types of immunity
Active immunity- makes its own antibodies.
requires exposure to antigen. takes a while for protection to develop. long term as memory cells are produced
Passive immunity- given antibodies from elsewhere eg child from mother
doesnt require exposure to antigen
immediate protection
short term as memory cells never produced
125
whats natural and artificial immunity
natural passive immunity- antibodies passed through placenta or breastfeeding
artifical passive immunity- antibodies injected into someone who has been infected with a dangerous disease they have no immunity yo
natural active- results from an infection by the disease
artificial active - vaccination
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whats vaccination
• Contains the antigen. Usually a dead/weakened form of the pathogen. which stimulates production of antigen presenting cells antibodies/plasma cells/memory cells
• Specific Helper T-cells detect the antigen and stimulate specific B-cells
• The B-cells divide by mitosis to give plasma cells which produce antibodies and memory cells
• A second dose could produce antibodies in a secondary immune response in higher
concentration and quickly Eg. attenuated strains: less virulent strains such as a mutated form that does not cause the disease. Used to combat Rubella. Subculture the rubella virus and select less virulent strains
• 'Herd effect' as in a population virus is destroyed in vaccinated people. Unvaccinated peopleunlikely to come into contact and spread disease.
• Sometimes parents refuse to get children vaccinated eg. MMR. But then numbers of eg.measles cases rise.
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How can vaccination control disease
• It provides (artificial) active immunity with memory cells etc
• Most children are vaccinated when young
• Herd immunity interrupts transmission through a population so unvaccinated people less likely to contact infected people.
• Little reservoir of infection in unvaccinated people
• Difficult for bacteria to spread as most people are immune
Ring vaccination: vaccinate all people round the victim to prevent spread
128
Whatre ethical issues with vaccination
• Use of testing on animals in development and production
• Testing: Risk to people in medical trials
Side effects - how can the risk of side effects be balanced against the risk of developing the disease?
Compulsory vaccination: Need herd immunity, Opt out, personal beliefs?
Expense: Vaccines are expensive so less money for other treatments
Priorities: Who should get the vaccine first in a new epidemic?
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whats antigenic variability
• Some pathogens can change their surface antigens
• Virus mutates (changes base sequences in DNA/RNA) so that the body fails to recognize it next
time
• Eg. Over 100 different strains of the influenza virus
• Primary response each time as no memory cells for new antigen
• If you are infected a second time, the memory cells produced from the first infection will not
recognise the different antigen because they are no longer complementary.
• This antigenic variability enables pathogens to evade recognition
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What're monoclonal antibodies
A single type of protein with the same tertiary structure artificially produced from a single clone of plasma cells.
Complementary to one antigen only, antibodies Al the same and fr9m 1 original plasma cells. Derived from used b lymphocyte and cancer cell
131
Uses of monoclonal antibodies
Medical treatment- targeting medication to specific cell types by attaching a therapeutic drug to an antibody
Medical diagnosis
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Uses of monoclonal antibodies in medical treatment
Cancer cells have antigens called tumour markets not found on normal body cells.
Specific monoclonal antibodies can bind to tumour markers.
You can attach anti cancer drugs to the specific antibodies
Drugs will only accumulate where there are cancer cells reducing side effects. Often called bullet drugs
133
Describe the role of antibodies in producing a positive result in an ELISA test. (4 marks)
antibody complementary in shape binds to antigen;
antibody with enzyme attached is added;
antibody attaches to antigen;
Substrate and colour changes;
134
Medical diagnostic test to detect specific antigens or antibodies in a eg blood plasma sample
1. An antigen is attached to the test well
2. The blood/plasma sample is added. Any complementary antibodies bind to the antigen. Well is washed
3. A second antibody with an enzyme attached is added. It binds to the first antibody if it is present and
attached to the antigen. Well is washed
4. A yellow substrate solution is added. If the enzyme linked antibody is present, then it turns into a blue
A control well is also used, with eg. salt solution rather than blood plasma. This shows that only the enzymeis causing the colour change, and that washing of the unbound antibody is effective
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Medical diagnosis eg pregnancy and COVID lateral flow tests
1.Urine applied. Hormone hcg in preg women urine• Mobile antibodies bind to complementary antibodies in control window. Build up creates visible blue line.
2.reaction zone, there are mobile antibodies specfic to hcg here, they can move and have blue dye attached to them. if hcg present, jt will bind to the antibodies and move up. Build up of the mobile antibodies, builds up the blue dye and creates a visible line.
3. Result window. Immobilised antibodies specific to hcg here.Mobile antibodies also bind to antigen.
4. Control window. Immobilised antibodies specific to mobile antibodies from the reaction zone. Antigen binds to complementary specific antibodies in result window.
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Medical diagnosis eg pregnancy and COVID lateral flow tests
• Antigen binds to complementary specific antibodies in result window.
• Mobile antibodies also bind to antigen.
• Build up of the mobile antibodies, builds up the blue dye and creates a visible line.
• Mobile antibodies bind to complementary antibodies in control window. Build up creates visible blue line.
137
2 functions of golgi apparatus 2 marks
Package proteins
Releases lysosomes/vesicles out of the cell
138
Describe phagocytosis of bacteria 4 marks
Phagocyte recognises antigens on bacteria as foreign.
Engulfs bacteria into a vesicle,
Lysosome fuses with vacuole
Bacteria hydrolysed
139
Eukaryotic cell eg human compared with prokaryotic
1.Bacterial cell is much smaller than a human cell
2. Bacterial cell has a cell wall but human cell does not
3. Bacterial cell lacks a nucleus but human cell has a nucleus
4. Bacterial cell lacks membrane-bound organelles but human cell has membrane-bound organelles
5. Bacterial ribosomes smaller than human ribosomes / bacteria have 70S ribosomes whereas humans have 80S
6. Bacterial DNA is circular but human DNA is linear
7. Bacterial DNA is ‘naked’ whereas human DNA is bound to histones/proteins
140
How to measure objects using an eyepiece graticule 3 marks
1. Use eyepiece graticule to measure the object e.g. nucleus or capillary
2. Calibrate eyepiece graticule against stage micrometer
3. Take a number of measurements and calculate the mean
141
Suggest why scientists can use
detergent to break open cells instead of
homogenisation (2)
1. Cell membranes made from phospholipid;
2. (Detergent) dissolves membranes / phospholipid (bilayer);
142
Bacteria -Describe how bacteria
divide.
1.Binary fission
2. Replication of (circular) DNA;
3. Division of cytoplasm to produce 2 daughter cells;
4. Each with single copy of (circular) DNA
143
What's a tumour
Mass of cells
Many cells in mitosis
144
Give evidence that the cell was undergoing mitosis (2)
1. The chromosomes are visible because they have condensed;
2. (Each) chromosome is made up of two chromatids because DNA has replicated;
3. The chromosomes are not arranged in homologous pairs, which they would be if it was meiosis;
145
Evidence for a cell in anaphase (2)
1. Chromosomes are at poles of spindle
2. V-shape shows that chromatids have been pulled apart at their centromeres
146
During the cell cycle, the amount of DNA in a cell changes Explain how the behaviour of chromosomes causes these changes in the amount of DNA per cell 2 marks
1.DNA replicates;
2.Sister chromatids separate
147
Suggest why the student soaked the
root tips in hydrochloric acid In req practical 2 mitosis
1. To separate cell walls;
2. Allowing the stain to pass into the cells
148
Describe how you would determine a reliable mitotic index (MI) from tissue observed with an optical microscope. Do not include details of how you would prepare the tissue observed with an optical microscope (3 marks)
1. Count cells in mitosis in field of view;
2. Divide this by total number of cells in field of view;
3. Repeat many times
149
Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate
1. Examine many cells;
2. To ensure representative sample;
3. Repeat count;
4. To ensure figures are correct;
5. count only whole cells;
6. To standardise counting;
150
Suggest and explain two ways the cell-surface
membranes of may be adapted to allow rapid transport of nutrients. (2)
1. Membrane folded so increased surface area
2. Large number of protein channels / carriers (in membrane) for facilitated diffusion
151
Why does inhibiting respiration/using cyanide prevent
active transport? (4)
1. Oxygen is required for aerobic respiration which releases ATP
2. ATP is needed to change the shape of the protein carrier
3. Which would cause the release of the transported ion/molecule
4. So no ATP, no Active Transport
152
Req prac 3- How do we find water potential of plant tissue practically? (3
1. Plot a graph with concentration on the x-axis and percentage change in mass on the y-axis;
2. Find concentration where curve crosses the x-axis/where percentage change is zero;
3. Use (another) resource to find water potential of sucrose concentration (where curve crosses x-axis)
153
Describe an experiment that you could do to investigate whether the mangrove root cells have a lower water potential than sea water.
1. Record mass before and after;
2. Place in sea water for equal time;
3. Remove surface water;
4. Increase in mass will show water has been absorbed by osmosis;
5. Repeat minimum of three times;
154
Req prac 4 - Give one way in which the student could ensure the first three beetroot cylinders were kept at 25 °C throughout her experiment. (1)
Measure temperature (in tube) at intervals and use appropriate corrective measure
155
How does alcohol disrupt
membranes (1)
ethanol dissolving phospholipid bilayer
156
Req prac 4 - Explain why it is important to control the volume of water in each test tube (1).
(Beetroot pigment practical)
If) too much water the concentration of pigment (in solution) will be lower
157
Non-specific - Phagocytosis (3
1. vesicle fuses with lysosome;
2. (pathogen) destroyed by lysozymes
3. Antigen (from pathogen) displayed on cell membrane
158
Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen
1. Helper T cell binds to the antigen (on the antigen-presenting cell / phagocyte);
2. This helper T cell stimulates a specific B cell;
3. B cell divides by mitosis;
4. (Forms) plasma cells that release antibodies;
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Antigen-Antibody complex formation (4)
1. Antibody has 4 polypeptide chains and has a quaternary structure
2. Antibody has a variable region which has a specific amino acid sequence
3. Shape of the binding site is complementary to the antigen
4. Forming an antigen-antibody complex
160
Describe and explain the role of antibodies in stimulating phagocytosis. Do not include details about the process of phagocytosis 2 marks
Bind to antigen
Cause agglutination
161
Compare active and passive immunity 6 marks
1. Active involves memory cells, passive does not;
2. Active involves production of antibody by plasma cells
3. Passive involves antibody introduced into body from outside
4. Active long term, because antibody produced in response to antigen;
5. Passive short term, because antibody (given) is broken down;
6. Active (can) take time to develop, passive fast acting;
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How a vaccine produces an immune response (7)
1. Vaccine contains antigen from pathogen;
2. Macrophage presents antigen on its surface;
3. T cell with complementary receptor protein binds to antigen;
4. T cell stimulates B cell;
5. (With) complementary antibody on its surface;
6. B cell/plasma cell secretes large amounts of antibody;
7. B cell divides to form clone all secreting/producing same
163
HIV treatment with anti-retroviral drug AZT (6)
1. Person (infected with HIV) has HIV DNA
2. New HIV (particles) still made;
3. (AZT) inhibits reverse transcriptase;
4. (AZT) stops replication of HIV;
5. Stops destruction of more infected T cells;
6. So immune system continues to work (and AIDS does not develop);
164
Describe how HIV is replicated (5)
1. Attachment proteins attach to receptors on helper T cell
2. Nucleic acid enters cell;(in hiv its rna)
3. Reverse transcriptase converts RNA to DNA;
4. Host cell produces, Viral protein produced;
5. Virus (particles assembled and released (from cell);
165
Describe how the human Immunodeficiency virus (HIV) is replicated once inside helper T cells
1. RNA converted into DNA using reverse transcriptase;
2. DNA inserted into (helper T cell) DNA;
3. DNA transcribed into (HIV m)RNA;
4. (HIV mRNA) translated into (new) viral proteins (for assembly into viral particles);
166
Explain how HIV affects the production of antibodies when AIDS develops in a person. (3)
1. Less/no antibody produced;
2. (Because HIV) destroys helper T cells;
3. No b cells activated
167
Explain why antibody will only bind to target cell. (4 marks)
1. antibody has a (specific) tertiary structure;
2. Has variable region that only binds to one antigen;
3. Antigen to this antibody (only) found on these nerve cells;
4. So, antibody (only) forms antigen-antibody complex with these cells
168
Explain why antibody will only bind to target cell
1. antibody has a (specific) tertiary structure;
2. Has variable region that only binds to one antigen;
3. Antigen to this antibody (only) found on these nerve cells;
4. So, antibody (only) forms antigen-antibody complex with these cells
169
Explain 2 further investigations that should be done before vaccine tested on human patients
Test in human tissue to check for no side effects
test on other mammals for side effects
170
explain why its important to wash the well when doing an antibody test
removed unbound antibodies, otherwise there may be a false positive
171
Describe the process of clonal selection
B cell collides with a help T cell receptor,
this activates the B cell to go through
clonal expansion and differentiation
B cells divide by mitosis and differentiate into plasma and memory cells
172
Memory B cells can live for decades in your body,whereas plasma cells are short-lived. Describe what happens when a memory B cell with an antigen that was previously encountered enters body again
Memory B cells will divide by mitosis and make plasma cells rapidly if they collide with an antigen they have previously encountered.
Large numbers of antibodies produced, pathogens destroyed before symtoms can occur
173
How would determining the genome of viruses allow scientists to develop a vaccine
(2marks)
1.(The scientists) could identify proteins (that derive from the genetic code)
2.(They) could (then) identify potential antigens (to use in the vaccine);
174
Give 2 ways pathogen may cause disease when it enters rhe body
damages cells
invades cells and produces toxins
175
State two precautions required when working with hydrochloric acid.
eye protection
wear goggles
176
In elisa test, explain what causes the line to appear in a positive test.
Antigen
enzyme substrate complex produces colour change
177
evaluate ethics of animal testing
Harmful but not killed
178
whys sem microscope 3d
electrons/bounce off (using SE
179
what does vaccination do
prevents infection to ensure herd inmmunity
180
Describe the cell surface membrane
Selectively permeable - enables control of passage of substances in / out of cell
• receptors on surface → allow cell recognition
181
Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells
Cell homogenisation to break open cells and remove cell debris
Filter to remove cell debris
use isotonic solution to prevent damage to mitochondria
ice cold solution to reduce enzyme activity to prevent digestion of organelle, buffered to maintain ph prevent mitochondria frok denaturing
Centrifuge at lower speed to separate heaviest organelles
respin supernatant at higher speed to get mitochondria in pellet
182
Describe and explain how centrifuging the culture allowed scientists to obtain a cell free liquid
Heavy cells form pellet when centrifuged
supernatant can be removed
A Level Biology
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