Cells 3.2 Flashcards
1
Q
Structure of eukaryotic cells (AO1)
What is a eukaryotic cell?
A
A cell with a nucleus AND membrane-bound organelles.
2
Q
Structure of eukaryotic cells (AO1)
Describe the structure of the nucleus (2 marks).
A
1. Nuclear envelope and pores
OR double membrane and pores;
2. Chromosomes/chromatin
OR DNA wrapped around histones;
3. Nucleolus/nucleoli
3
Q
Structure of eukaryotic cells (AO1)
Describe the function of the nucleus (2 marks).
A
1. Stores genetic information/material for polypeptides (production)
OR codes for proteins
OR codes for primary structure of polypeptides;
2. Site of (Semi-conservative) DNA replication;
3. Production of mRNA/tRNA
OR site of Transcription;
4. Production of rRNA/ribosomes;
4
Q
Structure of eukaryotic cells (AO1)
Eukaryotic cells contain linear DNA which is bound to which protein?
A
Histones
5
Q
Structure of eukaryotic cells (AO1)
Draw out and label the structure of a mitochondrion
A
6
Q
Structure of eukaryotic cells (AO1)
Mitochondrial DNA is linear OR circular?
A
Circular
7
Q
Structure of eukaryotic cells (AO1)
What size are mitochondrial ribosomes?
A
70S
This is smaller than cytoplasmic ribosomes which are 80S
8
Q
Structure of eukaryotic cells (AO1)
What process takes place in the mitochondria
A
Aerobic respiration
9
Q
Structure of eukaryotic cells (AO1)
What are the products of aerobic respiration?
A
Carbon dioxide, water AND ATP
10
Q
Structure of eukaryotic cells (AO1)
The cristae provide a large _________ _________ so more ATP synthase can be embedded into the inner mitochondrial membrane.
A
surface area
11
Q
Structure of eukaryotic cells (AO1)
Which organelle can be found on the outer surface membrane of the rough endoplasmic reticulum?
A
Ribosome
12
Q
Structure of eukaryotic cells (AO1)
What is the function of the rough endoplasmic reticulum?
A
Provide a large surface area for the synthesis of proteins via ribosomes on their surface.
Packages proteins into vesicles to be transported to the Golgi apparatus
13
Q
Structure of eukaryotic cells (AO1)
Why is the smooth endoplasmic reticulum ‘smooth’?
A
No ribosomes on its surface
14
Q
Structure of eukaryotic cells (AO1)
What is the function of the smooth endoplasmic reticulum?
A
- Synthesise lipids and packages them into vesicles.
- Synthesise carbohydrates and packages them into vesicles.
15
Q
Structure of eukaryotic cells (AO2)
A
1. Less phospholipids in rough
OR
More protein/glycoprotein in rough
OR
Presence of ribosomes in rough;
2. (More protein/glycoprotein/ribosomes)
Rough – production/transport of proteins;
3. (More phospholipid)
Smooth –production / modification / packaging / transport of lipids
16
Q
Structure of eukaryotic cells (AO1)
What is the function of the Golgi apparatus?
A
1. Sorts, modifies and packages proteins into vesicles.
E.g. adds a carbohydrate to a protein to form a glycoprotein.
E.g. forms chylomicrons
2. Forms lysosomes
17
Q
Structure of eukaryotic cells (AO1)
What is the name of enzyme contained by lysosomes?
A
Hydrolytic enzymes
(aka lysozymes)
18
Q
Structure of eukaryotic cells (AO1)
Describe how lysosomes destroy pathogens or damaged organelles (2 marks).
A
- Lysosomes fuse with vesicle
- Release its hydrolytic enzymes
- Which breakdown pathogens AND/OR damaged and worn out organelles
19
Q
Structure of eukaryotic cells (AO1)
What is the function of ribosomes?
A
Synthesise proteins
20
Q
Structure of eukaryotic cells (AO1)
Ribosomes are made up of……..
A
ribsomal RNA (rRNA)
Protein sub-units
21
Q
Structure of eukaryotic cells (AO1)
What size are cytoplasmic ribosomes?
A
80S
This is also the size of ribosomes on the rough ER
22
Q
Structure of eukaryotic cells (AO1)
Eukaryotic cells produce and release proteins. Outline the role of organelles in the production, transport and release of proteins from eukaryotic cells (4 marks).
A
- DNA in nucleus is code (for protein);
- Ribosomes/rough endoplasmic reticulum synthesis protein;
- Mitochondria produce ATP (for protein synthesis);
- Golgi apparatus modifies and packages protein;
- Vesicles transport protein
OR
- (Vesicles) fuse with cell(-surface) membrane;
Accept exocytosis at cell membrane
23
Q
Structure of eukaryotic cells (AO1)
What is the name of the process when a vesicle fuses with the cell surface membrane to release its content?
A
Exocytosis
24
Q
Structure of eukaryotic cells (AO1)
TRUE or FALSE
The nucleus can contain more than one nucleoli?
A
TRUE
25
# **Structure of eukaryotic cells (AO1)**
DNA in the eukaryotic nucleus is linear OR circular?
Linear
26
# **Structure of eukaryotic cells (AO1)**
The **cell-surface** membrane consists of a _________________.
Phospholipid bilayer
27
# **Structure of eukaryotic cells (AO1)**
Name the main polymer that forms the cell wall in plants.
Cellulose
28
# **Structure of eukaryotic cells (AO1)**
Name the main polymer that forms the cell wall in fungi.
Chitin
29
# **Structure of eukaryotic cells (AO1)**
Draw out and label the structure of a chloroplast.
| Chloroplasts also contain circular DNA, 70S ribosomes & starch grains.
30
# **Structure of eukaryotic cells (AO1)**
The **thylakoid membranes** provide a large surface area for more ______________.
chlorophyll
| this allows MORE light energy to be absorbed during photosynthesis
31
# **Structure of eukaryotic cells (AO1)**
The synthesis of glucose as a result of photosynthesis takes place in which part of the chloroplast?
Stroma
32
# **Structure of eukaryotic cells (AO1)**
Name the main polymer that forms the cell wall in algae.
Cellulose
33
# **Structure of eukaryotic cells (AO1)**
Algae are unicellular eukaryotic organisms that can ________________ .
Photosynthesise
34
# **Structure of eukaryotic cells (AO1)**
What is the function of the large permanent vacuole in plant cells?
1. Provide support, making cells turgid.
2. Store of sugars and amino acids
35
# **Structure of eukaryotic cells (AO2)**
U. marinum cells ingest bacteria and digest them in the cytoplasm.
Describe the role of one named organelle in digesting these bacteria (*3 marks*).
**1.** Lysosomes;
**2.** **Fuse** with vesicle;
**3.** (Releases) hydrolytic enzymes;
36
# **Structure of eukaryotic cells (AO2)**
Give **one** feature of the chloroplast that allows protein to be synthesised inside the chloroplast and describe **one** difference between this feature in the chloroplast and similar features in the rest of the cell.
Mark in pairs, 1 and 2 OR 3 and 4
1. DNA;
2. Is not associated with protein/histones but nuclear DNA is
OR is circular but nuclear DNA is linear
OR is shorter than nuclear DNA;
3. Ribosomes;
4. Are **smaller** (70S) than cytoplasmic ribosomes;
37
# **Structure of eukaryotic cells (AO1)**
Outline the **similarities** in the structures of chloroplasts and mitochondria.
**1.** **Both** double membrane;
**2.** **Both** contain (circular) DNA;
**3.** **Both** contain ribosomes;
38
# **Structure of eukaryotic cells (AO1)**
Outline the **differences** in the structures of chloroplasts and mitochondria.
**4.** Chloroplasts have thylakoids/grana **whereas** mitochondria have cristae;
**5.** Chloroplasts stroma **whereas** mitochondria matrix;
**6.** Chloroplasts pigments (chlorophyll) **whereas** no pigments in mitochondria;
**7.** Chloroplasts have starch grains **whereas** mitochondria have no starch grains;
39
# **Structure of eukaryotic cells (AO1)**
D - **Granum**/grana/thylakoid(s);
E - **starch** / lipid;
40
# **Structure of eukaryotic cells (AO1)**
B;
A;
E;
41
# **Structure of eukaryotic cells (AO2)**
Human breast milk is produced and secreted by gland cells. These gland cells have adaptations that include many mitochondria and many Golgi vesicles. The milk contains a high concentration of protein.
Explain the role of these cell adaptations in the production and secretion of breast milk (*2 marks*).
1. (Many mitochondria) release energy / ATP for movement of vesicles / synthesis of protein / active transport;
2. (Many Golgi) vesicles transport protein / glycoprotein / milk to cell membrane / out of cell;
42
# **Structure of eukaryotic cells (AO1)**
43
# **Structure of eukaryotic cells (AO1)**
B Golgi (body / apparatus);
C Mitochondria / mitochondrion;
44
# **Structure of eukaryotic cells (AO1)**
Name two structures present in plant cells that are not present in animal cells.
1. Chloroplasts
2. Cell wall
3. Cell vacuole
4. Starch grains
45
# **Structure of eukaryotic cells (AO1)**
A stroma
B granum
46
# **Structure of eukaryotic cells (AO1)**
W – chloroplast, photosynthesis;
Z – nucleus, contains DNA / chromosomes / holds genetic information of cell.
47
# **Structure of eukaryotic cells (AO1)**
Identify X
Crista/cristae
48
# **Structure of eukaryotic cells (AO1)**
L
H
N
49
# **Structure of eukaryotic cells (AO2)**
Membrane-bound organelle(s)
OR Mitochondrion/mitochondria
OR Vesicle(s)/lysosomes
OR Rough endoplasmic reticulum
OR Nucleus/(double) nuclear membrane/pore(s)/ nuclear envelope;
50
# **Structure of eukaryotic cells (AO1)**
Define a tissue
**Similar** specialised cells that perform a specific function
51
# **Structure of eukaryotic cells (AO1)**
Define an organ
**Different tissues** that work together to perform a specific / vital function
52
# **Structure of eukaryotic cells (AO1)**
Define an organ system
**Different organs** that work together to perform a specific / vital function
53
# **Structure of eukaryotic cells (AO1)**
In complex multicellular organisms, eukaryotic cells become _____________ for specific functions.
specialised
54
# **Structure of prokaryotic cells and of viruses (AO1)**
Prokaryotic cells are smaller OR larger than eurkaryotic cells
Smaller
55
# **Structure of prokaryotic cells and of viruses (AO1)**
Define a prokarytic cell
Cells that **DO NOT** contain a nucleus or membrane-bound organelles
56
# **Structure of prokaryotic cells and of viruses (AO1)**
Describe the structure of DNA in prokaryotic cells
**no nucleus**;
single **circular DNA** molecule that is free in the cytoplasm;
**not** associated with proteins/histones;
57
# **Structure of prokaryotic cells and of viruses (AO1)**
By what process do prokarytic cells replicate their DNA
Semi-conservative replication
| Meselson & Stahl used E.coli (a bacteria) for their experiments
58
# **Structure of prokaryotic cells and of viruses (AO1)**
What is the name of the glycoprotein that makes up the prokaryote cell wall?
**Murein**
(aka peptidoglycan)
59
# **Structure of prokaryotic cells and of viruses (AO1)**
What size are prokaryotic ribosomes?
70S
| This is smaller than cytoplasmic ribosomes in a eukarytic cell
60
# **Structure of prokaryotic cells and of viruses (AO1)**
What is the extra source of DNA called in a prokaryote
Plasmid(s)
61
# **Structure of prokaryotic cells and of viruses (AO1)**
What genes are typically found in plasmids
Genes that benefit prokaryote survival
e.g., antibiotic resistance
62
# **Structure of prokaryotic cells and of viruses (AO1)**
**TRUE or FALSE**
Prokaryotes can have more than one plasmid
TRUE
| Prokaryotes have a **variable** number of plasmids
63
# **Structure of prokaryotic cells and of viruses (AO1)**
What structure often surrounds the prokaryotic cell?
Capsule
64
# **Structure of prokaryotic cells and of viruses (AO1)**
Give two structures found in all prokaryotic cells and in all eukaryotic cells.
1. Cell(-surface) membrane;
2. Ribosomes;
3. Cytoplasm;
4. DNA;
65
# **Structure of prokaryotic cells and of viruses (AO1)**
Name two structures found in all bacteria that are not found in plant cells.
1. Circular DNA (molecule in cytoplasm);
2. Murein cell wall
OR Peptidoglycan cell wall
3. Smaller/70S ribosomes in cytoplasm;
66
# **Structure of prokaryotic cells and of viruses (AO1)**
Name two features of HIV particles that are not found in bacteria.
1. Capsid;
2. Reverse transcriptase;
3. RNA genome;
Accept ‘genetic material’ OR ‘genes’ for ‘genome’
4. Envelope;
5. Attachment proteins
67
# **Structure of prokaryotic cells and of viruses (AO1)**
**TRUE or FALSE:**
All prokaryotic cells have one or more flagella.
FALSE
| Some prokaryotes have **NO** flagella
68
# **Structure of prokaryotic cells and of viruses (AO1)**
All prokaryotic cells have ___________ ribosomes than eukaryotic cells.
smaller
69
# **Structure of prokaryotic cells and of viruses (AO1)**
Flagellum
70
# **Structure of prokaryotic cells and of viruses (AO1)**
Name an organelle found in both a chloroplast and a prokaryotic cell.
(70S) Ribosome
71
# **Structure of prokaryotic cells and of viruses (AO1)**
72
# **Structure of prokaryotic cells and of viruses (AO1)**
Second box ticked
B – statements 1, 2 and 4
73
# **Structure of prokaryotic cells and of viruses (AO1)**
W – (cell surface) membrane
X – cell wall
Y – capsule
Z – flagellum
74
# **Structure of prokaryotic cells and of viruses (AO1)**
Viruses are ________ and non-living.
**a**cellular
| This means they need a host cell to surivive and reproduce
75
# **Structure of prokaryotic cells and of viruses (AO1)**
**TRUE or FALSE**
Prokaryotes can have one or more flagella.
TRUE
76
# **Structure of prokaryotic cells and of viruses (AO1)**
Draw out and label the key structures of a virus
## Footnote
Structures in red, funtion in black
77
# **Structure of prokaryotic cells and of viruses (AO1)**
What is the function of the capsid in a virus?
Protects the viral genome (DNA or RNA)
78
# **Structure of prokaryotic cells and of viruses (AO1)**
What is the function of the viral genome (DNA or RNA)?
Codes for (viral) protein
79
# **Structure of prokaryotic cells and of viruses (AO1)**
RNA viruses (e.g. HIV) contain an enzyme that converts viral RNA into (c)DNA - what is the name of this enzyme?
Reverse transcriptase
80
# **Structure of prokaryotic cells and of viruses (AO1)**
What is the function of viral attachment proteins?
Binds to receptors (on cell);
81
# **Structure of prokaryotic cells and of viruses (AO1)**
**TRUE or FALSE**
Some viruses contain RNA as their genetic material
TRUE
| These are called RNA viruses or retroviruses e.g. HIV
82
# **Structure of prokaryotic cells and of viruses (AO1)**
Capsid and attachment protein
83
# **Methods of studying cells (AO1)**
What are the principles of light (aka optical) microscopy?
A thin specimen is illuminated with light;
This light is focussed using a glass lens;
Magnified and view using the eye piece and objective lenses;
Specimens can be alive or dead;
Cellular structures like the nucleus can be stained with dyes to make them visible;
84
# **Methods of studying cells (AO1)**
Explain why it is not possible to identify smaller organelles like mitochondria using an optical microscope (*2 marks*).
1. Wavelength of light is (too) long;
2. So has a low**er** resolution
85
# **Methods of studying cells (AO1)**
A section/slice (so nucleus in another part of cell)
OR
(Nucleus) not stained;
| A cell is 3D so slicing across the top or bottom may miss the nucleus
86
# **Methods of studying cells (AO1)**
Identify organelles S and T
S = Vacuole
T = Chloroplast;
87
# **Methods of studying cells (AO1)**
Give one advantage of viewing a biological specimen using a transmission electron microscope compared with using a scanning electron microscope (1 mark).
High**er** resolution
OR
View internal structures;
88
# **Methods of studying cells (AO1)**
A biologist separated cell components to investigate organelle activity. She prepared a suspension of the organelles in a solution that prevented damage to the organelles.
**Describe** three properties of this solution and **explain** how each property prevented damage to the organelles (*3 marks*).
1. **(Ice) cold** to prevent/reduce enzyme activity;
2. **Buffered** to prevent denaturing of enzyme/protein;
3. **Same water potential**/ Ψ to prevent lysis/bursting (of organelle);
Accept: **isotonic** for same water potential.
89
# **Methods of studying cells (AO2)**
Scientists investigated the role of a protein called CENP-W in mitosis. Their method involved cell fractionation and ultracentrifugation.
(a) The scientists began by lysing (breaking open) cells and organelles using a detergent that dissolves lipids in water.
Suggest how the detergent releases CENP-W from cells (*2 marks*).
1. Cell surface membranes made from phospholipid bilyar;
2. (Detergent) dissolves membranes / phospholipid (bilayer);
90
# **Methods of studying cells (AO2)**
Explain how ultracentrifugation separates a protein involved in mitosis CENP-W from other molecules.
1. **Spin** (liquid / supernatant) at (very) **high speed**;
2. Molecules / CENP-W separates depending on (molecular) mass / size / density;
| Densest molecules/organelles found at bottom of tube.
91
# **Methods of studying cells (AO1)**
Contrast how an optical microscope and a transmission electron microscope work (*3 marks*).
1. TEM use electrons **whereas** optical use light;
2. TEM focuses using magnets **whereas** optical uses (glass) lenses;
3. TEM allows a **greater** resolution;
4. (So with TEM) **smaller** organelles / named cell structure (e.g. mitochondria) can be observed
92
# **Methods of studying cells (AO1)**
Contrast the limitations of an optical microscope and a transmission electron microscope when studying cells (*3 marks*).
1. TEM view only dead / dehydrated specimens **whereas** optical (can) view live specimens;
2. TEM does not show colour **whereas** optical can;
3. TEM requires **thinner** specimens;
4. TEM requires a **more complex/time** consuming preparation;
93
# **Methods of studying cells (AO1)**
During cell fraction explain why biologists use a blender and then filtered the mixture (*2 marks*).
1. Break open cells / homogenise;
2. Remove unbroken cells / larger debris;
94
# **Methods of studying cells (AO1)**
Name the organelle that made up most of the first pellet after centrifuging at a lowest speed.
Nucleus / nuclei;
95
# **Methods of studying cells (AO1)**
Describe how a sample of chloroplasts could be isolated from leaves (*4 marks*).
1. Break open cells/tissue **and** filter
*Accept homogenise **and** filter*
2. In cold, isotonic, buffered solution;
3. Centrifuge/spin and remove nuclei/cell debris;
4. (Centrifuge/spin) at **high(er)** speed, chloroplasts settle out;
96
# **Methods of studying cells (AO1)**
Describe how you could make a temporary mount of a piece of plant tissue to observe the position of starch grains in the cells when using an optical (light) microscope (*3 marks*).
1. Add drop of water to (glass) slide;
2. Obtain **thin** section (of plant tissue) and place on slide / drop of water;
3. Stain with / add iodine in potassium iodide.
4. Lower cover slip using mounted needle.
*Allow any appropriate method that avoids trapping air bubbles*
97
# **Methods of studying cells (AO1)**
A student investigated the distribution of stomata on leaves from two species of plant. She removed small pieces from the lower surface of the leaves of each plant species. She mounted these pieces on separate microscope slides. She then counted the number of stomata in several parts of the epidermis on each piece of leaf tissue using an optical microscope.
**The pieces of leaf tissue examined were very thin**.
Explain why this was important.
1. Single layer(s) of cells;
2. So light can pass through;
98
# **Methods of studying cells (AO1)**
A student investigated the distribution of stomata on leaves from two species of plant. She removed small pieces from the lower surface of the leaves of each plant species. She mounted these pieces on separate microscope slides. She then counted the number of stomata in several parts of the epidermis on each piece of leaf tissue using an optical microscope.
Give *two* reasons why it was important that the student counted the number of stomata in several parts of each piece of leaf tissue.
1. Distribution may not be uniform
OR so it is a representative sample;
2. To obtain a (reliable) mean;
99
# **Methods of studying cells (AO1)**
**Describe** and **explain** how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells (*5 marks*).
1. Cell homogenisation to break open cells;
2. Filter to remove (large) debris / whole cells;
3. Use isotonic solution to prevent osmotic damage to mitochondria / organelles;
4. Keep cold to prevent / reduce damage by enzymes / use buffer to prevent protein / enzyme denaturation;
5. Centrifuge **at lower speed** to separate nuclei / cell fragments / heavy organelles;
6. Re-spin (supernatant / after nuclei / pellet removed) at **higher speed** to get mitochondria in pellet / at bottom.
100
# **Methods of studying cells (AO1)**
Describe the principles of using a transmission electron microscope to investigate cell structure
(*3 marks*).
1. Electrons pass through / enter (thin) specimen;
2. Denser parts absorb more electrons;
3. (So) denser parts appear darker;
4. Electrons have short wavelength so give high resolution;
101
# **Methods of studying cells (AO1)**
Describe the limitations of using a transmission electron microscope to investigate cell structure (*3 marks*).
5. Cannot look at living material / Must be in a vacuum;
6. Specimen must be (very) thin;
7. Artefacts present;
8. Complex staining method / complex / long preparation time;
9. Image not in 3D / only 2D images produced.
102
# **Methods of studying cells (AO1)**
The scientists used a transmission electron microscope to study the structure of the amoeba. Explain why (*2 marks*).
1. Shorter wavelength of electrons;
2. So high**er** resolution;
3. To see internal structures / organelles / named organelles (e.g. chloroplasts);
103
# **Methods of studying cells (AO1)**
Give one advantage of using a SEM rather than a TEM.
Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images;
104
# **Methods of studying cells (AO1)**
Describe how the student could use an eyepiece graticule to determine the mean diameter of stomata (3 marks).
1. Calibrate eyepiece graticule against stage micrometer;
2. Measure (each stoma) using eyepiece graticule;
3. Take a number of measurements
(to calculate a mean);
105
# **Methods of studying cells (AO1)**
Define resolution
The ability to distinguish between objects that are close together.
106
# **Methods of studying cells (AO1)**
Define magnification
The ability to make an object bigger (when using an optical or electron microscope)
107
# **Methods of studying cells (AO1)**
Describe the principles of using a scanning electron microscope to investigate cell structure (*3 marks*).
1. Specimens are **NOT** sliced
2. The electrons bounce off the **SURFACE** of the specimen.
3. This produces a 3D image / shows the surface of a cell
108
# **Methods of studying cells (AO2)**
**1.** Nucleus;
**2.** Nucleolus/nucleoli
OR Nuclear membrane/envelope;
**3.** Mitochondria/chloroplast contain DNA;
109
# **Structure of prokaryotic cells and of viruses (AO1)**
Explain why viruses are described as acellular and non-living (*2 marks*).
*Mark point 1 (Acellular) *
no cell(-surface) membrane;
OR
Not made of cells;
*Mark point 2 (Non-living)*
Cannot (independently) move/respire/replicate/
excrete
OR
have no metabolism/metabolic
reactions;
OR
(Have) no nutrition;
110
# **All cells arise from other cells (AO1)**
**TRUE or FALSE**
Within multicellular organisms, all cells retain the ability to divide.
FALSE
| Stem cells are the main cell type that can divide.
111
# **All cells arise from other cells (AO1)**
Eukaryotic cells that retain the ability to divide show a cell ______________.
cycle
112
# **All cells arise from other cells (AO1)**
DNA replication takes place during interphase OR mitosis in the cell cyle?
Interphase
| During s-phase which stands for semi-conservative replication
113
# **All cells arise from other cells (AO1)**
Draw out and label the cell cycle
114
# **All cells arise from other cells (AO1)**
Fill in the missing words:
[1] is the part of the cell cycle in which a eukaryotic cell divides to produce two daughter cells, each with [2] copies of DNA produced by the parent cell during DNA replication.
[1] Mitosis
[2] identical
115
# **All cells arise from other cells (AO1)**
List the stages of mitosis in the correct sequence.
Prophase
Metaphase
Anaphase
Telophase
116
# **All cells arise from other cells (AO1)**
What is the name for the process where division of the cytoplasm occurs, producing two new cells.
cytokinesis
117
# **All cells arise from other cells (AO1)**
Explain why mitosis is important
(3 marks)
- Growth of multicellular organisms
- Replacement of cells and repair of tissues
- Asexual reproduction
118
# **All cells arise from other cells (AO1)**
A, D, C, E, B
119
# **All cells arise from other cells (AO1)**
Prophase = C
Metaphase = A
Anaphase = D
Telophase = B
120
# **All cells arise from other cells (AO1)**
What are homologous chromosomes?
A pair of chromosomes which contain the same genes (but with different alleles)
| This is what makes cells diploid (2n)
121
# **All cells arise from other cells (AO1)**
Draw out and label a pair of homologous chromosomes after semi-conservative replication.
122
# **All cells arise from other cells (AO1)**
What holds sister chromatids together after DNA replication
The centromere
123
# **All cells arise from other cells (AO1)**
Describe the structure of a chromosome
**1.** DNA is associated with histones;
**2.** (During mitosis/when visible) chromosome
consists of two (sister) chromatids joined at a
centromere;
124
# **All cells arise from other cells (AO1)**
Describe the appearance and behaviour of chromosomes during **prophase**
**Chromosomes condense** / coil / shorten / thicken / become visible;
(Chromosomes) appear as (two sister) chromatids joined at the centromere;
125
# **All cells arise from other cells (AO1)**
Describe the appearance and behaviour of chromosomes during **metaphase**
Chromosomes line up on the equator / centre of the cell;
(Chromosomes) attached to spindle fibres;
By their centromere;
126
# **All cells arise from other cells (AO1)**
Describe the appearance and behaviour of chromosomes during **anaphase**
The centromere splits / divides;
(Sister) chromatids / chromosomes are pulled to opposite poles / ends of the cell;
127
# **All cells arise from other cells (AO1)**
Describe the appearance and behaviour of chromosomes during **telophase**
Chromatids / chromosomes uncoil / unwind / become longer / thinner.
128
# **All cells arise from other cells (AO1)**
Describe what happens to the chromosomes in anaphase (*2 marks*)
Spindle fibres shorten and centromere splits;
Sister chromatids separate;
Sister chromatids pulled to opposite poles of the cell (by spindle fibres);
129
# **All cells arise from other cells (AO1)**
What is the name of the organelle that produces the spindle fibres?
centriole
| There are two that move to opposite poles during prophase
130
# **All cells arise from other cells (AO1)**
1. Chromosomes (are) becoming visible/distinct;
2. Because (still) condensing;
Accept shorten or thicken for ‘condensed’
3. Chromosomes (arranged) at random/not lined up;
4. Because no spindle (activity);
OR
Because not attached to spindle fibres;
131
# **All cells arise from other cells (AO1)**
A
132
# **All cells arise from other cells (Maths)**
1.286
Rate is always DY / DX (time) (read off graph)
DY = 19 - 4 = 15 um
DX = 2500-1800 = 700 secs
min-1 (per minute), 700 / 60 = 11.67 mins
15 um / 11.67 mins = 1.286 um min-1
133
# **All cells arise from other cells (AO1)**
1. The (individual) chromosomes are visible because they have condensed;
*Accept ‘tightly coiled’ or ‘short and thick’ for condensed but do not accept ‘contracted’.*
2. (Each) chromosome is made up of two chromatids because DNA has replicated;
Accept ‘sister chromatids’ for ‘two chromatids’.
3. The chromosomes are not arranged in homologous pairs, which they would be if it was meiosis;
134
# **All cells arise from other cells (AO1)**
(D)CBEA.
135
# **All cells arise from other cells (AO1)**
What leads to the formation of tumours / cancers.
**Uncontrolled cell division** / mitosis / cell cycle
136
# **All cells arise from other cells (AO1)**
What is a tumour?
1. Mass of cells/tissue
OR Abnormal cells/tissue;
2. (As a result of) **uncontrolled** mitosis/cell division;
137
# **All cells arise from other cells (AO1)**
Many _____________ treatments are directed at controlling the rate of cell division.
cancer
138
# **All cells arise from other cells (AO2)**
**1.** 2 nuclei (in cells)
OR Cells (stopped) at telophase;
**2.** Cytokinesis prevented
OR Stopped cytoplasm dividing;
139
# **All cells arise from other cells (AO1)**
140
# **All cells arise from other cells (AO1)**
What is the name of the process by which prokaryotes divide?
Binary fission
141
# **All cells arise from other cells (AO1)**
Describe binary fission
1. Replication of (circular) DNA;
2. Replication of plasmids;
3. Division of cytoplasm (to produce daughter cells);
142
# **All cells arise from other cells (AO2)**
**Describe**
1. (Trend of) slowing growth from before birth to 21 days
OR (Trend of) decreasing percentage undergoing mitosis from before birth to 21 days
OR (Trend of) decreasing percentage undergoing DNA replication from before birth to 21 days;
**Explain**
2. DNA replication happens before mitosis
OR Heart growth slowing until (fully) developed
OR These cells lost the ability to divide;
143
# **All cells arise from other cells (AO2)**
1. No separation of chromatids/chromosomes/centromeres;
Accept anaphase prevented
2. Chromatids/chromosomes all go to one pole/end/sides of cell/not pulled to opposite poles;
3. Doubles chromosome number in cell OR one daughter cell gets no chromosomes or chromatids;
144
# **All cells arise from other cells (AO1)**
Centromere
145
# **Transport across cell membranes (AO1)**
Explain the arrangement of phospholipids in a cell-surface membrane (*3 marks*).
**1.** As a bilayer
**2.** Phospholipid both hydrophobic and hydrophilic OR Phospholipid polar
**3.** Triglycerides only hydrophobic
OR Fatty acid/triglyceride is non-polar;
**4.** Hydrophilic/phosphate group attracts water (to either side of bilayer)
OR Hydrophobic (fatty acid) tails point away/are repelled from water
146
# **Transport across cell membranes (AO1)**
Explain why the structure of a membrane is described as fluid-mosaic (*2 marks*).
Idea of molecules / named molecules moving (= Fluid);
Idea of both proteins and phospholipids (= Mosaic);
147
# **Transport across cell membranes (AO1)**
Draw out and label a diagram of the phospholipid bilayer (include different biological molecules)
148
# **Transport across cell membranes (AO1)**
What properties must a molecule possess to cross the cell surface membrane by simple diffusion
Lipid-soluble
AND/OR
Non-polar
| e.g. hormones, oxygen & carbon dioxide
149
# **Transport across cell membranes (AO1)**
Explain why phospholipids can form a bilayer but triglycerides cannot (*3 marks*).
**1**. Phospholipid both hydrophobic and hydrophilic
OR
Phospholipid polar
OR
Phosphate group is charged;
**2.** Triglycerides only hydrophobic
OR Fatty acid/triglyceride is non-polar;
**3.** Hydrophilic/phosphate group **attracts water** (to either side of bilayer)
150
# **Transport across cell membranes (AO1)**
What transport process do channel proteins allow?
Facilitated diffusion
151
# **Transport across cell membranes (AO1)**
Receptors are embebbed into the cell surface membrane and have a specific and ___________ shape to only one molecule that binds.
complementary
152
# **Transport across cell membranes (AO1)**
Cholesterol role
**Restricts** the movement of other molecules making up the cell surface membrane;
153
# **Transport across cell membranes (AO1)**
Q
P
S
154
# **Transport across cell membranes (AO2)**
*(Similarity)*
Both have a phospholipid bilayer OR
Both have protein;
*(Differences)*
No channel/carrier proteins, whereas fluid mosaic does
OR
Protein layer outside (phospholipids), fluid mosaic is 'dotted';
Accept only one type of protein whereas fluid mosaic has many (types)
Cholesterol is not present whereas it is present in fluid mosaic;
155
# **Transport across cell membranes (AO1)**
Channel proteins have a specific __________ structure
tertiary
156
# **Transport across cell membranes (AO1)**
______________ have a specific tertiary structure and allow the transport of larger polar molecules (e.g. glucose) by facilitated diffusion and active transport.
Carrier proteins
157
# **Transport across cell membranes (AO1)**
**TRUE or FALSE**
Receptors have active sites
FALSE
| Receptors have binding sites whereas only enzymes have active sites
158
# **Transport across cell membranes (AO1)**
Diffusion is a ____________ process – it does not require energy from ATP hydrolysis.
passive
159
# **Transport across cell membranes (AO1)**
Non-polar, lipid-soluble molecules like oxygen, carbon dioxide and hormones (e.g. oestrogen) can diffuse __________ a concentration gradient and cross the phospholipid bilayer.
DOWN
160
# **Transport across cell membranes (AO1)**
Explain how increasing temperature affects the rate of diffusion.
Increase kinetic energy therefore faster movement of molecules.
This leads to a **faster** rate of diffusion.
161
# **Transport across cell membranes (AO1)**
Explain how increasing surface area affects the rate of diffusion.
More cell surface membrane for molecules to pass through;
Therefore a **faster** rate of diffusion.
162
# **Transport across cell membranes (AO1)**
As a concentration gradient decreases, the rate of diffusion becomes ___________.
slower
163
# **Transport across cell membranes (AO1)**
The shorter the diffusion distance, the _______ the rate of diffusion.
faster
164
# **Transport across cell membranes (AO1)**
Facilitated diffusion is a passive process, it does not require ________.
ATP
165
# **Transport across cell membranes (AO1)**
Describe how substances move across cell-surface membranes by facilitated diffusion (*3 marks*).
1. Carrier / channel protein;
2. (Protein) specific / complementary to substance;
3. Substance moves **down** concentration gradient;
166
# **Transport across cell membranes (AO1)**
Pure water has the highest water potential and a value of _____ kpa.
0
(Zero)
167
# **Transport across cell membranes (AO1)**
Adding a solute (e.g. sucrose) makes the water potential of a solution _________.
negative
168
# **Transport across cell membranes (AO1)**
What is the name of the channel proteins required for the movement of polar water molecules by osmosis?
aquaporins
169
# **Transport across cell membranes (AO1)**
During osmosis, water moves from a [1] water potential to a [2] water potential, [3] a water potential gradient.
[1] high
[2] low
[3] down
170
# **Transport across cell membranes (AO1)**
Give two similarities in the movement of substances by diffusion and by osmosis.
1. (Movement) **down** a gradient
2. Passive processes;
OR Do not use energy from respiration / from ATP;
171
# **Transport across cell membranes (AO2)**
Concentration of sodium ions (outside cell);
As concentration increases so does the rate of (facilitated) diffusion;
172
# **Transport across cell membranes (AO2)**
1. Between A and B - Movement through carrier proteins (accept channel proteins);
OR Facilitated diffusion;
2. Between A and B - rate of uptake proportional to (external) concentration;
3. Between C and D - all channel / carrier proteins in use / saturated / limiting;
173
# **Transport across cell membranes (AO2)**
1. Rate of uptake is proportional / does not level off (so diffusion occurring);
*Accept as one increases the other increases*
2. (Lipid-soluble molecules) diffuse through / are soluble in phospholipid (bilayer);
174
# **Transport across cell membranes (AO1)**
Active transport only involves [1] proteins.
It involves moving molecules [2] the concentration gradient from low to high.
This requires energy from [3].
[1] carrier
[2] AGAINST
[3] ATP hydrolysis
175
# **Transport across cell membranes (AO2)**
Sodium ions from salt (sodium chloride) are absorbed by cells lining the gut. Some of these cells have membranes with a carrier protein called NHE3.
NHE3 actively transports one sodium ion into the cell in exchange for one proton (hydrogen ion) out of the cell.
Use your knowledge of transport across cell membranes to suggest how NHE3 does this.
1. Sodium ion and proton bind to the protein;
2. Co-transport;
3. Protein changes shape (to move sodium ion and / or proton across the membrane);
4. Uses (hydrolysis of) ATP;
176
# **Transport across cell membranes (AO1)**
Cells involved in active transport contain higher numbers of which organelle. Explain why.
Mitochondria;
To produce ATP;
**Energy from ATP hydrolysis**;
(used to change shape of carrier protein)
move molecules **against** concentration gradient;
177
# **Cell recognition and the immune system (AO1)**
Each type of cell has specific molecules on its surface that identify it. These molecules include proteins and enable the immune system to identify:
pathogens;
cells from other organisms of the same species;
abnormal body cells;
toxins;
178
# **Cell recognition and the immune system (AO1)**
Define antigen
A foreign molecule / protein;
stimulates an immune response;
results in the production of a specific antibody;
179
# **Cell recognition and the immune system (AO1)**
Which organelle do phagocytes contain many of?
Lysosomes
180
# **Cell recognition and the immune system (AO1)**
Describe how a phagocyte destroys a pathogen present in the blood (*3 marks*).
1. Engulfs;
2. Forming vesicle/phagosome **and fuses** with lysosome;
3. Enzymes digest/hydrolyse;
Accept lysozymes for ‘enzymes’
181
# **Cell recognition and the immune system (AO1)**
Cells that stimulate an
immune response
1. Pathogens e.g. bacteria / fungi
2. Cells from organisms / transplants of the **same** species;
3. Abnormal / cancer / tumour (cells);
4. (Cells) infected by virus;
5. Antigen-presenting cells
182
# **Cell recognition and the immune system (AO1)**
Describe how phagocytosis of a virus leads to presentation of its antigens (*3 marks*).
1. Phagosome / vesicle **fuses** with lysosome;
2. (Virus) destroyed by lysozymes / hydrolytic enzymes;
3. Antigens (from virus) are displayed on the cell **surface** membrane;
183
# **Cell recognition and the immune system (AO1)**
Which immune cells contain receptors which bind to antigens on antigen-presenting cells during the cellular response?
T helper cells
184
# **Cell recognition and the immune system (AO1)**
What are the roles of a T helper cell?
1) Stimulates B cells to divide by mitosis
2) Stimulates phagocytes
3) Stimulates cytotoxic T cells
185
# **Cell recognition and the immune system (AO1)**
Upon stimulation, what chemicals do T helper cells release?
Cytokines
186
# **Cell recognition and the immune system (AO1)**
Which part of the T helper cell is specific and complementary to the shape of the antigen?
Receptor
187
# **Cell recognition and the immune system (AO1)**
Cytotoxic T cells destroy which cells?
Virally-infected cells;
Cancerous cells;
188
# **Cell recognition and the immune system (AO1)**
What is the name of the chemical contained by cytotoxic T cells that damages its target cells?
Perforin
189
# **Cell recognition and the immune system (AO1)**
The humoral response results in the production of ____________ .
Monoclonal antibodies
190
# **Cell recognition and the immune system (AO1)**
Upon stimulation, the B cells divide
by _____________ to produce clones.
mitosis
191
# **Cell recognition and the immune system (AO1)**
Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen (*3 marks*).
1. Helper T cell cell binds to the antigen (on the antigen-presenting cell / phagocyte);
2. This helper T cell stimulates a specific B cell;
3. B cell clones
OR B cell divides by mitosis;
4. (Forms) plasma cells that release antibodies;
192
# **Cell recognition and the immune system (AO1)**
What is the primary response.
Some B cells differentiate into **plasma cells**;
which **produce and release large quantities of monoclonal antibodies** (secreted into the blood);
193
# **Cell recognition and the immune system (AO1)**
What is the secondary response.
Some B cells become memory cells;
which persist in the blood;
help to mount **a faster immune response upon re-infection**;
194
# **Cell recognition and the immune system (AO1)**
Define monoclonal antibody
Same tertiary structure;
produced by identical/cloned plasma cells;
195
# **Cell recognition and the immune system (AO1)**
Monoclonal antibodies are an example of a ______________ protein
quaternary
196
# **Cell recognition and the immune system (AO1)**
The 4 polypeptide chains (2 heavy and 2 light) in an antibody are joined together by _______________.
disulphide bridges
197
# **Cell recognition and the immune system (AO1)**
‘X’ written at either or both ends of Y shape;
198
# **Cell recognition and the immune system (AO1)**
Describe and explain the role of antibodies in stimulating phagocytosis.
1. Bind to antigen
OR Accept form (antibody-antigen) complexes/are complementary to antigen
2. (Antibodies) cause clumping/agglutination
OR Attract phagocytes;
199
# **Cell recognition and the immune system (AO1)**
What is formed when an antibody binds to an antigen.
Antibody-antigen complex
200
# **Cell recognition and the immune system (AO2)**
NMO is a disease that leads to damage to nerve cells in the spinal cord.
A person with NMO produces anti-AQP4 antibody that attacks only these nerve cells.
Explain why the anti-AQP4 antibody only damages these cells (*4 marks*).
1. (Anti-AQP4) antibody has a (specific) tertiary structure;
2. Has binding site that only binds to / complementary to one antigen;
3. Antigen to this antibody (only) found on these nerve cells;
4. So, antibody (only) binds to / forms antigen-antibody complex with these nerve cells (causing damage);
201
# **Cell recognition and the immune system (AO2)**
Collagen is a protein produced by cells in joints, such as the knee.
Rheumatoid arthritis (RA) is an auto-immune disease. In an auto-immune disease, a person’s immune system attacks their own cells. RA causes pain, swelling and stiffness in the joints.
Scientists have found a virus that produces a protein very similar to human collagen.
Suggest how the immune response to this viral protein can result in the development of RA (*2 marks*).
1. The antibody against virus (antigen) will bind to collagen;
2. This results in the destruction of the (human) cells / collagen;
202
# **Methods of studying cells (AO1)**
1. **3D** with SEM, but **2D** with TEM
OR
Only **surface** visible with SEM, but **internal structures** visible with TEM;
2. **Electrons bounce off** using SEM
OR
**Electrons pass through** using TEM;
203
# **Methods of studying cells (AO1)**
The resolution of an image obtained using an electron microscope is higher than the resolution of an image obtained using an optical microscope.
Explain why.
Short**er** wavelength between electrons;
OR
Long**er** wavelength in light rays;
204
# **Methods of studying cells (AO1)**
A student determined the size of a cell structure from a photograph obtained using a microscope.
He used a ruler and a calculator and gave the answer in μm.
Describe how the student determined the size of the structure (*2 marks*).
1. Measure length of structure and divide by magnification;
Accept correct equation making reference to a measurement
2. Correct conversion from measured length to µm e.g. ×1000 from mm;
OR
3. Measure (length of structure) and divide by (image) length of scale bar;
4. Multiply by actual length of scale bar;
205
# **Structure of prokaryotic cells and of viruses (AO1)**
Give two features of **all** prokaryotic cells that are not features of eukaryotic cells.
No membrane-bound organelles
Circular DNA OR DNA free in cytoplasm
DNA not associated with proteins/histones
No introns
Murein/peptidoglycan (in) cell wall;
Only have smaller 70S ribosomes
206
# **Transport across cell membranes (AO2)**
**1.** Hydrophobic side next to/in/face fatty acids/tails
OR
Hydrophobic side next to/in/face hydrophobic part of phospholipid/bilayer;
**2.** Hydrophilic sides allow ion movement through membrane
OR
Hydrophilic sides form a channel;
207
# **Structure of eukaryotic cells (AO1)**
**1.** Magnification (figures) show A is **bigger** than B;
**2.** A has a nucleus **whereas** B has free circular DNA;
**3.** A has mitochondria **whereas** B does not;
**4.** A has Golgi body/endoplasmic reticulum **whereas** B does not;
**5.** A has no cell wall **whereas** B has a murein/peptidoglycan cell wall;
**6.** A has no capsule **whereas** B has a capsule;
**7.** A has DNA is bound to histones/proteins **whereas** B has DNA not associated with histones/proteins
OR
A has linear DNA whereas B has circular DNA;
**8.** has **larger** ribosomes;
208
# **Cell recognition and the immune system (AO1)**
What does a vaccine contain?
A dead / weakened / attenuated form of the pathogen
A **specific antigen** or antigens
e.g. an attachment protein on a virus
*OFF-SPEC/AO2*
mRNA that could be used by ribosomes to produce a specific antigen
e.g. an attachment protein on a virus
209
# **Cell recognition and the immune system (AO1)**
The primary response
After taking a vaccine, stimulation of B cells will lead to mitosis and differentiation into [1] and the production of a small quantity of [2]. [3] cells are also produced.
[1] plasma cells
[2] antibodies
[3] Memory
210
# **Cell recognition and the immune system (AO1)**
The secondary response
When a vaccinated person is infected with the actual pathogen, [1] cells will help produce a [2] concentration of antibodies AND [3].
[1] memory
[2] higher
[3] faster
211
# **Cell recognition and the immune system (AO1)**
Why do some patient's receive boosters (a 2nd or 3rd dose of a vaccine)?
Produce **more** memory cells;
So **higher** concentration of antibodies produced;
At a **faster** rate;
212
# **Cell recognition and the immune system (AO1)**
What is herd immunity?
When the majority of the population is vaccinated;
Some unvaccinated individuals are also protected;
(this is because) vaccinated individuals are less likely to spread the pathogen to unvaccinated individuals;
213
# **Cell recognition and the immune system (AO2)**
Bacterial meningitis is a potentially fatal disease affecting the membranes around the brain. Neisseria meningitidis (Nm) is a leading cause of bacterial meningitis.
(a) In the UK, children are vaccinated against this disease. Describe how vaccination can lead to protection against bacterial meningitis
*(6 marks)*.
1. Antigen on surface of N. meninigitidis / bacterium binds to surface of T helper cell;
2. T helper cell release cytokines / stimulate B cells;
3. (Activated) B cell divides by mitosis;
4. B cells differentiate into plasma cells which release antibodies;
5. (Some) B cells become memory cells;
6. Memory cells produce plasma cells / antibodies faster and at higher concentration;
214
# **Cell recognition and the immune system (AO1)**
What causes antigen variability?
random mutations
215
# **Cell recognition and the immune system (AO1)**
What are the consequences of antigen variability on antibody effectiveness?
Antigen tertiary structure changes shape;
Antibody binding sites / t cell receptors;
No longer complementary to antigen;
216
# **Cell recognition and the immune system (AO1)**
Vaccines may have negative __________ .
side effects
| This is a common limitation of AO3 questions involving vaccines
217
# **Cell recognition and the immune system (AO1)**
New vaccines are typically developed and tested using animal models and cell cultures.
Explain why this is a limitation.
Even though antibodies may be produced, this does not mean it will have the same positive effect in humans.
218
# **Cell recognition and the immune system (AO1)**
What are the advantages of using animals during vaccine/drug research and development?
Stops human suffering through development of useful medicines.
219
# **Cell recognition and the immune system (AO1)**
When testing a new vaccine or drug, a vet closely observes the animals being used. Explain why.
A vet could stop the experiment to minimise any suffering;
The experiment may be repeated at lower concentration to reduce side effects
220
# **Cell recognition and the immune system (AO1)**
Give examples of active immunity
Natural infection with a pathogen;
Vaccine
221
# **Cell recognition and the immune system (AO1)**
Give examples of passive immunity
Maternal antibodies via breast feeding;
Antivenom
(contains antibodies against a specific pathogen)
222
# **Cell recognition and the immune system (AO1)**
Describe the difference between active and passive immunity (5 marks)
**1.** Active involves memory cells **whereas** passive does not;
**2.** Active involves production of antibody by plasma cells / memory cells **whereas** passive does not;
**3.** Passive involves antibody introduced into body from outside / named source (e.g. antivenom from horses);
**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 / work **whereas** passive fast acting.
223
# **Cell recognition and the immune system (AO2)**
When a person is bitten by a venomous snake, the snake injects a toxin into the person. Antivenom is injected as treatment. Antivenom contains antibodies against the snake toxin. This treatment is an example of passive immunity.
Explain how the treatment with antivenom works and why it is essential to use passive immunity, rather than active immunity (*2 marks*).
Antivenom antibodies bind to the toxin/venom/antigen and causes its destruction;
Active immunity would be too slow/slow**er**
OR
‘Passive immunity is fast**er**
224
# **Cell recognition and the immune system (AO2)**
During vaccination, each animal is initially injected with a small volume of venom. Two weeks later, it is injected with a larger volume of venom.
Use your knowledge of the humoral immune response to explain this vaccination programme.
**1.** B cells specific to the venom reproduce by **mitosis**;
**2.** B cells differentiate into plasma cells and memory cells;
**3.** The second dose produces antibodies (in secondary immune response) in **higher** concentration AND **faster**
225
# **Cell recognition and the immune system (AO2)**
**1.** May be different form of antigen/toxin (within one species)
OR Snakes (within one species) may have different mutations / alleles;
**2.** Different antibodies needed in the antivenom
OR Several antibodies complementary to several antigens;
226
# **Cell recognition and the immune system (AO1)**
Define monoclonal antibody
**Same tertiary structure** produced by **identical plasma cells**
227
# **Cell recognition and the immune system (AO1)**
What part of the monoclonal antibody makes it make it specific to a cell?
The antigen binding site
228
# **Cell recognition and the immune system (AO1)**
What can be attached to a monoclonal antibody?
therapeutic drugs (e.g. anti-cancer);
dye/stain/fluorescent marker;
229
# **Cell recognition and the immune system (AO2)**
The protein ZO-1 is found on the surface of ileum cells.
A scientist used an anti-ZO-1 monoclonal antibody to identify ileum cells in a sample of intestine observed using an optical microscope.
Suggest how the monoclonal antibody helped the scientist to identify ileum cells in the sample of intestine (*4 marks*).
**1.** ZO-1 is located in cell surface membrane;
**2.** Antibody is complementary (to ZO-1);
**3.** Binds/attaches to the ZO-1/protein;
Accept ‘forms antigen-antibody complex’
**4.** (Cells identified with) dye/stain/fluorescent marker linked to antibody;
230
# **Cell recognition and the immune system (AO1)**
Give one example of using monoclonal antibodies in a medical treatment.
Targets/binds/carries drug/medicine to specific cells/antigens/receptors
OR
Block antigens/receptors on cells;
Accept 'cancer cells' as a specific cell
231
# **Cell recognition and the immune system (AO1)**
Describe the role of antibodies in producing a positive result in an ELISA test (*4 marks*).
**1.** First antibody binds/complementary (in shape) to antigen;
**2.** Second antibody with enzyme attached is added;
**3.** Second antibody binds to antigen;
**4.** Substrate/solution added and colour changes;
232
# **Cell recognition and the immune system (AO1)**
What is a false positive?
Test is positive but there is NO antigen / pathogen present
233
# **Cell recognition and the immune system (AO1)**
What is a false negative?
Test is negative but there IS antigen / pathogen present
234
# **Cell recognition and the immune system (AO2)**
**1.** Cancer/fused cells divide / replicate rapidly / uncontrollably;
Accept mitosis
**2.** B cells produce monoclonal antibody;
235
# **Cell recognition and the immune system (AO1)**
A = Attachment protein;
B = Capsid
236
# **Cell recognition and the immune system (AO1)**
Describe the structure of the human immunodeficiency virus (HIV) (*4 marks*).
**1.** RNA genome / genetic material;
**2.** Reverse transcriptase;
**3.** Capsid;
**4.** (Phospho)lipid (viral) envelope
**5.** Attachment proteins;
237
# **Cell recognition and the immune system (AO1)**
What is the specific cell that HIV infects?
T helper cell
238
# **Cell recognition and the immune system (AO1)**
What does the HIV attachment protein bind to on the T helper cell?
receptor
| Note: receptors are proteins with a specific tertiary structure
239
# **Cell recognition and the immune system (AO1)**
Describe how HIV is replicated
(*4 marks*)
**1.** Attachment proteins bind to receptors on helper T cell;
**2.** Nucleic acid/RNA enters cell;
**3.** Reverse transcriptase converts RNA to DNA;
(viral DNA inserted into host cell genome)
**4.** Viral protein/capsid/enzymes produced;
**5.** Virus (particles) assembled and released (from cell);
240
# **Cell recognition and the immune system (AO1)**
Describe how the human immunodeficiency virus (HIV) is replicated **once inside** helper T cells (*4 marks*).
**1.** RNA converted into DNA using reverse transcriptase;
**2.** DNA inserted into (helper T cell) DNA/chromosome/genome/nucleus;
**3.** DNA transcribed into (HIV m)RNA;
**4.** (HIV mRNA) translated into (new) HIV/viral proteins (e.g proteins)
**5.** For assembly into viral particles;
241
# **Cell recognition and the immune system (AO1)**
What happens to t helper cells infected with HIV?
Destroyed;
Number of cells decrease;
242
# **Cell recognition and the immune system (AO1)**
What condition develops when T helper cells falls below a critical threshold?
AIDS
| Acquired Immunodeficiency Syndrome
243
# **Cell recognition and the immune system (AO1)**
**TRUE or FALSE:**
A virus with a double-stranded DNA genome requires reverse transcriptase.
FALSE
| **Virsues with a RNA genome (e.g. HIV) require reverse transcriptase**
244
# **Cell recognition and the immune system (AO1)**
How can AIDS be diagnosed?
Lower / decreasing number of T helper cells;
Using ELISAs to measure the concentration of HIV antibodies / antigens;
245
# **Cell recognition and the immune system (AO1)**
Explain how HIV affects the production of antibodies when AIDS develops in a person (*3 marks*).
**1.** Less antibody produced;
**2.** Because HIV destroys / reduces number of helper T cells;
**3.** few/no B cells activated / stimulated
OR
(So) few/no B cells undergo mitosis/differentiate/form plasma cells;
246
# **Cell recognition and the immune system (AO2)**
In Europe, viruses have infected a large number of frogs of different species. The viruses are closely related and all belong to the Ranavirus group.
Previously, the viruses infected only one species of frog.
Suggest and explain how the viruses became able to infect other species of frog (*2 marks*).
**1.** Mutation in the viral DNA/RNA/genome/genetic material;
**2.** Altered tertiary structure of viral attachment protein;
Accept causes antigenic variability
**3.** Allows it/attachment protein/virus to bind to receptors of other species;
247
# **Cell recognition and the immune system (AO1)**
How do antibiotics work?
Preventing bacteria from synthesising murein cell walls;
Directly damaging murein cell wall;
(Some) inhibit binary fission by preventing DNA replication and protein synthesis;
248
# **Cell recognition and the immune system (AO1)**
Give one reason why antibiotics are not effective against viruses.
Do not have a cell wall/murein;
OR
Do not have bacterial structures/enzymes
OR
Do not have metabolic processes
249
# **Cell recognition and the immune system (AO2)**
Collagen is a protein produced by cells in joints, such as the knee.
Rheumatoid arthritis (RA) is an auto-immune disease. In an auto-immune disease, a person’s immune system attacks their own cells. RA causes pain, swelling and stiffness in the joints.
Scientists have found a virus that produces a protein very similar to human collagen.
Suggest how the immune response to this viral protein can result in the development of RA (*2 marks*).
**1.** The antibody against virus (antigen) will bind to collagen;
**2.** This results in the destruction of the (human) cells / collagen;
250
# **Structure of prokaryotic cells and of viruses (AO1)**
Describe one difference between the structure of DNA in a prokaryotic cell and in a eukaryotic cell.
*(In prokaryotes)*
Circular not linear
OR
Not associated with proteins/histones
OR
No introns;
