Unit 2 - Cell Biology Flashcards
(73 cards)
1
Q
Compare and contrast Eukaryotic and Prokaryotic cells.
(7 marks)
A
- Prokaryotic cells are much smaller than eukaryotic cells
- Prokaryotic cells have a cell wall whereas eukaryotic cells do not
- Prokaryotic cells do not have a nucleus whereas eukaryotic cells do
- Prokaryotic cells do not have membrane-bound organelles whereas eukaryotic cells do
- Prokaryotic ribosomes are smaller (70S) than eukaryotic ribosomes (80s)
- Prokaryotic DNA is circular whereas eukaryotic DNA is linear
- Eukaryotic DNA is associated with histones whereas prokaryotic DNA is not
2
Q
Describe the structure and function of the nucleus.
(4 marks)
A
- Double membrane called the nuclear envelope
- Nuclear pores in the membrane so mRNA can leave
- Stores genetic information
- Is the site of transcription
3
Q
Name the main polymers that form;
- Plant cell walls
- Fungal cell walls
- Bacterial cell walls
(3 marks)
A
- Cellulose
- Chitin
- Meurin
4
Q
Describe the role of one named organelle in digesting bacteria.
(3 marks)
A
- Lysosome
- Fuses with the vesicle/phagosome
- Releases lysozymes/hydrolytic enzymes
5
Q
Identify two organelles in cells that enable the production of glycoproteins.
(2 marks)
A
- Rough endoplasmic reticulum/ribosomes
- Golgi apperatus
6
Q
Give four structures that are found in all prokaryotic cells and all eukaryotic cells.
(4 marks)
A
- Cell-surface membrane
- Ribosomes
- Cytoplasm
- DNA
7
Q
Give one feature of the chloroplast that allows proteins to be synthesised inside it and describe one difference between this and the same feature in a eukaryotic cell.
(2 marks)
A
- Ribosomes
- They are smaller than eukaryotic ribosomes
8
Q
Outline the role of organelles in the production, transport and release of proteins in eukaryotic cells.
(6 marks)
A
- DNA in the nucleus codes for the protein
- Ribosomes/RER produce the protein
- Mitochondria produces ATP
- The golgi apparatus modifies the protein and packages it into a vesicle
- The vesicle transports the protein
- The vesicle fuses with the cell-surface membrane so the protein can be released through exocytosis.
8
Q
Name the main biological molecule in the cell membrane.
(1 mark)
A
Phospholipids
9
Q
Describe the role of mitochondria in secreting a protein.
(1 mark)
A
Release of ATP to provide energy for vesicle movement/protein synthesis
10
Q
Describe the role of the golgi apperatus in lipid absorption.
(3 marks)
A
- Modifies triglycerides
- Combines them with proteins to form a chylomicron
- Packages them for release
11
Q
Give three features of all viruses.
(3 marks)
A
- Attachment proteins
- Protein capsid
- Nucleic acid (DNA/RNA)
12
Q
Why are viruses classed as non living?
(3 marks)
A
- Have no metabolic reactions
- Cannot independently replicate
- Have no nutrition
13
Q
Why are viruses classed as acellular?
(3 marks)
A
- No cell-surface membrane
- Not made of cells
- Have no cytoplasm/organelles
14
Q
How do you measure objects using an eyepiece graticule?
(3 marks)
A
- Use the eyepiece graticule to measure the object
- Calibrate the eyepiece graticule against the stage micrometer
- Take a number of measurements and calculate the meane
15
Q
What are the strengths and limitations of a transmission electron microscope?
(6 marks - 2 strengths, 4 limitations)
A
- Small objects (sub-cellular structures) can be seen
- High resolution as electrons have a shorter wavelength than light
- Cannot look at living cells
- Specimen must be very thin
- Preparation may create artefacts
- Does not produce a colour image
16
Q
Compare and contrast TEMs and optical microscopes.
(7 marks)
A
- TEMs use electrons whereas optical microscopes use light
- TEMs have a greater resolving power than optical microscopes
- TEMs can see sub-cellular structures whereas optical microscopes cannot
- Optical microscopes can view living specimens whereas TEMs cannot
- Optical microscopes can view specimen in colour whereas TEMs cannot
- TEMs require thinner specimen than optical microscopes
- TEMs require a much more complex staining process than optical microscopes
17
Q
Why do electron microscopes have a higher resolving power than optical microscopes?
(1 mark)
A
Electrons have a shorter wavelength than light
18
Q
Describe and explain the difference between TEMs and SEMs.
(2 marks)
A
- SEMs can produce a 3D image whereas SEMs can only produce a 2D image
- Because the transmitted electrons bounce off the structure
19
Q
What are the three conditions required for cell homogenisation?
(3 marks)
A
- Cold to reduce enzyme activity so no organelles are digested
- Buffered to maintain pH so that enzymes do not denature
- Isotonic to prevent osmosis so no shrinkage of organelles
20
Q
Describe how you would use homogenisation and ultracentrifugation to obtain mitochondira from a cell sample.
(4 marks)
A
- Grind/homogenise cells to break them open
- Filter to remove large cell debris
- Centrifuge at a slow speed to obtain highest density organelles in pellet
- Increase the speed until the mitochondria settle out into the pellet
21
Q
Suggest why scientists can use detergent to break open cells rather than homogenisation?
(2 marks)
A
- Cell membranes are made from phospholipids
- Detergent dissolves the phospholipid bilayer
22
Q
Describe viral replication.
(5 marks)
A
- Attachment proteins attach to receptors on the host cell
- Virus injects nucleic acid into the host cell
- The host cell replicates the nucleic acid
- The host cell produces viral proteins
- Virus particles reassemble and are released
23
Q
Describe how bacterial cells replicate.
(5 marks)
A
- Binary fission
- Replication of circular DNA
- Replication of plasmids
- Division of cytoplasm to produce daughter cells
- Each with a single copy of circular DNA
24
What is a tumour?
(2 marks)
- Mass of cells
- Formed by uncontrolled cell division
25
Describe the appearance and behaviour of chromosomes during mitosis.
(8 marks)
- In prophase chromosomes condense and become visible
- As two sister chromatids joined at the centromere
- In metaphase chromosomes line up on the equator of the cell
- And are attached to spindle fibres
- By the centromere
- During anaphase the centromere splits
- Sister chromatids are pulled to opposite poles of the cell
- During telophase the chromosomes become longer and thicken
26
Describe and explain the arrangement of genetic material in prophase.
(4 marks)
- Chromosomes are becoming visible
- As they condense
- Chromosomes are not lined up
- Because of no spindle activity
27
Suggest and explain how two environmental variables could be changed to increase the growth rate of cells.
(4 marks)
- Increase oxygen concentration
- Increases the rate of respiration
- Increase temperature
- Increases enzyme activity
28
Suggest and explain why the student soaked the root tips in HCl.
(2 marks)
- To break down links between cell walls
- Allowing the stain to pass into different cells
29
Explain why pressing the coverslip downwards allowed the student to observe the stages of mitosis more clearly.
(2 marks)
- To break down links between cell walls
- Allowing the cells to be squashed more easily
30
Explain why only the first 5mm of the root was used.
(1 mark)
It is where mitosis in plants occurs
31
Describe how you would obtain a reliable mitotic index from tissue observed with an optical microscope.
(3 marks)
- Count cells in field of view that are undergoing mitosis
- Divide this by the total number of cells in the field of view
- Repeat many times in other random areas of the sample
32
Describe and explain what the student should have done to make sure the mitotic index obtained was accurate.
(2 marks)
- Examine a large field of view
- To ensure a representative sample
33
Suggest why a different student may get a different mitotic index using the same methods.
(2 marks)
- Garlic may have been grown in different conditions
- Different species of garlic may have been used
34
Describe how proteins arrange themselves in a membrane.
(2 marks)
- Hydrophobic region towards the outside to sit within the fatty acid tails
- Hydrophilic region towards the inside as ions are charged
35
Describe the role of cholesterol in a membrane.
(1 mark)
To restrict the movement of the molecules that make up the membrane
36
Name and describe five ways substances can move across the cell-surface membrane into a cell.
(5 marks)
- Simple diffusion of small molecules down a concentration gradient
- Facilitated diffusion of molecules down a concentration gradient, using a carrier/channel protein
- Osmosis of water molecules down a water potential gradient
- Active transport against a concentration gradient, using a carrier protein with use of ATP
- Co-transport of at least two substances down an already existing concentration gradient, using a carrier protein
37
Describe how the movement of substances across a cell membrane is affected by membrane structure.
(5 marks)
- Phospholipid bilayer prevents the movement of larger, polar molecules
- Channel/carrier proteins allow facilitated diffusion, active transport and co-transport
- Number of channel/carrier proteins determine how much movement occurs
- Cholesterol affects the fluidity of the membrane
38
What two factors affect the rate of facilitated diffusion?
- External concentration of molecules
- Number of channel/carrier proteins
39
Suggest and explain two ways the cell-surface membrane is adapted to allow the rapid transport of nutrients.
(2 marks)
- Folded membrane for an increased surface area
- Large number of channel/carrier proteins for facilitated diffusion/active transport/co-transport
40
Describe how substances move across cell-surface membranes by facilitated diffusion.
(3 marks)
- Carrier/channel proteins
- That are complementary to the substance
- Substance moves across the membrane down a concentration gradient
41
How does using a respiratory inhibitor prevent active transport?
(4 marks)
- No oxygen for aerobic respiration
- No production of ATP
- The shape of the carrier protein cannot change
- No release of transporting ion/molecule
42
How would you find the water potential of plant tissue practically?
(3 marks)
- Plot a graph with concentration on the x-axis and percentage change in mass on the y-axis
- Find the concentration where the curve crosses the x-axis (% change = 0)
- Use another resource to find the water potential of the sucrose concentration
43
Give one way in which the student could ensure the first three beetroot cylinders were kept at 25°C.
(1 mark)
Measure the temperature in the tube at intervals and use an appropriate corrective measure if temperature does fluctuate
44
How does a high temperature disrupt membranes?
(2 marks)
- By denaturing membrane proteins
- By increasing the fluidity of the membrane
45
How does alcohol disrupt membranes?
(1 mark)
Ethanol dissolves the phospholipid bilayer
46
Explain why it is important to control the volume of water in each test tube.
(1 mark)
If there is too much water the pigment will be dilute and the absorbance would appear lower
47
Explain why a high temperature caused an increase in absorbance.
(2 marks)
- Higher absorbance means more pigment was released
- This means there was more membrane damage/permeability
48
Describe the process of phagocytosis.
(6 marks)
- Phagocyte recognises an antigen as foreign
- It engulfs the pathogen into a vesicle called a phagosome
- A lysosome fuses with the phagosome
- The lysosome releases lysozymes into the phagosome
- Lysozymes digest the pathogen
- Phagocyte displays the pathogen's antigens and becomes an APC
49
Describe how the presentation of an antigen leads to the secretion of an antibody against this antigen.
(5 marks)
- Specific T-helper cell binds to the antigen
- T-helper cell activates a specific B-cell
- The B-cell divides by mitosis to produce many clones
- These clones are either plasma cells or memory cells
- Plasma cells release specific antibodies for the antigen
50
What is an antigen?
(2 marks)
- A foreign protein
- That stimulates an immune response
51
What is an antibody?
(2 marks)
- A protein specific to a particular antigen
- Produced by B-cells
52
How are antibodies specific?
(4 marks)
- Antibodies have a specific tertiary structure
- They have a binding site that only binds to a particular antigen
- The antigen is only present on a particular pathogen
- So the antibody only forms an antigen-antibody complex with these antigens
53
How are antigen-antibody complexes formed?
(4 marks)
- Antibodies have four polypeptide chains so a quaternary structure
- They have a variable region with a specific amino acid sequence
- The shape of the binding site is complementary to the antigen
- So antigen-antibody complexes can form
54
Give two other types of cell (not pathogens) that can stimulate an immune response.
(2 marks)
- Abnormal body cells, e.g tumour cells
- Virally infected cells
55
Describe the structure (/draw a labelled diagram of) an antibody.
(3 marks)
- Y-shape showing two long and two short polypeptide chains
- Binding sites on both ends of each branch of the Y-shape
- Variable reigion/constant reigion labelled
56
Describe and explain the roles of antibodies in stimulating phagocytosis.
(2 marks)
- Bind to antigens and cause agglutination of pathogens
- Attracting phagocytes
57
Compare active and passive immunity.
(4 marks)
- Active immunity produces memory cells whereas passive immunity does not
- Active immunity involves antibody production in the body whereas passive immunity introduces antibodies from outside sources
- Active immunity is long-term whereas passive immunity is short-term because the antibody is broken down
- Active immunity can take time whereas passive immunity produces an immediate response
58
How does a vaccine produce an immune response?
(8 marks)
- Vaccine contains antigens from the pathogen
- Phagocytosis occurs, phagocyte becomes an antigen-presenting cell
- Specific T-cell with a complementary receptor protein binds to the antigen
- T-cell releases chemicals that stimulate a specific B-cell
- That has a complementary antibody on it's surface
- B-cell undergoes mitosis to produce many clones
- Plasma cells are formed that secrete large amounts of the specific antibody
- Memory cells store the antibody in case the person becomes properly infected
59
Explain why giving children more than one vaccination develops good immunity.
(2 marks)
- More memory cells produced
- Rapid production of antibodies in the case of further infection
60
How does determining the genome of viruses allow scientists to develop a vaccine.
(2 marks)
- Identification of proteins that derive from the genetic code
- Identification of potential antigens to be used in the vaccine
61
Describe how a B-lymphocyte would respond to vaccination.
(4 marks)
- B-cell antibody binds to a specific complementary antigen
- B-cell divides by osmosis to produce many clones
- Plasma cells produce antibodies for the virus
- Memory cells are produced
62
Describe HIV treatment with the anti-retroviral drug, AZT.
(6 marks)
- HIV present in patient's DNA
- New HIV particles are made
- AZT inhibits reverse transcriptase
- Replication of HIV is stopped
- Stops further destruction of T-cells
- The immune system continues to work and AIDS does not develop
63
Describe how HIV is replicated.
(5 marks)
- Attachment proteins bind to receptors on T-helper cell
- RNA is injected into the cell
- Reverse transcriptase converts RNA into DNA
- Viral proteins are produced by the T-cell
- HIV particles are assembled and released from the cell
64
Describe how HIV is replicated once inside T-helper cells.
(4 marks)
- RNA is converted into DNA using reverse transcriptase
- DNA is inserted into the T-cell genome
- DNA is transcribed into mRNA
- mRNA is translated into new viral proteins
65
Explain how HIV affects the production of antibodies when AIDS develops in a person.
(3 marks)
- HIV destroys T-helper cells
- So few B-cells are stimulated to produce plasma cells
- Less antibodies are produced
66
Describe the structure of HIV.
(5 marks)
- RNA as genetic material
- Reverse transcriptase
- Protein capsid
- Phospholipid viral envelope
- Attachment proteins
67
What is a monoclonal antibody.
(3 marks)
- Antibody is specific to one antigen only
- Antibodies are all the same and from one original plasma cell
- Derived from a hybridoma cell, a fused mouse B-lymphocyte and tumour cell
68
Suggest how monoclonal antibodies help scientists to identify target cells.
(4 marks)
- Monoclonal antibody has dye attached to it
- Antibody is complimentary to target cell's membrane-bound protein
- So it binds to the protein
- Dye acts as a marker
69
Suggest how one antibody can bind to two different molecules.
(2 marks)
- Molecules have a similar shape
- Antibody is complementary to both molecules
70
Explain why an antibody will only bind to a specific target cell.
(4 marks)
- Antibody has a specific tertiary structure
- It has a binding site that is only complementary to one antigen
- The specific antigen is only found on a particular cell
- So the antibody will only form an antigen-antibody complex with these cells
71
Describe the role of antibodies in producing a positive result in an ELISA test.
(4 marks)
- The first antibody binds to the antigen
- Second antibody (with enzyme attached) is added
- The second antibody attaches to the antigen
- Substrate is added and the colour changes
72
What are the differences between the cellular and humoral immune responses?
(6 marks)
- The cellular response involves primarily T-lymphocytes whereas the humoral response involves B-lymphocytes.
- In the cellular response the antigen is on an APC whereas in the humoral response the antigen is on a pathogen
- In the cellular response antibodies are not directly produced whereas in the humoral response they are
- The cellular response does not directly produce immunity whereas the humoral response produces primary and secondary immunity
- The type of protein on a T-lymphocyte is a receptor whereas the type of protein on a B-lymphocyte is an antibody
- In the cellular response T-lymphocytes are stimulated via binding to the APC whereas in the humoral response B-lymphocytes are stimulated via chemicals produced by T-helper cells
