Cells - Mark Scheme Based Flashcards
(87 cards)
1
Q
What organelles are involves in protein synthesis and trasnport?
A
- Ribosomes (makes proteins)
- RER (process/transport proteins)
- Golgi apparatus (modifies/sorts)
- Vesicles (transport)
2
Q
What is active transport and how does it differ from diffusion?
A
Moves substances against concentration gradient. Requires ATP. Uses carrier proteins
3
Q
How to calculate the mitotic index
A
(Number of cells in mitiosis / total number of cells) times 100
4
Q
Function of the cells-surface membrane
A
Controls movement of substances into and out of the cells. Contains receptors
5
Q
How does HIV infect human cells?
A
- Attachement protein binds to CD4 receptor on helper T cells
- RNA and enzymes enter
- Reverse transcriptase makes DNA copy
- Integrates into host DNA
6
Q
How do vaccines work?
A
Contain antigens to stimulate the production of memory cells. Allows faster secondary response if infected
7
Q
Maximum resolution of a TEM
A
Around 0.1 nm
8
Q
What is the function of ribosomes?
A
Site of protein synthesis
9
Q
Role of memory cells
A
- Remain in the body after infection
- Respond quickly on reinfection
- Enable faster, stronger secondary response
10
Q
A student sees no bacteria on an agar plate after applying antibiotics. What could they conclude
?
A
The antibiotic killed or inhibited all bacterial growth
11
Q
How do virues replicate
A
Attach to host cell, inject genetic material, hijack host machinery to make viral particles
12
Q
Why are thin sections of tissue used in microscopy?
A
To allow light or electrons to pass through to provide a clear image
13
Q
Define osmosis
A
Net movement of water molecules from high to low water potential through a selectively permeable membrane
14
Q
What is the role of the Rough ER?
A
Processes and transports proteins made by ribosomes
15
Q
Role of the vaculole
A
Contains sap; helps maintain pressure and support in cell
16
Q
What happens during interphase?
A
- DNA replication
- Organelle synthesis
- Cells grows
- Prepares for division
17
Q
Function of lysosomes
A
- Contain digestive enzymes
- Break down worn out organelles or pathogens
18
Q
Describe the function of the golgi apparatus
A
- Modifies and packages proteins
- Forms vesicles for transport or secretion
- Produces lysosomes
19
Q
What is the role of cholesterol in membranes?
A
Maintains membrane fluidity and stabilises membrane by binding to phospholipids
20
Q
What is the function of the nucleus?
A
Contains DNA; controls cells activities; site of transcription
21
Q
Why can’t antibiotics treat viral infections such as as HIV?
A
Viruses use host cells to replicate, antibiotics target bacterial structures not found in viruses
22
Q
What is the fluid mosaic of membrane?
A
Phospholipid bilayer with protein embedded
- fluid = phosphoslipids move
- mosaic = scattered proteins
23
Q
Explain how viruses cause disease
A
They replicate inside host cells, causing cell damage and triggering immune responses
24
Q
Why do cancer treatments target mitosis
A
They inhibit cell division, reducing tumour growth by preventing new cells from forming
25
What is a phagocyte and how does it work?
White blood cell that engulf pathogens, forms phagosome, lysosome fuses and digests pathogen, antigens are displayed on surface
26
Describe whats happens during anaphase
- Centromeres split
- Sister chromatids pulled to opposite poles
27
What is water potential & what affects it?
-Measure of water's ability to move
- Pure water has a water potential of 0
- Solutes lower water potential
28
Structures found in bacterial cells but not eukaryotic
Plasminds, circular DNA, capsule, flagellum
29
What happens during Anaphase?
- Centromeres split
- Sister chromatids are pulled to opposite poles of the cell
- Spindle fibre contracts
30
How does glucose enter a cell?
Facilitated diffusion via carrier proteins or active transport using carrier proteins and ATP
31
Function of the Smooth ER
Synthesises and processes lipids
32
What happens during prophase?
- Chromosomes condense and become visible
- Each chromosome consists of two sister chromatids joined by a centromere
- Nuclear envelope breaks down
- Spindle fibres begin to form from centrioles
33
Structure of cell wall
Made of cellulose; provides strength and prevents lysis
34
Compare prokaryotic and eukaryotic cells
Prokaryotic - No nucleus, smaller ribosomes (70S), circular DNA, no membrane bound organelles
Eukaryotic - nucleus, 80S ribosomes, linear DNA, membrane bound organelles
35
Key features of prokaryotic cells
No nucleus, circular DNA, plasmids, no membrane-bound organelles, smaller ribosomes (70S), cell walls (murein)
36
Why do we strain cells before viewing them under a microscope?
- Increase contrast
- Makes structures like chromosomes visible
37
Define faclilitated diffusion
Passive movement of large or changed molecules through channel or carrier protein
38
How do antibodies destroy pathogens?
Bind to antigens to form an antigen-antibody complex, causing agglutination or promote phagocytosis
39
Difference between active and passive immunity
Active: immune system produces own antibodies
Passive: antibodies given directly
active gives long-term immunity
40
Describe what happens in metaphase
- Chromosomes line up along equator
- Spindle fibres attach to centromeres
41
Explain how vaccines provide immunity
They introduce antigens, stimulating production of memory cells. When reinfection occurs, the response if faster and stronger
42
How does temperature affect membrane permeability?
High temp disrupts membrane. Proteins denature. Increased permeablility.
43
Why do electron microscopes have higher resolution than light microscopes?
Electrons have shorter wavelenghts than light allowing better resolution
44
How is the structure of the Rough ER related to its function?
Its covered with ribosomes which allow it to syntheisise proteins and transport them through its membrane-bound channels
45
What happens during cytokinesis?
- Division of the cytoplasm
- Occurs after telophase, completing cell division
- Results in two genetically identical daughter cells
46
Describe the role of T cells
Bind to antigen-presenting cells. Activate B cells and phagocytes. Cytotoxic T cells kill infected cells
47
Explain why a this section of tissue is needed of a light microscope
To allow light to pass though for a clear image
48
Function of plasmids
Carries genes for antibiotic resistance and can be passed between bateria
49
What happens during ultracentrifugation?
Spinning seperates organelles by mass, heavier organelles pellet first.
nuclei, mitochondria, ribosomes
50
Difference between optical and electron microscopes
Optical: uses light, lower resolution and magnification
Electron: uses electrons, higher resolution and magnification
51
How do antibodies help destroy pathogens?
They bind to antigens to form antigen-antibody complexes, leading to phagocytosis or neutralisation
52
What is the golgi apperatus?
Modifies, sorts and packages proteins and lipids for secretion or use in the cell
53
Describe what happens in telophase
- Chromatids reach poles
- Nuclear envelope reforms
- Chromosomes decondense
54
What happens during Telophase?
- Chromatidds reach opposite poles
- Chromatids decondense into chromatin
- Nuclear envelope reforms around each group of chromosomes
55
Role of B cells
- Recognise specific antigens
- Clone by mitosis
- Differenatiate into plasma cells
- Plasma cells make antibodies
56
Function of cell-suface (plasma) membrane
Regulates movement of substances in and out out of the cells; contains receptor molecules.
57
Function of lysosomes
Contain digestive enzymes to break down waste or damaged organelles
58
Describe what happens in prophase
- Chromosomes condense
- Nuclear envelope breaks down
- Spindle fibres form
59
Describe how a student could prepare a slide to observe mitiosis in a root tip.
Cut root tip, soften with HCL, stain with a DNA-specific dye, squash under coverslip, observe under microscope
60
How do small, non-polar substances move across membranes?
Diffuse directly through the phospholipid bilayer
61
What is the function of mitochondria?
Site of aerobic respiration and ATP production
62
What is co-transport?
Two substances transported together via the same protein
63
Structure of a virus
Genetic material, capsid, attachement proteins
64
How does cell fractionation seperate organelles?
- Homogenisation breaks the cells open
- Filtration removes debris
- Ultracentrifugation spins to seperate organelles by mass
65
Why must cells be in a cold, buffered, isotionic solution before cell fractionation?
Cold: slows enzyme activity
Buffered: maintains pH
Isotionic: prevents osmosis/damage
66
Stages of cell fractionation
Homogenisation, filtration, ultracentrifugation
67
A student sees many cells in interphase. Explain why
Interphase is the longest stage of the cell cycle; most cells are not actively divding
68
What happens during metaphase?
- Chromosomes line up along the equator of the cell
- Spindle fibres attach to the centromeres of chromosomes
69
What is an antigen?
Molecules on the surface of cells that trigger an immune respose
70
What does specific mean in terms of antigen-antibody interaction?
Antibodies have a unique variable region that is complementary in shape to a specific antigen
71
What is the role of phagocytes in the immune response?
- Engulf pathogens
- Enclose them in a phagosome.
- Fuse with lysosme to digest pathogen
- Present antigens on surface
72
What type of immume response involves phagocytes?
Non-specific immune response
73
What are the two main types of lymphocytes involved in the specific immune response?
T-cells & B-cells
74
Role of T-helper cells
Bind to antigens presented by APC's. Release cytokines to activate B-cells and phagocytes
75
What do plasma cells do?
Produce and secrete large quantities of antibodies
76
Difference between the primary and secondary immune response?
Primary: Slower, fewer antibodies
Secondary: faster, more antibodies due memory cells
77
What is active immunity?
Immunity resulting from the activation of the immune system and production of memory cells
78
What is passive immunity?
Immunity from the transfer of antibodies. Provides short-term protection
79
Why might a vaccine not work against some pathogens?
- Antigentic variation
- Antigens on the pathogen change
- Memory cells don't recognise new antigens
80
What is herd immunity?
When enough people are immune, reducing the spread of disease
81
Describe how the body responds to a foreign antigen (6 marks)
- Phagocytosis of pathogen
- Phagocyte presents antigens on its surface
- T-helper cell binds to antigen
- Activates B-cells which divide by mitosis
- B- cells differentiate into plasma cells
- Plasma cells produce specific antibodies
82
Explain how vaccination leads to immunity
- Vaccine contains antigens from the pathogen
- Stimulates an immune response
- B-cells divide to form plasma
- Also produces memory cells
- On reinfection, faster and stronger response with more antibodies
83
What is the role of antigen-presenting cells in the immune response?
- Display antigen from pathogen on their surface
- Allow recognition by T-helper cells
- T-cells bind and become activated
- Activate other immune cells
84
How do antibodies lead to the destruction of pathogens?
- Antibodies bind to specific antigens
- Form antigen-antibody complexes
- Cause agglutination of pathogens
- Makes it easier for phagocytes to engulf them
- Neutralise toxins
85
Explain how antigenic variation in a pathogen can make vaccines less effective
- Pathogen mutates, changes surface antigens
- Memory cells from previous infection/vaccine don't recognise new antigens
- No secondary immune response triggered
- Slower primary response needed again
- Pathogen replicates anhd causes illness
- New vaccine may be required
86
Describe how HIV replicates inside a helper T cell
- HIV binds to CD4 receptor on T-helper cell
- Capsid releases RNA anhd reverse transcriptase into host
- Reverse transcriptase makes DNA copy from RNA
- DNA integrated into host genome
- Host cell makes new viral proteins and RNA, assembles new viruses
87
Describe the difference between active and passive immunity.
Active:
- Immune system produces own antibodies
- Is long term due to memory cells
Passive:
- Antibodies given from other source
- Short term as no memory cells are formed
