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Biology > 3.2 Cells > Flashcards

3.2 Cells Flashcards

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1
Q

Explain why organisms with smaller sizes can be seen with a TEM but not with an optical microscope.

A

TEM has higher resolution as it uses a shorter wavelength of electrons, rather than a long wavelength of light

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2
Q

Why is a TEM microscope used to produce an image of a plant cell, including its mitochondria?

A
  • TEM has a higher resolution
  • Electron beam passes through the cell so that the internal structures of the cell can be seen
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3
Q

Describe the principles and limitations of TEM to investigate cell structure.

A
  • Short wavelength of electrons pass through sample, high resolution
  • Sample must be extremely thin to allow electrons to pass through
  • Sample cannot be living as it is carried out in a vacuum
  • Image produced is not in colour or 3D
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4
Q

Describe the structure and function of the nucleus.

A
  • Has nucleolus
  • Has nuclear envelope with pores (important for mRNA and ribsome movement)
  • Contains chromatin (DNA and histones)
  • Site of trancription
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5
Q

What organelle in a eukaryotic cell modifies proteins?

A

The golgi body

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6
Q

What is the function of the smooth ER?

A

Synthesises, stores and transports carbohydrates and lipids

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7
Q

What are the main structures of chloroplasts?

A

Stroma, thylakoid membrane, grana, lipid droplets, starch grain

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8
Q

What are the main structures of mitochondria?

A

Matrix, inner membrane, outer membrane, cristae, inter membrane space

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9
Q

Why do you use an ice-cold, isotonic buffer solution when preparing a solution for centrifuging?

A

Ice-cold = slows down the activity of hydrolytic enzymes

Isotonic = stops osmosis, cells are not damaged (burst, shrivel)

Buffer = control pH, slows down enzyme activity which may destroy organelles

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10
Q

Describe how you would use cell fractionation to isolate chloroplasts from leaf tissue.

A
  • Homogenate leaf tissue in cold, isotonic buffer solution.
  • Filter off any debris
  • Collect 2nd pellet after centrifuging
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11
Q

What organelles require the lowest speed for centrifuge and why?

A
  • Nuclei, mitochondria
  • They are the larger and heavier organelles
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12
Q

What organelles require the highest speed for centrifuge and why?

A
  • Lysosomes, ribosomes, endoplasmic reticulum.
  • Smallest organelles, have a low density
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13
Q

What are the two components once the mixture is centrifuged?

A

Pellet and supernatant

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14
Q

What are the cell walls of the following organisms primarily made up of:
a) bacteria
b) fungi

A

a) Murein
b) Chitin

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15
Q

What is the theory that relates prokaryotic cells to mitochondria and chloroplasts?

A

Endosymbiotic theory

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16
Q

What are the similarities between prokaryotes and mitochondria/chloroplasts?

A

Both:
- Contain 70s ribosomes
- Replicate by binary fission
- Have similar sizes
- Have circular DNA
- Have a double membrane

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17
Q

Describe the structure of a bacterial cell.

A

All:
- No membrane-bound organelles
- 70s ribosomes
- No nucleus, circular DNA instead that is not associated with histones
- Cell wall containing murein

Some have:
- Plasmids
- Capsules
- Flagellum

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18
Q

Describe the structure of a virus.

A
  • Nucleic acid core (RNA/DNA)
  • Protein coat/capsid
  • Attachment proteins (glycoproteins)
  • Phospholipid envelope
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19
Q

Why are viruses classed as acellular and non-living?

A
  • Invade host cell in order to reproduce
  • They contain no cellular structures like cytoplasm or cell membranes
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20
Q

What are the phases of the cell cycle?

A

Interphase, mitosis, cytokinesis

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21
Q

What are the phases of interphase? Describe what happens in each one.

A

G1 - organelles replicate, protein synthesis, cell grows
S - DNA replicates, sister chromatids created
G2 - DNA checked for errors, energy stores grow

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22
Q

What are the phases of mitosis? Describe what happens in each one.

A

Prophase:
- chromosomes condense
- centrioles move to form spindle fibres

Metaphase:
- nucleus disappears
- chromosomes line up along spindle fibres

Anaphase:
- centromere splits
- sister chromatids pulled apart to opposite poles

Telophase:
- chromosomes decondense
- nuclear envelope reforms

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23
Q

Where in plants does mitosis occur?

A

Meristems

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24
Q

Explain how the events in interphase and mitosis leads to the production of genetically identical daughter cells.

A
  • Semi-conservative replication during interphase produces two identical sister chromatids
  • Each chromatid seperated during anaphase and pulled to opposite poles
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25
Q

How many cells does mitosis produce and are they haploid or diploid?

A

Produces 2 genetically identical diploid cells

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26
Q

What two pieces of evidence show that a cell is in the anaphase stage of mitosis?

A
  1. V-shape of chromosomes show that they have been pulled apart at the centromere
  2. Chromosomes are at opposite poles of the spindle fibres
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27
Q

What occurs during cytokinesis in an animal plant? How does this differ in plant cells?

A
  • In animal cells, a cleavage furrow forms and separates the two cells, splitting the cell membrane in two.
  • In plant cells, a cell plate forms and new cell walls form once the cell plate reaches the old cell walls
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28
Q

What happens during binary fission?

A
  • Circular DNA and plasmids replicated
  • Parent cell divides into two new cells, cytoplasm split in two
  • Produces two daughter cells, each with one copy of the circular DNA and with a variable number of plasmids
29
Q

How does a virus replicate?

A
  • Virus attachment proteins bind to complimentary receptor proteins on the surface of a host cell
  • Virus injects DNA/RNA into the host cell
  • Host cell DNA changed and it begins to code for new virus particles
  • Virus particles then released by the cell (budding- leave one by one through membrane)
30
Q

What is cancer?

A

When cells break away from a primary tumour and form a secondary tumour elsewhere. (metastasis)

31
Q

What two types of tumours are there? Describe their differences.

A

Malignant and benign
- Malignant is usually cancerous and benign non-cancerous
- Malignant tumours grow and spread more quickly (rapidly dividing)
- Malignant tumours do more harm, however, benign can still put pressure on adjacent organs and tissues
- Symptoms of malignant tumours are systemic but localised with benign tumours

32
Q

What 4 ways can you treat cancer?

A
  1. Radiotherapy
  2. Chemotherapy
  3. Surgery
  4. Immunotherapy
33
Q

Why would a potato lose mass when placed in a sucrose solution for a period of time?

A
  • Sucrose solution had a lower water potential (hypertonic)
  • Water moves by osmosis from area of high w.p in potato to low w.p in solution
  • Loss of water in potato so smaller mass
34
Q

Describe how you would carry out an experiment to find the water potential of a potato tissue?

A
  • Evenly cut 5 potato cylinders, measure the mass of each one
  • Add each cylinder to a different conc. of sucrose solution for a set time
  • Remeasure the mass after patting each potato dry with paper towels
  • Calculate % change in mass
  • Plot graph:
    x-axis = conc. sucrose solution
    y-axis = % change in mass
  • Draw line of best fit, find where the line crosses 0% change in mass
  • Use an external resource to find the water potential of the potato at this conc. of sucrose solution
35
Q

What happens to a plant cell when it is placed in a hypertonic solution?

A
  • Cells shrink (flaccid) and become plasmolysed, cell membrane pulled away from cell wall
  • Plant wilts and possibly dies
36
Q

Predict what would happen to a sample of cheek cells that are placed into a test tube containing pure water. How does this differ with onion cells?

A
  • Cheek cells would burst, water moves into cell by osmosis from high water potential in test tube to low water potential in cell.
  • Onion cell will become turgid, but not burst as it has a cell wall
37
Q

State two functions of membranes in living cells.

A
  1. Compartmentalisation, separate organelles from one another and the reactions that occur in each
  2. Able to control what molecules leave and enter a cell
38
Q

What lipids are found in the phospholipid bilayer?

A
  • Cholesterol
  • Glycolipid
  • Phospholipid
39
Q

What proteins are found in the phospholipid bilayer?

A
  • Glycoprotein
  • Intrinsic proteins (channel, carrier)
  • Extrinsic proteins
40
Q

What is the purpose of cholesterol in the phospholipid bilayer?

A
  • Regulates fluidity of the membrane
41
Q

What is the purpose of glycoproteins and glycolipids in the phospholipid bilayer?

A

Act as receptor molecules:
- Signalling receptors for hormones/neurotransmitters
- Receptors involved in endocytosis

42
Q

Describe the phospholipid bilayer and how it forms?

A
  • Bilayer of phospholipids
  • Hydrophilic phosphate heads face outwards and hydrophobic fatty acid tails face inwards
43
Q

What is the impact of temperature on the phospholipid bilayer?

A

As temperature increases:
- Cell membrane permeability increases
- Increased movement of phospholipids
- Channel/carrier proteins denature

At very low temperatures:
- Membranes become damaged as ice crystals pierce the cell membrane
- Once the cells thaw, the membranes are highly permeable

44
Q

What can pass through the cell membrane by simple diffusion?

A

Small, non-polar, lipid-soluble molecules

45
Q

Describe how a molecule moves by facilitated diffusion across the cell membrane.

A
  • Molecule diffuses from area of high conc. to low conc. down the conc. gradient
  • Through a carrier/channel protein
46
Q

How does a protein enter a cell by facilitated diffusion?

A
  • Protein binds to receptor on the cell membrane surface
  • Protein travels through carrier/channel protein down conc. gradient
47
Q

What factors affect the rate of diffusion of a molecule across the cell membrane?

A
  • Temperature
  • Surface area
  • Steepness of conc. gradient
  • Property of molecule (size, charge etc)
48
Q

What is active transport and how does it work?

A
  • The movement of molecules against the conc. gradient from an area of low conc. to high conc.
  • Requires energy (provided by ATP) which allows the carrier protein to change shape
49
Q

Why is active transport important in cells? Give examples.

A
  • Absorbing glucose and amino acids from digestion
  • Loading sucrose into phloem sieve cells from companion cells in plants
  • Taking up inorganic ions from soil in root hair cells
50
Q

Describe the co-transport involved in the absorption of glucose.

A
  • Na+ actively transported into blood
  • Lower conc. of Na+ in cells
  • Na+ diffuses into cells by facilitated diffusion, taking with them glucose molecules
  • Glucose enters blood by facilitated diffusion
51
Q

Describe how cell-mediated immunity works.

A
  • Phagocyte/own cell presents antigens (antigen presenting cells)
  • T cell has specific receptors which bind to the antigen
  • This causes the T cell to divide by mitosis, producing T helper cells and cytotoxic T cells
52
Q

Describe how humoral immunity works.

A
  • Antigen taken up, processed and presented by B cell
  • T-helper cell binds to presented antigen and activates B cell, causing it to divide by mitosis.
  • Plasma cells produced which produce and secrete antibodies.
  • Antibodies bind to antigens, pathogen destroyed
  • Memory cells also produced (secondary response)
53
Q

What are the differences between B and T lymphocytes?

A

B:
- Humoral immunity
- Produced in bone marrow
- Respond to pathogens suspended in blood

T:
- Cell-mediated immunity
- Produced in thymus
- Respond to pathogens in own cells

54
Q

Describe the process of phagocytosis.

A
  • Phagocyte attracted to pathogen by chemicals released
  • Phagocyte engulfs pathogen, forming phagosome
  • Lysosome and phagosome fuse,hydrolytic enzymes from lysosome hydrolyse the pathogen
  • Products used or removed, antigens presented on outer membrane
55
Q

What is an antibody?

A

Protein produced by plasma cells which binds to specific foreign antigens

56
Q

What is an antigen?

A

Non- self/foreign protein which triggers an immune response

57
Q

Name the key structures of an antibody?

A

2 binding sites, variable/constant region, disulphide bridges, hinge region

58
Q

What is the benefit of antibodies having 2 binding sites?

A

Agglutination
- Antibody can bind to two pathogens/bacteria at once
- Groups of same pathogen clump together
- Acts like a marker to attract phagocytes to engulf and destroy

59
Q

What are monoclonal antibodies?

A

Antibodies produced by the same genetically identical plasma cell

60
Q

How would you produce monoclonal antibodies?

A
  • Mouse B cells fused with tumour cells using detergent (breaks down cell membrane)
  • Fused cells are tested and cloned
  • Antibodies are collected on large scale and modified for humans (humanisation)
61
Q

What are the ethical issues surrounding monoclonal antibodies?

A

Mice are given tumours (cancer) in order to produce fast dividing cells

62
Q

How are monoclonal antibodies used in an ELISA test?

A
  • Antigens fixed to surface
  • Add specific monoclonal antibodies. Linked to enzyme
  • Surface is washed to remove antibodies not attached to the antigen.
  • Enzyme substrate is added, detectable signal produced
63
Q

What is active and passive immunity?

A

Active = produce the antibodies yourself
Passive = antibodies injected

64
Q

What is herd immunity?

A
  • When a large enough proportion of the population is immune/vaccinated that the chance of spread of the pathogen is very small
65
Q

How does a vaccine work?

A
  • Given dead/inactive pathogen
  • Antigens cause immune response, T cells are activated and T helper cells stimulate B cells to divide by mitosis
  • Plasma cells (antibodies) and memory cells produced
  • Memory cells act as the vaccine and produce many more antibodies in a shorter period of time, this reduces the symptoms
66
Q

For what 3 reasons do vaccines not always work?

A
  • Antigen drift (mutations)
  • Immunosuppressed individuals (malnourished, drugs)
  • Antigenic concealment (hide)
67
Q

What is HIV and AIDS?

A
  • Human Immunodeficiency Virus
  • Acquired immune Deficiency Syndrome
68
Q

How does HIV replicate and how can this lead to AIDS?

A
  • Virus attachment proteins bind to complimentary receptor proteins on the surface of a host cell
  • Virus uses reverse transcriptase enzyme to make DNA from its RNA, which it can then insert into the T-helper cell (host cell).
  • T-helper cell produces HIV particles and releases these, when this happens the host cell is destroyed
  • When HIV particles start infecting more host cells, more T-helper cells are destroyed.
  • Weaker immune system as there are fewer T-helper cells to activate B cells and produce antibodies

Biology (10 decks)

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