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Biology A Level Content > 2.1.1 Cell Structure > Flashcards

2.1.1 Cell Structure Flashcards

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1
Q

What are the pros and cons of a light microscope?

A

Pros:
- Specimens can be alive or dead
- Natural colour
- Portable and easy to use
- Can see living processes

Cons:
- Long wavelength
- Low magnification
- Poor resolution
- 2D

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2
Q

What are the pros and cons of transmission electron microscopes (TEMs)?

A

Pros:
- Electrons instead of light
- Shorter wavelength
- High magnification
- High resolution
- Good detail

Cons:
- 2D
- Specimens must be dead (cut thin, in a vacuum)
- Black and white only
- Expensive

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3
Q

What are the pros and cons of scanning electron microscopes (SEMs)?

A

Pros:
- Electrons instead of light
- High magnification
- High resolution
- Good detail
- 3D

Cons:
- Specimens must be dead
- Black and white only
- Expensive

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4
Q

What is the difference between TEMs and SEMs?

A

TEMs - electrons pass through the specimen
SEMs - electrons bounce of the surface of the specimen

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5
Q

What are the pros of laser scanning confocal microscopes?

A
  • Laser light used
  • High resolution
  • 3D
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6
Q

What are the resolutions and magnifications of light microscopes, SEMs and TEMs?

A

Light - x1500, 200nm
SEM - x100,000, 0.2nm
TEM - x500,000, 0.02nm

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7
Q

What are dry mounts?

A
  • Thin slices or whole specimens
  • Just coverslip placed on top
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8
Q

What are wet mounts?

A
  • Water is added to specimen before lowering coverslip
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9
Q

What are squash slides?

A
  • Wet mounts which have had the coverslip pushed down to squash sample
  • Thin layer to enable light to pass through
    E.g. root tip
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10
Q

What are smear slides?

A
  • Edge of another slide smears sample across the slide
  • Creates a thin, smooth, evenly coated specimen
  • Coverslip placed on top
    E.g. blood cells
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11
Q

What is the process of preparing a specimen?

A
  1. Fixing
  2. Sectioning
  3. Staining
  4. Mounting
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12
Q

What is the eyepiece graticule?

A
  • A scaled used to measure the size of objects you are viewing under a microscope
  • When the objective lens and magnification is changed, the eyepiece must be calibrated
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13
Q

How do you calibrate an eyepiece graticule?

A
  1. Line up the stage micrometer and the eyepiece graticule whilst looking through the eyepiece
  2. Count how many divisions on the eyepiece graticule fit into one division on the micrometer scale
  3. Divide the micrometer number by the number of eyepiece graticule divisions
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14
Q

Why is staining used?

A
  • To increase contrast so cells become visible and distinguishable
  • Living cells are normally colourless and transparent so they have a low magnification and resolution
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15
Q

What is an example of a stain?

A

Methylene blue - all purpose, positively charged

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16
Q

What is differential staining?

A

A technique which involves many chemical stains being used to stain different parts of a cell different colours

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17
Q

What is gram staining and how does it work?

A
  • A type of differential staining using crystal violet and safranin
  • Crystal violet is added and gram positive bacteria appear blue/purple as thicker peptidoglycan cell wall retains the stain
  • Gram negative bacteria don’t absorb it as they have a thinner peptidoglycan cell wall so safranin is used as a counter stain turning them red
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18
Q

What are the rules of biological drawings?

A
  • Draw in a sharp pencil
  • Title the diagram
  • State the magnification
  • No shading
  • Smooth, continuous lines
  • Annotate cell components, cells and sections of tissue visible
  • white and unlined paper
  • Labels should be parallel to top of page with a ruler
  • Labels shouldn’t cross and have no arrowheads
  • Proportions must be correct
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19
Q

What are the two magnification formulae?

A

Magnification = size of image/size of real object

Magnification = eyepiece magnification x objective magnification

20
Q

What is magnification?

A

Measure of how many times larger the image is compared to the object

21
Q

What is resolution?

A

Minimum distance between two objects in which they can still be viewed as separate (determined by wavelength)

22
Q

What are eukaryotic cells?

A

Cells that contain membrane bound organelles

23
Q

What is the nucleus?

A
  • Site of DNA replication and transcription
  • Contains genetic code for each cell
  • Surrounded by a nuclear envelope (double membrane)
  • Outer membrane is continuous with the RER
  • Pores allow mRNA and ribosomes out and nutrients and hormones in
  • Chromosomes are in a loosely coiled state (chromatin) when cell is not dividing
  • The nucleolus is the site of ribosome synthesis
24
Q

What is the rough endoplasmic reticulum?

A
  • Intracellular transport system made up of extensive membranes present within cytoplasm
  • Studded with ribosomes
  • Large SA for ribsomes
  • Ribosomes make proteins which are then transported within the ER’s cisternae
25
Q

What is the smooth endoplasmic reticulum?

A
  • Contains enzymes involved with lipid metabolism (synthesis of lipids/phospholipids and synthesis of cholesterol)
  • Storage site for calcium in skeletal muscle cells
  • Involved with absorption, synthesis and transport of lipids from the gut
26
Q

What is the golgi apparatus?

A
  • A series of tightly packed, membrane-bound, flattened sacs (cisternae)
  • Collects and processes proteins
  • Adding sugar makes glycoproteins and adding lipids makes lipoproteins
  • Made from vesicles budded (from ER) which fuse at forming face
  • Vesicles bud off from maturing face to go to surface membrane for secretion or to be stored in the cell
27
Q

What is the plasma membrane?

A
  • Has a triliminar appearance
  • Selectively permeable
  • Controls entry and exit of materials
  • Made of phospholipid bilayer
28
Q

What is the vacuole?

A
  • Large fluid filled sac
  • Surrounded by a membrane called the tonoplast
  • Only plant cells have a permanent vacuole
  • Filled with water and solutes
  • Provides support by creating a pressure potential through osmosis
  • Pressure means cells become turgid
29
Q

What are the mitochondria?

A
  • Rod like structures with a double membrane
  • The inner membrane is highly folded to form cristae which project into the matrix
  • Completes the later stages of aerobic respiration and synthesizes ATP
  • Self replicating and abundant in metabolically active cells
  • DNA loop codes for enzymes needed for respiration
30
Q

What is the chloroplast?

A
  • Organelle only found in plant cells
  • Surrounded by a double membrane
  • Inner membrane is continuous with thylakoids which run through stroma
  • Thylakoids are stacked (grana)
  • Site of photosynthesis
  • Grana trap light energy used to fix carbon dioxide in the stroma
  • Stroma contain enzymes for photosynthesis
31
Q

What are the ribosomes?

A
  • Made of protein and rRNA
  • Site of protein synthesis
  • Two sizes (70s is smaller ribosome found in prokaryotes and 80s is a large ribosome found in eukaryotes)
  • Attached to RER or free in the cytoplasm
32
Q

What are the lysosomes?

A
  • Contain powerful hydrolytic enzymes for hydrolysis
  • Single membrane
  • Enzymes are kept separate from rest of the cell
  • Role is to destroy damaged cells and organelles
  • Present in white blood cells and acrosome of sperm head in large numbers
33
Q

What are the cilia?

A
  • Membranous cellular extensions
  • Move in a wave like manner
  • Contain microtubules and are formed from centrioles
34
Q

What is the centriole?

A
  • Two bundles of microtubules at 90 degrees to each other
  • Present just outside the nucleus
  • Triplets of microtubules form a ring
  • Microtubules are made from tubulin
  • Produce spindle fibres which attach to centromere of chromosome in cell division
  • Involved in the formation of cilia
35
Q

What is the cell wall?

A
  • High tensile strength to prevent the cell from bursting when turgid
  • Maintains cell shape
  • Contributes to structural strength and support of plant
  • Freely permeable
  • Cellulose in plants
  • Chitin in fungi
  • Peptidoglycan in prokaryotes
36
Q

What is the flagella?

A
  • A whip like structure
  • Aids mobility
37
Q

How do the organelles produce and secrete proteins?

A
  1. Nucleus contains DNA for protein synthesis
  2. DNA copied into mRNA which leaves nucleus
  3. Proteins are made by the ribosomes of the RER
  4. Transport vesicles bud off from the RER and travel to the forming face of the golgi body
  5. Material is modified/processed
  6. Vesicles bud off from the maturing face of the golgi body
  7. Vesicle either transport material within cell to form cellular structures or fuse with the cell membrane to export contents in exocytosis
38
Q

What is the importance of the cytoskeleton?

A
  • Network of protein structures (microfilaments, intermediate filaments and microtubules) in the cytoplasm
  • Provides cellular support
  • Involved in movement and cell division
39
Q

What are the microtubules?

A
  • The largest cytoskeleton fibres
  • Made of tubulin
  • Can grow or shrink by adding dimers
  • Form the track along which motor proteins walk and drag organelles
  • Form the spindle before a cell divides, which enable the chromosomes to be moved
  • Make up the cilia, undulipodia and centrioles
40
Q

What are the microfilaments?

A
  • Made of actin
  • Give support and mechanical strength
  • Keep cell’s shape stable
  • Allow cell movement
41
Q

What are the intermediate filaments?

A
  • Prevent collisions
  • Maintain position of organelles in cytoplasm
  • Anchor the nucleus within the cytoplasm
  • Extend between cells for cell signalling
42
Q

What are the motor proteins?

A
  • Myosins, kinesins and dynesins
  • Drag substances around the cell along the microtubules
43
Q

What are prokaryotic cells?

A

Cells that have no membrane bound organelles

44
Q

What structures are always present in a prokaryotic cell?

A
  • Cytoplasm
  • Plasma membrane
  • Cell wall
  • Circular loop of DNA
  • Ribosomes
45
Q

How is a prokaryotic cell different to a eukaryotic cell?

A
  • Cells are smaller
  • DNA is not contained with a nucleus
  • Smaller ribosomes
  • Capsule prevents bacteria from desiccating and protects bacteria from hosts immune system

Biology A Level Content (6 decks)

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