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Biology Paper 1 > 3.2.1 Cell structure > Flashcards

3.2.1 Cell structure Flashcards

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1
Q

Define magnification

A

how many times larger the image is compared to the object

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2
Q

Define resolution

A

minimum distance between two points on the sample in which they can still be viewed as separate

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3
Q

What is the formula for magnification ?

A

magnification = image size / object size

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4
Q

How can you calculate magnification of cell ?

A

measured length of scale / given length of scale
- must be in the same units

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5
Q

How can you convert between mm, micrometres and nm ?

A

Big to small = multiply by 1000
Small to big = divide by 100

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6
Q

What is an eyepiece graticule ?

A

a glass disc on the eyepiece with an etched on scale
-this can be used to measure the size of objects under the microscope
-Must be calibrated for each objective lens
- No fixed units

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7
Q

What is the stage micrometer ?

A

glass disc on the microscope slide which has fixed units and is used to callibrate the eyepiece graticule
- Divided into 100 equal units of 10 micrometres (Fixed units)

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8
Q

How can the stage micrometer be used to callibrate the eyepiece graticule ?

A
  1. Line up the stage micrometer and graticule
  2. Count the** number of divisions **on the graticule which fit into one micrometer division
  3. Find the **ratio **(eg 20 graticule divisions fit into 10 micrometer divisions) - 2:1 ratio
  4. Calculate the** size of one division** on the graticule at the current magnification
    (micrometer division / graticule divisions)
  5. Measure the object size ( Divisions x size of one division)
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9
Q

How does a light microscope work?

A

a beam of light is condensed to form an image

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10
Q

Give the advantages and limitations of a light (optical microscope)

A

Advantages:
- Colour images
- living samples
- simple preparation (less change of artefacts)
Limitations:
- Maximum resolution of 0.2 micrometres (cannot see ribosomes or lysosomes)
- Maximum magnification of x1500

Poorer resolution as light has a longer wavelength

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11
Q

How does a transmission electron microscope work?

A

electrons are fired from an electron gun and pass through a thin section of the specimen
- Electron beam is focused using an electromagnet
- Denser parts absorb more electrons so appear more dark
- Image produced is 2D and shows the internal cell structure

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12
Q

Give the advantages and limitations of a transmission electron microscope

A

Advantages:
- Higher resolution and magnification than light microscope
- Shows internal structure
Limitations:
- Thin samples needed
- In a vacuum so specimens must be dead
- Complex staining process could cause artefacts
- Black and white
- 2D image

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13
Q

How does a scanning electron microscope work?

A

Beam of electrons focused onto the** specimen surface,** these are scattered and detected to form an image
- Image is 3D and shows the cell surface

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14
Q

Give the advantages and limitations of a scanning electron microscope

A

Advantages:
-Can use thicker specimens
-Shows a 3D structure
Limitations:
-Lower resolution than TEM
-Does not show internal structures
-Black and white image
-Dead specimen

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15
Q

Define cell fractionation

A

cell is broken up so that organelles are released for separation, so structure and function can be studied

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16
Q

What are the three aspects the solution must have before fractionation ?

A
  1. Cold - reduces enzyme activity so they do not digest the released organelles
  2. Isotonic - same water potential, prevents osmosis which prevents organelles shrinking or bursting due to osmotic pressues
  3. Buffered - maintains a constant pH to stop enzymes/proteins denaturing
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17
Q

What is the first stage of cell fractionation ?

A

Homogenisation
- Cells are broken open in a blender (in the prepared solution)
- Breaks the plasma membrane and releases organelles

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18
Q

What is the second stage of cell fractionation ?

A

Filtration
- Solution is filtered to remove large debris, leaving a homogenate

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19
Q

What is the third stage of cell fractionisation ?

A

Ultracentrifugation (organelles separate based on density)
* Spun in a centrifuge at a high speed
* Heavy organelles form a thick sediment at the bottom (pellet)
* Supernatent forms
* Differential centrifugation - process is repeated at increasing speeds, removing the supernatent each time until all the organelles are separated out

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20
Q

Give the order of organelles based on density

A

Least dense (last to separate)
* ribosomes
* endoplasmic reticulum
* lysomes
* mitochondria
* nuclei
Most dense (first to separate)

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21
Q

What is an artefact ?

A

dust, air bubbles which occur during preparation and can impact the image seen
- To overcome this scientists need to prepare specimens in a different way

22
Q

Define eukaryotic cell

A

a complex cell with a membrane bound nucleus and chromosomes

Eg. animal, plant, fungi

23
Q

Give the structure of the cell surface membrane

A
  • surrounds the cell
  • formed from a phospholipid bi-layer
  • partially permeable
24
Q

Give the function of the cell surface membrane

A
  • regulates movement of substances in and out of the cell
  • has receptor molecules which allow it to respond to chemicals (hormones)
25
Q

Give the structure and function of the nucleus

A

Function - holds the cells genetic material
* * Nucleolus - site of RNA and ribosome production, site of DNA replication and transcription
* Nuclear pore - allows** MRNA and ribosomes to exit** and allow enzymes to travel in
* Nuclear envelope - double membrane with many pores
* Contains chromosomes (make of chromatin), sections of linear DNA tightly wound around proteins called histones

Visible with a light microscope

26
Q

Give the structure and function of mitochondria

A

Function - site of aerobic respiration and ATP production
* Cristae (folded inner membrane) - large surface area for attachment of enzymes and other proteins
* Matrix (fluid centre) - contains enzymes needed for aerobic respiration (ATP)
* Circular mitochondrial DNA - needed for replication

Just visible with a light microscope

27
Q

Give the structure and function of the chloroplasts

A

Function - site of photosynthesis
* Grana - stacks of thylakoids which contain chlorophyll (light dependent stage occurs)
* Lamellae - link the grana
* Stroma (fluid filled matrix) - contains enzymes for the **synthesis of sugars **which occurs here (Light independent stage)

visible with a light microscope

28
Q

Give the structure and function of the golgi apparatus and golgi vesicles

A

Main function - processes and packages new lipids and proteins
* folded and flattered sacs of memrane
* produces secretory enzymes
* secretes carbohydrates
* transports and stores lipids
* forms lysosomes
VESICLES - STORE the lipids and proteins before transporting them out of the cell (they are brought to the cell surface and fuse with the memrane before release)

visible with a light microscope

29
Q

Give the structure and function of the lysosomes

A

Function - break down pathogens and waste materials
* produced by the golgi apparatus (separated from the cell by a membrane
* contain digestive enzymes (lysozymes - hydrolytic enzymes)
* Lysozymes digest….
- pathogens
- worn out organelles (for reuse of materials)
- the cell after it dies

Not visible with a light microscope

30
Q

Give the structure and function of ribosomes

A

Function -** site of protein synthesis**
* float freely in the** cytoplasm **or are attached to the rough endoplasmic reticulum
* Make of rRNA and proteins
* Small and large subunits
* Two types
- 80s = eukaryotic cells
- 70s = prokaryotic cells

31
Q

Give the structure and function of the rough endoplasmic reticulum

A

Function -** folds and processes proteins**
* folded fluid-filled membranes called cisternae
* surface is covered in ribosomes - so protein synthesis occurs here

32
Q

Give the structure and function of the smooth endoplasmic reticulum

A

Function - **synthesises and stores lipids (phospholipids and cholesterol) and carbohydrates **
* No ribosomes

33
Q

Give the structure and function of the cell wall (in plants)

A

Function - structural support
* outside of the cell membrane
* made of cellulose microfibrils, plasmodesmata connect cytoplasm to neighbouring cells
* Support..
- mechanical strength to prevent the cell bursting under osmotic pressure (turgidity regulates the amount and rate at which water can enter)
- **gives rigidity **to the plant as a whole

34
Q

Give the structure and function of the permanent vacuole

A

surrounded by the tonoplast which is a selectively permeable membrane
* makes cells turgid (which prevents wilting)
* temporary store of sugars and amino acids
* pigments can attract pollinators

35
Q

Define cell diferentiation

A

process by which a cell becomes specialised to carry out a specific function

36
Q

Define cell

Give some examples

A

a membrane bound structure containing biomolecules such as nucleic acids, proteins and polysaccharides

sperm, goblet, neurone, muscle

37
Q

Define tissue

Give some examples

A

a group of SIMILAR specialised cells working together to perform a SPECIFIC function

epithelium, xylem, capilliary, nerves, elastic fibres, aorta, palispide mesophyll

38
Q

Define organ

Give some examples

A

a combination of DIFFERENT tissues working together to carry out a VARIETY of functions
-Different organs form an ORGAN SYSTEM

lungs, heart, artery, stomach, vein, brain, trachea, bronchiole, kidney, spinal chord

39
Q

Why are arteries and veins organs while capilliaries are tissues ?

A

capillaries are only made of epithelium whereas arteries and veins are made of epithelial AND muscle tissue so are organs

40
Q

Give the levels of organisation in the digestive system

A
  • Organs - Stomach, intestines, liver, pancreas
  • Stomach - Made of epithelial , muscular and glandular tissues etc
  • Epithelial tissue - made of epithelial cells
41
Q

Define prokaryotic cells

A

much smaller than eukaryotic cells and have…
* no nucleus
* no membrane-bound organelles

42
Q

How do prokaryotic cells differ from eukaryotic cells ?

A
  • smaller
  • no nucleus
  • no membrane-bound organelles
  • smaller ribosomes (70s)
  • cell wall made of murein
    MAY also contain (often in bacteria)
  • plasmids
  • slime capsule
  • flagella
43
Q

Give the structure and function of plasmids

A

Structure - small loops of DNA
Function - contain genetic material and can be passed between prokaryotes, genes are often ones which may aid survival (eg antibiotic resistance)

44
Q

Give the structure and function of the slime capsule

A

Structure - extra layer on the cell wall
Function:
* protects bacteria from attack (groups of bacteria can stick together which covers the antigens)
* stops cell drying out

45
Q

Give the structure and function of the flagellum

A

Structure - long tail
Function - rotates to enable cell movement

46
Q

Give the structure and function of the cell wall (prokaryotic)

A

Structure - made of murein
Function - supports cell and stops it bursting under osmotic pressure

47
Q

Give the function of pili

A

allow the bacterial cell to attach to specific surfaces on other cells

48
Q

What are the three main factors which define viruses ?

A
  1. Acellular and non-living
  2. Smaller than bacteria
  3. Invade and reproduce inside living cells

They are essentially just nucleic acids surrounded by protein

49
Q

Function of the nucleic acid core in viruses

A

asexual reproduction
(genomes are either DNA or RNA and can be single or double stranded)

50
Q

Function of the capsid in viruses

A

protein coat which contains two single strands of DNA and some enzymes

51
Q

Function of the attachment protein in viruses

A

allow the virus to identify and attach to host cells
* they bind to the complementary receptor proteins, which are specific so viruses can only infect one type of cell

Biology Paper 1 (15 decks)

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