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OCR Biology A Level > 2.1.1 Cell Structure > Flashcards

2.1.1 Cell Structure Flashcards

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1
Q

State differences between eukaryotic and prokaryotic cells

A
  • Prokaryotes don’t have a nucleus, eukaryotes do
  • Prokaryotes are bacteria, eukaryotes are animal and plant cells
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2
Q

Describe a virus

A
  • non-cellular
  • contains no cytoplasm or organelles
  • no chromosome, just DNA and RNA strands
  • enclosed in a protein coat
  • depends on cells for metabolism and reproduction
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3
Q

Name organelles of an animal cell

A
  • mitochondria
  • plasma membrane
  • centrioles
  • Golgi apparatus
  • nucleus
  • lysosome
  • rough er
  • smooth er
  • ribosome
  • cell surface membrane
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4
Q

Describe the structure and function of a nucleus

A

Structure
Nuclear envelope:
- outer membrane
- inner membrane
- pores in nuclear envelope

  • nucleoplasm (made from chromatin)
  • nucleolus (dark region of chromatin)
  • largest organelle

Function
- stores genetic information in DNA
- DNA replication occurs in the nucleus

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5
Q

Describe the structure and function of a ribosome

A

Structure
- very small
- mostly found on ER (makes it rough)
- made of RNA
- no membrane
- made from two subunits
- 70s (smaller) in prokaryotic cells
- 80s in eukaryotic cells

Function
- carries out protein synthesis

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6
Q

Describe the structure and function of the rough endoplasmic reticulum

A

Structure
- covered in ribosomes
- forms cisternae (flattened sacs)
- membrane made from phospholipid bilayer
- membranes are continuous with nuclear envelope

Function
- transports protein around the cell and the Golgi body
- holds ribosomes responsible for protein synthesis

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7
Q

Describe the structure and function of the smooth endoplasmic reticulum

A

Structure
- forms cisternae (flattened sacs)
- membrane made from phospholipid bilayer

function
- site of production and transport of lipids/steroids

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8
Q

Describe the structure and function of the Golgi body/apparatus

A

Structure
- flatterned membrane-bound sacs

Function
- receives proteins from ribosomes
- proteins and lipids then become modified to produce glycoproteins and glycolipids (carbohydrate is added) then packaged into vesicles
- vesicles transport glycoproteins and glycolipids to the cell membrane, to be secreted by exocytosis
- also produces lysosomes, which contain lytic enzymes which breakdown bacteria and worn out organelles

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9
Q

Describe the structure and function of the mitochondria

A

Structure
- outer + inner membrane
- matrix, where DNA is found (space inside)
- inner membrane is folded to form cristae
- sausage shaped

function
- site of aerobic respiration
- ATP is formed here
- have circular DNA and 70s ribosomes (suggest they could have evolved from bacteria)

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10
Q

Describe the structure and function of the cytoskeleton

A

Structure
- microfilaments of actin
- microtubules made of tublin

Function
- micro filaments move against each other allowing cellular movement
- provides strength
- stabilises, supports, strengthens the cell
- holds organelles in place
- transport within the cell
- make up the spindle fibres and centrioles used in cell devision
- used to move flagella and cilia

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11
Q

Describe and explain vesicle and lysosome transport

A
  • cytoskeleton (microtubules) provide a pathway
  • 2 motor types- dynein + kinesin, which use ATP
  • microtubules can be extended and broken down
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12
Q

Suggest processes that rely on the cytoskeleton for movement

A
  • movement of chromosomes in cell division
  • movement of cytoplasm in cytokinesis
  • movement of organelles
  • movement of RNA in protein synthesis
  • movement of proteins
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13
Q

Describe the structure and function of centrioles

A

Structure
- small tubes of protein fibres
- found near the nucleus in animal cells
- not found in plant cells

Function
- form spindle fibres for cell division
- move chromosomes during nuclear division

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14
Q

Describe the structure and function of flagella and cilia

A

Structure
- nine microtubules arranged in a circle with two at the centre

Function
- movement caused by ATP
- required mitochondria and cytoskeleton to function
- used by sperm cells and ciliated epithelial cells

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15
Q

Describe the structure and function of micro villi

A

Structure
- folds in the plasma membrane of animals cells

Function
- increases surface area for a faster rate of diffusion

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16
Q

Name the organelles of a plant cell

A
  • cell wall
  • cell surface membrane
  • large permanent vacuole
  • nucleus
  • chloroplasts
  • mitochondria
  • cytoplasm
  • lysosome
  • rough er
  • smooth er
  • ribosomes
  • Golgi body
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17
Q

Describe and explain the components of a chloroplast

A
  • outer and inner membrane
  • oil droplets contacting lipids used for making/ repairing membranes (as they are made from phospholipids)
  • grana made from stacks of disks called thylakoids
  • thylakoids contain the pigment chlorophyll
  • intergranal lamellae are membranes that link the grana together
  • the Stroma is fill with fluid + starch grains
  • contains 70s ribosomes and circular DNA (suggests they evolved from bacteria)
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18
Q

Name 3 important adaptations of chloroplasts

A
  • grana have a large surface area for attachment of lots of chlorophyll molecules
  • chloroplasts have DNA and ribosomes to quickly create protein when needed
  • chloroplasts have oil droplets for making more phospholioid membranes
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19
Q

Describe the structure and function of the cell wall in plant cells

A
  • made from cellulose (a polysaccharide) which is permeable
  • provides strength to the cell, as it has a high tensile strength to stop the cell bursting when water enters
  • makes the cell rigid, which prevents wilting
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20
Q

Describe the structure and function of the cell vacuole

A

Structure
- Membrane bound (tonoplast)
- contains cell sap (weak solution of sugar + salts)

Function
- helps maintain pressure inside cell and keep it rigid
- stop the plant wilting
- can isolate unwanted chemicals

21
Q

Name the parts of the cell protein manufacture requires

A
  • DNA and RNA molecules
  • rough endoplasmic reticulum
  • ribosomes
  • vesicles
  • Golgi body
22
Q

Explain the production of extracellular proteins

A
  1. Genes in nucleus are copied into mRNA (transcription)
  2. mRNA joins with rough ER and ribosome for translation/protein synthesis
  3. A protein is built in the ribosome
  4. Protein is put into a transport vesicle to be transported to the Golgi body
  5. Golgi body process, modifies and packages protein (e.g. makes a glycoprotein)
  6. Golgi body packages protein into a secretory vesicle which moves and fuses to the cell membrane, then released by exocytosis (using ATP)
  7. Golgi body also makes lysosomes which digest worn out organelles
23
Q

Give examples of extracellular proteins which are excreted (4)

A
  • enzymes - amylase/lipase/protease
  • protein hormones - insulin/ADH
  • glycoproteins for cell membrane
  • antibodies
24
Q

Describe the structure of DNA in eukaryotic and prokaryotic cells

A
  • eukaryotic DNA is linear as chromosomes
  • eukaryotic DNA has proteins called histones which organise it into chromosomes
  • prokaryotic DNA is circular
  • prokaryotic DNA has no histones so does not form chromosomes
25
Q

List similarities of eukaryotic and prokaryotic cells

A
  • plasma membrane which controls substances entering and exiting the cell
  • cytoplasm where most of the metabolic reactions occur
  • ribosomes for protein synthesis
  • DNA containing coded information for protein production
26
Q

List differences of prokaryotic and eukaryotic cells

A
  • Eukaryotic: larger cells (20-100um)
  • Prokaryotic: extremely small (less than 0.5 - 5um)
  • Eukaryotic: has membrane bound organelles
  • Prokaryotic: no membrane bound orangelles
  • Eukaryotic: nucleus containing DNA
  • Prokaryotic: no nucleus- DNA free in cytoplasm
  • Eukaryotic: DNA is linear as chromosomes - wound around histone proteins
  • Prokaryotic: DNA is circular and not wound around histone proteins
  • Eukaryotic: small 70s ribosomes (18nm)
  • Prokaryotic: large 80s ribosomes (22nm)
  • Eukaryotic: cellulose cell wall in plant cells, chitin fungal cell wall, no cell wall in animal cells
  • Prokaryotic: peptidiglycan cell wall
27
Q

Explain the makeup of cells, tissues, organs and systems

A
  • cells make up all living things
  • a tissue is a collection of similar cells that are specialised to work together to a particular function
  • an organ is a collection of different tissues working together to perform a common function
  • a system is a group of organs working together to perform a particular function
28
Q

What are the two lenses found in a compound light microscope, and how do they work?

A
  1. Objective lens - placed near the specimen
  2. Eyepiece (ocular) lens - lens through which the specimen is viewed
    Objective lens produces a magnified image, which is magnified again by the eyepiece lens
29
Q

What are dry and wet mounts?

A
  1. Dry mount - solid specimen either cut thin or whole with a cover slip on top
  2. Wet mount - specimens suspended in water or oil (with refractive index same as glass), cover slip placed at angle to prevent bubbles
30
Q

What are squash and smear slides?

A
  1. Squash slide - wet mount but using a lens tissue apply pressure to the cover slip to squash specimen
  2. Smear slide - edge of slide used to smear a specimen then a cover slip is added
31
Q

List important things to do when preparing an onion cell slide

A
  • use forcepts to obtain thin layer + place on slide
  • use pipette to place 2 stopds on stain on edge of sample
  • lower cover slip at angle using a mounted needle
  • use blotting paper to remove excess stain
32
Q

What rules must be followed when drawing a scientific drawing?

A
  • use a piece of plain paper
  • use a sharp pencil
  • use at leasat 50% of space
  • use correct proportions
  • continous lines
  • NO shading
  • use ruled label lines
  • labels outside diagram
  • lables don’t cross
  • include a title + magnification
33
Q

Why is staining used on samples?

A
  • makes cells/organelles visible by increasing contrast
  • allows recognition of different cell types + different organelles
34
Q

What is the difference between gram negative and gram positive bacteria?

A

Gram negative: Not killed by penicillin as the less vital peptidoglycan cell wall is thinner and covered by a lipopolysaccharide layer
Gram positive: Killed by penicillin as it works by reaking down the vital peptidoglycan cell wall

35
Q

When is a differential stain - gram stain used?

A

To determine whether bacteria are gram negative or gram positive

36
Q

What is the procedure of gram staining?

A
  1. Crystal violet stain applied
  2. Alcohol decolorization - alcohol is used to wash away the stain from gram negative cells, leaving them colorless. Gram-positive cells retain the stain due to their thicker peptidoglycan layer.
  3. Counterstaining - counterstain is applied to the smear, staining the decolorized Gram-negative cells pink while maintaining the purple color of the gram positive cells
  4. Observation - the slide is observed under a microscope to determine the gram reaction of the bacteria
37
Q

What colour does each bacteria stain and why?

A

Gram positive: Purple, as the alcohol doesn’t remove crystal violet because of the thick peptidoglycan wall
Gram negative: Pink, as the alcohol washes out the crystal violet due to the thin peptidoglycan cell wall covered by the lipopolysaccharide cell wall - pink counter-stain bindso the cell wall

38
Q

What is leishman’s stain used for?

A
  • provides contrast between the cytoplasm and the nucleus
  • allows the shape of the nucleus to be seen
  • allows different white blood cells with different shaped nuclei to be seen
  • red blooc cells not affected as have no nucleus for stain to bind to
39
Q

Define fixing, sectioning, staining and mounting

A

Fixing: Chemicals like formaldehyde are used to preserve specimens in as near-natural state as possible
Sectioning: Specimens are dehydrated with alcohols and then placed in a mould with wax/resin to form a hard block - thinly sliced with a knife
Staining: Specimens treated with multiple coloured chemicals to show different strutures
Mounting: Specimens secured to microscope slide and cover slide placed on top

40
Q

What are the advantages and disadvantages of using a light microscope?

A

Advantages
- portable
- takes up little space
- specimens easy to prepare
- can see cells and often nucleus
- colour visible

Disadvantages
- low resolution (200nm) as wavelength of light too long
- cannot see small organelles or details of organelles

41
Q

Define magnification and resolution

A

Magnification: The degree to which the size of an image is larger than the object itself
Resolution: The ability to see two objects tha are close together as separate objects and see in detail

42
Q

How do electron microscopes work and why do they have a higher resolution compared to a light microscopes?

A
  • beam of electrons focused by electromagnets through or onto the surface of a specimen
  • electron microscopes use electrons to take images, which have a much short wavelength (0.2nm), so have a higher resolution
43
Q

What are the two types of electron microscope, how do they work, and what type of image do they produce

A

Transmission electron microscope (TEM)
- a beam of electrons is transmitted through a specimen and focused to produce a 2D image
- used to view the ultra structure of cells and organelles

Scanning electron microscope (SEM)
- a beam of electrons is sent across a specimen and reflected electrons are collected to produce a 3D image
- used to view the 3D shape of the surface of cels and organelles and their surface features

44
Q

What is the magnification and resolution of each type of electron microscope and a light microscope?

A

Transmission electron microscope (TEM)
Magnification: x500,000
Resolution: 0.05 - 2nm

Scanning electron microscope (TEM)
Magnification: x100,000
Resolution: 5 - 50nm

Light microscope
Magnification: x1500
Resolution: 200nm

45
Q

What are the advantages and disadvantages of using an electron microscope?

A

Advantages
- higher resolution
- higher magnification
- shorter wavelength
- can see ultra structure

Disadvantages
- cannot view living cells
- must be in vacuum
- no colour images
- specimen must be thin
- artefacts may appear (structures produced during preparation process)
- have to be treated with metal (lead) salts

46
Q

List units used when measuring smaller specimens, their units and how to convert between them

A
  • milimetre (mm) - 1000μm
  • micrometre (μm) - 1000nm
  • nanometre (nm)
47
Q

How is magnification calculated?

A

Magnification = Image size / real object size

48
Q

What is an eyepiece graticule and stage micrometer?

A

Eyepiece graticule: Placed into the eyepiece lens - used to measure specimens seen udner the microscope. Will not change size when magnification is changed. Needs to be calibrated
Stage micrometer: Goes on the stage of the microscope - a microscope slide with a scale etched into it. Is a known size (e.g. 1mm). Used to calibrate eyepiece graticle

OCR Biology A Level (20 decks)

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