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AQA AS BIOLOGY: FLASHCARDS > 3.2 - CELLS > Flashcards

3.2 - CELLS Flashcards

1
Q

what is DNA like in a eukaryote? (4)

A
  • it is a linear, double helix shape
  • tightly wrapped around proteins called histones - these are called chromosomes
  • enclosed in a nucleus
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2
Q

what is DNA like in a prokaryote? (2)

A
  • non-linear, a single circular piece (a loop), as well as plasmids
  • not enclosed in a nucleus
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3
Q

what are the differences between active and passive transport? (4)

A

active transport:
* use energy
* against concentration gradient
* from area of low concentration to high concentration

passive transport:
* does not use energy
* from area of high concentration to low concentration
* e.g. diffusion

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4
Q

what are the 5 key structures that make up the nucleus? (5)

A

nuclear envelope:
- a double membrane, outer membrane is continuous with the rough endoplasmic reticulum
- it contains the reactions taking place in the nucleus

nuclear pores:
- holes in the surface of the nucleus
- allow passage of large molecules (e.g. mRNA)

nucleoplasm:
- a granular, jelly-like material
- makes up the bulk of the nucleus

chromatin:
- mixture of DNA and proteins that form chromosomes (linear, protein-bound DNA)

nucleolus:
- small spherical region, - manufactures & assembles ribosomal RNA and ribosomes
- can be more than 1

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5
Q

what is the function of the nucleus? (5)

A
  • controls the activities of the cells
  • contains nuclear reactions
  • manufactures ribosomes and ribosomal RNA
  • produces mRNA and tRNA for protein synthesis
  • contains genetic materials in the form of DNA and chromosomes
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6
Q

what is mRNA? what is its function? (2)

A

messenger RNA: a type of RNA that carries instructions from DNA in the nucleus to the ribosomes

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7
Q

what is tRNA? what is its function? (2)

A

transfer RNA: type of RNA that carries amino acids to the ribosome

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8
Q

what are the 3 key structures that make up the mitochondria? (3)

A

double membrane (envelope):
- controls entry and exit of substances

cristae:
- extensions of the inner membrane
- provide a large SA for attachment of enzymes & other proteins involved in respiration

matrix:
- contains proteins, lipids, ribosomes and DNA
- allows mitochondria to produce some of its own proteins and respiratory enzymes

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9
Q

what is the function of mitochondria? (2)

A
  • site of aerobic respiration
  • therefore responsible for production of ATP (a molecule that carries energy)
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10
Q

what is the structure of the cell membrane?

A
  • fluid mosaic model
  • plasma membrane
  • phospholipid bilayer
  • hydrophobic tails on the inside, hydrophilic heads on the outside
  • contains cholesterol
  • contains glycoproteins
  • contains proteins
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11
Q

what is the function of the cell membrane?

A
  • regulates the movement of materials into and out of the cell
  • barrier between the cell and its environment
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12
Q

what are the 5 key structures found in chloroplasts? (4)

A

double-membrane (envelope):
* plasma membrane, highly selective in what it allows in and out

grana/granum:
* stacks of thylakoids (up to 100)

thylakoids:
* folded membranes embedded with pigment (chlorophyll)
* can be linked to other grana by lamella (plural: lamellae)

the stroma:
* fluid-filled matrix
* second stage of photosynthesis occurs here (synthesis of sugars)
* contains starch grains
- contain DNA

  • 70S ribosomes
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13
Q

what is the function of chloroplasts? (2)

A
  • harvest sunlight to carry out photosynthesis
  • contain DNA and ribosomes, can manufacture some proteins needed for photosynthesis
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14
Q

what are the 4 key features of the Golgi apparatus and its vesicles? (4)

A

cisternae: compact stack of flattened sacs and stacked membranes

vesicles: transport molecules to and from the Golgi body

cis face: molecules can only join the Golgi here

trans face: molecules can only leave the Golgi here

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15
Q

what is the function of the Golgi apparatus and its vesicles? (6)

A
  • form glycoproteins by adding carbohydrates to proteins
  • produce secretory enzymes, such as those secreted by the pancreas (amylase, protease, lipase)
  • secrete carbohydrates, such as cellulose for plant cell walls
  • transport, modify and store lipids to form lysosomes

vesicles:
- transports proteins from rough ER to Golgi body
- transports modified proteins and lipids to the cell membrane, where they fuse with the membrane and then egest contents to the outside

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16
Q

what is the structure of lysosomes? (3)

A
  • formed when vesicles produced by Golgi contain digestive enzymes (proteases and lipase)
  • contain hydrolytic enzymes, such as lysozymes (enzymes that hydrolyse the cell wall of certain bacteria)
  • lysosomes isolate these enzymes from the rest of the cell before releasing them
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17
Q

what is the function of lysosomes? (3)

A
  • to break down (hydrolyse) foreign material ingested by phagocytic cells
  • release enzymes outside the cell to destroy materials around the cell (exocytosis)
  • digest worn out organelles so useful chemicals can be recycled
  • to break down cells after they die (autolysis)
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18
Q

what are the 2 key structures in a ribosome? what are the two types of ribosomes? (3)

A
  • composed of two sub-units (one large, one small)
  • found in all cells

80S:
- found in eukaryotic cells
- slightly larger

70S:
- found in prokaryotic cells
- slightly smaller

  • both types contain ribosomal RNA and proteins
  • small, but many, account for 25% of dry mass of cell
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19
Q

what is the function of ribosomes? (2)

A
  • site of protein synthesis
  • produce polypeptides
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20
Q

what is the structure of the smooth and rough endoplasmic reticulum? (4)

A
  • 3D system of sheet-like membranes
  • membrane consists of a network of tubules and flattened sacs called cisternae

rough:
- ribosomes on surface
- continuous with outer nuclear membrane

smooth:
- lacks ribosomes on surface
- often more tubular in appearance

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21
Q

what are the functions of the rough and smooth endoplasmic reticulum? (4)

A

rough:
- provides large SA for protein/glycoprotein synthesis
- provides pathway for transport of material, especially proteins

smooth:
- synthesises, stores and transports carbohydrates and lipids

  • cells that store lots of carbohydrates and proteins have an extensive ER (e.g. liver and secretory cells)
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22
Q

what is the structure of the vacuole?

A
  • fluid filled sac bounded
  • has a single membrane called a tonoplast
  • contains a solution of mineral salts, amino acids, sugars, wastes and sometimes pigments such anthocyanins
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23
Q

what is the function of the vacuole?

A
  • supports herbaceous plants, and herbaceous parts of woody plants by making cells turgid
  • the sugars and amino acids can act as a temporary food store
  • the pigments may attract pollinating insects due to their colour
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24
Q

what is the function of the cell wall?

A
  • to provide mechanical strength to prevent cell bursting under pressure created by osmotic entry of water (cellulose)
  • to provide mechanical strength to the cell as a whole
  • permeable, to allow water to pass through, to contribute to the movement of water through the plant
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25
Q

what is the structure of the cell wall?

A
  • consist of a number of polysaccharides
  • thin layer (middle lamella) marks the boundary between adjacent cell walls and cements adjacent cells together

plant cell wall: made from cellulose

algae: made up of either cellulose or glycoproteins, or a mixture

fungi: made of a mixture of nitrogen-containing chitin, glycan and glycoproteins.

prokaryotes: made of murein (a glycoprotein)

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26
Q

are there membrane-bound organelles in prokaryotes?

A
  • no, but it contains ribosomes (not membrane-bound)
  • contain mesosomes
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27
Q

what is the structure and function of mesosomes (2)

A
  • mesosomes are infoldings of the cell membrane
  • provide large SA for attachment of enzymes involved in respiration
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28
Q

what is the structure and function of the capsule around a pathogen?

A

structure:
- usually composed of polysaccharides but also contains water to protect against desiccation (drying out)

function:
- hides antigens on the surface to protect bacteria from viruses or attack from a host’s immune system
- protects bacterium from other cells
- helps bacteria stick together for further protection

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29
Q

what is the structure and function of plasmids?

A

structure:
- circular pieces of DNA in a prokaryote

function:
- contain a small number of genes that can aid the survival of bacteria in adverse conditions
- this can include genes that make a bacterium resistant to antibiotics

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30
Q

what are examples of eukaryotic cells?

A
  • animal cells
  • fungi cells
  • plant cells
  • protist cells
  • algae
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31
Q

what are examples of prokaryotic cells?

A
  • bacteria
  • cyanobacteria
  • blud-green bacteria
  • archaea
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32
Q

what is the typical structure of a eukaryotic cell?

A
  • DNA enclosed in a nucleus
  • membrane-bound organelles
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33
Q

what is the typical structure of a prokaryotic cell?

A
  • free DNA (not enclosed in a nucleus)
  • no membrane-bound organelles
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34
Q

what is the typical structure of a virus?

A
  • capsid: to protect viral RNA or DNA
  • attachment proteins: to attach to host cell
  • genetic material
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35
Q

what is magnification?

A

the number of times larger an image is compared with the real size of an object

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36
Q

what is resolution?

A
  • this is defined as the ability to distinguish between two separate points
  • if two points cannot be resolved they will be seen as one point
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37
Q

what are the principles and limitations of the optical microscope?

A

principles/advantages:
- uses a light beam
- uses glass lenses in pairs
- produces colour images
- can view living samples

limitations:
- poor resolution due to long wavelength of light
- low magnification: x1500
- 2D images
- internal structure of organelles cannot be seen, some smaller organelles cannot be seen at all

38
Q

what are the principles and limitations of the electron microscope?

A

principles/advantages:
- first developed in 1930s
- uses electron beam, this can be condensed using an electromagnet
- electrons have a short wavelength, so a higher resolving power
- higher magnification = x1.5 million
- can see internal structure of organelles
- two types: TEM & SEM

limitations:
- produces black and white images (samples must be stained)
- living specimens cannot be viewed as the sample must be contained in a vacuum (because electrons can be absorbed by air)

39
Q

what are the principles and limitations of the transmission electron microscope (TEM)?

A

principles/advantages:
- electron gun produces an electron beam which can be controlled using a condenser electromagnet
- the beam passes through parts of the specimen
- denser parts of the specimen absorb more electrons and therefore appear darker compared to other parts of the specimen
- the image produced can be photographed to produce a photomicrograph

limitations:
- the specimens have to be extremely thin so electrons can penetrate
- does not produce colour images
- takes place in a vacuum so living specimens cannot be observed
- 3D images can be produced but it is very slow and complex process
- images can contain artefacts due to long, complicated preparation process

40
Q

what are the principles and limitations of the scanning electron microscope (SEM)?

A

principles/advantages:
- electron beam directed from above the specimen
- then passed back and forth across a portion of the specimen in a regular pattern, can build 3D images with this
- 3D images can be produced quicker than TEM

limitations:
- does not produce colour images
- takes place in a vacuum so living specimens cannot be observed
- image can contain artefacts due to long, complicated preparation process

41
Q

what are artefacts in microscopy?

A

distortions that result from the way a specimen is prepared

42
Q

what is cell fractionation? what stages does it consist of? what is it needed for?

A
  • a process in which cells are broken up and the different organelles are spread out
  • a pure sample is needed to study function and structure

consist of two stages:
- homogenation: breaking open cells
- ultracentrifugation: separating organelles with the use of a spinning centrifuge

43
Q

why is the cell tissue placed in a cold, isotonic, buffered solution?

A

cold:
- to reduce enzyme activity that could break down the organelles

isotonic:
- to prevent organelles bursting or shrinking due to osmotic gain or loss of water

buffered:
- to maintain a constant pH to prevent enzymes from denaturing

44
Q

what is the method for cell fractionation?

A
  1. place tissue in cold, isotonic, buffer solution
  2. place solution in homogeniser to break open cells
  3. filter homogenate to remove insoluble tissue and large debris
  4. centrifuge at low speed to remove nuclei (most dense organelle)
  5. centrifuge supernatant at different speeds until you obtain your desired organelle (differential centrifugation)
45
Q

what is the order of organelle fractionation?

A

first to pellet: nuclei
- chloroplasts & mitochondria
- lysosomes, endoplasmic reticulum & Golgi (membrane-bound organelles)
last to pellet: ribosomes

46
Q

what are pellets?

A

fragments that have fallen and collected at the bottom of the test tube in the process of differential centrifugation

47
Q

what is the structure and function of the flagella and pilli?

A

flagella:
- some bacteria can have more than one flagellum
- a tail-like structure which rotates to allow the cell to move (locomotion)

pilli:
- hollow protein structures found on the surface of the flagella
- help to attach to surfaces and other bacteria
- when two bacteria are attached, DNA can be transferred from one to another

48
Q

what is mitosis?

A
  • mitosis is the division and replication of cells for growth and repair
  • the part of the cell cycle in which a eukaryotic cell divides to produce two daughter cells with identical copies of DNA produced by the parent cell during DNA replication.
49
Q

what cells do not retain the ability to divide?

A

specialised cells

50
Q

what is a cell cycle?

A

the sequence of events between one cell division and the next.

51
Q

what are the 3 overall stages of the cell cycle?

A
  1. interphase
  2. nuclear division
  3. cytokinesis
52
Q

how is the movement between different phases of the cell cycle triggered?

A

it is triggered by chemical signals called cyclins

53
Q

what is interphase? what occurs in it? (6)

A
  • longest stage in cell cycle (90%)
  • consists of G1, S and G2

G1:
- organelles double
- ATP increases to provide energy for the cell division
- receives signal to divide

S:
- DNA unravels and replicates (synthesis of DNA)
- when chromosomes duplicate, they attach to their copy, so they now consist of 2 strands called sister chromatids joined by a centromere

G2:
- cell growth continues
- newly synthesised DNA is checked for any errors

54
Q

what is nuclear division? what occurs in it?

A
  • can either involve mitosis (creating two identical diploid cells), or meiosis (creating four genetically different haploid cells)
  • nucleus divides into 2
  • chromatids separate from each other, they are redistributed as chromosomes in the nuclei of the 2 new daughter cells
55
Q

what is cytokinesis? when does it occur?

A
  • begins in anaphase and ends in telophase
  • the splitting of the cytoplasm
  • a cleavage furrow develops, deepens and eventually cuts the cell in two
  • this produces two identical daughter cells that contain identical copies of DNA produced by the parent cell during DNA replication
56
Q

what are the four stages in mitosis?

A

PMAT: prophase, metaphase, anaphase & telophase

57
Q

what happens in prophase?

A
  • chromosomes coil up, shorten, thicken, take up more stain, becoming more distinct
  • centrioles divide and migrate to opposite poles of the cell
  • nucleolus shrinks and disappears
  • nuclear envelope disintegrates so chromosomes are now free in the cytoplasm
58
Q

what are centrioles?

A

rod-like, protein molecules that are usually together

59
Q

what happens in metaphase?

A
  • the centrioles reach their respective poles, they grow/produce spindle fibres
  • the spindle fibres attach to the centromeres, each centromere is attached to both poles
  • chromosomes are pulled to the equator and lined up in the centre of the cell
60
Q

what happens in anaphase?

A
  • the spindle fibres contract, dividing centromeres, separating chromatids
  • chromatids were pulled to opposite poles of the cell
  • the energy for this process is provided by mitochondria
  • each half of the cell receives one of the genetically identical chromatids from each chromosome
  • this is the start of cytokinesis
61
Q

what happens in telophase?

A
  • chromatids reach the opposite poles
  • they uncoil, become longer and thinner, therefore less distinct
  • nuclear envelope and nucleolus reform
62
Q

explain what happens in binary fission. (3)

A

binary fission occurs in prokaryotic cells

1. circular DNA and plasmids are replicated
2. cell elongates (membrane grows)
3. the two circular DNA move to opposite sides of cell
4. cell pinches in middle to form septum, dividing cytoplasm into two
5. a new cell wall forms dividing it into two cells

63
Q

what is cancer? how does it occur? what are most cancer treatments aimed at (3)

A
  • cancer is a group of diseases caused by a growth disorder of cells
  • cancer and tumours form due to uncontrolled cell division
  • cancer starts from a malignant tumour
  • this is why many cancer treatments are directed at controlling the rate of cell division
64
Q

explain why the model for membrane structure is known the fluid-mosaic model (3)

A

fluid: phospholipid molecules can move freely laterally and makes the membrane fluid

mosaic: proteins are distributed throughout the membrane unevenly and in a mosaic pattern

model: the structure is based upon experimental and chemical evidence and so is classed as a model

65
Q

compare how polar and non-polar molecules pass through the membrane (2)

A
  • polar molecules require protein channels to enable them to pass through the membrane, however, non-polar molecules can diffuse directly through the phospholipid bilayer
66
Q

describe the structure and function of the glycocalyx (3)

A
  • consists of glycoproteins (proteins with added carbohydrate chains)
  • used for cell recognition
  • used as receptors
67
Q

explain why phospholipids form a bilayer in plasma membranes (4)

A
  • polar, hydrophilic phosphate group will face the aqueous solutions
  • fatty acid tails are non-polar and hydrophobic and will move away from an aqueous environment
  • both tissue fluid and cytoplasm is aqueous, so phospholipids form two layers with the hydrophobic tails facing inward and phosphate groups outwards interacting with the aqueous environment
68
Q

state three functions of membrane-bound proteins (3)

A
  • receptors
  • enzymes
  • carriers (carrier proteins)
69
Q

what are carcinogens? give an example (1)

A
  • carcinogens are cancer causing agents in the environment
  • for example, cigarettes
70
Q

state 3 ways of treating cancer (3)

A
  • chemotherapy
  • surgical removal of the tumour
  • radiotherapy
71
Q

how does radiotherapy work? (2)

A

radiotherapy uses x-rays or radiation from radioactive sources to destroy cancer cells

72
Q

what is chemotherapy? how does it work to treat cancer? (4)

A
  • using chemicals which kill dividing cells by blocking/disrupting part of the cell cycle so cell division stops, this included both cancerous and normal cells that are dividing
  • disruption is by either: preventing DNA from replicating or inhibiting metaphase by interfering with spindle formation
  • can specifically target cancerous cells using monoclonal antibodies
73
Q

what is facilitated diffusion?

A
  • the transport of substances across a biological membrane from anarea of high concentration to an area of low concentration with thehelp of transport molecules/channels
  • this uses channel proteins and carrier proteins
74
Q

explain why the diffusion of ions involves a membrane protein and the diffusion of oxygen does not (5)

A
  • chloride ions are charged/ water soluble/polar
  • so they cannot cross the bilayer
  • therefore, they are transported by facilitated diffusion, which involves the use of carrier proteins
  • however, oxygen is non-polar, so it can diffuse across the bilayer
75
Q

what molecules can freely pass through the phospholipid bilayer?

A

molecules that are:
- lipid soluble
- non-polar

76
Q

what molecules can not freely pass through the phospholipid bilayer?

A

molecules that are:
- not lipid-soluble
- too large to pass through
- have the same charge as the protein channels (they will be repelled)
- polar

77
Q

explain the importance of cholesterol in the membrane (5)

A
  • to help control membrane fluidity
  • the more cholesterol, the less fluid, and the less permeable the membrane
  • to help keep membranes at normal body temperature, without it, cells would burst open
  • due to their hydrophobic nature they help in preventing the loss of water and dissolved ions
78
Q

what is the function of membranes within the cell?

A
  • separate organelles from cytoplasm so that specific metabolic reactions can take place within them
  • in textbook
79
Q

what is cell signalling? what do cells use to do this?

A
  • communication between cells
  • direct contact
    or
  • messengers such as neurotransmitters or hormones
80
Q

write a detailed description of the formation of a glycoprotein in an eukaryotic cell (4)

A

rough endoplasmic reticulum: protein is assembled here, vesicles form around the protein and move to the Golgi apparatus where it is manufactured into a glycoprotein with the addition of a carbohydrate side chain, then
another Golgi vesicle is formed

81
Q

outline the role of organelles in the production, transport and release of proteins from eukaryotic cells (4)

A
  1. DNA in nucleus is code for protein
  2. rough endoplasmic reticulum produce protein
  3. mitochondria produce ATP for protein synthesis
  4. Golgi apparatus modify
  5. vesicles transport
  6. vesicles fuse with cell membrane to release proteins
82
Q

explain why it is not possible to identify certain (small) structures using an optical microscope (2)

A
  1. resolution of optical microscope is too low
  2. this is due to the long wavelength of light
83
Q

describe the role of lysosomes in digesting bacteria (2)

A
  1. Golgi body forms lysosomes
  2. release hydrolytic enzymes
84
Q

suggest one explanation why there is a faster rate of plasmid replication in cells growing in a culture with a high amino acid concentration (2)

A
  1. amino acids are used in protein synthesis
  2. so more enzymes for DNA/plasmid replication

OR

  1. amino acids used in respiration
  2. so more energy for ATP for DNA/plasmid replication
85
Q

explain the difference between the ribosomes in chloroplasts and the cytoplasm (2)

A

70S ribosomes in chloroplasts, these are smaller than the 80S ribosomes in cytoplasm

86
Q

suggest why _____ is not visible in the micrograph/image (1)

A
  1. not stained
    OR
  2. can only see a section, it might be in another part of the cell
87
Q

explain the link between mitochondria and muscle cells (3)

A
  • aerobic respiration takes place in the mitochondria
  • this releases ATP for muscle contractions
88
Q

explain the link between the rough endoplasmic reticulum and enzyme secreting cells from the salivary glands (2)

A
  • endoplasmic reticulum synthesis proteins
  • enzymes are proteins
89
Q

explain why large numbers of mitochondria and Golgi apparatus are found in mucus-secreting cells (2)

A
  • Golgi modifies mucus
  • mitochondria provides the ATP for this
90
Q

are the daughter cells produced by binary fission genetically identical? (2)

A

no, because the daughter cells have a single copy of the circular DNA but a variable number of plasmids

AQA AS BIOLOGY: FLASHCARDS (4 decks)

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