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A level Biology > unit 2 > Flashcards

unit 2 Flashcards

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1
Q

where is the dna kept in a eukaryotic cell?

A
  1. the dna is contained in a membrane bound nucleus
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2
Q

difference between eukaryote and prokaryote 3 points

A

1-alot smaller than eukaryotes
2-contains 70 s ribosomes
3-dna does not contain histone. dna is arranged in circular chromosomes with no free ends

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3
Q

3 key features of a plant cell

A

plant cells are the same as animal cells except 3 other key features
-a cellulose cell wall. with plasmoesmata which areer channels for exchanging substances with adjacent cells
-vacuole
chloroplasts

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4
Q

organelles in eukaryotic cell

A

membrane bound eg mitochondria

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5
Q

what type of ribosomes do eukaryotic cells have

A

3.eukaryotic cells contain 80S ribosomes

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6
Q

dna in eukaryotic cells

A

4- dna is tightly coiled around a protein called histone. dna and histones form chromatin
by tightly coiling the dna into chromosomes they can pack a lot of dna into its nucleus
5- dna is a linear molecule

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7
Q

what are plasmids

A

4 plasmids contain genetic material which is responsible for antibiotic resistance small, circular rings of double-stranded DNA.
can be passed between prokaryotes

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8
Q

what is a bacterial cell wall made out of

A

5-murein cell wall.

- amino acid and sugar

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9
Q

what do slime capsules do

A

slime capsules can protect the cell from phagocytosis from white blood cells

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10
Q

Mesosome proika

A

Mesosome – Permeable boundary that allows for entry and exit of nutrients and waste

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11
Q

what is pili

A

its a fine protein that can attach to surfaces and transfer dna

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12
Q

whats an artifact

A

artifact. Something artificial, a distortion that does not reflect normal anatomy or pathology,

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13
Q

specialised animal cell red blood cell

A

They are biconcave in shape which increases the surface area over which oxygen can be absorbed.
The cytoplasm contains high amounts of the pigment haemoglobin which can readily bind to oxygen. … Elastic membrane allows the cell to be flexible and change shape as it squeezes through narrow capillaries.

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14
Q

ciliated epithelial cells

A

Ciliated Epithelial Cells are column shaped cells, that cover many surfaces.
They have tiny projections on their exposed surface, called Cilia,
which beat in a synchronised pattern to move Mucus, produced by Goblet Cells, along the surface.

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15
Q

specialised cell: palisade cells

A

The Palisade Layer consists of long, thin Palisade Mesophyll Cells.
They are specialised for carrying out Photosynthesis since they contain large amounts of Chlorophyll,
and their long shape maximises light absorption.

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16
Q

Specialised plant cell 2: root hair cell

A

Root hair cells:
Are adapted for the absorption of water and mineral ions from soil
Have a specialised shape (the root ‘hair’) that increases the cell’s surface area so the rate of water uptake by osmosis is greater (can absorb more water and mineral ions than if the surface area was lower)
Have thinner walls than other plant cells so that water can move through easily (due to shorter diffusion distance)
Have a permanent vacuole containing cell sap, which is more concentrated than soil water. This ensures a high water potential gradient is maintained

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17
Q

plasma membrane

A

It is a fluid mosaic of lipids, proteins and carbohydrate.
The plasma membrane is composed of a bilayer of phospholipids, with their hydrophobic, fatty acid tails in contact with each other. The landscape of the membrane is studded with proteins, some of which span the membrane

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18
Q

nucleus

A

ouble membrane (the nuclear envelope) which has many pores
Nuclear pores are important channels for allowing mRNA and ribosomes to travel out of the nucleus, as well as allowing enzymes (eg. DNA polymerases) and signalling molecules to travel in
The nucleus contains chromatin (the material from which chromosomes are made)
Usually, at least one or more darkly stained regions can be observed – these regions are individually termed ‘nucleolus’ and are the sites of ribosome production

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19
Q

mitochondria

A

.The site of aerobic respiration within eukaryotic cells, mitochondria are just visible with a light microscope
.Surrounded by double-membrane with the inner membrane folded to form cristae
.The matrix formed by the cristae contains enzymes needed for aerobic respiration, producing ATP
.Small circular pieces of DNA (mitochondrial DNA) and ribosomes are also found in the matrix (needed for replication)

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20
Q

chloroplasts

A

Larger than mitochondria, also surrounded by a double-membrane
Membrane-bound compartments called thylakoids containing chlorophyll stack to form structures called grana
Grana are joined together by lamellae (thin and flat thylakoid membranes)
Chloroplasts are the site of photosynthesis:
-Also contain small circular pieces of DNA and ribosomes used to synthesise proteins needed in chloroplast replication and photosynthesis

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21
Q

Golgi apparatus

A
  • Flattened sacs of membrane similar to the smooth endoplasmic reticulum
  • Modifies proteins and packages them into vesicles or lysosomes
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22
Q

Golgi vesicle

A

Membrane-bound sac for transport and storage

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23
Q

cell membrane

A

.ll cells are surrounded by a cell surface membrane which controls the exchange of materials between the internal cell environment and the external environment
.The membrane is described as being ‘partially permeable’
.The cell membrane is formed from a phospholipid bilayer of phospholipids spanning a diameter of around 10 nm

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24
Q

cell wall

A

Cell walls are formed outside of the cell membrane and offer structural support to cell
Structural support is provided by the polysaccharide cellulose in plants, and peptidoglycan in most bacterial cells
Narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighbouring plant cells

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25
Q

ribosomes

A

Ribosomes are formed in the nucleolus and are composed of almost equal amounts of RNA and protein

.Found freely in the cytoplasm of all cells or as part of the rough endoplasmic reticulum in eukaryotic cells
.Each ribosome is a complex of ribosomal RNA (rRNA) and proteins
.80S ribosomes) are found in eukaryotic cells
.70S ribosomes in prokaryotes, mitochondria and chloroplasts
Site of translation (protein synthesis)

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26
Q

Rough Endoplasmic Reticulum (RER)

A

1Surface covered in ribosomes
2Formed from continuous folds of membrane continuous with the nuclear envelope
3Processes proteins made by the ribosomes

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27
Q

Smooth Endoplasmic Reticulum (ER)

A

1Does not have ribosomes on the surface, its function is distinct to the RER
2Involved in the production, processing and storage of lipids, carbohydrates and steroids

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28
Q

vacuole

A

Sac in plant cells surrounded by the tonoplast, selectively permeable membrane
Vacuoles in animal cells are not permanent and small

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29
Q

Lysosome

A

1 Specialist forms of vesicles which contain hydrolytic enzymes (enzymes that break biological molecules down)
2 Break down waste materials such as worn-out organelles, used extensively by cells of the immune system and in apoptosis (programmed cell death)

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30
Q

centriole

A

1 Hollow fibres made of microtubules, two centrioles at right angles to each other form a centrosome, which organises the spindle fibres during cell division
2 Not found in flowering plants and fungi

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31
Q

Microtubules

A

1 Makes up the cytoskeleton of the cell about 25 nm in diameter
2 Made of α and β tubulin combined to form dimers, the dimers are then joined into protofilaments
3 Thirteen protofilaments in a cylinder make a microtubule
The cytoskeleton is used to provide support and movement of the cell

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32
Q

microvilli

A

Cell membrane projections that increase the surface area for absorption
Cilia

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33
Q

cillia

A

Hair-like projections made from microtubules

Allows the movement of substances over the cell surface

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34
Q

flagella

A

Similar in structure to cilia, made of longer microtubules

Contract to provide cell movement for example in sperm cells

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35
Q

what are the two main microscopes

A

electron and optical

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36
Q

what is the optical microscope

A

Optical microscopes use light to form an image

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37
Q

limits for optical microscopes

A

This limits the resolution of optical microscopes
Using light, it is impossible to resolve (distinguish between) two objects that are closer than half the wavelength of light
2. maximum resolution of around 0.2 micrometres (µm) or 200 nm

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38
Q

what organelles can optical microscopes see

A

his means optical microscopes can be used to observe eukaryotic cells, their nuclei and possibly mitochondria and chloroplasts

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39
Q

what is a electron microscope

A

Electron microscopes use electrons to form an image

40
Q

why is an electron microscope better

A

beam of electrons has a much smaller wavelength than light, so an electron microscope can resolve (distinguish between) two objects that are extremely close together

41
Q

what can electron microscopes observe

A

This means electron microscopes can be used to observe small organelles such as ribosomes, the endoplasmic reticulum or lysosomes

42
Q

what are the two types of microscopes

A

Transmission electron microscopes (TEMs)

Scanning electron microscopes (SEMs)

43
Q

whats TEMs

A

TEMs use electromagnets to focus a beam of electrons

This beam of electrons is transmitted through the specimen

44
Q

advantages of TEMS

A

hey give high-resolution images (more detail)

This allows the internal structures within cells (or even within organelles) to be seen

45
Q

disadvantages of TEMS

A

1 They can only be used with very thin specimens or thin sections of the object being observed
2 They cannot be used to observe live specimens (as there is a vacuum inside a TEM, all the water must be removed from the specimen and so living cells cannot be observed, meaning that specimens must be dead, unlike optical microscopes that can be used to observe live specimens)
3 The lengthy treatment required to prepare specimens means that artefacts can be introduced (artefacts look like real structures but are actually the results of preserving and staining)
4 They do not produce a colour image (unlike optical microscopes that produce a colour image)

46
Q

what SEMS

A

EMs scan a beam of electrons across the specimen
This beam bounces off the surface of the specimen and the electrons are detected, forming an image
This means SEMs can produce three-dimensional images that show the surface of specimens

47
Q

advantages of SEMs

A

they can be used on thick or 3-D specimens

They allow the external, 3-D structure of specimens to be observed

48
Q

disadvantages of SEMs

A

They give lower resolution images (less detail) than TEMs
They cannot be used to observe live specimens (unlike optical microscopes that can be used to observe live specimens)
They do not produce a colour image (unlike optical microscopes that produce a colour image)

49
Q

how big is a prokaryotic cell

A

0.5-5 microm

50
Q

how big is a eukaryotic cell

A

100 micrometres

51
Q

how do eukaryotes undergo cell division vs prokaryotes

A

-mitosis or meiosis and involves spindle fibers to separate chromosomes were as prokaryotes undergo cell division by binary fission

52
Q

what is prokaryotic cell wall made out of

A

muerin or peptidoglycan

-polysaccharide and amino acids

53
Q

viruses

A

Viruses are non-cellular infectious particles

with diameters between 20 and 300 nm

54
Q

virus structure

A

A nucleic acid core (their genomes are either DNA or RNA, and can be single or double-stranded)
A protein coat called a ‘capsid’

55
Q

magnification equation

A

i

a x m

56
Q

converting units

A

When doing calculations all measurements must be in the same units. It is best to use the smallest unit of measurement shown in the question

57
Q

Converting units of measurement

A

There are 1000 nanometers (nm) in a micrometre (µm)
There are 1000 micrometres (µm) in a millimetre (mm)
There are 1000 millimetres (mm) in a metre (m)

58
Q

Cell Fractionation & Ultracentrifugation

A

The process of separating cell organelles from each other is known as cell fractionation
This process involves breaking up a suitable sample of tissue and then centrifuging the mixture at different speeds

59
Q

what are the three stages of cell fractionation

A

cell fractionation can be split into three stages:
Homogenisation
Filtration
Ultracentrifugation

60
Q

what is homogentasion

A

Homogenisation is the biological term used to describe the breaking up of cells

61
Q

conditions for homogenisation

A

ice-cold to reduce the activity of enzymes that break down organelles
Isotonic (it must have the same water potential as the cells being broken up) to prevent water from moving into the organelles via osmosis, which would cause them to expand and eventually damage them
Buffered (have a buffer solution added) to prevent organelle proteins from becoming denatured

62
Q

what is a homogenizer

A

This is a blender-like machine that grinds the cells up (the cells can also be vibrated until they break up)
This breaks the plasma membrane of the cells and releases the organelles into a solution called the homogenate

63
Q

what is a homogenate

A

homogeniser breaks the plasma membrane of the cells and releases the organelles into a solution called the homogenate

64
Q

filtration

A

The homogenate (containing the homogenised cells) is then filtered through a gauze

65
Q

what happens in filtration

A

This is to separate out any large cell debris or tissue debris that were not broken up
The organelles are all much smaller than the debris

66
Q

what is ultracentrifugation

A

The filtrate is placed into a tube and the tube is placed in a centrifuge
A centrifuge is a machine that separates materials by spinning

67
Q

stage one of ultracentrifugation

A

The filtrate is first spun at a low speed
This causes the largest, heaviest organelles (such as the nuclei) to settle at the bottom of the tube, where they form a thick sediment known as a pellet
The rest of the organelles stay suspended in the solution above the pellet
This solution is known as the supernatant

68
Q

what is a pellet

A

when filtrate is first spun at a low speed his causes the largest, heaviest organelles to settle at the bottom of the tube, where they form a thick sediment known as a pellet

69
Q

what is a supernatant

A

This causes the largest, heaviest organelles to settle at the bottom of the tube, where they form a thick sediment known as a pellet
The rest of the organelles stay suspended in the solution above the pellet
This solution is known as the supernatant

70
Q

what happens with the supernatant

A

The supernatant is drained off and placed into another tube, which is spun at a higher speed
Once again, this causes the heavier organelles (such as the mitochondria) to settle at the bottom of the tube, forming a new pellet and leaving a new supernatant

71
Q

how do you get the desired organelle to be separated out

A

The new supernatant is drained off and placed into another tube, which is spun at an even higher speed
This process is repeated at increasing speeds until all the different types of organelle present are separated out (or just until the desired organelle is separated out)

72
Q

what is an artifact

A

When looking at a prepared sample (e.g. a cell or a group of cells) under a microscope, you can sometimes see things that aren’t actually part of the specimen
These are known as artefacts
Artefacts can be a variety of things, such as:
dust
air bubbles
fingerprints

73
Q

the movement from one phase to another is triggered by what chemical signals

A

The movement from one phase to another is triggered by chemical signals called cyclins

74
Q

what is the cell cycle

A

The cell cycle is the regulated sequence of events that occurs between one cell division and the next

75
Q

what are the three stages of the cell cycle

A 
interphase
nuclear division (mitosis)
cell division (cytokinesis)
76
Q

what is interphase

A

During Interphase the cell increases in mass and size and carries out its normal cellular functions (eg. synthesising proteins and replicating its DNA ready for mitosis)

77
Q

what happends to the nucleus in the interphasse e

A

The DNA in the nucleus replicates (resulting in each chromosome consisting of two identical sister chromatids)

78
Q

g1 phase

A

Cells make the RNA, enzymes and other proteins required for growth during the G1 phase

79
Q

s phase

A

The DNA in the nucleus replicates (resulting in each chromosome consisting of two identical sister chromatids)
This phase of the interphase stage of the cell cycle is called the S phase

80
Q

g2

A

During the G2 phase, the cell continues to grow and the new DNA that has been synthesised is checked and any errors are usually repaired

81
Q

Nuclear division (mitosis)

A

follows interphase
Referred to as the M phase – M stands for mitosis
Cell growth stops during the M phase

82
Q

Cytokinesis

A

Once the nucleus has divided into two genetically identical nuclei, the whole cell divides and one nucleus moves into each cell to create two genetically identical daughter cells
In animal cells, cytokinesis involves constriction of the cytoplasm between the two nuclei and in plant cells a new cell wall is formed

83
Q

the importance of mitosis. Growth of multicellular organisms

A

Growth of multicellular organisms: his enables unicellular zygotes (as the zygote divides by mitosis) to grow into multicellular organisms

84
Q

the importance of mitosis.

Replacement of cells & repair of tissues

A

Damaged tissues can be repaired by mitosis followed by cell division
As cells are constantly dying they need to be continually replaced by genetically identical cells

85
Q

the importance of mitosis. Asexual reproduction

A

Asexual reproduction is the production of new individuals of a species by a single parent organism – the offspring are genetically identical to the parent
For unicellular organisms such as Amoeba, cell division results in the reproduction of a genetically identical offspring

86
Q

whats mitosis

A

Mitosis is the process of nuclear division by which two genetically identical daughter nuclei are produced that are also genetically identical to the parent nucleus

87
Q

mitosis is, in reality, one continuous process, it can be divided into four main stages

A

Prophase
Metaphase
Anaphase
Telophase

88
Q

prophase

A

Chromosomes condense and are now visible when stained

The chromosomes consist of two identical chromatids called sister chromatids (each containing one DNA molecule) that are joined together at the centromere

The two centrosomes (replicated in the G2 phase just before prophase) move towards opposite poles (opposite ends of the nucleus)

Spindle fibres (protein microtubules) begin to emerge from the centrosomes (consists of two centrioles in animal cells)

The nuclear envelope (nuclear membrane) breaks down into small vesicles

89
Q

Metaphase

A

centrosomes reach opposite poles

Spindle fibres (protein microtubules) continue to extend from centrosomes

Chromosomes line up at the equator of the spindle (also known as the metaphase plate) so they are equidistant to the two centrosome poles

Spindle fibres (protein microtubules) reach the chromosomes and attach to the centromeres

Each sister chromatid is attached to a spindle fibre originating from opposite poles

90
Q

anaphase

A

The sister chromatids separate at the centromere (the centromere divides in two)

Spindle fibres (protein microtubules) begin to shorten

The separated sister chromatids (now called chromosomes) are pulled to opposite poles by the spindle fibres (protein microtubules)

91
Q

telophase

A

Chromosomes arrive at opposite poles and begin to decondense

Nuclear envelopes (nuclear membranes) begin to reform around each set of chromosomes

The spindle fibres break down

92
Q

recognising prophase

A

Chromosomes are visible

The nuclear envelope is breaking down

93
Q

recognising Metaphase

A

Chromosomes are lined up along the middle of the cell

94
Q

recognising anaphase

A

Chromosomes are moving away from the middle of the cell, towards opposite poles

95
Q

recognising Telophase

A

Chromosomes have arrived at opposite poles of the cell
Chromosomes begin to decondense
The nuclear envelope is reforming

96
Q

motic indxx

A

mitotic index = number of cells with visible chromosomes ÷ total number of cells

97
Q

cell fractionation

A

Method used for isolating organelles from a tissue sample/cells is cell fractionation
Step 1 homogenisation: breaking up tissue and breaking open cells by mechanical force e.g. blender, pestle and mortar, homogeniser to release organelles
Solution used in homogenisation should be cold to reduce enzyme activity (to prevent damage to organelles)
Isotonic so organelles don’t burst/lyse or shrivel as no net movement of water in and out of organelle
pH buffered to preserve enzyme function/prevent enzymes being denatured
Step 2. Filtration of homogenate to remove unbroken tissue and cells/debris
Step 3. Centrifugation of organelles to separate by size/mass/density
First spin low speed gives nuclei in pellet and other organelles is supernatant/Supernatant can be centrifuged again at higher speed to obtain next largest organelle and so on

A level Biology (11 decks)

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