unit 2

Question 1

where is the dna kept in a eukaryotic cell?

Answer 1

1. the dna is contained in a membrane bound nucleus

Question 2

difference between eukaryote and prokaryote 3 points

Answer 2

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

Question 3

3 key features of a plant cell

Answer 3

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

Question 4

organelles in eukaryotic cell

Answer 4

membrane bound eg mitochondria

Question 5

what type of ribosomes do eukaryotic cells have

Answer 5

3.eukaryotic cells contain 80S ribosomes

Question 6

dna in eukaryotic cells

Answer 6

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

Question 7

what are plasmids

Answer 7

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

Question 8

what is a bacterial cell wall made out of

Answer 8

5-murein cell wall.

- amino acid and sugar

Question 9

what do slime capsules do

Answer 9

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

Question 10

Mesosome proika

Answer 10

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

Question 11

what is pili

Answer 11

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

Question 12

whats an artifact

Answer 12

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

Question 13

specialised animal cell red blood cell

Answer 13

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.

Question 14

ciliated epithelial cells

Answer 14

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.

Question 15

specialised cell: palisade cells

Answer 15

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.

Question 16

Specialised plant cell 2: root hair cell

Answer 16

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

Question 17

plasma membrane

Answer 17

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

Question 18

nucleus

Answer 18

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

Question 19

mitochondria

Answer 19

.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)

Question 20

chloroplasts

Answer 20

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

Question 21

Golgi apparatus

Answer 21

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

Question 22

Golgi vesicle

Answer 22

Membrane-bound sac for transport and storage

Question 23

cell membrane

Answer 23

.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

Question 24

cell wall

Answer 24

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

Question 25

ribosomes

Answer 25

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)

Question 26

Rough Endoplasmic Reticulum (RER)

Answer 26

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

Question 27

Smooth Endoplasmic Reticulum (ER)

Answer 27

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

Question 28

vacuole

Answer 28

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

Question 29

Lysosome

Answer 29

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)

Question 30

centriole

Answer 30

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

Question 31

Microtubules

Answer 31

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

Question 32

microvilli

Answer 32

Cell membrane projections that increase the surface area for absorption Cilia

Question 33

cillia

Answer 33

Hair-like projections made from microtubules | Allows the movement of substances over the cell surface

Question 34

flagella

Answer 34

Similar in structure to cilia, made of longer microtubules | Contract to provide cell movement for example in sperm cells

Question 35

what are the two main microscopes

Answer 35

electron and optical

Question 36

what is the optical microscope

Answer 36

Optical microscopes use light to form an image

Question 37

limits for optical microscopes

Answer 37

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

Question 38

what organelles can optical microscopes see

Answer 38

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

Question 39

what is a electron microscope

Answer 39

Electron microscopes use electrons to form an image

Question 40

why is an electron microscope better

Answer 40

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

Question 41

what can electron microscopes observe

Answer 41

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

Question 42

what are the two types of microscopes

Answer 42

Transmission electron microscopes (TEMs) | Scanning electron microscopes (SEMs)

Question 43

whats TEMs

Answer 43

TEMs use electromagnets to focus a beam of electrons | This beam of electrons is transmitted through the specimen

Question 44

advantages of TEMS

Answer 44

hey give high-resolution images (more detail) | This allows the internal structures within cells (or even within organelles) to be seen

Question 45

disadvantages of TEMS

Answer 45

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)

Question 46

what SEMS

Answer 46

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

Question 47

advantages of SEMs

Answer 47

they can be used on thick or 3-D specimens | They allow the external, 3-D structure of specimens to be observed

Question 48

disadvantages of SEMs

Answer 48

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)

Question 49

how big is a prokaryotic cell

Answer 49

0.5-5 microm

Question 50

how big is a eukaryotic cell

Answer 50

100 micrometres

Question 51

how do eukaryotes undergo cell division vs prokaryotes

Answer 51

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

Question 52

what is prokaryotic cell wall made out of

Answer 52

muerin or peptidoglycan | -polysaccharide and amino acids

Question 53

viruses

Answer 53

Viruses are non-cellular infectious particles | with diameters between 20 and 300 nm

Question 54

virus structure

Answer 54

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

Question 55

magnification equation

Answer 55

i | a x m

Question 56

converting units

Answer 56

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

Question 57

Converting units of measurement

Answer 57

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)

Question 58

Cell Fractionation & Ultracentrifugation

Answer 58

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

Question 59

what are the three stages of cell fractionation

Answer 59

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

Question 60

what is homogentasion

Answer 60

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

Question 61

conditions for homogenisation

Answer 61

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

Question 62

what is a homogenizer

Answer 62

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

Question 63

what is a homogenate

Answer 63

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

Question 64

filtration

Answer 64

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

Question 65

what happens in filtration

Answer 65

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

Question 66

what is ultracentrifugation

Answer 66

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

Question 67

stage one of ultracentrifugation

Answer 67

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

Question 68

what is a pellet

Answer 68

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

Question 69

what is a supernatant

Answer 69

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

Question 70

what happens with the supernatant

Answer 70

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

Question 71

how do you get the desired organelle to be separated out

Answer 71

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)

Question 72

what is an artifact

Answer 72

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

Question 73

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

Answer 73

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

Question 74

what is the cell cycle

Answer 74

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

Question 75

what are the three stages of the cell cycle

Answer 75

``` interphase nuclear division (mitosis) cell division (cytokinesis) ```

Question 76

what is interphase

Answer 76

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)

Question 77

what happends to the nucleus in the interphasse e

Answer 77

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

Question 78

g1 phase

Answer 78

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

Question 79

s phase

Answer 79

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

Question 80

g2

Answer 80

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

Question 81

Nuclear division (mitosis)

Answer 81

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

Question 82

Cytokinesis

Answer 82

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

Question 83

the importance of mitosis. Growth of multicellular organisms

Answer 83

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

Question 84

the importance of mitosis. | Replacement of cells & repair of tissues

Answer 84

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

Question 85

the importance of mitosis. Asexual reproduction

Answer 85

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

Question 86

whats mitosis

Answer 86

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

Question 87

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

Answer 87

Prophase Metaphase Anaphase Telophase

Question 88

prophase

Answer 88

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

Question 89

Metaphase

Answer 89

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

Question 90

anaphase

Answer 90

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)

Question 91

telophase

Answer 91

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

Question 92

recognising prophase

Answer 92

Chromosomes are visible | The nuclear envelope is breaking down

Question 93

recognising Metaphase

Answer 93

Chromosomes are lined up along the middle of the cell

Question 94

recognising anaphase

Answer 94

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

Question 95

recognising Telophase

Answer 95

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

Question 96

motic indxx

Answer 96

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

Question 97

cell fractionation

Answer 97

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