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biology a level > cells > Flashcards

cells Flashcards

1
Q

why do cells need to be small/ why is their size limited? (2)

A

1) in order to exchange materials with their surroundings.
2) SA:V ratio decreases as cell size increases (cells need a high SA:V ratio)

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2
Q

what is the typical diameter of a nucleus?

A

15 micrometers

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3
Q

what does a plant vacuole contain?

A

a solution of mineral salts, sugars, amino acids, wastes and sometimes pigments.

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4
Q

what are the functions of a plant vacuole? (3)

A

1) support herbaceous plants and herbaceous parts of woody plants by making cells turgid
2) sugars and amino acids stored in the vacuole may act as a temporary food source
3) pigments may colour petals to attract pollinating insects

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5
Q

what is the structure of a cell wall? (2)

A

1) made of cellulose microfibrils which are embedded in a matrix
2) has a middle lamella which is a thin layer which marks the boundary of and cements adjacent cell walls

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6
Q

what are the functions of the cell wall? (4)

A

1) provide mechanical strength to prevent the cell bursting under the pressure created by the osmotic entry of water
2) to provide structural support to the plant as a whole
3) to allow water to pass along it, contributing to the movement of water through the plant
4) physical barrier against pathogens

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7
Q

what are lysosomes? (2)

A

1) vesicles produced by the Golgi apparatus which have hydrolytic enzymes (proteases, lipases and lysozymes)
2) Lysosomes isolate these enzymes from the rest of the cell before releasing them either to the outside or into a phagocytic vesicle within the cell.

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8
Q

what are the functions of lysosomes? (5)

A

1) hydrolyse material ingested by phagocytes
2) exocytosis- release enzymes outside the cell in order to destroy material around the cell
3) digest worn out organelles so the useful chemicals they are made of can be re-used
4) autolysis- completely break down cells after they have died
5) all of the above is known as intracellular digestion

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9
Q

what are ribosomes and where are they typically found? (2)

A

1) composed of a large subunit and a small subunit (each contain rRNA and protein)
2) They can be found in the cytoplasm, attached to the ER as RER, or in groups called polyribosomes.

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10
Q

what happens in ribosomes?

A

site of protein synthesis

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11
Q

what are the two types of
ribosomes?

A

80S- found in eukaryotic cells around 25nm in diameter
70S- found in prokaryotic cells, mitochondria and chloroplasts

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12
Q

what is the endoplasmic reticulum? (2)

A

1) a network of flattened sacs and tubules (cisternae) that is spread through the cytoplasm and is continuous with the outer nuclear membrane.
2) it is involved in protein synthesis, lipid metabolism, and the maintenance of cellular homeostasis.

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13
Q

what is the structure of the RER? (2)

A

1) series of flattened sacs enclosed by a membrane with ribosomes on the surface
2) formed from continuous folds of membranes which are continuous with the nuclear envelope

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14
Q

what are the functions of the RER? (3)

A

1) folds and processes proteins made on the ribosomes.
2) provides a large surface area for the synthesis of proteins and glycoproteins
3) provides a pathway for the transport of materials, especially proteins throughout the cell.

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15
Q

what is the structure of the SER? (2)

A

1) system of membrane bound sacs
2) lack ribosomes on its surface and is often more tubular in appearance.

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16
Q

what are the functions of the SER?

A

1) to synthesise, store and transport lipids.
2) to synthesise, store and transport carbohydrates

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17
Q

what is the structure of the Golgi apparatus? (2)

A

1) a series of fluid filled, flattened and curved sacs
2) has vesicles surrounding the edges

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18
Q

what is the function of the Golgi apparatus? (3)

A

1) process and package proteins and lipids from the ER into vesicles.
2) vesicles transport the proteins and lipids to their required destination.
3) It also produces lysosomes.

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19
Q

how are the modified proteins/lipids made in the Golgi transported? (2)

A

1) transported in Golgi vesicles which are regularly pinched off from the ends of the Golgi cisternae
2) or the vesicles may move to the cell surface where they can fuse with the membrane and release their contents to the outside.

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20
Q

what are the main functions of the Golgi?

A

1) to add carbohydrates to proteins to form glycoproteins
2) to produce secretory enzymes
3) to secrete carbohydrates
4) to transport, modify and store lipids
5) to form lysosomes

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21
Q

what is the relationship between an organ system and specialised cells?

A

specialised cells which carry out a particular function are called tissues
->
organs are made of several tissue types
-> organ systems

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22
Q

what is the structure of a cell surface membrane? (2)

A

1) formed from a phospholipid bilayer
2) with extrinsic and intrinsic proteins embedded

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23
Q

what is the function of a cell surface membrane? (3)

A

1) to isolate cytoplasm from extracellular environment
2) to control the exchange of materials between the internal and external cell environment
3) involved in cell signalling/recognition

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24
Q

what are the cell walls of bacteria made of?

A

murein

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25
Q

what is the structure of the nucleus? (3)

A

1) surrounded by a nuclear envelope
(a semi-permeable double membrane)
2) has nuclear pores in the envelope to allow substances (mRNA and ribosomes) to enter/exit
3) dense nucleolus (made of rRNA and proteins) assembles ribosomes

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26
Q

what is the function of the nucleus? (2)

A

1) contains chromatin (genetic material)
2) controls cellular processes (gene expression determines specialisation, site of mRNA transcription and mitosis)

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27
Q

what is the structure of a mitochondrion? (3)

A

1) surrounded by a double membrane called the envelope
2) folded inner membrane forms cristae (site of electron transport chain)
3) fluid matrix (contains all enzymes needed for respiration)

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28
Q

what is the function of a mitochondrion? (3)

A

1) site of aerobic respiration
2) matrix contains enzymes needed for aerobic respiration, producing ATP
3) mitochondrial DNA and ribosomes are also found in the matrix (needed for replication)

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29
Q

what is structure of a chloroplast? (4)

A

1) disc shaped and surrounded by a double membrane
2) have membrane-bound compartments called thylakoids which contain chlorophyll
3) they stack to form structures called grana
4) these grana are joined together by lamellae (thin and flat thylakoid membranes)

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30
Q

what is the function of a chloroplast? (3)

A

1) site of photosynthesis
2) light dependent stage of photosynthesis takes place in the thylakoids
3) the light independent stage (Calvin cycle) takes place in the stroma.

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31
Q

why do chloroplasts contain small circular pieces of DNA and ribosomes?

A

they are needed to synthesise proteins used in chloroplast replication and photosynthesis

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32
Q

what usually happens to proteins which go through the Golgi apparatus? (4)

A

1) Proteins that go through the Golgi apparatus are usually exported (e.g. hormones such as insulin)
2) put into lysosomes (such as hydrolytic enzymes)
3) delivered to membrane-bound organelles
4) the Golgi usually modifies these proteins adding non protein components such as carbohydrates

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33
Q

What is a vesicle?

A

a membrane-bound sac for transport and storage

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34
Q

what is magnification?

A

the degree to which the size of an image is larger than the object itself

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35
Q

what is resolution?

A

the degree to which it is possible to distinguish between two objects that are very close together

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36
Q

what is the difference between electron microscopes and optical/light microscopes in terms of magnification and resolution?

A

electron microscopes have both a higher magnification and resolution

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37
Q

how do light microscopes work? (2)

A

1) use light to form an image
2) can be used to observe eukaryotic cells, their nuclei and possibly mitochondria and chloroplasts

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38
Q

what are the limitations of light microscopes (3)

A

1) poor and limited resolution as a result of the relatively long wavelength of light
2) can only distinguish between two objects if they are 0.2 micrometers or further apart
3) optical microscopes cannot be used to observe smaller organelles such as ribosomes, the endoplasmic reticulum or lysosomes

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39
Q

how do electron microscopes work? (2)

A

1) use electrons to form an image
2) electrons have a shorter wavelength- can distinguish objects only 0.1nm apart providing a more detailed image

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40
Q

how does the TEM work? (4)

A

1) use electromagnets to focus a beam of electrons
2) beam of electrons is transmitted through the specimen
3) Denser parts of the specimen absorb more electrons
4) these denser parts appear darker on the final image produced (produces contrast between different parts of the object being observed)

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41
Q

what are the limitations of the TEM? (4)

A

1) can only be used with very thin specimens or thin sections of the object being observed
2) cannot be used to observe live specimens (there is a vacuum inside a TEM, all the water must be removed from the specimen and so living cells cannot be observed)
3) lengthy treatment required to prepare specimens means that artefacts can be introduced
4) do not produce a colour image

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42
Q

what are artefacts (in microscopy)?

A

artefacts look like real structures but are actually the results of preserving and staining

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43
Q

what are the advantages of the TEM? (2)

A

1) high-resolution images
2) allows the internal structures within cells (or even within organelles) to be seen

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44
Q

how does the SEM work? (4)

A

1) scan a beam of electrons across the specimen
2) beam bounces off the surface of the specimen
3) electrons are detected, forming an image
4) This means SEMs can produce 3D images that show the surface of specimens

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45
Q

what are the advantages of the SEM? (2)

A

1) They can be used on thick or 3-D specimens
2) They allow the external, 3-D structure of specimens to be observed

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46
Q

what are the disadvantages of the SEM? (3)

A

1) They give lower resolution images (less detail) than TEMs
2) They cannot be used to observe live specimens
3) They do not produce a colour image

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47
Q

how do prokaryotic cells differ from eukaryotic cells? (5)

A

1) much smaller
2) cytoplasm that lacks membrane-bound organelles
3) Their ribosomes are structurally smaller (70 S) in comparison to those found in eukaryotic cells (80 S)
4) No nucleus (instead they have a single circular DNA molecule that is free in the cytoplasm and is not associated with proteins)
5) A cell wall that contains murein

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48
Q

what organelles do prokaryotic cells have that differentiate the species from others? (3)

A

1) one or more plasmids
2) a capsule surrounding the cell
3) one or more flagella.

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49
Q

what are viruses?

A

acellular and non-living particles

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50
Q

what are the key structures of viruses?

A

1) A nucleic acid core as genetic material (DNA or RNA)
2) A protein coat called a ‘capsid’
3) capsids will have attachment proteins which are essential to allow the virus to identify and attach to a host cell

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51
Q

what is the aim of differential centrifugation?

A

to isolate and collect large quantities of functional organelles in order to study their structure and function

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52
Q

how does differential centrifugation work? (2)

A

1) uses centrifugal force via spinning to separate out organelles of differing densities
2) works because the effect of gravity on each organelle will be different

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53
Q

what are the 3 conditions of the solution that the tissue/cell is placed into before being broken up?

A

1) isotonic- same water potential as tissue to prevent osmotic damage to organelles through lysis/bursting
2) cold- reduces enzyme activity to reduce organelle breakdown/damage
3) buffered- maintains optimum pH to prevent enzyme active site damage and so ensures the functioning of organelles

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54
Q

what is stage 1 of differential centrifugation? (6)

A

1) Homogenation (break open the cell)
2) grind/blend sample
3) cell membranes are broken down to release the cell contents
4) filter to remove non-organelle material e.g cellulose
5) remaining fluid is known as a homogenate/ homogenous solution
6) organelles are still in tact/functional

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55
Q

what is stage 2 of differential centrifugation? (4)

A

Ultracentrifugation
1) a variable speed centrifuge separates out organelles of differing densities using centrifugal force
2) largest and most dense organelles will be forced to the bottom of the test tubes first at the slowest speeds
(1000 rpm for 5-10 minutes)
3) this forms a sediment pellet
4) low speed for a short period of time

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56
Q

what is stage 3 of differential centrifugation? (4)

A

supernatant/pellet extraction
1) sediment pellet removed
2) this will contain functional nuclei
3) the supernatant fluid (remaining solution) is then respun at higher speeds for a longer period of time (3500 rpm for 10-20 minutes)
4) the next densest organelles then form a pellet (mitochondria, chloroplasts, lysosomes)

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57
Q

what is stage 4 of differential centrifugation? (3)

A

Lowest density organelles
1) higher speeds for longer periods of time
2) fragments of the endoplasmic reticulum and ribosomes can be extracted
3) following this, the supernatant will only contain soluble proteins

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58
Q

what phase happens before mitosis? (3)

A

interphase
1) DNA replication occurs
2) cell grows and organelles are replicated
3) each length of DNA forms a pair of identical strands called sister chromatids which are joined at the centromere

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59
Q

what do eukaryotic cells that retain the ability to divide show?

A

a cell cycle

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60
Q

what is mitosis? (2)

A

1) Mitosis is the part of the cell cycle in which a eukaryotic cell
divides to produce two genetically identical daughter cells
2) each with the identical copies of DNA produced by the parent cell during DNA replication.

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61
Q

how do chromosomes behave during interphase? (2)

A

1) genetic material in the nucleus exists as chromatin
2) each length of DNA forms a pair of identical strands called sister chromatids which are joined at the centromere

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62
Q

how do chromosomes behave during prophase? (2)

A

1) chromosomes condense and first become visible
2) chromosomes consist of two identical chromatids called sister chromatids (each containing one DNA molecule) that are joined together at the centromere

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63
Q

what happens during stage 1 of mitosis? (4)

A

stage 1- prophase
1) nuclear envelope and nucleolus breaks down leaving chromosomes free in the cytoplasm
2) chromosomes condense and first become visible
3) centrioles duplicate and move to opposite poles
4) spindle fibres begin to develop from the centrioles which span from pole to pole

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64
Q

what happens during stage 2 of mitosis? (5)

A

stage 2- metaphase
1) centrioles reach poles
2) spindle fibres continue to extend from centrioles
3) Chromosomes line up at the equator of the cell
4) spindle fibres reach the chromosomes and attach to the centromeres
5) each sister chromatid is attached to a spindle fibre originating from opposite poles

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65
Q

how do chromosomes behave during metaphase? (2)

A

1) chromosome line up at the equator of the cell
2) spindle fibres reach the chromosomes and attach to the centromeres

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66
Q

what happens during stage 3 of mitosis? (3)

A

stage 3- anaphase
1) The sister chromatids separate at the centromere/ the centromere divides in two
2) The separated sister chromatids (now called chromosomes) are pulled to opposite poles by the spindle fibres which contract
3) this process is energy dependent, provided by mitochondria which gather around the spindle fibres

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67
Q

how do chromosomes behave during anaphase? (2)

A

1) sister chromatids separate at the centromere and are pulled to opposite poles by the spindle fibres which contract
2) sister chromatids now referred to as chromosomes

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68
Q

what happens during stage 4 of mitosis? (3)

A

stage 4- telophase
1) Chromosomes arrive at opposite poles and begin to decondense/ become longer and thinner
2) nuclear envelopes (nuclear membranes) and nucleolus begin to reform around each set of chromosomes
3) The spindle fibres break down

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69
Q

how do chromosomes behave during telophase? (2)

A

1) chromosomes arrive at respective poles
2) chromosomes begin to decondense/ become longer and thinner, leaving only widespread chromatin

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70
Q

what happens after mitosis?

A

cytokinesis
Division of the cytoplasm usually occurs, producing two new daughter cells which are genetically identical to each other and the parent cell

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71
Q

what can happen due to uncontrolled cell division? (2)

A

1) the formation of tumours and cancers
2) any cancer treatments are directed at controlling the rate of cell division.

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72
Q

how does cell division take place in prokaryotic cells? (3)

A

1) Binary fission
2) replication of the circular DNA and of plasmids
3) division of the cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids.

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73
Q

do viruses undergo cell division? (2)

A

1) Being non-living, viruses do not undergo cell division.
2) Following injection of their nucleic acid, the infected host cell replicates the virus particles.

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74
Q

how is the cell cycle split up?

A

1) interphase- occupies most of the cell cycle, no division takes place
2) nuclear division (mitosis or meiosis)
3) cytokinesis

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75
Q

what does 2n represent? (2)

A

1) parent and daughter cells in mitosis are diploid= 2n
2) n= number in a set of chromosomes

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76
Q

why is mitosis important? (3)

A

1) increases cell numbers in an organism
2) growth and repair depends on mitosis
3) asexual reproduction relies on mitosis

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77
Q

on a graph what symbols represent which stages in the cell cycle?

A

1) G1- interphase (cell grows, organelles replicated)
2) S- DNA replication forming sister chromatids (included in interphase)
3) G2- replication of centrioles, second growth phase
4) M- mitosis

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78
Q

how does cancer form? (3)

A

1) result of damage to the genes that regulate mitosis and the cell cycle
2) leads to uncontrolled growth/ cell cycle
3) group of abnormal cells called a tumour develops

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79
Q

how do drugs used to treat cancer disrupt the cell cycle? (2)

A

1) preventing DNA from replicating
2) inhibit the metaphase of mitosis by interfering with spindle formation

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80
Q

what does the fluid mosaic model help to explain? (3)

A

1) Passive and active movement between cells and their surroundings
2) Cell-to-cell interactions
3) Cell signalling

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81
Q

what is a phospholipid monolayer?

A

when phospholipids are spread over the surface of water they form a single layer with the hydrophilic phosphate heads in the water and the hydrophobic fatty acid tails sticking up away from the water

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82
Q

what is a phospholipid bilayer? (3)

A

1) basic structure of a cell membrane
2) composed of two layers of phospholipids; their hydrophobic tails facing inwards and hydrophilic heads outwards
3) hydrophobic barrier to water-soluble molecules and ions

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83
Q

The phospholipid bilayers that make up cell membranes also contain…

A

proteins which can either be intrinsic or extrinsic

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84
Q

where are intrinsic proteins found? (2)

A

embedded in the membrane/ span the membrane from one side to the other

85
Q

where are extrinsic proteins found? (2)

A

1) extrinsic proteins are embedded in the outer or inner surface of the membrane
2) do not extend the width of the membrane

86
Q

why does the fluid mosaic model describes cell membranes as ‘fluid? (3)

A

1) The phospholipids and proteins can move around relative to each other within the structure which allows the structure to be fluid
2) The phospholipids mainly move sideways, within their own layers
3) many different types of proteins interspersed throughout the bilayer move about within it, although some may be fixed in position

87
Q

why does the fluid mosaic model describes cell membranes as ‘mosaics’?

A

the membrane contains a variety of different molecules to perform different functions

88
Q

what are the functions of extrinsic proteins? (4)

A

1) mechanical support
2) recognition sites (e.g for hormones for hormones to bind)
3) cell adhesion
4) usually glycoproteins

89
Q

what are the functions of intrinsic proteins?

A

can serve as a channel protein or carrier protein or hormone receptor

90
Q

what are the functions of carrier proteins in terms of active transport? (5)

A

1) molecule binds to carrier protein on one side of the membrane
2) ATP is hydrolysed to ADP and Pi
3) the phosphate binds to the carrier protein on the other side of the membrane, causing it to change shape
4) molecule travels through newly opened channel in the cell
5) carrier protein returns to its original shape

91
Q

what are the functions of channel proteins?

A

enable specific water soluble molecules to diffuse through and across the membrane.

92
Q

what are phospholipids?

A

the main components in the cell membrane which form the phospholipid bilayer arrangement

93
Q

how is the phospholipid bilayer formed? (2)

A

1) hydrophilic phosphate heads orientated outwards due to the attraction to water/ cytoplasm/ extracellular fluid
2) hydrophobic fatty acid tails orientated inwards toward the middle of the membrane due to being repelled by water/fluid on both sides

94
Q

what are the functions of cholesterol molecules within the phospholipid bilayer? (5)

A

1) hydrophobic
2) add mechanical strength
3) attract fatty acid ‘tails’ together which increases rigidity of structure
4) maintains membrane fluidity and flexibility
5) restricts the movement of other molecules making up the membrane.

95
Q

what are glycoproteins on the phospholipid bilayer?

A

CHO groups bonded to extrinsic proteins on the outer surface of the membrane

96
Q

what are the functions of glycoproteins on the phospholipid bilayer? (3)

A

1) perform cell recognition roles (lymphocytes recognising own body cells)
2) form specific receptor sites (largely for hormones and neurotransmitters)
3) also have cell adherence roles

97
Q

describe the permeability of cell membranes (4)

A

1) unless substances are lipid-soluble, they are regulated from entering cells
2) substances may be too large to pass through the channel proteins
3) specific proteins will transport specific substances and not others
4) polarised/ charged molecules are also repelled by phospholipid bilayer

98
Q

what are phospholipid bilayers permeable to?

A

lipid soluble substances which will diffuse freely across the phospholipids

99
Q

what are the main functions of the cell membrane? (6)

A

1) to form a boundary, separating the cytoplasm from external environment
2) control entry and exit of substances from cell and organelles
3) separate organelles from cytoplasm to enable biochemical functions (conc. gradient) to be maintained
4) to provide an internal transport system (ER)
5) to isolate potentially damaging enzymes (lysosomes)
6) to provide surfaces for biochemical reactions to occur on (grana in chloroplasts)

100
Q

what is diffusion?

A

the net movement of molecules or ions down a concentration gradient

101
Q

where can diffusion occur? (2)

A

1) across a membrane
2) not across a membrane e.g water vapour diffusing out through stomata

102
Q

what factors increase diffusion rate? (4)

A

1) large concentration gradient
2) large surface area (greater no. of molecules which can cross at any given moment)
3) higher temperature (more kinetic energy)
4) short diffusion pathway

103
Q

how do water soluble ions and molecules diffuse across membranes? give examples

A

through facilitated diffusion
e.g
glucose, amino acids, Na+, K+

104
Q

what are the 2 ways in which facilitated diffusion can occur?

A

1) using membrane channel proteins
2) using carrier proteins

105
Q

how does facilitated diffusion occur using membrane channel proteins? (3)

A

1) channel proteins are specific to only one ion
2) it is hydrophilic channel which allows ions to move through
3) ion channels can become saturated which limits rate of diffusion

106
Q

how does facilitated diffusion occur using carrier proteins? (3)

A

1) water soluble ion/ polar molecule will be specific to and bind to carrier protein
2) carrier protein changes shape
3) water soluble ion/molecule is released.

107
Q

what are 2 key things to remember about facilitated diffusion?

A

1) it still occurs down a concentration gradient
2) still a passive process (no ATP required)

108
Q

what is the limitation of facilitated diffusion? (2)

A

1) carrier/channel proteins can be saturated at a maximum rate
2) so rate of diffusion will stop/level off

109
Q

name the different types of movement across membranes? (5)

A

1) simple diffusion (involving limitations imposed by the nature of the phospholipid bilayer)
2) facilitated diffusion (the roles of carrier proteins and channel proteins)
3) osmosis (explained in terms of water potential)
4) active transport (the role of carrier proteins and the importance of the hydrolysis of ATP)
5) co-transport (the absorption of sodium ions and glucose by cells lining the mammalian ileum).

110
Q

explain the adaptations of specialised cells in relation to the rate of transport across their internal and external membranes? (3)

A

1) increase in the surface area of the internal membranes (stacks of golgi apparatus) or the cell surface membrane (such as the presence of microvilli)
2) increase in the no. of protein channels and carrier molecules in their membranes.
3) mechanisms to set up concentration/water potential gradients across membranes.

111
Q

how may cells be adapted for rapid transport across their internal or external cell membranes? (3)

A

1) Increase SA so more carrier proteins and channel proteins can be inserted therefore the faster the rate of diffusion.
2) Increase in the no. of channel or carrier proteins so more molecules/ions can get transported at a faster rate.
3) the greater the concentration gradient the faster the rate of diffusion/osmosis and therefore the rate of transport.

112
Q

how can we explain passive forms of transport? (2)

A

1) particles are constantly in random motion due to the kinetic energy that they possess
2) particles are constantly bouncing off each other

113
Q

what is osmosis?

A

the net movement of water from an area of higher water potential to an area of lower water potential/down a concentration gradient through a selectively permeable membrane.

114
Q

what can happen as a result of diffusion?

A

molecules/ions tend to reach an equilibrium situation where they are evenly spread within a given volume of space

115
Q

which substances cannot diffuse through the phospholipid bilayer of cell membranes? (2)

A

1) Large polar molecules such as glucose and amino acids
2) Ions such as sodium ions (Na+) and chloride ions (Cl-)

116
Q

what does a “partially permeable” membrane mean?

A

it allows small molecules (like water) to freely enter but not larger molecules (like solute molecules)

117
Q

explain the link between dilution and water potential and how this affects osmosis (3)

A

1) A dilute solution has a high water potential (less sugar, more water)
2) a concentrated solution has a low water potential (more sugar, less water)
3) osmosis always moves from dilute/more water to concentrated

118
Q

under standard conditions of temperature and pressure, pure water has a water potential of…

A

zero

119
Q

in osmosis, both the solute and water molecules are in random motion due to their…

A

kinetic energy

120
Q

what happens when the water potential on either side of the plasma membrane is equal? (2)

A

1) a dynamic equilibrium is reached
2) no net movement of water

121
Q

what is a hypertonic solution?

A

has a lower water potential than that of the cell/ higher concentration of solutes

122
Q

what is a hypotonic solution?

A

has a higher water potential than that of the cell/ lower concentration of solutes

123
Q

what is an isotonic solution?

A

a solution which has the same water potential of that of the cell/ equal concentration of solutes

124
Q

what will happen if a plant cell is placed in pure water or a dilute solution (high water potential) (2)

A

1) water will enter the plant cell through its partially permeable cell surface membrane by osmosis
2) as the pure water or dilute solution has a higher water potential than the plant cell

125
Q

what happens as water moves into a plant cell via osmosis? (3)

A

1) as water enters the vacuole of the plant cell, the volume of the plant cell increases
2) The expanding protoplast swells and pushes against the cell wall and pressure builds up inside the cell but the inelastic cell wall prevents the cell from bursting
3) The pressure created by the cell wall also stops too much water entering which also helps to prevent the cell from bursting

126
Q

why is turgidity important for plants? (3)

A

1) provides support and strength for the plant
2) makes the plant stand upright with its leaves held out to catch sunlight
3) If plants do not receive enough water the cells cannot remain rigid and firm (turgid) and the plant wilts

127
Q

what happens if a plant cell is placed in a solution with lower water potential than the plant cell?

A

water will leave the plant cell through its partially permeable cell surface membrane by osmosis

128
Q

what happens when water moves out of a plant cell via osmosis? (4)

A

1) As water leaves the vacuole of the plant cell, the volume of the plant cell decreases
2) The protoplast gradually shrinks and no longer exerts pressure on the cell wall
3) As the protoplast continues to shrink, it begins to pull away from the cell wall
4) This process is known as plasmolysis – the plant cell is plasmolysed

129
Q

what is active transport?

A

the movement of molecules and ions through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration

130
Q

what does active transport require? (3)

A

1) carrier proteins (each carrier protein being specific for a particular type of molecule or ion)
2) energy required to make the carrier protein change shape, allowing it to transfer the molecules or ions across the cell membrane
3) The energy required is provided by ATP released during respiration. The ATP is hydrolysed to release energy.

131
Q

how is active transport different to facilitated diffusion?

A

Although facilitated diffusion also uses carrier proteins active transport is different as it requires energy and goes against the concentration gradient

132
Q

how is the energy required for active transport provided? (2)

A

1) provided by ATP (adenosine triphosphate) released during respiration
2) The ATP is hydrolysed to release energy

133
Q

what is co transport? (3)

A

1) the coupled movement of substances across a cell membrane via a carrier protein
2) two types of molecule are moved across the membrane at the same time; the movement of one is dependent on the movement of the other
3) involves a combination of facilitated diffusion and active transport

134
Q

what is stage 1 of the absorption of sodium ions and glucose by epithelial cells lining the ileum? (3)

A

1) sodium ions are actively transported out of the epithelial cells into the blood via a sodium/potassium pump
2) this takes place one type of carrier protein found in the cell-surface membrane of the epithelial cells
3) active process

135
Q

what is stage 2 of the absorption of sodium ions and glucose by epithelial cells lining the ileum?

A

after sodium ions are actively transported out of the epithelial cell this results in a sodium concentration gradient between the lumen (high) and the epithelial cell cytoplasm (low)

136
Q

what is stage 3 of the absorption of sodium ions and glucose by epithelial cells lining the ileum? (6)

A

1) sodium ions diffuse from the lumen into the epithelial cell cytoplasm through a co-transport protein in the cell surface membrane by co-operative facilitated diffusion
2) they diffuse through this protein combined with glucose molecules and both diffuse through together
3) sodium diffuses down its conc. gradient
4) glucose diffuses up/ against its conc. gradient
5) sodium ion conc. gradient rather than ATP that powers the movement of glucose so it is the indirect active transport of glucose
6) passive process

137
Q

what is stage 4 of the absorption of sodium ions and glucose by epithelial cells lining the ileum?

A

glucose passes from the cytoplasm into the blood using another type of carrier protein by facilitated diffusion, down its concentration gradient

138
Q

how is rate of absorption increased in the small intestine? (5)

A

1) long small intestine
2) folded outer surface
3) presence of villi
4) presence of microvilli on villi
5) maintenance of a steep concentration gradient through the movement of blood, villi etc.

139
Q

how is indirect active transport used in the absorption of sodium ions and glucose by epithelial cells lining the ileum? (2)

A

1) indirect AT involves pumping a second molecule/ion and establishing a conc. gradient with this substance
2) this gradient is then used to co-transport the second molecule (glucose) by cooperative facilitated diffusion

140
Q

Each type of cell has specific molecules on its surface that identify it. These molecules include proteins and enable the immune system to identify… (4)

A

1) infected body cells
2) cells from other organisms of the same species
3) abnormal body cells
4) toxins

141
Q

what is an antigen? give examples

A

A cell surface molecule, usually a protein/glycoprotein with a specific tertiary structure that can trigger an immune response by lymphocytes
e.g Infected host cells, Cancer cells

142
Q

what is the effect of antigen variability on disease prevention? (2)

A

1) reduces the effectiveness of vaccines
2) antibodies are no longer complementary to antigens so no antigen-antibody complex forms
.

143
Q

what is antigen variability? (2)

A

1) pathogens DNA mutates regularly and can result in new shapes of antigens being made
2) memory cells do not detect the altered antigens and are no longer effective against the pathogen

144
Q

what is the effect of antigen variability on disease? (2)

A

1) makes organisms more susceptible to pathogenic disease
2) an organism with a resistance to a certain pathogen will only have memory B lymphocytes associated with the previous antigens of that pathogen

145
Q

outline the phagocytosis of pathogens (6)

A

1) phagocytes are attracted to the pathogen by chemoattractants
2) phagocytes attach themselves to the surface of the pathogen
3) phagocytes engulf the pathogen into a temporary vesicle called a phagosome
4) lysosomes move towards the phagosome and fuse with it
5) lysozymes (proteases etc) digest the pathogen by the hydrolysis of large insoluble molecules into small soluble molecules
6) the soluble breakdown products from the pathogen are absorbed into the cytoplasm of the phagocyte

146
Q

what adaptations do phagocytes have for phagocytosis? (3)

A

1) extra flexible cell membrane
2) multi-lobed nucleus
3) allows phagocytosis and shape change

147
Q

what are pathogens? give examples

A

micro organisms that cause disease
e.g bacteria, viruses, fungi

148
Q

what is phagocytosis?

A

The process by which a phagocyte surrounds and destroys foreign substances

149
Q

what are antigen presenting cells? give examples

A

any cell that presents a non self-antigen on their surface
e.g
infected body cells with viral antigens on their surface
cells of a transplanted organ
a macrophage which has engulfed and destroyed a pathogen
cancer cell

150
Q

why is the cellular response specific?

A

T-cells respond to antigens on the surface of cells

151
Q

why is it called the cellular response? (2)

A

1) T cells only respond to antigens which are present on antigen presenting cell
2) not antigens detached from cells and within bodily fluids

152
Q

what is stage 1 of the cellular response (3)

A

1) Helper T cells have receptors on their surface which are complementary to and can attach to the antigens on the antigen presenting cell
2) this activates the helper T cells and they divide by mitosis to replicate and make large numbers of clones of themselves

153
Q

after helper T cells divide by mitosis they can produce more helper T cells to: (3)

A

1) stimulate B cells to divide and secrete their antibody
2) stimulate macrophages to perform more phagocytosis
3) stimulate cytotoxic T cells (killer T cells) (most common)

154
Q

what are cytotoxic T cells?

A

destroy abnormal or infected cells

155
Q

how do cytotoxic T cells work? (2)

A

1) release a protein called perforin which embeds in the cell surface membrane of virus-infected cells and makes a pore so any substances can enter or exit the cell
2) this causes cell death

156
Q

what is the cellular response? (2)

A

1) involves the response of T lymphocytes to a foreign antigen.
2) They only respond to antigens on the surface of cells

157
Q

what are antibodies?

A

proteins produced by the immune system in response to foreign substances, such as viruses or bacteria.

158
Q

what is the structure of antibody? (4)

A

1) has a variable region which is where the antigen binding site is located which is a complementary shape to only one antigen - each antibody has a different tertiary structure
2) has a constant region which is the same tertiary structure in all antibodies
3) has a flexible ‘hinge’ which allows binding of 2 antigen molecules easily
4) S-S bonds hold the 4 polypeptide chains together

159
Q

what is immunity?

A

when a person has memory cells and antibodies against a pathogen

160
Q

why are antibodies described as having a quaternary structure?

A

4 polypeptide chains

161
Q

why do antibodies specifically bind to just 1 antigen? (3)

A

1) antibody has a specific amino acid structure
2) so the antigen binding site has a specific tertiary structure which is a complementary shape to the antigens
3) antibody-antigen complex forms

162
Q

how does the body form lymphocytes which don’t attack our own cells? (7)

A

1) the womb is sterile and no infection occurs so lymphocytes won’t encounter any foreign antigens
2) any antigens the lymphocytes do encounter will be ‘self’ antigens
3) lymphocytes that have receptors to bind to these ‘self’ antigens are destroyed or suppressed
4) nearly all of the remaining lymphocytes will be those that bind to ‘non-self’ antigens
5) in childhood, the bone marrow is also sterile so any immature lymphocytes being made will only encounter ‘self’ antigens
6) any immature lymphocyte in the bone marrow with receptors that bind to ‘self’ antigens will undergo apoptosis
7) as a result, only lymphocytes that have receptors that bind to ‘non-self’ antigens will ever appear in the blood

163
Q

what are B lymphocytes (2)

A

1) involved in the specific immune response/ humoral response
2) mature in the bone marrow

164
Q

what is the humoral response?

A

response involving B cells and making antibodies

165
Q

outline the humoral response (8)

A

1) A complementary T-helper cell binds to foreign antigen on APC
2) activated T helper cell divides by mitosis to clone itself
3) B cell collides with T helper cell receptor which activates the B cell to go through clonal expansion and differentiation (clonal selection)
4) activated B cells divide by mitosis and differentiate into B plasma cells or B memory cells
5) B plasma cells secrete antibodies using the ribosomes on the RER
6) antibodies bind to and agglutinate the pathogen and mark it for phagocytosis
7) B memory cells are made with receptors to bind to the same antigen. If they do not bind to antigen, they divide quickly to make B plasma cells that quickly make lots of antibodies.

166
Q

how do antibodies destroy antigens (3)

A

1) formation of antigen-antibody complex
2) results in agglutination as antibodies are flexible and can bind to multiple antigens to bind them together
3) which enhances phagocytosis/ easier for phagocytes to locate them.

167
Q

what are memory cells? (4)

A

1) specialised T helper/ B cells produced from the primary immune response
2) remain in very low levels in the blood
3) can live in the body for decades
4) do not make antibodies but can divide very rapidly by mitosis into B plasma cells if organism encounters the same pathogen again to make large numbers of antibodies rapidly before any symptoms occur

168
Q

describe what would happen if someone was given a poorly matched kidney? (8)

A

1) kidney cells will have foreign antigens on their cell surface membrane
2) kidney cells act as antigen presenting cells
3) T helper cells that bind to these specific antigens will become activated
4) these will then activate the correct B cells
5) B cells divide by mitosis to produce lots of B-plasma cells
6) these then produce millions of antibodies proteins using the many ribosomes on the RER
7) the antibodies only bind to the donated kidney because only the donated kidney cells have the foreign antigen
8) the antibody only binds to that one specific antigen due to the unique tertiary structure of its antigen binding site

169
Q

what is a log scale?

A

enables accurate plotting of data that has a very wide range of values on 1 reasonably-sized axis with a sensible scale

170
Q

compare the secondary immune response to the first (6)

A

1) secondary immune response is quicker
2) secondary immune response produces a much higher concentration of antibodies
3) secondary immune response is longer lasting
4) secondary immune response produces more memory cells so the tertiary response would be even stronger
5) this is because memory cells bind to the antigens and rapidly divide by mitosis to form a clone of B plasma cells
6) Antigen presentation and T helper cell activation are not required

171
Q

what is passive immunity?

A

produced by the introduction of antibodies into the individuals from an outside source

172
Q

give 3 features of passive immunity

A

1) no direct contact with the pathogen or its antigen is necessary to induce immunity
2) antibodies are not being produced by the individuals themselves so antibodies are not replaced when broken down
3) no memory cells formed so no lasting immunity

173
Q

give two examples of passive immunity (2)

A

1) anti venom given to snake bite victims
2) immunity acquired by the foetus when antibodies pass across the placenta from the mother

174
Q

how is active immunity achieved?

A

produced by stimulating the production of antibodies by the individual’s own immune system

175
Q

give 2 features of active immunity

A

1) direct contact with the pathogen or its antigen is necessary
2) long-lasting

176
Q

what are the two types of active immunity?

A

1) natural active immunity
- results from an individual becoming infected with disease under normal circumstances
- which causes the body to produce its own antibodies and may continue to do so for many years
2) artificial active immunity
- forms the basis of vaccination which involves inducing an immune response in an individual without them suffering the symptoms of the disease

177
Q

how do vaccines provide protection for individuals against disease? (4)

A

1) stimulate an immune response against a particular disease by injecting or ingesting a dead pathogen or weakened antigen
2) often contains one or more types of antigens from the pathogen
3) memory cells are produced which remain in the blood so allow a greater and more immediate response to a future infection with the same pathogen
4) results in a rapid production of antibodies so the new infection is overcome before it can cause any harm with few symptoms

178
Q

how do vaccines provide protection for populations against disease? (3)

A

1) when vaccines are carried out on a large scale, this provides protection for the whole population through herd immunity
2) it arises when a sufficiently large proportion of the population has been vaccinated which makes it difficult for a pathogen to spread within the population as pathogens spread from individual to individual when in close contact
3) this makes it highly unlikely that a susceptible individual will come in contact with an infected person so those who are not immune to the disease are still protected

179
Q

why is herd immunity important? (2)

A

1) because babies and very young children cannot be vaccinated as their immune system is not fully functional
2) it could also be dangerous to vaccinate those who are ill or have compromised immune systems (HIV)

180
Q

how is herd immunity achieved? (2)

A

1) vaccination is best carried out at one time
2) meaning that for a certain period there are very few individuals in the population with the disease and the transmission of the pathogen is interrupted

181
Q

what makes a successful vaccine? (5)

A

1) economically available in sufficient quantities to immunise most of the vulnerable population
2) few side effects- side effects may discourage individuals from being vaccinated
3) technologically advanced equipment as a means of producing, storing and transporting the vaccine
4) appropriately trained staff to administer the vaccine properly
5) must be possible to vaccinate the vast majority of the vulnerable population to produce herd immunity

182
Q

what are the ethical issues surrounding vaccines? (4)

A

1) animal testing
2) side effects which may cause long term harm
3) if vaccines should be compulsory (not in the UK)
4) how vaccines are tested (volunteers in the UK)

183
Q

why may vaccinations fail to eliminate a disease? (6)

A

1) vaccines will fail to induce immunity in people with defective immune systems
2) individuals may develop the disease immediately after vaccination but before their immunity levels are high enough to prevent it. These individuals may harbour the pathogen and reinfect others.
3) pathogen may mutate frequently so that antigens change suddenly meaning vaccines become ineffective as the new antigens on the pathogen are no longer recognised by the immune system. This means the immune system will not produce antibodies to destroy the pathogen so immunity is short-lived. (antigen variability)
4) may be many varieties of a particular pathogen that it is impossible to develop a vaccine that is effective against them all such as the common cold virus
5) certain pathogens ‘hide’ from the body’s immune system by concealing themselves inside cells or living in places out of reach such as cholera which hides in the intestines
6) individuals may have objections to vaccination for religious, ethical or medical reasons

184
Q

what are the economic costs and benefits of vaccines in the UK? (4)

A

cost:
1) prices of millions of vaccines
2) cost of trained nurses to give the vaccines
benefit:
1) fewer days off work with illness
2) the NHS has to treat fewer serious infections

185
Q

how do activated T helper cells activate Cytotoxic T-cells?

A

they have the same receptor

186
Q

where do T cells mature?

A

in the Thymus gland

187
Q

where do B cells mature?

A

in the Bone marrow

188
Q

T helper cell receptors, B cell receptors, Cytotoxic T cell receptors and antibodies all have a (1) (2) (3) to the (4) (5)

A

1) tertiary
2) structure
3) complementary
4) presented
5) antigen

189
Q

the cellular response happens (1) the humoral response

A

alongside

190
Q

outline the difference between the humoral and cellular response

A

humoral response- antibodies agglutinate viruses and tag them for phagocytosis
cellular response- kills body cells, usually infected with viruses

191
Q

how are monoclonal antibodies made?

A

In the lab from hydbridoma cells (a fusion of 1 cancer cell and 1 B plasma cell)

192
Q

what is a monoclonal antibody?

A

monoclonal antibodies bind to just one antigen made by hybridoma cells from just 1 B-plasma and 1 cancer cells in a laboratory

193
Q

how can monoclonal antibodies be used for immunotherapy? (5)

A

1) monoclonal antibodies against cancer/disease are made by injecting a mouse with a cancer/disease antigen
2) chemotherapy drug is attached to the other end of the monoclonal antibody
3) this is injected into the human and will only target the organ with the cancer cell antigens
4) higher drug concentration at cancer cells means there is a quicker effect
5) lower drug concentration elsewhere means there is fewer side effects

194
Q

how can monoclonal antibodies be used for diagnosis? (3)

A

1) inject a monoclonal antibody that binds to specific antigen which is attached to a dye, fluorescent or radioactive marker
2) antibody binds to antigen on the infected cells
3) antibody is detected by being radioactive or fluorescent using a gamma-ray camera etc

195
Q

in diagnosis, why will monoclonal antibodies only bind to infected cells? (2)

A

1) antigens are only found on infected body cells
2) monoclonal antibodies have a specific tertiary structure which is only complementary to the antigens

196
Q

outline the ELISA test for HIV (6)

A

1) attach antigens from a sample of the patient’s blood and place on a plastic slide
2) add monoclonal antibodies that specifically bind to the HIV antigen (produced by a mouse)
3) wash plastic slide to remove any unbound 1st antibodies to prevent false positive results
4) add 2nd monoclonal antibody that binds to the 1st antibody which has an enzyme attached to it
5) wash slide again to remove any unbound 2nd antibody to avoid any false positive results
6) add a colourless substrate which will react with the enzyme resulting in a blue product that indicates a positive result.

197
Q

outline the results of the ELISA test for HIV is the person is negative (3)

A

1) person will not have the HIV antigen so the first monoclonal antibodies won’t bind and will be washed away
2) second monoclonal antibodies will also have nothing to bind to and will be washed away
3) there will be no enzyme to react with the substrate so no blue product will be released, indicating a negative result

198
Q

outline the ELISA. test for pregnancy (5)

A

1) pregnant woman’s urine is added to monoclonal antibodies which will bind to the hcg
2) wash away the urine- the hcg will stay attached to the monoclonal antibodies
3) add 2nd monoclonal antibodies against hcg with an enzyme attached
4) wash away unbound 2nd antibody to avoid any false positive results
5) add colourless substrate which is turned blue by the enzyme, indicating a positive result

199
Q

why don’t other hormones give a positive result in the ELISA pregnancy test?

A

other hormones won’t have a complementary shape to bind to the first or second antibody

200
Q

why is HIV known as a retrovirus? (2)

A

1) contains reverse transcriptase
2) the consequent ability to make DNA from RNA means that HIV belongs to a group of viruses called retroviruses

201
Q

how does HIV replicate In T helper cells? (11)

A

1) HIV enters the bloodstream and circulates around the body
2) HIV attachment proteins bind specifically to CD4 proteins which are mostly found on T helper cells
3) HIV lipid envelope fuses with T helper cell membrane
4) capsid enters the T helper cell
5) capsid gets removed, releasing the HIV enzymes and RNA into the T helper cell cytoplasm
6) HIV reverse transcriptase makes a DNA copy of the HIV RNA
7) the DNA copy enters the T helper cell nucleus
8) DNA copy is transcribed into mRNA copies by RNA polymerase
9) this mRNA copy leaves the nucleus via nuclear pores
10) human cell ribosomes translate the HIV mRNA to make HIV proteins which then self-assemble into new HIV particles
11) New HIV particles burst out of the T helper cell, wrapping themselves in human cell membrane as they go to form their own lipid envelope

202
Q

describe how HIV is replicated once inside T helper cells (4)

A

1) HIV RNA converted into DNA using reverse transcriptase
2) DNA inserted into T helper cell nucleus
3) DNA transcribed into HIV mRNA
4) HIV mRNA translated into new HIV/viral proteins for assembly into viral particles

203
Q

explain how HIV affects the production of antibodies when AIDS develops in a person (3)

A

1) less/no antibody produced
2) Because HIV destroys/reduces number of helper T cells
3) So few/no B cells activated / stimulated so no/few B cells undergo mitosis and differentiate to form plasma cells which produce antibodies

204
Q

how does HIV cause the symptoms of AIDS? (6)

A

1) HIV specifically attacks T helper cells by killing them or interfering with their normal function
2) person with AIDS will have significantly less functioning T helper cells
3) without a sufficient amount of T helper cells the immune system cannot stimulate B cells to divide by mitosis to create B plasma cells which produce antibodies/ humoral response is limited
4) cellular response is limited as less T helper cells are able to stimulate cytotoxic T cells which kill infected body cells
5) body is unable to produce an adequate immune response and becomes susceptible to secondary diseases and cancers
6) these ultimately cause death

205
Q

why are antibiotics ineffective against viruses? (7)

A

1) antibiotics inhibit bacteria from making cross-links to their murein cell walls so they are much weaker meaning the bacteria burst and die when water enters them by osmosis
2) viruses aren’t affected as they do not have cell walls but have protein coats
3) other antibiotics inhibit the 70s ribosomes of bacteria
4) viruses use 80s human ribosomes to make their proteins so aren’t affected
5) viruses rely on the host cell to carry about their metabolic activities and so lack their own metabolic pathways and structures
6) antibiotics are ineffective because there are no metabolic mechanisms/ cell structures for them to interrupt
7) when viruses are within an organism’s own cells, antibiotics cannot reach them

206
Q

what are the ethical issues associated with the use of vaccines and monoclonal
antibodies? (4)

A

1) Use of animals: all vaccines are tested on animals before they can move onto human-trials
2) potentially dangerous side effects
3) compulsory or the choice to opt out
4) balancing individual health risks against herd immunity

207
Q

on a test strip, why does the soluble monoclonal antibody with a dye attached only bind to the specific antigen?

A

the tertiary structure of the antibody means that its antigen-binding site is a complementary shape only to the antigen from that disease

208
Q

on a test strip why is the control line important? (2)

A

1) prevents false negative results
2) shows that an antibody has successfully moved up the test strip

biology a level (12 decks)

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