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cells Flashcards

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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? (4)

A

1) formed outside the cell membrane
2) made of cellulose microfibrils which are embedded in a matrix
3) has a middle lamella which is a thin layer which marks the boundary of and cements adjacent cell walls
4) has narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata to connect the cytoplasm of neighbouring plant cells

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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 phagocytic vesicles
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) small cytoplasmic granules which are 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?

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? (3)

A

1) a series of fluid filled, flattened and curved sacs
2) has vesicles surrounding the edges
3) similar to SER in structure but more flattened.

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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 a eukaryotic cell?

A

a cell which contains membrane-bound specialised organelles and DNA is contained in a nucleus

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22
Q

what is a prokaryotic cell?

A

DNA is ‘free’ in the cytoplasm and there are no membrane bound organelles

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23
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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24
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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25
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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26
Q

what are the cell walls of bacteria made of?

A

murein

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27
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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28
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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29
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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30
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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31
Q

what is structure of a chloroplast? (5)

A

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

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32
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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33
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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34
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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35
Q

what are vacuoles like in animal cells?

A

not permanent and small

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36
Q

What is a vesicle?

A

a membrane-bound sac for transport and storage

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37
Q

what is magnification?

A

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

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38
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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39
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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40
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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41
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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42
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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43
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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44
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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45
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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46
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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47
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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48
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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49
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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50
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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51
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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52
Q

what are viruses?

A

acellular and non-living particles

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53
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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54
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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55
Q

how does differential centrifugation work?

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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56
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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57
Q

what is stage 1 of differential centrifugation?

A

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

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58
Q

what is stage 2 of differential centrifugation? (5)

A

Ultracentrifugation
1) a variable speed centrifuge separates out organelles of differing densities using centrifugal force
2) spins tubes of homogenate at certain speeds
3) 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)
4) this forms a sediment pellet
5) low speed for a short period of time

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59
Q

what is stage 3 of differential centrifugation?

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)
5) repeat the above steps (remove pellet and re-spin supernatant fluid

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60
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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61
Q

what phase happens before mitosis?

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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62
Q

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

A

a cell cycle

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63
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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64
Q

how do chromosomes behave during interphase? (2)

A

1) genetic material in the nucleus appears 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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65
Q

how do chromosomes behave during prophase?

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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66
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
1) chromosomes condense and first become visible
2) centrioles duplicate and move to opposite poles
3) spindle fibres (protein microtubules) begin to develop from the centrioles which span from pole to pole

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67
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 (protein microtubules) 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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68
Q

how do chromosomes behave during metaphase? (2)

A

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

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69
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 (protein microtubules) which contract
3) this process is energy dependent, provided by mitochondria which gather around the spindle fibres

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70
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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71
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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72
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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73
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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74
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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75
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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76
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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77
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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78
Q

what does 2n represent? (2)

A

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

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79
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

80
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
3) G2- replication of centrioles, second growth phase
4) M- mitosis

81
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

82
Q

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

A

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

83
Q

what does the fluid mosaic model of the membrane explain?

A

how biological molecules are arranged to form cell membranes

84
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

85
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

86
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

87
Q

The phospholipid bilayers that make up cell membranes also contain…

A

proteins which can either be intrinsic or extrinsic

88
Q

where are intrinsic proteins found? (2)

A

1) Intrinsic proteins are embedded in the membrane/ span the membrane from one side to the other
2) with their arrangement determined by their hydrophilic and hydrophobic regions

89
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

90
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

91
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

92
Q

what are the functions of extrinsic proteins? (5)

A

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

93
Q

what are the functions of intrinsic proteins?

A

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

94
Q

what are the functions of carrier proteins? (4)

A

1) involved in active transport
2) enable ATP and other molecules to bind
3) there is a conformational shape change
4) the molecule is moved across the membrane

95
Q

what are the functions of channel proteins?

A

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

96
Q

what are phospholipids?

A

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

97
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

98
Q

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

A

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

99
Q

what are glycoproteins on the phospholipid bilayer?

A

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

100
Q

what are the functions of glycoproteins on the phospholipid bilayer?

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

101
Q

describe the permeability of cell membranes (4)

A

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

102
Q

what are phospholipid bilayers permeable to?

A

lipid soluble substances which will diffuse freely across the phospholipids

103
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)

104
Q

what is diffusion?

A

the net movement of molecules or ions down a concentration gradient

105
Q

where can diffusion occur? (2)

A

1) across a membrane e.g lipid molecules or small molecules like O2
2) not across a membrane e.g water vapour diffusing out through stomata

106
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

107
Q

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

A

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

108
Q

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

A

1) using membrane channel proteins
2) using carrier proteins

109
Q

how does facilitated diffusion occur using membrane channel proteins? (4)

A

1) channel proteins are specific to only one ion, controlling the entry and exit of ions
2) hydrophilic channel which allows ions to move through
3) ion channels can become saturated which limits rate of diffusion
4) most channel proteins are ‘gated’, (part of the channel protein on the inside surface of the membrane can move in order to close or open the pore)

110
Q

how does facilitated diffusion occur using carrier proteins? (4)

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.
4) direction of movement of molecules diffusing across the membrane depends on relative concentration on each side of the membrane

111
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)

112
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

113
Q

The basic structure of all cell membranes, including cell-surface membranes and the membranes around the cell organelles of eukaryotes are…

A

the same

114
Q

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

A

1) increase in surface area of, or by
2) increase in the number of protein channels and carrier molecules in their membranes.

115
Q

how does movement across membranes occur?

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).

116
Q

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

A

1) Cells may be adapted for rapid transport across their internal/ external membranes by an 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 or gradients across membranes.

117
Q

How can you increase the rate of movement across 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) water will move by osmosis from a region of higher water potential to a lower water potential so the steeper/greater the concentration gradient the faster the rate of diffusion/osmosis and therefore the rate of movement.

118
Q

the shape and the composition of the membrane could…

A

alter for different cell/organelle types

119
Q

how can we explain passive forms of transport?

A

1) particles are constantly in motion due to the kinetic energy that they possess
2) this motion is random with no set pattern to the way the particles move around
3) particles are constantly bouncing off each other

120
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.

121
Q

what can happen as a result of diffusion?

A

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

122
Q

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

A

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

123
Q

What is facilitated diffusion?

A

substances can only cross the phospholipid bilayer with the help of certain proteins

124
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)

125
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

126
Q

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

A

zero

127
Q

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

A

kinetic energy

128
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

129
Q

what is a hypertonic solution?

A

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

130
Q

what is a hypotonic solution?

A

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

131
Q

what is an isotonic solution?

A

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

132
Q

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

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

133
Q

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

A

1) 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 – 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

134
Q

when does a plant cell become turgid?

A

When a plant cell is fully inflated with water and has become rigid and firm

135
Q

why is turgidity important for plants? (3)

A

1) the effect of all the cells in a plant being firm is to provide support and strength for the plant
2) making 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

136
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

137
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

138
Q

where does osmosis occur?

A

across cell membranes which are freely permeable to water and selectively permeable to other substances

139
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

140
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.

141
Q

how is active transport different to facilitated diffusion?

A

Although facilitated diffusion also uses carrier protein, active transport is different as it requires energ

142
Q

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

A

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

143
Q

why is active transport important? (4)

A

1) for the reabsorption of useful molecules and ions into the blood after filtration into the kidney tubules
2) absorption of some products of digestion from the digestive tract
3) loading sugar from the photosynthesising cells of leaves into the phloem tissue for transport around the plant
4) loading inorganic ions from the soil into root hairs

144
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

145
Q

what is stage 1 of the absorption of sodium ions and glucose by epithelial cells lining the ileum? (2)

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

146
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)

147
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

148
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

149
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) microvilli brush the border of epithelial cells bordering the lumen
5) maintenance of a steep concentration gradient through the movement of blood, villi etc.

150
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

151
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) pathogens
2) cells from other organisms of the same species
3) abnormal body cells
4) toxins

152
Q

what is an antigen? give examples (2)

A

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

153
Q

what is the effect of antigen variability on disease prevention? (3)

A

1) reduces the effectiveness of vaccines
2) antibodies are no longer complementary to antigens/ don’t bind
3) This means you won’t get a rapid response to a new infection like you would if you were vaccinated/had been previously exposed.

154
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

155
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

156
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

157
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

158
Q

what are pathogens?

A

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

159
Q

what is phagocytosis?

A

The process by which a phagocyte surrounds and destroys foreign substances

160
Q

what are antigen presenting cells?

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 will present the antigens on their surface, cancer cell

161
Q

why is the cellular response specific?

A

T-cells respond to antigens on the surface of cells

162
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

163
Q

what is stage 1 of the cellular response (3)

A

1) once a pathogen has been engulfed and destroyed by a phagocyte, the antigens are positioned on the cell surface. This is now called an antigen presenting cell
2) Helper T cells have receptors on their surface which can attach to the antigens on the antigen presenting cell
3) once attached this activates the helper T cells to divide by mitosis to replicate and make large numbers of clones of themselves

164
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)

165
Q

what are cytotoxic T cells?

A

destroy abnormal or infected cells

166
Q

how do cytotoxic T cells work? (4)

A

1) release a protein called perforin which embeds in the cell surface membrane and makes a pore so any substances can enter or exit the cell
2) this causes cell death
3) this is most common in viral infections as viruses infect body cells
4) body cells are sacrificed to prevent viral replication

167
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

168
Q

what are antibodies?

A

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

169
Q

what is the structure of antibody? (5)

A

1) has a variable region- 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) the variable region is where the antigen binding site is located which is a complementary shape to only one antigen
5) S-S bonds hold the 4 polypeptide chains together

170
Q

what is immunity?

A

when a person has memory cells and antibodies against a pathogen

171
Q

why are antibodies described as having a quaternary structure?

A

4 polypeptide chains

172
Q

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

A

1) antibody/variable region has a specific amino acid structure
2) so the antibodies have a specific tertiary structure which is a complementary shape to the antigens
3) antibody-antigen complex forms

173
Q

how does the body form lymphocytes which don’t attack our own cells? (8)

A

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

174
Q

what are B lymphocytes

A

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

175
Q

what is the humoral response?

A

response involving B cells and making antibodies

176
Q

outline the humoral response

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.

177
Q

how do antibodies destroy antigens? (2)

A

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

178
Q

what are monoclonal antibodies?

A

identical copies of one type of antibody produced from a single clone of B cells

179
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

180
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

181
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

182
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

183
Q

what is passive immunity?

A

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

184
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

185
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

186
Q

what is active immunity?

A

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

187
Q

give 2 features of active immunity

A

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

188
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

189
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

190
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

191
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)

192
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

193
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

194
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)

195
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

196
Q

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

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

biology a level (10 decks)

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