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IB Biology HL > Topic 1 > Flashcards

Topic 1 Flashcards

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1
Q

Cell theory

A
  1. all living things are composed of cells (or cell products)
  2. the cell is the smallest unit of life
  3. cells only arise from pre-existing cells
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2
Q

What common features do cells share?

A
  • every living cell is surrounded by a membrane, which separates the cell contents from everything else outside
  • cells contain genetic material which stores all of the instructions needed for the cell’s activities
  • many of these activities are chemical reactions, catalysed by enzymes produced inside the cell
  • cells have their own energy release system that powers all of the cell’s activities
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3
Q

What are the three levels of magnification on a typical high school microscope?

A
  • x40 (low power)
  • x100 (medium power)
  • x400 (high power)
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4
Q

What is the formula to calculate magnification?

A

size of image/actual size of specimen

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5
Q

Explain striated muscle as an atypical example which questions the cell theory

A
  • building blocks of striated muscle are muscle fibres (similar to cells)
  • muscle fibres are surrounded by a membrane and are formed by division of pre-existing cells; they have their own genetic material and their own energy release system
  • however, they have an average length of 30mm in humans, whereas other cells typically have a size of less than 0.03mm and have multiple nuclei
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6
Q

Explain fungi as an atypical example of a cell which questions the cell theory

A
  • fungi consists of narrow thread-like structures called hyphae
  • hyphae have a cell membrane and a cell wall
  • in some types of fungi, the hyphae are divided up into small cell-like sections by cross walls called septa
  • in other types of fungi, however, there are no septa and each hypha is an uninterrupted tube-like structure with many nuclei spread along it
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7
Q

Explain algae as an atypical example of a cell which questions the cell theory

A
  • algae are organisms that feed themselves by photosynthesis and store their genes inside nuclei
  • many algae consist of one microscopic cell
  • giant algae can grow to a length as much as 100mm despite only having one nucleus
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8
Q

Outline the seven functions of life

A
  1. Nutrition: obtaining food, to provide energy and the materials needed for growth
  2. Metabolism: chemical reactions inside the cell, including cell respiration to release energy
  3. Growth: an irreversible increase in size
  4. Response: the ability to react to changes in the environment
  5. Excretion: getting rid of the waste products of metabolism
  6. Homeostasis: keeping conditions inside the organism within tolerable limits
  7. Reproduction: producing offspring either sexually or asexually

Note: Unicellular organisms must carry out all functions of life in the one cell

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9
Q

Limitations on cell size

A
  • surface area to volume ratio is important in the limitation of cell size
  • large numbers of chemical reactions take place in the cytoplasm of the cells (metabolism)
  • the rate of the reactions (metabolic rate) is proportional to the volume of the cell
  • substances used for the reactions must be absorbed by the cell and the waste products must be removed; the rate at which substances cross this membrane depends on its surface area
  • surface area:volume ratio is also important for heat production and loss
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10
Q

Outline the ways in which Paramecium demonstrates the functions of life

A
  • Paramecia are surrounded by small hairs called cilia which allow it to move (responsiveness)
  • Paramecia engulf food via a specialised membranous feeding groove called a cytostome (nutrition)
  • Food particles are enclosed within small vacuoles that contain enzymes for digestion (metabolism)
  • Solid wastes are removed via an anal pore, while liquid wastes are pumped out via contractile vacoules (excretion)
  • Essential gases enter (e.g. O2) and exit (e.g. CO2) the cell via diffusion (homeostasis)
  • Paramecia divide asexually (fission) although horizontal gene transfer can occur via conjugation (reproduction)
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11
Q

Outline the ways in which Scenedesmus demonstrates the functions of life

A
  • Scenedesmus exchange gases and other essential materials via diffusion (nutrition / excretion)
  • Chlorophyll pigments allow organic molecules to be produced via photosynthesis (metabolism)
  • Daughter cells form as non-motile autospores via the internal asexual division of the parent cell (reproduction)
  • Scenedesmus may exist as unicells or form colonies for protection (responsiveness)
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12
Q

Emergent properties

A
  • multicellular organisms have properties that emerge from the interaction of their cellular components
  • multicellular organisms can be regarded as cooperative groups
  • the characteristics of the whole organism, including the fact that it is alive, are known as emergent properties
  • emergent properties arise from the interaction of the component parts of a complex structure
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13
Q

Cell differentiation

A
  • specialized tissues can develop by cell differentiation in multicellular organisms
  • different cells perform different functions
  • often a group of cells specialize in the same way to perform the same function (tissue)
  • the development of cells in different ways to carry out specific functions is called differentiation
  • involves the expression of some genes and not others in a cell’s genome (cells have all genes needed to specialize in every possible way but only expresses certain ones)
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14
Q

Stem cell

A
  • can divide again and again to produce copious quantities of new cells; good for the growth of tissues or the replacement of cells that have been lost/damaged
  • not fully differentiated; can differentiate in different ways to produce different cell types
  • essential in embryonic development for the above reasons
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15
Q

What is an example of a non-therapeutic use for embroynic stem cells

A
  • produce large quantities of striated muscle fibres/meat for human consumption
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16
Q

Use of stem cells to treat Stargardt’s disease

A
  • usually caused by a genetic mutation, the membrane protein used for active transport in the retina cells malfunction
  • as a result, photoreceptive cells in the retina degenerate; vision becomes progressively worse
  • can be treated by injecting retina cells derived from embryonic stem cells into the patient’s eyes
  • the cells attach themselves to the retina and improve the vision of the patient
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17
Q

Use of stem cells to treat leukemia

A
  • leukemia is a type of cancer; cancer is caused by mutations
  • leukemia involves the production of abnormally large numbers of white blood cells, which are produced in the bone marrow
  • to cure leukemia, the cancer cells in the bone marrow that are producing excessive white blood cells must be destroyed
  • this can be done via chemotherapy (using chemicals that kill dividing cells) but to remain healthy in the long term, the patient must be able to produce white blood cells needed to fight disease
  • stem cells that can produce blood cells must be present, but they are killed by chemotherapy
  • therefore, they extract stem cells from the patient by sticking a large needle into a large bone (ie. pelvis) and remove the fluid from the bone marrow; they perform chemotherapy, killing the cancer cells but also causing the bone marrow to lose its ability to produce blood cells; the stem cells that were extracted are returned to the patient’s body and they reproduce/re-establish themselves in the bone marrow
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18
Q

Outline the three sources of stem cells and the ethics of using them

A
  1. embryos –> embryonic stem cells
    - almost unlimited growth potential/can differentiate into any type of cell
    - less chance of genetic damage due to accumulation of mutations than with adult stem cells
    - more risk of becoming tumour cells than with adult stem cells
    - likely to be genetically different from an adult patient receiving the tissue
    - ethical controversy because removal of cells from the embyro is likely to kill it
  2. umbilical cord –> cord blood stem cells
    - easily obtained/stored
    - fully compatible with the adult individual that it comes from; no rejection issues
    - limited capacity to differentiate into different cell types (naturally develops into blood cells)
    - limited quantities of stem cells from one baby’s cord
    - ethical because umbilical cord is discarded whether or not stem cells are taken from it.
  3. bone marrow –> adult stem cells
    - difficult to obtain; very few and buried deep in tissues
    - limited capacity to differentiate/less growth potential than embryonic stem cells
    - less chance of malignant tumours developing
    - fully compatible with the individual it comes from; no rejection issues
    - ethical because removal of stem cells does not kill the adult it comes from
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19
Q

Electron microscopes

A
  • much higher resolution than light microscopes
  • reveal the ultrastructure of cells
  • needed to see viruses with diameter of 0.1 micrometres
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20
Q

Resolution

A

Making the separate parts of an object distinguishable by eye

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21
Q

Prokaryotes

A
  • simple cell structure without compartments
  • no nucleus; has nucleoid instead which contains DNA
  • DNA not associated with proteins
  • cell wall
  • do not have crytoplasmic organelles apart from ribosomes
  • ribosomes are 70S (smaller than those in eukaryotoes)
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22
Q

How do prokaryotes divide?

A
  • binary fission
  • used for asexual reproduction
  • circular chromosome is replicated and the two copies of the chromosome move to opposite ends of the cell
  • division of the cytoplasm
  • each of the daughter cells contains one copy of the chromosome so they are genetically identical
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23
Q

Eukaryotes

A
  • compartmentalized cell structure, meaning that the cell is divided up by single or double membranes into compartments
  • has nucleus
  • DNA associated with histone proteins
  • organelles in the cytoplasm (‘compartments’)
  • ribosomes are 80S (bigger than those in prokaryotes)
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24
Q

Advantages to being compartmentalized

A
  • enzymes and substrates for a particular process can be much more concentrated than if they were spread throughout the cytoplasm
  • substances that could cause damage to the cell can be kept inside the membrane of an organelle (ie. lysosome)
  • conditions such as pH can be maintained at an ideal lvel for a particular process, which may be different to the levels needed for other processes in a cell
  • organelles with their contents can be moved around within the cell
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25
Q

Recognition features and function of the nucleus

A
  • nuclear membrane is double and has pores through it
  • nucleus contains the chromosomes, consisting of DNA associated with histone proteins
  • uncoiled chromosomes are spread through the nucleus and are called chromatin
  • often densely straining areas of chromatin around the edge of the nucleus
  • DNA replication and transcription to form mRNA occurs in the nucleus (exported via the nuclear pores to the cytoplasm
  • constructs ribosomes
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26
Q

Recognition features and function of the rough endoplasmic reticulum

A
  • consists of flattened membrane sacs called cisternae, which have 80S ribosomes attached to them
  • main function is to synthesize protein for secretion from the cell
  • protein synthesized by the ribosomes passes into its cisternae and is then carried by vesicles, which bud off and are moved to the golgi apparatus
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27
Q

Recognition features and function of the golgi apparatus

A
  • consists of flattened membrane sacs called cisternae
  • unlike the rER, the cisternae are not as long are often curved, do not have attached ribosomes, and have many vesicles nearby
  • processes proteins brought in vesicles from the rER
  • most of these proteins are then carried in vesicles to the plasma membrane for secretion
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28
Q

Recognition features and function of a lysosome

A
  • approximately spherical with a single membrane
  • formed from golgi vesicles
  • contain high [protein] which makes them densely staining in electron micrographs
  • contain digestive enzymes which can be used to break down ingested food in vesicles or break down organelles in the cell or even the whole cell
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29
Q

Recognition features and function of a mitochondrion

A
  • surrounded by a double membrane
  • inner membrane invaginated to form structures called cristae
  • the fluid inside is called the matrix
  • the shape is variable but is usually spherical or ovoid
  • produce ATP for the cell by aerobic cell respiration
  • fat is digested here if it is being used as an energy source in the cell
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30
Q

Recognition features and function of free ribosomes

A
  • appear as dark granules in the cytoplasm and are not surrounded by a membrane
  • have the same size as ribosomes attached to the rER (80S)
  • synthesize protein, releasing it to work in the cytoplasm, as enzymes or in other ways
  • constructed in a region of the nucleus called the nucleolus
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31
Q

Recognition features and function of chloroplast

A
  • surrounded by double membrane
  • variable in shape, but usually spherical or ovoid
  • contains sacs of thylakoids, which are flattened sacs of membrane
  • produces glucose/other organic compounds by photosynthesis
  • starch grains may be present inside the chloroplasts if they have been photosynthesizing rapidly
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32
Q

Recognition features and function of vacuoles/vesicles

A
  • consist of a single membrane with fluid inside
  • many plant cells have large vacuoles that occupy more than half of the cell volume
  • some animals absorb foods from outside and digest them inside vacuoles
  • some unicellular organisms use vacuoles to expel excess water
  • vesicles are very small vacuoles used to transport materials inside the cell
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33
Q

Recognition features and function of microtubules/centrioles

A
  • microtubules are small cylindrical fibres with multiple roles, including moving chromosomes during cell division
  • animal cells have structures called centrioles, which consists of two groups of nine triple microtubules
  • centrioles form an anchor point for microtubules during cell division and also for microtubules inside cilia and flagella
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34
Q

Recognition features and function of cilia/flagella

A
  • whip-like structures projecting from the cell surface
  • contain a ring of nine double microtubules plus two central ones
  • flagella are larger and usually only one is present as a sperm
  • cilia are smaller and many are present
  • both can be used for locomotion
  • cilia can be used to create a current in the fluid next to the cell
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35
Q

What are exocrine gland cells of the pancreas and what organelles does it contain?

A
  • a type of gland cell in the pancreas that secretes digestive enzymes into a duct that carries them to the small intestine where they digest food
  • have organelles needed to synthesize/process/secrete proteins (ie. enzymes) in large quantities:
    1. plasma membrane
    2. mitochondrion
    3. nucleus
    4. rER
    5. golgi apparatus
    6. vesicles
    7. lysosomes
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36
Q

What are palisade mesophyll cells of the leaf and what organelles does it contain?

A
  • the cell type of the leaf that carries out the most photosynthesis
  • shape is rougly cylindrical
  • contains the following
    1. cell wall
    2. plasma membrane
    3. chloroplast
    4. mitochondrion
    5. vacuole
    6. nucleus
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37
Q

Hydrophilic

A
  • substances that are attracted to water
  • all substances that dissolve in water are hydrophilic, including polar molecules such as glucose and chloride ions
  • substances that water adheres to (ie. cellulose) are also hydrophilic
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38
Q

Hydrophobic

A
  • substances that are insoluble in water, but dissolve in other solvents
  • molecules that are non-polar are hydrophobic
  • all lipids are hydrophobic
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39
Q

Amphipathic

A

Substances that are partially hydrophilic and partially hydrophobic (ie. phospholipid)

40
Q

What is a phospholipid bilayer?

A
  • double layers formed by phospholipids
  • stable structure
  • form the basis of all cell membranes
41
Q

Why do phospholipids form bilayers in water?

A
  • phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules
  • phosphate group is hydrophilic
  • hydrocarbon tails are hydrophobic
  • when mixed with water, the phosphate heads are attacted to the water by the hydrocarbon tails are attracted to each other
  • thus, the phospholipids form double layers called phospholipid bilayers
42
Q

What was the Davson-Danielli model?

A
  • layers of protein adjacent to the phospholipid bilayer on both sides of the membrane
43
Q

What evidence was there to support the Davson-Danielli model?

A
  • appeared to be supported by electron micrographs of membranes which showed two dark lines with a lighter band between (railroad track appearance)
44
Q

What were the problems with the Davson-Danielli model?

A
  1. Freeze-etched electron micrographs
    - rapid freezing of cells and then fracturing them
    - fracture occurs along lines of weakness, including the centre of membranes
    - globular structures scattered through free-etched images of the centre of membranes were interpreted as transmembrane proteins
  2. Structure of membrane proteins
    - proteins extracted from membranes were found to be varied in size and globular in shape (unlike the type of structural proteiin that would form continuous layers)
  3. Fluorescent antibody tagging
    - red/green fluorescent markers were attached to antibodies that bind to membrane proteins
    - memrane proteins of some cells were tagged with red markers and others with green markers
    - the cells were fused together and within 40 minutes, the red/green were mixed together showing that membrane proteins are free to move within the membrane rather than being fixed in a peripheral layer
45
Q

What are some functions of membrane proteins?

A
  • Hormone binding sites
  • Enzymes
  • Electron carriers
  • Channels for passive transport
  • Pumps for active transport

(Happy Elephants Eat Chocolate Pie)

46
Q

Integral membrane proteins

A
  • hydrophobic on at least part of their surface
  • embedded in the hydrocarbon chains in the centre of the membrane
  • many are transmembrane (they extend across the membrane, with hydrophilic parts projecting through hte regions of phosphate heads on either side)
47
Q

Peripheral membrane proteins

A
  • hydrophilic on their surface
  • not embedded in the membrane
  • most are attached to the surface of integral proteins
  • attachment is often reversible
  • some have a single hydrocarbon chain attached to them which is inserted into the membrane, anchoring the protein to the membrane surface
48
Q

What are three components of animal cell membranes?

A

phospholipids, proteins, cholesterol

49
Q

What is cholesterol?

A
  • a component of animal cell membranes
  • a type of liquid belonging to a group of substances called ‘steroids’
  • most of the molecule is hydrophobic so it is attracted to the hydrophobic hydrocarbon tails, but one end of the cholesterol has a hydroxyl group which is hydrophilic (so it is attracted to the phosphate heads)
  • chloesterol molecules are therefore positioned between phospholipids in the membrane
50
Q

What is the role of cholesterol in membranes?

A
  • disrupts the regular packing of the hydrocarbon tails of phospholipids, so prevents them from crystallizing and behaving as a solid
  • however, it also restricts molecular motion and therefore the fluidity of the memrane
  • it also reduces the permeability to hydrophilic particles such as sodium ions and hydrogen ions
  • due to its shape, cholesterol can help membranes to curve into a concave shape, which helps in the formation of vesicles during endocytosis
51
Q

Endocytosis

A
  • a process by which large substances (or bulk amounts of smaller substances) enter the cell without crossing the membrane
  • results in the formation of a vesicle containing the materials that were outside of the cell
  • this process is also used by some types of white blood cells in order to ingulf pathogens and kill them
  • it is possible because of the fluidity of membranes
52
Q

What are the two main types of endocytosis?

A

Phagocytosis – The process by which solid substances are ingested (usually to be transported to the lysosome)
Pinocytosis – The process by which liquids / dissolved substances are ingested (allows faster entry than via protein channels)

53
Q

Exocytosis

A
  • a process by which large substances (or bulk amounts of small substances) exit the cell without crossing the membrane
  • a vesicle fuses with the membrane and the contents are released outside the cell
  • this process can be used to release useful enzymes (referred to as ‘secretion’) or expel waste products
  • it is possible because of the fluidity of membranes
54
Q

Difussion

A
  • the spreading out of particles in liquids and gases
  • occurs because particles are in random motion
  • more particles move from an area of higher concentration to an area of loewr cocnentration
  • therefore, movement down the concentration gradient
  • passive process (energy not consumed)
55
Q

List 4 methods by which particles can move across membranes

A

simple diffusion, facilitated diffusion, osmosis, active transport

56
Q

Simple difussion

A
  • movement of particles across the membrane, down the concentration gradient
  • involves particles passing between phospholipids in the membrane
  • can only occur if the phospholipid bilayer is permeable to the particles
  • non-polar particles (ie. oxygen) can diffuse into the cell esaily/passively if there is a higher concentration outside the cell than inside it
57
Q

Facilitated diffusion

A
  • some particles (ie. ions) cannot diffuse between phospholipids
  • channels help these particles to pass through the membrane from a higher concentration to a lower concentration
58
Q

Osmosis

A
  • water is able to move in and out of most cells freely
  • the net movement of water molecules is called osmosis
  • osmosis is caused by differences in the concentrations of substances dissolved in water
  • water moves from areas of low solute concentration to areas of high solute concentration
  • passive process
59
Q

Active transport

A
  • moving against the concentration gradient (ie. moving from an area of low concentration to an area of high concentration)
  • energy (ATP) and pump proteins are required
60
Q

What is the purpose/function of sodium-potassium pumps and potassium channels?

A
  • The axons of nerve cells transmit electrical impulses by translocating ions to create a voltage difference across the membrane
  • At rest, the sodium-potassium pump expels sodium ions from the nerve cell, while potassium ions are accumulated within
  • When the neuron fires, these ions swap locations via facilitated diffusion via sodium and potassium channels
61
Q

Explain how sodium-potassium pumps work

A
  • sodium-potassium pump is an integral protein that exchanges 3 sodium ions (moves out of cell) with two potassium ions (moves into cell) against the concentration gradient
  • thus, the process of ion exchange is active transport and requires energy
  • the following occurs:
    1. Three sodium ions bind to intracellular sites on the sodium-potassium pump
    2 .A phosphate group is transferred to the pump via the hydrolysis of ATP
    3. The pump undergoes a conformational change, translocating sodium across the membrane
    4. The conformational change exposes two potassium binding sites on the extracellular surface of the pump
    5. The phosphate group is released which causes the pump to return to its original conformation
    6. This translocates the potassium across the membrane, completing the ion exchange
62
Q

Explain how potassium channels work

A
  • each potassium channel conists of four protein subunits with a narrow pore between them that allows potassium ions to pass in either direction
  • while potassium ions are small enough to fit through the pores, if they dissolve and bond with water, they become too large to fit
  • thus, in order for the potassium ion to fit through the channel, energy is used to break the bond between the potassium ion and water
  • the potassium ion temporarily bonds to the amino acid sequence in the narrowest part of the channel pore
  • after the potassium ion passes through the channel, it bonds with water again
  • since the potassium channels in the axon are voltage gated, they only open when there is a net positive charge inside the axon
  • closes rapidly due to an extra globular protein subunit/ball, attached by a flexible chain of amino acids; the ball can fit inside the open pore milliseconds after it opens and then it remains there until the channel returns to its original state
63
Q

Hypotonic

A
  • has a lower osmolarity

- water moves by omosis out of the hypotonic solution

64
Q

Hypertonic

A
  • has a higher osmolarity

- water moves by osmosis to the hypertonic solution

65
Q

Isotonic

A
  • has the same osmolarity

- therefore, water does not move by osmosis

66
Q

Osmolarity

A

the total concentration of osmotically active solutes, measured in osmoles or milliosmoles

67
Q

Preventing osmosis

A
  • store tissues/organs in solutions that are isotonic to the cytoplasm
68
Q

How are cells formed?

A
  • division of pre-existing cells
69
Q

Pasteur’s experiments

A
  • proof that spontaneous generation of cells and organisms does not now occur on Earth
  • used swan-necked flasks and placed broth inside of them, melting the glass and bending it into a variety of shapes
  • broth in some flasks were boiled (to kill any organisms), some were left unboiled for controls
  • fungi/organisms appeared in the unboiled flasks but none appeared in the boiled flasks
  • this proved that even with contact to air, spontaneous generation would not occur
  • when the necks of the flasks were snapped, organisms/fungi began to grow in the boiled flasks
70
Q

Theories about the origin of the first cells

A
  • we know that the first cells must have arisen from non-living material
  • there are hypotheses for how some of the main stages could have occured:
  1. Production of carbon compounds such as sugars/amino acids
    - steam through a mixture of methane, hydrogen and ammonia (thought to be a representative of the atmosphere of the early Earth)
    - electrical discharges were used to simulate lightning
    - amino acids/carbon compounds needed for life were produced
  2. Assembly of carbon compounds into polymers
    - a possible site for the origin of the first carbon compounds is around deep-sea vents, which have gushing hot water carrying reduced inorganic chemicals such as iron sulphide
    - these chemicals represent readily accessible supplies of energy needed for the assembly of carbon compounds into polymers
  3. Formation of membranes
    - phospholipids/amphipathic carbon compounds which may have been produced in the previous step would naturally assembled into bilayers
    - this would allow different internal chemistry from that of the surroundings to develop
  4. Development of a mechanism for inheritance
    - living organisms currently have genes made of DNA and use enzymes as catalysts; however, enzymes require DNA to exist and DNA requires enzymes to exist, creating a paradoxical situation
    - there may have been a time when RNA was the genetic material as it can store information like DNA but is self-replicating and can itself act as a catalyst
71
Q

Endosymbiotic theory

A
  • states that mitochondria and chloroplasts were once free-living prokaryotic organisms
  • mitochondria had developed the process of aerobic cell respiration and chloroplasts had developed photosynthesis
  • larger prokaryotes that could only respire anaerobically took them in by endocytosis
  • instead of killing/digesting the smaller prokaryotes (ie. mitochondria/chloroplasts), they allowed them to continue to live in their cytoplasm
72
Q

Evidence for the endosymbiotic theory

A

chloroplasts/mitochondria:

  • have their own genes, on a circular DNA molecule like that of prokaryotes
  • have their own 70S ribosomes the size and shape typical of some prokaryotes
  • transcribe their DNA and use mRNA to synthesize some of their own proteins
  • can only be produced by division of pre-existing mitochondria and chloroplasts
73
Q

Mitosis

A
  • the division of the nucleus into two genetically identical daughter nuclei
74
Q

List the stages of mitosis in order

A

(interphase occurs before prophase but is not considered a stage of mitosis)
1. prophase
2. metaphase
3. anaphase
4. telophase
(cytokinesis occurs after telophase but is not considered a stage of mitosis)

75
Q

Interphase

A
  • a very active phase of the cell cycle with many processes occuring in the nucleus and cytoplasm
  • number of mitochondria in the cytoplasm increase
  • in plant/algae cells, the number of chloroplasts also increase; they also synthesize cellulose and use vesicles to add it to their walls
  • consists of three phases, G1 phase, S phase and G2 phase.
  • G1: cellular comtents apart from the chromosomes are duplicated
  • S: each of the chromosomes is duplicated
76
Q

Supercoiling

A
  • repeated coiling of the DNA molecule to make the chromosome shorter and wider
  • histones (protein) in eukaryote chromosomes help with supercoiling and enzymes are also involved
77
Q

List the phases of mitosis in sequential order

A

prophase, metaphase, anaphase, telophase

78
Q

Prophase

A
  • the chromosomes become shorter and fatter by coiling
  • to become short enough, they have to coil repeatedly (supercoiling)
  • the nucleolus breaks down
  • microtubules grow from structures called microtubule organizing centres (MTOC) to form a spindle-shaped array that links the poles of the cell
  • at the end of this phase, the nuclear membrane breaks down
79
Q

Metaphase

A
  • microtubules continue to grow and attach to the centromeres on each chromosome
  • the two attachment points on opposite sides of each centromere allow the chromatids of a chromosome to attach to microtubules from different poles
  • the microtubules are all put under tension to test whether the attachment is correct
  • this happens by shortening of the microtubules at the centromere
  • if attachment is correct, the chromosomes remain on the equator of the cell
80
Q

Anaphase

A
  • each centromere divides, allowing the pairs of sister chromatids to separate
  • the spindle microtubules pull them rapidly towards the poles of the cell
  • mitosis produces two genetically identical nuclei because sister chromatids are pulled to opposite poles
  • this is ensured by the way that the spindle microtubules were attached in metaphase
81
Q

Telophase

A
  • chromatids have reached poles and are now called chromosomes
  • at each pole, the chromosomes are pulled into a tight group near the MTOC and a nuclear membrane reforms around them
  • the chromosomes uncoil and a nucleolus is formed
  • by this stage, the cell is usually already dividing and the two daughter cells enter interphase again
82
Q

Mitotic index

A
  • the ratio between the number of cells in mitosis in a tissue and the total number of observed cells
  • can be calculated by dividing the number of cells in mitosis by the total number of cells
83
Q

Cytokinesis

A
  • refers to the process of cell division
  • occurs after mitosis
  • different in plant and animal cells
84
Q

Cytokinesis in animal cells

A
  • plasma membrane is pulled inwards around the equator of the cell to form a cleavage furrow
  • this is accomplished using a ring of contractile proteins, actin and myosin
  • when the cleavage furrow reaches the centre, the cell is pinched apart into two daughter cells
85
Q

Cytokinesis in plant cells

A
  • vesicles are moved to the equator where they fuse to form tubular structures across the equator
  • with the fusion of more vesicles, these tubular structures merge to form two layers of membrane across the whole of the equator, which develop into the plasma membranes of the two daughter cells and are connected to the existing plasma membranes at the sides of the cell, completeing the divison of the cytoplasm
  • next, pectins/other substances are brought in vesicles and deposited by exocytosis between the two new membranes
  • this forms the middle lamella that will link the new cell walls
  • both of the daughter cells bring cellulose to the equator and deposit it by exocytosis adjacent to the middle lamella
  • thus, each cell builds its own cell wall adjacent to the equator
86
Q

Cyclins

A
  • a group of proteins that is used to ensure that tasks are performed at the correct time and that the cell only moves to the next stage of the cycle when appropriate
  • bind to enzymes called cyclin-dependent kinases which then become active and attach phosphate groups to other proteins in the cell
  • the attachment of phosphate triggers the proteins to become active and carry out tasks specific to one of the phases of the cell cycle
  • four main types of cyclin in human cells
  • unless the cyclins reach a threshold concentration, the cell does not progress to the next stage of the cell cycle
  • thus, cyclins control the cell cycle and ensure that cells divide when new cells are needed, but not at other times
87
Q

Define tumour

A

abnormal groups of cells that develop at any stage of life in any part of the body

88
Q

Differentiate between a benign tumour and a malignant tumour

A
  • benign tumours are ones in which the cells adhere to each other and do not invade nearby tissues or move to other parts of the body; they are unlikley to cause much harm
  • malignant tumours can become detached and move elsewhere in the body and develop into secondary tumours; they are likely to be life-threatening
89
Q

Cancer

A

diseases due to malignant tumours

90
Q

Define carcinogen

A

chemicals and agents that can cause cancer

91
Q

Define mutagen

A

agents that cause gene mutations

92
Q

Define oncogenes

A
  • genes that can become cancer-causing after mutating

- normal cell oncogenes control cell cycle and cell division

93
Q

Define metastasis

A
  • movement of cells from a primary tumour to set up secondary tumours in other parts of the body
94
Q

Explain the development of primary and secondary tumours with reference to: mutagens, oncogenes, and metastasis

A
  • mutagens cause gene mutations in oncogenes
  • mutation in oncogenes results in uncontrolled cell division
  • uncontrolled cell division forms a tumour
  • tumour cell divides repeatedly to form a primary tumour
  • metastasis is the movement of cells from a primary tumour to set up secondary tumours in other parts of the body
95
Q

Evaluate the hypothesis that smoking causes cancer.

A
  • there is a positive correlation between smoking cigarettes and death by cancer
  • the more cigarettes smoked per day, the higher the death rate due to cancer
  • the result of the survey shows increases in death rate due to cancers of the mouth, lungs, larynx, pharynx; since these are the body parts that come into contact with the smoke from the cigaratte, this supports the hypothesis that smoking causes cancer
  • however, there is also an increase in death rate due to cancers of the esophagus, stomach, kidney, bladder, pancreas and cervix
  • correlation does not equal causation; just because there is a found correlation between smoking and cancer does not mean that one causes the other
  • however, it has been found that several substances in cigarette smoke are carcinogens, making it likely that smoking causes cancer

IB Biology HL (23 decks)

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