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Biology 1 > Module 4 > Flashcards

Module 4 Flashcards

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1
Q

What is a molecular clock used for?

A
  • DNA & protein sequences change through mutation over time
  • longer periods = more change
  • we estimate mutation rate & therefore the time of the last common ancestor of extant species
  • fossil record is used to “calibrate” molecular clock

ESTIMATES TIME OF DIVERGENCE OF PLANTS & ANIMALS

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2
Q

How many times has multicellularity evolved independently?

A

at least 6 times
fungi (x2)
animals
green algae
brown algae
red algae

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3
Q

Fossil evidence for multicellularity arose when?

A

about 600 mya

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4
Q

Propose possible steps leading to multicellularity

A
  • aggregation of cells into a cluster
  • intercellular communication within the cluster
  • specialisation of some cells within the cluster (cooperation)
  • organization of specialised cells into groups (tissues)
    A TRANSITION TO MULTICELLULARITY ALSO RESULTS IN INDIVIDUAL CELLS LOSING THE ABILITY TO LIVE INDEPENDENTLY
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5
Q

Possible first multicellular animal

A

placazoans

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6
Q

What are consequences of multicellularity?

A
  • allows for more specialized systems
  • e.g. in volvox
  • outer cells have coordinated flagella for movement
  • outer cells create an inner space to protect reproductive cells
  • big inner cells are specialized for reproduction
  • leads to change in size too (not prey to certain predators)
  • FUNCTIONAL SPECIALIZATION (e.g. cells work in unison e.g. beating of flagella)
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7
Q

What does multicellularity enable?

A
  • cell specialization allows cells to adopt new functions
  • integration & cooperation b/w cells allowing for development of tissues & organs
  • structurally & functionally complex bodies
  • creation of a stable internal env.
  • increase in size
  • more efficient gathering of resources & adapting to specific environments
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8
Q

How do multicellular organisms develop?

A

develop from zygote as a result of embryogenesis
- during embryogenesis there are multiple rounds of cell division producing specific cell types along major spatial axes

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9
Q

Describe the pattern of cell fate

A

it is highly ordered & reflects the position of cells in the developing embryo - instructive cues (cytoplasmic factors / cell signalling molecules
- change in cell potency

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10
Q

Each cell has the same set of genes so how do they become so different?

A

cell properties are determined by the subset of genes that are expressed - therefore, the specification of cell fate involves gene regulation

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11
Q

Which essential genes are expressed in every cell?

A

housekeeping genes

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12
Q

What is morphogenesis?

A
  • process by which cells & tissues organize & arrange themselves to create the final form of the body
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13
Q

Outline key processes in morphogenesis

A
  • division
  • changing shape (expansion)
  • moving (not seen in plant embryogenesis)
  • adhering to one another (not seen in plant embryogenesis)
  • death (apoptosis)
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14
Q

Define body plan

A

general structure of organism, arrangement of organs systems, integrated functioning of its parts

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15
Q

How can you categorize body plan in animals?

A

according to symmetry, body cavity structure, segmentation, type of appendages, & type of nervous system

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16
Q

Describe body plan in plants

A
  • body plan is modular
  • aerial structures (shoot)- subterranean structures (roots) have a modular arrangement of organs (phytomers / rhizomers)
  • plants have a radial arrangement of tissue types
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17
Q

Difference in growth b/w plants & animals

A

animals = determinate growth (predetermined body form)
plants = flexible body form - most plant development occurs after embryogenesis

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18
Q

Challenges faced by multicellular organisms

A
  • surface area to vol ratio of a multicellular organism is SMALL
  • distance of internal cells to external env. is LARGE
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19
Q

SOLUTIONs to large size of cells of multicellular organisms

A
  • close to external env. so diffusion occurs directly
  • might have central cavity which brins ex env into the animal
  • large surface area of exchange organs (long, flat, folded, branched)
  • thin surface area with small diffusion distances –> ensures maximal rate of exchange
  • circulatory system solves diffusion limit (movement of extracellular fluids around body – maintains high concentration gradients for diffusion)
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20
Q

Difference b/w transport systems of animals & plants

A
  • circulatory systems of animals - active (pumps)
  • transport system of plants - passive
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21
Q

What solves the diffusion limit?

A
  • a circulatory system
  • movement of extracellular fluids around the body to ensure exchanged substances from exchange organs reach cells of body (BULK FLOW)
  • maintains high concentration gradients for diffusion
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22
Q

To maintain a high level of metabolism large multicellular organisms. . .

A
  • need highly branched internal transport system
  • rapid movement of exchange substances
  • considerable force required to move fluids through these transport systems
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23
Q

Examples of cells in multicellular organisms communicating

A
  • through use of INTERCELLULAR SIGNALLING
  • conveying positional info during development
  • maintaining a stable internal env (homeostasis)
  • ensuring cells work in unison (beating of Volvox flagella)
  • physical / chemical signals arising from external env.
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24
Q

chemical signals

A

can activate receptors on nearby cells (e.g. ligans) or secreted into bloodstream & activate cells throughout body (e.g. hormones)

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25
Q

electrical signals

A

passed long distances very rapidly via neurons to very specific targets

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26
Q

Adaptations of plants to a sedentary lifestyle

A
  1. have organ systems that allow them to capture limited resources (root + shoot system)
  2. grow continuously to exploit new areas & respond to environmental cues (primary vs secondary growth)
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27
Q

Adaptation of root system

A

primary vs lateral roots
- absorbing water & mineral nutrients
- anchorage, storage, transport, hormones

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28
Q

Adaptation of shoot system

A
  • photosynthesis & gas exchange
  • hormones
  • reproduction
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29
Q

primary growth of plants

A

longitudinal

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30
Q

secondary growth

A

radially

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31
Q

What is continuous growth associated with in plants?

A

repeated formation of modules (phytomers)
– includes the leaf, axillary bud, & internode

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32
Q

Differences b/w plant & animal cells

A
  • plants have large vacuole but animals lack vacuoles
  • plants are immobile but animal cells are mobile
  • plants have cell walls, animals do not
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33
Q

Describe the plant cell walls

A

semi-rigid cell wall composed of cellulose fibers

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34
Q

Describe the outside of animal cells

A

surrounded by an extracellular matrix with collagen & proteoglycans as major components

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35
Q

Functions of plant cell wall

A
  • provides semi-rigid support
  • provides a barrier to prevent infection
  • contributes to plant form by growing as plant cell grows
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36
Q

Plant cell wall molecular structure

A
  • primary cell wall is composed of polysaccharides, cellulose, hemicellulose, & pectin
  • cellulose fibrils are formed via H bonds
  • extremely high tensile strength
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37
Q

Where else is pectin found in plant cells?

A

a major component of the middle lamella

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38
Q

If plant cells are surrounded by a semi-rigid cell wall, how do they grow?

A
  1. cell takes up water
  2. vacuole expands
  3. increase in turgor pressure
  4. cell expansion resisted by cell wall
  5. increased turgor pressure triggers release of enzymes to soften wall
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39
Q

What is expansin?

A

allows slippage b/w cellulose microfibrils by interfering w/ non-covalent binding of cellulose & the glycans, hemicellulose, & pectin

binds to “tensioned” glycans & makes them “relaxed” & vice versa

40
Q

Plane of cell division determines. . .

A

direction of tissue growth

41
Q

Difference b/w primary & secondary cell walls

A

primary: semi-rigid & expansion is possible
SECRETION OF WALL MATERIAL AFTER EXPANSION –>
secondary: thick & rigid & unable to expand

composed of lignin + cellulose

42
Q

Difference b/w primary & secondary cell walls

A

primary: semi-rigid & expansion is possible
SECRETION OF WALL MATERIAL AFTER EXPANSION –>
secondary: thick & rigid & unable to expand

composed of lignin + cellulose

43
Q

Define tropism

A

growth towards or away from a stimulus - light, gravity, water, touch

44
Q

Define phototropism

A

differential growth in response to light

45
Q

Define heliotropism

A

growth that follows the path of the sun

46
Q

How does auxin hormone regulate phototropism & gravitropism?

A
  • during phototropism auxin accumulates on shaded side
  • during gravitropism auxin accumulates on lower side
  • in both cases auxin-dependent growth bends the plant
47
Q

How does auxin control growth via expansin activity?

A
  • auxin promotes the activity of a proton pump
  • lower pH in the cell wall activates expansin
  • expansin loosens up the cell wall & makes it more flexible
48
Q

Early steps of plant embryogenesis

A
  1. Begin as zygote
  2. Undergoes first division which is asymmetric
  3. Daughter cells are diploid (apical and basal) –> two-cell stage
  4. Cell undergo more orientated cell division (embryo vs suspensor)–> octant stage
  5. More orientated cell divisions + cell expansion –> heart stage
  6. Further elongation of cotyledons & the main axis of the embryo –> mature embryo (contains shoot apical & root apical meristems)
49
Q

Define determination

A

commitment to a particular cell fate before cellular characteristics become apparent (at the octant stage for plants)

50
Q

Define differentiation

A

cells acquire specific functions & characteristics due to differential gene expression (at heart + embryo stage in plants)

51
Q

Define morphogenesis

A

the process by which differentiating cells organize to form the tissues & organs of the body

52
Q

Define growth

A

increase in size of the body & organs due to cell proliferation & cell enlargement

53
Q

Steps of plant development

A
  1. determination
  2. differentiation
  3. morphogenesis
  4. growth
54
Q

What are the 2 principle axes of plant body?

A

apical-basal: arrangement of tissues along the shoot-root axis

radial: concentric (circular) arrangement of tissues

during early embryogenesis, the plant body is mapped out along 2 principle axes

55
Q

Post-embryonic devel. of plants (dif b/w plants & animals)

A

plants continually make new organs as they grow - leaves, roots, flowers
- these structures are NOT produced during embryogenesis but arise post-embryonically from meristems
- animals usually have them produced embryogenically

56
Q

Shoot vs root apical meristems

A
  • shoot apical meristem: generates aerial structures –> phytomer (leaf, internode, axillary bud)
  • root apical meristem: generates subterranean structures –> roots
57
Q

Apical meristems must be kept inactive . . .

A

prior to seed disposal (imagine a strawberry with tiny leaves coming out of the seeds)

58
Q

What are the 3 primary meristems?

A
  • protoderm
  • ground meristem
  • procambium
59
Q

Features of shoot apical meristems

A
  • associated with primary growth of shoot
  • source of cells for primary tissues of shoot
  • branches will form indirectly from activity of axillary buds
60
Q

What are the 3 ‘zones’ in the root

A

zone of maturation
zone of elongation
zone of cell division

61
Q

Features of root apical meristems

A
  • associated with primary growth of root
  • source of cell for primary tissues of root
  • source of cells for root cap formation
  • lateral roots arise from internal tissue at some distance from RAM (root apical meristem)
62
Q

How is continuous activity of apical meristems maintained?

A

self-renewing undifferentiated cells (stem cells)

63
Q

Purpose of secondary growth

A

increases plant thickness by producing wood & bark

64
Q

What generates secondary growth?

A

lateral meristems called cambium
stem cells are also present in these lateral meristems

65
Q

Tree rings are affected by??

A

seasonal environmental conditions produce annual rings of secondary growth (wood)
- sprint: water is plentiful so light ring
- summer: water less available so dark ring
- winter: no growth

66
Q

3 main tissue systems in plants

A
  • dermal tissue system: forms outer covering of plant
  • ground tissue system: carries out photosynthesis, stores photosynthetic products, & helps support the plant
  • vascular tissue system: conducts water & solutes throughout plant
67
Q

Dermal tissue system

A
  • forms epidermis which is usually a single layer of cells
  • epidermal cells may differentiate into (stomata, trichomes (leaf/stem hairs), root hairs)
  • epidermis of aerial structures (leaves & stem) have a waxy cuticle
68
Q

Function of waxy cuticle

A
  • limits water loss & is gas impermeable
  • protects against physical damage, UV radiation, & pathogens
69
Q

Ground tissue system

A
  • located b/w dermal & vascular tissue –> represents bulk of plant body
  • classified according to cell wall structure:
    1. parenchyma
    2. collenchyma
    3. sclerenchyma
70
Q

Describe parenchyma

A

thin cells walls
large vacuoles
photosynthesis, storage (proteins, starch, fats, oil) in seeds & roots, nutrient transport

71
Q

Describe collenchyma

A

unevenly thickened cell walls
(bendy) support e.g. strings of celery

72
Q

Describe sclerenchyma

A

thick cell walls w/ secondary cell walls
very rigid support
fiber cells

73
Q

Vascular tissue system

A

conducting (transporting) tissue that forms a network throughout the plant
xylem vs phloem

74
Q

xylem

A

carries water & mineral ions from roots to shoots
- 2 cell types (tracheids & vessel elements)
- mainly composed of dead cells w/ secondary cell walls

75
Q

phloem

A

moves sugars & nutrients from shoots to roots (or other places)
- sieve tube element cells & companion cells
- composed of living cells
companion cells help to keep the simple sieve tube elements alive

76
Q

Role of water in plants

A
  • photosynthesis in leaves
  • transporting solutes b/w plant organs
  • cooling the plant
  • structural support (turgor pressure)
77
Q

Role of water in plants

A
  • photosynthesis in leaves
  • transporting solutes b/w plant organs
  • cooling the plant
  • structural support (turgor pressure)
78
Q

Roots are a . . .

A

net source of water
net sink (??) of sugar

79
Q

Shoot is a . . .

A

net sink of water
net sink for sugars

80
Q

Examples of macronutrients needed by plants

A

nitrogen + phosphorus

81
Q

Example of micronutrient

A

iron

82
Q

Define water potential

A

tendency of a solution to take up water from pure water across a selectively permeable membrane

83
Q

Golden rule about water potential

A

water ALWAYS moves across a selectively permeable membrane towards regions of LOWER (more negative) water potential

84
Q

2 components of water potential

A
  1. solute potential - the greater the concentration of solutes, the lower the potential
  2. pressure potential - the greater the internal pressure, the higher the potential
85
Q

In plant cells, turgor pressure is equivalent to. . .

A

pressure potential

86
Q

Describe movement of water based on water potential

A

under low turgor pressure, water will enter a plant cell by osmosis due to a low solute potential
when turgor pressure balances solute potential, there is no net flow of water in/out of the cell

87
Q

What does a reduction in turgor pressure lead to?

A

plant cells become less rigid (flaccid cells)
causes plants to wilt

88
Q

apoplast (water uptake by cells of the root)

A

interconnected cell wall & intercellular spaces b/w cells - movement is rapid & unregulated

89
Q

symplast

A
  • interconnected cytoplasm via plasmodesmata
  • movement is SLOW & regulated
  • water & solutes gain entry into symplast by first crossing a membrane
90
Q

Casparian strip

A

forms a (diffusion) barrier to the apoplastic flux, forcing ions to pass through the selectively permeable plasma membrane into the cytoplasm, rather than move along the cell wall

91
Q

Explain the movement of water through the root

A
  1. water & solutes enter root by osmosis (move through symplast + apoplast)
  2. water & solutes in the apoplast forced into endodermal cells (symplast)
  3. water & solutes remain in symplast
  4. solutes are actively transported out of the cell into the apoplast & water follows passively by osmosis
92
Q

adhesion

A

interaction b/w the water molecules & the xylem wall (capillary action)

93
Q

Stomata

A

opening through epidermis to allow gas exchange; opening controlled by 2 guard cells that open when turgid
regulated by light, CO2, temp, & water availability

94
Q

Explain the activity of stomata & guard cells in presence of light

A
  • protons are pumped out
  • ions (K+ & Cl-) enter, lowering solute potential
  • H2O enters by osmosis, increasing turgor pressure
  • pore opens
95
Q

Explain the activity of stomata & guard cells in absence of light

A
  • proton pumps becomes less active
  • K+ & Cl- ions diffuse out passively
  • H2O followed by osmosis
  • pressure goes down
  • pore closes
96
Q

How is osmosis controlled by light?

A
  1. light activates photoreceptor
  2. signaling cascade activates proton pump (H+ ATPase)
  3. H+ pumped out of cell
  4. electrochemical gradient drives K+ ions in through potassium channel
  5. symport protein also imports Cl- ions along w/ H+ ions to maintain electrical balance
  6. intracellular K+ & Cl- go up, decreasing solute potential
  7. H2O enters via osmosis

Biology 1 (10 decks)

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