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biology > topic 9 - Plant Biology > Flashcards

topic 9 - Plant Biology Flashcards

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1
Q

How does the structure of a plant (leaves, roots, stems) relate to its various functions?

A

• Leaves contain chloroplasts and stomatal pores
(for photosynthesis and gas exchange respectively)
• Roots are highly branched, with a high SA:Vol ratio (necessary for water and mineral uptake)
• Stems transfer essential materials in vascular bundles (transpiration of water and translocation of nutrients)

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2
Q

A leaf possesses two layers of inner tissue. Describe these two layers.

A

• Palisade mesophyll – upper layer of tightly packed
cells that are rich in chloroplasts (⬆︎︎ light absorption)
• Spongy mesophyll – lower layer of cells interspersed
by space and located near the stomata (⬆ gas exchange)

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3
Q

Root systems display extensive branching in order to maximize the available surface area for material uptake. Describe 2 root system.

A
  • Fibrous (adventitious) root systems contain many branching roots that are thin and very spread out
  • Tap root systems have a deeply penetrating central root (for stability) with many connected lateral branches
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4
Q

The root epidermis additionally may have many small extensions called _________.

What does it do?

A

The root epidermis additionally may have many small extensions called root hairs (to further increase available surface area)

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5
Q

What are vascular bundles? Why are they important?

A

In vascular plants, the vessels of xylem and phloem are arranged into bundles that extend from the roots to the shoots
• The organisation of these vascular bundles differ according to the plant section (root vs stem) and plant type (monocot vs dicot)

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6
Q

Describe vascular bundles in roots.

A

Roots
• Vascular bundles are radially arranged within a big stele in monocots, but are centrally arranged within a small stele in dicots

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7
Q

Describe vascular bundles in stems.

A

Stems

• Vascular bundles are scattered haphazardly in monocots, but form a ring around a circular cambium in dicots

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8
Q

What is transpiration?

A

Transpiration is the loss of water vapor from a plant

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9
Q

Describe the process of transpiration.

A
  • Active uptake of ions by roots promotes water uptake
  • Water moves up the stem of a plant by mass flow
  • Water is evaporated from leaves (via stomatal pores)
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10
Q

What is transpiration stream?

A

The flow of water from root to leaf is the transpiration stream

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11
Q

What are the features that are commonly present in xylem structures? What do they look like?

A

The vessel elements form a continuous tube
The remnants of fused end walls are shown as indents The xylem lining contains pits and pores
It is reinforced with lignin (spiral or annular)

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12
Q

Describe Root Uptake

A

Active uptake of mineral ions in the roots causes absorption of water by osmosis. Plants take up water and mineral ions from the soil via their roots and thus need a maximal surface area to optimise this uptake

Soil contains anionic clay particles to which minerals attach
• Examples of cationic minerals include K+, Na+,
Ca2+
Roots pump H+ ions into the soil to displace the minerals
• Displaced minerals diffuse into root (indirect active transport)
• Water follows mineral ions into the root via osmosis

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13
Q

Water moves up the stem via mass flow in vessels called ______

A

xylem

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14
Q

Water moves up the stem via mass flow in vessels called xylem. Describe the pressure in the xylem.

A
  • Pressure is high in root (water in) and low in leaf (water out)
  • The pressure differential results in the mass flow of water
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15
Q

Water moves up the stem via mass flow in vessels called xylem. This capillary action is mediated by two forces. What are they?

A

• Cohesion (water molecules stick together by H-bonding) • Adhesion (water molecules adhere to the xylem wall)

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16
Q

Plants have adaptions to reduce water loss (aka. to conserve water due to transpiration). How do Xerophytes (desert plants) do this?

A
  • Reduced leaves (lowers evaporative surface area)
  • Thick, waxy cuticles (reduces water loss from leaves)
  • Stomata in pits with hairs (traps vapor = ⬇ evaporation)
  • CAM physiology (only opens stomata at night)
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17
Q

Plants have adaptions to reduce water loss (aka. to conserve water due to transpiration). How do Halophytes (salt water plants) do this?

A
  • Cellular sequestration (salt is stored within the vacuoles)
  • Tissue partitioning (abscission of leaves containing salt)
  • Salt excretion (salt is actively removal from the plant)
  • Root level exclusion (roots avoid salt uptake)
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18
Q

What are the ways water transport can be modelled in xylems?

A
  • Capillary tubing (water moves along tubing via surface tension)
  • Filter paper (absorbs water due to adhesive properties)
  • Porous pots (semi-permeable containers can model osmosis)
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19
Q

Transpiration rates in plants are measured with potometers. What are potometers? What does more movement represent?

A
  • Potometers measure movement of air bubble/meniscus

* More movement represents increased transpiration rate

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20
Q

Describe the importance of evaporation in plants.

A

The vapor diffuses out of stomata, resulting in transpiration (transpiration is a consequence of gas exchange in the leaf)
• Transpiration rate is regulated by the stomatal guard cells
• Guard cells occlude the stomatal opening when flaccid

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21
Q

Potometers can be used to test a number of variables that may affect the rate of transpiration in plants. What are these variables and how would they affect the rate of transpiration?

A

Temperature: increase in temperature = increase in rate of transpiration (due to more evaporation)

Humidity: increase in humidity = decrease in rate of transpiration. Humidity is the amount of water vapour in the air – less vapour will diffuse from the leaf if there is more vapour in the air

Light Intensity: increase in light intensity = increase in rate of transpiration. Increasing light exposure will cause more stomata to open in order to facilitate photosynthetic gas exchange

Wind Exposure: increase in level of wind exposer = increase in rate of transpiration. Wind / air circulation will function to remove water vapour from near the leaf, effectively reducing proximal humidity

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22
Q

What is Translocation?

A

It is the movement of plants transporting organic molecules from source to sink

  • Source: Photosynthetic tissues (e.g. leaves)
  • Sink: Storage organs (e.g. fruits, seeds, roots)
23
Q

Describe the process of active translocation within plants.

A

Organic molecules are transported via vessels called phloem • Organic molecules are loaded and unloaded into the
phloem by companion cells at the source and sink
The active loading of solutes at the source creates high solute concentrations within the viscous phloem fluid (sap)
• Water is drawn into the phloem from the xylem (osmosis)
The incompressibility of water causes the sap volume to be increased, creating a pressure gradient (i.e. mass flow)
• Mass flow drives sap along the phloem (source to sink)

24
Q

What is a common occurrence of active translocation?

A

Carbohydrates are usually transported in the phloem as sucrose, but are typically stored within the sink as starch

25
Q

Organic molecules are actively unloaded at the sink, which ________________

Loss of water __________

A

Organic molecules are actively unloaded at the sink, which lowers solute concentrations (and water returns to the xylem)
• Loss of water
lowers the hydrostatic pressure at the sink,
maintaining the pressure gradient (and mass flow)

26
Q

Compare and Contrast Xylem and Phloem.

A

Xylem:
Process: Transpiration
Materials: water, minerals
transport: undirectional
Composition: vessel element and tracheid
Structure: Composed of a perforated inner layer of dead cells that are fused into a continuous tube (vessel element). The cell walls have thickened cellulose are reinforced with lignin (spiral or annular arrangement)
Location: Inner or central region of bundle

Phloem:
Process: Translocation
Materials: organic nutrients
transport: bidirectional
Composition: sieve element and companion cell
Structure: Composed of living cells connected by porous plates at their transverse ends (sieve elements). Are supported by companion cells that are connected via plasmodesmata to mediate material exchange
Location: outer region of vascular bundle

27
Q

How are translocation rates measured?

A

Measured using aphid stylets

• If the stylet is severed, the sap will continue to flow
from the plant and can be collected and measured
• Plants exposed to radioactive carbon dioxide will
produce radioactively labelled sugars within the phloem
• The rate of translocation can be identified by the time
taken for radioisotopes to be detected along the phloem

28
Q

What are aphid stylets?

A

Aphids are insects that feed on the sap in phloem via a

protruding mouthpiece called a stylet

29
Q

What are companion cells?

A

Provide metabolic support for sieve element cells and facilitate the loading and unloading of materials at source and sink

30
Q

What are sieve element cells?

A

long and narrow cells that are connected together to form the sieve tube, porous to enable flow between cells

31
Q

What are meristems?

A

Meristems are undifferentiated cells in plants that are capable of indeterminate growth (analogous to totipotent stem cells)
• They have specific regions of growth or development and allow for regrowth and vegetative propagation

32
Q

Meristematic tissue can be characterised as either:

A
  • Apical – Occurs in shoots and roots and is responsible for primary growth (i.e. lengthening) and leaf development
  • Lateral – Occurs at the cambium and is responsible for secondary growth (i.e. widening) and the production of bark
33
Q

What are auxins?

A

Plant hormones that control growth in the shoot apex by stimulating or inhibiting cell division (mitosis)

released by the shoot apical meristem and coordinates both apical growth and directional growth (tropism)

influences cell growth rates by changing the pattern of gene expression within the plant tissue

34
Q

What are auxin efflux pumps?

A

Auxin efflux pumps can set up concentration gradients of auxin in plant tissues to allow for differentiated growth rates

35
Q

What is apical growth?

A

Growth in the shoot apex allows for the extension of the stem and the development of leaves (primary growth)

36
Q

True or False?

In the stem, growth occurs in sections called nodes, with the remaining meristem tissue forming inactive axillary buds
• Axillary buds have the potential to form new shoots

A

TRUE

37
Q

What is apical dominance?

A

Auxins promote growth in apex but inhibit growth in buds

38
Q

What is a tropism?

A

A tropism is the turning of an organism in response to a directional external stimulus (e.g. light = phototropism)

39
Q

How are plant tropisms caused?

A

Plant tropisms are caused by the differential elongation of plant cells (plant turns away from side with cell elongation)

40
Q

Tropisms may differ according to the type of plant tissue
• In plant shoots, auxin ______________
• In plant roots, auxin _________________

A

Tropisms may differ according to the type of plant tissue
• In plant shoots, auxin promotes cell elongation
• In plant roots, auxin inhibits cell elongation

41
Q

What is micropropagation?

A

Micropropagation is an in vitro technique used to produce large numbers of identical plants (i.e. clones) from a selected stock plant
• Tissue sample (explant) is grown in agar and treated with growth hormones
• Growing shoots are divided and transferred to soil to form new plants

42
Q

How is micropropagation used?

A

Micropropagation can be used for the rapid bulking up of new plant varieties, the production of virus-free stains of existing varieties and the propagation of rare plant species (e.g. certain types of orchids)

43
Q

True or False?

Flowers are the reproductive organs of certain types of plants and develop from changes to gene expression in the shoot apex

A

TRUE

44
Q

Sexual reproduction in flowering plants (angiosperms) involve three key stages. Identify and describe these three stages.

A
  • Pollination – The transfer of pollen from the anther to the stigma (usually occurs between different plants)
  • Fertilisation – The fusion of the male gamete nuclei (in pollen) with the female gamete nuclei (in ovule)
  • Seed Dispersal – The fertilised ovule (seed) moves away from the parent plant to reduce the competition for growth
45
Q

True or False

Most flowering plants will employ a mutualistic relationship with pollinators (e.g. birds, bees) in order to reproduce
• The plant gains a mechanism of pollen transfer, while the animal gains a source of nutrition (plant nectar)

A

TRUE

46
Q

What is the general name for the female plant reproductive organs? Identify these parts.

A

General: Pistil

Parts: stigma, style, ovule

47
Q

What is the general name for the male plant reproductive organs? Identify these parts.

A

General name: Stamen

Parts: anther, filament

48
Q

Identify the parts of the seed.

A 
Epicotyl
Radicle
Micropyle
Testa
Cotyledon
49
Q

What is germination?

A

Germination is the process by which a seed emerges from a period of dormancy and sprouts (forming a new plant)

50
Q

What are the conditions for germination seeds?

A
  • Oxygen (to produce ATP via aerobic respiration)
  • Water (to metabolically activate the cells)
  • Suitable temperature and pH (for enzyme activity)
51
Q

What is photoperiodism?

A

Flowering in plants is controlled by photoperiodism

• The response of a plant to the length of day or night

52
Q

Flowering is regulated by phytochrome which exist in 2 forms. What are these 2 forms?

A
  • Inactive red form (Pr) absorbs red light (to become Pfr)

* Active far red form (Pfr) absorbs far red light (forms Pr)

53
Q

Sunlight contains more red light. How does this effect the active far red during the day versus night?

A
  • The active far red form is predominant during the day

* Reverts to mainly the inactive red form at night

54
Q

Flowering is triggered by the active form, but effects differ • Flowering requires a set length of uninterrupted darkness

True or False

A

TRUE

biology (11 decks)

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