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APS 137 Plant Physiology > Lecture 1 - Beth Dyson > Flashcards

Lecture 1 - Beth Dyson Flashcards

Lecture

1
Q

What macronutrients do plants need to survive? [3]

A

Phosphorous, Nitrogen and Potassium

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2
Q

What is homeostasis and how is it maintained? [2]

A

The tendency towards a relatively stable equilibirum, physiologically maintained.

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3
Q

What is adaptation? [1]

A

Adaptation is heritable changes in genes.

NATURAL SELECTION!!

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4
Q

What is acclimination? [1]

A

Acclimination is non-heritable changes in gene expression and metabolism.

…Usually they’re reversible and non heritable.

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5
Q

What makes plant acclimation different from animals? [1]

A

They’re stationary so need to respond quicker to environmental change

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6
Q

What percentage of plants are water? [1]

A

Up to 95%, because plants have less structures than animals (humans have 75% water)

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7
Q

Why do plants need water? [4]

A 
Plants need water to:
Maintain cell turgidity.
Force cell elongation and growth.
Aid in transport.  
Water-based reactions (E.g. in photosynthesis)
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8
Q

What is transpiration? [2]

A

Transpiration is the unidirectional movement of water. From roots, up the stem and out of the leaves.

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9
Q

What is evapotranspiration? [1]

A

The process of water moving land -> atmosphere via evaporation or transpiration.

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10
Q

What percentage of precipitation/rainfall worldwide is due to transpiration? [1]

A

40% of worldwide rainfall is a consequence of transpiration.

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11
Q

How much water can a single mature oak transpire in one year? [1]

A

150,000/L per year.

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12
Q

How much water can a single acre of corn lose in a day? [1]

A

An acre of corn can lose up to 15,000 L/day in water.

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13
Q

What areas of the world have more evaporation? [1]

A

Areas with lots of plants tend to have higher rates of evaporation.

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14
Q

Why is water a greenhouse gas? [1]

A

Water is considered a greenhouse gas as after evaporation, some may stay in the atmosphere for a bit.

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15
Q

What is water more potent than in regards to greenhouse gases? [1]

A

Water is more potent than carbon dioxide, so changes in water balance is important for climate change.

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16
Q

How does climate impact waters role as a greenhouse gas? [3]

A

In warmer climates more water gets held up the atmosphere. Water causes more thermal energy to become absorbed, which further increases the temperature (further influencing the cycle).

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17
Q

What is humidity and what conditions are more ‘humid’? [1]

A

The amount of water present in the air, warmer air holds more water.

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18
Q

What is plant-water balance primarily controlled by? [1]

A

Plant-water balance is mainly controlled by altering the rate of transpiration.

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19
Q

Why are flood-tolerant plants being researched? [1]

A

Flooding can cause plant death as a consequence of drowning by ‘overwatering’.

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20
Q

What’s the vascular bundle in plants made of? [2]

A

The xylem and phloem.

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21
Q

How is water transported through the xylem? [2]

A

In the Xylem water is transported unidirectionally from roots -> top of leaf cells.

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22
Q

What are xylem made from? [3]

A

Xylem are made from a long tube of dead cells, which become lignified after maturation making them water proof.

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23
Q

Why are the xylem a long tube? [1]

A

The ends of xylem cells are broken down, hence the whole xylem being a long tube.

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24
Q

How are solutes transported in the phloem? [2]

A

In the phloem, solutes are transported bidirectionally between a ‘source’ and a ‘sink’.

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25
Q

What is a source in regards to plants? [1]

A

A ‘source’ is a nutrient-rich region. Such as the leaves (as they generate sugar via photosynthesis).

26
Q

What are sinks when regarding plants? [1]

A

A ‘sink’ is an area of a plant in need of nutrients. For example, growing roots.

27
Q

Why are vascular bundles an important structure? [2]

A

Vascular bundles are important structures, as they allow the regular transport of solutes/water and provide structural support to the plant.

28
Q

Where are the phloem and xylem located (relative to each other)? [2]

A

The xylem is located in the middle of the structure in an ‘X’ shape, while the phloem is packed between xylem cells..

29
Q

How does root, stem and leaf structure vary between plants? [2]

A

Root structure is typically similar between plants. Leaf and stem structure may vary greatly.

30
Q

Where do vascular bundles appear in monocot plants? [1]

A

Plant vasculature occurs throughout the plant in monocots.

31
Q

Where do vascular bundles appear in dicotyl plants? [1]

A

Vascular bundles appear in a ring along the outside of dicotyl plants.

32
Q

What are root hairs? [2]

A

Cute fluffy things which expand the roots surface area:volume ratio to take up water.

33
Q

What percentage of water is taken into a plant via the root hairs… and how? [2]

A

99% of water enters a plant via root hairs, through osmosis of course.

34
Q

What four types of cells must water pass through in the root? [From outer to inner] [4]

A

The root structure is in four layers - the epidermis, cortex, endodermis and pericycle.

35
Q

What is the epidermis? [3]

A

The epidermis is the outermost root layer.

It’s the toughest layer, providing structural support for the plant and even is strong enough to pierce the soil when elongating. It’s also capable of nutrient regulation.

36
Q

What is the cortex of a plant root? [1]

A

The cortex simply provides structure to the root and the ‘flesh’ of root vegetables (like the orange of a carrot).

37
Q

What is the endodermis of a plant root? [3]

A

The endodermis is a single cell layer and it’s role is in water regulation both in loss and gain.

This is as the Casparian strip runs through the endodermis’ cell wall.

38
Q

What’s unique about the endodermis cell wall? [2]

A

The endodermis cell wall is unique as it is made from suberin (which regular cell walls don’t have) which allows its waterproofness (it’s highly hydrophobic).

39
Q

What is the pericycle of the root? [4]

A

The pericycle is the innermost root layer, between the pericycle and the xylem.

The pericycle is involved in root development and its

It’s the final layer, separating the endodermis from the xylem. It’s the area involvled in root development and is named as it’s one of the closest type of stem cells that is found in the plant root.

40
Q

What does the pericycle do? [1]

A

The pericycle constantly divides and makes the other types of root cell!

41
Q

What are the two pathways of entering a root? [2]

A

The two pathways involved in entering the root are the symplastic and apoplastic pathways.

42
Q

What are the features of the symplastic route of transport? [2]

A

The symplastic route moves through the cytoplasm, so water has to pass through a membrane which contains aquaporins.

This allows filtering of things like heavy metals, bacteria etc. from the water.

43
Q

What are the features of the apoplastic route of transport? [1]

A

The apoplastic route has no filter - as it goes through the cell wall, which are mostly open!

44
Q

What is the Casparian strip and why is it useful? [3]

A

Located in the endodermis, the strip is a waterproof layer.

As a consequence it ensures water must pass through a cell membrane to reach the pericycle.

Additionally it also prevents backflow of water from the root to the soil.

45
Q

How many aquaporins do humans and Arabidopsis have? [2]

A

Humans have 4 aquaporins, expressed in the kidneys.

Arabidopsis has 35 mostly expressed in the root (but can be elsewhere). Other plants may have 100+ aquaporins.

46
Q

What happens when water reaches the leaves? [1]

A

When water reaches the leaves, it travels through the cytoplasm of mesophyll cells and out through the stomata.

47
Q

What are mesophyll cells? [1]

A

Mesophyll cells are specialised cells for photosynthesis.

48
Q

Why is transpiration at its highest during photosynthesis? [2]

A

Transpiration is at its highest during photosynthesis because its stomata are open to let carbon dioxide in, which means more water will also be lost.

49
Q

What conditions increase the rate of transpiration? [4]

A

Warm conditions increase energy for evaporation.

Windy conditions blow water off the leaf.

Dry conditions change the osmotic balance between the air and the stomata.

Light causes the stomata to open for photosynthesis as it requires CO2, giving more room for water to also leave.

All of these cause an increased rate of water loss, hence transpiration is increased.

50
Q

How do guard cells influence stomata opening and closing? [2]

A

When guard cells are turgid, its inner cell wall becomes more rigid and bends away from the opposite guard cell ‘opening’ a pore.

When the cells aren’t full of water they return to a ‘closed’ shape.

51
Q

How do ATP driven proton pumps in guard cells work? In regard to opening. [3]

A

ATP-driven proton pumps in guard cells efflux protons, hyperpolarising the plasma membrane.

When hyperpolarised, inward K+ channels are opened allowing K to enter and decrease the water potential of the cell.

The decreased water potential causes water to enter and the cell to become turgid and ‘open’.

52
Q

How do anions influence guard cell closing? [3]

A

Anions, like C- are released via channels to depolarise the membrane and deactivate inward K+ channels.

These K+ channels efflux K+ from the cell and this increases water potential.

The increased water potential causes water to leave via osmosis, leading to a loss of turgor and the guard cell ‘closing’.

53
Q

What is the cohesion-tension theory? [2]

A

The cohesion-tension theory suggests water molecules are ‘stuck’ via hydrogen bonds.

This gives the movement of water tension hence the high pressure up the xylem.

54
Q

How does humidity affect transpiration? [2]

A

High humidity increases the amount of water in the air, so the rate of evaporation (hence transpiration) is reduced.

Low humidity does the opposite.

55
Q

What is the worlds largest terrestrial biome and what characterises them? [1]

A

Boreal forests, which are characterised by coniferous forests.

56
Q

Where do boreal forests form a belt across? [1]

A

Boreal forests form a circumpolar belt across N. America and Eurasia at latitudes above 50 degrees.

57
Q

What % of world surface do boreal forests cover? [1]

A

14% of the worlds surface is covered by boreal forests.

58
Q

What temperatures can boreal forests go down to? [1]

A

Boreal forests may fall to -70 degrees celcius.

All water available is frozen, it’s a pretty extreme scenario.

59
Q

Why can boreal forests be dry as a desert? [1]

A

As all water is frozen.

60
Q

What issues come with freeze-thaw cycles in the xylem of plants? [4]

A

Freeze-thaw cycles refer to the continuous freezing and thawing of water within a plant.

Dissolved solutes in these cycles will cause bubbles to be formed during freezing, disrupting hydrogen bonding.

A big enough gap can break the chain of water in the xylem, this known as an embolism reducing transport efficiency.

61
Q

What xylem adaptations are suited to cold environments? [2]

A

Short and narrow xylem are adaptations suited to extreme cold environments.

62
Q

Why would xylem adaptations evolve towards this? [1]

A

The adaptation towards ‘bubble’ defence is touted to have occurred as a consequence of low-water environments, in which water was forced through the roots causing bubbles to form.

APS 137 Plant Physiology (19 decks)

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