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Biology > Module 3: Exchange And Transport 2 > Flashcards

Module 3: Exchange And Transport 2 Flashcards

(107 cards)

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1
Q

Why do plants need a transport system??

A

Plants need to exchange CO2 in and O2 out

Water and minerals in

Waste products out

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2
Q

Why is there no need for specialised gas exchange surfaces in plants??

A

Leaves are adapted to allow gas exchange by diffusion

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3
Q

What are the 2 vascular tissues in a plant?

A

Xylem and phloem

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4
Q

Xylem

A

Upwards transport of water and mineral ions

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5
Q

Phloem

A

Bidirectional transport of organic food molecules

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6
Q

Vascular tissue structures of stems and roots

A

Share similar vascular tissue structures

But arrangement and position differs

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7
Q

Root structure: epidermis

A

Single layer of cells

Often have long extensions called root hairs

Increase surface area

A single plant may have 10^10 root hairs

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8
Q

Root structure: cortex

A

Thick layer of packaging cells often containing stored starch

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9
Q

Root structure: endodermis

A

Single layer of tightly packed cells containing a waterproof layer called the casparian strip

Prevents movement of water between cells

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10
Q

Root structure: pericycle

A

Layer of undifferentiated menstematic (growing) cells

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11
Q

Root structure: vascular tissue

A

Contains phloem and xylem cells

Continuous with stem vascular bundles

Arrangement is different

Xylem usually forms a star shape with 2-6 arms

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12
Q

Stem structure: epidermis

A

One cell thick

In young plants the epidermis cells may secrete a waterproof cuticle

In older plants, the epidermis may be absent replaced by bark

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13
Q

Stem structure: cortex

A

Composed of various ‘packaging’ cells

Give young plants strength and flexibility

Source of plant fibres such as sisol and hemp

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14
Q

Stem structure: vascular tissue

A

Contains phloem and xylem tissue

Grows out from the combium

In young plants the vascular tissue is arranged in vascular bundles

Phloem on the outside and xylem on the inside

In older plants the xylem bundles fuse together to form the bulk of the stem

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15
Q

Stem structure: parenohyma

A

The central region of a stem

Used for food storage in young plants

May be absent in older plants

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16
Q

Stem structure: cambium

A

Unspecialised meristem that can divide to form vascular tissues

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17
Q

Vascular tissue in the leaf: parenchyma

A

Relatively unspecialised cells

Make up the bulk of soft internal tissues of leaves, stem, roots and fruits

Thin flexible cell walls

Large water-filled vacuole

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18
Q

Vascular tissue in the leaf: Collenchyma

A

Living at maturity, never lignified

Support tissue in growing plant parts

Cell walls strengthened by cellulose and pectin but distortable when stretched

Found in strands beneath the epidermis

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19
Q

Vascular tissue in the leaf: schlerenchyma

A

Thick walled dead cells, heavily lignified

Fibres frequently grouped in bundles:

  • elongated cells, often with pointed ends
  • associated with vascular tissue
  • high load-bearing capacity and easily processed fibres
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20
Q

What is transported in xylem vessels

A

Water

Soluble mineral ions

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21
Q

What is a tissue

A

A group of cells working together to perform a particular function

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22
Q

What is the dual function of xylem tissue?

A

Has the dual functions of support and transport

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23
Q

Xylem as a tissue - what does it do?

A

Transport water and other minerals from the soil up to the roots and stem of a plant

Contain long elongated cells called Tracheids and shorter and wider cells called vessel elements

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24
Q

What are xylem vessels made up of?

A

Vessels are made up of elongated vessel elements arranged end to end

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25
How does the xylem structure form?
Each element began as a normal plant cell Substance called lignin is laid down As lignin builds up around the cell, the cell dies which leaves an empty space inside The end walls of neighbouring vessel elements would break down completely to form a continuous tube
26
What is lignin??
A hard strong substance which is impermeable to water
27
What are pits in the xylem??
In the area where plasmodesmata is present, no lignin would be laid down These non-lignified areas can be seen as gaps in the walls of xylem vessels
28
Water movement in a plant
In the root, water crosses the cortex, endodermis and pericycle and moves into the xylem through the pits in their walls Will then move towards the leaves and up the vessels Water and dissolved minerals only move in one direction through the plants
29
Similarities between tracheids and xylem vessel elements
Both conduct water Both are dead Both develop lignin
30
What are tracheids
Spindle shapes cells with pits through which water flows from cell to cell They have tapered ends and a function in support as well as water transport
31
What are pits
Thinner regions where water can pass through from cell to cell
32
What does TS mean
Transverse section
33
What does LS mean
Longitudinal section
34
Why is xylem a tissue?
Because it contains a variety of specialised, water conducting cells known as tracheory elements
35
What is the role of parenchyma cells
Fibres lend support
36
What is the role of fibres in the xylem??
Lend support to tissues
37
What is the difference between a tracheid and a xylem vessel??
Tracheids are thinner than xylem vessels
38
What is the purpose of lignin in xylem vessel cell walls?
Plays a crucial part in conducting water in plant stems Gives support Prevents collapse of xylem vessel Prevents escape of water
39
What is the effect of the lignin on the xylem cells?
Prevents water loss from xylem cells as it is impermeable
40
What are the 4 basic ways that molecules can be transferred??
Diffusion Osmosis Active transport Bulk transport
41
What is water potential??
Water potential is a measure of the ability of water molecules to move freely in solution
42
How does water move?
Water moves from a solution with high water potential to one of lower water potential
43
How is water potential decreased?
Decreased by the presence of solutes
44
How is water transported from the root hair to the xylem?
Water is taken up by the root hair and crosses the cortex Then it enters the xylem in the centre of the root
45
Why does water move from the root hair to the xylem??
There is a lower water potential in the xylem vessels than there is in the root hairs Water moves down the water potential gradient
46
Does soil have a high or low water potential??
High
47
Does the root hair cell have a high or low water potential??
Low
48
The apoplast pathway
The cells of a cortex are surrounded by cell walls made of several layers of cellulose fibres criss crossing one another Water can soak into these walls Water can then deep across the root cortex from cell wall to cell wall until it reaches the xylem
49
The symplast pathway
Water moves into the cytoplasm of a cortical cell and then into adjacent cells through their interconnecting plasmodesmata The continuum of cytoplasm within a plant tissue requires only the crossing of a plasma membrane
50
The vascular pathway
Similar to the symplast pathway except fluid can move into and out of the vacuoles
51
What are the three pathways?
The apoplast pathway The symplast pathway The vascular pathway
52
What is a casparian strip??
A bond which forms an impenetrable barrier to water in cell walls
53
At the stele how does water cross the endodermis
Through the cytoplasm of cells
54
What happens as the endodermis cells get older??
The Suberin deposits become more extensive
55
What happens inside the stele
Once across the endodermis, water continues to move down the water potential gradient across the pericycle and towards the xylem vessels
56
What is transpiration?
Loss of water by evaporation from the aerial parts of the plant
57
In leaves where does water evaporate from?
Cell walls
58
In leaves how does water evaporate?
The vapour accumulates in the air spaces and then diffuse out through open stomata
59
What happens to the leaf cells as water evaporates??
The leaf cells are cooled
60
Transpiration process
Water evaporates from the leaf cells Water is drawn by osmosis from the xylem vessels of the leaf veins to replace the lost water As a consequence water is drawn up through the plant
61
What 3 processes does Transpiration involve??
1) osmosis from the xylem to the mesophyll cells 2) evaporation from the surface of the mesophyll cells into intercellular spaces 3) diffusion of water vapour from the intercellular spaces out through the stomata
62
What is cohesion?
Attraction of molecules for other molecules of the same kind
63
Why do water molecules have strong cohesive forces??
Because of the ability to form hydrogen bonds with one another
64
What is Adhesion
Attraction of molecules of one kind, to molecules of a different kind
65
Why is the attraction of molecules quite strong for water
Because other molecules bear positive or negative charges
66
In what ways is the movement of water useful to the plant??
Water is required in the leaves for photosynthesis Water is needed to enable cells to grow and elongate Water keeps cells turgid so that stomata will open The flow of the water passively carries minerals up the plant Evaporation of water keeps the plants cool
67
What is the transpiration pull
As water leaves the xylem in the leaf it must be replaced from below Water moves up the xylem from the roots to replace the lost water This is because it is under tension
68
How is water moved up the xylem from the roots to the leaves?
Low pressure at the top, water is under tension Adhesion of water molecules to the xylem Water moves up through the xylem by mass flow
69
Are the cells living or dead in a xylem??
Dead
70
Are phloem sieve tube elements living or dead??
Living
71
Do xylem vessels have bordered pits?
Yes
72
Do phloem sieve tube elements have bordered pits??
No
73
Is lignin present or absent in a xylem vessel
Present
74
Is lignin present or absent in phloem sieve tube elements??
Absent
75
What does the xylem vessel transport??
Water Mineral ions
76
What does the phloem sieve tube elements transport??
Organic solutes such as sugars and amino acids
77
What direction is transport in a xylem vessel??
One way
78
What direction of transport is the phloem sieve tube element??
Either direction
79
What evidence the scientist might expect to see in companion cells, using an electron microscope??
Many mitochondria Plasmodesmata between companion cell and sieve tube Many ribosomes
80
What are the 5 environmental factors that affect the rate of transpiration
Light Temperature Humidity Wind Soil water
81
Affect of light on rate of transpiration
Plants transpire more rapidly in the light than in the dark This is because light stimulates the opening of the stomata
82
What is the affect of temperature on the rate of transpiration??
Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises
83
What is the affect of humidity on the rate of transpiration??
The rate of diffusion of any substance increase as the difference in concentration of the substances in two regions increases When the surrounding air is dry diffusion of the water out of the leaf goes on more rapidly
84
What is the affect of wind on transpiration??
When there is no breeze, the air surrounding a leaf becomes increasingly humid thus reducing the rate of transpiration
85
What occurs when a breeze is present
The humid air is carried away and replaced by drier air
86
Effect of soil water on rate of transpiration
When absorption of water cannot equal the transpiration rate, the stomata close which reduces transpiration rate. Therefore it is important that there is water present in the soil
87
Describe two xeromorphic features
Hairs on the lower surface trap water vapour and reduce water potential gradient Thick waxy cuticle reduces evaporation of water
88
What is the cohesion tension theory??
As leaves transpire, the continual removal of water from the xylem vessels generates a pulling force that allows for water to be drawn through the root tissues and into the xylem
89
Three possible routes for water to get into the xylem
The apoplast pathway The symplast pathway The vacuolar pathway
90
What happens at the stele
As the endodermal cells get older, the Suberin deposits become more extensive, except in certain passage cells
91
What is a xerophyte??
A plant that is adapted to very dry conditions
92
Examples of xerophytes
Succulents Bromeliads Cacti
93
How do cacti reduce water loss in their leaves
Their leaves are reduced to spines which reduces the surface area of the leaf in water loss Thick, waxy cuticle covers the plants surfaces which reduces transpiration
94
How do cacti reduce water loss in their stem
Tick and fleshy with numerous water storage cells to retain water absorbed by roots
95
How do cacti reduce water loss in their root
Shallow, spreading root system to quickly absorb any water from rainfall
96
What is the effect of a round and compact shape
Reduces surface area for water loss
97
What is the effect of a shiney surface
Reflect heat and light
98
What is the effect of stomata in reducing water loss
Closed during the day, reduces water loss Open at night, absorb CO2, used for photosynthesis during the day
99
What is the effect of rolling up leaves??
Protects the lower epidermis from the outside helps to trap air within the leaf As this region becomes saturated with water, the water vapour potential is reduced
100
What is the effect of hairy leaves??
Trap moist air next to leaf surface Reduces water potential gradient between outside and inside the leaf Less water loss by transpiration
101
What is the effect of stomata in pits??
Traps water vapour in pits reducing water vapour potential gradients
102
What are hydrophytes??
Plants which grow submerged or partially submerged in water
103
Adaptations of a hydrophytes
Extensive system of air spaces in stems and leaves Gases diffuse quickly Provide buoyancy to keep the plants close to the light and are a resource of O2 and CO2
104
Which vessels in the vascular bundle will water be moving in?
The xylem
105
What is the purpose of the reservoir of water
Reset the apparatus so that multiple readings can be taken
106
Other than transpiration, what may a very small percentage of water be used for in the plant?
Photosynthesis Maintaining all turgour
107
What precautions must be taken in setting up a potometer to ensure your results are valid?
Set up the apparatus under water to eliminate air bubbles Avoid wetting leaves, ensure leaves are dry before taking readings Consistent external environment conditions

Biology (7 decks)

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