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Transport in Plants Flashcards

1
Q

What are the main features of dicotyledonous plants?

A

Two cotyledons, veins usually net-like, vascular bundles arranged in ring, taproot is usually present, floral parts usually in multiples of 4 or 5

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2
Q

How do plants meet their needs?

A

Sugar is made in leaves, but is needed in all parts of the plant, so sugars can move upwards and downwards in the stem via phloem
Water is absorbed from the soil, but is needed in all parts of the plant, so water and minerals move up the stem in the xylem
Gas exchange is by diffusion through stomata and lenticels (in woody trunks)

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3
Q

What is the endodermis?

A

Single layer of tightly packed cells inside the roots of vascular plants

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4
Q

What is pericycle?

A

Thin layer of meristem tissue between the endodermis and the phloem in plant roots

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5
Q

What is parenchyma?

A

Packing tissue in plants which fills spaces between other tissues

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6
Q

What is collenchyma?

A

Cells that have thick cellulose walls and strengthen vascular bundles and outer parts of stems whilst allowing some flexibility in these regions

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7
Q

What is sclerenchyma?

A

Plant cells that have lignified walls and are used to strengthen stems and leaf midribs

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8
Q

How is vascular tissue arranged in the roots?

A

Xylem forms star shape in centre, phloem between points, in middle of plant to help plant withstand strain

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9
Q

How is vascular tissue arranged in the stem?

A

Vascular bundles in ring by edge of plant, xylem inside, phloem outside

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10
Q

What are the main features of xylem vessels?

A

Transports water and ions up the plants (roots to leaves)
Dead cells alligned end to end to form continuous tube
Narrow tubes prevent water column breaking easily so capillary action can be effective
Walls have deposits of lignin, a waterproof, tough substance which supports the tissues
Pits/pores allow sideways movement of water
Water flow is not impeded because there are no end walls, no cell contents, and lignin prevents the walls collapsing
Mature xylem walls are almost completely impregnated with lignin, there are pores or pits in the walls to allow movement between cells

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11
Q

What is the name of the cells that make up xylem vessels?

A

Vessel elements

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12
Q

Why is lignin laid down in spirals, annular and reticulate patterns in immature stems and roots?

A

Provides support, allows plants to flex in the wind, allows cells to elongate during growth, waterproof

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13
Q

Why is it important to have pits in highly lignified xylem?

A

So water can still move out of xylem, as lignin is waterproof, so without pits no water could pass out of xylem

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14
Q

What are the main features of phloem?

A

Composed of sieve tube elements and companion cells
Sieve tube elements transport assimilates (sucrose and amino acids, sap) up and down: translocation
Elongated cells positioned end to end, form tubular structure
Very little cytoplasm - little obstruction to movement
No nucleus to prevent obstruction
Perforated end walls (sieve plates) to allow sap to flow
Companion cells carry out metabolic processes

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15
Q

In what form is sugar transported around the plant?

A

Sucrose

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16
Q

What is vascular tissue?

A

Transport tissue, usuallly found as bundles containing xylem and phloem

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17
Q

What is xylem tissue?

A

Xylem vessels and other cells. Transports water and dissolved ions, support the plant

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18
Q

What is phloem tissue?

A

Used to transport dissolved sugars and other substances. Contains sieve tube elements and companion cells

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19
Q

What is a vascular bundle?

A

A bundle of tissues containing xylem and phloem. For transport and support

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20
Q

What is the endodermis?

A

A ring of cells between the root cortex and vascular tissue

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21
Q

What is the meristem?

A

Undifferentiated plant cells capable of rapid cell division. Found at tips of roots and shoots

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22
Q

What is the cambium?

A

Plant tissue in the stem and root forming new cells by cell division

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23
Q

What is the pericycle?

A

A layer of cells in the root that lies just inside the endodermis

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24
Q

What is the stele?

A

The central region of a root, contains xylem and phloemW

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25
What is the epidermis?
Outer layer of cells
26
What is the plasmodesma (plural plasmodesmata)?
Cytoplasmic connections between adjacent plant cells, passing through pits in cell wall
27
What is the root cortex?
Tissue between epidermis and endodermis, made up of round cells with large vacuoles and thin walls.
28
Why is water important for the plant?
Turgor pressure: support for the plant, also helps drive roots through soil or even tarmac and concrete Loss of water from leaf through evaporation helps cool plants Mineral ions and assimilates are transported in aqueous solutions Needed for photosynthesis
29
Describe how water moves into the root from the soil.
Water potential in root hair cells and other root hair cells and is lower than soil water. Minerals and other solutes in higher concentration in the cytoplasm than the soil, water moves down water potential gradient into root hair cells.
30
What is the symplastic pathway?
The movement of water from one cell to another cell by plasmodesmata, which are cytoplasmic connections between adjacent plant cells, passing through pits in cell wall
31
How does water enter the xylem?
Water moves via apoplast or symplast pathway Casparian strips - band of waxy material (suberin) prevents apoplast pathway Water forced into cytoplasm Prevents toxins reaching rest of plant (no transport proteins in plasma membrane) Solute concentration in endodermal cells is relatively dilute - high water potential Water potential of xylem cells now lower than endodermal cells Water moves by osmosis into xylem cells This process results in root pressure, and gives water a small push up the xylem
32
What is the apoplastic pathway?
Water is transported from root hair to xylem through the cell wall of intervening cells
33
What are casparian strips and what do they do?
Casparian strips - band of waxy material (suberin), prevents apoplast pathway
34
What is guttation?
Water is secreted from tips of leaves of plants (from pores called hydrathodes) and excess xylem leaks when the pressure in the xylem is too high
35
How are root hair cells adapted for their function?
Large surface area to increase rate of absorbtion
36
Describe the process of transpiration
Water diffuses out of stomata through substomatal airspace Water vapour evaporates from cell walls of the spongy mesophyll cells into substomatal airspace (concentration gradient) Reduces water potential of those cells compared to cells next to them Water moves by osmosis down water potential gradient from neighbouring cell Eventually water moves from the xylem to the cells next to the xylem Water is drawn up the xylem in a continuous stream to replace water lost
37
Describe movement of water through the plant
Movement of water through leaf from xylem results in transpiration stream Results in tension in the xylem and helps move water across the root Movement of water through plant is known as transpiration stream Model of moving water known as cohesion tension theory
38
What is transpiration?
Loss of water from leaf
39
What is transpiration pull?
Loss of water from the leaf, draws water from xylem
40
What is transpiration stream?
Movement of water up the xylem from the roots to replace that lost by transpiration
41
What is cohesion-tension?
The pull of water from above and the attraction between water molecules causing tension in the xylem vessels which brings about movement.W
42
What evidence is there for the cohesion-tension theory?
When transpiration is at its greatest, diameter of tree trunk reduces due to the pressure, at night it increases If stem is cut: -Air is immediately drawn into xylem as column of water 'pings' up, like cutting an elastic band -Plant will wilt as water can no longer be drawn up, column broken
43
What is the effect of temperature on transpiration?
Higher temperature, more evaporation, more diffusion as more kinetic energy, decreases humidity so more diffusion out of leaf
44
What is the effect of light on transpiration?
More gas exchange as stomata open
45
What is the effect of humidity on transpiration?
High humidity, less transpiration
46
What is the effect of wind on transpiration?
More wind, more transpiration
47
What is the effect of water availability on transpiration?
Less water in soil, less transpiration (in winter, plants lose leaves for example)
48
What is translocation?
The movement of assimilates from source to sink, energy requiring process
49
What is a source, and give some examples.
Part of a plant which loads sucrose into phloem For example: green leaves and stems, storage organs such as tubers - unloading a store at the beginning of growing season Food stores in seeds when germinating
50
What is a sink, and give some examples
Part of plant which removes sucrose from phloem For example: growing roots, roots actively transporting mineral ions, meristems actively dividing, any part of plant laying down stores, seeds, fruit, storage organs
51
Process of phloem loading
Companion cell actively pumps out H+ ions These build up forming a proton gradient Protons move back into companion cell by co-transport, bringing sucrose into the companion cell Sucrose then diffuses into sieve elements Some water follows down a water potential gradient from the xylem Increases hydrostatic pressure Movement in phloem by mass flow High hydrostatic pressure to low hydrostatic pressure
52
Process of phloem unloading
Sucrose moves at the sieve elements into surrounding cells (eg, converted to glucose for respiration or starch for storage) Water potential gradient will increase in sieve elements Water will leave by osmosis into surrounding cells or into transpiration stream in the xylem
53
Is a nectary in a flower a sink or a source, and why?
Sink Removing sucrose to make nectar
54
Is a developing fruit a sink or a source, and why?
Sink Storing sugars in fruit to attract birds to spread seeds
55
Is a potato tuber early in the spring a sink or a source, and why?
Source Stored starch hydrolysed and taken to growing regions
56
Is a potato tuber in late summer a sink or a source, and why?
Sink Sugars converted to starch for storage over winter
57
Is a mature leaf a sink or a source, and why?
Source Produces more sugars in photosynthesis than used in respiration
58
Is a growing leaf a sink or a source, and why?
Sink Uses more sugars than produced
59
In what ways are terrestrial plants adapted to conserve water?
Waxy cuticle on leaf reduces water loss due to evaporation through epidermis Stomata found on underside of leaf, not on top so reduces evaporation due to direct heat from the sun Most stomata close at night as no light for photosynthesis Deciduous plants lose leaves in winter when ground may be frozen (less water available) when temp too low for photosynthesis
60
What are xerophytes?
Plant adapted to living in arid conditions
61
What are the adaptations of Marram grass?
-Leaf rolled longitudinally -Thick waxy cuticle -Stomata on inner side of rolled leaf -Stomata in pits on lower epidermis -Spongy mesophyll dense
62
What are the adaptations of cacti?
Succulents, store water in stems, become fleshy and swollen Stem often ribbed/fluted so can expand Leaves reduced to spines, reduces surface area, less water lost by transpiration Stem often green ----> photosynthesis Roots widespread, take advantage of any rain fall
63
What are some other features of Xerophytes?
Closing stomata when water availability is low, reduces water loss Some plants have low water pot. in leaf cells, maintain high salt concentration, reduces evaporation of water as WPG between cells and air spaces maintained Long tap root that can reach water deep underground
64
What are hydrophytes?
Plants that live in water
65
How are water lilies adapted to their environment?
Many large air spaces in the leaf, keeps leaf afloat so they are in air, absorb sunlight Stomata on upper epidermis, exposed to air to allow gas exchange Leaf stem has many air spaces, helps with buoyancy, also allows oxygen to diffuse quickly to roots for aerobic respiration
66
What is mass flow?
A theory that explains the movement of water and solutes from high to low concentration across a selectively permeable membrane movement of fluids down a pressure or temperature gradient

Biology (12 decks)

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