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Plants Flashcards

1
Q

Why do plants need a transport system?

A

Cells in a multicellular plant require a regular inflow of water and nutrients
Only the exterior cells can obtain nutrients and water through diffusion
Roots can obtain water but not sugars from the soils
The leaves can make sugars by photosynthesis but cannot obtain water

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2
Q

What do vascular bundles consist of?

A

Xylem vessels
Phloem vessels
Cambium tissue

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3
Q

Where are the vascular bundles usually located in woody plants?

A

Near the outer edge creating a ring that provides flexibility and strength to withstand bending
The cambium tissue is sandwiched by the phloem tissue on the outside and the xylem vessels on the inside

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4
Q

What are the veins like in a dicotyledon leaf?

A

The veins branch out and get steadily thinner

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5
Q

What do xylem vessels transport?

A

Water and minerals

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6
Q

What do phloem vessels transport?

A

Sucrose and most macromolecules

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7
Q

What is the structure of xylem vessels like?

A

Walls are impregenated with lignin
Long colomn of dead cells like a straw
Lignification prevents the vessel from being too rigid and allows flexibility
Pitted with pores to allow adjacent movement of water

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8
Q

What is the structure of phloem vessels like?

A

Made up of sieve tube elements and companion cells

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9
Q

What is the structure of sieve tube elements like?

A

Contain very little cytoplasm and no nucleus
Joined end to end to form a tube for sap to flow through
Seperated by sieve plates with pores

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10
Q

What is the structure of companion cells like?

A

Have a dense cytoplasm and a large nucleus
Contains a lot of mitochondria to handle the loading of sucrose molecules
Have extensions called plasmodesmata that allow communication and flow of minerals

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11
Q

What is plasmodesmata?

A

Extensions of the cell cytoplasm

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12
Q

How are most macromolecules made in the plant?

A

Through photosynthesis and the absorbtion of minerals from the soil

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13
Q

What evidence is there for phloem as the tissue for translocation

A

Injecting radioactive carbon into soluble carbohydrates during photosynthesis and examining later with autoradiographs
Electron microscopy has shown a greater concentration of sucrose molecules in phloem
Removing a ring of bark and seeing the bottom half of the tree die due to a lack of sucrose
Cyanide injections into phloem stop translocation but not when injected into the xylem
Aphid mouthparts may be removed and examined for sucrose

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14
Q

What is phototropism?

A

The growth response which allow choots to grow towards a light source to optimise illumination of leaves

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15
Q

How is leaf structure adapted to photosynthesis and gas exchange?

A 
Large surface area to volume ratio
Thin leaves
Leaf mosaic
Phototrophic abilities
Extensive root system
Etiolation
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16
Q

What is the greatest risk factor for plants reagarding water loss?

A

Sunlight

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17
Q

What is the function of the waxy cuticle?

A

Reduces water loss

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18
Q

What is the function of the upper epidermis?

A

Reduce water loss
Traps moisture by epidermal hairs and reflects sunlight
Sterile to prevent pathogenic infection

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19
Q

What is the function of the palisade mesophyll

A

Creates glucose by photosynthesis

Contain many chloropasts that move to the optimum position for photosynthesis

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20
Q

What is the function of the spongy mesophyll?

A

Permit the diffusion of gases out of the leaf

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21
Q

What is the function of the stomata?

A

To control the diffusion of the respiratory gases in and out of the leaf

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22
Q

What is the function of guard cells?

A

To open and close the stomata by changing shape

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23
Q

How do guard cells change shape?

A

Guard cells contain chloroplasts
As theses guard cells have a lower potential, water moves in
Due to the spirals in the walls of the inner edges, the outer walls stretch
As the cell bulges out at both ends, the pore opens between them

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24
Q

What are the requirements for photosynthesis?

A

Light
A supply of water
A supply of carbon dioxide
Presence of chlorophyll

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25
What are the four main categories of animal tissues?
Epithelial tissue Connective tissue Muscle tissue Nervous tissue
26
What is transpiration?
The loss of water by evaporation from the aerial parts of a plant
27
What three processes make up transpiration?
Osmosis from the xylem to mesophyll cells Evaporation from the mesophyll cells into the intracellular spaces Diffusion of water vapour from the intracellular spaces out through the stomata
28
Why is the movement of water up the stem useful for plants?
``` For photosynthesis So cells can grow and elongate Maintain turgidity Carrying minerals Keep the plant cool through evaporation ```
29
What does a photometer measure?
The rate of water uptake
30
How much water is actually used by the plant
Around 2% to use in photosynthesis and the building of the cytoplasm
31
What is the reservoir of water for in the photometer?
To prevent air bubble from entering the plant | To move the air bubble back along the capillary tube
32
What features of a plant affect water loss?
``` Number of leaves Number, size and position of stomata Presence of cuticle Light Temperature Relative humidity Air movement or wind ```
33
What happens if the plant loses too much water?
If water loss is greater than water uptake, plant cells will lose turgidity and the plants will wilt and die
34
What is translocation?
The transports of assimilates throughout the plant, in the phloem tissue
35
What is a source?
Where sucrose is loaded into the phloem
36
What is a sink?
Where sucrose is removed from the phloem
37
What is mass flow?
The phenomenon where sucrose is continuously moving along the phloem due to differences in hydrostatic pressure
38
Why does translocation occur in two directions?
During summer more sucrose is pumped to the roots for active transport to maintain hydration levels In the winter, there is less photosynthesis so sucrose moves from the roots to the leaves
39
What are the steps of loading?
Protons are pumped from clarion cells into surrounding cells This generates a proton gradient between the two cells Protons diffuse back across into the companion cell cotransporting sucrose Sucrose diffuses into the phloem down a concentration gradient Sucrose decreases the water potential of the sieve tube and so water diffuses from the companion cell into the sieve tube, increasing hydrostatic pressure
40
What are the steps of unloading?
Sucrose molecules diffuse across into surrounding cells as the surrounding cells have used the sucrose for respiration so have a lower concentration of sucrose compared to the sieve tube This increase the concentration of sucrose in the surrounding cellscand decreases the water potential of these cells This causes water to move in down the concentration gradient into the surrounding cells This decreases hydrostatic pressure in the roots Due to this pressure gradient, mass flow can occur
41
What are the three ways in which water can move across the root into the xylem?
Apoplast pathway Symplast pathway Vacuolar pathway
42
How does water travel in the Apoplast pathway?
Through the cell walls until it reaches the campaign strip (least resistance)
43
How does water move in the symplast pathway?
Through the cytoplasm connected between each cell by pasmodesmata
44
What are the types of lignification
Spiral Annular Reticulate Pitted
45
Why does water travelling in the apoplast pathway move into the cytoplasm in the endodermis?
The casparin strip is impregnated into the cell wall | It is made of suburin that is impermeable to water
46
What is the importance of the casparin strip?
Gives the plant the ability to control the inflow of water
47
How are xylem vessels made?
Xylem cells elongate and are impregnated with lignin Cells die as water cannot reach the cell The cell wall breaks down to form a xylem vessel
48
What are the ways in which water can travel up the xylem?
Root pressure | Capiliarity transpiration stream pull
49
How does root pressure move water up the xylem?
An increased concentration of water and mineral ions pushes the water up the stem
50
How does the transpiration pull move water up the xylem vessels?
Water is lost via transpiration | This water has to be replaced so the cohesive forces of the water molecules pulls the whole column of water up the xylem
51
How does capillary action move water up the stem?
The adhesive forces in the narrow xylem are strong enough to pull the water up the stem
52
What is a xerophyte?
A plant that is adapted to reduce water loss so that it can survive in very dry conditions
53
Why is loss of water in a plant unavoidable?
The stomata have to open to allow the exchange of respiratory gases so water vapour always diffuses out
54
How are plants adapted to reduce water loss?
Presence of a waxy cuticle Stomata are found on the underside of a leaf Stomata are closed during night Leaves are lost during winter
55
How are xerophytes adapted to reduce water loss?
``` Small leaves Densely packed spongy mesophyll Thick waxy cuticle Closing stomata when water availability.is low Hairs trap a barrier of saturated air Pits trap a barrier of saturated air around the stomata Rolling up the leaves Maintaining a low water potential ```
56
How are the vascular bundles in a dicotyledonous root organised?
The xylem vessels are organised in a X shape around the centre The phloem vessels fill the gaps between each wing of the X shape
57
How are the vascular bundles organised in a monocotyledonous root?
The xylem vessels are in a ring structure around the central part of the root within the endodermis The phloem vessels are located around the xylem but do not fill the centre of the endodermis
58
What tissues in the plant contain stem cells?
Meristem and cambium
59
Why does the trunk swell above the cut?
Sugar cannot pass the cut Decreased water potential causes water to move into cells Damage triggeres cell division to produce more cells to store sugars Cut causes infection
60
What is the purpose of spiral band lignification?
Provides structural support for xylem wall Lignin makes xylem vessels waterproof Improves adhesion of water molecules Spiral pattern allows flexibility
61
What is the function of the pits in the xylem vessels?
``` Prevents the collapse of xylem Waterproofing allows water to be under tension at low pressures Reduces water loss through walls Increases capillarity Prevents stem breaking Pits allow lateral movement of water Can bypass blockage ```
62
Precautions to take with a potometer
``` Make sure shoot is healthy Assemble apparatus under water Cut stem at an angle Check there are no air bubble in the apparatus Make sure apparatus is air tight Make sure leaves are dry ```
63
Why does the potometer only give an estimate of the rate of transpiration?
Potometer measures water uptake Not all water taken up is transpired Some water is used for photosynthesis or making the cytoplasm
64
How is water moved up the xylem from the roots to the leaves
Water moves into xylem down a water potential gradient High hydrostatic pressure at the bottom of the xylem Transpiration creates low hydrostatic pressure at the top of the xylem Column of water is pulled up by cohesive forces between water molecules Adhesion of water molecules Capillary action Water moves up by mass flow

Biology (18 decks)

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