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Biology Unit 2 > Plant Transport > Flashcards

Plant Transport Flashcards

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1
Q
  1. The vascular tissue of plants consists of xylem and phloem. What do xylem and phloem do?
A
  • Xylem vessels transport water and inorganic ions from the roots to the leaves * Phloem tubes transport organic molecules (sucrose and amino acids) from the leaves to growing points (where carbohydrates are used for energy and amino acids for growth) and to the roots (where storage occurs). Known as TRANSLOCATION.
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2
Q
  1. Where are vascular tissues found in a ROOT?
A

Xylem and phloem are found in the centre of a root as a central stele (or vascular cylinder)

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3
Q
  1. Which tissue makes up the majority of the stele
A

Xylem

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4
Q
  1. What is the name of the single layer of cells that surrounds the stele?
A

Endodermis

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5
Q
  1. What is the name for the general undifferentiated cells between the endodermis and the epidermis in a root?
A

Cortex (also referred to as packing tissue or parenchyma - may be used for starch storage or maintaining turgidity)

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6
Q
  1. Where are the vascular tissues found in a STEM?
A

Vascular tissue is arranged as vascular bundles around the outside of the stem

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7
Q
  1. How is the xylem adapted for transport of water and ions?
A
  1. It is made from vessels with no end walls and no cell contents, therefore transport is not restricted 2. The walls are thickened with impermeable lignin (as well as cellulose which: * is waterproof so prevents leakage of water * provides the strength needed to prevent collapse due to tension created by transpiration stream * provides structural support for the plant
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8
Q
  1. Give 5 difference between xylem and phloem (apart from the materials transported)
A
  1. Xylem cells are non-living (no cytoplasm) but phloem tubes are living (thin layer of cytoplasm) 2. Transport in xylem is in one direction (upwards), transport in phloem is bi-directional (from source to sink) 3. Cell wall material is lignin and cellulose in xylem, just cellulose in phloem 4. Xylem vessels have no end walls, but phloem sieve tubes do, in the form of sieve plates 5. Flow in xylem is faster
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9
Q
  1. What patterns of lignification is found in the more immature protoxylem and what is significant about this?
A

Annular and spiral lignification - allows expansion and elongation during growth

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10
Q
  1. What patterns of lignification are found in the more mature metaxylem?
A

Reticulate and pitted - the pits allow movement of water between adjacent vessels and surrounding cells

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11
Q
  1. How is the phloem adapted for transporting organic substances (eg. sucrose and amino acids)
A
  1. They have companion cells that have a dense cytoplasm, rich in mitochondria which support the sieve tube cells by carrying out the metabolic activities associated with transport of organic substances 2. They have microtubules that extend through the pores of sieve plates (found between the sieve tube elements) that help with continuous translocation 3. Companion cells are linked to sieve tube elements via plasmodesmata enabling transport between the two cells 4 Sieve tube elements only have a thin cytoplasm which reduces friction to the flow of organic substances
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12
Q
  1. What are the 3 main stages in the transport of water and ions through a plant?
A
  1. Movement into root hairs and across the root 2. Transport up the stem in the xylem 3. Transport through the leaf and evaporation from the leaf
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13
Q
  1. What is TRANSPIRATION?
A

Transpiration is the evaporation of water from the spongy mesophyll cells followed by the diffusion of water through the stomata and into the atmosphere

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14
Q
  1. How do water and ions enter the plant?
A
  • Water is taken up by root hair cells by osmosis (high Y to lower Y) * Mineral ions are taken up by root hair cells by ACTIVE UPTAKE or FACILITATED DIFFUSION The root hair cells provide a thin surface membrane, a permeable wall and a large surface area for this
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15
Q
  1. Water and ions move across the root cortex cells and into the xylem via the APOPLAST pathway and the SYMPLAST pathway. Describe the APOPLAST PATHWAY.
A
  • Apoplast pathway - water moves along the cellulose microfibrils of the cell walls of the cortex cells * This is aided by the parallel arrangement of the microfibrils and the mesh-like arrangement of the walls * Cohesion between the water molecules (due to H-bonds) helps pull the water column along
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16
Q
  1. Describe the SYMPLAST PATHWAY across the root cortex
A
  • Symplast pathway - water moves by osmosis from cell to cell via the cytoplasm and plasmodesmata of each cell of the cortex * It moves by osmosis along the water potential gradient
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17
Q
  1. Which pathway is faster, apoplast or symplast
A

The apoplast pathway, as there is limited resistance to water flow

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18
Q
  1. What is the endodermis?
A

The endodermis is a layer of cells just outside the stele of the root which have walls embedded with a waxy, circular layer of suberin called the CASPARIAN STRIP.

19
Q
  1. What happens at the Casparian strip?
A

Water is forced out of the apoplast pathway and into the symplast pathway. To do this it must cross the plasma membrane.

20
Q
  1. What is the importance of the Casparian Strip?
A

The Casparian strip provides a means of metabolic control over which ions enter the xylem

21
Q
  1. What provides the force needed to transfer water and ions from the endodermis into the xylem?
A
  • Energy is used to pump ions into the xylem from the endodermis * This creates a water potential gradient to draw water into the xylem by osmosis * This creates a ROOT PRESSURE FROM BELOW to help push water up through the xylem
22
Q
  1. Water (and ions) travel up the xylem of the stem in the transpiration stream. What is the transpiration stream AND WHAT CAUSES IT?
A

The transpiration stream is the continual unbroken column of water in the xylem due to: 1. COHESION: The sticking together of the water molecules due to hydrogen bonds between them 2. NEGATIVE PRESSURE OR TENSION: Caused by the evaporation of water out of the leaves creating a (transpirational) pull upwards 3. ADHESION: The attraction between the water molecules and the xylem walls NOTE - THE ABOVE ALSO DESCRIBES THE COHESION-TENSION THEORY

23
Q
  1. Why does the diameter of a tree trunk decrease in the middle of the day?
A

This is when transpiration is at its greatest and the tension or negative pressure caused by it pulls the walls of the xylem vessels inwards. This in turn, reduces the diameter of the tree

24
Q
  1. How does water enter the leaf?
A

It travels from the xylem (in the veins) to the spongy mesophyll cells via apoplast and symplast pathways

25
Q
  1. What happens to the water that enters the leaf?
A
  • Some is used in photosynthesis * Some provides turgor in cells * Most is lost in transpiration
26
Q
  1. How is the transpirational pull created in the leaf?
A

Water evaporates from the cell membranes of the spongy mesophyll cells into the air spaces and then the vapour diffuses out of the stomata, creating a water potential gradient

27
Q
  1. Give 3 internal factors i.e. leaf characteristics that affect transpiration rate
A
  1. Stomatal density (the more there are, the more evaporation/transpiration there is) 2. Leaf surface area (the bigger the surface area, the more evaporation there is) 3. Cuticle thickness - the thicker it is, the less water is lost by evaporation
28
Q
  1. Give 5 external factors that affect the rate of transpiration
A

Wind speed, Temperature, Humidity, Light intensity, Soil Water availability

29
Q
  1. How does wind speed affect transpiration?
A

As wind speed increases, rate of transpiration increases as diffusion shells are blown away more quickly which maintains a steep Y gradient and therefore increases the rate of evaporation from spongy mesophyll cells (followed by diffusion through stomata)

30
Q
  1. How does light intensity affect transpiration?
A

As light intensity increases, rate of transpiration increases as more stomata tend to be open during day-time, enabling more diffusion outwards

31
Q
  1. How does humidity affect transpiration rate?
A

As humidity increases rate of transpiration DECREASES as air surrounding the leaf and in sub-stomatal air spaces has a higher concentration of water vapour which decreases the water potential gradient for evaporation

32
Q
  1. How does temperature affect transpiration rate?
A

As temperature increases rate of transpiration increases as kinetic energy of water molecules increases, leading to a faster rate of evaporation from SM cells

33
Q
  1. What is translocation?
A

Translocation is the movement of organic substances (amino acids and sucrose from the leaves to the growing regions and roots (where sugars are stored) in the phloem

33
Q
  1. How does soil water availability affect transpiration?
A

As soil water availability increases, rate of transpiration increases, however in times of drought, evaporation and transpiration will decrease due to stomata closing to conserve water.

33
Q
  1. How do we know translocation of sucrose in the phloem is bi-directional?
A

When a branch is supplied with radioactively labelled CO2, the sugars made by photosynthesis take up the radioactively labelled carbon. These sugars are subsequently found both above the branch in growing regions and below the branch in storage organs of roots

34
Q
  1. Translocation is energy requiring. How do we know this and how do we know companion cells are involved?
A
  • The companion cells which are found beside the phloem sieve tube elements have high metabolic rates and have MANY mitochondria * When treated with a respiratory poison, like cyanide, translocation is disrupted
35
Q
  1. In what way does translocation demonstrate MASS FLOW?
A

The build-up of sugars in “SOURCE” areas such as leaves helps to build up a hydrostatic pressure between these source areas and “SINK” areas such as the roots, where the sugars are respired or stored and hydrostatic pressure is lower. This drives transport in the phloem.

36
Q
  1. What water conservation features do typical land-dwelling (mesophytic plants) have?
A
  • Waterproofed cuticle * Stomata that can be opened or closed * Exchange surfaces that are protected within the leaf to prevent excess evaporation (spongy mesophyll cells)
37
Q
  1. What is a xerophyte?
A

A xerophyte is a plant adapted to conditions in which there is a lack of water (and therefore it needs to decrease transpiration to try and prevent desiccation EXAMPLE - MARRAM GRASS)

38
Q
  1. List the typical xerophytic leaf adaptations
A
  • Leaf Curvature: The fold creates an area of humid air which decreases the water potential gradient for evaporation and transpiration (between inside and outside of the leaf) * Reduced Leaf Surface Area: Structures such as spines or needles reduce the area over which transpiration can take place * Sunken Stomata: Pits or grooves allow diffusion shells of humid air to build around the stomata, which reduces the water potential gradient and therefore reduces evaporation and transpiration Leaf hairs: Found on the lower surface, again these trap a layer of humid air in a diffusion shell and reduce the water potential gradient between the inside and outside of the leaf * Thick Cuticle: Helps to reduce evaporation * Succulent leaves and tissues: Store large amounts of water for periods of drought
38
Q
  1. What other adaptations might a xerophytic plant have?
A

Deep roots to reach the water well or extensive shallow roots to absorb as much surface moisture from rainfall as possible

38
Q
  1. What is a hydrophyte? Eg Waterlily
A

A hydrophyte is a plant which is adapted for living in or on water i.e. is found in a wet habitat

38
Q
  1. What adaptations do hydrophytes have?
A
  • Stomata found mainly on upper surface: Enables gas exchange to occur between leaf and air whilst preventing water from entering air spaces and submerging the leaves * Aerenchyma (large air spaces): These store gases and allow plant to float, enabling them to obtain maximum light for photosynthesis * Lack of or very thin cuticle: Water is abundant so loss is not a problem * Sclereids: Act as an internal skeleton

Biology Unit 2 (5 decks)

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