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Ib biology > Topic 9 > Flashcards

Topic 9 Flashcards

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1
Q

What is transpiration the inevitable consequence of?

A

Gas exchange in the leaf

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2
Q

What is photosynthesis?

A

The synthesis of carbohydrates using light energy

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3
Q

Photosynthesis word equation

A

6C02+6H20–C61206+602

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4
Q

Where does absorption of CO2 take place?

A

In the stomata, which are pores in the epidermis

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5
Q

What gases are exchanged in the leaves?

A

CO2 and O2

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6
Q

What happens in the stomata is open and allows CO2 absorption?

A

Water vapour escapes

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7
Q

What is transpiration?

A

The loss of water vapour from the leaves and stems

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8
Q

What minimises water loss?

A

Guard cells that control the stomata cells and adjust from open to closed. Found in all land plants except liverworts

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9
Q

What do potometers show?

A

Similarities in structures to plants and measures water uptake in plants

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10
Q

Xylem structure

A
  • Withstand low pressure and allow water transport under tension
  • long continuous tubes with thick walls made of lignin ( strengthens the walls so can withstand low pressure w/o collapsing)
  • non living so flow of water must be passive and pressure inside xylem vessels must be lower than the atmospheric pressure
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11
Q

How is water pulled up from the xylem?

A

In a continuous stream due to cohesion and adhesion

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12
Q

What is adhesion?

A

When water is attracted to hydrophillic parts of the xylem

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13
Q

What is cohesion?

A

Water is attracted to other water molecules

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14
Q

What does active intake of mineral ions cause?

A

Water absorption by osmosis

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15
Q

Why is osmosis able to happen?

A

The solute concentration inside the root cells great than the water in the soil ( solute = mineral ions)

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16
Q

How are concentration gradients established?

A

Active transport using protein pumps

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17
Q

Mineral ions

A
  • Can be absorbed by active transport if they make contact with the right pumps
  • cells like fungus on the surface of roots and hyphae of the fungus grow out into the soil and absorb mineral ions
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18
Q

Xerophytes

A
  • Dry condition plants
  • Reduced leaves
  • Thick and waxy cuticles
  • Low growth
  • Rolled leaves
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19
Q

Halophytes

A
  • Salty conditions
  • Leaves are reduced to small scaly structures
  • Thick cuticle and multi-layered epidermis
  • Sunken stomata
  • Long roots which search for water
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20
Q

What are the three ways that water transport can be modelled?

A

-Filter paper, Porous pots, Capillary tubing

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21
Q

Porous pots

A
  • water fills the pores within the pot to show adhesion to clay molecules
  • water being drawn in and cohesion causes water to be drawn up the glass tubing
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22
Q

Capillary tubing

A
  • Capillary tubes are dipped in water with dye and mercury
  • There is no adhesion to the mercury glass and no cohesion between mercury molecules so mercury does not climb up the glass
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23
Q

Filter paper

A

-Folded paper with one end in water will transport the water into an empty container by capillary action

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24
Q

What is humidity?

A

Amount of water vapour in the air

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25
Q

What is the relationship between transpiration and humidity?

A

High humidity = low transpiration

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26
Q

How can we test humidity?

A

Encasing the plant in a plastic bag with variable levels of water vapour

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27
Q

What generates tension force in the leaves?

A

Adhesive property of water and evaporation

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28
Q

Adhesive tension force

A
  • When water evaporates adhesion causes water to be drawn up through the cell wall from the nearest supply to replace water loss
  • force of adhesion is strong enough to suck water out of the xylem which decreases the pressure
  • The now low pressure generates a pulling force that is transmitted through the water in the xylem down the stem and to the ends of the xylem = transpiration pull
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29
Q

Transpiration pull

A
  • The pulling force that is generated through the water in the xylem down the stem and into the ends of the xylem in the roots
  • strong enough to draw water up against the force of gravity
30
Q

Why do plants transport water from the roots to the leavea?

A

To replace water loss from transpiration

31
Q

How is water replaced after transpiration?

A
  • water in the xylem climbs up the stem through the transpiration pull force, adhesion and cohesion
  • water moves from soil into roots by osmosis
  • travels to the xylem by the cell wall
32
Q

Draw a xylem vessel

A
33
Q

What is transpiration in terms of gas exchange?

A

The inevitable consequence of gas exchange in the leaf

34
Q

What do plants do in order to replace water loss from transpiration?

A

Water will move from the roots to the leaves

35
Q

Where does transpiration take place and why?

A

In the stomata which remains open to allow CO2 in and O2 out ( gas exchange) which also leads to loss of water vapour

36
Q

What generates tension forces in the leaves?

A

Adhesion and evaporation of water

37
Q

Describe the process of replacing water loss in the leaves

A
  • water diffuses of the leave through the stomata creating a negative gradient
  • Negative gradient creates a tension force that causes water to be drawn up through the xylem ( transpiration pull)
  • water is pulled up under tension due to adhesion
38
Q

What are the factors that affect transpiration rate?

A
  • Humidity
  • Wind
  • Stomata opening and closing
  • Light intensity and temperature
39
Q

What do the cohesive property of water and structure of the xylem allow for?

A

Transport under tension

40
Q

What is cohesion?

A

Cohesion is the force of attraction between two particles of the same substance (e.g. between two water molecules). Allows for water to be drawn up the xylem in a continuous stream.

41
Q

What is adhesion?

A

Adhesion is the force of attraction between particles of different substances. As water moves upwards they pull inwards on the xylem walls

42
Q

What is the structure of the xylem?

A
  • It is a tube composed of dead cells that are hollow (no to allow for the free movement of water
  • Dead cells so the movement of water is passive and in one direction
  • The cell wall contains numerous pores (called pits), which enables water to be transferred between cells
  • Walls are thickened with lignin to provide strength as water is transported under tension
43
Q

What does active uptake of mineral ions cause?

A

absorption of water by osmosis

44
Q

Describe the process of mineral uptake

A

-Root cells contain proton pumps that actively expel H+ ions into the surrounding soil
-The H+ ions displace the positively charged mineral ions from the clay, allowing them to diffuse into the root along a gradient
-

45
Q

What follows after the mineral ions?

A
  • water which will follow the mineral ions into the root by osmosis
46
Q

What is a potometer?

A

A device to measure transpiration rates

47
Q

How do you use potometers to measure the rate of transpiration?

A
  • transpiration can be indirectly identified by the movement of water towards the plant
  • This water movement can be assessed as a change in meniscus level or by the movement of an air bubble towards the plant
  • The initial starting position of the meniscus or air bubble can be adjusted by introducing additional water from a reservoir
48
Q

From where to where do plants transport organic compounds and what is this process called?

A

From source to sink by translocation

49
Q

What is the difference between sources and sinks?

A 
Sources = where organic molecules are synthesised (  leaves)
SInks = where the organic compounds are used/ stored ( roots/fruits/leaves)
50
Q

What transports organic compounds?

A

Phloem

51
Q

What are the two main cells in phloem sieve tubes?

A

Sieve element cells and companion cells

52
Q
A

Temperature:

Increasing the ambient temperature is predicted to cause an increase in the rate of transpiration
Higher temperatures lead to an increase in the rate of water vaporisation within the mesophyll, leading to more evaporation
The effect of temperature variation can be tested experimentally by using heaters or submerging in heated water baths

Humidity:

Increasing the humidity is predicted to cause a decrease in the rate of transpiration
Humidity is the amount of water vapour in the air – less vapour will diffuse from the leaf if there is more vapour in the air
The effect of humidity can be tested experimentally by encasing the plant in a plastic bag with variable levels of vapour

Light Intensity:

Increasing the light intensity to which a plant is exposed is predicted to cause an increase in the rate of transpiration
Increasing light exposure will cause more stomata to open in order to facilitate photosynthetic gas exchange
The effect of light intensity can be tested experimentally by placing the plant at variable distances from a lamp

Wind Exposure:

Increasing the level of wind exposure is predicted to cause an increase in the rate of transpiration
Wind / air circulation will function to remove water vapour from near the leaf, effectively reducing proximal humidity
The effect of wind can be tested experimentally by using fans to circulate the air around a plant

53
Q

Structure of sieve element cells

A

Sieve element cells
-Sieve elements are long and narrow cells that are connected together to form the sieve tube

Sieve elements are connected by sieve plates at their transverse ends, which are porous to enable flow between cells
-have no nuclei to maximise space for translocation
The sieve elements also have thick and rigid cell walls to withstand the hydrostatic

54
Q

Structure of the companion cells

A

-Provide metabolic support for sieve element cells and facilitate the loading and unloading of materials at source and sink

Possess an infolding plasma membrane which increases SA:Vol ratio to allow for more material exchange
Have many mitochondria to fuel the active transport of materials between the sieve tube and the source or sink
Contain appropriate transport proteins within the plasma membrane to move materials into or out of the sieve tube

55
Q

What is active transport used for?

A

To load organic compounds into the sieve tube

56
Q

Describe active transport

A
  • Hydrogen ions (H+) are actively transported out of phloem cells by proton pumps (involves the hydrolysis of ATP)
  • The concentration of hydrogen ions consequently builds up outside of the cell, creating a proton gradient
  • Hydrogen ions passively diffuse back into the phloem cell via a co-transport protein, which requires sucrose movement
  • This results in a build up of sucrose within the phloem sieve tube for subsequent transport from the source
57
Q

Describe active translocation by mass flow

A

-The active transport of solutes (such as sucrose) into the phloem by companion cells makes the sap solution hypertonic
-This causes water to be drawn from the xylem via osmosis
-Due to the incompressibility of water, this build up of water in the phloem causes the hydrostatic pressure to increase
This increase in hydrostatic pressure forces the phloem sap to move towards areas of lower pressure (mass flow)
-Hence, the phloem transports solutes away from the source (and consequently towards the sink)
The solutes within the phloem are unloaded by companion cells and transported into sinks (roots, fruits, seeds, etc.)
-This causes the sap solution at the sink to become increasingly hypotonic (lower solute concentration)
-Consequently, water is drawn out of the phloem and back into the xylem by osmosis
-This ensures that the hydrostatic pressure at the sink is always lower than the hydrostatic pressure at the source
Hence, phloem sap will always move from the source towards the sink
When organic molecules are transported into the sink, they are either metabolised or stored within the tonoplast of vacuoles

58
Q

What do aphids do?

A

Aphids possess a protruding mouthpiece (called a stylet), which pierces the plant’s sieve tube to allow sap to be extracted
The penetration of the stylet into the sieve tube is aided by digestive enzymes that soften the intervening tissue layers
If the stylet is severed, sap will continue to flow from the plant due to the hydrostatic pressure within the sieve tube

59
Q

What do undifferentiated cells in the meristem allow for?

A

Indeterminate growth

60
Q

What are the two types of meristems ( apical and lateral)

A

Apical meristem
-responsible for plant lengthening i.e. primary growth) and occur at the roots and shoots to produce new leaves
lateral meristems ( responsible for widening/ thickening i.e. secondary growth, occurs at the cambium and produces new bark

61
Q

What is needed in the shoot apex for extension of the stem and development of the leaves?

A

Celll divison and mitosis

62
Q

How does growth occur in the stem?

A

In sections called nodes with the remaining inactive tissue forming an inactive auxillary bud

63
Q

Auxin

A
  • controls growth in the shoot apex
  • via elongation and cell division
  • prevents growth in lateral (axillary) buds, a condition known as apical dominance
  • Apical dominance ensures that a plant will use its energy to grow up towards the light in order to outcompete other plants
  • Different species of plants will show different levels of apical dominance
64
Q

What do auxin efflux pumps set up?

A

A concentration gradient of auxin inside the plant tissue

65
Q

Auxin efflux pumps

A

-Auxin efflux pumps can set up concentration gradients within tissues – changing the distribution of auxin within the plant
- control the direction of plant growth by determining which regions of plant tissue have high auxin levels
Auxin efflux pumps can change position within the membrane (due to fluidity) and be activated by various factors

  • In the shoots, auxin stimulates cell elongation and thus high concentrations of auxin promote growth (cells become larger)
  • In the roots, auxin inhibits cell elongation and thus high concentrations of auxin limit growth (cells become relatively smaller)
66
Q

How does auxin change patterns of gene expression

A
  • Auxin activates a proton pump in the plasma membrane which causes the secretion of H+ ions into the cell wall
  • The resultant decrease in pH causes cellulose fibres within the cell wall to loosen (by breaking the bonds between them)
  • With the cell wall now more flexible, an influx of water (to be stored in the vacuole) causes the cell to increase in size
67
Q

Tropisms

A
68
Q

Micropropagation

A
69
Q

Draw the internal structure of a seed

A
70
Q

Describe how water is carried through a flowering plant.

A

active transport of solutes from soil into roots;

b. draws water by osmosis
c. root hairs provide a large surface area for water uptake;
d. carried through xylem vessels;
e. transpiration is the loss of water (vapour) from leaves and stems / stomata;
f. (transpiration) creates suction/pull/negative pressure;
g. cellulose wall with rings of lignin give strength to resist (low) pressure;
h. water pulled up due to capillary action/cohesion/adhesion;
i. continuous column of molecules/transpiration stream;

71
Q

Define the term transpiration and explain the factors that can affect transpiration in a typical terrestrial plant.

A

(transpiration is) loss of water vapour from the leaves/stomata (and stems) of plants;
temperature, humidity, light (intensity) and wind all affect transpiration;
high temperatures increase evaporation rate of water/transpiration; (accept converse)
high humidity lowers the rate of water evaporation/transpiration; (accept converse)
air currents/wind increase water evaporation/transpiration; (accept converse)
high light (intensity)/sunlight (usually) increases photosynthesis/water evaporation through the stomata/transpiration;
stomata open to allow gaseous exchange/entry of CO2;
abscisic acid stimulates closing of stomata;
guard cells open/close the stomata;
adaptations of (xerophyte) plant structures reduce water loss/transpiration;
one example;
(thicker leaf cuticle / reduced surface area/rolled leaves/spines / sunken/reduced stomata / close stomata in day / low growth form / CAM / C4 physiology)

72
Q

Explain how flowering is controlled in long-day and short-day plants.

A

flowering affected by light;
phytochrome;
exists in two (interconvertible) forms/Pfr and Pr;
Pr (red absorbing/660 nm) converted to Pfr (far-red/730 nm absorbing) in red or day light;
sunlight contains more red than far red light so Pfr predominates during the day;
gradual reversion of Pfr to Pr occurs in darkness;
Pfr is active form / Pr is inactive form;
in long-day plants, flowering induced by dark periods shorter than a critical length / occurs when day is longer than a critical length;
enough Pfr remains in long-day plants at end of short nights to stimulate flowering;
Pfr acts as promoter of flowering in long-day plants;
short-day plants induced to flower by dark periods longer than a critical length/days shorter than a critical value;
at end of long nights enough Pfr has been converted to Pr to allow flowering to occur;
Pfr acts as inhibitor of flowering in short-day plants;

Ib biology (11 decks)

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