3.1.3 ( part 2 ) - Transportation in plants

Question 1

define the term ‘assimilates’ ?

Answer 1

Assimilates - The products of photosynthesis that are transported through the plant

Question 2

Define the term ‘translocation’ ?

Answer 2

Translocation - The movement of organic solutes around the plant in the phloem

Question 3

Explain how assimilates are transported around the plant ?

Answer 3

Plants transport organic compounds/ assimilates in the phloem from the sources ( where they are made ) to the sinks ( where they are required by the plant )

Question 4

Name the main sources of the plant ?

Answer 4

• Green leaves/ stems
• Storage organs ( e.g tubers and tap roots ) that unload stores at the start of a growth period
• Food stores in seeds when they germinate

Question 5

Name the main sinks of the plant ?

Answer 5

• Roots that are growing/ absorbing mineral ions
• Meristems that are actively dividing
• Any part of plant that are laying food stores

Question 6

What is phloem loading ?

Answer 6

An active process by which assimilates are moved into the phloem from the sources

Question 7

describe the process of phloem loading ?

Answer 7

1 ) Sucrose from the sources travels through the apoplast route to the companion cell via diffusion down the concentration gradient
2 ) In the companion cells, sucrose is moved into the cytoplasm across the cell membrane through an active process
3 ) Hydrogen ions are active pumped out of companion cell using ATP
4 ) The Hydrogen ions return to companion cells down a concentration gradient via a co-transport protein. Sucrose is the molecule which is co-transported
5 ) This increases the sucrose concentration in the companion cells through the many plasmodesmata between the two linked cells
6 ) This results in build up of sucrose and water which also moves in by osmosis in companion cells
7 ) This causes the turgor pressure in companion cells to increase causing water carrying assimilates to move into tubes of sieve tube elements
8 ) Water then moves up and down the plant to regions of lower pressure such as the sinks

Question 8

Explain the process of phloem unloading ?

Answer 8

• Sucrose is unloaded from the phloem at any point where the cells need it via diffusion or by being converted into another substance ( eg. glucose )
• This maintains curse concentration between phloem and surrounding cells
• Loss of solutes in phloem leads to increase in water potential and for water to move into surrounding cells via osmosis

Question 9

What evidence is there for phloem loading/ unloading ?

Answer 9

• Advances in microscopes allow us to see adaptations of companion cells for active transport
• If mitochondria in companion cells are poisoned, translocation stops
• Flow of sugars is much faster than if it solely relied on diffusion indicating it is an active process
• Aphids can demonstrate the translocation process causing mass flow in phloem

Question 10

Define the term ‘Xerophytes’ ?

Answer 10

Xerophytes - Plants with adaptations that enable them to survive in dry habitats or habitats where water is in short supply in the environment

Question 11

Name examples of xerophytes ?

Answer 11

• Conifers
• Marram grass

Question 12

Define the term ‘Hydrophytes’ ?

Answer 12

Hydrophytes - Plants with adaptations that enable them to survive in very water habitats or submerged or at surface of water

Question 13

Name examples of hydrophytes ?

Answer 13

• Water lilies
• Water cress

Question 14

What are some adaptations of xerophytes that help them conserve water ?

Answer 14

• A thick waxy cuticle
• Sunken stomata
• Reduced number of stomata
• Reduced leaves
• Haiti leaves
• Curled leaves
• Succulents
• Leaf loss
• Root adaptations ( long or shallow )
• Able to avoid the problem

Question 15

Explain how a thick waxy cuticle helps xerophytes conserve water ?

Answer 15

this helps minimise water loss by transpiration through the cuticle

Question 16

Explain how sunken stomata helps xerophytes conserve water ?

Answer 16

• This means stomata are located in pits
• This reduces air movement creating a humid microclimate
• This reduces the water vapour concentration gradient leading to reduced water loss via transpiration

Question 17

Explain how a reduced number of stomata helps xerophytes conserve water ?

Answer 17

A reduced number of stomas a means the is less water loss via transpiration

Question 18

Explain how reduced number of leaves helps xerophytes conserve water ?

Answer 18

Reduced number of leaves means there is less leaves off which water can be lost via transpiration

Question 19

Explain how hairy leaves helps xerophytes conserve water ?

Answer 19

The hairs on the leaves create a humid microclimate reducing the water vapour potential gradient and minimising water loss via transpiration

Question 20

Explain how curled leaves help xerophytes conserve water ?

Answer 20

The curled shape of the leaf causes all stomata to be confined in humid microclimate reducing the water vapour potential gradient leading to reduced loss of water via transpiration

Question 21

Explain how succulents helps xerophytes conserve water ?

Answer 21

• Succulent plants store water in specialised parenchyma tissue in stems/ roots when water is in plentiful supply
• This water is used during time of drought

Question 22

Explain how leaf loss helps xerophytes conserve water ?

Answer 22

• Some plants simply lose leaves when water is not available
• This means there are less stomata through which water can be lost via transpiration

Question 23

Explain how root adaptations helps xerophytes conserve water ?

Answer 23

• Root adaptations help plants absorb as much water as possible from the soil
• Long plant roots can penetrate several rtes and access water a long way below the surface
• Shallow roots with a large surface area are able to absorb any available water

Question 24

Explain how the ability to avoid the problem helps xerophytes conserve water ?

Answer 24

Some plants avoid the problem by losing leaves, becoming dormant or dying, leaving seeds behind to germinate/ grow when rain falls

Question 25

What are some adaptations of hydrophytes ?

Answer 25

• Very thin/ no waxy cuticle
• Many ‘always-open’ stomata
• Reduced structure to plant
• Wide, flat leaves
• Small roots
• Large surface area of stem/ roots underwater
• Air sacs
• Aerenchyma

Question 26

Explain the effect of a very thin/ no waxy cuticle for hydrophytes ?

Answer 26

• Water is always in plentiful supply
• Therefore water being lost via transpiration is not a problem

Question 27

Explain the effect of many ‘always-open’ stomata for hydrophytes ?

Answer 27

• The large number of ‘always-open’ stomata maximises gas exchange
• Water is always available so no loss of turgor pressure and stomata often are always open

Question 28

Explain the effect of reduced structure to plant for hydrophytes ?

Answer 28

Strong support structure is not needed since water supports leaves/ flowers

Question 29

Explain the effect of wide, flat leaves for hydrophytes ?

Answer 29

Wide flat leaves have large surface area which maximises light absorbance for photosynthesis

Question 30

Explain the effect of small roots for hydrophytes ?

Answer 30

Water can diffuse directly into stem/ leaf tissue so there is no need for uptake by roots

Question 31

Explain the effect of large surface area of stem/roots underwater for hydrophytes ?

Answer 31

The large surface area of stem/ roots maximises area for photosynthesis and gas exchange

Question 32

Explain the effect of air sacs for hydrophytes ?

Answer 32

Enable the leaves/ flowers to float to waters surface

Question 33

Explain the effect of aerenchyma for hydrophytes ?

Answer 33

• Makes the stem and leaves more buoyant
• Forms a low-resistance internal pathway for the movement of substances such as oxygen to tissues below the water. This helps the plant to cope with anoxic (extreme low oxygen conditions) conditions in the mud, by transporting oxygen to the tissues.

Question 34

What is aerenchyma ?

Answer 34

• It is specialised parenchyma (packing) tissue formed in the leaves, stems and roots of hydrophytes
• It has many large air spaces

Question 35

What is a potometer ?

Question 36

What precautions must be taken when setting up a photometer ?

Answer 36

• Photometer should be air tight/ set up underwater
• Cut stem under water
• Have apparatus under water
• Insert stem under water
• Joints must be sealed/ tight

Question 37

Why is it important that a potometer is air tight/ set up underwater ?

Answer 37

• This prevents air blocking and ensures there is a continuous column of water
• Bubble could block the xylem

Question 38

Describe how a potometer can be used to calculate rate of transpiration ?

Answer 38

• Set up the potometer so it is air tight/ water tight
• Ensure leaves of plant are dry
• Cut shoot under water
• Measure the distance air bubble traveled per time interval ( minute/ 3 minutes … )
• Calculate volume of water uptake
• Maintain constant conditions ( air movement, humidity, light intensity, temperature ) g