Transport in plants

Question 1

what are the two main types of transport vessels found in dicotyledonous plants

Answer 1

xylem and phloem

Question 2

why do plants require specialised transport systems

Answer 2

To ensure nutrients reach all tissues.
To allow diffusion across large distances
To overcome the low surface area to volume ratio
To meet the high metabolic demand

Question 3

what are vascular bundles

Answer 3

transport tissues arranged in stems, leaves and roots of plants

Question 4

how are the vascular tissues arranged in a stem of a dicotyledonous plant

Answer 4

arranged in a circle around the edge of the stem

Question 5

how are the vascular tissues arranged in the roots of dicotyledonous plants

Answer 5

arranged in a bundle in the centre of the root

Question 6

what are stomata

Answer 6

The stomata are pores, usually found in the lower epidermis of a leaf, through which gases such as oxygen and carbon dioxide diffuse.

Question 7

what happens to stomata in the day

Answer 7

they are open and both respiration and photosynthesis occur

Question 8

what happens to the stomata during the night

Answer 8

they are closed and only respiration occurs

Question 9

what is transpiration

Answer 9

the evaporation of water through stomata down a water potential gradient

Question 10

what increases the rate of transpiration

Answer 10

increased temperature and wind, decreased humidity

Question 11

what are plasmodesmata

Answer 11

Plasmodesmata are small channels connecting the cytoplasm of adjacent plant cells.

Question 12

What is the name of the pathway by which water uses plasmodesmata to move across adjacent cells through the cytoplasm?

Answer 12

the symplast pathway

Question 13

What is the name of the pathway by which water moves through the cellulose fibres in the cell walls of connecting cells?

Answer 13

the apoplast pathway

Question 14

Describe the cohesion-tension theory of water transport in the xylem.

Answer 14

First, the loss of water by transpiration decreases the water potential in mesophyll cells.
This pulls water up the xylem, which puts it under tension.
Inside the column, water molecules adhere to the walls, and they’re stuck together by hydrogen bonds.

Question 15

What term is used to describe plants that have adapted to survive in habitats where water supply is limited?

Answer 15

Xerophytes

Question 16

List 4 adaptations shown by the leaves of xerophytes which help reduce water loss.

Answer 16

Thick waxy cuticle
Stomata in sunken pits
Leaves which are curled
Leaves covered in hairs

Question 17

What term is used to describe plants adapted to grow partly under water or in wet habitats?

Answer 17

hydrophytes

Question 18

List three adaptations of hydrophytes to survive in wet habitats.

Answer 18

1. No waxy cuticle
2. Increased number of stomata
3. Wide, flat leaves to capture light

Question 19

what does a potometer measure

Answer 19

the rate of water uptake

Question 20

what are the limitations of using a potometer to measure the rate of transpiration

Answer 20

Assumes that all of the plants water will be transpired and requires all the roots of a plant to be removed so the calculated rate doesn’t take into account water uptake in the roots

Question 21

Define osmosis

Answer 21

The movement of water across a partially permeable membrane, from an area of high water potential to an area of low water potential.

Question 22

what can lead to a decrease in water potential

Answer 22

addition of solutes and removal of water

Question 23

what water potential does pure water have

Answer 23

0

Question 24

which transport vessel do assimilates travel through

Answer 24

the phloem

Question 25

what is translocation

Answer 25

the process by which substances are transported from a source to a sink

Question 26

why do plants use sucrose rather than glucose to transport

Answer 26

because glucose is more reactive than sucrose and could react with other substances in the other phloem which would prevent it from being transported to the cells that it needs to go to

Question 27

what is hydrostatic pressure

Answer 27

pressure exerted by a liquid inside a container

Question 28

what is the hypothesis that is used to explain translocation in plants

Answer 28

the mass flow hypothesis

Question 29

define co transport

Answer 29

when a carrier protein transports two substances at once

Question 30

how does sucrose move through companion cells

Answer 30

active transport

Question 31

describe the mass flow hypothesis

Answer 31

1. First, sucrose moves into the sieve tube element. 2. This causes the water potential in the sieve tube element to decrease. 3. Water moves from the xylem into the sieve tube element by osmosis. 4. This causes the hydrostatic pressure in the sieve tube element to increase. 5. At the sink cell, the hydrostatic pressure decreases as a result of water moving out of the sieve tube element. 6. As a result, the sucrose solution moves down the hydrostatic pressure gradient. 7. Finally, sucrose moves into the sink cell.

Question 32

what is the theory for how sucrose moves through the companion cells from source to sieve tube elements

Answer 32

First, a co transport protein moves H+ ions from the cytoplasm of the companion cell to the cell wall, using active transport . This creates a concentration gradient, allowing the H+ ions to be returned to the cytoplasm along with sucrose, via active transport. Once the sucrose is inside the companion cell, it diffuses into the sieve tube element.

Question 33

how does an increase in wind speed cause increased rates of transpiration

Answer 33

higher wind speeds remove water on the surface of the leaf which creates a higher concentration gradient which causes more water to diffuse out the stomata, water is pulled up the xylem as the water molecule stick together

Question 34

what does the xylem have which makes it more adapted to water transportation

Answer 34

it has lignin in the cell walls to make them waterproof, it has no organelles or end cell walls which results in less obstruction to the water and allows the water to form a continuous column