Y12 MS - Plant Transport (Complete)

Question 1

What is the name of a plant adapted for survival in an environment with little water?

Answer 1

A xerophyte

Question 2

What are the adaptations of xerophytic plants?

Answer 2

Waxy cuticle - prevents water loss by evaporation
Spines - leaves rolled up into spines to reduce the surface area so there is little loss of moisture
Leaves covered in hair - the hair traps a layer of moisture around the leaf so a water potential gradient is not created, preventing the rapid loss of water
Sunken stomata - increases the humidity around the stomata
Reduced number of stomata - reduced surface area for water loss

Question 3

How are the stomata and guard cells adapted in plants?

Answer 3

Stomata - controlled by the guard cells which allow them to open and close so water doesn’t move out by osmosis
Guard cells - when turgid, the guard cells are closed to prevent water loss (when flaccid they open)

Question 4

How are spongy mesophyll and palisade mesophyll cells adapted in plants?

Answer 4

Spongy mesophyll - cells separated by air spaces to allow efficient gas exchange
Palisade mesophyll - cells contain a high number of chloroplasts so a higher rate of photosynthesis can take place

Question 5

What is the structure of the xylem vessel?

Answer 5

Made up of hollow, dead cells strengthened with rings of lignin

The ends of the cell walls have broken down to form xylem vessels which allow a continuous column of water

There are gaps in the walls called pits which allow movement between vessels / nearby tissues

Question 6

What is the function of the xylem?

Answer 6

To transport water and dissolved mineral ions

Question 7

What does the xylem and phloem make up?

Answer 7

Vascular bundle

Question 8

What is transpiration?

Answer 8

The loss of water vapour from a plant through the stomata by diffusion

Question 9

What environmental conditions make the rate of transpiration higher?

Answer 9

Low humidity
High temperatures
High light intensity
High wind intensity

Question 9

What environmental conditions make the rate of transpiration higher?

Answer 9

Low humidity
High temperatures
High light intensity
High wind intensity

Question 10

What is the process of transpiration?

Answer 10

Water evaporates from mesophyll cells in the leaf
Water vapour diffuses out of the stomata, lowering the water potential of the leaf cells
Moving down the water potential gradient, water moves up the xylem and into the leaf cells
This creates tension on the column of water in the xylem
The water molecules are joined by hydrogen bonds, these do not break due to adhesion with the xylem walls
Moving down the water potential gradient, water moves by osmosis into the root hair cells and through the root to the xylem

Question 11

How does a potometer measure the rate of transpiration of a plant?

Answer 11

The time an air bubble in the capillary tube takes to move a certain distance is measured

Question 12

What is cohesion tension theory and what does this mean can happen?

Answer 12

Water is cohesive because of the hydrogen bonds which join molecules together. This means that in the xylem, a continuous column of water can form. During transpiration, the xylem is put under tension

Question 13

How and why does the diameter of a tree trunk change throughout the day?

Answer 13

At midday, the diameter of the trunk decreases. This is because, the light intensity and temperature is higher so the rate of transpiration is higher. Therefore, the adhesion between the water molecules and the xylem vessel walls pulls the xylem in

Question 14

What is the function of the phloem?

Answer 14

To transport dissolved substances such as sugars and amino acids up or down the plant

Question 15

What is the structure of the phloem?

Answer 15

Made up of living cells with perforated end walls which form sieve plates
Companion cells are on the side of the sieve tube elements which structurally support the phloem and provide energy for translocation

Question 16

What is translocation?

Answer 16

The transport of assimilates such as sucrose from source to sink cells with the use of ATP

Question 17

What is the process of translocation?

Answer 17

Source cells in the leaf produce sucrose and assimilates (by photosynthesis) which are actively transported into the phloem by the companion cells
This lowers the water potential in the phloem so water enters by osmosis
This produces high hydrostatic pressure, causing mass flow of water and assimilates to the sink cells
The assimilates are actively transported into the sink cells where they are used for respiration or stored as starch
The water potential gradient increases when the assimilates are removed so the water moves down the water potential gradient and moves out by osmosis

Question 18

What are the different methods for and against translocation?

Answer 18

Ringer experiments - F
Tracer experiments - F
Phloem cutting - F

Not all solutes move as the same speed as the mass flow theory would suggest - A

Question 19

What is the ringer experiment?

Answer 19

This is a type of experiment to investigate mass transport in plants
As the phloem is located towards the outside of the stem and the xylem near the centre, rings of surface tissue are removed from the outside of the stem. After being left for a period of time, the area above where the tissue was removed will swell with liquid. Non-photosynthetic cells here will continue to live while the ones below die

This proves the phloem is responsible for translocation

Question 20

What is the tracer experiment?

Answer 20

This is a type of experiment to investigate mass transport in plants
Plants are grown in conditions with radioactive isotopes e.g radioactive C02 so they are incorporated into the sugars through photosynthesis. They can then be traced moving through the plant using a radioactive tracer. Results from this is that the bulk flow of phloem sap is in one direction and occurs at the same rate

Therefore, the phloem is responsible for translocation