UNIT 8 Transport in Plants + EXAM QUES

Question 1

Functions of xylem

Answer 1

transport of water and mineral ions [taken up from the soil by the roots to the stem and leaves]

& support

Question 2

Functions of phloem

Answer 2

transport of sucrose and amino
acids in plants AWAY from leaf to the rest of the plant

Question 3

Identify in diagrams and images the position of
xylem and phloem as seen in sections of roots,
stems and leaves of non-woody dicotyledonous
plants

Answer 3

Xylem - when looking like pills, lower part is xylem

Larger, towards centre, at the top otherwise = xylem

Question 4

Relate structure of xylem vessels to their function

a) walls

b) contents

c) tube

Describe how the structure of this water-conducting tissue is adapted to its function.

Answer 4

a) thick walls with lignin

(b) no cell contents

(c) cells joined end to end with no cross walls to form a long continuous tube

// exam mark scheme:

thick /lignified, cell walls;
for support;

lignin;
cell walls are waterproof/no water leaks out;

long/hollow/no cytoplasm/no organelles/no end walls;
water passes through easily/low resistance (to flow);

pits;
for lateral movement;

Question 5

Identify in diagrams and images root hair cells

STATE root hair cells functions

Answer 5

The rectangle with the tube protruding from the right side.

Functions:

⭐ single-celled extensions of EPIDERMIS cells in the root

⭐️ absorb water and minerals from the soil

⭐️ water enters the root hair cells by osmosis

⭐️ happens because soil water has a higher water potential than the cytoplasm of the root hair cell

Question 6

What does large surface of root hairs do? Another adaptation?

Answer 6

large surface area of root hairs

increases the uptake of water and mineral ions

/ increases the rate of the absorption of water by osmosis and mineral ions by active transport

⭐️ Mitochondria release energy for active transport

Question 7

Pathway taken by water through root, stem & leaf?

Answer 7

pathway taken by water through the root, stem and leaf as:

soil
root hair cells,
root cortex cells,
xylem,
mesophyll cells / layer
air pockets
stomata
atmosphere

Question 8

Investigate, using a suitable stain, the pathway of
water through the above-ground parts of a plant

Question 9

What is transpiration?

Answer 9

the loss of water vapour
from leaves

Question 10

Water evaporates from…

Answer 10

water evaporates from the surfaces of the mesophyll cells

into the air spaces

and then diffuses out of the leaves through the stomata as
water vapour

Question 11

Rhabdostyla is a single-celled organism that has no cell wall and no chlorophyll.
Gases are exchanged across the cell membrane of Rhabdostyla.

The gas produced by Rhabdostyla

Answer 11

carbon dioxide

Question 12

the process that produces the gas

Answer 12

(aerobic) respiration

Question 13

the method of removal of the gas

Answer 13

(simple) diffusion

Question 14

Rhabdostyla lives in freshwater habitats, such as ponds, lakes and rivers.
Freshwater has a very low concentration of solutes.
Rhabdostyla has a contractile vacuole that fills with water and empties at intervals as shown in
Fig. 4.1. The contractile vacuole removes excess water

(b) Explain, using the term water potential, why Rhabdostyla needs to remove excess water.

Answer 14

Water enters by osmosis

Down a water potential gradient (high to low water potential)

through partially permeable membrane ;

needs to remove water to prevent bursting

Question 15

In an investigation, individual Rhabdostyla were placed into different concentrations of sea water.
The rate of water excreted by the contractile vacuole of each organism was determined. The results
are shown in Fig. 4.2.

(c) Explain the results shown in Fig. 4.2.

Answer 15

as concentration of sea water increases the removal of water decreases ;

as concentration of sea water increases the water potential gradient decreases ;

therefore less water enters at higher concentrations of sea water ;

less excess water ;

Question 16

(d) Single-celled organisms with cell walls do not have contractile vacuoles.

Suggest why. [3]

Answer 16

cell walls inelastic/keep shape of cell ;

cells are turgid/ have high turgor pressure ;

the cells will not burst ;

Question 17

Explain how the root hair cell carries out its function [3]

Answer 17

Mineral ions are taken up by active transport

This water potential inside the root hair cell decreases

Water then enters the root hair cell by osmosis

Question 18

Function of STOMATA [2]

Answer 18

movement of gas / oxygen/ carbon dioxide, into and out of leaf ;

for, photosynthesis /respiration ;

allows transpiration ;

Question 19

Under identical environmental conditions the rate of water uptake in plant A is higher
than plant B.

Explain why. [3]

Answer 19

more stomata in variety A ;

more transpiration in variety A ;

greater opportunity for loss of water vapour through stomata in variety A ;

by evaporation, from surfaces of (mesophyll) cells / into air spaces
(in leaf) ;

loss of water from leaf (cells) lowers water potential ;

Question 20

The density of stomata is an example of a leaf adaptation to the environmental conditions.

State two other adaptations of leaves for survival in a dry environment. [2]

Answer 20

hairs ;

thick cuticle ;

small surface area ;

Question 21

Water lost from the leaves enters the atmosphere.

Describe how water is recycled from the atmosphere back to the roots. [2]

Answer 21

water vapour condenses to form clouds

precipitation ;

rainwater drains into rivers ;

seeps into soil ;

Question 22

water-conducting tissue

Answer 22

xylem

Question 23

Describe how the structure of this water-conducting tissue is adapted to its function [2]

Answer 23

thick /lignified, cell walls;

for support;

long/hollow, no end walls;

water passes through easily/low resistance (to flow);

Question 24

Explain the mechanism of water movement from the roots up the tree to the leaves.

[4]

Answer 24

1 transpiration;

2 creates a, tension/negative pressure;

3 water potential gradient;

4 osmosis into leaf cells;

8 water evaporates, into airspaces (in mesophyll);

9 water (vapour), diffuses/passes, out through stomata;

Question 25

Fig. 4.2 shows the rate of water conduction up three different trees in a forest over 24 hours.

(i) Describe the rate of water conduction in tree A, during this 24 hour period.
You will gain credit for using the data in Fig. 4.2 to support your answer [3]

Answer 25

two peaks;

at 10h, and 14/15h;

no water conduction before 4h;

slow/gradual, increase from 4h to 6h/7h;

Question 26

Suggest how the ecologists used the data in Fig. 4.2 to calculate the total volume of
water used by a tree in 24 hours

Answer 26

calculate area under curve

Question 27

(iii) In Fig. 4.2, tree A is a tall tree, tree B is a medium-height tree and tree C is a short tree.
Suggest reasons for the different rates of water conduction in the three trees.

Answer 27

different rates of transpiration;

factors affecting transpiration:
(sun)light/shade;
temperature/heat;

different species;
different diameters of xylem

Question 28

(d) Loggers often cut down the tall trees in a forest.
Describe the effects on the forest ecosystem of cutting down trees. [4]

Answer 28

increase in carbon dioxide, concentration;

habitat/ecosystem, loss;

disruption to food webs;

less biodiversity;

Question 29

Stomata allow the movement of gases into and out of the leaf. During the daytime oxygen
passes out and carbon dioxide passes in.

(i) Explain why oxygen passes out of the leaf during the daytime.

Answer 29

oxygen is a (waste/ by) product of photosynthesis ;

concentration inside the leaf is greater than outside ;

oxygen moves down its concentration gradient ;

by diffusion ;

idea that the rate of photosynthesis is greater than the rate of respiration ;

Question 30

Describe the path taken by a carbon dioxide molecule after it has passed through the
stomata during the daytime until it becomes part of a glucose molecule. [3]

Answer 30

passes through air spaces ;

carbon dioxide dissolves in water (in cell wall) ;

diffuses, through, cell membrane ;

diffuses, through, cytoplasm ;

enters chloroplast/ used in chloroplast ;

reacts with water (to form glucose) ;