Chapter 9 - Plants

Question 1

Why do plants require specialised transport tissue?

Answer 1

To overcome the limitations of diffusion over large distances

Question 2

A group of students wants to observe the position of xylem vessels in the leaf stalks of celery.
Describe a procedure they could use to do this.

Answer 2

Cut a thin cross section of the plant
Add a stain - toluidine blue
Observe with a microscope under a low power

Question 3

State one similarity between the structure of xylem and phloem

Answer 3

Both are made up of cells joined end to end

Question 4

State two differences between the structure of xylem and phloem

Answer 4

D1. Phloem has companion cells whereas Xylem do not

D2. Phloem tubes have cellulose cell walls, Xylem vessels have lignified cell wall

Question 5

A student designed an investigation into the rate of transpiration in plants.
They use 8 leaves of the same size, age and species.
Why did the student take readings from 8 different leaves?

Answer 5

To assess the repeatability of their data

Question 6

Water Starwort is a hydrophyte. It is an aquatic plant which has its stems fully submerged in water.
Cholla is a cactus. Growing over 4 metres tall.
Give one way in which you would expect the walls of the xylem vessels

Answer 6

Water Starwort - walls of the xylem vessels to be quite thin compared to deciduous plant; less lignin

Cholla - walls of the xylem vessels would be quite thick to preserve water; more lignified.

Question 7

How do hydrogen ions move out of companion cell

Answer 7

active transport

Question 8

How do sucrose move into companion cells

Answer 8

Facilitated diffusion

Question 9

How do sucrose move out of companion cell

Answer 9

Diffusion

Question 10

The use of cyanide prevents the change in pH occuring. What conclusion can be made

Answer 10

Cyanide prevents active transport as ATP cannot be produced

Question 11

A scientist used an electron microscope to look for evidence in loading sucrose.
What evidence might the scientists see

Answer 11

It has a large mitochondria to proudce ATP.

Plasmodesmata between companion cell and sieve tube element

Question 12

What is the pathway water is transported along the cells walls and between cells in plants

Answer 12

Apoplast pathway

Question 13

What is the function of the pits in xylem tissue

Answer 13

Lateral movement of water

Question 14

Xylem forms part of a plant’s transport system.

Explain why large multicellular plants need a transport system.

Answer 14

Small surface area to volume ratio
Long distance from external surface to cells
Simple diffusion is not enough to meet the demands

Question 15

Suggest and explain 2 likely adaptations of the leaves of the plant with lots of air spacs

Answer 15

Large Surface area to maximise photosynthesis

Many stomata to increase gas exchange

Question 16

What is the most common pathway of water

Answer 16

Apoplast

Question 17

What is meant by the term resolution of a microscope

Answer 17

Resolution is the ability to differentiate between two things

Question 18

Phloem sap mainly consists of carbohydrate in the form of sucrose
Suggest why it is beneficial to the plant for the carbohydrate to be transferred throughout the plant in the form of sucrose rather than an alternative carbohydrate

Answer 18

Sucrose is soluble so can be transported in sap.

It is metabolically inactive

Question 19

How is the transport in the phloem similar to the transport in the xylem.

Answer 19

Both use mass flow generated by hydrostatic pressure

Question 20

Explain with a suitable example how some parts of the plant can act as both a source and a sink

Answer 20

Certain parts can store and then release carbohydrates when needed.
Leaf can act as a sink or source at different times of year.

Question 21

Explain the process of loading of sucrose into the phloem and its movement in the phloem

Answer 21

Sucrose is pumped from companion cell into phloem tube by active transport.
H+ is a co transporter for sucrose.
This reduce water potential in sieve tube

Water also enters from the companion cell to the sieve tube

Water also enters from the xylem this increases pressure so sap flows down the phloem and goes through the pores

Question 22

How are meristems producing new plant tissues?

Answer 22

Meristems can generate new plant tissues.
Xylem tissue is formed, lignin impregnates the cell walls making them impermeable to water. Cytoplasm is lost.
Phloem tube is formed by the sieve tube elements becoming elongated and lost most of their cytoplasm

Question 23

which macromolecule does a plant need both nitrogen and phosphorus.

Answer 23

DNA

Question 24

How would flooding from sea water affect soil water potential?

Answer 24

It makes it more negative

Question 25

How does casparian strip prevent ions such as Na+ and CL- from reaching the xylem of the plant by the apoplast pathway.

Answer 25

The phospholipid bilayer in the strip repels charged particles
It forces water to pass through plasma membrane

Question 26

halophytes are plants that have the ability to live in soils with a very low water potential .
Suggest and explain how the root hairs of halophytes are able to absorb water by osmosis from the soil of the salt marsh

Answer 26

there is a lower water potential inside root hair cells

actively transport ions into root hairs

Question 27

Explain how mass flow of the phloem sap occurs in plants with a vascular system.

Answer 27

sucrose enters the sieve tube which lowers the water potential
water enters by osmosis from xylem and the companion cell , this increases hydrostatic pressure.
Assimilates move from high to low down the pressure gradient .

Question 28

Cells in the phloem are specialised so that translocation can occur.
What is meant by translocation?

Answer 28

The movement of assimilates from source to sink

Question 29

State one adaptation that leaves might have to conserve water

Answer 29

Thick waxy cuticle to prevent water loss

Fewer Stomata

Question 30

One environmental factor that affects the loss of water vapour from the leaves is air movement.
Explain how increased air movement increases the loss of water vapour from the leaves.

Answer 30

Water vapour around the stomata is blown away so a steeper water potential gradient

Question 31

The leaves of moss plants are usually one cell thick and are attached to a thin stem. Neither the leaves nor the stem contain vascular tissue.
Suggest and explain how the absence of vascular tissue might affect the size to which moss plants can grow.

Answer 31

The plant will remain small as there is no support from vascular tissue.
The only transport is diffusion . Therefore for large plants diffusion would be too slow so the plant will remain small

Question 32

Describe how the guard cells surrounding the leaf pores are adapted to their role.

Answer 32

They have an unevenly thickened cell wall. (Thick inner and thin outer walls).
This means they can change shape - bend when turgid.
Also contains chloroplasts to provide ATP

Question 33

Name one other part of the leaf from which water may be lost.

Answer 33

Stomata

Cuticle

Question 34

Why does a plant wilt

Answer 34

if there is a lot of water lost from the leaf cell, then turgidity is lost and the plant wilts.

Question 35

The cohesion tension theory is often used to explain the mechanism by which water moves up the xylem from the roots to the leaves.
Use this theory to explain how water moves from the roots to the leaves.

Answer 35

Evaporation from the top of the plant causes tension in xylem.
Water molecules are cohesive and when pulled up the column by tension, the water molecules stick and followup the column to the leaves.

Question 36

Name 2 types of cell that can be found in phloem tissue

Answer 36

Parenchyma
Sieve tube element
Companion cell

Question 37

Multicellular organisms such as plants have evolved internal transport systems.
Explain the benefit to plants of internal transport systems.

Answer 37

Surface area to volume ratio is too small so diffusion is not fast enough therefore transport systems ensure molecules reach all tissues at a high metabolic rate.

Question 38

Give an example of what substance root hair cells transport

Answer 38

Nitrate ions

Question 39

Mosses are small plants with no true roots. Each plant is anchored by simple root-like structures which do not contain vascular tissue.

Although a moss plant has no vascular tissue, water still moves through the plant from the root-like structures to the leaves.

Use your knowledge of the mechanisms of water transport to explain the movement of water through the moss plant.

Answer 39

Water is lost by evaporation. It is transported by symplast and apoplast pathways.
Apoplast pathway is along cell walls.
Symplast partway, water is transported by osmosis from a high concentration to a low concentration

Question 40

Leaves of dicotyledonous plants contain types of cells that are not found in the leaves of mosses

Other than the cells found in vascular tissues, name two types of cell found in the leaves of dicotyledonous plants that are not found in the leaves of mosses

Answer 40

Palisade cells

Spongy Mesophyll

Question 41

How is transport in the phloem similar to and different from transport in the xylem?

Answer 41

Similar - Both use mass flow

Different -
transport in phloem can take place in different directions and transport in xylem only takes p

Question 42

Explain the benefit to plants of internal transport systems.

Answer 42

ensures molecules / nutrients / sugars / water, reach all tissues at a high metabolic rate

Question 43

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

Answer 43

potometer airtight / watertight
 dry leaves 
cut shoot under water
 measure distance air bubble travels per  time interval
calculate volume of water uptake 

maintain constant conditions - wind, temp, sunlight

Question 44

Suggest why it might be considered better to use a capillary tube rather than a calibrated pipette to measure water uptake

Answer 44

capillary tube:

measures smaller volumes

Question 45

Besides safety precautions, explain one practical precautions that should be taken when using a potometer

Answer 45

Keep abiotic factor (temp) constant as it affects rate of transpiration

Question 46

They placed the leaves on graph paper and then counted squares to obtain an estimate of leaf area.
State two things the student would have to do to ensure that the estimate of leaf area was accurate

Answer 46

Flatten leaf on graph paper

Only count squares more than 50% covered

Question 47

Neonicotinoid insecticide molecules are absorbed by the roots and leaves of maize plants.
Describe how once these molecules have been absorbed they may be transported to the fruits of the maize plant

Answer 47

in xylem (by),cohesion-tension / transpiration (stream);
in phloem (by), translocation / mass flow;