Topic 4 - plant cells and transport

Question 1

Which structures does a plant cell contain that an animal cell doesn’t?

Answer 1

Cell wall
Plasmodesmata
Chloroplasts
Amyloplasts
Vacuole

Question 2

Function of the chloroplasts and explanation

Answer 2

Site of photosynthesis
Have stacks of thylakoids called a grana, containing chlorophyll
These grana are connected by extensions of thylakoid membranes called lamellae
Grana are surrounded by a colourless fluid called stroma which contain the enzymes required for photosynthesis
Chloroplasts are bound by a membrane

Question 3

Function of amyloplasts

Answer 3

Produces and stores starch
Surrounded by a double membrane

Question 4

Features of vacuole

Answer 4

Contains cell sap and is surrounded by a tonoplast (single membrane). Provides the cell with strength and support

Question 5

Features of the cell wall

Answer 5

Rigid outer covering made of peptidoglycan which provides the cell with strength and support

Question 6

Features of the plasmodesmata

Answer 6

An extension of cytoplasm between the cell wall of adjacent cells involved in the transport of substances between them

Question 7

What are plasmodesmata?

Answer 7

Gaps between cells

Question 8

Describe the structures in a chloroplast that are involved in the light dependent reactions of photosynthesis (3 marks)

Answer 8

Granum provides increased SA for photosynthesis

A granum is a stack of thylakoids

Thylakoid membrane contains proteins and chlorophyll

Question 9

Explain the features of the chloroplast

Answer 9

Have a double membrane
Site of photosynthesis
Contain stacks of thylakoid membranes called grana
Grana are connected by lamella
Grana are surrounded by a colourless fluid called stroma which contains all the enzymes required for photosynthesis

Question 10

What causes plant fibres to have so much strength?

Answer 10

The arrangement of microfibrils in a mesh-like pattern

Secondary thickening which results in a thick secondary cell wall developing which often contains lignin

Question 11

What is the function and structure of the xylem vessel?

Answer 11

Vascular tissue that transports dissolved minerals and water around that plant

Structural support - lignin allows the vessel to withstand high pressure created by the moving column of water

Xylem vessels form long, hollow straw like structures that are formed by dead cells

Don’t contain any cytoplasm or organelles that could slow down the flow of water

Question 12

Describe the structure and function of a plants cell wall

Answer 12

Made of cellulose. Outer layer is called middle lamella. Holds adjacent cells together as well as providing support and protection

Question 13

Structure and function of sclerenchyma

Answer 13

Sclerenchyma fibres provide support

They consist of bundles of dead cells
They form long, hollow tubes, but they do have end walls present

Lignification of cell walls occur, but they do not have pits like xylem vessels

They have more cellulose in their walls compared to other plant cells

Question 14

Structure and function of phloem tissue

Answer 14

Transport organic compounds (assimilates), particularly sucrose, from sources (e.g. leaves) to sinks (e.g. roots).

The transport of these compounds can occur up and down the plant. This is known as translocation

No support function in a plant

Phloem is a complex tissue made up of various cell types; its bulk is made up of sieve tube elements which are the main conducting cells and companion cells

Question 15

Function of the vascular bundles in a stem

Answer 15

Vascular bundles consist of xylem vessels which are group together with phloem tissue

In a stem, xylem vessels are always located towards the middle of the stem, while the phloem is located closer towards the outside of the stem

Sclerenchyma fibres are associated with the vascular bundles and provide additional support to the stem

Question 16

Relate the structure of cellulose to its function

Answer 16

Made of long beta glucose chains which are held together by hydrogen bonds to form microfibrils. Hydrogen bonds are strong meaning cellulose is suitable for providing structural support within the cell walls

Question 17

Relate the structure of xylem and sclerenchyma fibres to their function

Answer 17

Cellulose microfibrils form an arrangement of net like structures in the cell walls of the fibres

Secondary thickening further strengthens the fibres by adding lignin

Question 18

Explain starch

Answer 18

Starch is the storage polysaccharide of plants
It is stored as granules in plastids (e.g. chloroplasts) and amyloplasts (small, membrane bound organelles containing starch granules)
Due to starch molecules being large polymers consisting of thousands of glucose monomers, starch takes longer to digest than glucose

Starch contains:

Amylose (10 - 30% of starch)
-Unbranched helix-shaped chain with 1,4 glycosidic bonds between α-glucose molecules
-The helix shape enables it to be more compact and thus it is more resistant to digestion

Amylopectin (70 - 90% of starch):
-1,4 glycosidic bonds between α-glucose molecules (as found in amylose) but also 1,6 glycosidic bonds form between glucose molecules creating a branched molecule

Question 19

Explain features/structure of cellulose

Answer 19

Cellulose is a polymer consisting of long chains of β-glucose joined together by 1,4 glycosidic bonds

Component of well walls in plants and is composed of long, unbranched chains of beta glucose which are joined by glycosidic bonds.

Microfibres formed of microfibrils are strong threads which are made up of long cellulose chains joined together by hydrogen bonds and they provide structural support in plant cells

Due to the inversion of the β-glucose molecules many hydrogen bonds form between the long chains, giving cellulose it’s great strength

Question 20

Explain the function of cellulose

Answer 20

Cellulose is the main structural component of cell walls due to its strength, which is a result of the many hydrogen bonds found between the parallel chains of microfibrils
The high tensile strength of cellulose allows it to be stretched without breaking which makes it possible for cell walls to withstand turgor pressure
The cellulose fibres and other molecules (e.g. lignin) found in the cell wall form a matrix which increases the strength of the cell walls
These strengthened cell walls provide support to plants

Question 21

What conditions do bacterial cells require for growth?

Answer 21

-Nutrients
-Sufficient supply of oxygen for bacteria which respire aerobically
-Temp and PH cant be too high or too low so that enzymes that control metabolic processes to function optimally

Question 22

Explain the relationship between the structure and functions of a granum in photosynthesis (3)

Answer 22

-Granum is formed from many layers of thylakoid membranes to increase surface area for absorbing light
-Thylakoid membranes contain chlorophyll to absorb light
-Electron carrier molecules in thylakoid membrane involved in ATP production

Question 23

Some plant cells contain the polymer starch.
Explain how the structure and properties of starch are related to its function as a storage molecule (3)

Answer 23

-Contains glucose needed for respiration/energy
-Insoluble so there is no osmotic effect
-Amylose is coiled making starch compact so more can be stored
-Amylopectin is branched/has 1-4 and 1-6 glycosidic bonds so it can be rapidly hydrolysed

Question 24

What is meant by tensile strength?

Answer 24

The total amount of force a fibre can withstand without breaking

Question 25

Compare and contrast the structure of cellulose and amylopectin (3)

Answer 25

Similarities:
-Both are polysaccharides
-Both contain 1,4 glycosidic bonds

Differences:
-Cellulose contains beta glucose whereas amylopectin contains alpha glucose
-Cellulose is not branched and doesn’t contain 1,6 glycosidic bonds

Question 26

Explain why seedlings need a supply of magnesium ions (2)

Answer 26

-Magnesium is used to make chlorophyll
-Chlorophyll is required for photosynthesis

Question 27

Function of magnesium ions in plants

Answer 27

Involved in chlorophyll production

Question 28

Functions nitrogen ions in plants

Answer 28

Making DNA,RNA, proteins and chlorophyll

Question 29

Function of calcium ions in plants

Answer 29

Component of the plants cell wall - they form calcium pectate and are also essential for plant growth

Question 30

Uses of plant fibres

Answer 30

Sustainable and renewable resource
Very strong so can be used to make fabrics and ropes

Question 31

Describe how the tensile strength of plant fibres can be measured (3)

Answer 31

-Add weight to a fibre
-Measure the weight that is require to break the fibre
-Calculate cross sectional area

Question 32

Explain the effects of a shortage of magnesium ions on a plant (3)

Answer 32

-Magnesium shortage limits the production of chlorophyll
-Lack of glucose produced due to less photosynthesis
-Therefore plant leaves may turn yellow and the plant may be small

Question 33

Compare the structure of a cellulose molecule with the structure of starch.

Answer 33

-Both have 1-4 glycosidic bonds
-Starch is alpha glucose, cellulose is beta glucose
-Both made of glucose
-Starch is composed of more than one type of molecule (amylose and amylopectin)