Topic 9 Plants Unit

Question 1

Describe xylem’s structure and how it allows water transport. [2 marks]

Answer 1

1. Dead, hollow cells stacked ends to ends allows water movement.
2. Lignin-impregnated walls allows it to withstand low pressure for water transport.

Question 2

Describe how water’s properties relates to its transport in xylem. [ 2 marks]

Answer 2

1. Its adhesion to the mesophyl cell walls, allows tension force to exert on the water column in the xylem when water evaporates.
2. Its cohesion allows the tension force to be transmitted from shoot to root without caviation.

Question 3

Describe water’s movement in leaves during gas exchange. [2 marks]

Answer 3

1. Water evaporates when stomata opens for gas exchanges, causing transpiration.
2. New water molecules replaced the evaporated one from the xylem water column due to water adhesion to mesophyl cell wall.

Question 4

Describe the process whereby water enter the roots and xylem. [4 marks]

Answer 4

1. Active transport of ions into root cells causes water to enter the roots via osmosis.
2. Water might reach the Caspian strip through plasmodaeta symplastically or between cell walls apoplastically.
3. All pathways of water is absorbed into the Caspian strip before being moved into the xylem.
4. This is called mass flow.

Question 5

Define halophytes and state how they conserves water. [3 marks]

Answer 5

1. Halophytes are plants living in saline conditions.
2. They have specialized tissues to remove salt.
3. They uses stems to photosynthesize.

Question 6

Define xerophytes and describe how they converved water. [5 marks]

Answer 6

1. Xerophytes are plants living in dry habitats.
2. Ephemeral ones conserves water by being active only in rainy seasons.
3. Perrenials ones hoards water in specialized tissues.
4. Some other plants restrict transpiration by shielding stomata with needled-sized or closed, sunken leaves.
5. Some plants transform carbon dioxide into malic acid at night to limits gas exchange during the day. This is called the Crusselean acid metobolism, and occurs in C4 physiology.

Question 7

What effect does increased soil salinity have on water transport in the plant roots?

A. Decreases movement of water from soil into the root
B. Absorption of water with a higher solute concentration
C. Increases movement of water from soil into the root
D. Absorption of water with a lower solute concentration

Answer 7

A

Question 8

Which process and cause are responsible for water uptake by the roots?

A. Simple Diffusion
B. Osmosis since [roots solute] is greater than [soil]
C. Osmosis since [roots solute] is less than [soil]
D. Cohesion

Answer 8

B

Question 9

Outline active transport in phloem tissue. [2 marks]

Answer 9

1. Proteins pumps employs ATP to move protons out. When the protons diffuse back in through protons channels, sucrose is co-transport into the companion cell from apoplastic pathway.
2. Proteins pumps then moved the sucrose into the sieve tube cell actively.
3. Loading and unloading at sources and sinks.

Question 10

Explain how a plant replaces the water it loses in transpiration. [3 marks]

Answer 10

[Any 3 of 5]
1. Water evaporating due to transpiration causes another one to take its place from the xylem.
2. Its adhesion property causing tension the xylem water column causing water to be drawn out.
3. The tension is transmitted down to the roots with water’s cohesion.
4. To avoid caviation root pressure causes water to enter the cell.
5. These waters entered the roots via osmosis when ions are actively transport into the roots.

Question 11

Explain gas exchange in plants and its contribution to repsiration. [2 marks]

Answer 11

1. Gas exchange is neccesary to supply photosyntheis with CO2 and replace O2.
2. It also allows substance to exit the leaves through stomata.

Question 12

Outline roots absorption of water. [3 marks]

Answer 12

1. A 100x higher solute concentration is established in roots by protein pumps.
2. Water osmosis into the cells, either apoplastically or symblasticly through the plasmodeta.
3. Water is absorbed by the Caspian strip then moved to the xylem.

Question 13

Outline how plants absorbed ions attached to soil’s surface using fungi. [2 marks]

Answer 13

[Any 2 out of 3]
1. Some plants allows fungi to grow over or into the roots cells.
2. The fungi collects ions like phosphate, in exchange for sugars and nurtrients.
3. Plants are able to grow in minerally deficit soils.

Question 14

Which plants store water in specialized tissues to conserve water in dry climates?

Answer 14

Perrenial Xerophytes

Question 15

Which plants only become active in short rainy seasons to conserve water in dry habitats?

Answer 15

Ephemeral Xerophytes

Question 16

Which plants process allows plants to conserve water by being active at night to limit respiration during the day? [2 marks]
What substance is involved? [1 mark]

Answer 16

1. Crusselean Acid Metabolism
2. C4 physiology
3. Malic Acid

Question 17

States all adaptions that conserve waters employed by xerophytes. [4 marks]

Answer 17

1. Being active only during rainy seasons.
2. Store water only in specialised tissues.
3. Convert CO2 into malic acid at night so that no respiration and thus transpiration occured during the day.
4. Curled up leaves with stomata at the curl bottom reduce opening OR hair around stomata stop air movement and prevent respiration.

Question 18

States halophytic adaptions to conserve water in salty conditions. [4 marks]

Answer 18

1. Scaly leaves and stem
2. Internal water storage
3. Thickened cuticles & epidermis
4. Salt removing structure.

Question 19

Draw a xylem structure.

Answer 19

Check textbook.

Question 20

States components of a phloem sieve tubes cells. [3 marks]

Answer 20

1. Sieve tube
2. Peforated sieve tube plates between each sieve tubes.
3. Companion Cell

Question 21

State functions of phloem. [2 marks]

What it transports, and from where to where?

Answer 21

1. Phloem transport sugars and amino acids, called translocation.
2. Phloem transport them from source to sink.

Question 22

Differientiate source and sink. [2 marks]

Answer 22

1. Sources is where there is a suplus of amino acids and sugars. Sink is where there is a deficite.
2. Souces is where substance is loaded, sink is where it is unloaded.

Question 23

Explain how phloem maintain flow in any direction. [1 marks]

Answer 23

1. Phloem actively expend energy to maintain a pressure gradient that allows translocation to occured.

Question 24

Define translocation. [1 marks]

Answer 24

1. It is the transport of organic solutes from sources to sink.

Question 25

Explain why sucrose is employed for phloem loading. [2 marks]

Answer 25

1. It is most prevelant in sap, up to 30%.
2. It doesn’t metabolized during transport.

Question 26

Outline how apoplast sucrose is loaded during phloem loading. [3 marks]

Answer 26

1. H+ is actively pumped out with ATP, creating a concentration gradient.
2. H+ diffusing back in operates a sucrose channel that allows sucrose to enter the cell.
3. The sucrose is passed onto the sieve tube cells.

Question 27

Outline how symplast sucrose is loaded during phloem loading. [3 marks]

Answer 27

1. Sucrose travel in the plasmodesmata reached the companion cell.
2. Sucrose is converted into oligosaccharides before passing onto the sieve tube.
3. The low [sucrose] in the companion cell allows more to diffuse in.

Question 28

Outline how sucrose and water is unloaded at sink. [2 marks]

Answer 28

1. Sugar diffuse from the sieve tube into the companion cell, due to low [sucrose] in the cell.
2. Water follows via osmosis.

Question 29

State the two properties that allows translocation to occured in the phloem. [2 marks]

Answer 29

1. Water’s incompressibility
2. Cell walls’ rigidity

Question 30

Outline water’s movement and contributions to translocation in phloem. [3 marks]

In terms of hydrostatic pressure.

Answer 30

1. High [sucrose] in source companion cell causes water to osmosis in, creating high hydrostatic pressure.
2. Sucrose consumption at sink, means water osmosis out and into the xylem, creating high hydrostatic pressure.
3. Water flows from high to low pressure, and tus from sources to sink.

Question 31

Describe the phloem sieve tubes cells’ structure and function. [4 marks]

Answer 31

1. Sieve tubes cells are separated by perforated sieve plates.
2. Sieve tubes cell have no nucleus and much less cytoplasm.
3. This lessened the resistance to the flow of phloem sap.
4. Rigid cell wall to maintain hydrostatic pressure.

Question 32

Describe the phloem companion cells’ structure and functions. [3 marks]

Answer 32

1. High number of mitochondria for active sucrose transport and its conversion to oligosaccharides.
2. Plenty of membrane folding to increase phloem loading capacities.
3. Nucleus to perform the genetic and metabollic function for itself and the sieve tube cell.

Question 33

Draw a half-view diagram of a flower.[5 marks]

Answer 33

Look at the mark scheme.

Question 34

Explain the process of flowering control in short-day plants. [5 marks]

and in lond-day plants [2 marks]

Answer 34

1. Phytochrome P_FR are formed from P_R in the presence of far-red light during the day.
2. At night or under red light, P_FR diminished into P_R due to the latter’s stability.
3. In short-day plants, P_FR acts as a flowering inhibitors.
4. After long nights, all P_FR is diminished and dissapeared, and as such flowering occured.

1. In long-day plants, P_FR acts as a flowering inhibitors.

Question 35

State the period where flowers are developed in plants. [1 marks]

Answer 35

Reproductive phase

Question 36

State the precursor to flower and the conditions that causes it to flower. [2 marks]

Answer 36

1. Shoot apical meristem
2. Duration of darkness

Question 37

Explain the change in gene expressions done by phytochrome P_FR [3 marks]

Answer 37

1. P_FR causes transcription of Ft (flowering time) gene.
2. Ft mRNA is transported into the shoot apical meristem.
3. Ft mRNA is made into Ft protein, which togther with transcription factors causes the meristems to developed into the shoot.

Unsure whether Ft protein is the transcription factor or act in tandem w

Question 38

Define pollination. [1 marks]

Answer 38

Pollination is the transfer of pollen between flowers during sexual reproduction.

Question 39

Explain the purpose behind dormancy before germination. [1 marks]

Answer 39

Dormancy inhibits seed growth in presence of sufficient nuritients to allows seeds to be dispersed.

Question 40

State and explain the things needed for seed to germinate.

Answer 40

1. Water is needed to wash away growth inhibitors, rehydrate the seed and fuel its growth.
2. Oxygen is needed to restart the halted metabollic processes.
3. Warmth is needed for enzymes to catalyze effectively.
4. Gibberellin is needed to start cell division and mitosis, synthesisation of amylase to convert starch until usable glucose and saccacharides.

Question 41

Explain how plants elongates using acid growth hypothesis. [5 marks]

Answer 41

1. Auxin causes the plasma proteins to pump H⁺ out.
2. This causes the voltage acorss the membrane to increase while the pH decreases.
3. The lowered pH disrupt the H-bonds between cellulose microfibrils, allowing them to slide past each other.
4. The increased membrane potential allows more water to be uptake and water osmosis in.
5. The more flexible cell wall, and water-filled cell allows the cell to elongates.