9. Plant Sciences

Question 1

Draw & Label showing distribution of tissues in stem and leaf of dicotyledous plant.

Answer 1

Question 2

What are the differences in structure of monotyledons and dicotuyledons?

(at least 3)

Answer 2

1. Number of cotyledon: 1 vs.2
2. Leaf veins: Parallel venation vs. Reticulateral ventaion
3. Roots: Fibrous adventitious vs. Tap roots w/ lateral branches
4. Floral organs: x3 vs. x4/x5
5. Stem vascular arrangement: Scattered vs. In a ring
6. Pollen: Single furrow/pore(monosulcate) vs. 3 furrows (trisulcate)

Question 3

Explain the relatioship between tissue distribution and structure in leaf.

Answer 3

**1. Upper epidermis **

F: Water conservation (Secrete cuticle => Waxy outer boundary)

D: Top of laeves where light I + heat highest (Transperant)

**2. Palisade Mesophyll **

F: Photosynthetic tissue; absorption of light - cell contains chloroplast

D: Upper half of leaf; light I greatest

**3. Spongy mesophyll **

F: Gas exchange

D: Loosely packed cells with spaces, lower half, near stomatal pores (where gases and water exchanged w/ atmosphere)

4. Vascular Tissue

F: Transport water(xylem) + products of photosynthesius (phloem)

D: Middle of leaf => All cells optimal access

Question 4

Identify modification of roots + stems = leaves for dfferent function.

Answer 4

1. Storage roots: Modified roots -> Store H2O/food
   e. g. carrots
2. Stem Tubers: Horizontal underground stems that store carbohydrates
   e. g. potato
3. Bulbs: Modified leaf bases (ex.underground vertical shoots) that contains layers called scales
   e. g. onion
4. Tendrils: Modified leaf/stem for climbing support attachement
   e. g. Vines

Question 5

What are meristems?

What are the two types of meristems in dicotyledonous plants?

Answer 5

Meristem = Tissue(plant) w/ undofferentiated cells, found in zones where growth take place

The two types of meristems are apical and lateral.

Question 6

Compare growth due to apical vs. lateral meristems in dicotyledonous plants

Answer 6

Similarity

1. Composed of totipotent cells
2. Found in dicotyledounous plant

**Differences **

1. Occue @ Tip of root + shoot vs. Cambum
2. Vertical growth (root/shoot) vs. Lateral (stem)
3. Primary growth vs. Secondary
4. Primary xylem/phloem vs. Secondary
5. Produce leaves + flowers vs. Bark

Question 7

Explain the role of auxin in phototroposim.

Answer 7

1. Phototropism = growing/turning (organism) response unilateral light
2. Auxin (IAA) = plant hormone produced by tup of shoot and control 1). Destory by light
3. Auxin => Cell enlarge/grow
4. Accumulation(IAA) -> Shaded area cause shaded side legnthen, => shoot bend towards ligth
5. Auxin => cell elongation by activating proton pumps => expel H+ ions from cytoplasm -> Cell wall
6. Decrease pH (Cell wall) => cellulose fibre lossen (break bonds)
7. Cell wall ^flexible + capable(stretching). H2O influx promote cell turgor.
8. Auzin also alter gene expression => Cell growth (upregulation of expansins)

Question 8

Explain how root systems provides larger SA for mineral ion + H2O uptake.

Answer 8

1. Function of root = Absorb H20, minerals, support
2. Monotyledon: Root = fibrous, highly branched structure ^SA
3. Dicotyledon: Main top root (deep penetration) soil access deep reseviour.

Lateral branches max. SA

4. Root epidermis extension = root hairs
5. Root hair: Carreier protein + ion pumps in plasmomembrane + mitochondria in cytoplasm => Aid active transport
6. Cortex cell wall permeable <=> osmosis
7. 6) absorb by capillary action
8. Mineral / H2O transport other parts <=> xylem

Question 9

List 3 ways which mineral ion in soil move to the root

Answer 9

1. Diffusion: [gradient]
2. Mass flow: hydrostatic pressure gradient
   a) Water -> Root via osmosis => -ve hyrostatic pa. in soil
   b) mineral H Bond w/ H2O & dragged to root, []ing for absorbtion
3. Fungal Hyphae: Mutualism - Exchange w/ sugar

Question 10

Explain process of mineral ion absorption from soil into roots by active transport.

Answer 10

• Minerals = K+, Na+, Ca2+, NH4+, PO₄^3-, NO3-
• Fertile soil = -ve clay particle + +ve minerals
  1. Root cell proton pump H+ -> Soil

Cation: Ion exchange: Displace the mineral => Absorbtion

Anion: Symport: -ve mineral bind H+ => Reabsorb w/ proton

2. 1) = Indirect active tranport: energy ( + proton pump) => electrochemical gradient by which mineral ion absorbed via diffusion
3. Direct active transport: Proton pump translocate ion against [gradient]

Question 11

How do terrestrial plants support themselves?

Answer 11

1) Thickened cellulose: Cell wall = structural support
2) Cell turgor: ^hydrostatic pa. w/in cell exert pa. -> cell wall => Cells turgid
3) Lignified xylem: Stem to Branch = extra support

Question 12

Define transpiration

Answer 12

Transpiration is the loss of water vapour from the leaves and stems of plants

Question 13

Explain how H2O is carried by transpiration stream.

Answer 13

1. Light => Leaf => Heat

H2O(spongy mesophyll) -> Vapour

2. Vapour =>(diffusion, stomata) evaporate => -ve pa. gradient in leaf
3. New H2O drawn from xylem (mass flow), replaced by H2O from roots (from soil via. osmosis)
4. Roots —–H2O—-(Xylem)—> Leaf = Transpiration Stream
5. H2O Rise becasue of
   a) Cohesion: Weakly attract ea. other via. H-Bond
   b) Adhesion H2O form H-bond w/ xylem cell wall
6. a)+b) = sunction effect / Transpiration pull in xylem
   7) Xylem specialised structure:
   a) Inner lining = dead cells fused => Continuous tube
   b) a) lack cell membrane, H2O enter xylem freely
   c) Perforated (contain pores) outer later, allow H2O move out -> leafs
   d) Outer cell wall : Annular lignin rings

=> Strengthen xylem against tension

from transpiration stream

Question 14

Guard cells. Why are they?

Answer 14

Guard cells can regulate transpiration by opening/closing stomata:

1. Transpiration pull by -ve hydrostatic pa.

by evaporation (water vapour) from leaf

2. Guard cell lines stomata, regulate transpiration by control n(water vapour) exit leaf
3. Stomata open => ^ r.o. transpiration

close => Decrease r.o.t.

Question 15

Abscisic acid. Why are they?

Answer 15

1. Plant wilt from H2O stress, dehydrated mesophyll cells release plant hormone abscisic acid (ABA)
2. Abscisic acid trigger efflux of potassium from guard cell, decrease H2O pa. w/in cells -> Flaccid
3. Stomotal pane closes

Question 16

Explain how abiotic factor - light, temp, wind, humudity affect r.o.transpiration in typical terestrial plant.

Answer 16

**1. Light **

a) ^lux ^r.o.t.
b) Light => stimulate stomata open

(gas exchange for photosynthesis)

c) Light => Heat ^r.o.evaporation

**2. Temperature **

a) ^C ^ r.o.t.
b) ^Temp => ^ H2O vaporisation in spongy mesophyll

^ evaporation from surface of leaf

c) ^ Diffusion H2O vapour out of laef (via stomata)

^ r.o.t.

**3. Wind **

a) ^ Air flow ^ r.o.t.
b) Wind removes H2O vapour ( decrease [vapour] ) on leaf surface

^ rate of diffusion from w/in spongy mesophyll

4. Humidity

a) ^ Humidity, decrease r.o.t.
b) Humidity = H2O vapour in air

^ Humidity = ^ [H2O Vapour] in air

c) Decrease r.o.diffusion(H2O Vapour) from inside leaf smaller [gradient] => decrease net flow

Question 17

Outline 4 adaptions of xerophytes that help decrease transpiration

Answer 17

• Xerophytes tolerate dry conditions (desert/high attitude):

1. Reduced leaves

Decrease SA, Decrease H2O loss,

Decrease Transpiration

**2. Rolled levaes **

Lower epidermis inside, decrease exposore (stomata) to air (decrease transpiration)

3. Thick waxy cutcile

Prevent H2O loss from surface of leaf

**4. Stomata in pits **

Surrounded by hairs, concentrate H2O vapour near stomata

5. Low growth

Decrease exposure to wind + shaded

**6. C4/CAM physiology **

Requires less CO2, stomata stay closed longer

Question 18

Outline role of phloem in active translocation of sugars + amino acid from source to sink

Answer 18

1. Organic molecule(sugar,amino acid) : source(photosynthetic tissue/storage organ) -> tube system = phloem
2. Sugar transport as sucrose (soluble + metabolically inert) in fluid of phloem (sap)
3. Actively loaded by companion cells => [High] draw H2O from xylem via osmosis
4. Sap (Vol. + pa) increase => mass flow

=> drive sap along phloem

5. Actively unloaded by companion cells

=> store in sink (fruit, seed, root)

6. Sucrose stored as starch (insoluble), H2O in phloem released and return to xylem.

Question 19

Draw and label structure of dicotyledonous animal-pollinated flower structure.

Answer 19

Question 20

Define

1. Pollination
2. Fertilisation
3. Seed dispersal

Answer 20

Pollination : Transfer (pollen grain: anther -> sigma(usually other plant) )

facilated by animal/wind/H2O movement/

Fertilisation: Fusion(male gamete nuclei(in pollen grain) w/female gamate(in ovule) to form zygote

Seed dispersal: Fertilised ovules form seded, move away from parental plant before germination. (Fruit, wind, water, animals)

Decrease competition for resources.

Question 21

Draw & Label external + internal structure of named dicotyledonous seed.

Answer 21

Question 22

Explain the conditions for germination

Answer 22

Germination: Process = seed emerge from period of dormancy => starts to sprout

1) O2 : Aerobic respiration (ATP to grow)
2) H2O: Metabolically active cells, stimulate release of gibberalin
3) Temp: Optimal enzyme function
4) Other speciliased conditions
- Fire, burning
- Light/darkness
- Freezing, period of cold temperature
- Prior animal digestion
- Erosion(seed coat)
- Washing/removal of inhibitors

Question 23

Outline the metabolic process during strachy seed germination

Answer 23

1. Absorption of H2O, regydrate seed, cause production of gibberellin / gibberellic acid (GA)
2. GA cause amylase synthesis -> Break strach => Maltose
3. Maltose transport -> amylase
   a) hydrolysed to glucose (energy)
   b) polymerised to cellulose (formation of cell wall)
4. Stored protein + lipid —hydrolysed, addition of H2O—-> enzymes, triglycerides, phospholipids
5. Food stored in cotyledon used as energy source until shoot reach light + begin photosynthesis.

Question 24

Explain how flowering is controlled in long day & short day plants and the role of phytochrome

Answer 24

• Control by phytochrome (affected by light = photoperiodicitiy)
• 2 forms(phytochrome)
  a) Inactive 1. Red Pr absorb red light, covert to Pfr
  b) Active 2. Far red Pfr absorb far red light => Pr
• Sunlight more red light, Pfr dominant during day
• Night: Gradual reversino to Pr
• Long day plants: Active Pfr form promotor(flowering)

Flowering induced when

a) night period < critical length
b) Pfr high
- Short day plants: Active Pfr inhibitor(flowering)

Flowering induced when

a) night > critical legnth
b) Pfr low