module 4

Question 1

Provide argument suggesting multicellularity arose independently in plants and animals

Question 2

Propose possible steps leading to multicellularity

Answer 2

1. Divided and stayed in a cluster
2. inter and intracellular communication
3. differentiation and specialisation
4. specialised cells seperate into groups

Question 3

Benefits of multicelluarity

Answer 3

• cell specialisation allows cells to adopt new functions
• integration and co-operation between cells allowing for the development
• structurally and fucntionally complex bodies
• creation of a stable internal environment
• increase in size
• more efficient gathering of resources and adapting to specific environment

Question 4

Primary and secondary growth

Answer 4

Primary is vertical and secondary is radical

Question 5

Role of expansin

Answer 5

allows slippage between cellulose microfibrils by temperarily disrupting non-covalent bonds of celluse and glycan, hemicellulose and pectin

Question 6

difference between primary and secondary cell division

Answer 6

primary cell wall is sem-rigid and can expand whereas secondary cell wall is thick, rigid, rich in lignin and cannot expand

Question 7

Auxin hormone and its role in regulating phototropism and gravitropism

Answer 7

-auxin is a growth hormone in plants
-phototropism: auxin accumulates on the exposed side
-gravitropism: auxim accumulated on the lower side

Question 8

Key steps in plant embryogenesis

Answer 8

1. asymmetrical division of zygote into a smaller apical cell and a larger basal cell
2. octant stage: apical cell further divides to become the embryo and basal cell divides to form the suspensor
3. heart stage: cell expansion and division
4. mature embryo: embryo fold over in the seed

Question 9

Shoot apical and root apical meristem

Answer 9

shoot apical meristem generates aerial structures (leaf, axillary bud, internode)
root apical merstem: subterranean structures (roots)

Question 10

Tissue systems in plants - dermal tissue system

Answer 10

single layer of cell forming the epidermis
epidermal cells can differentiate into stomata, trichomes and root hairs

Question 11

Tissue systems in plants - Ground

Answer 11

makes up most of plant tissue and is located between dermal and vascular tissue
classifications based on cell wall structure
1. parenchyma: round cell, thin cell wall
2. collenchyma: flexible structural support
3. sclerenchyma: have a secondary cell wall, rigid tissue and thicken cell wall

Question 12

Tissue systems in plants - vascular

Answer 12

Network of transporting systems
Xylem: carrier for water and mineral ions from roots to shoots
- dead cells with secondary walls
pholem: move sugar and nutrients from shoot to roots
- living cells
- sieve tuble element cells
companion cells

Question 13

Water potential

Answer 13

refers to the tendency of a solution to take up water from pure water across a selectively permeable membrane
water always moves for high to low potential reigons

Question 14

Water uptake by root cells

Answer 14

1. water enters root via osmosis and moves through symplast or apoplast
2. when reaching the casparian strip, water and solute in apoplast forced into endothermal cells
3. water and solute remain in the symplast
   solute is actively transportd out of the cell and into apoplast and follows passively by osmosis

Question 15

difference between apoplast and symplast

Answer 15

apoplast: rapid and unregulated movement on interconnected cell wall and intercellular spaces between cells
symplast: slow and regulated movement in interconnected cytoplasm via plasmodesmata

Question 16

Transpiration process

Answer 16

1. water diffuses out of leaf via stomata
2. water evaporates from mesophyll cell walls
3. Tension pulls water from veins and into apoplast surrounding mesophyll cells
4. This subsequently pulls water in leaf vers upwards he outwards
5. which subsequently pulls water column in xylem of shoot and root upwards PASSIVELY
6. cohesion between water molecules allow continuous water column from root to leaves
7. Water enters xylem via osmosis
8. water enters root via Osmosis

Question 17

control of osmosis by light

Question 18

translocation

Answer 18

movement of carbohydrates and other solutes through the pholem

Question 19

Mass flow hypothesis

Answer 19

Sucrose and other solutes are actively transported into sieve tubes elements via the companion cell - loading

Sucrose accumulation makes potential, more negative in sieve tube elements causing water to enter the cells by osmosis from adjacent tissue

Increase in pressure (Y) causes ‘mass’ in the phloem to move away from the pressure

Active transport of sucrose into sink cells cases an increase in the Yw of sieve tube elements

Water leaves the phloem by osmosis - reinforcing the pressure gradient

Question 20

key stages of animal embryogenesis

Question 21

3 germ layers

Answer 21

ectoderm: external surfaces and vervous system
mesoderm: internal tissue
endoderm: cells lining organs
tripoblast = 3, dipoplast=2