plant nutrition & transport !

Question 1

upper epidermis

Answer 1

made up of a single layer of closely packed cells
no chloroplasts

covered by a layer of cuticle : transparent & waxy

• allows light to pass through
• prevents excessive water loss from upper epidermis

Question 2

palisade mesophyll !

Answer 2

closely packed cells that are long & cylindrial
contains many chloroplasts : located near the top surface of leaf -> light is most abundant -> maximum absorption of light energy

Question 3

spongy mesophyll !

Answer 3

cells are irregularly shaped

have lesser chloroplasts than palisade mesophyll cells

contains the vascular bundle (xylem & phloem tissues)

cells : covered in a thin layer of moisture
- for CO2 to dissolve in before diffusing into the cells

have numerous large intercellular air spaces among the cells
-allowing transport of water, sucrose & amino acids within the plants

Question 4

lower epidermis !

Answer 4

consists of a single layer of closely packed cells
no chloroplasts : no photosynthesis
covered with a layer of cuticle : prevent excessive water loss

Question 5

guard cells !

Answer 5

control size of stomata : regulate gaseous exchange between plant & surroundings

day : guard cells photosynthesis - convert light energy -> chemical energy

• chemical energy : pump K+ ions into the guard cells from neighbouring epidermal cells -> water potential of guard cells to decrease -> water from neighbouring epidermal cells enter guard cells by osmosis
• turgidity of guard cells increase -> becomes curved -> pulls stoma open

night : K+ ions diffuse out of guard cells to epidermal cells -> water potential of guard cells increase -> water leaves by osmosis
- turgidity decreases -> becomes flaccid -> stoma closes

Question 6

carbon dioxide - entering leaves !

Answer 6

day : photosynthesis occurs

• CO2 : rapidly used up -> concentration is lower than atmospheric air -> diffusion gradient established
• surfaces of mesophyll cells : covered by thin film of moisture -> CO2 dissolves -> diffuse into cells

Question 7

lamina!

Answer 7

large surface area : maximise absorption of sunlight for photosynthesis + allows rapid diffusion of CO2 to reach inner cells of leaf

thin : allowing for a shorter diffusion distance for gases during gaseous exchange

Question 8

petiole !

Answer 8

positions lamina away from stem : allows lamina to absorb maximum sunlight & carry out gaseous exchange

Question 9

veins !

Answer 9

allow transport of water & mineral salts to the cells in the lamina
transports manufactured food (glucose) from cells in the leaves to the other parts of the plant
main vein : gives off branches repeatedly -> forming network of fine veins

Question 10

leaf arrangement !

Answer 10

organised around the stem in a regular pattern : grow in pairs
- opposite one another or singly in an alternative arrangement

• > ensures that the leaves are not blocking each other from sunlight
• > ensures that each leaf receives optimum light

Question 11

photosynthesis formulas !

Answer 11

6CO2 + 12H20 (light energy & chlorophyll) -> C6 H12 O6 + 602 + 6H2O

carbon dioxide + water (light energy & chlorophyll) -> glucose + oxygen + water

Question 12

conditions - photosynthesis !

Answer 12

light intensity 
presence of chloroplasts
carbon dioxide
suitable temperature 
water

Question 13

light-dependent stage !

Answer 13

enzymes are involved
light energy : absorbed by chlorophyll in leaves & converted into chemical energy

12 H20 (photolysis of water) -> 6O2 + 24H

Question 14

light-independent stage !

Answer 14

enzymes involved
does not require light energy
hydrogen atoms produced by light-dependent stage : used to reduce CO2 into glucose

Question 15

limiting factors !

Answer 15

a factor that directly affects or limits a process if its quantity or concentration is altered

affects rate of photosynthesis !

• light intensity
• CO2 concentration
• temperature

Question 16

pathway of water !

Answer 16

root hair : fine tubular outgrowth of an epidermal cell that grows between soil particles
- close contact with surrounding soil particles

soil particle : thin film of liquid surrounding it

cell sap in root hair cell : more concentrated due to presence of mineral salts
- lower water potential than soil solution -> water enters root hair by osmosis

entry of water : dilutes root hair cell cap

• 1st root hair cell : higher water potential than 2nd root hair cell -> water passes from 2nd to 3rd to cortex …
• process continues until water enters xylem vessels

Question 17

root hair cell !

Answer 17

has numerous mitochondria : release energy from aerobic respiration
- allow uptake (active transport) of mineral salts

long narrow protrusion : increases surface area to volume ratio
- increases rate of absorption of water & mineral salts

large central vacuole with concentrated cell sap : creates water potential gradient for quicker movement of water molecules by osmosis

Question 18

root pressure !

Answer 18

pressure resulting from the constant entry of water from the roots
root cells surrounding xylem causes water potential in xylem to lower -> water moves into xylem

Question 19

capillary action !

Answer 19

tendency of water to move up very narrow capillary tubes

• forces of cohesion : attached by water molecules
• forces of adhesion : stick to wall

Question 20

transpiration pull !

Answer 20

suction force caused by transpiration which results in water moving up the xylem against gravity

Question 21

transpiration !

Answer 21

loss of water vapour from the aerial parts of the plant, especially through the stomata of the leaves

evaporation of water from cells in the leaf by transpiration
- removes latent heat of vaporisation -> cools the plant, preventing it from being scorched

water transported to the leaves can be used in photosynthesis

• keeps cells turgid
• replaces water lost by the cells

Question 22

water movement in leaves !

Answer 22

water that moves out of the mesophyll cells : form a thin film of moisture around the cells

water from the thin film of moisture : evaporates to form water vapour in the intercellular air spaces
- water vapour : diffueses out of the stomata to the drier air outside the leaf - transpiration

movement of water out of the calls to replace the thin film of moisture that has evaporated
- causes the cell sap’s water potential to decreases

mesophyll cells : absorb water via osmosis from the cells deeper in the leaf
- results in the production of a suction force : transpiration pull

Question 23

temperature - transpiration factors !

Answer 23

increase in temperature -> increases rate of evaporation of water from the cell surfaces -> increases water vapour in air spaces -> increase rate of transpiration

Question 24

light intensity - transpiration factors !

Answer 24

presence of light : stomata size increases -> increased rate of evaporation of water -> increases rate of transpiration

absence of light : stomata size decreases -> decreased rate of evaporation of water -> decreases rate of transpiration

Question 25

humidity - transpiration factors !

Answer 25

the drier / less humid the air outside the leaf is, the steeper the concentration gradient between leaf & atmosphere -> increases rate of transpiration

high humidity : lower vapour concentration gradient between leaf & atmosphere -> decreases rate of transpiration

Question 26

wind - transpiration factors !

Answer 26

wind : blows away water vapour that accumulates outside the stomata
- helps maintain water vapour concentration gradient between the leaf & the atmosphere -> increases transpiration rate

still air : water vapour that diffuses out of the leaf makes the air outside the leaf more humid -> decreases transpiration rate

Question 27

wilting !

Answer 27

occurs when rate of water loss (transpiration) exceeds rate of water absorption

vacuole + cytoplasm of plant cells : shrink
- plant cells : lose their turgor -> becomes flaccid

Question 28

factors - wilting !

Answer 28

strong light -> increases rate of transpiration -> wilting occurs

too much fertiliser in soil : root hair cells -> higher water potential than surrounding soil solution -> water leaves the root hairs by osmosis -> wilting occurs

Question 29

advanatages of wilting !

Answer 29

reduces rate of transpiration
prevents excessive water loss : guard cells are flaccid -> stomata closed -> lesser transpiration
cools plant down

• leaf folds up -> surface area to volume ratio decreases

Question 30

disadvanatges - wilting !

Answer 30

stomata close : amount of CO2 decreases
leaves will droop :
- absorption of sunlight decreases -> photosynthesis decreases
- lesser surface area to volume ratio that is exposed to sunlight -> photosynthesis decreases