chap12: nutriton & transport in plants

Question 1

describe the upper epidermis

Answer 1

irregular
closely packed cells
covered in a waxy cuticle that is water proof to prevent water loss and transparent to allow sunlight to enter for photosynthesis
do not contain chloroplasts

Question 2

describe the palisade mesophyll layer

Answer 2

cells are closely packed
contains many chloroplasts to absorb as much sunlight as possible for photosynthesis

Question 3

describe the spongy mesophyll layer

Answer 3

cells are irregular shaped
contains many intercellular air spaces to allow for fast rate of diffusion of carbon dioxide which enters via the stomataa
contain lesser chloroplasts than palisade mesophyll layer
has a thin film of moisture for carbon to dissolve in it
contains the vascular bundles

Question 4

describe the vascular bundles

Answer 4

vascular bundle contains xylem and phloem
this brings the transport tissues in closer contact to the photosynthetic tissue, allowing water and mineral salts to be distributed efficiently to the photosynthetic cells and food products to be brought to other parts of the plant

Question 5

describe guard cells and their purpose

Answer 5

contains chloroplast
control the opening and closing of the stomata

Question 6

describe the stomata

Answer 6

allows carbon dioxide to diffuse in and oxygen to diffuse out
allows water vapor to escape during transpiration

Question 7

how does temperature affect the rate of photosynthesis

Answer 7

• photosynthesis involved enzymes
  at low temperatures, rate of photosynthesis is low as enzymes have not enough energy for effective collisions for photosynthesis

at optimum temperature, rate of photosynthesis is high as enzymes have sufficient energy for effective collisions

beyond an optimum temperature, the rate of photosynthesis decreases sharply as enzymes become denatured

Question 8

what are the functions of the xylem

Answer 8

transport water and mineral salts from the roots to the leaves
provide mechanical support to the plant

Question 9

how is the xylem adapted for it’s functions

Answer 9

absence of cytoplasm and cross walls
lignin on the cell walls strengthen the vessel walls, providing support

Question 10

what are the functions of the pholem

Answer 10

transports glucose made in the leaves during photosynthesis to all parts of the plant
move up leaves
move down to roots

Question 11

how is the root hair cell adapted to it’s functions

Answer 11

elongated protrusion: increases surface area to volumes ratio to increase absorption of water and minerals
one cell thick: decreases diffusion distance of mineral salts
lower water potential in the cell than the soil: maintaining concentration gradient for osmosis/diffusion

Question 12

define transpiration

Answer 12

transpiration is the loss of water vapour from the stomata pod the leaves to the surrounding through diffusion

Question 13

how does transpiration occur and how does it result in transpiration pull

Answer 13

during photosynthesis, when the stomata open for carbon dioxide intake, transpiration occurs as water vapour from the intercellular air spaces in the leaves diffuses out of the cell and into the air outside which has a lower water vapour concentration than inside the leaf

transpiration results in transpiration pull which is the suction force that pulls water up the xylem, from the roots and to other parts of the plant

Question 14

factors affecting rate of transpiration

Answer 14

humidity: humidity affects the concentration gradient of water vapour between the intercellular air spaces in the leaf and the external environment. higher humidity = higher concentration of water vapour in the external air + less steep diffusion gradient for water vapour = lower rate of transpiration

air movement: wind removes water vapour that accumulates outside the stomata due to transpiration. this maintains steep diffusion gradient of water vapour = higher rate of transpiration

light intensity: light induces stomatal opening. sine transpiration takes place mainly through the stomata, increased light intensity = increased rate of transpiration

Question 15

how does transpiration take place

Answer 15

water vapour in the intercellular air space diffuses out of the stomata.
evaporation from the thin film of water that coats the mesophyll cells replaces the water lost through the transpiration. as water evaporates from the mesophyll cells, the water potential of the cell sap decreases. the mesophyll cells absorb water form the neighbouring cells closer to the vascular bundles by osmosis. these cells then absorb water from the xylem vessels.
this creates a suction forces that pulls the entire column of water up the xylem vessels.

Question 16

definition of translocation

Answer 16

translocation is the process of transporting sugars from leaves to other parts of the plants via phloem tissues.

Question 17

how is the leaf adapted for photosynthesis

Answer 17

waxy cuticle on upper and lower epidermis: transparent for light to enter, waterproof to prevent water loss
stomata present in the epidermal layer: allows gaseous exchange, co2 diffuse in, o2 diffuse out
many chloroplasts in upper mesophyll tissue: more light can be absorbed near the upper leaf surface
chloroplasts containing chlorophyll in all mesophyll cells
air spaces in the spongy mesophyll: allows co2 to diffuse in and o2 to diffuse out of mesophyll cells
veins connecting xylem and phloem close to mesophyll cells: xylem can transport water no mineral salts to mesophyll cells, phloem transport sucrose away from the leaf and to other parts of the plant.

Question 18

how is phloem adapted for it’s functions

Answer 18

phloem consists of many sieve tubes and companion cells
cross wall that contains sieve plates helps transport sucrose and amino acids
cross wall: provides nutrients
companion cells: contains cytoplasm and nucleus, contain mitochondria which provides energy for companion cells to load sugar from mesophyll cells to sieve tubes via active transport

Question 19

describe the vascular bundle

Answer 19

xylem inside, phloem outside, cambium in between
stem is covered by a layer of cells called the epidermis. it is protected by a waxy, waterproof cuticle that reduces water loss by evaporation

Question 20

why is photosynthesis important

Answer 20

sunlight is the ultimate source of energy for living organisms. during photosynthesis plants take in sunlight to make food. this eventually becomes food for other organisms and they obtain chemical energy indirectly or directly from plants because plants are the producers in food chains

removes co2, replenishes o2

energy stored in fossil fuels come from photosynthesis

Question 21

describe wilting

Answer 21

in strong light, the rate of transpiration is higher than the rate of absorption, this results in cells losing its turgor. they become flaccid and the plant wilts.

Question 22

what are the advantages of wilting

Answer 22

during wilting, the leaf closes up and the surface area that is exposed to sunlight is reduced. this reduces the exposure of stomata to the atmosphere and this reduces the rate of water loss through the stomata.
excessive water loss causes guard cells to become flaccid and the stomata to close which reduces rate of transpiration

Question 23

what are the disadvantages of wilting

Answer 23

as the stomata closes, the amount of carbon dioxide entering the leaf is reduced which decreases rate of photosynthesis
folding of leaf also reduces the surface area exposed to light, reducing rate of photosynthesis.

Question 24

how is the xylem adapted for its functions

Answer 24

hollow and long
empty lumen, no cytoplasm and cross walls
lignin to provide mechanical support

Question 25

what is the importance of translocation

Answer 25

keeping the plant cool
keeps cells turgid

Question 26

how does water enter a plant

Answer 26

when water enters the cell sap via the root hair, it dilutes the cell sap which increases the water potential to much higher than the water potential of the cell next to it. this results in a concentration gradient which allows water to pass by osmosis from one cell to the other. this process continues until the water reaches the xylem vessels and moves up the plant.

Question 27

describe the move to of water through the leaf via transpiration

Answer 27

water evaporates from the thin film of moisture that surrounds the mesophyll cells to form water vapour in the intercellular air spaces
water vapour then diffuses through the stomata to the drier air outside the leaf (transpiration)
as water evaporates from the thin film of moisture, more water moves out of the mesophyll cells to replenish it.
as water is lost from the mesophyll cells, the water potential of their cell sap decreases and becomes lower than the neighbouring mesophyll cells
the mesophyll cells draw water form cells deeper inside the leaf by osmosis
the cells deeper inside the leaf then draws water from the xylem by osmosis. this causes transpiration pull which pulls water up the xylem vessels.

Question 28

what are external features that helps leaves carry out photosynthesis

Answer 28

leaf surface area to volume ratio: obtain max. amount of sunlight for photosynthesis, higher vol of co2 can reach cells of the leaf
leaf stalk: holds the leaf blade away from the stem so it can obtain sufficient air and light
leaf arrangement: prevents leaves from overlapping and blocking each other from sunlight needed for photosynthesis
network of veins: veins carry water and mineral salts to the cells in the leaf blade