organisation (in plants)

Question 1

what movement are xylem vessels involved in

Answer 1

they are involved in transpiration.

the movement of water through a plant from ROOTS —> LEAVES

Question 2

what movement are phloem vessels involved in

Answer 2

they are involved in translocation.

the movement of food substances from stems to growing tissues + storage tissues

Question 3

why do plants require a transport system

Answer 3

to move food, water and minerals

Question 4

describe how translocation works

Answer 4

plants make their sugars through photosynthesis - this happens in the leaves. so to share the sugars with the rest of the plant, they have to be transported.

phloem cells are tubes arranged end to end forming a phloem tube.

in between adjacent cells, there are small pores which allow cell sap (mixture of water and sugar) - this means that the sugars made in the leave can be transported long distances through multiple cells

once the sugar has ended up wherever it needs to go, 1 of 2 things can happen:
- the sugar can be used directly for energy
- the sugar can be stored to be used for energy later

Question 5

describe how transpiration works

Answer 5

stomata allows gas exchange between the leaf and the atmosphere.

when the stomata are open they let in carbon dioxide and also allow water vapour to leave the leaf through evaporation

this is what drives the movement of water up through the plant

Question 6

describe how the transpiration stream works

Answer 6

water (by osmosis) and mineral ions (by active transport) are absorbed from the soil through root hair cells

(the transported water is needed for photosynthesis which mostly takes place in the leaves)
(the mineral ions are needed to make proteins and other molecules)

it is then transported through the xylem vessels UP the stem to the leaves

the water then evaporates from the leaves (transpiration)

Question 7

how are root hair cells adapted for transpiration

Answer 7

they have a large surface area to increase the rate of absorption

Question 8

all about xylem

Answer 8

• physical process
• transports water + minerals from roots to leaves via transpiration
• transports upwards (one way only)
• thick walls stiffened with lignin
• no end wall between cells (hollow)

Question 9

all about phloem

Answer 9

• requires energy
• transports amino acids dissolved in water from the leaves to the rest of the plant and to storage organs via translocation
• transports upwards and downwards
• cells have end walls with perforations

Question 10

features of a leaf (from top to bottom)

Answer 10

• waxy upper epidermis
• upper palisade mesophyll cells
• spongy mesophyll
• guard cell - stomata - guard cell
• waxy layer
• lower epidermis

Question 11

upper epidermal tissue adaptation + function

Answer 11

• it is transparent
• it protects the plant from infection and water

Question 12

palisade mesophyll adaptation + function

Answer 12

• packed with chloroplast
• absorbs light for photosynthesis

Question 13

spongy mesophyll adaptation + function

Answer 13

• packed loosely
• diffusion of gases (CO2)

Question 14

lower epidermal tissue adaptation + function

Answer 14

• lots of stomata to prevent excess transpiration
• allows CO2 to enter the leaf and O2 + excess water to exit

Question 15

vascular bundles adaptation + function

Answer 15

• has xylem + phloem
• transport critical substances to plant

Question 16

features of an OPEN stomata (6)

Answer 16

1 - stomatal pore
2 - inner thick wall
3 - nucleus, chloroplast, vacuole
4 - outer thin wall
5 - guard cells (from 2 - 4)
6 - epidermal cell

Question 17

how do guard cells work

Answer 17

when the plant wants to open, ions are pumped into the guard cell

this creates a concentrated region and water moves into the guard cell - osmosis - causing them to become turgid (swollen/no more water can get in)

due to the different wall thickness, the outsides of the cell becomes longer than the insides and so the cells curve - this creates a space

when the stomata needs to close, the water moves out of the cells - osmosis - and they become flaccid (opposite of turgid/floppy)
the cell returns to normal shape and the space between them closes

Question 18

what needs to be transported in plants (5)

Answer 18

WATER - taken in primarily at the roots and needs to get all the way around the plant

IONS AND NUTRIENTS - taken in by roots and needs to get all the way round the plant

GLUCOSE - made by chloroplast ; needs to be transported to all cells for respiration

CARBON DIOXIDE - diffuses in through stomata to be used in photosynthesis

OXYGEN - diffuses out through stomata

Question 19

measuring transpiration

Answer 19

you use a potometer
–> this indicates how quickly transpiration occurs
–> how far the bubble moves shows how much water has been taken up

transpiration happens at different rates in different environmental conditions

Question 20

what affects transpiration

Answer 20

light intensity -
the brighter the light intensity, the more photosynthesis can take place –> this means more stomata will have to be open to let in the CO2 (required for photosynthesis) so more water can evaporate resulting in a higher rate of transpiration
so when it is nighttime, there is no photosynthesis happening because is it dark –> closed stomata so little transpiration

temperature - the warmer it is the higher the rate of transpiration because the particles of water will have more energy –> more likely to evaporate and diffuse out of the stomata

FOR AIRFLOW AND HUMIDITY –>

because water is constantly being brought up from the roots, the inside of the leaf is going to have a much higher concentration of water than the outside
–> concentration gradient where the water can diffuse out the leaf SO rate of transpiration will depend on gradient

airflow - when airflow is high (windy) the water molecules that leave the leaf are quickly going to be blown away –> so the concentration gradient between inside and outside will stay high, increasing the rate of transpiration

humidity (how much water vapour is in the air) - more humid air will decrease the rate of transpiration because the large amount of water in the moist air will decrease the concentration gradient –> so less water will diffuse out so there will be less overall evaporation