topic 6

Question 1

photosynthesis + photosynthetic organisms

Answer 1

• the main producers of food and therefore biomass
• photosynthesis occurs in plants and algae
• it is an endothermic reaction - it takes in more energy than it releases

Question 2

adaptations of root hair cells

Answer 2

• specialised to take up water by osmosis and mineral ions by active transport
• the millions of root hairs on each branch of a root give them a large surface area
• mitochondria provide energy from respiration for active transport

Question 3

adaptations of xylem cells

Answer 3

• dead lignified cells
• hollow and joined end-to-end to form a continuous tube for water to flow through
• lignin is deposited in spirals, helping the cells withstand the pressure of the movement of water

Question 4

adaptations of phloem cells

Answer 4

• cell walls of each cell form sieve plates when the break down, allowing movement of substances between cells
• living cells missing many sub-cellular structures - kept alive by energy released by mitochondria of companion cells
• the energy is used to transport sucrose around the plant

Question 5

how does transpiration work

Answer 5

• it is the loss of water/water vapour from leaves and stems of a plant because of gaseous exchange through the stomata
• water molecules evaporate at the open stomata, as water molecules are attracted to each other, when some leave the plant the rest are pulled through the xylem
• this causes more water to be taken up from the soil - resulting in a continuous transpiration stream through the plant

Question 6

purpose of guard cells

Answer 6

• they open and close stomata
• kidney shaped with thin outer walls and thick inner walls
• if there’s lots of water the cells become turgid and open the stomata vs flaccid - they’re also light sensitive
• this allows gases to be exchanged and water to leave the plant by transpiration

Question 7

where are stomata found

Answer 7

• more are found on the bottom of a leaf

* gases can be exchanged whilst minimising water loss by evaporation because it’s cooler

Question 8

what is translocation

Answer 8

its the movement of food substances (eg. sucrose) through the phloem from the sources (where it’s made) to the sinks (where it’s stored)

the location of the source and sink can vary depending on the season

Question 9

factors affecting rate of water uptake

Answer 9

•increases temp - molecules move faster so evaporation occurs at a faster rate and rate of transpiration increases

• photosynthesis rate increases so more stomata are open for gaseous exchange, so more evaporation and increased transpiration rate
• relative humidity
• air movement
• light intensity - high light intensity increases rate of photosynthesis, so more stomata open for gaseous exchange, more water evaporates and more transpiration

Question 10

adaptations of plants to live in extreme environments

Answer 10

• small/no leaves - reduces amount of water lost from transpiration for desert plants
• curled leaves - reduces air flow close to the leaf, trapping water vapour
• waxy cuticle - again prevents water evaporating
• thick, fleshy stem to store water

• stomata - in sunken pits, reducing air flow close by
- fewer/only open at night

Question 11

positive phototropism with auxin

Answer 11

• auxin diffuses in solution to the shaded side of the shoot
• the cells are stimulated to elongate faster
• the shoot bends towards the light, so photosynthesis can occur faster and the plant can grow faster

Question 12

negative gravitropism with auxin

Answer 12

• auxin moves to the lower side of the Shoot due to gravity
• it stimulates the growth of cells where there’s more auxin
• this makes the shoot bend away from the ground, beneficial bc light levels are likely higher further from the ground

Question 13

positive gravitropism with auxin

Answer 13

• auxin moves to the lower side of the Root
• the auxin inhibits growth and the cells on top elongate faster
• the root bends and grows downwards
• beneficial because there’s likely to be more water and nutrients lower down and it also provides stability

Question 14

hormone used in weed killers

Answer 14

auxin

• weed killers with auxin have been synthesises to only affect broad-leaved plants
• increased amount of auxin causes rapid growth of cells and the weed dying

Question 15

hormone used as rooting powders

Answer 15

auxin
• a cutting is taken from the og plant

• rooting powder with auxin is put on it and it’s placed in the ground
• roots grow and the new plant begins growth speedily

CLONES!

Question 16

hormone used to promote growth in tissue culture

Answer 16

auxin
• cells from the plant are taken and places in a growth medium with lots of nutrients

• auxins are added and the cells begin forming roots and shoots

Question 17

hormone used in germination

Answer 17

gibberellins

• they break seed dormancy when seeds haven’t been through certain conditions yet that are normally required for germination
• treating seeds with gibberellins can make them germinate at times of year that they wouldn’t usually
• it also helps to ensure all seeds in a batch germinate together

Question 18

hormone used in food industry

Answer 18

ethene

• fruit is picked before its ripe, it’s firm and doesn’t get as bruised and damaged transport
• before selling it is exposed to ethene and warmer temperatures
• then helps control cell devision and stimulates enzymes resulting in fruit ripening

Question 19

how can you estimate transpiration rate

Answer 19

• using a potometer, it measures a plants water uptake but its assumed that water uptake and transpiration are directly related
• use a stopwatch to estimate distance moved by the bubble per unit time and then find the speed
• a photometer can be used to show how light intensity, temperature/air flow affect rate of transpiration

Question 20

order of layers in a leaf

Answer 20

waxy cuticle
upper epidermis
palisade mesophyll tissue 
spongy mesophyll tissue + air spaces
lower epidermis
stomata + guard cells

Question 21

palisade layer

Answer 21

lots of chloroplasts, so near the top of the leaf to get maximum light

Question 22

upper epidermis

Answer 22

transparent so that light can reach the palisade layer

Question 23

xylem and phloem

Answer 23

network of vascular bundles, providing the leaf with water for photosynthesis, taking away glucose and helping to support structure

Question 24

spongy mesophyll tissue

Answer 24

contains air spaces allowing for increased rate of diffusion into and out of the leafs cells

Question 25

negative phototropism with auxin

Answer 25

• when a root is exposed to light, auxin accumulates on the shaded side
• auxin inhibits elongation and the root bends towards the ground

Question 26

shoots growing in the dark

Answer 26

• auxin on the tip makes them elongate quickly on all sides

* a taller shoot has more chance of finding light

Question 27

hormone for controlling flower and fruit formation

Answer 27

gibberellins

• they can be used to make plants flower earlier/in conditions where they wouldn’t usually
• they can also be used to reduce flower formation which can improve fruit quality - fewer flowers = fewer fruits, so they can grow bigger and slay more

Question 28

hormone used for producing seedless fruit

Answer 28

gibberellins

• usually fruit with seeds is only grown on flowering plants that have been pollinated by insects
• applying gibberellins to the unpollinated flowers of some plant types can cause the fruit to grow without seeds (eg. some citrus fruits)