topic 6 Flashcards
(28 cards)
photosynthesis + photosynthetic organisms
- 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
adaptations of root hair cells
- 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
adaptations of xylem cells
- 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
adaptations of phloem cells
- 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
how does transpiration work
- 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
purpose of guard cells
- 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
where are stomata found
- more are found on the bottom of a leaf
* gases can be exchanged whilst minimising water loss by evaporation because it’s cooler
what is translocation
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
factors affecting rate of water uptake
•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
adaptations of plants to live in extreme environments
- 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
positive phototropism with auxin
- 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
negative gravitropism with auxin
- 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
positive gravitropism with auxin
- 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
hormone used in weed killers
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
hormone used as rooting powders
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!
hormone used to promote growth in tissue culture
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
hormone used in germination
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
hormone used in food industry
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
how can you estimate transpiration rate
- 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
order of layers in a leaf
waxy cuticle upper epidermis palisade mesophyll tissue spongy mesophyll tissue + air spaces lower epidermis stomata + guard cells
palisade layer
lots of chloroplasts, so near the top of the leaf to get maximum light
upper epidermis
transparent so that light can reach the palisade layer
xylem and phloem
network of vascular bundles, providing the leaf with water for photosynthesis, taking away glucose and helping to support structure
spongy mesophyll tissue
contains air spaces allowing for increased rate of diffusion into and out of the leafs cells
