CB6 - Plant structure + function Flashcards
word and symbol equation for photosynthesis
carbon dioxide + water —> oxygen + glucose
6C02 + H2O —> O2 + C6H12O6
what happens to the products of photosynthesis?
the glucose cannot be transported, so it is built up into sucrose or becomes a starch polymer
oxygen leaves the plant through its stomata and enters the earths atmosphere
why is photosynthesis classed as an endothermic reaction?
it takes in energy from its surroundings
what is the difference between starch and glucose
starch is a polymer of glucose molecules and is insoluble, while glucose is soluble
what might sucrose in a plant be used for
starch in a storage organ
glucose for respiration
other molecules in the plant
what is the structure of a leaf and how is it adapted for photosynthesis?
wax cuticle - prevents loss of water upper epidermis - to allow light through palisade cells spongey mesophyll - air spaces for gas exchange lower epidermis guard cells stomata phloem vascular bundle xylem
how do guard cells open and close stomata?
in light, water flows into the guard cells and open the stomata
when there is less light (at night), water flows out of the guard cells and the stomata closes
what gas exchanges happen through the stomata?
carbon dioxide enters the leaf and oxygen leaves
why do the stomata close at night?
there is no light, so water flows out of the guard cells and close stomata
why are mountain plants so small?
- photosynthesis is slower higher up
- fewer molecules of air per cm3 higher up, lowering rate of photosynthesis
- less carbon dioxide particles being taken in by the plants, not as much photosynthesis occurring
- higher up mountain areas are also colder, makes photosynthesis slower
- colder temps mean enzymes have less energy, not as many reactions occurring
what is a limiting factor and what are the three involved in photosynthesis
a limiting factor is a factor that prevents a rate increasing
for photosynthesis they are:
- temperature
- carbon dioxide concentration
- light intensity
how does temperature affect photosynthesis
- affects activity of enzymes involved in photosynthesis
- too high temperatures denature the enzymes so photosynthesis will slow down and eventually stop
- too low temps mean enzymes dont have enough energy to create reactions
how does carbon dioxide affect photosynthesis
- limit the rate of photosynthesis
- not enough carbon dioxide to take in to produce oxygen + glucose
- in the air the concentration of CO2 is 0.04%
how does light intensity affect photosynthesis
- provides energy to drive photosynthesis
- on cloudy days light can be a limiting factor
describe a root hair cell
- cell membrane
- cell wall
- vacuole
- mitochondria
- nucleus
- cytoplasm
- thin cell walls to easily absorb water (for photosynthesis)
- no chloroplasts because its underground
what is the function of water going into the plant
- carries dissolved mineral ions
- keeps cells rigid so they dont wilt
- cooling the leaves
- photosynthesis
compare and contrast osmosis and diffusion
- both occur down concentration gradient
- both passive
- osmosis is the movement of only water
- diffusion can be movement of liquid/gas particles
- osmosis occurs across a semi-permeable membrane
- diffusion doesnt need a membrane
how does transport in the plants occur
1) water enters the root hair cells through osmosis, water moves down a water potential gradient, from soil to root cells
2) active transport of mineral ions from the soil into the root hair cells, helps lower water potential of root hair cells
3) water moves from one root hair cell to another, mainly through cell walls
4) water + mineral ions moves into xylem vessels from root cells
5) water moves up xylem from root to stem, upward movement of water in the xylem is known as a transpiration stream
what is active transport
moving against the concentration gradient, so its active and requires energy
more ions inside root hair cells so they get pumped into the cell
nitrate ions are needed to make proteins
why cant mineral ions move into root hair cells through diffusion
mineral ions are very low in concentration, so would only be able to move through active transport and not diffusion
describe the role of a xylem and explain how its well adapted to its job
it transports water up the stem and to the rest of the plant. its lack of cell walls allow fast water flow, thick side walls provide support and do not burst/ collapse, no cytoplasm, so lots of area for water to flow through
describe the structure of a xylem
- thick side walls + rings of lignin form rigid tubes that wont burst or collapse + provide support
- tiny pores allow water + mineral ions to enter and leave xylem vessels
- dead cells have no cytoplasm so an empty tube for water to flow through is formed
- lack of cell walls between cells mean water flow is not slowed down
describe the structure of a phloem
- sieve tubes in the phloem tissue
- holes in end of cell walls allow liquids to flow from one sieve cell to the next
- very small amount of cytoplasm and no nucleus means there is more room for central channel
- has pores in which sucrose solution can be pumped
why do sieve cells have so little cytoplasm and no nucleus?
why do companion cells have so many mitochondria?
to allow as much sugar as possible to flow through and more room for a central channel
they need enough energy to pump sucrose in and out of sieve cells for active transport. mitochondria releases energy during respiration so there is enough energy for active transport.
describe transpiration and translocation
transpiration - the flow of water into a root, up the stem and out of the leaves. water moves up the xylem in an unbroken chain due to forces of attraction between each molecule. as water evaporates from the leaves more gets pulled from the stem
translocation - the movement of sucrose (a sugar) through the phloem in a plant
what factors affect transpiration and how
wind - decrease, moves water molecules away from the stomata
humidity - decrease, more water vapour in the air
temperature - increase, particles move faster in higher temp, diffuse faster
light intensity - increase, stomata are wider in greater light intensity
