Topic 6 - Plant Structures and Their Functions Flashcards
what is photosynthesis
- energy transferred by the light from the Sun is trapped
- energy is then transferred to molecules of a sugar called glucose
- when animals eat plants they get the energy from these stores
biomass
The materials in an organism
Photosynthesis word equation
Carbon dioxide + water -> glucose + oxygen
Where and how does photosynthesis occur?
Chloroplasts which contain a green substance called chlorophyll that traps energy transferred by light
Is photosynthesis endothermic or exothermic?
Endothermic because energy enters from the surroundings so the products of photosynthesis have more energy than the reactants
How is sucrose made in a plant?
The glucose molecules that are made linked together to form a polymer starch. This stays in the chloroplast until photosynthesis stops, the starch is then broken down into simple substances which are moved into the cytoplasm and used to make sucrose.
What can sucrose be used to make?
- Starch
- other molecules for the plant (such as cellulose, lipids or proteins)
- glucose for respiration (to release energy)
What is the adaptation of the palisade cells?
Packed with chloroplasts so they can absorb a great deal of light
Function of stomata
Allows carbon dioxide to diffuse into the leaf
Also allows the oxygen produced by photosynthesis to escape into the air
Function of Guard cells
Cells that open and close the water stomata
How does the stomata open in the day but close at night
- in the light water flows into pairs of guard cells making them rigid this opens a stoma (plural stomata)
- At night water flows out of the guard cells they lose their rigidity and closes a stoma
What are basic leaf adaptations?
- Leaves are broad and flat giving them a large surface area
- Leaves are thin so carbon dioxide does not have far to diffuse into the leaf before reaching cells that need it
Structure of a leaf
Why is photosynthesis slower at the top of a mountain and then at the bottom?
- reduce concentration of air molecules causes a lower rate
- Photosynthesis is catalysed by enzymes at work better at warmer temperatures (the top of the mountain is cold)
Limiting factor
Factor that prevents a rate increasing
What are the 3 limiting factors for photosynthesis?
- carbon dioxide Concentration
- temperature
- light intensity
How do we calculate the new light intensity (I) (I(new)) when the distance (d) of light source changes from d(orig) to d(new)
I(new) = I(orig) x d2 (orig)
d2 (new)
- light intensity is inversely proportional to the new distance squared
What is the method for the core practical of light intensity and photosynthesis?
- Decide on the different distances between the algae and the lamp you are going to use and for each distance you will need one clear glass bottle. You will also need one extra bottle.
- Add 20 of the algal balls to each bottle.
- Add the same amount of indicator solution to each bottle, and put on the bottle caps - Compare the colour in your tubes with this pH range to work out the pH at the start.
- Set up a tank of water between the lamp and the area where you will place your tubes. Take extreme care not to spill water near electrical apparatus (such as a lamp).
- Cover one bottle in kitchen foil, so that it is in the dark.
- Measure the different distances from the lamp. Place your bottles at those distances. Put the bottle covered in kitchen foil next to the bottle that is closest to the lamp.
- Turn on the lamp and wait until you can see obvious changes in the colours in your bottles. The longer you can wait, the more obvious your results are likely to be.
- Compare the colours of all your bottles with the pH range bottles. Write down the pHs of the solutions in your bottles.
- For each bottle, calculate the ‘change in pH/hour.
- Plot a suitable graph or chart of your results.
What are the functions of roots in plants?
absorb water and dissolve the mineral ions from the soil
Buttress roots adaptation
help stop the tall trees falling over - provide support
What is the water absorbed by plant roots used for?
- Carrying dissolved mineral ions
- keeping cells rigid (otherwise the plants were wilt - the leaves and stems droop)
- cooling the leaves (when it evaporates from them)
- Photosynthesis
Function of root hair cells
- The ‘hairs’ are extensions of the cell that provide a large surface areas that water and mineral ions can be quickly absorbed
- ‘hairs’ also have been cell wall at the flow of waters that cells is not slowed down
What are the two pathways that water can take through a plant root?
- Water enters by osmosis through tiny tubes that join the cytoplasm of cells together allowing waters to diffuse
- water enters by diffusion - it diffuses through the cell walls
Why can mineral ions not diffuse into root hair cells?
As the concentration of ions inside the root hair cell is greater than the soil so they cannot diffuse against this concentration gradient so active transport is used instead
what transport is used to pump ions from the soil into the root hair cell?
active transport
how does water flow from the soil into the cytoplasm of a root cell?
Through osmosis as the cell membrane is a semipermeable
transpiration
Flow of water into a root, up the stem and out of the leaves
what’s the meaning for the evaporation of water from the leaves
to keep them cool and helps move water (and dissolved mineral ions) up the plant
what do xylem vessels form?
Tiny continuous pipes leading from a plants roots up into the leaves - inside the vessels is an unbroken chain of water, due to the weak forces of attraction between water molecules
how does the water move out of a leaf
- water vapour diffuses out of the leaf (water evaporates from the xylem inside the leaf)
- the concentration of water vapour in the air spaces inside a leaf is greater than outside of it -> water diffuses down the concentration gradient, out of the leaf
If the concentration difference is bigger what does this mean for the diffusion
bigger difference between concentrations makes the gradient steeper so diffusion is faster
what are factors that increase transpiration
- more wind - moves water molecules away from stomata - reducing the concentration of water molecules outside the stomata
- low humidity - little water vapour in the air - reducing the concentration of water molecules outside the stomata
- higher temp - particles move faster and so diffuse faster
- greater light intensity - make the stomata wider - more water vapour can evaporate
function of xylem cells
transport water upward from the roots to parts of the plants such as stems and leaves, also transports nutrients
function of phloem cells
moves food substances that the plant has produced by photosynthesis
how do xylem cells form an empty tube in the middle
during their development, xylem cells die and their top and bottom cell walls disintegrate
function of xylem cell adaptation (empty tube)
- lack of cell walls between cells allow water flow not to be slowed down
- no cytoplasm allows water to flow through easily
function of xylem cell adaptation (thick side walls and rings of lingnin)
this makes the cell rigid meaning water pressure inside the vessels does not burst or collapse them and it gives support
functions of sieve cell in phloem cells (holes in the end)
to translocate (transport) sucrose using the holes in the end of the cell wall which allows liquids to flow from one sieve cell to the next
function of phloem cell adaptation (large central channel)
no cytoplasm and no nucleus means more room for central channel for sucrose to flow
function of companion cells in phloem cells
actively pump sucrose into or out of the sieve cells that form the sieve tubes
what causes the sucrose solution to move in a leaf
as sucrose is pumped into sieve tubes, the increased pressure cause the sucrose solution to flow up to the growing shoots or down to storage organs
what can chloroplasts do to protect damage by very bright light
chloroplasts in a cell can move towards light or away from it to protect or enhance light
function of irregular spongy cells in plants
they do not fit together well and create air spaces allowing gases to diffuse easily
epidermis cells function
form the outer layers of a leaf holding the leaf together and protecting the cells inside
In winter, why does some broadly deciduous plants lose all their leaves?
To prevent water loss when soil water may be frozen
How are cacti adapted to living in dry environments?
- spines instead of leaves to minimise the surface area of the plant and protect the stem from herbivores
- Cacti stomata only opens at night - carbon dioxide is taken at night and stored fees during the day
stimulus
change in the environment that causes a response by an organism
tropism
Responding to stimulus by growing towards or away from it
phototropism
a tropism caused by light
positive tropism
a tropism towards the stimulus
negative tropism
the growth of a plant away from a stimulus
What do plants use to respond to a stimuli?
Plant hormones
auxin
Plant hormone that causes growth of a plant shoot/root towards the stimulus e.g. towards gravity/light
where are auxins produced in shoot
Produced in a tip of a shoot and move down the shoot
Process auxins in shoots
- auxins are produced at the very tip of the shoot and move down the shoot
- As auxins move downwards, they move to the shaded parts of the shoot
- The auxins cause cell elongation which causes the shoot to grow towards the light
gravitropism
The way plants grow in response to gravity
process of auxin in roots
auxins are pulled downwards by gravity and slows down cell elongation growth in the root and makes it grow downwards by moving to the lower side so the other side grows faster (grows down) and inhibit cell elongation -> it helps roots to anchor the plant in place and to reach moisture underground
gibberellins
- Help seeds to germinate and start to grow roots and shoots
- also be sprayed on some plants to make them produce bigger fruits
- Can cause some plants to produce fruit without being pollinated so gives us seedless fruits
ethene gas
Helps fruits to ripen
why is ethene used to ripen plants
Fruits that are not ripe are easier to transport than ripe fruits without damaging them and they can also be kept longer in cold storage without going off so ethene gas is used to ripen it so that fruit reaches the shops in ‘just ripened’ condition
Why do farmers use gibberellins to help seeds to germinate and start to grow
As some seeds need a period of darkness or cold before they can germinate but plant growers can use gibberellins to make the seeds germinate without this
photoperiodism
The response of an organism to the number of daylight hours in a day
In xylem cells, what helps to strengthen the cell walls
lignin
translocation
the movement of food in plants from the leaves to other parts of the plant
spongy mesophyll function
Contains many air spaces, which help with gas exchange throughout the leaf.
epidermis cell adaptation
they are transparent which allows light to pass through them easily and they also produce a waterproof waxy cuticle which helps to prevent the water loss - cuticle also helps to stop microorganisms and water entering the leaf
How can auxins be used as weed killers?
if large amount of auxins are added to plants, it can disrupt their growth process by overstimulating them - this can kill the plant
benefits of selective weed killers
they kill some plants but not all
dormancy
seeds are inactive and do not grow or develop
what is rooting powder and what does it contain
It is used to encourage plant growth and contains auxins to stimulate growth
