biology - plant structures & their functions (6.1 - 6.17)

biomass

materials in an organism

6.1 photosynthetic organisms

produce their own biomass - main producers of food & biomass

6.2 photosynthesis in plants & algae

endothermic reaction - energy enters from surroundings, products have more energy than reactants

carbon dioxide + water —energy transferred by light→ glucose + oxygen

6.3 temp. effect as limiting factor on rate of photosynthesis

temp. increases = rate of photosynthesis increases

reactions in photosynthesis catalysed by enzymes - work better at warmer temps.

6.3 light intensity effect as limiting factor on rate of photosynthesis

light intensity increases = rate of photosynthesis increases

light needed for reaction

6.3 CO₂ conc. effect as limiting factor on rate of photosynthesis

CO₂ conc. increases = rate of photosynthesis increases

CO₂ needed for reaction

limiting factor

factor that prevents rate increasing

6.4 interactions of temp., light intensity & CO₂ conc. in limiting rate of photosynthesis

changing supply of limiting factor changes rate of photosynthesis

in graph:

• lower line levels off - temp. is limiting factor

• increase temp. - higher rates of photosynthesis (upper line)

6.5 core practical: investigate effect of light intensity on rate of photosynthesis

1. choose diff. distances between algae & lamp to use

2. need one clear glass bottle for each distance & one extra bottle

3. add 20 algal balls to each bottle

4. add same amount of indicator solution to each bottle & put bottle caps on

5. compare colour in bottle with pH range (from range of bottles showing colours of indicator at diff. pHs) to find pH at start

6. place tank of water between lamp & area you will place bottles

7. cover one bottle in foil

8. measure diff. distances from lamp & place bottles at those distances

9. place bottle in foil next to bottle closest to lamp

10. turn on lamp & wait until you can see obvious changes in colours in bottles

11. compare colours of bottles with pH range bottles & record pHs of solutions in bottles

12. for each bottle, calculate: change in pH/hour

13. plot suitable graph/chart of results

6.6 how is rate of photosynthesis is directly proportional to light intensity?

straight line = linear relationship between 2 variables

line goes through origin = 2 variables in direct proportion

rate of photosynthesis directly proportional to light intensity until limiting factor starts to effect

6.6 how is rate of photosynthesis is inversely proportional to distance from light source? (inverse square law)

l_new inversely proportional to d²_new

double distance from light source: light intensity = 1/2² = 1/4 times og.

halve distance from light source: light intensity = 1/1/2² = 1/1/4 = 4 times og.

6.7 how is structure of root hair cells adapted to absorb water & mineral ions?

outer surfaces of roots covered with root hair cells

hairs have:

• large surface area - water & mineral ions absorbed quickly

• thin cell walls - flow over water into cells not slowed down

6.8 how is structure of xylem adapted to its function?

lignified dead cells in xylem transport water & minerals through plant

thick side walls & rings of hard lignin form rigid tubes - won’t burst/collapse from water pressure, provide support

dead cells have no cytoplasm - form empty tube for water to flow through

tiny pores - allow water & mineral ions to enter & leave xylem vessels

no cell walls between cells - water flow not slowed down

6.8 how is structure of phloem adapted to its function?

living cells in phloem use energy to transport sucrose around plant

holes in ends of cell walls - liquids flow from one sieve to next

pore - sucrose solution pumped through

very small amount of cytoplasm (& no nucleus) - more room for central channel

6.9 how are water & mineral ions transported through plant by transpiration (xylem vessels)?

xylem vessels form tiny continuous pipes - roots → leaves

inside vessels - unbroken chain of water (weak forces of attraction between water molecules)

water evaporates from xylem vessels in leaf - water pulled up xylem vessels

water vapour diffuses out leaf - more water evaporates from xylem in leaf

6.9 stomata structure & function

stoma/stomata: microscopic pore on leaves

let CO₂ diffuse into leaf

opened & closed by specialised guard cells (light sensitive)

when light/lots water:

• don’t need to conserve water

• guard cells turgid (osmosis - water flows in)

• stoma open

• CO₂ diffuses in for photosynthesis

when night/little water:

• need to conserve water

• guard cells flaccid (osmosis - water flows out)

• stoma closed

• conserves water vapour

• no photosynthesis at night - no CO₂ needed

transpiration definition

flow of water into root → up stem → out leaves

6.10 how is sucrose transported around plant by translocation?

sucrose translocated in holes in sieve tubes of phloem

large central channel in each sieve cell connected to next sieve cell by holes

companion cells actively pump sucrose into/out of sieve cells that form sieve tubes

sucrose pumped into sieve tubes → increased pressure → sucrose solution flows up to growing shoots/down to storage organs

where does sucrose come from?

made from glucose & starch made by photosynthesis

translocation definition

transport of sucrose in phloem

6.11 how is structure of leaf adapted for photosynthesis?

large surface area - maximise light absorption

chlorophyll - traps energy transferred by light

chloroplasts move towards/away from light - protection from damage by very bright light

network of xylem vessels - provides water for photosynthesis

epidermis cells (outer layer of leaf) are transparent - light passes through easily

6.11 how is structure of leaf adapted for gas exchange?

stomata - lets CO₂ for photosynthesis diffuse into leaf through it

thin - short diffusion distance for CO₂ before reaching photosynthesising cells

irregularly shaped spongy cells - don’t fit together well, create air spaces → gases diffuse easily

6.12 effect of light intensity on water uptake by plant

greater light intensity → stomata wider → faster diffusion of water → more water pulled up plant

6.12 effect of air movement on water uptake by plant - wind, humidity

water molecules diffuse down concentration gradient out of leaf - water vapour conc. in air spaces in leaf > outside

bigger difference between concs. = steeper gradient → faster diffusion

wind - windy → moves water molecules away from stomata → faster diffusion

humidity - low humidity → less water vapour in air → faster diffusion

6.12 effect of temp. on water uptake by plant

higher temp. → particles move faster → diffuse faster

6.13 rate calculations for transpiration

distance moved by bubble/time taken

e.g. mm/min

6.14 plants adapted to survive in extreme environments - leaf size & shape

broad-leaved deciduous plants lose leaves in winter - prevents water loss when soil frozen

conifers have needle-shaped leaves - smaller surface area, very thick cuticle, less wind resistance, collect less snow

6.14 plants adapted to survive in extreme environments - cuticle

waxy & waterproof

helps prevent water loss

helps stop microorganisms & water entering leaf

6.14 plants adapted to survive in extreme environments - stomata

reduce water loss - trap water vapour close to leaves → slows rate of diffusion out of leaves

conifers have stomata in small pits - water vapour collects (less exposed to air movement)

(other plants - tiny hairs trap water vapour)

epidermis cells

hold leaf together, protect cells inside, produce waterproof waxy cuticle

(outer layers of leaf)

stimulus

change in environment that causes response by organism

tropism - positive & negative

respond to stimulus - grow towards/away from it

positive - tropism towards stimulus

negative - tropism away from stimulus

phototropism definition

tropism caused by light

gravitropism definition

tropism caused by gravity

6.15 how do auxins control & coordinate plant growth & development - phototropism?

shoots - positively phototrophic; roots - negatively phototrophic

auxins cause positive phototropism

how auxins work:

• produced in tip of shoot

• cause cell elongation

• shoot grown with light only from one direction

• auxins move to shaded side of shoot

• cells on shaded side elongate more

• shoot grows towards light

6.15 how do auxins control & coordinate plant growth & development - gravitropism?

auxins cause positive gravitropism

helps roots anchor plant in place & reach moisture underground

how auxins work:

• found in root tips

• have opposite effects to in shoots

• inhibit cell elongation

• pulled downwards by gravity

• cells stop elongating

• root grows down

6.16 commercial uses of auxins in plants

make some plants grow uncontrollably - can kill them

selective weedkillers (artificial auxins):

• kill plants with broad not narrow leaves

• farmers can kill weeds in wheat field without affecting crop

rooting powders:

• make plant cuttings develop roots quickly

• lots of identical plants produced quickly using cuttings (vs seed)

6.16 commercial uses of gibberellins in plants

naturally released inside seed - start germination

germination:

• some seeds need darkness/cold before germination

• make plants germinate without this

fruit & flower formation:

• photoperiodism: organism’s response to number of daylight hours in day

• some plants use this to flower at certain time - e.g. suitable pollinators around, not too cold

• flower growers override photoperiodism

producing seedless fruit:

• many plants only produce seeds after pollination

• make some plants produce fruit without this

can produce bigger fruits

6.16 commercial uses of ethene in plants

fruit ripening

• unripe fruits (vs ripe) - easier to transport without damaging, kept longer in cold storage without going off

• pick unripe fruit & ripen it when needed with ethene gas