OCR Biology Module B4 IT’S A GREEN WORLD
B4a – Who planted that there?
Leaf – for photosynthesis
Leaf cells – efficient photosynthesis
Palisade cells
B4b Water, water everywhere
Osmosis
Osmosis
Partially permeable membrane
Support in plants
Plant wilting
Plasmolysed cells
Animal cells
Root hairs
Transpiration
Transpiration water
Leaf adaptations
Stomata control
B4c Transport in plants
Plant structure
Xylem
Phloem
Xylem vessels
Phloem vessels
Vascular bundles
Transpiration
Transpiration
Transpiration
Transpiration
rate
rate
rate
rate
–
–
–
–
light
temperature
air movement
humidity
broad so large surface area; thin so short distance for gases to travel; contain chlorophyll to absorb light;
have a network of veins for support and transport; stomata for gas exchange (by diffusion)
epidermis (transparent); palisade layer (at top – has most chloroplasts); spongy mesophyll (air spaces for
diffusion between stomata and photosynthesising cells); internal surface area / volume ratio very large
have many chloroplasts absorb light energy for photosynthesis
movement of water molecules from an area of high water concentration (dilute solution) to an area of low water
concentration (concentrated solution) across a partially-permeable membrane
special type of diffusion – result of the random movement of individual molecules
allows only certain things to diffuse through it (small molecules such as water)
inelastic cell wall and water pressure (turgor pressure) inside the cell; swollen, firm cell = turgid
lack of water causes lack of turgor pressure  flaccid cells
cytoplasm shrinks so much the membrane pulls away from the cell wall
no cell wall; cells absorb too much water  burst (lysis); loses too much water  shrivels (crenation)
increase surface area for roots to take up more water by osmosis
evaporation (diffusion) of water through stomata in leaves (to ‘pull’ water up from the roots)
for: cooling; photosynthesis; support; movement of minerals
water loss reduced by: waxy cuticle; small number of stomata on upper surface; smaller stomata
changes in guard cell turgidity (due to light intensity and availability of water) to regulate stomata opening
stem (support/transport); leaf (photosynthesis); flower (reproduction); root (water/mineral uptake; anchorage)
transpiration - movement of water and minerals from the roots to the shoot and leaves
phloem - translocation - movement of food substances (sugars) up/down stems to growing and storage issues
carry water; thick strengthened cellulose cell wall with a hollow lumen (dead cells)
carry sugar solution; columns of living cells
‘veins’ of xylem and phloem; roots (centre – resist pulling); stem (edge/tube – resist bending); leaf (network –
support thin tissue)
stomata open in light/day; brighter light  increase in transpiration rate
warmer particles have more energy  diffuse/evaporate faster; warmer  increase in transpiration rate
windier  sweeps away water molecules from leaf; windier  increase in transpiration rate
damper  higher concentration of water molecules around leaf; damper  decrease in transpiration rate
B4d Plants need minerals too
Fertilisers – provide
Nitrates (nitrogen)
Phosphates (phosphorus)
Potassium
Magnesium
Mineral deficiency
Nitrate
Phosphate
Potassium
Magnesium
Minerals in soil
Active transport
Active transport – needs
nitrates, phosphates, potassium, magnesium
for amino acids and proteins which are needed for cell growth
for respiration and growth; to make DNA and cell membranes
for enzymes (in photosynthesis and respiration)
to make chlorophyll for photosynthesis
cause poor plant growth
poor growth and yellow leaves
poor root growth and discoloured leaves
poor flower and fruit growth and discoloured leaves
yellow leaves
present in very low concentrations; concentrations lower than minerals inside plant root hair cells
can move substances from low concentrations to high concentrations (against the concentration gradient)
active transport uses energy from respiration; roots need air/oxygen from soil
B4e Energy Flow
Producer
Consumers
Trophic level
Pyramid of numbers
Pyramid of biomass
Energy flow
Efficiency
Efficiency calculation
Biomass – energy from
Biofuels
Biofuels – uses
green plants; produces food by photosynthesis; base of food chain/web/pyramid
animals; eat/need food
feeding level
bars show numbers of organisms at each feeding level; bottom bar is the producers
bars show the mass of living material at each stage; bottom bar (producers)
main energy source = Sun; energy lost at each energy level – respiration/heat/movement; droppings (egestion)
of energy transfer from one feeding level to the next; energy loss at each level limits length of food chain
efficiency= energy available to next level X 100 ÷ energy available to previous level
burning fast growing trees; fermenting biomass using bacteria or yeast
renewable; reduces air pollution; energy self-reliance
eating it; feeding it to livestock; using it as a fuel; growing the seeds
B4f Farming
Intensive farming
Intensive farming – efficiency
Energy transfer
Intensive farming – issues
Pesticides
Hydroponics
Hydroponics – advantages
Hydroponics – disadvantages
Organic farming
Organic farming – techniques
Organic farming – advantages
Organic farming – disadvantages
Biological control
Biological control – advantages
Biological control – disadvantages
methods to increase productivity: fish farming; glasshouses; hydroponics; battery farming
intensive food production improves efficiency of energy transfer by reducing energy transfer
competing plants; pests; heat from battery animals (kept penned indoors – warm and less movement)
intensive farming methods may be efficient but they raise ethical dilemmas e.g. use of pesticides
may enter and accumulate in food chains; may harm organisms which are not pests
plants grown without soil; glasshouse tomatoes; plant growth in areas of barren soil
better control of mineral levels; better control of disease
lack of support for plant; required addition of fertilisers
no artificial fertilisers; no herbicides; no pesticides
animal manure and compost; crop rotation; nitrogen-fixing crops; weeding; varying seed planting times
no chemicals; not harm wildlife; treatment of animals
needs more space; needs more labour; less intensive; lower yield
use of living organisms (predator/parasite/disease) to control a pest
specific (only pest affected); no chemical pollution; long lasting (predator reproduces so always present)
slower (time for control organism numbers to build); not kill all pest types; control organism can become pest
B4g Decay
Key factors
Factors affect
Decomposers
Saprophytes
Use of decomposers
Detritivores
Detritivores – effect
Food preservation techniques
Canning
Cooling – fridge
Freezing – freezer
Drying
Adding salt / sugar
Adding vinegar
presence of microorganisms; temperature; oxygen; water
microbial respiration; growth and reproduction of microorganisms
bacteria; fungi
feed on dead/decaying material by extracellular digestion (secrete digestive enzymes); bacteria/fungi
break down human waste (sewage); break down plant waste (compost)
feed on dead and decaying material (detritus): earthworms, maggots, woodlice
rate of decay by producing larger surface area
reduce the rate of decay: canning; cooling; freezing; drying; adding salt / sugar; adding vinegar
airtight can keeps decomposers/air out
slows respiration; slows reproduction; doesn’t kill cells
stops respiration; stops reproduction; freezing water in cells can kill some cells
stops respiration; stops reproduction
causes water loss by osmosis; damages/kills cells
acidic; stops enzymes working in cells
B4h Recycling
Carbon cycle
 plants
 feeding
 plants/animals
 bacteria/fungi
 fossil fuels
 in sea
 volcanic activity
Nitrogen in air
Nitrogen cycle

plants

feeding

decomposers

proteins

ammonia

nitrates

nitrogen-fixing
carbon is moved between the atmosphere, soil and living things
remove carbon dioxide from the air by photosynthesis
passes carbon compounds along a food chain or web
release carbon dioxide into the air, as a product of respiration
in soil act as decomposers, release carbon dioxide into the air by respiration
combustion (burning) releases carbon dioxide
marine organism make shells made of carbonates; shells become limestone;
carbon returns to air as carbon dioxide during volcanic eruption or weathering
78% of air is nitrogen; too unreactive to be used directly by animals and plants
importance of soil bacteria
take in nitrates from the soil to make protein for growth
passes nitrogen compounds along a food chain or web
nitrogen compounds in dead plants/animals – broken down into nitrates and returned to the soil
soil bacteria and fungi, acting as decomposers, convert proteins and urea into ammonia
nitrifying bacteria convert ammonia to nitrates
denitrifying bacteria convert nitrates to nitrogen gas
fixing of nitrogen gas by nitrogen-fixing bacteria living in root nodules or the soil or by the action of lightning