Transcript OCR_B4_biology

Biology Revision
B4 It’s a Green World
4a Who Planted that there?
 Plants carry out photosynthesis in
leaves:
 Leaves are adapted
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by:
Broad – large s.a.
Thin – short diffusion
distance
Chlorophyll – absorb light
Veins – support &
transport
Stomata – gas exchange
Transparent epidermis
Palisade contain most
chloroplasts
Air spaces in spongy
mesophyll
Large internal s.a.
4b Water, water everywhere?
 Osmosis – the net movement of water across a
partially permeable membrane from an area of high
water concentration to low as a consequence of
random movement of particles
 Effect of osmosis on animal cells:
Lysis
Crenation
4b Water, water everywhere?
 Effect of osmosis on plant cells:
 Inelastic cell wall provides support & prevents cell
bursting
4b Water, water everywhere?
 Plants use water to:
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Keep cool
Transport minerals
Photosynthesise
Keep cells firm & supported
 Water is:
 Absorbed through root hair cells (large s.a.)
 Transported through stem
 Lost by evaporation/transpiration from leaves
 Water loss reduced by:
 Waxy cuticle; small number of stomata on upper
surface; guard cells
4c Transport in Plants
 Transpiration – diffusion & evaporation of water from a
leaf
 Rate is effected by:
 Light – more light increases p/s & transpiration
 Temperature – hotter increases p/s & transpiration
 Air movement – air removes water vapour from around leaves,
maintaining diffusion gradient
 Humidity – high water vapour in air reduces diffusion gradient
Potometer
measures
rate
4c Transport in Plants
 Vascular bundles – arrangement of xylem & phloem
Xylem
Phloem
Transpiration
Translocation
Movement of water &
minerals
Movement of dissolved
sugar
From roots to leaves
From leaves to rest of plant
Vessels – thick cellulose
strengthened cell wall, dead
cells so hollow lumen
Vessels – column of living
cells
4d Plants need minerals too
 Minerals are absorbed by root hairs by active
transport – using energy from respiration to move
substances against concentration gradient
Mineral
Purpose
Deficiency
Nitrates
Amino acids/proteins for
growth
Poor growth, yellow
leaves
Phosphates
DNA & cell membranes,
respiration & growth
Poor root growth &
discoloured leaves
Potassium
Enzymes for respiration &
photosynthesis
Poor flower & fruit
growth, discoloured
leaves
Magnesium
Chlorophyll
Yellow leaves
4e Energy flow
 Food chain – shows transfer of energy
Producer – green plant
Consumer – organism
that eats another
organim
 Pyramid of numbers – the numbers
of organisms at each trophic level
4e Energy Flow
 Pyramid of biomass – the mass of living material
at each trophic level
 Always pyramid shaped
because of efficiency of
energy transfer i.e.
 Energy is lost as less useful
forms at each trophic level e.g. by heat from
respiration, egestion of undigested food, not all
organism being eaten
 Energy efficiency = energy converted to biomass X 100
total energy taken in
4e Energy Flow
 Biomass/Biofuels
 Fuels – wood, biogas from manure, alcohol from corn or
sugar cane, bioethanol
 Energy can be transferred by:
 Eating it
 Burning it
 Feeding to livestock
 Growing seeds to produce more biomass
 Advantages of biofuels
 Renewable, reduces air pollution, energy self-reliance
4f Farming
 Intensive Farming – to produce as much food as
possible from the land, plants & animals available
 Improves energy transfer efficiency
Farming Method
Reduction of energy
transfer
Problems
Pesticides: herbicide,
insecticide, fungicide
To competing plants & pests
Pesticides bioaccumulate
in food chains or harm
non target organisms
Fertilisers
Battery farming/fish
farming
Eutrophication
Limited movement
Temperature control
Moral/ethical – poor
quality of life
Spread of disease
4f Farming
 Alternatives to intensive farming
 Hydroponics – growing plants in solution without soil
Advantages
Disadvantages
Minerals added can be
carefully controlled
Expensive addition of
fertilisers
Reduced risk of disease
Lack of support/anchorage
 Organic Farming – high quality produce whilst maintaining
welfare of animals & minimising environmental impact
Advantages
Disadvantages
Food uncontaminated
Less efficient – crops lost
Limited soil erosion
Manure takes time to rot & doesn’t
provide specific balance of minerals
Biodiversity promoted
Biological control of pests difficult to
control & expensive
Animal welfare
4g Decay
 Breakdown of complex substances into simpler ones
 Detritivores – feed on dead organisms or waste
(detritus), form larger surface area – e.g. worms, woodlice,
maggots
 Decomposers – feed on waste left by detritivores
 Saprophytes – secrete enzymes on to material then
absorb digested products
4g Decay
 Rate effected by:
1. Temperature – microorganisms work best at 40°C,
but enzymes denatured above this
2. Oxygen – needed for respiration
3. Water – grow best in moist conditions
 Food Preservation
Method
Explanation
Canning
Sealed to remove oxygen & prevent entry of microbes
Cooling
Low temperatures slow growth
Drying
Reduces moisture needed for growth
Preserving (salt/sugar)
Conditions are too concentrated for survival
Pickling in vinegar
Low pH denatures enzymes in microbes
4h Recycling
 Decay recycles chemicals e.g. carbon & nitrogen
 Carbon cycle
0.04% CO2
in air
4h Recycling
 Nitrogen Cycle
78% N2 in air
N2 gas is too
unreactive to use
directly