B4: It

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B4 Its a Green World

• Plant Structure and adaptations
• Osmosis and plant support
• Transpiration and reducing water loss
• Plant Minerals
• Pyramids of number and biomass
• Farming
• Decay
• Carbon and Nitrogen Cycles

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for each topic. Then try the revision questions
and mark them yourself. Easy!
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B4a Plant Structure and Adaptations

• Leaves are made of the epidermis and waxy
  cuticle, palisade layer, spongy layer veins,
  stomata and guard cells
• Palisade cells have many chloroplasts for
  photosynthesis
• Guard cells surround the stomata (holes in the
  underside of the leaf) and can open or close them
  to let water out and gases in
• Leaves need water, carbon dioxide and light for
  photosynthesis

Adaptations for Photosynthesis include Broad
leaves large surface area for sun Thin leaves
for gas diffusion Chlorophyll pigment to absorb
sunlight Veins to transport sucrose and
water Stomata allow gases to diffuse (oxygen
and carbon dioxide both in and out) Epidermis
transparent skin on top of leaf allowing light
through Palisade layer for photosynthesis Air
spaces gas diffusion
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Test your knowledge of leaf structure- click the
mouse for the answers
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B4b Osmosis and Plant Support

• Diffusion is the random movement of particles
  from a high to low concentration
• Osmosis is the same as diffusion, except it only
  involves water
• Water will move from where there is lots of water
  molecules (a dilute solution) to a solution that
  is concentrated with salt (a concentrated
  solution) with less water in it.
• Water also travels through a semi (or partially)
  permeable membrane (a thin skin with tiny holes
  big enough for water)
• We say water moves down a concentration gradient
  from high to low

Animal cells have a concentrated cytoplasm with
many salts etc- when they are in pure water, the
water moves in and they burst (lysis) when put in
a really concentrated solution, water moves out
of the animal cell and it shrinks (crenated)
Plant cells have a concentrated cytoplasm with
many salts etc- when they are in pure water, the
water moves in but they dont burst as they have
a cell wall (turgid) When put in a really
concentrated solution, water moves out of the
plant cell and the cytoplasm shrinks (flaccid
then plasmolysed)
Plant cells rely on this turgor pressure to
keep them upright like an inflatable chair, if
you dont water them all their cells become
flaccid and the leaves go floppy- to absorb water
the roots have lots of tiny root hair cells to
give a bigger surface area
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Plants also have phloem tubes that carry sucrose
from the leaves all around the plant- this is
called translocation- phloem is alive
B4c Transport in Plants

• Water enters through roots and root hair cells
  by osmosis
• Water then moves into the xylem which are dead,
  long, narrow and join up end to end like a
  drainpipe, they are also made of lignin which
  supports the plant and stops water leaking out
• Next, the water moves up the xylem vessels and
  evaporate from the cells in the leaf into the air
  spaces, then diffuses out of the stomata at the
  bottom surface of the leaf-
• The whole movement of water up the plant and
  evaporating at the leaf is called transpiration
• A potometer (shown below) can be used to measure
  transpiration (water uptake)

Cacti cut down transpiration by having sunken
stomata and rolled leaves in dry places

• Transpiration can be speeded up by
• Hot days faster evaporation
• More light stomata are open more
• Air movement wind blows the water away so more
  evaporates (greater diffusion gradient)
• Low Humidity the drier the air, the faster
  evaporation

Stem
Root
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B4d Plants Need Minerals Too

• Plants need the following minerals
• Nitrate for proteins, growth and repair NO3-
• Phosphate for DNA and cell membranes
• Potassium for enzymes in photosynthesis
• Magnesium for chlorophyll

Fertilisers can be added to soil to help plants
grow better NPK fertilisers contain nitrogen,
phosphate and potassium Adding fertilisers can be
bad as it leads to eutrophication Framers can use
GPS to see where to apply fertiliser
Plants absorb minerals through their roots from a
low concentration in the soil to a high
concentration- this needs energy as it is against
the concentration gradient- this is called active
transport
nitrate poor growth and yellow leaves
phosphate poor root growth and discoloured
leaves potassium poor flower and fruit
growth and discoloured leaves magnesium
yellow leaves.
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B4e Energy Flow

• Food chains show the direction of energy flow
• The plant is always the producer as it produces
  food by photosynthesis
• All the other organisms are consumers, the first
  one in the chain is the primary consumer, then
  the secondary and tertiary

A pyramid of numbers show how many organisms
there are. They can be shaped strangely A pyramid
of biomass shows the amount of biomass (the
amount of living material)
Biomass (living material) is a renewable fuel It
can be burnt to heat water in electricity power
plants Fast growing trees are grown then
harvested by coppicing (cutting trees then
letting them re-grow) Coppicing is carbon
neutral- it doesnt add any extra carbon dioxide
into the environment
Number
Biomass
At every stage (trophic level) of the food chain
or pyramid, energy is lost, this is because the
animals use some energy to move around or
respire. Some is also lost through egestion (poo)
Biomass can be used to make biogas by putting
yeast and bacteria inside a digester where
fermentation takes place Bioethanol can also be
made by letting yeast ferment biomass- this can
be used for cars in developing countries
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B4f Farming
There are many problems after using chemicals on
fields Pesticides kill animals that you dont
want to kill and affects the food
chain Pesticides and herbicides can be harmful to
humans and make them ill if sprayed near homes,
or if they remain on fruit and vegetables Some
pesticides are persistent like DDT that can build
up in an animals body and cause death- we now use
biodegradable pesticides that can be broken down

• Intensive farming means getting the highest
  yield possible from your land by putting
  fertilisers etc onto crops
• Weedkillers or herbicides kill plants, selective
  weedkillers only kill certain plants and dont
  harm the others
• Pesticides kill pests
• fungicides kill fungus
• insecticides kill insects like
• aphids (greenfly)

Biological control using predators to kill
pests No harm to food chain, lasts for a long
time, and only one type of prey harmed - Pest not
completely gone, might not work, predator might
leave or become a pest itself
Crops in glasshouses Grower can control temperature, light and reduce the problem of pests and weeds
Hydroponics Same as glasshouses but grows plants without soil, plants grown in nutrient solution- can be grown in desert
Battery Farming Keeping animals in small spaces indoors so no energy is wasted- some people think its cruel
Fish Farming Fish kept in cages in lochs, food, pesticides and faeces can drop to bottom causing pollution
Organic Farming Use nitrogen fixing bacteria, crop rotation and weed by hand, but less crops so more expensive to buy
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B4g Decay

• Food can be preserved by
• canning - boiling to kill microbes then sealing
  in air tight can
• cooling/ freezing - slowing down the microbes
  chemical reactions
• drying deprives microbes of water so they
  cant grow
• Adding salt/ sugar water moves out of the
  microbes by osmosis
• adding vinegar to acid for microbes enzymes

• Biodegradable items are things that can decay
  like paper, bodies and poo
• Micro-organisms need water, oxygen and a
  suitable temperature for their enzymes in order
  to decay materials

Making compost requires food waste e.g. potato
peelings, air spaces, warm temperature and a
little water
Decomposers all organisms that cause
decay Detritivores big decomposers like worms
and woodlice- create a larger surface area for
smaller decomposers Saprophytes fungi that have
threads called hyphae, they secrete enzymes and
digest food

• It is important to treat sewage as
• it might contain pathogenic (disease causing)
  bacteria
• It contains food for bacteria to reproduce
• it contains chemicals which may harm other
  living things
• sewage is changed into sludge, methane and clean
  water called effluent that goes back into the sea

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B4h Recycling

• The Nitrogen Cycle
• Nitrogen goes into the atmosphere through
  denitrifying bacteria and lightning
• Nitrogen is removed from the atmosphere by
  nitrogen fixing bacteria and nitrifying bacteria-
  soil bacteria and fungi convert protein and urea
  to ammonia

• The Carbon Cycle
• carbon goes into the atmosphere through
  respiration, decomposers, detritivores, burning
  fossil fuels, volcanoes
• Carbon is removed from the atmosphere by
  photosynthesis by plants and phytoplankton,
  calcium carbonate shells from sea creatures
  forming limestone under the sea bed

Nitrogen fixing bacteria turn nitrogen gas into
nitrates e.g. rhizobium bacteria in root
nodules Nitrifying bacteria turn ammonia into
nitrates e.g. nitrobacter Denitrifying bacteria
turn nitrates into nitrogen gas
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