GCSE Biology Revision
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Transcript of GCSE Biology Revision
BiologyBiologyJust an introduction or summery – whatever way you look at itI don’t know what is needed and not needed but it covers most things
ContentsContents
PLANT PROCESSESPLANT PROCESSES
Leaf structurePhotosynthesis
Limiting Factors
Uses of GlucosePlants and Water
Osmosis
Osmosis in Different CellsTranspirationPlant Growth and Fertilisers
Plant Senses and their Commercial Uses
Response to Water
Response to Gravity
Response to Light
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The Leaf StructureThe Leaf StructureBack to Contents
The LeafThe LeafBack to Contents
Leaves and Leaves and PhotosynthesisPhotosynthesis
A leaf has an upper and lower epidermis covered with a waxy cuticle
The spongy mesophyll and palisade cells contain chloroplasts
Guard cells surround the stomata Leaves are adapted for efficient photosynthesis by having
a large surface area, being thin and having veins Photosynthesis occurs mainly in the leaves Water enters the root hairs by osmosis Carbon dioxide enters and oxygen leaves by diffusion
through stomata The leaf is very efficient in photosynthesising because it
has a large internal surface area, internal air spaces and many chloroplasts in the palisade layer
There are three main limiting factors that affect the rate of photosynthesis. They are:◦ Light◦ Carbon dioxide◦ Temperature
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Limiting FactorsLimiting Factors
45°C
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Uses of GlucoseUses of GlucoseSome glucose is used in respiration to
obtain energyOther uses include converting it to:
◦ Insoluble starch stored in the roots, particularly in the winter. In this form it does not cause too much water to move into the cells by osmosis, as it doesn’t contribute to the concentration inside the cells
◦ Cellulose, needed for cell walls◦ Lipids and oils are formed from glucose
and stored in seeds◦ Glucose can also be combined with other
substances, such as nitrates obtained from the oil and turned into proteins
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Plants and WaterPlants and Water Plant cells are supported by their cell walls and turgor
pressure in the cell sap Water enters the root hairs by osmosis Osmosis is the movement of water from a high
concentration to a low concentration through semi-permeable membrane
A semi-permeable membrane only allows the movement of small molecules
Water moves both in and out of the root to try to even the concentrations. Therefore we use the net movement of water
Osmosis is a type of diffusion A plant must balance its water uptake and water loss Water is needed for photosynthesis, cooling and
transport A leaf is adapted to reduce water loss Leaves lose water because a leaf is adapted for
photosynthesis
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OsmosisOsmosis Root hairs take in water by
osmosis Water moves along the cells
of the root and up the xylem to the leaf
All the time the water is moving to areas of lower water concentration
Osmosis makes plant cells swell up
The water moves into the plant cell vacuole and pushes against the cell wall making it turgid
It is useful as it gives the stem support
When there is little water the cells become flaccid as water has moved out of the cell
If a lot of water leaves the cell, the cytoplasm started to peel away from the cell wall which is called plasmolysis
The cell will behave differently in an animal cell because there is no cell wall to prevent the cell from bursting (haemolysis)
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Osmosis in Different Osmosis in Different CellsCells
In a
Pla
nt
In a
n A
nim
al
NormalToo Much Water Too Little Water
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TranspirationTranspiration Water loss from a plant is called transpiration The water evaporates and exits the leaves by diffusion Water travels from the roots, through the stem to the leaves in
xylem cells Dissolved food travels downwards in phloem cells The rate of transpiration is speeded up by a higher
temperature, more wind, a low humidity and more light More light will increase the transpiration rate because the
stomata will be open A higher temperature will increase the transpiration rate by
increasing the diffusion rate A low humidity will allow more water vapour to diffuse out of
the leaves Xylem cells are dead because they have extra lignin
thickening The flow of water up the xylem to the leaves is called the
transpiration stream The transpiration stream also draws minerals into the plant as
well as water As water is lost, the transpiration stream replaces it so there is
a constant flow
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Fertilisers and Plant Fertilisers and Plant GrowthGrowth Plants need minerals in fertilisers such as nitrates,
phosphates, potassium and magnesium compounds Minerals are needed only in small quantities Nitrates are needed to make proteins for growth Phosphates are needed for root growth Potassium is needed for flower formation Magnesium is needed to make chlorophyll If minerals are missing from the soil water, the plant
shows that it is mineral-deficient Minerals are taken up from the soil water by active
transport Minerals are taken up against a concentration
gradient Active transport uses energy An NPK fertiliser contains nitrogen (N), phosphorus
(P) and potassium (K)
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Plant Senses and Commercial Plant Senses and Commercial UsesUses
Plant Senses Commercial Uses
Plants respond to their surroundings to give them a better chance of survival
Plant responses are called tropisms and are controlled by a hormone
Plants respond to light, gravity and water
Remember: unequal distribution of auxin speeds up growth in shoots and slows down growth in roots
1. Growing Cuttings◦ Rooting powder contains synthetic
auxins◦ A cutting is taken from a plant and
dipped in this powder. This stimulates the roots to grow quickly and enables gardeners to grow lots of exact copies of a particular plant
2. Killing Weeds◦ Synthetic auxins are used as
selective weed-killers◦ They only affect the broad-leaved
weeds; narrow-leaved grasses and cereals are not affected
◦ They kill the weed by making the weed grow to quickly
3. Seedless Fruits◦ Synthetic auxins are sprayed on
unpollinated flowers◦ Fruits form without fertilisation and
thus form without pips
4. Early Ripening◦ Plant hormones can also be used to
ripen fruit in transport
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Responses to Water and Responses to Water and GravityGravity
Response to Water Response to Gravity
A plant’s response to water is called hydrotropism
Roots always grow to a certain extent towards water, even if it means ignoring the pull of gravity and growing sideways
An uneven amount of moisture will cause more auxin to appear on the side with more water
This inhibits the growth of cells on this side
The root cells on the outside will grow quicker and will bend towards the moisture
A plant’s response to gravity is called geotropism
Even if you plant a seed the wrong way up, the shoot always grows up, away from gravity and the root grows down towards gravity
If a plant is put on its side, auxin gathers on the lower half of the shoot and root
Auxin slows down the growth of root cells, so the root curves downwards
Auxin speeds up the growth of the shoot cells so the shoot curves up
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Response to LightResponse to LightA plant’s response to light is called phototropismPlants need light for photosynthesis and thus grow
towards the lightNormally light shines from above. Auxin is spread
evenly and the shoot grows upwards If light comes from one side, auxin accumulates
down the shaded side. Auxin makes these cells grow faster
The result is that the shoot bends towards the light
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BIOMASS, FARMING BIOMASS, FARMING AND DECAYAND DECAY
BiomassPyramid of Numbers
Pyramid of BiomassIntensive Farming and Organic Farming
Pesticides
Fertilisers
EutrophicationDecay and Food PreservationRecycling of CarbonRecycling of Nitrogen
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BiomassBiomass Energy enters food chains in photosynthesis Plants are producers because they produce food Animals are consumers A pyramid of numbers show the number of
organisms in each link (trophic level) in a food chain
A pyramid of biomass shows the mass of living material in each link (trophic level) in a food chain
Energy is transferred along a food chain or food web
Some energy is transferred into less useful forms such as hear or body waste
Biomass fuels are wood (by burning), alcohol (by fermentation) and biogas (from decay)
Biomass fuels are renewable, produce less pollution and are energy self-reliant
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Pyramids of NumbersPyramids of NumbersA pyramid of numbers tells us how
many organisms are involved at each stage in the food chain
At each trophic level the number of organisms get less
However, sometimes a pyramid of numbers doesn’t look like a pyramid at all because it doesn’t take into account the size of the organisms◦E.g. There are many fleas on a single fox
which would make the pyramid ‘top heavy’
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Pyramids of BiomassPyramids of BiomassA biomass pyramid takes into
account the size of an organism at each level unlike the pyramid of numbers
It looks at the mass of the organismYou can take the information from
the pyramid of numbers and multiply it by the organism’s mass which will achieve the pyramid shape again
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Intensive and Organic Intensive and Organic FarmingFarming Intensive farming uses pesticides (insecticide and
fungicide) to kill pests and herbicides to kill weeds Intensive farming produces more food but also
causes problems such as pesticides accumulation in food chains
Fish farming, glasshouses, hydroponics and battery farming are all examples of intensive farming
Organic farming does not use artificial fertilisers, herbicides or pesticides
Organic farming uses animal manure, crop rotation, hand-weeding and biological control of pests
Intensive farming improves the efficiency of energy transfer in food chains
Hydroponics gives better control of fertilisers and diseases
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Intensive FarmingIntensive Farming
Intensive farming can produce more food because it is designed to provide more food for the given land
Many people regard intensive farming of animals as cruel
In order to produce more food from the land, fertilisers and pesticides are needed
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PesticidesPesticidesPesticides are used to kill insects
that damage cropsThey also kill harmless insects, then
insect-eating birds have a shortage of food
The pesticides can get washed into rivers and lake which can then get into our food chains
This was the case in the 60s when a pesticide, DDT, got into the food chain and threatened populations of animals
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FertilisersFertilisersPlants need nutrients from the soil
to growArtificial fertilisers are used to
replace the nutrients in the soil because there isn’t enough because of intensive farming
Fertilisers enable farmers to crop more crops in a smaller space.
Less countryside will be lost for farming but eutrophication is caused because of fertilisers
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EutrophicationEutrophication If too much fertiliser is used and it rains, it
goes into rivers and lakesThe water plants grow quicker as a result
of this and they quickly cover the surface of the water
There is then more competition for light and some plants die
Microbes break down the dead plants and use the oxygen for respiration
The amount of oxygen in the water is then reduced and animals die through suffocation
Untreated sewage can also cause eutrophication
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Organic FarmingOrganic FarmingPeople need to limit their needsIntensive farming produces quality food
and enough to supply people’s needs in Europe but has its problems – alternative is organic farming
Organic farming produces less food per area of land but is kinder to the environment
Organic farming uses manure as a fertiliser and has land for wild plants and animals to flourish.
Biological control of pests are also used where animals eat the pests, it’s not as effective but it isn’t harmful
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Decay and Food Decay and Food PreservationPreservation Decomposers such as fungi and bacteria cause
decay Decay breaks down sewage and compost Decay is affected by temperature and the
amount of oxygen and water Detritivores are animals that feed on dead and
decaying material Earthworms, maggots and woodlice are
Detritivores Saprophytes are plants that live on dead and
decaying material Food can be preserved by stopping or reducing
decay Food preservation methods include canning,
freezing, drying and adding salt, sugar or vinegar
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Recycling of Nitrogen and Recycling of Nitrogen and CarbonCarbon When plants and animals die, their chemicals, such as
nitrogen and carbon, are recycled Plants remove carbon fro the air by photosynthesis Respiration and the burning of fossil fuels releases carbon
in the form of carbon dioxide Carbon is recycled through marine shells, limestone and
eventual weathering There is 78% nitrogen in the atmosphere but it is
unreactive Plants take in nitrogen as nitrates Dead bodies decay, releasing nitrates Decomposers convert proteins and urea into ammonia Ammonia is converted into nitrates by nitrifying bacteria Some nitrates are converted into nitrogen by denitrifying
bacteria Nitrogen-fixing bacteria in the soil and root nodules fix
atmospheric nitrogen (This is further explained on the next few slides...)
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THE CARBON THE CARBON CYCLECYCLE
Feeding
Decomposers
Death but no decay
Death and Decay
Photosynthesis
Burning and Combustion
Respiration
The atmosphere
Fossil Fuels
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THE CARBON CYCLE IN THE CARBON CYCLE IN DETAILDETAIL
Added Notes:Decomposition
•Decomposers are bacteria and fungi which break down dead material•They help recycle carbon into the atmosphere and recycle nutrients into the soil•Plants use this nutrients dissolved in water during photosynthesis.•Animals eat plants, and both animals and plants die, making the cycle start from the beginning again•Decomposition happens everywhere in nature, in compost heaps and even sewage works•The perfect conditions are:
• Warm• Moist• Plenty of oxygen
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THE NITROGEN CYCLETHE NITROGEN CYCLE
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THE NITROGEN CYCLETHE NITROGEN CYCLEBack to Contents
THE NITROGEN CYCLETHE NITROGEN CYCLEADDED NOTESADDED NOTES
•The atmosphere contains 78% nitrogen gas•Nitrogen is needed to make protein•Plants and animals cannot use nitrogen as a gas – it has to be converted into nitrates•Animals get protein by eating plants which plants make from nitrates•It is a continuous cycle•There are four ways that nitrogen is converted into nitrates and only two ways that nitrogen is taken out of the soil•There are three different types of bacteria involved in this cycle:
• Nitrifying bacteria• Nitrogen-fixing bacteria• Denitrifying bacteria
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Key/ Scientific WordsKey/ Scientific Words
PhotosynthesisRespirationCombustionCarbonFossil fuelsDecomposers/
decompositionNutrientsWarmthMoistureOxygen
LighteningNitratesNitrogenNitrogen-fixing bacteriaRoot nodulesProteinDetritivoresDecomposersNitrifying bacteriaLeachingDenitrifying bacteria
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More Key/ Scientific More Key/ Scientific Words...Words...
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