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B4 It’s a Green World
Biology Revision
Habitats
Plants need different amounts of light, water and minerals.
Factors such as soil pH, temperature, light intensity and the availability of water can be measured.
Samples are taken to get a picture of what the habitat is like
Measurements
Quadrats (identification keys; percentage growth)
Random (removes bias)
Transect (how species change across landscapes)
Light meters
Mark, capture and recapture
Trap animals and mark in a harmless wayRelease and then recaptureRecord animals with and without marks
number in 1st sample x number in 2nd sample number in 2nd sample with marks
Photosynthesis
Capturing energy from sunlight, used to make molecules for growth – sugars, starch, enzymes and chlorophyll.
These molecules feed others in the food chain
Equation
light6CO2 + 6H2O C6H12O6 + 6O2 chlorophyll Glucose is made up of CHO so is a carbohydratePhotosynthesis takes place in chloroplasts.
Contain chlorophyll which absorbs light and uses the energy to start photosynthesis
Energy from light splits water molecules into H2 and O2 atoms. The H2 is combined with CO2 from the air to make glucose. O2 is released as a waste product
Glucose and Starch
Glucose can be converted into starch for storage or cellulose to make new cell walls. Both are polymers of glucose
Glucose can also be built up into fats, proteins and chlorophyll
Glucose molecules are broken down by respiration, releasing energy to power chemical reactions in cells
Storage
Glucose made by photosynthesis
Glucose transported from leaves together cells where is stored until it is needed for respiration. Water would move to this area unless stored as starch
Insoluble starch grains
4a Who Planted that there?
Plants carry out photosynthesis in leaves:
Leaves are adapted 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.
Diffusion
Molecules of liquids and gases move around randomly, collide with each other and spread out.
They move from areas of high to low concentration
Passive processTo increase diffusion: Greater conc gradientShorter distanceLarger surface area
Osmosis
Special type of diffusionMove water molecules
in and out of cells across a partially permeable membrane
Water moves from area of high concentration to area of low concentration of water molecules
Drives uptake of waterLack of water - wilting
4b Water, water everywhere?
Effect of osmosis on plant cells:
Inelastic cell wall provides support & prevents cell bursting
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
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
4b Water, water everywhere?
Plants use water to: 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
Need Nitrogen!
Proteins are long chains of amino acids
Nitrogen needs to be combined with carbon, hydrogen and oxygen from glucose made in photosynthesis
Absorbed from soil as nitrate ions
Absorbed by root hair cells
What else do plants need?
Magnesium to make chlorophyll
Phosphates to make DNA
Proteins are needed to build cells and make enzymes, so nitrates are needed in the highest quantities
Fertilisers contain minerals such as phosphates and nitrates
4d Plants need minerals too
Minerals are absorbed by root hairs by active transport – using energy from respiration to move substances against concentration gradientMineral 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
Active Transport
Nitrate ions are at a higher concentration inside the root cells, compared to the surrounding soil
Diffusion should move ions out into soil.
Plants use active transport to overcome this
Cells use energy from respiration to transport molecules across the membrane
Yields
The amount of product a farmer has to sell
Limiting factors of photosynthesis – temperature, light intensity, carbon dioxide, water and chlorophyll
Stomata may close to conserve water, but stops carbon dioxide entering the leaf
4f Farming
Intensive Farming – to produce as much food as possible from the land, plants & animals available
Improves energy transfer efficiencyFarming Method Reduction of energy
transferProblems
Pesticides: herbicide, insecticide, fungicide
To competing plants & pests
Pesticides bioaccumulate in food chains or harm non target organisms
Fertilisers Eutrophication
Battery farming/fish farming
Limited movementTemperature control
Moral/ethical – poor quality of lifeSpread of disease
4f Farming
Alternatives to intensive farmingHydroponics – growing plants in solution without soil
Organic Farming – high quality produce whilst maintaining welfare of animals & minimising environmental impact
Advantages Disadvantages
Minerals added can be carefully controlled
Expensive addition of fertilisers
Reduced risk of disease Lack of support/anchorage
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 this2.Oxygen – needed for respiration3.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