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