# Biology B4 - it's a green world

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## Estimating Population Sizes

• POPULATION is all the organisms of one species in a habitat.
• COMMUNITY is populations of different species in a habitat
• There are different types of sampling methods such as...
• A Quadrat is a square frame (1m x 1m) used to study a small area. You can use it to estimate the population of a large area.
• Count all organsims in the quadrat then multipy it by the total area of the habitat.
• You can estimate poulation size using the capture-recapture method.
• Capture a sample of the population, mark the animals then release them.After a certain time recapture another sample of the population and count how many of this sample are marked.
• Then use this equation to estimate the population size:
• Population size = ( no. in first sample x no. in second sample) / ( no. in second sample previously marked).
• Sample size affects the accuracy of the estimate.
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## Ecosystems and Distribution

• An ECOSYSTEM is all the organisms living in a paticular area, as well as all the non-living (abiotics) conditions.
• Ecosystems are self-supporting.
• DISTRIBUTION is where organisms are found within a particular area.
• You can investigate distribution using lines called transects.
• To do a transect you mark out a line and place quadrats next to each other along the line. You can then count and record the organisms in the quadrats.
• You can plot results on kite diagrams.
• The abundance of each organism is shown by the thickness of the shape.
• The x-axis shows the distance along the transect line.
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## Zonation

• Abiotic factors are all the non-living and physical factors in an environment.
• They affect the distribution of organisms because...
• Organisms are adpated to live in certain conditions so are more likely to survive and reproduce in areas with these conditons.
• Many organisms can only survive in conditons their adapted to.
• ZONATION is the gradual change in distribution of species across a habitat e.g.
• In a costal habitat salinity and soil depth result in zones where different types of plants grow.
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## Biodiversity

• BIODIVERSITY is a measure of the variety of life in an area.
• Biodiversity includes...
• The variation between individuals of the same species in an area.
• The number of different species in an area.
• The number of different habitats within an area.
• Natural Ecosystems have a higher biodiversity than artificial ones.
• Native woodlands have a higher biodiversity than forestry plantations.
• Lakes have a higher biodiversity than fish farms.
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## Photosynthesis

• Photosynthesis takes place in chloroplasts in plant cells they contain pigments like chloropyll that absorb light energy.
• Carbon dioxide + water ----> glucose + oxygen
• 6CO2 + 6H2O ----> C6H12O6 +6O2
• Glucoseis converted into other substances fo different processes
• Resperation - releases energy so thee plant can convert the rest of the glucose into useful substances.
• Glucose is converted into cellulose to make cell walls.
• Glucose is turned into lipids (fats and oils) for storing in seeds.
• Glucose is turned into starch to be stored for when photosythesis isn't happening. Starch is insoluble which makes it good for storing because it can't dissolve and move away and it doesn't affect water conecentration.
• Glucose is combined with nitrates to make amino acids which are then used to make proteins. These are then used for growth and repair.
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## Photosynthesis +

• Greek scientists concluded that plants gain mass by taking in minerals from soil.
• In 1648 Jan Van Helmont said that plants gain mass by taking in water.
• In the 1770s Joseph Priestly showed that plants produce oxygen by placing a plant and a candle in a sealed container. The oxygen from the plant kept the candle alight.
• In photosynthesis oxygen comes from water in the plant.
• There are three limiting factors that control the rate of photosynthesis:
• Light provides the energy needed for photosythesis. If the light energy is increased the rate of photosynthesis increases howver only up to a certain point because then other factors will limit the rate.
• Too little carbon dioxide slows down the rate of photosynthesis but like light only up to a certain point.
• Temperature affects the rate, if it's increased the rate of photosynthesis, however at 45*C the plants enzymes become denatured.
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## Diffusion

• DIFFUSION is the net movement of particles from an area of higher concentration to lower concentration.
• Diffusion happens in liquids and gases.
• Cell membranes let small molecules in and out of the plant.
• The rate of diffusion depends on three things..
• Distance - substances diffuse quicker if they haven't got far to move.
• Concentration gradient - substances diffuse qicker if there is a large concentration difference.
• Surface area - the more surface area there is available for molecules to move across the faster they can get from side to side.
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## Leaves and Photosynthesis

• Leaves are adapted for diffusion...
• They're broad so that there's a large surface area for gases to diffuse.
• They're thin so that gases only have to diffuse a short distance.
• The lower surface of the leaf is full of holes called stomata which let gases in and out. They have guard cells surrounding them to control when the stoma open and close.
• There are air spaces in the spongy mesophyll layer to allow gases to move between the stomata and the photosythesising cells.
• Leaves are adapted to absorb light...
• They're broad which means there's a large surface area exposed to light.
• They contain lots of chloroplasts which contain chlorophyll to absorb light energy.
• Different pigments absorb different wavelengths of light so the plant can make the most of the Sun's energy.
• The cells containing the most chloroplasts are arranged in the pallisade layer at the top of the leaf where they can get the most light. The upper epidermis layer is transparent to let light pass through to the pallisade layer.
• Leaves have vascular bundles whcih contain transport vessels, xylem and phloem.
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## Osmosis

• Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration.
• A partially permeable membrane has small holes that molecules such as water can pass through but larger molecules e.g. sucrose can't pass through.
• The water molecules can pass both ways through the membrane during osmosis.
• However because there are more water molecules on one side than on the other there's a steady net flow of water into the region with fewer water molecules. This means the concentrated solution gets more dilute.
• Osmosis is a type of diffusion - net movement of particles from an area of high concentration to one of low concentration.
• Turgor pressure is when the water in a cell pushes against the cell wall, this gives support.
• If a cell doesn't have enough water it becomes flaccid and if it becomes vey short of water the cytoplasm starts to shrink and pull away from the cell wall. It is now plasmolysed.
• Changes in water amounts don't affect plant cells to much because they have a cell wall however if an animal cell has to much water it can burst, this is called lysis. If an animal cell loses to much water it is known as crenation.
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## Transport Systems in Plants

• Plants have two transport systems xylem and phloem. They are both contious and they go to every part of the plant but are seperate.
• Phloem tubes transport food...
• They are made up of columns of living cells with perforated end-plates which allow substances to flow through.
• They transport food, mainly sugars, up and down the stem to growing and storage tissues.
• This is known as translocation.
• Xylem vessels take water up...
• They are made of dead cells joined end to end, they have no end walls and have a lumen down the middle.
• They have thick side walls mde of cellulose that support the plant.
• They carry water and minerals from the roots up the shoot to the transpiration stream.
• The xylem and phloem run alongside each other in vascular bundles. They are found in roots, stems and leaves.
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## Water Flow Through Plants

• The cells on plant roots grow into long hairs, each root will have millions of these hairs.
• This gives the plant a big surface area for absorbing water from the soil.  If there's a higher concentration of water in the soil water is drawn into the root hair cells through osmosis.
• Transpiration is the loss of water from the plant, it is caused by evaporation and diffusion of water vapour from inside the leaves.
• This creates a shortage of water in the leaf so the xylem vessels bring more water to the leaves through the roots. This creates a constant transpiration stream of water entering the plant and exiting the plant.
• This is a side effect of the way leaves are adapted for photosynthesis. They have stomata which alows gases to be exchanged easily but this also means that water escapes from the leaves through the stomata.
• Transpiration has some benifits: it keeps the plant cool, provides a constant suppy of water, creates turgor pressure which supports the plant and minerals from the soil that the plant needs are brought in with the water.
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## Water Flow Through Plants +

• Transpiration rate is affected by four main things...
• Light intensity - the brighter the light the faster transpiration is because when it's dark stomata close because photosynthesis can't happen. This means water can't escape.
• Temperature - the higher the temeperature the greater the rate of transpiration because the water particles have more energy to evaporate and diffuse out the stomata.
• Air movement - if there's lots of wind around a leaf transpiration increases becasue water vapour is blown away from the leaf. Therefore there is a low concentration of water particles outside the leaf so diffusion happens quickly.
• Humidity - if the area around the leaf is dry then transpiration rate increases because there will be a lower concentration of water outside the leaf so diffusion happens quickly.
• Plants are adapted to reduce water loss in several ways...
• They have a waxy cuticle covering the upper epidermis making it waterproof.
• Stomata are on the lower surface where it's dark and cool this reduces diffusion. Plants in hot areas have no stomata on the upper epidermis and only a few on the lower layer. Stomata open and close automatically when water supplies dry up.
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## Minerals Needed for Healthy Growth

• Nitrates contain nitrogen that make amino acids and proteins that're needed for cell growth. If a plant doesn't get enough nitrates its leaves will be yellow and it'll have poor growth.
• Phosphates are needed for resperation and growth, they contain phosphorus, this makes DNA and cell membranes. Without phosphate plants have poor root growth and discoloured leaves.
• Potassium helps enzymes that are needed for photosynthesis and resperation. If the plant doesn't have enough potassium the it will have poor flower and fruit growth and discoloured leaves.
• Magnesium is also needed but in smaller amounts than the other three elements.
• It makes chlorophyll, if a plant doesn't have enough magnesium it will have yellow leaves.
• Root hair cells take in minerals using active transport.
• The concentration of minerals in the soil is usually low but higher in the root hair cell. Therfore normal diffusion doesn't work so a different process called active transport happens. Energy from resperation pulls minerals into the root against the concentration gradient.
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## Decay

• Decomposition is done by microrganisms like soil bacteria and fungi.
• The rate of decay depends on three main things.
• Temperature - warm conditions speeds up resperation in the microorgaisms.
• Water - microorganisms need water to decay.
• Oxygen - microorganisms respire areobically which provides more energy.
• There are two types of organisms that're important in decay, detritivores and saprophytes.
• Detritivores (earthworms, woodlice) feed on decaying materials and break them up into smaller pieces which gives a smaller surface area for other decomposers to work on.
• Saprophytes (fungi) feed on decaying material by extracellular digestion (secreating digestive enzymes on to the material outiside their cells).
• The enzymes break down materials into smaller bits which are then abosorbed.
• Preservation methods such as, canning, cooling, freezing, drying, adding salt/sugar and adding vinegar help to preserve food.
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## Intensive Farming

• Intensive farming is trying to get the most out of your land, animals and plants by...
• Using herbicides to kill weeds and using pesticides to kill insects,
• Battery farming animals. this is where animals are kept close together indoors in small pens  so they're warm and can't move about. This saves wasting energy.
• Hydrophonics is where plants are grown in nutrient solutions.
• It is often used to grow glasshouse tomatoes and plants in areas with poor soil.
• Advantages - mineral levels and diseases can be controlled.
• Disadvantages - lots of fertilisers need to be added and there's no soil to anchor the roots and support the plants.
• Intensive farming can destroy the environment.
• Removal of hedges destroyes habitats and can lead to soil erosion.
• Eutrophication can occur this is where fertilisers get into rivers.
• Pesticides can disturb food chains.
• Intensive farming is cruel and the animals suffer.
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## Pesticides and Biological Control

• Pesticides are used to kill creatures that damage crops but sometimes they kill other animals such as bees and ladybirds.
• This can cause a shortage of food further up the food chain.
• Sometimes pests aren't killed by the pesticide therefore the pestiide is passed up the food chain. The toxicity then builds up throughout the food chain causing problems fro the animals at the top.
• Biological control is used instead of pesticides, it's where a living thing controls pests. Eg...
• People release ladybirds into their fields to eat aphids that eat roses and vegatables.
• Some wasps and flies produce larvae which develop on or in a host insect and kill them, lots of pests have parasites like this.
• In Australia the myxoma virus was released to kill rabbits that were ruining crops.
• Advantages - no chemicals are used which means there's less polution, less disruption to food chains and less harm to humans. The process doesn't need to be repeated.
• Disadvantages - the predator might not eat the pest, it could eat useful species, it's population might increse and it might not stay in the right area.
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## Alternatives to Intensive Farming

• Intensive farming produces lots of food but organic methods are still effective.
• Using organic fertilisers such as manure and compost recycles nutrients left in plant and animal waste.
• Crop rotation is where crops are grown in different fields each year to stop pests and disease building up and stop nutrients from running out.
• Weeding is used instead of using herbicides however it involves lots of physical labour.
• Varying seed planting times avoids major pests developing.
• Advantages of organic farming methods...
• They use fewer chemicals so there's less risk of toxic chemicals staying on food.
• They're better for the enivronment as they don't pollute rivers or disrupt food chains.
• For a farm to be classed as organic they have to follow ethical guidelines on animals which means no battery farming.
• Disadvantages of organic farming methods...
• They take up more space so there's less space for wildlife.
• It's more labour-intensive which provides more jobs but makes food expensive
• You can't grow as much food.
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