B4- It's a Green World

A population is all the organisms of a new species in a habitat. Populations of a different in a habitat make up a community

• A Quadrat is a square frame enclosing a known area. You can study the small area within a quadrat and scale up your findings to make estimates for larger areas. You count all the organisms within the quadrat and then you multiply it by the total area of the habitat
• The Capture-Recapture method. You capture a sample of the populaytion and mark the animals in a harmless way, you then release them. You recapture them and count how many were marked and then estimate it using the equations
• Population Size= number in first sample x number in second sample
•                                 number in second sample previously marked
• The sample size affects the accuracy of the estimate because the bigger your sample the more accurate that the estimate is likely to be, when using the capture-recapture you have to assume there have been no changes, the sampling methods used were identical and the marking hasn't affected their survival

An ecosystem is all the organisms living in a particular area as well as all the non- living conditions e.g. the temperature, salinity and soil quality. It isn't the same as a habitat as it is just the place where the organism lives. They are self supporting and contain everything they need to maintain. The only thing from outside is an energy source which is usually the sun

Distribution is where organisms are found within a particular area and you can investigate this using transects. To do this you mark out a line using a tape measure and place quadrats next to eachother all the way along the line and place quadrats next to one another and record and count all the way along. It is difficult to count all the way along so you calculate the percentage cover which means estimating the percentage area of the quadrat. You can plot the results in a kite diagram which allows you to map the distribution.

The distribution of organisms is affected by these factors because they are adapted to live in certain physical conditions which means they are more likely to survive and reproduce. Many organisms can only survive in the conditions they're adapted to, mosquitos are adapted to live in warm climates.

ZONATION IS THE GRADUAL CHANGE IN THE DISTRIBUTION OF A SPECIES ACROSS A HABITAT.

A gradual change in the abiotic factors can lead to the zonation of organisms in a habitat. In a costal habitat, changes in salinity and soil depth result in zones where different types of plants grow.

Biodiverity includes: the varitation between individuals of the same species, the number of different species in an area, the number of different habitats in an area. It is important because ecosystems with a high level of biodiversity are healthier.

Natural Woodlands have a higher biodiversity than artificial ones. They maintain themselves with little interference from humans but artificial ecosystems are made and maintained by humans. Native Woodlans have a higher biodiversity than forestry plantations. Lakes also have a higher biodiversity than fish farms. This can be because they have many different species, all different sizes, variety of plant species and variety of habitats

• Photosynthesis uses energy from the sun to change carbon dioxide and water into glucose and oxygen. It takes place in the chloroplasts in plant cells that contain pigments like chlorophyll that absorb light energy.
• 6CO2 + 6H2O -> C6H12O6

Glucose is converted into other substances

• Plants use some of the glucose for respiration. This releases energy so they can convert the rest of the glucose into various other substances
• Glucose is turned into lipids for storing in seeds. Sunflower seeds contain alot of oil and we get cooking oil and margarine from them
• Glucose combined with nitrates to make amino acids which are made into proteins for growth and repair
• Glucose is converted into cellulose for making cell walls, especially in a rapidly growing plant
• Glucose is turned into starch and stored in roots, stems, leaves ready for when photosynthesis isn't happening at night. Starch doesn't effect the water concentration inside cells

Greek scientists concluded that plants gain mass from soil minerals as this was the only thing that touched plants

Van Helmont

• In the 1600s dried soil, and planted a tree and added rainwater. 5 years later he removed the tree from the pot and it had gained 74.5kg of mass. He dried the soil and weighed it and it had only changed a little so the tree must have gained mass from somewhere else, he had only added water so it must have been the water.

Priestley

• In the early 1770s he placed a burning candle in a sealed container and the flame went out and then he placed it into a container with a living plant and the flame went out but after a few weeks it could be re-lit. He concluded that the burning candle used up something. He filled another container with exhaled air and a mouse but it only survived a few seconds. He thought breathing had taken something out of the air and the living plant had restored the air. After these experiments he concluded plants restore something. We now now this is oxygen

LIGHT:

Light provides the energy for photosynthesis, if the light energy is raised the rate will increase but only up to a certain point. After it will be temperature or carbon dioxide which are the limiting factors

CARBON DIOXIDE:

As the light intensity the amount of carbon dioxide will increase the rate of photosynthesis but only to a certain point. As long as light and CO2 are in plentiful supply then the factor limiting photosynthesis will be temperature

TEMPERATURE:

Photosynthesis works best when its warm but not too hot. As the temperature increases so does the rate but if it is too hot then the plants enzymes will be denatured so the rate will rapidfly decrease. This happens at around 45'c. Usually though it temperature is the limiting factor its because it is too low

Diffusion is the gradual movement of particles from places where there are lots of them to places where there are fewer of them. DIFFUSION IS THE NET MOVEMENT OF PARTICLES FROM AN AREA OF HIGHER CONCENTRATION TO AN AREA OF LOW CONCENTRATION.

Cell Membranes are clever

• They are clever because they hold the cell together but they let stuff in and out as well, only small molecules like simple sugars, water or ions. Big molecules like starch and proteins can't pass through the membrane
• Just like with diffusion in the air, particles flow through the cell membrane from where there is a higher conentration to where there is a lower concentration
• They only move randomly so they go both waays but if there are alot more particles on one side of the membrane there's obviously movement from one side.

The rate of diffusion depends on three things:

Distance (substances diffuse more quickly when there isn't far to move), Concentration Gradient (substances diffuse faster if there's a big difference in concentration) and surface area

During the day the plant make more oxygen by photosynthesis than they use in respiration so in daylight they release oxygen and take in carbon dioxide. At night though plants only respire, there's no light for photosynthesis which means they take in oxygen and release carbon dioxide

PHOTOSYNTHESIS:

When the plant is photosynthesising it uses up lots of carbon dioxide so there's hardly any inside the leaf. This makes more carbon dioxide move into the leaf by diffusion and at the same time lots of oxygen is being made as a waste product of photosynthesis. Some is used in respiration and the rest diffuses out of the leaf.

RESPIRATION:

At night there is no photosynthesis going on because there's no light. Lots of carbon dioxide is made in respiration and lots of oxygen is being used up. There's a lot of carbon dioxide in the leaf and not alot of oxygen so now it's mainly carbon dioxide diffusing out and oxygen diffusing in

Leaves are broad so they have a large surface area for gases to diffuse, they are also thin which means carbon dioxide and water vapour only have to diffuse a short distance to reach the cells. The lower surface is full of little holes called stomata which are they're to let gases in and out and water to escape. They have guard cells surrounding each stoma to control when the stoma opens and closes and allows the guard cells to control gas exchange. There are air spaces in the spongy mesophyll layer which allows gases to move between the photosynthesis cells. They have a large surface area for gas exchange

Leaves contain lots of chloroplasts which contain chlorophyll to absorb light energy. Different pigments absorb different wavelengths of light so they can absorb as much as possible. The cells that contain the most are arranged in the palisade layer near the top of the leaf where they can get the most light.

The Upper Epidermis is transparent so that light can pass through it to the palisade layer

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.

The water molecules actually pass both ways through the membrane during osmosis. There are more water molecules on one side so there's a steady net flow of water into the region with fewer water molecules. These means the concentrated sucrose solution gets more dilute.

When a plant is well watered all its cells wil draw water in by osmosis and become plump and swollen, when the cells are like this they are said to be turgid. The contents of the cell push aganst inelastic cell wal which is call turgor pressure. When cells lose water they become flaccid. If the plant is short of water the cells become to shrink and the cell is now said to be plasmolysed.

Phloem Tubes transport food:

• Made of columns of living cells with perforated end-plates to allow stuff to flow through
• They transport the food substances both up and down the stem to growing and storage tissues
• This movement of food substances around the plant is known as translocation

Xylem Vessels take water up:

• Made of dead cells joined end to end with no end walls between them and a lumen (hole) down the middle
• The thick side walls are made of cellulose, they're strong and stiff which gives the plant support
• They carry water and minerals from the roots up the shoot to the leaves in the transpiration stream

Transpiration is caused by evaporation and diffusion of water vapour from inside the leaves. This creates a slight shortage of water in the leaf and so more water is drawn up from the rest of the plant through the xylem vessels to replace it. This in turn means more water is drawn up from the roots and so there's a constant transpiration stream of water through the plant

Transpiration is just a side effect of the way leaves are adapted for photsynthesis, they have to have a stomata in them so that gasses can be exchanged easily. Because there's more water inside the plant than the air outside the water escapes from the leaves through the stomata.

The benefits of the transpiration stream:

• The constant stream of water from the ground helps to keep the plant cool
• It provides the plant with a constant supply of water for photosynthesis
• The water creates turgor pressure in the plant cells, which helps support the plant and stops it wilting
• Minerals needed by the plant can be brought in from the soil along with the water

Transpiration Rate is increased by four main things:

• An increase in light intensity, the brighter the light the greater the rate. The stomata begin to close as it gets darker. Photosynthesis can't happen in the dark so they don't need to be open to let it in.
• An increase in temperature, the warmer it is the faster transpiration happens. When it's warm particles have more energy to evaporate and diffuse out of the stomata.
• An increase in air movement, if there is alot of air movement around a leaf transpiration happens faster. If there is little water vapour just surrounds the leaf and doesn't move away. This means there is a high concentration of water particles outside the lead as well as inside the leaf so diffusion doesn't happen quickly
• A decrease in air humidity, if the air around the leaf is very dry, transpiration happens more quickly. This is like what happens with air movement. If the air is humid there's alot of water already so there's not much of a difference between the inside and the outside of the leaf. Diffusion happens fastest if there is a really high concentration in one place and a low concentration in the other

Nitrates: contain nitrogen for making amino acids and proteins, these are needed for cell growth. If a plant can't get enough nitrates its growth will be poor and it'll have yellow older leaves

Phosphates: needed for respiration and growth, contain phosphorus for making DNA and cell membranes. Plants without enough phosphate have poor root growth and discoloured older leaves

Potassium:to help enzymes needed for photosynthesis and respration, if there's not enough potassium in the soil, plants have poor flower and fruit growth and discoloured leaves

Magnesium:is needed in small amounts. It is significant as it's required for making chlorophyll and plants without enough magnesium have yellow leaves

Root Hairs take in minerals using active transport. They give the plant a big surface area for absorbing minerals from the soil but the concentration of minerals in the soil is usually pretty low. It is normally higher in the root hair cell than the soil around it. Active transport is responsible because it uses energy from respiration to help the plant pull minerals into the root hair against the concentration gradient.

The rate of decay depends on three main things:

• Temperature: a warm temperaure makes things decay faster because it speeds up the respiration imicroorganisms
• Amount of water: things decay faster when they're moist because microorganisms need water
• Amount of oxygen: decay is faster when there's oxygen avaliable. The microorganisms can respire aerobically

Detrivores: detrivores feed on dead and decaying material. Examples of this includes earthworms, maggots and woodlice. They break it into smaller bits whcih gives them a bigger surface area to work on and so speeds up decay. Saprophytes also feed on decaying material but they do so by extracellular digestion. The enzymes break down the material into smaller bits which can be absorbed by the saprophyte

Food preservation methods reduce the rate of decay:

Canning, cooling, freezing, drying, adding salt/sugar, adding vinegar

• Intensive farming can be used to produce more food:
• Using herbicides to kill weeds, this means more energy from the sun falling on the field goes to the crops and not to any other competing plants that aren't wanted
• Using pesticides to kill insects that eat the crops, this makes sure no energy is transferred into a different food chain- it's all saved for growing the crops
• Battery farming animals, they are kept close together so they are kept warm and don't move about which saves energy and keeps them warm

Hydroponics is where plants are grown without soil. They are grown in nutrient solutions and are often used to grow glasshouse tomatoes on a commercial scale. Advantages: mineral levels can be controlled more accurately, diseases can be controlled more effectively. Disadvantags: lots of fertilosers need to be added, there's no soil to anchor the roots and support the plants

Intensive farming can destroy the environment: the removal of hedges to make huge great fields destroys the natural habitat which can lead to soil erosion, careless use of fertilisers can pollute rivers and lakes, pesticides disturb food chains and lots of people think that it is cruel to animals

Pesticides are sprayed onto crops to kill the creatures that damage them, this can cause a shortage of food for animals further up the food chain, some pesticides are persistant so they are hard to get rid of, there is a danger of pesticides being passed along the food chain and killing animals further up

Biological Control means using living things instead of chemicals to control a pest.

• Aphids= are a pest because they eat roses and veg, ladybirds are aphid predators so people release them into their fields
• Certain types of wasps and flies produce larvae which develop on a host insect which kills it
• Myxomatosis= is a disease that kills rabbits

Advantages: no chemicals are used so there is less pollution, there is no need to keep retreating the treatment

Disadvantages: the predator that you introdue might not eat the pest, the predatr could eat useful species, the predator's population might increase and get out of control, the predator might not stay in the are where it is needed

• Use of organic fertilisers
• Crop rotation
• Weeding
• Varying seed planting times
• Biological Control

Advantages and Disadvantages of organic farming

Advantages: it uses fewer chemicals which reduces toxic chemicals being on food, it is better for the environment, it has ethical treatment of animals

Disadvantages: it takes up more space, it is labour-intensive so it provides more jobs for people but this makes the food very expensive, you can't grow as much food