B4 - Its a green world

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Distribution of Organsims

Habitat - Where a plant or animal lives.

Community - All the plants and animals living in the area.

Population - Number of a PARTICULAR organism in its community.

Biodiversity - variety of plants and animals

Natural ecosystems usually have good biodiversity as they have a wide variety of plants and animals.

Artificial ecosystems have bad biodiversity because only one species is kept to remove any other organism that could reduce the amount of that species.

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Transect Lines

Distribution of organisms can be mapped using a transcent line:
  A long length of string is layed across an area. At regular intervals you use a quadrat to count how many organisms are in the square(animals) or percentage cover (plants).

A transect line can show zonation(zones) in distibution of organisms. This could be due to being trampled on if near a path.

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Kite Diagrams

Kite diagrams can be used to show data from transect line.

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Food Chains and Food Webs

Food Chains & Food Webs show the cycle of energy between organisms. It show who eat who to survive.

The exchange of gasses in Photosynthesis and Respiration ensures an overall balance of these gases.

An ecosystem is therefore self-supporting in all factors apart from having to have the sun as an energy source.

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Population Size

You can calculate the size of the population by:

using a capture and recapture method. To do this you:

1. Do a method to collect your organisms (e.g. pitfall trap)
2. Then mark all the organisms you capture ( e.g. a dot / line)
3. then you let them go
4.You redo your method and you see how many organisms you have this time. Also how many are marked

Population Size = Nom. of organisms in 1st sample X Nom. of organisms in 2nd Sample
                          ---------------------------------------------------------------------------------------------------                                                  Nom. in second sample already marked 

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Population Size - 2

The larger the scale you use to collect your organisms, the more accurate it is going to be
(e.g. Larger Quadrat)

Using a Capture and Recapture method assumes:

  • There are no deaths / reproduction / movement in or out of area 
  • Identical sampling methods are used for both samples
  • The marking doesnt affect survival of organisms
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6CO2 +  6HO  ---> C6H12O6 + 6O2   

The simple sugars such as glucose can be:

  • Used in respiration, releasing energy
  • Converted into cellulose to make cell walls
  • Converted into proteins for growth and repair
  • Converted into starch, fats and oils for storage

Starch is used for storage because it is insoluble and doesn't move from storage areas.

 Also unlike glucose it doesn't affect water concentration of cells & cause osmosis.

Photosynthesis is a two-stage process:

  • Water is split up by light energy releasing oxygen and hydrogen ions.
  • Carbon Dioxide gas combines with hydrogen ions producing glucose and water 
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Rate of Photosynthesis

The rate of photosynthesis can be increased by:

  • More Carbon Dioxide
  • More Light
  • Higher Temperature - Increases enzyme action 

Photosynthesis only take place at day, when it is light.

Plants respire all day (release energy)
They take in oxygen and release it as carbon dioxide.

During the day they carry out photosynthesis, they take in carbon dioxide and release it is as oxygen.

The rate is higher in photosynthesis, so respiration is only noticed at night.

Since photosynthesis depends on light, temperature and carbon dioxide,  a lack of one of these will limit the rate of photosynthesis. They are called limiting factors.

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Leaf cells have many specialised cells. The cell is adapted so photosynthesis is efficient.

  • The outer epidermis lacks chloroplast (so it is transparent) there are no barriers to light.
  • The upper palisade layer contains most of the leafs chloroplasts as they will receive most of the light
  • The spongy mesophyll cells - loosely spaced so diffusion of gasses between cells and atmosphere can take place
  • The arrangement of mesophyll cells create a large surface area so large amount of gasses can enter and exit
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Leaf Adaptations

Leaves are adapted so photosynthesis become more efficient:

  • BROAD - gives them a large surface area so as much light as possible hits the leaf
  • THIN - gasses can easily diffuse through them and light can easily get in
  • CHLOROPHYLL - they can use light from a broad range of lights 
  • VASCULAR BUNDLES (Veins) - support and transport of chemicals such as water and glucose
  • SPECIALIZE GUARD CELLS - control opening and closing of the stomata, regulating the flow of co2 and o2 as well as water loss
  • PIGMENTS - the plants cells can maximise the use of suns energy. Each pigment absorbs light of different wavelengths 
    (Pigments = Chlorphyll A & B, Carotene and Xanthophylls) 
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Diffusion = movement of particles (in a gas or liquid) from an                         area of high concentration to an area of low                         concentration. Resulting in random movement of particles.

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Diffusion in cells

Diffusion is how molecules of water, oxygen and carbon dioxide can enter and leave through cell membrane

If plant cell is using up carbon dioxide, then there is a low concentration of it. therefore carbon enters to replace it, it enter by diffusion

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Diffusion in Leaves

Leave are adapted to increase diffusion of CO2 and O2 by having...

  • Large Surface Area
  • Specialised openings (Stomata), which are spaced out
  • Gaps between the spongy mesophyll cells 
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Rate of Diffusion

Rate of diffusion is not a fixed quantity.

You can increase the rate of diffusion by having....

  • Shorter distance for molecules to travel
  • Greater difference in concentration between the two areas.
  • Greater surface area for molecules to diffuse from.
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Osmosis is a type of diffusion.

Osmosis depends on there being a Partially-Permeable Membrane that allows the passage of water molecules.

Osmosis doesn't allow the passage of large molecule such as gas..

Osmosis is movement of water across a partially-permeable membrane from an area of high water concentration (dilute solution) to an area of low water concentration (concentrated solution).

Osmosis is a consequence of the random movement of water molecules, which is nor restricted by a partially-permeable membrane. the net movement of water molecules will be from an area where there are many to one where there are few.

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Osmosis - 2


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Water in Plant Cells

Entry of water into plant cells increases pressure pushing on the cell wall. (Which is rigid and not elastic) This turgor pressure supports the cell, stopping it from entering and the whole plant from collapsing.

When a plant is full of water it is called turgid.
When the cell loses water, the cell content shrinks and becomes plasmolysed and the cell is called flaccid.

Animal cells also shrink and collapse when they lose too much water. They swell up when there is too much water.

Animal cells don't have a cell wall, so when too much water enters, they will swell up and burst (lysis). When too much water leaves an animal cell, it shows crenation by shrinking into a scalloped shape.

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Xylem and Phloem Cells

Xylem and Phloem are made up of specialised plant cells. Both types of tissues are continuous from the root, through the stem and into the leaf.

Both xylem and phloem form vascular bundles inborad-leaved plants.


 - Carries water and minerals from the roots to the leaves.
 - Ivolved in transpiration
 - Xylem cells are called vessels - dead cells and have a gollow lumen (from having a lack of cytoplasm)
 - Their cellulose walls have extra thickening of lignin, which gives great strength and support 


 - Carries food substances (e.g. sugars) up and down the stem to growinf and storage tissues.
 - Transportation of food is called translocation
 -  Living cells
 - Arranged in columns 

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Transpiration explains how water moves up the plant against gravity in tubes made of dead xylem cells without the use of a pump.

Water on the surface of spongy and palisade cells (inside the leaf) evaporates and then diffuses out of the leaf. This is called transpiration. More water is drawn out of the xylem cells inside the leaf to replace what's lost. As the xylem cells make a continuous tube from the leaf, down the stem to the roots, this acts like a drinking straw, producing a flow of water and dissolved minerals from roots to leaves.

Factors that speed up transpiration will also increase the rate of water uptake from the soil. When water is scarce, or the roots are damaged, it increases a plant’s chance of survival if the transpiration rate can be slowed down. Plants can do this themselves by wilting, or it can be done artificially, like removing some of the leaves from cuttings before they have chance to grow new roots.
(source BBC) 

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Root hairs have a large surface area for water to uptake by osmosis.

Transpiration ensures that plants have water for cooling by evaporation, photosynthesis and support from cells turgor pressure and for transport of minerals.

The structure of a leaf is adapted to prevent too much water loss, which could cause wilting if not prevented.
Water loss is reduced by having a waxy cuticle covering the outer epidermal and by most stomata openings being situated on the shaded lower surface

Leaves are adapted for photosynthesis by having stomata for entry and exit for gases.
The sponge mesophyll cells are also covered with a film of water in which the gasses can dissolve. 

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Rate of Transpiration

Rate of transpiration can be increased by:

 - an increase in light intensity, which returns in stomata being opened

 - Increse in temperature, causing an increase in evaporation of water

 - Increase in air movement, blowing away air containing a lot of evaporated water

 - Decrease in humidity, allows more water to evaporate 

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Plants need minerals such as:

  • nitrates - make proteins, which plants use for cell growth
  • phosphates - involved in respiration and growth
  • potassium compounds - involved in respiration and photosynthesis
  • magnesium compounds - involved in photosynthesis

Elements from soil minerals are used to produce useful compounds.

 - Nitrogen (from nitrates) = used to produce amino acids
 - Phosphorus (from phosphates) = used to make DNA, contains plants genteic code and cell membranes
 - Potassium (from potassium compounds) - used to help enzyme action in photosynthesis and respiration
 - Magnesium (from magnesium compounds) - used to make chlorophyll, which is essential for photosynthesis 

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Mineral Deficiency

Lack of certain minerals results in different outcomes:

lack of...

  • Nitrate = poor growth and yellow leaves
  • Phosphate = poor root growth and discoloured leaves
  • Potassium = poor flower and root growth and discoloured leaves
  • Magnesium = yellow leaves
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Mineral Uptake

Minerals are usually present in soil in low concentrations

Minerals are taken up by the root hair cells by a process called active transport. Rather than osmosis or diffusion.

A system of carriers transport selected minerals across the cell membrane.

Active transport enables minerals in the soil in low conncentration to enter the root hair cells which contain high conentration of minerals.

The minerals move from low concentration to high concentration. This uptake of minerals require energy to go up against the gradient. The energy comes from respiration.

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Earthworms, maggots and woodlice are called Detritivores because they feed on dead and decaying material (detritus)

Detritivores increase the rate of decay by breaking up the detritus and so increasing the surface area for further microbial breakdown.

How to increase the rate of decay?

  • by having detritivores in the soil
  • increasing the temperate - by increasing the temperature to 37°C (bacteria) or 25°C (fungi) will increase their rate of respiration. Too high temperature the enzymes will denature
  • increasing the amount of oxygen - bacteria will use aerobic respiration to grow and reproduce faster
  • increasing the amount of water - allows material to be digested and absorbed more efficiently and increase growth and reproduction of bacteria and fungi.
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Fungus and Decay

Saprophyte = an organism that feed on dead and decaying materials

Fungi is an example of a Saprophyte.

Fungi produce enzymes to digest food outside their cells and then reabosorb the simple soluble substances. This type of digestion is called extracellular digestion.

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Food Preservation

Food preservation reduces the rate of decay.

 - Canning foods -  food are heated to kill bacteria and then sealed in a vacuum to prevent oxygen getting in

 - Cooling foods - slows down bacterial and fungal growth and reproduction

 - Freeing foods - kills some bacteria and fungi and also slow down the growth and reproduction

 - Drying foods - removes water so bacteria can not feed or grow

 - Adding salt or sugar - kill some bacteria and fungi, as the high osmotic concentration will remove water from then

 - Adding vinegar - produce very acidic condition killing most bacteria and fungi

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The use of pesticdes, herbicides and insecticides has its disadvantages.


 - they can enter the accumulate in food chain cauisng illness to the predators

 - they can harm other organisms living nearby which are not pests

 - some are pesrsistent (take a very long time to break down and become harmless)

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Organic Farming

Organic farming does not use artificial fertilisers or pesticiders

It uses animal manure and compost (instead of artificial fertilisers), crop rotation (to avoid build-up of soil pasts)

It avoids expensive fertilisers and there disadvantages, however the crops are smaller and the produce is more expensive and take longer. 

However people think organic crops are healthier and tastier.

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Biological Control

Biologic Control is where you use living organisms to control pests.

e.g. ladybirds and wasps are used to eat aphids which destroy plants

Biological control avoids all of the diasdvantages of using fertilisers so it is good.

However some of the useful biological contols organisms have started eating other biological controlling organisms. The population of biological control organisms has rapidly increased and started to make them pests and then spread into other areas.

Introducing a species into a habitat to kill another species can upset the food chain.

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Intensive farming

Intensive farming makes use of fertilisers and pesticides to produce large crop yields cheaply.

However they have raised concerns about animal cruelty as animals are kept in small areas. And also about the effect of chemicals on soil structures.

Intensive farming improves the efficiency of energy transfer in food chains involving humans by reducing or removing competing organisms such as animal pests and weeds

Also by keeping animals in sheds or barns (battery farmign) they use less energy to keep warm and moving. They focus more energy on growth (cattle) or egg production (hens)

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Plants can be grown without using soil using hydroponics. This system uses a regulated recycled mineral water and is usually done in green houses and poly-tunnels.

Hydroponics is a type of intense farming that is especially useful in areas of barren soil or low rainfall. Tomatoes are a common crop grown in this way.

Being a soil free system, hydroponics has a better control over mineral levels. Many plants can be grown in the tight spaces as there is no anchorage into the soil.

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A  good set of notes with some useful, coloured diagrams which cover a wide range of topics such as diffusion, energy flow, water transport, decomposers,food chains and photosynthesis. Students could take out the cards they need to make a useful set or combine them with some of their own to make a set for their specification.


Thanks. Really helpful

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