B4

Population Size = number in 1st sample × number in 2nd sample/ number in 2nd sample previously                                                             marked

The bigger the quadrat and the more samples you take, increases the accuracy

Using a capture-recapture method assumes that:

• There are no deaths, reproduction or movement of animals in and out of the area
• Identical sampling methods are used fro both samples
• The marking does not affect the survival rate

Sampling Methods:

• Line Transect-Record plants/animals under tape measure at intervals
• Random Sampling
• Pooter- Used to collect small animals
• Sweep Net
• Pitfall trap
• Kite diagrams

Ecosystem= A group of living animals and their environment

Habitat= An area where one animal/plant lives, that reflects its characteristics/niche

Community= All the animals and plants in an ecosystem

Population= Is the number of organisms of the same species in a specific area/community

The distribution of organisms can be mapped using a transect line. A long length of string is laid across an area. At regular intervals, the organisms in a quadrat would be counted

Food chains show that plants/animals are self-sufficient, with energy being transferred from one organism to another. An ecosystem is, therefore, self-supporting in all factors apart from having the sun as an energy source.

Abiotic Factors= Non-living factors

Zonation= Each group of organisms require specific conditions so grow in particular areas. A transect line can show zonation in the distribution of organisms. Changes in abiotic factors such as exposure on a sea shore cause zonation.

Natural Ecosystem= When an ecosystem has been naturally formed, not man made, meaning there is a high species diversity. eg a native woodland or lake

Artificial Ecosystem= An ecosystem made/changed by man, herbicides and fertilisers may be used and biodiversity decreases. eg Forestry plantations and fish farms

In artificial ecosystems, human deliberately keep and protect only one species and remove any other organisms that would compete with it and lower the yield. This does not happen in a natural ecosystem

Balanced Symbol Equation for Photosynthesis:

Development In understanding:

• the view of Greek scientists that plants gained mass only by taking in minerals from the soil

• Van Helmont’s experimental conclusion that plant growth cannot be solely due to nutrients from the soil • Priestley’s experiment which showed that oxygen is produced by plants.

• Priestley’s experiment which showed that oxygen is produced by plants.

• Modern experiments using a green alga called Chlorella and an isotope of oxygen 18^0 as part of a water molecule, show that the light energy is used to split water, not carbon dioxide. The water is split up into oxygen gas and hydrogen ions. Carbon dioxide gas combines with the hydrogen to make glucose.

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, this means that it doesn't move away in solution from storage areas. And unlike glucose, it doesn't affect the water concentration of cells and cause osmosis.

The rate of photosynthesis can be increased by:

• More Carbon dioxide
• More Light
• A higher temperature which increases enzyme action

• Plants carry out respiration at all times- by taking in oxygen and releasing Carbon Dioxide, because they are a living thing and must respire at all times releasing energy.
• Whereas Photosynthesis will only take place in the daytime (in the light) .
• During the day plants carry out photosynthesis, taking in Carbon Dioxide and releasing oxygen - the same gas exchange as respiration but in reverse.
• But the rate of gas exchange in photosynthesis is more than that of respiration in terms of quantity.
• So respiration can only be noticed at night

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

How leaves are adapted for photosynthesis:

• Usually broad, so have large surface area to get as much light a possible
• Thin, so gases can diffuse easily and light can get to all cells
• Contain chlorophyll so that they can use light from a broad range of the light spectrum
• Network of vascular bundles for support and transport of chemicals such as water and glucose
• Specialised guard cells which control the opening/closing of the stomata, therefore regulating flow of carbon dioxide, oxygen and water loss

How cells are adapted for efficient photosynthesis:

• Outer epidermis lacks chloroplasts, so is transparent, so no barriers for light entry
• Upper palisade contains most of the leaf's chloroplasts, as they receive most light
• The spongy mesophyll cells are loosely spaced, so diffusion of gases between cells and outside atmosphere can take place
• Arrangement of mesophyll cells creates a large surface area to volume ratio so large amounts of gases can exit and enter the cells

Diffusion= The net movement of particles from an area of high concentration to an area of low concentration, due to the random movement of particles

Molecules of water, oxygen and carbon dioxide enter and leave cells through the cell membrane due to Diffusion. eg If a plant is using carbon dioxide, there is a lower concentration of carbon dioxide inside the cell, so carbon dioxide will enter by diffusion.

The rate of diffusion can be increased by having:

•  A shorter distance for the molecules to travel
•  A steeper concentration gradient
• Greater surface area for molecules to diffuse from/into

Osmosis= A type of diffusion, that depends on the presence of a partially permeable membrane that allows the passage of water molecules but not large molecules like glucose, from an area of high water concentration to an area of low water concentration (i.e. concentrated solution).

Partially permeable Membrane= a membrane that allows some small molecules to pass through but not larger molecules

Flaccid=Soft and floppy-No water

Turgid=Hard and rigid- Full of Water

Plasmolysed cell= A cell that has lost water and its membrane has pulled away from the cell wall

The entry of water into plant cells increases the pressure pushing on the cell wall, which is rigid. The turgor pressure sports the cell, stopping the plant from collapsing. When too much water leaves it looses its pressure and the plant wilts.

Turgor Pressure= The pressure exerted on the cell membrane by the cell wall when the cell is fully inflated

Animal cells also react to intake and loss of water. However, they don't have a supporting cell wall. When too much water enters they will swell up and burst (lysis). When too much water leaves, it shows crenation by shrinking into a scalloped shape.

Crenation= when red blood cells shrink in concentrated solutions, they look partly deflated

Xylem – Transpiration – movement of water and minerals from the roots to the shoot and leaves

Phloem – Translocation – movement of food substances (sugars) up and down stems to growing and storage tissues

Xylem and Phloem are made of specialised plant cells. Both types of tissue are continuous from the root, through the stem and up into the leaf. Together they form vascular bundles in dicotyledonous (broad-leaved) plants

The xylem cells are called vessels, they are dead cells and the lack of cytoplasm leaves a hollow lumen. They have thick strengthened cellulose walls- thickened with ligin, giving strength and support

Phloem cells are living cells and are arranged in columns 

Transpiration= The evaporation and diffusion (changing from a liquid to a gas) of water from inside leaves

Loss of water from leaves helps to create a continuous flow of water from the roots to the leaves in xylem cells

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

Plant leaves are adapted for efficient photosynthesis by having stomata for entry and exit of gases. the spongy mesophyll cells are covered with a film of water in which gases can dissolve. This water can therefore readily escape through the stomata

The rate of transpiration can be increased by:

• An increase in light intensity, which results in stomata being open
• An increase in temperature, causing an increase in the evaporation of water
• An increase in air movement, blowing away air containing a lot of evaporated water
• A decrease in humidity, allowing more water to evaporate

Transpiration provides plants water for:

• Cooling
• Photosynthesis
• Support
• Movement of minerals

Root hairs are projections from root hair cells. they produce a large surface area for water uptake by osmosis

A leaf is adapted to reduce water loss by:

• Having a waxy cuticle covering the outer epidermal cells 
• Most stomatal openings being situated on the shaded lower surface
• Guard cells are able to change the size of the stomatal openings
• Having fewer stomata, smaller stomata, the position of the stomata and their distribution

Guard cells can change the size of the openings because they contain chloroplasts. So photosynthesis in the presence of water and light will produce sugars, which will increase the turgor pressure causing the cells walls to swell. Due to differential thickness of their walls, the guard cells curve, opening the stomata

Plants need minerals such as:

• nitrates: for proteins which are needed for cell growth
• phosphates: for respiration and growth
• potassium compounds: for respiration and photosynthesis
• magnesium compounds: for photosynthesis.

Elements in the soil are used to produce useful compounds:

• Nitrogen, from nitrates, used to produce amino acids, which combine to form proteins. 
  Lack of nitrate causes poor growth and yellow leaves
• Phosphorus, from phosphates, used to make DNA which contains the plant's genetic code. Lack of phosphate causes poor root growth and discoloured leaves
• Potassium, from potassium compounds, used to help enzyme action in photosynthesis and respiration. Lack of potassium causes poor flower and root growth and discoloured leaves
• Magnesium, from magnesium compounds, used to make chlorophyll

Minerals are usually present in the soil in low concentrations.

So minerals must be taken up by root hair cells by active transport

Active transport requires energy (as ATP) from respiration. Molecules and ions can travel against the concentration gradient. It is a system of carrier transport selected minerals across the cell membrane. 

Active transport enables minerals present in the soil in low concentrations to enter root hairs already containing high amounts of minerals.

Factors that increase the rate of Decay:

• Increasing temperature
• Increasing oxygen levels
• increasing water levels

Because increasing the temperature to an optimum of 37 degrees celsius for bacteria and 25 degrees celsius for fungi will increase their rate of respiration. Higher than optimum temperatures will denature enzymes

Increasing the amount of water will allow for material to be digested and absorbed more efficiently and increase growth and reproduction

Increasing the oxygen level will allow bacteria to aerobically respirate to grow and reproduce faster

Detritivores= Organisms that eat dead and semi-decayed remains of living things (detritus) eg. Earthworms, Maggots and Woodlice. 

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

Saprophyte= Organisms that break down dead organic matter (carbon compounds) outside its body and then absorb the products if digestion eg fungus

Fungi produce enzymes to digest food outside their cells and then reabsorb the simple soluble substances, this is called extracellular digestion

Food preservation methods reduce the rate of decay:

• Canning, foods are heated to kill bacteria and then sealed in a vacuum to prevent entry of oxygen and bacteria
• Cooling foods will slow down bacterial and fungal growth/reproduction
• Freezing foods will kill some bacteria and fungi and slow down their growth/reproduction
• Drying foods removes water so bacteria can't feed and grow
• Adding sugar or salt will kill some bacteria/fungi, as the high osmotic concentration will remove water from them
• Adding vinegar will produce very acidic conditions killing most bacteria/fungi

Disadvantages of using pesticides:

• They can enter and accumulate in food chains
• May harm organisms that aren't pests
• Some pesticides are persistent (Take a long time to break down)

Organic farming doesn't use artificial fertilisers or pesticides

Organic farming techniques:

• Use of animal manure and compost
• Crop rotation including the use of nitrogen-fixing crops
• Weeding
• Varying seed planting times. 

Organic farming avoids the expensive of fertilisers and pesticides and their problems, however, the crops are smaller and more expensive. Some people believe organic crops are healthier and tastier

Plants can be grown without soil using hydroponics. It is a regulated recycling flow of aerated water containing minerals and is usually done in greenhouse/polytunnels. It is a type of intensive farming, especially useful in areas of barren soil or low rainfall. Tomatoes are a common crop

Advantages of Hydroponics:

• Better control of mineral levels and disease
• Many plants can be grown in a small space
• More efficient

Disadvantages:

• No support for plants, so artificial plants used
• Fertilisers still must be added

Intensive farming improves the efficiency of energy transfer in food chains, by reducing/removing competing organisms such as pests and weeds. And by keeping animals indoors they are warm and move around less , so they waste less energy and more energy on growth. However, this does bring ethical dilemma

Biological control uses living organisms to control pests. eg ladybirds to eat aphids which damage plants

Advantages of Biological Control:

• No need for chemical pesticides
• No need for repeated treatment

Disadvantages:

• Predator may not eat pest
• May eat useful species
• May increase out of control
• May not stay in area where needed

Introducing a species into a habitat to kill another species can affect the food sources of other organisms in a food web.